A Study on A Sensor Skin Using Wire-Free Tactile Sensing Elements Based on Optical Connection

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In this project we proposed a new structure of tactile sensing device. The tactile sensing chip operates with optical power, and sends optical codes of 6 stress components around the chip. Since the sensing device includes no metal wire, the integration process of tactile sensing elements and a tactile sensor body is simple that enables us to implant high density of tactile sensing elements without loss of elasticity and toughness of the sensing device. The results of the study are summarized as follows.1) We showed the chip design and the 6 stress sensing principle, and examined it experimentally. The tactile sensing chip consists of a VLSI chip and an elastic structure attached on it that deforms by the stress around it. The VLSI chip detects the light intensity that reaches on it through the elastic structure, and it detects the deformation of the elastic structure from the detected light intensity. Using its symmetry of the structure it detects 6 components of stress tensor by the 8 photo-detectors formed on the VLSI chip.2) The detected sensing date are sent with digital codes of optical signal. We fabricated VLSI chip with communication functions including automatic ID assignment to each sensing chip. The circuit based on CMOS 0.35 μm rule occupied 1 mm by 1.4 mm on the chip, and we confirmed the 10 MHz operation.3) Energy consumption with large number of tactile sensing elements with sufficient throughput for tactile sensing was evaluated. This research exposed wireless connection requires inevitable energy consumption that is not suitable for practical tactile sensor. This will motivate a new research area of communication among sensing chips.