Abstract:
A device for producing a printing form includes a printing form carrier, a holder and an imaging head fixed to the holder. The imaging head has at least one radiation source and is positionable along a printing form blank for directing radiation onto the printing form blank for producing printing ink-accepting image points in accordance with an image. A tempering or temperature control configuration is provided for the holder.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to a device for producing a printing form, including a printing form carrier having an imaging head, and a holder to which the imaging head is fixed. The imaging head has at least one radiation source and is positionable along a printing form blank for directing radiation onto the printing form blank to produce printing ink-accepting image points in accordance with an image.  
           [0003]    Heretofore-known devices for producing a printing form employ an imaging or imagesetting head with a radiation source, in particular with a laser diode array. The radiation source is controlled in accordance with an image. When a laser is activated, an image point or a non-image point is produced on a printing form blank coated with a light-sensitive material. The printing form blank, in the form of a plate, film or sleeve, is accommodated on a cylinder or is disposed on a flat support table. The imaging head is moved relative to the printing form blank in order to be able to cover the entire surface of a printing form blank.  
           [0004]    In order to increase productivity, it has become known heretofore to use a plurality of imaging heads in parallel. For that purpose, the imaging heads are mounted on a common holder and are positioned relative to the printing form blank together in a linear guide, for example on a carriage. During the operation of imaging heads equipped with laser diode arrays, heat is produced, which has to be dissipated by a cooling device. Optically imaging elements having properties which are highly temperature-dependent serve for producing image points and non-image points, respectively. In order to ensure that the image points or non-image points are placed accurately on the printing form blank in the micron range, it is necessary to temper or control the temperature of the optoelectrical subassemblies. Usually, a streaming or flowing tempering medium, which is fed by suitable lines to the imaging heads, is provided for that purpose. The temperature of the tempering or temperature control medium is regulated or controlled in such a manner that the desired temperature is provided on the optoelectronic subassemblies. An interfering variable which appears during the control or regulation of the temperature is the ambient temperature of the imaging or imagesetting head. In particular, if devices for producing printing forms are integrated into printing presses, severe fluctuations of the ambient temperatures occur, which can only be inadequately compensated for. The ambient temperature fluctuations additionally effect longitudinal expansions in a holder for a plurality of imaging heads, so that impermissible changes occur in the spacing or distance of the optoelectronic subassemblies from one another, resulting in the occurrence of image errors during imaging or imagesetting.  
           [0005]    In order to stabilize the printing process, it has become known heretofore to set up printing presses or printing devices in air-conditioned rooms. Furthermore, it has become known heretofore to encapsulate printing presses with respect to the outside and to maintain a dedicated climate in the interior. Such globally acting tempering or temperature control devices are incapable of satisfying the special requirements in the temperature control of imaging or imagesetting devices, which are required to operate accurately in the micron range.  
           [0006]    In further heretofore-known improvements, temperature-sensitive optoelectronic components are isolated thermally from possible interfering sources. Improved embodiments of that type are complicated and require a large amount of installation space.  
         SUMMARY OF THE INVENTION  
         [0007]    It is accordingly an object of the invention to provide a device for producing a printing form, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known devices of this general type and which permits improved tempering or temperature control of components that can be influenced by temperature.  
           [0008]    With the foregoing and other objects in view, there is provided, in accordance with the invention, a device for producing a printing form, comprising a printing form carrier having an imaging head, and a holder to which the imaging head is fixed. The imaging head has at least one radiation source and is to be positioned along a printing form blank for directing radiation onto the printing form blank to produce printing ink-accepting image points in accordance with an image. A tempering or temperature control configuration is provided for the holder.  
           [0009]    In accordance with another feature of the invention, the printing-form producing device further includes a tempering or temperature control configuration for the imaging head. Both the tempering or temperature control configuration of the holder and the imaging head are provided with a common tempering or temperature control medium.  
           [0010]    In accordance with a further feature of the invention, the tempering or temperature control medium is a liquid. In accordance with an added feature of the invention, the liquid is water. In accordance with an additional feature of the invention, the water has a corrosion-prevention and/or antifreeze additive.  
           [0011]    In accordance with yet another feature of the invention, the holder is formed with at least one respective forward flow and return duct for the water.  
           [0012]    In accordance with yet a further feature of the invention, the imaging head is formed with at least one coolant duct connected to the forward flow and the return duct.  
           [0013]    In accordance with yet an added feature of the invention, the tempering or temperature control configuration includes a control device to which a nominal temperature value is to be fed for controlling the temperature of the imaging head.  
           [0014]    In accordance with a concomitant feature of the invention, the holder is horizontally disposed with at least two ducts for a tempering or temperature control medium disposed therein vertically above one another at the respective top and bottom of the holder. The medium in the respective duct located at the bottom of the holder has a lower temperature than the medium in the respective duct located at the top of the holder.  
           [0015]    Due to the provision of a tempering or temperature control configuration for a holder of one or more imaging heads, it thus becomes possible to control the temperature of the surroundings of an imaging head over a large space. Furthermore, it is possible to deform the holder, such as a crossmember, specifically for compensating for impermissible bending. The temperature gradient between an imaging head and the surroundings thereof is reduced considerably, so that the control of the temperature of an imaging head and the optoelectronic components contained therein can be carried out more quickly, more accurately and with less use of a temperature control medium than has been necessary heretofore. If only one circuit for a temperature control medium, such as water, is provided, flow can take place during forward flow and during return flow both through the holder and the components of an imaging head. Temperature-induced expansions and tolerances on the imagesetting head, on the holder and on a positioning system for an imaging head are reduced to a minimum. Virtually all imaging heads are always operated at a constant temperature, assisted by a housing which is encapsulated with respect to the outside.  
           [0016]    In the case of systems with spindle positioning of the imaging heads, virtually no temperature-induced longitudinal change takes place, so that the positioning accuracy of an imaging head is improved. A constant operating temperature of an imaging head also improves the dissipation of heat from electronic components within an imaging head.  
           [0017]    In the case of systems wherein a plurality of imaging heads are held jointly on a carriage, the distances between the imaging heads do not change. Consequently, no so-called line connection errors are produced in the printed image between two lines which are produced by different imaging heads.  
           [0018]    Tempering or controlling the temperature of the holder of imaging heads achieves the result of reducing the expenditure for lines for the tempering or temperature control of components within an imaging head. The ducts for circulation of a tempering or temperature control medium in the holder can serve simultaneously as forward flow and return lines for tempering or controlling the temperature of one or more imaging heads. The holder itself represents a heat storage device which does not permit any rapid temperature fluctuations. As a result, the tempering or temperature control becomes more independent of fluctuations which are caused by a tempering or temperature control unit itself or by other interfering sources in the surroundings.  
           [0019]    The tempering or temperature control medium provided for the holder can advantageously be water, preferably with a corrosion-prevention and/or antifreeze additive.  
           [0020]    Other features which are considered as characteristic for the invention are set forth in the appended claims.  
           [0021]    Although the invention is illustrated and described herein as embodied in a device 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.  
           [0022]    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  
       [0023]    [0023]FIG. 1 is a diagrammatic perspective view of a temperature control system for a device for producing a printing form in accordance with the invention;  
         [0024]    [0024]FIG. 2 is a side-elevational view of a crossmember formed of an aluminum extruded section;  
         [0025]    [0025]FIG. 2A is a cross-sectional view of FIG. 2, taken along a line IIA-IIA thereof, in the direction of the arrows;  
         [0026]    [0026]FIG. 3 is a side-elevational view of a crossmember formed of gray cast iron;  
         [0027]    [0027]FIG. 3A is a cross-sectional view of FIG. 3, taken along a line IIIA-IIIA thereof, in the direction of the arrows; and  
         [0028]    [0028]FIGS. 4 and 5 are side-elevational views of crossmembers having compensation for bending of a crossmember. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]    Referring now to the figures of the drawings in detail and first, particularly, to FIG. 1 thereof, there is seen a carriage or holder  1  whereon two imaging or imagesetting heads  2  and  3  are held at a fixed spaced distance a from one another. The carriage or holder  1  runs in a linear guide between two side walls of a printing press. The carriage  1  is coupled to a nut  4  of a spindle drive. The spindle drive has a spindle  5  which is connected to a stepping motor  6 . The stepping motor  6  and the spindle drive serve for positioning the carriage  1  in a lateral direction represented by an arrow  7  between the side walls of the printing press. The direction represented by the arrow  7  extends parallel to the axis of rotation of a printing form cylinder or carrier  8  which is mounted in the non-illustrated side walls of the printing press. A printing form blank  9  is clamped onto the circumferential surface of the printing form cylinder or carrier  8 . Each imaging or imagesetting head  2 ,  3  has a respective laser diode array  10 ,  11 , electronic components for power supply and control of the lasers, and optoelectric components for focusing respective laser beams  12  and  13  onto the surface of the printing form blank  9 . As the printing form cylinder  8  rotates in the direction of an arrow  14 , driven by a motor  60 , the laser diode arrays  10  and  11  are controlled in accordance with an image. In this regard, image points which accept printing ink are produced in tracks  15  and  16  on the printing form blank  9 .  
         [0030]    During imaging or imagesetting, heat is produced in the imaging or imagesetting heads  2  and  3  and is dissipated by a water cooling system. The water cooling system includes a water treatment or preparation device  17 , flow lines  18  and  19 , return lines  20  to  23  and a flow duct  24  and return ducts  25  and  26  within the carriage  1 . The carriage  1  is implemented as a metallic extruded section or as a casting. The ducts  24  to  26  have end covers with connections for the flow and return lines  18  to  23 . The cooling water is brought to a predetermined temperature in the water treatment device  17  and fed to the imaging heads  2  and  3  via the flow line  18 , the flow duct  24  and the flow line  19 . In the imaging heads  2  and  3 , the cooling water flows through a respective heat exchanger to which the heat surrendering components are thermally coupled. In this regard, the water is heated and flows back to the water treatment device  17  via the return lines  22  and  23 , the return ducts  25  and  26  and the return lines  20  and  21 , respectively.  
         [0031]    Due to the fact that the cooling water flows through the ducts  24  to  26  both during forward flow and during return flow, the carriage  1  assumes the temperature of the cooling water. The carriage  1  is a large-area component, so that the surroundings approximately assume the temperature of the carriage  1  by heat exchange. Therefore, the temperature of the imaging heads  2  and  3  is pre-controlled by the carriage  1 . The temperature gradient between a respective imaging head  2 ,  3  and the carriage  1  is small, so that the tempering or regulation of the temperature of the imaging heads  2  and  3  is improved. The carriage  1  itself and the spindle  5  influenced by the temperature of the carriage  1  have a low thermal expansion due to the tempering or temperature control, so that no disruptive positioning errors of the imaging heads  2  and  3  in the lateral direction represented by the arrow  7  occur. Leading the lines to the water treatment device  17  and the imaging heads  2  and  3  is simplified by providing the ducts  24  to  26 . In order to regulate the cooling water temperature, a control device  51  can be provided, which is connected to the water treatment device  17 . Furthermore, respective temperature sensors  52 ,  53  and  54  can be provided on the imaging heads  2  and  3  and on the carriage  1 , and can be connected to the control device  51 .  
         [0032]    [0032]FIGS. 2, 2A,  3 ,  3 A and  4  show different embodiments of crossmembers or traverses according to the invention. Ducts disposed vertically above one another are provided for cooling water, in order to additionally compensate for the deflection of a respective crossmember.  
         [0033]    [0033]FIGS. 2 and 2A illustrate a crossmember or holder  27  which is formed of an aluminum extruded section. The crossmember  27  is held on a fixed bearing  28  and a sliding bearing  29 . The crossmember  27  has a longitudinal guide  30  for a carriage  31  with an imaging or imagesetting head  32 . The carriage  31  is reciprocatingly positionable in the direction of arrows  33  and  34  during imaging. As is shown in FIG. 2A, which is a cross-sectional view of FIG. 2 taken along a line IIA-IIA, the crossmember  27  is formed with rectangular ducts  35  to  40  which are closed by end plates and through which, to some extent, tempered or temperature-controlled water  41 ,  42  flows.  
         [0034]    [0034]FIGS. 3 and 3A show a crossmember or holder  43  of gray cast iron formed with circular bores  44  to  47 , as is shown in the cross-sectional view of FIG. 3A taken along a line IIIA-IIIA of FIG. 3. The circular bores  44  to  47  are closed by end plates.  
         [0035]    The crossmembers  27  and  43 , the carriages  31  and the imaging heads  32  have a weight which would cause deflection of the crossmembers  27  and  43 . Furthermore, forces and moments which can cause deflection act upon a respective crossmember  27 ,  43 . In order to compensate for a deflection, the temperature of the water  41  in the upper ducts  35  and  36  or bores  44  and  45  located at the top of the respective crossmembers  27  and  43  can be set to be higher than the water  42  in the lower ducts  37  and  38  or bores  46  and  47 . Without any weight forces, an opposite deformation, illustrated by a broken line in FIG. 4, would result in the crossmember  27  or  43 . The opposite deformation is based upon different longitudinal expansions of the material of the respective crossmember  27 ,  43  in the regions above and below a neutral longitudinal center line. When the respective crossmember  27 ,  43  is loaded with usual weights  50 , forces and moments, the respective crossmember  27 ,  43  will be directed or aligned rectilinearly, as is shown in FIG. 5. It is therefore possible to use crossmembers  27  and  43  which have a low flexural rigidity, resulting in a conservation of weight and material.  
         [0036]    The tempering or temperature control of the crossmember  27 ,  43  can be coupled to the tempering or temperature control of a respective carriage  1  and  31 . Therefore, cooling water flows through the respective crossmember  27 ,  43 , the respective carriage  1 ,  31  and the respective imaging or imagesetting heads  2 ,  3 ,  32 .