Proxy-based guidance virtual fixtures with orientation constraints

Abstract

Aiming at the problem of defining the shortest distance between poses in traditional virtual fixtures, this paper proposes a proxy-based guidance virtual fixtures with orientation constraints, which can assist operators in the path following task. By designing the dynamics of the proxy and then connecting it to the robot using a spring-damping model, the end-effector position can be constrained within the pipeline and cone, and the stiffness coefficients of the virtual forces can be adjusted linearly or nonlinearly. To overcome the cumulative errors, we then propose a discretized improved algorithm, which applies the virtual fixtures on a discretized reference curve. Furthermore, the orientation constraints are defined, and hence the end-effector orientation can also be constrained within a specific range to comply with ergonomics. An experiment was conducted using a Franka Emika Panda robot and involving 9 subjects. The results show that compared to the gravity compensation mode, the pipeline virtual fixtures and the virtual fixtures with the pipeline and cone, as proposed in this paper, reduced task completion time by 38% and 44.7%, respectively. Additionally, they reduced the total mental burden obtained from NASA-TLX by 29.96% and 47.42%, respectively.