This invention relates generally to a method and apparatus for automated regulation of the contact pressure being exerted when the printed image is being formed in a rotary type printing press and more particularly to providing a novel automated control system in doing so for any corrective action needed.
The contact pressure being exerted between rotating printing plates during operation of a rotary printing press, such as an offset press, a lithograph press and the like, is well recognized to undergo significant variation reducing the quality of the printed image. For example, too little contact pressure results in a printed image being faint or missing details and which can require further press operation for avoidance of additional spoilage. Such corrective action taken by the press operator can understandably be carried out long after needed thereby causing considerable loss of the various objects on which the printed image is applied, such as metal cans, plastic containers and the like. In a similar manner, the application of excessive contact pressure when the printed image is being applied causes the liquid ink to smear upon deposition and thereby require the press operator to make the necessary adjustments for reducing the amount of this operating factor during continued press operation. Such variation in contact pressure between the printing plates during operation of a rotary printing press can also be caused by a wide variety of operating conditions, including temperature changes, rotational speeds of operation, materials employed to produce the printed image and still other operating factors. A commonly experienced temperature change affecting contact pressure between the rotating printing plates occurs during press start-up after customary periods of press inactivity which causes critical printing surfaces to avoid physical contact due to experiencing lower temperatures while being inactive. It remains desirable, therefore, to provide improved means whereby the printing contact pressure in a rotary printing press can be more effectively controlled during press operation.
In my recently issued U.S. Pat. No. 6,543,350B2, there is disclosed a measurement system enabling the operator of a rotary printing press to continuously discern the contact pressure being exerted during press operation. Said measurement system require the pressure sensing components being employed to cooperate with further sensing components detecting angular position of the printing plates when the pressure measurements are being carried out to produce a continuous visual display for the press operator. An automated control system to regulate the contact pressure during rotary type press operation is also disclosed in U.S. Pat. No. 5,275,099 wherein automated roller adjustment is carried out. In doing so, the contact pressure between a rotating plate roller and a form roller physically abutting said rotating plate roller is detected with multiple strain gage sensors mounted on a mechanical pivot arm. Continued correction of the contact pressure during press operation to a predetermined or preestablished contact pressure value is said to be achieved automatically with a feedback type servomechanism employing comparator means.
To overcome the difficulties experienced with manual contact pressure adjustment as well as automated control of the printing contact pressure by said prior art regulation means, there is now provided a novel fully automated system to regulate visual image formation in a rotary type printing press by still further improved means. In the present control method, the actual contact pressure between pairs of operationally cooperating printing plates in an offset type rotary printing press is controlled by novel means. In doing so, the apparatus continually senses when a first printing plate disposed on the outer surface of the rotating plate roller comes into registration with a second printing plate disposed on the outer surface of the rotating blanket roller and concurrently measures the dynamic contact pressure being exerted between said rotating printing plates while remaining in registration. Said measured contact pressure values are next compared with preestablished contact pressure values to generate an electrical feedback control signal which is applied to conventional programmed controller means for fully automated control of the actual printing plate contact pressure during continued press operation. A more direct control of said dynamic printing plate contact pressure in this manner can understandably improve the operating efficiency of various type rotary printing presses to include those having single and multiple printing heads as well as those producing single and multicolored printed images.
It is an object of the present invention, therefore, to provide an automated control system for operation of a rotary printing press to improve the visual quality of the printed image.
It is another object of the present invention to provide such presently improved actual printing plate contact pressure in a manner requiring only a relatively simple modification to the existing rotary printing press apparatus.
A still further object of the present invention is to provide a rotary printing press incorporating the presently improved control system for increased operating efficiency.
It is yet another object of the present invention to provide a novel method for automated control of a rotary printing press to increase the quality of the printed image.
These and still further objects of the present invention will become more apparent upon considering the following more detailed description of the present invention.
It has now been discovered by the present applicants that the printed image quality produced in a rotary type printing press can be significantly improved with novel fully automated control means. Generally, the presently improved control system is incorporated in a rotary printing press having pairs of rotating printing plates disposed on the outer surface of rotating plate and blanket rollers and which further includes a pair of upper and lower form rollers transferring ink to the printing plates disposed on said plate roller. The present automated control method first senses during press operation when the printing plates disposed on the plate and blanket rollers come into registration and continuously measures the contact pressure being exerted between the plate and blanket rollers during the time period when the physically contacting printing plates remain in registration, next determines the difference between the measured contact pressures and preestablished contact pressure values to generate an electrical feedback control signal, and employs said electrical feedback control signal to automatedly vary the contact pressure between the plate and blanket rollers during continued press operation. Since the present fully automated control system can be utilized with the particular type rotary press apparatus described in the aforementioned U.S. Pat. No. 6,543,350B2, the entire contents of said issued patent are incorporated herein by reference. In accordance therewith, many of the same position and contact pressure sensing devices can be employed in the present control system in order to generate the now further required electrical feedback control signal. Registration between the paired printing plates on the plate and blanket rollers in the present control system can thereby employ the same proximity or position sensing devices disclosed in the referenced patent. Likewise, the same previously disclosed pressure sensing devices, such as strain gages and the like, can be employed in the present control system for the contact pressure measurements. Both of said type sensing devices cooperate in a particular manner for development of the further required electrical feedback control signal in the present control system. More particularly, said electrical feedback control signal is produced with programmed electrical controller means that operates upon these measured values.
In a representative embodiment, a Microstar Model DAP1200a controller device is employed for closed loop control of the printing plate contact pressure although still other commercially available controller devices of the proportional/integral/derivative type (PID) are considered equally suitable. The programmed sequence of operations for said controller in the present control system is initiated by the position sensing devices indicating when the paired printing plates come into registration. Contact pressure measurements from the pressure sensing devices are then continuously applied to the controller device during the time period when the paired printing plates remain in registration. In doing so, the analog strain gage values are converted to digital signals for input to said controller. Said applied force measurements are then averaged in the controller for comparison with preestablished contact pressure values previously entered by the press operator and with any difference detected therebetween forming an error signal which is further applied to corrective pressure adjustment means included in the present apparatus. Any needed contact pressure adjustment with the present control system is thereby carried out automatically in the press apparatus by adjusting the contact pressure being exerted between the form rollers and the plate roller. Having customary electric stepper motor and gear box arrangements or the like which are physically secured to the press frame for said purpose have already proven acceptable. Any change needed to meet said preestablished contact pressure values in said manner will be provided by the number of steps and direction of the stepper motor device when actuated by the output error signal from the operatively associated controller device. Such operational control can be further carried out by employing individual stepper motor and gearbox arrangements to adjust each form roller in the press apparatus.
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It will be apparent from the foregoing description that a broadly useful and novel means has been provided to continuously control the contact pressure being exerted when the actual printed image is being formed in a rotary printing press. It is contemplated that various modifications can be made in the present method for controlling print quality as well as the apparatus means being employed to do so other than herein specifically illustrated, however, without departing from the spirit and scope of the present invention. For example, other position sensors denoting proper registration between the rotating printing plates on the plate and blanket rollers can be employed as well as substituting other pressure sensing devices than mechanical strain gages. Similarly, other data processors and controller devices are contemplated for use in the present closed loop control procedure than herein illustrated for even more extensive control of the printing contact pressure leading to still further improved print quality. Accordingly, it is intended to limit the present invention only by the scope of the appended claims.
This application relates to Provisional Application Ser. No. 60/508,498 filed by the present applicants on Oct. 3, 2003.
Number | Date | Country | |
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60508498 | Oct 2003 | US |