A High Performance Thermal Control for Simulation of Different Materials in a Fingertip Haptic Device

In this work we present an advanced thermal control for a miniaturized fingertip haptic device: the aim is to achieve high fidelity in following temperature references, in order to accurately simulate contact with different materials. The thermal module is designed to be mounted in a wearable device called Haptic Thimble, which is able to render surface orientation and fast contact transition through a linear electromagnetic actuator. The thermal module is expected to simulate the relatively fast thermal transients occurring at the contact with virtual materials. By means of a thin plate design of the device, and of a specific control implementation presented in this paper, we were able to achieve fast and accurate temperature tracking of temperature transients simulating different real materials. The control implementation and algorithm, making use of an inner current control loop and of an asymmetric temperature control loop is presented in this work and experimentally validated, also in presence of disturbance of the user’s fingerpad. Particularly good results (comparable to non-portable, bulky thermal stages) have been obtained in terms of dynamics and accuracy of the temperature tracking (1 Hz bandpass frequency). Moreover, a perception experiment with seven subjects involving discrimination of contact with different virtual materials (copper, glass, urethane) has been conducted. The aim of the experiment was to assess the capability of the fully wearable device to properly render thermal transients when virtual contact occurs.