Evaluation of Position and Velocity Based Forward Dynamics Compliance Control (FDCC) for Robotic Interactions in Position Controlled Robots

TL;DR

This paper compares position and velocity control modes for implementing forward dynamics compliance control (FDCC) in robotic manipulators, demonstrating that velocity control yields smoother compliance and better force regulation.

Contribution

It provides an empirical evaluation of FDCC on a UR10e robot, highlighting the advantages of velocity control over position control for compliance tasks.

Findings

Velocity control results in smoother compliant behavior.

Velocity control reduces interaction forces during contact.

Experimental results favor velocity control for compliance in robotic manipulation.

Abstract

In robotic manipulation, end-effector compliance is an essential precondition for performing contact-rich tasks, such as machining, assembly, and human-robot interaction. Most robotic arms are position-controlled stiff systems at a hardware level. Thus, adding compliance becomes essential. Compliance in those systems has been recently achieved using Forward dynamics compliance control (FDCC), which, owing to its virtual forward dynamics model, can be implemented on both position and velocity-controlled robots. This paper evaluates the choice of control interface (and hence the control domain), which, although considered trivial, is essential due to differences in their characteristics. In some cases, the choice is restricted to the available hardware interface. However, given the option to choose, the velocity-based control interface makes a better candidate for compliance control because of smoother compliant behaviour, reduced interaction forces, and work done. To prove these points, in this paper FDCC is evaluated on the UR10e six-DOF manipulator with velocity and position control modes. The evaluation is based on force-control benchmarking metrics using 3D-printed artefacts. Real experiments favour the choice of velocity control over position control.