Wrist-detection algorithm

Patent metadata

Field	Value
Publication number	US-9766370-B2
Application number	US-201514845156-A
Country	US
Kind code	B2
Filing date	Sep 3, 2015
Priority date	May 18, 2015
Publication date	Sep 19, 2017
Grant date	Sep 19, 2017

Abstract

Algorithms for detecting whether a device is properly secured to a user's skin are described. The operation of a device, such as a wearable device, can be adjusted based on whether the device is properly secured to a user's skin (e.g., on-wrist) or not properly secured to the user's skin (e.g., off-wrist). For example, certain functions can be disabled for power-saving, security or other purposes if the device is off-wrist. In order to avoid falsely identifying the device as off-wrist or on-wrist, algorithms for detecting whether the device is on-wrist or off-wrist can calculate one or more variances based on signals measured by a light sensor and compare the one or more variances with one or more thresholds. Comparing the one or more variances to the one or more threshold can improve the accuracy of wrist-detection algorithms.

First claim

The invention claimed is:

1. A device comprising:
a sensor comprising a light emitter and a light detector configured to generate signal samples, wherein each signal sample includes a first signal generated when the light emitter is on and a second signal generated when the light emitter is off; and
processing circuitry capable of:
performing one or more variance calculations for each signal sample;
predicting a condition of the device based on the one or more variance calculations for each signal sample; and
determining that the device is not secured to an object when the predictions of the condition of the device for the signal samples meet a threshold.

2. The device of claim 1 , wherein the one or more variance calculations comprises a first variance calculation of a variance of a difference between the first signal and the second signal of the signal sample.

3. The device of claim 2 , wherein predicting the condition of the device based on the one or more variance calculations for each signal sample comprises, predicting a first condition of the device when the first variance calculation is below a first variance threshold and predicting a second condition of the device when the first variance calculation meets or exceeds the first variance threshold.

4. The device of claim 2 , wherein the one or more variance calculations comprises a second variance calculation of a difference between a variance of the first signal of the signal sample and a variance of the second signal of the signal sample.

5. The device of claim 4 , wherein predicting the condition of the device based on the one or more variance calculations for each signal sample comprises:
predicting a first condition of the device when the first variance calculation is below a first variance threshold;
predicting the first condition of the device when the first variance calculation meets or exceeds the first variance threshold, the first variance calculation is below a second variance threshold, and the second variance calculation is below a third variance threshold;
predicting a second condition of the device when the first variance calculation meets or exceeds the first variance threshold and the first variance calculation meets or exceeds the second variance threshold; and
predicting the second condition of the device when the first variance calculation meets or exceeds the first variance threshold, the first variance calculation is below the second variance threshold, and the second variance calculation meets or exceeds the third variance threshold.

6. The device of claim 4 , wherein predicting the condition of the device based on the one or more variance calculations for each signal sample comprises:
predicting a first condition of the device when the first variance calculation is below a first variance threshold and the first variance calculation is below a third variance threshold;
predicting the first condition of the device when the first variance calculation is below the first variance threshold, the first variance calculation meets or exceeds the third variance threshold, and the second variance calculation is below a fourth variance threshold;
predicting a second condition of the device when the first variance calculation meets or exceeds the first variance threshold and the first variance calculation meets or exceeds the second variance threshold; and
predicting the second condition of the device when the first variance calculation is below the first variance threshold, the first variance calculation meets or exceeds the third variance threshold, and the second variance calculation meets or exceeds the fourth variance threshold.

7. The device of claim 1 , wherein predicting the condition of the device based on the one or more variance calculations for each signal sample comprises predicting a first condition of the device or predicting a second condition of the device, wherein the first condition corresponds to a prediction that the device is not secured to the object and wherein the second condition corresponds to a prediction that the device is secured to the object.

8. The device of claim 7 , wherein determining that the device is not secured to the object when the predictions of the condition of the device for the signal samples meet the threshold comprises predicting the first condition for a threshold number of consecutive predictions.

9. A method for determining that a device is not secured to an object, the method comprising:
generating a plurality of signal samples, wherein each signal sample includes a first signal generated when a light emitter is on and a second signal generated when the light emitter is off;
performing one or more variance calculations for each signal sample;
predicting a condition of the device based on the one or more variance calculations for each signal sample; and
determining that the device is not secured to the object when the predictions of the condition of the device for the signal samples meet a threshold.

10. The method of claim 9 , wherein the one or more variance calculations comprises a first variance calculation of a variance of a difference between the first signal and the second signal of the signal sample.

11. The method of claim 10 , wherein predicting the condition of the device based on the one or more variance calculations for each signal sample comprises, predicting a first condition of the device when the first variance calculation is below a first variance threshold and predicting a second condition of the device when the first variance calculation meets or exceeds the first variance threshold.

12. The method of claim 10 , wherein the one or more variance calculations comprises a second variance calculation of a difference between a variance of the first signal of the signal sample and a variance of the second signal of the signal sample.

13. The method of claim 12 , wherein predicting the condition of the device based on the one or more variance calculations for each signal sample comprises:
predicting a first condition of the device when the first variance calculation is below a first variance threshold;
predicting the first condition of the device when the first variance calculation meets or exceeds the first variance threshold, the first variance calculation is below a second variance threshold, and the second variance calculation is below a third variance threshold;
predicting a second condition of the device when the first variance calculation meets or exceeds the first variance threshold and the first variance calculation meets or exceeds the second variance threshold; and
predicting the second condition of the device when the first variance calculation meets or exceeds the first variance threshold, the first variance calculation is below the second variance threshold, and the second variance calculation meets or exceeds the third variance threshold.

14. The method of claim 12 , wherein predicting the condition of the device based on the one or more variance calculations for each signal sample comprises:
predicting a first condition of the device when the first variance calculation is below a first variance threshold and the first variance calculation is below a third variance threshold;
predicting the first condition of the device when the first variance calculation is below the first variance threshold, the first variance calculation meets or exceeds the third variance threshold, and the second variance calculation is below a fourth variance threshold;
predicting a second condition of the device when the first variance calculation meets or exceeds the first variance threshold and

Assignees

• Apple Inc

Inventors

• Aloe Robert T
• Saha Sankalita
• Waydo Stephen J
• Culbert Daniel J

Classifications

• A61B2562/0219

  Inertial sensors, e.g. accelerometers, gyroscopes, tilt switches · CPC title

• A61B5/6844

  Monitoring or controlling distance between sensor and tissue · CPC title

• A61B5/0059

  using light, e.g. diagnosis by transillumination, diascopy, fluorescence (photoacoustic A61B5/0093; optical measurement of heart rate A61B5/02416; optical measurement of blood flow A61B5/0261; optical measurement of analytes A61B5/1455) · CPC title

• G01V8/12 Primary

  using one transmitter and one receiver · CPC title

• A61B5/11

  Measuring movement of the entire body or parts thereof, e.g. head or hand tremor or mobility of a limb {(A61B5/1038 takes precedence; motion detection to correct for motion artifacts in physiological signals A61B5/721)} · CPC title