Abstract
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.
Highlights
The advent of powered prosthetic legs has demonstrated great promise to significantly improve the mobility of people with lower limb amputations [1,2,3,4,5]
For W!RA/RD, the critical timing was defined as the beginning of swing phase (i.e. SWF_1 in Fig 4), which was within the safe window; for RA/RD!W, the critical timing, defined as the initial ground contact of the prosthetic foot (i.e. IDS_2 in Fig 4), fell within the safe window for mode switching
In the transition W!stair ascent/descent (SA/SD), the critical timing was defined as the beginning of swing phase, which was the timing SWF_1 in this study
Summary
The advent of powered prosthetic legs has demonstrated great promise to significantly improve the mobility of people with lower limb amputations [1,2,3,4,5]. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript
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