This paper reports on the existing robot force control algorithms and their composition based on the review of 75 papers on this subject. The objective is to provide a pragmatic exposition with speciality on their differences and different application conditions, and to give a guide of the existing robot force control algorithms. The previous work can be categorized into discussion, design and/or application of fundamental force control techniques, stability analysis of the various control algorithms, and the advanced methods. Advanced methods combine the fundamental force control techniques with advanced control algorithms such as adaptive, robust and learning control strategies.

An overview of robot force control

An adaptive motion/force controller is developed for unilateral or bilateral teleoperation systems. The method can be applied in both position and rate control modes, with arbitrary motion or force scaling. No acceleration measurements are required. Nonlinear rigid-body dynamics of the master and the slave robots are considered. A model of the flexible or rigid environment is incorporated into the dynamics of the slave, while a model of the human operator is incorporated into the dynamics of the master. The master and the slave are subject to independent adaptive motion/force controllers that assume parameter uncertainty bounds. Each parameter is independently updated within its known lower and upper bounds. The states of the master (slave) are sent to the slave (master) as motion/force tracking commands instead of control actions (efforts and/or flows). Under the modeling assumptions for the human operator and the environment, the proposed teleoperation control scheme is L/sub 2/ and L/sub /spl infin// stable in both free motion and flexible or rigid contact motion and is robust against time delays. The controlled master-slave system behaves essentially as a linearly damped free-floating mass. If the parameter estimates converge, the environment impedance and the impedance transmitted to the master differ only by a control-parameter dependent mass/damper term. Asymptotic motion (velocity/position) tracking and force tracking with zero steady-state error are achieved. Experimental results are presented in support of the analysis.

Stability guaranteed teleoperation: an adaptive motion/force control approach

From the Publisher:
Nonlinear Control of Engineering Systems is a research monograph on Lyapunov-based control design and analysis techinques for nonlinear systems. The basic idea is to illustrate how recent Lyapunov-based techniques can be utilized to develop control designs for nonlinear systems including: mechanical systems, electrical systems, robotic systems, aerospace systems, and underactuated systems. The introduction presents: (i) motivation for the Lyapunov-based design and analysis techniques, (ii) an overview of the book, (iii) some simple examples as an aid to the less experienced reader. The book presents a complete and detailed theoretical treatment of the stated control objective, and contains a detailed description of the experimental testbed and the results obtained by implementing the developed control algorithms. The experimental results will serve to complement the theoretical content of the book by: (i) demonstrating the feasibility of implementing "complex" nonlinear control algorithms with current computational hardware, (ii) guiding the reader towards adapting these techniques to his/her own needs or for further research, and (iii) bridging the gap between theoretical design and analysis and real-time implementation.

Nonlinear Control of Engineering Systems

In this article, a new sensor-referenced control method using positive acceleration feedback together with a switching control strategy is developed for robot impact control and force regulation. The robot dynamic model is feedback-linearized and decoupled for the free-motion mode, the phase-transition mode, and the constrained-motion mode. Considering the detection of the impact as an event, the event-driven switching control strategy is used to deal with the inadvertent loss of contact of the robotic manipulator. Bouncing can be eliminated after finite switches. A stable transition can be achieved with a nonzero impact velocity; large impact forces can be avoided and the output force can be regulated after contact is established. Stability analysis based on the Lyapunov-like method is given for the proposed system. The scheme was implemented and tested on a 6 DOF PUMA 560 robot arm.

Force regulation and contact transition control

This paper presents an adaptive impedance control scheme for an $n$-link constrained rigid robot manipulator without using the regressor. In addition, inversion of the estimated inertia matrix is also avoided and the new design is free from end-point acceleration measurements. The dynamics of the robot manipulator is assumed that all of the matrices in robot model are unavailable. Since these matrices are time-varying and their variation bounds are not given, traditional adaptive or robust designs do not apply. The function approximation technique is used here to represent uncertainties in some finite linear combinations of the orthogonal basis. The dynamics of the output tracking can thus be proved to be a stable first order filter driven by function approximation errors. Using the Lyapunov stability theory, a set of update laws is derived to give closed loop stability with proper tracking performance. A 2 DOF planar robot with environment constraint is used in the computer simulations to test the efficacy of the proposed scheme.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0263574704000190

Adaptive Impedance Control of Robot Manipulators based on Function Approximation Technique

In this paper, a new method of design of position/force controller for robots with parametric uncertainty is presented. An adaptive control scheme is proposed for constrained robot motion control. The proposed control scheme possesses an important practical feature: under the suggested controller, position, velocity, acceleration and force errors converge to zero without requiring measurements or estimates of acceleration and force derivative. Computer simulation results are also presented for illustration.

An adaptive approach to constrained robot motion control

In this paper, two sliding mode based control schemes in joint space are developed for robust control of constrained robot motion in the presence of dynamic uncertainties. One of the proposed control schemes is developed by using two sliding surfaces; the other scheme is derived by employing only one sliding surface, Under the proposed control schemes, both position and contact force are simultaneously controlled. Computer simulation results are presented for illustration. >

Robust position and force control of robots using sliding mode

This paper presents a solution based on robust control approach for asymptotic position/force control of constrained robots with parametric uncertainty. Important practical feature is that position, velocity, acceleration and force errors converge to zero without requiring measurements or estimates of acceleration and force derivative. In this control scheme, a variable structure controller combined with a PI controller is used to guarantee the convergence of position and force errors without control chattering. Compared with adaptive position/force controllers in the literature, the proposed robust controller is less sensitive to force measurement noise.

R.R.Y. Zhen

Papers

An adaptive approach to constrained robot motion control

Robust position and force control of robots using sliding mode

Asymptotic robust constrained robot motion control