Foot presence sensing using magnets in footwear

Abstract

An article of footwear can include a ferromagnetic body disposed in the article, and a magnetometer to measure a strength or direction of a magnetic field that is influenced by a position of the ferromagnetic body. One of the ferromagnetic body and the magnetometer can be configured to move relative to the other one of the ferromagnetic body and the magnetometer, for example according to movement of a foot in the article. In an example, the ferromagnetic body is disposed in a compressible insole and the ferromagnetic body moves in response to compression or relaxation of the insole. The magnetometer can be disposed in a platform or sole portion of the article that is relatively stationary compared to the ferromagnetic body. Rate of change information about the magnetic field can be used to control article functions or to provide information about a foot strike or step rate.

What is claimed is: 
     
         1 . An article of footwear comprising:
 a ferromagnetic body disposed in the article of footwear;   a magnetometer configured to provide a magnetometer signal that indicates a strength or direction of a magnetic field measured by the magnetometer, wherein the magnetometer signal indicates a position of the ferromagnetic body; and   a processor circuit configured to receive the magnetometer signal from the magnetometer and determine a foot impact characteristic using the magnetometer signal;   wherein one of the ferromagnetic body and the magnetometer is configured to move relative to the other one of the ferromagnetic body and the magnetometer according to movement of a foot in the article.   
     
     
         2 . The article of footwear of  claim 1 , wherein in response to the magnetometer signal indicating a specified change in the position of the ferromagnetic body, the processor circuit is configured to initiate data collection from one or more other sensors in or associated with the article of footwear. 
     
     
         3 . The article of footwear of  claim 1 , wherein in response to the magnetometer signal indicating a specified change in the position of the ferromagnetic body, the processor circuit is configured to actuate a drive mechanism to tighten or loosen the article of footwear about the foot. 
     
     
         4 . The article of footwear of  claim 3 , further comprising the drive mechanism, wherein the drive mechanism is configured to tighten or loosen the article of footwear about the foot in response to actuation instructions from the processor circuit. 
     
     
         5 . The article of footwear of  claim 1 , wherein the magnetometer signal comprises a time-varying signal that indicates a changing position of the ferromagnetic body while the article is worn and while the article is moved by a foot; and
 the processor circuit is configured to determine the foot impact characteristic based on a rate of change of the time-varying signal.   
     
     
         6 . The article of footwear of  claim 5 , wherein the processor circuit is configured to determine a foot impact force characteristic based on the time-varying signal. 
     
     
         7 . The article of footwear of  claim 5 , wherein the processor circuit is configured to determine a step timing characteristic based on the time-varying signal. 
     
     
         8 . The article of footwear of  claim 5 , wherein the processor circuit is configured to determine a step count using the foot impact characteristic as-determined. 
     
     
         9 . The article of footwear of  claim 1 , further comprising multiple ferromagnetic bodies disposed in the article of footwear, wherein the magnetometer signal indicates a change in a position of one or more of the multiple ferromagnetic bodies, and wherein the multiple ferromagnetic bodies are spaced apart from each other and from the magnetometer. 
     
     
         10 . The article of footwear of  claim 1 , wherein the ferromagnetic body is embedded in a compressible material that is configured to be worn underfoot in the article of footwear. 
     
     
         11 . A method comprising:
 using a magnetometer, measuring a strength or direction of a magnetic field generated by a ferromagnetic body that is disposed in an article of footwear; and   using a processor circuit:
 receiving a signal from the magnetometer indicating the strength or direction of the magnetic field as-measured; and 
 determining a foot impact characteristic, corresponding to movement of a foot inside of the article of footwear, using the signal. 
   
     
     
         12 . The method of  claim 11 , wherein receiving the signal from the magnetometer includes receiving a time-varying signal from the magnetometer, the time-varying signal indicating a change in the strength or direction of the magnetic field over time. 
     
     
         13 . The method of  claim 12 , further comprising determining a rate of change of the time-varying signal as-received;
 wherein determining the foot impact characteristic includes using the rate of change as-determined.   
     
     
         14 . The method of  claim 13 , further comprising using the processor circuit, determining a foot impact force characteristic using the rate of change as-determined. 
     
     
         15 . The method of  claim 13 , further comprising using the processor circuit, determining a step timing characteristic using the rate of change as-determined. 
     
     
         16 . The method of  claim 13 , further comprising using the processor circuit, determining a step count using the rate of change as-determined. 
     
     
         17 . The method of  claim 13 , further comprising using the processor circuit, determining a gait characteristic using the rate of change as-determined. 
     
     
         18 . The method of  claim 13 , further comprising using the processor circuit, selectively actuating a lace drive mechanism based on the rate of change as-determined. 
     
     
         19 . An article of footwear comprising:
 a ferromagnetic body disposed in the article of footwear;   a magnetometer configured to provide a magnetometer signal that indicates a strength or direction of a magnetic field measured by the magnetometer, wherein the magnetometer signal indicates a position of the ferromagnetic body;   an automatic lacing engine; and   a processor circuit configured to receive the magnetometer signal from the magnetometer, determine a rate of change of the magnetometer signal over time, and selectively actuate the automatic lacing engine to tighten or relax the article of footwear about a foot based on the rate of change as-determined;   wherein one of the ferromagnetic body and the magnetometer is configured to move relative to the other one of the ferromagnetic body and the magnetometer according to movement of the foot in the article.   
     
     
         20 . The article of footwear of  claim 19 , wherein the processor circuit is further configured to classify an activity type based on the rate of change as-determined, and wherein the processor circuit is configured to actuate the automatic lacing engine based on the activity type.