Abstract:
The disclosed technique relates to an insert for footwear and to a composite orthotic insole comprising said insert, wherein the insert is embedded with a plurality of force (or pressure) sensors, and may be used to provide feedback on important information regarding the wearer&#39;s gait biomechanics. The layer of sensors may be used to assist in monitoring the wearer&#39;s health via foot pressure tracking. The insole can use a relative large number of sensors, which together provide broad coverage of the human foot impact area.

Description:
CLAIM FOR PRIORITY 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 62/199,818 of the same title and filed on Jul. 31, 2015, which is incorporated by reference herein. 
     
    
     TECHNICAL FIELD 
       [0002]    The technique introduced here relates to the field of electronic sensor systems for footwear. 
       BACKGROUND 
       [0003]    The use of orthotic inserts in footwear to assist in the therapy and alignment of the wearer&#39;s neuromuscular and skeletal systems is known. One refinement to such orthotics contemplates their use in combination with electronic pressure sensors so that the wearer can be assessed and/or monitored. 
       SUMMARY 
       [0004]    Disclosed herein is an orthotic insert configured with an improved electronic sensor layer that provides feedback on important information regarding the wearer&#39;s gait mechanics (such as the force and pressure distribution on substantially the complete footprint of the wearer) during walking and other physical activities. The layer of sensors is used to assist in monitoring the wearer&#39;s health via foot pressure tracking. 
         [0005]    Known existing sensing systems for footwear to date are limited to 8 sensors; in other words, the force/pressure signals from no more than 8 sensors (distributed around the wearer&#39;s foot) can be tracked. This is because the signals are processed through an analog-to-digital converter (ADC) device, and presently such ADC devices typically have an 8 channel limit. The technique introduced here is able to utilize  9  or more (substantially more, where appropriate) sensors on the sensor layer. At least one embodiment of the disclosed system incorporates the use of one or more 32-channel analog multiplexers (or multiplexer switches) and Bluetooth 4.0 low-energy technology (the latter being used to transmit/communicate the data), to significantly increase the number of sensors that can be handled. Using a large quantity of standardized sensors allows the sensor layer to be more readily customizable and robust to different foot and gait biomechanics. 
         [0006]    Furthermore, existing sensing systems that are used with footwear are generally either impractically thick or not customizable. The manufacturing process disclosed, coupled with the selection of suitable sensors and materials, enables sensor layers having a thickness of less than 2.6 mm to be produced. 
         [0007]    The technique introduced here relates to an insert for footwear and to a composite orthotic insole comprising said insert, wherein the insert (or sensor layer) is embedded with a plurality of force (or pressure) sensors, and may be used to gather the wearer&#39;s foot pressure data (such as gait biomechanics) during various physical activities. The insert can include 9 or more embedded sensors, which together will provide broad coverage and precise sensing of the human foot impact area. In at least one embodiment, the insert comprises a polydimethylsiloxane (PDMS) covering to seal and protect the layer of sensors, thus providing flexibility, durability and waterproofing of the insert. The applicable data collected from the sensors will be passed to a proximally-located, battery-powered microcontroller (which may be concealed within or beneath the orthotic insole, such as in the area of the foot arch) which can use standard Bluetooth (4.0) communications technology to communicate such data to external devices. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    Embodiments of teachings introduced here are described below with reference to the accompanying drawings in which: 
           [0009]      FIG. 1  is a simplified top view of the composite orthotic insole and sensor layer, illustrating the layout of the sensors in the sensor layer. 
           [0010]      FIG. 2  is a cross-sectional view of an embodiment of an orthotic insole having multiple layers. 
           [0011]      FIG. 3  is a schematic diagram illustrating the wiring for the sensors in the sensor layer and illustrating the multiplexer function. 
           [0012]      FIG. 4  is a top view of the sensor sheet, along with an enlarged fragmentary view of a section thereof, illustrating the wiring of the sensors. 
           [0013]      FIG. 5A and 5B  are a simplified diagram (top view) of two differently sized sensor sheets, illustrating how each can be trimmed to form a sensor layer for different-sized feet. 
           [0014]      FIG. 6  is a side view of an embodiment of an orthotic insole including a number of electronic components. 
           [0015]      FIG. 7  is a block diagram of a system including an external user device and an application server. 
           [0016]      FIG. 8  is a cross-sectional view of an embodiment of an orthotic insole having a support pillar in an air gap layer. 
           [0017]      FIG. 9  is a flowchart of a method for customization of an orthotic insole. 
           [0018]      FIG. 10  is a flowchart of a method of receipt and transmission of signals from an orthotic insert. 
       
    
    
     DETAILED DESCRIPTION 
       [0019]      FIG. 1  is a simplified top view of the composite orthotic insole and sensor layer, illustrating the layout of the sensors in the sensor layer. A schematic top view of a smart orthotic insert  20  is shown. The orthotic insert  20  includes a number of layers. Displayed is a sensor layer  22  and a surface layer  24  which the sensor layer is placed on top of. The surface layer  24  would go around the exterior of the orthotic insert  20  and is the surface upon which users contact with their feet. The sensor layer  22  is generally in the shape of a wearer&#39;s foot, and is made up of a plurality of electronic pressure or force sensors  26  wired together in a network. The sensor  26  themselves may merely be conductive contacts that make up a portion of a pressure sensor or switch. The surface layer  30  serves to completely seal and protect the sensor layer (among other layers), and may be made from a material such as PDMS, or other suitable plastics or gel materials which are flexible, durable and waterproof. 
         [0020]    Each of the active sensors  26  is shown as having a hexagonal shape (although it should be understood that other shapes of sensors are also possible, such as circular). The general layout of the sensors  26  in relation to a wearer&#39;s foot shape is shown in  FIG. 1 . The number of sensors  26  and their placement/coverage around the shape of the foot is such that all important areas of the foot will be measured, regardless of the wearer&#39;s foot shape specifics, as well as regardless of the wearer&#39;s gait mechanic changes during the orthotic lifetime. 
         [0021]    An embodiment of the technique introduced here is described herein in the form of a sensor layer  22  of an orthotic insert  10 . However, it should be understood that the sensor layer could instead be used in combination with a regular insole or insert, or by itself as an insert for footwear. 
         [0022]      FIG. 2  is a cross-sectional view of an embodiment of an orthotic insole having a number of layers. The sensor layer  22  interacts with a number of layers, including a pressure-sensitive resistor layer (“PSR layer”)  28 . The PSR  28  may comprise a layer of Velostat as manufactured by the  3 M Company. Other materials are suitable so long as the material used has a variable electrical resistance which is controlled by the amount of pressure applied to the material. The electrical resistance is reduced when pressure is applied. Between the sensor layer  22  and the pressure-sensitive resistor layer  28  is an air gap layer  30 . The air gap layer  30  is established through the structure of the surface layer  24  which keeps the PSR layer  28  and the sensor layer  22  split apart. After the orthotic insert  20  is constructed, the air pressure of the air gap layer  30  maintains the integrity of the air gap layer  30 . 
         [0023]    Below the sensor layer  22  are electronic components. The electronic components include a microcontroller  32 , and a wireless communicator  34 . Optionally a multiplexer  36  is connected to the microcontroller  32 . The sensors  26  are connected to either the microcontroller  32  or the multiplexer  36 . There is also a differential contact  38  that runs between the microcontroller  32  and the PSR layer  28  that completes the circuit. The circuit is powered by a battery  40 . The battery  40  may be rechargeable or replaceable. 
         [0024]    The general functionality of the layers is as follows. The differential contact  38  carries the voltage difference from the battery  40  to the PSR layer  28 . The PSR layer  28  changes its resistance when bent, compressed or is otherwise deformed by external forces (in this case, foot impact). The air gap layer  30  is placed below the PSR layer  28  to provide cushioning and support for the PSR layer  28 , and therefore regulate how much pressure is required to alter the shape of the PSR layer  28 . In other words, The air gap layer  30  regulates how much force or pressure is required to create the resistance difference in the circuit. Where the PSR layer  28  contacts the sensor layer  22  (the particular sensors  26 ) a circuit is completed. The changing resistance is measured in the microcontroller  32 , and converted into digital data points for software interpretation. The recorded voltage enables calculation of the magnitude of pressure applied to the sensor as well as the timing for the applied pressure. 
         [0025]    Based on the number of sensors  26 , the orthotic insert  20  makes use of the multiplexer  36 . Where the microcontroller  32  is configured to accept all of the inputs on the of the sensors  26  directly, no multiplexer  36  is required. Where the number of sensors  26  is greater than the number of sensor inputs on the microcontroller  32 , a multiplexer  36  enables additional sensor input to the microcontroller  32 . In at least one embodiment, the sensor coverage will be such that a minimum of nine sensors  26  providing pressure data points at all times. 
         [0026]    In at least one embodiment, the complete pressure sensors are composed of a Velostat™ layer, an air gap layer, sensor layer and electronic components. Sensors  26  can be sized as desired, possibly in the 5 mm to 40 mm range. The sensors are semi-custom, in that the sensors  26  are based on a standard set of layers, and customized in terms of shape and size to fit the design of the sensor sheet. An example of a suitable off-the-shelf complete pressure sensor that utilizes a usable pressure-sensor configuration is the Teksan™ FlexiForce™ A201. 
         [0027]    The sensor sheet can be used in contact with a human foot and placed above an orthotic insert (which itself is preferably one that has been customized to a shape or profile to provide the wearer with specific biomechanical improvements). The sensor layer can provide gait and stride force/pressure feedback to validate these improvements, and predict future orthotic refinements. The gathered data could be used for performance analysis, performance improvement recommendation, health tracking, injury prevention, and various other biomechanical applications. 
         [0028]      FIG. 3  is a schematic diagram illustrating the wiring for the sensors  26  in the sensor layer  22  and illustrating the multiplexer  36  function. The schematic diagram illustrates the wiring  42  of nine separate sensors  26  and the multiplexer  36  function. To enable 9+ channels of data logging, one or more multiplexer switches  36  is used. 
         [0029]    The sensors are wired through one or more multiplexer switch  36 , which can be analog 32-channel switches, for example. From the multiplexer switch  36 , the wiring  42  runs to a microcontroller  32 , which is limited to 8 inputs. It may be preferable that a particular sensor sheet be made up of sensors  26  that are standardized and the same size, since this makes the sensor sheet more readily customizable and facilitates comparisons (and provides for uniformity) of the various sensor signals from the same foot or from different wearers; however, sensors  26  of differing sizes could be used. 
         [0030]    The multiplexer  36  will switch between the sensors  26  rapidly, i.e., fast enough to ensure that any measurable pressure changes can be detected and recorded. The multiplexer  36  switches one of multiple inputs to the common output, determined by a unique binary address lines (samples are marked on each sensor  26 ). 
         [0031]    For 9-16 sensors, a 16-channel analog multiplexer can be used, switching one of 16 inputs to one, determined by four-bit binary address lines (in this case, a 32-channel analog multiplexer could also be used). For 17-32 sensors, a 32-channel analogy multiplexer can be used, switching one of 32 inputs to one, determined by five-bit binary address lines. Alternatively, where appropriate, two or more multiplexers  36  can be used in combination. The signal from the sensors is passed to a microcontroller  32 , which can include a microcontroller and associated electronic equipment (including battery unit and communication hardware). 
         [0032]    The above-described approach involving relatively large numbers of sensors is practical in combination with the use of electronics that consume small amounts of power (such as low-power sensors) and that require low-power for communication through the wireless communicator  34 . Bluetooth 4.0 standard technology, compatible with iBeacon™, for example, can be used to conserve battery life. Other forms of wireless communicators  34  are also suitable such as WiFi or cellular (GSM, CDMA, GPRS, etc . . . ) so long as the wireless communicator  34  is compact. 
         [0033]      FIG. 4  is a top view of a sensor sheet  44 , along with an enlarged fragmentary view of a section thereof, illustrating the wiring  42  of the sensors  26 . The sensor sheet  44  itself can be designed to allow trimming and customizing for each unique footprint. The sensors  26 A and peripheral sensors  26 B are placed and wired in such a way that the electrical wires  42  are directed generally towards the center of the basic foot shape. This enables adding or subtracting to the sensor sheet  44  design without disrupting the wiring  42  of the sensor  26 . This also provides the advantage of being able to trim/customize each sheet to a specific foot shape, by cutting through some of the peripheral sensors  26 B, without significantly affecting the functionality of the sensor layer  26  as a whole. In  FIG. 4 , the trim line  46  for the sensor layer  22  for a particular foot-size indicates that certain peripheral sensors  26 B will be compromised by the trimming and would not function; other active sensors  26 A; however would continue to be able to record pressure data. 
         [0034]    The production process can start with a set of standard sensor sheets  44 . In some embodiments these sensor sheets  44  are categorized for one or more shoe sizes. In some embodiments, the sensor sheets  44  are suitably large to be used for all shoe sizes. The customization of the orthotic inserts  20  begins with the sizing of the sensor sheet  44 . Where customized foot sized data is received by the manufacturer, a very particular foot shape may be cut into the sensor sheet  44  matching foot of the intended user as accurately as possible. This is technique is highly customizable, in part, as a result of the repeating, pattern of the sensors  26  on the sensor sheet  44 , and that the wiring  42  for each of the sensors  26  is routed towards the center of the sensor sheet  44 . Routing the wiring  42  to the center of the sensor sheet  44  enables large variation in the foot size cut  46  into the sensor sheet  44  while still enabling the wiring  42  to function for all remaining sensors  26 . 
         [0035]    This is illustrated in  FIG. 5A and 5B , which show two differently sized sensor sheets  44 A and  44 B, and illustrate how each could be trimmed to be formed into a sensor layer for two different-sized feet (in this case, sensor sheet  44 A for a relatively larger foot, and sensor sheet  44 B for a relatively smaller foot). It also may be preferable that the sensor sheet  44  be made relatively thin—in practice, a thickness of less than about 2.6 mm may be considered optimal. 
         [0036]    The optimal sized sheet is chosen, then trimmed/customized along the trim lines  46 A and  46 B respectively for the individual foot shape. Each standard sheet size could be produced in bulk using a packaging machine, or produced using additive manufacturing with a modified 3D printer. It also may be preferred to determine sensor spacing based on foot size. For example, relatively smaller foot sizes may require less spacing between sensors than larger sizes. In cases where a standardized sensor sheet  44  is used, there is a positive correlation between a number of sensors  26  to the foot size trim lines  46 . Further, in those embodiments there is a static density of sensors  26  despite variance to the foot size trim lines  46 . 
         [0037]      FIG. 6  is a side view of an embodiment of an orthotic insole including a number of electronic components. In addition to a set of pressure sensors  26 , additional instruments  48  can be inserted in the orthotic insert  20  to provide data. The additional instruments  48  may include, for example: a geolocation sensor (such as a GPS), a thermometer, an accelerometer, an ultrasonic sensor, a heartbeat sensor and/or a gyroscope. More than one of the additional instruments  48  may be placed within the orthotic insert  20 . The additional instruments feed collected data to the microcontroller  32  which in turn feeds data to the wireless communicator  34  for transmission. The additional instruments  48  provide additional data that help shape the machine understood story of the travel a foot, a pair of feet, or even a whole body take. 
         [0038]    In some embodiments, the additional instruments  48  are socketed into an insole without the pressure sensors. Rather than use a layered pressure sensor, the additional instruments  48  are inserted into sockets in the surface layer  24 . Between the sockets wiring connects the microcontroller  32  and the wireless communicator  34  and the battery  40 . 
         [0039]      FIG. 7  is a block diagram of a system including an external user device and an application server. The orthotic insert  20  uses the internal wireless communicator  34  to transmit data and signals  49  collected and processed by the microcontroller  32  to an external device  50 . The external device  50 , may be a number of devices including but not limited to a smart phone, a tablet, a laptop or desktop computer, a virtual reality interface, a augmented reality interface, and a suitable control module known in the art. 
         [0040]    Processed data and signals  49  are either used directly by the external device  50 , or forwarded to an applications server  52 . The external device  50  may be connected to the application server  52  through wireless, network, or wired connections. In some embodiments, the processed data and signals  49  are used to construct analytical models of the wearer&#39;s gait, physical stresses, and body health. 
         [0041]    Another possible application for the disclosed system is for entertainment purposes. For example, the foot pressure on the wearer may be tracked through the layer of sensors and used as inputs to a connected user-interactive processing device (such as a video game system or a virtual reality hardware device). The wearer can provide instructions to or otherwise control the processing device, at least in part, via the foot pressure communicated (e.g. the wearer may represent/simulate actions such as jumping, walking, hopping, balancing, etc.). 
         [0042]      FIG. 8  is a cross-sectional view of an embodiment of an orthotic insole  20  having a support pillar  54  in an air gap layer  30 . In order to increase the resistance of the air layer  30  beyond air pressure, one or more collapsible support pillars  54  or substrate may be affixed within the air gap layer  30  increasing the amount of pressure required upon the PSR layer  38  in order to make contact with the sensor layer  22 . 
         [0043]      FIG. 9  is a flowchart of a method for customization of an orthotic insole. In step  902 , a insole manufacturing station receives foot size parameters. The scope of insole manufacturing station is general. Included examples of a insole manufacturing station are a corporate entity with the purpose of manufacturing insoles, a 3D printer, a single machine that assembles insoles, or a group of machines that assemble insoles. The foot size parameters pertain to the size of a customer&#39;s foot as measured by an external method. In step  904 , the insole manufacturing station determines the correct sensor sheet  44  to use for the particular customer&#39;s foot size parameter. 
         [0044]    In step  906 , the insole manufacturing station cuts the sensor sheet to the foot size parameter. In doing so, extraneous sensors  26 B and wiring  42  for those sensors are stripped away leaving only the sensors  26 A which will remain in the sensor layer  22 . In step  908 , the remainder of the sensor matrix is completed: the PSR layer  28  and the air gap layer  30  are formed. The electronic components (microcontroller  32 , multiplexer  36 , and wireless communicator  34 ) are connected to the wiring  42  and the differential contact  38  is connected to the PSR layer  28 . 
         [0045]    In step  910 , any additional instruments  48  are added as suitable. In step  912 , the layers, including the surface layer  24  are fixed into positon and a completed custom orthotic insert  20  is ready to ship to the customer. 
         [0046]      FIG. 10  is a flowchart of a method of receipt and transmission of signals from an orthotic insert. In step  1002 , the orthotic insert  20  receives a footfall, the footfall imparting pressure upon the insert  20 . In step  1004 , the imparted pressure increasing the conductivity of the PSR layer  28  of the insole  20 . In step  1006 , the imparted pressure further causes the air gap layer  30  to at least partially collapse. The collapse of the air gap layer  30  causes the PSR layer  28  to contact one or more sensors  26  on a sensors layer  22  of the insert  20 . 
         [0047]    In step  1008 , the orthotic insert  20  completes one or more circuits between the one or more sensors  26  and the PSR layer  28 . In step  1010 , each completed circuit delivers a signal to a microcontroller  32 , each signal including a unique identifier associated with each of the one or more sensors that complete the one or more circuits. In inserts  20  with a multiplexer  36  the unique identifier is determined by a binary code corresponding to the input on the multiplexer  36 . In inserts  20  without a multiplexer, the unique identifier is indicated by the input used on the microcontroller  32 . 
         [0048]    In step  1012 , the microcontroller  32  processes the received signals. In step  1014 , the microcontroller  32  delivers the processed signals to the wireless communicator  34  for transmission. In step  1016 , the signals are analyzed with a measured voltage to determine the magnitude of the pressure supplied by the footfall across each sensor  26  receiving pressure. Step  1016  may be performed either by the microcontroller  32  prior to step  1014 , or after step  1014  by an external device  50  or an application server  52 . 
         [0049]    Depending on how the transmitted data is to be used by the external device  50  or application server  52 , the method proceeds to step  1018  or  1020 . In step  1018 , the external device  50  or application server  52  uses the transmitted signals to develop analytical models of footfalls. In step  1020 , the transmitted signals provide user input to an entertainment apparatus such as a game system or virtual/augmented reality apparatus. 
         [0050]    The embodiments described herein are not, and are not intended to be, limiting in any sense. One of ordinary skill in the art will recognize that the disclosed technique(s) may be practiced with various modifications and alterations, such as structural and logical modifications. Although particular features of the disclosed technique(s) may be described with reference to one or more particular embodiments and/or drawings, it should be understood that such features are not limited to usage in the one or more particular embodiments or drawings with reference to which they are described, unless expressly specified otherwise.