referring now to fig1 and 2 , there is shown a shoe 10 containing a force sensor array 100 and an electronic circuit module 500 connected thereto by means of a flat ribbon cable 102 . force sensor array 100 is arranged to cover a substantial area of contact between the bottom of the wearer &# 39 ; s foot and foot apparel ( e . g ., shoe ) 10 . although the use of a force sensor array in a shoe represents a preferred embodiment of the present invention , many similar types of foot apparel may utilize the same type of system . for example , the force sensor array may be used inside a sock , bootie , or attached to a prosthetic device to accomplish the same result of measuring and monitoring forces applied by the user &# 39 ; s foot . additionally , although the preferred embodiment involves the measurement of forces between a foot and shoe , it should be appreciated that this device could be used to measure other forces , such as between the end of an amputated limb and a prosthetic device . electronic circuit module 500 is preferably clipped or otherwise attached to the side of shoe 10 that is opposite the other foot and slightly forward of the center thereof , where it is least likely to be damaged or to interfere with the normal physical activities of the wearer . referring now to fig3 covering layers 112 and 142 are used to hold the remaining parts of the force sensor array 100 together and to isolate them from contamination . covering layers 112 and 142 can include , for example , a 1 / 16 - inch thick , adhesive coated , closed cell vinyl foam tape such as 3m scotchfoam 4726 ™. a conductive trace layer 122 includes a multiplicity of conductive traces , each of which is electrically connected through a substrate 124 to each line of a multiplicity of lines of sensor electrodes ( 123 in fig4 ) that are formed by a conductive trace layer 126 and a like number of contact points that are also formed by conductive trace layer 126 . similarly , a conductive trace layer 132 includes a multiplicity of conductive traces , each of which is electrically connected through a substrate 134 to each line of a multiplicity of lines of sensor electrodes ( 123 in fig4 ) formed by another conductive trace layer 136 . conductive trace layers 122 , 126 , 132 , and 136 can be fabricated from any suitable electrically conductive material capable of being printed or otherwise deposited on substrates 124 , 134 . substrates 124 , 134 are dielectric films and can be fabricated from , for example , du pont kapton ™ polyimide film material . other films can also be used . preferably , substrates 124 and 134 are fabricated from materials which are too rigid to operatively conform to a user &# 39 ; s foot when no portions have been removed therefrom . however , when selected portions of substrates 124 and 134 are removed , as shown in fig5 and 13 , the substrates are capable of operatively conforming to the user &# 39 ; s foot , while simultaneously avoiding undesirable wrinkling . pressure sensitive coating layers 128 , 138 can comprise a commercially available partially conductive pressure sensitive coating , such as one of those designated as numbers 4407 and 4408 produced by chomerics , inc . of woburn , mass . referring now to fig4 hexagonal areas 130 of the substrates 124 , 134 are removed to increase the flexibility of the assembled force sensor array 100 , allow it to operatively conform to the user &# 39 ; s foot , provide mechanical isolation for the individual sensors 123 comprising force sensor array 100 , and allow contact of the adhesive coatings 114 , 144 . although hexagonal cutouts 130 are a preferred embodiment of the present invention , any suitable geometric shape of cutout can be utilized which enhances the flexibility of the force sensor array 100 . the actual geometric configuration is dependent on a number of variables including the substrate material , thickness of the substrate and total length and width of the material necessary for each particular application . conductive trace layers 126 , 136 , which form individual force sensor electrodes 123 , are prevented from directly contacting each other by the position and shape of pressure sensitive coatings 128 , 138 . the areas of the partially conductive pressure sensitive coatings 128 , 138 are slightly larger than the sensor electrode areas , and the conductive traces connecting the individual force sensor electrodes 123 not covered by the pressure sensitive coatings 128 , 138 do not come into contact because their positions are not coincident . the film substrates 124 , 134 between the hexagonal or other geometric removed areas are wide enough to accommodate the various conductive traces , electrodes , and sensor areas . narrower bands of the film substrates 124 , 134 between the individual force sensors 123 of force sensor array 100 result in greater flexibility and provide better mechanical isolation of the individual sensors . referring now to fig5 and 6 , conductive trace layer 122 on the top surface of film substrate 124 connects each line 121 of individual force sensor electrodes 123 formed by conductive trace layer 126 on the bottom surface of film substrate 124 to the electronic circuit module 500 of fig1 and 2 . electrical connections through the film substrate to conductive trace layer 126 on the bottom surface of film substrate 124 are represented as enlarged areas 117 at both ends of each conductive trace 101 of conductive trace layer 122 . referring now to fig6 conductive trace layer 126 forms diagonal lines 121 of sensor electrodes 123 and contact areas for connection to the electronic circuit module 500 . electrical connections through the substrate 124 to conductive trace layer 122 on the top surface of film substrate 124 are represented as enlarged areas 127 located firstly between consecutive force sensor electrodes 123 and secondly under the contact areas 125 in connector tab 104 . thus , all of the individual force sensor electrodes 123 in a diagonal line 121 are commonly connected through a single conductive trace 101 of conductive trace layer 122 to electronic circuit module 500 . referring now to fig7 conductive trace layer 136 forms lines of individual force sensor electrodes and contacts for connection to the electronic circuit module 500 . electrical connections through the substrate 134 to conductive layer 132 are represented as enlarged areas located firstly between consecutive individual force sensor electrodes and secondly under the contact areas of conductive trace layer 136 in connector tab 104 . thus , all of the individual force sensor electrodes in a line are commonly connected through a single conductive trace of conductive trace layer 132 to electronic circuit module 500 . referring now to fig8 conductive traces of conductive trace layer 132 connect each line of individual force sensor electrodes formed by conductive trace layer 136 to the electronic circuit module 500 . electrical connections through the substrate 134 to conductive trace layer 136 are represented as enlarged areas at both ends of each trace of layer 132 . referring now generally to fig5 - 8 , the layout of the force sensors 123 , lines of individual force sensor electrodes formed by conductive traces of conductive trace layers 126 , 136 , and conductive traces 122 , 132 permit trimming the array to fit any shape or size of a user &# 39 ; s foot or shoe . the diagonal arrangement of force sensors 128 , 138 results in a smaller number of electrical leads in conductive trace layers 122 , 132 than would be required if the sensors 128 , 138 were perpendicularly arranged . this is because the ratio of the length to width of the human foot is about 3 . 5 , and a similar ratio of rows to columns would result . in the diagonal sensor layout of the present invention , the ratio of rows to columns can be closer to unity . the honeycomb pattern of the substrates produces meandering nonlinear courses for electrical conductive leads in conductive trace layers 122 , 132 . this prevents a stiff conductive material such as copper from excessively restricting the flexing of the force sensor array 100 along the general direction of the leads . referring now to fig9 and 10 , a portion of a standard two - sided printed circuit board 550 extends to the exterior periphery of electronic circuit module 500 , together with conductive leads 552 to form contacts arranged to coincide with contact areas of electrode lines formed by conductive trace layers 126 , 136 . the connector portion of force sensor array 100 and the printed circuit board 550 are clamped between facing halves 502 of electronic circuit module 500 . any conventional mechanical fastening device may be used to hold the facing halves 502 of electronic circuit module 500 together . elastic material 504 evenly distributes the clamping force . a thickened center of elastic material 504 compensates for any bending that may take place in the two facing halves 502 of electronic circuit module 500 . guides 506 position the end portions of the force sensor array 100 , while the two facing halves 502 of electronic circuit module 500 are tightened . the clearance between the connector parts 104 of substrates 124 , 134 to guides 506 is small enough to assure alignment between each of the connector contact areas of electrode lines formed by conductive trace layers 126 , 136 and contact areas 552 . the conductive traces of conductive trace layers 122 , 132 are as closely spaced as practical to make the cable 102 portion of substrates 124 , 134 as narrow as possible . curving the re - entrant edges of substrates 124 , 134 reduces fatigue stress . referring now to fig1 , force sensor array 100 is connected to electronic circuit module 500 , which contains scanning circuitry 210 controlled by a central processing unit ( cpu ) 220 . cpu 220 executes software routines stored in a read - only memory ( rom ) 230 during system boot and thereafter executes software programs stored in a random access memory ( ram ) 250 . an interface 240 is used to upload data stored in ram 250 to an external personal computer ( pc ) and to down - load operational data and software programs from a pc to ram 250 . a time of day and calendar clock 260 provides time and date information to cpu 220 . an annunciator 270 is controlled by cpu 220 for signalling , for example , the occurrence of measured forces exceeding preset thresholds , hardware fault conditions , and operator errors . in addition , a wireless data transmitter ( not shown ) may be included to interface electronic circuit module 500 to external electronic equipment for the purpose of transferring data and other information between electronic circuit module 500 and the external electronic equipment . referring now to fig1 , there is shown a software program executed by cpu 220 contained within electronic circuit module 500 to facilitate operation of the foot force measurement system of the present invention as a weight monitor . initialization step 302 can be a conventional software initialization step involving setting memory areas to proper values , checking hardware configurations , etc . step 304 reads one byte of data from the scanning circuitry 210 . this data represents either the result of a single instantaneous reading from an individual sensor within force sensor array 100 or a special synchronizing value to mark the beginning or end of a scan of the entire force sensor array 100 . step 306 tests the data byte for the special value . when this value is the special synchronizing value , the next byte of data read will be force data from a known sensor of force sensor array 100 . the next byte is not read until it is time to do so , as determined by steps 307 and 308 . the force sensor array 100 can be scanned many times per second . the loop formed by steps 310 - 318 is executed as many times as there are individual sensors within the force sensor array 100 . the current through each of the sensors of force sensor array 100 is measured in a predetermined order and consequently the individual force sensor being addressed can be associated to stored data representing its location within the force sensor array 100 . step 312 tests for the special synchronizing byte , and if it is found at this point in the routine , it is a clear error . step 314 makes an appropriate data record for future reference , annunciates the error , and resets a loop counter to point to the first sensor . step 316 extracts information stored in ram 250 for the particular sensor of force sensor array 100 currently being evaluated . this information is used to translate the measured current through an individual sensor to a value accurately representing the force being placed on that sensor . this is necessary because the output voltage of each sensor of the force sensor array 100 is inversely and logarithmically proportional to the applied force , and the response varies between individual sensors due to unavoidable manufacturing variances . more specifically , within the ram 250 is stored a two - vector data array previously loaded by use of a pc and other suitable test equipment . in this array , a first vector applies to each sensor , and a second vector applies to each possible input data value from a particular sensor . contained in each storage location within the data array is the appropriate output value . stated in other words , a counter incremented with each iteration of the loop comprising steps 310 , 312 , 314 , 316 and 318 is taken as a first pointer and the value from the sensor measurement is taken as a second pointer to the proper output data stored in the two - vector data array . the value pointed to is added to the value representing the total weight measured by the force sensor array 100 . following execution of the loop comprising steps 310 , 312 , 314 , 316 and 318 , a single scan of the force sensor array 100 has been completed , and the total force on the force sensor array 100 has been computed . steps 320 , 322 , 324 , 326 , 328 , and 330 serve to test the total instantaneous force from the scan of the force sensor array 100 against two preset values stored in ram 250 . if a &# 34 ; maximum allowable force &# 34 ; ( maf ) has been exceeded , a recognizable tone is produced by the annunciator 270 . if the total force is less than the maf , but greater than a predetermined proportion of the maf , a clearly different tone is produced . if the total force is less than the predetermined proportion of the maf , no tone is produced . alternatively , the program can be designed to monitor forces in desired localized areas rather than over the entire foot . step 305 clears the storage location for total force . since the next byte should be a synchronizing byte , it must be wasted . this is done by step 304 before beginning execution of the next loop comprising steps 310 , 312 , 314 , 316 and 318 . referring now to fig1 , modified hourglass cutouts 199 are removed from the film substrate 124 , 134 to increase the flexibility of the force sensor array and allowing it to operatively conform to the user &# 39 ; s foot yet provide mechanical isolation for the pressure sensitive coating layers 128 , 138 . the actual geometric configuration of the cutout may change depending on the substrate material used and the length , width and thickness of the material . in use , the foot force measurement system described above is capable of measuring the instantaneous force on all of the individual force sensors within force sensor array 100 during a scan that takes place at regular , predetermined time intervals . the scan rate is fast enough to assure a multiplicity of scans for any foot strike and thus capture any significant instantaneous force value . consequently , a time - based plot of force on the entire foot or any part thereof may be produced for each foot strike . the force centroid or balance point of forces placed on a foot or portions of a foot may be computed for each scan of force sensor array 100 because the relative position of each of the sensors within force sensor array 100 is fixed . therefore , a time - based two - coordinate plot of the path of the centroid may be produced for each foot strike . force placed on the foot in excess of that required to counteract the individual &# 39 ; s weight may be assumed to be due to acceleration resulting from work done by that individual . this acceleration can be used to compute an instantaneous resultant velocity from which the mechanical power produced by the individual can be computed . using these primary measurements and computations , information can be produced which is useful in circumstances including but not limited to those discussed below . the foot force measurement system of the present invention may be used as a foot force monitor by persons with prosthetic bone or joint implants and fractures who need to carefully control the weight placed on an affected leg during a recovery period . the individual uses crutches or a walker for physical support and , guided by audible tones from the annunciator 270 , can control the amount of weight placed on the affected leg . in addition to annunciating individually set optimum and excessive weight thresholds , the foot force measurement system of the present invention also has the capability of generating and storing computer data records which , for example , may include the date and time of system turn on and turn off , and the number of foot strikes of a minimum useful force . when the stored data is reviewed following a period of usage that may extend for several weeks , for example , clear indications are provided regarding the extent of system usage and adherence by the wearer to a prescribed course of therapy . the foot force measurement system of the present invention may also be used to alert the staff of a nursing center when patients who are prone to confusion or are otherwise at risk of falling attempt to stand and walk without assistance . when the patient first places weight on either foot in an effort to stand , the force is detected by the force sensor array 100 fitted into flexible footwear typically worn by such patients . this would trigger a suitable display and annunciator on a computer console located at the central nurses &# 39 ; station to provide an early warning of a patient &# 39 ; s attempt to rise from his or her bed . the foot force measurement system of the present invention may also find application as a guide to fitting and adjustment of a prosthetic leg . it may also be used in training a patient in use of a prosthesis . in this instance , the force sensor array 100 can be placed between the prosthetic foot and a shoe or between the end of the limb and the prosthetic device . the foot force measurement system of the present invention may also be used to provide runners and other athletes instantaneous and continuous measurements of their power output and pace , as measured by frequency of foot strikes . these measurements can be compared to historical values for the current wearer and others so that appropriate and timely adjustments in pace or other running techniques may be made . deviations of force centroid path or force - time curve from normal values for the individual wearer can be detected . such deviations imply impending injury , and when they occur , a warning may be sounded in time to avoid an injury . the foot force measurement system of the present invention may also find application in weight loss programs to monitor the wearer &# 39 ; s compliance with an established exercise schedule . the foot force measurement system of the present invention may be used to detect lower extremity abnormalities or improper footwear and to monitor the result of corrective measures . this is done by comparing a patient &# 39 ; s force - time plot ( s ) and / or the force centroid path plot with normal plots of these parameters . the precise functional information provided by the system of the present invention can be used to quantify and display well - understood anatomical conditions . use of the present invention to measure and chart a statistically significant number of subjects could produce detailed standards for subsequent comparison not otherwise available . by comparing individual plots with known standards developed through use of the foot force measurement system of the present invention , a wider range of problems could be detected earlier and more accurately than is presently possible . while the invention has been described in combination with specific embodiments thereof , it is evident that many alternatives , modifications and variations will be apparent to those skilled in the art in light of the foregoing description . accordingly , it is intended to embrace all such alternatives , modifications , and variations as fall within the spirit and broad scope of the claims .
a self - contained system for measuring forces applied by the foot of a user includes a force sensor array positioned within the user &# 39 ; s shoe between the foot and the inner sole of the shoe . the force sensor array including a multiplicity of individual force sensors arranged in a pattern that covers the area of contact between the sole of the user &# 39 ; s foot and the inner sole of the shoe , and a substrate material which is so rigid that it will not operatively conform to the user &# 39 ; s foot unless a plurality of shaped cutout portions of the substrate material is removed in order to allow the force sensor array to operatively conform to the user &# 39 ; s foot when force is applied . an electronic circuit module is removably attached to the side of the shoe and a flat interconnecting cable electrically couples the force sensor array to the electronic circuit module . an annuniciator audibly signals the user when a force on the foot greater than a predetermined threshold force is sensed .