Abstract:
This disclosure provides for an impression scanner system having improved calibration having a housing and a calibration plate of known geometry. The calibration plate has a plurality of different shapes thereon. The system also has a radiation source for emitting radiation towards the shapes on the plate and a surface for reflecting images created by the radiation on the shapes. A sensor for receiving the images of the shapes as the plate moves relative to the housing is also provided. A processor compares known geometry of the plate to the images received by the sensor and calibrates the sensor based upon the known geometry and images to reduce system aberration and distortion.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims benefit of expired U.S. Provisional Patent Application Ser. No. 61/002,141 filed on Nov. 7, 2007, the contents of which are incorporated by reference herein. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This disclosure relates to a system for obtaining and scanning an impression of the plantar surface of the foot. This disclosure further relates to a system for obtaining and scanning a contour of an impression of the plantar surface of the foot that uses a self-contained laser scanning technology to digitize the contour of the impression for orthotics manufacture. This disclosure further relates to a system for obtaining and scanning an impression of the plantar surface of the foot that uses a calibration plate that reduces aberration and distortion of the scanned image. 
     2. Description of Related Art 
     Traditionally, devices for the purpose of capturing the three dimensional (3-D) shape or contour of the plantar surface of the foot require a foam impression that is filled with plaster. The resulting plaster is used to produce a model of the subject foot of the patient. The model can then be measured using a pin digitizer or a laser scanner to accurately create a representation of the plantar surface of the foot for orthotics manufacture. Systems that use plaster are inconvenient, require numerous steps and are time consuming. The laser scanning systems, while not requiring plaster, are not generally self contained or efficient. 
     Systems using optical digitization of a three dimensional (3-D) contour using a camera coupled with a light source for triangulation are known. Typically, the light source is structured or beamed; a beamed source would include a laser line projected at a proscribed incident angle onto an object within the camera field of view. Optical digitization systems are typically calibrated to map observed line location to contour data. Placing a predefined geometrical object in the camera field of view and mapping each point in the image to the known location on the object can realize the calibration. The recorded image data is compared with the known geometry of the object in the field of view to determine and assign geometry values to the observed location in the camera&#39;s image data. In this fashion, the system learns how to derive geometric data from point locations in the camera image. That is, the digitization system is calibrated. 
     There are a number of variations of the above-discussed concept. For example, one variation uses a calibration plate disposed between the light source and the surface to be scanned. The light passing through the calibration plate forms a pattern, such as a matrix of lines, a grid pattern, dots, etc. on the surface to be scanned. Alternatively, the digitization system may use a polar axis rather than a linear axis for the transport of the object being measured through the field of view of the camera and the structured light source. Such systems often have problems related to aberration and distortion of the image that is viewed by the camera, as well as inconsistency in brightness due to distance and angle of reflection. 
     Systems using the basic optical digitization discussed above are known. However, heretofore such systems have been large, expensive to build time and consuming to operate. This and other disadvantages limit the application of the laser scanning technology to applications where expense and size are not relatively important factors such as applications like high-end medical applications and service bureaus. 
     Other technologies may be used to measure the geometry of the undersurface of the object to be measured, such as a foot. These technologies include (1) contact digitizing wherein gauge pins spaced at known intervals are urged upward beneath the foot and sample the contour periodically, and (2) optical triangulation where radiation of a known characteristic is projected against the subject foot such that the resulting shape of the radiation as it contacts the foot is observed by a sensor, typically a camera. A processor is used to evaluate the observed image to determine the contour data of the object (e.g., the foot) being measured. 
     Contact digitizing is generally the preferred method of obtaining the underside of a foot when the merits of the resulting data are the exclusive criterion. A contact digitizer supports the foot while measuring. Supporting the foot allows a full weight bearing measurement to be made, while not allowing the foot to completely collapse against the flat, top surface of the scanner. This yields a supportive data set that captures the extension of the foot when weight is applied. 
     A laser scanner has a clear plate between the scanning mechanism and the subject being measured. In the instance of measuring a foot, if the foot is suspended above the glass plate the data produced by the scanner matches the shape of the foot. However, this technique requires that the foot be measured in an unweighted position. The contour data obtained from the foot in the unweighted position is not very desirable since the foot can expand by as much as size and one-half when weight is applied thereto in the course of walking. The contour produced by an unweighted measurement will over-support the foot and cause discomfort. Yet, if the foot is placed against the clear plate to simulate the weight bearing of the foot, the bottom of the subject foot is completely flat. This produces an uncomfortable and unnatural, distorted shape. 
     Laser scanners also have a number of other problems associated with placing the foot against the clear plate such as (1) fogging where, if the foot is not completely dry, a fog is produced on the glass that tends to compromise the measurement accuracy of the foot since the shape of the subject foot is at least partially obscured by the fog; and (2) surface refraction caused by a lack of contrast of the subject foot due to, for example a light skin tone of a bare foot placed against the clear glass plate that disperses the projected radiation when it contacts the foot. The projected light disperses inside the body. It then refracts back through the clear plate. This produces an ambiguous radiation observation, as the radiation is diffused. 
     Accordingly, there is a need for a system that obtains a impression of the plantar surface of the foot coupled with the advantages of a laser scanning systems, as discussed above. Such a system would be of similar efficacy in acquiring data from any kind of medium used to capture a foot impression. 
     Alternative mediums to the use of foam for obtaining an impression of the foot, and particularly the plantar surface of the foot, also exist. One such common alternative medium is a sock casting, often called a “slipper cast”. This technique involves encasing the foot in a casting material that hardens when activated. Once hardened, the casting is cut and removed from the foot. Removing the top portion of the casting then produces an impression of the foot. At that point it can be processed identically to a foam impression using a scanner. 
     SUMMARY OF THE INVENTION 
     This disclosure provides for an impression scanner system having improved calibration having a housing and a calibration plate of known geometry. The calibration plate has a plurality of different shapes thereon. The system also has a radiation source for emitting radiation towards the shapes on the plate and a surface for reflecting images created by the radiation on the shapes. A sensor for receiving the images of the shapes as the plate moves relative to the housing is also provided. A processor compares known geometry of the plate to the images received by the sensor and calibrates the sensor based upon the known geometry and images to reduce system aberration and distortion. 
     A scanner system for capturing an impression having improved calibration includes an object of known geometric values having a plurality of different shapes thereon and a radiation source for emitting radiation towards the plurality of different shapes. The system also provides for a surface for reflecting an image of the plurality of different shapes and a sensor for capturing reflected images of the plurality of different shapes and for outputting data responsive to the image of the plurality of different shapes. A processor that compares the outputted data to the known geometric values of the object and stores differences between the data and the values to minimize aberration of scanned objects. 
     A method of measuring the contour of an impression provides for calibrating a sensor using a plate having a plurality of different shapes thereon to derive calibration data and placing an object against in a medium to obtain an impression of the object. The method provides for scanning the impression with radiation emitted from a radiation source and sensing reflected light from the impression during the scanning and calculating spatial values representing the contour of the impression using the derived data from the calibration of the sensor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other and further benefits, advantages and features of the present invention will be understood by reference to the following specification in conjunction with the accompanying drawings, in which like reference characters denote like elements of structure and: 
         FIG. 1  illustrates a perspective view of the system according to the present invention; 
         FIG. 2  illustrates a section view of the system of  FIG. 1  taken along line  2 - 2 , according to the present invention; 
         FIG. 3  illustrates a section view of the system of  FIG. 1  taken along line  3 - 3 , according to the present invention; 
         FIG. 4  illustrates a section view of the the system of  FIG. 1  taken along line  4 - 4 , according to the present invention; 
         FIG. 5  illustrates a side view of the sliding mechanism of the system, according to the present invention; 
         FIG. 6  illustrates a perspective view of the system of the present invention with the drawer in an extended position; and 
         FIG. 7  illustrates a view of the calibration plate of  FIG. 3 , according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention provides a novel architecture for laser scanning. The embodiment described herein is designed to be illustrative of the architecture rather than a comprehensive, exhaustive listing of all possible implementations of the present invention. 
     The present invention preferably uses inexpensive components and technologies. These include, for example commodity cameras such as those used with personal computers (i.e., a digital camera). Such cameras are relatively inexpensive and designed for easy interfacing with a computer. 
     The camera used in an illustrative and exemplary application of the present invention can be a commercially available “webcam”. The camera connects to a personal computer using a USB, serial, or other (preferably standardized) interface. The camera is preferably equipped with a pass filter. The filter can be a band-pass, high-pass, or low-pass filter to allow the passage of the desired spectrum of the radiation (e.g., light) of the structured emission source to pass through to the camera, but rejecting to a great degree other emissions that may come into the camera&#39;s view. For example, the camera can be outfitted with a filter to reject ambient light that may come into the field of view of the camera. 
     In one aspect hereof, a structured emission source is provided by a laser diode having a convex plastic lens at the emission end of the laser. The lens spreads the laser emission outwards in an axis to produce a line on a surface intersected by the laser emission. Laser diodes are relatively inexpensive and are also widely available. 
     The present invention is preferably compatible with and uses standard computing interfaces and communication protocols, thereby facilitating connection to commercially available computers and other processing peripherals using standard communication interface protocol(s). The USB interface is one such interface, as it is ubiquitous and requires little or no special skills to connect to. The ease of connection makes the present invention all the more useful. The USB interface facilitates use of an off-the-shelf, commercially available digital camera having a USB interface. 
     In an aspect of the present invention, an interface was designed to allow the USB connection to be used for the control of miscellaneous functions of the compact optical contour digitizer of the present invention. This aspect of the present invention contributes towards maintaining low costs and improves the practicality and reliability of the present invention. 
     The control electronic aspects of the present invention provide for control of motion along an axis, control of the radiation source, positioning control, and control of projection means used to illuminate the subject matter having its contour digitized. The projection means allows for direct imaging of the subject matter, as well as contour measurement. Direct imaging is desirable to derive metrics of the subject matter. In one aspect hereof, metrics are used to determine a length and a width of the foot (or any other subject matter being measured). 
     As discussed above, measuring an unweighted foot does not provide a complete set of data desirable for fully capturing the contour of the foot since the foot expands when weighted. Also, placing the foot on the glass plate of the scanner introduces other problems (e.g., fogging and over-flattening of the foot). Yet it is desirable to fully understand the contour of a weighted foot for the purpose of, for example, manufacturing customized orthotic supports. 
     The embodiment shown in  FIG. 1  is a contour digitizer designed to measure the shape of the plantar surface of a human foot. This particular application of the present invention uses the digitizer to measure the foot for the purpose of fabricating an orthosis for the foot. 
     Referring to the figures and, in particular to  FIGS. 1 through 3 , a perspective view and section views, respectively, of the scanning system according to the present invention are shown and referenced generally using reference numeral  10 . System  10  has a housing  12  that contains a pair of sensors such as, for example, cameras  15 , a pair of reflective surfaces, such as mirrors  20 , and a pair of radiation sources for emitting radiation. Radiation sources are preferably laser line generators  25 . Laser line generators  25  each include a laser diode having a convex plastic lens at the emission end. The lens spreads the laser emission outwards in an axis to produce a line  27  against either a calibration plate or an impression that will be discussed below. The present disclosure has particular application to measuring the plantar surface of the foot for the purpose of fabricating orthotics for the foot. While radiation source is shown as a laser line generator  25 , other devices such as photodiodes, a light, an infrared generator and an acoustic wave generator are also within the scope of this invention. While sensors are shown as being cameras, other sensors such as for example digital camera, a photodiodes and CCDs, could also be used. 
     System  10  contains a pair of multi-part sliding tracks  30  that are connected to inner surface of opposite sides of housing  12 . A drawer  40  slides in tracks  30  for smooth movement relative to housing  12 . Drawer  40  carries foam block  34  housed in containers  35  of drawer  40 . Foam block  34  is preferably phenolic foam, an ultra low density expanded polystyrene material commonly used for insulation that is a pressure sensitive material which compress when a person&#39;s feet are pressed into containers  35 . Foam block  34  is easily deformed, with little or no memory, and retains the deformed shape of impression  36  indefinitely. A slipper casting could also be used to capture the contour of the plantar surface of a foot. A slipper casting would also retain a negative impression of the plantar surface of the foot for orthotics manufacture. Motor  45  provides the motive force to enable drawer  40  to slide via sliding track  30  to move foam containers  35 . 
       FIG. 3  also shows two templates  60  on which a user may place her feet in the respective foam containers  35 . Additionally, as shown in  FIG. 4 , various connection ports are also associated with system  10  for electrical connection with processor  37  and/or graphical display device  38  to compute and graphically present, respectively, the results of the scanned foam impression  36  in the foam containers  35 . The present invention is preferably compatible with and uses standard computing interfaces and communication protocols, thereby facilitating connection to commercially available computers and other processing peripherals using standard communication interface protocol(s). 
       FIGS. 2 through 6  show the positioning of drawer  40  inside housing  12 . Cameras  15  and laser liner generators  25  are positioned almost directly above respective foam blocks  34  in containers  35 . Drawer  40  supports foam containers  35  during the measurement process and during storage. As shown in  FIG. 2 , drawer  40  moves in sliding tracks  30  of  FIG. 5  using a series of ball bearings, although other friction minimizing methods could also be used. Sliding tracks  30  are on each side of housing  12 . Each track  30  has an inner component and an outer component  32 . Inner component is affixed to drawer  40  and outer component is affixed to housing  12 . Inner component and outer component  32  slide relative to one another to insure that full extension of drawer  40  from box  10  is possible. This configuration also ensures that the entire length of foam block  34  within foam container  35  will be scanned. Significantly, tracks  30  also conserve space reduce overall length of system  10  for more convenient use. 
     Generally, aberration and distortion that occurs in cameras causes physical points of equal distance apart captured in a camera image to appear to be non-equidistant. To compensate for this phenomenon the process of calibrating to known points across the entire width of the field of view compensates for such lens aberration and distortion. 
     System  10  also has a calibration plate  50  having a plurality of high contrast different shapes, as shown in  FIGS. 2 and 7 . Inclined calibration plate  50  is marked with a plurality of different shapes that are exactly measured isosceles trapezoids  53  or gradually tapered lines. The axes of the plurality of trapezoids and lines are equidistant apart in real space but do not appear so in the image of camera  15 . Mapping this difference across the width of the image minimizes the effect of lens aberration upon the scanned object. Plurality of trapezoids  53  include a central trapezoid  54  and lateral trapezoids  55  disposed on opposite sides of central trapezoid  54 . Each of the plurality of trapezoids  53  extends along the entire length of plate  50 . Each of the plurality of trapezoids  53  also has a base  58  and a top  59 . Plate  50  has lateral edges  62 , a top edge  63  and a bottom edge  64 . Base  58  and top  59  are parallel. Top  59  has a shorter dimension than base  58 , thus creating a taper in each of the plurality of trapezoids at the top edges closest to cameras  15 . Each of the plurality of trapezoids  53  is filled with a highly reflective color. In contrast, the area surrounding and between each of the plurality of trapezoids  53  is colored to be non-reflective. During the scanning process line  27  that is projected against plate  50  will be received by camera as a series of white dots or points, representing the reflected portions of each of the plurality of trapezoids. 
     The spacing and shape of each of the plurality of trapezoids  53  on plate  50  reduces aberration and distortion that is due lens of camera  25 . A central trapezoid  54  of the plurality of trapezoids  53  is placed exactly in the physical center of plate  50  at a central axis thereof. Central trapezoid  54  and each of the lateral trapezoids  55  has a central axis that is equidistant from the axes of adjacent trapezoids. While the axes of the plurality of trapezoids  53  have an equidistant spacing, lateral trapezoids  55  that are progressively closer to lateral edges  62  have broader bases  58 , and are thus wider. Thus, the image of points that are observed by camera  15  of the points from the lateral trapezoids will be appear brighter than they would if they were not broadened. The broadening of lateral trapezoids  55  compensates for dimming on the lateral edges of images due to lens aberration. 
     The shape of each of the plurality of trapezoids  53  also compensates for the disproportionate brightness of images from the points of the trapezoids closest to camera  15 . The reflected brightness of line  27  from inclined plate  50  is non-linear relative to the distance of plate  50  to the camera  15 . Plate  50  of the present invention compensates for this distorted appearance so that the images of points received by the cameras  15  during calibration will have uniform brightness and size for greater resolution and accuracy. The compensation in size of reflected image points will compensate for the greater brightness that is received by images that are closer to the camera than those that are further away. 
     Thus, the trapezoidal shapes on calibration plate  50  compensate for aberration as well as disproportionate appearance of brightness and size of reflected points. 
     Calibration plate  50  is positioned at a predetermined angle  51  from the horizontal defined by base plate  52  in drawer  40 . In this embodiment of the invention, angle  51  is approximately 12° from the horizontal. Predetermined angle  51  of calibration plate  50  and the size of the image field of view  21  as observed by camera  15  will determine the maximum possible scanning height or depth of the impression. While a large angle  51  relative to base plate  52  allows for a higher maximum calibrated height or depth of the impression, field of view  21  that can be observed by camera  15  may be limited. As predetermined angle  51  increases, a loss of resolution occurs because fewer points created by line  27  against plate  50  from the scanning process can be captured in a longitudinal direction of movement. Conversely, a shallow angle, while providing a large field of view  21 , may not offer as great a level of perspective from which to collect images of points for mapping during calibration. Thus, angle  51  of plate  50  varies for the specific requirements of an impression or size of drawer  40 . While angle  51  is variable, it is preferably between a range of 8° and 25° relative to the horizontal or base plate  52 . 
     Calibration plate  50  is movable in order to accommodate multiple cameras as well as different impressions or drawer sizes. System  10  also has a belt  65  operatively associated with motor  45  to enable controlled linear advancement of drawer  40  and foam container  35  on sliding track  30  during laser scanning. 
     The operation of system  10  according to the present invention will now be addressed in conjunction with other aspects of the present invention, as with reference to  FIGS. 1 through 7 . Foam containers  35  each contain a foam block  34 , such as, for example, phenolic foam, that is easily deformed. Alternatively, a casting from a slipper casting could also be placed in drawer  40  for scanning. When drawer  40  is pulled away from housing  12 , the user places her feet in the respective containers  35  to provide an impression  36  in block  34  of the plantar surfaces of the feet. The feet must be placed in a crossed-over fashion to prevent excessive pressure from being applied in any one of the foam containers  35 . Such excessive pressure could yield inaccurate scanning results that would potentially result in improperly fitted orthotics. After the user removes her feet from the foam containers  35  and impressions  36  have been made in foam block  34 , drawer  40  is fully re-positioned in housing  12 . Foam block  34  retains the contour of impressions  36  of plantar surface of the foot for scanning at a later time. 
     Prior to scanning unknown geometries, a calibration to a known geometry is required for each camera/laser unit. This calibration is needed only once per unit the lifetime of the device. Before calibration, the calibration plate  50  is secured in drawer  40 . Motor  45  and belt  65  can be selectively activated to move drawer  40  and thus foam containers  35  away from housing  12 . Belt  65  moves drawer  40  containing calibration plate  50  at a selected rate precisely in a longitudinal direction directly under laser line  27  and camera  15 . Laser line generator  25  generates a line  27  that is projected against calibration plate  50  at a predetermined angle of incidence  28 . Predetermined angle  28  is determined within a possible range of angles in order to accommodate the necessary depth of the impression and to minimize the loss of visible object surface due to shadowing. 
     As calibration plate  50  moves relative to line  27 , reflected points are visible in the mirror  20  and captured as images by camera  15  as they come in field of view  21 . Computer vision software processes each image to locate the previously described points produced by plurality of tapered trapezoids  53 . Because the center axis of each of the plurality of shapes is at a known position in three-dimensional space, the pixel position of its rendering in the camera image can be used to represent that three-dimensional point. By obtaining a series of images while traversing plate  50  along its length, each possible pixel in camera field of view  21  is mapped to an actual point in three-dimensional space using known trigonometric functions. Thus a calibration map is developed and saved in persistent storage of scanning system  10  as a data lookup table. Software can load the table at any time, providing rapid data lookups to retrieve the physical point in space for any point in subsequent images. In this way, when laser line  27  projects upon an unknown object such as an impression, the reflection of that line can be found by software in the camera image and translated into three-dimensional points in space using data lookup table. Thus calibration of any camera/laser unit is required only once per lifetime of the device, as long as persistent storage of the calibration map remains intact. After calibration, plate  50  is removed. 
     It is to be understood that the scanning system of the present invention includes storage as well as processing and applications to carry out the present invention. 
     After contour of impressions  36  have been made and are returned to housing  12 , scanning commences. Laser line generator  25  projects a line across an approximately 6 inch width of impression  36  in foam block  34 . Mirror  20  is used to fold or reflect view  21  observed by camera  15  of the projection of laser line  27  against contour in foam block  34 . By folding view  21 , the overall dimensions of the housing, both height and length, are greatly reduced. In addition, the use of mirror  20  enables a longer focal length and allows the use of less expensive camera optics and minimizes aberrations. In the present application, the scanning system  10  acts directly on the impression  36  left by the foot within foam container  35 . Camera  15  supplies an image used to read the position of the laser line  27  on impression  36 . The contour of impression is captured and the spatial orientation of points that are received by camera  15  are stored by system  10 . The development of contour is computed by using the found laser points in the image to look up the corresponding three dimensional spatial point in the calibration map. 
     Generally, scanning of one contour completes with inward drawer traversal, and scanning of the second contour completes with outward drawer traversal. 
     Significantly, the size and geometry of system  10  is designed such that line  27  reflects as a series of horizontal points across the center of the camera field of view  21  at the mid-height  70  of the inclined calibration plate  50 . As well, this design ensures that the middle of field of view  21  correlates to 50% of the dynamic range, or depth of impression, for data acquisition. When light beam  27  is focused at a location of calibration plate  50  that correlates to half of the depth of the impression, not only is the aberration reduced, but also the entire impression can be viewed in a single pass of drawer  40 . The efficiency of scanning system  10  is optimized by having the middle of field of view located at this position. 
     System  10  allows accurate calibration and subsequent quick and precise scanning of the plantar surface of the foot without the use of plaster. Additionally, the scanning can be performed by a single unitary device to save time and expense for the manufacture of orthotics. Further, the calibrating system compensates both for camera lens aberration in the image of the field of view  21 , as well as non-linear brightness of points in the image due to varying distance of calibration plate  50  from camera  15 . 
     The present invention having been thus described with particular reference to the preferred forms thereof, it will be obvious that various changes and modifications may be made therein without departing from the spirit and scope of the present invention as defined in the appended claims.