Abstract:
A method of detecting the relative skew between a reference beam and transparent lenticular material of the type having a repeating pattern of cylindrical lenses, comprising the steps of: forming a beam of light; focusing the beam of light into a line with a width smaller than the pitch of the cylindrical lenses onto the lenticular material; moving the lenticular material relative to the beam in a direction such that the beam crosses the longitudinal axes of the cylindrical lenses to modulate the angle of reflection or refraction of the beam of light; and sensing the position of the line of modulated beam of light along a line parallel to the longitudinal axes of the cylindrical lenses to determine the skew or relative angular location of lenticular material to the focused line.

Description:
FIELD OF THE INVENTION 
     The invention relates generally to the field of manufacturing lenticular images and more particularly to detecting and measuring the relative skew of a writing laser beam to lenticular material which is used for producing the lenticular images. More specifically, the invention relates to the detection of the skew between the writing laser beam and the lenticules as the material is transported in a scanning laser printer. 
     BACKGROUND OF THE INVENTION 
     Lenticular images include an array of cylindrical lenses (or lenticules) in a lenticular material and a sequence of spatially multiplexed images that are viewed through 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 stereoscopic image where the lenticules are oriented vertically and 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 both eyes, while changing the angle at which the image is viewed. In this image effect the lenticules are oriented in the horizontal direction and the lenticular material is rotated about the long axis of the lenticules. 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 stereoscopic images by providing a lenticular material having a color photographic emulsion thereon. The stereoscopic images are exposed onto the lenticular material 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 material must be very precisely positioned under each lenticule. If the separate image lines produced by the writing laser beam of the laser scanner and the lenticules on the material are not aligned parallel, the resulting skew misalignment will degrade the image quality. There is a need therefore for an improved manufacturing process for making lenticular image products from lenticular material of the type having a lenticular lens array coated with photographic emulsion. 
     The following patents disclose various arrangements for aligning a lenticular overlay with a lenticular print which do not address the problem of aligning a writing laser beam with the lenticules of a photosensitive lenticular material. 
     U.S. Pat. No. 5,729,332, issued Mar. 17, 1998, inventors Fogel et al. 
     U.S. Pat. No. 5,633,719, issued May 27, 1997, inventors Oehlbeck et al. 
     U.S. Pat. No. 5,699,190, issued Dec. 16, 1997, inventors Young et al. 
     U.S. Pat. No. 5,424,553, issued Jun. 13, 1995, inventor Morton. 
     It is known to scan a non actinic laser beam across a lenticular array in a direction perpendicular to the axes of the lenticules, and to sense the deflection of the beam by the lenticules to produce an output clock for modulating a writing laser 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 lenticular skew relative to the writing laser beam for the purpose of printing accurate images on the material. It is another object of the invention to provide a method and apparatus for minimizing skew 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 line whose width is smaller than the pitch of the cylindrical lenses onto the lenticular material. The line of the second beam of light is directed parallel and adjacent to or overlapping the first beam of light in the direction of the long axis of the cylindrical lenses of the lenticular material. The lenticular material is moved through the beam to provide a page scan motion across the short axes of the lenticules of the material and to modulate the angle of reflection or refraction of the second beam of light caused by the lenticules. The position of the angularly modulated second beam of light is sensed along a line parallel to the longitudinal axis of a lenticule and the sensed position is used to control the rotational position of a pivoting cylinder mirror assembly or the rotational position of a platen supporting the lenticular material. As a result, the skew between the writing laser beam and the longitudinal axis of the cylindrical lens is minimized and the parallel alignment of the writing laser beam to the lenticule is maintained. 
     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 and apparatus for either mapping lenticular skew or detecting skew which can be compensated in a laser printer, thereby enabling efficient production of high quality lenticular image products using lenticular material having photographic emulsion coated thereon. The invention is cost effective and automated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A-4F are diagrammatic views useful in explaining the present invention. 
     FIG. 5 is a diagrammatic view of an apparatus employed to produce lenticular image products according to the present invention; 
     FIG. 6 is a diagrammatic view of an alternate apparatus similar to FIG. 4, employed to produce lenticular image products according to the present 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 
     FIG. 1A illustrates a line of light  100  as it passes through a lenticule  102  of transparent lenticular material  104 . Lenticules  102  form cylindrical lenses. As shown, the line of light  100  is parallel to the longitudinal axis  106  of lenticule  102 . The light that is transmitted through lenticule  102  forms a line of light  108  which is also parallel to longitudinal axis  106  of lenticule  102 . This line of light  108 , falls on surface  107  to form an imaged line  105 . As the lenticular material  104  is moved in the direction of arrow A, the incident line of light  100  falls on different positions of lenticule  102 , and the transmitted line of light  108  is refracted to different positions on surface  107 , but remains parallel to axis  106 . The resulting refraction of line of light  108  as the lenticular material  104  is moved in the direction A, causes the position of imaged line  105  to move in the direction B across surface  107 . This same effect will be produced if the incident line of light  100  is translated as shown in FIG. 1A in the direction of arrow AA and the lenticular material  104  is held stationary. 
     FIG. 1B shows a top view of surface  107  and the imaged line  105  of line of light  108  on surface  107 . In order to clearly show the imaged line  105 , the lenticular material  104  has been left out. FIG. 1B further illustrates how the imaged line  105  of the refracted line of light  108  moves along surface  107  as the lenticular material  104  is moved in direction A. In accordance with the position of the incident line of light  100  on the lenticule  102 , the resulting refraction of line of light  108  causes imaged line  105  to sweep from imaged line position  101  to imaged line position  103  on surface  107  in the direction of arrow B. The motion of imaged line  105  has a fixed extent and is shown by upper limit  109  and lower limit  111 . The motion of imaged line  105  will not go beyond this extent because at these limits the incident line of light  100  has moved off one lenticule and onto to the next adjacent lenticule. As other lenticules of lenticular material  100  move under incident line of light  100 , the imaged line  105  will jump back to imaged line position  101  and the sweeping motion of imaged line  105  will repeat. 
     FIG. 2A shows what happens to the transmitted line of light  108  when the incident line of light  100  is slightly skewed (i.e., skewed within one lenticule) with respect to longitudinal axis  106 . The transmitted and refracted line of light  108  will again produce imaged line  105 , but this time imaged line  105  will be at an angle with respect to longitudinal axis  106 . As either the lenticular material  104  is moved in direction A or the incident line of light  100  is translated in direction AA while lenticular material  104  is held stationary, the incident line of light  100  falls on different positions of the lenticule  102 . The resulting refraction of transmitted line of light  108  produces imaged line  105  on surface  107  which is skewed relative to longitudinal axis  106  and which moves in the direction of arrow B. 
     FIG. 2B further illustrates the movement of imaged line  105  on surface  107  when incident line  100  is skewed relative to longitudinal axis  106 . Similar to FIG. 1B, surface  107  is shown from the top with lenticular material  104  removed. Imaged line  105  is shown on surface  107  with skew angle Θ relative to longitudinal axis  106  produced by the relative skew between incident line of light  100  and longitudinal axis  106 . As lenticular material  100  is moved in direction A, skewed imaged line  105  will sweep in direction B starting from imaged line position  101  to imaged line position  103  on surface  107 . Skew angle Θ of imaged line  105  will remain constant as imaged line  105  moves in direction B. As portions of imaged line  105  move to upper and lower limits  109  and  111 , imaged line  105  will be truncated due to the fact that the incident line of light  100  has moved off of the lenticule and on to the next adjacent lenticule of lenticular material  104 . Further, when imaged line  105  is at imaged line position  103  a new imaged line has already formed back at imaged line position  101 . This new imaged line is produced by the fact that the incident line  100  is beginning to cross into the next adjacent lenticule of lenticular material  104 . As other lenticules of lenticular material  104  move under incident line of light  100 , the imaged line  105  will form back at imaged line position  101  and the sweeping motion of imaged line  105  will repeat. 
     FIG. 3A shows an incident line of light  100  that is so skewed that it crosses several lenticules  102 . The light transmitted through lenticules  102  forms several discontinuous imaged line segments  110  which are imaged onto surface  107 , none of which are parallel to lenticule axis  106 . Each imaged line segment  110  starts when the incident line of light  100  crosses over to another lenticule  102 . As the incident line of light  100  falls on different positions of the lenticular media  104  as it is moved in a direction perpendicular to the axis  106 , it continues to cross over multiple lenticules  102  producing transmitted light formed of angled, discontinuous imaged line segments. 
     FIG. 3B shows a top view of the discontinuous imaged line segments  110  on surface  107  similar to FIG.  1 B and FIG. 2B where lenticular material  104  has been omitted. Imaged line segments  110  are formed on surface  107  with severe skew angle Θ relative to longitudinal axis  106 . Multiple imaged line segments are formed simultaneously onto surface  107  because incident light  100  falls across multiple lenticules. As lenticular material  104  is moved in direction A of FIG. 3A, discontinuous imaged line segments  110  will move in the direction B. Skew angle Θ of imaged line segments  110  will remain constant as imaged line segments  110  move in direction B. As portions of imaged line segments  110  move to upper and lower limits  109  and  111 , imaged line segments  110  will be truncated due to the fact that the incident line of light  100  has moved off of the lenticule and on to the next adjacent lenticule of lenticular material  104 . This same effect will be produced if the incident line of light  100  is translated as shown in FIG. 1A in the direction of arrow AA and the lenticular material  104  is held stationary. 
     According to the present invention, the line of light transmitted through a transparent lenticular media is detected by a linear light detector placed beyond the lenticular media to detect the transmitted light. FIG. 4A shows a linear light detector  114  placed onto surface  107  where the transmitted lines of light form imaged lines. As shown, the linear light detector  114  is dimensioned to extend the length of a lenticule, although this is not a requirement to detect skew between an incident line of light and the lenticules on the lenticular material. The longitudinal axis of the linear light detector  114  is placed parallel to an incident line of light which is a reference. 
     FIG. 4B shows the linear light detector  114  on surface  107  while refracted and transmitted lines are imaged both on surface  107  and linear light detector  114 . In this figure the imaged lines  105  have no skew because the incident line of light is aligned parallel to the lenticules of the lenticular material. While the linear detector stays in a fixed position on surface  107 , either the reference incident line of light is moved relative to the lenticular material or the lenticular material is moved relative to the reference incident line of light in a direction perpendicular to the long axis of the lenticules. The movement of the lenticular material or incident line of light in a direction perpendicular to the long axis of the lenticules causes the imaged line  105  to sweep across the linear light detector  114 . The location of the imaged line  105  is shown at three positions, I, J and K as the imaged line  105  sweeps. At imaged line positions I and K the imaged line  105  does not fall on the linear light detector  114  and hence no signal is generated. At imaged line position J the imaged line  105  falls completely on the linear light detector  114  and a signal is generated. The output signal of linear light detector  114  is shown at the bottom of FIG. 4B with the positions I, J and K that correspond to that part of the generated signal. Because the imaged line  105  is parallel to longitudinal axis  106  at imaged line position J, the imaged line falls completely on the linear light detector  114  and the signal amplitude is high and the width of the amplitude is narrow as the imaged line  105  sweeps. Therefore, a generated signal from linear light detector  114  that has a high amplitude and narrow width is an indication of an imaged line  105  that is parallel to linear light detector  114  and therefore that the incident line of light is parallel to the long axis of the lenticules. 
     FIGS. 4C and 4D further illustrate this principal where the incident line of light is skewed relative to the long axis of the lenticules and the resulting imaged lines  105  are therefore skewed relative to the linear light detector  114 . In FIG. 4C, the skew between the imaged line of light  105  and linear light detector  114  at the imaged line positions I, J and K is shown with the generated signal from linear light detector  114 . At imaged line position J, the imaged line  105  no longer completely overlaps the area of the linear light detector  114  and therefore the amplitude of the signal is reduced from the one generated in FIG.  4 B. The width of the generated signal from linear light detector  114  is also greater than the signal of FIG. 4B because imaged line  105  will fall on linear light detector  114  for a greater portion of the sweep that occurs as either the lenticular material or the incident line of light is moved perpendicular to the long axis of the lenticules. FIG. 4D shows the effect of extreme skew when the incident line of light crosses several lenticules at one time. The resulting skew of imaged lines  105  is so great that imaged lines  105  will always cross linear light detector  114 . Due to the extreme skew angle between imaged lines  105  and linear light detector  114  the overlapped areas of imaged lines  105  on linear light detector  114  are very small resulting in a low amplitude signal as shown. Because the linear light detector  114  always has an imaged line  105  crossing as the image lines  105  sweep, the signal will have a very broad width and may be flat as shown at the bottom of FIG.  4 D. 
     The lenticular material is then rotated while either the lenticular material or the incident line of light is moved perpendicular to the long axis of the and the linear detector signal is monitored. If the line of light is parallel to the lenticules, the transmitted light beam will walk on and off the photodetector yielding a detection signal having maximum amplitude and minimum pulse width. If the line of light is skewed with respect to the lenticules, much of the transmitted light will not hit the detector resulting in a lower amplitude signal a very wide width. By using this method the lenticular material is aligned with the incident line of light and thus the skew between the lenticules and the writing beam is minimized. 
     An improvement to the above method can be accomplished by replacing the linear light detector whose output is proportional to the amount of energy falling on its surface area, with a light sensor whose output is proportional to the position of the centroid of light falling on its surface. Such a sensor is commonly called either a PSD ‘Position Sensing Detector’ or LEP ‘Lateral Effect Photodiode’. The previously described skew minimization method using the linear light detector is not able to give information as to the direction of the skew of the imaged line of light that falls on it. Therefore minimizing skew requires an integrative nulling technique where the lenticular material is arbitrarily rotated one direction to see if the detector signal amplitude becomes greater. If it does the rotation of the material is continued until a peak is found. If the first direction of rotation does not cause an increase in the amplitude, the direction of rotation must be reversed to determine if there is an increase in amplitude. This lack of directional information increases the correction time and the complexity of the control algorithm used to minimize the skew. 
     As shown in FIG. 4E the waveform produced using a PSD has direction information provided by the slope of the signal. As imaged line  105  moves across the PSD  115  the output signal is proportional to the position of the centroid of the intersection of the imaged line  105  and the detector surface. As the imaged line  105  moves in direction B, the point of intersection moves from location S to R due to the positive skew angle Θ. The output signal waveform is shown below with the corresponding points R and S on the signal noted. FIG. 4F shows the skew of the lenticules opposite to that shown in FIG. 4E where the skew angle Θ is now negative. As the imaged line  105  moves in the direction B the intersection of the imaged line  105  and PSD sensor  115  moves from location R to S and the resulting waveform is inverted as shown at the bottom of FIG.  4 F. By detecting the slope of the generated signal waveform it can be determined which way the lenticular material needs to be rotated to minimize the skew between the lenticular material and the writing beam. The degree of skew can also be determined from the magnitude of the slope of the generated signal waveform, with less skew producing greater slope. This is due to the fact that as the skew of imaged line  105  becomes less its intersection with PSD  115  will move across the sensor surface faster for the same displacement in the direction B. 
     It can be appreciated by anyone skilled in the art that other light detectors could be substituted in this application, including but not limited to, CCD array sensors or a line array of photo diodes to accomplish the same purpose. 
     Referring to FIG. 5, lenticular image product production apparatus  10  includes a platen  12  for supporting lenticular material  14 . Lenticular material  14  is placed with the lenticules down on the top of transparent platen  12  so that the emulsion side of the lenticular material  14  faces up. A suitable mounting structure (not shown) is provided to fixedly mount linear photodetector or position sensing detector  44  under the area where lenticular material  14  is exposed, while platen  12  and lenticular material  14  are moved. 
     The lenticular material  14  is transported by platen  12  in the direction of arrow A by a linear transport system that is suitably driven, typically by a motor system (not shown) such as a direct drive linear motor or leadscrew. These drive systems are well understood and known in the art. The lenticular material  14  is exposed with a writing laser beam  22  from a modulated laser  24 . The writing laser beam  22  is focused onto a scanning polygon  26  by optics  28 . The scanning polygon  26  rotates in direction C causing the reflected writing laser beam  22  to scan in the D direction. The writing laser beam  22  is reflected from a cold mirror (reflects visible light and transmits infrared light)  32  onto pivotable cylinder mirror  34 . Cylinder mirror  34  focuses the writing laser beam  22  onto the surface  13  of the lenticular material  14  thereby exposing the color photographic emulsion. (It will be understood that any type of emulsion can be used, black and white, color, monochromatic.) 
     An infrared laser  36 , located at a distance from the surface of the material identical to the distance to the scanning face of the polygon  26 , forms a second beam of light  38 , of a wavelength that can be transmitted through and which does not expose the lenticular material  14 . The second beam of light is reflected by mirror  40  through cold mirror  32  onto cylinder mirror  34 . Cylinder mirror  34  focuses the second beam  38  onto the surface  13  of the lenticular material  14  in a line parallel to the. Linear detector or position sensing detector  44  is sensitive to the wavelength of second beam  38  and made insensitive to writing laser beam  22  by suitable filters placed over the detector during the manufacturing process. Second beam  38  passes through lenticular material  14  and is refracted by the lenticules of lenticular material  14  and impinge on fixed detector  44 . Thus, the skew of second beam  38  is sensed by detector  44  relative to the lenticules of lenticular material  14 . 
     Pivotable cylinder mirror  34  is mounted so that it is rotatable about a pivot axis  35  in the direction arrow E at the center of the scan line of writing laser beam  22 . Cylinder mirror  34  rotates both the first and second laser beams  22  and  38  about pivot axis  35  and assures that the line of second beam  38  and the scan line of writing laser beam  22  are maintained parallel. The scanning polygon  26  works in conjunction with cylinder mirror  34  to cause the writing laser beam  22  to scan the lenticular material in the direction of arrow B, parallel to the longitudinal axes of the lenticules of lenticular material  14 . The motion of the lenticular material  14  caused by platen  12  in the direction of arrow A provides scanning in the orthogonal or page scan direction. 
     Further, the angular position of pivotable mirror  34  is measured by position sensor  20  whose moving member  21  is fixedly mounted to the end portion of pivoting mirror  34 . This sensor may be of any suitable type of position sensor known and employed in the art such as an LVDT, capacitive probe or potentiometer. At the other end of mirror  34  is attached a means for displacing or rotating the mirror  34 . In this embodiment, a D.C. motor  19  and leadscrew  18  are employed to produced a controlled displacement of the end portion of pivotable mirror  34  in the direction of arrow F, and thus an angular displacement E about pivot axis  35 . Control  48  receives signals from detector  44  and sensor  20  and sends control signals to motor  19 . 
     It can be appreciated by those skilled in the art that any number of other suitable means may employed to produce the same displacement including but not limited to, a cam actuator, voice coil or mechanical link. Thus, by the above described means, mirror  34  can be accurately controlled to change the angle of writing laser beam  22  and second beam  38  with respect to the lenticules on lenticular material  14  and therefore to minimize any skew misalignment between them. 
     According to the present invention, diode  36  is oscillated in the vertical direction I to cause beam  38  to be translated orthogonal to the longitudinal axis of the lenticules of media  14 . The mechanical actuator to move diode  36  is not shown but can be any of several typical mechanisms to accomplish this type of motion, such as cam actuator or motor driven leadscrew. Cylinder mirror  34  is rotated until beam  38  is aligned the longitudinal axes of the lenticules of media  14 . This is effected when a maximum pulse amplitude and minimum pulse width is detected using a linear photodetector  44 . If photodetector  44  is a position sensing device, a minimum amplitude and or maximum slope of the signal waveform is detected. Alignment of beam  38  results in proper alignment of beam  22 . Alternately, diode  36  may be held fixed while platen  12  is moved in direction A to cause the media to move orthogonally through beam  38 . Cylinder mirror  34  is rotated until beam  38  is aligned with the longitudinal axis of the lenticules of media  14  by detecting the signal waveform from photodetector  44  as previously described. 
     FIG. 6 illustrates an alternate method for aligning a writing laser beam  22  and lenticular material  14 . In this alternate method the optical elements described and depicted in FIG. 5 are the same but cylinder mirror  34  is held in a fixed mount  27 . Motor  19  and leadscrew  18  along with sensor  20  and its moving member  21  are not used. Movable platen  12  is mounted on a rotating mechanical stage  17  which is fixedly mounted on a stage base  23 . Stage base  23  is transported in the direction A by the same type of linear transport means discussed in FIG.  5 . 
     Rotational skew alignment of beam  38  and writing laser beam  22  to the lenticules of lenticular material  14  is accomplished by the rotational movement of mechanical stage  17  in the indicated direction G. Rotation of mechanical stage  17  in direction G produces rotational movement of platen  12  and lenticular material  14  about axis  25  of mechanical stage  17 . Movement of lenticular material  14  about axis  25  changes the relative angular position of the lenticules of lenticular material  14  and writing laser beam  22  and second beam  38 . The relative angular position of the lenticules of lenticular material  14  and second beam  38  is detected by fixedly mounted linear detector  44  by translating the platen and media back and forth or in one direction. Thus, the angular skew alignment of the lenticules of lenticular material  14  and writing laser beam  22  can be sensed and corrected to a minimum or any desired angular skew alignment by this means. 
     The means for rotational movement of mechanical stage  17  can be any of the known means used in the art, such as: motor driven worm and pinion gear, lever arm or manual adjustment. 
     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  lenticular image product production apparatus 
       11  transparent inserts 
       12  platen 
       13  top layer of lenticular material 
       14  lenticular material 
       15  curved surface of the lenticular material 
       17  rotating mechanical stage 
       18  leadscrew 
       19  pivoting cylinder mirror motor 
       20  pivoting cylinder mirror position sensor 
       21  moving member 
       22  writing laser beam 
       23  rotational stage base 
       24  modulated laser 
       25  rotating mechanical stage axis 
       26  polygon 
       27  cylinder mirror fixed mount 
       28  optics 
       32  cold mirror 
       33  exiting beam 
       34  pivoting cylinder mirror 
       35  pivot axis 
       36  infrared laser 
       38  second beam of light 
       40  IR turning mirror 
       44  linear position detector 
       46  control