Acceleration-based force-impedance control of a six-dof parallel manipulator

Purpose - This paper seeks to present an acceleration-based force-impedance controller, applied to a six-dof parallel mini-manipulator: the robotic controlled impedance device (RCID). Design/methodology/approach - The proposed control strategy involves three cascade controllers: an inner acceleration controller, built as a set of six single input/single output acceleration controllers (one per manipulator axis), an impedance task-space controller, and an outer force controller. Findings - The control strategy enables two kinds of manipulator behaviour: force-limited impedance control and position-limited force control. The type of behaviour depends only on the chosen manipulator trajectories. Practical implications - The RCID may be used as a force-impedance controlled auxiliary device, coupled in series with a position-controlled commercial industrial robot. The two manipulators combined behave as a single manipulator, having the impedance and force control performance of the RCID, as well as the workspace and trajectory tracking performance of the industrial manipulator. The industrial manipulator should perform free space motion trajectory tracking, the RCID being kept in a "home" position, preserving its small workspace for impedance and force control. Originality/value - A robust control strategy that enables good performance, while the robot executes tasks that involve interaction with the environment, is being proposed. Experimental results on a force-impedance controlled six-dof parallel mini-manipulator are presented.