Ergonomic design of a wrist robot : The influence of hyperstaticity on reaction forces and motor strategies

Abstract

Purpose

The purpose of this paper is to propose a method to avoid hyperstaticity and eventually reduce the magnitude of undesired force/torques. The authors also study the influence of hyperstaticity on human motor control during a redundant task.

Design/methodology/approach

Increasing the level of transparency of robotic interfaces is critical to haptic investigations and applications. This issue is particularly important to robotic structures that mimic the human counterpart's morphology and attach directly to the limb. Problems arise for complex joints such as the wrist, which cannot be accurately matched with a traditional mechanical joint. In such cases, mechanical differences between human and robotic joint cause hyperstaticity (i.e. over-constrained) which, coupled with kinematic misalignment, leads to uncontrolled force/torque at the joint. This paper focusses on the prono-supination (PS) degree of freedom of the forearm. The overall force and torque in the wrist PS rotation is quantified by means of a wrist robot.

Findings

A practical solution to avoid hyperstaticity and reduce the level of undesired force/torque in the wrist is presented. This technique is shown to reduce 75 percent of the force and 68 percent of the torque. It is also shown an over-constrained mechanism could alter human motor strategies.

Practical implications

The presented solution could be taken into account in the early phase of design of robots. It could also be applied to modify the fixation points of commercial robots in order to reduce the magnitude of reaction forces and avoid changes in motor strategy during the robotic therapy.

Originality/value

In this paper for the first time the authors study the effect of hyperstaticity on both reaction forces and human motor strategies.

Citation

Esmaeili, M., Jarrassé, N., Dailey, W., Burdet, E. and Campolo, D. (2014), "Ergonomic design of a wrist robot : The influence of hyperstaticity on reaction forces and motor strategies", International Journal of Intelligent Computing and Cybernetics, Vol. 7 No. 3, pp. 289-306. https://doi.org/10.1108/IJICC-10-2013-0047