Abstract:
A method for detecting steps taken by a person in locomotion on foot having a step-detection apparatus carried on the person. The step-detection apparatus generates a signal in response to locomotion of the person. The signal is compared to the timing characteristics of human gait to identify steps taken. The step-detection apparatus can be carried in a front pants pocket of the person.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of provisional patent application Ser. No. 60/668,387, filed 2005 Apr. 5 by the present inventor. 
    
    
     FEDERALLY SPONSORED RESEARCH 
     Not Applicable 
     SEQUENCE LISTING OR PROGRAM 
     Not Applicable 
     BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     This invention relates to pedometers, specifically to an improved method for detecting strides for a pedometer. 
     2. Prior Art 
     In many recreational endeavors and occupations a need exists for persons to be able to measure distances by walking from one point to another. For example, exercise walkers often record their daily mileage in a diary. Golfers and hunters often want to know the distance between two landmarks. Real estate agents often need to know the length and width of a building or field. 
     Prior art pedometers do not support these distance-measuring needs with an acceptable level of accuracy.  Consumer Reports  magazine (pp. 30-31, October, 2004) recently tested a number of pedometers and found that most were inaccurate by 5 to 10 percent, and some were inaccurate by 20 percent or more. “The worst were so inaccurate that if you walked five miles, they might say you&#39;d covered three to seven.” This is not satisfactory for an exerciser wanting to know the number of miles traveled to within a fraction of a mile, let alone a golfer or real estate agent wanting to know a distance to within a few yards or feet. 
     Pedometers calculate distance by multiplying the length of the user&#39;s step (or stride) times the number of steps (or strides) the user takes. A stride is one step by each leg, or two steps total. Any given pedometer is designed to count either steps or strides. 
     The accuracy of the distance measured by a pedometer is a function of: (1) the accuracy of the step/stride length entered into the pedometer for a given person, and (2) the accuracy with which that pedometer counts steps/strides. Researchers of human gait have determined that a person&#39;s step/stride length is the same from one step/stride to the next and from one day to the next when that person walks at their self-selected speed (Inman et al,  Human Walking , p. 22, 1981). Self-selected walking speed, also called free- or natural-walking speed, is the speed that a walker unconsciously uses when walking without any particular purpose. Accurately determining a person&#39;s step/stride length for their self-selected walking speed is a straightforward exercise of counting the number of steps/strides taken for a measured distance and then dividing the distance by the number of steps/strides. So the distance-measuring accuracy of any given electronic pedometer is determined by the accuracy of the step/stride detection mechanism for that pedometer, assuming an accurate step/stride length is used. 
     The prior art uses a number of different mechanisms to detect steps and strides. U.S. Pat. No. 4,053,755 to Sherrill (1977) is an example of a mechanism for sensing the up-and-down motion of the torso. It uses an electrically conductive leaf spring with a small weight on its free end for momentary engagement with a mating electrically conductive contact. This switch is normally open, and each step taken by the user causes the weight to be jarred downward to bring the contacts together and close the switch. U.S. Pat. No. 4,144,568 to Hiller et al (1979) improves this by replacing the ordinary on/off switch with a magnetic reed switch. U.S. Pat. No. 5,117,444 to Sutton et al (1992) teaches “Ordinary switches, however, are prone to intermittent operation” and “Reed switch pedometers are much more reliable and give fewer false readings than other prior art devices.” 
     Other mechanisms are used to detect steps and strides. U.S. Pat. No. 4,175,446 to Crowninshield (1979) uses a strain gauge to sense foot strike with the ground and detect strides. U.S. Pat. No. 4,371,945 to Karr et al (1983) uses an ultrasonic generator and detector to sense (lower) leg swing and detect steps. U.S. Pat. No. 4,855,942 to Bianco (1989) uses a mercury switch to sense arm swing and detect strides. U.S. Pat. No. 5,485,402 to Smith et al (1996) uses an accelerometer to sense lower-leg swing and detect strides. The prior art teaches away from using an inexpensive, ordinary tilt switch as a sensor for a pedometer. 
     All of the prior art has the step- or stride-detection mechanism attached to a body part or an item of clothing of the user. Some of the prior art asserts that body motions other than that specifically described can detect steps with a certain detection mechanism. For instance, U.S. Pat. No. 4,223,211 to Allsen et al (1980) states, “The said motions accompanying foot motions of the subject may be motions of any part of the body.” This patent, like others making similar statements, does not describe how the other body motions actually detect steps taken. No prior art detects strides by sensing the motion of a user&#39;s upper leg with a stride-detection mechanism in the front pants pocket of the user that is unattached to either the pocket or the user. 
     Prior art pedometers assume that each pulse in the electrical signal produced by the sensor corresponds to a single step or stride. U.S. Pat. No. 4,387,437 to Lowery et al (1983) recognizes the problem of switch bounce giving false step indications and incorporates a debounce circuit to attempt to eliminate false indications. U.S. Pat. No. 5,684,284 to Lee et al (1997) uses an electronic filter to prevent “extraneous mechanical vibration of the unit from registering as a player&#39;s stride.” No prior art uses the timing of human gait to interpret step/stride-sensor signals and differentiate step/stride indications from switch bounce and non-step/stride motion artifacts. 
     OBJECTS AND ADVANTAGES 
     Accordingly, several objects and advantages of the present invention are: 
     (a) to provide an accurate stride-detection mechanism for a pedometer; 
     (b) to provide a method to differentiate stride indications from switch bounce and non-stride motion artifacts in the signal generated by the stride sensor in a pedometer; 
     (c) to provide a convenient-to-use front pants-pocket format for pedometers; 
     (d) to provide for using an inexpensive, ordinary tilt switch as a stride sensor for a pedometer. 
     Further objects and advantages will become apparent from a consideration of the ensuing description and drawings. 
     SUMMARY 
     In accordance with the present invention a pedometer comprises an electronic system with a tilt switch used as a stride sensor housed in an enclosure dimensioned to fit in a front pants pocket of a user. The user&#39;s walking causes the stride sensor electrical contacts to open and close with the forward then backward motion of the user&#39;s leg. The electronic system uses the timing of human gait to interpret tilt switch stride sensor signals and differentiate stride indications from switch bounce and non-stride motion artifacts. 
    
    
     
       DRAWINGS 
       Figures 
         FIG. 1  is a block diagram of the electronic system of the present pedometer invention. 
         FIG. 2  is a perspective view showing the present pedometer invention in the front pants pocket of a user. 
         FIGS. 3   a - 3   b  are lateral cross-sectional views of the present pedometer invention. 
         FIG. 4  is a waveform illustrating the opening and closing of the tilt-switch stride sensor in the present pedometer invention. 
         FIG. 5  is a flow chart of a method to interpret the signal generated by the sensor in the present pedometer invention. 
     
    
    
     REFERENCE NUMERALS 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 10 
                 microcomputer 
               
               
                 12 
                 pushbutton switches 
               
               
                 14 
                 LCD display 
               
               
                 16 
                 tilt-switch stride sensor 
               
               
                 18 
                 battery 
               
               
                 20 
                 user 
               
               
                 22 
                 enclosure 
               
               
                 24 
                 front pants pocket 
               
               
                 30 
                 circuit board 
               
               
                 32 
                 electrically-conductive ball 
               
               
                 34 
                 enclosed, non-conducting tube 
               
               
                 36 
                 electrical contacts 
               
               
                 41 
                 first long-open period 
               
               
                 42 
                 first long-closed period 
               
               
                 43 
                 second long-open period 
               
               
                 44 
                 second long-closed period 
               
               
                 45 
                 third long-open period 
               
               
                 46 
                 third long-closed period 
               
               
                 50 
                 routine 
               
               
                 52 
                 first step of routine 
               
               
                 54 
                 second step of routine 
               
               
                 56 
                 third step of routine 
               
               
                 58 
                 fourth step of routine 
               
               
                   
               
             
          
         
       
     
     DETAILED DESCRIPTION 
     FIGS.  1 - 3 —Preferred Embodiment 
       FIG. 1  is a block diagram of an electronic system for the present pedometer invention. A microcomputer  10  consists of a CPU, RAM, input/output, and a ROM containing a control program to implement pedometer and other functions. A plurality of pushbutton switches  12  supply input to microcomputer  10  to enter data such as stride length, to enter commands such as start or stop pedometer distance measurement or stride counting, and to enter information for other functions microcomputer  10  may perform. A LCD display  14  displays distance walked, strides taken, stride length, or information from other functions microcomputer  10  may perform. A tilt-switch stride sensor  16  detects strides and supplies a signal to microcomputer  10 . A battery  18  provides power to the system. 
       FIG. 2  is a perspective view showing the present pedometer invention, contained in an enclosure  22 , in a front pants pocket  24  of a user  20 . Enclosure  22  is not attached to pocket  24  and is free to move around within pocket  24 . Enclosure  22  is rectangular shaped and dimensioned to fit in front pants pocket  24  and not rotate or flip in any direction to change its orientation in the pocket. A range of dimensions will satisfy these requirements. Enclosure  22  has distinctive markings such that a user knows the correct orientation with which to place it in pocket  24 . 
       FIGS. 3   a - 3   b  are lateral cross-sectional views of the present pedometer invention. Enclosure  22  contains a circuit board  30  to which sensor  16 , and other electronic components, are mounted. Sensor  16  consists of an electrically-conductive ball  32  in an enclosed, non-conducting tube  34  with electrical contacts  36  at one end. Sensor  16  is oriented slightly less than perpendicular to circuit board  30 . The angle is such that, when enclosure  22  is in pocket  24  of user  20  and user  20  is standing still, enclosure  22  is vertical as shown in  FIG. 3   a  and gravity forces ball  32  into contact with contacts  36 , closing the switch. In  FIG. 3   b , user  20  has moved the leg forward to begin a stride, and enclosure  22  has tilted away from vertical and ball  32  has moved away from contacts  36 , opening the switch. When user  20  completes the stride enclosure  22  returns to the position shown in  FIG. 3   a  where gravity has returned ball  32  into contact with contacts  36 . 
     Operation— FIGS. 4 ,  5   
     Forward and backward leg motion of user  20  is not the only cause of the opening and closing of sensor  16 . Sensor  16  is an ordinary switch that exhibits switch bounce. Non-stride motion artifacts can produce opening and closing of sensor  16  as a result of enclosure  22  moving around within pocket  24 . Loose-fitting pants such as walk shorts produce more non-stride motion artifacts than tight-fitting pants such as jeans. 
     Human gait has timing properties that can be used to interpret the opening and closing sequences of sensor  16 . Research has found that walking step rates are within the range of 75 to 140 steps per minute for adult men, and 80 to 150 steps per minute for adult women, with the typical being about 110 steps per minute (Inman et al,  Human Walking , p. 28, 1981). Elite distance runners run at approximately 180 steps per minute (Daniels,  Daniels&#39; Running Formula , p. 93, 1998). It is reasonable to expect that humans will not walk faster than the 90 strides per minute rate of world-class runners, so walking strides will not occur faster than once every 750 milliseconds. It is also reasonable to expect that with a stride taking at least 750 milliseconds, the forward movement of the leg will produce some minimum open period for sensor  16 , followed by some minimum closed period for the backward movement of the leg. Shorter opens and closes can then be attributed to either switch bounce or non-stride motion artifacts. 
       FIG. 4  is a waveform illustrating the opening and closing of sensor  16  as user  20  walks three strides. A first long-open period  41  followed by a first long-closed period  42  comprises the first stride. A second long-open period  43  followed by a second long-closed period  44  comprises the second stride. A third long-open period  45  followed by a third long-closed period  46  comprises the third stride. The shorter open and closed periods in the waveform are the result of switch bounce and non-stride motion artifacts. 
       FIG. 5  is a flow chart of a routine  50  that interprets the signal generated by sensor  16  in the present pedometer invention and differentiates stride indications from switch bounce and non-stride motion artifacts. This routine is implemented as a portion of the control program executed by microcomputer  10 . Routine  50  begins at a step  52 , where routine  50  waits until sensor  16  is open for at least 85 milliseconds continuously. After this condition is met, routine  50  proceeds to a step  54 , where routine  50  waits until sensor  16  is closed for at least 65 milliseconds continuously. After this condition is met, routine  50  proceeds to a step  56 , where the time elapsed since the last stride is compared to 750 milliseconds. If the time elapsed is more than 750 milliseconds, routine  50  proceeds to a step  58  where a stride is added to the current stride count, and then routine  50  returns to step  52 . If the time elapsed is less than 750 milliseconds, the potential stride indication is ignored and routine  50  returns to step  52 . 
     The times of 85 and 65 milliseconds in steps  52  and  54  respectively of routine  50  were selected after numerous observations of sensor  16  for a number of different users, wearing a number of different tight- and loose-fitting pants, walking at a number of various high and low speeds. The times were chosen such that they were longer than observed switch bounce and non-stride artifacts under the worst-case conditions of fast walking and loose-fitting pants. 
     CONCLUSIONS, RAMIFICATIONS, AND SCOPE 
     Accordingly the reader will see that this invention provides an accurate stride-detection mechanism for a pedometer, a method to differentiate stride indications from switch bounce and non-stride motion artifacts in the signal generated by the stride sensor in a pedometer, a convenient-to-use front pants-pocket format for pedometers, and the ability to use an inexpensive, ordinary tilt switch as a stride sensor for a pedometer. 
     While the above description contains many specificities, these should not be construed as limiting the scope of the invention but as merely providing illustrations of the presently preferred embodiment of the invention. Many other ramifications and variations are possible within the teachings of the invention. For example, 
     (a) the enclosure can have other shapes, such as oval, oblong, or any other shape, including those that may aide in correct orientation of the enclosure in the user&#39;s pocket; 
     (b) any other type of controller, either programmable or hard-wired, can be used instead of a microcomputer; 
     (c) any other type of sensor, such as a mercury switch, reed switch, or an accelerometer, can be used to sense the forward and backward motion of a user&#39;s upper leg; 
     (d) the method to differentiate strides from switch bounce and non-stride motion artifacts can be used with any other type of step/stride-detection mechanism for a pedometer, including those that detect up-and-down motion of the torso, foot strike, arm swing and lower leg swing; 
     (e) the minimum stride duration of 750 milliseconds is not a precise limit, and can vary by 50 or more milliseconds; 
     (f) the open and closed times of 85 and 65 milliseconds respectively are not precise, and other times will work for the present pedometer invention. The times can also vary with different types of tilt switches, different angles between tilt switch and the circuit board, and different sized and shaped enclosures from those used in the present pedometer invention. 
     Thus the scope of the invention should be determined by the appended claims and their legal equivalents, and not by the examples given.