Surface haptics render textures, dials: on-the-fly

January 20, 2020 // By Julien Happich
Chicago-based startup Tanvas is gearing up to deliver cost-competitive reconfigurable multi-touch haptics to automotive displays, rendering dials, sliders and any 3D textures, with a pixel-level resolution.

Spun out of Northwestern University in 2011 when company's co-founders Ed Colgate and Michael Peshkin first described their haptic solution in a CHI 2011 paper titled "Enhancing Physicality in Touch Interaction with Programmable Friction”, the startup engineered its haptics around electroadhesion. This effect only relies on surface electrostatic forces interacting with the skin at the tip of your fingers, which under increased touch friction, perceive the same signal as a texture or a pattern protruding out of the touch surface. In effect, the changes in friction are perceived as fine textures, edges and bumps that can be felt without looking although they can be tied to visual representations.

"The way we create electroadhesion is by applying an electric field below the touch interface, which creates an inverse polarity, attracting more of your finger to the surface of the screen. We can modulate that electroadhesion at high frequency and pixel by pixel" explained Tanvas' CEO Phill LoPresti when interviewed by eeNews Europe. "Physically, when the skin is pulled closer to the screen, it experiences more friction as it slides across the screen."

In the touch-display stack, the added cost for haptics is marginal as the company leverages the existing patterned Tx and Rx ITO traces below the glass of the touch-panel and only puts additional ITO lines on top of the same cover glass.

Tanvas’ touch and haptics stack.

The bottom layer is for touch detection, and the top layer consists of floating electrodes for haptics, which couple with the bottom electrodes to turn the touch sensors into haptics actuators, explained LoPresti. "We drive the haptics with the same touch sensing lines, capacitively coupled through the glass to the top electrodes, closing the circuit. The glass provides galvanic isolation to it is very safe" the CEO continued. "We don't complicate the touch panel very much, so the cost differential is negligible" LoPresti added, noting that Tanvas owns the IP (through multiple patents) on how the top electrodes must be patterned relative to the bottom electrodes to properly maximize the electroadhesion effects.

Another important part of the IP is the firmware and software necessary to deliver these haptic effects. The startup has developed a complete development kit with all the tools to design the haptics for any touch interface with ready to use widgets for scroll buttons, sliders or rotating knobs. It also offers to train design engineers with its haptics solution or to design bespoke haptics solutions.

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