Patent Publication Number: US-2006016040-A1

Title: Device for cleaning surfaces, especially of printing machine cylinders

Description:
The invention concerns a device for cleaning surfaces, especially of printing machine cylinders, with the aid of a cleaning cloth which is transported from a supply shaft to a winding shaft for soiled cleaning cloth and is pressed with the help of a rubber bar against the surface to be cleaned, with a drive to rotate the winding shaft.  
      It many cases it has been possible to automate the cleaning of surfaces, whether flat or cylindrical surfaces, by drawing a cleaning cloth, possibly with the addition of cleaning agents, across the surface to be cleaned. The use of a web-shaped, automatically transported cleaning cloth with a large width permits the cleaning of a large surface area. Devices of this type are already known of in connection with the cleaning of printing machine cylinders, for example for cleaning the rubber cylinders used in offset printing machines. The description below will therefore be based essentially on this particular application without this implying any limitation in the subject-matter of the application.  
      In offset printing machines a cylinder wrapped with a rubber blanket serves to transfer the image onto the actual printing cylinder. Once printing starts, the rubber blanket gradually becomes soiled, essentially with residues of printing ink and dust. These unwanted residues have to be removed from time to time to ensure printing of impeccable quality. It is customary, therefore, to clean the rubber blanket from time to time.  
      This is usually done with the aid of a cleaning cloth in the form of a piece of web-shaped material which is drawn off a supply shaft and, when soiled, collected on a winding shaft. This cleaning cloth is drawn across the rubber blanket with the application of slight pressure, or vice versa, and once a certain degree of soiling has occurred, is fed forward step by step or continuously, and is wound up again.  
      For the purpose of pressing the cleaning cloth against the rubber blanket a rubber bar is used which extends across the entire length of the rubber blanket cylinder. As a rubber bar possesses no appreciable resistance to bending, the rubber bar is disposed on, and attached to, a support bar in the form of a metal or plastic profile configured to be as stiff as possible.  
      As the cleaning cloth absorbs the dirt removed from the rubber cylinder, it gradually becomes dirtier itself. When the cleaning cloth has absorbed a certain amount of dirt from the rubber blanket, it is moved forward and wound onto the winding shaft as a result of the winding shaft being rotated, whilst at the same time being unwound from the supply shaft in an equal quantity. This necessitates a drive for the winding shaft.  
      The winding shaft is usually rotated by motors with suitable gears. The motors used have to be large enough to supply the relatively high torque required to pull the cleaning cloth through the cleaning position and then wind up the cleaning cloth. Furthermore, the motors which are usually used do not readily offer any means of knowing what length of soiled cleaning cloth has already been wound up, unless relatively costly servomotors are used.  
      The invention is therefore based on the task of creating a device of the above-mentioned type which, with simple means and relatively low costs, allows the length of already wound-up soiled cleaning cloth to be monitored and hence indicate in this way the remaining supply of cleaning cloth and the end thereof.  
      For the purpose of solving this task, the device according to the invention is characterised in that at each end of the winding shaft for soiled cleaning cloth there is a free-running bearing (bearing with non-reverse ratchet mechanism), the outer ring of which is in contact with the piston rod of a reset cylinder in such a way that the winding shaft is rotated in the direct of winding when the piston rod moves forward but is held stationary by the free-running effect when the piston rod moves backwards.  
      According to the invention the winding shaft can therefore be made to rotate with relatively simple fluid cylinders, in particular air cylinders.  
      These are substantially less costly than motors with equivalent driving power and associated control electronics. The stroke of the piston rod of the reset cylinder can be converted relatively easily into rotation angles of the winding shaft. Suitable tests can then be carried out to ascertain what lengths of cleaning cloth have already been wound up so that information concerning how much cleaning cloth is still available, and when the supply will be expended, can be displayed.  
      Attached to the outer ring of the free-running bearing there is preferably a lever with which the piston rod of the reset cylinder is connected.  
      This allows the driving force of the cylinder to be transmitted in such a way that a smaller-sized reset cylinder can be used. The strokes of the reset cylinder can be relatively easily detected and communicated to a central control element by end switches, reed switches or similar equipment.  
      Preferably provided at each end of the supply shaft there is a toothed ratchet wheel whose pawl is released each time the reset cylinder moves forward and then re-engages thanks to spring pretensioning after the reset cylinder moves backward. In this way the supply shaft is kept blocked outside each reset phase of the cleaning cloth so that unintentional unwinding of the cleaning cloth cannot occur. 
    
    
      Preferred embodiments of the invention will be described below with reference to the enclosed drawings, in which  
       FIG. 1  is a perspective overall view of a device according to the invention;  
       FIG. 2  is a similar view, but shows the drive according to the device for the winding shaft. 
    
    
      A device according to the invention has a housing designated overall as  10 , which is an elongated box-shaped structure whose length is the same as the length of the associated rubber blanket cylinder (not shown).  
      The inside of head element  14  houses the elements of the drive for the winding shaft  24 , more details of which will be given below.  
      Head elements  12 , 14  are attached to both outer ends. The head element  14  positioned in the forefront of  FIG. 1  is shown uncovered. Screw channels  16 , 18  serve to accommodate screws to attach a cover (not shown here).  
      Head elements  12 , 14  project parallel to each other over the elongated centre element  20  of housing  10 . Extending between the head elements there is a supply shaft  22  for a supply reel (not shown) of a cleaning cloth, a winding shaft  24  to accommodate soiled cleaning cloth after contact with the rubber blanket (not shown), and a stiffening rod  26 . The stiffening rod  26  facilitates the handling of the device and may be provided with handles  27 .  
      The cleaning cloth (not shown) is pulled from the supply shaft  22  around the elongated centre part  20  of housing  10  then back down underneath this centre part and on to winding shaft  26  for soiled cleaning cloth.  
       FIG. 2  shows a view of the inside of the front head element  14  in  FIG. 1 . A free-running bearing  28  is attached to the end of winding shaft  24 . The outer ring of the free-running bearing is designated as  30 . When this outer ring  30  is rotated anticlockwise the winding shaft  24  is also rotated anticlockwise. When outer ring  30  is rotated backwards, winding shaft  24  remains stationary.  
      Attached to outer ring  30  there is a radially projecting lever arm  32 . The outer end of this lever arm  32  is connected via an articulation  34  to the outer end of the piston rod  36  of a reset cylinder  38 . The housing of this reset cylinder  38  is fixed to the housing of the device in an axis  40  and can thus be pivoted up and down in  FIG. 1  to adjust to the arc-shaped path of lever arm  32 .  
      The stroke of the piston (not shown) of the reset cylinder  38  can be monitored in an appropriate way, e.g. with the help of end switches, teed switches, etc. From the stroke executed by the reset cylinder  38  the rotation angle of winding shaft  24  can be calculated for each stroke, or determined by means of tests. The stroke of the piston (not shown) of reset cylinder  38  can be continuously recorded and in this way it is relatively easy to ascertain what length of cleaning cloth has already been wound up and what length of unsoiled cleaning cloth remains on supply shaft  22 .  
      On supply shaft  22  there is a ratchet wheel  42 , in whose teeth a pawl  44  engages, said pawl being pivotably mounted in axis  46 . The pawl  44  is spring pretensioned in the direction of ratchet wheel  42  in a manner not shown. This prevents the cleaning cloth on supply shaft  22  from being unwound in an uncontrolled manner. The cleaning cloth is thus held taut on its way from supply shaft  22  to winding shaft  24  and around the centre part  20  of the housing.  
      At its free end, pawl  44  has a downward pointing arm  48  which is contacted by the advancing piston rod  36  in such a way that, when winding shaft  24  is rotated with the help of reset cylinder  38 , pawl  44  is released from the ratchet wheel and the ratchet wheel  42  is free to rotate together with supply shaft  22 .