Abstract
This article describes the application and comparison of three nonlinear feedback controllers for low-level control of soft actuators driven by a pressure source and single high-speed on/off solenoid valve. First, a mathematical model of the pneumatic system is established and the limitations of the open-loop system are evaluated. Next, a model of the pneumatic system is developed using Simscape Fluids to evaluate the performance of various control strategies. In this article, State-Dependent Riccati Equation control, sliding mode control, and feedback linearization are considered. To improve robustness to model uncertainties, the sliding mode and feedback linearization control strategies are augmented with integral action. The model of the pneumatic system is also used to develop a feedforward component, which is added to a PI controller with anti-windup. The simulation and experimental results demonstrate the effectiveness of the proposed controllers for pressure tracking.
Highlights
Soft robotics is a rapidly growing field in which the robots are elastically deformable (Rus and Tolley, 2015; Bao et al, 2018; Xu and Wang, 2021)
MOSFETs allow the use of Pulse-Width Modulation (PWM) to control the pressure of fluid passing through the valves
Using this second-order equation, sliding mode controllers are developed in the works of Skorina et al (2015), Luo et al (2017), and Khan and Li (2020) to control the bending angle of soft actuators governed by high-speed on/off solenoid valves
Summary
Soft robotics is a rapidly growing field in which the robots are elastically deformable (Rus and Tolley, 2015; Bao et al, 2018; Xu and Wang, 2021). Relying on the electrical circuit equivalence of pneumatic systems, the dynamic behavior of a bending soft actuator can be approximated as a lumped second-order dynamic equation (Onal and Rus, 2013; Skorina et al, 2015) Using this second-order equation, sliding mode controllers are developed in the works of Skorina et al (2015), Luo et al (2017), and Khan and Li (2020) to control the bending angle of soft actuators governed by high-speed on/off solenoid valves. In the work of Chen et al (2020), a pneumatic model is included to control the bending angle of a fiber-reinforced actuator using two three-way, two-position on/ off valves with a backstepping-based adaptive robust controller and sliding mode controller.
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