Haptic perception mechanism of softness-second report, relationship between stiffness of an object and softness sensation

A palpation is a useful method to detect cancer and to evaluate skin or under skin conditions. However, the palpation is a skillful method. Doctor's mental and physical conditions affect diagnoses by the palpation. Additionally, it is hard to share the feeling of palpation with other people because palpation is subjective skill. Therefore, the development of the sensor that can measure the skin and under skin condition of the body like softness as a doctor's palpation is demanded. In this paper, we focus on a haptic perception mechanism of human for evaluating the softness. Six objects are made to conduct sensory tests. The silicone rubber part of the objects has two kinds of thickness and three kinds of Young's modulus. Relationships between physical properties of evaluated objects and the softness that human feel in active touch are investigated. After that, to control the contact condition between objects and finger, a passive touch evaluation system is fabricated. Using the system, relationships between the stiffness of the objects and evaluated haptic softness are investigated under passive touch condition.