七自由度冗余机械臂避障控制

基于冗余机械臂零空间的自运动特性,提出了一种新的七自由度冗余机械臂避障控制方法.该方法引入臂平面和避障面来参数化表达冗余机械臂的零空间运动;基于这种描述,利用人工势场法实现碰撞检测;根据检测结果得出的虚拟排斥力推导零空间运动方程,改进具有位置内环的逆动力学控制方法,使机械臂避障时的动态性能具有类似质量-阻尼系统的物理特性.该方法可以在控制末端执行器运动的同时实现冗余机械臂避障.为了验证所提出方法的性能,利用在轨自维护实验平台完成了实验.实验结果表明,机械臂与障碍物的最近距离大于40 mm,末端执行器位置动态误差小于10 mm,稳态误差小于2 mm.这些结果显示,所提出的方法通过合理地自运动行为实现了冗余机械臂的避障控制,而且在避障过程中不影响末端执行器的操作.     

A compliance control strategy for robot manipulators under unknown environment

In this paper, a compliance control strategy for robot manipulators that employs a self-adjusting stiffness function is proposed. Based on the contact force, each entry of the diagonal stiffness matrix corresponding to a task coordinate in the operational space is adaptively adjusted during contact along the corresponding axis. The proposed method can be used for both the unconstrained and constrained motions without any switching mechanism which often causes undesirable instability and/or vibrational motion of the end-effector. The experimental results involving a two-link direct drive manipulator interacting with an unknown environment demonstrates the effectiveness of the proposed method.     

Cooperative compliance control of the dual-arm manipulators with elastic joints

Journal of Mechanical Science and Technology - Cooperative compliance control of dual-arm manipulators with elastic joints carrying a constrained object is addressed in this paper. The well-known...     

A study on avoiding joint limits for inverse kinematics of redundant manipulators using improved clamping weighted least-norm method

Journal of Mechanical Science and Technology - A general method is presented for the inverse kinematics resolution of redundant manipulators with joint limits. The success of avoiding joint angular...     

一种新的机器人分散完全自适应前馈反馈控制方法

针对多关节刚性串联机器人多输入多输出特点,提出了一种新的分散完全自适应前馈反馈控制方法.该方法仅需知道机器人关节数目,即可设计控制器,能够保证系统渐近稳定.由于采用分散控制形式,该方法具有结构简单,运算效率高,易于实现等特点.运用Lyapunov方法分析了系统稳定性,最后通过数值仿真验证了该方法的有效性.     

On the fail-safe design of tendon-driven manipulators with redundant tendons

Journal of Mechanical Science and Technology - A tendon-driven manipulator having redundant tendons may possess more flexibility in operation, such as optimizing the performance of tendons,...     

Rapid optimization of tension distribution for cable-driven parallel manipulators with redundant cables

The solution of tension distributions is infinite for cable-driven parallel manipulators(CDPMs) with redundant cables. A rapid optimization method for determining the optimal tension distribution is presented. The new optimization method is primarily based on the geometry properties of a polyhedron and convex analysis. The computational efficiency of the optimization method is improved by the designed projection algorithm, and a fast algorithm is proposed to determine which two of the lines are intersected at the optimal point. Moreover, a method for avoiding the operating point on the lower tension limit is developed. Simulation experiments are implemented on a six degree-of-freedom(6-DOF) CDPM with eight cables, and the results indicate that the new method is one order of magnitude faster than the standard simplex method.The optimal distribution of tension distribution is thus rapidly established on real-time by the proposed method.     

用于桥梁检测的冗余度机器人设计及避障能力分析

针对桥梁检测设备的现状,提出一种新的具有冗余自由度的桥梁检测机器人方案,以实现检测摄像机在桥底的定位。对所提出的桥梁检测机器人进行了构型设计和运动学分析,利用可操作椭球和避障操作椭球的概念对其可操作度和避障能力进行了评估及仿真,以等高线图的形式直观地表示了机构主要参数对机器人可操作度及避障能力的影响,为机器人机构参数优化以及避障路径规划提供了依据。     

Robust control using recursive design method for flexible joint robot manipulators

A flexible joint robot manipulator can be regarded as a cascade of two subsystems: link dynamics and the motor dynamics. Using this structural characteristic, we propose a robust nonlinear recursive control method for flexible manipulators. The recursive design is done in two steps. First, a fictitious robust control for the link dynamics is designed as if it has a direct control input. As the fictitious control, a nonlinear H _∞-control using energy dissipation is designed in the sense of L ₂-gain attenuation from the disturbance caused by uncertainties to performance. In the process, Hamilton-Jacobi (HJ) inequality is solved by a more tractable nonlinear matrix inequality (NLMI) method. In the second step, the other fictitious and the actual robust control are designed recursively by using the Lyapunov’s second method. The proposed robust control is applied to a two-link robot manipulator with flexible joints in computer simulations. The simulation results show that the proposed robust control has robustness to the model uncertainty caused by changes in the link inertia and the joint stiffness.     

A preview approach to force control of robot manipulators

Automated assembly operations that utilize robots tend to constrain the robot's motion due to the task geometry. This constrained motion is termed compliant motion. Complaint motion can be actively controlled using a method of force feedback based upon servo-loop compensation, or it can be passively controlled by mechanical devices integrated into the robot structure. The “preview approach” to force control presented in this paper is a scheme based on predictive calculation of the contact forces that develop at the interface between mating parts. The preview approach utilizes predicted, present and past information to execute motion control. Contact forces are calculated using a mathematical model of the assembly process and are then used to control the compliant motion through suitable compensation torques. The control algorithm used here is more efficient than the standard methods that rely on data from force sensors and use no preview.     

基于RBF神经网络和二次规划的冗余机械臂避障问题研究

针对冗余机械臂的运动灵活性问题,提出了一种基于径向基函数(RBF)神经网络模型和二次规划技术的避障方法。该方法通过建立避障模型来对障碍物和机械臂的关节转角极限等约束进行描述,通过采用调整神经网络输出权值的方法使机械臂逐渐达到最佳运动构型;结合Lyapunov稳定性分析原理,验证了该方法的有效性;利用预选关键杆件方法和离线训练出了机械臂在任意构型下的网络权值模糊查询表,极大地提高了网络的收敛速度,从而可以将该方法应用到机械臂的动态避障规划中;最后,利用一种新型7自由度机械臂对该方法进行了仿真验证,并结合基于雅克比矩阵伪逆的方法进行了对比研究。研究结果表明,该方法计算效率高,适合解决使机械臂在准确跟踪轨迹的同时避开关节转角极限和避障的问题。     

A simple method of accuracy enhancement for industrial manipulators

A robot calibration method which includes identification of kinematic parameters and error compensation is presented. The parameter identification process features an easy-to-perform measurement procedure using a low-cost, instrumented, articulated linkage, and with proper planning of the data collection process, the measurement of actual end effector positions can be performed automatically. The basis of the parameter identification approach is akin to that of closed-loop mechanism synthesis. For error compensation, a computation scheme based on the nominal model as opposed to the calibrated one is presented. The resulting algorithm, allowing the exploitation of the closed-form inverse kinematics solutions available for most industrial robots, is computationally efficient and therefore suited for on-line applications. Examples based on simulation studies, devised to include realistic operating conditions, are presented to demonstrate the feasibility of this method. The effects are also investigated of the number of measurements and of the sensor resolution on the overall quality of the identification.     

Improvement of the control performance of pneumatic artificial muscle manipulators using an intelligent switching control method

Problems with the control, oscillatory motion and compliance of pneumatic systems have prevented their widespread use in advanced robotics. However, their compactness, power/weight ratio, ease of maintenance and inherent safety are factors that could be potentially exploited in sophisticated dexterous manipulator designs. These advantages have led to the development of novel actuators such as the McKibben Muscle, Rubber Actuator and Pneumatic Artificial Muscle Manipulators. However, some limitations still exist, such as a deterioration of the performance of transient response due to the changes in the external inertia load in the pneumatic artificial muscle manipulator. To overcome this problem, a switching algorithm of the control parameter using a learning vector quantization neural network (LVQNN) is newly proposed. This estimates the external inertia load of the pneumatic artificial muscle manipulator. The effectiveness of the proposed control algorithm is demonstrated through experiments with different external inertia loads.     

New control concept of anthropomorphic manipulators

In this paper is presented a new control concept of anthropomorphic manipulators for industrial application. A new algorithm is given for finding the dynamic equations of open kinematic chains using a digital computer. The synthesis of the programmed dynamics has been performed via prescribed motion kinematics. The synthesis of the compensating movement level was proposed too, by measuring contact forces between the object and the terminal device. The presented example of a 6 degrees-of-freedom anthropomorphic manipulator illustrates the proposed approach to manipulator control.     

Dynamic control of manipulators using load-feedback

In the paper is proposed a procedure for introducing feedback with respect to forces, measured in the contact points between the manipulator gripper and working onject. Information about the dynamic reactions serve as data for the realization of a very efficient algorithm, which calculates the supplementary manipulator movements and the corresponding supplementary loads (driving forces) for their realizations. The problem of controlling the complete dynamic model in that way is solved without on-line calculations of the dynamics based on the complex system of differential equations.     

冗余度机器人的非接触阻抗控制

机器人与运动物体接触的过程包括非接触、接触过渡和接触3个部分。对于机器人与高速运动目标接触等存在较大冲击的应用实例，进行有效的非接触阻抗控制是实现机器人稳定、安全作业的必然要求。这方面的研究是实现机器人捕捉运动物体的关键技术，在工业、军事和航天等领域均有重要意义。本文对冗余度机器人非接触阻抗控制的理论和应用研究的现状进行了详细的综述，并提出了需要进一步深入研究的一些问题。     

柔性机器人动力学分析与控制策略综述

综述了柔性机器人动力学分析和控制等相关问题,对柔性机器人动力学分析中变形场的离散化、建模方法、近似分析等问题进行了系统分析。详细介绍了被动控制、PID控制、模糊控制、神经网络控制、自适应控制、鲁棒控制、变结构控制、奇异摄动控制和非线性控制等在柔性机器人控制中的应用情况。指出了在柔性机器人动力学建模和控制中应解决的问题,这对包括柔性机器人在内的多柔体系统动力学建模与控制问题的研究有一定的促进作用。     

A disturbance observer-based adaptive control approach for flexure beam nano manipulators

This paper presents a systematic modeling and control methodology for a two-dimensional flexure beam-based servo stage supporting micro/nano manipulations. Compared with conventional mechatronic systems, such systems have major control challenges including cross-axis coupling, dynamical uncertainties, as well as input saturations, which may have adverse effects on system performance unless effectively eliminated. A novel disturbance observer-based adaptive backstepping-like control approach is developed for high precision servo manipulation purposes, which effectively accommodates model uncertainties and coupling dynamics. An auxiliary system is also introduced, on top of the proposed control scheme, to compensate the input saturations. The proposed control architecture is deployed on a customized-designed nano manipulating system featured with a flexure beam structure and voice coil actuators (VCA). Real time experiments on various manipulating tasks, such as trajectory/contour tracking, demonstrate precision errors of less than 1%.     

Design and analysis of a class of redundant collaborative manipulators with 2D large rotational angles

The parallel spindle heads with high rotational capability are demanded in the area of multi-axis machine tools and 3D printers. This paper focuses on designing a class of 2R1T (R: Rotation; T: Translation) parallel spindle heads and the corresponding collaborative 5-axis manipulators with 2-dimension (2D) large rotational angles. In order to construct 2D rotational degrees of freedom (DOFs), a platform with 2D revolute joints is proposed first. Based on the constraint screw theory, the feasible limbs that can be connected in the platform are synthesized. In order to provide constant rotational axis for the platform, a class of redundant limbs are designed. A class of redundant 2R1T parallel spindle heads is obtained by connecting the redundant limbs with the platform and the redundant characteristics are verified by the modified Grübler-Kutzbach criterion. The corresponding 5-axis collaborative manipulators are presented by constructing a 2-DOF series translational bottom moving platform. The inverse kinematics and the orientation workspace as well as the decoupling characteristics of this type of 2R1T parallel spindle heads are analyzed. The results show that these manipulators have large 2D rotational angles than the traditional A3/Z3 heads and can be potentially used in the application of multi-axis machine tools and the 3D printers.