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Tactile Shape Displays for Small Scale Shape Feedback

Parris Wellman, Bill Peine, R. D. Howe

Support provided by the Whitaker Foundation

The tactile display in our prototype system consists of a line of 10 individually actuated pins that are raised against the fingerpad.  Shown below is  a drawing of our design.  A line configuration was chosen since the palpation instrument will be scanned across the tissue allowing motion to provide the other dimension.  This also simplifies the design.  SMA wires are used to drive the pins.  As electric current heats the wire, it goes through a phase transformation and shortens, thus pushing the pin up.  With this design, each pin can move 3 mm and produce over 1 N of force.  A primary problem with SMA is the slow response times.  We overcame this by using water cooling and position feedback for each pin from optical sensors.   Figure 5 shows the response of the pin as a function of desired position frequency.   The output displacement drops by 30% (-3 db point) at 40 Hz.  This satisfies the design specification set by the finger speed experiments.

Shape Display Design.  The upper figure shows the top view of the display and a user’s finger.  The lower figure shows the side view of the display.  Electrical current heats the SMA wires, which undergo a phase transformation and shorten.  This forces the pin up against the fingerpad.  The pin's position is measured optically. 
Frequency Response of the Tactile Display.   Maximum output response of pin motion divided by desired maximum motion of the pin as a function of temporal frequency. 

Related Publications

Peine, W.J., Wellman, P.S., and Howe, R.D., Temporal Bandwidth Requirements for Tactile Shape Displays, Proceedings of the IMECE Haptics Symposium, Dallas, TX, November 1997.

Wellman, P.S., Peine, W.J., and Howe, R.D., “Mechanical Design and Control of a High-Bandwidth Shape Memory Alloy Tactile Display,” proceedings of the International Symposium of Experimental Robotics,  Barcelona, Spain, June 1997.

Also see Simulating Soft Tissue with a Tactile Shape Display

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