Adaptive force and position control of manipulators

The article presents simple methods for the design of adaptive force and position controllers for robot manipulators within the hybrid control architecture. The force controller is composed of an adaptive PID feedback controller, an auxiliary signal, and a force feedforward term, and achieves tracking of desired force setpoints in the constraint directions. The position controller consists of adaptive feedback and feedforward controllers as well as an auxiliary signal, and accomplishes tracking of desired position trajectories in the free directions. The controllers are capable of compensating for dynamic cross-couplings that exist between the position and force control loops in the hybrid control architecture. The adaptive controllers do not require knowledge of the complex dynamic model or parameter values of the manipulator or the environment. The proposed control schemes are computationally fast and suitable for implementation in online control with high sampling rates. The methods are applied to a two-link manipulator for simultaneous force and position control. Simulation results confirm that the adaptive controllers perform remarkably well under different conditions.     

Stable Switching PD Control Using Hunt-Crossley Model for a Press Platform

This study proposes a switching proportional-derivative (PD) controller for a press platform for inspecting the surfaces of a wind turbine blade. We use the Hunt-Crossley model to represent the probe shape or the nonlinearity of the inspection platform. This model consists of a nonlinear spring and a damper; therefore, it is more accurate than linear spring-damper models. We prove the global asymptotic stability of a PD force feedback controller and a PD position feedback (force) controller. However, both the controllers suffer from implementation-related problems. Specifically, the PD force feedback controller makes the impact force large, and the PD position feedback controller cannot easily measure small position changes when the platform contacts the surface. These problems of each controller are solved by switching the two controllers. The PD force feedback control and PD position feedback control are used when the platform is in the contact and noncontact states, respectively. We prove that the proposed switching PD force/position feedback controller is globally asymptotically stable. Further, simulations show satisfactory performance resulting from stable switching between the two control schemes.

     

Adaptive neuro fuzzy based hybrid force/position control for an industrial robot manipulator

In this paper an ANFIS-PD+I (AFSPD+I) based hybrid force/position controller has been proposed which works effectively with unspecified robot dynamics in the presence of external disturbances. A constraint is put to limit the movement of manipulator in XY Cartesian coordinates. The validity of the proposed controller has been tested using a 6-degree of freedom PUMA robot manipulator. The performance comparison have been done with the fuzzy proportional derivative plus integral, fuzzy proportional integral derivative and conventional proportional integral derivative controllers subjected to the same data set with proposed controller. The projected AFSPD+I controller adhered to the desired path closer and smoother than the other mentioned controllers.     

Vibration control of the flexible manipulator with input constraints and external disturbances based on Nussbaum function

In this paper, a boundary control scheme based on the partial differential equation (PDE) model is proposed for the vibration control problem of the flexible manipulator with input constraints and external disturbances. Based on the backstepping method, two boundary controllers are designed to stabilize the position loop subsystem and the attitude loop subsystem, respectively, and auxiliary systems based on the smooth hyperbolic tangent function and Nussbaum function are designed in the controllers to deal with the input saturation and external disturbances. The Nussbaum function can overcome the difficulties in controller design and stability analysis caused by the derivatives of smooth hyperbolic tangent functions. The well-posedness of the closed-loop system is proven by employing the semigroup theory, and the uniformly bounded stability is proved by Lyapunov direct method. Finally, the performance of the proposed control laws is verified by numerical simulations.     

Decentralized adaptive control of manipulators

This article presents two new adaptive schemes for motion control of robot manipulators. The first controller possesses a partially decentralized structure in which the control input for each task variable is computed based on information concerning only that variable and on two “scaling factors” that depend on the other task variables. The need for these scaling factors is eliminated in the second controller by exploiting the underlying topology of the robot configuration space, and this refinement permits the development of a completely decentralized adaptive control strategy. The proposed controllers are computationally efficient, do not require knowledge of either the mathematical model or the parameter values of the robot dynamics, and are shown to be globally stable in the presence of bounded disturbances. Furthermore, the control strategies are general and can be implemented for either position regulation or trajectory tracking in joint-space or task-space. Computer simulation results are given for a PUMA 762 manipulator, and these demonstrate that accurate and robust trajectory tracking is achievable using the proposed controllers. Experimental results are presented for a PUMA 560 manipulator and confirm that the proposed schemes provide simple and effective real-time controllers for accomplishing high-performance trajectory tracking. © 1994 John Wiley & Sons, Inc.     

QFT-based design of force and contact transition controllers for a flexible link manipulator

This paper deals with the modeling, system identification and robust control of flexible link manipulators that are required to perform contact task operations. For a single flexible link (SFL) manipulator in contact, two infinite dimensional models are developed and dynamic differences with respect to the force sensing devices are examined. Generalized orthonormal basis functions (GOBFs) are adopted for system identification and new algorithms are developed that improve the identification of resonant systems. The identification results, combined with estimated measures of model uncertainties, are directly used in the design of robust controllers. For the contact transition control, a switching condition is proposed based on robust position and force controllers. The stability of the switching controller is examined using a piecewise quadratic Lyapunov approach. Both simulation and experimental results are presented showing the effectiveness of the proposed technique.     

Robust Flight Control Using Nonsmooth Optimization for a Tandem Ducted Fan Vehicle

This work addresses the aerodynamic modeling and near‐hover‐flight control design for an unconventional aerial robot of the tandem ducted fan configuration, which is intended to be prototypical of a flight service vehicle. The main model elements of this novel unmanned vehicle, which exhibit highly nonlinear and unstable open‐loop modes, are presented. A frequency‐domain controllability analysis concerning the plant's behavior around the hovering flight condition is then adopted to determine the expected control performance, which is of important practical significance to controllability improvement through vehicle design changes. A robust controller that stabilizes the unmanned vehicle under wind disturbances is designed using a newly developed nonsmooth optimization algorithm, which rigorously and efficiently tunes the arbitrarily predefined structured controller against multiple control requirements. A successive two‐loop architecture is employed in the designed controller. In this architecture, the inner loop provides stability augmentation and decoupling, and the outer loop guarantees the desired velocity tracking performance. Simulation results under stochastic wind gusts are presented to verify the performance of the proposed controllers. Preliminary flight tests are also carried out to demonstrate the performance of the system.     

接触作业型飞行机械臂系统的力/位置混合控制

针对飞行机械臂系统移动接触作业问题,使用了一个力/位置混合控制框架,用以控制飞行器系统持续可靠地接触外部环境同时保持一定大小的接触力,并实现在接触过程中的期望轨迹跟踪.首先将作业空间分成2个子空间--约束空间和自由空间,并分别进行力控制和位置控制.对于力控制问题,证明闭环无人机系统是一个类弹簧-质量-阻尼系统,然后在约束子空间中设计逆动力学控制器来实现接触力控制.自由飞行空间中的运动控制依靠轨迹规划和位置控制器来实现.最后,开发了基于六旋翼飞行机器人的单自由度飞行机械臂系统,在飞行状态下进行接触墙面并跟踪倾斜直线轨迹的实验.结果显示本文所使用方法能够保证在平稳移动的同时控制期望的接触力.     

Adaptive stabilization and tracking control of electrically driven manipulators

This article presents two new adaptive strategies for motion control of uncertain rigid-link, electrically driven manipulators. The first controller is a position regulation scheme that ensures (semiglobal) asymptotic convergence of the position error if no external disturbances are present, and convergence to an arbitrarily small neighborhood of zero in the presence of bounded disturbances. It is shown that the regulation scheme can be modified to provide accurate trajectory tracking control through the introduction of adaptive feedforward elements in the control law; this second control strategy retains the simple structure of the first controller and ensures arbitrarily accurate tracking in the presence of bounded disturbances. Each of the adaptive schemes is computationally efficient and requires virtually no information concerning either the manipulator or actuator models. Computer simulation results are given for a PUMA 560 manipulator and demonstrate that accurate and robust motion control can be achieved by using the proposed controllers. Experimental results are presented for an IMI Zebra Zero manipulator and confirm that the proposed approach provides a simple and effective means of obtaining high performance motion control. © 1996 John Wiley & Sons, Inc.     

Neural network-based position synchronised internal force control scheme for cooperative manipulator system

More complex problems of simultaneous position and internal force control occur with cooperative manipulator systems than that of a single one. In the presence of unwanted parametric and modelling uncertainties as well as external disturbances, a decentralised position synchronised force control scheme is proposed. With a feedforward neural network estimating engine, a precise model of the system dynamics is not required. Unlike conventional cooperative or synchronised controllers, virtual position and virtual synchronisation errors are introduced for internal force tracking control and task space position synchronisation. Meanwhile joint space synchronisation and force measurement are unnecessary. Together with simulation studies and analysis, the position and the internal force errors are shown to asymptotically converge to zero. Moreover, the controller exhibits different characteristics with selected synchronisation factors. Under certain settings, it can deal with temporary cooperation by an intelligent retreat mechanism, where less internal force would occur and rigid collision can be avoided. Using a Lyapunov stability approach, the controller is proven to be robust in face of the aforementioned uncertainties.     

Bilateral parallel force/position teleoperation control

The extension of parallel force/position control to teleoperation systems is considered in this article. In the proposed four‐channel bilateral controller, higher priority is granted to position control at the master side and to force control at the slave side. The primary goal of this control architecture is the enhancement of force and position tracking performance in the presence of uncertainties in the system and environment. The stability and performance of the proposed controller is investigated by analyzing the three decoupled single‐degree‐of‐freedom systems obtained from decoupling and projecting the closed‐loop system dynamics onto the slave task‐space orthogonal directions. Experimental results demonstrate significant improvement in transparency. © 2002 Wiley Periodicals, Inc.     

机器人位置/力控制系统的稳定性

本文通过一个简单的两自由度机器人,分析了 Raibert 和 Craig 提出的位置/力混合控制器的不稳定性问题,提出了力微分反馈控制和在力控制方向引入位置反馈这两种克服不稳定性的方法;在此基础上,对一般机器人提出了一种有效的位置/力控制结构。大量的仿真研究显示了该控制结构的有效性,并给出了关于力控制器设计的一些重要结论.     

Adaptive Jacobian force/position tracking for space free-flying robots with prescribed transient performance

This paper presents a tracking control with guaranteed prescribed performance (PP) for space free-flying robots with uncertain kinematics (Jacobian matrix) and dynamics, uncertain normal force parameter, and bounded disturbances in a compliant contact with a planar surface. Given the orientation of the surface and a nonlinear model of the elastic force, a controller is designed requiring no information on the robot parameters and the disturbances. This controller will guarantee that the tracking errors satisfy PP indexes such as the maximum steady-state errors and overshoots, and the minimum convergence rates. Thus, contact maintenance can be ensured as prescribed. An approximation of the Jacobian is utilized in the presence of uncertain robot kinematics, and PP position/attitude tracking of the free-flying base is achieved in addition to the PP force/position tracking of the manipulator’s fingertip. The proposed controller is based on an error transformation technique, and a directly tunable gain for the transformed error feedback is introduced in the control to trade off between the tracking performance and control effort. Numerical simulations and comparisons demonstrate the effectiveness and superiority of the proposed controller.     

Simulation of a SCARA robot with PD and learning controllers

In this study, a SCARA robot manipulator is simulated under PD and learning based controllers. The trajectory following performance of the robot is studied against these controllers. The adaptive/learning hybrid controller scheme and learning controller method are utilized as learning based controllers. The results of simulations show that, learning algorithm based controllers reduce the position tracking error effectively. The hybrid adaptive/learning controller has similar performance as the learning controller although it uses partial state information and compensates both mechanical and electrical dynamics, whereas the learning controller needs both position and velocity measurements neglecting electrical dynamics.     

Dynamic hybrid position/force control of a two degree-of-freedom flexible manipulator

In this article, a method is proposed whereby both contact force exerted by a flexible manipulator and position of end-effector while in contact with a surface are controlled. We approximate elastic deformations by means of B-spline functions and derive dynamic equations of joint angles, vibration of the flexible link, and constraint force. A controller for the hybrid position/force control of the flexible manipulator is designed on the basis of the singular perturbation method. Simulation results confirm that the controller performs remarkably well. © 3994 John Wiley & Sons, Inc.     

A Modular Scheme for Controller Design and Performance Evaluation in 3D Visual Servoing

In this paper we present a modular scheme for designing and evaluating different control systems for position based dynamic look and move visual servoing systems. This scheme is particularly applied to a 6 DOF industrial manipulator equipped with a camera mounted on its end effector. The manipulator with its actuators and its current feedback loops can be modeled as a Cartesian device commanded through a serial line. In this case the manipulator can be considered as a decoupled system with 6 independent loops. The use of computer vision as feedback transducer strongly affects the closed loop dynamics of the overall system, so that a visual controller is required for achieving fast response and high control accuracy. Due to the long delay in generating the control signal, it is necessary to carefully select the visual controller. In this paper we present a framework that allows the study of some conventional and new techniques to design this visual controller. Besides an experimental setup has been built and used to evaluate and compare the performance of the position based dynamic look and move system with different controllers. Some criterions for selecting the best strategy for each task are established. Quite a lot of results relative to different trajectory tracking control strategies are presented, showing both simulation and real platform responses.     

On the force control problem for flexible joint manipulators

It is shown, using a singular perturbation model of the elastic joint manipulator dynamics and the concept of corrective control. how force control techniques developed for rigid manipulators can be extended to the flexible joint case. It is shown that the overall control law can be implemented in an inner loop/outer loop structure, where the inner loop is a nonlinear control that linearizes the system restricted to a suitable integral manifold in state space and the outer loop is a linear control that can be designed independently of the nonlinear inner loop, using any number of force control schemes designed for rigid manipulators to extend all of the standard techniques for force control of rigid manipulators to the flexible joint case, including hybrid position/force control, impedance control, or any other suitable design     

机械臂的位置与力的混合控制方法

本文研究关于机械臂的位置与力的混合控制方法.为了实现混合控制,首先应用一对被 称为"任务规范投影算子"建立了机械臂混合控制的动态方程.在此基础上,提出了两种控制器 的设计方法,一种是计算力矩方法控制器,另一种是动态补偿变结构控制器.后者不但具有更 好的鲁棒性,并且可以分别调整运动与约束力的跟踪精度.     

基于Matlab机械臂力控系统仿真研究

以位置控制为主的机械臂控制方法已不能满足某些复杂环境（装配、抛光、去毛刺）的应用要求,控制机械臂与环境间的接触力已成为机器人学研究的一个热点。提出一种在Matlab/SimMechanics环境下平面二自由度机械臂力控制的仿真研究方法。在平面中模拟机械臂与环境的接触面,设计振荡抑制控制器,实现机械臂与环境间接触力的控制,以及机械臂与刚性环境碰撞接触过程中冲击振荡阶段的振荡抑制,生成机械臂期望的运动轨迹。仿真结果表明,该方法可实现特定作业下机械臂与环境间接触力的控制。     

Adaptive compliant motion control of manipulators without velocity measurements

This article presents two adaptive schemes for compliant motion control of uncertain manipulators. The first strategy is developed using an adaptive impedance control approach and is appropriate for tasks in which the dynamic character of the end-effector/environment interaction must be controlled, while the second scheme is an adaptive position/force controller and is useful for those applications which require independent control of end-effector position and contact force. The proposed controllers are very general and computationally efficient, require virtually no information regarding the manipulator dynamic model or the environment, and are implementable without velocity measurements. It is shown that the schemes ensure semiglobal boundedness of all signals in the presence of bounded disturbances, and that the ultimate size of the system errors can be made arbitrarily small. The capabilities of the proposed control strategies are illustrated through both computer simulations and laboratory experiments with a 6 degree-of-freedom (DOF) IMI Zebra Zero manipulator. ©1997 John Wiley & Sons, Inc.