Programmable and Portable Vibrotactile Feedback for Intuitive Virtual Grasping: A Preliminary Study Towards Upper Limb Rehabilitation

Wearable hand exoskeleton systems have been developed with virtual reality (VR) and force feedback for upper limb rehabilitation. However, force feedback does not provide intuitive guidance feedback regarding state of a virtual object grasping. To address this issue, we developed vibrotactile feedback interface to provide more intuitive way of guidance feedback for a virtual grasping task. This initial study began by implementing haptic driver circuit to drive two different types of haptic actuators, linear resonant motors (LRMs) and coin brushless motors (CBMs), with AD9850 signal generator that uses advanced direct digital synthesis (DDS) theory and L298N (H-bridge motor driver). Based on a pilot study, we determined identifiable frequencies and amplitudes for LRMs and pulse width modulation (PWM) for CBMs to design vibrotactile patterns with haptic actuators and adequate intensity of a haptic glove force. With five conditions, four vibrotactile feedback conditions with two vibration patterns and one force feedback condition with the haptic glove, we focused on which conditions provide more intuitive guidance feedback when grasping the virtual eggshell without breaking. From both quantitative and qualitative results, the results demonstrated that vibrotactile feedback provides more intuitive guidance feedback than force feedback in the virtual grasping task.