EP2159050A2 - Method for operating a printing machine with a central cylinder - Google Patents

Abstract

The method involves employing a common central cylinder (10) with multiple impression cylinders (14). The pressure cylinders are propelled in an appropriate operating phase during the printing operation. The central cylinder runs with the impression cylinder only by frictional engagement.

Description

The invention relates to a method for operating a printing press with a plurality of printing cylinders, which are employed on a common central cylinder.

In some known printing methods, for example in gravure printing, it is desirable that no slippage occurs between the printing cylinders and the substrate as possible. If several printing cylinders are provided, for example, for different inks, also the angular velocities of all printing cylinders must match, so that the repeat of the images printed by these cylinders is maintained. Known gravure printing machines are therefore constructed as multi-stand machines in which a printing cylinder and an associated impression roller is provided in each inking unit, which presses the printing material against the printing cylinder. Only the printing cylinders are actively driven while the impression rollers free. This ensures that the web tension is effected solely by frictional engagement between the printing material web and the printing cylinders and thus the transport speed of the web coincides exactly with the peripheral speed of the printing cylinder. If all printing cylinders are driven at the same angular velocity, there may be some differences in peripheral speeds due to tolerances in the radii of the printing cylinders. So that these do not lead in the long run to excessive tensile stresses in the printing material web, the web is deflected between the individual inking with the help of dancers or the like, so that their length is variable and slight differences in speed can be compensated during the printing run.

The object of the invention is to provide a method that allows a new operation and use of a central cylinder engine.

This object is achieved in that at least in a certain phase of operation during the printing operation, the printing cylinder can be driven and you can run the central cylinder only by frictional engagement with the printing cylinders.

If the printing cylinders are machined so that their radii are exactly the same, or if certain tolerances in the radii of the printing cylinders are compensated in some other way, a central cylinder machine can be operated with the aid of this method so that there is no slippage between the printing material web and the printing cylinders, since the central cylinder is not actively driven, but only by frictional engagement of the pressure cylinder is taken, so that its peripheral speed is always adapted to the peripheral speed of the impression cylinder.

Advantageous developments and refinements are specified in the subclaims.

Preferably, the operation described above is applied only during the printing run when the central cylinder has already reached its target speed. In the start-up phase, on the other hand, the central cylinder, which has a relatively large moment of inertia, is actively driven. This allows a faster acceleration of the central cylinder to the target speed.

According to another embodiment of the method, a central cylinder is used, which has an elastic surface layer on its peripheral surface, and the tolerances in the radii of the individual printing cylinders are compensated by the fact that the impression cylinder are made with elastic deformation of the surface layer of different amounts against the central cylinder.

In the following an embodiment will be explained in more detail with reference to the drawing.

Fig. 1

eine schematische Ansicht einer Zentralzylinder-Tiefdruckmaschine, mit der das erfindungsgemäße Verfahren ausführbar ist;

Fig. 2

eine schematische Teilansicht eines Zentralzylinders mit mehreren daran angestellten Druckzylindern in einer unkorrigierten Anstellposition;

Fig. 3

die Druckzylinder nach Fig. 1 in einer korrigierten Anstellposition; und

Fig. 4

ein Flußdiagramm für das erfindungsgemäße Verfahren.

Show it:

Fig. 1

a schematic view of a central cylinder gravure printing machine, with which the inventive method is executable;

Fig. 2

a schematic partial view of a central cylinder with several employed pressure cylinders in an uncorrected setting position;

Fig. 3

the impression cylinder after Fig. 1 in a corrected setting position; and

Fig. 4

a flow chart for the inventive method.

In Fig. 1 a central cylinder 10 is shown, which has on its peripheral surface an elastomeric surface layer 12 and is wrapped by a printing substrate B. Several pressure cylinders 14 are arranged on the circumference of the central cylinder 10 and employed against the central cylinder, that with them various print images, for example, different color separation images, can be successively printed on the substrate web B. So that the repeat is maintained during the printing operation, all printing cylinders 14 are driven at the same speed.

Based on Fig. 2 and 3 Now, a method will be explained with which any manufacturing differences in the radii of the printing cylinder 14 can be compensated so that for all printing cylinder slippage between the peripheral surface of the printing cylinder and the surface of the printing material 10 is avoided.

In Fig. 2 one half of a central cylinder 10 is shown, which has an elastomeric surface layer 12, whose thickness is greatly exaggerated here.

A plurality of impression cylinders 14-1, 14-2 and 14-3 are set against the circumference of the central cylinder 10 so far as to slightly depress the elastomeric surface layer 12, again exaggerated in the drawing. Due to this deformation of the surface layer of the central cylinder 10 has at the location of the printing cylinder 14-1 the effective radius R _1, at the location of the printing cylinder 14-2 the effective radius R _2, and the point of the printing cylinder 14-3 the effective radius R ₃ ,

The radii of the printing cylinders are r ₁ , r ₂ and r ₃ .

As an example was in Fig. 1 Suppose that the radii r ₁ and r ₃ (at both ends of the respective cylinder) exactly match the nominal radius r of the impression cylinder. The radius r _{2 of} the impression cylinder 14-2 gives way on the other hand due to production-related inaccuracies by a factor (1 + k) of the nominal value r ab: r ₂ = (1 + k) r. In the example shown in the drawing, k has the unrealistically high value 0.1. In practice, the size deviations of the printing cylinders are typically of the order of a few μm, so that realistic values for k are approximately of the order of 10 ^-5 .

Due to the slightly too large radius r _{2 of} the impression cylinder 14-2, the elastomeric layer 12 is pressed in more strongly here, so that the effective radius R _{2 is} smaller than the effective radii R ₁ and R ₃ .

In this situation, the position of the axis of the impression cylinder 14-2 is corrected as shown in FIG Fig. 2 is shown. The pressure cylinder 14-2 has been further moved away from the central cylinder 10, and just so far that the effective radius R _{2 is} now by the factor (1 + k) greater than R ₁ and R ₃ . The ratio between the impression cylinder radius and the respective effective radius of the central cylinder 10 is therefore the same for all impression cylinders: R ₁ / r ₁ = R ₂ / r ₂ = R ₃ / r ₃ .

In practice, the actual radii r _{1 of} all printing cylinders (the index i identifies the individual printing cylinders) will deviate from the nominal value r, and the axes of all printing cylinders will then be adjusted so that R _i / r _i has the same value for all i. In principle, since the impression cylinders may also have a slightly conical shape so that their radius at the opposite ends may be different, the radii are measured at least at both ends of the impression cylinder and the adjustment is made for the opposite ends of the impression cylinders (the opposite sides the printing press) made independently.

In order to maintain the repeat of the color separations printed with the various printing cylinders during the printing process, all printing cylinders 14-1,... Are driven at the same angular velocity w. The peripheral speed v _{i of} the printing cylinder with the index i is accordingly v _i = w * r _i . So that each printing cylinder rolls without slippage on the surface of the central cylinder 10 (possibly slightly dented surface layer 12), also the central cylinder 10 at the point of contact must each Pressure cylinder have this peripheral speed v _i . If W is the angular velocity of the central cylinder, then: $${\mathrm{v}}_{\mathrm{i}}\mathrm{=}\mathrm{W}\mathrm{*}{\mathrm{R}}_{\mathrm{i}}\mathrm{=}\mathrm{w}\mathrm{*}{\mathrm{r}}_{\mathrm{i}}$$

gilt somit $$\mathrm{W}\mathrm{*}{\mathrm{R}}_{\mathrm{i}}\mathrm{=}\mathrm{w}\mathrm{*}\mathrm{r}\mathrm{*}\left(\mathrm{l}\mathrm{+}{\mathrm{k}}_{\mathrm{i}}\right)$$

und folglich $${\mathrm{R}}_{\mathrm{i}}\mathrm{=}\left(\mathrm{w}\mathrm{/}\mathrm{W}\right)\mathrm{*}\left(\mathrm{l}\mathrm{+}{\mathrm{k}}_{\mathrm{i}}\right)\mathrm{*}\mathrm{r}\mathrm{=}\left(\mathrm{w}\mathrm{/}\mathrm{W}\right){\mathrm{r}}_{\mathrm{i}}$$

If ki are the dimensional tolerances in the radii of the printing cylinders, so: $${\mathrm{r}}_{\mathrm{i}}\mathrm{=}\left(\mathrm{l}\mathrm{+}{\mathrm{k}}_{\mathrm{i}}\right)\mathrm{*}\mathrm{r}\mathrm{.}$$

is valid $$\mathrm{W}\mathrm{*}{\mathrm{R}}_{\mathrm{i}}\mathrm{=}\mathrm{w}\mathrm{*}\mathrm{r}\mathrm{*}\left(\mathrm{l}\mathrm{+}{\mathrm{k}}_{\mathrm{i}}\right)$$

and consequently $${\mathrm{R}}_{\mathrm{i}}\mathrm{=}\left(\mathrm{w}\mathrm{/}\mathrm{W}\right)\mathrm{*}\left(\mathrm{l}\mathrm{+}{\mathrm{k}}_{\mathrm{i}}\right)\mathrm{*}\mathrm{r}\mathrm{=}\left(\mathrm{w}\mathrm{/}\mathrm{W}\right){\mathrm{r}}_{\mathrm{i}}$$

That is, the effective radii R _{i of} the central cylinder 10 must be proportional to the actual radii r _{i of} the impression cylinders. With this setting, an exact synchronization of all printing cylinders, ie, a run with the same angular velocity and the same peripheral speed can be achieved, so that no pressure cylinder slip occurs relative to the central cylinder or the printing material guided thereon and no tensile stresses are exerted on the printing material.

As Fig. 1 shows, for driving the central cylinder 10, an electric motor Mz is provided, which is connected in the example shown via a mechanical coupling 16 with the central cylinder. Each pressure cylinder 14 has its own electric motor Md for driving. All motors Md and Mz and the clutch 16 are controlled by an electronic control unit 18.

The essential steps of the operation are in Fig. 4 shown as a flow chart. The starting point is a situation in which the printing press is prepared for a printing run but is still standing still. In step S1, the clutch 16 is then engaged, ie, the motor Mz is connected to the central cylinder 10, and the motors Mz and Md are turned on, to accelerate both the central cylinder and the pressure cylinders to their respective desired speeds. The ratio w / W of the angular velocities is kept constant by electronic control of the motors.

In step S2, it is checked whether the central cylinder 10 has reached its target speed. As long as this is not the case, this step is repeated cyclically. Once the target speed is reached, the clutch 16 is disengaged in step S3, and the motor Mz for the central cylinder 10 is turned off. Thus, only the motors Md remain active for driving the printing cylinders 14, and these motors are controlled so that all printing cylinders run at the same angular velocity w.

Due to the frictional engagement between the printing cylinders 14 and the printing substrate B and the frictional engagement of this printing material web with the surface layer 12 of the central cylinder, the central cylinder 10 is maintained at its desired rotational speed. For this purpose, only a very small torque is needed, which compensates for the friction losses. This torque can be easily transferred by friction, so that there is no slippage between the printing cylinders and the printing material. The basis of Fig. 2 and 3 explained employment of the impression cylinder also ensures that all pressure cylinders have the same tendency to keep the central cylinder at the same angular velocity.

In the Fig. 1 shown mechanical coupling 16 can be omitted if the motor Mz has a construction that allows to connect this motor so that it exerts virtually no torque on the rotating central cylinder. Alternatively, it is also possible to regulate the motor Mz so that it exerts virtually no torque on the central cylinder or that it exerts such a small torque, which compensates only the friction losses, so that the speed is leztlich determined solely by the pressure cylinder.

After completion of a print run, either the clutch 16 can be engaged again or the motor Mz can be operated so that it actively brakes the central cylinder.

Claims (5)

Method for operating a printing machine having a plurality of printing cylinders (14) which are set to a common central cylinder (10), characterized in that the printing cylinders (14) are driven during printing operation at least in a specific operating phase and the central cylinder (10) is actuated. only by friction with the pressure cylinders (14) can run along. Method according to Claim 1, in which an engine (Mz) for driving the central cylinder (10) is controlled in said operating phase so that the torque exerted by this engine at most compensates for frictional losses such that the rotational speed of the central cylinder is determined solely by frictional engagement The torque transmitted to the printing cylinders is determined. Method according to Claim 1, in which a motor (Mz) for driving the central cylinder (10) is mechanically decoupled from the central cylinder during said operating phase. Method according to one of the preceding claims, wherein a central cylinder (10) is used, which has an elastic surface layer (12), and in which each pressure cylinder (14) is set against the central cylinder with elastic deformation of said surface layer (12). in that the effective radii (R _i ) of the central cylinder at the locations of the respective impression cylinders are proportional to the actual radii (r _i ) of these impression cylinders. A method according to any one of the preceding claims, wherein the impression cylinders (14) are gravure cylinders.

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