Inker controller for a can decorator

Abstract

A controller for controlling roller segments of a vibrating roller of a can decorator. The controller obtains a decorator speed and an inking percentage defining a percentage ink transfer for the roller segment up to a maximum inking percentage. The controller further determines from said data and the corresponding inking percentage, an applied ink pulse duration defining a first time period during which each roller segment is in the first position and an applied ink pulse spacing defining a second time period during which each roller segment is in the second position, and generates for each roller segment a periodic control signal based on the applied ink pulse duration and spacing determined for that roller segment. The controller outputs the generated control signals to actuators of the respective roller segments.

Description

[0001] Inker Controller for a Can Decorator

[0002] Technical field

[0003] The present invention relates to an inker controller for a can decorator and to an inker control method.

[0004] Background

[0005] Metal cans such as steel and aluminium beverage cans are commonly manufactured in two pieces. A first part comprises a generally cylindrical container body with integral base, formed from a circular metal disk using a drawing and ironing process. A second part comprises an end having a tab or ring-pull formed therein. The can is filled, e.g. with beverage, and the end subsequently fixed to the body using a seaming process.

[0006] Can decorators are known in the art for applying decoration to the external surface of a can body, for example see W02020 / 092841. A typical decorator is used to apply decoration to the can body prior to filling of the can body and prior to seaming of the end. Figure 1 shows a mandrel wheel assembly 1 comprising a set of mandrels 2 each of which is rotatable about a central axis. Unprinted or “blank” can bodies 3 are loaded onto the mandrels 2 via the can infeed conveyor 4. The unprinted can bodies 3 are then conveyed into a printing zone 5 where the can bodies are brought into contact, i.e. rolled across, pre-inked blankets (not shown) mounted on a blanket wheel 6 via respective blanket segments. Printed cans then pass through an over varnish unit 7 and onwards onto a can transfer assembly 8 before transferring onto a pin chain conveyor 9.

[0007] Figure 1 also illustrates eight ink stations 10, each comprising an ink reservoir or ink fountain 11 , a printing plate (not shown) having an image provided thereon, e.g. using a computer to plate (CtP) technology, and attached to a plate cylinder 12, and a delivery mechanism 13 for ensuring even application of ink from the reservoir to the printing plate. Traditionally the delivery mechanism comprises one or more inker rollers. Each blanket passes through the ink stations 10 in sequence such that a blanket leaving the final ink station has a composite (in this case, eight colour) ink

[0008] 38191232-1 image formed on a printing surface thereof. This composite image is transferred to a blank can body 3 in the printing zone 5.

[0009] In order to deliver an even and consistent coating of ink from the ink fountain of each inker station to the printing plate, whilst at the same time minimising ink usage, it is known to implement the delivery mechanism 13 as a sequence of inker rollers including a fountain roller that is adjacent to the ink fountain and one or more transfer rollers that transfer ink from the fountain roller to the print cylinder.

[0010] Ink is of course ultimately transferred from the fountain roller to the can bodies. However, the removal of ink from the fountain roller is discontinuous along its axis. Consider for example an inker station configured to provide red ink decoration to a can body. Ink will be taken up by the corresponding printing plate only in those regions where red is to be applied. Traditional blanket decorators may provide some means to account for this by providing a series of manually adjustable blades along the edge of the ink fountain and which can be moved independently towards and away from the fountain roller. These allow the amount of ink transferred to the fountain roller to be varied along the axis of that roller. Manual adjustment is of course time consuming and prone to error.

[0011] Figure 2 illustrates an improved ink delivery mechanism including a fountain roller 101 and a transfer roller 102. The fountain roller is a driven roller and is located adjacent to the ink fountain 103. The transfer roller is also driven. Ink flows over an edge of the ink fountain and into contact with the fountain roller as it rotates. The edge of the ink fountain forms a single continuous blade 104. The blade may be a movable towards and away from the fountain roller 103 by manual adjustment such that the gap therebetween, which defines the amount of ink transferred to the fountain roller, can be precisely controlled, e.g. to fix the gap during normal operations. In order to reduce the amount of ink taken from the ink fountain 103 a further roller 105 is located between the fountain roller 101 and the (first) transfer roller 102. This further roller 105 is referred to here as the “vibrating roller”. Such use of a vibrating roller is described for example in US5688217A and US11292244B2 in the context of a printing press.

[0012] The vibrating roller 105 comprises a series (in this example seven) of axially spaced roller segments 106 located on a common axle 107 and which are each essentially

[0013] 38191232-1 “free-wheeling”. The segments 106 are movable independently of one another, by respective electromechanical actuators, away from the axle 107 under the control of a computer controller such that each roller segment may rotate eccentrically about the common axle 107. This allows the roller segments 106 to be moved dynamically into and out of contact with the fountain roller 101 and the transfer roller 102 such that each segment contacts only one of the fountain roller and the transfer roller at any given time. In this way, the volume of ink may be tailored for each colour and along the length of each print plate, as indicated in Figure 3 which shows from left to right the inked green (a), red (b), black (c), cyan (d), yellow (e) and blue (f) printing plates and, beneath each plate, ink levels applied to sequential circumferential regions of the plates. By controlling the contact time of a roller segment 106 with the fountain roller 101 and with the transfer roller 102 (i.e. the duty cycle of the segment), the amount of ink transferred from the ink fountain 103 to the transfer roller 102 can be precisely controlled both axially and in time. Maximum ink transfer for a given roller segment, from the fountain roller to the transfer roller, i.e. 100% transfer, is achieved with a 50% duty cycle, that is when the vibrating roller segment is in contact with the fountain roller for 50% of the time and in contact with the transfer roller for the other 50% of the time (subject to the transit time of the segment during each change of position).

[0014] This maximum ink transfer is illustrated schematically in Figure 4 which effectively shows time along the horizontal axis, where time is measured in terms of encoder counts and one cycle corresponds to 48 encoder counts, i.e. the contact time of the roller segment with the transfer roller is 24 counts followed by a contact time of 24 counts with the fountain roller.

[0015] The patent document number EP4072857 discloses an image control system for a can decorator that includes an electronic can decorator control assembly, a mechanical can decorator control assembly, and a number of sensors. The electronic can decorator control assembly includes a programmable logic circuit and a number of modules. The mechanical can decorator control assembly is structured to be, and is, operatively coupled to at least one of an ink fountain ink application adjustment assembly, a ductor roll assembly duty cycle adjustment assembly, a printing plate cylinder assembly axial adjustment assembly, or a printing plate cylinder assembly circumferential adjustment assembly. The electronic can decorator control assembly is structured to be operatively coupled to the mechanical can decorator control assembly. Each sensor in the number

[0016] 38191232-1 of sensors is structured to measure a can body applied image characteristic and to generate an image signal including data representing the can body applied image characteristic.

[0017] Summary

[0018] Embodiments of the invention may address the problem of inconsistent ink transfer during the can decoration process, which can otherwise lead to variations in print quality and inefficiencies in ink usage.

[0019] Embodiments may provide solutions for controlling the independent movement of roller segments in a vibrating roller system of a can decorator, allowing for precise adjustments in ink transfer based on the decorator speed and the specific requirements of the can decoration. By dynamically determining the applied ink pulse duration and spacing for each roller segment, the controller may ensure that the volume of ink transferred between the fountain roller and the transfer roller is optimized according to the decoration segments, thereby addressing the challenges of maintaining uniform ink application across varying production speeds and decoration designs.

[0020] According to a first aspect of the present invention there is provided a controller for controlling roller segments of a vibrating roller of a can decorator, each of the roller segments being movable independently under control of the controller between a first position in which the roller segment contacts a fountain roller of the can decorator and a second position in which the roller segment contacts a transfer roller of the can decorator to thereby control the volume of ink transferred between the fountain roller and the transfer roller. The controller comprises an input for receiving an input indicative of a decorator speed and a processor for obtaining for each roller segment an inking percentage defining a percentage ink transfer for the roller segment up to a maximum inking percentage, determining, for each roller segment, from said data and the corresponding inking percentage, an applied ink pulse duration defining a first time period during which the roller segment is in the first position and an applied ink pulse spacing defining a second time period during which the roller segment is in the second position, and generating for each roller segment a periodic control signal based on the applied ink pulse duration and spacing determined for that roller segment. The controller further comprises an output for providing the generated control signals to actuators of the respective roller segments.

[0021] 38191232-1 The processor may be configured to determine a period of said periodic control signal as a standard cycle period for inking percentages above a predefined inking percentage and to determine the period as greater than the standard cycle period for inking percentages equal to or less than the predefined inking percentage. The standard cycle period may be a time taken to transfer a capacity of the mandrel wheel assembly through the printing zone. The mandrel wheel assembly capacity may be a number of mandrels configured to hold can bodies.

[0022] The processor may be configured to define a minimum ink pulse duration and to define the applied ink pulse duration as the minimum ink pulse duration for inking percentages equal to or less than a predefined inking percentage.

[0023] The determining, by the processor, of the applied ink pulse duration and the applied ink pulse spacing from said data and the corresponding inking percentage may comprise adjusting the inking percentage in dependence upon the decorator speed. The adjusting may comprise applying one of a pre-defined set of correction factors associated with respective decorator speed bands. The processor may be configured to determine the compensation factor from a pre-defined compensation factor profile.

[0024] The pre-defined compensation factor profile may define one of: a constant compensation factor, for example 1 ; a compensation factor that increases substantially linearly with increasing decorator speed up to a defined decorator speed and is constant at higher decorator speeds; and a compensation factor that decreases substantially linearly with decreasing decorator speed down to a defined decorator speed and is constant at lower decorator speeds.

[0025] The defined decorator speed may be a most commonly used decorator speed. A compensation factor at the most commonly used decorator speed may be 1 .

[0026] The input may be further configured to receive a can infeed conveyor start signal indicative of a starting of the can infeed conveyor, the controller being configured to react to the can infeed start signal by commencing generating the control signal after a predefined delay.

[0027] 38191232-1 The input may be configured to receive a can infeed conveyor stop signal indicative of a stopping of the can infeed conveyor, the can infeed conveyor being configured to react to the can infeed stop signal by ceasing generation of the control signal. The stop signal may be received at some interval prior to stopping of the can infeed conveyor, and the can infeed conveyor being configured to react to the can infeed stop signal by ceasing generation of the control signal at some predefined delay prior to the last can of the sequence entering the printing zone.

[0028] The data may comprise a sequence of pulses each associated with the passage of a mandrel past a fixed point, and a predefined delay is defined in terms of a predefined number of pulses.

[0029] According to a second aspect of the present invention there is provided method of controlling roller segments of a vibrating roller of a can decorator, each of the roller segments being movable independently between a first position in which the roller segment contacts a fountain roller of the can decorator and a second position in which the roller segment contacts a transfer roller of the can decorator to thereby control the volume of ink transferred between the fountain roller and the transfer roller. The method comprises receiving data indicative of a decorator speed, obtaining for each roller segment an inking percentage defining a percentage ink transfer for the roller segment up to a maximum inking percentage, determining, for each roller segment, from said data and the corresponding inking percentage, an applied ink pulse duration defining a first time period during which the roller segment is in the first position and an applied ink pulse spacing defining a second time period during which the roller segment is in the second position, generating for each roller segment a periodic control signal based on the applied ink pulse duration and spacing determined for that roller segment, and providing the generated control signals to actuators of the respective roller segments.

[0030] The method may comprise determining a period of said periodic control signal as a standard cycle period for inking percentages above a predefined inking percentage and to determine the period as greater than the standard cycle period for inking percentages equal to or less than the predefined inking percentage. The standard cycle period may be a time taken to transfer a capacity of the mandrel wheel assembly

[0031] 38191232-1 through the printing zone. The conveyor capacity may be a number of mandrels configured to hold can bodies.

[0032] The method may comprise defining a minimum ink pulse duration and the applied ink pulse duration as the minimum ink pulse duration for inking percentages equal to or less than a predefined inking percentage.

[0033] The determining of the applied ink pulse duration and the applied ink pulse spacing from said data and the corresponding inking percentage may comprise adjusting the inking percentage in dependence upon the decorator speed. The adjusting may comprise applying one of a pre-defined set of correction factors associated with respecting decorator speed bands. The compensation factor may be determined from a pre-defined compensation factor profile.

[0034] The pre-defined compensation factor profile may define one of: a constant compensation factor, for example 1 ; a compensation factor that increases substantially linearly with increasing decorator speed up to a defined decorator speed and is constant at higher decorator speeds; and a compensation factor that decreases substantially linearly with decreasing decorator speed down to a defined decorator speed and is constant at lower decorator speeds.

[0035] The defined decorator speed may be a most commonly used decorator speed. A compensation factor at the most commonly used decorator speed may be 1 .

[0036] The method may comprise receiving a can infeed conveyor start signal indicative of a starting of the can infeed conveyor, and reacting to the can infeed start signal by commencing generating the control signal after a predefined delay.

[0037] The method may comprise receiving a can infeed conveyor stop signal indicative of a stopping of the can infeed conveyor, the can infeed conveyor being configured to react to the can infeed stop signal by ceasing generation of the control signal. The stop signal may be received at some interval prior to stopping of the can infeed conveyor, and the can infeed conveyor being configured to react to the can infeed stop signal by

[0038] 38191232-1 ceasing generation of the control signal at some predefined delay prior to the last can of the sequence entering the printing zone.

[0039] The data may comprises a sequence of pulses each associated with the passage of a mandrel past a fixed point, and a predefined delay is defined in terms of a predefined number of pulses.

[0040] According to a further aspect of the present invention there is provided computer implemented method of determining a percentage ink transfer for a roller segment of a vibrating roller of an inking station of a can decorator, up to a maximum inking percentage. The method comprises receiving an electronic data file defining a can decoration to be applied to can bodies by the can decorator at the inking station, for a given ink colour, segmenting the can decoration into decoration segments aligned with respective roller segments, and, for each decoration segment, determining an inking percentage based on the fractional coverage of the segment by the decoration.

[0041] The disclosed controller may enable precise control of ink volume transfer to the can bodies by independently adjusting the position of each roller segment, thereby ensuring consistent print quality across the production line. By receiving data indicative of the decorator speed, the controller may dynamically adjust the ink transfer process in realtime, accommodating variations in production speed and maintaining optimal printing conditions. The generation of periodic control signals for each roller segment may allow for a synchronized and efficient operation of the can decorator, reducing ink wastage and improving the overall efficiency of the printing process.

[0042] Brief description of the drawings

[0043] Figure 1 illustrates a known beverage can decorator with a sequence of eight inker stations delivering respective inks (of different colour);

[0044] Figure 2 illustrates schematically a known inker station delivery mechanism comprising a fountain roller, a vibrating roller and a transfer roller;

[0045] Figure 3 shows from left to right inked green (a), red (b), black (c), cyan (d), yellow (e) and blue (f) printing plates and, beneath each plate, ink levels applied to sequential circumferential regions of the plates;

[0046] 38191232-1 Figure 4 illustrates schematically a maximum ink transfer showing time along the horizontal axis, where time is measured in terms of encoder counts;

[0047] Figure 5 illustrates schematically an exemplary controller for controlling the vibrating rollers of a can decorator;

[0048] Figure 6 illustrates in the uppermost trace, a sequence of mandrel pulses and, in the lower traces, exemplary ink pulses for respective roller segments;

[0049] Figure 7 illustrates calculated ink pulse durations at a decorator speed of 1200 cpm; Figure 8 illustrates calculated ink pulse durations at a decorator speed of 600 cpm; Figure 9 illustrates calculated ink pulse durations at a decorator speed of 1800 cpm; Figure 10 is a flow diagram illustrating a method of controlling a vibrating roller;

[0050] Figure 11 illustrates an operating mode in implementing a can feed start delay;

[0051] Figure 12 illustrates an operating mode in implementing a can feed stop delay;

[0052] Figure 13 is a flow diagram illustrating a method of determining an inking percentage to be applied to a roller segment of a vibrating roller; and

[0053] Figure 14 to 17 illustrate various different decorator speed dependent inking percentage compensation profiles.

[0054] Detailed description

[0055] The following disclosure relates generally to a can decorator apparatus of a type already described in general terms with reference to Figure 1. The decorator apparatus includes in particular: a mandrel wheel assembly 1 for delivering can bodies 3 in sequence to a printing zone 5; a blanket wheel 6; and a series of ink stations 10. Other components of the can decorator apparatus will be known to the skilled person and will not be described here. Each inker station further comprises a vibrating roller as described with reference to Figures 2 to 4.

[0056] A controller and method for controlling the vibrating roller, and specifically the positions of the vibrating roller segments by way of respective electromechanical actuators, will now be described. An exemplary controller 200 for controlling the vibrating rollers of a can decorator 201 is illustrated schematically in Figure 5 and comprises a processor 202, a memory 203 and a user interface 204, for example a graphical user interface comprising a display and user input devices, for example a keyboard and / or pointer device. The controller further includes data input / output interfaces including a first input / output interface 205 and a second input / output interface 206.

[0057] 38191232-1 Can decorators are designed to run optimally at a chosen speed, e.g. at a fixed speed of 2200cpm (cans-per-minute) with a speed ramp-up and ramp-down at the beginning and end of a can production run. Line constraints upstream or downstream of the decorator may further define or refine the speed at which the decorator is normally run during print runs. Environmental conditions such as temperature may also be a factor. The speed may be measured using a physical encoder by detecting the passage of each mandrel past a given circumferential position within the mandrel wheel assembly 1. Any suitable means may be used to detect this passage, for example using magnetic or optical detection means. In one embodiment, a virtual encoder in communication with a decorator programmable logic controller (PLC) is used. The decorator PLC generates a “mandrel pulse” signal 207 that is provided to the first input / output interface 205 of the controller. A typical decorator may comprise 24 mandrels located on a rotating mandrel wheel, and this number is considered here to define a “standard” cycle. The cycle time is the time taken to count 24 mandrel pulses.

[0058] The controller 200 presented here implements, by way of the processor 202, a virtual encoder 202a which generates a high frequency count by dividing the cycle time by 4800. This is fixed and is selected to give good resolution / accuracy for the inking calculations, although other encoder counts may be used. The controller provides a control signal 208 to the can decorator via the second input / output interface 206. The control signal 208 specifies, inter alia, operations of the roller segments of the vibrating roller.

[0059] Consider the can decorator 201 running at the appropriate decorator speed. At the beginning of each standard cycle time period, or at some predefined time interval after that, each vibrating roller segment is brought into a position adjacent the fountain roller to begin the transfer of ink to the segment (of course if no ink is to be transferred to a segment that segment is permanently located away from the fountain roller). The contact duration between a segment and the fountain roller, or “ink pulse”, measured in terms of virtual encoder pulses, may be different for different rollers.

[0060] As noted above with reference to Figure 4, 100% inking corresponds to a 50% duty cycle of a vibrating roller segment. For low inking percentages, for example less than 5%, a minimum ink pulse duration is employed. This may be in the region of 20ms to

[0061] 38191232-1 25ms. The minimum ink pulse is calculated based on the time it takes for the vibrating roller segment to cross the gap to the fountain roller. For example, if solenoid valves are used to actuate the vibrating roller segment, it may be determined by the latency of the solenoid valve. The amount of ink transferred to a vibrating roller segment for low inking percentages is therefore adjusted by varying the ink pulse spacing, as will be described further below, such that an ink pulse may not be applied in every can cycle (e.g. every 24 cans).

[0062] As the inking percentage increases above 5%, the ink pulse duration increases. This is implemented in a stepwise manner. For example, at decorator speeds below 1300 cpm, each 0.03% change in the inking percentage above 5% produces an increase in the ink pulse duration of 0.18ms. For decorator speeds above 1300 cpm, the ink pulse duration increases by 1 ms for each 0.18% increase in the inking percentage.

[0063] At a rate above OOcpm, a standard cycle of 24 cans is counted whereas, below OOcpm, a reduced can count is used instead giving more inking control at lower speeds.

[0064] Figure 6 illustrates the described approach, where the uppermost trace 300 indicates mandrel pulses and specifically a standard cycle time of 24 mandrel pulses. The second trace 301 illustrates exemplary ink pulses for a given roller segment. As the inking percentage for this roller exceeds 5%, the start of the ink pulse coincides with the start of the cycle time. The third trace 302 illustrates exemplary ink pulses for a second roller segment for which the inking percentage is less than 5%. In this case the ink pulse duration is set to the minimum duration, e.g. 25ms, and pulses have a spacing that exceeds the cycle time. As such the start of an ink pulse may not coincide with the start of the cycle time and indeed not every cycle will include an ink pulse.

[0065] Figure 7 illustrates calculated ink pulse durations at a decorator speed of 1200 cpm, i.e. a can cycle (at 24 cans) of 1 .2 seconds and a virtual encoder pulse spacing of 0.25ms. The ink pulse spacing (or interval) is determined as follows. Assume the total encoder count is set to be 4800. A can speed of 1200 cpm is equivalent to 20 cans per second so one can cycle (i.e. one Pulse interval) of 24 cans will take 1 .2 seconds. 1 .2 seconds divided by the total encoder count of 4800 gives 0.25ms, which is the virtual encoder pulse spacing. For 100% inking, the vibrating roller segment is in contact with

[0066] 38191232-1 the fountain roller 50% of the time, equivalent to 2400 encoder ticks and a ‘Time on’ interval of 600 ms (i.e. 0.25 ms multiplied by 2400 encoder ticks). It will be apparent that, for inking percentages below 5%, the minimum pulse duration of 25ms (or 100 virtual encoder pulses at this can speed) is applied.

[0067] Figure 8 illustrates calculated ink pulse durations at a decorator speed of 600 cpm. If a 24 can cycle were to be applied, this cycle would be 2.4 seconds with a virtual encoder pulse spacing of 0.5ms. As this is relatively slow, a reduced can cycle is in practice applied. It has been found that, at or below a low-speed threshold (optionally 1000 cpm), implementing a hypothetical reduced can cycle within the controller of 50% to 80%, preferably 60% to 70%, works well in practice and produces good inking results. In this example, the reduced can cycle applied is 16, resulting in a cycle time of 1.6 seconds and a virtual encoder pulse spacing of 0.333ms. It is noted that, with 4% inking, the ink pulses occur within every cycle. This is not the case for lower inking percentages.

[0068] Figure 9 illustrates calculated ink pulse durations at a decorator speed of 1800 cpm, i.e. a 24 can cycle time (i.e. one Pulse interval) of 0.8 seconds and a virtual encoder pulse spacing of 0.166ms. It is noted that, at an ink percentage of 5%, the ink pulse spacing is 1.12ms such that the ink pulses are no longer synchronised with the can cycle. This is also true of course for inking percentages below 5% and where the minimum pulse duration (25ms) is applied.

[0069] Figure 10 is a flow diagram illustrating a method of controlling a vibrating roller of the type discussed above. The following steps are included:

[0070] 51 . Receiving data indicative of a decorator speed.

[0071] 52. Obtaining for each roller segment an inking percentage defining a percentage ink transfer for the roller segment up to a maximum inking percentage.

[0072] 53. Determining, for each roller segment, from said data and the corresponding inking percentage, an applied ink pulse duration defining a first time period during which the roller segment is in the first position and an applied ink pulse spacing defining a second time period during which the roller segment is in the second position.

[0073] 38191232-1 54. Generating for each roller segment a periodic control signal based on the applied ink pulse duration and spacing determined for that roller segment.

[0074] 55. Providing the generated control signals to actuators of the respective roller segments.

[0075] Operation of the controller as described above assumes a steady state operation of the can decorator, i.e. running at the desired decorator speed. It is however often necessary to stop and restart production. On most decorators, the can feed input signal switches just as cans enter the printing area. This provides a well-timed start and stop ink sequence. However, in some plants, the can feed input sensor is located slightly upstream of entry to the printing area and so it is desirable for the can feed input signal to switch slightly earlier. This can be adjusted accordingly for each plant.

[0076] In order to avoid under or over inking of an initial sequence of the cans, a can feed start delay may be implemented such that a first ink pulse is generated for each roller segment (of the multiple vibrating rollers) only after some initial time delay. This mode of operation is illustrated in Figure 11 which illustrates in the upper trace 400 the mandrel pulses and in the lower three traces 401 ink pulse signals for respective roller segments of a vibrating roller. It will be noted that all ink pulses commence on the seventh mandrel pulse.

[0077] In order to avoid under inking on the final sequence of cans through the decorator, a can feed stop delay may be implemented such that a last ink pulse is generated for each roller segment (of the multiple vibrating rollers) some count before the last can of the sequence. The stop delay allows time for the cans being carried by / within the mandrel wheel to reach the printing zone. This mode of operation is illustrated in Figure 12 which illustrates in the upper trace 500 the mandrel phases and in the lower three traces 501 ink pulse signals for respective roller segments of the vibrating roller.

[0078] As already noted, the controller 200 will typically comprise a user interface 204, for example a graphical use interface, which allows an operator to configure parameters of the system, specifically the inking percentage to be applied for each roller segment for all of the vibrating rollers (one vibrating roller for each ink station). This may be done based upon the skill and experience of the operator taking into account a visual

[0079] 38191232-1 inspection of the design to be printed. However, a more efficient and systematic approach may rely on an automated analysis of the design.

[0080] Conventionally, once a customer has approved the final label artwork for their product at a design studio, a corresponding colour separation is provided to the can production facility as electronic data files by the design studio. These have a standardised format and will comprise one design per ink colour. They are used for plate making. Some plants have their own plate making facilities, while others use a centralised plate making service. In accordance with one of the claimed methods, a computer analysis tool may be applied to inspect each colour file (or a duplicate thereof), splitting the design into segments aligned with the roller segments of the vibrating roller. Preferably, the computer analysis tool is applied to each CtP (computer to plate) file where CtP technology is implemented. An inking percentage is determined for each segment (of each design). This might be based on a percentage coverage of the given colour. For example, a 100% coverage may result in a 50% inking percentage, whilst a 50% coverage might result in a 25% inking percentage. Of course, these values are merely exemplary. Once determined, the inking percentage for each roller segment of each vibrating roller may be provided to the controller. Collectively, the inking percentages form a recommended template for the label artwork, to act as a guide when the label artwork is first loaded onto the decorator. The template settings may be implemented unchanged or adjusted as necessary for a particular decorator by the operator and saved for future use. Provided that the inks and the gap between the ink fountain and the fountain roller remains fixed, the template settings can be used repeatedly, thereby reducing label set-up times in the future. Changeover times between labels are also reduced.

[0081] The computer analysis tool may incorporate machine learning so that, over time, recommended ink levels may be set based on ink coverage within similar historical artwork. Equally, artificial intelligence may be incorporated into the controller to take account of further environmental variables such as temperature and humidity that might otherwise affect ink volume usage at different decorator speeds or for different ink compositions.

[0082] Figure 13 is a flow diagram illustrating a method of determining an inking percentage to be applied to a roller segment of a vibrating roller. The following steps are shown:

[0083] 38191232-1 5100. Receiving an electronic data file defining a can decoration to be applied to can bodies by the can decorator at the inking station, for a given ink colour;

[0084] 5101. Segmenting the can decoration into decoration segments aligned with respective roller segments; and

[0085] 5102. For each decoration segment, determining an inking percentage based on the fractional coverage of the segment by the decoration.

[0086] This method is repeated for each inking station / colour and the resulting data save to a memory. The data may be transferred or otherwise made available to the above described controller prior to operation of the can decorator (to decorate cans with the desired design).

[0087] The controller 200 may be configured to allow even further adjustment of the ink volumes. Speed bands may be used to enable fine tuning of the ink volume depending on the production rate. For example, with a maximum decorator speed of around 2400cpm, and a minimum decorator speed of around 100cpm (some decorators rarely ever completely stop), and a normal running speed somewhere therebetween, including a banding of 100cpm gives 24 bands or intervals to enable incremental adjustments. The adjustment can be fine-tuned for each band if required, or only certain bands adjusted if needs be. The inking changes are relatively small and gradual, e.g. 1 , 0.99, 0.9909, 0.9918, 0.99272 etc, so changes to the ink calculation will not be dramatic, thus maintaining ink control as speed changes. This may be useful if higher ink volumes are normally experienced at higher decorator speeds; they can be mitigated using the controller 200.

[0088] The controller 200 may be configured to allow yet further adjustment of the ink volume with the implementation of a speed compensation ratio / factor that is applied to the predefined inking percentages. This factor takes into account the real-time decorator (e.g. 400cpm) speed relative to the ‘normal’ steady state running speed of the decorator and alters the ink volume accordingly so that ink volume is transferred consistently at all production speeds. A speed compensation ratio / factor of 1.0 means that no speed compensation is applied. Optionally, the speed compensation ratio / factor of 1.0 is applied at the decorator speed most commonly used for any given decorator. Figure 14 shows that the speed compensation ratio / factor set at a constant 1.0 across the operating speed range including 1200cpm.

[0089] 38191232-1 In some production plants, a non-constant speed compensation profile is advantageous. In a first profile and as shown in Figure 15, a speed compensation factor in the range of 0.9 to 1.1 is centred on a normal decorator speed of, e.g. 1200cpm. In a second profile and as shown in Figure 16, the speed compensation factor increases incrementally up to 1.0, coinciding with 1.0 at the normal decorator running speed (e.g. OOcpm), or another set threshold, as the decorator speed increases. It then remains at 1.0 even if the decorator speed increases further. In a third profile and as shown in Figure 17, the speed compensation factor decreases incrementally down to 1.0, coinciding with 1.0 at normal decorator running speed (or another set threshold) as the decorator speed increases up to normal running speed. It then remains at 1 .0. In this example, increased inking occurs at very slow speeds, and there is no compensation above 800cpm. It will be appreciated by the person of skill in the art that various modifications may be made to the above described embodiment without departing from the scope of the present invention.

[0090] 38191232-1

Claims

CLAIMS:

1. A controller for controlling roller segments of a vibrating roller of a can decorator, each of the roller segments being movable independently under control of the controller between a first position in which the roller segment contacts a fountain roller of the can decorator and a second position in which the roller segment contacts a transfer roller of the can decorator to thereby control the volume of ink transferred between the fountain roller and the transfer roller, the controller comprising: an input for receiving data indicative of a decorator speed; a processor for obtaining for each roller segment an inking percentage defining a percentage ink transfer for the roller segment up to a maximum inking percentage, determining, for each roller segment, from said data and the corresponding inking percentage, an applied ink pulse duration defining a first time period during which the roller segment is in the first position and an applied ink pulse spacing defining a second time period during which the roller segment is in the second position, and generating for each roller segment a periodic control signal based on the applied ink pulse duration and spacing determined for that roller segment; and an output for providing the generated control signals to actuators of the respective roller segments.

2. A controller according to claim 1 , said processor being configured to determine a period of said periodic control signal as a standard cycle period for inking percentages above a predefined inking percentage and to determine the period as greater than the standard cycle period for inking percentages equal to or less than the predefined inking percentage.

3. A controller according to claim 2, wherein said standard cycle period is a time taken to transfer a capacity of a mandrel wheel assembly through the printing zone.

4. A controller according to claim 3, wherein the mandrel wheel assembly capacity is a number of mandrels configured to hold can bodies.38191232-15. A controller according to any one of the preceding claims, the processor being configured to define a minimum ink pulse duration and to define the applied ink pulse duration as the minimum ink pulse duration for inking percentages equal to or less than a predefined inking percentage.

6. A controller according to any one of the preceding claims, wherein the determining, by the processor, of the applied ink pulse duration and the applied ink pulse spacing from said data and the corresponding inking percentage comprises adjusting the inking percentage in dependence upon the decorator speed.

7. A controller according to line claim 6, wherein the adjusting comprises applying one of a pre-defined set of correction factors associated with respective decorator speed bands.

8. A controller according to claim 7, the processor being configured to determine the compensation factor from a pre-defined compensation factor profile.

9. A controller according to claim 8, wherein the pre-defined compensation factor profile defines one of: a constant compensation factor, for example 1 ; a compensation factor that increases substantially linearly with increasing decorator speed up to a defined decorator speed and is constant at higher decorator speeds; and a compensation factor that decreases substantially linearly with decreasing decorator speed down to a defined decorator speed and is constant at lower decorator speeds.

10. A controller according to claim 9, wherein said defined decorator speed is a most commonly used decorator speed.

11. A controller according to claim 10, wherein a compensation factor at the most commonly used decorator speed is 1 .38191232-112. A controller according to any one of the preceding claims, said input being further configured to receive a can infeed conveyor start signal indicative of a starting of the can infeed conveyor, the controller being configured to react to the start signal by commencing generating the control signal after a predefined delay.

13. A controller according to any one of the preceding claims, said input being further configured to receive a can infeed conveyor stop signal indicative of a stopping of the can infeed conveyor, the can infeed conveyor being configured to react to the stop signal by ceasing generation of the control signal.

14. A controller according to claim 13, said stop signal being received at some interval prior to stopping of the can infeed conveyor, and the can infeed conveyor being configured to react to the stop signal by ceasing generation of the control signal at some predefined delay prior to the last can of the sequence entering the printing zone.

15. A controller according to claim 12 or 14, wherein said data comprises a sequence of pulses each associated with the passage of a mandrel past a fixed point, and a predefined delay is defined in terms of a predefined number of pulses.

16. A method of controlling roller segments of a vibrating roller of a can decorator, each of the roller segments being movable independently between a first position in which the roller segment contacts a fountain roller of the can decorator and a second position in which the roller segment contacts a transfer roller of the can decorator to thereby control the volume of ink transferred between the fountain roller and the transfer roller, the method comprising: receiving data indicative of a decorator speed; obtaining for each roller segment an inking percentage defining a percentage ink transfer for the roller segment up to a maximum inking percentage; determining, for each roller segment, from said data and the corresponding inking percentage, an applied ink pulse duration defining a first time period during which the roller segment is in the first position and an applied ink pulse spacing defining a second time period during which the roller segment is in the second position; generating for each roller segment a periodic control signal based on the applied ink pulse duration and spacing determined for that roller segment; and38191232-1providing the generated control signals to actuators of the respective roller segments.

17. A computer implemented method of determining a percentage ink transfer for a roller segment of a vibrating roller of an inking station of a can decorator, up to a maximum inking percentage, the method comprising: receiving an electronic data file defining a can decoration to be applied to can bodies by the can decorator at the inking station, for a given ink colour; segmenting the can decoration into decoration segments aligned with respective roller segments; and for each decoration segment, determining an inking percentage based on the fractional coverage of the segment by the decoration.38191232-1

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