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.
Highlights
Day-by-day increase in the use of electrically driven vehicles will eventually lead to an increase in the number of depleted lithium-ion batteries (LIBs) to recycle
We presented a primary attempt to automate the task of nut unfastening by means of robotic surface exploration
Our method solely depends on the self-contained proprioception of the robot, and eliminates the need for external expensive hardware. We have demonstrated this in the context of dismantling an EV battery pack, where individual cell modules are to be separated from their stack
Summary
Day-by-day increase in the use of electrically driven vehicles will eventually lead to an increase in the number of depleted lithium-ion batteries (LIBs) to recycle. This is one of the major challenges at the forefront of automotive industries [1]. Unfastening hexagonal nuts to dismantle LIB components as well as to separate storage cells is a crucial step in this recycling process This is being performed manually by trained workers, who follow safety protocols while dismantling. One way to deal with this is by robotising the dismantling process This increases the safety levels, and reduces the operating costs.
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