Abstract:
A quick release pallet for a screen printing machine in which the pallet has locating recesses at either ends which locate the pallet on the pallet arm of the screen printing machine by engaging locating lugs on the pallet arm. A toggle clip secures the pallet in position. The advantages are that the pallet has no attachments and can be very quickly positioned and released. Because there are no screw holes in the top surface of the pallet it has a larger print area. The pallet can be modified to a vacuum pallet with a perforated or porous top plate and a vacuum manifold connected to the base plate and air spaces being provided by machined channels in the base plate or a mesh interposed between the base plate and the top plate.

Description:
This application is a continuation in part to application Ser. No. 09/828,880, filed Apr. 10, 2001, now U.S. Pat. No. 6,575,091, which I turn is a continuation in part to Ser No. 09/359,115, filed Jul. 23, 1999, now U.S. Pat. No. 6,237,488. 
    
    
     This invention relates to improvements in screen printing machines particularly to the pallet and pallet arm constructions used in such machines. 
     BACKGROUND OF THE INVENTION 
     Garments such as tee shirts are decorated using multi printing head, screen printing machines. The number of heads correspond to the number of colours to be printed. U.S. Pat. Nos. 3,795,189 [Jaffa] and 5,031,527 [Eppinger] disclose examples of the type of machines used in printing garments. 
     The garments are supported on a pallet, which in turn is supported, for registry with the printing head, on a pallet arm. The pallet is moved successively past the desired number of printing heads until the printing is complete. Different size garments require correspondingly different sized pallets. Usually pallets are of the same length but vary in width from a garment sleeve width to a large body width. 
     This means that the pallets need to be removed from the pallet arms on a frequent basis. 
     The positioning of the pallet on its pallet arm needs to be precise and secure to ensure that registration with successive printing heads is maintained. 
     Conventionally one means of removably securing pallets to pallet arms has been to use 2 or 3 counter sunk screws at each end of the pallet. This is quite adequate in terms of registration accuracy and retention of alignment but involves extensive labour time to fit a new set of pallets to a machine. A number of quick release mechanisms have been proposed. Some use a key and keyhole type arrangement where either the pallet or the pallet arm has a keyhole slot and the other has a complementary waisted head that can be locked into the narrow part of the slot. 
     Another quick release means relies on the use of a rail and complementary track arrangement with either the pallet or the pallet arm having a rail and the other having a channel track of complementary cross section to the rail and a securing means to lock the two relative to one another for registration relative to the length of the arm. In most of these devices several wing nuts or bolts need to be tightened to secure the aligned pallet to the pallet arm. 
     FIG. 13 illustrates a further embodiment of the invention in which the pallet is a vacuum pallet consisting of a machined aluminium base  140   
     U.S. Pat. No. 4,031,825 [Jaffa] discloses a pallet which fits sleeve-like over the pallet arm and is held in place by springs in the side edges of the pallet arm. Even though the pallet appears to be simple it needs to be fabricated or machined extensively as does the pallet arm. 
     U.S. Pat. No. 5,592,877 in part discloses a pallet which can be installed and released quickly and utilises a pneumatic release mechanism to free the pallet. The pallet comprises two plates screwed together with the lower plate having lugs and slots that cooperate with recesses and a pin in the pallet arm to locate the pallet. 
     Although these quick release arrangements are an improvement they do have short comings in terms of convenience and operator simplicity. Also they all involve additional manufacturing steps in preparing the pallets. 
     It is desirable that a pallet be adapted for use with a vacuum system which creates a vacuum through the surface of the pallet to retain the garment in position during the printing process. 
     BRIEF DESCRIPTION OF THE INVENTION 
     To this end the present invention provides, in a screen printing machine of the type having a pallet mounted on a pallet arm which is successively brought into registry with a series of printing heads the improvement comprising 
     a) a pallet having a longitudinal axis and leading and trailing edge portions extending laterally at each end of the longitudinal axis; 
     b) a pallet arm to support said pallet along its longitudinal axis; 
     c) at least one edge recess in either the leading or trailing edge of said pallet and at least one location recess in or adjacent to the other of said leading or trailing edges; 
     d) at least one fixed locating stop on said pallet arm adapted to fit said at least one edge recess; and 
     e) at least one locating means mounted on said pallet arm remote from said at least one fixed locating stop, said locating means being of complementary shape to said at least one location recess in or adjacent to said leading or trailing edge of said pallet. 
     The pallet of this invention is unique in that it is an integral pallet devoid of parts welded or otherwise fixed to it and having no fixing holes or recesses in its upper surface. 
     In contrast to prior art quick release systems, the pallet of this invention requires no additional device or protrusion to be welded mounted or adhered to its surface. 
     The only precision machining required is to machine recesses into the edge of one end of the pallet and into the opposite edge or the base of the pallet adjacent the opposite edge. The pallets can in other respects be of the same shape and materials as is conventional for screen printing pallets. 
     Although two location points are adequate it is preferred to use 3 points. Preferably one adjustable point is located at the free end of the pallet arm and two adjacent the leading edge of the pallet when it is secured to the pallet arm. The recesses in the edges may be into the edge or into the top surface of the pallet at the edge. If the locating recess is into the base of the pallet it is preferably into underneath surface of the pallet adjacent the trailing edge and shaped to fit over a lug or bolt head protruding from the surface of the pallet arm adjacent its free end. 
     In order to press the pallet securely into its register position the surfaces of the recesses and the corresponding contact surfaces of the locating stops on the pallet arm are angled in complementary fashion so that the pallet is pressed along its longitudinal axis and also pressed onto the pallet arm. The final securing force can be provided by a spring clip or toggle clamp acting on the edge of the pallet opposite the edge which abuts the fixed stops on the pallet arm. 
     To fit the pallet, it is simply placed onto the pallet arm so that the locating stops are aligned with the recesses and then the spring clip or toggle is locked into place. 
     Only one fastening action is needed in contrast to the need to fasten several bolts in the prior art devices. Because there are no screw or bolt holes in the top surface of the pallet, a larger surface area of the pallet is available for printing than is the case for prior art pallets. Because there are no protrusions or rails mounted on the pallet as is the case with prior art quick release pallets, the pallets of this invention pack flat and are easier to store, transport and clean. 
     In a modification of the pallet of this invention the pallet is adapted for use with a vacuum manifold. The pallet is formed in two parts the upper surface being perforated to enable air flow through the surface and the lower surface incorporating a recess communicating with a vacuum outlet connected to a manifold. The manifold may be a third part of the vacuum pallet or it can be a part of the pallet arm which mates with the pallet. 
     The present invention in a further aspect provides a pallet for supporting an item to be screen printed having 
     a) a longitudinal axis and leading and trailing edge portions extending laterally at each end of the longitudinal axis; 
     b) a perforated top plate 
     c) a recessed bottom plate adapted for connection to a vacuum line 
     d) at least one edge recess in either the leading or trailing edge of one or both of said top plate and said bottom plate 
     e) at least one location recess in or adjacent to the other of said leading or trailing edges in either or both the top plate and said bottom plate 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A preferred embodiment of this invention will now be described with reference to the drawings in which: 
     FIG. 1 is an isometric view of the assembled pallet arm and pallet of this invention; 
     FIG. 2 is a view of the pallet arm; 
     FIGS. 3A and 3B are views of the upper and lower surfaces of the pallet of this invention; 
     FIG. 4 is a sectional view of the pallet and pallet arm of a second embodiment of this invention and; 
     FIG. 5 is a partial exploded view of the leading edge of the pallet and its associated pallet arm of the same embodiment as shown in FIG.  4 . 
     FIG. 6 is a side elevation of a screen printing machine incorporating a vacuum line for applying a negative air pressure to the upper surface of the pallets; 
     FIG. 7 is a plan view of a vacuum pallet of this invention; 
     FIG. 8 is a side view and detail along the line A—A of the pallet of FIG. 7; 
     FIG. 9 is a detailed plan view of the perforated top plate of the pallet of FIG. 7; 
     FIG. 10 is a detailed plan view of the bottom plate of the pallet of FIG. 7; 
     FIG. 11 is a plan view of a manifold used in the pallet of FIG. 7; 
     FIG. 12 is a side view of the manifold of FIG. 11; 
     FIG. 13 is a further embodiment of a vacuum pallet; 
     FIG. 14 is another embodiment of a vacuum pallet in which a spacer material such as mesh creates an air space. 
    
    
     The pallet  10  is a flat aluminium cast plate of a size matched to the garment to be printed. The pallet has an upper surface  12  and a lower surface  11 . The leading edge incorporates two recesses  13  of semicircular shape with chamfered or inclined faces  14 . The trailing edge incorporates a clip recess  16 . On the underneath surface adjacent the trailing edge is the location or key recess  15 . The recess  15  is centred over the longitudinal centre line of pallet  10  which passes through the mid point between the recesses  13 . 
     The pallet arm  20  has an upper surface  21  and a side portion  22 . Counter sunk bolt heads  24  protrude from the upper surface  21  of the pallet arm  20 . The bolts  24  can be adjustable in height above the surface  21  and on the under sides of the screw heads  24  are inclined faces  25  which engage the surfaces  14  of the recesses  13  in pallet  10 . Adjacent the free end of the pallet arm is the key protrusion  26  preferably of plastic and screwed into the surface  21  so that it can be removed. The protrusion  26  is slightly shorter in length than the corresponding locating recess  15  on the underside of pallet  10 . The protrusion  26  is preferably centred on the longitudinal centre line of the pallet arm which centre line also passes through the midpoint between the stops  24 . 
     Under the free end of the pallet arm  20  is the preferred locking mechanism a toggle clip comprising the over centre toggle arm  27  and the clip  29 . The end  28  of clip  29  seats in the recess  16  of pallet  10 . The portion  30  of clip  29  engages underneath edge of the pallet arm surface  21  to exert spring pressure onto the edge recess 16  of pallet  10 . The curved portion  31  of clip  29  applies a longitudinal force to the trailing edge of pallet  10  via the end  28  of the clip  29  engaging the recess 16 . These two forces ensure that the pallet  10  is held securely in registry with the centre line of arm  20 . 
     The side  22  has a portion  23  cut away at the free end of arm  20  to improve access to the toggle  27  and clip  29 . The clip end  28  is placed into engagement with the recess  16  of pallet  10  and the toggle  27  closed to lock the pallet into position. By making fine adjustments to the height of the screws  24  the longitudinal alignment of pallet  10  can be adjusted. 
     Instead of the toggle mechanism a spring loaded stop can be located on the free end of the pallet arm which engages a recess in the centre of the pallets trailing edge. In such an arrangement the protrusion  26  and recess  15  may not be needed. The pallet in that construction would be pressed against the spring stop to locate the stops  24  in recesses  13  and then released so that the spring would press the pallet into position. 
     The recesses  13 ,  15  and  16  in the pallet are all subject to wear. The wear surface may be incorporated In a plate which fits within a recess in the pallet so that the surface of the pallet and the adjacent surfaces of the plate are flush. This enables the wear surfaces of the pallet to be replaced when wear affects their function. The plates containing the recesses  13 ,  15  and/or  16  may be secured to the plate by counter sunk screws or adhesives. 
     In the embodiment shown in FIGS. 4 and 5 an alternative fixing arrangement is shown. The pallet  35  is held to the pallet arm  40  at two positions. The leading edge of pallet  35  has a rectangular inclined recess  38  which incorporates a centering groove  39 . The pallet arm  40  has stop  47  with an inclined facing edge  50  which engages the inclined recess  38  of pallet  35 . The pin  49  on stop  47  engages the centering groove  39 . The stop  47  is fixed to the pallet arm by the counter sunk screws  48 . 
     The second securing position is shown in FIG. 4 where recesses  36 in the undersurface of pallet  35  are engaged by the grips  42 . The recesses  36  incorporate in the inner edges wedged grooves  37  which are engaged by the wedged ribs  43  on the grips  42 . The grips  42  are mounted on the pallet arm  40  by a screw threaded shaft  41 . Rotation of the shaft  41  by turning handle  44  tightens or loosens the grips  42 . This alternative need not have any clamp on the trailing edge of the pallet. The pallet  35  is placed over the pallet arm  40  so that the grips  42  enter the recesses  36 , then the pallet is urged against stop  47  so that pin  39  fits in groove  39  and then the grips are tightened by turning handle  44  so that the ribs  43  are urged into the grooves  37 . 
     FIG. 6 illustrates a typical screen printing machine having print heads  101  which rotate with the central support  102  and print garments loaded on pallets  112 . The pallets  112  are supported on pallet arms  111 . The machine control panel  106  is situated at the load/unload stations which don&#39;t have associated print heads. The vacuum pallet  112  is connected to a vacuum line  107  which communicates with the central vacuum region  108  within the central support  102 . The vacuum region  108  is connected to a vacuum pump [not shown] via the external line  109 . 
     The vacuum pallet  112  as shown in FIGS. 7 to  12  consists of a top plate  121  as seen in detail in FIG. 9 with a grid of perforations  122  to create an even suction on the top surface of the top plate  121 . This top plate has the two semi circular edge recesses  13  at one end and the clip recess  16  in the other end. The top plate  121  sits on the bottom plate and may be made from cold rolled aluminium or rubber. 
     The bottom plate  126  as seen in detail in FIG. 10 has a series of transverse slots or channels  127  into the surface to provide air flow channels from the perforations in the top plate. The holes  128  in the channels  127  provide air flow communication to the manifold  131 . The fastening holes  129  are for screws or bolts to attach the two manifolds  131  to the base of the bottom plate  126 . The bottom plate also incorporates the semicircular location recesses  13  at one end and the clip recess  16  at the other end. The bottom plate  126  is preferably machined from Aluminium tooling plate. 
     Each manifold  131  as shown in FIGS. 11 and 12 comprises a channel section  132  dimensioned to cover one of the rows of air holes  128  in the bottom plate. The fastening holes  133  correspond to the fastening holes  129  in the bottom plate. The vacuum outlet hole  134  in the channel  132  is adapted to receive the end of the vacuum line  107 . The manifold  131  is preferably machined from Aluminium. 
     FIG. 13 illustrates a further embodiment of a vacuum pallet according to this invention. The pallet base  140  is similar to the base  126  of FIG.  10  and is machined from an aluminium plate to incorporate the semicircular location recesses  143  at one end and the clip recess  146  at the other end as well as the channels  142  to low comunication with the vacuum line. The top plate  147  is a sheet of a porous material such as cork which allows air to bedrawn through to create a suction to hold the garment in place. 
     FIG. 14 is another embodiment of a vacuum pallet. The pallet base  150  is only machined to form the location recesses and clip recesse  153 . An expanded aluminium mesh  157  is partially glued to the pallet base  150 . overlying the mesh  157  is a sheet of porous material  158  such as cork which is lightly glued to the mesh  157 . The cork and mesh are secured to the pallet base  150  by an edge frame  159  screwed to the pallet base  150  by pan head screws  160 . 
     From the above description it can be seen that this invention provides 
     1) a pallet that is simple to machine with no added devices or protrusions. 
     2) The pallet is simple to assemble to the pallet arm. 
     3) The pallet has a larger free surface for printing because there are no screw holes through its top surface 
     4) The pallet and arm can be made from off the shelf components which reduces the costs of production. 
     5) The pallet is adapted for use with a vacuum line.