Design and Analysis of Pneumatic 2-DoF Soft Haptic Devices for Shear Display

Haptic devices use touch to enable communication in a salient and private manner. While most haptic devices are held or worn at the hand, there is recent interest in developing wearable haptic devices for the arms. This frees the hands for manipulation tasks, but creates challenges for wearability. One approach is to use pneumatically driven soft haptic devices that, compared to rigid devices, can be more readily worn due to their form factor and light weight. We propose a two-degree of freedom (2-DOF) pneumatic soft linear tactor that can be mounted on the forearm and provide shear force. The tactor is comprised of four soft fiber-constrained linear pneumatic actuators connected to a dome-shaped tactor head. The tactor can provide fast, repeatable forces on the order of 1 N in shear, in various directions in the plane of the skin surface. We demonstrate the tradeoffs of two housing schemes, one soft and one rigid, that mount the pneumatic soft linear actuator to the forearm. A user study demonstrated the performance of both versions of the device in providing directional cues, highlighting the challenges and importance of grounding soft wearable devices and the difficulties of designing haptic devices given the perceptual limits of the human forearm.