Abstract:
A method and apparatus are provided for the manipulation of a sleeve onto and off of a cylinder. A sleeve mounted on a handling shaft is equipped with a substantially airtight slideable end cap at its distal end. During mounting, axial alignment is provided when the handling shaft is engaged with the free end of the cylinder. A plurality of apertures on the cylinder&#39;s exterior surface conduct pressurized air, which expands the sleeve by exerting radial fluid pressure on its inside surface. A vacuum source actively evacuates the air from the sleeve&#39;s interior drawing the sleeve onto the cylinder. To remove the sleeve fluid pressure is reasserted exerting an axial force against the substantially airtight end cap. An auxiliary air supply is selectively activated to aid in sleeve removal.

Description:
REFERENCE TO RELATED APPLICATION  
       [0001]     This application claims the benefit of U.S. application 60/504,975 filed on 23 Sep. 2003, which is hereby incorporated herein by reference in its entirety and claims priority from Canadian patent application No. 2,442,051 filed on 22 Sep. 2003. 
     
    
     TECHNICAL FIELD  
       [0002]     This invention relates to the preparation and handling of printing sleeves for a printing press.  
       BACKGROUND  
       [0003]     Hollow cylindrical sleeves are often employed in flexographic printing as a means of quickly mounting and dismounting plates on imaging cylinders, printing press cylinders, storage cylinders, and other cylinder-based equipment. For various reasons, it is generally desirable to avoid touching the surface of the un-processed media normally mounted on the sleeve&#39;s outer cylindrical surface. Avoiding touching the media surface is particularly difficult while the sleeve is being handled during mounting and dismounting from the cylinder. With the more recent desire to image the media directly on the sleeve, the care required in handling the sleeve is even more critical.  
         [0004]     Typically, the sleeves used in flexographic printing are tubular in form and made of composite, polymer, or metal. Sleeves are commonly affixed to the printing cylinder using an interference fit i.e. the free-state circumference of the sleeve&#39;s interior surface is less than or equal to the circumference of the exterior surface of the cylinder. The requirement for an interference fit presents problems related to the mounting and dismounting of sleeves from the cylinder.  
         [0005]     A common method for mounting and dismounting sleeves is described in U.S. Pat. No. 4,903,597 to Hoage at. al. Hoage et al. disclose introducing fluid pressure between the exterior cylindrical surface of the cylinder and the interior cylindrical surface of the sleeve. This method is schematically depicted in  FIG. 1 . Cylinder  11  is supported in a cantilevered condition with a free end  11   a  ready to receive a sleeve  12 . The proximate end  12   a  of a sleeve  12  is initially forced onto free end  11   a  of a cylinder  11 . After the sleeve  12  has been pushed a short way onto cylinder  11 , a fluid pressure is established via small apertures  13  in the exterior surface of cylinder  11 . The fluid pressure (commonly pressurized air) exerts radial force on the sleeve  12 , expanding it slightly and creating an air bearing on which the sleeve  12  may be slid onto the cylinder  11 . When the sleeve  12  is in the desired location relative to the cylinder  11 , the fluid pressure is removed and the sleeve  12  shrinks to its regular size, forming an interference fit on the cylinder  11 . It is advantageous if the apertures  13  are located relatively close to the free end  11   a  of the cylinder  11 , so that the fluid pressure may be applied in the region where the sleeve initially engages the free end  11   a  of cylinder  11 .  
         [0006]     There are some problems with this method. One such problem is that the proximate end  12   a  of the sleeve  12  must initially be forced onto the free end  11   a  of cylinder  11  before the air bearing created by the apertures  13  can overcome the interference between the sleeve  12  and cylinder  11 . This initial mounting requires accurate axial alignment of sleeve  12  and cylinder  11 . Any binding will make it difficult to push sleeve  12  far enough onto cylinder  11  to allow the air bearing to form. As mentioned earlier, the media (not shown) on the exterior surface of the sleeve  12  is sensitive and may not be physically manipulated during this procedure. Even if the sleeve  12  is only manipulated by its distal end  12   a , there is a significant chance that such manipulation will damage the media on the sleeve&#39;s external surface, or damage the sleeve itself.  
         [0007]     On completion of imaging the sleeve is usually removed from the imaging cylinder. An air bearing is once again established via apertures  13 . The only way to remove sleeve  12  from cylinder  11  is to apply a force to the very thin edge of its proximate end  12   a . This can damage the printing media, the image carried on the media, or even cylinder  11 . Another problem occurs when the proximate end  12   a  of the sleeve  12  gets closer to the free end  11   a  of the cylinder  11   a  during the removal process. In this condition a substantial portion of the sleeve  12  overhangs the cylinder  11 , which may cause the sleeve  12  to bind or lock on the cylinder  11 . If the sleeve  12  binds on the cylinder  11 , one may need to push the sleeve  12  back onto the cylinder  11  and try to remove it again. Obviously, such remounting and dismounting substantially increases the amount of manipulation of (and potential damage to) the sleeve  12  and the sensitive media on its outer surface.  
         [0008]     There remains a need for better apparatus and methods for mounting and dismounting sleeves on cylinders.  
       SUMMARY OF INVENTION  
       [0009]     A sleeve, sealed at one end to create a substantially air tight cavity, is drawn onto a cylinder by lowering the pressure in the cavity using a vacuum source and removed from the cylinder by increasing the pressure in the cavity using pressurized air. An auxiliary supply of pressurized air aids in the removal of the sleeve.  
         [0010]     In a first aspect of the present invention an apparatus for mounting a tubular sleeve on a cylinder is provided. The cylinder has an open end with at least one air aperture formed in the outer surface of the cylinder proximate the open end for radially expanding the sleeve and providing air bearing flotation thereto. An end cap sealingly engages an end of the sleeve distal to the cylinder open end so that at least a portion of the sleeve is free to engage the open end of the cylinder thus forming a substantially closed cavity between the end cap, the sleeve, and the open end of the cylinder. A vacuum source is provided for selectively evacuating air from the cavity to draw the sleeve onto the cylinder. An auxiliary air supply is provided for introducing air into the cavity to aid in removing the sleeve from the cylinder.  
         [0011]     Another aspect of the invention provides a method for mounting a tubular sleeve onto a cylinder. The cylinder has an open end with at least one air aperture formed in the cylinder outer surface proximate the open end. The air aperture is for radially expanding the sleeve and providing air bearing flotation thereto. The open end of the sleeve is engaged on the open end of the cylinder and the end of the sleeve distal to the open end of the cylinder is sealed to create a cavity between the distal end, the sleeve and the cylinder. The sleeve is drawn onto the cylinder by establishing a vacuum in the cavity. The sleeve is removed using pressurized air from the air aperture. Removal is aided by selectively applying auxiliary pressurized air between the cylinder and the sealed end.  
         [0012]     Further aspects of the invention and features of embodiments of the invention are set out below. 
     
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0013]     In drawings which illustrate, by way of example only, embodiments of the invention:  
         [0014]      FIG. 1  is a perspective view illustrating a prior art sleeve mounting technique;  
         [0015]     FIGS.  2 -A- 2 -D are side views of a sleeve mounting apparatus according to the invention;  
         [0016]     FIGS.  3 -A- 3 -C are further side views of the sleeve mounting apparatus;  
         [0017]      FIG. 4  is a partial side view of the end cap portion of the sleeve mounting apparatus; and  
         [0018]      FIG. 5  is a perspective view of an imaging device according to an embodiment of the invention. 
     
    
     DESCRIPTION  
       [0019]     Throughout the following description, specific details are set forth in order to provide a more thorough understanding of the invention. However, the invention may be practiced without these particulars. In other instances, well known elements have not been shown or described in detail to avoid unnecessarily obscuring the invention. Accordingly, the specification and drawings are to be regarded in an illustrative, rather than a restrictive, sense.  
         [0020]      FIG. 2 -A, depicts apparatus according to one embodiment of the invention. Sleeve  12  is completely detached from cylinder  11 . Sleeve  12  may be made, for example, of composite material, polymer or metal and may carry sensitive imaging media (not shown) on its exterior cylindrical surface  12   c . Cylinder  11  is the imaging cylinder on which the sleeve-mounted media is to be imaged prior to processing.  
         [0021]      FIG. 2 -A shows sleeve  12  in a state in which it may be stored prior to use. Sleeve  12  is mounted on a handling shaft  16 . An end cap  14   a  is located at the proximate end  12   a  of sleeve  12 . A second end cap  14   b  is located at the distal end  12   b  of sleeve  12 . End caps  14   a  and  14   b  are annular in shape and each engage an interior cylindrical surface  12   d  of sleeve  12 . End caps  14   a  and  14   b  are capable of slideably moving along the exterior surface of handling shaft  16 . Distal end cap  14   b  forms a substantially airtight seal with distal end  12   b  of sleeve  12 . End cap  14   b  defines one end of a cavity  19  within sleeve  12 . End cap  14   a  is not necessarily sealed to sleeve  12  although, for convenience, end caps  14   a  and  14   b  may be the same as one another.  
         [0022]     One construction for securing end cap  14   b  to sleeve  12  while maintaining a seal is depicted in  FIG. 4 . End cap  14   b  has a wedge-shaped groove extending around its circumference. An o-ring  22  is retained in wedge shaped groove  23 . In the illustrated embodiment groove  23  is asymmetrical and has a proximal, more gently sloping, sidewall  23   a  and a steeper sidewall  23   b . The pressure in cavity  19  during dismounting generates an outward air pressure indicated by arrow  26  that tends to push end cap  14   b  out of the sleeve  12 . Groove  23  helps o-ring  22  to maintain the seal in the face of increasing air pressure  26  in cavity  19  inside sleeve  12 . As this force  26  is applied, end cap  14   b  tends to move outward, causing o-ring  22  to roll or move up the more gently angled wall  23   a  of groove  23 . In this manner, o-ring  22  becomes more tightly wedged between end cap  14   b  and inner surface  12   d  of sleeve  12 , providing a stronger gripping force against the inside cylindrical surface  12   d  of sleeve  12 . The harder the air pressure  26  pushes against end cap  14   b , the more strongly end cap  14   b  grips the inside cylindrical surface of sleeve  12 .  
         [0023]     Returning again to  FIG. 2 -A, an intermediate disk  15  is provided to support sleeve  12  at a point near end  12   a . Intermediate disk  15  is annularly shaped and made from a ferromagnetic metal and is slideably located on handling shaft  16 . The outer circumference of the intermediate disk engages the inside surface  12   d  of sleeve  12 . Intermediate disk  15  is placed on the handling shaft  16  near the end  12   a  when mounting sleeve  12  and is retained by a plurality of magnets  17  recessed into the surface of handling shaft  16 .  
         [0024]     FIGS.  2 -B to  2 -D show steps in a method for mounting sleeve  12  to the cylinder  11 . Proximate end cap  14   a  is first removed so that the sleeve  12  is supported by distal end cap  14   b  and intermediate disk  15 , thus leaving sleeve end  12   a  open. The proximate end  16   a  of the handling shaft  16  is engaged in a socket  18  or other engagement mechanism in the free end  11   a  of cylinder  11 . The engaging mechanism  18  on the cylinder  11  and the proximate end  16   a  of the handling shaft  16  are fitted, such that when they engage, the axial center of the sleeve  12  is substantially the same as the axial center of the cylinder  11 . This concentric orientation of the sleeve  12  and the cylinder  11  is referred to herein as being aligned.  
         [0025]     Once handling shaft  16  and the cylinder  11  are engaged and aligned, a flow of air or other suitable fluid is established through apertures  13 . The next stage in mounting the sleeve  12  onto the cylinder  11  is depicted in  FIG. 2 -C. Sleeve  12  is initially pushed onto the proximate edge  11   a  of cylinder  11  by pushing on distal end cap  14   b . There is no need to handle the sensitive exterior surface  12   c  of sleeve  12 , or media mounted thereon. Once the proximate end  12   a  of sleeve  12  has been pushed past apertures  13 , the pressurized air being expelled from apertures  13  exerts radial force on the interior cylindrical surface  12   d  of sleeve  12 . This radial force expands sleeve  12  slightly in a radial direction, forming an air bearing and making it significantly easier to slide sleeve  12  farther onto cylinder  11 .  
         [0026]     The air coming out of the apertures  13  and forming the air bearing must escape somewhere. Some air escapes from the air bearing near the proximate end  12   a  of the sleeve  12  and vents into the atmosphere. The remaining air escapes between the sleeve  12  and the cylinder  11  near its free end  11   a  and flows into the closed cavity  19  formed by sleeve  12 , distal end cap  14   b  and the free end  11   a  of cylinder  11 . The air building up in the cavity  19  is mostly vented through an aperture  20  into handling shaft  16 , which has a conduit formed therethrough. Some air may vent through the small gap between the end cap  14   b  and the handling shaft since if this seal is made too tight, end cap  14   b , will have difficulty sliding on handling shaft  16 .  
         [0027]     Referring now to  FIG. 4 , handling shaft  16  has an internal conduit  52  between aperture  20  and a port  21  at its distal end  16   b . Port  21  is connected to a vacuum source  32  via a coupler  36  and an in-line adjustable valve  34 . When valve  34  is open and vacuum source  32  is operating, air from cavity  19  is evacuated at a faster rate than the airflow from apertures  13 , thus lowering the pressure within cavity  19 . The lowered pressure in cavity  19  draws sleeve  12  onto cylinder  11 . The advance rate of sleeve  12  may be controlled by adjusting the vacuum established by source  32  by operating adjustable valve  34 . In this manner, sleeve  12  may be loaded onto the cylinder  11  with virtually no touching or manipulation, even via end cap  14   b.    
         [0028]     As sleeve  12  is drawn further onto cylinder  11 , intermediate disk  15  is held by magnets  17 . As sleeve  12  advances, intermediate disk  15  is eventually contacted by end cap  14   b  and moved off magnets  17  to be sandwiched between the free end  11   a  of cylinder  11  and end cap  14   b . End cap  14   b  has a plurality of magnets  50  for contacting the intermediate disk  50 , the function of which is explained below.  
         [0029]      FIG. 2 -D shows sleeve  12  fully engaging cylinder  11 . The pressurized air coming from apertures  13  is shut-off, reducing the axial pressure on the interior surface  12   d  of sleeve  12  and eliminating the air bearing. As a result, sleeve  12  shrinks and forms an interference fit on the exterior surface of cylinder  11 . Handling shaft  16  is removed at this stage and a tailstock (not shown) engages the free end  11   a  of cylinder  11  with the end cap  14   b  and the intermediate disk  15  still in place. The sensitive media on the exterior surface of the sleeve  12  may now be imaged or used in a conventional manner.  
         [0030]     After imaging or use, sleeve  12 , which bears the imaged media must be removed from cylinder  11 . The media is still susceptible to handling damage at this point. A sleeve removal process is depicted in  FIG. 3 . The preliminary steps for removal of sleeve  12  are shown in  FIG. 3 -A. The proximate end  16   a  of handling shaft  16  is engaged with the free end  11   a  of the cylinder  11  to align the two. Valve  34  in  FIG. 4  is closed and pressurized air is applied via apertures  13  causing radial pressure on the interior surface of the sleeve  12  thus creating an air bearing. The air venting into cavity  19  causes an increase in pressure in cavity  19 . This results in an axial force being applied against the interior surface of the substantially airtight end cap  14   b . This axial force pushes sleeve  12  away from cylinder  11  and along the handling shaft  16  towards its distal end  16   b . The axial force in combination with the air bearing support allows the sleeve  12  to be removed from cylinder  11  without physically manipulating any part of its exterior surface.  
         [0031]     As sleeve  12  is pushed along handling shaft  16 , the intermediate disk  15 , attached to the end cap  14   b  via magnets  50 , moves with the end cap  14   a  until it reaches magnets  17  in handling shaft  16 . Magnets  17  provide a stronger attractive force than magnets  50  thus retaining intermediate disk  15  at the position of magnets  17  in order to support the open end of the sleeve  12 .  
         [0032]     It has been found that under the force of the pressurized air venting from apertures  13 , sleeves may from time to time stick while being removed. This would necessitate handling of the proximate end  12   a  in order to release sleeve  12 , which is highly undesirable. This problem may be resolved by incorporating an auxiliary pressurized air supply  38  as shown in  FIG. 4 . The auxiliary air supply  38  is connected to vented end  21  of handling shaft  16  via a branch in coupler  36 . A valve  40  allows selective introduction of additional blasts of pressurized air to cavity  19  via coupler  36 . Under normal sleeve removal conditions sleeve  12  is allowed to blow off the cylinder  11  under the forces exerted by pressurized air venting from apertures  13  only. Should a sleeve stick during removal, valve  40  maybe opened to provide additional pressurization of cavity  19  and thus additional force to the sleeve  12 . As soon as sleeve  12  becomes unstuck, valve  40  may be closed. In the illustrated embodiment the auxiliary air supply valve  40  is controlled via a small push button switch located on a larger lever controlling valve  34 .  
         [0033]      FIG. 3 -C depicts sleeve  12  completely removed from cylinder  11 . Handling shaft  16  is now carrying sleeve  12  and is disengaged from cylinder  11 . The proximate end cap  14   a  is reinserted into the proximate end  12   a  of the sleeve  12 . By manipulating the ends of the handling shaft  16 , the sleeve  12  may then be handled without touching the media. After imaging, the media on the exterior surface of the sleeve  12  may be further processed, if necessary, to develop the image.  
         [0034]      FIG. 5  depicts a flexographic imaging device  60  according to the invention. Device  60  comprises a cylinder  11  supported in a cantilevered condition by a headstock  62  so that the cylinder has an open end  64  which is partially engaged by sleeve  12 . The device is further equipped with a moveable tailstock  64  that is pivoted out of engagement with cylinder  11  for the loading of a sleeve  12 . An imaging head  66  is disposed to imagewise expose a media loaded on cylinder  12  as is well known in the art. Sleeve  12  is sealed at its distal end by end cap  14   b  which is slideably located on a handling shaft  16 . Handling shaft  16  is rigidly cantilevered from a support  68  attached to a base  70  which is bolted to the floor of the plant housing device  60 . A lever  72  controls the air supply as previously described, activating evacuation of cavity  19  to draw sleeve  12  onto cylinder  11 . A push button  74  on lever  72  further activates the auxiliary air supply to aid in removing a sleeve that becomes stuck when dismounting. Support  68  may be selectively rotatable to align the handling shaft to more than one sleeve device such as an imaging device, a media mounting device, or a printing press.  
         [0035]     As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. For example: 
        Pressurized air may be replaced by some other pressurized fluid.     While the vacuum source and auxiliary air supply in the described embodiment are shown attached via handling shaft  16 , this is not mandated. The vacuum and auxiliary air supply may equally well be applied through suitable passages in cylinder  11 .     Although the invention is described above with reference to use on an imaging cylinder the invention may be applied in association with printing press cylinders, sleeve mounting cylinders, and other cylinder and sleeve applications.     The described embodiment of the invention shows only one set of apertures  13  at the free end  11   a  of the exterior cylindrical surface of the cylinder  11 . However, the invention is not limited to having apertures in that location alone. For example, apertures located otherwise along the exterior cylindrical surface of the cylinder  11  may be provided. Such apertures may conduct pressurized air from a single source or from multiple sources. The vacuum source may be connected to the sleeve cavity via a conduit through the cylinder.     While in the preferred embodiment the sleeve is supported by a slideable end cap and intermediate disk on a handling shaft other means of supporting the sleeve may easily be envisaged that employ other well known mechanical devices or hardware.     The cylinder could be expandable to grip the sleeve. In this case it may be unnecessary to provide air to expand the sleeve or to make an air bearing between the sleeve and the cylinder.     Intermediate disk  15  need not be made entirely of ferromagnetic material. Disk  15  may comprise ferromagnetic material embedded within or attached to another material.     End cap  14   b  could be supplied as a part of cylinder  12 .     The handling shaft could comprise a socket which is fittingly engageable with a projection on the end of the cylinder such that engagement of the socket on the projection supports the handling shaft in an aligned relationship with the cylinder.        
 
         [0045]     Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.