Effects of Shear Stress in Teletaction and Human Perception

Ideally, a tactile stimulator presents information through control of surface normal stress and surface shear stresses. Psy-chophysical experiments measured the eeect of shear stress information on the perception of static stimuli applied normal to the surface. Wax gratings in two diierent orientations and various spatial frequencies were used as stimuli. Elastic layers, representing the anti-aliasing lter on a tactile display, were placed over the stimuli. Using an elastic layer which reduces shear stress transmission improved perception compared to standard elastic layers. Spatial resolution diierences due to diierent elastic layers are explained by modulation indices determined from the predicted sub-surface strain using an elastic half-plane model. INTRODUCTION Information about texture, local compliance, and local shape is important in applications such as telesurgery or handling of fragile objects in telerobotics. Figure 1 shows a general connguration of a teletaction system. One possible application is on a robotic laparoscopic telesurgery system. The tactile sensor is mounted on the end eeector (the laparoscopic instrument), and the tactile stimulator display is mounted on the master ma-nipulator (the user interface). The tactile stimulator presents information recorded by the tactile sensor to the user. Ideally, the patterns felt by the user would be indistinguishable from direct contact with the environment. The tactile stimulator needs to generate surface stresses that realistically represent data collected by the tactile sensor. To fully control surface stress, the ideal tactile display system would be an innnite density array of 3 DOF actuators. This paper examines the perceptual diierence between a 1 DOF and 3 DOF tactile display for simple grating patterns. Tactile displays can control either displacements or forces. In a displacement display, an array of pins is shaped into a con