D'Arsonval Movement-Based Precise Milligram Force Control for Individual Touch Sense Assessment

Abstract

Humans cannot feel the contact (or touching) force when it is too weak and falls in a specific range. For instance, if it is between several dozens and hundreds of milligram force, then humans may not be able to distinguish whether the object has come in contact with their skin or not. The minimum contact force that the human can feel is called the light touch threshold (LTT). This paper presents a novel apparatus to measure the LTT, which is referred to as an active von Frey (AVF) in this paper. To the best of the authors' knowledge, an LTT measurement device with a precise weak force range is proposed for the first time in this paper. It is possible for the AVF to provide the touching force range from 1 to 400 [mgf]. In order to provide a precise touching force for individual subjects, D'Arsonval movement is chosen as an actuator to rotate the touching AVF pin. Both an electric current applied to the D'Arsonval movement and a rotational angle of the AVF pin are utilized to calculate the touching force by the electromechanical statics. As outcomes of this paper, we found out that the LTTs are very different from individual to individual and they are approximately proportional to the vibration perception thresholds with the results of 13 participants. It is expected that the AVF for LTT measurement can be utilized to design or control the personalized haptic device and, furthermore, to research the human nervous system diseases.