A basic study on two-axial piezoelectric actuator for tactile display using illusions

In this study, we intend to enhance a tactile display composed of two-axial micro actuators, using tactile illusions such as comb illusion and velvet hand illusion (VHI). The comb illusion causes a feeling of unevenness to the finger surfaces touching a comb´s teeth tips by scratching the sides of the teeth. In VHI, a person rubs his/her hands together on either side of wires strung through a frame, producing the sensation of rubbing a very smooth and soft surface like velvet. According to our investigation, tactile illusions can be controlled by tangential stimuli, which are generated by two-axial micro actuator array. This paper mainly describes the actuator, which is composed of two bimorph piezoelectric elements and two small links connected by three joints. A control system for the two-axial micro actuator is designed based on a multi-layered artificial neural network to compensate for the hysteresis of piezoelectric elements. The neural network is outfitted with a feedback loop including an integral element to reduce the number of neurons. If the result of the left piezoelectric element is compared to that of the right element, the displacement amplitudes and the inclinations coincide on the right and left piezoelectric elements. Although precise hysteresis characteristics such as loop width are considerably different, the present neural system can follow the difference.