A Handheld Haptic Robot for Large-Format Touchscreens

This paper presents a handheld surface robot built around a single steerable wheel that can direct the user's motion or modulate the interaction forces with the touchscreen. Steering control is used to render spatial constraints on a touchscreen surface in coordination with the displayed visual objects. A force sensor using flexures and Hall effect sensors is integrated into the device design for economic two-dimensional force sensing. The flexure array and device frame are built a single part out of nylon using the selective laser sintering additive manufacturing process. The position and orientation of the device are supplied by touchscreen eliminating the need for a grounded external frame and resulting in a more compact form. Potential applications include upper limb stroke therapy, gaming, and touchscreen accessibility for disabled individuals. The device exerts up to 10.6 ± 1.0 N of friction force and has a 90° peak-to-peak sine tracking bandwidth of 7.0 Hz. The embedded force sensor has a 6.5% full-scale force magnitude error with an average 4.0° load angle error. The device tracks force-sensitive compliant haptic boundaries with a stiffness range between 0.1 N/mm and 2.0 N/mm. Also demonstrated is stiffness tracking of a 0.175 N/mm boundary (near maximum stable deflections) with mean error 9.4% of the maximum desired deflection.