CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    This is a continuation-in-part application of co-pending application Ser. No. 09/090,485, filed Jun. 3, 1998. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates to an apparatus for printing, and more particularly to an apparatus having a displaceable print cylinder for printing on board or cut sections of board.  
         BACKGROUND OF THE INVENTION  
         [0003]    Apparatus for printing on board or cut sections of board, such as corrugated board, commonly include a number of print stations through which the board is directed to successively receive print images from one or more of the print stations.  
           [0004]    In such apparatus, each print station commonly includes a print cylinder fitted with one or more printing plates for receiving ink from, for example, an anilox roll, and for transferring appropriate print images to the board or board sections. The printing plate or plates on each print cylinder need to be replaceable to enable different printing requirements to be satisfied. The present invention is concerned with an arrangement for enabling the printing plates to be changed on one print cylinder without requiring the entire printing apparatus to be stopped.  
           [0005]    In addition, existing apparatus typically exhaust air from their vacuum transfer table fans directly into overhead centralized take-away systems or to a bag filter. Bag filters eventually clog, and the resulting back pressure decreases the vacuum level of the transport table. This decrease in vacuum level affects the accuracy of registration from one print unit to another. The present invention incorporates a self cleaning filter unit directly on the print unit&#39;s vacuum fan&#39;s exhaust to satisfy clean air requirements for operating personnel.  
         SUMMARY OF THE INVENTION  
         [0006]    According to the present invention, at least one of the print stations comprises a print cylinder mounted in a laterally displaceable carriage which can be moved laterally (in a direction parallel to the longitudinal axis of the print cylinder) away from the board travel line, leaving in place substantially all the remaining parts of the print station, to allow changing of the printing plate or plates on the print cylinder while the printing apparatus can continue to operate with one or more of the other print stations.  
           [0007]    Each print station is preferably a top printer: that is to say, it applies print to the upper surface of the board or board sections. In a preferred arrangement for flexographic printing, the print cylinder receives ink on its printing plate or plates from an anilox roll which remains in position (except for being moved slightly away from the print cylinder) when the print cylinder carriage is displaced laterally to allow the printing plate or plates to be changed.  
           [0008]    Each print station preferably includes conveyors, for example rollers, for conveying the board through the station, and those conveyors remain in place when the print cylinder carriage is displaced laterally. Thus the conveyors remain available to convey board through the print station so as to allow the printing apparatus to continue operating while any given print station is being altered in preparation for applying the print needed for a subsequent order.  
           [0009]    This invention contrasts with, and is an improvement over, prior proposals, for example one providing for the entire printer or the top portion thereof to be lifted vertically to allow the operator (who must then work on an overhead gantry) to change the printing plates. Another prior proposal involved displacing laterally the entire print station; this involves a number of problems, not least of which is the fact that the printing apparatus cannot then readily be kept in operation while one of the print stations is out of position. The provision, in accordance with the present invention, for displacing essentially only the print cylinder and leaving the remainder of the printing station in position is a significant improvement over such prior proposals. 
       
    
    
       [0010]    An example of a print station according to this invention is shown in the accompanying drawings.  
       BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is an isometric view of the print station of the present invention;  
         [0012]    [0012]FIG. 2 is a side schematic view of the print station of FIG. 1;  
         [0013]    [0013]FIG. 3 is a enlarged partial schematic side view of the upper portion of the print station of FIG. 1;  
         [0014]    [0014]FIG. 4 is a front view of the print station of FIG. 1;  
         [0015]    [0015]FIG. 5 is an isometric view of the print station of FIG. 1 showing the print cylinder carriage in the laterally displaced position;  
         [0016]    [0016]FIG. 6 is a enlarged partial isometric view of the dust collection system of the print station of FIG. 1; and  
         [0017]    [0017]FIG. 7 is a flow chart illustrating a preferred method of operating an apparatus incorporating the print station of FIGS.  1 - 6 . 
     
    
       [0018]    Additional features and advantages of the invention will become apparent to those skilled in the art upon consideration of the following detailed description of the preferred embodiment exemplifying the best mode of carrying out the invention as presently perceived. The detailed description particularly refers to the accompanying drawings.  
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]    [0019]FIG. 1 illustrates a print station  10  comprising a print cylinder  12  carrying printing plates (not shown) for applying print images to corrugated board sections  100  conveyed in the direction of the arrow  11  through the print station.  
         [0020]    Referring now to FIGS. 1 and 2, ink is applied to the printing plates by means of an anilox roll  14  which is uniformly coated with ink by means of a chambered doctor blade assembly  16 . An impression roll  18  located below the print cylinder  12  holds the moving board sections  100  against the printing plates on the print cylinder  12 . A plurality of rolls  20  are also provided for conveying the board sections  100  through the print station  10 . The conveying rolls  20  are mainly located in a suction chamber  22  whereby suction in the chamber  22  draws the board section  100  downwards into driving engagement with the rolls  
         [0021]    It is contemplated that a different conveyor arrangement may be utilized. For example, the conveyor system may involve rolls above the board line and a vacuum chamber above the board line for drawing the board sections upwards into engagement with the conveying rolls.  
         [0022]    The print station  10  comprises a main frame  24  and a displaceable print cylinder carriage  26 . The main frame  24  includes an operator side sub-frame  24   a  and drive-side sub-frame  24   b.  A transverse bracket  28  connects operator-side sub-frame  24   a  and a drive-side sub-frame  24   b.  As best seen in FIG. 4, each end  28   a  and  28   b  of the transverse bracket  28  overhangs beyond both the respective sub-frames  24   a  and  24   b.  The suction chamber  22 , impression roll  18 , rolls  20 , anilox roll  14 , and the chambered doctor blade  16  are carried by the main frame  24 .  
         [0023]    As best seen in FIGS. 1 and 2, a guide rail  30  is mounted on the front face  32  of the main frame bracket  28  and extends substantially the entire length thereof. The rail  30  comprises upper  30   a  and lower  30   b  tracks.  
         [0024]    The print cylinder  12  is mounted in the print cylinder carriage  26 . The carriage  26  includes an operator-side sub-frame  26   a  and a drive-side subframe  26   b.  A bracket  34  is secured to the top of the carriage  26 , extending the entire length of the print cylinder  12 . As best seen in FIG. 4, the bracket  26  carries an upper and a lower row of spaced wheels  36 . The upper row of wheels engage with and travel along the upper track  30   a  while the lower row of wheels  36  engage with and travel along the lower track  30   b.  The wheel and track configuration enables the carriage  26  to be displaced laterally to carry the print cylinder  12  clear of the board line: that is to say, to the position shown in FIG. The wheels  36  may have V-shaped peripheral cross-sections and in that case the tracks  30   a  and  30   b  would have corresponding V-sectioned grooves for locating the wheels.  
         [0025]    As best seen in FIG. 3, when the print cylinder  12  is in position above the board line (FIG. 1), the carriage  26  may be secured to the main frame  24  by a clamping device  40  mounted on each sub-frame of main frame  24 . The clamping device  40  includes a pivoting lever  42  mounted to the main frame  24  at pivot  44 . An actuator  46  is connected to one end  42   a  of the lever  42 . A cam follower  47  is located on the other end  42   b  of the lever  42 . An inclined ramp  48  is located on each lower inner comer of the frame  26  such that the inclined surface  48   a  of the ramp  48  is engageable by the cam follower  47 . To clamp the carriage  26  on the main frame  24 , the actuator  46  is retracted, pivoting the lever  42  about pivot  44 . The follower  47  engages the inclined surface  48   a  of the ramp  48 , applying both a horizontal and a vertical force to the ramp  48  to secure the carriage  26  to the main frame  24 . The clamping device  40  is released by extending the piston rod of the actuator  46 . When the clamping device  40  is released the print cylinder carriage  26  may be displaced laterally to allow for printing plate changing.  
         [0026]    Before the carriage  26  can be displaced laterally it is necessary to lift the print cylinder  12  clear of the impression cylinder  18 . It is also necessary to lift the anilox cylinder  14  clear of the print cylinder  12  before the print cylinder can be lifted from the impression cylinder  18 . An anilox roll lifting device  50  is incorporated in the main frame  24  and a print cylinder lifting device  60  (FIG. 1) is incorporated in the carriage  26  to accomplish these functions.  
         [0027]    As best seen in FIG. 3, the anilox lifting device  50  comprises a frame  52  pivotably attached to the main frame  24  at pivot  54 . The anilox roll  14  is mounted on the pivotable frame  52 . A spring  56  located on the main frame  24  biases the pivotable frame  52 , and the anilox roll  14 , away from the print cylinder  12 . An eccentric  58  is rotated to force the pivotable frame  52  against the spring  56  such that the anilox roll  14  is engaged with the print cylinder  12 .  
         [0028]    A releaseable lock member  59  is provided to secure the pivotable frame  52  in an operating position in which the anilox roll  14  is engaged with the print cylinder  12 . In the operating position, the eccentric  58  is rotated until its thickest portion is in contact with contact pads  53  on frame  52  to force the frame  52  against the spring  56  and engage the anilox roll  14  with the print cylinder  12 . The locking member  59  is clamped against the eccentric  58  by means of a hold-down cylinder (not shown) to secure the frame  52  in the operating position.  
         [0029]    When it is necessary to displace the print cylinder carriage  26  laterally, the anilox roll  14  must be lifted off the print cylinder  12 . To accomplish this, the locking member  59  is disengaged from the eccentric  58 . The eccentric  58  is then rotated until its thinnest portion is engaged with the contact pads  53 . This permits the frame  54  to pivot away from the print cylinder  12  under the force of the spring  56 . In this position there is sufficient clearance between the anilox roll  14  and the print cylinder  12  to allow the carriage  26  to be displaced laterally, as explained in greater detail below.  
         [0030]    It should also be recognized that the eccentric  58  can be rotated to an intermediate position in which the anilox roll  14  is disengaged to a lesser degree from the print cylinder  12 , permitting a jam to be cleared or the print cylinder  12  to be cleaned.  
         [0031]    The print cylinder lifting device  60  is best seen in FIG. 1 and comprises an eccentric  62  on which the print cylinder  12  is mounted. The periphery of the eccentric  62  has a toothed surface  64 . A series of gears  66  engage the toothed surface  64  of the eccentric  62 . The gears  66  are driven to rotate the eccentric  62  and lift the print cylinder  12  from the impression cylinder  18 . In this raised position, the print cylinder carriage  26  can be displaced laterally.  
         [0032]    A drive device  70  is provided for displacing the print cylinder carriage  26  laterally. The drive device  70  comprises a linear actuator  72  mounted to the bracket  28  of the main frame  24 . The linear actuator  72  is preferably in the form of a telescoping slide. The linear actuator  72  is driven by a drive motor  74  through a gear reducer  76 . The linear actuator is coupled to the bracket  34  of the frame  26 . The drive motor  74  extends and retracts the linear actuator  72 , displacing the print cylinder carriage  26  laterally from the operating position shown in FIG. 1 to the fully displaced configuration shown in FIG. 5. In the fully displaced position, the print cylinder carriage  26  is cantilevered on the end  28   a  of the main frame bracket  28 . The drive motor  74  is torque-limited to provide a beneficial safety feature. The motor  74  will stall when resistance to movement is applied to the carriage  26 , for example in the event that the carriage were to encounter an obstruction such as a person, during displacement of the carriage. The drive device  70  also includes a reversing contactor, which provides for alternative extension or retraction of the linear actuator  72  by drive motor  74 . A suitable motor for drive motor  74  is the Reliance Electric DC drive Model 1DN1001, made by Rockwell Automation of Greenville, S. C.  
         [0033]    A wire raceway  78  is provided for containing the various electrical wires for the print cylinder carriage  26 . The electrical wires are located in a flexible wire harness  79  which lays in the raceway  78 . As the print cylinder carriage  26  is displaced laterally, the wire harness  79  progressively bends and doubles over itself allowing the electrical wires contained therein to follow the printing cylinder carriage  26  without risk of tangling, kinking, or accidental breaking. When the print cylinder carriage  26  is retracted, the wire harness  79  is returned back into the raceway  78 .  
         [0034]    It is contemplated that a pair of sensors may be provide to assist in retracting the print cylinder carriage  26 . The sensors (not shown) can be used to enable the slowing down of the linear actuator drive in order to slow down the carriage  26  down just before reaching the operational or fully retracted position. The sensors can also be used to signal when the carriage reaches the home position so the carriage lock down mechanism  40  can be actuated to secure the carriage  26  to the main frame  24 .  
         [0035]    As shown in FIG. 1, the print cylinder  12  has an associated drive motor  80  which is an independent drive such as a servo motor for rotating the print cylinder. The motor  80  preferably remains connected to the print cylinder  12  when the carriage  26  is displaced laterally, as shown in FIG. 5. Preferably, when the print cylinder is not in the down and ready-to-run condition, a contactor of the drive motor  80  is de-energized to ensure against inadvertent cylinder rotation, for operator safety. However, the drive motor  80  can be “jogged” in a low torque mode when not in the down and ready-to-run condition to slowly rotate the cylinder  12  forward and reverse. The ability to jog the cylinder  12  facilitates changing of die plates or other cylinder maintenance, for example. The cylinder  12  may be jogged while the carriage is lifted with the carriage in the retracted condition. Alternatively, the cylinder can also be jogged after the carriage has been displaced laterally to the cantilevered position previously described. As an additional safety feature, the cylinder drive motor  80  is torque-limited to provide for stalling of the motor and stoppage of the cylinder when resistance to rotation is applied the cylinder, for example by the hand of an operator.  
         [0036]    The conveyor rolls  20  may also have an independent drive; that is to say, independent of the drive (not shown) to the anilox roll  14  and of the drive  80  to the print cylinder  12 . The drive for the rolls  20  of each print station may be controlled to ensure proper registration of the print images applied to the board sections at successive print stations.  
         [0037]    [0037]FIGS. 2 and 4 also show an ink pail  82  from which, during printing, ink is pumped into the ink chamber of the assembly  16 . Adjacent to the pail  82  there is a container  84  for holding washing liquid. A washing operation may be carried out on the anilox roll  14  by pumping washing liquid into the chamber of the assembly  16  while the print cylinder carriage  26  is in the laterally displaced position for printing changing purposes. Separate washing provisions may be provided for the printing plates on the cylinder  12 .  
         [0038]    For the sake of lightness, the print cylinder  12  may comprise mainly a composite non-metallic material.  
         [0039]    In FIG. 6 there is shown a dust collection apparatus  90  in combination with the print station  10  of the present invention. It should be understood that the dust collection apparatus  90  can be adapted for use in many different types of corrugated box making machinery and is not limited to the embodiment disclosed herein. The dust collection apparatus extracts dust from the exhaust air of the vacuum transfer table  22 . In order to provide vacuum level at the wheel surface of the transport table  22 , air is extracted through an inlet duct  91  by a fan  92 . The air is exhausted into a dust collection system  93 .  
         [0040]    In side the dust collection system  93 , the air is pushed through filters  94  where dust is removed and expelled out of a silencer  95 . At a sequence time throughout the operation, rotating nozzles  96  located inside the filters  94  are powered by high pressure air which blows collected dust off the surface of the filters  94 . This airborne dust eventually settles into a removable dust pan  97 . This “self cleaning” filter sequence eliminates the back pressure produced by “clogged” filters and keeps the vacuum level at the transport table  22  at a maximum condition. By incorporating a self-cleaning filter system  93  directly on the print unit&#39;s  10  vacuum fan&#39;s exhaust, air is cleaned of dust and expelled directly into the plant without the inconvenience of coupling to a central system or the inefficiency of using a bag filter arrangement.  
         [0041]    The preferred method of operating the print station  10  of FIGS.  1 - 6  is best understood with reference to the flow diagram of FIG. 7. As described previously, devices for printing on board material, such as corrugated board, typically include a series of print stations arranged for sequentially printing on a length of board that is directed through the series of print stations. Accordingly, in the preferred method of operating the print station  10 , the print station is operated as part of a device having a series of print stations. The device preferably includes a control system which governs the lateral displacement for each of the print cylinders and coordinates the series of print stations in the manner to be described.  
         [0042]    In the “ready to print” condition  100 , the actuator is retracted so that the carriage  26  is in the fully-in position, with the carriage clamping devices  40  locking the carriage  26  to the frame  24 . The cylinder  12  and anilox roll  14  are in their lowered positions to position the print cylinder  12  for contact with the corrugated board to be printed. When roll-out of the print cylinder  12  of print station  10  is desired, the initial step  102  is to raise anilox roll  14  and print cylinder  12  in the manner described previously. However, before anilox roll  14  and print cylinder  12  can be raised, a safety  104  of the control system requires that the carriage be in the fully-in position. The position of carriage  26  could be verified, for example, by a proximity switch between the carriage  26  and frame  24  to provide a signal to the control system to indicate that the carriage is in the fully-in position.  
         [0043]    Once the carriage  26  is in the fully-in position, it can be moved to an “up and locked” position  106 . In the up and locked position, the anilox roll  14  and print cylinder  12  have been raised and the clamp device  40  remains engaged to the carriage  26 . With the carriage  26  in the up and locked position, print cylinder  12  may be rotated intermittently, or “jogged” as shown at  108 , to perform die plate changing or other cylinder maintenance, for example, which does not require roll-out of the carriage  26 .  
         [0044]    When it is desired to roll out the carriage, the clamp device  40  is disengaged from the carriage  26 , as illustrated in step  110 , to unlock the carriage and place the print station  10  in a “ready to roll out” condition  112 .  
         [0045]    To roll out the carriage  26 , as illustrated in step  114 , the carriage drive motor  74  is energized to extend actuator  72  to roll out carriage  26 . However, another control safety  116  prevents roll-out of the cylinder carriage  26  if the cylinder is in the process of being raised or lowered. As an additional control safety, the control system will not allow carriage roll-out if any other print station has a carriage that is not in its fully-in position.  
         [0046]    In a “carriage fully-out” condition  118 , the actuator  72  has been extended such that the carriage  26  is cantilevered from the print station frame  24  as shown in FIG. 5. In the fully-out condition  118 , the print cylinder drive  80  can be jogged to slowly rotate the print cylinder  12  as indicated in optional step  120 .  
         [0047]    To return the carriage  26  to the “ready to roll-out” condition  112 , the contactor of carriage drive motor  74  is reversed (step  122 ) such that energization of the carriage drive motor  74  results in retraction of the actuator  72  (step  124 ).  
         [0048]    The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicating the scope of the invention.
A device for printing board or cut sections of board comprising a number of print stations through which the board is arranged to pass successively to receive print images from one or more of the print stations and at least one print station. The print station comprising a print cylinder mounted in a laterally displaceable carriage which can be moved laterally away from the board travel line, leaving in place substantially all the remaining parts of the at least one print station, to allow changing of printing plate or plates on the print cylinder while the printing apparatus can continue to operate with one or more of the other print stations.