The Touch Thimble: Providing Fingertip Contact Feedback During Point-Force Haptic Interaction

Touching a real object with your fingertip provides simultaneous tactile and force feedback, yet most haptic interfaces for virtual environments can convey only one of these two essential modalities. To address this opportunity, we designed, prototyped, and evaluated the Touch Thimble, a new fingertip device that provides the user with the cutaneous sensation of making and breaking contact with virtual surfaces. Designed to attach to the endpoint of an impedance-type haptic interface like a SensAble Phantom, the Touch Thimble includes a slightly oversize cup that is suspended around the fingertip by passive springs. When the haptic interface applies contact forces from the virtual environment, the springs deflect to allow contact between the user's fingertip and the inner surface of the cup. We evaluated a prototype Touch Thimble against a standard thimble in a formal user study and found that it did not improve nor degrade subjects' ability to recognize smoothly curving surfaces. Although four of the eight subjects preferred it to the standard interface, overall the Touch Thimble made subjects slightly slower at recognizing the presented shapes. Detailed subject comments point out strengths and weaknesses of the current design and suggest avenues for future development of the device.