Force sensing system and method
A force sensing system for determining if a user input has occurred, the system comprising: an input channel, to receive an input from at least one force sensor; an activity detection stage, to monitor an activity level of the input from the at least one force sensor and, responsive to an activity level which may be indicative of a user input being reached, to generate an indication that an activity has occurred at the force sensor; and an event detection stage to receive said indication, and to determine if a user input has occurred based on the received input from the at least one force sensor.
1. A device, comprising:
at least one sensor; and
a controller operable, in a classification operation, to determine whether a candidate input sensor signal derived from the at least one sensor has a given characteristic,
wherein:
the classification operation comprises employing a classification model to determine whether a signal sequence extracted from the candidate input sensor signal belongs to one or more categories defined by the classification model;
the controller is operable to:
populate a feature vector by extracting defined features from the signal sequence;
once the feature vector has been populated, determine whether the signal sequence belongs to said one or more categories based on the populated feature vector; and then
clear the feature vector so that it can be repopulated for a subsequent signal sequence.
2. The device of claim 1 , wherein the controller is operable to start populating the feature vector if the candidate input sensor signal rises above a first threshold.
3. The device of claim 2 , wherein:
where a waveform defined by the signal sequence rises through said first threshold and then falls through a second threshold, the feature vector is populated to contain features which define a profile or shape of the waveform; or
where the waveform defines a pulse, the feature vector is populated to contain the length of the pulse, a gradient to a maximum peak of the pulse, a time from a point the waveform crosses said first threshold to the maximum peak, and/or a maximum value of the maximum peak.
4. The device of claim 1 , wherein the controller is operable to determine whether a defined core event or a defined anomalous event has occurred based on a said category to which the signal sequence is determined to belong.
5. The device of claim 1 , wherein the controller is operable to carry out the classification operation for a set of said signal sequences extracted from the candidate input sensor signal in a given order.
6. The device of claim 5 , wherein the controller is operable to determine whether a defined gesture event has occurred based on a combination of categories to which the plurality of said signal sequences are determined to belong,
optionally based on timings at which the plurality of signal sequences were obtained by the at least one sensor and/or the at least one sensor from which the plurality of signal sequences were obtained.
7. A sensing system for determining if a user input has occurred, the system comprising:
an input channel, to receive an input from at least one sensor;
an activity detection stage, to monitor an activity level of the input from the at least one sensor and, responsive to an activity level which may be indicative of a user input being reached, to generate an indication that an activity has occurred at the sensor; and
an event detection stage to receive said indication, and to determine if a user input has occurred based on the received input from the at least one sensor,
wherein:
the sensing system comprises a configurable input path from the input channel to the activity detection stage and the event detection stage; and
a mode of operation of the input path is different depending on whether activity detection or event detection is being performed.
8. The system of claim 7 , wherein the input channel is arranged to provide at least one of the following:
gain control adjustment of the input from the at least one sensor;
bias voltage adjustment of the input from the at least one sensor;
duty cycling of the at least one sensor;
sensitivity adjustment of the at least one sensor;
polarity adjustment of the at least one sensor; and
offset adjustment of the at least one sensor.
9. The system of claim 7 , wherein the system further comprises:
a sensor conditioning stage, to perform conditioning of an input received from the input channel to provide a conditioned sense signal, wherein the activity detection stage performs the activity level monitoring on the conditioned sense signal.
10. The system of claim 7 , comprising a plurality of sensors, wherein a signal path between the sensors and the stages may be switched to affect power consumption or latency.
11. A device, comprising:
at least one sensor; and
a controller operable, based on a candidate input sensor signal derived from the at least one sensor to:
derive a noise threshold for use with the candidate input sensor signal based on a running estimate of the noise in that signal; and
control, based on a comparison between the candidate input sensor signal and the noise threshold derived for use with that signal, one or more of:
an operation mode of the controller;
a sample rate at which the at least one sensor is sampled;
a system parameter such as a performance parameter; and
which of a plurality of units of the controller are disabled or operating in a low-power mode.
12. The device of claim 11 , wherein the controller is configured to recursively calculate the noise threshold based on current and previous values of the input sensor signal.
13. The device of claim 11 , wherein the controller is configured to calculate a current value of the noise threshold based on a combination of a previous value of the noise threshold and a current value of the input sensor signal.
14. A method of adaptively deriving a noise threshold for use with a given signal, the method comprising calculating the noise threshold based on a running estimate of the noise in the signal.
15. The method of claim 14 , comprising recursively calculating the noise threshold based on current and previous values of the signal.
16. The method of claim 14 , comprising calculating a current value of the noise threshold based on a combination of a previous value of the noise threshold and a current value of the signal, optionally wherein said combination is a sum such as a weighted sum, optionally wherein the weighted sum is defined by a first weighting when the values of the signal are falling and a second weighting different from the first weighting when the values of the signal are rising.
17. The method of claim 14 , comprising constraining the threshold value within upper and lower limit values.
18. The device of claim 1 , wherein the at least one sensor is a force sensor.
19. The system of claim 7 , being a force sensing system, wherein the at least one sensor is a force sensor.
20. The device of claim 1 , wherein the at least one sensor is a force sensor.