On the Design of Miniature Haptic Devices for Upper Extremity Prosthetics

We have developed three different versions of a multifunction haptic device that can display touch, pressure, vibration, shear force, and temperature to the skin of an upper extremity amputee, especially the one who has undergone targeted nerve reinnervation (TR) surgery. In TR patients, sensation from the reinnervated skin is projected to the missing hand. This paper addresses the design of the mechanical display, the portion responsible for contact, pressure, vibration, and shear force. A variety of different overall design approaches satisfying the design specifications and the performance requirements are considered. The designs of the fully prototyped haptic devices are compared through open-loop frequency response, closed-loop force response, and tapping response in constrained motion. We emphasize the tradeoffs between key design factors, including force capability, workspace, size, bandwidth, weight, and mechanism complexity.

I. Introduction

The DESIGN of upper extremity prostheses often gives precedence to cosmesis, grasping, and manipulation. Also important, however, is haptic perception. Haptics subserves a wide variety of manual activities, including stable grasping, activating buttons, knobs, and other interface devices, detecting shape, compliance, texture, etc. The problem of restoring haptic perception to an amputee, however, is a difficult one. Human skin, especially the glabrous skin of the fingertips, is richly innervated by a variety of specialized mechanoreceptors and free nerve endings. The musculoskeletal system is also rich in sensors. All of this information is lost when a limb is amputated. While a prosthetic device can be outfitted in sensors (though certainly not the number of sensors found in the intact limb), it is by no means clear how best to convey sensor data to the nervous system.