Abstract:
An apparatus for producing a printing form which, with little expenditure, permits exact beam alignment and positioning. The apparatus for producing the printing form contains a holder for at least one printing form blank, and at least one imaging module, which can be moved relative to the printing form blank and which contains at least one radiation source which, in order to produce image elements that accept printing ink, is aimed at the surface of the printing form blank and whose beam direction can be adjusted. The imaging module being accommodated in a six-point mounting in three bearing locations, each bearing location containing a spherical element and an associated bearing element and in each case the spherical element rests on it and, in order to adjust the beam direction, at least one element of one bearing location being disposed adjustably.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    Field of the Invention  
           [0002]    The invention relates to an apparatus for producing a printing form. The apparatus contains a holder for at least one printing form and at least one imaging module which can be moved relative to the printing form blank and which contains at least one radiation source. The radiation source, in order to produce image elements that accept printing ink, is aimed at a surface of the printing form blank and whose beam direction can be adjusted.  
           [0003]    In order to produce the printing form, use is made of radiation sources, in particular lasers, whose beams are aimed at a radiation-sensitive layer on the printing form blank. When the radiation source is activated, an image point is produced or, in the negative process, a non-image point. The printing form blank can be fixed to a flat substrate, to the surface of a printing form cylinder or to the inner side of a hollow cylinder. In order to be able to cover the entire surface of the printing form blank, the radiation sources and the printing form blank are positioned relative to one another. In order to increase productivity, a plurality of radiation sources are used simultaneously.  
           [0004]    In an apparatus shown in U.S. Pat. No. 5,717,451, four imaging heads are used, each of which contains a laser diode array. The imaging heads, together with the laser diode arrays, can in each case be positioned independently of one another in linear guides in a direction parallel to the axis of rotation of a printing form cylinder by a slide. While the printing form cylinder rotates, the imaging heads are positioned in the lateral direction, it being possible for a strip to be imaged by each imaging head. In order to avoid imaging errors, in particular connecting errors between two strips, the imaging heads are aligned exactly before imaging. In order to align the imaging heads, these are moved into a calibration position and the laser diodes are activated. The locations of the laser beams on a calibration surface are registered by a detector. If the beam direction of a laser diode array deviates from a predefined value, the relevant imaging head is pivoted in such a way that the deviations are corrected. Following pivoting, the position of an imaging head on a slide is fixed. The adjustment of the beam direction and the fixing of the imaging head have to be carried out accurately to a few microns and reproducibly. In order to implement this, extremely fine precision mechanical adjustments and highly accurate mountings are known. In an imaging configuration according to U.S. Pat. No. 5,367,323, the mount of a deflection mirror is mounted in an articulated manner by a sphere and tilted to a certain extent by two adjusting screws. Each adjusting screw has the effect of tilting about one axis in each case, the axes being at right angles to one another. U.S. Pat. No. 5,331,343 shows an imaging apparatus in which a lens configuration is accommodated in a v-shaped groove such that it can be rotated and displaced in the direction of the groove.  
         SUMMARY OF THE INVENTION  
         [0005]    It is accordingly an object of the invention to provide an apparatus for producing a printing form that overcomes the above-mentioned disadvantages of the prior art devices of this general type, which, with little expenditure, permits exact beam alignment and positioning.  
           [0006]    With the foregoing and other objects in view there is provided, in accordance with the invention, an apparatus for producing a printing form. The apparatus contains a holder for at least one printing form blank and at least one imaging module disposed movable relative to the printing form blank. The imaging module has at least one radiation source for producing image elements that accept printing ink. The radiation source is disposed aimed at a surface of the printing form blank and has an adjustable beam direction. A six-point mounting having three bearing locations accommodates the imaging module. The bearing locations have elements including spherical elements and bearing elements. The spherical elements rest on the bearing elements with one to three points, and for adjusting the beam direction, at least one of the elements of one of the bearing locations is disposed adjustably and defines an adjustable element.  
           [0007]    The invention permits extremely fine adjustment of the point of incidence of write beams on a printing form blank. In the case of the simultaneous use of a plurality of radiation sources, it is ensured that no offset errors between the lines of adjacent write lines are produced. The setting of the point of incidence on the printing form blank is carried out once during a calibration operation during assembly. When a radiation source is replaced, only slight readjustment is necessary. The radiation sources are in each case mounted at three bearing locations on a total of six points. The bearing parts consist of hard materials, so that material deformations have no influence on the accuracy of the mount. It is advantageous if the bearing forces for an imaging module are introduced in such a way that the magnitudes of the force vectors acting on the six bearing points are virtually identical. The forces applied during fixing of an imaging module are accurately defined.  
           [0008]    In accordance with an added feature of the invention, the bearing locations lie at corners of an isosceles triangle, in particular an equilateral triangle. The bearing locations lie in a plane located at right angles to the surface of the printing form blank, and one corner of the isosceles triangle faces the surface. Preferably, the bearing elements each contain two parallel cylindrical rollers. Alternatively, the bearing elements are prismatic shaped, in particular V-shaped.  
           [0009]    In accordance with an additional feature of the invention, the bearing elements are fixed to the imaging module, and one of the spherical elements is displaceable.  
           [0010]    In accordance with another feature of the invention, the spherical elements are fixed to the imaging module, and one of the bearing elements is displaceable.  
           [0011]    In accordance with a further feature of the invention, the bearing elements have a common point of intersection. From the common point of intersection, the bearing elements exhibit an angle of 120 degrees to each other.  
           [0012]    In accordance with another further feature of the invention, the adjustable element of one of the bearing locations faces the surface of the printing form blank and can be moved in a direction parallel to the surface.  
           [0013]    In accordance with another added feature of the invention, the imaging module rests in the bearing locations by a spring force provided by a spring. The spring is connected between the imaging module and the bearing locations, the imaging module resting in the bearing locations by the spring force.  
           [0014]    In accordance with a concomitant feature of the invention, a common slide is provided and the imaging module is one of a plurality of imaging modules disposed adjustably on the common slide. One of the spherical elements and the bearing elements is disposed on the common slide, and it being possible for the common slide to be positioned parallel to an axis of rotation of the holder carrying the printing form blank. The imaging modules are preferably disposed at equal intervals along the common slide, and the holder is preferably a printing form cylinder.  
           [0015]    Other features which are considered as characteristic for the invention are set forth in the appended claims.  
           [0016]    Although the invention is illustrated and described herein as embodied in an apparatus for producing a printing form, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.  
           [0017]    The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0018]    [0018]FIG. 1 is a diagrammatic, plan view of an apparatus for producing a printing form according to the invention;  
         [0019]    [0019]FIG. 2 is a sectional view of a detail of the apparatus taken along the line II-II shown in FIG. 1;  
         [0020]    [0020]FIG. 3 is a schematic drawing of an apparatus for imaging with laser diodes;  
         [0021]    [0021]FIG. 4 is a sectional view of a bearing location containing two cylinders and a sphere;  
         [0022]    [0022]FIG. 5 is a plan view of a detail of the bearing location according to FIG. 4;  
         [0023]    [0023]FIG. 6 is a perspective view of a six-point mounting with three prisms;  
         [0024]    [0024]FIG. 7 is a schematic drawing of a mounting for a laser module;  
         [0025]    [0025]FIG. 8 is a perspective view of the six-point mounting with one corner, one prism and a surface; and  
         [0026]    [0026]FIG. 9 is a schematic drawing relating to the adjustment of the six-point mounting according to FIG. 8. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]    Referring now to the figures of the drawing in detail and first, particularly, to FIGS. 1 and 2 thereof, there is shown a schematic drawing relating to the production of a printing form. Between two sidewalls  1 ,  2  connected firmly to each other, a printing form cylinder  3  is rotatably mounted with its axle journals  4 ,  5  in bearings  6 ,  7 . The axle journals  4  and  5  are coupled to a motor  8  and a rotary encoder  9 . The printing form cylinder  3  bears a printing form blank  10 . The sidewalls  1 ,  2  are connected by a cross-member  11 , on which there are guide tracks  12 ,  13  for a slide  14 . The slide  14  is mounted in the guide tracks  12 ,  13  by eight ball bearings  15 - 22  such that it can be displaced. The guide tracks  12 ,  13  lie parallel to an axis of rotation  23  of the printing form cylinder  3 . The slide  14  has a U-shaped cross section, between whose limbs a screw drive is accommodated. The screw drive contains a threaded spindle  24 , which is held in bearings  25 ,  26  in the sidewalls  1 ,  2 . The ends of the threaded spindle  24  are coupled to a motor  27  and a rotary encoder  28 . Seated on the threaded spindle  24  is a nut  29 , which is coupled to the slide  14 . Fixed to the slide  14  are four laser modules  30 - 33 , which are each seated on three bearing locations  34 - 45 . The bearing locations  34 - 45  lie in a plane that runs parallel to the axis of rotation  23 . In the plan view according to FIG. 1, the bearing locations  34 - 45  of each laser module  30 - 33  form an isosceles triangle, the bearing locations  34 ,  35 ;  37 ,  38 ;  40 ,  41  and  43 ,  44  lying on the base of the respective triangle lying parallel to the axis of rotation  23 . The bearing locations  36 ,  39 ,  42  and  45  located at the point of intersection of the equally long limbs face the printing form blank  10 . The laser modules  30 - 33  are held in the bearing locations  34 - 45  by springs  46  (FIG. 2). The points of action  47 - 50  of the springs  46  on the respective laser module  30 - 33  lie centrally in the isosceles triangle that in each case is formed by the bearing locations  34 - 45 . As shown in more detail in FIG. 2, the springs  46  are tension springs, which are in each case anchored on the laser module  30 - 33  and on the slide  14  and which pull the laser modules  30 - 33  against the slide  14  in each case with a force F F . In each laser module  30 - 33  there is a radiation source  51  with at least one laser, an optical system  52  for beam shaping and beam deflection and a protective lens  53 . The beam direction  54  of a beam leaving a laser module  30 - 33  intersects the axis of rotation  23 , apart from slight deviations.  
         [0028]    [0028]FIG. 3 shows a configuration of the radiation source  51  having a laser diode array  55 . The laser diode array  55  contains a bar  56  on which a large number of individually driveable laser diodes  57  are disposed. The laser diodes  57  are at equal intervals and lie on a line that is parallel to the axis of rotation  23 . The laser diodes  57  are connected to a control device  58 . When the laser diode  57  is activated by the control device  58 , a laser beam  59  is emitted, which is focused onto a surface of the printing form blank  10  by the optical system  52  and produces an image point  60  that accepts printing ink on the surface. The beam directions of the laser beams  59  are all parallel.  
         [0029]    During the assembly of the apparatus for producing a printing form, and in the event of replacement of a defective laser module  30 - 33 , it must be ensured that the distances a between two image points  60  produced by different laser modules  30 - 33  correspond to a predefined value in the y direction. If, during test imaging, the result is that there are deviations from a predefined value, then readjustment of at least one laser module  30 - 33  is necessary, for which purpose the laser modules  30 - 33  are disposed such that they can be adjusted. In order to adjust the laser modules  30 - 33  on the slide  14 , adjusting screws  61 - 64  in holding blocks  65 - 68  are provided (FIG. 1). The adjusting screws  61 - 64  engage without play on a bearing element of one of the bearing locations  36 ,  39 ,  42 ,  50  in each case which faces the printing form blank  10 . When an actuating screw  61 - 64  is operated, the corresponding bearing element on the laser module  30 - 33  is carried along, so that the laser module  30 - 33  completes a rotation about the z-axis. The beam direction  54  can therefore be adjusted over an angular range a, which lies in the x-y plane.  
         [0030]    Each of the bearing locations  34 - 35  contains two bearing elements, which are each assigned to the slide  14  and the laser module  30 - 33 . In the exemplary embodiment in FIGS. 1 and 2, spheres  69  and cylindrical rollers  70 ,  71  are provided as bearing elements. The spheres  69  are embedded with an adhesive  72  in the slide  14  or in a component connected to the slide  14 . The cylindrical rollers  70 ,  71  are embedded with an adhesive  73  in a parallel groove  74  such that their axes  75 ,  76  are parallel. The axes  75 ,  76  lie in a plane at right angles to the z-axis. The lines of symmetry of the axes  75 ,  76  intersect at the center of the circumcircle of the triangle that is formed by the three bearing locations  34 - 45  of a laser module  30 - 33 . At each bearing location  34 - 45 , a laser module  30 - 33  rests on two points of contact  77 ,  78  on the sphere  69 . Therefore, each laser module  30 - 33  is mounted on six points of contact  77 ,  78 . If, by using an adjusting screw  61 - 64 , a laser module  30 - 33  is rotated about the z-axis, then the contact between the spheres  69  and the cylindrical rollers  70 ,  71  is maintained while maintaining the force F F  of the spring  46 . The points of contact  77 ,  78  move slightly on the surface of the spheres  69 . The point of incidence of the laser beam  59  on the surface of the printing form blank  10  is corrected in the y-direction. Since the laser module  30 - 33  does not carry out a pure rotation about the z-axis, the position of the point of incidence also changes in the z and x directions, but this can readily be corrected by controlling the time of activation of the laser diode  57  and by a focusing configuration in the laser beam path.  
         [0031]    A further variant of a six-point mounting for a laser module is illustrated in a perspective illustration in FIG. 6. Use is made of spheres  79 - 81 , which are fixed to a laser module in a plane  82 . The spheres  79 - 81  are mounted in three v-shaped prisms  83 - 85  with the force F F  of a spring. The result is six points of contact  86 - 91 . If, as shown in detail in FIG. 7, one of the prisms  83 - 85  is disposed such that it can be displaced, rotation of a laser module  92 ,  93  can be achieved.  
         [0032]    [0032]FIG. 7 shows in schematic form two laser modules  92 ,  93  having six spheres  94 - 99 , which are seated on six prisms  83 - 85 ,  100 - 102 . The spheres  94 - 99  and the prisms  83 - 85 ;  100 - 102  form bearing locations at the corners of equilateral triangles, an adjustable bearing location facing the surface of a printing form  103 . On the laser module  92 , it is demonstrated how a displacement of the prism  83  acts in the y-direction. If, for example by an adjusting screw  104 , the sphere  94  is displaced in the y-direction by an amount Δa, then the points of contact  105 ,  106  on the prism  83  are substantially likewise offset in the y-direction. The point of contact  107 - 110  and the force introduction point  111  experience an offset both in the y and in the x-direction. The shifted position of the laser module  92  is illustrated dashed. As a result of the force acting at the force introduction point  111 , the contact between the laser module  92  and the prisms  83 - 85 ,  100 - 102  connected to a slide at the points of contact  105 - 110  is maintained. Following the adjustment of the laser module  92 , the point of incidence  112  has the predefined distance a from the point of incidence  113  of the adjacent laser module  93 .  
         [0033]    [0033]FIG. 8 shows a further variant of the six-point mounting. A corner  114 , a prism  115  and a supporting plane  116  are formed on a non-illustrated slide. Fixed to a laser module  117  are three spheres  118 - 120 , which rest with three points of contact  121 - 123  on the corner  114 , with two points of contact  124 - 125  on the prism  115 , and with one point of contact  126  on the supporting plane  116 . The laser module  117  is acted on by clamping forces F 1 -F 3  such that when the corner  114  is displaced in the direction y, the contact at the six points of contact  121 - 126  is always maintained. The clamping force F 3  running in the direction of the corner  114  is in this case chosen to be greater than the clamping force F 2  in the direction of the prism  115 . The clamping force F 2  in the direction of the prism  115  is greater than the clamping force F 1  in the direction at right angles to the supporting plane  116 .  
         [0034]    [0034]FIG. 9 shows the adjustment of the laser module  117  by the six-point mounting according to FIG. 8. The corner  114  is disposed in such a way that two walls  127 ,  128  standing in the z-direction form an acute angle, which points in the direction of the surface of a printing form blank  129 . The base of the corner  114  lies in a plane with a side surface of the prism  115  and the supporting plane  116 . The corner  114  is disposed on a slide such that it can be displaced in the y-direction. When the corner  114  is displaced by a small amount Δa, the result is the position of the laser module  11  illustrated by dots. The point of incidence  130  of a laser diode is likewise displaced in the y-direction, so that the result is a new point of incidence  131 . While the points of contact  121 - 123  are displaced substantially in the y-direction, the points of contact  124 - 126  are given displacement components in the x and y directions.  
         [0035]    The invention is not limited to the exemplary embodiment illustrated. For example, the radiation source can be provided once or many times. Individual radiant sources or a large number of radiant sources may be present in a radiation source, and experience common adjustment. In addition to lasers, LEDs or other radiant sources can also be used which have the capacity of setting an image point or a non-image point on a printing form blank. The printing form blank can be clamped on a printing form cylinder or formed in the manner of a sleeve. The positive or negative imaging can likewise take place on the surface of a suitable printing form cylinder. The invention can likewise be used in flat bed exposers and internal drum exposers. The apparatus according to the invention can be integrated in printing presses. The rotation of the spindle  24  and of the printing form cylinder  3  by the motors  8 ,  27 , the processing of the rotary encoder signals and the driving of the laser diodes  57  can be controlled in a synchronized manner by the common control device  58 . It is possible to register the position of the laser modules  30 - 33  by measurement and to carry out the adjustment automatically by actuating motors. In this case, the position of the laser modules  30 - 33  can be readjusted continuously if deviations occur during imaging operation.