Abstract:
The invention relates to an apparatus for correctly registering mounting of a printing plate. Task of the invention is to provide an apparatus to control the correctly registered position of a printing plate, which can be realized with simple means and can withstand abrupt load changes of the printing plate. The task is solved according the invention by inserts allocated to registering elements, which are contacting the printing plate electrically isolated from the registering elements and are connected to a control unit.

Description:
FIELD OF INVENTION  
         [0001]    The invention relates to an apparatus for correctly registering mounting of a printing plate on a plate cylinder of a sheet fed offset press. The plate cylinder has in the plate cylinder gap a plate clamping apparatus consisting of a front plate clamping device and a rear plate clamping and tensioning device. Registering elements for the lateral and circumferential direction are located in the front plate clamping device. These registering elements coinciding with the registering punches in the printing plate and are connected with a control unit.  
         BACKGROUND OF INVENTION  
         [0002]    An apparatus with electrically isolated registering pins at the front plate clamping device is known from DE-GM 77 28 905. The registering pins are connected with an electrical source and a signal transmitter. An electrical circuit is closed and the signal transmitter is activated when the registering pins contacting the printing plate in the registering holes.  
           [0003]    It is disadvantageous that the signal transmitter is also activated if the printing plate is not correctly registered. This is for instance the case when deformations or too large tolerances in the registering hole are causing skewing of the printing plate. The signal transmitter is also activated if for instance the printing plate is laterally misaligned so that the registering pins are touching the front edge of the printing plate. Is also possible that the registering pins are not touching the bottom but the side of the U-shaped at the front edge open registering and an incorrectly registered printing plate activates the signal transmitter.  
           [0004]    The apparatus according to EP 581 212 B1 eliminates these disadvantages. The registering pins are also electrically isolated and connected to an electrical source and a signal transmitter. The registering pins have an additional partial isolation on its surface that only a certain conductive section is detecting the bottom part of the registering hole. Disadvantage of the apparatus are the expensive manufactured registering pins. The isolated surface carries high loads and therefore either the surface or the entire registering pin are made from ceramics. This material can not withstand the occurring abrupt load changes, which might cause breakage of the registering pin.  
         SUMMARY DESCRIPTION OF INVENTION  
         [0005]    Task of the invention is to provide an apparatus to control the correctly registered position of a printing plate, which can be realized with simple means and can withstand abrupt load changes of the printing plate.  
           [0006]    The task is solved according the invention by inserts allocated to registering elements, which are contacting the printing plate electrically isolated from the registering elements and are connected to a control unit.  
           [0007]    Advantages of the invention are especially a wear resistant and fracture-proof registering element, which can be manufactured with low costs and guarantees a secure function. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0008]    The invention is described below in greater detail by embodiments of the invention, by reference being had to the drawing, wherein:  
         [0009]    [0009]FIG. 1: Schematic drawing of a plate cylinder with an open clamping rail during insertion of the printing plate  
         [0010]    [0010]FIG. 2: Schematic of the register-proof position of the printing plate at the registering pins  
         [0011]    [0011]FIG. 3 Schematic of a registering pin with a flat touching head (top view)  
         [0012]    [0012]FIG. 4 Schematic of a registering pin with a round touching head (top view) 
     
    
     DETAILED DESCRIPTION  
       [0013]    [0013]FIG. 1 shows a printing plate  1  stored in a printing plate magazine  2 . The printing plate  1  rests in two pre-registering pins  21   a ,  21   b  which are corresponding to the registering punches  12   a ,  12   b  (see FIG. 2) of the printing plate. The registering pins  21   a ,  21   b  are in a certain distance to each other.  
         [0014]    The registering punches  12   a ,  12   b  have a different shape. The registering punch  12   a  has a flat bottom; the registering punch  12   b  has a radius at the bottom (see FIG. 2). Both have the same insertion bevel  121   a ,  121   b . The pre-registering pins  21   a ,  21   b  have an appropriate shape to the registering punch  12   a ,  12   b . This means that a round pre-registering punch  12   b  fits the round pre-registering pin  21   b  (not shown) whereby its radius matches the radius of the registering punch  12   b . The registering punch  12   a  takes the pre-registering pin  21   a  which is flat as the contact zone in the registering punch  12   a  in the printing plate  1 . The sides of the registering punch  12   a  do not have contact with the pre-registering pin  21   a.    
         [0015]    The printing plate magazine  2  is in its resting position mounted to the not shown frame of the printing press.  
         [0016]    The plate cylinder  4  is also arranged in this frame. The printing cylinder  4  carries on its surface the printing plate  1  supplied from the printing plate magazine  2  and has on its circumference a plate cylinder gap  41  stretching in axial direction. A plate clamping device  7  is located in the plate cylinder gap  4 . It consists of a front clamping device  5  and a rear clamping and tensioning device  6  for the plate end. The front clamping device  5  has an upper clamping rail  52  and a lower clamping rail  51 . The upper clamping rail  52  is fixed mounted at the plate cylinder gap  41 . The lower clamping rail  51  can be moved against the upper clamping rail  52  for clamping of the printing plate  1 .  
         [0017]    The front clamping device  5  has registering elements embodied as registering pins  54   a ,  54   b  in the area of clamping rails  51 ,  52 . FIG. 2 shows that the registering pins  54   a ,  54   b  are in a finite distance from each other as the pre-registering pins  21   a ,  21   b  from each other. The registering pin  54   a  has as the pre-registering pin  21   a  a flat contact area to the bottom of the registering punch  12   a . The registering pin  54   b  has as the pre-registering pin  21   b  a radius to accommodate the radius of the contact area of the registering punch  12   b.    
         [0018]    The design of the registering pins  54   a ,  54   b  is shown in FIG. 3 and FIG. 4. Both registering pins  54   a ,  54   b  have a foot  547   a ,  547   b  carrying the guiding body  541   a ,  541   b . FIG. 3 and FIG. 4 are showing a top view in the direction of the registering pins  54   a ,  54   b  whereby FIG. 3 and FIG. 4 are a section through the guiding body  541   a ,  541   b . Rectangular to the axis of the registering pins  54   a ,  54   b  is in transportation direction of the printing plate  1  a bore in the guiding body  541   a ,  541   b  for the insert  542   a ,  542   b . These inserts  542   a ,  542   b  are electrically isolated to the guiding body  541   a ,  541   b  by an isolation sleeve  544   a ,  544   b . They have an electrical connection  548   a ,  548   b . The electrical connection  548   a ,  548   b  is connected to a not shown control unit. In the embodiment the insert  542   a ,  542   b  is fixed on the guiding body  541   a ,  541   b  by a hex nut  546   a ,  546   b , which fastens the insert  542   a ,  542   b  via an isolating washer  545   a ,  545   b  to the guiding body  541   a ,  541   b.    
         [0019]    Both inserts  542   a ,  542   b  have a touching head  543   a ,  543   b . The touching heads  543   a ,  543   b  have a different shape. The touching head  543   a  has a flat surface in its contact area to match the flat bottom of registering punch  12   a . The touching head  543   b  has a contact area with a radius to accommodate the radius of registering punch  12   b.    
         [0020]    The printing plate  1  is secured in its position analogue to the positioning in printing plate magazine  2 : The guiding body  542   b  and the touching head  543   b  of the registering pin  54   b  have contact to the registering punch  12   b  in the printing plate  1  and the registering punch  12   a  has contact at its bottom to the touching head  543   a.    
         [0021]    To the operation of apparatus:  
         [0022]    The printing plate magazine  2  equipped with a printing plate  1  is moved from its resting position into the position for a printing plate change. The plate cylinder  4  is positioned to enable the insertion of the printing plate  1  in the front clamping device  5 . FIG. 1 shows this position.  
         [0023]    The printing plate  1  is pre-registered by the pre-registering system in the printing plate magazine  2 . It is released from the printing plate magazine  2  by retracting the pre-registering pins  21   a ,  21   b  during the printing plate change. The transport device is moving the printing plate  1  for instance in the embodiment with sucker  3 . Transportation by wheels or other means is also possible.  
         [0024]    The sucker  3  gets the printing plate  1  and transports it from the printing plate magazine  2  in the direction of the opened front clamping device  5 . In this position the upper clamping rail  52  is removed from the lower clamping rail  51  to the utmost distance.  
         [0025]    The printing plate  1  with its registering punches  12   a ,  12   b  is moved inside the front clamping device  5  to the registering pins  54   a ,  54   b . The electrical contact between the conductive printing plate  1  and the registering pins  54   a  and  54   b  is closed if the printing plate  1  reaches the registering position (see FIG. 2). An electrical signal to the printing machine control is generated when the set registering position analogue to FIG. 2 is obtained and the front clamping device  5  closes. Further steps for plate change  1  can now follow.