Lens adjustment assembly for electronic digital imaging apparatus

Abstract: An electronic digital imaging apparatus includes an intensity-modulated light source (80) for emitting a light beam along an optical path, an adjustment block (100) to which the light source (80) is fixed and which is movable along the optical path to move the light source (80) along the optical path, and means for scanning the light beam along a recording surface. The adjustment block (100) has two opposed ends (102, 104) and a central region (103); one of the opposed ends being fixed relative to the optical path, the other of the opposed ends being adjustable in the general direction of the optical path, and the central region (103) carries the light source (80); whereby adjustment of the other of the opposed ends (102, 104) in the general direction of the optical path by a given distance is effective to move the light source 80) along the optical path by a fraction of the given distance. Projection optics (31) are detachably integral with the light source (80) in the optical path for focusing the light beam at the recording surface. The projection optics (31) being detachable from the light source (80) without effecting the position of the light source along the optical path so as to not disturb the focus of the imaging apparatus upon re-attachment of the projection optics (31) to the light source (80).

Description: BACKGROUND OF THE INVENTION Technical Field This invention relates generally to the field of electronic digital imaging and, specifically, to such imaging systems that utilize a light source write head to record information by scanning photosensitive media. Background Art Electronic digital imaging, such as for example in copiers and/or printers, is accomplished by modulating the intensity of a light beam that forms a writing spot on photosensitive media as the beam moves relative to the photosensitive media. One type of electronic digital imager uses a modulated array of light emitting diodes (LED's) positioned on a write head assembly resident on a rotor which is simultaneously rotated about a fixed axis and linearly translated past stationary photosensitive recording media mounted on the inner surface of a cylindrical "support shoe" to form a plurality of writing spots moving across the photosensitive material in a fast scan direction and in a slow scan direction. When using such imagers, the optics must remain focused under high rotational gravitational forces, and yet be easily re-focused in the field. Dismounting the lens during LED array changes causes a loss of focus, so provision must also be made for easy and repeatable replacement of the LED array. The optical elements must be light weight to minimize inertia because they are mounted on a spinning rotor. U.S. Patent No. 4,703,334 to Mochimaru, et al. reflecting the preamble of claim 1 discloses an optical recording apparatus including an array of light-emitting elements for recording an image on a belt-shaped recording medium. More specifically, the Mochimaru patent discloses an optical recording head including an image forming unit. The image forming unit includes a lens array. Adjustment of focusing conditions of the lens array is carried out using an adjustment fixture prior to assemblage into the main apparatus. U.S. Patent No. 5,177,502 to Schreyer, et al. relates to an arrangement for detachably fastening modules to a module carrier. More specifically, the Schreyer, et al. patent discloses a character generator having imaging optics. The imaging optics is integrated in a cover and is centrally positioned over an exposure line. DISCLOSURE OF THE INVENTION It is an object of the present invention to provide an improved lens adjustment assembly that can be easily focused onto the predicted media surface, both in the factory during final assembly and in the field. It is another object of the present invention to provide an improved lens adjustment assembly that is light in weight and low in inertia so that the rotor motor requirements are small, large size component use is minimized, and the rotor reaches operating speed quickly. It is still another object of the present invention to provide an improved lens adjustment assembly that is sufficiently rigid to maintain focus at high speeds. It is yet another object of the present invention to provide an improved lens adjustment assembly that maintains lens focal length adjustment during LED array replacement. Preferably, this is accomplished by independent removal of the lens and LED array, resulting in no loss of lens focus adjustment when the LED array is removed. Other objects of the present invention include having only a very few tight-tolerance parts, and an assembly with good heat dissipation properties. With the above objects in view, the invention is defined by the several claims appended hereto. According to a feature of the present invention, an electronic digital imaging apparatus includes an intensity-modulated light source for emitting a light beam along an optical path, an adjustment block to which the light source is fixed and which is movable along the optical path to move the light source along the optical path, and means for scanning the light beam along a recording surface. According to another feature of the present invention, the adjustment block has two opposed ends and a central region; one of the opposed ends being fixed relative to the optical path, the other of the opposed ends being adjustable in the general direction of the optical path, and the central region carries the light source, whereby adjustment of the other of the opposed ends in the general direction of the optical path by a given distance is effective to move the light source along the optical path by a fraction of the given distance. In a preferred embodiment, adjustment of the other of the opposed ends by a given distance is effective to move the light source by approximately one-half of the given distance. According to yet another feature of the present invention, the adjustment block is a pantograph linkage comprising a first arm forming the one of the opposed ends of the adjustment block, a second arm forming the other of the opposed ends of the adjustment block, and a third arm forming the central region of the adjustment block; the three arms being flexibly connected to top and bottom links, whereby adjustment of the second arm in the general direction of the optical path by a given distance is effective to move the third arm along the optical path by a fraction of the given distance. According to still another feature of the present invention projection optics are detachably integral with the light source in the optical path for focusing the light beam at the recording surface. The projection optics being detachable from the light source without effecting the position of the light source along the optical path so as to not disturb the focus of the imaging apparatus upon re-attachment of the projection optics to the light source. The invention, and its objects and advantages, will become more apparent in the detailed description of the preferred embodiments presented below. BRIEF DESCRIPTION OF THE DRAWINGS In the detailed description of the preferred embodiments of the invention presented below, reference is made to the accompanying drawings, in which: Fig. 1 is a perspective view of a rotary printing system according to the prior art; Fig. 2 is a schematic illustration of a printer incorporating a preferred embodiment of the present invention; Fig. 3 is an enlarged view of a portion of the printer of Fig. 2; Fig. 4 is an exploded view of the lens adjustment assembly with the optical elements shown in section for clarity according to a preferred embodiment of the present invention; and Fig. 5 is an assembly view in section of the lens adjustment assembly of Fig. 4. BEST MODE FOR CARRYING OUT THE INVENTION The present description will be directed in particular to elements forming part of, or cooperating more directly with, apparatus in accordance with the present invention. It is to be understood that elements not specifically shown or described may take various forms well known to those skilled in the art. It is also to be understood that the lens adjustment assembly of the present invention has applications in types of imaging apparatus other than the rotary printer of the illustrated preferred embodiment. For example, the light weight of the assembly may lend itself particularly to a moving structure, but the invention would also be applicable to a stationary assembly with scanning optics such as for example a rotating polygon mirror. A prior art rotary printing system employing an adjustable-position lens assembly is illustrated in Fig. 1, and includes a rotor 1 coupled to a drive motor, not shown, supported by a rotor support member 2 which hangs from a carriage assembly 3 which is supported for movement along a pair of guide rods 4 and 4'. The rotor is arranged to spin and move axially within a cylindrical support shoe 5 which is adapted to receive a sheet of photosensitive material on the inner surface 6 thereof. Rotor 1 is attached to a linear translation assembly comprising rotor support member 2, carriage assembly 3, and a lead screw 7 driven by a stepper motor. The rotor is simultaneously rotated by the drive motor in a fast scan direction and is translated past the cylindrical support shoe in the slow scan direction (axially) by the stepper motor and lead screw 7, thereby achieving a raster scan pattern on the photosensitive media held within the support shoe. An LED printhead assembly 8 is mounted in rotor 1 and comprises a plurality of mono-color light sources such as an array of LED's and a projection lens assembly. The printhead assembly is located within the body of rotor 1 with the LED array package positioned so that the LED aperture output surface is located in a plane which is perpendicular to the optical axis of the projection lens assembly. The projection lens assembly is arranged to simultaneously image (focus) all of the LED's in the array onto a surface located in close proximity above the outer surface of the rotor, and more particularly, onto the inner surface of the photosensitive material held by support shoe 5. A single projection lens array thereby images the plurality of LED's onto the photosensitive material as a plurality of individual images which constitute the writing beams that expose the image pixels. Fig. 2 is a schematic illustration of a printer incorporating a preferred embodiment of the present invention. Access into a light-tight cabinet 10 is attained through a door 12, which pivots about a hinge 14. A web of photographic light sensitive media 16 is fed from a roll 18 around an anti-backup device 20. From anti-backup device 20, paper is lead to a write station 22. The write station includes a metering mechanism 24, a cylindrical support shoe 26 (corresponding to support shoe 5 in the prior art device of Fig. 1), an exit guide 28, a web-cutting mechanism 30 including a pair of knives, and an exit media guide member. Referring now to Fig. 3, the arcuate inner surface of cylindrical support shoe 26 is precisely bored so that an LED array in a lens assembly 31 mounted on a rotor 32 focuses on the emulsion side of media 16. A translator base assembly 34 is attached to framework to support guide rods 36 and 38. A plurality of wheels 40 are rotatably attached to a carriage 42 which translates along guide rods 36 and 38 by means of a lead screw 44 turned by a lead screw motor, not shown. A rotor support member 46 (corresponding to rotor support member 2 in the prior art device of Figure 1) is rigidly attached to carriage 42, and carries rotor 32. Also attached to rotor support member 46 is a media guide disc 48 arranged such that a space gap is created between the outer diameter of the media guide disc and the arcuate inner surface of support shoe 26. Referring to Fig. 4 and 5, lens assembly 31 includes a cover 60 that receives an upper mirror 62 and a lower mirror 64 separated by a mirror spacer 66. The spacer carries a diaphragm 68 and a diaphragm spacer 70. This cover subassembly is held together by a jam nut 72. An array post 76 has a threaded head 78 with four locating pins that are received in mating holes of an LED array 80. The array may be secured to the post head by screws. A cover lock 82 is secured on post 76 by an E-ring 84. Rotation of cover lock 82 is limited by a pin 86 depending from head 78 into a slot 88 in the cover lock. The cover subassembly is screwed onto threaded head 78 of array post 76. When jam nut 72 bottoms out on threaded head 78, a tab 92 on cover lock 82 falls into one of several castellations 94 around the bottom of cover 60. A lens adjustment block 100 includes three arms 102-104 connected to top and bottom links 106 and 108, respectively, by narrow webs 110 to form a pantograph linkage. Vertical movement of arm 104 relative to arm 102 by a given distance will cause central arm 103 to move relative to arm 102 half the given distance that arm 104 moved. Lens adjustment block 100 is preferably extrusion-formed as a single unit because an extrusion is light weight and requires little machining compared to sheet metal fabrication. During assembly, array post 76 is inserted through a hole 112 in top link 106 and is received by "v" shaped walls in central arm 103, where it is secured by a screw 114. Adjustment block 100 is attached to rotor 32 by a screw 116. A lens adjustment screw 118 compresses a spring 120. As best seen in Fig. 5, the lens assembly can be focused by merely turning lens adjustment screw 118 to raise or lower arm 104 relative to rotor 32. Central arm 103 follows arm 104, moving one half the distance of arm 104. Accordingly, very fine adjustment can be easily effected, both in the factory during final assembly and in the field. The improved lens adjustment assembly is light in weight and low in inertia so that the rotor motor requirements are small, large size component use is minimized, and the rotor reaches operating speed in less time; yet the lens adjustment assembly is sufficiently rigid to maintain focus at speed. As can best be seen in Fig. 5, The cover subassembly including cover 60, mirrors 62 and 64, diaphragm 68, and jam nut 72 can be removed as an assembled unit from array post 76 so that LED array 80 can be reached for replacement without unduly affecting lens focal length adjustment during LED array replacement.

Claims: An electronic digital imaging apparatus having an intensity-modulated light source (80) for emitting a light beam along an optical path and means for scanning the light beam along a recording surface, an adjustment block (100) to which the light source is fixed and which is movable along the optical path to move the light source along the optical path, characterized by : the adjustment block having two opposed ends (102,104) and a central region (103), one (104) of the opposed ends being fixed relative to the optical path and the other (102) of the opposed ends being adjustable in the general direction of the optical path; and the central region (103) carrying the light source, whereby adjustment of said other of the opposed ends in the general direction of the optical path by a given distance is effective to move the light source along the optical path by a fraction of the given distance. An electronic digital imaging apparatus as set forth in Claim 1 wherein the light source is carried by the central region of the adjustment block approximately midway between the two opposed ends, whereby adjustment of said other of the opposed ends in the general direction of the optical path by a given distance is effective to move the light source along the optical path by approximately one-half of the given distance. An electronic digital imaging apparatus as set forth in Claim 1 wherein the adjustment block is a pantograph linkage characterized by : a first arm forming said one of the opposed ends of the adjustment block; a second arm forming said other of the opposed ends of the adjustment block, and a third arm forming said central region of the adjustment block, said three arms being flexibly connected to top and bottom links, whereby adjustment of said second arm in the general direction of the optical path by a given distance is effective to move the third arm along the optical path by a fraction of the given distance. An electronic digital imaging apparatus as set forth in Claim 1 wherein the adjustment block is an extrusion formed as a single unit. An electronic digital imaging apparatus as set forth in Claim 1 further characterized by projection optics detachably coupled to the light source in the optical path for focusing the light beam at the recording surface, said projection optics being detachable from the light source as an assembled unit without affecting the position of the light source along the optical path so as to not disturb the focus of the imaging apparatus upon re-attachment of the projection optics to the light source.

Inventors: BRIDGES MARK EDWARD, BRIDGES, MARK EDWARD, Bridges, Mark Edward, c/o Eastman Kodak Co.
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1996
Main classification: G06K15
IPC codes: G03G15, G02B7, H04N1, B41J2