Department of Control Engineering, Electrical Engineering School, Shahid Rajaee Teacher Training University, Lavizan, Tehran, Iran.
Neuromodulation. 2021 Dec;24(8):1467-1474. doi: 10.1111/ner.13126. Epub 2020 Feb 21.
One significant challenge of developing a controller for functional electrical stimulation systems is the time-variant nonlinear dynamics of the neuromusculoskeletal system. In the conventional methods, the stimulation intensity is adjusted by a controller; however, the stimulation frequency is always constant. The previous studies have shown that the stimulation frequency is effective in fatigue formation.
A simultaneous modulation of the stimulation intensity and frequency is proposed to improve the joint controllability and muscle endurance. The presented control method determines pulse width (PW), amplitude, and frequency of the electrical stimulation signal, synchronously. Three different modulations are applied for control of the knee joint to show the superiority of the proposed modulation.
The stimulation intensity is controlled by the PW and pulse amplitude of the electrical signal using an adaptive fuzzy terminal sliding mode controller and a fuzzy logic controller, respectively. Also, a fuzzy logic controller is applied to adjust the stimulation frequency. The proposed method is utilized to control the knee joint movement using quadriceps femoris muscles for ten paraplegic subjects.
Two different test protocols are defined to evaluate the presented method: A protocol for testing the controllability and another protocol for evaluating the produced muscle endurance. The average value of the root mean square of the tracking error was 6.4° for the proposed method which is 5.1° and 9.6° less than PW modulation and synchronous PW and amplitude modulation, respectively. The average time duration of the knee full extension was 96 sec for the proposed method which is 17 and 26 sec more than PW modulation and synchronous PW and amplitude modulation, respectively.
The experimental results show that control performance and tracking ability of the joint reference trajectory are improved by using the simultaneous modulation of PW, amplitude, and frequency.
为功能性电刺激系统开发控制器的一个重大挑战是神经肌肉骨骼系统的时变非线性动力学。在传统方法中，通过控制器调整刺激强度；然而，刺激频率始终是恒定的。先前的研究表明，刺激频率对疲劳形成有效。
提出同时调制刺激强度和频率以提高关节可控性和肌肉耐力。所提出的控制方法同步确定电刺激信号的脉冲宽度 (PW)、幅度和频率。应用三种不同的调制方法来控制膝关节，以显示所提出的调制方法的优越性。
使用自适应模糊终端滑模控制器和模糊逻辑控制器分别通过 PW 和电信号的脉冲幅度控制刺激强度。还应用模糊逻辑控制器来调整刺激频率。使用所提出的方法控制 10 名截瘫受试者的股四头肌的膝关节运动。
定义了两种不同的测试协议来评估所提出的方法：一种用于测试可控性的协议和另一种用于评估产生的肌肉耐力的协议。对于所提出的方法，跟踪误差的均方根的平均值为 6.4°，分别比 PW 调制和同步 PW 和幅度调制少 5.1°和 9.6°。对于所提出的方法，膝关节完全伸展的平均时间持续时间为 96 秒，分别比 PW 调制和同步 PW 和幅度调制多 17 和 26 秒。
实验结果表明，通过同时调制 PW、幅度和频率，提高了关节参考轨迹的控制性能和跟踪能力。
