Unfastening of hexagonal headed screws by a collaborative robot

Ruiya Li, Duc Pham, Jun Huang, Yuegang Tan, Mo Qu, Yongjing Wang, Mairi Kerin, Kaiwen Jiang, Shizhong Su, Chunqian Ji, Quan Liu, Zude Zhou

Research output: Contribution to journalArticlepeer-review

4 Citations (Scopus)
1024 Downloads (Pure)


Disassembly is a core procedure in remanufacturing. Disassembly is currently carried out mainly by human operators. It is important to reduce the labor content of disassembly through automation, to make remanufacturing more economically attractive. Threaded fastener removal is one of the most difficult disassembly tasks to be fully automated. This article presents a new method developed for automating the unfastening of screws. An electric nutrunner spindle with a geared offset adapter was fitted to the end of a collaborative robot. The position of a hexagonal headed screw in a fitted stage was known only approximately, and its orientation in the hole was unknown. The robot was programed to perform a spiral search motion to engage the tool onto the screw. A control strategy combining torque and position monitoring with active compliance was implemented. An existing robot cell was modified and utilized to demonstrate the concept and to assess the feasibility of the solution using a turbocharger as a disassembly case study. Note to Practitioners-Remanufacturing is known to generate substantial economic, social, and environmental benefits. Disassembly is the first operation in a remanufacturing process chain. Unfastening threaded parts ('unscrewing') is a common disassembly task accounting for approximately 40% of all disassembly activity. Like other disassembly tasks, often, unscrewing has to be carried out manually in remanufacturing due to difficulties caused by the variable and unpredictable condition of the end-of-life (EoL) products to be remanufactured. Automating unscrewing operations should reduce the labor content of disassembly, thus lowering remanufacturing costs and promoting the adoption of remanufacturing. This article proposes the use of a collaborative robot to perform autonomous unfastening of hexagonal headed screws. Collaborative robots have built-in force sensors and can be programed to carry out operations involving not only position but also active force and compliance control. They can work safely alongside human operators, enabling the latter to focus on jobs requiring high cognitive or manipulation abilities. The article presents a novel spiral search technique developed to improve the rate of successful engagement between the robot end effector and the screw heads despite uncertainties in the location of the screws. The technique was successfully demonstrated on the dismantling of a turbocharger but can readily be applied to other EoL products with hexagonal headed screws. It can also be used with other kinds of screws (e.g., Phillips screws and slotted-head screws) simply by changing the tool and tuning the robot control parameters. A limitation of the proposed technique is that it can only deal reliably with undamaged screws. In our future research, we will consider screws that are in imperfect conditions through usage and develop appropriate solutions for their removal by robots.

Original languageEnglish
Article number8954893
Pages (from-to)1455-1468
Number of pages14
JournalIEEE Transactions on Automation Science and Engineering
Issue number3
Early online date9 Jan 2020
Publication statusPublished - 9 Jan 2020

Bibliographical note

Funding Information:
Manuscript received August 2, 2019; accepted November 25, 2019. Date of publication January 9, 2020; date of current version July 2, 2020. This article was recommended for publication by Associate Editor B. Fidan and Editor B. Vogel-Heuser upon evaluation of the reviewers’ comments. This work was supported in part by EPSRC under Grant EP/N018524/1, in part by Innovate U.K. under Contract 103667, and in part by the China Scholarship Council under Grant 201706950023. (Corresponding author: Jun Huang.) R. Li is with the Department of Mechanical Engineering, School of Mechanical and Electronic Engineering, Wuhan University of Technology, Wuhan 430070, China, and also with the Department of Mechanical Engineering, School of Engineering, University of Birmingham, Birmingham B15 2TT, U.K. (e-mail: liruiya@whut.edu.cn).

Publisher Copyright:
© 2004-2012 IEEE.

Copyright 2020 Elsevier B.V., All rights reserved.


  • Automated unfastening
  • collaborative robot
  • disassembly
  • human–robot collaboration
  • remanufacturing
  • unscrewing
  • human-robot collaboration

ASJC Scopus subject areas

  • Electrical and Electronic Engineering
  • Control and Systems Engineering


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