Design and evaluation of a measuring system for human force perception parameters

Abstract

The investigation of vibrotactile perception has been a common area of haptic research for some decades. Nevertheless has haptic sensation been fairly examined metrologically. This is probably due to the high demands on the design of a measurement system regarding the combination of bandwidth, accuracy (<1 mN) and disposable energy (several 100 W for high frequency, high amplitude forces). In this paper, a force perception measurement system based on a dynamic force source is presented. It is designed to deliver sinusoidal forces with amplitude of up to 10 N at frequencies of up to 1000 Hz, while deflection is depending on mass load. For example, a mass of 50 g can still be driven with deflections of 100 μm at 1 kHz. Forces are generated using an electrodynamic actuator. An analogue PID controller in combination with a force prediction model based on concentrated network parameters ensures an accuracy of less than 1 mN at the driving point. Despite force, deflection and velocity of the system's moving parts are monitored. The system is in use to measure the absolute threshold of force perception with a bandwidth of up to 1000 Hz. Super-threshold measurements will include the Just Noticeable Difference (JND) and curves of equal perception. The system is designed to measure normal and lateral forces at the fingertip of a single finger and of precision and power grips of the human hand. First measurements of vibrotactile perception thresholds prove the systems capability to cover the relevant bandwidth and dynamics for human haptic interaction.