2012 Vol.25(2)
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2012, 26(2).
Abstract:
Many performance indices for parallel mechanism are put forward in the phase of dimensional synthesis, except for identifiability index, which determines the difficulty of kinematical calibration. If the dimensional parameters are inappropriately selected, the existing methods for optimizing identifiability will not effectively work. Thus, with the aim of studying identifiability optimization in dimensional synthesis for 3-PRS mechanism, kinematics with structural errors is analyzed to provide theoretical bases for kinematical model. Then through a comparison of two 3-PRS mechanisms with different dimensional parameters, identifiability performance is proved to be necessary and feasible for optimization in the phase of dimensional design. Finally, an index δ is proposed to scale the identifiability performance. With the index, identifiability analysis and dimensional synthesis simulation in the whole workspace is completed. The index is verified to be correct and feasible, and based on the index, a procedure of dimensional synthesis, as well as an example set of non-dimensional parameters of 3-PRS mechanism, is proposed. The proposed identifiability index and design method can effectively introduce identifiability optimization into dimensional synthesis, and will obviously benefit later kinematical calibration.
Many performance indices for parallel mechanism are put forward in the phase of dimensional synthesis, except for identifiability index, which determines the difficulty of kinematical calibration. If the dimensional parameters are inappropriately selected, the existing methods for optimizing identifiability will not effectively work. Thus, with the aim of studying identifiability optimization in dimensional synthesis for 3-PRS mechanism, kinematics with structural errors is analyzed to provide theoretical bases for kinematical model. Then through a comparison of two 3-PRS mechanisms with different dimensional parameters, identifiability performance is proved to be necessary and feasible for optimization in the phase of dimensional design. Finally, an index δ is proposed to scale the identifiability performance. With the index, identifiability analysis and dimensional synthesis simulation in the whole workspace is completed. The index is verified to be correct and feasible, and based on the index, a procedure of dimensional synthesis, as well as an example set of non-dimensional parameters of 3-PRS mechanism, is proposed. The proposed identifiability index and design method can effectively introduce identifiability optimization into dimensional synthesis, and will obviously benefit later kinematical calibration.
2012, 26(2).
Abstract:
Cutouts are inevitable in structures due to practical consideration. In order to investigate the free vibration of functionally graded plates with multiple circular and non-circular cutouts, finite element method is used. The volume fraction of the material constituents is assumed to follow a simple power law distribution. The parameters considered in this paper are as follows: cutout size, cutout location, number of cutouts and different boundary conditions. It should be mentioned that free vibration for FG plates(such as rectangularskewtrapezoidalcircular plates) with multiple cutouts has not been studied yet and hence the results out coming from this paper may be used as bench marks for future works.
Cutouts are inevitable in structures due to practical consideration. In order to investigate the free vibration of functionally graded plates with multiple circular and non-circular cutouts, finite element method is used. The volume fraction of the material constituents is assumed to follow a simple power law distribution. The parameters considered in this paper are as follows: cutout size, cutout location, number of cutouts and different boundary conditions. It should be mentioned that free vibration for FG plates(such as rectangularskewtrapezoidalcircular plates) with multiple cutouts has not been studied yet and hence the results out coming from this paper may be used as bench marks for future works.
2012, 26(2).
Abstract:
Error modelling and compensating technology is an effective method to improve the processing precision .The position and orientation deviation of workpiece is caused by the fixing and manufacturing errors of the fixture. How to reduce the position and orientation deviation of workpiece has become a technical problem of improving the processing quality of workpiece. In order to increase machining accuracy，an implementation scheme of fixture system comprehensive errors (FSCE) compensation is proposed. A FSCE parameter model is established by analyzing the influence of contact points on the position and orientation of workpiece. Meanwhile, a parameter identification method for FSCE parameter model is presented by using the 3-2-1 deterministic positioning fixture, which determines the model parameters. Moreover, a FSCE compensation model is formulated to study the compensation value of the cutting position. By using RenishawOMP60 Probe and combining vertical machining centre (SKVH850) equipment with SKY2001 Open CNC System, on-machine verification system (OMVS) is built to measure FSCE successfully. The processing error can be reduced by analyzing the cutting position of the tool with the homogeneous transformation of space coordinate system. Finally, the compensation experiment of real time errors is conducted, and the cylindricality and perpendicularity errors of hole surface are reduced by 30.77% and 28.57%, respectively. This paper provides a new way of realizing the compensation of FCSE, which can improve the machining accuracy of workpiece largely.
Error modelling and compensating technology is an effective method to improve the processing precision .The position and orientation deviation of workpiece is caused by the fixing and manufacturing errors of the fixture. How to reduce the position and orientation deviation of workpiece has become a technical problem of improving the processing quality of workpiece. In order to increase machining accuracy，an implementation scheme of fixture system comprehensive errors (FSCE) compensation is proposed. A FSCE parameter model is established by analyzing the influence of contact points on the position and orientation of workpiece. Meanwhile, a parameter identification method for FSCE parameter model is presented by using the 3-2-1 deterministic positioning fixture, which determines the model parameters. Moreover, a FSCE compensation model is formulated to study the compensation value of the cutting position. By using RenishawOMP60 Probe and combining vertical machining centre (SKVH850) equipment with SKY2001 Open CNC System, on-machine verification system (OMVS) is built to measure FSCE successfully. The processing error can be reduced by analyzing the cutting position of the tool with the homogeneous transformation of space coordinate system. Finally, the compensation experiment of real time errors is conducted, and the cylindricality and perpendicularity errors of hole surface are reduced by 30.77% and 28.57%, respectively. This paper provides a new way of realizing the compensation of FCSE, which can improve the machining accuracy of workpiece largely.
2012, 26(2).
Abstract:
Round method is the common method for discrete variable optimization in optimal design of complex mechanical structures; however, it has some disadvantages such as poor precision, simple model and lacking of working conditions’ description, etc. To solve these problems, a new model is constructed by defining parameterized fuzzy entropy, and the rationality of parameterized fuzzy entropy is verified. And a new multidirectional searching algorithm is further put forward, which takes information of actual working conditions into consideration and has a powerful local searching capability. Then this new algorithm is combined with the GA by the fuzzy clustering algorithm (FCA). With the application of FCA, the optimal solution can be effectively filtered so as to retain the diversity and the elite of the optimal solution, and avoid the structural re-analysis phenomenon between the two algorithms. The structure design of a high pressure bypass-valve body is used as an example to make a structural optimization by the proposed HGA and finite element method (FEM), respectively. The comparison result shows that the improved HGA fully considers the characteristic of discrete variable and information of working conditions, and is more suitable to the optimal problems with complex working conditions. Meanwhile, the research provides a new approach for discrete variable structure optimization problems.
Round method is the common method for discrete variable optimization in optimal design of complex mechanical structures; however, it has some disadvantages such as poor precision, simple model and lacking of working conditions’ description, etc. To solve these problems, a new model is constructed by defining parameterized fuzzy entropy, and the rationality of parameterized fuzzy entropy is verified. And a new multidirectional searching algorithm is further put forward, which takes information of actual working conditions into consideration and has a powerful local searching capability. Then this new algorithm is combined with the GA by the fuzzy clustering algorithm (FCA). With the application of FCA, the optimal solution can be effectively filtered so as to retain the diversity and the elite of the optimal solution, and avoid the structural re-analysis phenomenon between the two algorithms. The structure design of a high pressure bypass-valve body is used as an example to make a structural optimization by the proposed HGA and finite element method (FEM), respectively. The comparison result shows that the improved HGA fully considers the characteristic of discrete variable and information of working conditions, and is more suitable to the optimal problems with complex working conditions. Meanwhile, the research provides a new approach for discrete variable structure optimization problems.
2012, 26(2).
Abstract:
Euler angles are commonly used as the orientation representation of most two degrees of freedom (2-DOF) rotational parallel mechanisms (RPMs), as a result, the coupling of two angle parameters leads to complexity of kinematic model of this family of mechanisms. While a simple analytical kinematic model with respect to those parameters representing the geometrical characteristics of the mechanism, is very helpful to improve the performance of RPMs. In this paper, a new geometric kinematic modeling approach based on the concept of instantaneous single-rotation-angle is proposed and used for the 2-DOF RPMs with symmetry in a homo-kinetic plane. To authors’ knowledge, this is a new contribution to parallel mechanisms. By means of this method, the forwards kinematics of 2-DOF RPMs is derived in a simple way, and three cases i.e. 4-4R mechanism (Omni-wrist III), spherical five-bar one, and 3-RSR&1-SS one demonstrate the validity of the proposed geometric method. In addition, a novel 2-DOF RPM architecture with virtual center-of-motion is presented by aid of the same method. The result provides a useful tool for simplifying the model and extending the application of the RPMs.
Euler angles are commonly used as the orientation representation of most two degrees of freedom (2-DOF) rotational parallel mechanisms (RPMs), as a result, the coupling of two angle parameters leads to complexity of kinematic model of this family of mechanisms. While a simple analytical kinematic model with respect to those parameters representing the geometrical characteristics of the mechanism, is very helpful to improve the performance of RPMs. In this paper, a new geometric kinematic modeling approach based on the concept of instantaneous single-rotation-angle is proposed and used for the 2-DOF RPMs with symmetry in a homo-kinetic plane. To authors’ knowledge, this is a new contribution to parallel mechanisms. By means of this method, the forwards kinematics of 2-DOF RPMs is derived in a simple way, and three cases i.e. 4-4R mechanism (Omni-wrist III), spherical five-bar one, and 3-RSR&1-SS one demonstrate the validity of the proposed geometric method. In addition, a novel 2-DOF RPM architecture with virtual center-of-motion is presented by aid of the same method. The result provides a useful tool for simplifying the model and extending the application of the RPMs.
2012, 26(2).
Abstract:
Dynamically adapt to uneven ground locomotion is a crucial ability for humanoid robots utilized in human environments. However, because of the effect of current pattern generation method, adapting to unknown rough ground is limited. Moreover, to maintain large support region by four-point contact during the landing phase is usually a key problem. In order to solve these problems, a landing phase control and online pattern generation in three dimensional environments is proposed. On the basis of robot-environment non-planar interactive modes, a method of landing control based on optimal support region is put forward to realize stable four-point contact by flexible foot, and a controller is employed to adapt to the changes of ground without using prior knowledge. Furthermore, an adaptable foothold planning is put forward to the online pattern generation considering walking speed, uneven terrain, and the effect of lateral movement to the locomotion stability. Finally, the effectiveness of landing control and online pattern generation is demonstrated by dynamic simulations and real robot walking experiments on outdoor uneven ground. The results indicate that the robot kept its balance even though the ground is unknown and irregular. The proposed methods lay a foundation for studies of humanoid robots performing tasks in complex environments.
Dynamically adapt to uneven ground locomotion is a crucial ability for humanoid robots utilized in human environments. However, because of the effect of current pattern generation method, adapting to unknown rough ground is limited. Moreover, to maintain large support region by four-point contact during the landing phase is usually a key problem. In order to solve these problems, a landing phase control and online pattern generation in three dimensional environments is proposed. On the basis of robot-environment non-planar interactive modes, a method of landing control based on optimal support region is put forward to realize stable four-point contact by flexible foot, and a controller is employed to adapt to the changes of ground without using prior knowledge. Furthermore, an adaptable foothold planning is put forward to the online pattern generation considering walking speed, uneven terrain, and the effect of lateral movement to the locomotion stability. Finally, the effectiveness of landing control and online pattern generation is demonstrated by dynamic simulations and real robot walking experiments on outdoor uneven ground. The results indicate that the robot kept its balance even though the ground is unknown and irregular. The proposed methods lay a foundation for studies of humanoid robots performing tasks in complex environments.
2012, 26(2).
Abstract:
In order to overcome the drawbacks of traditional rehabilitation method, the robot-aided rehabilitation has been widely investigated for the recent years. And the hand rehabilitation robot, as one of the hot research fields, remains many challenging issues to be investigated. This paper presents a new hand exoskeleton system with some novel characteristics. Firstly, both active and passive rehabilitative motions are realized. Secondly, the device is elaborately designed and brings advantages in many aspects. For example, joint motion is accomplished by a parallelogram mechanism and high level motion control is therefore made very simple without the need of complicated kinematics. The adjustable joint limit design ensures that the actual joint angles don’t exceed the joint range of motion (ROM) and thus the patient safety is guaranteed. This design can fit to the different patients with different joint ROM as well as to the dynamically changing ROM for individual patient. The device can also accommodate to some extent variety of hand sizes. Thirdly, the proposed control strategy simultaneously realizes the position control and force control with the motor driver which only works in force control mode. Meanwhile, the system resistance compensation is preliminary realized and the resisting force is effectively reduced. Some experiments were conducted to verify the proposed system. Experimentally collected data show that the achieved ROM is close to that of a healthy hand and the range of phalange length (ROPL) covers the size of a typical hand, satisfying the size need of regular hand rehabilitation. In order to evaluate the performance when it works as a haptic device in active mode, the equivalent moment of inertia (MOI) of the device was calculated. The results prove that the device has low inertia which is critical in order to obtain good backdrivability. The experiments also show that in the active mode the virtual interactive force is successfully feedback to the finger and the resistance is reduced by one-third; for the passive control mode, the desired trajectory is realized satisfactorily.
In order to overcome the drawbacks of traditional rehabilitation method, the robot-aided rehabilitation has been widely investigated for the recent years. And the hand rehabilitation robot, as one of the hot research fields, remains many challenging issues to be investigated. This paper presents a new hand exoskeleton system with some novel characteristics. Firstly, both active and passive rehabilitative motions are realized. Secondly, the device is elaborately designed and brings advantages in many aspects. For example, joint motion is accomplished by a parallelogram mechanism and high level motion control is therefore made very simple without the need of complicated kinematics. The adjustable joint limit design ensures that the actual joint angles don’t exceed the joint range of motion (ROM) and thus the patient safety is guaranteed. This design can fit to the different patients with different joint ROM as well as to the dynamically changing ROM for individual patient. The device can also accommodate to some extent variety of hand sizes. Thirdly, the proposed control strategy simultaneously realizes the position control and force control with the motor driver which only works in force control mode. Meanwhile, the system resistance compensation is preliminary realized and the resisting force is effectively reduced. Some experiments were conducted to verify the proposed system. Experimentally collected data show that the achieved ROM is close to that of a healthy hand and the range of phalange length (ROPL) covers the size of a typical hand, satisfying the size need of regular hand rehabilitation. In order to evaluate the performance when it works as a haptic device in active mode, the equivalent moment of inertia (MOI) of the device was calculated. The results prove that the device has low inertia which is critical in order to obtain good backdrivability. The experiments also show that in the active mode the virtual interactive force is successfully feedback to the finger and the resistance is reduced by one-third; for the passive control mode, the desired trajectory is realized satisfactorily.
2012, 26(2).
Abstract:
Rising concern in environmental issues on global scale has made energy saving in powered equipment a very important subject. In order to improve the energy efficiency and driving range of a motor hoist, a regenerative braking system is designed and discussed. The system takes a unique ultracapacitor-only approach to energy storage system. The bi-directional bride DCDC converter which regulates current flow to and from the ultracapacitor operates in two modes: boost and buck, depending on the direction of the flow. In order to provide constant input and output current at the ultracapacitor, this system uses a double proportional-integral (PI) control strategy in regulating the duty cycle of PWM to the DCDC converter. The permanent magnet synchronous motor (PWSM) drive system is also studied. The space vector pulse width modulation (SVPWM) technique, along with a two-closed-loop vector control model, is adopted after detailed analysis of PMSM characteristics. The overall model and control strategy for this regenerative braking system is ultimately built and simulated under the MATLAB and Simulink environment. A test platform is built to obtain experimental results. Analysis of the results reveals that more than half of the gravitational potential energy can be recovered by this system. Simulation and experimentation results testify the validity of the double PI control strategy for interface circuit of ultracapacitor and SVPWM strategy for PMSM.
Rising concern in environmental issues on global scale has made energy saving in powered equipment a very important subject. In order to improve the energy efficiency and driving range of a motor hoist, a regenerative braking system is designed and discussed. The system takes a unique ultracapacitor-only approach to energy storage system. The bi-directional bride DCDC converter which regulates current flow to and from the ultracapacitor operates in two modes: boost and buck, depending on the direction of the flow. In order to provide constant input and output current at the ultracapacitor, this system uses a double proportional-integral (PI) control strategy in regulating the duty cycle of PWM to the DCDC converter. The permanent magnet synchronous motor (PWSM) drive system is also studied. The space vector pulse width modulation (SVPWM) technique, along with a two-closed-loop vector control model, is adopted after detailed analysis of PMSM characteristics. The overall model and control strategy for this regenerative braking system is ultimately built and simulated under the MATLAB and Simulink environment. A test platform is built to obtain experimental results. Analysis of the results reveals that more than half of the gravitational potential energy can be recovered by this system. Simulation and experimentation results testify the validity of the double PI control strategy for interface circuit of ultracapacitor and SVPWM strategy for PMSM.
2012, 26(2).
Abstract:
Surface lowdistortion is one of the most challenging surface deflections that have a great effect on the exterior appearance of automobiles. Most studies on surface distortiondeflection have focused on evaluation and visualization techniques, the research work on correction or prevention of surface lowdistortion is limited, and there is no perfect surface lowdistortion corrective method that can satisfy the needs of the engineering. A B-spline based geometry morphing algorithm is proposed and then a new program based on UG-NX platform is developed to modify the die face in the surface lowdistortion areas. To verify this developed system, the experimental dies that can replicate the surface lowdistortion phenomenon successfully is put to use. Five geometric variables are introduced to describe the basic geometry of typical depression features of automotive outer panels. The experimental dies are then designed to reflect various combinations of these geometric parameters. The stamping experiments are conducted on cold rolled grade 5(CR5) sheet steel and various static measurements, such as oil-stoning, laser scanner, etc, are performed to measure and record the surface lowdistortions. Three approaches including good bearing, holds in blank and die face morphing that aim to correct lowdistortions are tried out and surface lowdistortions are observed in the specimen with reverse draw depth of 10 mm. The measurement results show that die morphing is a practical and effective method to correct the surface lowdistortion. The correction method proposed can be used to minimize the occurrence of surface lowdistortion in die manufacturing, which has certain reference significance to the correction of surface lowdistortion.
Surface lowdistortion is one of the most challenging surface deflections that have a great effect on the exterior appearance of automobiles. Most studies on surface distortiondeflection have focused on evaluation and visualization techniques, the research work on correction or prevention of surface lowdistortion is limited, and there is no perfect surface lowdistortion corrective method that can satisfy the needs of the engineering. A B-spline based geometry morphing algorithm is proposed and then a new program based on UG-NX platform is developed to modify the die face in the surface lowdistortion areas. To verify this developed system, the experimental dies that can replicate the surface lowdistortion phenomenon successfully is put to use. Five geometric variables are introduced to describe the basic geometry of typical depression features of automotive outer panels. The experimental dies are then designed to reflect various combinations of these geometric parameters. The stamping experiments are conducted on cold rolled grade 5(CR5) sheet steel and various static measurements, such as oil-stoning, laser scanner, etc, are performed to measure and record the surface lowdistortions. Three approaches including good bearing, holds in blank and die face morphing that aim to correct lowdistortions are tried out and surface lowdistortions are observed in the specimen with reverse draw depth of 10 mm. The measurement results show that die morphing is a practical and effective method to correct the surface lowdistortion. The correction method proposed can be used to minimize the occurrence of surface lowdistortion in die manufacturing, which has certain reference significance to the correction of surface lowdistortion.
2012, 26(2).
Abstract:
Beveloid gears, also known as conical gears, gain more and more importance in industry practice due to their abilities for power transmission between parallel, intersected and crossed axis. However, this type of gearing with crossed axes has no common plane of action which results in a point contact and low tooth durability. Therefore, a geometry design approach assuming line contact is developed to analyze the tooth engagement process of crossed beveloid gears with small shaft angle for marine transmission applications. The loaded gear tooth contact behavior is simulated by applying a quasi-static analysis to study the effects of gearing parameters on mesh characteristics. Using the proposed method, a series of sensitivity analyses to examine the effects of critical gearing parameters such as shaft angle, cone angle, helix angle and profile-shift coefficient on the theoretical gear mesh is performed. The parametric analysis of pitch cone design shows that the dominant design parameters represented by the angle between the first principle directions (FPD) and normal angular factor are more sensitive to the shaft and cone angles than they are to the helix angle. The theoretical contact path is highly sensitive to the profile-shift coefficient, which is determined from the theoretical tooth contact analysis. The FPD angle is found to change the distribution of contact pattern, contact pressure and root stress as well as the translational transmission error and the variation of the mesh stiffness significantly. The contact pattern is clearly different between the drive and coast sides due to different designed FPD angles. Finally, a practical experimental setup for marine transmission is performed and tooth bearing test is conducted to demonstrate the proposed design procedure. The experimental result compared well with the simulation. Results of this study yield a better understanding of the geometry design and loaded gear mesh characteristics for crossed beveloid gears used in marine transmission.
Beveloid gears, also known as conical gears, gain more and more importance in industry practice due to their abilities for power transmission between parallel, intersected and crossed axis. However, this type of gearing with crossed axes has no common plane of action which results in a point contact and low tooth durability. Therefore, a geometry design approach assuming line contact is developed to analyze the tooth engagement process of crossed beveloid gears with small shaft angle for marine transmission applications. The loaded gear tooth contact behavior is simulated by applying a quasi-static analysis to study the effects of gearing parameters on mesh characteristics. Using the proposed method, a series of sensitivity analyses to examine the effects of critical gearing parameters such as shaft angle, cone angle, helix angle and profile-shift coefficient on the theoretical gear mesh is performed. The parametric analysis of pitch cone design shows that the dominant design parameters represented by the angle between the first principle directions (FPD) and normal angular factor are more sensitive to the shaft and cone angles than they are to the helix angle. The theoretical contact path is highly sensitive to the profile-shift coefficient, which is determined from the theoretical tooth contact analysis. The FPD angle is found to change the distribution of contact pattern, contact pressure and root stress as well as the translational transmission error and the variation of the mesh stiffness significantly. The contact pattern is clearly different between the drive and coast sides due to different designed FPD angles. Finally, a practical experimental setup for marine transmission is performed and tooth bearing test is conducted to demonstrate the proposed design procedure. The experimental result compared well with the simulation. Results of this study yield a better understanding of the geometry design and loaded gear mesh characteristics for crossed beveloid gears used in marine transmission.
2012, 26(2).
Abstract:
With the rapid development of engineering component with integration, high-speed and multi-parameter, traditional techniques haven’t met practical needs in extreme service environment. Laser welding, a new welding technology, has been widely used. However, it would generate the drop of mechanical properties for laser welded joint due to its thermal effect. Laser shock processing (LSP) is one of the most effective methods to improve the mechanical properties of laser welded ANSI 304 stainless steel joint. In this paper, the effects of LSP on the mechanical properties of laser welded ANSI 304 stainless steel joint have been investigated. The welded joint on the front of the tensile samples is treated by LSP impacts, and the overlapping rate of the laser spot is 50%. The tensile test of the laser welded joint with and without LSP impacts is carried out, and the fracture morphology of the tensile samples is analyzed by scanning electron microscope (SEM). Compared with the yield strength of 11.70 kN, the tensile strength of 37.66 kN, the yield-to-tensile strength ratio of 0.310 7, the elongation of 25.20%, the area reduction of 32.68% and the elastic modulus of 13 063.876 MPa, the corresponding values after LSP impacts are 14.25 kN, 38.74 kN, 0.367 8, 26.58%, 42.29% and 14 754.394 MPa, respectively. Through LSP impacts, the increasing ratio of the yield strength and tensile strength are 121.79% and 102.87%, respectively; the elongation and area reduction are improved by 5.48% and 29.38%, respectively. By comparing with coarse fracture surface of the welded joint, the delamination splitting with some cracks in the sharp corner of the welded joint and asymmetric dimples, LSP can cause brighter fracture surface, and finer and more uniform dimples. Finally, the schematic illustration of dimple formation with LSP is clearly described. The proposed research ensures that the LSP technology can clearly improve the yield strength, tensile strength, yield-to-tensile strength ratio, elongation, area reduction and elastic modulus of the welded joint. The enhancement mechanism of LSP on laser welded ANSI 304 stainless steel joint is mainly due to the fact that the refined and uniform dimples effectively delay the fracture of laser welded joints.
With the rapid development of engineering component with integration, high-speed and multi-parameter, traditional techniques haven’t met practical needs in extreme service environment. Laser welding, a new welding technology, has been widely used. However, it would generate the drop of mechanical properties for laser welded joint due to its thermal effect. Laser shock processing (LSP) is one of the most effective methods to improve the mechanical properties of laser welded ANSI 304 stainless steel joint. In this paper, the effects of LSP on the mechanical properties of laser welded ANSI 304 stainless steel joint have been investigated. The welded joint on the front of the tensile samples is treated by LSP impacts, and the overlapping rate of the laser spot is 50%. The tensile test of the laser welded joint with and without LSP impacts is carried out, and the fracture morphology of the tensile samples is analyzed by scanning electron microscope (SEM). Compared with the yield strength of 11.70 kN, the tensile strength of 37.66 kN, the yield-to-tensile strength ratio of 0.310 7, the elongation of 25.20%, the area reduction of 32.68% and the elastic modulus of 13 063.876 MPa, the corresponding values after LSP impacts are 14.25 kN, 38.74 kN, 0.367 8, 26.58%, 42.29% and 14 754.394 MPa, respectively. Through LSP impacts, the increasing ratio of the yield strength and tensile strength are 121.79% and 102.87%, respectively; the elongation and area reduction are improved by 5.48% and 29.38%, respectively. By comparing with coarse fracture surface of the welded joint, the delamination splitting with some cracks in the sharp corner of the welded joint and asymmetric dimples, LSP can cause brighter fracture surface, and finer and more uniform dimples. Finally, the schematic illustration of dimple formation with LSP is clearly described. The proposed research ensures that the LSP technology can clearly improve the yield strength, tensile strength, yield-to-tensile strength ratio, elongation, area reduction and elastic modulus of the welded joint. The enhancement mechanism of LSP on laser welded ANSI 304 stainless steel joint is mainly due to the fact that the refined and uniform dimples effectively delay the fracture of laser welded joints.
2012, 26(2).
Abstract:
Prognosis is a key technology to improve reliability, safety and maintainability of products, a lot of researchers have been devoted to this technology. But to improve the predict accuracy of remaining life of products has been difficult. To predict the lifetime specification of pneumatic cylinders with high reliability and long lifetime and small specimen, this paper put forward the prognosis algorithm based on the path classification and estimation (PACE) model. PACE model is based entirely on failure data instead of failure threshold. Pneumatic cylinders normally characterize with failure mechanism wear and tear. Since the minimum working pressure increases with the number of working cycles, the minimum working pressure is chosen as degradation signal. PACE model is fundamentally composed of two operations: path classification and remaining useful life (RUL) estimation. Path classification is to classify a current degradation path as belonging to one or more of previously collected exemplary degradation paths. RUL estimation is to use the resulting memberships to estimate the remaining useful life. In order for verification and validation of PACE prognostic method, six pneumatic cylinders are tested. The test data is analyzed by PACE prognostics. It is found that the PACE based prognosis method has higher prediction accuracy and smaller variance and PACE model is significantly outperform population based prognostics especially for small specimen condition. PACE model based method solved the problem of prediction accuracy for small specimen pneumatic cylinders’ prognosis.
Prognosis is a key technology to improve reliability, safety and maintainability of products, a lot of researchers have been devoted to this technology. But to improve the predict accuracy of remaining life of products has been difficult. To predict the lifetime specification of pneumatic cylinders with high reliability and long lifetime and small specimen, this paper put forward the prognosis algorithm based on the path classification and estimation (PACE) model. PACE model is based entirely on failure data instead of failure threshold. Pneumatic cylinders normally characterize with failure mechanism wear and tear. Since the minimum working pressure increases with the number of working cycles, the minimum working pressure is chosen as degradation signal. PACE model is fundamentally composed of two operations: path classification and remaining useful life (RUL) estimation. Path classification is to classify a current degradation path as belonging to one or more of previously collected exemplary degradation paths. RUL estimation is to use the resulting memberships to estimate the remaining useful life. In order for verification and validation of PACE prognostic method, six pneumatic cylinders are tested. The test data is analyzed by PACE prognostics. It is found that the PACE based prognosis method has higher prediction accuracy and smaller variance and PACE model is significantly outperform population based prognostics especially for small specimen condition. PACE model based method solved the problem of prediction accuracy for small specimen pneumatic cylinders’ prognosis.
2012, 26(2).
Abstract:
Multi-sensor vision system plays an important role in the 3D measurement of large objects. However, due to the widely distribution of sensors, the problem of lacking common fields of view (FOV) arises frequently, which makes the global calibration of the vision system quite difficult. The primary existing solution relies on large-scale surveying equipments, which is ponderous and inconvenient for field calibrations. In this paper, a global calibration method of multi-sensor vision system is proposed and investigated. The proposed method utilizes pairs of skew laser lines, which are generated by a group of laser pointers, as the calibration objects. Each pair of skew laser lines provides a unique coordinate system in space which can be reconstructed in certain vision sensor’s coordinates by using a planar pattern. Then the geometries of sensors are computed under rigid transformation constrains by taking coordinates of each skew lines pair as the intermediary. The method is applied on both visual cameras with synthetic data and a real two-camera vision system; results show the validity and good performance. The prime contribution of this paper is taking skew laser lines as the global calibration objects, which makes the method simple and flexible. The method need no expensive equipments and can be used in large-scale calibration.
Multi-sensor vision system plays an important role in the 3D measurement of large objects. However, due to the widely distribution of sensors, the problem of lacking common fields of view (FOV) arises frequently, which makes the global calibration of the vision system quite difficult. The primary existing solution relies on large-scale surveying equipments, which is ponderous and inconvenient for field calibrations. In this paper, a global calibration method of multi-sensor vision system is proposed and investigated. The proposed method utilizes pairs of skew laser lines, which are generated by a group of laser pointers, as the calibration objects. Each pair of skew laser lines provides a unique coordinate system in space which can be reconstructed in certain vision sensor’s coordinates by using a planar pattern. Then the geometries of sensors are computed under rigid transformation constrains by taking coordinates of each skew lines pair as the intermediary. The method is applied on both visual cameras with synthetic data and a real two-camera vision system; results show the validity and good performance. The prime contribution of this paper is taking skew laser lines as the global calibration objects, which makes the method simple and flexible. The method need no expensive equipments and can be used in large-scale calibration.
2012, 26(2).
Abstract:
Paris law can reflect the failure mechanism of materials and is usually used to be a method to predict fatigue life or residual fatigue life. But the variable which can represent the health of machine is hardly measured on line. To a degree, the difficulty of on-line application restricts the scope of application of Paris law. The relationship between characteristic values of vibration signals and the variable in the Paris equation which can describe the health of machine is investigated by taking ball bearings as investigative objects. Based on 6205 deep groove ball bearings as a living example, historical lives and vibration signals are analyzed. The feasibility of describing that variable in the Paris equation by the characteristic value of vibration signals is inspected. After that vibration signals decomposed by empirical mode decomposition(EMD), root mean square(RMS) of intrinsic mode function(IMF) involving fault characteristic frequency has a consistent trend with the diameter of flaws. Based on the trend, two improved Paris models are proposed and the scope of application of them is inspected. These two Paris Models are validated by fatigue residual life data from tests of rolling element bearings and vibration signals monitored in the process of operation of rolling element bearings. It shows that the first improved Paris Model is simple and plain and it can be easily applied in actual conditions. The trend of the fatigue residual life predicted by the second improved Paris model is close to the actual conditions and the result of the prediction is slightly greater than the truth. In conclusion, after the appearance of detectable faults, these improved models based on RMS can predict residual fatigue life on line and a new approach to predict residual fatigue life of ball bearings on line without disturbing the machine running is provided.
Paris law can reflect the failure mechanism of materials and is usually used to be a method to predict fatigue life or residual fatigue life. But the variable which can represent the health of machine is hardly measured on line. To a degree, the difficulty of on-line application restricts the scope of application of Paris law. The relationship between characteristic values of vibration signals and the variable in the Paris equation which can describe the health of machine is investigated by taking ball bearings as investigative objects. Based on 6205 deep groove ball bearings as a living example, historical lives and vibration signals are analyzed. The feasibility of describing that variable in the Paris equation by the characteristic value of vibration signals is inspected. After that vibration signals decomposed by empirical mode decomposition(EMD), root mean square(RMS) of intrinsic mode function(IMF) involving fault characteristic frequency has a consistent trend with the diameter of flaws. Based on the trend, two improved Paris models are proposed and the scope of application of them is inspected. These two Paris Models are validated by fatigue residual life data from tests of rolling element bearings and vibration signals monitored in the process of operation of rolling element bearings. It shows that the first improved Paris Model is simple and plain and it can be easily applied in actual conditions. The trend of the fatigue residual life predicted by the second improved Paris model is close to the actual conditions and the result of the prediction is slightly greater than the truth. In conclusion, after the appearance of detectable faults, these improved models based on RMS can predict residual fatigue life on line and a new approach to predict residual fatigue life of ball bearings on line without disturbing the machine running is provided.
2012, 26(2).
Abstract:
In order to improve the fuel consumption and exhaust emission for gasoline engines, gasoline direct injection (GDI) system is spotlighted to solve these requirements. Thus, many researchers focus on the investigation of spray characteristics and the fuel formation of GDI injector. This paper presents a complete numerical and experimental characterization of transient gasoline spray from a high pressure injection system equipped with a modern single-hole electric controlled injector in a pressurized constant volume vessel. The numerical analysis is carried out in a one-dimensional model of fuel injection system which is developed in the AVL HYDSIM environment. The experimental analyses are implemented through a self-developed injection rate measurement device and spray evolution visualization system. The experimental results of injection rate and spray dynamics are taken to tune and validate the built model. The visualization system synchronize a high speed CMOS camera to obtain the spray structure, moreover, the captured images are taken to validate the injector needle lift process which is simulated in the model. The reliability of the built model is demonstrated by comparing the numerical results with the experimental data. The formed vortex structure at 0.8 ms is effectively disintegrated at 6.2 ms and the spray dynamics become rather chaotic. The fuel flow characteristics within injector nozzle extremely influence the subsequent spray evolution, and therefore this point should be reconsidered when building hybrid breakup GDI spray model. The spray tip speed reach the maximum at 1.18 ms regardless of the operation conditions and this is only determined by the injector itself. Furthermore, an empirical equation for the spray tip penetration is obtained and good agreement with the measured results is reached at a certain extent. This paper provides a methodology for the investigation of spray behavior and fuel distribution of GDI engine design.
In order to improve the fuel consumption and exhaust emission for gasoline engines, gasoline direct injection (GDI) system is spotlighted to solve these requirements. Thus, many researchers focus on the investigation of spray characteristics and the fuel formation of GDI injector. This paper presents a complete numerical and experimental characterization of transient gasoline spray from a high pressure injection system equipped with a modern single-hole electric controlled injector in a pressurized constant volume vessel. The numerical analysis is carried out in a one-dimensional model of fuel injection system which is developed in the AVL HYDSIM environment. The experimental analyses are implemented through a self-developed injection rate measurement device and spray evolution visualization system. The experimental results of injection rate and spray dynamics are taken to tune and validate the built model. The visualization system synchronize a high speed CMOS camera to obtain the spray structure, moreover, the captured images are taken to validate the injector needle lift process which is simulated in the model. The reliability of the built model is demonstrated by comparing the numerical results with the experimental data. The formed vortex structure at 0.8 ms is effectively disintegrated at 6.2 ms and the spray dynamics become rather chaotic. The fuel flow characteristics within injector nozzle extremely influence the subsequent spray evolution, and therefore this point should be reconsidered when building hybrid breakup GDI spray model. The spray tip speed reach the maximum at 1.18 ms regardless of the operation conditions and this is only determined by the injector itself. Furthermore, an empirical equation for the spray tip penetration is obtained and good agreement with the measured results is reached at a certain extent. This paper provides a methodology for the investigation of spray behavior and fuel distribution of GDI engine design.
2012, 26(2).
Abstract:
Fatigue life and reliability of aero-engine blade are always of important significance to flight safety. The establishment of damage model is one of the key factors in blade fatigue research. Conventional linear Miner’s sum method is not suitable for aero-engine because of its low accuracy. A back propagation neutral network (BPNN) based on the combination of Levenberg-Marquardt (LM) and finite element method (FEM) is used to describe process of nonlinear damage accumulation behavior in material and predict fatigue life of the blade. Fatigue tests of standard specimen made from TC4 are carried out to obtain material fatigue parameters and S-N curve. A nonlinear continuum damage model (CDM), based on the BPNN with one hidden layer and ten neurons, is built to investigate the nonlinear damage accumulation behavior, in which the results from the tests are used as training set. Comparing with linear models and previous nonlinear models, BPNN has the lowest calculation error in full load range. It has significant accuracy when the load is below 500 MPa. Especially, when the load is 350 MPa, the calculation error of the BPNN is only 0.4%. The accurate model of the blade is built by using 3D coordinate measurement technology. The loading cycle in fatigue analysis is defined from takeoff to cruise in 10 min, and the load history is obtained from finite element analysis (FEA). Then the fatigue life of the compressor blade is predicted by using the BPNN model. The final fatigue life of the aero-engine blade is 6.55 104 cycles (10 916 h) based on the BPNN model, which is effective for the virtual design of aero-engine blade.
Fatigue life and reliability of aero-engine blade are always of important significance to flight safety. The establishment of damage model is one of the key factors in blade fatigue research. Conventional linear Miner’s sum method is not suitable for aero-engine because of its low accuracy. A back propagation neutral network (BPNN) based on the combination of Levenberg-Marquardt (LM) and finite element method (FEM) is used to describe process of nonlinear damage accumulation behavior in material and predict fatigue life of the blade. Fatigue tests of standard specimen made from TC4 are carried out to obtain material fatigue parameters and S-N curve. A nonlinear continuum damage model (CDM), based on the BPNN with one hidden layer and ten neurons, is built to investigate the nonlinear damage accumulation behavior, in which the results from the tests are used as training set. Comparing with linear models and previous nonlinear models, BPNN has the lowest calculation error in full load range. It has significant accuracy when the load is below 500 MPa. Especially, when the load is 350 MPa, the calculation error of the BPNN is only 0.4%. The accurate model of the blade is built by using 3D coordinate measurement technology. The loading cycle in fatigue analysis is defined from takeoff to cruise in 10 min, and the load history is obtained from finite element analysis (FEA). Then the fatigue life of the compressor blade is predicted by using the BPNN model. The final fatigue life of the aero-engine blade is 6.55 104 cycles (10 916 h) based on the BPNN model, which is effective for the virtual design of aero-engine blade.
2012, 26(2).
Abstract:
Heavy-payload forging manipulators are mainly characterized by large load output and large capacitive-load input. The relationship between outputs and inputs, which will greatly influence the control and the reliability, is the key issue in type design for heavy-payload forging manipulators. In this paper, a type design method by considering the incidence relationship between output characteristics and actuator inputs is presented and used to design the mechanism for forging manipulators. The concept of modeling method based on the outputs tasks is defined and investigated. The principle of type design from the viewpoints of the relationship between output characteristics and actuator inputs is discussed. An idea of establishing the incidence relationship between output characteristics and actuator inputs is proposed. The incidence relationship matrix between outputs and inputs is also given. The design flow is obtained, and the incidence relationship between outputs and inputs for heavy-payload forging manipulators is divided into three parts after detailed understanding of the functional properties. Four types of mechanisms for heavy-payload forging manipulators are given, and the corresponding spatial mechanical sketches are also drawn, some new designed mechanisms have been adopted by company or used as prototype. These novel forging manipulators which satisfy certain functional requirements provide an effective help for the design of forging manipulators and patent application.
Heavy-payload forging manipulators are mainly characterized by large load output and large capacitive-load input. The relationship between outputs and inputs, which will greatly influence the control and the reliability, is the key issue in type design for heavy-payload forging manipulators. In this paper, a type design method by considering the incidence relationship between output characteristics and actuator inputs is presented and used to design the mechanism for forging manipulators. The concept of modeling method based on the outputs tasks is defined and investigated. The principle of type design from the viewpoints of the relationship between output characteristics and actuator inputs is discussed. An idea of establishing the incidence relationship between output characteristics and actuator inputs is proposed. The incidence relationship matrix between outputs and inputs is also given. The design flow is obtained, and the incidence relationship between outputs and inputs for heavy-payload forging manipulators is divided into three parts after detailed understanding of the functional properties. Four types of mechanisms for heavy-payload forging manipulators are given, and the corresponding spatial mechanical sketches are also drawn, some new designed mechanisms have been adopted by company or used as prototype. These novel forging manipulators which satisfy certain functional requirements provide an effective help for the design of forging manipulators and patent application.
2012, 26(2).
Abstract:
Cylinder pressure fluctuation during combustion process of internal combustion engine is closely related to combustion noise and knock. The current studies are based on cylinder pressure test to obtain information on combustion noise and knock, but there is little for simulation of combustion pressure fluctuation. Based on effects of combustion process in the combustion chamber on cylinder pressure by using wave equation, the mechanism of pressure fluctuation during combustion is researched with three-dimensional acoustic wave equation and flow field model of KIVA program. The cylinder pressure fluctuation curve, temperature field and acoustic field are obtained from the coupled calculation of the wave equation and KIVA program. The frequency spectrum analysis is taken with the cylinder pressure oscillation of cylinder pressure measured and calculated. The calculation result is consistent with the experimental result. This indicates that the cylinder pressure fluctuation can be correctly calculated with the wave equation. Analysis of calculation results of temperature field and acoustic field shows that sound field changes faster than flame propagates, and distribution of sound field is more complicated. Combustion pressure oscillation in the diesel engine is under highly unstable condition. This indicates that the combination of cylinder pressure fluctuation model and combustion model is an effective method to study the pressure oscillations and a new method to study the combustion noise and knock.
Cylinder pressure fluctuation during combustion process of internal combustion engine is closely related to combustion noise and knock. The current studies are based on cylinder pressure test to obtain information on combustion noise and knock, but there is little for simulation of combustion pressure fluctuation. Based on effects of combustion process in the combustion chamber on cylinder pressure by using wave equation, the mechanism of pressure fluctuation during combustion is researched with three-dimensional acoustic wave equation and flow field model of KIVA program. The cylinder pressure fluctuation curve, temperature field and acoustic field are obtained from the coupled calculation of the wave equation and KIVA program. The frequency spectrum analysis is taken with the cylinder pressure oscillation of cylinder pressure measured and calculated. The calculation result is consistent with the experimental result. This indicates that the cylinder pressure fluctuation can be correctly calculated with the wave equation. Analysis of calculation results of temperature field and acoustic field shows that sound field changes faster than flame propagates, and distribution of sound field is more complicated. Combustion pressure oscillation in the diesel engine is under highly unstable condition. This indicates that the combination of cylinder pressure fluctuation model and combustion model is an effective method to study the pressure oscillations and a new method to study the combustion noise and knock.
2012, 26(2).
Abstract:
Arc sound is well known as the potential and available resource for monitoring and controlling of the weld penetration status, which is very important to the welding process quality control, so any attentions have been paid to the relationships between the arc sound and welding parameters. Some non-linear mapping models correlating the arc sound to welding parameters have been established with the help of neural networks. However, the research of utilizing arc sound to monitor and diagnose welding process is still in its infancy. A self-made real-time sensing system is applied to make a study of arc sound under typical penetration status, including partial penetration, unstable penetration, full penetration and excessive penetration, in metal inert-gas (MIG) flat tailored welding with spray transfer. Arc sound is pretreated by using wavelet de-noising and short-time windowing technologies, and its characteristics, characterizing weld penetration status, of time-domain, frequency-domain, cepstrum-domain and geometric-domain are extracted. Subsequently, high-dimensional eigenvector is constructed and feature-level parameters are successfully fused utilizing the concept of primary principal component analysis (PCA). Ultimately, 60-demensional eigenvector is replaced by the synthesis of 8-demensional vector, which achieves compression for feature space and provides technical supports for pattern classification of typical penetration status with the help of arc sound in MIG welding in the future.
Arc sound is well known as the potential and available resource for monitoring and controlling of the weld penetration status, which is very important to the welding process quality control, so any attentions have been paid to the relationships between the arc sound and welding parameters. Some non-linear mapping models correlating the arc sound to welding parameters have been established with the help of neural networks. However, the research of utilizing arc sound to monitor and diagnose welding process is still in its infancy. A self-made real-time sensing system is applied to make a study of arc sound under typical penetration status, including partial penetration, unstable penetration, full penetration and excessive penetration, in metal inert-gas (MIG) flat tailored welding with spray transfer. Arc sound is pretreated by using wavelet de-noising and short-time windowing technologies, and its characteristics, characterizing weld penetration status, of time-domain, frequency-domain, cepstrum-domain and geometric-domain are extracted. Subsequently, high-dimensional eigenvector is constructed and feature-level parameters are successfully fused utilizing the concept of primary principal component analysis (PCA). Ultimately, 60-demensional eigenvector is replaced by the synthesis of 8-demensional vector, which achieves compression for feature space and provides technical supports for pattern classification of typical penetration status with the help of arc sound in MIG welding in the future.
2012, 26(2).
Abstract:
The β-FeSi2 thin film has been applied in the research field of the solar cell, and the thickness of β-FeSi2 absorption layer was chosen through the experiments. However, Up to now neither the optimal thickness of β-FeSi2 absorption layer nor the relationship between the thickness of β-FeSi2 absorption layer and the solar photo wavelength has been theoretically studied. In this paper, the relationship between the thickness of the absorption layer of β-FeSi2 thin film solar cell and the solar photo wavelength is calculated and analyzed by theory. The results show that the thickness of the absorption layer of β-FeSi2 is at least 200 nm when the optical absorption efficiency of the solar energy reaches 90%, and that the optimal thickness range is from 200 nm to 250 nm, and that the optimal wavelength of the photon absorbed by β-FeSi2 thin film solar cell is from 0.46 μm0.6 μm. Furthermore, two formulas are put forward to indicate the relationship between the thickness of the absorption layer of β-FeSi2 thin film solar cell and the solar photo wavelength. The thickness of the absorption layer of β-FeSi2 thin film solar cell increases linearly with the solar photo wavelength within the optimal photo wavelength. The formulas provide a reliable theoretical basis of determining the thickness of the β-FeSi2 thin film in the solar cell.
The β-FeSi2 thin film has been applied in the research field of the solar cell, and the thickness of β-FeSi2 absorption layer was chosen through the experiments. However, Up to now neither the optimal thickness of β-FeSi2 absorption layer nor the relationship between the thickness of β-FeSi2 absorption layer and the solar photo wavelength has been theoretically studied. In this paper, the relationship between the thickness of the absorption layer of β-FeSi2 thin film solar cell and the solar photo wavelength is calculated and analyzed by theory. The results show that the thickness of the absorption layer of β-FeSi2 is at least 200 nm when the optical absorption efficiency of the solar energy reaches 90%, and that the optimal thickness range is from 200 nm to 250 nm, and that the optimal wavelength of the photon absorbed by β-FeSi2 thin film solar cell is from 0.46 μm0.6 μm. Furthermore, two formulas are put forward to indicate the relationship between the thickness of the absorption layer of β-FeSi2 thin film solar cell and the solar photo wavelength. The thickness of the absorption layer of β-FeSi2 thin film solar cell increases linearly with the solar photo wavelength within the optimal photo wavelength. The formulas provide a reliable theoretical basis of determining the thickness of the β-FeSi2 thin film in the solar cell.
2012, 26(2).
Abstract:
The motional payloads on stabilized platform must be linked by some cable harnesses with other immobile apparatus. During the operation of stabilized platform, these cable harnesses can create spring disturbance torque which is exerted on the stabilized platform and then reduce the stabilizing precision. None of current studies can deal with the spring disturbance torque problem. To analyze the spring disturbance toque, a dynamic thin rod model is presented for simulating the motional cable harness which is based on the Kirchhoff rod theorem and can consider the geometrically non-linear effects. The internal bending and torsion restoring torques are simulated and then a predictive analysis of the disturbance torque can be performed in motional cable routing design. This model is solved with differential quadrature method (DQM). By using zeros of the Chebyshev polynomial as the grid points, the arc-coordinate is discretized to obtain a set of ordinary differential equations in time domain which is solved by implied method to obtain the profile and internal force of cable harness. The accuracy of this model is validated by comparing the simulation results and the experiment results (both the spring force and the deformed profile of the motional cable harness). In the experiment, a special optical measuring instrument based on binocular vision is developed. The comparison of experimental and simulated results shows that the simulation model can represent the real motional cable harness well, and the spring disturbance force simulation results are precise enough for spring disturbance torque analysis. This study will be helpful to obtain an optimized motional cable harness layout design with small spring disturbance torque.
The motional payloads on stabilized platform must be linked by some cable harnesses with other immobile apparatus. During the operation of stabilized platform, these cable harnesses can create spring disturbance torque which is exerted on the stabilized platform and then reduce the stabilizing precision. None of current studies can deal with the spring disturbance torque problem. To analyze the spring disturbance toque, a dynamic thin rod model is presented for simulating the motional cable harness which is based on the Kirchhoff rod theorem and can consider the geometrically non-linear effects. The internal bending and torsion restoring torques are simulated and then a predictive analysis of the disturbance torque can be performed in motional cable routing design. This model is solved with differential quadrature method (DQM). By using zeros of the Chebyshev polynomial as the grid points, the arc-coordinate is discretized to obtain a set of ordinary differential equations in time domain which is solved by implied method to obtain the profile and internal force of cable harness. The accuracy of this model is validated by comparing the simulation results and the experiment results (both the spring force and the deformed profile of the motional cable harness). In the experiment, a special optical measuring instrument based on binocular vision is developed. The comparison of experimental and simulated results shows that the simulation model can represent the real motional cable harness well, and the spring disturbance force simulation results are precise enough for spring disturbance torque analysis. This study will be helpful to obtain an optimized motional cable harness layout design with small spring disturbance torque.
2012, 26(2).
Abstract:
Coupled-plate structures are widely used in the practical engineering such as aeronautical, civil and naval engineering etc. Limited works can be found on the vibration of the coupled-plate structure due to the increased mathematical complexity compared with the single plate structure. In order to study analytically the vibration characteristics and power transmission of the coupled-plate structure, an analytical model consisting of three coupled plates elastically restrained along boundary edges and elastically coupled with arbitrary angle is considered, in which four groups of springs are distributed consistently along each edge of the model to simulate the transverse shearing forces, bending moments, in-plane longitudinal forces and in-plane shearing forces separately. With elastic coupling condition and general boundary condition of both flexural and in-plane vibrations taken into account by setting the stiffness of corresponding springs, the double Fourier series solution to the dynamic response of the structure was obtained by employing the Rayleigh-Ritz method. In order to validate the model, the natural frequency and velocity response of the model are firstly checked against results published in literatures and the ANSYS data, and good agreement was observed. Then, numerical simulation of the effects of several relevant parameters on the vibration characteristics and power transmission of the coupled structure were performed, including boundary conditions, coupling conditions, coupling angle, and location of the external forces. Vibration and energy transmission behaviors were analyzed numerically. The results show that the power transmission can be significantly influenced by the boundary restraints and the location of excitation. When the excitation is located at the central symmetry point of the model, the energy flow shows a symmetrical distribution. Once the location deviates from the central symmetry point, the power circumfluence occurs and the vortex energy field is formed at high frequency.
Coupled-plate structures are widely used in the practical engineering such as aeronautical, civil and naval engineering etc. Limited works can be found on the vibration of the coupled-plate structure due to the increased mathematical complexity compared with the single plate structure. In order to study analytically the vibration characteristics and power transmission of the coupled-plate structure, an analytical model consisting of three coupled plates elastically restrained along boundary edges and elastically coupled with arbitrary angle is considered, in which four groups of springs are distributed consistently along each edge of the model to simulate the transverse shearing forces, bending moments, in-plane longitudinal forces and in-plane shearing forces separately. With elastic coupling condition and general boundary condition of both flexural and in-plane vibrations taken into account by setting the stiffness of corresponding springs, the double Fourier series solution to the dynamic response of the structure was obtained by employing the Rayleigh-Ritz method. In order to validate the model, the natural frequency and velocity response of the model are firstly checked against results published in literatures and the ANSYS data, and good agreement was observed. Then, numerical simulation of the effects of several relevant parameters on the vibration characteristics and power transmission of the coupled structure were performed, including boundary conditions, coupling conditions, coupling angle, and location of the external forces. Vibration and energy transmission behaviors were analyzed numerically. The results show that the power transmission can be significantly influenced by the boundary restraints and the location of excitation. When the excitation is located at the central symmetry point of the model, the energy flow shows a symmetrical distribution. Once the location deviates from the central symmetry point, the power circumfluence occurs and the vortex energy field is formed at high frequency.
2012, 26(2).
Abstract:
Conical spiral tube bundle are universally used in heat transfer enhancement in heat exchangers. The heat transfer and resistance of the tube bundle are affected greatly by the conical structure, so the analysis of it is necessary. In order to a further evaluation, the heat transfer and resistance characteristics of conical spiral tube bundle are investigated with regression analysis based on numerical simulation data. The correlations of heat transfer and pressure drop of conical spiral tube bundle are proposed both in laminar and turbulent fluid flow. On the based of the field synergy principle, the synergy of four vectors, the velocity, the velocity gradient, the temperature gradient and the pressure gradient, are calculated and discussed via the user defined function (UDF) program. The synergy angles β and θ, which respectively denote the performance of heat transfer enhancement and pressure drop of the conical spiral tube bundle, are analyzed. Finally, the comprehensive performance of the conical spiral tube is evaluated by the synergy angle γ and all of the three synergy angles of conical spiral tube bundle are compared to both bare tube and thin cylinder-interpolated tube. The analysis of the synergy angles shows that the heat transfer enhancement and pressure drop of conical spiral tube bundle are smaller than that of the thin cylinder-interpolated tube, while the comprehensive performance of conical spiral tube bundle is greater. The analysis of the heat transfer and pressure drop of conical spiral tube is valuable and instructional on the design and optimum of conical spiral tube bundle heat exchangers.
Conical spiral tube bundle are universally used in heat transfer enhancement in heat exchangers. The heat transfer and resistance of the tube bundle are affected greatly by the conical structure, so the analysis of it is necessary. In order to a further evaluation, the heat transfer and resistance characteristics of conical spiral tube bundle are investigated with regression analysis based on numerical simulation data. The correlations of heat transfer and pressure drop of conical spiral tube bundle are proposed both in laminar and turbulent fluid flow. On the based of the field synergy principle, the synergy of four vectors, the velocity, the velocity gradient, the temperature gradient and the pressure gradient, are calculated and discussed via the user defined function (UDF) program. The synergy angles β and θ, which respectively denote the performance of heat transfer enhancement and pressure drop of the conical spiral tube bundle, are analyzed. Finally, the comprehensive performance of the conical spiral tube is evaluated by the synergy angle γ and all of the three synergy angles of conical spiral tube bundle are compared to both bare tube and thin cylinder-interpolated tube. The analysis of the synergy angles shows that the heat transfer enhancement and pressure drop of conical spiral tube bundle are smaller than that of the thin cylinder-interpolated tube, while the comprehensive performance of conical spiral tube bundle is greater. The analysis of the heat transfer and pressure drop of conical spiral tube is valuable and instructional on the design and optimum of conical spiral tube bundle heat exchangers.
2012, 26(2).
Abstract:
As an essential component of a servo system, mechanical properties of high precision planetary servo gearhead direct influence on the validation, stability and accuracy of the servo control system. However, mechanical properties measurement and assessment for high precision planetary servo gearhead is a time-consuming and tedious work, since current methodologies typically rely on various different specified systems. An integrated multifunctional measurement system SFJC-I is developed, which employs a torque sensor and a laser displacement transducer to simultaneously measure torque applied on servo gearhead and its corresponding torsional deformation. The measurement system depends on the accurate measurement of the relative displacement between input clamping system and output shaft of servo gearhead with a lever-type enlarging mechanism, rather than traditional optical dividing head and optical multisurface prism. Using interchangeable fixture system, the developed system capability to measure almost all series and specifications of high precision planetary servo gearhead is demonstrated. With proposed hardware platform configuration and developed measuring software, mechanical properties such as backlash, torsional stiffness, hysteresis plot and emergency stop torque, can be measured accurately and assessed reliably. A torsion test with standard circular specimen is carried out with the multifunctional measurement system. The result of test shows that the measurement error is within ±3σ and the measurement reliability is more than 99.97%. The problem of accurate measurement and reliable assessment of mechanical properties for high precision planetary servo gearhead is fully solved with the developed multifunctional measurement system.
As an essential component of a servo system, mechanical properties of high precision planetary servo gearhead direct influence on the validation, stability and accuracy of the servo control system. However, mechanical properties measurement and assessment for high precision planetary servo gearhead is a time-consuming and tedious work, since current methodologies typically rely on various different specified systems. An integrated multifunctional measurement system SFJC-I is developed, which employs a torque sensor and a laser displacement transducer to simultaneously measure torque applied on servo gearhead and its corresponding torsional deformation. The measurement system depends on the accurate measurement of the relative displacement between input clamping system and output shaft of servo gearhead with a lever-type enlarging mechanism, rather than traditional optical dividing head and optical multisurface prism. Using interchangeable fixture system, the developed system capability to measure almost all series and specifications of high precision planetary servo gearhead is demonstrated. With proposed hardware platform configuration and developed measuring software, mechanical properties such as backlash, torsional stiffness, hysteresis plot and emergency stop torque, can be measured accurately and assessed reliably. A torsion test with standard circular specimen is carried out with the multifunctional measurement system. The result of test shows that the measurement error is within ±3σ and the measurement reliability is more than 99.97%. The problem of accurate measurement and reliable assessment of mechanical properties for high precision planetary servo gearhead is fully solved with the developed multifunctional measurement system.
2012, 26(2).
Abstract:
Morphing wing has attracted many research attention and effort in aircraft technology development because of its advantage in lift to draft ratio and flight performance. Morphing wing technology combines the lift and control surfaces into a seamless wing and integrates the primary structure together with the internal control system. It makes use of the wing aeroelastic deformation induced by the control surface to gain direct force control through desirable redistribution of aerodynamic forces. However some unknown mechanical parameters of the control system and complexity of the integrated structure become a main challenge for dynamic modeling of morphing wing. To solve the problem, a method of test data based modal sensitivity analysis is presented to improve the morphing wing FE model by evaluating the unknown parameters and identifying the modeling boundary conditions. An innovative seamless morphing wing with the structure integrated with a flexible trailing edge control system is presented for the investigation. An experimental model of actuation system driven by a servo motor for the morphing wing is designed and established. By performing a vibration test and the proposed modal sensitivity analysis, the unknown torsional stiffness of the servo motor and the boundary condition of the actuation mechanism model is identified and evaluated. Comparing with the test data, the average error of the first four modal frequency of the improved FE model is reduced significantly to less than 4%. To further investigate the morphing wing modeling, a wing box and then a whole morphing wing model including the skin and integrated with the trailing edge actuation system are established and tested. By using the proposed method, the FE model is improved by relaxing the constraint between the skin and actuation mechanism. The results show that the average error of the first three modal frequency of the improved FE model is reduced to less than 6%. The research results demonstrate that the presented seamless morphing wing integrated with a flexible trailing edge control surface can improve aerodynamic characteristics. By using the test data based modal sensitivity analysis method, the unknown parameter and boundary condition of the actuation model can be determined to improve the FE model. The problem in dynamic modeling of high accuracy for a morphing wing can be solved in an effective manner.
Morphing wing has attracted many research attention and effort in aircraft technology development because of its advantage in lift to draft ratio and flight performance. Morphing wing technology combines the lift and control surfaces into a seamless wing and integrates the primary structure together with the internal control system. It makes use of the wing aeroelastic deformation induced by the control surface to gain direct force control through desirable redistribution of aerodynamic forces. However some unknown mechanical parameters of the control system and complexity of the integrated structure become a main challenge for dynamic modeling of morphing wing. To solve the problem, a method of test data based modal sensitivity analysis is presented to improve the morphing wing FE model by evaluating the unknown parameters and identifying the modeling boundary conditions. An innovative seamless morphing wing with the structure integrated with a flexible trailing edge control system is presented for the investigation. An experimental model of actuation system driven by a servo motor for the morphing wing is designed and established. By performing a vibration test and the proposed modal sensitivity analysis, the unknown torsional stiffness of the servo motor and the boundary condition of the actuation mechanism model is identified and evaluated. Comparing with the test data, the average error of the first four modal frequency of the improved FE model is reduced significantly to less than 4%. To further investigate the morphing wing modeling, a wing box and then a whole morphing wing model including the skin and integrated with the trailing edge actuation system are established and tested. By using the proposed method, the FE model is improved by relaxing the constraint between the skin and actuation mechanism. The results show that the average error of the first three modal frequency of the improved FE model is reduced to less than 6%. The research results demonstrate that the presented seamless morphing wing integrated with a flexible trailing edge control surface can improve aerodynamic characteristics. By using the test data based modal sensitivity analysis method, the unknown parameter and boundary condition of the actuation model can be determined to improve the FE model. The problem in dynamic modeling of high accuracy for a morphing wing can be solved in an effective manner.
2012, 26(2).
Abstract:
For at least the past five decades, structural synthesis has been used as a main means of finding better mechanisms with some predefined function. In structural synthesis, isomorphism identification is still a problem unsolved well, and to solve this problem is very significant to the design of new mechanisms. According to the given degree of freedom (DOF) and link connection property of planar closed chain mechanisms, vertex assortment is obtained. For solving the isomorphism problem, a method of the adding sub-chains is proposed with the detailed steps and algorithms in the synthesizing process. Employing this method, the identification code and formation code of every topological structure are achieved, therefore many isomorphic structures could be eliminated in time during structural synthesis by comparing those codes among different topological graphs, resulting in the improvement of synthesizing efficiency and accuracy, and the approach for eliminating rigid sub-chains in and after the synthesizing process is also presented. Some examples are given, including how to add sub-chains, how to detect simple rigid sub-chains and how to obtain identification codes and formulation codes et al. Using the adding sub-chain method, the relative information of some common topological graphs is given in the form of table. The comparison result is coincident with many literatures, so the correctness of the adding sub-chain method is convinced. This method will greatly improve the synthesizing efficiency and accuracy, and has a good potential for application.
For at least the past five decades, structural synthesis has been used as a main means of finding better mechanisms with some predefined function. In structural synthesis, isomorphism identification is still a problem unsolved well, and to solve this problem is very significant to the design of new mechanisms. According to the given degree of freedom (DOF) and link connection property of planar closed chain mechanisms, vertex assortment is obtained. For solving the isomorphism problem, a method of the adding sub-chains is proposed with the detailed steps and algorithms in the synthesizing process. Employing this method, the identification code and formation code of every topological structure are achieved, therefore many isomorphic structures could be eliminated in time during structural synthesis by comparing those codes among different topological graphs, resulting in the improvement of synthesizing efficiency and accuracy, and the approach for eliminating rigid sub-chains in and after the synthesizing process is also presented. Some examples are given, including how to add sub-chains, how to detect simple rigid sub-chains and how to obtain identification codes and formulation codes et al. Using the adding sub-chain method, the relative information of some common topological graphs is given in the form of table. The comparison result is coincident with many literatures, so the correctness of the adding sub-chain method is convinced. This method will greatly improve the synthesizing efficiency and accuracy, and has a good potential for application.
2012, 26(2).
Abstract:
Sundial solar tracking machines are machines that tracking the sun, and can promote sunshine receiving efficiency of solar panels. Their operations are strongly influenced by wind load. Previous studies were focused on tracking accuracy and tracking methods, the influence of wind load to the operation of the tracking machines has not caused enough attention, so that many tracking machines did not have the reasonable design basis, which led to unreasonable design and high maintenance costs, and had seriously influenced the application and popularization of the tracking machines. Therefore, the 16 m2 sundial solar tracking machine is taken as research object from the perspective of wind load. A series of computational fluid dynamics (CFD) analyses are carried out on the model of the 16 m2 sundial solar tracking machine. Firstly, in order to make CFD analyses carry on smoothly, after the three-dimensional solid model is established, the model is simplified, and grids are meshed on the simplified model. Then, in the virtual environment, to make the simulation closer to real but at the same time not too complex to make simulation hard to realize, assumptions of the nature of air flow are conducted, boundary conditions of the analyses are set reasonably, and appropriate CFD analysis solver is also chosen. Finally, the results of the CFD analyses are also analyzed and sorted; and limit requirements (i.e., force conditions of limit case), such as the maximum load and the maximum total torque, are provided for the further finite element analyses (FEA) and the optimization design of the products. This paper presents an effective computer simulation analysis method for the design and optimization of this type of solar tracking machine, and this method can greatly shorten the development cycle and cost.
Sundial solar tracking machines are machines that tracking the sun, and can promote sunshine receiving efficiency of solar panels. Their operations are strongly influenced by wind load. Previous studies were focused on tracking accuracy and tracking methods, the influence of wind load to the operation of the tracking machines has not caused enough attention, so that many tracking machines did not have the reasonable design basis, which led to unreasonable design and high maintenance costs, and had seriously influenced the application and popularization of the tracking machines. Therefore, the 16 m2 sundial solar tracking machine is taken as research object from the perspective of wind load. A series of computational fluid dynamics (CFD) analyses are carried out on the model of the 16 m2 sundial solar tracking machine. Firstly, in order to make CFD analyses carry on smoothly, after the three-dimensional solid model is established, the model is simplified, and grids are meshed on the simplified model. Then, in the virtual environment, to make the simulation closer to real but at the same time not too complex to make simulation hard to realize, assumptions of the nature of air flow are conducted, boundary conditions of the analyses are set reasonably, and appropriate CFD analysis solver is also chosen. Finally, the results of the CFD analyses are also analyzed and sorted; and limit requirements (i.e., force conditions of limit case), such as the maximum load and the maximum total torque, are provided for the further finite element analyses (FEA) and the optimization design of the products. This paper presents an effective computer simulation analysis method for the design and optimization of this type of solar tracking machine, and this method can greatly shorten the development cycle and cost.
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