Printing – Processes – Condition responsive
Reexamination Certificate
2001-07-16
2003-07-29
Nolan, Jr., Charles H (Department: 2854)
Printing
Processes
Condition responsive
C226S001000, C226S010000, C226S045000, C226S100000, C101S483000
Reexamination Certificate
active
06598529
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a method for detecting faults during transport of a web, in particular, for detecting a web break during the transport of a paper web in a web-fed rotary printing machine, wherein the speed of the web is determined by contact-free or contactless measurement, in accordance with the Doppler principle, and is evaluated thereafter.
The invention also relates to a device for detecting a fault during a web transport, in particular, for detecting a web break during the transport of a paper web in a web-fed rotary printing machine, the device including a detector for determining the speed of the web free of any contact, in accordance with the Doppler principle, and supplying the determined speed value to an evaluation unit disposed downline therefrom, as viewed in the transport direction of the web.
The published German Patent Document DE 196 11 878 A1 discloses a method for detecting faults during the transport of a continuous paper web in a printing machine, wherein a determination of the speed of the web is performed in accordance with a classic, contact-free method by an optical route or with the aid of sound, and is then evaluated. The instantaneous speed of the web, determined in this manner, is compared either with a virtual speed of the web determined from the mechanical speed of the printing machine, with the average speed of the web measured during the time before the measurement of the instantaneous speed, or with a speed of the web at a time immediately before measuring the instantaneous speed. The difference between the instantaneous speed and the comparison speed is then compared with a predefined threshold. If the threshold is exceeded, a web-catching device can be triggered and/or the printing machine can be stopped.
A disadvantage of the aforedescribed method wherein changes in the speed of the web, which are not caused by a web break and are brought about, for example, by longitudinal oscillations of the web, trigger a machine stoppage and can activate a Web-catching device. The aforedescribed method, because it determines the speed at only one point on the web, is unable to distinguish such an oscillation of the web from a change in the speed which results from a web break. However, a machine stoppage leads to an enormous time loss for the pressman and to considerable costs which, as a result of the breakdown in production of the printing machine which occurs, are produced during the stoppage by accumulating rejects during the rethreading of a new printing material web into the machine and also during the removal of the previously printed and torn printing material web from the machine. Furthermore, a web break conceals the risk of the paper web winding up on printing-unit cylinders and, thus, the risk of massive damage to the printing units.
It is also disadvantageous that devices wherein the determination of the speed is performed with optical methods generally require very high purchasing costs and, in operation, are very sensitive to soiling and therefore require intensive maintenance. Devices wherein the measurement is performed with the aid of sound waves are additionally quite inaccurate and unreliable.
A further difficulty of the aforedescribed method results from the fact that, when optical methods are used, the measurement accuracy is not independent of the printed subject, because the reflectance level of the web varies as a function of the printed image.
SUMMARY OF THE INVENTION
It is therefore an object of the invention of the instant application to provide a method for detecting faults during the transport of a web, which overcomes the aforementioned disadvantages and which, in particular when web oscillations occur during which there is no risk of a web break, rules out the detection of a fault.
It is a further object of the invention to provide a device for detecting a fault during the transport of a web which overcomes the aforementioned disadvantages of the prior art and which, in particular, detects as a fault only those changes in the movement of the web which conceal the risk of a web break.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, a method for detecting faults during transport of a web, wherein web speed is determined by contact-free measurement, in accordance with the Doppler principle, which comprises the following method steps: by applying microwaves, determining a first local speed of the web at a first measurement position; by applying microwaves, determining at least a second local speed of the web at a second measurement position spaced apart from the first measurement position in a direction of web transport; determining an actual value from the first local speed and at least the second local speed; determining any deviation of the actual value from a predefined desired value; and comparing the deviation of the actual value from the predefined desired value with a predefined threshold.
In accordance with another mode, the method of the invention includes detecting a web break, as a fault, during the transport of a paper web in a web-fed rotary printing machine.
In accordance with a further mode, the method of the invention includes determining the first local speed of the web and at least the second local speed of the web virtually simultaneously.
In accordance with an added mode, the method of the invention includes generating a control signal if the deviation of the actual value from the predefined desired value is greater than the predefined threshold.
In accordance with an additional mode, the method of the invention includes applying a computer program for calculating at least one of the actual value and the deviation of the actual value from the predefined desired value, in order to evaluate the local speeds of the web.
In accordance with yet another mode, the method of the invention includes varying at least one of the predefined desired value and the predefined threshold as a function of operating parameters of the printing machine.
In accordance with yet a further mode, the method of the invention includes transporting the web in a web-fed printing machine, and calculating the predefined desired value as a theoretical web speed based upon the mechanical speed of at least one subassembly in the printing machine.
In accordance with yet an added mode, the method of the invention includes at least one of triggering a machine stoppage and actuating at least one web-catching device in response to the control signal.
In accordance with another aspect of the invention, there is provided a device for detecting a fault during the transport of a web in a web-fed rotary printing machine, comprising a detector assembly for determining contact-free the speed of the web, in accordance with the Doppler principle, and for feeding information regarding the web speed to an evaluation unit disposed downline from the detector assembly in the transport direction of the web, the detector assembly including a first microwave detector located at a first measurement position, for determining a first local speed of the web and for feeding the determined information to the evaluation unit, at least a second microwave detector located at a second measurement position spaced apart from the first measurement position in the web transport direction, for determining a second local speed of the web and for feeding the determined information to the evaluation unit, the evaluation unit being capable of applying the determined information regarding the first and at least the second local speeds for determining an actual value, for determining a deviation of the actual value from a predefined desired value, and for comparing the deviation of the actual value from the predefined desired value with a predefined threshold.
In accordance with a further feature of the invention, at least one of the microwave detectors has a microwave antenna serving as a transmitter and a receiver.
In accordance with an added feature of the
Heidelberger Druckmaschinen AG
Mayback Gregory L.
Nolan, Jr. Charles H
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