Advancing material of indeterminate length – With material-responsive control means – To regulate longitudinal movement of material
Reexamination Certificate
1998-12-31
2001-04-10
Walsh, Donald P. (Department: 3653)
Advancing material of indeterminate length
With material-responsive control means
To regulate longitudinal movement of material
C226S024000
Reexamination Certificate
active
06213367
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the field of printing technology. It is based on a method of controlling the drive for transporting a paper web in a printing machine according to the preamble of the first claim.
2. Discussion of Background
The invention is particularly advantageously used for shaftless rotary printing machines. A shaftless rotary printing machine having blanket and plate or forme cylinders combined in pairs to form cylinder groups is described in DE 43 44 896 A1. A method of operating a drive system which is suitable, in particular, for shaftless rotary printing machines is described by DE 196 26 287 A1. According to this method, the torque control of the driven axles has superimposed on it speed control (rotational speed control) or position control (angular position controls). In this case, in order to control the individual drives for printing cylinders and folders under the stringent requirements for angularly synchronised running which rotary printing machines have to meet, use is preferably made of position controls.
A significant advantage of individually driven rotary printing machines is that these machines are capable of carrying out a product change while the machine is running. Such product changes include the throwing on and throwing off of printing points, as well as changes of paper graded while the machine is running, which may lead to considerable and impermissible changes in the paper web tensions.
During the operation of drive groups which are controlled in this way—and in particular when products changes are also carried out while the machine is running, or when changes of paper grade take place within continuous production—undesired subsidiary phenomena occur, such as excessively fluctuating web tensions and, as a result of this, for example paper breaks.
The conventional methods of controlling the drive for transporting a paper web primarily involve two modes of operation: the drives are controlled either to constant speed or to constant web tension. These methods have, in either form, the disadvantage that:
The paper draw between the threading mechanism and the printing unit builds up only very slowly when the machine is being started up.
The web tension fluctuates to a relatively pronounced extent during normal operation.
During a change of paper grade or of production sequence, the web tension fluctuates to an extremely pronounced extent, which can be attributed to the abruptly changed paper web lengths when throwing on or throwing off the printing units. This applies both when the web is guided over a plurality of printing towers and also when it is guided within one printing tower, a turning tower or the folder.
The web tension is not maintained if the machine is stopped in an emergency.
All these disadvantages can be attributed to the fact that
on the one hand, the paper properties of the running web change and, in the case of constant speed control, frequent and large-scale control compensation operations necessarily have to be carried out and
on the other hand, the machine is not able to compensate for such control deviations in the desired time, from the point of view of control dynamics, and in addition has a tendency to an oscillatory behavior.
SUMMARY OF THE INVENTION
Accordingly, one object of the invention is to provide a novel method of controlling the drive of the paper web in a printing machine, in which method in all possible modes of operation of the rotary printing machine, and with or without a change of paper grade or in the content of the printed product while the machine is running, the web tension does not exhibit any noticeable fluctuations and deviations are compensated for rapidly. This object is achieved by the features of the first claim.
The core of the invention is that the control of the drives of the paper web, for example in the pretensioning units or the turning towers of a rotary printing machine, takes into account both speed and web tension in a flexible manner. This enables considerably better paper guidance with controlled web tension, both in static and in dynamic operation. In the simplest case, this is achieved by means of settings of the speed controller, with the result that the latter shows a distinct dependence of the drive torque on the deviation between desired and actual speed. This controller deviation is taken into account in the reference desired value, and a suitable operating point is thereby set. In the event of a production-induced variation in the machine configuration, the current operating point is displaced along a curve (loading curve), both the speed actual value and the drive torque being changed. The slope of this curve is a measure of the influence of the load change on speed and torque. It is preferably selected such that the drive torque and hence the web tension are kept within the operating limits. The reference desired value determines the static and dynamic guiding behavior to a large extent.
A distinction may be drawn between pre-controlled and controlled operation. In the simpler case of pre-controlled operation (open loop), known influencing variables of the process to be controlled are taken into account. In a first step, therefore, the steady-state operating case and acceleration-dependent variables are preset. In the optional controlled operation (closed loop), the web tension, for example, is measured; it acts on the reference desired value via a control algorithm. This ensures that residual errors are controlled out.
Clear-cut advantages are achieved in comparison with operation according to the prior art:
In pre-controlled operation, high static accuracy of the web tension is achieved, this having a low sensitivity to interfering variables.
Since the abovedescribed loading curve is part of the speed controller, the behavior exhibits extremely high dynamics. Characteristic reaction times of less than one millisecond are therefore possible. This is significantly faster than in the case of conventional web tension control.
Furthermore, the loading curve leads to damping of mechanical oscillations. This property is important above all in the case of mechanical stimuli, such as those which occur when the paper grade or the production sequence is changed.
Further advantageous embodiments emerge from the corresponding dependent claims.
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Asea Brown Boveri AG
Burns Doane Swecker & Mathis L.L.P.
Walsh Donald P.
Webb Colling A.
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