EP2921441B1

EP2921441B1 - Sheet handling apparatus for sheet processing apparatus

Info

Publication number: EP2921441B1
Application number: EP14160570.9A
Authority: EP
Inventors: James Anthony GRAHAM
Original assignee: Crabtree of Gateshead Ltd
Current assignee: Crabtree of Gateshead Ltd
Priority date: 2014-03-18
Filing date: 2014-03-18
Publication date: 2016-07-27
Anticipated expiration: 2034-03-18
Also published as: WO2015139786A1; EP2921441A1

Description

The present invention relates to a sheet handling apparatus, and relates particularly, but not exclusively, to a metal sheet handling apparatus for use in a metal sheet printing or coating apparatus.
US7011305 B2 discloses an apparatus according to the preamble of claim 1.
In printing machines in which registration of a sheet of metal with a printing cylinder, i.e. accurate location of the sheet in position on the cylinder, occurs at line speed, the position of the sheet in a direction transverse to the feeding direction of the sheet is controlled by sidelay apparatus. The sheet is pushed by suitable pushers, acting on one side of the sheet, against register stops on the opposite side of the sheet.
However, such mechanisms suffer from the drawback that their operation causes compressive stresses in the sheet, which can cause buckling or distortion of the sheet, which in turn can adversely affect registration accuracy. In addition, because of movement of the sheet relative to the sidelay apparatus in the direction of travel of the sheet relative to the cylinder, while in contact with the sidelay apparatus, any significant deviation of the sheet from perfect rectangular shape can cause the front edge of the sheet to move laterally relative to front lays controlling the position of the front edge of the sheet. This in turn can create disturbances and destabilising torques on the sheet, which again can adversely affect registration accuracy and cause distortion of the sheet, thereby causing a deterioration of printing quality.
Preferred embodiments of the present invention seek to overcome one or more of the above disadvantages of the prior art.
According to an aspect of the present invention, there is provided a sheet handling apparatus for handling a sheet of material in a sheet processing apparatus, the sheet handling apparatus comprising:-

at least one engaging portion for engaging an edge of a sheet of material being fed in a feeding direction relative to a sheet processing component of a sheet processing apparatus; and
magnetic flux generating means for generating magnetic flux passing through an edge region of the sheet of material such that a first magnetic force is applied to said sheet to urge said sheet towards at least one said engaging portion.

By providing magnetic flux generating means for generating magnetic flux passing through an edge region of the sheet of material such that a first magnetic force is applied to said sheet to urge said sheet towards at least one said engaging portion, this provides the advantage of enabling a force to be applied to the sheet to control its position without contact between the sheet handling apparatus and the sheet. This in turn reduces the occurrence of compressive stresses in and destabilising torques on the sheet, which in turn improves the accuracy of registration and therefore improves the print quality. In addition, by avoiding contact between the sheet handling apparatus and the sheet, the complexity and cost of the sheet handling apparatus is reduced, since complicated mechanisms to reduce the effect of compressive stresses or torques is no longer necessary.
The magnetic flux generating means may be adapted to generate magnetic flux passing through an edge region of said sheet such that opposed second and third magnetic forces are applied to said sheet in a direction transverse to a surface of said sheet.
By providing magnetic flux generating means adapted to generate magnetic flux passing through an edge region of said sheet such that opposed second and third magnetic forces are applied to said sheet in a direction transverse to a surface of said sheet, this provides the advantage of reducing the friction between the sheet and the sheet processing apparatus, thereby simplifying material handling.
The magnetic flux generating means may be adapted to provide at least one pair of first magnetic poles of a first polarity, and at least one second pole of a second polarity, opposite to said first polarity, such that magnetic flux passing from a said first magnetic pole to a said second magnetic pole passes through said sheet.
This provides the advantage of enabling a large attractive force to be generated by means of an apparatus of compact construction.
The magnetic flux generating means may have a magnetic flux concentrating portion for concentrating magnetic flux therein and defining at least one pair of said first poles and at least one said second pole.
At least one pair of said first magnetic poles may be arranged such that said sheet can pass therebetween.
This provides the advantage of enabling a strong attractive force, and substantially equal and opposite forces in a direction transverse to a plane of the sheet, to be applied to the sheet by means of a compact construction.
The magnetic flux generating means may comprise at least one first coil and at least one second coil.
At least one said first coil may be arranged in use on a first side of said sheet and at least one said second coil may be arranged in use on a second side of said sheet
This provides the advantage of enabling substantially equal and opposite forces to be applied to the sheet in a direction transverse to a plane of the sheet by means of an apparatus of simplified construction.
At least one said first coil and at least one said second coil may be connected in parallel.
This provides the advantage of simplifying electrical control of the apparatus.
The apparatus may further comprise mechanical gripper means for gripping said sheet.
According to another aspect of the present invention, there is provided a sheet processing apparatus including at least one sheet handling apparatus as defined above.
At least one said sheet handling apparatus may be adapted to apply a force to said sheet adjacent a side edge thereof relative to a feeding direction of the sheet.
At least one said sheet handling apparatus may be adapted to apply a force to said sheet adjacent a rear edge thereof relative to a feeding direction of the sheet.
At least one said sheet handling apparatus may be adapted to apply a force to said sheet adjacent a leading edge thereof relative to a feeding direction of the sheet.
This provides the advantage of enabling the sheet to be applied to a sheet processing component of a sheet processing apparatus under tension, thereby minimising the risk of buckling of the sheet, thereby maximising print quality. In addition, because of the strong attractive force generated by the sheet handling apparatus of the present invention, especially when the distance between the sheet handling apparatus and the sheet is small, the advantage is further provided that the sheet is rapidly and securely located on the sheet processing apparatus, thereby minimising any deterioration of print quality.
Preferred embodiments of the present invention will now be described, by way of example only and not in any limitative sense, with reference to the accompanying drawings in which:

Figure 1 is a schematic view of a sheet processing apparatus embodying the present invention;
Figure 2 is a cross sectional view of a first sheet handling apparatus of the sheet processing apparatus of Figure 1;
Figure 3 is a schematic side view of the sheet handling apparatus of Figure 2 in operation applying force to a sheet of material;
Figure 4 is a perspective front and side view of the sheet handling apparatus of Figure 2;
Figure 5 is a perspective side and rear view of the sheet handling apparatus of Figure 2;
Figure 6 is a perspective view of a second sheet handling apparatus of the sheet processing apparatus of Figure 1;
Figure 7 is a plan view of the second sheet handling apparatus of Figure 6 with a gripper blade thereof removed; and
Figure 8 is a perspective view of a magnet and coil assembly of the apparatus of Figures 6 and 7.

Referring to Figure 1, a sheet processing apparatus 2 such as a sheet printing apparatus or a sheet coating apparatus embodying the present invention applies ink or coating material to a metal sheet 4 at a gap 6 between a blanket cylinder 8 and an impression cylinder 10. Registration of a leading edge 14 of the sheet 4 with the impression cylinder 10 is achieved by means of a pair of front lay devices 16 with accompanying gripper blades 60 (Figure 6) which cooperate with respective notches 18 in the impression cylinder 10 to limit forward travel of the sheet 4 in the direction of arrow A and move with the impression cylinder 10 to cause registration of the leading edge 14 of the sheet 4 with the cylinder 10.
At the same time, a first sheet handling apparatus in the form of a sidelay assembly 20 embodying the present invention applies a tensile attractive force to each side edge 24 of the sheet 4 to limit movement of the sheet 4 in a direction transverse to arrow A, while allowing movement of the sheet 4 in the direction of arrow A. The sheet 4 is fed to the gap 6 between the rollers 8, 10 by means of a feeder apparatus including pushers 28, 30.
Referring to Figures 2 to 5, each sidelay assembly 20 is controlled by controller 22 and has an upper sheet guide plate 32 and a lower sheet guide plate 34 forming a tapering gap 36 for location of the side edge 24 of the sheet 4 therein such that the sheet 4 moves out of the plane of the drawing in Figures 2 and 3. The sidelay assembly 20 is provided with a soft iron core 38 around which a first coil 40 and a second coil 42 are wound, the first 40 and second 42 coils being connected in parallel such that they generate generally identical magnetic flux. The soft iron core 38 defines a pair of north poles 44, 46 which face each other through respective apertures 48, 50 in the upper 32 and lower 34 guide plates, and a south pole 52 adjacent to which a pair of registration rollers 54 is rotatably mounted. When the first 40 and second 42 coils are energised, they produce respective magnetic fluxes 56, 58 passing from their respective north poles 44, 46 through the sheet 4 to the south pole 52 such that substantially equal and opposite vertical forces are applied to the sheet 4 in the region between the north poles 44, 46, and a strong attractive force is applied laterally to the sheet 4 by the south pole 52 which draws the sheet 4 into engagement with the registration rollers 54.
The sidelay assemblies 20 also control the pushing force of the feeder apparatus 28, 30, improving the reliability of insertion of the sheet 4 by preventing the sheet 4 moving away from the pushers 28, 30 as they travel on their respective forward paths. Alternatively, the pushers 28, 30 can be replaced by a sheet handling assembly 20 as shown in Figures 2-5 which applies a gripping force to rear edge 58 (Figure 1) of the sheet 4, thereby removing the need for complex friction controlling devices to prevent the sheet 4 from moving away from the pushers 28, 30.
Referring to Figures 6 to 8, a front lay device 16 of Figure 1 is described in greater detail. The front lay device 16 is a complete assembly that is pivoted about pivot axis 62. A soft iron core 66, around which a first coil 68 and a second coil 70 are wound, is mounted to the body 64 and defines a pair of north poles 72 and a south pole 74 arranged between the north poles 72.
In operation, the gripper assembly 16 is pivoted about pivot axis 62 to expose a slot 76 at the level of the poles 72, 74 at the upper part of inclined surfaces 78. When the first 68 and second 70 coils are energised, the leading edge of the sheet 4 is attracted towards the poles 72, 74 and slides over inclined surfaces 78 to come into abutment with carbide tips 80 arranged between respective north 72 and south 74 pole pairs. The gripper assembly 16 is then pivoted to mechanically grip the sheet 4 against the impression cylinder 10, ready to be printed in the correct position/orientation.
It will be appreciated by persons skilled in the art that the above embodiment has been described by way of example only and not in any limitative sense, and that various alternations and modifications are possible without departure from the scope of the invention as defined by the appended claims. For example, the sidelay assembly 20 shown in Figure 1 as stationary relative to the frame of the apparatus 2 could move with the sheet 2 such that there is zero relative velocity between the sheet 4 and the sidelay assembly 20. Alternatively, or in addition, the use of the sheet handling apparatus embedded into front lay devices 16 enables the feeder apparatus 28, 30 to be dispensed with, thereby minimising the risk of buckling of the sheet and maintaining a positive force during register, wherein the magnet can be switched off before sheet release.

Claims

A sheet handling apparatus for handling a sheet (4) of material in a sheet processing apparatus, the sheet handling apparatus comprising:-
at least one engaging portion (36, 54) for engaging an edge (24) of a sheet of material being fed in a feeding direction relative to a sheet processing component of a sheet processing apparatus; and

characterized by magnetic flux generating means for generating magnetic flux passing through an edge region of the sheet of material such that a first magnetic force is applied to said sheet to urge said sheet towards at least one said engaging portion.
An apparatus according to claim 1, wherein said magnetic flux generating means is adapted to generate magnetic flux passing through an edge region of said sheet such that opposed second and third magnetic forces are applied to said sheet in a direction transverse to a surface of said sheet.
An apparatus according to claim 1 or 2, wherein the magnetic flux generating means is adapted to provide at least one pair of first magnetic poles of a first polarity, and at least one second pole of a second polarity, opposite to said first polarity, such that magnetic flux passing from a said first magnetic pole to a said second magnetic pole passes through said sheet.
An apparatus according to claim 3, wherein the magnetic flux generating means has a magnetic flux concentrating portion for concentrating magnetic flux therein and defining at least one pair of said first poles and at least one said second pole.
An apparatus according to claim 3 or 4, wherein at least one pair of said first magnetic poles is arranged such that said sheet can pass therebetween.
An apparatus according to any one of the preceding claims, wherein the magnetic flux generating means comprises at least one first coil and at least one second coil.
An apparatus according to claim 6, wherein at least one said first coil is arranged in use on a first side of said sheet and at least one said second coil is arranged in use on a second side of said sheet.
An apparatus according to claim 6 or 7, wherein at least one said first coil and at least one said second coil are connected in parallel.
An apparatus according to any one of the preceding claims, further comprising mechanical gripper means for gripping said sheet.
A sheet processing apparatus including at least one sheet handling apparatus according to any one of the preceding claims.
An apparatus according to claim 10, wherein at least one said sheet handling apparatus is adapted to apply a force to said sheet adjacent a side edge thereof relative to a feeding direction of the sheet.
An apparatus according to claim 10 or 11, wherein at least one said sheet handling apparatus is adapted to apply a force to said sheet adjacent a rear edge thereof relative to a feeding direction of the sheet.
An apparatus according to any one of claims 10 to 12, wherein at least one said sheet handling apparatus is adapted to apply a force to said sheet adjacent a leading edge thereof relative to a feeding direction of the sheet.