Virtual reality for mechanical button feeling

It is a well-known disadvantage of modern HMIs like touch screens or –pads that the operator does not receive a mechanical feedback from the unit upon his input. This may lead to irritation of the operator, double input, etc. and finally faulty operation.

An approach to solve this problem was the implementation of vibration after the operator touches the respective HMI. However, this could by far not replace the perception of a mechanical knob or button.

Kyoceras HAPTIVITY technology now enables the simulation of a real mechanical button by a distinctive surface vibration.

Biological circle of human reception of a haptic event

► Haptics are a complex interaction of information provided from several nerves and a constructive motion control of finger or any other receptor. The integrated result is the human perception of the respective touch.

Human nerves involved in this process

Just vibration of the surface cannot provide a realistic mechanical button feeling. Necessary technical conditions for an authentic button feeling are:

1. Pressure feeling by a specified pressure detection threshold before the switch event starts.   
2. Specified frequency vibration of the touched surface with one rapid shot wave and natural damping wave.
3. Short timing of the wave output after sensing finger pressure.
4. Different frequencies and waves realize different button feelings.

The human finger cannot distinguish between a vertical movement / vibration of the surface and a horizontal movement / vibration of the surface. Only the scalar value of acceleration is recognized. Considering this, there are two basic approaches to realize a surface vibration:

In order to realize the respective mechanical vibration, an actuator is needed. Kyocera is using specific rod-like shaped multi-stack piezos. 

Principle technical design of an HMI with HAPTIVITY based on piezos

This is an example incorporating an LCD with touch panel. The number of piezos depends on size and design. The core of the unit is the Haptic controller with following key functions:

  • receive the voltage input from the piezos and interpret the pressure load
  • trigger the pressure threshold, generate and amplify the actuation voltage
  • get the local information of the touch from the touch panel controller and adopt the output signal according to the location

In order to achieve an authentic button feeling with flexible adoption to different kind of HMIs it has the following specific features:

Specific features of the KYOCERA HAPTIVITY control IC:

  • 7 "hold down" stages
    → allow multi step operation
  • 256 hold down threshold values
    → precise adjustment of pressure strength
  • 14 different wave patterns
    → realization of differnt knob feelings
  • vibration output strength adjustable in steps from 1 - 100
    → precise actuation control
  • local correction ("weighting") for
    → threshold value level
    → vibration output strength
    → frequency characteristic

Advantages of a piezo based HAPTIVITY system:

  • piezos are thin and light weight (20 mm x 2 mm x 0,5 mm)
    → very limited requirements regarding construction space
  • piezos are very fast (resonse time µs)
    → allow immediate actuation
  • piezos have low power consumption
    → important for mobile devices
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