Method for determining when a force sensor signal baseline in a force-based input device can be updated
Disclosed is a method for determining a force sensor signal baseline in a force-based input device. The method includes accepting a signal associated with touch activity and determining a signal range, wherein the signal range decays with time and is reset when the signal exceeds the current range. A touch event is declared when the signal range exceeds a predetermined activity threshold. A previously determined baseline is held when a touch event is declared, and updated when a touch event is not declared.
1. A method for determining when a force sensor signal baseline in a force-based input device can be updated, the method comprising:
accepting a force sensor signal associated with a touch activity;
determining a force sensor signal range comprising a difference between a decaying maximum of the force sensor signal and a decaying minimum of the force sensor signal, wherein the force sensor signal range decays with time and the force sensor signal range is reset when the force sensor signal exceeds a current range;
declaring a touch event when the force sensor signal range exceeds a predetermined activity threshold;
determining a baseline for the force sensor signal;
holding the previously determined baseline for the force sensor signal when a touch event is declared;
updating the previously determined baseline for the force sensor signal when a touch event is not declared; and
outputting a conditioned force sensor signal that is adjusted based on the updated baseline for the force sensor signal.
2. The method of claim 1 , wherein accepting a force sensor signal associated with a touch activity comprises summing a plurality of force sensor signals from a plurality of force sensors in the force-based input device to form the force sensor signal associated with the touch activity.
3. The method of claim 1 , wherein updating the previously determined baseline for the force sensor signal further comprises filtering the force sensor signal.
4. The method of claim 1 , wherein outputting the conditioned force sensor signal further comprises subtracting the previously determined baseline from the force sensor signal to produce the conditioned force sensor signal.
5. The method of claim 4 , wherein subtracting the previously determined baseline is performed before determining the force sensor signal range.
6. The method of claim 1 , wherein accepting a force sensor signal associated with touch activity further comprises accepting a plurality of force sensor signals from a plurality of force sensors in the force-based input device.
7. The method of claim 6 , further comprising:
determining a plurality of force sensor signal ranges, one for each of the force sensor signals; and
declaring a touch event when any one or more of the force sensor signal ranges exceeds the predetermined activity threshold.
8. The method of claim 1 , further comprising accepting the force sensor signal associated with the touch activity wherein the force sensor is of a piezoelectric type.