Method for Operating a Winding Device

Abstract

A method for operating a winding device of a processing machine for processing a material web is disclosed. A winding device is provided for winding or unwinding the material web. The winding device is operated to specify a web tension, wherein a switch occurs from a first web tension specification procedure to a second web tension specification procedure during the processing of the material web.

Description

The present invention relates to a method for operating a winding device of a processing machine for processing a material web and to an associated computing unit.

Although in the following text reference will primarily be made to printing presses, the invention is not restricted thereto but instead is directed to all types of processing machines in which a product web or material web is processed. However, the invention can be used in particular in printing presses such as newspaper printing presses, commercial printing presses, gravure printing presses, in-line flexographic printing presses, packaging printing presses or valuable document printing presses and also in processing machines such as bag-making machines, envelope-making machines or packaging machines. The material web can be formed from paper, fabric, paperboard, plastic, metal, rubber, in the form of film or foil and so on.

PRIOR ART

In material web processing machines, winding devices are used optionally as winders or unwinders. A winding device normally comprises at least one driven shaft, for example a winding shaft of a center winder, a drive shaft of a circumferential winder, a pull roll or the like, an associated actuating or controller function, for example in a motion control system or memory-programmable controller (PLC) and, if appropriate, measuring elements for determining the web tension. The winders are normally operated in such a way that a web tension is impressed on the material web, both control and also merely setting of the web tension being used. In the prior art, different methods for controlling or setting web tension are known in the winders of web-processing machines.

For example, a dancer control system or else a dancer position control system is used, in which the web tension is typically impressed on the web by a gravitational force or pressure on the dancer. The object of the dancer position control system is to keep the dancer within predefined limits, the set point of the dancer position normally being set to a central position. A dancer position control system is normally used to compensate for sudden disturbances, non-roundness in the coil or non-uniform web transport. A method or structure with a dancer position controller is mostly used when the material web does not run continuously or sudden disturbances have to be compensated for. In particular in the case of a flying reel change, a dancer is usually imperative.

In addition, it is known to set or control the web tension by means of tensile force control of the driven winder shaft. In this case, the controller typically specifies either the drive torque or the rotational speed of the shaft. Control of the drive torque is expediently used in the case of stiff material with a high modulus of elasticity, such as paper, metal, whereas control of the rotational speed is expediently used in the case of elastic material, such as foil, film or fabric. Tensile force control, as compared with dancer position control, offers the advantage of the ability to be implemented more simply and of lower expenditure on components.

Finally, feedback-free setting of the web tension, for example by setting rotational speed or setting drive torque, is also known. The setting or open-loop control offers the advantage of simplicity, since no kinds of mechanism, such as dancers or force transducers, or measuring elements, such as dancer height measurement or force measurement, are needed. However, it is relatively inaccurate, since disturbances are not registered and cannot be compensated for by a controller.

The structure or method with tensile force control/setting is normally used instead of dancer position control when a constantly running web transport without great disturbances is to be expected.

The known methods are relatively inflexible and cannot easily be adapted to changed conditions, for example of new material. In addition, in the case of production in which a flying reel change is provided, complicated dancer position control is always needed.

DISCLOSURE OF THE INVENTION

According to the invention, a method for operating a winding device of a processing machine for processing a material web having the features of patent claim 1 is proposed. Advantageous refinements are the subject matter of the subclaims and of the following description.

ADVANTAGES OF THE INVENTION

The invention is based substantially on the finding that flexible web tension control or setting that can be adapted to the respective conditions can be provided for a winding device if a switch is made online, i.e. during the production, from a first web tension specification method to a second web tension specification method. The term “specification method” comprises both control and setting methods.

Therefore, for example by switching as a function of the material, the control structure can be matched particularly well to the material web material. In particular in the case of production with a flying reel change, particular advantages can be achieved. Expediently, during normal production, web tension specification without a dancer is used for this purpose. A switch to dancer position specification is made before the reel change in order to be able to compensate particularly effectively for the disruption which is caused by the reel change. A switch back from the dancer position specification to the original web tension specification is finally made after the reel change has been carried out.

Likewise, a switch from rotational speed specification to drive torque specification can advantageously be made during a change to a material with a greater modulus of elasticity (stiffer material). A switch from drive torque specification to rotational speed specification is conversely made during a change to a material with a lower modulus of elasticity (softer material). Thus, during a change in the material, the respectively optimal specification method, i.e. control or setting method, can be selected.

A computing unit according to the invention, e.g. a control device of a printing press, is equipped, in particular by programming, to carry out a method according to the invention.

In addition, the implementation of the invention in the form of software is advantageous, since this permits particularly low costs, in particular if an executing computing unit is used for further tasks and is therefore present in any case. Suitable data carriers for providing the computer program are in particular floppy disks, hard drives, flash memories, EEPROMs, CD-ROMs, DVDs and many more. Downloading a program via computer networks (Internet, Intranet and so on) is also possible.

Further advantages and refinements of the invention can be gathered from the description and the appended drawing.

It goes without saying that the features mentioned above and those still to be explained below can be used not only in the respectively specified combination but also in other combinations or on their own without departing from the scope of the present invention.

The invention is illustrated in the drawing by using an exemplary embodiment and will be described extensively below with reference to the drawing.

FIGURE DESCRIPTION

FIG. 1 shows a winding device with a dancer position control system in schematic form.

FIG. 2 shows the winding device according to FIG. 1 after a switch to a rotational speed specification method has taken place.

FIGS. 1 and 2 will be described conjointly and in an overlapping manner, the same elements being provided with the same designations. Shown in FIGS. 1 and 2 is a winding device 100 which, according to a preferred embodiment of the invention, can be operated using different web tension specification methods. The intention is to explain below how, for example after a flying reel change, a switch is made from dancer position specification, as illustrated in FIG. 1, to rotational speed specification, as illustrated in FIG. 2.

The winding device 100 has a winding shaft 101, onto which a material web 102 is wound. It goes without saying that the invention can likewise be used during an unwinding operation. The winding device 100 has a dancer 110 for specifying a web tension and a force transducer 120 for measuring the web tension. The web tension value measured by the force transducer 120 is transmitted to a control device 130, which is provided for web tension control. The control device 130 activates a dancer drive 111 which exerts a specific pressure on the dancer 110 pneumatically, for example. The dancer position is detected by a dancer position controller 131, which specifies and controls the rotational speed or the drive torque of the drive shaft 101 on this basis. It goes without saying that the web tension controller 130 and the dancer controller 131 can also be embodied in a common control device.

It can be seen that the dancer position control system requires a multiplicity of elements and is therefore to be viewed as over-dimensioned for conventional operation. The substantial advantage of the dancer position control system consists in the possibility, in particular during a flying reel change, of intercepting the disturbance in the web tension behavior, brought about by the reel change, through the web material stored in the dancer, and of avoiding damage to the material web. After the reel change has been carried out, rotational speed control is often more practical. According to the present embodiment of the invention, after the reel change has been carried out, a switch is therefore made to rotational speed or drive torque specification (control), as illustrated by using FIG. 2.

During the online switchover to dancer-free operation, first of all the dancer position setpoint is set to a value which corresponds to the dancer stop. As illustrated in FIG. 2, the dancer 110 is, for example, fixed at the upper stop. After the dancer stop has been reached, a start is made on the structure or method switch. At the same time, the dancer pressure is reduced since, following the switchover, the web tension is no longer specified by the dancer pressure. After the switch, the web tension controller 130 will control the rotational speed or the drive element of the shaft 101 on the basis of the web tension measured by the force transducer 120.

The structure switch during the production operation is expediently carried out in such a way that, at the time of the switch, no steps occur in the control loop. For example, in the case of a PID controller and in the case of a force transducer structure with specification of a drive torque, the instantaneous drive torque is read and the integral term of the controller is predefined in such a way that, following the switch, the same reference torque appears at the controller output. In the case of a force transducer structure with pre-definition of a drive rotational speed, the instantaneous drive rotational speed is expediently read and the integral term of the controller is predefined in such a way that, following the switch, the same reference rotational speed appears at the controller output. A switch to dancer position specification can also be carried out in a comparable way by the integral term being predefined in accordance with the current rotational speed.

During a switch from rotational speed specification to dancer position specification, the dancer position setpoint can be set to the dancer center, for example, and as the switch in the control is made, the dancer pressure can also be set appropriately at the same time. Alternatively, instead of moving to the dancer stop, mechanical fixing of the dancer, for example by means of a mechanical brake, at another point, for example at the dancer center, can also be carried out. In this refinement, the dancer advantageously does not first have to be moved to the stop and later moved back into the central position.

Claims

1. A method for operating a winding device of a processing machine for processing a material web, comprising:

(a) processing the web material so as to wind up or unwind the material web with a winding device,

(b) operating the winding device so as to specify a web tension during the processing step,

(c) during the processing step, switching from a first web tension specification method to a second web tension specification method.

2. The method as claimed in claim 1, wherein the first and/or second web tension specification method is selected from the group comprising control and setting of a dancer position, of a rotational speed and of a drive torque.

3. The method as claimed in claim 1, further comprising:

(d) carrying out a flying reel change, and

wherein each of steps (a), (b), and (c) are carried out before step (d).

4. The method as claimed in claim 3, wherein:

the second tension specification method is a a dancer position specification method, and

step (c) is carried out before step (d).

5. The method as claimed in claim 3, wherein:

the second tension specification method is a dancer position specification method, and

step (c) is carried out after step (d).

6. The method as claimed in claim 5, wherein the dancer is fixed before step (c).

7. The method as claimed in claim 1, further comprising:

(d) carrying out a change in the material, and

wherein each of steps (a), (b), and (c) are carried out before step (d).

8. The method as claimed in claim 7, wherein:

the second tension specification method is a rotational speed specification method, and

step (c) is carried out during a change to a material with a lower modulus of elasticity.

9. The method as claimed in claim 7, wherein:

the second tension specification method is a drive torque specification method, and

step (c) is carried out during a change to a material with a greater modulus of elasticity.

10. A computing unit configured to carry out a method for operating a winding device of a processing machine for processing a material web, comprising:

(a) processing the web material so as to wind up or unwind the material web with a winding device,

(b) operating the winding device so as to specify a web tension during the processing step, and

(c) during the processing step, switching from a first web tension specification method to a second web tension specification method.

11. The method as claimed in claim 1, further comprising:

(d) carrying out—a flying reel change, and

wherein each of steps (a), (b), and (c) are carried out after step (d).

12. The method as claimed in claim 1, further comprising:

(d) carrying out a change in the material, and

wherein each of steps (a), (b), and (c) are carried out after step (d).