Specifying the natural stiffness of an exoskeleton arm used as haptics device

D. Chakarov, I. Veneva, M. Tsveov

Abstract: The natural dynamics of an active exoskeleton of upper limb used as haptics device for applications in virtual reality is studied in this work. It is important this device to possess naturally low impedance in order to achieve natural safety in the mutual interaction “human-robot”. On the other hand, the natural dynamics of the device detract from the realism of the haptic feedback, so we are looking for ways to reduce the natural dynamics of the haptic device. To meet these requirements an exoskeleton with actuation system based on pneumatic muscle actuators is revealed, which allows feed-forward planning the parameters that determine the exoskeleton stiffness. The equations of joint stiffness and of operation stiffness are presented, that can be used in the model feedforward compensations and for the feedforward stiffness specification. Computer simulations are carried out using the dimensions of a real exoskeleton.Тabular and graphic examples of the actuator stiffness and joint stiffness description are presented as well as examples of the end-effector compliance specification. The results are derived for the stiffness as a function of the structural parameters such as muscles number, pressure and contraction of muscles, etc.

Series on Biomechanics, Vol.30, No.2 (2016), 3-12

Keywords: compliance; Exoskeleton; haptics device; natural stiffness; pneumatic muscle; safety requirements

Date published: 2017-02-03