EP0805021A2 - Process for the regulation of the temperature within a device for the inscription of printing plates using a laser radiation particularly for an offset printing machine - Google Patents

Abstract

The method involves operating a heat source (18) placed close to the laser light source (10) so that the temp. of the light source, which is switched on and off according to the image to be reproduced, is held as constant as possible. The heat generated by the heat source per time unit is increased when the light source is off and is reduced when the light source is on. The heat generated by the heat source per time unit essentially corresp. to that generated by the light source.

Description

The invention relates to a method and a device for regulating the temperature in a printing plate labeling unit working with laser light, in particular an offset printing machine, according to the preamble of claims 1 and 8.

For the labeling of printing plates that are used in printing presses, in addition to the conventional method of exposure using films, digitally working labeling units are now being used, to which the image information is supplied in the form of digital bit patterns generated in the prepress stage, which are supplied by the labeling units are transferred to the printing plate. For this purpose, the labeling units have a light source, the light of which is focused by an optical lens system on the respective location on the printing plate and which is switched on or off depending on whether an image point is to be generated on the printing plate at the corresponding location.

From US 5,351,617 a labeling unit working with laser light for the printing plate provided with a special coating and clamped onto the printing plate cylinder of an offset printing press is known, in which the laser light is generated by a laser diode unit and then via an optical fiber cable an optical arranged near the printing plate cylinder Focusing unit is supplied, which is moved by motor parallel to the longitudinal axis of the printing plate cylinder over the surface of the printing plate cylinder and which focuses the laser light on the corresponding locations on the printing plate. By rotating the printing plate cylinder accordingly, the printing plate clamped on the cylinder is imaged over its entire surface.

No. 5,351,617 furthermore shows a device in which a plurality of optical focusing units, which are connected to corresponding laser light sources via optical fiber cables, are moved over a flat printing plate and expose it at the corresponding points.

In the described labeling or imaging units working with laser diodes, the problem arises that the intensity of the laser light is influenced to a large extent by the temperature of the respective laser light source, in this case a laser diode. Because of the known exponential dependence of the intensity of the generated laser light on the temperature in a laser diode, temperature fluctuations in the range from 0.5 ° to 2 ° C are sufficient to adversely affect the labeling result in such a way that the resulting quality losses in the finished product Print image can be easily perceived by the human eye.

The loss of quality results from the fact that with a fluctuating light intensity of the laser light, which is due to a too low or too high temperature of the respective laser diode, the pixels to be generated on the printing plate vary greatly, so that the printing image generated with the printing plate has errors which lead to the perceptible loss of quality described above.

The temperature fluctuations of the laser diodes are generated when a printing plate is labeled, in particular in that the laser diodes convert a large part of the electrical energy supplied to them into Joule heat in the switched-on state, and in the switched-off state, i.e. in those places where no imaging takes place, no heat is generated by the laser diodes. In practice, this results in high quality losses, in particular in the areas of the printing plate in which only a few pixels are set by the corresponding laser diode unit, since the laser diode unit which has been switched off for a longer period of time cools down and therefore when switched on again, due to the heating of the laser diode necessary time, a lower light intensity generated.

The object of the invention is to provide a method for regulating the temperature in a printing plate labeling unit working with laser light, with which the temperature of the laser light source generating the laser light, in particular a laser diode, can be kept constant to a high degree and with simple means can.

It is also an object of the present invention to provide a device with which the temperature of the laser light source of a printing plate labeling unit, in particular a laser diode, can be kept constant in a simple and efficient and cost-effective manner.

This object is achieved according to the invention by the features of claims 1 and 8.

Further features of the invention are contained in the subclaims.

The invention has the particular advantage that even with labeling units with a larger number of individual laser diode units and associated focusing optics, a high degree of constancy and, in connection therewith, high quality in the generation of the individual pixels on the printing plate can be achieved over the entire image.

Furthermore, the device according to the invention has the advantage that it can be retrofitted in a simple and inexpensive manner to existing printing plate labeling units, both for flat printing plates and for printing plates clamped on a printing plate cylinder.

The invention is described below with reference to the drawings based on preferred embodiments.

Fig. 1

eine schematische Darstellung von zwei an einem Druckplattenzylinder einer Druckmaschine angeordneten Druckplatten-Beschriftungseinheiten mit erfindungsgemäßen Temperaturregelungsvorrichtungen,

Fig. 2

einen elektrischen Schaltplan einer bevorzugten Ausführungsform der erfindungsgemäßen Temperatur-Regelungsvorrichtung,

Fig. 3

einen Verlauf der am Widerstand beziehungsweise an der Laserdiode anliegenden elektrischen Spannung beziehungsweise der vom Widerstand bzw. der Diode abgegebenen Wärmemenge bei einer ersten Ausführungsform der Erfindung, bei der die am Widerstand anliegende Spannung bei Einschalten der Laserdiode auf Null heruntergefahren wird,

Fig. 4

eine weitere Ausführungsform der Erfindung, bei der am Heizelement bei ausgeschalteter Laserdiodeneinheit eine bestimmte Wärmemenge erzeugt wird, die nach Einschalten der Laserdiodeneinheit um eine vorherbestimmten Wert verringert wird.

Show in the drawings

Fig. 1

2 shows a schematic illustration of two printing plate labeling units arranged on a printing plate cylinder of a printing press with temperature control devices according to the invention,

Fig. 2

an electrical circuit diagram of a preferred embodiment of the temperature control device according to the invention,

Fig. 3

a course of the electrical voltage applied to the resistor or to the laser diode or the amount of heat given off by the resistor or the diode in a first embodiment of the invention, in which the voltage applied to the resistor is reduced to zero when the laser diode is switched on,

Fig. 4

a further embodiment of the invention, in which a certain amount of heat is generated on the heating element when the laser diode unit is switched off and is reduced by a predetermined value after the laser diode unit is switched on.

The device 1 shown in FIG. 1 for labeling a printing plate 4 clamped on a printing plate cylinder 2 of a printing press has one or more, for example 16 individual printing plate labeling units 5, of which only two units are shown in FIG. 1 for reasons of illustration technology. In the same way as for labeling a printing plate 4 clamped on a printing press cylinder 2, the labeling units 5 can also be used for labeling flat printing plates. Each of the labeling units 5 comprises focusing optics 6 which are arranged in the vicinity of the printing plate 4 and which are connected to a laser diode unit 10 via an optical light guide 8. The optical focusing optics 6 focus the laser light generated by the laser diode unit 10 onto an image point to be generated on the printing plate 4, where it removes an area corresponding to the image point from the surface layer of the printing plate 4, so that an underlying ink-accepting layer is exposed. The structure and the composition of such a printing plate are known, for example, from US Pat. No. 5,351,617 and are not described further here.

The control of the laser diode unit 10 takes place via a control device 12, which switches the laser diode unit on or off depending on a pixel to be set or not to be set in accordance with a bit pattern generated in the prepress stage.

In the preferred embodiment of the invention shown in FIG. 1, the laser diode units 10 are accommodated in a housing 14 which is fastened on a base or carrier body 16. A heating element 18, which is actuated by the control device 12, is arranged in the vicinity of the laser diode unit 10, preferably inside the housing 14. The heating element 18 is actuated by the control device 12 alternately or in push-pull with the laser diode unit 10 in such a way that when the laser diode unit 10 is switched off, the heating element 18 is actuated and this heats the switched off laser diode unit 10. When turning on the laser diode unit 10, i.e. when the printing plate 4 is labeled with a pixel, the heating element 18 is switched off, so that no heat energy is generated by it during the time in which the laser diode unit 10 is switched on. In the preferred embodiment of the invention, the heating element 18 is formed by an ohmic resistor, which is alternately connected to the high or low electrical voltage in alternation with the laser diode unit 10. In the same way, the heating element 18 can be formed by any other electronic component that generates Joule heat and is connected to a corresponding current and / or voltage source in opposition to the laser diode unit 10. Such a component can be, for example, a transistor, a diode or a so-called Peltier element, etc.

In the same way as in the arrangement of the heating element 18 shown in FIG. 1 in the housing 14 of the laser diode unit 10, the heating element 18 can also be arranged outside the housing 14, for example on this or on the base body 16. In a further embodiment of the invention, it can further be provided that the base body 16 carrying the labeling unit 5 Constantly cooling or heating device 1, for example by virtue of the fact that the base body 16 is hollow on the inside and the interior is flowed through by a corresponding cooling or heat transport medium of the desired temperature, as indicated by the arrows 20, 22. Instead of a base body 16 through which a cooling or heating medium flows, it can also be electrically heated in the same way. As a result, an independent pre-temperature can be imparted independently of the regulation of the temperature by the heating element 18 of the laser diode unit 10 and / or the heating element 18, so that, for example, the operating point is one of several, e.g. B. from 16 printing plate labeling units 5 printing plate labeling device 1, for example depending on the respective ambient temperature for all labeling units 5 can be changed together.

The temperature of the laser diode unit 10 can be regulated by the heating element 18 using, for example, an electronic circuit arrangement 30 shown in FIG. 2. The circuit arrangement 30 has a current and / or voltage source 32, to whose one pole, for example the positive pole, the control device 12 and the heating element 18 and, in parallel, the laser diode unit 10 are connected. The heating element 18 and the laser diode unit 10 are also connected to the second pole of the current and / or voltage source 32 via respectively assigned power transistors 34 and 36. The base of the power transistor 34 of the heating element 18 is preferably connected to the control device 12 via a fixed or adjustable resistor 35. The base of the power transistor 36 of the laser diode unit 10 is preferably connected to the control device 12 via a second fixed or controllable resistor 37 and an inverting Schmitt trigger circuit 38. The control device 12 controls the bases of the Power transistors 34 and 36 in push-pull operation, so that when the laser diode unit 10 is switched off, a current flows through the heating element 18, the size of which can be set accordingly via the resistor 35 for the respective heating element 18 of a printing plate labeling unit 5. Due to the inverting Schmitt trigger 38, the signal present at the base of the power transistor 36 of the laser diode unit 10 is inverted, so that the power transistor 36 blocks and the laser diode unit 10 remains switched off. To switch on the laser diode unit 10, a signal of reversed polarity is generated by the control device 12 and, accordingly, the power transistor 34 of the heating element 18 is blocked and the power transistor 36 is switched on due to the inverting effect of the Schmitt trigger circuit 38, so that a current flows through the laser diode unit 10, whose size is adjustable via the resistor 37. The control device 12 generates the signals as a function of a pixel to be set on the printing plate 4.

The course of the voltage U _R applied to the heating element 18 and the voltage U _LD applied to the laser diode unit 10 at the same time are shown in idealized form in FIG. 3. As can be seen from FIG. 3, the heating element 18 is connected to the voltage source 32 during the preheating phase V or in an equivalent manner to a corresponding current source and emits a certain amount of heat Q _R , the size of which is preferably regulated in this way via the adjustable resistor 35 becomes that the temperature of the laser diode unit 10 switched off at this time adjusts to a desired working temperature. The voltage U _LD applied to the laser diode unit 10 during the preheating phase V in this embodiment of the invention is preferably 0 volts, so that the amount of heat generated by the laser diode unit 10 per unit of time is also corresponding to 0 J (joules). In the subsequent labeling phase B, the laser diode unit 10 is switched on by applying the voltage U _LD and the heating element 18 is switched off at the same time, that is to say alternately or in opposition to it. In this embodiment of the invention, the amount of heat emitted by the laser diode unit 10 per unit of time Q _LD and the amount of heat emitted by the heating element 18 per unit of time Q _{R are} preferably essentially the same, depending on the arrangement of the heating element 18 or the preheating of the base body 16 or total radiated thermal power, the heat quantity Q _R radiated by the heating element 18 can also be smaller or larger than the heat quantity Q _LD radiated by the laser diode unit 10. The amounts of heat can be adjusted, for example, via the adjustable resistors 35, 37 of the circuit arrangement shown in FIG. 2, the adjustment preferably being carried out in such a way that the temperature fluctuations between switching the laser diode unit on and off are as small as possible.

wobei vorzugsweise die Wärmemenge Q_R2 kleiner als die l'ärmemenge Q_LD ist.In a further embodiment of the invention, the heating element 18, as shown in FIG. 4, is supplied with a preferably adjustable basic voltage U _R1 , or a corresponding basic current, even when the laser diode unit 10 is switched on, and emits a first basic heat quantity Q _R1 , which is shown in the upper diagram 4 is shown as a dashed line. When the laser diode unit 10 is switched off, the heating element 18 is connected to a second higher voltage U _R2 , as a result of which it generates the amount of heat Q _R2 per unit of time. The difference between the amounts of heat Q _R1 and Q _R2 emitted by the heating element 18 in this embodiment of the invention is preferably selected such that the temperature fluctuations or the temperature difference of the Laser diode unit 10 between the off and on state is minimal. Preferably, _R1 has the amount of heat generated by the heating element 18 is switched on laser diode unit 10 Q a value whose magnitude of the heat quantity Q _R2 reduced by the difference between the output from the laser diode unit 10, heat quantity Q _LD and the amount of heat Q _R2 corresponds; or expressed in formulas: $${\text{Q}}_{\text{R1}}{\text{= Q}}_{\text{R2}}{\text{- (Q}}_{\text{LD}}{\text{- Q}}_{\text{R2}}\text{),}$$

wherein the amount of heat Q _{R2 is} preferably less than the amount of heat Q _LD .

However, the heat quantities Q _R1, Q _R2 and Q _LD as well as the corresponding voltages U _R1 , U _R2 and U _LD , in particular the difference between Q _R2 and Q _R1 , can also have a different value, depending on the radiation emitted to the environment Amount of heat per unit of time, the thermal conductivity of the individual components, the arrangement and design of the heating element 18, the preheating of the carrier body 16 or housing 14 etc. preferably empirically by adjusting the voltage and / or the current via the adjustable resistors 35, 37 in the manner it is determined that the temperature differences of the laser diode unit 10 become as small as possible.

The switching on of the laser diode unit 10 and the corresponding switching off of the heating element 18 are preferably carried out simultaneously. However, it can also be provided that the periods of time in which the laser diode unit 10 is switched on and the heating element 18 is switched off overlap, so that the heating element 18 z. B. can be turned on a short time before switching off the laser diode unit 10. In the same way, the heating element 18 can then remain switched on for a short period of time beyond the time at which the laser diode unit 10 is switched on.

In a further embodiment of the invention, not shown in the drawings, it can further be provided to provide the base body 16 or the laser diode units 10 and / or their housing with a layer of thermal insulation material, so that fluctuations in the ambient temperature result in less or almost none Have an influence on the temperature of the laser diode units 10.

Reference list

1

Printing plate labeling device

2nd

Printing press cylinder

4th

printing plate

5

Printing plate labeling unit

6

optical focusing device

8th

optical light guide

10th

Laser diode unit

12th

Control device

14

casing

16

Support body

18th

Heating element

20th

arrow

22

arrow

30th

Circuit arrangement

32

Current / voltage source

34

Power transistor for heating element

35

adjustable resistance for heating element

36

Power transistor for laser diode unit

37

adjustable resistance for laser diode unit

38

inverting Schmitt trigger circuit

V

Preheating phase

B

Labeling phase

Claims (13)

Method for regulating the temperature in a printing plate labeling unit of a printing machine, in particular an offset printing machine, which works with laser light, the laser light being generated by a laser diode unit which is switched on and off as a function of the image pattern to be generated on the printing plate,
characterized by
that a heat source arranged in the vicinity of the laser diode unit is operated alternately with the laser diode unit in such a way that the temperature of the laser diode unit is as constant as possible. Method according to claim 1,
characterized by
that the amount of heat given off by the heat source per unit of time is increased when the laser diode unit is switched off and reduced when the laser diode unit is switched on. The method of claim 1 or 2,
characterized by
that the amount of heat given off by the heat source per unit of time essentially corresponds to the amount of heat given off by the laser diode unit per unit of time. The method of claim 1 or 2,
characterized by
that the heat source with a switched on laser diode unit emits a predetermined basic heat quantity per unit time, which is smaller than the heat quantity emitted by the laser diode unit per unit time and that the heat source emits a second larger amount of heat when the laser diode unit is switched off, the first and second amounts of heat being selected in such a way that the temperature difference of the laser diode unit between the on and off state becomes minimal. Method according to claim 4,
characterized by
that the difference between the first and the second amount of heat essentially corresponds to the difference between the amount of heat emitted by the switched-on laser diode unit and the second amount of heat. Method according to one of the preceding claims,
characterized by
that the laser diode unit and / or the heat source are heated or cooled to a predetermined pre-temperature. Method according to one of the preceding claims,
characterized by
that the laser diode units and / or the heat sources are thermally isolated from the environment. Device for regulating the temperature in a printing plate labeling unit of a printing machine, in particular an offset printing machine, which works with laser light, in which the laser light is generated by at least one laser diode unit which is switched on and off as a function of the dot pattern to be generated on the printing plate,
characterized by
that in the vicinity of the laser diode unit (10) an electric heating element (18) is arranged, which alternates with the laser diode unit 10 when switched on Laser diode unit (10) generates a first amount of heat (Q _R1 ) and when the laser diode unit (10) is switched off a second, larger amount of heat (Q _R2 ). Device according to claim 8,
characterized by
that the second amount of heat (Q _R2 ) essentially corresponds to the amount of heat (Q _LD ) generated by laser diode unit (10) and that the first, smaller amount of heat (Q _R1 ) has a value of 0. Device according to claim 8,
characterized by
that the second quantity of heat (Q _R2 ) generated by the heating element (18) when the laser diode units (10) are switched off is of such a size that the temperature of the laser diode unit (10) corresponds to a predetermined target value. Apparatus according to claim 10,
characterized by
that the first amount of heat (Q _R1 ) generated by the heating element (18) when the laser diode unit (10) is switched on has a value, the size of the second amount of heat (Q _R2 ) reduced by the difference from the amount of heat generated by the laser diode unit (10) (Q _LD ) and the second amount of heat (Q _R2 ). Device according to one of claims 8 to 11,
characterized by
that the heating element (18) is formed by a Joule heat-generating electrical component which is connected to an electrical voltage and / or current source (32) in accordance with the amount of heat to be generated. Device according to claim 12,
characterized by
that an electronic push-pull circuit (30) with a first power transistor (34) controlled by the control device (12) and determining the current flow through the heating element (18) and one controlled by the control device (12) via an inverting Schmitt trigger circuit (38), the second power transistor (36) determining the current through the laser diode unit (10) is provided.

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