Smoothly Connected Preemptive Impact Reduction and Contact Impedance Control

Abstract

This article proposes novel control methods that lower impact force by preemptive movement and smooth transition to conventional contact-based impedance control. These techniques are suggested for application in force-control-based robots and position/velocity-control-based robots. Strong impact forces have a negative influence on multiple robotic tasks. Recently, preemptive impact reduction techniques that expand conventional contact impedance control using proximity sensors have been examined. However, a seamless transition from impact reduction to contact impedance control has yet to be demonstrated. It has, therefore, been necessary to switch control strategies or perform complicated parameter tuning. In contrast, our proposed methods utilize a serial combined impedance control framework to solve these problems. The preemptive impact reduction feature can be added to an already-implemented impedance controller because the parameter design is divided into impact reduction and contact impedance control. There is no discontinuity or abrupt alteration in the contact force, nor are there any excessively large contact forces that exceed the intended repulsive force established by the contact impedance control during the transition. Furthermore, although the preemptive impact reduction uses a crude optical proximity sensor, the influence of reflectance is minimized by employing a virtual viscous force. Analyses and real-world experiments with a 1-D mass model confirm these features, which are useful for many robots performing contact tasks.