2008

Tactile Feedback for Touch-input Devices

As products become more featurerich, manufacturers are looking at ways to improve the human-computer interface (HCI). Touchscreens, with intuitive operation and software flexibility, and screen-printed touch surfaces, with refined aesthetics and better sealing, have become extremely popular. But what these touch-input devices do not supply is tactile confirmation of (1) a button’s location and (2) pressing it. The loss of this tactile information can be detrimental to user engagement and understanding, productivity, completion of transactions, safety, and satisfaction. In some applications, the lack of tactile feedback has been enough of a problem to prevent the conversion from mechanical switches to digital controls. The solution is simple — add tactile feedback to secure the best features of touch-input devices.

altWith the TouchSense® system from Immersion Corporation, tactile feedback (also known as haptic feedback) can be added to no- or low-travel touch surfaces. This technology makes virtual onscreen or graphical panel buttons feel real. They seem to press and release like mechanical buttons, which can improve some usability problems and enhance other aspects of use.

How It Works — The Perception of Pressing Mechanical Buttons

To provide tactile feedback, the system components may vary, depending on the mass of the touch-input device, but the basic architecture is the same, allowing high-speed control over an actuator. When the user presses a graphical button, the haptic feedback system drives the actuator according to a preprogrammed tactile effect. The actuator’s vibrations supply the perception that the graphical button moves, seeming to press and release as if it were mechanical. Because of the high speed and small displacement of the touch-input device, haptic feedback does not interfere with the visual qualities of the display.

The processor load to support a haptics system today is trivial. Touch-input technologies are virtual commodities, and actuator solutions are available off the shelf. A common initial assumption about haptic technology for touch-activated controls is that, to be effective, the full motion of a button or switch has to be replicated. However, the human finger is not that discriminating. Thousands of hours of research have revealed that neurons in the human finger detect very small amounts of motion... if combined with moderate acceleration. Just 0.1 mm of motion, combined with an acceleration of at least 1.5 gee, supplies a sensation perceived as a confirming response. The low threshold of 1.5 gee of acceleration, however, does not necessarily produce the best tactile feedback. A more effective result is created by generating an acceleration and displacement profile that induces a stronger stimulus. These acceleration and displacement profiles can be visualized through “phase portraits”. Phase portraits can be generated after successful electromechanical integration of haptic technology into a touch interface device.

Tactile vibrations or “effects” can be synchronized with sound and display changes, creating a more engaging, multisensory experience. A wide range of tactile effects is possible, from those that reproduce the press and push-away characteristics of various mechanical switches to complex nonlinear vibrations. By varying the frequency, waveform, amplitude, and duration of the effect, the response can be changed to support various user interface features:

  • A brief and subtle tactile effect can be used to help the user find their location on the keypad, similar in purpose to the small bump on a phone’s ‘5’ button and the J and F keys on a standard keyboard.
  • Often-used function buttons (for example, Enter, Start, Back, Next) could have a unique feel, which provides unmistakable confirmation and also helps alert the user when they unintentionally press a button.
  • Controls like fast forward and reverse could provide a subtle vibration that increases or decreases according to speed.
  • Scrolling through lists could be accompanied by a ticking or detent sensation as each entry is passed, giving the user more sense of control.