Printing – Processes
Reexamination Certificate
2001-11-20
2003-12-30
Hirshfeld, Andrew H. (Department: 2854)
Printing
Processes
C101S148000, C516S198000
Reexamination Certificate
active
06668723
ABSTRACT:
Priority to German Patent Application No 100 58 550.7, which is hereby incorporated by reference herein, is hereby claimed.
BACKGROUND OF THE INVENTION
The present invention relates to a method for regulating the ink-to-wetting agent equilibrium in a rotary offset printing machine, the quantity of wetting agent being determined specifically using the signals of a sensor which measures the light reflectance of an area that is wetted using wetting agent on a printing form of the rotary printing machine.
If in an offset printing machine, i.e., for example in a sheet-fed rotary offset printing machine or in a web-fed rotary offset printing machine, the printing forms are supplied with too little wetting agent, then the following problem can occur: areas of the printing form that are generally supposed to be ink-free for a specific printing job, in order to generate a print image that is composed of the four primary colors black, yellow, cyan, and magenta, acquire ink. The appearance of ink in the basically ink-free areas of the printing form, caused by a lack of wetting agent, is known in the field of printing technology as smearing, and the quantity of wetting agent supplied, hereinafter termed wetting solution, at which no smearing occurs or at which the smearing begins, is also known as the smearing threshold.
In addition, for an optimal printing result, it is necessary that the so-called ink-to-wetting agent equilibrium be maintained during the offset process, so that an optimal emulsion made of wetting agent and ink, necessary for the printing process, is generated on the printing forms.
From German Patent 44 36 582 C2, it is known to regulate the wetting agent quantity for a printing form of an offset rotary printing machine that is in operation, a number of measuring values being repeatedly measured when there is a change in the quantity of wetting agent at a given rotational angle of the printing form. The dispersion value of the measuring values is calculated from them, differential amounts of the dispersion values being arrived at, and the smearing threshold being established when one of the differential amounts exceeds a preestablished differential value. Thereupon the wetting agent quantity for the continued printing is increased by a preestablished amount and is maintained such that the measuring values on average remain constant. The German '582 Patent provides no information as to combining wetting solution regulation with a change in the ink control, specifically an ink regulation, as a result of which the quantity of ink in the printing areas of a printing form occupied by ink are controlled or regulated during the continued printing operation.
Furthermore, from German Patent Application No. 29 31 579, a device is known for the zonal regulation of the wetting agent supply, in which the actuators for the zonal ink metering—hereinafter also known as ink zone screws—are coupled to the actuators for the wetting agent control, which are assigned to the ink zone screws and which correspond to zones. In this context, the coupling takes place in a mechanical manner using a mechanical control gear. The publication provides no information as to calibrating the wetting agent quantity when the ink quantity is essentially maintained at a constant level.
SUMMARY OF THE INVENTION
Accordingly, it is one objective of the present invention to create a method for regulating the ink-to-wetting agent equilibrium in a rotary offset printing machine, which makes it possible to adjust the optimum emulsion of ink and wetting agent in the shortest possible time and with a high degree of reproducibility.
The present invention provides a method for regulating the ink-to-wetting agent equilibrium in a rotary offset printing machine, the wetting agent quantity being determined especially using the signals of a sensor which measures the light reflectance of an area on the printing form of the rotary printing machine that is wetted by a wetting agent. The method includes:
presetting the wetting agent quantity supplied to the printing form,
calibrating the wetting agent quantity supplied at an ink quantity that is essentially kept constant,
adjusting the wetting agent quantity to a wetting agent quantity setpoint value that is characteristic for the specific print job,
increasing or decreasing the ink quantity from an ink quantity setpoint value to an ink quantity target value that is desirable for the printing job to be processed, and a corresponding increasing or decreasing of the wetting agent quantity setpoint value in the same direction to a wetting agent quantity target value, and
regulating the wetting agent quantity supplied in a closed control loop as a function of the wetting agent quantity target value.
According to the method in accordance with the present invention for regulating the ink-to-wetting agent equilibrium in a rotary offset any machine, the method preferably being realized by appropriate control and regulation software in a known printing machine controlling and regulating device, the wetting agent quantity supplied to a pressure plate or printing form is determined by the signals of a sensor. The sensor advantageously determines the light reflectance of an area on the printing form that is wetted by a wetting agent and that is preferably not to be printed. For this purpose, the sensor can detect, for example, the reflected light of a laser, which is oriented in the normal direction or at an angle to the area of the printing form not to be printed. As a function of the detected light intensity, the sensor then can generate a sensor signal which represents a measure for the light reflectance of the pressure plate, which in turn is a function of the quantity of wetting agent in the area. According to the present invention, the quantity of wetting agent to be supplied to the printing form for the specific printing job is preset, which can take place, for example, in the familiar manner by interconnection or by varying the application pressure between the rollers controlling the wetting agent in the wetting apparatus of the printing machine, or in another familiar manner. Presetting the wetting agent quantity supplied to the printing form and/or presetting the ink quantity supplied to the printing form is preferably accomplished, in this context, when the printing machine is at a standstill, or is in crawling mode, as a result of which the amount of spoilage is reduced in an advantageous manner.
Presetting the wetting agent quantity, in this context, is preferably accomplished on the basis of a presetting signal value, which corresponds to the signal value of the sensor for the wetting agent target value, which was determined by the sensor during a preceding printing job. The wetting agent quantity target value of the preceding printing job, or the signal value of the sensor assigned thereto, essentially corresponding to the wetting agent quantity that is optimal for the preceding job, can be stored, for example, in a storage unit. In this way, the advantage is achieved that presetting the wetting agent quantity can be accomplished in a simple manner by increasing the wetting agent quantity until the signal value measured by the sensor corresponds to the stored signal value.
In the same way, it is possible to carry out the presetting of the wetting agent quantity on the basis of a calculated presetting signal value, which is advantageously determined by averaging the signal values of the sensor for the wetting agent quantity target values during two or more preceding printing jobs. In this context, it is assumed that the wetting agent quantity target values of the preceding printing jobs essentially correspond to the optimal wetting agent quantity at the ink quantity set in the given case, the wetting agent quantity having resulted in an optimal ink-wetting agent emulsion in the preceding printing jobs. As a result of the averaging, the influence is reduced of the signal values of the sensor which have been measured at a non-optimal setting of the ink-to-wetting agent eq
Berton Philippe
Blanchard Alain
Boillot Dominique
Chevalier Antoine
Lepeltier Patrick
Davidson Davidson & Kappel LLC
Heidelberger Druckmaschinen AG
Hirshfeld Andrew H.
Nguyen Hoai-An D.
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