Redundant serial robot kinematic chains with seven axes are an extension of classical 6-axis ones. The structural synthesis of these structures is useful to provide a working basis, including for the promotion of new ...Redundant serial robot kinematic chains with seven axes are an extension of classical 6-axis ones. The structural synthesis of these structures is useful to provide a working basis, including for the promotion of new structures with 7 axes, besides some already existing and applied structures. This paper summarizes kinematic chain structures using a combinatorial method by listing all possible variants of the structures with 7 axes, obtained by adding a rotational or translational coupling, in a parallel or perpendicular position, against the guiding structure with 6 axes consisting of two distinct modules： positioning module （3 axes） and orientation module （3 axes）. Representation of proper workspaces can help the designer in choosing the structure with maximum functionality for a given application.展开更多
This paper adopts the Global Workspace Theory as a neuro-scientifically plausible theory for developing conscious cognitive architecture.The Global Workspace Theory’s compatibility with the working mechanisms underne...This paper adopts the Global Workspace Theory as a neuro-scientifically plausible theory for developing conscious cognitive architecture.The Global Workspace Theory’s compatibility with the working mechanisms underneath human brains is enhanced by the implementation of different cognitive features based on this framework.Amongst the topics in the literature for intelligent systems,we start with attention,memory and learning mechanisms,and corresponding experiments are summarized here.We also discuss how other topics of cognitive robotics could be developed based on these three basic components,and their correlations.This provides a foundation for future long-term development of cognitive architectures of cognitive robots.The research in this paper follows the incremental research pathway for the architecture implementation,which is consistent with the Biologically Inspired Cognitive Architecture roadmap.展开更多
This paper presents a classification on the workspaces of planar serial three-link manipulators, that is, position workspace and orientation angle workspace. Position workspace indicates the region reached by the refe...This paper presents a classification on the workspaces of planar serial three-link manipulators, that is, position workspace and orientation angle workspace. Position workspace indicates the region reached by the reference point on the end-effector. Orientation angle workspace indicates a set of angle ranges by which the end-effector can reach with certain orientation for every point in the reachable position workspace. By introducing a virtual equivalent mechanism, reachable position workspace can be di- vided into several Grashof intervals and non-Grashof intervals. The calculation equations of orientation angle workspace are deduced in three situations according to the relationships among four link lengths in the virtual four-bar chain. Three examples are given for three kinds of relationship of link lengths. The orientation angle workspace of extended groups, that is, two of the three link lengths equal, and the orientation angle workspace when the reference point on the end-effector moves along a non-radial direction are also discussed. A program is developed to calculate orientation angle workspaces and output variation curves of orientation angle workspace and key data within the position workspace. The approach and program in this paper can be used for fast calculation and identification of the variation rule of the orientation angle workspace of any given planar serial three-link manipulator on the basis of its link parameters, and for the design of a highly dexterous serial manipulator with proposed link rela- tions.展开更多
At present,the cranes used at sea have several shortcomings in terms of flexibility,efficiency,and safety.Therefore,a floating multi-robot coordinated lifting system is proposed to fulfill the offshore lifting require...At present,the cranes used at sea have several shortcomings in terms of flexibility,efficiency,and safety.Therefore,a floating multi-robot coordinated lifting system is proposed to fulfill the offshore lifting requirements.First,the structure of the lifting system is established according to the lifting task,the kinematic model of the system is developed by using the D–H coordinate transformation,and the dynamic model is developed based on rigid-body dynamics and hydrodynamics.Then,the static and dynamic workspace of the lifting system are analyzed,and the solving steps of the workspace are given by using the Monte–Carlo method.The effect of the load mass and the maximum allowable tension of the cable on the workspace is examined by simulation.Results show that the lifting system has limited carrying capacity and a data reference for selecting the structural parameters by analyzing the factors affecting the workspace.Findings provide a basis for further research on the optimal design of structural parameters and the determination of safe configurations of the lifting system.展开更多
A new three dimensional simulation method is introduced to study the workspace of a 6 PSS (P denotes a prismatic kinematic pair, S denotes a spherical kinematic pair) parallel machine tool. This algorithm adopts the...A new three dimensional simulation method is introduced to study the workspace of a 6 PSS (P denotes a prismatic kinematic pair, S denotes a spherical kinematic pair) parallel machine tool. This algorithm adopts the method of numerical analysis to investigate the boundary points in a series of sections which form the surface of the workspace. That is, to study such points that have the largest polar radius on a certain section in a system of polar coordinates according to conditions of constraint. The constraint conditions considered in the article include the maximum and minimum displacements of each dieblock, the maximum and minimum angles of oscillation in each hinge. By converting the constraint inequalities into constraint equations, the largest polar radius corresponding to every constraint condition can be evaluated and the minimum one is used to decide the boundary point. This algorithm greatly simplifies the computational process and can be used to analyze any section of the workspace. It provides a theoretical basis for the structural design of such a machine tool.展开更多
Parallel Kinematic Machines(PKMs)are being widely used for precise applications to achieve complex motions and variable poses for the end effector tool.PKMs are found in medical,assembly and manufacturing industries w...Parallel Kinematic Machines(PKMs)are being widely used for precise applications to achieve complex motions and variable poses for the end effector tool.PKMs are found in medical,assembly and manufacturing industries where accuracy is necessary.It is often desired to have a compact and simple architecture for the robotic mechanism.In this paper,the kinematic and dynamic analysis of a novel 3-PRUS(P:prismatic joint,R:revolute joint,U:universal joint,S:spherical joint)parallel manipulator with a mobile platform having 6 Degree of Freedom(Do F)is explained.The kinematic equations for the proposed spatial parallel mechanism are formulated using the Modified Denavit-Hartenberg(DH)technique considering both active and passive joints.The kinematic equations are used to derive the Jacobian matrix of the mechanism to identify the singular points within the workspace.A Jacobian based sti ness analysis is done to understand the variations in sti ness for different poses of the mobile platform and further,it is used to decide trajectories for the end effector within the singularity free region.The analytical model of the robot dynamics is presented using the Euler-Lagrangian approach with Lagrangian multipliers to include the system constraints.The gravity and inertial forces of all links are considered in the mathematical model.The analytical results of the dynamic model are compared with ADAMS simulation results for a pre-defined trajectory of the end effector.展开更多
Although the parallel mechanisms have the advantages of high accuracy, velocity, stiffness, and payload capacity, the shortcomings of the space utilization and workspace limit the applications in the confined space. A...Although the parallel mechanisms have the advantages of high accuracy, velocity, stiffness, and payload capacity, the shortcomings of the space utilization and workspace limit the applications in the confined space. A novel 3 degrees of freedom spatial parallel manipulator 3-PSR-O（prismatic-spherical-revolute） is proposed, which possesses a compact architecture and extended workspace while maintaining the inherent advantages of the parallel mechanisms. The direct-inverse position, singularity and workspace are investigated. The mapping method is adopted in the position analysis, and the closed form solution is derived in the form of a six order equation. The singularity analysis of the mechanism is also carried out based on the geometrical constraints, including six singularity boundaries. A feature boundary, which is independent of the prismatic joints＇ stroke limit, is obtained by integrating the six singularity boundaries. According to the formation of the reachable workspace, a concept of basic workspace is also introduced and presented in the analytical way. By demarcating the basic workspace along the central height with the feature boundary, the reachable workspace can be derived and analyzed more efficiently. Finally, a comparative study on the space utilization between the 3-PSP parallel mechanism and the new mechanism is also presented. The area of feature boundary of the new mechanism is about 140% of the 3-PSP parallel mechanism, while its installation radius is only 1/2 of the 3-PSP parallel mechanism. The proposed parallel mechanism shows great space utilization, and is ideally suited for applications in confined space occasions such as immersion lithography, nano-imprint etc.展开更多
Parallel mechanisms are widely used in various fields of engineering and industrial applications such as machine tools, flight simulators, earthquake simulators, medical equipment, etc. Parallel mechanisms are restric...Parallel mechanisms are widely used in various fields of engineering and industrial applications such as machine tools, flight simulators, earthquake simulators, medical equipment, etc. Parallel mechanisms are restricted to some limitations such as irregular workspace, existence of singular points and complexity of control systems which should be studied and analyzed for effective and efficient use. In this research, a new machine tool with parallel mechanism which has three translational degrees of freedom is studied and the workspace and singular points are determined by deriving analytical equations and then utilizing of Matlab software. To do so, forward and inverse kinematics of the mechanism are obtained and workspace and singular points are calculated using a search algorithm. Afterward in order to validate the results, the proposed mechanism is simulated in automatic dynamics analysis of mechanical systems （ADAMS） software. Moreover, in order to investigate the quality of robot performance and dexterity of the mechanism in its workspace, global dexterity index （GDI） of the robot is calculated using Jacobean matrix at different positions of the mobile platform.展开更多
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 k...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-RSR1-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.展开更多
The direct use of the determinant of Jacobian matrix being equal to zero for the singularity analysis is generally difficult which is due to complexity of the Jacobian matrix of 6-DOF parallel manipulators,especially ...The direct use of the determinant of Jacobian matrix being equal to zero for the singularity analysis is generally difficult which is due to complexity of the Jacobian matrix of 6-DOF parallel manipulators,especially for Stewart platform.Recently,several scholars make their great contribution to the effective solution of this problem,but neither of them find the right answer.This paper gives a brief analysis of the kinematics of the Stewart platform and derives the Jacobian matrices of the system through the velocity equation.On the basis of the traditional classification of singularities,the second type of singularity is investigated.An assumption of any three of the six variables of the Stewart platform as constant is made,then the analytical expression of singularity locus equation of the second type singularity which contains another three pose variables is obtained.The singularity locus is represented in the three-dimensional space through the derived equation.The correctness and validity of the proposed method are verified through examples.Finally,the singularity analysis of an electric Stewart platform in its desired workspace and reachable workspace is implemented.Thus,one can easily identify whether singularity exists in a given workspace of a Stewart platform and determine whether the existed singularity can be avoided through the proposed method.The proposed method also provides theoretical principle for the design and application of the Stewart platform and has great significance for the trajectory planning and control.展开更多
The 4TPS-PS parallel platform designed for a stabilization and automatic tracking system is a novel lower-mobility parallel mechanism. In the first part of this paper, the structure of the platform is described and th...The 4TPS-PS parallel platform designed for a stabilization and automatic tracking system is a novel lower-mobility parallel mechanism. In the first part of this paper, the structure of the platform is described and the kinematics model is built. The workspace of the platform is defined as the full reachable rotation workspace when the Z coordinate dimension of the upper plate varies continuously. A fast searching method of the full reachable workspace is presented, after which the inverse kinematics of the platform is deduced. The forward and inverse solutions of the speed and force of the platform are deduced. According to the characteristic of the 4TPS-PS platform’s structure, a fast searching algorithm of the maximum generalized speed and maximum generalized force output by the upper plate is put forward based on the forward and inverse solutions of the platform’s speed and force. The 4TPS-PS platform prototype built by the State Key Laboratory of Fluid Power Transmission and Control of China is taken as the research subject. The full reachable rotation workspace of the prototype is computed out and analyzed. The curves of maximum generalized speed and maximum generalized force of the prototype are computed out and plotted. Finally, the com- puting and analyzing results of the operating characteristics are confirmed through the experiment.展开更多
This paper presents a novel 1T2R three degrees of freedom redundantly actuated and overconstrained ■parallel machining head(■denotes the active prismatic joint), which can construct 5-axis hybrid machine to complete...This paper presents a novel 1T2R three degrees of freedom redundantly actuated and overconstrained ■parallel machining head(■denotes the active prismatic joint), which can construct 5-axis hybrid machine to complete high speed freedom surface milling for large complex structural components in aerospace. Firstly, based on the screw theory, the mobility of the proposed parallel manipulator is briefly analysed. Secondly, the kinematic inverse position and the parasitic motion of the parallel manipulator are explicitly expressed. Furthermore, motion-force transmission performance evaluation indices are derived in detail via an alternative approach based on the screw theory. More importantly, a simple method for quickly solving the maximum virtual power coefficient is proposed, and the motion-force transmission performance evaluation index is greatly improved. To evaluate the kinematic performance, its workspace is calculated. With numerical examples, performance distribution atlases of the manipulator are depicted visually. The corresponding results illustrate that the proposed parallel manipulator has better orientation workspace and superior motion-force transmission performance than the 2 PRU-PRS parallel manipulator, which proves the validity and applicability of applying this manipulator as a machining head.展开更多
To assist an amputee in regaining his or her daily quality of life,based on analysis of the motion characteristics of the human hip,a 2-UPR/URR parallel mechanism with a passive limb was designed.The inverse kinematic...To assist an amputee in regaining his or her daily quality of life,based on analysis of the motion characteristics of the human hip,a 2-UPR/URR parallel mechanism with a passive limb was designed.The inverse kinematics of this mechanism was analyzed based on a closed-loop vector method.The constrained Jacobian matrix and kinematic Jacobian matrix of each limb were then analyzed,and a 6×6 fully Jacobian matrix was constructed.Based on this,kinematic performances were analyzed and summarized.Finally,the dynamic model of the mechanism was constructed based on the virtual work principle,and its theoretical solution was compared with the numerical results,which were obtained in a simulation environment.Results showed that the prosthetic mechanism had a larger rotating workspace and better mechanical performance,which accorded a range of motion and bearing capacity similar to that of the human hip in multiple gait modes.Moreover,the validity of the dynamic model and inverse kinematics were verified by comparing the theoretical and simulation results.Furthermore,with flexion and extension,the torque change in the hip prosthetic mechanism was similar to that of the human hip,which demonstrated the feasibility of the hip prosthetic mechanism and its good dynamic performance.展开更多
This paper presents a kinematic analysis of the locomotion of a gecko,and experimental verification of the kinematic model.Kinematic analysis is important for parameter design,dynamic analysis,and optimization in biom...This paper presents a kinematic analysis of the locomotion of a gecko,and experimental verification of the kinematic model.Kinematic analysis is important for parameter design,dynamic analysis,and optimization in biomimetic robot research. The proposed kinematic analysis can simulate,without iteration,the locomotion of gecko satisfying the constraint conditions that maintain the position of the contacted feet on the surface.So the method has an advantage for analyzing the climbing motion of the quadruped mechanism in a real time application.The kinematic model of a gecko consists of four legs based on 7-degrees of freedom spherical-revolute-spherical joints and two revolute joints in the waist.The motion of the kinematic model is simulated based on measurement data of each joint.The motion of the kinematic model simulates the investigated real gecko's motion by using the experimental results.The analysis solves the forward kinematics by considering the model as a combination of closed and open serial mechanisms under the condition that maintains the contact positions of the attached feet on the ground. The motions of each joint are validated by comparing with the experimental results.In addition to the measured gait,three other gaits are simulated based on the kinematic model.The maximum strides of each gait are calculated by workspace analysis.The result can be used in biomimetic robot design and motion planning.展开更多
Current research on robotic dexterous hands mainly focuses on designing new finger and palm structures,as well as developing smarter control algorithms.Although the dimensional synthesis of dexterous hands with tradit...Current research on robotic dexterous hands mainly focuses on designing new finger and palm structures,as well as developing smarter control algorithms.Although the dimensional synthesis of dexterous hands with traditional rigid palms has been carried out,research on the dimensional synthesis of dexterous hands with metamorphic palms remains insufficient.This study investigated the dimensional synthesis of a palm of a novel metamorphic multi-fingered hand,and explored the geometric design for maximizing the precision manipulation workspace.Different indexes were used to value the workspace of the metamorphic hand,and the best proportions between the five links of the palm to obtain the optimal workspace of the metamorphic hand were explored.Based on the fixed total length of the palm member,four nondimensional design parameters that determine the size of the palm were introduced;through the discretization method,the influence of the four design parameters on the workspace of the metamorphic hand with full-actuated fingers and under-actuated fingers was analyzed.Based on the analysis of the metamorphic multi-fingered hand,the symmetrical structure of the palm was designed,resulting in the largest workspace of the multi-fingered hand,and proved that the metamorphic palm has a massive upgrade for the workspace of underactuated fingers.This research contributed to the dimensional synthesis of metamorphic dexterous hands,with practical significance for the design and optimization of novel metamorphic hands.展开更多
With the increasingly more extensive application of the medical surgical robot in the clinic,higher requirements have been put forward for medical robots.The bone-attached robot,a popular orthopedic robot in recent ye...With the increasingly more extensive application of the medical surgical robot in the clinic,higher requirements have been put forward for medical robots.The bone-attached robot,a popular orthopedic robot in recent years,has a tendency of miniaturization and refinement.Thus,a bone-attached parallel manipulator(PM)based on 6-UCU(universalcylindrical-universal)configuration is proposed,which is characterized by small volume,compact structure,high precision and six-dimensional force feedback.To optimize the structure and make it more compact,the workspace of the 6-UCU PM is analyzed based on the analysis of three kinds of constraint,and workspace model is established through spherical coordinate search method.This study also analyzes the influence of structural parameters on workspace,which may contribute to improving the efficiency of design and ensuring small-sized robots possess relatively large workspace.Moreover,to improve the motion accuracy,an error modeling method is developed based on the structure of 6-UCU PMs.According to this established error model,the output pose error curves are drawn using MATLAB software when the structure parameters change,and the influence of the structure and pose parameters change on the output pose error of PMs is analyzed.The proposed research provides the instruction to design and analysis of small PMs such as bone-attached robots.展开更多
A wearable force-feedback glove is a promising way to enhance the immersive sensation when a user interacts with virtual objects in virtual reality scenarios.Design challenges for such a glove include allowing a large...A wearable force-feedback glove is a promising way to enhance the immersive sensation when a user interacts with virtual objects in virtual reality scenarios.Design challenges for such a glove include allowing a large fingertip workspace,providing a desired force sensation when simulating both free-and constrained-space interactions,and ensuring a lightweight structure.In this paper,we present a forcefeedback glove using a pneumatically actuated mechanism mounted on the dorsal side of the user’s hand.By means of a triple kinematic paired link with a curved sliding slot,a hybrid cam-linkage mechanism is proposed to transmit the resistance from the pneumatic piston rod to the fingertip.In order to obtain a large normal component of the feedback force on the user’s fingertip,the profile of the sliding slot was synthesized through an analysis of the force equilibrium on the triple kinematic paired link.A prototype five-fingered glove with a mass of 245 g was developed,and a wearable force-measurement system was constructed to permit the quantitative evaluation of the interaction performance in both free and constrained space.The experimental results confirm that the glove can achieve an average resistance of less than 0.1 N in free-space simulation and a maximum fingertip force of 4 N in constrained-space simulation.The experiment further confirms that this glove permits the finger to move freely to simulate typical grasping gestures.展开更多
文摘Redundant serial robot kinematic chains with seven axes are an extension of classical 6-axis ones. The structural synthesis of these structures is useful to provide a working basis, including for the promotion of new structures with 7 axes, besides some already existing and applied structures. This paper summarizes kinematic chain structures using a combinatorial method by listing all possible variants of the structures with 7 axes, obtained by adding a rotational or translational coupling, in a parallel or perpendicular position, against the guiding structure with 6 axes consisting of two distinct modules： positioning module （3 axes） and orientation module （3 axes）. Representation of proper workspaces can help the designer in choosing the structure with maximum functionality for a given application.
基金Supported by the European Union’s Horizon Europe research and innovation program(101120727-PRIMI).
文摘This paper adopts the Global Workspace Theory as a neuro-scientifically plausible theory for developing conscious cognitive architecture.The Global Workspace Theory’s compatibility with the working mechanisms underneath human brains is enhanced by the implementation of different cognitive features based on this framework.Amongst the topics in the literature for intelligent systems,we start with attention,memory and learning mechanisms,and corresponding experiments are summarized here.We also discuss how other topics of cognitive robotics could be developed based on these three basic components,and their correlations.This provides a foundation for future long-term development of cognitive architectures of cognitive robots.The research in this paper follows the incremental research pathway for the architecture implementation,which is consistent with the Biologically Inspired Cognitive Architecture roadmap.
基金Supported by the Natural Science Foundation of Shanxi Province (Grant No. 20041070)
文摘This paper presents a classification on the workspaces of planar serial three-link manipulators, that is, position workspace and orientation angle workspace. Position workspace indicates the region reached by the reference point on the end-effector. Orientation angle workspace indicates a set of angle ranges by which the end-effector can reach with certain orientation for every point in the reachable position workspace. By introducing a virtual equivalent mechanism, reachable position workspace can be di- vided into several Grashof intervals and non-Grashof intervals. The calculation equations of orientation angle workspace are deduced in three situations according to the relationships among four link lengths in the virtual four-bar chain. Three examples are given for three kinds of relationship of link lengths. The orientation angle workspace of extended groups, that is, two of the three link lengths equal, and the orientation angle workspace when the reference point on the end-effector moves along a non-radial direction are also discussed. A program is developed to calculate orientation angle workspaces and output variation curves of orientation angle workspace and key data within the position workspace. The approach and program in this paper can be used for fast calculation and identification of the variation rule of the orientation angle workspace of any given planar serial three-link manipulator on the basis of its link parameters, and for the design of a highly dexterous serial manipulator with proposed link rela- tions.
基金Supported by the National Natural Science Foundation of China under Grant No.51965032the National Natural Science Foundation of Gansu Province of China under Grant No.22JR5RA319+1 种基金the Science and Technology Foundation of Gansu Province of China under Grant No.21YF5WA060the Excellent Doctoral Student Foundation of Gansu Province of China under Grant No.23JRRA842。
文摘At present,the cranes used at sea have several shortcomings in terms of flexibility,efficiency,and safety.Therefore,a floating multi-robot coordinated lifting system is proposed to fulfill the offshore lifting requirements.First,the structure of the lifting system is established according to the lifting task,the kinematic model of the system is developed by using the D–H coordinate transformation,and the dynamic model is developed based on rigid-body dynamics and hydrodynamics.Then,the static and dynamic workspace of the lifting system are analyzed,and the solving steps of the workspace are given by using the Monte–Carlo method.The effect of the load mass and the maximum allowable tension of the cable on the workspace is examined by simulation.Results show that the lifting system has limited carrying capacity and a data reference for selecting the structural parameters by analyzing the factors affecting the workspace.Findings provide a basis for further research on the optimal design of structural parameters and the determination of safe configurations of the lifting system.
基金Ministerial Level Foundation(96J185 .1BQ0150) Fund for Reasearch on Doctoral Programs in Institutions of Higher Learning(1997000716)
文摘A new three dimensional simulation method is introduced to study the workspace of a 6 PSS (P denotes a prismatic kinematic pair, S denotes a spherical kinematic pair) parallel machine tool. This algorithm adopts the method of numerical analysis to investigate the boundary points in a series of sections which form the surface of the workspace. That is, to study such points that have the largest polar radius on a certain section in a system of polar coordinates according to conditions of constraint. The constraint conditions considered in the article include the maximum and minimum displacements of each dieblock, the maximum and minimum angles of oscillation in each hinge. By converting the constraint inequalities into constraint equations, the largest polar radius corresponding to every constraint condition can be evaluated and the minimum one is used to decide the boundary point. This algorithm greatly simplifies the computational process and can be used to analyze any section of the workspace. It provides a theoretical basis for the structural design of such a machine tool.
文摘Parallel Kinematic Machines(PKMs)are being widely used for precise applications to achieve complex motions and variable poses for the end effector tool.PKMs are found in medical,assembly and manufacturing industries where accuracy is necessary.It is often desired to have a compact and simple architecture for the robotic mechanism.In this paper,the kinematic and dynamic analysis of a novel 3-PRUS(P:prismatic joint,R:revolute joint,U:universal joint,S:spherical joint)parallel manipulator with a mobile platform having 6 Degree of Freedom(Do F)is explained.The kinematic equations for the proposed spatial parallel mechanism are formulated using the Modified Denavit-Hartenberg(DH)technique considering both active and passive joints.The kinematic equations are used to derive the Jacobian matrix of the mechanism to identify the singular points within the workspace.A Jacobian based sti ness analysis is done to understand the variations in sti ness for different poses of the mobile platform and further,it is used to decide trajectories for the end effector within the singularity free region.The analytical model of the robot dynamics is presented using the Euler-Lagrangian approach with Lagrangian multipliers to include the system constraints.The gravity and inertial forces of all links are considered in the mathematical model.The analytical results of the dynamic model are compared with ADAMS simulation results for a pre-defined trajectory of the end effector.
基金Supported by National Natural Science Foundation of China(Grant No.51221004)National Hi-tech Research and Development Program of China(863 Program,Grant No.2012AA040605)
文摘Although the parallel mechanisms have the advantages of high accuracy, velocity, stiffness, and payload capacity, the shortcomings of the space utilization and workspace limit the applications in the confined space. A novel 3 degrees of freedom spatial parallel manipulator 3-PSR-O（prismatic-spherical-revolute） is proposed, which possesses a compact architecture and extended workspace while maintaining the inherent advantages of the parallel mechanisms. The direct-inverse position, singularity and workspace are investigated. The mapping method is adopted in the position analysis, and the closed form solution is derived in the form of a six order equation. The singularity analysis of the mechanism is also carried out based on the geometrical constraints, including six singularity boundaries. A feature boundary, which is independent of the prismatic joints＇ stroke limit, is obtained by integrating the six singularity boundaries. According to the formation of the reachable workspace, a concept of basic workspace is also introduced and presented in the analytical way. By demarcating the basic workspace along the central height with the feature boundary, the reachable workspace can be derived and analyzed more efficiently. Finally, a comparative study on the space utilization between the 3-PSP parallel mechanism and the new mechanism is also presented. The area of feature boundary of the new mechanism is about 140% of the 3-PSP parallel mechanism, while its installation radius is only 1/2 of the 3-PSP parallel mechanism. The proposed parallel mechanism shows great space utilization, and is ideally suited for applications in confined space occasions such as immersion lithography, nano-imprint etc.
文摘Parallel mechanisms are widely used in various fields of engineering and industrial applications such as machine tools, flight simulators, earthquake simulators, medical equipment, etc. Parallel mechanisms are restricted to some limitations such as irregular workspace, existence of singular points and complexity of control systems which should be studied and analyzed for effective and efficient use. In this research, a new machine tool with parallel mechanism which has three translational degrees of freedom is studied and the workspace and singular points are determined by deriving analytical equations and then utilizing of Matlab software. To do so, forward and inverse kinematics of the mechanism are obtained and workspace and singular points are calculated using a search algorithm. Afterward in order to validate the results, the proposed mechanism is simulated in automatic dynamics analysis of mechanical systems （ADAMS） software. Moreover, in order to investigate the quality of robot performance and dexterity of the mechanism in its workspace, global dexterity index （GDI） of the robot is calculated using Jacobean matrix at different positions of the mobile platform.
基金supported by National Natural Science Foundation of China (Grant No. 50875008)
文摘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-RSR1-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.
基金supported by Program for New Century Excellent Talents in University of Ministry of Education of China(Grant No.NCET-04-0325)
文摘The direct use of the determinant of Jacobian matrix being equal to zero for the singularity analysis is generally difficult which is due to complexity of the Jacobian matrix of 6-DOF parallel manipulators,especially for Stewart platform.Recently,several scholars make their great contribution to the effective solution of this problem,but neither of them find the right answer.This paper gives a brief analysis of the kinematics of the Stewart platform and derives the Jacobian matrices of the system through the velocity equation.On the basis of the traditional classification of singularities,the second type of singularity is investigated.An assumption of any three of the six variables of the Stewart platform as constant is made,then the analytical expression of singularity locus equation of the second type singularity which contains another three pose variables is obtained.The singularity locus is represented in the three-dimensional space through the derived equation.The correctness and validity of the proposed method are verified through examples.Finally,the singularity analysis of an electric Stewart platform in its desired workspace and reachable workspace is implemented.Thus,one can easily identify whether singularity exists in a given workspace of a Stewart platform and determine whether the existed singularity can be avoided through the proposed method.The proposed method also provides theoretical principle for the design and application of the Stewart platform and has great significance for the trajectory planning and control.
基金Project (No. 50375139) supported by the National Natural Science Foundation of China
文摘The 4TPS-PS parallel platform designed for a stabilization and automatic tracking system is a novel lower-mobility parallel mechanism. In the first part of this paper, the structure of the platform is described and the kinematics model is built. The workspace of the platform is defined as the full reachable rotation workspace when the Z coordinate dimension of the upper plate varies continuously. A fast searching method of the full reachable workspace is presented, after which the inverse kinematics of the platform is deduced. The forward and inverse solutions of the speed and force of the platform are deduced. According to the characteristic of the 4TPS-PS platform’s structure, a fast searching algorithm of the maximum generalized speed and maximum generalized force output by the upper plate is put forward based on the forward and inverse solutions of the platform’s speed and force. The 4TPS-PS platform prototype built by the State Key Laboratory of Fluid Power Transmission and Control of China is taken as the research subject. The full reachable rotation workspace of the prototype is computed out and analyzed. The curves of maximum generalized speed and maximum generalized force of the prototype are computed out and plotted. Finally, the com- puting and analyzing results of the operating characteristics are confirmed through the experiment.
基金supported by the Fundamental Research Funds for the Central Universities (Nos. 2018JBZ007, 2018YJS136 and 2017YJS158)China Scholarship Council (CSC) (No. 201807090079)National Natural Science Foundation of China (NSFC) (No. 51675037)
文摘This paper presents a novel 1T2R three degrees of freedom redundantly actuated and overconstrained ■parallel machining head(■denotes the active prismatic joint), which can construct 5-axis hybrid machine to complete high speed freedom surface milling for large complex structural components in aerospace. Firstly, based on the screw theory, the mobility of the proposed parallel manipulator is briefly analysed. Secondly, the kinematic inverse position and the parasitic motion of the parallel manipulator are explicitly expressed. Furthermore, motion-force transmission performance evaluation indices are derived in detail via an alternative approach based on the screw theory. More importantly, a simple method for quickly solving the maximum virtual power coefficient is proposed, and the motion-force transmission performance evaluation index is greatly improved. To evaluate the kinematic performance, its workspace is calculated. With numerical examples, performance distribution atlases of the manipulator are depicted visually. The corresponding results illustrate that the proposed parallel manipulator has better orientation workspace and superior motion-force transmission performance than the 2 PRU-PRS parallel manipulator, which proves the validity and applicability of applying this manipulator as a machining head.
基金Supported by Beijing Natural Science Foundation(Grant No.L172021)National Natural Science Foundation of China(Grant No.51875033).
文摘To assist an amputee in regaining his or her daily quality of life,based on analysis of the motion characteristics of the human hip,a 2-UPR/URR parallel mechanism with a passive limb was designed.The inverse kinematics of this mechanism was analyzed based on a closed-loop vector method.The constrained Jacobian matrix and kinematic Jacobian matrix of each limb were then analyzed,and a 6×6 fully Jacobian matrix was constructed.Based on this,kinematic performances were analyzed and summarized.Finally,the dynamic model of the mechanism was constructed based on the virtual work principle,and its theoretical solution was compared with the numerical results,which were obtained in a simulation environment.Results showed that the prosthetic mechanism had a larger rotating workspace and better mechanical performance,which accorded a range of motion and bearing capacity similar to that of the human hip in multiple gait modes.Moreover,the validity of the dynamic model and inverse kinematics were verified by comparing the theoretical and simulation results.Furthermore,with flexion and extension,the torque change in the hip prosthetic mechanism was similar to that of the human hip,which demonstrated the feasibility of the hip prosthetic mechanism and its good dynamic performance.
基金supported by the Brain Korea 21 Project and SNU-IAMD.
文摘This paper presents a kinematic analysis of the locomotion of a gecko,and experimental verification of the kinematic model.Kinematic analysis is important for parameter design,dynamic analysis,and optimization in biomimetic robot research. The proposed kinematic analysis can simulate,without iteration,the locomotion of gecko satisfying the constraint conditions that maintain the position of the contacted feet on the surface.So the method has an advantage for analyzing the climbing motion of the quadruped mechanism in a real time application.The kinematic model of a gecko consists of four legs based on 7-degrees of freedom spherical-revolute-spherical joints and two revolute joints in the waist.The motion of the kinematic model is simulated based on measurement data of each joint.The motion of the kinematic model simulates the investigated real gecko's motion by using the experimental results.The analysis solves the forward kinematics by considering the model as a combination of closed and open serial mechanisms under the condition that maintains the contact positions of the attached feet on the ground. The motions of each joint are validated by comparing with the experimental results.In addition to the measured gait,three other gaits are simulated based on the kinematic model.The maximum strides of each gait are calculated by workspace analysis.The result can be used in biomimetic robot design and motion planning.
基金Supported by National Natural Science Foundation of China(Grant No.51535008).
文摘Current research on robotic dexterous hands mainly focuses on designing new finger and palm structures,as well as developing smarter control algorithms.Although the dimensional synthesis of dexterous hands with traditional rigid palms has been carried out,research on the dimensional synthesis of dexterous hands with metamorphic palms remains insufficient.This study investigated the dimensional synthesis of a palm of a novel metamorphic multi-fingered hand,and explored the geometric design for maximizing the precision manipulation workspace.Different indexes were used to value the workspace of the metamorphic hand,and the best proportions between the five links of the palm to obtain the optimal workspace of the metamorphic hand were explored.Based on the fixed total length of the palm member,four nondimensional design parameters that determine the size of the palm were introduced;through the discretization method,the influence of the four design parameters on the workspace of the metamorphic hand with full-actuated fingers and under-actuated fingers was analyzed.Based on the analysis of the metamorphic multi-fingered hand,the symmetrical structure of the palm was designed,resulting in the largest workspace of the multi-fingered hand,and proved that the metamorphic palm has a massive upgrade for the workspace of underactuated fingers.This research contributed to the dimensional synthesis of metamorphic dexterous hands,with practical significance for the design and optimization of novel metamorphic hands.
基金National Natural Science Foundation of China(Grant Nos.51775052,52175019)Beijing Municipal Natural Science Foundation of China(Grant No.21C10109)Beijing Municipal Key Laboratory of Space-ground Interconnection and Convergence of China.
文摘With the increasingly more extensive application of the medical surgical robot in the clinic,higher requirements have been put forward for medical robots.The bone-attached robot,a popular orthopedic robot in recent years,has a tendency of miniaturization and refinement.Thus,a bone-attached parallel manipulator(PM)based on 6-UCU(universalcylindrical-universal)configuration is proposed,which is characterized by small volume,compact structure,high precision and six-dimensional force feedback.To optimize the structure and make it more compact,the workspace of the 6-UCU PM is analyzed based on the analysis of three kinds of constraint,and workspace model is established through spherical coordinate search method.This study also analyzes the influence of structural parameters on workspace,which may contribute to improving the efficiency of design and ensuring small-sized robots possess relatively large workspace.Moreover,to improve the motion accuracy,an error modeling method is developed based on the structure of 6-UCU PMs.According to this established error model,the output pose error curves are drawn using MATLAB software when the structure parameters change,and the influence of the structure and pose parameters change on the output pose error of PMs is analyzed.The proposed research provides the instruction to design and analysis of small PMs such as bone-attached robots.
基金the National Key Research and Development Program(2016YFB1001200)the National Natural Science Foundation of China(61572055 and 61633004).
文摘A wearable force-feedback glove is a promising way to enhance the immersive sensation when a user interacts with virtual objects in virtual reality scenarios.Design challenges for such a glove include allowing a large fingertip workspace,providing a desired force sensation when simulating both free-and constrained-space interactions,and ensuring a lightweight structure.In this paper,we present a forcefeedback glove using a pneumatically actuated mechanism mounted on the dorsal side of the user’s hand.By means of a triple kinematic paired link with a curved sliding slot,a hybrid cam-linkage mechanism is proposed to transmit the resistance from the pneumatic piston rod to the fingertip.In order to obtain a large normal component of the feedback force on the user’s fingertip,the profile of the sliding slot was synthesized through an analysis of the force equilibrium on the triple kinematic paired link.A prototype five-fingered glove with a mass of 245 g was developed,and a wearable force-measurement system was constructed to permit the quantitative evaluation of the interaction performance in both free and constrained space.The experimental results confirm that the glove can achieve an average resistance of less than 0.1 N in free-space simulation and a maximum fingertip force of 4 N in constrained-space simulation.The experiment further confirms that this glove permits the finger to move freely to simulate typical grasping gestures.
