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Analysis of a Customized Clutch Joint Designed for the Safety Management of an Ultrasound Robot

School of Biomedical Engineering & Imaging Sciences, King’s College London, 4th Floor, Lambeth Wing, St Thomas’ Hospital, London SE1 7EH, UK
Xtronics Ltd., Gravesend, Kent DA12 2AD, UK
Department of Informatics, King’s College London, Strand, London WC2R 2LS, UK
Faculty of Science & Engineering, Queen Mary University of London, Mile End Rd, London E1 4NS, UK
Author to whom correspondence should be addressed.
Appl. Sci. 2019, 9(9), 1900;
Received: 19 March 2019 / Revised: 29 April 2019 / Accepted: 5 May 2019 / Published: 9 May 2019
(This article belongs to the Section Mechanical Engineering)
PDF [4378 KB, uploaded 9 May 2019]


Robotic systems have great potential to assist ultrasound (US) examination. Currently, the safety management method to limit the force that a US robot can apply mostly relies on force sensing and software-based algorithms. This causes the concern that the potential failure of sensors, electrical systems, or software could lead to patient injuries. In this paper, we investigated a customized spring-loaded ball clutch joint designed for a newly developed US robot to passively limit the force applied. The working mechanism of the clutch was modelled and the kinematic-based analysis was performed to understand the variation of the limited force at different postures of the robot. The triggering torque of the clutch was found to be 3928 N·mm, which results in the mean limited force 22.10 ± 1.76 N at the US probe end based on potential postures. The real measurement of the implemented design indicated that the limited force could be set between 17 and 24 N at the neutral posture depending on the preload. With the maximum preload, the mean limited force was found to be 21.98 ± 0.96 N based on 30 repeated measurements. The practically measured results meet the expectation from the theoretical calculation, and the resulting small variation has indicated a good repeatability of the clutch. Based on this evidence, it is concluded that the proposed clutch meets the design aim that it can limit the force applied within a safe range while at the same time ensuring that the required force is applied at different postures. View Full-Text
Keywords: ultrasound robot; robot safety; force control; ball clutch; mechanism design ultrasound robot; robot safety; force control; ball clutch; mechanism design

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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).

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Wang, S.; Housden, R.J.; Noh, Y.; Singh, A.; Lindenroth, L.; Liu, H.; Althoefer, K.; Hajnal, J.; Singh, D.; Rhode, K. Analysis of a Customized Clutch Joint Designed for the Safety Management of an Ultrasound Robot. Appl. Sci. 2019, 9, 1900.

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