Periodic robust robotic rock chop via virtual model control

TL;DR

A new active virtual-model control scheme is introduced that enables knife rocking motion for robot manipulators, without pre-planned trajectories or precise information of the environment, to demonstrate robustness and platform independence.

Abstract

Robotic cutting is a challenging contact-rich manipulation task where the robot must simultaneously negotiate unknown object mechanics, large contact forces, and precise motion requirements. We introduce a new active virtual-model control scheme that enables knife rocking motion for robot manipulators, without pre-planned trajectories or precise information of the environment. Motion is generated and controlled through switching virtual coupling with virtual mechanisms, given by virtual springs, dampers, and masses arranged in a suitable way. Through analysis and experiments, we demonstrate that the controlled robot behavior settles into a periodic motion. Experiments with a Franka manipulator demonstrate robust cuts with five different vegetables, and sub-millimeter slice accuracy from 1 mm to 6 mm at nearly one cut per second. The same controller survives changes in knife shape and cutting board height, and adaptation to a different humanoid manipulator, demonstrating robustness and platform independence.

Figures (13)

• Figure 1: Robotic arm with knife ridigly attached, and snapshots of robotic cutting experiments.
• Figure 2: $20$ N saturated nonlinear spring force profile.
• Figure 3: Virtual mechanism design for rocking motion.
• Figure 4: Phase plane of a mass spring damper system with switching references $r_1=-1$ and $r_2=1$ and positions $z_1=-0.8$ and $z_2=0.8$. Trajectories with different initial conditions converge to the same limit cycle.
• Figure 5: Work done for each cutting cycle. Red: cutting a carrot, blue: no food