Combined Admittance Control With Type II Singularity Evasion for Parallel Robots Using Dynamic Movement Primitives

• Published in: IEEE transactions on robotics Vol. 39; no. 3; pp. 1 - 16
• Main Authors: Escarabajal, Rafael J., Pulloquinga, Jose L., Valera, Angel, Mata, Vicente, Valles, Marina, Castillo-Garcia, Fernando J.
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.06.2023; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Behavioral sciences; Control systems design; Controllers; Couplings; Damping; Dynamic movement primitives (DMPs); Electrical impedance; Force; force control; Human motion; Motion perception; parallel robot (PR); Rehabilitation; rehabilitation robotics; Robot control; Singularities; singularity avoidance; Task analysis; Trajectory; Trajectory control
• ISSN: 1552-3098; 1941-0468
• DOI: 10.1109/TRO.2023.3238136

This article addresses a new way of generating compliant trajectories for control using movement primitives to allow physical human-robot interaction where parallel robots (PRs) are involved. PRs are suitable for tasks requiring precision and performance because of their robust behavior. However, two fundamental issues must be resolved to ensure safe operation: first, the force exerted on the human must be controlled and limited, and second, Type II singularities should be avoided to keep complete control of the robot. We offer a unified solution under the dynamic movement primitives (DMP) framework to tackle both tasks simultaneously. DMPs are used to get an abstract representation for movement generation and are involved in broad areas, such as imitation learning and movement recognition. For force control, we design an admittance controller intrinsically defined within the DMP structure, and subsequently, the Type II singularity evasion layer is added to the system. Both the admittance controller and the evader exploit the dynamic behavior of the DMP and its properties related to invariance and temporal coupling, and the whole system is deployed in a real PR meant for knee rehabilitation. The results show the capability of the system to perform safe rehabilitation exercises.