Tap Detection

• US 20110087454A1
• Filed: 10/01/2009
• Published: 04/14/2011
• Est. Priority Date: 10/21/2008
• Status: Active Grant

• Current Assignee: Analog Devices, Inc.
• Original Assignee: Analog Devices, Inc.
• Inventors: Williams, Jon Austen, Lee, James M.
• Granted Patent: US 8,326,569 B2
• Time in Patent Office: Days
• US Class Current: 702/124
• CPC Class Codes: G06F 2200/1636 Sensing arrangement for detection of a tap gesture on the housing
• CPC Class Codes: G06F 3/017 Gesture based interaction, e.g. based on a set of recognized hand gestures interaction based on gestures traced on a digitiser G06F3/04883
• CPC Class Codes: G06F 3/033 Pointing devices displaced or positioned by the user , e.g. mice, trackballs, pens or joysticks; Accessories therefor digitisers characterised by the transducing means G06F3/041
• CPC Class Codes: G06F 3/0346 with detection of the device orientation or free movement in a 3D space, e.g. 3D mice, 6-DOF [six degrees of freedom] pointers using gyroscopes, accelerometers or tilt-sensors

Abstract

Methodology and circuitry for determining if a device, such as a cellular phone or personal digital assistant has been tapped is disclosed. The device includes an accelerometer and in response to an acceleration, the accelerometer outputs an acceleration signal. The accelerometer may continuously output an acceleration signal even if no acceleration occurs. A tap detection device receives the temporally sampled acceleration signal and takes the first derivative of the temporally sampled acceleration signal producing one or more derivative values. The tap detection system compares each derivative value to a threshold value and if the derivative value exceeds the threshold a tap is detected. By taking the derivative of the acceleration signal, the noise floor for the acceleration signal is reduced leading to more accurate results with less false positives and less positive negatives.

Claims

1. A computer implemented method for determining taps on a surface of a device having an accelerometer, the method comprising:

in a computer process;

receiving as input a temporally sampled acceleration signal;

taking a first derivative of the temporally sampled acceleration signal producing derivative values; and

comparing at least one derivative value to at least one threshold to determine if a tap has occurred based upon the derivative value exceeding the threshold.

2. The computer implemented method according to claim 1, wherein the device is a cellular phone.

3. The computer implemented method according to claim 1, wherein the device is a personal digital assistant.

4. The computer implemented method according to claim 1, wherein comparing the derivative values further comprises:

determining when two taps have occurred within a predetermined period and outputting a signal to a processor when two taps have occurred within the predetermined period.

5. The computer implemented method according to claim 1, wherein the device is a phone and an identification of a tap causes the phone to mute.

6. The computer implemented method according to claim 1, further comprising:

after a tap has been detected, determining when a subsequent derivative value falls below the threshold value indicating that the tap has ended.

7. The computer implemented method according to claim 1, wherein the absolute value of the at least one derivative value is used when comparing the at least one derivative value to the threshold.

18. The system according to claim 6 wherein at least the accelerometer, register, and subtraction circuit are housed within the same packaging.

27. A computer implemented method according to claim 1, wherein comparing includes comparing each derivative value to the threshold to determine both if the device has been tapped and the total number of derivative values that exceed the threshold.

8. A system for determining if a device has been tapped, the system comprising:

an accelerometer circuit for outputting a temporal acceleration signal;

a register for storing the temporal acceleration signal at time N−

1;

a subtraction circuit receiving from the register the temporal acceleration signal at time N−

1 and subtracting the temporal acceleration signal at time N−

1 from the temporal acceleration signal at time N producing a derivative signal;

a computation module receiving the derivative signal and comparing the derivative signal to at least one threshold to determine if the device has been tapped.

9. The system according to claim 8 wherein the accelerometer outputs a digital acceleration signal sampled at a sample rate.

10. The system according to claim 8 wherein the accelerometer circuit outputs an analog acceleration signal and the system further comprises:

a sampling circuit for sampling the analog acceleration signal at a sample rate producing a sampled acceleration signal.

11. The system according to claim 8, wherein when a derivative signal is indicative of a tap, the computation module stores an indicator of the tap in associated memory.

12. A system for determining if a device has been tapped, the system comprising:

an accelerometer circuit for outputting a temporal acceleration signal; and

a computation module receiving the temporal acceleration signal, taking the derivative of the temporal acceleration signal producing a derivative signal and comparing the derivative signal to at least one threshold to determine if the device has been tapped.

13. The system according to claim 12 wherein the accelerometer outputs a digital acceleration signal sampled at a sample rate.

14. The system according to claim 12 wherein the accelerometer outputs an analog acceleration signal and the system further comprises:

a sampling circuit for sampling the analog acceleration signal at a sample rate producing a sampled acceleration signal.

15. The system according to claim 12, wherein when a derivative signal is indicative of a tap, the computation module stores an indicator of a tap in associated memory.

16. The system according to claim 15, wherein the computation module determines a temporal period between taps and compares the temporal period to a threshold to determine if a double tap has occurred.

17. The system according to claim 12, wherein the accelerometer and the computation unit are housed within the same packaging.

19. A computer program product including a tangible computer readable medium having computer executable code thereon for determining if a tap has occurred on a surface of a device that includes an accelerometer the computer code comprising:

computer code for receiving as input from the accelerometer a temporally sampled acceleration signal;

computer code for taking a first derivative of the temporally sampled acceleration signal producing derivative values; and

computer code for comparing at least one derivative value to at least one threshold to determine if a tap has occurred based upon the derivative value exceeding the threshold.

20. A computer program product according to claim 19, wherein the computer code for comparing includes computer code for comparing each derivative value to the threshold to determine both if the device has been tapped and the total number of derivative values that exceed the threshold.

21. The computer program product according to claim 19, wherein the device is a cellular phone.

22. The computer program product according to claim 19, wherein the device is a personal digital assistant.

23. The computer program product according to claim 19, wherein the computer code for comparing the derivative values further comprises:

computer code for determining when two taps have occurred within a predetermined period and outputting a signal to a processor when two taps have occurred within the predetermined period.

24. The computer program product according to claim 19, wherein the device is a phone and an identification of a tap causes the phone to mute.

25. The computer program product according to claim 19, further comprising:

computer code that operates after a tap has been detected for determining when a subsequent derivative value falls below the threshold value indicating that the tap has ended.

26. The computer program product according to claim 19, wherein the absolute value of the at least one derivative value is used when comparing the at least one derivative value to the threshold.