Abstract
Haptic interaction is essential for the dynamic dexterity of animals, which seamlessly switch from an impedance to an admittance behaviour using the force feedback from their proprioception. However, this ability is extremely challenging to reproduce in robots, especially when dealing with complex interaction dynamics, distributed contacts, and contact switching. Current model-based controllers require accurate interaction modelling to account for contacts and stabilise the interaction. In this manuscript, we propose an adaptive force/position controller that exploits the fractal impedance controller's passivity and non-linearity to execute a finite search algorithm using the force feedback signal from the sensor at the end-effector. The method is computationally inexpensive, opening the possibility to deal with distributed contacts in the future. We evaluated the architecture in physics simulation and showed that the controller can robustly control the interaction with objects of different dynamics without violating the maximum allowable target forces or causing numerical instability even for very rigid objects. The proposed controller can also autonomously deal with contact switching and may find application in multiple fields such as legged locomotion, rehabilitation and assistive robotics.
Highlights
Haptic interaction is essential for the dynamic dexterity of animals, which seamlessly switch from an impedance to an admittance behaviour using the force feedback from their proprioception
If we look at these tasks in the context of robotics, they all continue to be open research questions [1]–[8]
The feasibility of available architectures so far has focused on small scale scenarios with controlled interaction conditions. These optimisation algorithms and controllers exhibited a lack of robustness, which is connected to the need for accurate task models to guarantee interaction stability [1]–[3], [6]. Improving both interaction robustness and haptics is of interest for robotics at large
Summary
Through the force sensor, which is typically used in industrial application and prosthetics. Optimised Port-Hamiltonian controllers have been proposed to make the robots safe for interaction [2], [6], [19] They drive robots using an equivalent mechanical system that guarantees the robustness of interaction by trading-off tracking accuracy and interaction force. The passivised controllers use a virtual spring to evaluate the non-conservative exchange with the environment to guarantee passivity, and exploit the Port-Hamiltonian representation to perform a line integral of this energy [19], [22], [23] They allow velocity tracking as long as there is energy in the reservoir. The Haptic module modifies the planned trajectory to adjust the desired pose of the Task Space Fractal Impedance Controller (TS-FIC) to generate the desired interaction behaviour.
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