Operator-Based Nonlinear Control for a Miniature Flexible Actuator Using the Funnel Control Method

• Main Authors: Keisuke Ueno, Shuhei Kawamura, Mingcong Deng
• Format: Article
• Language: English
• Published: MDPI AG 2021-02-01
• Series: Machines
• Subjects: soft actuator; modeling; operator theory; nonlinear control; right coprime factorization; passivity
• Online Access: https://www.mdpi.com/2075-1702/9/2/26

Recently, the studies of soft actuators have been getting increased attention among various fields. Soft actuators are very safe for fragile objects and have an affinity to humans because they are composed of flexible materials. A miniature flexible actuator is a kind of pneumatically driven soft actuator. It has a bellowed shape and asymmetrical structure. This shape can generate a curling motion in two ways under positive and negative pressures with only one air tube. In the previous article, a control system using adaptive <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mi>λ</mi></semantics></math></inline-formula>-tracking control was proposed. This control gain can become too large as time tends to infinity because the adaptive law exhibits a non-decreasing gain. To solve this problem, the funnel control method is proposed. The adaptive gain of this method not only increases but also decreases; however, the design scheme of the boundary function which is needed to decide on adaptive gain is not proposed here. In this article, an operator-based nonlinear control system’s design and the design scheme of the boundary function using an observer are proposed. Then, the effectiveness of the proposed method is verified by a simulation and an experiment.