Method of Operating a Printing Machine During Start-Up or Run-on and Optically Testing a Printed Image

Reference to related publication: German Patent 31 36 703.

The present invention relates to eliminating production of scrap copy during start-up or run-on of a printing machine, and to apparatus for carrying out the method.

Printing machines require an adjustment phase before they can provide perfectly printed copy. This start-up phase is independent of the type of printing machine, that is, whether it is a sheet-fed or web-fed machine, and whether the printing method is letterpress, gravure or planographic. During the start-up phase, adjustments are to be made so that the inking will be uniform, register accurate, and, in all other respects, the print is perfect. To do so, test samples are printed which are visually inspected by experienced personnel. Additionally, measurements can be taken of density of ink, register and the like, of the substrate on which printing is carried out. Apparatus to preset circumferential register, lateral register, diagonal register, and all other parameters relating to printing can reduce the production of scrap printed material, but could not entirely eliminate it. Test samples still had to be printed. If the number of printed production is to be small, the time to produce a perfectly printed sample can become a major production cost factor. This factor can be particularly high when the printing method is an offset process, since it is then necessary not only to control lateral and circumferential and other register parameters, but, additionally, the application of damping fluid so that the appropriate damping fluid-ink balance is obtained. This, also, increases start-up time and, hence, production costs. German Patent 31 36 703 describes arrangements to preset various registers, which, however, still have to be checked visually.

It is an object to provide a method and an apparatus in which the production of scrap during the start-up phase of a printing machine is reduced to a minimum or entirely eliminated.

Briefly, during start-up of the machine, and preliminarily in advance of a printing run, the information to be printed is transferred from a printing cylinder on a control or test cylinder which, preferably, has a surface which simulates the surface of the substrate on which printing is to be effected, i.e. is an analog of the substrate surface, for example white, with a surface characteristic similar to paper. The information which is transferred to the control cylinder will form an image on the control cylinder. This image is then optically tested, at a first partial circumferential range of the control cylinder subsequent to the printing line. The image transfer from the printing cylinder thus is examined, and information is derived fherefrom relative to parameters affecting the printing quality, based on adjustment of the operating system of the printing machine; such parameters are register, ink-water balance, inking density, color, and the like. The image which had been transferred to the control cylinder is then removed from the control cylinder at a second partial circumferential range, subsequent to the first range, for example by an erasing or cleaning apparatus in engagement with the control cylinder.

The use of a control cylinder on which the image to be reproduced is transferred, and, then again erased or washed off, permits reduction or entire elimination of test prints being made; thus, production of printed products which cannot be used approaches or becomes zero. This not only saves paper; the erasing or cleaning apparatus can readily be combined with a recycling apparatus so that ink which was used during the test run, as well as damping fluid, if an offset process is used, can be reconstituted and recycled.

FIG. 1 is a schematic illustration of an offset rotary printing machine having three cylinders, and employing the method in accordance with the present invention;

FIG. 2 is a schematic representation of a printing station of a gravure printing machine; and

FIG. 3 is a schematic representation of a letterpress printing machine and employing the present invention.

The offset printing station shown in FIG. 1 includes a plate cylinder 1, a rubber blanket cylinder 2, i.e. a cylinder which has a yielding or soft surface, an inker 3, and a damper 4. In a printing run, a substrate 6 is passed between the blanket cylinder 2 and an impression cylinder 5, which has an unyielding or hard surface, e.g. a ceramic surface. Upon continued printing, the web or sheet 6 which is passed between the blanket cylinder 2 and the impression cylinder 5 receives the printed image, which is transferred or offset from the plate cylinder 1 to the blanket cylinder 2.

In accordance with the present invention, the printed information is preliminarily transferred from the blanket cylinder 2 not onto a substrate 6 but, rather, at the printing or cylinder contact line from the blanket cylinder 2 on the impression cylinder 5. In this instance, the impression cylinder 5 functions as a control or test cylinder. The surface of the impression cylinder 5, under run-on or start-up conditions, is so constituted that its roughness and, preferably, its color, is comparable or similar to, or an analog of that of the roughness and color of the substrate 6 which, later on, is to be used as the printed product. A white ceramic surface is particularly suitable.

In accordance with a feature of the invention, a first circumferential range 7, downstream--with respect to the direction of rotation of cylinder 5, as shown by the arrows in the cylinders--is used to permit optical examination and testing of the transferred image, which permits the formation of judgments with respect to the adjustment of parameters affecting the printed image, that is, which influence the quality of printing and the position of the printed image. Such parameters are, as well known for example, the preadjustment of the circumferential and lateral register, or registers, the adjustment of inked zones, thickness of the damping fluid film and the like. In the specification and claims, these parameters, or any one of them, will be referred to as "print quality parameters".

The optical examination in the first circumferential zone 7 can be carried out by observation of the printed transferred image by a printer. In accordance with the printer's judgment and observation, manual change of printing parameters can be carried out. Alternatively, the optical examination of the transferred image on the first range of cylinder 7 can be carried out by optical sensors, the test results of which are indicated at a central control panel, from which the various parameters affecting the image transfer can also be changed, either manually or automatically. Further, the optical examination of the transferred image can be done by means of opto-electronic sensors 8, see FIG. 1, which transfer electrical signals representative of optically sensed conditions of the printed image, for example position of register markers, characteristic elements of the printed image, inking density at characteristic points in the printed image and the like, as input signals to a control unit, typically formed by a computer 9. The computer 9 can access and read command or desired values from a memory 10 for the particular printing to be carried out, while considering characteristics of the substrates to be used, such as paper, for example, and the materials used in printing, for example the ink, color of the ink and the like, and provides error or difference signals 11 which are applied to the printing machine to change the respective parameter by controlling suitable adjustment elements, not shown, and well known in the printing machinery field. Such adjustment elements may, for example, be positioning motors to change the lateral, circumferential, or up-down register, control the inking in zones, control and, if necessary, change the speed of inker rollers in an inker train, the frequency of lifter rollers, and the like, until there is a zero or null difference between the actual value sensed by sensor 8 and command values supplied by memory 10.

In accordance with a further feature of the invention, a second circumferential range 12 follows the first circumferential range 7, in the direction of rotation of the control cylinder 5. An erasing or image extinguishing device 13 can be engaged against the control cylinder 5 which completely extinguishes the printed image on the control cylinder after the optical examination has taken place. The extinguishing or erasing apparatus 13, which can be a cleaning system, includes a housing 14, a first doctor blade 15, a first drainage duct 16, a roller brush 17 supplying a washing fluid to the test or control cylinder 5, a second doctor blade 18, a second drainage channel 19, and a dryer 20 located subsequent to the housing 14.

The first doctor blade 15 strips off, preferably the entire, or essentially entire quantity of printing ink on the control cylinder 5 and drains that ink into the first drainage duct 16, from which it can be supplied to a printing ink recycling system shown schematically at IR. In the chamber or space formed between the first doctor blade 15 and the second doctor blade 18, any remaining ink is cleaned off the control cylinder 5 by the rotating roller brush 17, under supply of washing fluid. Any remnant portions of ink and washing fluid, still on the control cylinder 5, are removed by the second doctor blade 18 and conducted to a second recycling system FR via duct 19, for reconstituting washing and damping fluid and separating remanent ink therefrom, for reuse, as shown schematically at the fluid recycling unit FR, and for reuse or return of ink to the ink recycling unit IR, as shown schematically by the broken-line connection F/I.

The dryer 20 may be a hot air dryer, a heat radiator, or a similar arrangement, for example a tube extending parallel to the test or control cylinder 5 and blowing hot air against the surface thereof.

The cleaned and dried surface of the control cylinder can, upon continued rotation, receive another new, or the same printed image.

When all printing parameters are appropriately adjusted to the satisfaction of the printer or machine operator, printing on the substrate, that is, a printing run can now be started. The erasing or extinguishing system 13 is disengaged from the printing cylinder 5, and the printing cylinder 5 is disengaged from the blanket cylinder 2. The substrate 6, if in web form, can now be pulled into the printing machine or, if the machine is a sheet-fed machine, the sheet supply can be enabled. The impression cylinder 5 is then again engaged against the blanket cylinder, with the substrate 6 therebetween, or arranged to be fed therebetween, and the printing run may commence.

In accordance with a preferred feature of the invention, the opto-electronic sensor 8 is positioned on a pivotable support, pivotable about an axis P, which, during the start-up and testing phase, directs the opto-electronic sensor against the first circumferential range 7 of the control cylinder 5 and which can move the sensor to the position shown at 8', where optical examination of the printed image can be checked. FIG. 1 illustrates this movable positioning only schematically, by positioning the sensor 8, when at 8', in the back of the substrate which, for example, may be transparent or at least translucent. This permits continued optical examination of the printed image of the substrate 6 during normal printing.

Testing the printed image on the control cylinder is not limited to offset printing machinery. FIG. 2 illustrates an application of the method of the present invention to a gravure printing machine. Basically, a control cylinder or testing cylinder can be used with any kind of printing system, and, for example, the impression cylinder can be used for this purpose, by directly transferring the printed image thereon. Transfer of the printed image in an offset printing machine on the impression cylinder is carried out by transferring the image, at least indirectly, via a cylinder with a soft or yielding surface. Indirect gravure printing, indirect letterset or flexo-printing, likewise are suitable applications. If necessary, an additional cylinder can be used as a control or testing cylinder, as will be described in connection with the embodiments of FIGS. 2 and 3.

FIG. 2, schematically, illustrates a printing station of a gravure printing machine. A forme cylinder 21 accepts printing ink upon dipping into an ink trough 22; excess ink is stripped off by the doctor blade 23 and returned to the ink trough 22. An impression cylinder 24 is engageable against the forme cylinder 21. The impression cylinder 24 has a soft surface. During normal printing, a substrate 25 is passed between the forme cylinder 21 and the impression cylinder 24. The substrate may be a continuous web, or may be sheets suitably fed between cylinders 21 and 24, for prime printing by cylinder 21.

During the start-up phase, when there is no substrate between cylinders 21 and 24, a control cylinder 26 is engaged against the impression cylinder 24. Control cylinder 26, preferably, has a hard or unyielding surface, the structure of which is similar to that of the substrate 25. Preferably, a white ceramic surface is used. In a first circumferential region 27, downstream of the printing line to the impression cylinder 24, optical sensor 28 senses, optically, the printed image transferred to the control cylinder, similar to the sensing by sensor 8, explained in connection with FIG. 1. A second circumferential range 29 follows the first range 27 which has an extinguishing, cancelling or cleaning system 30 engageable thereagainst which, in general construction, may be identical to the system 13, described and explained in connection with FIG. 1.

In operation, and during start-up, the image transferred to the control cylinder is first tested optically and then completely removed by the extinguishing system 30. A new image can then be applied to the cylinder 26 via the cylinder 24 at the impression line.

Evaluation circuitry to evaluate and, based on the evaluation, correcting or controlling the parameters affecting the printed image, based on signals derived from sensor 28, have been omitted from FIG. 2 since they can be similar to those explained in connection with FIG. 1.

FIG. 3, schematically, shows a letterpress printing machine which has a plate cylinder 31, inked by an inker 32 and, upon normal printing, prints the subject matter on a substrate 33, guided between cylinder 31 and an impression cylinder 34.

In accordance with a feature of the invention, a control or test cylinder 35 is provided, engaged against the impression cylinder 34 during start-up or run-on of the printing system and when there is no substrate 33 between the cylinders 31, 34. The control cylinder 35 will receive the image transferred to the impression cylinder 34.

An opto-electronic sensor optically tests the image transferred in a first circumferential range 36 on the test cylinder 35, range 36 following, downstream, the printing line of cylinder 35 with respect to the impression cylinder 34. Sensor 37 is directed to the surface of the test cylinder 35. Electronic evaluation, comparison and control apparatus control the parameters affecting the transferred image; none of that apparatus is shown in detail since it can be similar to the system 9, 10, 11 explained in connection with FIG. 1.

An erasing, extinguishing or cleaning apparatus 39 is located in a second circumferential range 38, downstream, with respect to the direction of rotation of cylinder 35. The extinguishing system 39 operates similarly to that of system 13, FIG. 1.

The extinguishing system 39 completely removes the image transferred by the impression cylinder 34 on the control cylinder 35, so that, upon each revolution, newly transferred information can be checked and tested on the first circumferential range 36 thereof.

Various changes and modifications may be made within the scope of the inventive concept.