Plate cylinder shaft assembly for a can decorator

Abstract

A plate cylinder shaft assembly for a beverage can decorator is disclosed herein. The assembly comprises an axially rotatable plate cylinder shaft member for mounting a print plate cylinder thereon, and a rotationally driven hub member, connected to the plate cylinder shaft member via a torque transfer mechanism for axially rotating the plate cylinder shaft member upon rotation of the hub member. The torque transfer mechanism is arranged to allow axial translation thereof relative to the hub member, and for angularly adjusting the plate cylinder shaft member about its axis relative to the hub member upon said axial translation for circumferential registration of the print plate cylinder mountable on the plate cylinder shaft member.

Description

[0001] PLATE CYLINDER SHAFT ASSEMBLY FOR A CAN DECORATOR

[0002] The present invention relates to a plate cylinder shaft assembly for a can decorator, such as a beverage can decorator, and to a can decorator comprising such a plate cylinder shaft assembly. The present invention further relates to a registration member for forming such a plate cylinder shaft assembly, to a method of upgrading an existing can decorator, and to a method of circumferentially registering a print plate cylinder.

[0003] Graphics and text are intricately printed on cans, particularly beverage cans, using high-speed industrial machines called decorators. These decorators employ various components to effectively transfer print designs onto the cylindrical surface of cans. One critical element is the plate cylinder shaft assembly, responsible for mounting and rotating a print plate cylinder, which is integral to the printing process.

[0004] Typically, in a decorator, cans are fed onto a mandrel wheel or spindle disk, where they are drawn onto mandrels using vacuum. As the cans rotate with the mandrel wheel, they come into contact with printing blankets on a rotating blanket wheel. Ink is transferred from print plates on a print plate cylinder to these printing blankets, which then imprint the graphics and text onto the cans. An over-varnish unit further applies a protective layer to the printed designs before the cans are cured.

[0005] The Rutherford Decorator is an example of such a decorator and comprises a drum assembly with blanket segments, ink station assemblies with plate cylinder shaft assemblies for applying ink to the blanket segments, a main drive gear for synchronously rotating the plate cylinder shafts as the blanket segments are rotated past the ink station assemblies, and a mandrel wheel assembly for can rotation for transferring ink from the blanket segments onto the cans. However, a drawback of this decorator is the need to pause operation for circumferential registration of the print plate cylinder. Circumferential registration is the process of angularly adjusting the print plate cylinders about their respective rotation axes for mutual alignment of the print plate cylinders. Pausing operation for circumferential registration limits productivity.

[0006] In previous attempts to address this limitation, a circumferential registration system was introduced, including a slider mechanism linked to the helical gear that is mounted on the plate cylinder shaft and meshes with the helical bull gear of the decorator, wherein translation of the slider is transmitted to the helical gear such that, due to the helicality of the gear teeth, the plate cylinder shaft is rotated by the movement of the slider. For example, US Patents 4,741,266 and 11,298,934 disclose a circumferential registration system wherein axial movement of the helical gear causes rotation of the shaft due to engagement of the helical teeth of the gear with the helical teeth of the bull gear. However, it has been found that this solution, when put into practice, leads to undesirable play within the assembly during operation.

[0007] It is an object of the present invention, amongst other objects, to provide a plate cylinder shaft assembly that enables circumferential registration of the print plate cylinder during operation of the can decorator while minimising play.

[0008] Hereto, a plate cylinder shaft assembly for a can decorator, such as a beverage can decorator, is provided, wherein the assembly comprises: a plate cylinder shaft member for mounting a print plate cylinder thereon, wherein the plate cylinder shaft member is axially rotatable about a main axis for rotating a print plate cylinder mounted on the plate cylinder shaft member; a hub member, arranged to be rotationally driven about a first axis and connected to the plate cylinder shaft member via a torque transfer mechanism for axially rotating the plate cylinder shaft member upon rotation of the hub member about the first axis, wherein the torque transfer mechanism is arranged to allow axial movement thereof relative to the hub member, and for angularly adjusting the plate cylinder shaft member about the main axis relative to the hub member upon said axial movement for circumferential registration of the print plate cylinder mountable on the plate cylinder shaft member.

[0009] By arranging the torque transfer mechanism this way, circumferential registration of the print plate cylinder without axially translating the gear or hub driven by the main drive gear of the can decorator is enabled. By not translating the driven gear or hub, the driving forces exerted on the driven gear or hub by the main drive gear can be efficiently transferred to the plate cylinder shaft member while minimising play within the assembly during operation of the can decorator. Furthermore, if the driven member is not axially translated, the driven member and the main drive gear do not have to be dimensionally configured for accommodating the axial translation of the driven member.

[0010] Preferably, the assembly comprises a registration member, arranged axially rotatable about a second axis and connected to the hub member via a first torque transfer mechanism and to the plate cylinder shaft member via a second torque transfer mechanism for axially rotating the plate cylinder shaft member upon rotation of the hub member about the first axis, wherein the first and second torque transfer mechanisms are jointly arranged to allow translation of the registration member along the second axis relative to the hub member and the plate cylinder shaft member, and for angularly adjusting the plate cylinder shaft member about the main axis relative to the hub member upon translation of the registration member along the second axis for circumferential registration of the print plate cylinder mountable on the plate cylinder shaft member.

[0011] By angularly adjusting the plate cylinder shaft member by means of axial translation of the registration member, circumferential registration of the print plate cylinder during operation of the can decorator can be achieved in a highly efficient and robust manner.

[0012] By transferring torque from the hub member to the plate cylinder shaft member not directly but indirectly via the registration member, the torque can be transferred to the plate cylinder shaft member at a location on the plate cylinder shaft member that is not the location of the hub member. For instance, the torque may be transferred to the plate cylinder shaft member at a location between the hub member and the section of the plate cylinder shaft member where a print plate cylinder is to be mounted. Thus, the hub member does not have to be provided with a keyway for coupling to the shaft but can be coupled to the plate cylinder shaft member via the registration member connected to the hub member via the first torque transfer mechanism. As the hub member is not coupled to the shaft by means of the usual keyed joint, the plate cylinder shaft member can be angularly adjusted about the main axis relative to the hub member.

[0013] The main, first and second axes are to be understood as mathematical axes serving as references for describing the movements of the various components of the system. The second axis may be parallel to the main axis and / or the first axis. Preferably, the second axis coincides with the main axis and / or the first axis. That is, the axes may be identical to each other.

[0014] According to a preferred embodiment of the plate cylinder shaft assembly, one or each of the hub member and the registration member is arranged around the plate cylinder shaft member. By arranging the hub member and / or the registration member on the plate cylinder shaft member, the mechanism for circumferential registration of the print plate cylinder can be made considerably compact. Preferably, the registration member is arranged between the hub member and the print plate cylinder mounting section of the plate cylinder shaft member.

[0015] According to a further preferred embodiment of the plate cylinder shaft assembly, the torque transfer mechanism or at least one, preferably each, of the first and second torque transfer mechanisms is formed by at least one mating pair of a protrusion, provided on one of the respective members, and a recess provided in the other of the respective members, wherein the protrusion is configured to engage in the recess. The torque transfer mechanism is preferably formed by a plurality of such mating pairs. Preferably, the at least one mating pair extends helically about the respective axis (i.e., along a space curve with tangent lines at a substantially constant angle to the respective axis) for angularly adjusting the respective members relative to each other about the respective axis upon relative axial movement of the torque transfer mechanism.

[0016] A helix is a highly effective shape for converting, e.g., axial translation of the registration member to axial rotation of the plate cylinder shaft member. Preferably, the protrusion is a helical tooth element, and the recess is a helical groove.

[0017] For instance, the first torque transfer mechanism may be formed by at least one mating pair of a protrusion, provided on one of the registration member and the hub member, and a recess provided in the other of the registration member and the hub member, wherein the protrusion is configured to engage in the recess, wherein the at least one mating pair extends helically about the second axis for angularly adjusting the registration member about the second axis relative to the hub member upon translation of the registration member relative to the hub member along the second axis. Alternatively, or additionally, the second torque transfer mechanism may be formed by at least one mating pair of a protrusion, provided on one of the registration member and the plate cylinder shaft member, and a recess provided in the other of the registration member and the plate cylinder shaft member, wherein the protrusion is configured to engage in the recess, wherein the at least one mating pair extends helically about the second axis for angularly adjusting the plate cylinder shaft member about the main axis relative to the registration member upon translation of the registration member relative to the plate cylinder shaft member along the second axis.

[0018] The helix angle may be in the range of, e.g., 10 to 40 degrees, preferably 20 to 30 degrees. If both the first and the second torque mechanism are formed by helical mating pairs as described above, the sum of the respective helix angles is preferably in the range of 20 to 80 degrees.

[0019] According to a further preferred embodiment of the plate cylinder shaft assembly, the torque transfer mechanism or at least one, preferably each, of the first and second torque transfer mechanisms is formed by a set of internal gear tooth elements, provided on one of the respective members, and a set of external gear tooth elements, provided on the other of the respective members, wherein the set of internal gear tooth elements is configured to mesh with the set of external gear tooth elements. Preferably, the gear tooth elements of at least one, preferably each, of the sets extend helically about the second axis for angularly adjusting the respective members relative to each other about the second axis upon relative translation of the registration member along the second axis. As the respective members are provided with meshing sets of internal and external helical gear teeth, the externally geared member can close-fittingly mate with the internally geared member such that any play within the torque transfer mechanism is minimised and the angular position of the plate cylinder shaft member relative to the hub member can be accurately and reliably adjusted by axial movement of the torque transfer mechanism.

[0020] The first or second torque transfer mechanisms may be a spline coupling. Preferably, the first torque transfer mechanism is a helical gear tooth coupling formed by gear teeth extending helically about the second axis. Additionally, or alternatively, the second torque transfer mechanism is a spline coupling formed by splines extending parallel to the second axis. In some cases, when retrofitting the assembly to an existing can decorator having a plate cylinder shaft with splines, the plate cylinder shaft of the existing assembly can be used for forming the retrofit assembly by using the splines of the shaft for forming the second torque transfer mechanism.

[0021] Alternatively, the first torque transfer mechanism may be a spline coupling formed by splines extending parallel to the second axis, and the second torque transfer mechanism may be a helical gear tooth coupling formed by gear teeth extending helically about the second axis.

[0022] According to a further preferred embodiment, the plate cylinder shaft assembly further comprises a circumferential registration operating system arranged for selectively translating the registration member along the second axis. The circumferential registration operating system may comprise an operatively movable slider and a bearing member connected to the slider and arranged for transmitting translation of the slider to translation of the registration member along the second axis and for allowing rotation of the registration member relative to the slider. For example, the bearing member may comprise a forked part and a pair of cam followers provided respectively on the mutually opposite fork ends of the forked part. The registration member may be provided with a circumferential groove, forming a cam, wherein the cam followers are arranged in the groove respectively on either side of the registration member. This way, translation of the slider can be transmitted to the registration member while still allowing the registration member to rotate for axially rotating the plate cylinder shaft member upon rotation of the hub member during operation of the can decorator.

[0023] According to a further preferred embodiment of the plate cylinder shaft assembly, the hub member comprises a gear part arranged to mesh with a main drive gear of the can decorator. Preferably, the gear part is a helical gear part. According to a further aspect, a registration member for forming a plate cylinder shaft assembly as described herein is provided, wherein the registration member is configured to be arranged around a plate cylinder shaft member axially rotatable about a main axis. Preferably, the registration member is a registration member as described above. In particular, the registration member is preferably provided with a set of internal spline elements for forming part of the second torque transfer mechanism of the assembly, wherein the set of internal spline elements is configured to mesh with a set of external spline elements provided on the plate cylinder shaft member and extending parallel to the main axis. Preferably, the registration member is further provided with at least one engaging structure extending helically about the main axis for forming part of the first torque transfer mechanism of the assembly. The engaging structure is, e.g., a protrusion or a recess.

[0024] Further, a kit-of-parts for forming a plate cylinder shaft assembly as described herein is provided, wherein the kit-of-parts comprises a registration member as described above and a hub member arranged to be rotationally driven about the main axis, wherein the registration member is arranged to be connected to the hub member via the first torque transfer mechanism. Preferably, the first torque transfer mechanism is formed by at least one mating pair of a protrusion, provided on one of the registration member and the hub member, and a recess provided in the other of the registration member and the hub member, wherein the protrusion is configured to engage in the recess, wherein the at least one mating pair extends helically about the main axis for angularly adjusting the registration member about the main axis relative to the hub member upon translation of the registration member relative to the hub member along the main axis. Preferably, the protrusion is a helical tooth element, and the recess is a helical groove. It is then further preferred if the first torque transfer mechanism is a helical gear tooth coupling formed by gear teeth extending helically about the main axis, and the second torque transfer mechanism is a spline coupling formed by splines extending parallel to the main axis.

[0025] According to a further aspect, a method of upgrading an existing can decorator is provided, the decorator comprising a plurality of ink station assemblies, each comprising a plate cylinder shaft assembly and arranged for supplying ink to a print plate cylinder mounted on the plate cylinder shaft assembly, and a main drive gear rotatably arranged for synchronously rotating the plate cylinder shaft assemblies, wherein the method comprises the step of adapting at least one, preferably each, of the ink station assemblies of the existing can decorator such that the at least one ink station assembly is provided with a plate cylinder shaft assembly as described herein.

[0026] The method preferably comprises the steps of providing at least one plate cylinder shaft assembly, preferably a plurality of plate cylinder shaft assemblies, as described herein and replacing the plate cylinder shaft assembly of the at least one ink station assembly with the at least one provided plate cylinder shaft assembly.

[0027] Further provided is a can decorator, comprising a plurality of ink station assemblies, each comprising a plate cylinder shaft assembly and arranged for supplying ink to a print plate cylinder mounted on the plate cylinder shaft assembly, and a main drive gear rotatably arranged for synchronously rotating the plate cylinder shaft assemblies, wherein at least one of the plate cylinder shaft assemblies is a plate cylinder shaft assembly as described herein.

[0028] A preferred embodiment of the can decorator further comprises: a drum assembly circumferentially provided with a plurality of blanket segments for receiving ink, wherein each ink station assembly is arranged for supplying ink to the plurality of blanket segments via the print plate cylinder mounted on the plate cylinder shaft assembly, wherein the drum assembly is rotatably arranged for rotating the plurality of blanket segments past the plurality of ink station assemblies to supply ink to the plurality of blanket segments; an infeed device arranged for feeding cans into the decorator; a mandrel wheel assembly arranged for receiving the cans from the infeed device, for holding the cans by means of vacuum, and for rotating the held cans from the infeed device to the drum assembly to apply the ink from the blanket segments to the cans.

[0029] Further, a method of circumferentially registering a print plate cylinder is provided, the method comprising the steps of: providing a can decorator as described above, wherein said print plate cylinder is mounted on the plate cylinder shaft member of the assembly as described herein; angularly adjusting the plate cylinder shaft member about the main axis relative to the hub member by translating the registration member along the second axis.

[0030] The method preferably further comprises the step of rotating the main drive gear, wherein the registration member is translated along the second axis during rotation of the main drive gear.

[0031] In the following, a preferred embodiment of the present invention is illustrated with reference to the accompanying drawings, wherein:

[0032] Figure 1 schematically represents a beverage can decorator known in the art;

[0033] Figure 2 represents a sectional side view of a known plate cylinder shaft assembly;

[0034] Figures 3A-D represent a plate cylinder shaft assembly according to the present disclosure; Figure 4 represents a registration member of the assembly shown in Figures 3A-D; Figure 5 represents a hub member of the assembly shown in Figures 3A-D.

[0035] In Figure 1, a beverage can decorator 100 of the Rutherford-type is schematically shown. The decorator 100 comprises an infeed conveyor 101 for feeding undecorated beverage cans 102 into the decorator 100 and a rotating mandrel wheel assembly 103 for receiving the cans 102 from the infeed conveyor 101. The mandrel wheel assembly 103 sucks the cans 102 onto mandrels along its circumference by means of vacuum and is mounted onto a rotating horizontal drive shaft 104 for rotating the held cans 102 from the infeed conveyor 101 to a rotating drum assembly 105 of the decorator 100.

[0036] The drum assembly 105 is circumferentially provided with a plurality of blanket segments 106 for receiving ink to be applied to the cans 102. Hereto, the decorator 100 further comprises a plurality of ink station assemblies 107 positioned around the drum assembly 105, wherein each ink station 107 is configured for supplying ink to the blanket segments 106. In each ink station assembly 107, ink from an ink container at the top of the ink station 107 is applied to a printing plate cylinder via one or more polyurethane or rubber rolls 108. The blanket segments 106 are rotated past the ink station assemblies 107 to supply the ink to the blanket segments 106 via the printing plate cylinders. The ink stations 107 are each configured for supplying a different colour of ink in a respective image pattern to the blanket segments 106. Combined, these image patterns form the multicolour image to be applied onto the cans 102. That is, e.g., for a can decoration with eight colours, eight ink stations are used with eight different printing plates. Likewise, for a can decoration with four colours, four ink stations are used with four different printing plates. The decorator 100 shown in Figure 1 comprises six ink stations 107. Where the undecorated cans 102, rotated by the mandrel wheel assembly 103, meet the blanket segments 106, the cans 102 are brought into engagement with the blanket segments 106 such that the multicolour ink image on each blanket segment 106 is unrolled onto a respective can 102. That is, the entire image on a blanket segment 106 is unrolled onto a single can 102.

[0037] After ink is applied onto a can 102, a layer of varnish may be applied on the printed image in an over-varnish unit 109. Decorated and varnished cans 102 are transferred from the mandrels of the mandrel wheel assembly 103 via a transfer unit 110 to horizontal pins 111 carried by a chain-type conveyor 112, which carries the cans 102 through a curing oven (not shown).

[0038] As the blanket segments 106 are rotated past the ink station assemblies 107, the printing plate cylinders are rotated to unroll the ink image from the plate cylinders onto the blanket segments 106. Hereto, each plate cylinder is mounted on an axially rotated plate cylinder shaft of the ink station assembly 107. In Figure 2, such a plate cylinder shaft assembly 1’ is shown in longitudinal section. The plate cylinder shaft assembly 1’ comprises the plate cylinder shaft 2’, on which the print plate cylinder 3 is mounted, and a helical gear member 4’ that is keyed to the plate cylinder shaft 2’. The decorator 100 comprises a helical bull gear that simultaneously engages with the helical gear members 4’ of the different plate cylinder shaft assemblies 1’ around the drum assembly 105 for synchronously rotating the plate cylinder shafts 2’ around their respective longitudinal axes A. The bull gear in such decorators is often about 1.5 metre in diameter. Each shaft 2’ is rotatably mounted in two frame plates 5 via roller bearings 6.

[0039] The process of printing beverage cans requires precise mutual alignment of the different image patterns to ensure quality of the printed image. Circumferential registration is the process of angularly adjusting the print plate cylinder 3 about the main axis A. At a mounting end plate 7’, wherein the print plate cylinder 3 is mounted on the shaft 2’ , the print plate cylinder 3 can be manually adjusted relative to the shaft 2’ when operation of the decorator 100 is paused. However, pausing operation limits productivity.

[0040] Figure 3C represents a side view of a plate cylinder shaft assembly 1 according to the present disclosure. In Figure 3D, the plate cylinder shaft assembly 1 is shown in longitudinal section. The plate cylinder shaft assemblies 1’ of the existing decorator 100 can be replaced by plate cylinder shaft assemblies 1 according to the present disclosure. Figures 3A-B represent an isometric view of the plate cylinder shaft assembly 1 according to the present disclosure in an installed state. The plate cylinder shaft assembly 1 comprises a plate cylinder shaft member 2 for mounting a print plate cylinder 3 thereon, a hub member 4 and a registration member 10. These members 2, 4, 10 are axially rotatable about a main axis A, wherein the shaft member 2 is rotatably mounted in two frame plates 5 via roller bearings 6 while the hub member 4 and the registration member 10 are arranged around the shaft member 2. The hub member 4 comprises a helical gear part 41 arranged to mesh with the helical bull gear of the existing decorator 100. The registration member 10 is connected to the hub member 4 via a first torque transfer mechanism 8 and to the plate cylinder shaft member 2 via a second torque transfer mechanism 9 such that, when the hub member 4 is rotationally driven about the main axis A by the bull gear of the decorator 100, also the plate cylinder shaft member 2 and a print plate cylinder 3 mounted thereon are axially rotated. That is, rotation of the hub member 4 is transferred to the shaft member 2 only via the registration member 10.

[0041] As illustrated in more detail in Figure 4 in conjunction with Figure 5, the first torque transfer mechanism 8 is a helical gear tooth coupling formed by external gear teeth 12 provided on the registration member 10 and internal gear teeth 42 provided on the hub member 4, wherein the gear teeth 12, 42 extend helically about the main axis A. As shown in Figure 4, the second torque transfer mechanism 9 is a spline coupling formed by internal splines 13 provided on the registration member 10 and external splines 21 provided on the shaft member 2, wherein the splines 13, 21 extend parallel to the main axis A. As such, the first and second torque transfer mechanisms 8, 9 are jointly arranged such that, upon relative translation of the registration member 10 along the main axis A in the direction indicated by arrow Ti, the plate cylinder shaft member 2 is angularly adjusted about the main axis A relative to the hub member 4 in the direction indicated by arrow Ri. Reversely, translation in the opposite direction, indicated by arrow Tz, results in an angular adjustment in the direction indicated by arrow Rz. This way, circumferential registration of a print plate cylinder 3 mounted on the plate cylinder shaft member 2 during operation of the decorator 100 is enabled.

[0042] The plate cylinder shaft assembly 1 further comprises a circumferential registration operating system 70, comprising a rotatable handle 71 and an axially rotatable spindle 72 connected to the handle 71 at one end and forming a leadscrew at the other end. The operating system 70 further comprises a slider 73 connected to the leadscrew end of the spindle 72 and axially movable by turning the handle 71 (indicated by arrows Ci, C2). The operating system 70 further comprises a linear guide 74 for guiding axial translation of the slider 73 (indicated by arrows Si, S2), a forkshaped arm 75 attached to the slider 73, and a pair of rollers 76 provided respectively on the mutually opposite fork ends 77 of the fork-shaped arm 75. The registration member 10 is provided with a circumferential groove or cam 11. The rollers 76 are fittingly arranged in the groove 11 respectively on either side of the registration member 10. By turning the handle 71, the slider 73 axially translates along the guide 74, which translation is transmitted via the arm 75 and rollers 76 to translation of the registration member 10 along the main axis A. As such, the operating system 70 is arranged for selectively shifting the registration member 10 into or out of the hub member 4 for angularly adjusting the plate cylinder shaft member 2 about the main axis A relative to the hub member 4 due to the helicality of the gear teeth 12, 42 as explained above.

[0043] The drawings and the above description serve to illustrate specific embodiments of the invention and do not limit the scope of protection defined by the appended claims.

Claims

CLAIMS1. A plate cylinder shaft assembly for a can decorator, such as a beverage can decorator, the assembly comprising:- a plate cylinder shaft member for mounting a print plate cylinder thereon, wherein the plate cylinder shaft member is axially rotatable about a main axis for rotating a print plate cylinder mounted on the plate cylinder shaft member;- a hub member, arranged to be rotationally driven about a first axis;- a registration member, arranged axially rotatable about a second axis and connected to the hub member via a first torque transfer mechanism and to the plate cylinder shaft member via a second torque transfer mechanism for axially rotating the plate cylinder shaft member upon rotation of the hub member about the first axis, wherein the first and second torque transfer mechanisms are jointly arranged to allow translation of the registration member along the second axis relative to the hub member and the plate cylinder shaft member, and for angularly adjusting the plate cylinder shaft member about the main axis relative to the hub member upon translation of the registration member along the second axis for circumferential registration of the print plate cylinder mountable on the plate cylinder shaft member.

2. Plate cylinder shaft assembly according to claim 1, wherein the second axis is parallel to the main axis and / or the first axis.

3. Plate cylinder shaft assembly according to claim 2, wherein the second axis coincides with the main axis and / or the first axis.

4. Plate cylinder shaft assembly according to claim 3, wherein one or each of the hub member and the registration member is arranged around the plate cylinder shaft member.

5. Plate cylinder shaft assembly according to claim 3 or 4, wherein at least one of the first and second torque transfer mechanisms is formed by at least one mating pair of a protrusion, provided on one of the respective members, and a recess provided in the other of the respective members, wherein the protrusion is configured to engage in the recess, wherein the at least one mating pair extends helically about the second axis for angularly adjusting the respective members relative to each other about the second axis upon relative translation of the registration member along the second axis.

6. Plate cylinder shaft assembly according to claim 5, wherein the protrusion is a helical tooth element, and the recess is a helical groove.

7. Plate cylinder shaft assembly according to any of the preceding claims, wherein at least one of the first and second torque transfer mechanisms is formed by a set of internal gear tooth elements, provided on one of the respective members, and a set of external gear tooth elements, provided on the other of the respective members, wherein the set of internal gear tooth elements is configured to mesh with the set of external gear tooth elements, wherein the gear tooth elements of at least one of the sets extend helically about the second axis for angularly adjusting the respective members relative to each other about the second axis upon relative translation of the registration member along the second axis.

8. Plate cylinder shaft assembly according to any of the preceding claims, wherein the first or second torque transfer mechanism is a spline coupling.

9. Plate cylinder shaft assembly according to claim 8, wherein the first torque transfer mechanism is a helical gear tooth coupling formed by gear teeth extending helically about the second axis, and the second torque transfer mechanism is a spline coupling formed by splines extending parallel to the second axis.

10. Plate cylinder shaft assembly according to any of the preceding claims, further comprising a circumferential registration operating system arranged for selectively translating the registration member along the second axis.

11. Plate cylinder shaft assembly according to claim 10, wherein the circumferential registration operating system comprises an operatively movable slider and a bearing member connected to the slider and arranged for transmitting translation of the slider to translation of the registration member along the second axis and for allowing rotation of the registration member relative to the slider.

12. Plate cylinder shaft assembly according to any of the preceding claims, wherein the hub member comprises a gear part arranged to mesh with a main drive gear of the can decorator.

13. Plate cylinder shaft assembly according to claim 12, wherein the gear part is a helical gear part.

14. A registration member for forming a plate cylinder shaft assembly according to any of the preceding claims, wherein the registration member is configured to be arranged around a plate cylinder shaft member axially rotatable about a main axis, wherein the registration member is provided with a set of internal spline elements for forming part of the second torque transfer mechanism of the assembly, wherein the set of internal spline elements is configured to mesh with a set of external spline elements provided on the plate cylinder shaft member and extending parallel to the main axis, wherein the registration member is further provided with at least one engaging structure extending helically about the main axis for forming part of the first torque transfer mechanism of the assembly.

15. A method of upgrading an existing can decorator, the decorator comprising a plurality of ink station assemblies, each comprising a plate cylinder shaft assembly and arranged for supplying ink to a print plate cylinder mounted on the plate cylinder shaft assembly, and a main drive gear rotatably arranged for synchronously rotating the plate cylinder shaft assemblies, wherein the method comprises the step of adapting at least one of the ink station assemblies of the existing can decorator such that the at least one ink station assembly is provided with a plate cylinder shaft assembly according to any of the preceding claims 1-13.

16. Method according to claim 15, comprising the steps of providing at least one plate cylinder shaft assembly according to any of the preceding claims 1-13 and replacing the plate cylinder shaft assembly of the at least one ink station assembly with the at least one provided plate cylinder shaft assembly.

17. A can decorator, comprising a plurality of ink station assemblies, each comprising a plate cylinder shaft assembly and arranged for supplying ink to a print plate cylinder mounted on the plate cylinder shaft assembly, and a main drive gear rotatably arranged for synchronously rotating the plate cylinder shaft assemblies, wherein at least one of the plate cylinder shaft assemblies is a plate cylinder shaft assembly according to any of the preceding claims 1-13.

18. Can decorator according to claim 17, further comprising:- a drum assembly circumferentially provided with a plurality of blanket segments for receiving ink, wherein each ink station assembly is arranged for supplying ink to the plurality of blanket segments via the print plate cylinder mounted on the plate cylinder shaft assembly, wherein the drum assembly is rotatably arranged for rotating theplurality of blanket segments past the plurality of ink station assemblies to supply ink to the plurality of blanket segments;- an infeed device arranged for feeding cans into the decorator;- a mandrel wheel assembly arranged for receiving the cans from the infeed device, for holding the cans by means of vacuum, and for rotating the held cans from the infeed device to the drum assembly to apply the ink from the blanket segments to the cans.

19. A method of circumferentially registering a print plate cylinder, comprising the steps of:- providing a can decorator according to claim 17 or 18, wherein said print plate cylinder is mounted on the plate cylinder shaft member of the assembly according to any of the preceding claims 1-13;- angularly adjusting the plate cylinder shaft member about the main axis relative to the hub member by translating the registration member along the second axis.

20. Method according to claim 19, further comprising the step of rotating the main drive gear, wherein the registration member is translated along the second axis during rotation of the main drive gear.

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