Genliang Chen

Optimum selection of mechanism type for heavy manipulators based on particle swarm optimization method

The mechanism type plays a decisive role in the mechanical performance of robotic manipulators. Feasible mechanism types can be obtained by applying appropriate type synthesis theory, but there is still a lack of effective and efficient methods for the optimum selection among different types of mechanism candidates. This paper presents a new strategy for the purpose of optimum mechanism type selection based on the modified particle swarm optimization method. The concept of sub-swarm is introduced to represent the different mechanisms generated by the type synthesis, and a competitive mechanism is employed between the sub-swarms to reassign their population size according to the relative performances of the mechanism candidates to implement the optimization. Combining with a modular modeling approach for fast calculation of the performance index of the potential candidates, the proposed method is applied to determine the optimum mechanism type among the potential candidates for the desired manipulator. The effectiveness and efficiency of the proposed method is demonstrated through a case study on the optimum selection of mechanism type of a heavy manipulator where six feasible candidates are considered with force capability as the specific performance index. The optimization result shows that the fitness of the optimum mechanism type for the considered heavy manipulator can be up to 0.578 5. This research provides the instruction in optimum selection of mechanism types for robotic manipulators.

A Kind of Kinematically Redundant Planar Parallel Manipulator for Optimal Output Accuracy

Theoretically, parallel manipulators perform higher precision than their serial counterparts. However, the output accuracy is sensitive to their configurations and dimensions. This paper presents a kind of parallel manipulator with kinematically redundant structure, which can improve the output accuracy by optimizing the error transmission from the active joints to the end-effector. With the kinematic redundancy, free redundant variables can be defined as second task variables, which provide the possibility to select a proper configuration for least error transmission at any pose (the position and orientation) of the end-effector for a given task. Contrast to non-redundant manipulators, the output errors of the proposed manipulator, caused by the active joints input errors, can be optimized rather than determined. By this goal, new limbs with redundant parallel structures are introduced to non-redundant planar parallel manipulators. Numerical example shows that the new architecture has the potential to enhance the output accuracy for a given pose or prescribed trajectory of the end-effector.Copyright

Performance Analysis of a Forging Manipulator Based on the Composite Modeling Method

This paper presents the performance analysis of one type of forging manipulator based on a new approach for the calculation of Jacobian matrices. The Jacobian matrix based evaluation criterions in robotics literature are studied to characterize the kinematic and dynamic manipulability, as well as the force capability of the studied manipulator. The performance measures with respect to the joint space are illustrated to describe the kinematic and dynamic capability of the manipulator intuitively. The ellipses at the best condition points are obtained. The research in this paper can be served as fundamentals of design and optimization of forging manipulators, and predict the best work conditions.

An approach of topology optimization of multi-rigid-body mechanism

Abstract Topology synthesis of multi-rigid-body mechanisms has always been a very important stage in the mechanism design process. In most cases, the topology of the multi-rigid-body mechanism for particular task is obtained by designers’ experience and ingenuity, rather than automatic approach. In this work, an approach of topology optimization of multi-rigid-body mechanisms is investigated. The core process of the approach is an automatic optimization design process. In this approach, we construct kinematics mapping from truss structures to the joint-linked mechanisms, which transforms the topology optimization problem of multi-body system into the truss structure optimization problem. We also develop a new strategy for topology optimization of statically determinate truss, the advantage of which lies in the ability dealing with statically determinate truss topology optimization problem compared to the existing methods. By automatically optimizing the topology of the truss structure, the topology of the multi-rigid-body mechanism is optimized automatically, accordingly. Here, we utilize the investigated approach to design suitable layout for multi-rigid-body micro-displacement amplifying mechanisms (MMAMs) with a large amplification ratio (>50). The layout consists of not only the topology information of the mechanism, but also the dimension parameters of the mechanism. The procedure of the approach is carried out in steps, and a human–computer interaction program has been developed for it. Using the developed program, different MMAMs are achieved. Meanwhile, the direct kinematics analysis of the MMAMs is achieved automatically, the existence of dead point position in the mechanism within movement range is checked and the micro-displacement amplification ratio is calculated out. The computing results are validated by the ADAMS® motion simulation, which proves that the achieved MMAMs fully fulfill the functional requirement. Along with two of the achieved MMAMs, the approach is explained, its functionality is shown, its advantages, limitations, some open problems and future works are discussed.

Conceptual Design and Kinematic Analysis of the Diamobot: A Homogeneous Modular Robot

Nature is the source of inspiration for human invention. As known to all, allotropes of carbon include diamond, graphite and charcoal, all with the same component unit. Inspired by this, we propose a conceptual design of the Diamobot, which is a homogeneous modular robot, with a diamond-like lattice. It can metamorphose as a quite different lattice-type modular robot, with a steadier skeleton than others. Besides, it can be used as a chain-type modular robot, and meanwhile, has a variety of mobile robot configurations. Passive complaint universal joints are equipped to each module, which can greatly enhance the Diamobot’s reconfigurability. In this paper, the Diamobot’s characteristics will be discussed, including the design features, kinematics and metamorphosis with a number of modules.

Design of an electromagnetic prismatic joint with variable stiffness

This paper aims to propose an electromagnetic prismatic joint with variable stiffness. The joint can absorb the sudden shocks and improve the natural dynamics of robotics. The ability of regulating the output stiffness can also be used for force control in industrial applications.,Unlike some existing designs of variable stiffness joints (VSJs) in which the stiffness regulation is implemented using the stiffness adjustment motor and mechanisms, the main structure of the electromagnetic VSJ is a permanent magnet (PM) arranged inside coaxial cylinder coils. The adjustment of input current can cause the change of magnetic force between the PM and the cylinder coils, and thus leads to the variation of output stiffness.,According to the theoretical model, the output stiffness of the electromagnetic VSJ is linearly proportional to the input current. The experiments further indicate that the current-controlled stiffness can make the stiffness variation response of this VSJ more rapid for practical applications. Due to the large damping introduced by the copper-based self-lubrication bearings, the VSJ shows good properties in motion positioning and trajectory tracking.,In summary, the electromagnetic VSJ is compact in size and light in weight. It is possible to realize the online adaptability to work conditions with dynamic load by using this VSJ.

An Experimental Comparison for the Accuracy Improvement of a 6-PSS Parallel Manipulator by Choosing Different Sets of Measurement Data

An experiment of kinematic calibration is conducted to improve the positioning accuracy of a 6-PSS parallel manipulator for large components assembly. To ensure the positioning accuracy of the manipulator with a higher level, the end effector’s pose and position data, which are obtained by the laser tracker, are respectively used in the calibration. The accuracy improvements are compared between the usages of poses and position data and the result shows that though the measurement device has the capability of obtaining the six dimensional poses of the end effector, it is still better to use the position data rather than the pose data to do the kinematic calibration, especially for some large scaled components positioning, for the orientation error may make a bigger influence than the position error in the positioning of the end effector.

Design and kinematic analysis of a spherical parallel manipulator using concurrent planar parallelogram linkages

This paper presents the design of a novel spherical parallel manipulator. The spherical parallel manipulator consists of three identical limbs and each of them is formed by a planar parallelogram linkage, a universal joint, and a revolute one, successively. Its mobility is analyzed using the reciprocal screws. After that, the kinematics is analyzed in detail, including inverse kinematic modeling, which is validated by a numerical example, inverse Jacobian analysis, singularity analysis, and manipulability analysis, which shows a relatively good performance of force transmission. Then based on the analysis, one prototype is fabricated to validate the effectiveness and feasibility of the design. In the end, some conclusions are drawn and future works are discussed.

A General Discretization-Based Approach for the Kinetostatic Analysis of Closed-Loop Rigid/Flexible Hybrid Mechanisms

This paper presents a general approach for the kinetostatic modeling and analysis of closed-loop mechanisms consisting of both rigid and flexible links. Based on the principal axes decomposition of structural compliance matrix, the flexible links are approximated by hyperredundant linkages with rigid bodies connected by passive elastic joints. Hence, the kinetostatic analysis of rigid/flexible hybrid mechanisms can be formulated as static equilibrium problems of the approximate linkages which are regarded as hyperredundant underactuated multibody systems. By taking advantage of mechanism kinematics/statics, the large deflection problems of flexible links can be efficiently solved using the presented discretization-based approach. In order to demonstrate the effectiveness of the proposed method, a hybrid planar four-bar mechanism is provided as an example. And FEA simulations have been conducted to verify the correctness of obtained results.

Design of an Actuation Device With the Capability of Automatically Distributing External Load Based on Stability Theorems

Actuation redundancy is widely used to enhance load-carryingcapability of robot manipulators; however, it also causes theproblems of uneven load distribution and internal forces. Thispaper presents a redundant actuation device which can automati-cally distribute the external load to the actuators equally. A struc-ture, which has two additional rotational degree-of-freedom(DOF), is introduced to coordinate the inconsistent forces andmotions of the redundant actuators. By an appropriate design ofthe coordinating structure, the proposed redundant actuationdevice can work stably at its equilibrium position, even when thesystem is imperfectly actuated. The automatic distribution prop-erty of the proposed actuation device is theoretically proved basedon two stability theorems in classical mechanics, namely, theLagrange’s and the Chetaev’s. Then, numerical simulations areperformed to validate the effectiveness of the design by means ofthe observation of the phase planes and the load distribution. Thisstudy provides an alternative way to design redundant actuationdevices with the capability of automatically distributing the exter-nal loads, such that the stability characteristics can be guaranteedin a mechanical way, rather than control strategies.[DOI: 10.1115/1.4030426]Keywords: actuator, load distribution, stability, redundantlyactuated manipulator