Abstract:
In a printing press, an adjustment system for positioning a rolling element such as a form roller or an impression cylinder relative to a first cylinder having a first diameter and relative to at least a second cylinder adapted to replace the first cylinder and having a second diameter different than the first diameter, the system comprising an actuating member operable to displace the rolling element relative to the first cylinder and having a pivotable fixed first end and a second end mechanically linked to the rolling element, the actuating member providing sufficient displacement to bring the rolling element into contact with the first cylinder such that a predetermined contact pressure therebetween is reached, the actuating member also being operable to bring the rolling element into contact with the second cylinder such that the predetermined contact pressure therebetween is reached. A method for displacing a rolling element is also presented.

Description:
TECHNICAL FIELD 
   The present invention relates generally to printing presses, and more particularly to a rolling element adjustment system for an offset printing press. 
   BACKGROUND OF THE INVENTION 
   Offset printing presses are well known in the art. Typically, water and ink are supplied to a printing plate cylinder, and are then transferred to a blanket cylinder for printing onto sheets or web, fed between the blanket cylinder and an impression cylinder. The water supply to the plate cylinder usually comprises a dampening unit having a dampening form roller which contacts the plate cylinder and is fed water from a water pan through intermediate water transferring rollers. Similarly, an inking unit transfers ink through one or more ink form rollers contacting the plate cylinder, the ink form rollers receiving ink from an ink supply through a series of ink transfer rollers. 
   While such presses have fixed lateral dimensions, and as such printed products wider than the length of the cylinders cannot be produced, the circumference of the rotating cylinders determines the length of each repeated pattern being printed onto the web or sheets passing therethrough. Accordingly, the larger the circumference of the plate and blanket cylinders being used, the longer the printed pattern that can be produced. Therefore, in order to permit a press to be modified to permit printing of different lengths of printed patterns, standard variable size presses provide a changeable insert comprising plate, blanket and impression cylinders. Replacement inserts comprising cylinders of different diameters can therefore be used with the same press. 
   An important parameter determining printing quality is the line of contact between two cylindrical rollers in contacting engagement, otherwise known as the contact stripe. Standard adjustment mechanisms between rollers and cylinders include mechanical means such as bolts or screws and single pneumatic actuators, to allow fine tuning of the contact stripe between, for example, the inking or dampening form roller and the plate cylinder. However, conventional adjustment mechanisms are usually adapted to be used with plate and blanket cylinders of fixed diameter. 
   On standard variable size presses, mechanical stoppers are usually included in the insert in order to adapt the adjustment mechanisms of the form rollers and cylinders to the plate and blanket cylinder diameter. Such stoppers offer only an adjustment having a limited precision. 
   Sleeve offset presses, such as the one disclosed in U.S. Application No. 60/457,295 by the applicant and incorporated herein by reference, provide for replacing only the plate and blanket cylinders, thereby eliminating the need for the various inserts. While the elimination of the inserts minimizes the complexity of changing cylinder sizes and reduces the storage space previously required for replacement inserts, it also eliminates the support for the prior mechanical stoppers. Integrating the stoppers directly on the cylinder bodies greatly increases their weight and cost. Alternatively, providing a different adjustment mechanism for each cylinder size can be very costly as well as increase the storage space necessary for spare parts and the down time when the cylinders are changed. 
   Accordingly, there is a need for a unique adjustment mechanism providing an adequate contact stripe adjustment between rolling elements in a printing press and being able to accommodate various dimensions of plate and blanket cylinders. 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide an improved adjustment system for rolling elements in an offset printing press. 
   Therefore, in accordance with the present invention, there is provided in a printing press an adjustment system for positioning a rolling element relative to a first cylinder having a first outer diameter and relative to at least a second cylinder adapted to replace the first cylinder and having a second outer diameter different than the first outer diameter, the adjustment system comprising an actuating member operable to displace the rolling element relative to the first cylinder, the actuating member having first and second ends, the first end being pivotally connected to a frame of the printing press and the second end being mechanically linked to the rolling element, the actuating member providing sufficient displacement to bring the rolling element into contact with the first cylinder such that a predetermined contact pressure therebetween is reached, the actuating member also being operable to bring the rolling element into contact with the second cylinder such that the predetermined contact pressure therebetween is reached. 
   Also in accordance with the present invention, there is provided a method for displacing a rolling element relative to at least a cylinder in a printing press, the rolling element being mechanically linked to an adjustment system composed of first and second independently controllable adjustment mechanisms, the method comprising the steps of setting the first adjustment mechanism to a predetermined length so that a total length of the adjustment system is such that the rolling element is out of contact with the cylinder, and extending the second adjustment mechanism such as to bring the rolling element in contact with the cylinder until a desired contact pressure therebetween is reached. 
   Further in accordance with the present invention, there is provided an offset printing press including at least a first cylinder and a rolling element mounted in a frame structure in serial contactable engagement, the printing press comprising an adjustment mechanism operable to displace the rolling element between a predetermined printing position, wherein the rolling element and the first cylinder are in contacting engagement, and a disengaged position, wherein the rolling element is removed from contacting engagement with the first cylinder, the adjustment mechanism being selectively actuable and providing controlled variable displacement of the rolling element relative to the first cylinder. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Having thus generally described the nature of the invention, reference will now be made to the accompanying drawings, showing by way of illustration a preferred embodiment thereof and in which: 
       FIG. 1  is a schematic side elevation view of an offset printing press including form rollers adjustment systems according to a preferred embodiment of the present invention; and 
       FIG. 2  is a schematic side elevation view of an offset printing press including a cylinder adjustment system according to an alternative embodiment of the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Referring to  FIG. 1 , an offset printing press  10  generally comprises a plate cylinder  12 , a blanket cylinder  14  and an impression cylinder  16 , all supported within a common frame structure  18 . At least the plate and blanket cylinders  12 , 14  are adapted to be completely removed from the printing press  10 , such that corresponding replacement cylinders having a different diameter can be re-engaged in the press in their place. Water and ink are supplied to the plate cylinder  12  by the dampening unit  22  and the inking unit  20  respectively. 
   The inking unit  20  generally comprises at least one ink transfer roller  26  receiving ink from an ink supply. The inking unit also comprises ink form rollers  28  in direct contacting engagement with the transfer roller  26  receiving the ink, and in direct contacting engagement with the plate cylinder  12  to transmit the ink thereto. The dampening unit  22  generally comprises a dampening form roller  30  in direct contacting engagement with the plate cylinder  12  and with dampening fluid transfer rollers  32 , 33 , which transfer the dampening fluid from the dampening supply  34  to the dampening form roller  30 . A series of transmission rollers  27  can also transfer ink from the ink supply to the dampening form roller  30 , so that the dampening form roller  30  applies both water and ink to the plate cylinder  12 . 
   The plate cylinder  12  generally comprises a circumferentially disposed printing plate on the outer surface thereof, the circumference of the plate cylinder corresponding to the length of the print repeat produced by the printing plate. The water and ink fed to the plate cylinder  12  are transferred from the exterior surface thereof to the blanket cylinder  14 , which is in contacting engagement with the plate cylinder  12 . Either sheets or a continuous web are fed between the blanket cylinder  14  and an impression cylinder  16 , which is similarly in contacting engagement with the blanket cylinder  14 . All cylinder rollers are rotatable and in precise contacting engagement with each adjacent roller along a contact stripe, such that fluid is transferred from one roller to the next. This contact stripe is precisely set, to ensure exact and uniform contact pressure along the entire length of the rollers. 
   The present invention concerns an adjustment mechanism for rolling elements of the printing press. The term rolling element as used herein is defined to comprise any substantially cylindrical and rotatable press element, including both rollers, such as ink or dampening form rollers, and cylinders, such as plate, blanket or impression cylinders. 
   In a preferred embodiment, illustrated in  FIG. 1 , the adjustment system  90   a,b  is adapted to be used with form rollers  28 , 30 . Although a single adjustment system  90   a  is shown for the ink form roller  28  and a single adjustment system  90   b  is shown for the dampening form roller  30 , two separate adjustment systems  90   a,b  are preferably used for each, one disposed at each end thereof. The adjustment systems  90   a,b  used with the inking and dampening units  20 , 22  being similar in geometry and function, they will be described simultaneously herein. However, it is to be understood that the adjustment system  90   a  for the inking form roller  28  and the adjustment system  90   b  for the dampening form roller  30  are independently operable from one another. 
   Each adjustment system  90   a,b  generally comprises an integrated multiple pneumatic actuator assembly having a first pneumatic actuator  92   a,b  and a second pneumatic actuator  94   a,b . The first pneumatic actuator  92   a,b  includes an integral locking mechanism  96   a,b . The adjustment system  90   a,b  also comprises a fixed end  91   a,b  which is pivotally engaged to the press frame structure  18 , and an opposed translating free end  93   a,b  which is pivotally engaged to a support or link member  98   a,b . The link member  98   a,b  rotationally supports the form roller  28 , 30  and rotates about a fixed pivot  99   a,b  which is preferably located at the central axis of the transfer roller  26 , 32 . 
   The adjustment system  90   a,b  permits the form roller  28 , 30  to be “thrown on” or “thrown off”, such that the form roller  28 , 30  can be selectively engaged or disengaged from contact with the plate cylinder  12 . The adjustment system  90   a,b  also allows for the location of the form roller  28 , 30  to be variable while remaining in contact with the transfer roller  26 , 32 , which permits the form roller  28 , 30  to accommodate displacement of the plate cylinder  12  or an alternate plate cylinder having a different diameter. The adjustment system  90   a,b  also permits fine contact stripe adjustment between the form roller  28 , 30  and the plate cylinder  12 . 
   In operation, the form roller  28 , 30  is correctly positioned in contact with the plate cylinder  12  according to the following. With the second pneumatic actuator  94   a,b  fully extended to the end of its stroke, the first pneumatic actuator  92   a,b  is extended by air pressure and is precisely adjusted until a desired contact stripe is achieved between the form roller  28 , 30  and the plate cylinder  12 . The air pressure in the first pneumatic actuator  92   a,b  of each form roller adjustment system  90   a,b  is preferably set by an independent air regulator. The air regulators can be programmed to different fixed values, corresponding to different plate cylinder diameters, so that only a fine adjustment may be required by the operator to obtain a desired contact stripe. Once the desired contact stripe is obtained, the air-actuated locking mechanism  96   a,b  is engaged to lock the output rod of the first pneumatic actuator  92   a,b  in position, thereby fixing the distance between the translating free end  93   a,b  and the fixed end  91   a,b  of the form roller adjustment system  90   a,b . Accordingly, the air pressure which regulates the first pneumatic actuator  92   a,b  can be statically adjusted (ie: when the press is not running) such that a desired contact stripe width between the form roller  28 , 30  and the plate cylinder  12  is achieved, and the brake or locking mechanism  96   a,b  is then locked to fix the first pneumatic actuator in position. Thus, during operation of the press, the locking mechanism  96   a,b  provides a mechanical stop which correctly positions the form roller in contacting engagement with the plate cylinder such that a desired contact pressure therebetween is achieved. 
   The form roller  28 , 30  is disengaged from the plate cylinder  12  according to the following. With the first pneumatic actuator  92   a,b  locked by the locking mechanism  96 , the second pneumatic actuator  94   a,b  is actuated to retract, thereby shortening the overall length of the form roller adjustment system  90   a,b . This causes the link member  98   a,b  to rotate about the transfer roller  26 , 32 , lifting the form roller  28 , 30  out of contacting engagement with the plate cylinder  12 . Since the contact stripe before the disengagement of the form roller  28 , 30  from the plate cylinder  12  was determined with the second pneumatic actuator  94   a,b  fully extended, and since the first pneumatic actuator  92   a,b  is locked during that disengagement, a simple return to full extension of the second pneumatic actuator  94   a,b  will place the form roller  28 , 30  back in contact with the plate cylinder  12  with the same contact stripe. 
   The form roller adjustment system  90   a,b  alternately includes an integral locking mechanism in the second pneumatic actuator, so that the desired contact stripe can be set by the first pneumatic actuator with the second pneumatic actuator being locked at a chosen length. Retraction of the second pneumatic actuator from the chosen length thus breaks contact between the form roller and the cylinder, and extension of the second pneumatic actuator back to the chosen length returns the set contact stripe between the two rollers. In this case, the second pneumatic actuator is adapted to retain a memory of the chosen length to be able to automatically return thereto after retraction. 
   Referring to  FIG. 2 , an alternative embodiment of the adjustment system  190  of the present invention is illustrated, adapted to be used to adjust the position of the impression cylinder  16  with respect to blanket cylinders  14  of various sizes, as well as to “throw-on” or “throw-off” the impression cylinder  16  with respect to the blanket cylinder  14  when the printing process is to be stopped. This permits printing to be interrupted, without having to drastically displace the impression cylinder and blanket cylinder relative to one another, and permits printing to be easily re-started without having to precisely reset the contact stripe between these cylinders. 
   The impression cylinder  16  rotates about its center  144  which is displaceable along an adjustment arc  142  by the action of first link members  198  which rotate about a pivot  141 . The impression cylinder adjustment system  190  comprises a first pneumatic actuator  192  having a first translating end  193  which is pivotably engaged to the impression cylinder first link member  198 . A second, opposed end  185  of the first actuator  192  is pivotably engaged to an eccentric mounting assembly  187  which is rotatable within the frame structure  18  of the printing press  10 . The eccentric rotating assembly  187  of the first actuator  192  is rotatable by a second actuator  194 , which is preferably a smaller pneumatic cylinder. A first translating end  195  of the second actuator  194  is engaged to the eccentric rotating assembly  187  by a second link member  188 . Opposed ends of the second link member  188  are respectively pivotably connected with the translating end  195  of the second actuator  194  and the second end  185  of the first actuator which is eccentrically engaged to the rotating assembly  187 . A second end  197  of the second actuator  194  is not displaceable, but is pivotably connected to the frame structure  18 . 
   Accordingly, and similarly to the first embodiment of the adjustment system  90   a,b  previously described, the first actuator  192  is used for impression adjustment, such that the impression cylinder can be displaced to accommodate the particular size of blanket and plate cylinders being employed, and to control the contact pressure between the impression cylinder  16  and the blanket cylinder  14 . By extending or retracting the first translating end  193  of the first actuator  192 , the impression cylinder first link member  198  is thus pivoted such that the impression cylinder  16  displaced as required. The first actuator  192  preferably has a relatively large travel, such that plate and blanket cylinder of various sizes can be accommodated. However, the first actuator is also preferably precisely controlled, such that a desired contact pressure between the impression cylinder  16  and the blanket cylinder  14  can be set. Once this is set, the first actuator  192  is locked, such that the relative positions of the first and second ends thereof are fixed. 
   The second actuator  194  of the impression cylinder adjustment system  190  is used to “throw-on” or “throw-off” the impression cylinder  16 , such that printing can be started or stopped when required. Displacing the translating end  195  of the second actuator  194  acts to rotate the eccentric rotating assembly  187  within the frame structure  18 , thereby slightly displacing the second end  185  of the locked first actuator  192  by a slight distance, which accordingly disengages the impression cylinder  16  from contact with the blanket cylinder  14  by said slight distance. This slight distance generally corresponds to the eccentricity of the second end  185  of the first actuator  192  relative to the center of rotation of the rotating assembly  187 . Thus, the precise location of the impression cylinder and the contact stripe relative to the blanket cylinder can be preset by the first actuator  192  and then locked in position, and the second actuator  194  can be activated to easily engage and disengaged the impression cylinder  16  with the blanket cylinder  14 , without having to reset the position and contact stripe each time. A dial-adjusted mechanical stop for the piston of the second actuator  194  is preferably also provided, such that slight displacement of the impression cylinder  16  relative to the blanket cylinder  14  is possible to allow for the particular thickness of the web or sheet substrate passing therebetween. 
   Accordingly, the pneumatically actuated and controlled roller and cylinder adjustment system  90   a,b  and  190  permits the elimination of mechanical stoppers, which have typically been used in the past to locate the form rollers relative to the plate cylinder and the impression cylinder relative to the blanket cylinder. The form roller and cylinder adjustment systems  90   a,b  and  190  provide the ability to throw on or off the form rollers  28 , 30  and the impression cylinder  16 , and further permits more accurate adjustment of the contact stripe. It also enables the positioning of the form rollers  28 , 30  and impression cylinder  16  as required regardless of the plate and blanket cylinder size used. 
   Although pneumatic actuators were described as being the preferred kind of actuator for the adjustment systems  90   a,b  and  190 , it is understood that other appropriate kinds of actuating members may be used, such as hydraulic or electric linear actuators for example. Particularly, in one alternate embodiment of the present invention, the first pneumatic actuator  192  is alternately a ball screw actuator. If hydraulic actuators are used, hydraulic fluid pressure would have to be adjusted to obtain the desired contact stripes. 
   Also, the adjustment systems as described herein can be used to similarly adjust other rolling elements in the printing press as required. 
   The embodiments of the invention described above are intended to be exemplary. Those skilled in the art will therefore appreciate that the forgoing description is illustrative only, and that various alternatives and modifications can be devised without departing from the spirit of the present invention. Accordingly, the present is intended to embrace all such alternatives, modifications and variances which fall within the scope of the appended claims.