Zero Moment Two Edge Pushing of Novel Objects With Center of Mass Estimation

Abstract

Pushing is one of the fundamental nonprehensile manipulation skills to impart to an object changes in position and orientation. To exploit this skill to manipulate novel objects, explicit knowledge of their physical properties should be given a priori. In this work, we estimate the center of mass (CoM) of an object by narrowing down its probable location with a deep learning model and Mason’s voting theorem. In addition, we propose the Zero Moment Two Edge Pushing (ZMTEP) method to translate a novel object without rotation to a goal pose. The proposed method enables a pusher to select the most suitable two-edge-contact configuration for a given object using the estimated CoM and the geometrical shape of the object. Notably, neither the friction between the object and its support plane nor the friction between the object and the pusher are assumed to be known. We evaluate the proposed CoM estimation and ZMTEP methods through a series of experiments in both simulation and real robotic pusher settings. The result shows that the CoM estimation method has good mean squared error properties and small standard deviation, and the ZMTEP method significantly outperforms competitive baseline methods. <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Note to Practitioners</i> —This article aims to endow robotic arms with the capability of moving or aligning objects by pushing, which is much more simple and secure than pick-and-place or in-hand manipulations. Most in-demand manipulation skills require sophisticated hand design and control, which might not be affordable for industrial applications staying cost-competitive. In contrast, robot pushing can be implemented with different types of simple pushers and straightforwardly applied to pre-grasp manipulation. This article makes the estimation of an object’s CoM location practical. Building upon the estimation method, a robust and noise-tolerant two-edge-contact pushing configuration selection method is presented to translate an arbitrarily shaped unknown object to its goal pose.