Patent Description:
Printing is the process of transferring an image onto a substrate using ink. In gravure printing, a roller engraved with an image to be printed is partially immersed in a quantity of ink and rotated. The ink collects in the engraved parts of the roller. Excess ink is scraped away by a doctor blade as the roller rotates, so that only the ink within the engraved parts of the cylinder remains. Once the excess ink has been scraped away, the roller is brought into contact with a substrate, for example paper. The substrate is typically pressed against the cylinder using a pressure roller positioned on an opposite side of the substrate to the cylinder. The ink contained in the engraved parts of the cylinder is transferred onto the substrate to form the image. In flexographic printing, ink is transferred to a fountain roller by at least partially submerging the fountain roller in a quantity of ink or by using an ink chamber having doctor blades. The fountain roller transfers ink to an anilox roller, which comprises a matrix of identical cells engraved onto its outer surface. As the anilox roller rotates, excess ink is scraped away using a doctor blade such that only the ink within the cells remains. The anilox roller transfers the ink to a print roller, which is engraved with the imaged desired to be printed. The print roller contacts a substrate to transfer the image onto the substrate. Typically, the substrate is typically pressed against the print roller using an impression roller on an opposite side of the substrate to the print roller.

The volume of ink in the engraved parts of the image carrying rollers must be precisely controlled so as to ensure consistent print quality. Over time, however, dried ink builds up within the engraved parts of the rollers. The dried ink acts to reduce the volume of the engraved parts of the rollers, which degrades the quality of the printed image. For example, the printed image may appear fainter, the image may be the wrong colour, or the edges of the printed image may be less precise. It is known to mitigate this problem by cleaning the engraved rollers so as to remove the dried ink. Known cleaning processes require that the engraved roller is removed from the printing machine and immersed in a bath of cleaning fluid containing a surfactant. In some cleaning processes, transducers are used to induce ultrasonic waves within the cleaning fluid which acts to loosen the dried ink from the surface of the engraved roller.

However, removing a roller from a printing machine is a complex task which requires detailed knowledge of the operation of the printing machine and as such can only be performed by skilled workers. The rollers may be up to around <NUM> in length and may weigh up to <NUM> tonne, and thus specialist lifting machinery may be required to remove the roller which adds additional expense to the cleaning process. Furthermore, depending upon the complexity of the printing machine, the amount of down time required to remove a roller to be cleaned may be relatively long, often taking an hour or more. This problem is compounded for full colour printing machines, which typically comprise seven or more rollers that require cleaning. The printing machine cannot be used to generate revenue whilst it is being cleaned, and therefore cleaning of the engraved rollers is relatively expensive in terms of lost revenue. In addition, removing the engraved roller from the printing machine runs the risk that it will be damaged and must therefore be replaced.

It is preferable to empty the bath between each cleaning operation so that subsequent cleaning operations can be performed with fresh cleaning fluid. However, the amount of cleaning fluid contained in the bath is typically significantly greater than the volume of the roller itself. Each cleaning operation therefore consumes a large quantity of cleaning fluid which is environmentally wasteful. Furthermore, because the volume of the bath is relatively large, the ultrasonic waves induced in the cleaning fluid dissipate and lose strength before they are reflected from the surface of the roller being cleaned. As such, the cleaning operation is typically not able to remove all of the dried ink from the roller. The cleaning operation is therefore inefficient in terms of time taken, dissipation of ultrasonic energy and consumption of cleaning fluid.

In some flexographic printing machines, cleaning fluid can be fed to the ink chamber in place of the ink to be printed. The cleaning fluid contacts the surface of the roller to be cleaned and removes dried ink. However, this requires that the ink chamber is emptied, often causing ink to be wasted. Furthermore, in such machines the cleaning fluid is continuously circulated through the ink chamber (that is to say, the cleaning fluid is supplied to the ink chamber at the same rate that it is removed from the ink chamber). However, continuously circulating cleaning fluid through the ink chamber results in a large amount of cleaning fluid being used which is environmentally wasteful.

<CIT> relates to a cleaning apparatus, cleaning method, pattern forming apparatus, and pattern forming method. According to the abstract of this document, a pattern formation apparatus has a drum-like intaglio rolling along a transferred medium. After the intaglio is charged by a charger, a pattern of toner particles is formed by supplying a liquid developer of each colour to the intaglio via a developing machine and an electric field is formed between the intaglio and the transferred medium by rolling the intaglio along the transferred medium to transfer charged toner particles to the transferred medium. A cleaning apparatus which cleans the intaglio after the pattern in each colour being transferred to the transferred medium has nozzles at an angle for blowing a cleaning liquid against recesses and removal rollers for removing toner particles liberated from the recesses together with the cleaning liquid.

<CIT> relates to a roller cleaning apparatus on a rotary printing press. According to the abstract of this document, for cleaning a rotatable roller dipping into a liquid medium and having a rastered or porous surface, an ultrasonic transducer is fitted to the chamber, e.g. to the floor of a chamber doctor. By means of this in the press, an intensive cleaning of the roller can be carried out without having to remove it from the press.

<CIT> relates to an ultrasonic cleaning apparatus. According to the abstract of this document, the ultrasonic cleaning apparatus washes the alkaline ink that is adhered at the bottom of the recessed part of a material (roller) to be washed with the maximum effect by irradiating ultrasonic vibration from an ultrasonic element to a liquid in a nozzle chamber through a vibration plate which is in contact with the ultrasonic element to produce an ultrasonic washing liquid and by maintaining the material to be washed to a constant distance of an integer multiple of <NUM>/<NUM> of one wave length from the vibration plate in accordance with frequency at the ultrasonic washing liquid within the nozzle chamber. The apparatus has a positioning device to determine the position with the material to be washed.

It is an object of the invention to obviate or mitigate the problems associated with prior art systems for cleaning rollers of printing machines, whether identified herein or elsewhere. It is a further object of the invention to provide an alternative and/or environmentally friendly system for cleaning rollers of printing machines.

To achieve the above-mentioned objects, a method and a system according to the present invention as defined in claims <NUM> and <NUM>, respectively, are provided.

According to a first aspect of the invention, there is provided a method of cleaning a print roller, comprising:.

When the trough is filled with cleaning fluid and the ultrasonic energy source is activated, ultrasonic oscillations are generated within the cleaning fluid. The oscillations of the cleaning fluid mechanically vibrates solid contaminant matter that has dried onto the surface of the print roller. The vibrations cause the contaminant matter to break up and detach from the ink-carrying surface.

It has been found that if the cleaning routine is run at least two times in succession the cleaning process is improved significantly. In particular, when the first cleaning routine is executed, relatively large particles of contaminant are removed from the ink-carrying surface. When these large particles are suspended in the cleaning fluid, they act to dampen the ultrasonic oscillations and prevent smaller particles from being removed. Additionally, if too many contaminant particles are removed, the cleaning fluid can become saturated making it more difficult to hold further contaminant particles in suspension even if the period of time that the ultrasonic energy source is activated is prolonged. However, when the cleaning fluid containing the contaminants is drained and replaced with new, contaminant-free cleaning fluid, the ultrasonic vibrations are not dampened and the ability of the cleaning fluid to contain a suspension of contaminant particles is maximised. As such, the second cleaning operation is able to more effectively remove smaller contaminant particles from the ink-carrying surface. This is particularly effective for removing particles that are contained at the bottom of the ink cells of an anilox roller. Consequently the use of two cleaning routines is able to better restore the print roller to its original geometry and ensure that every cell has the same volume for containing printing ink. The cleaning process therefore ensures that metering of ink by the print roller is more accurate and the performance of the print roller is improved.

It will be appreciated that because the trough is filled at the start of the cleaning routine and emptied only at the end of the cleaning routine, the fluid in the trough is not continuously replaced. As such, only the volume of fluid necessary to fill the trough is used during each cleaning routine. It has been found that even when the cleaning routine is repeated a number of times, the volume of cleaning fluid required is reduced significantly in comparison to alternative systems in which fluid is continuously replaced during cleaning or where the print roller is entirely submerged in a bath. The reduction in the amount of cleaning fluid conserves water and produces a smaller volume of ink-contaminated waste, and is therefore less environmentally harmful than alternative methods.

The term "print roller" encompasses substantially any roller within a printing system which may require cleaning due to contact with ink. The print roller may be, for example, an anilox roller.

The term "ultrasonic energy source" encompasses substantially any means of generating ultrasonic waves within the cleaning fluid. This may include, for example, an ultrasonic transducer.

The term "ink-carrying surface" encompasses substantially any surface of the print roller that is configured to contact ink and which may have become contaminated. This may include, for example, an outer surface of the print roller, and more particularly a cylindrical outer surface of the print roller. The ink-carrying surface may include concavities, for example in the case of an anilox roller the ink-carrying surface may comprise one or more ink-metering cells.

The term "trough" encompasses a region of space for containing a fluid that is partially defined by the ink-carrying surface and partially defined by the ultrasonic cleaning bar. That is to say, at least one of the surfaces defining the trough is the ink-carrying surface, and the other surface(s) defining the trough is (are) part of the ultrasonic cleaning bar.

The term "contaminants" encompasses any foreign matter that does not form part of the print roller. This primarily encompasses ink from the printing process in which the print roller is used that has solidified on the ink-carrying surface of the print roller. However, other possible contaminants that are removed during cleaning includes, for example dust, dirt, grease or the like.

The term "draining" encompasses removing the suspension of cleaning fluid and contaminants from the ultrasonic cleaning bar such that the ultrasonic cleaning bar is substantially empty.

The term "in succession" encompasses executing the cleaning routine a number of times in a row without using the print roller in a printing operation. That is to say, running the multiple cleaning routines consecutively in such a manner that the print roller is not used in any intermediate processes that would be likely to cause the ink-carrying surface to be contaminated. For example, where the print roller is within a printing machine, the printing machine is not used to perform a printing operation between cleaning routines. Alternatively, if the print roller has been removed from the printing machine and placed on a separate driving apparatus, the print roller is not replaced within the printing machine until all of the cleaning routines are complete.

The method may comprise executing the cleaning routine three times in succession before cleaning of the print roller is complete. In particular, the cleaning routine may be executed only (and not more than) three times in succession before cleaning of the roller is complete. When the cleaning routine is executed three times, even smaller particles of contaminant are removed from the ink-carrying surface of the print roller and the cleaning process is further improved. Generally speaking, increasing the number of times that the cleaning routine is executed increases the amount of contaminant that is removed from the ink-carrying surface, however the increase in the amount of ink removed decreases asymptotally with each additional cleaning routine. It has been found by experimentation that executing the printing routine three times optimises the overall time taken to clean the print roller versus the amount of contaminant that is removed. Nevertheless, in alternative embodiments, the cleaning routine may be executed four, five or more times in succession.

According to the invention, the method comprises preventing cleaning fluid draining from the trough whilst the ultrasonic energy source is activated. In particular, the method may further comprise providing an outlet valve to control the flow of fluid leaving the trough, and executing the cleaning routine may comprise maintaining the outlet valve in a closed configuration to prevent cleaning fluid draining from the trough whilst the ultrasonic energy source is activated. When the outlet valve is closed during the cleaning routine, the cleaning fluid captured within the trough is not flowing and therefore the vibrations produced by the by the ultrasonic energy source are better able to permeate through the cleaning fluid to reach the ink-carrying surface of the print roller.

The method may comprise rotating the print roller whilst the cleaning routine is being executed. By rotating the print roller when the cleaning routine is being executed, the area of the ink-carrying surface that is cleaned may be increased.

The period of time may be chosen based upon based upon the angular velocity of the print roller, such that the period of time is at least equal to the amount of time taken for the roller to complete one full rotation. The print roller may be driven by surface contact between a roller driver (comprising, for example, a motor and a drive wheel) rotating at a constant speed. As such, the angular velocity of the print roller will be dependent upon the diameter of the print roller (smaller-diameter print rollers will rotate at a faster angular velocity than larger-diameter print rollers). When the period of time is longer than the amount of time taken for the roller to complete one full rotation, this ensures that the entire surface of the roller is cleaned during the cleaning routine. In alternative embodiments, the period of time may be chosen based upon the amount of time taken for the print roller to complete two, three, four or substantially any number of rotations.

The print roller may be rotated such that the ink-carrying surface has a linear velocity in the range of around <NUM>. min-<NUM> to around <NUM>. min-<NUM>, more preferably in the range of around <NUM>. min-<NUM> to around <NUM>. min-<NUM>, or most preferably around <NUM>. In some embodiments the print roller may be rotated such that the ink-carrying surface has a linear velocity of up to <NUM>. The linear velocity of the ink-carrying surface is the tangential velocity of a point on the ink-carrying surface relative to an axis of rotation, for example a central axis of the print roller. When the print roller is rotating, the ink-carrying surface moves past the trough of the ultrasonic cleaning bar such that only a portion of the ink-carrying surface is in contact with the cleaning fluid at any one time. If the ink-carrying surface is moving too quickly relative to the trough, the portion of the ink-carrying surface being cleaned will not be in contact with the cleaning fluid long enough for the ultrasonic vibrations to shake contaminants loose from the ink-carrying surface. However, if the ink-carrying surface is moving too slowly cleaning may take too long. It has been found that when the linear velocity of the ink-carrying surface is within the ranges specified above the relative velocity of the ink-carrying surface to the though provides enough time for contaminants to be shaken loose as the ink-carrying surface moves past the trough without the cleaning process taking too long.

The period of time may be at least around three minutes. Generally, it is only preferable to start draining the cleaning fluid once the cleaning fluid has become saturated with contaminants. Waiting until the cleaning fluid is saturated ensures that the entire capacity of the cleaning fluid to absorb contaminants is used, and therefore less cleaning fluid is wasted. It has been found by experiment that three minutes is generally the fastest period of time it may take for the cleaning fluid to become saturated with contaminants and therefore it is preferable that the period of time is at least around three minutes. Additionally, for the majority of print rollers, around three minutes is sufficient time to allow the print roller to complete at least one full rotation.

The period of time may be no more than around seven minutes. Generally, the longer that the ultrasonic energy source is activated for, the more contaminants that removed from the ink-carrying surface. However, at some point the cleaning fluid will become saturated with contaminants and the ability of the cleaning fluid to absorb more contaminants is diminished. It has been found by experimentation that increasing the period of time beyond around seven minutes provides little extra benefit as the cleaning fluid is likely to have become saturated by this point. Therefore it is preferable if the period of time is not more than around seven minutes. More preferably, the period of time may be in the range of around three minutes to around seven minutes.

The period of time may be around five minutes. It has been found by experimentation when the period of time is around five minutes this provides a good balance between allowing the cleaning fluid to become saturated with contaminants but without wasting additional time once the cleaning fluid as become saturated.

The method may further comprise, before the first cleaning routine is executed, attaching the ultrasonic cleaning bar to a printing machine. In addition, the method may comprise, after the final cleaning routine is executed, removing the ultrasonic cleaning bar from the printing machine. That is to say, the ultrasonic cleaning bar may be used in-situ within the printing machine, such that the ultrasonic cleaning bar is only present within the printing machine for the duration of the cleaning operation, and is removed when the printing machine is used for printing. As such, the ultrasonic cleaning bar does not need to be present on the printing machine at all times, and therefore one ultrasonic cleaning be can be used to clean multiple print rollers.

The method may comprise, before the first cleaning routine is executed, removing the print roller from a printing machine and placing the print roller within a driving apparatus. In addition, the method may comprise, after the final cleaning routine is executed, replacing the print roller within the printing machine. That is to say, the print roller may be removed from the printing machine and cleaning away from the printing machine. In some printing machines it may not be possible to attach the ultrasonic cleaning bar to the printing machine and therefore the roller must be removed from the printing machine before it can be cleaned.

The method may comprise monitoring the volume of cleaning fluid in the trough and preventing execution of the cleaning routine if the amount of cleaning fluid is less than a fill volume. When the volume of cleaning fluid in the trough is less than the fill volume, there may not be enough cleaning fluid in the trough to absorb the ultrasonic vibrations from the ultrasonic energy source. Executing the cleaning routine in such circumstances may therefore cause damage to the ultrasonic cleaning bar. By ensuring the fill volume is reached before the cleaning routine is executed, accidental damage to the ultrasonic cleaning bar can be avoided.

The method may further comprise monitoring the volume of cleaning fluid in the trough whilst the cleaning routine is being executed, and introducing cleaning fluid to the trough to compensate for any leakage of cleaning fluid out of the trough whilst the cleaning routine is being executed. During execution of the cleaning routine, some fluid may leak from the trough, for example around any sealing members such as doctor blades or gaskets as the print roller rotates. Introducing new cleaning fluid to the trough may ensure that the amount of cleaning fluid in the trough is equal to or greater than the fill volume when the cleaning routine is being executed. As such, damage to the ultrasonic cleaning bar is avoided.

The method may comprise forming a seal between the ultrasonic cleaning bar and the ink-carrying surface. When a seal is formed between the ink-carrying surface and the ultrasonic cleaning bar this ensures that cleaning fluid leakage out of the trough is minimised.

The method may comprise introducing a surfactant to the cleaning fluid. In some embodiments, the cleaning fluid may comprise a surfactant when it is delivered to the trough.

According to a second aspect of the invention, there is provided a system for cleaning a print roller, comprising:.

That is to say, the system executes the cleaning routine at least twice before cleaning of the print roller is complete.

The system may be configured to execute the cleaning routine three times in succession before cleaning of the print roller is complete.

The ultrasonic cleaning bar may comprise the outlet valve. In alternative embodiments, the outlet valve may be a separate component to the ultrasonic cleaning bar (e.g. part of a control unit).

The system may comprise a drive wheel configured to contact the ink-carrying surface of the print roller to cause the print roller to rotate whilst the cleaning routine is being executed.

The period of time may be chosen based upon based upon the angular velocity of the print roller, such that the period of time is at least equal to the amount of time taken for the roller to complete one full rotation. The period of time may be. at least around three minutes, and/or or not more than around seven minutes. The period of time may be around five minutes.

The ultrasonic cleaning bar may comprise a fluid sensor configured to detect the presence of cleaning fluid in the trough.

The ultrasonic cleaning bar may define a fill volume, and the fluid sensor may be aligned with the free surface of the cleaning fluid when the cleaning fluid has filled the trough to the fill volume. That is to say, the fluid sensor may be positioned level with the free surface of the cleaning fluid when the trough has been filled to the fill volume. In some embodiments, the trough may, in practice, be filled with more cleaning fluid than the fill volume so that the free surface of the cleaning fluid is above the fluid sensor.

The system may be configured to monitor the volume of cleaning fluid in the trough using the fluid sensor and is further configured to prevent execution of the cleaning routine if the amount of cleaning fluid is less than the fill volume.

The ultrasonic energy source may be positioned between the fluid sensor and the base of the trough. In particular, the ultrasonic energy source may be spaced vertically below the fluid sensor and vertically above the base of the trough. When the ultrasonic energy source is positioned between the fluid sensor and the base of the trough this ensures that the ultrasonic energy source is aligned with the cleaning fluid, and the ultrasonic vibrations permeate into the cleaning fluid. As such, accidental damage to the ultrasonic cleaning bar is avoided.

The system may be configured to monitor the volume of cleaning fluid in the trough whilst the cleaning routine is being executed, and is further configured to introduce cleaning fluid to the trough to compensate for any leakage of cleaning fluid out of the trough whilst the cleaning routine is being executed.

The ultrasonic cleaning bar may comprise a sealing member configured to form a substantially fluid-tight seal against the ink-carrying surface of the print roller. The sealing member may comprise, for example, a doctor blade.

The system may further comprise a driving apparatus configured to support the print roller for rotation when it has been removed from a printing machine, and wherein the system is configured to execute the cleaning routine when the print roller is supported by the driving apparatus.

It will be appreciated that the above advantages and optional features of the first aspect of the invention may apply equally to the second aspect of the invention and vice versa.

<FIG> shows a cleaning system <NUM> for cleaning a roller <NUM> of a printing machine <NUM>. The print roller may be, for example, an engraved roller, and in particular may be an anilox roller. The print roller <NUM> comprises an axle <NUM> configured to support the print roller <NUM> for rotation. The cleaning system <NUM> comprises a control unit <NUM>, an ultrasonic cleaning bar <NUM>, a first bracket <NUM>, a second bracket <NUM> and a roller driver <NUM>. The ultrasonic cleaning bar <NUM> comprises a plurality of ultrasonic energy sources in the form of ultrasonic transducers <NUM> that are configured to generate ultrasonic vibrations. The control unit <NUM> receives fluid from a first fluid line <NUM> and dispenses fluid from a second fluid line <NUM>. The first fluid line <NUM> is connected to a fluid source, such as, for example, a factory water supply. The ultrasonic cleaning bar <NUM> receives fluid from the second fluid line <NUM> and dispenses fluid from a third fluid line <NUM>. The third fluid line <NUM> removes waste fluid from the ultrasonic cleaning bar <NUM>, and is typically connected to a drain or a factory waste disposal system.

The control unit <NUM> is connected to an electrical power source by a first power line <NUM>. The ultrasonic cleaning bar <NUM> is connected to the control unit <NUM> by a second power line <NUM> so as to supply electrical power to the ultrasonic cleaning bar <NUM>. The ultrasonic cleaning bar <NUM> is further connected to the control unit <NUM> by a first communications line <NUM> so that the ultrasonic cleaning bar <NUM> and the control unit <NUM> may send and receive control signals therebetween. The control unit <NUM> is connected to the roller driver <NUM> by a third power line <NUM> so as to supply electrical power to the roller driver <NUM>. The control unit <NUM> is further connected to the roller driver <NUM> by a second communications line <NUM> so that the roller driver <NUM> and the control unit <NUM> may send and receive control signals therebetween. In the illustrated embodiment the control signals sent between the control unit <NUM>, ultrasonic cleaning bar <NUM> and roller driver <NUM> are electrical control signals, however the control signals may additionally or alternatively comprise optical or wireless control signals.

<FIG> shows a side view of the ultrasonic cleaning bar <NUM> in an assembled state within a printing machine <NUM>. The ultrasonic cleaning bar <NUM> is generally elongate and defines a longitudinal axis extending generally parallel to the axle <NUM> of the roller <NUM>. The printing machine <NUM> further comprises an ink chamber <NUM>. The ink chamber <NUM> is pivotally mounted within the printing machine <NUM> so that it can be moved into and out of contact with the roller <NUM>. In the position shown in <FIG>, the ink chamber <NUM> has been pivoted away from the roller <NUM>. However, in normal use the ink chamber <NUM> engages the roller <NUM> in approximately the same position as the position of the ultrasonic cleaning bar <NUM> shown in <FIG>.

With reference to <FIG>, the ultrasonic cleaning bar <NUM> comprises a first pin <NUM>, a second pin <NUM>, a third pin <NUM> and a fourth pin <NUM>. The first and second pins <NUM>, <NUM> are co-linear and are positioned at longitudinally opposite ends of the ultrasonic cleaning bar <NUM>. Likewise, the third and fourth pins <NUM>, <NUM> are co-linear and are positioned at longitudinally opposite ends of the ultrasonic cleaning bar <NUM>. The first and second pins <NUM>, <NUM> are spaced apart from the third and fourth pins <NUM>, <NUM> in a lateral direction perpendicular to a longitudinal axis of the ultrasonic cleaning bar <NUM>. The first pin <NUM> and the third pin <NUM> are configured to be received by the first bracket <NUM>. The second pin <NUM> and the fourth pin <NUM> are configured to be received by the second bracket <NUM>. The first and second brackets <NUM>, <NUM> are mountable to the printing machine <NUM> either side of the roller <NUM>.

<FIG> shows a perspective view of the first bracket <NUM>. The bracket <NUM> comprises a rear surface <NUM>, a front surface <NUM> and a raised surface <NUM> which are generally coplanar. The front surface <NUM> and the raised surface <NUM> are connected by a guide surface <NUM> which extends in a normal direction relative to the front and raised surfaces <NUM>, <NUM>. The front surface <NUM>, raised surface <NUM> and guide surface <NUM> co-operate to define a lower channel <NUM>, an upper channel <NUM> and a neck region <NUM>. The lower channel <NUM> terminates in a lower end face <NUM> defined by the guide surface <NUM>, and the upper channel <NUM> terminates in an upper end face <NUM> also defined by the guide surface <NUM>. The lower channel <NUM> and upper channel <NUM> are connected by the neck region <NUM>, such that the lower channel <NUM> and upper channel <NUM> form a generally U-shaped recess relative to the raised surface <NUM>. The lower channel <NUM> defines a sloping portion <NUM> of the guide surface <NUM> which extends from the neck <NUM> to the lower end face <NUM>.

The bracket <NUM> comprises a plurality of mounting holes <NUM> which are configured to receive fasteners for securing the mounting bracket to a frame of the printing machine <NUM>. The mounting holes <NUM> comprise countersunk openings configured to receive corresponding countersunk screws, which ensures correct centring of the bracket relative to the frame of the printing machine <NUM>. Different models of printing machine <NUM> have different frame geometries, and therefore the exact positions of the mounting holes <NUM> may be chosen in dependence upon the geometry of the printing machine <NUM>.

The second bracket <NUM> is substantially identical to the first bracket <NUM>, but is mirrored in a plane defined by the raised surface <NUM>. The first and second brackets <NUM>, <NUM> are mounted to a frame of the printing machine <NUM> either side of the roller <NUM>. In particular, the brackets <NUM>, <NUM> are mounted such that the lower and upper channels <NUM>, <NUM> face generally towards the roller <NUM> whilst the necks <NUM> face generally away from the roller <NUM>. During use, the user orients the ultrasonic cleaning bar <NUM> so that its longitudinal axis extends generally parallel to the axle <NUM> of the roller <NUM>. The user then slides the third and fourth pins <NUM>, <NUM> through the necks <NUM> of the brackets <NUM>, <NUM> and into the lower channels <NUM> until the second and fourth pins <NUM>, <NUM> engage the lower end faces <NUM>. In this position, the first and second pins <NUM>, <NUM> rest upon the sloping portions <NUM> of the brackets <NUM>, <NUM>. In this position, the ultrasonic cleaning bar <NUM> is held in a resting configuration by the brackets <NUM>, <NUM> in which the ultrasonic cleaning bar <NUM> is supported by the printing machine <NUM> but is not in contact with the roller <NUM>. The user then pivots the ultrasonic cleaning bar <NUM> about the third and fourth pins <NUM>, <NUM> such that the first and second pins <NUM>, <NUM> are received within the upper channels <NUM> and contact the upper end faces <NUM>. In this position, the ultrasonic cleaning bar <NUM> is held in a cleaning configuration by the brackets <NUM>, <NUM> in which the ultrasonic cleaning bar <NUM> engages the roller <NUM>.

The lower and upper channels <NUM>, <NUM> act to guide the ultrasonic cleaning bar <NUM> into the resting and cleaning configurations and therefore assist the user when mounting the ultrasonic cleaning bar <NUM> to the printing machine <NUM>. In particular, the geometries of the lower and upper channels <NUM>, <NUM> prevent the ultrasonic cleaning bar <NUM> from being fitted incorrectly. Fitting and removal of the ultrasonic cleaning bar <NUM> from the printing machine <NUM> using the brackets <NUM>, <NUM> is therefore simple and fast. Due to their relatively small size, the brackets <NUM>, <NUM> may be left in place within the printing machine <NUM> when the ultrasonic cleaning bar <NUM> has been removed so as to save time during the next cleaning operation.

<FIG> shows a perspective cross-sectional view of the ultrasonic cleaning bar <NUM> mounted within the printing machine <NUM>. The ultrasonic cleaning bar <NUM> further comprises a pair of arms <NUM> at either end of the ultrasonic printing bar <NUM> (only one arm <NUM> is shown in <FIG>). The arms <NUM> are configured to engage a frame <NUM> of the printing machine <NUM>. It will be appreciated that different models of printing machine <NUM> will have different frame geometries, and therefore the specific shape of the arms <NUM> will be dependent upon the model of printing machine <NUM>. In the illustrated embodiment, the printing machine <NUM> is a Göpfert Evolution. Each arm <NUM> comprises a bolt <NUM> extending from an end of the arm <NUM>, the bolt <NUM> being configured to act as a catch to receive a corresponding latch of the printing machine <NUM>. During use, when the ultrasonic cleaning bar <NUM> is pivoted from the resting configuration to the cleaning configuration, the latch of the printing machine <NUM> engages the bolt <NUM> of the arm <NUM> to hold the ultrasonic cleaning bar <NUM> in the cleaning configuration. The arm <NUM> therefore prevents accidental pivoting of the ultrasonic cleaning bar <NUM> out of the cleaning configuration.

The brackets <NUM>, <NUM> are manufactured as single integral piece and in particular are manufactured from a polymer such as nylon, polyurethane, polytetrafluoroethylene, or the like. However, it will be appreciated that the brackets <NUM>, <NUM> may be manufactured from any suitable material. In alternative embodiment, the brackets <NUM>, <NUM> may not be made from a single integral piece. For example, the rear surface <NUM> and front surface <NUM> may be manufactured from a single flat plate, and the raised surface <NUM> and the guide surface <NUM> may be manufactured from a block of material that is subsequently attached to the flat plate.

Although the ultrasonic cleaning bar <NUM> described above comprises pins <NUM>, <NUM>, <NUM>, <NUM> which engage the brackets <NUM>, <NUM>, it will be appreciated that in alternative embodiments the ultrasonic cleaning bar <NUM> may comprise substantially any formation which is able to engage the brackets <NUM>, <NUM> so as to hold the ultrasonic cleaning bar <NUM> in the cleaning or resting configuration. For example, such formations may comprise rails configured to be received within grooves. Furthermore, in some embodiments the brackets <NUM>, <NUM> may be replaced with pins, and the pins <NUM>, <NUM>, <NUM>, <NUM> of the ultrasonic cleaning bar <NUM> may be replaced with geometry equivalent to the brackets <NUM>, <NUM> of the embodiment described above. That is to say, the printing machine may comprise a "male" formation and the ultrasonic cleaning bar may comprise a "female" formation configured to receive the "male" formation.

The ultrasonic cleaning bar <NUM> may comprise one or more switches configured to detect when the ultrasonic cleaning bar has been mounted to the brackets. For example, a switch may be positioned on one the end of the ultrasonic cleaning bar <NUM> adjacent one of the formations. The switch may be positioned such that the switch is actuated when the ultrasonic cleaning bar <NUM> is received by the brackets <NUM>, <NUM> in the cleaning configuration. The switch may communicate with the control unit <NUM>, and the control unit <NUM> may be configured to prevent the ultrasonic transducers <NUM> from being activated and/or the trough <NUM> from being filled when the switch is not actuated. As such, the switches ensure that the ultrasonic cleaning bar is only filled with cleaning fluid when it is in the correct position in relation to the roller <NUM>.

<FIG> shows a schematic cross-sectional side view of the ultrasonic cleaning bar <NUM> in the cleaning configuration relative to the roller <NUM>. The ultrasonic cleaning bar <NUM> comprises a body <NUM>, a doctor blade <NUM>, a pair of end caps <NUM>, a cover member <NUM>, and a plurality of ultrasonic transducers <NUM>. The body <NUM> is generally L-shaped and defines a base <NUM> having a lip <NUM>. The lip <NUM> extends upwardly from the base <NUM>, and is inclined at an obtuse angle relative to the base <NUM>. The doctor blade <NUM> extends generally upwards from the lip <NUM> so as to form a generally U-shaped channel along the longitudinal axis. The doctor blade <NUM> is mounted to the lip <NUM> by a fastener <NUM>. The interface between the doctor blade <NUM> and the lip <NUM> is sealed by a pair of gaskets <NUM> such that fluid cannot leak between the doctor blade <NUM> and the lip <NUM>. In alternative embodiments substantially any suitable mounting arrangement may be employed to fix the doctor blade <NUM> to the lip <NUM> in a fluid tight fashion. The doctor blade <NUM> engages the roller <NUM> when the ultrasonic cleaning bar <NUM> is in the cleaning configuration (as shown in <FIG>) and forms a fluid tight seal therebetween.

The end caps <NUM> are positioned at longitudinally opposite ends of the ultrasonic cleaning bar <NUM>. The end caps <NUM> are mounted to the body <NUM> and are configured to provide a fluid tight seal between the body <NUM>, the doctor blade <NUM> and the roller <NUM>. The end caps <NUM> are generally planar, and define a curved side edge having a corresponding radius of curvature to the roller <NUM>. The end caps <NUM>, body <NUM> and doctor blade <NUM> co-operate to define a trough <NUM> configured to contain a cleaning fluid. The body <NUM> comprises an inlet port <NUM> which is connected to the second fluid line <NUM> which is configured to deliver fluid to the trough <NUM> and an outlet port <NUM> and an outlet valve <NUM> connected to the third fluid line <NUM>. The outlet valve <NUM> is preferably electronically actuable in response to a control signal from the control unit <NUM>.

The ultrasonic cleaning bar <NUM> further comprises a level sensor <NUM> (i.e. a fluid sensor) configured to detect the presence of cleaning fluid within the trough <NUM>. The level sensor <NUM> is positioned close to the top of the body <NUM> vertically above the ultrasonic transducers <NUM>. In particular, the position of the level sensor corresponds to the position of the free surface <NUM> of the cleaning fluid when the trough <NUM> has been filled to a fill volume. The fill volume is the minimum volume of fluid that the trough <NUM> should contain before the ultrasonic transducers <NUM> are activated. The level sensor <NUM> may be any suitable sensor for detecting the presence of a fluid, for example an ultrasonic sensor, a contact sensor, a float sensor or the like.

During use, when the ultrasonic cleaning bar <NUM> is in the cleaning position, the system performs a cleaning routine. To begin the cleaning routine, the outlet valve <NUM> is closed and the trough <NUM> is filled with cleaning fluid until it reaches the level sensor <NUM>. The cleaning fluid comprises, for example, a mixture of heated water and a surfactant or detergent or the like. When the cleaning fluid reaches the level sensor <NUM>, this indicates that the trough <NUM> has reached the fill volume. The cleaning system <NUM> (via the control unit <NUM>) is configured so that the ultrasonic transducers <NUM> are not activated until the cleaning fluid has been detected by the level sensor <NUM>. Because the level sensor <NUM> is positioned above the ultrasonic transducers <NUM>, the ultrasonic transducers <NUM> cannot be activated until they are below the free surface <NUM> of the cleaning fluid. This ensures that the vibrational energy produced by the ultrasonic transducers <NUM> is dissipated within the cleaning fluid. If the cleaning fluid is not present, the ultrasonic vibrations will be conducted away from the ultrasonic transducers <NUM> primarily by the body <NUM>, which may cause damage to the body <NUM> and/or the ultrasonic transducers <NUM>.

Once the trough <NUM> has been filled to the fill volume, the ultrasonic transducers <NUM> are activated for a period of time and the roller driver <NUM> is activated to begin rotation of the print roller <NUM>. As described above, when the ultrasonic transducers <NUM> are active, the ultrasonic vibrations permeate the cleaning fluid and dislodge the contaminants from the outer surface <NUM> of the print roller <NUM>. The surfactant acts to weaken the surface tension between the cleaning fluid and the contaminants, thus enabling the contaminants to be dislodge more easily.

The period of time for which the ultrasonic transducers <NUM> are active is preferably in the range of around three minutes to around seven minutes, and is more preferably around five minutes. The period of time is preferably chosen to be longer than the length of time it takes for the roller driver <NUM> to rotate the print roller <NUM> by one whole rotation.

In some embodiments, the period of time is chosen in dependence upon the volume of the cells of the print roller <NUM> being cleaned. It has been found that the smaller the volume of the cells, the more difficult it is for the ultrasonic waves to shake contaminant loose from the outer surface <NUM> and therefore the longer it takes to clean the print roller <NUM>. However, for most commercial print rollers, it has been found that a period of around five minutes provides enough cleaning time even if the cells are relatively small.

Often a small amount of cleaning fluid will leak beyond the end caps <NUM> and/or the doctor blade <NUM> when the print roller <NUM> is rotating. Whilst the ultrasonic transducers <NUM> are active, the level sensor <NUM> monitors the volume of fluid in the trough <NUM>. If the free surface <NUM> drops below the level sensor <NUM>, the cleaning system <NUM> (via the control unit <NUM>) will supply additional cleaning fluid via the inlet port <NUM> to compensate for the leaked cleaning fluid.

Once the period of time has elapsed, the cleaning fluid will be saturated with contaminants (i.e. dried ink, dirt, grease or the like) and must be removed from the trough <NUM>. To do so, the outlet valve <NUM> is opened and the cleaning fluid is emptied from the trough <NUM> via the outlet port <NUM>. By maintaining the outlet valve <NUM> as closed during the cleaning operation, the cleaning fluid captured within the trough <NUM> is not flowing and therefore the vibrations produced by the by the ultrasonic transducers <NUM> are better able to permeate through the cleaning fluid. Furthermore, because the amount of cleaning fluid used is not more than the volume of the trough <NUM>, and therefore cleaning of the roller <NUM> can be performed using a relatively small amount of fluid.

Once substantially all of the cleaning fluid has been emptied from the trough <NUM>, the cleaning routine is completed. However, in the majority of cases some contaminant will have remained on the print roller <NUM>. This is because the cleaning fluid becomes saturated with contaminant during the cleaning routine and this can impede the transmission of ultrasonic vibrations to the outer surface <NUM>, thus limiting the removal of further contaminant from the roller <NUM>. Additionally, the cleaning fluid may reach a point where it is no longer possible or it becomes increasingly difficult to hold further particles of contaminant in suspension.

It has been found that if the cleaning routine is repeated at least twice in succession (i.e. without using the print roller <NUM> for a printing operation between cleaning routines) the cleaning process is improved significantly. In particular, repeating the cleaning routine provides fresh (i.e. uncontaminated) cleaning fluid to the trough <NUM> which will be more effective at removing contaminant from the print roller <NUM>. Generally speaking, increasing the number of consecutive cleaning routines increases the cleaning performance, however the effect diminishes as the number of cleaning routines increases. It has been found that running the cleaning routine three times consecutively provides a good balance between cleaning performance and the overall length of time taken to clean the roller.

The flow of fluid through the second fluid line <NUM> to the trough <NUM> is controlled by control unit <NUM>. In some embodiments, the control unit <NUM> is configured so that as soon as the level sensor <NUM> detects the presence of cleaning fluid, fluid flow through the second fluid line <NUM> is turned off, thus preventing the trough <NUM> from being over-filled. In alternative embodiments, the control unit <NUM> may be configured to wait for a predetermined period of time after the level sensor <NUM> detects the presence of cleaning fluid before turning off fluid flow through the second fluid line <NUM>. This will provide additional cleaning fluid within the trough <NUM> to account for any accidental leakage during the cleaning operation. In other embodiments, the ultrasonic cleaning bar <NUM> may comprise a pair of level sensors <NUM> spaced vertically apart from one another, and the control unit <NUM> may be configured to ensure that the free surface <NUM> stays between the two level sensors <NUM>. For example, when an upper one of the level sensors <NUM> detects the presence of cleaning fluid the fluid flow through the second fluid line <NUM> may be switched off, and if a lower one of the fluid sensors subsequently detects that the cleaning fluid is no longer present the fluid flow through the second fluid line <NUM> may be switched on.

The ultrasonic transducers <NUM> are spaced apart along the longitudinal axis of the ultrasonic cleaning bar <NUM> (i.e. from left to right in <FIG>) and are encased by the cover member <NUM>. The ultrasonic transducers <NUM> may be mounted to the body <NUM> in any suitable way so that when the ultrasonic transducers <NUM> are activated, vibrational energy from the ultrasonic transducers <NUM> is transferred through the body <NUM> and into the fluid contained in the trough <NUM>. For example, the ultrasonic transducers <NUM> may each comprise a housing which is mounted to the body <NUM> by bonding, and may further comprise piezoelectric elements which are secured within the housing by a fastener, such as a bolt. However, substantially any suitable configuration of ultrasonic transducer may be used, provided that ultrasonic energy is can be imparted upon the fluid contained in the trough <NUM>. The body <NUM> is preferably made from a metal such as stainless steel. It has been found that the use of non-metallic materials such as carbon fibre for the body <NUM> dampens the ultrasonic vibrations generated by the ultrasonic transducers <NUM>, whereas the use of metal, and in particular stainless steel, in fact promotes resonance of the ultrasonic vibrations thereby enhancing the cleaning effect.

The ultrasonic transducers <NUM> are positioned so that they are vertically above the doctor blade <NUM>. As such, when the trough <NUM> is filled with cleaning fluid, there is a large area between the roller <NUM> between a free surface <NUM> (i.e. top surface) of the cleaning fluid and the doctor blade <NUM> in which the cleaning fluid directly contacts the roller <NUM>. During use, the ultrasonic vibrations permeate the cleaning fluid and impinge upon an outer surface <NUM> (i.e. an ink-carrying surface) of the roller <NUM>. Where the roller <NUM> is an anilox roller, the outer surface <NUM> of the roller <NUM> will comprise a plurality of engraved cells within which may contain dried contaminants, such as for example dried ink, dirt, grease or the like. The ultrasonic vibrations are transmitted into the cells and act to dislodge the contaminants, thus cleaning the roller <NUM>. Preferably, the ultrasonic transducers <NUM> a primary vibrational frequency which is variable up to <NUM>, and further harmonic frequencies in the range <NUM> to <NUM> and <NUM> to <NUM>. Due to the shape of the body <NUM> of the ultrasonic cleaning bar <NUM>, the ultrasonic transducers are positioned relatively close to the outer surface <NUM> of the roller <NUM>. Typically, during use the ultrasonic transducers are around <NUM> to <NUM> away from the outer surface <NUM> of the roller <NUM>. As such, the amplitude of the ultrasonic vibrations in the cleaning fluid is still strong at the outer surface <NUM> of the roller <NUM>. As such, the ultrasonic cleaning bar <NUM> provides improved cleaning of the roller <NUM>.

Preferably, the ultrasonic transducers <NUM> are spaced apart from one another at regular intervals along the longitudinal axis. For example, the ultrasonic transducers <NUM> may be spaced apart by around <NUM> to <NUM>. However, it will be appreciated that in alternative embodiments the ultrasonic transducers <NUM> may be spaced apart from one another at irregular intervals. The ultrasonic transducers <NUM> may be operated simultaneously, or may be operated individually in a staggered fashion.

As shown in <FIG>, the roller driver <NUM> comprises a drive wheel <NUM> which is rotatable about an axle <NUM> under the action of a motor (not shown). The roller driver <NUM> is mounted to the frame of the printing machine <NUM> such that an outer surface <NUM> of the drive wheel <NUM> frictionally engages an outer surface <NUM> of the roller <NUM>. In particular, the roller driver <NUM> may be mounted to the frame of the printing machine <NUM> via a mounting. The mounting may comprise, for example, a stud attached to the frame of the printing machine <NUM> and the roller driver <NUM> may comprise a bracket configured to connect the roller driver <NUM> to the stud. The mounting is preferably configured to permit the roller driver <NUM> to move between an engaged position and a rest position. In the engaged position, the drive wheel <NUM> of the roller driver <NUM> frictionally engages the outer surface <NUM> of the roller <NUM>, and in the rest position the drive wheel <NUM> of the roller driver <NUM> is not in contact with the roller <NUM>.

However, it will be appreciated that in alternative embodiments the roller driver <NUM> may be secured in any suitable manner. For example, the roller driver <NUM> may be mounted to a frame which is independent of the printing machine <NUM>, so as to place the drive wheel <NUM> in contact with the roller <NUM>. In some embodiments the drive wheel <NUM> of the roller driver <NUM> may define a width in the direction of the axle <NUM> which is relatively narrow in comparison to the roller <NUM> of the printing machine (such as for example a few centimetres). For example, the drive wheel <NUM> may have a diameter of around <NUM> and a width of around <NUM> to <NUM>. In general, it will be appreciated that the roller driver may have any configuration which is suitable for imparting rotation on the roller <NUM> by frictional contact.

During use, the motor of the roller driver is activated, causing the drive wheel <NUM> to rotate, and transferring rotational motion to the roller <NUM> via frictional contact between the outer surface <NUM> of the drive wheel <NUM> and the outer surface <NUM> of the roller <NUM>. As such, the roller <NUM> rotates relative to the ultrasonic cleaning bar <NUM> about the axle <NUM>. By rotating the roller <NUM>, different parts of the outer surface <NUM> of the roller <NUM> come into contact with the cleaning fluid in the trough <NUM>. The rotation of the roller <NUM> therefore ensures that the whole surface of the roller <NUM> is cleaned by the ultrasonic cleaning bar <NUM> after one full rotation of the roller <NUM>. The roller <NUM> may be rotated in either direction about the axle <NUM> without affecting the ability of the doctor blade <NUM> to seal against the roller <NUM>.

In alternative embodiments, the roller driver <NUM> may not be present, and instead the printing machine <NUM> may be operated to rotate the print roller at a desired speed (e.g. using the internal drive components of the printing machine <NUM>). The control unit <NUM> may communicate with the printing machine <NUM> to drive the rotation of the print roller <NUM> at the desired speed.

The outer surface <NUM> of the drive wheel <NUM> is coated with a layer of material that is soft in comparison to the material of the roller <NUM>, and which provides good frictional contact with the outer surface <NUM> of the roller <NUM>. In the present embodiment, the outer surface <NUM> of the drive wheel <NUM> comprises a <NUM> shore hardness rubber, however it will be appreciated that any suitable material may be used, for example a polymer material, a nitrile material, a polyurethane or the like. Because the material of the outer surface <NUM> of the drive wheel <NUM> is soft in comparison to the roller <NUM>, this minimises the risk that the drive wheel <NUM> and roller <NUM> will damage the outer surface <NUM> of the roller <NUM>. Furthermore, because the material of the outer surface <NUM> of the drive wheel <NUM> provides good frictional contact, this minimises the risk that the drive wheel <NUM> will slip relative to the roller <NUM>, which may reduce the cleaning performance.

The ultrasonic cleaning bar <NUM> may be used with rollers <NUM> of different diameters. When the roller driver <NUM> is used, the roller <NUM> is driven by surface contact between the outer surface <NUM> of the drive wheel <NUM> and the outer surface <NUM> of the roller <NUM>, the velocity of the outer surface <NUM> of the roller <NUM> is directly controlled by the rotational input of the roller driver <NUM>. As such, for a given rotational speed of the drive wheel <NUM>, the outer surface <NUM> of the roller <NUM> will advance past the trough <NUM> of the ultrasonic cleaning bar <NUM> at the same rate regardless of the diameter of the roller <NUM>. Therefore, the roller driver <NUM> provides the advantage that it is able to precisely control the surface velocity of the roller <NUM> so as to ensure that the roller <NUM> advances at the correct surface velocity for the cleaning operation. This avoids the need to re-program the control unit <NUM> when the ultrasonic cleaning system <NUM> is used with rollers of different sizes (for example, where the ultrasonic cleaning system <NUM> is used with different models of printing machine).

<FIG> shows a second embodiment of an ultrasonic cleaning bar <NUM>' according to the present invention. The second embodiment of the ultrasonic cleaning bar <NUM>' differs from the first embodiment in that the ultrasonic cleaning bar comprises body <NUM>' having a pair of longitudinally extending sides <NUM>'. The sides <NUM>' define a pair of longitudinally extending lips <NUM>'. A lower one of the lips <NUM>' extends generally upwards and a second, opposite, one of the lips <NUM>' is extends generally downwards. The lips <NUM>' support a pair of doctor blades <NUM>' which face towards one another and engage the outer surface <NUM> of the roller <NUM>. The doctor blades <NUM>' are mounted to the lips <NUM>' via fasteners <NUM>' and sealed by sealing members <NUM>'. The sides <NUM>', lips <NUM>' and doctor blades <NUM>' co-operate to define a trough <NUM>' therebetween. The ends of the trough <NUM>' are sealed by end plates <NUM>' so as to prevent leakage of fluid out of the trough. The trough <NUM>' is therefore sealed on all sides. As such, the trough can be oriented in any direction with respect to gravity, without causing fluid leakage. This is advantageous where the geometry of the printing machine <NUM> is such that it would not be possible to orient the trough <NUM> of the first embodiment of the ultrasonic cleaning bar <NUM> in an upright position.

<FIG> shows a schematic view of a control unit <NUM> according to an embodiment of the present invention. The control unit <NUM> comprises a housing <NUM>, a controller <NUM>, a pulse generator <NUM>, a heater <NUM>, a dosing unit <NUM> and a user input panel <NUM>. The housing <NUM> comprises a fluid inlet port <NUM> which is connectable to the first fluid line <NUM> and a fluid outlet port <NUM> which is connectable to the second fluid line <NUM>. The housing <NUM> further comprises a power inlet socket <NUM> connectable to the first power line <NUM>, a first outlet socket <NUM> connectable to the second power line <NUM> and the first communications line <NUM>, and a second outlet socket <NUM> connectable to the third power line <NUM> and the second communications line <NUM>.

Fluid is received by the fluid inlet port <NUM> and is channelled to the heater <NUM>. Movement of the fluid is driven by the pressure of the fluid from the first fluid line <NUM> (i.e. the pressure of the factory water supply). However, in alternative embodiments the control unit <NUM> may additional comprise a pump and/or a tank for driving movement of the cleaning fluid. The control unit <NUM> additionally comprises a valve (not shown) for selectively permitting fluid flow to the second fluid line <NUM>. For example, the valve may be part of or coupled to the fluid inlet port <NUM> and/or the fluid outlet port <NUM>. The heater <NUM> is an in-line heater configured to heat the fluid as it moves. However, in alternative embodiments, the heater <NUM> may comprise a tank having heating elements for heating fluid contained in the tank. The heater <NUM> is configured to heat the fluid to around <NUM>. However, in yet further embodiments the control unit <NUM> may not comprise a heater <NUM>. In such embodiments, the fluid inlet port <NUM> may be connected directly to the dosing unit <NUM>.

Once heated, the fluid is passed to the dosing unit <NUM>. The dosing unit <NUM> introduces a predetermined amount of surfactant into the heated fluid. Typically, the amount of surfactant required is <NUM> per litre of fluid. The temperature of the heated fluid may be chosen so as to ensure that the surfactant will rapidly dissolve into the fluid so that it is evenly dissipated. Furthermore, it has been found that heating the fluid, cleaning performance is increased and dried ink is more easily dislodged. The dosing unit <NUM> is accessible via a door <NUM> of the housing <NUM>. The door <NUM> permits the surfactant in the dosing unit <NUM> to be refilled once it has been consumed. Once the surfactant has been introduced into the cleaning fluid, the cleaning fluid is channelled out of the control unit <NUM> via the fluid outlet port <NUM> and into the trough <NUM> of the ultrasonic cleaning bar <NUM>.

Electrical power is received by the power inlet socket <NUM> and is used to power the controller <NUM> and the pulse generator <NUM>. The controller <NUM> communicates with the ultrasonic cleaning bar <NUM> via the first outlet socket <NUM>. In particular, the controller <NUM> is configured to send and receive control signals from the ultrasonic transducers <NUM> and the level sensor <NUM>. The controller <NUM> communicates with the roller driver <NUM> via the second outlet socket <NUM> and is configured to activate, deactivate and control the speed of the drive wheel <NUM> of the roller driver <NUM>. The controller <NUM> is further configured communicate with the pulse generator <NUM> and the user input panel <NUM>.

During use, once the user has mounted the ultrasonic cleaning bar <NUM> to the printer <NUM>, the user inputs a "start" command to the user input panel <NUM>. The control unit <NUM> then begins to fill the trough <NUM> with cleaning fluid via the second fluid line <NUM>. The control unit <NUM> continues to fill the trough <NUM> until the presence of the cleaning fluid is detected by the level sensor <NUM>. The level sensor <NUM> communicates that cleaning fluid has been detected to the controller <NUM>, and subsequently the controller <NUM> shuts off fluid flow to the trough <NUM> (for example by deactivating the second fluid line <NUM>). The controller <NUM> communicates with the pulse generator <NUM> which produces an oscillating electrical power output which drives the ultrasonic transducers <NUM>. The frequency of the electrical power output from the ultrasonic generator <NUM> is chosen so as to cause the ultrasonic transducers to generate a primary vibrational frequency which is variable up to <NUM>, and further harmonic frequencies in the range <NUM> to <NUM> and <NUM> to <NUM>. The control unit <NUM> then communicates with the roller driver <NUM> to cause the drive wheel <NUM> to rotate at a predetermined angular velocity. The roller driver <NUM> causes the roller <NUM> to rotate, thereby cleaning the whole surface of the roller <NUM>.

Typically, the roller <NUM> is driven so that the outer surface <NUM> of the roller <NUM> has a surface velocity of around <NUM>. min-<NUM> (metres per minute), however this speed may be within the range of around <NUM>. min-<NUM> to around <NUM>. min-<NUM>, or more preferably in the range of around <NUM>. min-<NUM> to around <NUM>. In some embodiments the outer surface <NUM> may be rotated with a linear velocity of up to <NUM>. It has been found that a surface speed of around <NUM> metres per minute (or within the ranges above) is fast enough that the cells of the roller <NUM> can be cleaned in a short amount of time, but slow enough to that the cells of the roller <NUM> are exposed to ultrasonic vibrations for long enough to ensure that contaminant is shaken loose from the outer surface <NUM> such that the cells are cleaned. At such speeds, activating the ultrasonic transducers <NUM> for cycles of three to seven minutes, or more preferably five minutes removes enough contaminant from the outer surface <NUM> to saturate the cleaning fluid. Once the cleaning fluid is saturated, the cleaning fluid can be drained and replaced and a subsequent cleaning routine can be executed.

The control unit <NUM> continues to drive the ultrasonic transducers <NUM> and the roller driver <NUM> until either the user inputs a "stop" command into the user input panel <NUM>, or until a predetermined cleaning period has elapsed. The predetermined cleaning period is chosen so that the whole surface of the roller <NUM> has been cleaned. In particular, the predetermined cleaning period may be chosen in dependence upon the diameter of the roller <NUM> and the desired surface speed produced by the roller driver <NUM> (which may be input into the controller <NUM> by the user). The predetermined cleaning period may be input by the user, or may selected from a database stored by or associated with the controller <NUM> of the control unit <NUM>. Typically the predetermined cleaning period is around <NUM>, <NUM>, <NUM> or <NUM> minutes. Once the "stop" command is received by the controller <NUM> or the predetermined cleaning period elapses, the controller <NUM> deactivates the pulse generator <NUM> and stops driving the ultrasonic transducers <NUM>. The controller <NUM> communicates with the ultrasonic cleaning bar <NUM> and causes the outlet valve <NUM> of the ultrasonic cleaning bar <NUM> to open, permitting the cleaning fluid in the trough <NUM> to empty via the third fluid line <NUM>.

The cleaning system <NUM> may be used with rollers <NUM> of different lengths. In order to support the ultrasonic cleaning bar <NUM> either side of the roller <NUM>, the length of the ultrasonic cleaning bar <NUM> must be approximately the same as the length of the roller <NUM>. As such, the cleaning system <NUM> may comprise ultrasonic cleaning bars <NUM> of various different lengths. However, in order to provide cleaning along the whole length of the roller <NUM>, the ultrasonic transducers <NUM> should not be spaced apart too far. Therefore, longer ultrasonic cleaning bars <NUM> will require more ultrasonic transducers <NUM> in order to provide adequate cleaning. However, it will be appreciated that the pulse generator <NUM> may only be able to provide sufficient energy to power a number of ultrasonic transducers <NUM>. Typically a single pulse generator <NUM> is able to supply enough electrical energy to power four pulse generators <NUM>. As such, the control unit <NUM> may comprise more than one pulse generator <NUM>. For example, the control unit <NUM> may comprise two, three or any suitable number of pulse generators <NUM>. Where the control unit <NUM> comprises more than one pulse generator <NUM>, it is able to provide power to ultrasonic cleaning bars <NUM> having more than four ultrasonic transducers <NUM>.

With reference to <FIG>, each ultrasonic cleaning bar <NUM> comprises a plug configured to be received by the first outlet socket <NUM>. The plug <NUM> comprises six electrical contact pins 120a-c arranged in pairs. The pins <NUM> are received by corresponding receptacles of the first outlet socket <NUM> to create an electrical connection therebetween. Each pair of pins 120a-c comprises a first pin for feeding electrical current from the control unit <NUM> to the ultrasonic cleaning bar <NUM> and a second pin for returning the electrical current from the ultrasonic cleaning bar <NUM> to the control unit <NUM> (e.g. a "live" pin and a "neutral" pin). Each pair of pins 120a-c is electrically connected to four ultrasonic transducers <NUM>. Furthermore, each pair of pins 120a-c is electrically powered by a separate pulse generator <NUM>. For example, a first pair of pins 120a is powered by a first pulse generator <NUM>, a second pair of pins 120b is powered by a second pulse generator <NUM> and a third pair of pins is powered by a third pulse generator <NUM>. Because the plug <NUM> of <FIG> comprises three pairs of pins 120a-c, the plug <NUM> is able to connect the control unit <NUM> to an ultrasonic cleaning bar <NUM> comprising twelve ultrasonic transducers <NUM> (such as the ultrasonic cleaning bar <NUM> shown in <FIG>).

In alternative embodiments each pair of pins 120a-c may be connected any suitable number of ultrasonic transducers <NUM>, for example one to six ultrasonic transducers. Furthermore, the plug <NUM> may be used with an ultrasonic cleaning bar comprising fewer than twelve ultrasonic transducers. For example, the plug <NUM> may be used with an ultrasonic cleaning bar <NUM> comprising eight ultrasonic transducers <NUM>. However, because each pair of pins 120a-c powers four ultrasonic transducers <NUM>, all eight ultrasonic transducers <NUM> can be powered using only the first pair of pins 120a and the second pair of pins 120b. As such, the plug <NUM> may be manufactured without the third pair of pins 120c, or the third pair of pins 120c may be present but electrically disconnected from any other components. The plug <NUM> is therefore configured to automatically connect the correct number of pulse generators <NUM> to the ultrasonic transducers <NUM>. This means that the user does not need to make any adjustments to the control unit <NUM> where the control unit <NUM> is used with different ultrasonic cleaning bars <NUM> having different numbers of ultrasonic transducers <NUM>. In practice, the user is able to simply plug any ultrasonic cleaning bar <NUM> into the control unit <NUM>, as the configuration of the plug <NUM> will ensure that the correct amount of power is drawn from the control unit <NUM>.

The user input panel <NUM> may comprise one or more buttons in communication with the controller <NUM>. Additionally or alternatively, the user input panel <NUM> may comprise a screen, and in particular a touch screen, configured to display a graphical user interface. The user input panel <NUM> provides a means for the user to adjust the parameters of the cleaning operation, for example the frequency of the electrical pulses generated by the pulse generator <NUM>, the duration of the cleaning cycle itself, the speed of the roller driver <NUM> etc..

In alternative embodiments, the control unit <NUM> may comprise additional fluid outlet ports and outlet sockets configured to connect the control unit <NUM> to additional ultrasonic heating bars <NUM>. As such, the control unit <NUM> can be used to control a plurality of separate ultrasonic heating bars <NUM>. For example, a user may mount a first ultrasonic heating bar <NUM> to a first roller <NUM> of a printing machine <NUM> and initiate an ultrasonic cleaning cycle. Whilst the first roller <NUM> is being cleaned, the user may mount a second ultrasonic cleaning bar <NUM> to a second roller <NUM> of the same or a different printing machine <NUM>. Once the cleaning cycle of the first roller <NUM> is complete, the user can use the control unit <NUM> to initiate the cleaning cycle for the second roller <NUM>. Whilst the second roller <NUM> is being cleaned, the user can dismount the first ultrasonic cleaning bar <NUM> and mount it to a third roller <NUM> of the same or a different printing machine. As such, by using a plurality of ultrasonic cleaning bars <NUM> the user can save time when cleaning multiple rollers <NUM>.

Claim 1:
A method of cleaning a print roller (<NUM>), comprising:
providing an ultrasonic cleaning bar (<NUM>) having at least one ultrasonic energy source (<NUM>);
engaging the ultrasonic cleaning bar (<NUM>) with an ink-carrying surface (<NUM>) of the print roller (<NUM>), the ultrasonic cleaning bar (<NUM>) and the ink-carrying surface (<NUM>) defining a trough (<NUM>) therebetween for containing a cleaning fluid;
the method being characterized by executing a cleaning routine, the cleaning routine comprising
filling the trough (<NUM>) with the cleaning fluid so that the cleaning fluid contacts the ink-carrying surface (<NUM>);
activating the ultrasonic energy source (<NUM>) for a period of time to remove contaminants from the ink-carrying surface (<NUM>) of the print roller (<NUM>) so that the contaminants become suspended in the cleaning fluid;
preventing cleaning fluid draining from the trough (<NUM>) whilst the ultrasonic energy source (<NUM>) is activated; and
draining the suspension of cleaning fluid and contaminants from the trough (<NUM>);
wherein the method comprises executing the cleaning routine at least two times in succession before cleaning of the print roller (<NUM>) is complete.