Event-Triggered Sliding-Mode Control for a Discrete-Time Muscle-Driven Musculoskeletal System

Bionic muscle-driven musculoskeletal systems can dynamically adjust the stiffness between active and antagonistic muscles to improve stability. However, they retain many problems, such as difficulty with sensory feedback control, which arises from the strong coupling of models and large computational loads encountered when optimizing the muscle force online. In this study, based on a bionic muscle model, an event-triggered-sliding-mode controller for a discrete-time-muscle-driven musculoskeletal system (MDMS) was designed to drive the system into a bounded region. Specifically, based on the Hamilton principle and discretization of muscle contraction dynamics, a new discrete-time-muscle-driven musculoskeletal model was constructed to facilitate the decoupling of the muscle model, feedback of the muscle state, and improvement of model control accuracy. Second, to guarantee the boundedness of the closed-loop system, an even-triggered-sliding-mode control law was established by introducing the input-to-state stable (ISS) method to a new type of discrete-time MDMS. The design ensured the convergence of different triggering cases, and an event-triggered-sliding-mode control law was established to obtain faster and smoother response characteristics. Finally, stability was ensured using the Lyapunov synthesis principle. The experimental results demonstrated that the proposed controller could effectively reduce the computational load while maintaining the same performance using a time-based approach. Note to Practitioners - The motivation of this study is to delve into the utilization of the Lyapunov control theory to enhance the control performance of the bionic muscle model. Additionally, it aimed to explore the initial application of the event-trigger mechanism within the musculoskeletal system. The primary focus is on discrete musculoskeletal system modeling, which facilitates the achievement of sensory feedback control for nonlinear muscle models characterized by strong coupling and a multi-segment structure. Using the proposed method, it is possible to regulate the muscle force based on sensory feedback using the principles of Lyapunov control theory. Furthermore, the application of event triggering mechanisms is explored with the goal of reducing the communicational load within musculoskeletal systems.