Adaptive impedance control of robot manipulators based on Q-learning and disturbance observer

Abstract

In this paper, an adaptive impedance control combined with disturbance observer (DOB) is developed for a general class of uncertain robot manipulators in discrete time. The impedance control is applied to realize the interaction force control of robot manipulators in unknown, time-varying environments. The optimal reference trajectory is produced by impedance control, and the impedance parameters are achieved using Q-learning technique, which is implemented based on trajectory tracking errors. The position control with DOB of robot manipulators is implemented to track the virtual desired trajectory, and the DOB is designed to compensate for unknown compounded disturbance function by bounding both tracking error inputs and compounded disturbance inputs in a permitted control region, of which the compounded disturbance function is taken into account of all uncertain terms and external disturbances. The appropriate DOB parameters are selected applying linear matrix inequalities (LMIs) method. Both the impedance control and the bounded DOB control can well guarantee semiglobal uniform boundness of the closed-loop robot systems based on Lyapunov analysis and Schur complement theory. Simulation results are performed to test and verify effectiveness of the investigated combining adaptive impedance control with DOB.

NC controlled robot for adaptive and constant force 3D polishing

“…Lee and Buss [24] proposed a control scheme that achieves a contact force regulation control by adjusting the target stiffness of the Impedance Controller, as an analogy of human arm force control over an object. In the last years, more complex learning-based approaches like [25] and [26] have been investigated with the aim to provide a more humanized and intelligent interaction with the environment.…”

FAT-Based Robust Adaptive Control of Electrically Driven Robots in Interaction with Environment

“…Result 1. Suppose a sufficient number of basis functions are used and the approximation error can be ignored, then it is not necessary to include the σ -modification terms in (29). Hence, (30) can be reduced toV…”

“…28 However, many previous approaches on impedance control of robot manipulators have excluded actuator dynamics from their controller design. [29][30][31] In other words, their control laws compute the applied torques to the robot joints. In practical implementations, these controllers should be modified by converting the torque signals to motor voltage signals.…”

Variable Impedance Control for Bipedal Robot Standing Balance Based on Artificial Muscle Activation Model

“…To make robotic joints present a "gloppy" or "springy" compliant control behavior similar to human joints, the concept of impedance control in the field of robots has been proposed by Hogan [13]. Impedance control is extensively employed in robotic control and its robustness and feasibility have been acknowledged by many research studies [14,15]. However, a fixed impedance model may not suffice in many applications, and variable impedance is necessary to achieve optimal performance of the system [16]; for example, human beings have the ability to adjust their joint impedance through muscle contraction.…”