Capacitive force sensing is already a proven technology: Synaptics’ invention and implementation of force sensing is in use in the portable computing market today including ForcePad technology for the notebook PCs touchpad, and ClearForce for smartphone touchscreens. Apple later helped to commercialise force sensing with its 3D Touch. Force sensing depends on precise mechanical specification of the touchpad itself and a lower layer in close proximity to the touch surface. The touch surface flexes as the user presses it, bringing the two layers closer together, and changing the capacitance of the two surfaces. By configuring the threshold at which the change in capacitance is recognised as a press, the automobile OEM or tier 1 system supplier can calibrate the force with which the user must press the touchpad in order to activate a function.
This technology is proven, robust and simple in its conception. The most difficult aspect of its implementation is the precise mechanical assembly of the force sensing layers, to tolerances specified in microns. Extremely accurate and repeatable mechanical assembly, however, is a core competence of the automotive sector, and so this technology is particularly suitable for use in vehicles.
A demonstration of a touchpad with force sensing and haptic feedback was presented by Synaptics at the Consumer Electronics Show in January 2016 (see Figure 3). It draws on knowledge acquired in the development of the ForcePad product. But the ForcePad portable computing product is