A new touch sensor for material discrimination and detection of thickness and hardness

This paper reports the development of a new touch sensor for material discrimination and detection of thickness and hardness. Ultrasonic and electrical properties of objects are simultaneously measured by the proposed sensor using a pair of piezoelectric ceramic transducers. The properties are also measured under two contact conditions (i.e., two different sensor weights). The material is discriminated and the thickness and hardness are detected from the measured values. In the experiment, four kinds of materials – aluminium, polymer gel, silicone rubber, and acrylic resin – were prepared. Three thicknesses – 1 cm, 2 cm, and 4 cm – were prepared for each material. Additionally, four grades of hardness of polymer gel and silicone rubber were used. Discrimination of the materials including the detection of thickness and hardness was demonstrated by the measured values of capacitance and propagation time under the two contact conditions. The results indicate that the proposed touch sensor could discriminate four kinds of materials and detect thicknesses between 1 cm and 4 cm, and hardness in silicone and polymer gel.