From Force Feedback Manipulanda to Surface Haptics: Part II
(In which we establish that Surface Haptics = Awesome!)
In the last post, I described the earliest devices known as “haptic interfaces.” These were graspable robots that let people interact with really complex and interesting 3D virtual environments. My colleague Michael Peshkin and I had the vision of bringing this same sort of rich and interesting haptics to bare fingertips as they moved on touchscreens. We called this surface haptics: programmable haptic effects on physical surfaces.
The only problem was that we had no idea how to actually do surface haptics. Early on we explored various approaches, including selectively making certain areas of the surface harder or softer, but we eventually circled back to force feedback (the basis of those early robotic devices). We had good reasons. One, forces enable physics: graphic objects on the screen can be given heft, stretchiness (feel the slingshot!), and so on. Two, certain patterns of forces can fool the brain into feeling shapes rise out of, or dip into, the surface. Three, forces can actually change what the fingers do; for example, they can push the fingers toward the centers of those tiny keyboard keys. Four, forces can emulate an incredibly wide range of textures, from the smooth and ripply to the rough and prickly and everything in between.
But the question remained: how? Motors make use of magnetism, but our fingers aren’t magnetic. Eventually it became clear that there was little option except to exploit friction.
Friction, I must admit, lacks a certain sex appeal. I am reminded of men’s room graffiti from my undergraduate days in physics: “Ruth is stranger than friction.” Indeed. Yet the fact remains that, when two surfaces come into contact, friction is there. It keeps your fork in your hand and your car from sliding off the road. It is to be respected.
Friction control
The trick to making surface haptics work is to control the friction at the finger-surface interface. There are two parts to this: the amount of friction, and the direction in which it acts. It turns out that, when we started our work, two methods of controlling the amount were already known, although neither was well understood. One method used very high frequency vibrations to reduce friction, and the other method used electric fields to increase friction. For the better part of a decade now, our lab has worked to develop scientific and engineering understanding of both methods, and then to adapt both to glass surfaces.
Eventually, Michael and I founded Tanvas to commercialize our surface haptics technology. Tanvas has developed an advanced form of the electric field method that provides exquisite control over the amount of friction that a finger experiences.
Controlling the amount of friction without changing the direction doesn’t let you do all of the things I listed above, but it lets you do a LOT. For instance, Tanvas’ technology supports an infinite variety of virtual textures, many forms of virtual physics, and the illusion of out-of-plane shape. One thing that always amazes me about the Tanvas solution is that it is solid state — nothing moves! Despite that, it controls the forces on a fingertip in nearly endless ways. If you happen to be at CES this January, stop by the Tanvas booth in Eureka Park to feel for yourself. I think you’ll be pleased that you did.
And yet, as powerful as this technology is, an even more powerful form of surface haptics is coming. In the next part of this blog, I’ll talk about the future: controlling both the amount and the direction of friction at the finger-surface interface.
