Apple wants its touch sensitive devices to function properly even when wet. The tech giant has been granted a patent for “Touch Sensing With Water Rejection.”
About the patent
The patent relates generally to touch sensor panels, and more particularly to techniques for rejecting water droplets located near the edges of a device’s touch sensor panels.
(2) Many types of input devices are presently available for performing operations in a computing system, such as buttons or keys, mice, trackballs, joysticks, touch sensor panels, touch screens and the like.
In the patent Apple notes that, in general, touch screens can recognize a touch and the position of the touch on the touch sensor panel, and the operating system can then interpret the touch in accordance with the display appearing at the time of the touch, then perform one or more actions based on the touch.
And in the case of some touch sensing systems, a physical touch on the display is not needed to detect a touch. For example, in some capacitive-type touch sensing systems, fringing electrical fields used to detect touch can extend beyond the surface of the display, and objects approaching near the surface may be detected near the surface without actually touching the surface.
However, Apple says that not all touches detected on a touch sensor panel are intended user input. For example, water droplets on the surface of the touch sensor panel can be detected as touches. In particular, water droplets that are capacitively coupled to ground via the housing or other conductive structures within a device can appear as a touch.
As a result, water droplets can result in unintended behavior by the device. This can negatively affect user experience, particularly in wet environments. Apple’s patent is designed to to deal with such issues.
Summary of the patent
Here’s Apple’s abstract of the patent: “Techniques for rejecting apparent (but false) touches caused by objects such as water droplets located in areas with parasitic capacitive paths to ground are disclosed. To minimize these false touches, one or more guard conductors can be located in proximity to the housing and driven with a stimulation signal to shield objects from being capacitively coupled to ground through the housing.
“In some examples images of touch can be obtained from a non-bootstrapped or bootstrapped scan and also an extended bootstrapped scan wherein the guard conductor is driven with a stimulation signal that has the same characteristics as the stimulation signal being applied to the sensed touch nodes. In some examples, the results of the extended bootstrapped scan can be subtracted from the non-bootstrapped or bootstrapped scan to identify and reject apparent touches resulting from capacitive coupling to ground.”
