Event-based haptic vibration synthesis using a recursive filter for lower limb prosthetics

Providing a safe and rich environment to achieve ambulatory rehabilitation of the elderly, accident victims, or physically impaired patients, has motivated many researchers to develop lower limb prosthetic systems able to transmit physical stimuli at the skin surface. To this end, we propose a novel event-based method of synthesizing the vibratory characteristics of different types of material, such as broken stone, concrete, snow, sand, and earth, during walking, by using automatically generated Infinite Impulse Response (IIR) filters with pseudo-randomized coefficients to ensure a unique vibration at every step. As a first step, theoretical results were obtained by providing a simulated force input signal into the IIR filter's Real-Time Simulink model. The outcomes proved to be promising and demonstrated that the synthesized signals are highly comparable to the measured material response in both time and frequency domains. A comparison of the signals obtained by the proposed IIR filter approach and a physical model based technique is presented. Finally, this paper presents a new lower limb prosthetic-skin interface with the capabilities of rendering interactions measured at the foot such as vibrations and pressure points.