Sensory feedback for artificial hands

Abstract

Executing daily chores with missing limbs is undoubtedly very challenging. For a person who has lost his lower arm, it is highly desirable to replace this loss with a device that not only identical in appearance, but closely mimics its capabilities. While there are many prosthetic products of multiple functionalities in the current market, the capability of the device to replicate the tactile sensory system, the sensation largely felt at the fingertips and palm, is often neglected.

The motivation of this work is to provide a sense of embodiment to prosthetic users by supplementing their devices with a sensory feedback to the residual arm using haptic technology. A piezoelectric sensor attached to a fingertip of a Southampton Hand, is used to acquire vibration signals as a textured surface slides past the finger. With an upgraded data acquisition strategy, the piezoelectric sensor has been able to detect signal frequencies generated during the exploratory movement that reliably correlate to all the widths of grooves and ridges of the surface textures under investigation. The same signal frequencies become input signals to the Eccentric Rotation Mass (ERM), a haptic actuator selected to produce vibration to the upper arm, in accordance with the sensation felt by a finger when exploring the surface textures. A prototype that includes the ERM miniature motor and a specially designed brass platform has been fabricated to work at 250 Hz, the optimum frequency of mechanoreceptors underneath the skin of the upper arm. Results from the psychophysical investigation demonstrated that participants were able to associate the vibration patterns perceived at their upper arms with the surface textures felt on their fingertips. The findings from this work provide optimistic possibility that touch sensations that was previously lost could be ‘felt’ by the users. This would undeniably enhance their appreciation towards a well-designed device that feels more natural due to its ‘life-like’ quality.

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