A tactile sensor with 5-D deformation sensing element

This paper describes a new tactile sensor using acoustic cell structure based on the detection of ultrasound wavefronts in a flexible medium. The acoustic cell consists of a 2×2 ultrasonic transmitter matrix and a 2×2 ultrasonic sensing matrix which are placed face to face with an interval of a few tens of wavelength. These cells are embedded in flexible spherical finger-tip-like body of a tactile sensor. First, we show an ultrasonic transduction principle to discriminate small deformation of the cell in five dimensions, i.e. 3D displacement and a pair of surface angles of the transmitter matrix relative to the receiver. We then describe a tactile sensor using a single element of the cell, and show that the sensor can measure: 1) 10 μm displacement by 18.5 mm cell height, and 2) 0.001 rad change of surface inclination. We apply the sensor to a robot finger which can sense not only its contact force with arbitrary orientation but also predict the slip of the grasped object