Optimal Impedance Force-Tracking Control Design With Impact Formulation for Interaction Tasks

Abstract

The letter presents a force-tracking impedance controller granting a free-overshoots contact force (mandatory performance for many critical interaction tasks such as polishing) for partially unknown interacting environments (such as leather or hard-fragile materials). As in many applications, the robot has to gently approach the target environment (whose position is usually not well-known), then execute the interaction task. Therefore, the algorithm has been designed to deal with both the free space approaching motion (phase a.) and the succeeding contact task (phase b.) without switching from different control logics. Control gains have to be properly calculated for each phase in order to achieve the target force tracking performance (i.e., free-overshoots contact force). In detail, phase a. control gains are optimized based on the impact collision model to minimize the force error during the following contact task, while phase b. control gains are analytically calculated based on the solution of the LQR optimal control problem. The analytical solution grants the continuous adaptation of the control gains during the contact phase on the estimated value of the environment stiffness (obtained through an on-line extended Kalman filter). A probing task has been carried out to validate the performance of the control with partially unknown contact environment properties. Results show the avoidance of force overshoots and instabilities

Adaptive Variable Parameter Impedance Control for Apple Harvesting Robot Compliant Picking

“…After all creep experiments are completed, the data are averaged. e MATLAB fitting toolbox is used to fit the data by equation (2). e fitting results are shown in Figure 1.…”

“…In order to solve the problem of rapid compliant picking, many scholars have conducted a lot of research studies, and many studies have applied impedance control to it. For example, based on the optimal control theory, the set value of the internal impedance control layer was calculated by using the external admittance control layer, and the gain of the impact model was optimized to achieve the control performance with estimated error [2]. To realize the flexible adjustment of force and position of the manipulator under high-speed clamping and achieve good tracking effect, a robust impedance control method was proposed [3].…”

A Dynamical-System-Based Approach for Controlling Robotic Manipulators During Noncontact/Contact Transitions

“…Indirect force control architectures address the problem of switching between controllers [14]. [15] proposed a two layers controller which consists of an impedance and an admittance controllers. The parameters of the latter are calculated by solving a Linear Quadratic Regulator problem to minimize the force overshooting.…”

“…if 0 < q δẋ, (25a) is monotonically decreasing and (25b) is monotonically increasing. Hence, based on (25b), q 1Tẋ (t * ) = δẋ at t * = −ln( ν ν+δẋ −q Tẋ δẋ, substituting (5),(15) and t * into (25a) yieldsq 1 T x(t * ) = (δẋ + ν)(−ω −1 ln( ν ν + δẋ − q 1 Tẋ )) + (q δẋ)ω −1 + q 1 T x 0 = (−(δẋ + ν) ln( ν ν + δẋ − q 1 Tẋ 0 ) − δẋ + q…”

Optimal Trajectory Planning and Compliant Spacecraft Capture Using a Space Robot

“…Similar to the contact force estimation, research in the field of impedance control extends beyond the field of spacecraft capture. One such example is the research perfomed by Roveda et al [36], who presented a forcetracking impedance controller which granted an overshoot-free contact force to allow interactions with partially-unknown environments using a modified linear quadratic regulator to analytically determine the optimal gains. A probing task was carried out and results have shown that the controller avoids force overshoots and instabilities.…”