This paper presents an anthropomorphic prosthetic hand, which has a thumb and four fingers, all the fingers of which are driven by servomotors built into the fingers and the palm. A novel flexible three-axis tactile sensor array have been investigated for their suitability to measure the grip forces exerted upon an object held by a prosthetic hand. The tactile sensor array are placed at the thumb of prosthetic hand with the capability of measuring both normal and shear force distribution using quantum tunneling composite (QTC) as a base material. A joystick-like mesa was attached to a sensor base to transfer external force, and there are four fan-shaped electrodes in a cell to decompose the contact force into normal and shear components. The sensor has been realized in a 2 × 6 array of unit sensors, and each unit sensor responds to normal and shear stresses in all three axes, respectively. The zero potential method is used to avoid crosstalk effect by setting all drive lines (row electrodes), which do not involve the measuring point at zero voltage and also by setting all output lines (column electrodes) at zero voltage. Measurement of a single sensor shows that the full-scale range of detectable force are about 10, 10 and 22 N for the x-, y- and z-directions, respectively. The sensitivities of a cell measured with a current setup are 0.47, 0.45 and 0.16 mV/mN for the x-, y- and z-directions, respectively. The sensor showed a high repeatability, low hysteresis, and min tactile cross-talk. The proposed flexible three-axial tactile sensor array can be applied in a curved or compliant surface that requires slip detection and flexibility, such as a prosthetic hand.
Ultra-Thin Silicon based Piezoelectric Capacitive Tactile Sensor
