Abstract:
A stable, continuous, high-speed roll film media path is established between supply and take-up film reels. Supply and take-up path segments isolate a core transport path section from significant non-linear forces, thereby enabling continuous, high-speed, high-accuracy scan line imaging of the media. The supply and take-up path segments each operate to continuously maintain open decoupling loops in the film media while accurately controlling the speed, tension and alignment of the film media as transported through the core transport path section. A microcontroller operates two motor driven capstans to establish the film media speed and tension within the core transport path section. Optical sensors provide feedback to the microcontroller in managing two additional motor driven capstans to maintain the decoupling loops. The film media within the core transport path section is thereby isolated from frictive, inertial, and skewing forces that could otherwise degrade the media imaging.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention is generally related to continuous scan film readers and strip digitizer systems and, in particular, to a high-speed, continuous linear film transport system enabling continuous, highly accurate media-based image recognition. 
   2. Description of the Related Art 
   Substantial libraries of documents and related graphical image forms of information have been archived over the years on roll film media. In particular, there are a considerable number of large archives of imaged documents stored on roll microfilm. Conversion to a digital form is generally desired to prevent loss of the information due to aging of the film media and to fundamentally improve and ensure permanent access to the documents and information. 
   Many different roll film transport systems, using either a stop-motion or continuous feed architecture, have been developed over the years. These systems have met with varying degrees of success, depending on the nature of the intended application, when considered based on criteria including accurate image reproduction, total throughput, media wear, ease of operation, and both system and operational cost. Stop-motion systems are typically employed where accurate reproduction and high image resolution are required. Media transport mechanics intermittently decelerate the film media to allow static, frame-by-frame projection and, for digitization, two-dimensional image capture. In general, film loops are required to account for the frame-by-frame deceleration requirement for projection. U.S. Pat. No. 4,022,525 employs uncontrolled loops only presumed to provide sufficient slack to account for the individual frame deceleration and projection times. U.S. Pat. No. 6,120,151 provides an improved system where the individual film media frames are compressed into mechanical cartridges and from which the frames are decelerated for individual projection. 
   Generally, stop-motion systems are disfavored in many different applications due to not least the mechanical complexity and substantial media wear incurred by such systems. The repeated, high-frequency impulse flexion of the film media is well-recognized to directly limit the useful life of the film media. Additionally, the mechanics required to achieve the high deceleration rates necessary for nominal operating throughput rates are themselves a substantial source of non-linear media skew or weave and vibration, directly impacting the accuracy of reproduction. 
   Continuous transport systems are generally preferred where high-throughput is desired and, in many cases, to avoid the problems associated with stop-motion systems. These systems typically employ constant tensioning systems to align and control the speed of the film media through a film gate. A high-speed digital line scanner is typically positioned transverse to the film gate and configured with a line scan orientation perpendicular to the transport direction of the film media. As the film continuously passes through the film gate, digital scan lines are aggregated and images of the film media contents extracted. 
   By the nature of the line scanner and related electronics, potentially high throughput rates can be achieved by continuous transport systems. As film media speeds are increased, however, the quality of the image produced by conventional continuous transport systems is progressively compromised. Image accuracy is lost predominantly due to the increasing impact of media transport speed variations and associated randomly varying skew imposed on the media as the media passes through the film gate. Conventional attempts to alleviate these problems have been made by augmenting continuous film media feed systems with a perforation detector, as shown in U.S. Pat. No. 6,091,446, and improved speed control electronics, as shown in U.S. Pat. No. 6,169,571. Use of a perforation detector allows associated electronics to measure the weave movement of the media, at least as between successive sprocket holes, and thereby permit a corresponding correction in the physical positioning of the line scanner. The speed of the film media can be better maintained by actively monitoring, using suitable electronics, the speed and phase relationship of both the sprocket drive and a tensioning capstan positioned at either end of the film gate. 
   Increasing speed also tends to impose increasing tensional loads on the film media, both intended to better maintain media positioning and unintended as a consequence of proportionally increased speed variation. Additionally, increased speed also increases both mechanical and media wear. Although generally less than the impulse loads and wear imposed by stop-motion systems, increased speed factors directly into an increased risk of loss of information and throughput should the film media be damaged or break. Short of catastrophic media failures, higher speeds conventionally result in increased routine maintenance requirements, increased unscheduled repairs, and decreased overall media life. 
   A somewhat related throughput problem is that the typical complexity of the film transport path leads to difficulties in loading and aligning new film rolls. Often, the film media must be threaded through and carefully aligned over a complex set of rollers and bails. The direct result is an effective loss of throughput due to the significant time taken to load new rolls and to reload rolls in the event of misalignment errors. The complexity of conventional film transport paths also leads to increased operator costs, particularly due to the need for increased system training and to continually monitor system operations. 
   Consequently, the practical maximum throughput speed of conventional continuous film media transport systems has been rather limited. Consequently, there is a clear need for a high-speed linear film transport system enabling continuous, highly accurate image recognition. 
   SUMMARY OF THE INVENTION 
   Thus, a general purpose of the present invention is to provide an efficient continuous linear film transport system that is operable at high-speeds and at low costs without loss of image accuracy and resolution while imposing minimal wear on the film media and transport system mechanics. 
   This is achieved in the present invention by providing a stable, continuous, high-speed roll film media path between supply and take-up film reels. Supply and take-up path segments, adjacent the ends of a core transport path section, each operate to continuously maintain open decoupling loops in the film media while accurately controlling the speed, tension and alignment of the film media as transported through the core transport path section. A microcontroller operates two motor driven capstans to establish the film media speed and tension within the core transport path section. Optical sensors provide feedback to the microcontroller in managing two additional motor driven capstans to maintain the decoupling loops. The film media within the core transport path section is thereby isolated from frictive, inertial, and skewing forces that could otherwise degrade the media imaging. 
   An advantage of the present invention is that greatly increased media transport speeds can be achieved without incurring any significant loss in the accurate reproduction of the documentary information present on the film roll. The film loops decouple the portion of the media passing through the film gate from the randomly varying frictive, inertial, and skewing forces introduced by the film reels, including the film roll bulk, bail arms, and various rollers outside of the core film gate transport path. Consequently, the media moves continuously at a controlled high speed through the film gate without incurring any significant loss of image quality. 
   Another advantage of the present invention is that the decoupling film loops are readily established and maintained in a relatively open atmosphere. Drive capstan to roller offsets are used to reliably orient the creation of the film loops. Infrared emitters and detectors are used to continuously measure the height of the loops. A feedback control routine, interoperating with the film transport motor speed control routines, is used to dynamically adjust the film transport speed outside of the core film gate transport path to maintain the height of the decoupling loops within defined tolerance ranges. 
   A further advantage of the present invention is that, within the core film gate transport path, high-tolerance film guides are able to maintain a highly linear orientation of the film media through the film gate. The guides and a single, well controlled tensioning roller apply an essentially non-varying friction force on the film media and, therefore, allow a highly linear transport speed to be maintained through the core film gate transport path. 
   Still another advantage of the present invention is that the film transport path is simple and direct. New film rolls can be loaded with minimal complication. The closure of the roller assembly against the capstans provides for both a self alignment of the film media to the guides within the core film gate transport path and an automatic, controlled offsetting of the drive rollers to drive capstans appropriate to provide for the creation and maintenance of the decoupling loops. Further, due to the reduced frictive and inertial forces imposed on the core film gate transport path, there is minimal operational wear on the tolerance critical rollers, capstans, motors and other parts of the film transport system. Consequently, a film transport system implementing the present invention will be able operate at significantly higher continuous speeds for longer periods of time between routine maintenance servicing. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a schematic view of the continuous film transport path and line scanner system of the present invention; 
       FIG. 2  is a schematic view of the continuous film transport path of the present invention further detailing the supply, core, and take-up path segments; 
       FIG. 3  is a software block diagram illustrating the principle control flows utilized in managing operation of the continuous film transport path of the present invention; 
       FIG. 4  is a full front view of the continuous film transport path and line scanner system of the present invention; 
       FIG. 5  is a front detail view of the pinch roller clamp assembly and film media guide path assembly as constructed in accordance with the present invention; 
       FIG. 6  is a perspective view of the film media guide path assembly as constructed in accordance with the present invention; 
       FIG. 7  is a perspective detail view of the reversible film media guides as constructed in accordance with the present invention; and 
       FIG. 8  is a perspective detail view of the pinch roller clamp assembly as constructed in accordance with the present invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention is applicable to the continuous digital line scanning and image conversion of various forms and formats of optical image film media, including motion picture film. The preferred embodiments of the present invention are specifically directed to the accurate, high-throughput image recovery and digitization of documents optically captured on roll microfilm media. The following description of the preferred embodiments should therefore not be construed as limiting the present invention only to roll microfilm use. 
   Referring to  FIG. 1 , an overall view of a microfilm scanner system  10 , constructed in accordance with a preferred embodiment of the present invention, is shown. Roll microfilm media  12  is streamed from a supply reel  14 , through a supply tensioner system  16 , a guide path  18  including a film gate, a take-up tensioner system  20 , and collected onto a take-up reel  22 . A light source  24  projects a narrow field image from the film media present within the film gate through a focusing lense  26  for capture by a line image digitizing camera  28 . Preferably, the focusing lense  26  and camera  28  are separately adjustable, in line with the light source  24  and film gate, by microprocessor automated control of servo motor driven lead screws  30 ,  32 . 
   A detailed schematic view of the central transport path  40 , representative of the implementation of a preferred embodiment of the present invention, is shown in  FIG. 2 . The central transport path  40  includes supply  42 , core  44 , and take-up  46  segments. The supply and take-up segments  42 ,  46  operate, in accordance with the present invention, to isolate the core path segment  44  from frictional and inertial loads arising from or otherwise associated with the supply and take-up reels  14 ,  22  and the supply and take-up tensioner systems  16 ,  20 . The core path segment  44  provides a controlled tension, low friction guide path for film media through a central film gate  48  defined by two scroll bars  50 . The supply and take-up segments  42 ,  46  each operate to create open-air decoupling loops  52 ,  54  in the film media  12 . Preferably, drive capstans  56 ,  58 ,  60 ,  62  are inset relative to opposing pinch rollers  64 ,  66 ,  68 ,  70  sufficient to define the orientation of the loops  52 ,  54 . An elevation of about 7.5 degrees in the film path is established by the scroll bars  50  relative to the inner capstans  58 ,  60 . 
   In operation, a microprocessor controller  72  defines the speed of the supply drive capstan  56  using a direct connect supply capstan drive motor  74 . Closed-loop speed management is performed using a rotary quadrature encoder-based motor speed controller  76 . The speed of the film tensioning drive capstan  58 , in the currently preferred embodiment, is managed open-loop by control of a pulse-width drive signal provided by the microprocessor controller  72  to tensioning drive motor  78  by a motor speed controller  80 . In an alternate preferred embodiment, a rotary quadrature encoder-based motor speed controller  80  is used to allow the speed of the film tensioning drive capstan  58  to be managed closed-loop by the microprocessor controller  72 . The speed of the film gate speed drive capstan  60  and film take-up drive capstan  62  are separately controlled closed-loop by the microprocessor controller  72  through a film gate speed drive motor  82  and rotary quadrature encoder-based motor speed controller  84 , and take-up drive motor  86  and rotary quadrature encoder-based motor speed controller  88 . 
   Preferably, the motor speed controllers  76 ,  84 ,  88 , and speed controller  80  in the alternate embodiment, implement quadrature encoders configured to produce approximately 3.5 counts per micron (87,000 counts per inch). The encoder signals are processed by the microprocessor controller  72  using a conventional proportional, integral, and derivative (PID) feedback filter, to provide 4,000 capstan drive motor power corrections per second to each of the capstan drive motors  74 ,  80 ,  82 ,  86 . This level of speed control has been found sufficient obtain a high-degree of image resolution accuracy in terms of both absolute film speed accuracy and repeatability. Given the 48× optical reduction ratio used on typical duplex microfilm roll media and a conventional target image output resolution of 300 dots per inch (dpi), a true resolution of 14,400 dpi is required. Empirically, a deviation of more than one pixel over a short distance, such as the size of a single imaged character, will appear as an evident flaw in the scanning process. The PID feedback filter control loop is capable of maintaining film speed to within an error rate of about seven quadrature counts or about 0.6 pixels. 
   The motor speed control accuracy is obtainable absent dynamic forces that impose variable loads, such as due to variable friction and inertial loads. Constant loads will not adversely affect the resultant accuracy of a scanned image because the motor speed control via the PID filter will always be the same amount behind the desired position, and so the resultant output will be linear and accurate, even though delayed by several pixels. Variable loads, conventionally arising from the dynamic characteristics of the transport bail arms, film spools, and film guides, can introduce multi-pixel errors over short distances. These errors can easily surpass five pixels over 20 pixel ranges, which are plainly noticeable to the unaided human eye. 
   In accordance with the present invention, the film media loops  52 ,  54  operate to decouple any variable forces imposed on the film media  12  outside of the central transport path  40 . Referring to  FIG. 3 , the control operation  100  of the microprocessor controller  72  is performed by a real-time control executive kernel  102 . The control operation  100  provides independent control flows to monitor and adjust the speed of the capstan drive motors  74 ,  82 ,  86 , and capstan drive motor  78  in the alternate embodiment. Preferably, the speed of the film gate speed drive motor  82  is determined  104  from the motor speed controller  84  and adjusted  106  to achieve a target film media transport speed. Film media transport speeds of 15 inches per second or more without significant loss of image resolution are achievable by the present invention. 
   The tensioning drive motor  78  is preferably connected to the film tensioning drive capstan  58  through a friction slip connection  59 , allowing the speed and direction of the tensioning drive motor  78  to define a constant tensioning force that is applied as the film media  12  enters the core path segment  44 . Preferably, the direction of rotation is set counter to the normal forward direction of the film media movement. For the preferred embodiment, the open-loop controlled film tensioning drive capstan  58  is preferably driven at fixed speeds, selected according to the target speed of the film media, to provide a constant tensioning force to the film media. While the specific tensioning force is not critical, a smooth and continuous force level of between four and six ounces is preferred. In the alternate embodiments, this tensioning force is calculated  108  based on the drive power levels applied to the film gate speed drive motor  82  and tensioning drive motor  78 . The speed of the tensioning drive motor  78  is then adjusted  110  to set a desired tensioning force on the film media  12  sufficient to hold the film media stable through the film gate  48 . In both embodiments, the tension level is intended to ensure that the film media travels linearly and remains flat across the scroll bars  50  through the film gate  48 . 
   The supply capstan drive motor  74  is operated to provide a continuous supply of the film media  12  while maintaining the effective height of the supply decoupling loop  52 . An optical sensor assembly  90 , preferably implemented using a short range infra-red LED emitter, provides a distance proportionate range signal to the microprocessor controller  72 . The range signal is sampled  112  and a loop height value computed  114 . The speed of the supply drive capstan  56  is then adjusted to maintain the height of the loop  52  within target tolerance levels. The height of the loop is generally not critical and will be different depending on a number of factors including the width and material composition of the film medial  2 , the target speed of the media  12  through the film gate  48 , and the variability of frictive and inertial forces active outside of the central transport path  40 . Maintaining a 0.5 inch to 1.5 inch loop height between capstans spaced at approximately three inches is generally sufficient for purposes of the present invention. 
   The take-up capstan drive motor  86  is similarly operated to maintain the height of the take-up decoupling loop  54 . An optical sensor assembly  92  provides a range signal that is sampled  118  and used to compute the height of the take-up decoupling loop  54 . The speed of the take-up capstan drive motor  86  is adjusted  122  to maintain the height of the decoupling loop  54  within target tolerances. Generally, the some 0.5 inch to 1.5 inch loop height is preferred for the take-up decoupling loop  54 . 
   In accordance with the present invention, the decoupling loops  52 ,  54  are formed in free air, without requiring any complex of arc loop guides, atmospheric shields, or pressure controls. Film media guides are preferably provided only at the capstans to control the loop release and recapture of the film media  12 . The open formation and operation of the decoupling loop  52  maximizes the isolation of variable frictive and inertial forces from the core path segment  44 . The intrinsic strength of the film media  12 , though variable depending on the width and material composition of the film media  12 , is sufficient for at least the preferred heights of the loops  52 ,  54 , to be insensitive to ordinary air pressure variations within the general system cover of the central transport path  40 . Furthermore, the preferred use of infra-red LED emitters prevents interference with the height sensing of the loops  52 ,  54  by ordinary visible light sources. 
   As generally shown in  FIG. 4 , the roll film path control mechanics  130 , as implemented in a preferred embodiment of the present invention, are mounted as a unitary plate  132 . The lense  26  and camera  28  are mounted on a common slide rail  134  that permits independent focal adjust by operation of servo motor driven lead screw assemblies  30 ,  32 . Supply and take-up film media reels  14 ,  22  are driven by motors  136 ,  138 . Bail arms  140 ,  142  are spring loaded to bail pivot mounts  144 ,  146 . The bail arms  140 ,  142  are maintained in a centered range using potentiometer feedback control based on bail arm  140 ,  142  position to speed control the supply and take-up motors  136 ,  138 . 
   A capstan and film gate guide assembly  148  is mounted to the plate  132  in a fixed position, generally as shown. A pinch roller assembly  150  is mounted to slide rails  152 ,  154  in parallel opposition to the capstan film gate guide assembly  148 . The pinch roller assembly  150  is driven between an open position, as shown, and a closed position that places the pinch rollers in pressured contact with the capstans of the capstan and film gate guide assembly  148 . Movement of the pinch roller assembly  150  is controlled by a lead screw  156  operated by a gear motor mounted on the back side of the plate  132 . 
   A detail view  160  of the roll film path control mechanics  130  is shown in  FIG. 5 . The detail view  160  illustrates the preferred positioning of the pinch rollers  64 ,  66 ,  68 ,  70  in the open and closed positions. In accordance with the present invention, in the closed position the pinch rollers  64 ,  66  and  68 ,  70  are outwardly offset from the capstans  56 ,  58  and  60 ,  62  to control the orientation of the film media loops  52 ,  54 . In a preferred embodiment of the present invention, the center to center spacing  162  of the capstans  56 ,  58  and  60 ,  62  is three inches. In the closed position, the pinch rollers  64 ,  66  and  68 ,  70 , having a nominal diameter of one inch, are provided with an approximately 3.25 inch center to center spacing  164 . The optical sensors  90 ,  92  are mounted to capstan and film gate guide assembly  148  at points centered between the capstans  56 ,  58  and  60 ,  62 . 
   A perspective view  170  of the capstan and film gate guide assembly  148  is shown in  FIG. 6 . The drive shafts of the capstans  56 ,  60 ,  62  are extended, in the preferred embodiments, to connect directly to the drive shafts of the capstan drive motors  74 ,  82 ,  86 , which are mounted on the back side of the plate  132 . The drive shaft of the tensioning drive capstan  58  is connected through a friction slip connection  59  to the drive shaft of the tensioning drive motor  78 , which is also mounted on the back side of the plate  132 . Opening in the base of the capstan and film gate guide assembly  148  are provided through which the optical sensors  90 ,  92  extend. 
   Film media guide units  172 ,  174 ,  176 ,  178  are mounted concentric to the capstans  56 ,  58 ,  60 ,  62 . As shown in  FIG. 7 , each film guide unit  182  includes end bearing surfaces  184  that supports the guides  172 ,  174 ,  176 ,  178  and allows rotation independent of the capstans  56 ,  58 ,  60 ,  62 . Detent positions preferably enable the guide units  172 ,  174 ,  176 ,  178  to be reversibly oriented to present either 16 millimeter guide surfaces  186  or 35 millimeter guide surfaces  188 . Preferably, the film guide units  172 ,  174 ,  176 ,  178  are machined to a tolerance of 0.001 inches and plated to have a surface hardness twice that of conventional stainless steel. The concentric mounting of the film guide units  172 ,  174 ,  176 ,  178  and capstans  56 ,  58 ,  60 ,  62  preferably places the inner edges of the guide surfaces  186 ,  188  to within a tolerance of approximately 0.004 inches of the capstan  56 ,  58 ,  60 ,  62  surfaces. 
   A detail view  190  of the pinch roller assembly  150  is shown in  FIG. 8 . The pinch rollers  64 ,  66 ,  68 ,  70  are mounted in individual bracket arms  192 ,  194 ,  196 ,  198  that are connected through centering, spring loaded pivots to the frame of the pinch roller assembly  150 . Each pinch roller  64 ,  66 ,  68 ,  70  has a designed width to fit within the 35 millimeter guide surfaces  188 . A pair of grooves  200  are provided in each pinch roller  64 ,  66 ,  68 ,  70  to accommodate insertion of the 16 millimeter guide surfaces  186 . The axial mounting of the pinch roller  64 ,  66 ,  68 ,  70  preferably permits compression adjustment to minimize the roller outer edge to guide surface  188  and groove to guide surface  186  spacing to ensure that the film media edges remain flat on the capstans  56 ,  58 ,  60 ,  62  perpendicular to the guide surfaces  186 ,  188  during operation. 
   Thus, a high-speed continuous linear film media transport system has been described. While the present invention has been described particularly with reference to microfilm media, the present invention is equally applicable to the scanning of cinematic and other continuous strip film media generally for purposes of display and digitization. 
   In view of the above description of the preferred embodiments of the present invention, many modifications and variations of the disclosed embodiments will be readily appreciated by those of skill in the art. It is therefore to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as specifically described above.