Investigation of Timing to Switch Control Mode in Powered Knee Prostheses during Task Transitions

PLOS ONE, Dec 2019

Current powered prosthetic legs require switching control modes according to the task the user is performing (e.g. level-ground walking, stair climbing, walking on slopes, etc.). To allow prosthesis users safely and seamlessly transition between tasks, it is critical to determine when to switch the prosthesis control mode during task transitions. Our previous study defined critical timings for different types of task transitions in ambulation; however, it is unknown whether it is the unique timing that allows safe and seamless transitions. The goals of this study were to (1) systematically investigate the effects of mode switch timing on the prosthesis user’s performance in task transitions, and (2) identify appropriate timing to switch the prosthesis control mode so that the users can seamlessly transition between different locomotion tasks. Five able-bodied (AB) and two transfemoral (TF) amputee subjects were tested as they wore a powered knee prosthesis. The prosthesis control mode was switched manually at various times while the subjects performed different types of task transitions. The subjects’ task transition performances were evaluated by their walking balance and success in performing seamless task transitions. The results demonstrated that there existed a time window within which switching the prosthesis control mode neither interrupted the subjects’ task transitions nor disturbed their walking balance. Therefore, the results suggested the control mode switching of a lower limb prosthesis can be triggered within an appropriate time window instead of a specific timing or an individual phase. In addition, a generalized criterion to determine the appropriate mode switch timing was proposed. The outcomes of this study could provide important guidance for future designs of neurally controlled powered knee prostheses that are safe and reliable to use.

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Investigation of Timing to Switch Control Mode in Powered Knee Prostheses during Task Transitions

July Investigation of Timing to Switch Control Mode in Powered Knee Prostheses during Task Transitions Fan Zhang 0 2 3 4 Ming Liu 0 2 3 4 He Huang 0 2 3 4 0 Funding: This work was funded by National Science Foundation , NSF 1 1361549, to HH; National Institute on Disability and Rehabilitation 2 Data Availability Statement: The data presented in this study are available upon request for researchers who meet the IRB criteria at the University of North Carolina at Chapel Hill for access to confidential data. Interested researchers should send requests for data to He (Helen) Huang, Ph.D. Associate Professor, NCSU/UNC Department of Biomedical Engineering , North Carolina State , University & University of North 3 Editor: Jean L. McCrory, West Virginia University , UNITED STATES 4 Joint Department of Biomedical Engineering, North Carolina State University and University of North Carolina at Chapel Hill , Raleigh, North Carolina , United States of America Current powered prosthetic legs require switching control modes according to the task the user is performing (e.g. level-ground walking, stair climbing, walking on slopes, etc.). To allow prosthesis users safely and seamlessly transition between tasks, it is critical to determine when to switch the prosthesis control mode during task transitions. Our previous study defined critical timings for different types of task transitions in ambulation; however, it is unknown whether it is the unique timing that allows safe and seamless transitions. The goals of this study were to (1) systematically investigate the effects of mode switch timing on the prosthesis user's performance in task transitions, and (2) identify appropriate timing to switch the prosthesis control mode so that the users can seamlessly transition between different locomotion tasks. Five able-bodied (AB) and two transfemoral (TF) amputee subjects were tested as they wore a powered knee prosthesis. The prosthesis control mode was switched manually at various times while the subjects performed different types of task transitions. The subjects' task transition performances were evaluated by their walking balance and success in performing seamless task transitions. The results demonstrated that there existed a time window within which switching the prosthesis control mode neither interrupted the subjects' task transitions nor disturbed their walking balance. Therefore, the results suggested the control mode switching of a lower limb prosthesis can be triggered within an appropriate time window instead of a specific timing or an individual phase. In addition, a generalized criterion to determine the appropriate mode switch timing was proposed. The outcomes of this study could provide important guidance for future designs of neurally controlled powered knee prostheses that are safe and reliable to use. - The advent of powered prosthetic legs has demonstrated great promise to significantly improve the mobility of people with lower limb amputations [1–5]. With powered devices, lower limb amputees are now capable of performing a variety of locomotion tasks more easily and Competing Interests: The authors have declared that no competing interests exist. efficiently, such as staircase climbing and slope walking, which are difficult or even impossible to perform with a passive prosthesis. This is mainly because powered prosthetic legs can generate positive net power over gait cycles during ambulation, a feature that is absent in traditional passive devices. Current commercialized powered lower limb prostheses employ intrinsic control, i.e. control based on intrinsic mechanical feedback [1–2]. Such control is mode-based. Each control mode corresponds to one type of locomotion task (e.g. level-ground walking, stair climbing, walking on slopes, etc.). To allow prosthesis users to transition from one task to another, prosthesis modes need to be switched accordingly. Traditional manual mode switching, such as using a remote key fob [6] or performing extra body motions [1], is functionally viable; however, the manual approaches are cumbersome and sometimes unreliable. To make the prostheses easy to use, a hierarchical prosthesis controller has been proposed and adopted [5, 7, 8]. The hierarchical control structure mainly consists of (1) a high-level controller in which an intent recognition interface is designed to recognize the user’s intended locomotion tasks, and (2) a low-level intrinsic controller that generates the appropriate joint motions according to the user’s task. In the design of high-level controllers, significant efforts have been focused on improving the accuracy in identifying the user’s locomotion tasks and predicting the user’s task transitions [5, 7, 9–13]. Various approaches based on EMG signals from residual muscles [3, 9, 14, 15], intrinsic mechanical measurements [7], and neuromuscular-mechanical fusions [5, 10, 12] have been explored. In the design of hierarchical prosthesis control, det (...truncated)


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Fan Zhang, Ming Liu, He Huang. Investigation of Timing to Switch Control Mode in Powered Knee Prostheses during Task Transitions, PLOS ONE, 2015, 7, DOI: 10.1371/journal.pone.0133965