Abstract:
In a device for point-by-point and line-by-line scanning of masters chucked on scanner drums having different diameters with an optoelectronic scanner element, which converts the scan light modulated with the content of the master and focused with the scanner objective into an image signal, a scanner element comprising a reflected light illumination is provided for generating an illumination spot on an opaque original. The scanner objective for correction of the focusing of the scan light onto the scanner element given employment of scanner drums having different diameters—is seated displaceable on the optical axis of the scanner element into radial working positions determined by the diameter of the respective scanner drums. The reflected light illumination can be displaced in the direction of the optical axis by the focal intercept change of the scanner objective for the purpose of optimizing the illumination spot given employment of scanner drums of different sizes.

Description:
BACKGROUND OF THE INVENTION 
     The invention is in the field of electronic reproduction technology and is directed to a device for pixel-by-pixel and line-by-line, optoelectronic scanning of masters chucked on a scanner drum. Such a scanner drum device, referred to as a drum scanner below, can be designed for scanning black-and-white or chromatic masters in reflected light and/or transmitted light. 
     A drum scanner for scanning transparency masters is composed, for example, of a rotating, transparent scanner drum onto which a transparency master to be scanned is chucked, of a light source for pixel-by-pixel illumination of the transparency master and of a scanner element having a scanner objective, a scanner diaphragm and an optoelectronic transducer for converting the scan light the transparency master allows to pass into an image signal, which represents the luminance values of the scanned picture elements. 
     The light required for the pixel-by-pixel illumination of the transparency master is transported, for example, from a light source located outside the scanner drum through a light conductor into the hollow-cylindrical interior of the scanner drum and is imaged thereat onto the transparency master as an illumination spot with a matching objective and a deflection mirror. The scan light modulated with the image content of the transparency master proceeds through the scanner objective into the scanner element located outside the scanner drum and is converted thereat into an image signal by optoelectronic conversion. 
     The scanner element on the one hand and the optical elements on the other hand are respectively secured to an arm of a U-shaped feed support, whereby the arm carrying the optical elements projects into the scanner drum at the end face. 
     For planar scanning of the transparency master, the feed support moves in the axial direction of the rotating scanner drum. 
     In order to be able to scan masters having different formats, the standard scope of a drum scanner comprises scanner drums having different diameters that are chucked in the drum scanner dependent on the format of the master to be scanned. In this case, lens systems must be manually replaced at the feed support for optimum setting of the size of the illumination spot on the transparency master in order to compensate the different radial distances between the central arm of the feed support and the generated surface of the respective scanner drum. For optimum focusing of the luminance-modulated scan light coming from the transparency master onto the scanner diaphragm, the scanner element is equipped with interchangeable lenses that must be manually pivoted into the beam path dependent on the diameter of the scanner drum employed. The employment of such sets of lenses and interchangeable objectives is relatively complicated. 
     SUMMARY OF THE INVENTION 
     It is therefore an object of the invention to improve a device for pixel-by-pixel and line-by-line, optoelectronic scanning of transparency and opaque masters chucked on scanner drums such that optical adaptations, particularly given employment of scanner drums having different diameters, can be implemented in a simple way and automatically to the farthest-reaching extent. 
     According to the apparatus of the invention for point-by-point and line-by-line opto-electronic scanning of a master, a scanner drum is provided for chucking a master to be scanned. An illumination unit is provided for the master. A scanner objective is provided, and a scanner element converts the scan light modulated with the content of the master and then the scan light is focused with the scanner objective into an image signal. A feed support is provided in which the scanner objective in the scanner element are arranged, the feed support executing a feed motion in the direction of a rotational axis of the scanner drum for scanning of the master. The scanner comprises a reflected light illumination for generating an illumination spot on an opaque master. The scanner objective corrects focusing of the scan light onto the scan element given employment of scanner drums having different diameters and is seated displaceable into a radial working position on an optical axis of the scanner element determined by a diameter of the respective scanner drum. Reflective light illumination is displaceably arranged for optimizing the illumination spot given employment of scanner drums having different diameters. 
     The invention is explained in greater detail below with reference to FIGS.  1  through  5 . 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows the fundamental structure of a drum scanner; 
     FIG. 2 is an exemplary embodiment of the devices for axial displacement of a light conductor and for radial displacement of a scanner objective, as well as the positioning of the light conductor and of the scanner objective given employment of a scanner drum having a small diameter; 
     FIG. 3 illustrates the positioning of the light conductor and of the scanner objective given employment of a scanner drum having a large diameter; 
     FIG. 4 is an exemplary embodiment of a scanner element having a reflected illumination for scanning opaque masters as well as the positioning of the scanner element given employment of a scanner drum having a small diameter; and 
     FIG. 5 shows the positioning of the scanner element given employment of a scanner drum having a large diameter. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows the fundamental structure of a drum scanner. A transparent scanner drum  1  having, for example, a vertical rotational axis  2  is coupled to a rotational drive  4  with a clamp mechanism  3 . The rotational axis  2  of the scanner drum  1  can also be arranged horizontally or at an arbitrary angle relative to the floor space of the drum scanner. 
     A transparency master  5  is mounted on the scanner drum  1 . For scanning transparency masters  5  having different formats, scanner drums  1  having different diameters are chucked in the drum scanner with the assistance of the clamp mechanism  3 . The clamp mechanism  3  is constructed, for example, according to German Utility Model 296 23 523, and the rotational drive is constructed according to German Published Application 196 01 524. 
     For pixel-by-pixel illumination of the transparency master  5 , an illumination unit  7 ,  8 ,  10 ,  11  is provided in the hollow-cylindrical interior of the scanner drum  1 , this illumination unit being supplied from a light source  6  located outside the scanner drum  1 . A light beam generated by the light source  6  is transported by a light conductor  7  into the illumination unit and emerges through a light exit face  8  of the light conductor  7  in radial direction of the rotational axis  2 . The light beam  9  that has emerged is deflected in the radial direction onto the transparency master  5  with a matching objective  10  in the rotational axis  2  and deflection mirror  11  arranged at 45° relative to the rotational axis  2 , as a result whereof a light spot  8 ′ in the light exit face  8  of the light conductor  7  is imaged onto the transparency master  5  as an illumination spot  12 . 
     The scan light  13  that is allowed to pass by the transparency master  5  and modulated with the luminance values of the scanned picture elements proceeds through a scanner objective  14  into a scanner element  15  located outside the scanner drum  1  and having a scanner diaphragm  16  and an optoelectronic transducer not shown, whereby illumination spot  12  and scanner objective  14  lie on the optical axis  15 ′ of the scanner element  15  proceeding radially relative to the scanner drum  1 . 
     In the scanner element  15 , the scanned light  13  is converted with the optoelectronic transducer into an image signal B for further-processing. Scanner element  15  and light source  6  are structurally united in the illustrated exemplary embodiment. Scanner objective  14 , scanner element  15  and light source  6  move axially along the rotating scanner drum  1  for planar scanning of the master. 
     So that the illumination spot  12  in the planar master scanning always lies in the optical axis  15 ′ of the scanner element  15 , at least the deflection mirror  11 —the illumination unit with light conductor  7 , matching objective  10  and deflection mirror  11  in the exemplary embodiment—must be entrained synchronously with the scanner objective  14  and the scanner element  15  in the axial direction. For that purpose, a U-shaped feed support  17  having an inner arm  18  and an outer arm  19  is present, this being moved in the axial direction of the scanner drum  1  during the scanning of the master by a feed drive  20  with the assistance of a spindle  21  and a nut segment  22  located at the feed support  17 . The inner arm  18  of the feed support  17  is guided by the rotational drive  4 , projects into the scanner drum  1  at the end face, and extends along the rotational axis  2 . The inner arm  18  carries the illumination unit  7 ,  8 ,  10 ,  11 . The outer arm  19  of the feed support  17  proceeding parallel to the inner arm carries the scanner objective  14 , the scanner element  15  and the light source  6 . 
     For scanning opaque masters, a reflected light illumination not shown in FIG. 1 is present that generates a corresponding illumination spot  12  on the opaque master  5 ′. In this case, the modulated scan light  13  reflected from the opaque master to be scanned is converted in the scanner element  15  into an image signal B. 
     When scanner drums  1 ,  1 ′ having different diameters are chucked in the drum scanner, the distance between the deflection mirror  11  and the transparency master  5  mounted on the scanner drum  1  as well as the distance between the transparency master  5  and the scanner diaphragm  16  in the scanner element  15  change. In this case, the size of the illumination spot  12  on the transparency master  5  and the focusing of the scan light  13  coming from the transparency master  5  onto the scanner diaphragm  16  must be corrected. 
     The size correction of the illumination spot  12  on the transparency master  5  advantageously occurs with an automatic change of the imaging scale with which the light spot  8 ′ of the light exit face  8  of the light conductor  7  is imaged on the transparency master  5  as an illumination spot  12 . The modification of the imaging scale is preferably achieved by modifying the distance between the light exit face  8  of the light conductor  7  and the matching objective  10  secured stationarily to the inner arm  18 , preferably by displacing the light conductor  7  on the inner arm  18  in the direction of the rotational axis  2  of the scanner drum  1  into axial working positions A k  and A g , which are predetermined by the diameter of the scanner drums  1 ,  1 ′ respectively employed, as a result whereof an optimum illumination of the transparency master  5  is achieved given employment of scanner drums  1 ,  1 ′ having different diameters. 
     The recorrection of the focusing of the scanned light  13  onto the scanner diaphragm  16  in the scanner element  15  occurs by modifying the radial distance between the generated surface of the respective scanner drum  1 ,  1 ′ and the scanner objective  14  by displacing the scanner objective  14  into radial working positions B k  and B g , that are predetermined by the diameter of the scanner drums  1 ,  1 ′ respectively employed. 
     FIG. 2 shows an exemplary embodiment of the devices for axial displacement of the light conductor  7  at the inner arm  18  and for radial displacement of the scanner objective  14  at the outer arm  19  of the feed support  17 , as well as the positioning of the light conductor and of the scanner objective given employment of a scanner drum  1  having a smaller diameter. 
     The end region of the light conductor  7  with the light exit face  8  is enveloped by a cylindrical light conductor mount  24  that is seated in sliding fashion in the hollow-cylindrical inner arm  18  of the feed support  17 . A compression spring  26  is arranged between a recess  25  at the inside wall of the inner arm  18  and the light conductor mount  24 . A radial finger  27  is attached to the light conductor mount  24 , the radial finger being connected to a controllable actuating drive  29  via a tension cable  28  proceeding in the direction of the inner arm  18 . The actuating drive  29  is, for example, a stepping motor that drives a cable drum. The actuating drive  29  is preferably attached to the feed support  17 . The light conductor mount  24  and, thus, the light exit face  8  of the light conductor  7  is automatically displaced opposite the force of the compression spring  26  into one of the two axial working positions A k  and A g  corresponding to the diameter of the scanner drum  1 ,  1 ′ used at the moment—into the axial working position A k  for the scanner drum  1  having a small diameter in the illustrated example—and is fixed thereat. 
     The scanner object  14  is mounted on an objective holder  30  that is displaced with an actuating drive not shown with guides  31  onto one of the two radial working positions B k  or B g , corresponding to the diameter of the scanner drum  1 ,  1 ′ employed at the moment—into the radial working position A k  for the scanner drum  1  having a small diameter in the illustrated example—and is fixed thereat. 
     FIG. 3 shows the positioning of the light conductor  7  and of the scanner objective  14  given employment of a scanner drum  1 ′ having a large diameter. In this case, the exit face  8  of the light conductor  7  is displaced into the axial working position A g , and the objective holder  30  with the scanner objective  14  is displaced into the radial working position B g . 
     It can be seen from FIGS. 2 and 3 that an optimum size of the illumination spot  12  and an optimum focusing of the scan light  13  onto the scanner element  15  are respectively achieved in an advantageous way given different diameters of the scanner drums  1 ,  1 ′. 
     FIG. 4 shows an exemplary embodiment of the scanner element  15  with a reflected light illumination  34  for scanning opaque masters  5 ′, as well as the positioning of the reflected light illumination  34  given employment of a scanner drum  1  having a small diameter, whereas the positioning given employment of a scanner drum  1 ′ with a large diameter is shown in FIG.  5 . 
     By displacing the scanner objective  14  for the purpose of adaptation to scanner drums  1 ,  1 ′ having different diameters according to FIGS. 2 and 3, the focal intercept of the scanner objective  14  changes because the scanner diaphragm  16  is stationary in the scanner element  15 . For this reason, the reflected light illumination  34  when scanning opaque masters  5 ′ must be readjusted in adaptation to different diameters of the scanner drums  1 ,  1 ′ such that the reflected light illumination is also optimum given an optimum sharpness setting of the scanner objective  14 . 
     The objective holder  30  is essentially composed of an objective carrier  35  carrying the scanner objective  14  that slides on the guides  31 , and of an illumination carrier  36  carrying the reflected light illumination  34 . The illumination carrier  36  is connected to the objective carrier  35  via resilient parallel guides  37 ,  38 . Objective carrier  35  and illumination carrier  36  are displaceable in common with the guides  31  in radial direction relative to the respective scanner drum  1 ,  1 ′ onto the predetermined, radial working positions B k  and B g . The common displacement of the objective carrier  35  and illumination carrier  36  occurs with a traction spindle  39  attaching at the objective carrier  35  that is driven by the actuating drive  32 . The traction spindle  39  is surrounded by a coil spring  40  whose ends are supported at the objective carrier  35  and at the actuating drive  32 . 
     With the parallel guides  37 ,  38 , the illumination carrier  36  can implement a parallel motion with reference to the objective carrier  35  into two stable limit positions. The parallel motion is limited by two adjustable detents  41 ,  42  at the objective carrier  35  in the region of the optical axis  15 ′ of the scanner objective  14 , whereby the spacing of the detents  41 ,  42  on the optical axis  15 ′ corresponds to the deriving change in focal intercept of the scanner objective  14  given employment of a scanner drum  1  having a small diameter FIG. 4 and a scanner drum  1 ′ having a large diameter FIG.  5 . 
     The play of forces between the coil spring  40  and a leaf spring  44 , which is secured to the objective carrier  35  and presses against the illumination carrier  36  in the direction of the coil spring  40 , defines—dependent on the respectively assumed, radial working position B k  and B g —which of the limit positions defined by the detents  41 ,  42  the illumination carrier  36  assumes given its parallel motion. 
     In the radial working position B k  shown in FIG. 4 that the scanner objective  14  assumes given a scanner drum  1  having a small diameter, the coil spring  40  is relaxed and the force of the leaf spring  44  is greater than the force of the coil spring  40 . In this case, the illumination carrier  36  is pressed with the differential force into the limit position defined by the detent  42 . 
     The scanner objective  14  and the reflected light illumination  34  are adjusted relative to one another such that, in the limit position of the illumination carrier  36  defined by the detent  42 , the optical axis  15 ′ of the scanner objective  14  and the optical axis  45  of the reflected light illumination  34  intersect on the master  5  to be scanned in the focal intercept distance of the scanner objective  14 , as a result whereof the sharpness and illumination optimum is achieved in the intersection of the optical axes  15 ′,  45  given a scanner drum  1  having a small diameter. 
     In the radial working position B g  shown in FIG. 5 that the scanner objective  14  assumes given a scanner drum  1 ′ with a large diameter, the coil spring  40  is tensed and the force of the leaf spring  44  is lower than the force of the coil spring  40 . In this case, the illumination carrier  36  is pressed with the differential force into the limit position defined by the detent  41 . 
     In the limit position defined by the detent  41 , the intersection of the optical axis  45  of the reflected light illumination  34  with the optical axis  15 ′ of the scanner objective  14  is automatically shifted by the focal intercept change of the scanner objective  14  deriving given sharp focus onto the scanner drum  1 ′ having a large diameter, so that the sharpness and illumination optimum is also advantageously automatically achieved given employment of a scanner drum  1 ′ with a large diameter. 
     Although various minor modifications might be suggested by those skilled in the art, it should be understood that our wish to embody within the scope of the patent warranted hereon all such modifications as reasonably and properly come with the scope of our contribution to the art.