Department of Health Science and Technology, Aalborg University, Frederik Bajers Vej 7D, 9220, Aalborg Ø, Denmark.
Department of Computing and Control Engineering, Faculty of Technical Sciences, University of Novi Sad, Trg Dositeja Obradovica 6, 21000, Novi Sad, Serbia.
J Neuroeng Rehabil. 2021 May 25;18(1):87. doi: 10.1186/s12984-021-00877-5.
Despite important advancements in control and mechatronics of myoelectric prostheses, the communication between the user and his/her bionic limb is still unidirectional, as these systems do not provide somatosensory feedback. Electrotactile stimulation is an attractive technology to close the control loop since it allows flexible modulation of multiple parameters and compact interface design via multi-pad electrodes. However, the stimulation interferes with the recording of myoelectric signals and this can be detrimental to control.
We present a novel compact solution for simultaneous recording and stimulation through dynamic blanking of stimulation artefacts. To test the system, a feedback coding scheme communicating wrist rotation and hand aperture was developed specifically to stress the myoelectric control while still providing meaningful information to the subjects. Ten subjects participated in an experiment, where the quality of closed-loop myoelectric control was assessed by controlling a cursor in a two degrees of freedom target-reaching task. The benchmark performance with visual feedback was compared to that achieved by combining visual feedback and electrotactile stimulation as well as by using electrotactile feedback only.
There was no significant difference in performance between visual and combined feedback condition with regards to successfully reached targets, time to reach a target, path efficiency and the number of overshoots. Therefore, the quality of myoelectric control was preserved in spite of the stimulation. As expected, the tactile condition was significantly poorer in completion rate (100/4% and 78/25% for combined and tactile condition, respectively) and time to reach a target (9/2 s and 13/4 s for combined and tactile condition, respectively). However, the performance in the tactile condition was still good, with no significant difference in path efficiency (38/8%) and the number of overshoots (0.5/0.4 overshoots), indicating that the stimulation was meaningful for the subjects and useful for closed-loop control.
Overall, the results demonstrated that the developed system can provide robust closed-loop control using electrotactile stimulation. The system supports different encoding schemes and allows placing the recording and stimulation electrodes next to each other. This is an important step towards an integrated solution where the developed unit will be embedded into a prosthetic socket.
尽管在肌电假肢的控制和机电一体化方面取得了重要进展，但由于这些系统无法提供体感反馈，用户与仿生肢体之间的通信仍然是单向的。电触觉刺激是一种有吸引力的技术，可以通过多电极实现多个参数的灵活调制和紧凑的接口设计，从而实现闭环控制。然而，刺激会干扰肌电信号的记录，这可能会对控制产生不利影响。
我们提出了一种新颖的紧凑解决方案，通过动态屏蔽刺激伪影来实现同时记录和刺激。为了测试该系统，我们专门开发了一种反馈编码方案，通过该方案可以传达手腕旋转和手开口度的信息，从而在提供有意义的信息给受试者的同时，对肌电控制进行强调。十位受试者参与了一项实验，通过控制二维目标追踪任务中的光标来评估闭环肌电控制的质量。将具有视觉反馈的基准性能与结合视觉反馈和电触觉刺激以及仅使用电触觉反馈的性能进行了比较。
在成功到达目标、到达目标的时间、路径效率和过冲次数方面，视觉反馈和组合反馈条件之间的性能没有显著差异。因此，尽管存在刺激，但肌电控制的质量得以保持。正如预期的那样，触觉条件在完成率方面明显较差（组合和触觉条件下分别为 100/4%和 78/25%）和到达目标的时间（组合和触觉条件下分别为 9/2 s 和 13/4 s）。然而，触觉条件下的性能仍然很好，路径效率（38/8%）和过冲次数（0.5/0.4 个过冲）没有显著差异，这表明刺激对受试者有意义，对闭环控制有用。
总体而言，结果表明，所开发的系统可以使用电触觉刺激提供稳健的闭环控制。该系统支持不同的编码方案，并允许将记录和刺激电极彼此靠近放置。这是朝着集成解决方案迈出的重要一步，开发的单元将嵌入到假肢插座中。
