欠驱动冗余度空间机器人优化控制

欠驱动控制是空间技术中容错技术的重要方面.本文研究了被动关节中有制动器的欠驱动冗余度空间机器人系统的运动优化控制问题.从系统动力学方程出发,分析了欠驱动冗余度空间机器人的优化能力和控制方法;给出了主、被动关节间的耦合度指标;提出了欠驱动冗余度空间机器人系统的“虚拟模型引导控制”方法,在这种方法中采用与欠驱动机器人机构等价的全驱动机器人作为模型来规划机器人的运动,使欠驱动系统在关节空间中逼近给出的规划轨迹,实现了机器人末端运动的连续轨迹运动优化控制;通过末关节为被动关节的平面三连杆机器人进行了仿真,仿真的结果证明了提出算法的有效性.     

On the local fault tolerance of a kinematically redundant manipulator

This work examines the local fault tolerance of a kinematically redundant manipulator to failures that result in the immobilization of one or more joints. Immobilizing a joint results in additional singularities, which are called locally fault intolerant configurations. These configurations are characterized by the null space of the manipulator Jacobian. The effect that joint failures have on manipulator dexterity is then investigated. It is shown that the reduction in the manipulator's dexterity is also related to the null space of the manipulator Jacobian. © 1996 John Wiley & Sons, Inc.     

Dynamic and stable reconfiguration of self-reconfigurable planar parallel robots

This paper discusses dynamic and stable reconfigurations of self-reconfigurable planar parallel robots that can be done by coupling and decoupling of two underactuated robots on a horizontal plane. The limbs of the parallel robots are 2R open kinematic chains with their second joints unactuated. Two types of self-reconfigurable parallel robots are considered. One is formed by two limbs, and the other is by a limb and an underactuated robot consisting of two limbs and a platform. Uncertainty singularities enable them to self-reconfigure without additional actuators at their coupling mechanism. In this paper, we propose dynamic contact motion control to move them from an initial contact configuration to an uncertainty singular configuration while maintaining their contact. This paper also considers dynamic stability at their uncertainty singularities as equilibrium and shows that there exist geometrically stable configurations without feedback control, which are useful for decoupling. Experiments with real robots are carried out to verify the effectiveness of the dynamic contact motion control and stability analysis.     

Robust adaptive control of an underactuated free-flying space robot under a non-holonomic structure in joint space

This paper introduces a robust adaptive control scheme for an underactuated free-flying space robot under non-holonomic constraints. An underactuated robot manipulator is defined as a robot that has fewer joint actuators than the number of total joints. Because, if one of the joints is out of order, it is so hard to repair the joint, especially in space, the control of such a robot manipulator is important. However, it is difficult to control an underactuated robot manipulator because of the reduced dimension of the input space, i.e. the non-holonomic structure of the underactuated system. The proposed scheme does not need to assume that the exact dynamic parameters must be known. It is analysed in joint space to control the underactuated robot mounted on the space station under parametric uncertainties and external disturbances. The simulation results have shown that the proposed method is very feasible and robust for a two-link planar free-flying space robot with one passive joint.     

Redundant robot control using task based performance measures

The joint velocities required to move the end-effector of a redundant robot with a desired linear and angular velocity depend on its configuration. Similarly, the joint torques produced due to the force and moment at the end-effector also depend on its configuration. When the robot is near a singular configuration, the joint velocities required to attain the end-effector velocity in certain directions are extremely high. Similarly, in some configurations the joint torque produced at certain joints may be high for a relatively small magnitude of external force. An infinite number of trajectories in the joint space can be used to achieve a desired end-effector trajectory for redundant robots. However, a joint trajectory resulting in robot configurations requiring lower joint velocities or joint torques is desired. This may be achieved through a proper utilization of redundancy. Local performance measures for redundant robots are defined in this article as indicators of their ability to follow a desired end-effector trajectory and their ability to apply desired forces at the end-effector. Thus, these performance measures depend on the task to be performed. Control algorithms which can be efficiently applied to redundant robots to improve these performance measures are presented. These control algorithms are based on the gradient projection method. Gradients of the performance measures used in the control schemes result in simple symbolic expressions for “real world” robots'. Feasibility and effectiveness of these control schemes is demonstrated through the simulation of a seven-degree-of-freedom redundant robot derived from the PUMA geometry.     

基于扩展雅可比矩阵的冗余液压驱动四足机器人运动控制

针对冗余液压驱动四足机器人运动学逆解问题,提出一种基于扩展雅可比矩阵的冗余液压驱动四足机器人运动控制方法.该方法既能解决冗余自由度带来的逆解多解问题,还能使机器人足端入地角度满足摩擦锥要求避免足端滑动.首先,规划机器人足端轨迹得到机器人足端速度,在分析机器人足端入地角度对机器人运动性能影响的基础上,结合机器人腿部结构几...     

含有未驱动关节的空间机器人控制

含有未驱动关节的自由潭浮空间机器人具有不可积分的速度和加速度约束，因而是一个二阶非完整系统，通过分析系统的动力学结构，本文设计了一种全 基于速度控制的方法控制未驱动关节，然后采用多步混合控制策略实现空间机器人的定位跟踪。     

Trajectory Tracking Control of an Underactuated Underwater Vehicle Redundant Manipulator System

The purpose of this study is to control the position of an underactuated underwater vehicle manipulator system (U‐UVMS). It is possible to control the end‐effector using a regular 6‐DOF manipulator despite the undesired displacements of the underactuated vehicle within a certain range. However, in this study an 8‐DOF redundant manipulator is used in order to increase the positioning accuracy of the end‐effector. The redundancy is resolved according to the criterion of minimal vehicle and joint motions. The underactuated underwater vehicle redundant manipulator system is modeled including the hydrodynamic forces for the manipulator in addition to those for the autonomous underwater vehicle (AUV). The shadowing effects of the bodies on each other are also taken into account when computing the hydrodynamic forces. The Newton‐Euler formulation is used to derive the system equations of motion including the thruster dynamics. In order to establish the end‐effector trajectory tracking control of the system, an inverse dynamics control law is formulated. The effectiveness of the control law even in the presence of parameter uncertainties and disturbing ocean currents is illustrated by simulations.     

An improved trajectory planner for redundant manipulators in constrained workspace

This article studies the trajectory planning of redundant robots performing tasks within an enclosed workspace. Configuration control of kinematically redundant manipulators using the pseudo‐inverse with null‐space projection method is a well‐known scheme. One advantage of this method is that the gradient of an objective function can be included in the homogeneous term to optimize the objective function without affecting the position of the end‐effector. Using different objective functions, this method can achieve redundancy resolution such as obstacle or joint limits avoidance. Along this line of redundancy resolution, a switching objective function is proposed. We modify Liegeois' joint angle availability objective function so that the midpoints of each joint are switched at a series of prespecified key path points for the end‐effector to achieve. These key path points are planned beforehand according to the geometry of the constrained workspace. The trajectory planning problem can then be viewed as a series of proper postures (i.e., midpoints) determination problems at the key path points. The proper postures are determined using a combination of the potential field method and the elastic model method that takes into account joint operating ranges and the motion tendency of the end‐effector. A variable weighting technique to achieve the proper postures effectively is also presented. Simulations of a planar eight‐link robot in a constrained workspace illustrate the effectiveness of the switching objective function with the variable weighting approach in trajectory planning problems. ©1999 John Wiley & Sons, Inc.     

Differentially Flat Designs of Underactuated Open-Chain Planar Robots

A fully actuated system can execute any joint trajectory. However, if the system is underactuated, not all joint trajectories are attainable. For such systems, it is difficult to characterize attainable joint trajectories analytically. Numerical methods are generally used to characterize these. This paper investigates the property of differential flatness for underactuated planar open-chain robots and studies dependence on inertia distribution within the system. It is shown that certain choices of inertia distributions make an underactuated open-chain planar robot with revolute joints feedback linearizable, i.e., also differentially flat. Once this property is established, trajectory between any two points in the state space can be planned, and a controller can be developed to correct for errors. To demonstrate the proposed methodology in hardware, experiments with an underactuated 3-DOF planar robot are also presented.      

Stiffness characteristics and kinematics analysis of two‐link elastic underactuated manipulators

This article investigates the stiffness characteristics of two‐link underactuated manipulators, examines the effect on the torque resulting in the passive joint, and develops a stiffness model in analysing the behaviors of the manipulators. The kinematic analysis leads to the trajectory of the end‐effector, which is associated with the stiffness coupled between the active and passive joints and with the constraint forces, and the kinematic coupling is shown in the angular displacement and in the resulting torque. The stiffness characteristics are illustrated in the directional stiffness mapping, which gives a quantitative measure of stiffness with respect to displacement direction. © 2002 Wiley Periodicals, Inc.     

Redundancy resolution and obstacle avoidance for cooperative industrial robots

Planning methods for effective manipulation of single or multiple redundant arm systems must take account of DOF, the task, constraints, and joint drifts. Here, a new approach to redundancy resolution and obstacle avoidance for cooperative robot arms is proposed. In this development, a relative Jacobian and a relative dexterity measure for cooperative robot arms are derived. A nonlinear programming method is used to optimize the relative dexterity while satisfying cooperative task requirements, limits on joint angles, and obstacle avoidance. With this approach, it is not necessary to balance the weightings between the cost term to be optimized and the penalty from constraints. Configuration jumps over obstacles are avoided. Further, since globally optimal joint configurations are produced, drifts in joint configurations will be absent from the resulting configurations. This article includes several illustrative examples to demonstrate the effectiveness and usefulness of this approach. Results have indicated the benefits of both the relative dexterity and the sum of individual arm dexterities in planning of cooperative tasks. ©1999 John Wiley & Sons, Inc.     

Indirect robot model learning for tracking control

Learning task-space tracking control on redundant robot manipulators is an important but difficult problem. A main difficulty is the non-uniqueness of the solution: a task-space trajectory has multiple joint-space trajectories associated, therefore averaging over non-convex solution space needs to be done if treated as a regression problem. A second class of difficulties arise for those robots when the physical model is either too complex or even not available. In this situation machine learning methods may be a suitable alternative to classical approaches. We propose a learning framework for tracking control that is applicable for underactuated or non-rigid robots where an analytical physical model of the robot is unavailable. The proposed framework builds on the insight that tracking problems are well defined in the joint task- and joint-space coordinates and consequently predictions can be obtained via local optimization. Physical experiments show that state-of-the art accuracy can be achieved in both online and offline tracking control learning. Furthermore, we show that the presented method is capable of controlling underactuated robot architectures as well.     

Series of Multilinked Caterpillar Track‐type Climbing Robots

Climbing robots have been widely applied in many industries involving hard to access, dangerous, or hazardous environments to replace human workers. Climbing speed, payload capacity, the ability to overcome obstacles, and wall‐to‐wall transitioning are significant characteristics of climbing robots. Here, multilinked track wheel‐type climbing robots are proposed to enhance these characteristics. The robots have been developed for five years in collaboration with three universities: Seoul National University, Carnegie Mellon University, and Yeungnam University. Four types of robots are presented for different applications with different surface attachment methods and mechanisms: MultiTank for indoor sites, Flexible caterpillar robot (FCR) and Combot for heavy industrial sites, and MultiTrack for high‐rise buildings. The method of surface attachment is different for each robot and application, and the characteristics of the joints between links are designed as active or passive according to the requirement of a given robot. Conceptual design, practical design, and control issues of such climbing robot types are reported, and a proper choice of the attachment methods and joint type is essential for the successful multilink track wheel‐type climbing robot for different surface materials, robot size, and computational costs.     

A Reconfigurable Robot With Lockable Cylindrical Joints

This paper presents a new conceptual design for reconfigurable robots. Unlike conventional reconfigurable robots, our design does not achieve reconfigurability by utilizing modular joints. Rather, the robot is equipped with passive joints, i.e., joints without actuator or sensor, which permit changing the Denavit–Hartenberg (DH) parameters such as the link length and twist angle. The passive joints will become controllable when the robot forms a closed kinematic chain. Also, each passive joint is equipped with a built-in brake mechanism that is normally locked, but the lock can be released whenever the parameters are to be changed. Such a versatile and agile robot is particularly suitable for space application for its simple, compact, and light design. The kinematics and recalibration of this kind of reconfigurable robot are thoroughly analyzed. A stable reconfiguration-control algorithm is devised to take the robot from one configuration to another by directly regulating the passive joints to the associated, desired DH parameters. Conditions for the observability and the controllability of the passive joints are also derived in detail.      

A biomimetic approach to inverse kinematics for a redundant robot arm

Redundant robots have received increased attention during the last decades, since they provide solutions to problems investigated for years in the robotic community, e.g. task-space tracking, obstacle avoidance etc. However, robot redundancy may arise problems of kinematic control, since robot joint motion is not uniquely determined. In this paper, a biomimetic approach is proposed for solving the problem of redundancy resolution. First, the kinematics of the human upper limb while performing random arm motion are investigated and modeled. The dependencies among the human joint angles are described using a Bayesian network. Then, an objective function, built using this model, is used in a closed-loop inverse kinematic algorithm for a redundant robot arm. Using this algorithm, the robot arm end-effector can be positioned in the three dimensional (3D) space using human-like joint configurations. Through real experiments using an anthropomorphic robot arm, it is proved that the proposed algorithm is computationally fast, while it results to human-like configurations compared to previously proposed inverse kinematics algorithms. The latter makes the proposed algorithm a strong candidate for applications where anthropomorphism is required, e.g. in humanoids or generally in cases where robotic arms interact with humans.     

Optimal control of manipulators with any number of passive joints

This article discusses the problem of controlling robot manipulators with passive joints, when the number of passive joints is larger than the number of active joints. Assuming that brakes and position sensors are available at each passive joint, we investigate the following issues: (1) what is a sufficient condition for controllability of the passive joints via dynamic coupling with the active joints and how can we quantify the controllability at a given configuration; (2) what is the optimal control and locking sequence of the passive joints; and (3) how can we control both passive and active joints to an equilibrium point in joint space. We propose an optimal control method and demonstrate its validity with both simulation and experimental results. The work presented here is significant because it provides a better understanding and a guideline for utilizing manipulators with passive joints for energy efficiency and fault-tolerant design in applications such as space robotics, hyperredundant robots, and sport mechanics. © 1998 John Wiley & Sons, Inc. 15: 115–129, 1998     

Modified Transpose Effective Jacobian Law for Control of Underactuated Manipulators

Underactuated manipulators consist of active and passive joints, and developing a control technique that can manage such systems is an attractive, challenging problem. Most works in this area present model-based control laws that require a full dynamics model, and are consequently affected from uncertainties and time delays due to massive computations. Non-model-based control approaches provide an efficient alternative for practical implementation. The Modified Transpose Jacobian (MTJ) algorithm is one of these controllers that has been recently proposed for fully actuated manipulators with a square matrix Jacobian. Based on an approximated feedback linearization approach, the MTJ does not need a priori knowledge of the plant dynamics. In this paper, this scheme is extended to the complicated control problem of underactuated robots in Cartesian space. To this end, the notion of the Transpose Effective Jacobian (TEJ) is presented and so the proposed algorithm is called the Modified TEJ (MTEJ) algorithm. The MTEJ control law employs stored data of the control command in the previous time step, as a learning tool to yield an improved performance. Therefore, the proposed law needs just to a portion of mass matrix that corresponds to passive joint(s), and it is much less affected by inaccuracies in system properties. The gains of the proposed MTEJ can be selected more systematically and do not need to be large; hence, the noise rejection characteristics of the algorithm are improved. Also, no need for the pseudo-inversion of the Jacobian matrix in the proposed controller makes further convenience in the underactuated cases. In addition, the relationship between kinematic and dynamic manipulability measures is discussed for underactuated manipulators. Obtained results show its superior performance even compared to that of the model-based algorithms that need full dynamics models, while the proposed MTEJ requires much lower computation effort.     

Adaptive control of redundant multiple robots in cooperative motion

A redundant robot has more degrees of freedom than what is needed to uniquely position the robot end-effector. In practical applications the extra degrees of freedom increase the orientation and reach of the robot. Also the load carrying capacity of a single robot can be increased by cooperative manipulation of the load by two or more robots. In this paper, we develop an adaptive control scheme for kinematically redundant multiple robots in cooperative motion.In a usual robotic task, only the end-effector position trajectory is specified. The joint position trajectory will therefore be unknown for a redundant multi-robot system and it must be selected from a self-motion manifold for a specified end-effector or load motion. In this paper, it is shown that the adaptive control of cooperative multiple redundant robots can be addressed as a reference velocity tracking problem in the joint space. A stable adaptive velocity control law is derived. This controller ensures the bounded estimation of the unknown dynamic parameters of the robots and the load, the exponential convergence to zero of the velocity tracking errors, and the boundedness of the internal forces. The individual robot joint motions are shown to be stable by decomposing the joint coordinates into two variables, one which is homeomorphic to the load coordinates, the other to the coordinates of the self-motion manifold. The dynamics on the self-motion manifold are directly shown to be related to the concept of zero-dynamics. It is shown that if the reference joint trajectory is selected to optimize a certain type of objective functions, then stable dynamics on the self-motion manifold result. The overall stability of the joint positions is established from the stability of two cascaded dynamic systems involving the two decomposed coordinates.     

Design of a spherical parallel kinematic machine for ankle rehabilitation

Existing ankle rehabilitation robots have the limitations of insufficient motion ranges and coupled translations. An improved spherical robot has been proposed to overcome these limitations. The forward and inverse kinematic problems of this new machine are formulated and solved; the dexterity of the workspace is evaluated and the workspace has been optimized with the consideration of the motion ranges of passive joints. The operation of machine has been simulated; it will be further expanded as a control program to run the rehabilitation robot.