Nut Unfastening by Robotic Surface Exploration

Abstract

In this paper, we present a novel concept and primary investigations regarding automated unfastening of hexagonal nuts by means of surface exploration with a compliant robot. In contrast to the conventional industrial approaches that rely on custom-designed motorised tools and mechanical tool changers, we propose to use robot fingers to position, grasp and unfasten unknown random-sized hexagonal nuts, which are arbitrarily positioned in the robot’s task space. Inspired by how visually impaired people handle unknown objects, in this work, we use information observed from surface exploration to devise the unfastening strategy. It combines torque monitoring with active compliance for the robot fingers to smoothly explore the object’s surface. We implement a shape estimation technique combining scaled iterative closest point and hypotrochoid approximation to estimate the location as well as contour profile of the hexagonal nut so as to accurately position the gripper fingers. We demonstrate this work in the context of dismantling an electrically driven vehicle battery pack. The experiments are conducted using a seven degrees of freedom (DoF)–compliant robot fitted with a two-finger gripper to unfasten four different sized randomly positioned hexagonal nuts. The obtained results suggest an overall exploration and unfastening success rate of 95% over an average of ten trials for each nut.

Roadmap for a sustainable circular economy in lithium-ion and future battery technologies

“…The developed framework is a proof of concept tested in a simulation environment, and it proposed a trajectory-independent robotic path following for cutting, where the properties of the environment are uncertain. In another work, Rastegarpanah et al proposed a tactile based method for nut unfastening and this method was validated by unfastening the nuts of a Nissan Leaf LIB module [92]. The authors recognized unfastening as a main task in disassembly and showed the generalizability of the proposed method for unfastening the nuts in different sizes and shapes.…”

Enabling Future Closed‐Loop Recycling of Spent Lithium‐Ion Batteries: Direct Cathode Regeneration

“…[52] Some reviews provide a summary of disassembly approaches and related analysis of automation assessments for disassembly operations of spent LIBs, which can increase the circularity during the recycling and stress the necessity of technical developments in robotic disassembly. [53][54][55] After that, nearly all Li-ion batteries today are recycled through a process called "shredding," where the obtained components are shredded into very small pieces. [49,56] These shredding methods, involving multi-stage crushing, air classification, and fine screening, will produce a tremendous amount of impurities that are hard to separate in the subsequent process.…”

Design of an Energy-Aware Cartesian Impedance Controller for Collaborative Disassembly

“…Unscrewing is achieved with the help of a standard Cartesian impedance control scheme in combination with a custom nut-runner, which encloses the hexagonal-shaped screw head. Another unscrewing strategy for screws with a hexagonal shaped screw head was proposed in [13], where screw location and orientation are detected and the unscrewing makes use of a standard Cartesian impedance controller and a conventional 2-fingers gripper. In [14], an unscrewing robotic system for the automatic disassembly of electronic devices was developed.…”