Haptic Mushroom: a 3-DoF shape-changing encounter-type haptic device with interchangeable end-effectors

This paper presents the Haptic Mushroom, a grounded encounter-type haptic device with interchangeable end-effectors. It is composed of a three-leg parallel self-constrained mechanism connecting a lower static platform to an upper moving platform. The upper platform moves over the surface of a sphere centered on the lower one. The legs are attached to the moving platform through three joints, which are in turn driven through a spiral cam, finally actuating the chosen end-effector. As a representative example, we consider a soft end-effector, able to change its curvature, and a rigid origami-inspired end-effector, able to change its shape from flat to sharp. However, the device is designed to support a wide range of end-effectors. The paper describes the device and presents the kinematic characterisation of the two end-effectors. We carry out a perceptual experiment, enrolling 12 participants, evaluating the capability of the soft end-effector to render curvatures. Finally, we present a use case where the device is used as an encounter-type haptic interface during interactions with virtual objects.