Abstract:
The invention includes both a method and apparatus for measuring the shape of a surface of an object, such as a human foot. The apparatus includes a support for holding a compliant sheet of known color and retro-reflectivity. The compliant sheet conforms to the shape of the undersurface of the foot. A scanner scans a light beam along the undersurface of the compliant sheet from a vantage point that is below the compliant sheet. A sensor detects reflected light from the undersurface of the compliant sheet and feeds corresponding light value signals to a processor. The processor analyzes the signals and determines distance values to portions of the compliant sheet. The distance values enable a contour to be derived that is representative of the undersurface of the foot.

Description:
FIELD OF THE INVENTION 
     This invention relates in general to the precise measurement of a contoured surface and, more specifically, to measurements of the contour of the undersurface of the foot. 
     BACKGROUND OF THE INVENTION 
     Every foot is different and all require proper fitting of footwear in order to maintain good foot health. Measurement of the foot has long been done using length and width measurements. Those measurements yield a fair characterization of the general attributes of the foot, but fail to address the unique shape of the undersurface of the foot. 
     A number of prior art devices have, with varying degrees of success, measured the undersurface of the foot. Optical scanners that use a laser line optic that is projected onto the underside of a foot and a video camera that records the modified location of the reflected line, produce accurate contours. This technique only works well in a non-weightbearing circumstance. The reason is that the foot increases in length by approximately one size (the width also expands) when weight is applied. Measurement of the foot using such a scanner in a non-weight bearing arrangement will result in a data set that does not allow for this natural expansion of the foot in gait. 
     U.S. Pat. No. 5,689,446 to Sundman et al. and assigned to the same Assignee as this Application, describes a foot contour digitizer wherein a foot is first placed on an array of gauge pins which are in turn deflected to reflect the contour of the underside of the foot. The gauge pins are urged upward by a diaphragm that is moved by air pressure. The deflected gauge pins are then scanned to derive a data set that defines the foot contour. 
     While the aforementioned measurement device has the advantage of supporting the foot while measurement takes place, the device is inherently expensive, with its hundreds of gauge pins. Details of the gauge pin structure are found in U.S. Pat. No. 4,876,758 to Rollof and assigned to the same Assignee as is this Application. 
     Franks, in U.S. Pat. No. 4,858,621 discloses a foot pressure measurement system wherein a transparent flat surface is edge-lighted and supports a pliable material on which is placed a foot to be imaged. When the foot applies pressure to the pliable material, an increase in light intensity results in proportion to the pressure, which is sensed by a scanner. The light intensity variations are converted to foot pressure data. 
     If one places a foot against a transparent flat surface and uses a laser scanner to measure the contour of the undersurface of the foot, the resultant image reflects a contour with large unnatural flat areas of the foot where the foot contacts the transparent surface. Such a device is described in U.S. Pat. Nos. 5,128,880 and 5,237,520 to White. 
     White discloses a scanner that is similar to a flat plate document scanner, where the undersurface of the foot is imaged in color and the image data is processed to produce elevation data. The White device uses the principle that surfaces that are further away from the contact surface of the scanner will appear darker in the image data. 
     A problem with the White device is that there is no way to accurately determine the exact distance from the support surface of portions of the foot, using the data which results from the scanned foot image intensities. The variables which act to vary the intensity data include: variations in skin tone and color, ambient light, whether the subject foot is wearing a sock, and the amount of weight applied to the foot. Further, the lowest foot surfaces are whiter in relation to other areas of the foot due to reduced blood flow. Nevertheless, the White structure does exhibit the advantages of: use of an inexpensive flat bed scanner; providing an accurate perimeter of the foot; and providing enough information to characterize certain portions of the foot, e.g. high, low, or sheet arch height. 
     Even allowing for the variables discussed above, the intensity information acquired from an optical scanner is the sum of three components: 
     1. The position of the light source relative to the subject surface. 
     2. The incident angle of light projected onto the subject surface. 
     3. The distance of the subject surface from the reference surface. 
     To measure the contour of an object, such as a human foot, the above three components must be taken into consideration. Other variables must be eliminated, or allowed for, to derive accurate elevation data. 
     Accordingly, it is an object of the invention to provide an improved system for characterizing the undersurface of a foot. 
     It is another object of the invention to provide an improved system for characterizing the undersurface of a foot that provides consistent intensity data and enables accurate contour data to be derived. 
     It is a further object of the invention to provide an improved system for characterizing the undersurface of a foot that provides highly accurate foot contour data and enables the production of custom foot supports in accordance therewith. 
     SUMMARY OF THE INVENTION 
     The invention includes both a method and apparatus for measuring the shape of a surface of an object, such as a human foot. The apparatus includes a support for holding a compliant sheet of known color and retro-reflectivity. The compliant sheet conforms to the shape of the undersurface of the foot. A scanner scans a light beam along the undersurface of the compliant sheet from a vantage point that is below the compliant sheet. A sensor detects reflected light values from the undersurface of the compliant sheet and feeds corresponding signals to a processor. The processor analyzes the signals and determines distance values to portions of the compliant sheet. The distance values enable a contour to be derived that is representative of the undersurface of the foot. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded perspective view of a preferred embodiment of an apparatus that incorporates the invention. 
     FIG. 2 a  is an expanded schematic view of a scan mechanism. 
     FIG. 2 b  is an expanded view of a first preferred scan mechanism for use with the invention. 
     FIG. 2 c  is an expanded view of a second preferred scan mechanism for use with the invention. 
     FIG. 3 illustrates a retro-reflective bead on a compliant sheet. 
     FIG. 4 is a block diagram of elements of the processor shown in FIG.  1 . 
     FIGS. 5 a - 5   d  illustrate the operation of the apparatus of FIG. 1, during the process of acquiring contour data of the underside of a foot. 
     FIG. 6 is a schematic side view of a further embodiment of the invention. 
     FIG. 7 is a perspective view of an insole that is constructed using data achieved through operation of the invention. 
     FIG. 8 is a contour illustration of the underside of a foot using data acquired through operation of the invention 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, an optical scanner  10  is configured much the same as a flat plate document scanner. In that regard, optical scanner  10  includes a housing  12  and an upper, transparent plate  14  which may be either glass or a polymer/acrylic material. An optical scan structure  15  is positioned within housing  12  and includes a light source  16  and a linear detector array  18 , both of which are mounted for movement on a pair of rails  20  (only one rail is shown). A measure bar  21  is positioned on transparent plate  14  and is used to obtain a measure of the length of a foot being imaged. Motor means are present within housing  12  (not shown) and enable the optical scan structure  15  to move beneath transparent plate  14  in substantially the same manner as in prior art document scanners. 
     As indicated above, the position of the light source is an important consideration in achieving reliable elevation information. First, the light source must provide uniform illumunation from the camera&#39;s viewpoint. Most commercially available flatbed document scanners use a light source  16  on one or the other side of an active scanning opening. This yields a light source that is suited to the purpose for which the scanner was designed (namely scanning a flat sheet of paper a known distance from the active scanner opening), but yields a light source that will unevenly light an uneven surface. 
     FIG. 2 a  shows a measured surface  21  that is more perpendicular to the light source&#39;s emitted light and is more efficient at reflecting that light towards the scanner&#39;s active scanning element opening  19 . This is aided by addition of a “reflex light source”, as shown in FIG. 2 b.    
     The arrangement of FIG. 2 b  reflects the source light off of a 50% reflective mirror  23  located directly in the active scanning area of the scanner. Mirror  23  reflects 50% of the source&#39;s light directly at surface  21 . Light not reflected by mirror  23  is sent to light sink  25 , to prevent stray light from interfering with the scanning. The embodiment of FIG. 2 b  makes the apparent light location the same as the scanner&#39;s location and yields a near perfect lighting configuration. 
     A further scanner embodiment is shown in FIG. 2 c  and includes a collimated light source  100  whose output beam  102  is passed through a prism  104  which converts light beam  102  into a beam  106  comprising a rainbow of colors. Rainbow beam  106  is then reflected upwardly by mirror  108  onto the body being imaged. Any contoured item in the projection path of rainbow beam  106  will reflect a color back to color detector  110  that is a function of the distance of the body from reference surface  14 . For instance, if the reflecting surface is positioned at level A, color  112  is reflected along axis  114  to detector  110 . If the reflecting surface is positioned at level B, color  116  is reflected along axis  114  to detector  110 , etc. So long as the field of view of detector  110  is restricted to the immediate region of axis  114 , the other reflected colors are ignored. 
     As an alternative design, a strip of differing color film and a lens can be substituted for prism  104 . 
     Returning to FIG. 1, a processor  22  receives signals from linear detector array  18  that are indicative of intensities of reflected light from a surface being imaged. The operations of processor  22  will be considered in detail below. 
     A slanted support structure  24  is positioned on an uppermost surface of housing  12  and is affixed thereto. A flange  26  extends about the outer periphery of support structure  24  and mates with the outer edges of a compliant sheet  28  that rest thereupon. Compliant sheet  28  is preferably a flexible sheet of known color and retro-reflectivity. A surface that is retro-reflective has the property that it sends incident light rays back to the direction from where they came. By incorporating a retro-reflective surface, the slope of the reference surface relative to the reference surface has little impact in gray scale image data at slope angles of less than 30 degrees. At slope angles in excess of 30 degrees, the flexible sheet is less efficient at reflection. The reduced efficiency is compensated for in software post-processing. 
     A preferred method for achieving retro-reflectivity is by embedding glass microspheres  27  into the undersurface of compliant sheet  28  (see FIG.  3 ). Microspheres  27  are adhered to compliant sheet  28  using an elastic coating  29 . Glass microspheres  27  are slighty mirrored and have an index of refraction of approximately 1.5. Ambient incident light  33  that enters a microsphere  27  from off axis angles of over about 60 degrees is rejected and the rest is accepted. The accepted light that enters a microsphere  27  bounces off an interior reflective surface and is emitted at the same angle from whence it came. 
     In an alternative embodiment, the undersurface of compliant sheet  28  need not be continuously coated with microspheres  27  and embedding ink  29 . They need only be applied periodically (as in a dot pattern for instance). This will allow compliant sheet  28  greater flexibility than a continuous coating, as well as offering greater potential lifetime. 
     In a further embodiment, the microspheres can be embedded directly into compliant sheet  28 . This is accomplished during manufacture of the complaint sheet. The method of embedding can be by heating to slightly melt the surface of compliant sheet  28  and thereafter embedding microspheres  27  therein. 
     Regardless of the method employed, for optimum retro-reflectivity, microspheres  27  should be embedded to approximately ½ of their diameter, and the sheet into which they are embedded should have a uniform color or reflectivity. 
     In yet another embodiment, the compliant sheet need not have embedded microspheres but should preferably have a highly reflective coloration. Software processing is then needed to compensate for non-linearities in the image data intensity vs. elevation. 
     Returning to FIG. 1, a frame  30  sandwiches and seals the outer edges of compliant sheet  28  against flange  26 . A series of holes  32  are present in transparent plate  14  and enable the attachment of frame  30 , and an underlying edge of compliant sheet  28  directly to transparent plate  14 . 
     When frame  30 , compliant sheet  28  and support structure  24  are assembled on the upper surface of housing  12 , an air-tight volume  31  is created between the lower surface of compliant sheet  28  and the upper surface of transparent plate  14 . An air compressor  34  is positioned within housing  12  and is coupled, via a tube  36 , to an outlet  38  which leads into air-tight volume  31 . Air compressor  34  is controlled to maintain a level of pressure within volume  31  such that when a foot, or other object, is placed upon compliant sheet  28 , compliant sheet  28  remains sufficiently flexible to form around the foot/object but is maintained just out of contact with transparent plate  14 . 
     Turning now to FIG. 4, the block diagram shown therein illustrates the major components of processor  22 . Signals from detector array  18  are fed through an analog to digital (A/D) converter  40  and an input/output module  42  and are stored in a memory  44  in the form of pixel/intensity data  46 . Also stored within memory  44  is a calibration table  48  which equates intensity levels to distances from a reference or datum surface (e.g., transparent plate  14  or the flat surface defined by a plane resident on flange  26 , FIG.  1 ). 
     Memory  44  further includes a contour detection procedure  50  which enables the derivation of contour values from the pixel/intensity data  46  derived during a scan action of optical scan structure  15 . In the latter regard, contour detection procedure  50 , in combination with central processing unit (CPU)  52 , operates upon the pixel intensity data  46  and utilizes the distance entries in calibration table  48  to arrive at the contour data. CPU  52  also issues signals to a motor/light control module  54  which, in turn, controls the operation of light source  16  and the motor which moves optical scan structure  15  beneath transparent plate  14 . 
     Referring to FIGS. 5 a - 5   d , the method of the invention will be described. FIG. 3A illustrates a cutaway side view of optical scanner  10 , prior to volume  31  having been pressurized by operation of air compressor  34 . At this stage, compliant sheet  28  is uninflated and droops into volume  31  of support structure  24 . As shown in FIG. 3B, when air compressor  34  is energized by a signal from CPU  52 , airflow into the volume  31  causes compliant sheet  28  to extend upwardly as a result of a pressure build-up in volume  31 . 
     As shown in FIG. 5 c , a foot  60  is about to be placed on compliant sheet  28 . Note that both the heel and the arch of foot  60  are positioned directly above the uppermost regions of support structure  24 . Thus, when foot  60  is in full contact with compliant sheet  28  (as shown in FIG. 5 d ) compliant sheet  28  molds itself to the shape of the arch and heel in an enveloping fashion. The air pressure within volume  31  is maintained at a level that allows the portion of compliant sheet  28  that is immediately below the heel of foot  60  to either just touch or, preferably, be just offset from the upper surface of transparent plate  14 . 
     Accordingly, compliant sheet  28  molds itself to the bottommost surface of foot  60  and provides a uniformly colored surface for subsequent scanning. Note that the arrangement shown in FIG. 5 d  enables the imaging of the heel and arch (behind the metatarsels) as those are the regions of a foot whose dimensions must be known in order to enable the configuration of an orthotic support structure therefor. 
     Once foot  60  is in place, as shown in FIG. 5 d , processor  22  is instructed to commence a scan action. Accordingly, CPU  52  issues a signal to motor/light control module  54  to commence movement of optical scan structure  15  (FIG.  1 ). Accordingly, light source  16  is energized and projects a beam upwardly onto the undersurface of compliant sheet  28 . The reflections from compliant sheet  28  are sensed by linear detector array  18 , causing analog light intensity signals to be fed to A/D converter  40 , which converts those signals to digital intensity values. Those digital intensity values are then stored in pixel/intensity data region  46  of memory  44 . 
     Once a complete scan has been accomplished, contour detection procedure  50  causes each intensity value to be used to address calibration table  48  which, in turn, returns a distance value that is indicative of the distance of the respective pixel position from the datum surface. Once those distance values are accumulated, an accurate contour of the underside of foot  60  has been created which can later be used in constructing an orthotic foot support. For instance, the contour values can be used to determine the amount of a conformable material to be injected into a mold to create an orthotic or an insole that matches the underside of the foot. Further, the contour values can be used to control the machining of a blank to produce an orthotic matched to the underside of a user&#39;s foot. 
     The light intensity values derived during a scan exhibit a progressively darker value as the distance increases between the scanned surface of compliant sheet  28  and transparent plate  14 . Since the slope of support structure  24  is known, and the change in elevation between successive scan lines is also known, the elevation for any light intensity level observed at any given point can be derived. It is preferred that calibration table  48  be derived initially to enable a table lookup operation to be performed when converting from intensity values to distance values. In addition to the contour data, a sensing of the marking increments on measuring bar  21  during the scanning action enables a length dimension of the foot to be acquired. 
     To calibrate the system, a flat plate (not shown) is placed at an angle relative to the reference surface (e.g., transparent plate  14 ) and air is introduced into interior  31  of support structure  24 . Compliant sheet  28  is thus forced against the undersurface of the flat plate. Thereafter, a gray scale scan is performed of the underside of compliant sheet  28 . The digitized image is processed and saved. 
     The area recorded with the slanted flat plane in view exhibits a progressively darker image as the plane moves further away from the reference surface, (or in the event no reference surface is used), the scanning plane. Since the size of the flat calibration plane is known and the angle at which it was placed relative to the reference surface or scanning plane is known, the elevation for any given intensity can be derived. Those elevation distances are then stored in calibration table  48 , which correlates the distance values to the respective light intensity values which gave rise thereto. Then, when a foot is scanned, the resulting intensity values derived from the underside of compliant sheet  28  are used to address the calibration table  28 , enabling read-out of the corresponding distance values. 
     There are other methods that can be used to calibrate the system. Instead of a flat plane, a sphere can be used with a known radius. The sphere is placed against compliant sheet  28  such that it is tangent to the reference surface or the scanning plane. Air is then introduced into support structure  24  and the compliant sheet  28  is caused to assume the shape of the sphere. Compliant sheet  28  is scanned and the resulting image analyzed. Each elevation represented by an observed intensity can be readily derived when the radius of the sphere is known. 
     Once contour image data is acquired, contour detection procedure  50  performs image processing actions to capture the portion of the image directly related to the foot contour. More particularly, contour detection procedure  50  finds the active areas of the foot in the image by sensing edge pixels which encompass the contour image (e.g., by looking for pixels which, after a run of constant intensity pixels, commence a change of intensity—indicating a boundary between a non-stressed portion of compliant sheet  28  and a stressed portion thereof). The image is then trimmed so that a portion behind the heel is eliminated. 
     Thereafter, the heel area is centered in the image area and it is then rotated so that the forefoot is also in the middle of the image area. Next, any image areas outside of the image boundary are trimmed. Thereafter, the pixel intensity values within the now-captured foot contour region are converted to height values by referring the pixel intensity values to calibration table  48  and reading out the respective height data. 
     Turning now to FIG. 6, a further embodiment of the invention is illustrated wherein support structure  70  is arranged so that compliant sheet  28  is held parallel to transparent plate  14 . Accordingly, when a foot is thereafter placed on compliant sheet  28 , the sheet stretches and assumes the shape of the foot surface. An air supply is optional in this embodiment, but is preferred so as to enable pressurization of volume  72  so as to enable control of of the amount of deflection of compliant sheet  28 . 
     FIG. 7 illustrates a three dimensional view of an insole that is configured through use of the foot contour data derived as described above. FIG. 8 illustrates a contour image that is constructed from the foot contour data. It is preferred that the individual contours be shown in different colors to enable the user to better visualize foot surface differences. 
     It should be understood that the foregoing description is only illustrative of the invention. Various alternatives and modifications can be devised by those skilled in the art without departing from the invention. Accordingly, the present invention is intended to embrace all such alternatives, modifications and variances which fall within the scope of the appended claims.