Method for aligning a lenticular material for printing
FIELD OF THE INVENTION 
     This invention relates to the field of 3-D imaging using conventional printing press methods and more particularly to a technique for aligning a lenticular material with respect to an image to be printed on the lenticular material. 
     BACKGROUND OF THE INVENTION 
     There are a variety of ways to make three-dimensional images using lenticular material. These include exposing photographic film through the lenticular material and then developing the film, accurately writing the required image on photographic film using digital printing techniques and then aligning the film after developing to the lenticular material. 
     One disadvantage of the photographic approaches when a high volume of images is required, is that of cost. Attempts have been made to use high volume printing presses with very small half-tone dots to make low cost 3-D lenticular images. Examples of this approach being employed by a company called Quad Graphics. 
     However, a problem arises because of the difficulty of achieving registration to the lenticular material when printing directly on the material. The demands for accurate lenticular registration are very precise. Typically to produce a high quality image, the image must be registered to lenticules with an accuracy of plus or minus 0.0005 inches. If the misregistration exceeds this figure image quality drops significantly. 
     SUMMARY OF THE INVENTION 
     The present invention involves aligning the lenticular material prior to having it passed through a printing press for printing the image on the lenticular material. One preferred method for aligning a lenticular material for the printing of an image onto a printing surface of the lenticular material, comprises the steps of: 
     a) directing a radiation beam to the lenticular material such that at least one of the lenticules focuses the radiation beam at the printing surface of the lenticular material; 
     b) positioning a radiation sensitive array at a reference position that will yield a maximum sensed radiation when the position of the focused radiation beam on the printing surface of the lenticular material is in correct printing alignment; and 
     c) adjusting the position of the lenticular material to maximize the radiation sensed by the radiation sensitive array. 
     Another alignment technique involves manipulation of the lenticular material at the feed point of the press by sensing the position of the lenticules. 
     Another technique involves machining reference slots in the edge of the lenticular material that engage fixed reference projections to insure the alignment of the lenticules with the to be printed image. 
     Yet another technique is to sense the alignment of the lenticules on the fly and automatically adjust the phasing of the press to insure that the half-tone, image-printing plate comes into registration with the lenticular material at a point corresponding to the correct lenticule position. 
     The basic principle of this invention is to sense the position of the lenticule material by using an optical method to take advantage of the fact that a lenticule is, in fact, a lens and then position the lenticular material so that it is in accurate registration with the image-printing plate. 
     From the foregoing it can be seen that it is a primary object of the present invention to provide an improved method for aligning the position of a lenticular with respect to a printing press in order to increase the accuracy of placement of a printed image on the lenticular material. 
     It is another object of the present invention to provide an improved 3-D image by increasing the accuracy of alignment between a lenticular material and the image segments forming the image. 
     The above and other objects of the present invention will become more apparent when taken in conjunction with the following description and drawings wherein like characters indicate like parts and which drawings form a part of the present invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 illustrates the lenticule configuration and optical rays of a depth image. 
     FIG. 2 illustrates a system for sensing the position of a lenticule using a microscope objective. 
     FIG. 3 illustrates a system for sensing the position of a first piece of lenticule material by using a second piece of lenticular material. 
     FIG. 4A illustrates a servo technique for aligning lenticular material to a machine for making slots in the lenticular material. 
     FIG. 4B illustrates the direction of motion for the lenticular sheet. 
     FIG. 5 illustrates a technique for aligning the lenticular material at the feed point of the press. 
     FIG. 6 illustrates a technique for aligning the lenticular material with respect to fingers on a roll on the press. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Three-D imagery depends on the ability to project distinct images in different viewing directions. This can be seen in FIG. 1, where an image view is projected to lenticule 101 along ray 102 from image position 103. Similarly for lenticule 111, viewing ray 112 is projected from point 113. A number of points (depending on the number of views behind each lenticule), such as points 104, 105, and 106, correspond to different views of the image producing rays 107, 108, and 109, respectively. It can be appreciated that a very high degree of alignment is required between the position of the lenticular material 120 and the position of the media 121. Any small variation in these positions results in a angular displacement of the rays and therefore results in a substantial loss of image quality. 
     In order to accurately print the image on the smooth side of the lenticular material with the required alignment when using a printing press, it is necessary that the lenticular material be fed into the press with high accuracy and in synchronism with the printing roll. To achieve this synchronism, it is first necessary to determine accurately the position of the lenticules. 
     FIG. 2 illustrates a technique for sensing the position of a lenticule using a microscope objective. Parallel light from lamp 201 and condenser lens 202 passes to lenticule 203. This parallel light focuses on the back side of the lenticule. The microscope objective 204 images the focal point back to a multi-position sensor 205. This sensor is formed as number of individual light sensitive areas 206 through 210, which can be either separate light sensitive cells or a single CCD (charge coupled device) sensor. The signal from these sensors passes to an A/D converter 212, for conversion to a digital form and therefrom to a computer interface 213. These signals are then passed to a computer 214, whose program determines the position of the sensor receiving the maximum amount of light, thereby determining the position of the lenticule with respect to the microscope objective. 
     It will be appreciated that sensing the position of the lenticule at one point is insufficient to achieve the positioning registration along the whole length of the lenticule. It is therefore necessary to use multiple objectives across the width of the lenticular material with a spacing sufficiently close that given the angular uncertainties of the angular position of the lenticular material all adjacent objectives will be looking at the same lenticule. Consequently the series of microscope objectives aligned along a given lenticule are, when sensing that the lenticule is in the same position, in fact, looking at the same lenticule. 
     Referring to FIG. 3, another technique for sensing the alignment of the lenticular material is to use a second piece of lenticular material of slightly different pitch. The entire area of the lenticule is illuminated using, for example, a diffuse illuminator 301, which produces diffuse light. Lenticular material 303, whose position it is desired to determine, is brought into close alignment with a small piece of lenticular material 304 of slightly different pitch than the lenticular material 303. A lens 305 images the MOIRE pattern formed from the interaction of lenticular material 303 with lenticular material 304 onto a CCD camera 306. A computer interface 307 receives the video signal from the CCD camera 306 and passes information describing the scene to a computer processor 308. The output of computer 308 controls a servo system 309 which positions lenticular sheet 303 through motors (for example 310) to bring the lenticular sheet into correct positioning with respect to the fixed lenticular sheet 304. The position is considered correct when the local intensity of the MOIRE pattern is at its maximum value. (Alternatively a present intensity can be used as a reference because the purpose of this alignment method is to establish a fixed phase relationship between the two pieces of lenticular material and, then having established a stable phase relationship, it is possible to adjust the press for optimal image quality.) 
     FIG. 4a shows a system for machining reference marks on a lenticular sheet using the positioning techniques already described. A grinding wheel 402 is positioned near the edge of the lenticular material 401 so that the motor 410 controlling the position of the lenticular material through shaft 411 and drive wheel 412 drives the lenticular material against the grinding wheel. A second grinding wheel 403 machines a second notch in lenticular sheet 401. A second motor 413 also controlled by computer 308 (computer 214), positions the lenticular material 401 in the vicinity of grinding wheel 403 by turning shaft 414 and drive wheel 415. It would be appreciated that these two motors 410 and 413 are, in fact, adjusting both the position and the orientation of lenticular sheet 401 so that the two notches (420 and 421, see FIG. 4b) made by grinding wheels 401 and 403 occur in alignment with the direction of the lenticules. This direction is shown in FIG. 4b by arrow 422. 
     The notches 420 and 421 may then be used in two possible ways to correctly align and position the lenticular material in the printing press. Referring to FIG. 5, the first way is to position these notches against a finger 501 and 502 to establish correct alignment of the sheet 401. This alignment is performed by having a drive motor 503 operate a shaft 504 to a drive wheel 505 to establish pressure between the lenticular material 401 and finger 501. A similar arrangement (not shown) of motor, drive shaft and drive wheel is used to establish pressure against finger 502. Once the lenticular sheet 401 is correctly positioned, the fingers are withdrawn and the sheet moves on into the press. 
     Alternatively, the arrangement shown in FIG. 2 or 3, may be used to position the lenticular sheet 401 at the feed point of the press. 
     It can also be possible to establish a reference edge in alignment with the lenticules during the compression moulding or extrusion process used to make the lenticular sheets. Once the reference notches or the reference edge is established, they are used in the feed process of the printing press to establish correct positioning of the lenticular material. 
     A specific example of this technique is shown in FIG. 6 where the drum 601 within the press receives the lenticular material 602. Fingers 604 and 605 on the drum provide reference points corresponding to notches 420 and 421. The feed mechanism pushes the lenticular material against these fingers to accurately position the lenticular material with respect to the drum. 
     While there has been shown what are considered to be the preferred embodiments of the invention, it will be manifest that many changes and modifications may be made therein without departing from the essential spirit of the invention. It is intended, therefore, in the annexed claims, to cover all such changes and modifications as may fall within the true scope of the invention. 
     Parts List 
     101 Lenticule 
     102 Ray 
     103 Image position 
     111 Lenticule 
     112 Viewing ray 
     113 Point 
     104 Point 
     105 Point 
     106 Point 
     107 Ray 
     108 Ray 
     109 Ray 
     120 Position of lenticular material 
     121 Position of media 
     201 Lamp 
     202 Condenser lens 
     203 Lenticule 
     204 Microscope objective 
     205 Multi-position sensor 
     206 Light sensitive area 
     207 Light sensitive area 
     108 Light sensitive area 
     109 Light sensitive area 
     210 Light sensitive area 
     212 A/D converter 
     213 Computer interface 
     214 Computer 
     Parts List Cont&#39;d 
     301 Diffuse illuminator 
     303 Lenticular material 
     304 Lenticular material 
     305 Lens 
     306 CCD camera 
     307 Computer interface 
     308 Computer 
     309 Servo system 
     401 Lenticular material 
     402 Grinding wheel 
     403 Grinding wheel 
     410 Motor 
     411 Shaft 
     412 Drive wheel 
     413 Motor 
     414 Turning shaft 
     415 Drive wheel 
     420 Notch 
     421 Notch 
     422 Arrow 
     501 Finger 
     502 Finger 
     503 Drive motor 
     504 Shaft 
     505 Drive wheel 
     601 Drum 
     602 Lenticular material 
     604 Finger 
     605 Finger