Abstract:
A method of sensing the pitch or relative location of a lenticular lens on a sheet of transparent lenticular material of the type having a repeating pattern of cylindrical lenses on one side and a flat opposite side, comprising the steps of: forming a beam of light; focusing the beam of light into a spot smaller than the pitch of the cylindrical lenses onto the lenticular material; moving the lenticular material relative to the beam in a direction perpendicular to the axes of the cylindrical lenses to modulate the angle of reflection or refraction of the beam of light; and sensing the position of the modulated beam of light to determine the pitch or relative location of lenticular material to the focused spot.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation application of U.S. patent application Ser. No. 09/033,212, filed Mar. 2, 1998 now abandoned, which is a Continuation-in-Part application of U.S. patent application Ser. No. 08/828,637 filed Mar. 31, 1997, now U.S. Pat. No. 5,835,194, issued Nov. 10, 1998. 
    
    
     FIELD OF THE INVENTION 
     This invention relates in general to the field of manufacturing lenticular images and more particularly to detecting and measuring the pitch of lenticular material which is used for producing the lenticular images. More specifically, the invention relates to the detection of a change in pitch of the lenticular lenses as the material is transported in a scanning laser printer. 
     BACKGROUND OF THE INVENTION 
     Lenticular images include an array of cylindrical lenses in a lenticular material and a sequence of spatially multiplexed images that are viewed throughout the lenticular material so that different ones of the multiplexed images are viewed at different angles by the viewer. One image effect produced by the lenticular image is a depth or 3D image where one eye views one image of a stereo pair or sequence from one angle and the other eye views another image from the stereo pair. Another image effect is a motion image where different images in a motion image sequence are viewed by changing the angle at which the image is viewed. Other effects that combine these two effects, or form collages of unrelated images that can be viewed from different viewing angles can be provided. 
     It has been proposed to create lenticular images by providing a lenticular material having a color photographic emulsion thereon. The spatially multiplexed images are exposed onto the lenticular media by a laser scanner and the material is processed to produce the lenticular image product. See for example, U.S. Pat. No. 5,697,006, issued Dec. 9, 1997 to Taguchi et al. 
     The image that is exposed on the lenticular media must be very precisely positioned under each lenticule. Unfortunately, the manufacturing and keeping tolerances of lenticular media result in significant changes in the pitch of the lenticular lenses in the media. If the pitch of the lenticular lenses on the material varies or is different from what is expected, the image quality will be comprised. There is a need therefore for an improved manufacturing process for making lenticular image products form lenticular media of the type having a lenticular lens array coated with photographic emulsion. 
     It is known to scan a non actinic laser beam across a lenticular array in a direction perpendicular to the axes of the lenticular lenses, and to sense the deflection of the beam by the lenticular lenses to produce an output clock for modulating a writing beam. See U.S. Pat. No. 5,681,676, issued Oct. 28, 1997 to Telfer et al. 
     It is one object of this invention to provide a method and apparatus for detecting and/or measuring any variation of lenticular pitch for the purpose of printing accurate images on the media. It is another object of the invention to provide a method and apparatus for compensating for such variations during manufacture of a lenticular image product. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to overcoming one or more of the problems set forth above. Briefly summarized, according to one aspect of the present invention, a lenticular image product is formed from a lenticular material having an array of cylindrical lenses and a photographic emulsion coated thereon, by scanning the lenticular material with an intensity modulated first beam of light in a direction parallel to the long axes of the cylindrical lenses to form a latent lenticular image in the photographic emulsion. A second beam of light having a wavelength outside of the range of sensitivity of the photographic emulsion is focused into a spot smaller than the pitch of the cylindrical lenses onto the lenticular material. The lenticular material is moved through the beam in a direction perpendicular to the axes of the cylindrical lenses to provide a page scan motion of the lenticular material and to modulate the angle of reflection or refraction of the second beam of light. The position of the angularly modulated second beam of light is sensed and the sensed position is used to control the motion of the lenticular material. 
     These and other aspects, objects, features, and advantages of the present invention will be more clearly understood and appreciated from a review of the following detailed description of the preferred embodiments and appended claims, and by reference to the accompanying drawings. 
     ADVANTAGEOUS EFFECT OF THE INVENTION 
     The invention provides an accurate method for either mapping lenticular pitch or detecting pitch variations which can be compensated in a laser printer, thereby enabling efficient production of lenticular image products using lenticular media having photographic emulsion coated thereon. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic diagram of an apparatus employed to produce lenticular image products according to the present invention; 
     FIGS. 2A,  2 B, and  2 C are schematic diagram illustrating the effect of the lenticular medium on the second beam of light; 
     FIG. 3A is a schematic block diagram illustrating the control of media transport according to the present invention. 
     FIG. 3B is a diagrammatic view useful in exploring the present invention. 
     FIG. 4 is a plot showing the output of the sensor shown in FIG. 3; 
     FIG. 5 is a schematic diagram illustrating apparatus for generating a correction signal for controlling the motion of the lenticular medium according to a preferred embodiment of the invention; 
     FIG. 6 is a schematic diagram illustrating apparatus for generating a correction signal for controlling the motion of the lenticular medium according to an alternate embodiment of the invention. 
     FIG. 7 is a schematic diagram illustrating apparatus for generating a correction signal for controlling the motion of the lenticular medium according to a further alternative embodiment of the invention. 
     FIG. 8 is a schematic diagram illustrating apparatus for generating a correction signal for controlling the motion of the lenticular medium according to a still further embodiment of the invention. 
     To facilitate understanding, identical reference numerals have been used where possible, to designate identical elements that are common to the figures. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIG. 1, lenticular image product production apparatus  10  includes a platen  12  for supporting lenticular media  14 . Lenticular media  14  is transported past platen  12  in the direction of arrow A by a pitch roller drive system  16  that is driven by motor  18 . An encoder  20  is provided on the shaft of motor  18  to provide a measurement of the distance that the lenticular media  14  is transported. The lenticular media  14  is exposed with a laser beam  22  from a modulated laser  24 . The laser beam  22  is focused onto a scanning polygon  26  by a pair of beam shaping mirrors  28  and  30 . The laser beam  22  is reflected from a cold mirror (reflects visible light and transmits infrared light)  32  onto a cylindrical mirror  34 , which refocuses the laser beam  22  onto the media  14 . The scanning polygon  26  causes the laser beam  22  to scan the lenticular media in the direction of arrow B, parallel to the long cylindrical axes of the lenticular lenses in the media. The motion of the media past platen  12  provides scanning in the orthogonal direction. 
     An infrared laser  36 , located at distance from the surface of the media identical to the distance to the scanning face of the polygon  26 , forms a second beam of light  38 , of a wavelength that does not expose the lenticular media  14 . The second beam of light is reflected by a mirror  40  through cold mirror  32  onto cylindrical mirror  34 . Cylindrical mirror  34  focuses the second beam  38  onto the surface of the lenticular material  14 . In response to motion of lenticular media  14 , a sensor  44  detects the angular displacement caused by the lenticular lenses in the lenticular material  14  of the second beam  38  to provide a pitch indication signal to control electronics  46 . 
     Control electronics  46  employs the pitch correction signal and the signal from encoder  20  as described below to control the motor  18  so that the media  14  travels past platen  12  at a constant pitch rate. 
     FIGS. 2A,  2 B, and  2 C illustrate how the lenticular material deflects the beam  38  of infrared light as it passes through different portions of one of the lenticular lenses in the lenticular material. As the beam  38  first encounters a lenticule, as shown in FIGS. 2A, it is refracted at a large angle to the left and impinges on the left side of the position sensing detector  44 . The angle depends upon the position of the lenticule with respect to the beam  38 . When the beam is at the center of a lenticule FIG. 2B, it is minimally deflected as shown in the illustration in the center and falls on the center of the position sensor  44 . As the lenticular material is moved further to the right, as shown in FIG. 2C, the beam is deflected to the right and impinges on the right side of the position sensor  44 . The position sensor  44  may be, for example, a PSD S3932 position sensitive detector available from Hamamatsu Photonics KK, Hamamatsu, Japan. 
     Referring now to FIG. 3A, the control electronics is shown in further detail. A beam of light  38  is focused onto a flat surface  13  of the lenticular material  14 . The lenticular material  14  is moved relative to the beam  38  by a transport mechanism  16  which contains an encoder  20 . When the beam  38  passes through the curved surface  15  of the lenticular material  44  it refracts at a large angle. The centroid of the exiting beam  33  is axially displaced from the original beam  38  by a distance d (see FIG.  3 B). This distance d is measured by a position sensing detector  44 . As the transport mechanism  16  moves the lenticular material  14 , the distance d changes. This creates an output signal  48  which is then supplied to a zero crossing comparator  50 . As soon as a zero crossing is detected by the comparator, a zero crossing signal  52  is sent to the pitch detection electronics  54 , triggering the counting of encoder pulses  56 . The output of pitch detection electronics  54  is a signal proportional to encoder pulse counts per lenticule which defines the lenticular pitch error  58 . The pitch error  58  is supplied to the digital servo control  46  as a velocity correction signal to the nominal velocity command  64 . The output of digital servo controller  46 , control signal  62 , is sent to power amplifier  60  to drive media transport motor  18 . FIG. 4 shows waveform  48  produced by position detector  44 . 
     Turning now to FIG. 5, a preferred arrangement for pitch detection electronics  54  will be described. The effective error in the lenticular pitch is computed by counting the cycles of the output signal  48  from the position sensing detector  44  (see FIG. 3A) which occur over a predetermined distance as measured by counting a pre-determined number of encoder pulses  56 . The measurement occurs after the media transport  16  has reached its nominal transport speed. At this point, a counter  66 , DIV has been preset to a predetermined value and is enabled to count down one count per encoder pulse. During the period defined by the pre-determined value, a GATE pulse signal  68  is produced which enables the gated counter  70 . The output signal  48  is applied to a zero crossing comparator  50  which produces a square wave CLK IN  52 . The gated counter  70  counts one count per each rising edge of the signal  52  at CLK IN thus accumulating the number of full cycles of the output signal  48 . The gated counter  70  could likewise be configured to count on the falling edge of the CLK IN signal  52 . The ideal choice of edge is that which corresponds to the zero crossing associated with the beam  38  at the center of the lenticular lens  14  illustrated in of FIG.  2 B. At the next GATE pulse  68 , the output of the gated counter  70  is latched and output to a difference circuit  72  which computes the pitch difference. The pitch difference  74  is the difference between the measured lenticule count and the nominal lenticule count  78 . This pitch difference is then applied to the Gain or LUT block  76 , which adjusts this pitch difference signal to a scaled value which is then sent as a pitch error signal  58  to the digital servo controller  46  to correct the transport speed of the media  14 . The desired result of this correction to the transport speed is to move the lenticular media at a constant lenticular pitch rate, thereby compensating for lenticular media pitch imperfections. Subsequently, the gated customer  70  is zeroed when the next gate pulse  68  from the divider circuit  66  and begins counting on the next appropriate edge of the zero crossing comparator output  52 . 
     Turning now to FIG. 6, an alternate arrangement for pitch detection electronics  54  will be described. The effective error in the lenticular pitch is computed by dividing the number of predetermined cycles of the output  48  of position detector  44  by the distance within the media as measured by counting the number of encoder pulses  56  generated. The measurement occurs after the media transport  16  has reached its nominal transport speed. The output signal  48  is fed to a zero crossing comparator  50  to produce a square wave  52 . The square wave  52  us fed to the counter  66  DIV, which has been preset to a predetermined value and is enabled to count down one count per rising edge of the square wave  52 . As explained above, the counter could likewise be configured to count on the falling edge of the square wave  52 . Gate pulse signal  68  initiates counting by the gated counter  70 . In this embodiment, the encoder pulses  56  are directed to the input referred to as CLKN IN. The gated counter  70  counts one count per each rising edge of the signal at CLKN IN thus accumulating the number of encoder pulses  56  within the pre-determined number of cycles of output  48 . At the occurrence of the next GATE pulse, the output of the gated counter  70  is latched to the difference circuit  72  which computes the pitch difference  74 . The pitch difference  74  is the difference between the measured encoder count and the nominal pitch in encoder pulses  80 . This pitch difference is then applied to the Gain or LUT block  76 , which adjusts this pitch difference signal to a scaled value which is then sent as a pitch error signal  58  to the digital servo controller  46  to correct the transport speed of the media  14 . The desired result of this correction to the transport speed is to move the lenticular media at a constant lenticular pitch rate, thereby compensating for lenticular media pitch imperfections. Subsequently, the gated counter  70  is zeroed and beings counting after the next appropriate edge of the zero crossing comparator output  52 . 
     Turning now to FIG. 7, alternate arrangement for pitch detection electronics  54  will be described. The signal  48  from the position sensor  44  produced by the second beam of light  38 , as its angle is modulated by the lens of the lenticular media  14 , is applied to a Zero Crossing Comparator  50  which produces a square wave logic signal  52 . The rising and falling edges of this square wave signal correspond to the transitions through zero of the position sensor waveform  48 . The ideal choice of edge is that which corresponds to the zero crossing associated with the beam  38  at the center of the lenticular lens  14  illustrated in the center view (B) of FIG.  2 . This square wave logic signal  52  is then applied to a divider circuit  66  which counts a predetermined number of lenticule appropriate zero crossings of waveform  48 . At the occurrence of this pre-determined number of zero crossings the divider circuit  66  outputs a gating pulse signal  68  to the gated counter circuit  70 . 
     The function of the gated counter circuit  70  is to count the clock pulses  82  applied to its clock input from the reference clock source  84 , during the time that occurs between the gate input pulses  68  from the divider circuit  66 . At the end of a counting cycle, which is terminated by a new gate pulse  68  from the divider circuit  66 , the current count is latched and output to the next block which is the difference circuit  72 . At the same time the count is latched, the gate counter  70  is zeroed and begins again counting the reference clock pulses  82  applied to its clock input. The latched count output is applied to the difference circuit  72  which subtracts the count from the expected nominal pitch period in clock counts  86 . The output  74  of the difference circuit  72  is the pitch difference of the latest measured count or pitch period with respect to the expected nominal pitch period  86 . This pitch difference  74  is then applied to the gain or LUT block  76  which adjusts this pitch difference signal  74  to a scaled value  58 . The scaled value  58  is the pitch error, which is then sent to the digital servo controller  46  to correct the transport speed of the media  14 . The desired result of this correction to the transport speed is to move the lenticular media  14  at a constant lenticular pitch rate thereby compensating for lenticular media pitch imperfections. 
     Turning now to FIG. 8, a still further alternate arrangement for pitch detection electronics  54  will be described. The signal  48  from the position detector  44  produced by the second beam of light  38 , as its angle is modulated by a lenticule of the lenticular media  14 , is applied to a zero crossing comparator  50  which produces a square wave logic signal  52 . The rising and falling edges of this square wave signal  52  correspond to the transitions through the zero of the position detector signal  48 . This square wave signal  52  is applied to a minus input of a phase comparator circuit  88 . The purpose of the phase comparator circuit  88  is to determine the phase error occurring between the output of the zero crossing comparator  50  and a reference phase clock  90 . 
     The reference phase clock  90  is generated from a clock reference  84  and is the desired frequency of the signal  48  produced by the lenticular media  14  as its moved by the transport  16 . The reference phase clock  90  is applied to the plus input of the phase comparator  88 . The phase comparator  88  which is commonly known and understood in the art, produces an output signal  92  representing the phase difference of the two input signals over a range of plus or minus 180 degrees of phase shift between the two input waveforms. This output phase error signal  92  is applied to the gain or LTJT block  76  which adjusts the signal to a scaled value. The scaled value  58  represents the pitch error, which is then sent to the digital servo controller  46  to correct the transport speed of the media  14 . The desired result of this correction to the transport speed is to move the lenticular media  14  at a constant lenticular pitch rate, thereby compensating for lenticular media pitch imperfections. 
     The invention has been described with reference to a preferred embodiment, however, it will be appreciated that variations and modifications can be effected by a person of ordinary skill in the art without departing from the scope of the invention. 
     
       
         
               
             
               
               
             
           
               
                   
               
               
                 PARTS LIST 
               
               
                   
               
             
             
               
                   
               
             
          
           
               
                 10 
                 Image product production apparatus 
               
               
                 12 
                 Media platen 
               
               
                 14 
                 Lenticular media 
               
               
                 16 
                 Pinch roller drive system 
               
               
                 18 
                 Drive motor 
               
               
                 20 
                 Encoder 
               
               
                 22 
                 Writing laser beam 
               
               
                 24 
                 Modulated laser 
               
               
                 26 
                 Scanning polygon 
               
               
                 28 
                 Beam shaping mirror 
               
               
                 30 
                 Beam shaping mirror 
               
               
                 32 
                 Cold mirror 
               
               
                 34 
                 Cylindrical mirror 
               
               
                 36 
                 Infrared laser 
               
               
                 38 
                 Infrared laser bean 
               
               
                 40 
                 Mirror 
               
               
                 44 
                 Position sensing detector 
               
               
                 46 
                 Control electronics 
               
               
                 48 
                 Position sensing detector output signal 
               
               
                 50 
                 Zero crossing comparator 
               
               
                 52 
                 Signal output from zero crossing comparator 
               
               
                 54 
                 Pitch detection electronics 
               
               
                 56 
                 Encoder pulses 
               
               
                 58 
                 Lenticular pitch error 
               
               
                 60 
                 Power amplifier 
               
               
                 62 
                 Control signal 
               
               
                 64 
                 Nominal velocity command signal 
               
               
                 66 
                 Pulse divider 
               
               
                 68 
                 Gate pulse signal 
               
               
                 70 
                 Gated counter 
               
               
                 72 
                 Difference circuit 
               
               
                 74 
                 Pitch difference signal 
               
               
                 76 
                 Gain or LUT block 
               
               
                 78 
                 Nominal puck period in lenticule counts 
               
               
                 80 
                 Nominal pitch in encoder pulses 
               
               
                 82 
                 Reference clock pulses 
               
               
                 84 
                 Reference clock source 
               
               
                 86 
                 Nominal pitch period in clock counts 
               
               
                 88 
                 Phase comparator 
               
               
                 90 
                 Reference phase clock 
               
               
                 92 
                 Phase error