Predicting the Post-Impact Velocity of a Robotic Arm via Rigid Multibody Models: an Experimental Study

Abstract

Accurate post-impact velocity predictions are essential in developing impact-aware manipulation strategies for robots, where contacts are intentionally established at nonzero speed mimicking human manipulation abilities in dynamic grasping and pushing of objects. Starting from the recorded dynamic response of a 7DOF torque-controlled robot that intentionally impacts a rigid surface, we investigate the possibility and accuracy of predicting the post-impact robot velocity from the pre-impact velocity and impact configuration. The velocity prediction is obtained by means of an impact map, derived using the framework of nonsmooth mechanics, that makes use of the known rigid-body robot model and the assumption of a frictionless inelastic impact.The main contribution is proposing a methodology that allows for a meaningful quantitative comparison between the recorded post-impact data, that exhibits a damped oscillatory response after the impact, and the post-impact velocity prediction derived via the readily available rigid-body robot model, that presents no oscillations and that is the one typically obtained via mainstream robot simulator software. The results of this new approach are promising in terms of prediction accuracy and thus relevant for the growing field of impactaware robot control. The recorded impact data (18 experiments) is made publicly available, together with the numerical routines employed to generate the quantitative comparison, to further stimulate interest/research in this field.

Robot Control for Simultaneous Impact tasks via Quadratic Programming-based Reference Spreading

“…Posture task: To address redundancy when tracking a 6DOF impedance task using 7DOF robots, an additional degree of freedom has to be prescribed to preserve uniqueness of the QP solution, while enforcing stable null-space behaviour. We also want to make sure that the null-space configuration at the time of impact is identical between teleoperation and autonomous control, as the impact dynamics are configuration-dependent [40]. We opt to do so by formulating a so-called posture task that defines a desired acceleration β i,r for a given joint as…”

Repeated Collision of a Planar Robotic Arm with a Surface Using Generalized Active Forces

“…Hurmuzlu [25] studied the impact of the kinematic chain's complementarity conditions at the contacting ends and critical configurations of rigid-body kinematic chains where the effect of the impulsive force transmitting a link to link vanishes in a chain. Aouaj et al [26] proposed a procedure to predict the post-impact velocity of a robotic arm based on the idea of removing the post-impact oscillation component, and they acquired good agreement with the experiments.…”

Refined Post-Impact Velocity Prediction for Torque-Controlled Flexible-Joint Robots

“…[3], [4]). This ambitious goal requires a new holistic framework including modeling [5], learning [6], planning [7], sensing [8], and control aspects [9], supported by collision-tolerant hardware [10]- [12].…”

“…These jumps, when they are not addressed directly [9] or indirectly [13] by the control strategy, are seen as a sudden large disturbance in the system which results in poor tracking and even cause instability [14]. When employing an impact-aware strategy such as reference spreading [9], [15], [16], the availability of experimentally-validated post-impact velocity prediction models for robotic manipulators is of high relevance [5]. Other recent research in this direction, but for velocity-controlled robots, includes [17], [18].…”