Smooth transition-based control of encounter-type haptic devices

Encounter-type devices have been introduced to solve one of the main drawbacks of common haptic interfaces i.e. their limited transparency in free space and their restricted ability to render realistic transitions between free space and contact. Advantageously, encounter-type interfaces collide with fingers and display interaction forces only if a contact occurs in the virtual environment. In free space, their end-effectors are mechanically detached from the operator and closely track his fingers, allowing for a perfect transparency. This paper introduces a control scheme that handles the transition between tracking and force display modes in a smooth way. Experimental results using a custom encounter-type interface are also given. The obtained results show the efficiency of the proposed control law when compared to the conventional switch-based control usually found in the literature.