Calibration device and method of calibration utilising such a device

Abstract

A calibration roll 300 provides a visible indication to an operative of printing apparatus whether, and to what extent the applicator rolls 400 of that apparatus are: not cylindrical, parallel or axia

Description

Field of the Invention The present invention relates to a calibration device and a method of calibration utilising such a device. More specifically, the present invention relates to a calibration roller or sleeve predominantly for use with printing and coating apparatus wherein a liquid printing ink or coating fluid is applied to a plate cylinder, blanket cylinder or other applicator roll for subsequent transfer to a substrate to be printed or coated, and wherein it is desired to improve the precision, accuracy, and uniformity of the application of the ink or coating fluid, as well as the repeatability between successive applications by performing suitable calibration of the printing or coating apparatus in advance in order to quickly identify deficiencies or inaccuracies in the current positions, orientations and physical characteristics of the primary inking or coating rollers. Although the present invention is particularly suited to the calibration and adjustment of the various individual inking stations provided on and around conventional metal decoration apparatus, it is certainly not exclusively restricted to this field of application. Indeed it is certainly envisaged that the present invention may be used to similarly calibrate a wide variety of other rotary substrate printing and coating apparatus wherein there is at least one rotary cylindrical component having a rubberised or otherwise flexible resilient outer layer which repeatedly receives and then transfers an amount of an operative liquid to some other component or a substrate within or passing through the apparatus, and for which an easy, simple and speedy means of identifying deficiencies in the position, orientation or some other characteristic of said cylindrical component can be quickly and easily identified, and then corrected. Background to the Invention Metal decoration machinery has been in existence for over 50 years, and metal decoration is thus already a well established art. However, in more recent times, and as with all modern manufacturing, machinery customers, end users and consumers alike are becoming increasingly demanding as regards the quality, price, and production efficiency of the products being manufactured, and metal decoration is no exception. There is naturally a continual striving towards to achieving a superlative product at the lowest possible price point, and one particular aspect of the production of decorated metal cans of particular relevance hereto is the overall throughput in cans per minute which modern metal decoration machinery can achieve. Modern metal decoration equipment commonly now achieve can throughput rates in excess of 2000 cans per minute (CPM), and when it is considered that the cans are fed into and emerge from generally rotary decorator equipment individually, one after another, and are both printed within the decorator with an image consisting of 1, 2, 4, 6, or in some cases 8 different coloured inks, and then fully coated at least once with a varnish or lacquer, the skilled reader will immediately understand that modern metal decoration equipment can be not only complex, but must also be capable of delivering both inks and coatings with extreme accuracy and precision in a highly repeatable, consistent and reliable manner. To provide the reader with a basic understanding of modern metal decoration equipment, and to provide some useful context for the present invention, most metal decorators are designed around the fundamental requirements of • receiving individual usually open-topped (i.e. closed at one end) cans in high volumes / numbers, for example delivered on a conveyor belt, • transferring each and every such can onto a (rotating) supporting mandrel wheel, each can being slid, open end first, onto one of a plurality (typically 20-30 or more) of can body pin mandrels circumferentially evenly spaced around the mandrel wheel, • printing the exterior (usually cylindrical) surface of each can by transferring a wet ink image from a blanket wheel, disposed immediately adjacent the mandrel wheel, to the can by means of mutual contacting rotation of said can and said blanket wheel, the wet ink images on the blanket wheel often comprising 1, 2, 4, 6, or even possibly 8 different colour printing inks, depending on the number of active inking stations provided peripherally around the blanket wheel, • completely covering or coating the printed cylindrical surface of the can with a varnish or lacquer to stabilise the wet ink image having been immediately previously transferred to the can, so as to provide some fixing of, and / or protective coating for the wet-ink image and optionally or additionally to provide the decorated can with a lustrous quality or some other desired finish, • removing the decorated, coated cans from the mandrel for subsequent delivery to an oven to dry, and thus set the coating and printed image underneath. Therefore, many self-contained metal decorator machines (such as those manufactured by the Stolle Machinery Company, LLC, Colorado, USA, and others) consist of some form of can infeed transfer mechanism, a mandrel wheel, an ink blanket wheel surrounded by multiple inking stations, an overvarnish ("OV") unit, and an outgoing can disc transfer wheel. The present invention is primarily concerned with ensuring that the performance of the various inking stations disposed around the blanket wheel is optimised as far as possible, and in particular with ensuring that the position, orientation and ink transfer surface characteristics of specific rollers within each inking station are either optimised or quickly identified as being deficient. The present inventions is particularly suited to the calibration of the or each ink transfer roll provided within each inking station, as it is this particular roll that ultimately delivers ink to the plate cylinder which in turn delivers a single ink in a specific pattern onto a relevant portion of the blanket wheel. In to facilitate greater understanding of the invention, specific relevant aspects of existing metal decorating apparatus are now described. As the delivery of cans into and removal of printed, coated cans from the apparatus are not relevant to the present invention, further description thereof is omitted, except where necessary or appropriate, in the interests of brevity. Most commonly, the mandrel wheel and the ink blanket wheel are, in modern high-throughput decorators, generally independent large rotary sub-assembles mounted on their own frames or frameworks and adjacently disposed so that where they are most proximate one another, the ink blanket wheel kisses a single one of many identical can-carrying pin mandrels provided on the mandrel wheel (often 16, but mandrel wheels have been designed that can carry 24, or 36 cans depending on size). It is this kissing contact that, during operation, allows each one of the many identical adjacent composite patterns of printing inks to be directly transferred to a single can as the mandrel wheel and ink blanket wheel mutually rotate (in opposite directions) relative to one another. In some cases, the blanket wheel may be of a significantly larger diameter (often of the order of 2m or more when 6 or 8 ink stations are provided therearound) than the mandrel wheel it serves, because the inking stations can themselves be very substantial and highly accurate pieces of equipment and are consecutively arranged around it, usually over about one third, one half or possibly two thirds of the total circumference of the blanket wheel. Given the common requirement for the application of (usually) multiple different inks in different patterns to create the final composite wet ink pattern to be applied to any individual can, and the fact that the can diameter is always very much smaller than the blanket wheel diameter, it is common for the blanket wheel to be provided with many identical complete wet ink patterns adjacent one another around its surface to increase printing capacity. Naturally, the length of the circumferential arc of any one of the 16 (or so) inked sectors that the blanket wheel is notionally divided into corresponds exactly to the total circumferential dimension of the can to be printed. Thus, at any one instant, although only one (of the many) wet ink patterns can be transferred to one can as a result of the relative rotation of the blanket wheel and mandrel wheel, driving both the blanket wheel and the mandrel wheel at precisely synchronised angular velocities naturally increases the overall printing throughput at the point of contact between the two wheels in direct proportion to the diameters of the respective wheels. Finally, after any one wet ink pattern is transferred to any one can, both blanket wheel and mandrel wheel rotate further such that the now printed can moves, usually downwardly, away from the area of printing contact, and the particular previously fully wet inked area of the blanket wheel moves upwardly back towards the various inking stations positioned around the blanket wheel where that area may again be consecutively re-inked at each of said inking stations. Turning now to the inking stations, typically there will be at least 4, and sometimes as many as 8 individual inking stations mounted in close proximity to, and at evenly spaced apart positions around a good proportion, e.g. one third, a half or possibly even two thirds, of the exterior circumferential surface of the blanket wheel of the decorating apparatus. Each inking station will usually include at least the following specific components: • an ink tray or fountain provided at that end of the inking station which is radially most remote from the exterior surface of the blanket wheel, • a train of ink transfer rolls disposed inside the inking station and laterally mounted therein, arranged one after another so that the train extends in a generally radial direction away from the ink fountain and towards the exterior surface of the blanket wheel, a first roll in the train being in contact with the ink fountain itself and one succeeding roll, with further succeeding rolls in the train being disposed thereafter and each being in contact with the immediately preceding roll; there may be as many as 5-8 ink transfer rolls provided within the train, and usually at least two of the said rolls are provided with laterally acting cam means, typically provided at one or both of their end mountings, such that not only can both rotate freely or be driven rotationally, but these particular rolls also laterally oscillate within the inking station having the effect of more evenly and widely spreading the ink over these and subsequent ink transfer rolls, leading to an overall more uniform coating of ink ultimately being applied to the terminal roll in the assembly, this being... • one or in some cases a pair of ink applicator or form rolls provided at the terminal end of the train of transfer rolls and in contact with the final ink transfer roll, by means of which a typically consistent and uniformly thin layer of ink is thus applied to... • a plate cylinder around which one or possibly two (e.g. on Stolle Concord™ decorator machines) printing plates are circumferentially mounted, typically magnetically, and which is releasably mounted within or immediately adjacent the inking station at a proximal end thereof so that the plate cylinder is disposed immediately adjacent the exterior surface of the blanket wheel and against which, in use, said plate cylinder exerts some slight contact pressure against a relevant area of the circumferential surface of said blanket wheel, and • various (usually hydraulic) rotary drive and fluid cooling systems which both drive at least one or more of the transfer rolls, and also deliver a cooling fluid (most commonly water) into and through many if not all of the ink transfer rolls and the applicator roll to maintain the temperature of those rolls, and indeed the temperature of the inking station as a whole, at a relatively constant level while in use. As the skilled reader may appreciate, the aim and purpose of any ink station is to deliver ink to the plate cylinder, or more specifically to the raised surfaces of the one or more printing plates thereon and which thus define the pattern of ink to be applied to the blanket wheel, in a highly accurate, reliable, repeatable and consistent manner, so that the amount of ink applied is, for each and every rotation of the plate cylinder and thus each and every application, of a consistent, constant and uniform thickness or weight across the entire length of the printing plate. However, in practice, such consistency of ink application to the printing plates on the plate cylinder is rarely achieved, for a variety of reasons. Firstly, although any ink station is well engineered and thus a relatively robust subsystem of the overall metal decoration apparatus, an operative ink station is naturally subjected to significant pressure by virtue of the requisite contact pressure between the blanket wheel and the plate cylinder, which is then transmitted in turn through to the form roller(s) and then (if not entirely dissipated therein) on through preceding ink transfer rolls within the ink station. As previously mentioned, modern metal decoration apparatus can operate at can throughput speeds of the order of 2000 CPM. In any single revolution therefore, the blanket wheel may be required to print 24 cans (on the mandrel wheel) each having a circumference of (typically) 200mm and would therefore need to be capable of bearing a corresponding number of discrete separate spaced apart wet ink images each having a similar length (albeit at various stages of creation). This dictates that, allowing for a reasonable separation distance between each of the images of 100mm, the blanket wheel circumference must be at least 7.3m, giving a blanket wheel diameter of 2.32m. Thus the blanket wheel is by any measure a somewhat massive component, and in order to achieve the stated throughput CPM rates, this component is often required to rotate at speeds in excess of 80rpm, so the inertial and radial forces which can be created by the blanket wheel, even with only relatively small eccentricities in either the mounting or the overall circular cross-section of the blanket wheel and in particular its ink-receiving exterior periphery, can be significant. In any event, whether as a result of these forces or as a result of other rigours of production, the position and orientation of the plate cylinders and, especially, the form rolls can be prone to change. Additionally, depending on the nature of the inks which are to be used in a particular production run, and natural manufacturing tolerances in the dimensions of the plate cylinders and the printing plates mounted thereon, it is often necessary to manually adjust these and various other components in the inking station and in the decorator as a whole as part of the standard preliminary set up procedures prior to any print run. Thus, It is generally considered essential to perform some preliminary calibration of at least the form rolls of each operative inking station so as to achieve, in production, optimum accuracy and uniformity of ink transfer to each respective adjacent plate cylinder. In particular, the aim of this calibration is to primarily to ensure that sufficient and uniform contact pressures are achieved betwixt the or each form roll in any operative inking station and the respective plate cylinders associated therewith. Additionally, it is of course necessary that any and all plate cylinders are in exact registration with each other and with each of the (12, 14, 16, 24 or more) specific areas of the exterior surface of the blanket wheel that they are to deliver ink to during the print run, such that with each full rotation of any single plate cylinder, the one (or two, when the plate cylinder carries two printing plates, as is the case in the Concord™ decorator machine) wet ink pattern(s) carried by the inked printing plate(s) is / are applied in exactly the correct position on the exterior surface of the blanket wheel. Although the registration of the plate cylinders as regards each other and the blanket wheel is beyond the scope of this application, the position and orientation of the terminal form rolls within the ink stations is a very important part of the initial set up procedure, because it is these rolls that ultimately apply a coating of ink to the or each printing plate on the plate cylinders with every revolution thereof. If this coating of ink is deficient in any way, then such deficiencies immediately translate to the wet ink pattern that is ultimately transferred from the printing plate to the blanket wheel, and thence onto the exterior surface of the can body itself. The two main inking issues are 1. over- or under-inking, i.e. the overall application oftoo much ortoo little inkto the printing plate, resulting in tonal imbalance in the resulting wet ink and printed image due to the weight of one or more colours therein being excessive or insufficient respectively, 2. laterally non-uniform inking, i.e. when there is some variation in the thickness of the layer of ink applied to the printing plate along its width, resulting in tonal variation in the resulting wet ink image pattern transferred to the blanket wheel, from one side or end of the image to the other; As the skilled reader may appreciate, both these issues can either be systemic (when the same tonal imbalance exists in all the wet ink patterns and thus the resulting printed images, and the deficiency is generally uniformly manifested in all such images) or periodic, varyingly progressive and regressive, or even sporadic (when the extent of tonal imbalance that exists in some or all the printed images varies between successive images or successive sets of images, usually either in some periodic way, or sporadically). For issue (1), the primary cause is usually related to the contact pressure between the or each form roll and the or each printing plate on the plate cylinder. At one extreme, if there is zero contact pressure, then there is little no contact between the respective roll(s) and plates, and there can be little or no ink transferred to the latter, with obvious consequences. At the other extreme, if the contact pressure is too great, and taking into account that the exterior ink-bearing surface of the form roll is at least to some extent resilient and deformable, then this can have various consequences. In most cases, increasing the contact pressure results in a greater ink transfer efficiency, and therefore, in most cases, if the contact pressure is too great, then an excess of ink is transferred, and this reduces the resolution of the pattern of wet ink which is then subsequently transferred from the printing plate to the blanket wheel. If an excess of ink is present on the printing plate, this can result in a blurred or blotchy wet ink pattern being applied to blanket wheel, and where it is desired to print image with a desired resolution, this can have severe consequences. For example, if a bar code or a so-called quick-response (QR) codes form part of the image which is to be printed, and in the resulting wet ink image these are insufficient well resolved, then they cannot be subsequently sufficiently well discerned by digital scanning equipment, rendering these types of code useless. In general, over-inking of the printing plate such as described above usually always results in some compromise in the resolution of the wet ink pattern. In more extreme cases, where the contact pressure between the or each form roll and the or each printing plate on the plate cylinder is much too large, then this can result in more significant deformation of the resilient ink-bearing surface of the form roll. In such circumstances, not only can such excess contact pressure irreparably damage the form roll, for example through plastic deformation thereof or even tearing the surface thereof, but it can also result in the wholly undesirable transfer of ink therefrom into the interstitial regions of the printing plate, i.e. those regions between the raised portions thereof which are intentionally relieved such that they should never receive ink, again resulting in a partially or completely compromised wet ink pattern. In the most extreme case, it is conceivable that a largely solid block of ink could be subsequently transferred from the printing plate to the blanket wheel, which would of course completely destroy the final printed image. For issue (2) above, the primary causes are more varied, but the consequences for the resulting wet ink pattern which is ultimately transferred from the printing plate to the blanket wheel are no less severe, in terms of the overall quality of the resulting composite wet ink pattern carried by the blanket wheel, and thus overall rejection rates of the can bodies to which those wet ink patterns are subsequently applied. One of the main causes of laterally non-unform inking is that there is some discrepancy in alignment between the rotational axis of the plate cylinder and that of the or each form roller. Ideally, these two axes of rotation should be exactly parallel and horizontal relative to some similarly horizontal datum level, typically an exactly level support surface on top of which the entire machine is installed. In practice however, and especially after completing a print run print of any significant length wherein - substantial quantities of ink will have been delivered through each operative ink station, and - all the various interacting rotary components will have already undergone many thousands of rotations, the initial perfectly parallel alignment of these two axes, for some if not all of the form rolls and plate cylinders, can be prone to natural operational and production drift, whether as a result of ink residue build up, or for some other reason. Further factors which can result in these types of positional inaccuracies, or other causes of lateral inking variations, are: - the natural and often uneven wear of the surfaces of the components, particularly of the elastomeric resilient exterior layer provided on the form roll(s); such wear can of course be compounded somewhat by the fact that there can be significant contact pressures between both the form roll(s) and the plate cylinder, and between the plate cylinder and the blanket wheel; - any play or give which may inherently exist in the bearings and / or mountings and which may have arisen over time and previous lengthy production runs, or the tendency of these components or any part thereof to yield somewhat under the intensively repeated cyclical loading they are subjected to during production, and as a result become fractionally displaced from their optimum position as production continues, or as a result of natural progressive wear, - aggressive or inappropriate treatment of the components by unskilled or poorly trained machine operatives; (it is to be noted here that the inks and varnishes used in modern metal decoration are unpleasant chemicals and many have a tendency to congeal; this can make the removal and replacement of components at the end of a print run very difficult without using increased or in some cases extreme force; such changeovers are of course essential, both for cleaning and when setting the machine up for a new print run; with ever-increasing production demands, rarely is very much time or care taken during a changeover, and these components, critical though they, their mounting and dispositional accuracy are to the printing process, are often subjected to very rough treatment); - the natural build up and subsequent coagulation of ink residues (or varnish in coating apparatus) in the extremity and end regions of the components outside the contact areas thereof, and which always tends to compromise the inertial symmetry as compared to a corresponding clean or new component, leading to a tendency of that component to rotate eccentrically, - the tendency of the elastomeric resilient exterior layer provided on the form roll(s) to swell and become otherwise permanently deformed as a result of the prolonged periods when covered in ink, varnish or lacquer, and which can, over time, begin to chemically interact with the elastomer causing slight dimensional changes therein; such dimensional changes are usually manifested in a slight swelling in and around the middle of the roll where ink or varnish is generally permanently in contact with the elastomeric layer, as opposed to the more remote ends lying to the outside of the contact area with the plate cylinder and whereat ink or varnish can be more easily released from the surface of the roll, for example centrifugally. As will be immediately understood from the above, the form roll(s) of any inking station within metal decoration machinery, and indeed any applicator roll for any liquid ink or coating wherever employed and for which there is a requirement for extremely precise and uniform application of that liquid, are particularly vulnerable components and while the distortions, displacements, dislodgements and other positional and dimensional abnormalities may be relatively physically small (e.g. deviations of the order of only a few 10s-100s of microns from the ideal), such imperfections can nevertheless have a serious impact on overall operational effectiveness. Notwithstanding the importance of these components, within the metal decoration industry at least, it is currently common practice for initial setup adjustments to the physical position and axial orientation of the form rolls in each and every operative inking station relative to the plate cylinders to be conducted largely only manually, by eye, and / or based on some test print run results. This of course requires conducting at least one and in some cases two or three test print runs of very short duration to establish which of the various form rolls are delivering ink to their respective plate cylinders effectively, and which are not performing adequately enough. Not only does this practice take significant amounts of time, but it also results in large amounts of wastage, as those can bodies which are printed in the preliminary print runs will of course, almost by definition, be deficient. As will be readily understood from the foregoing, there is a clear need for some means whereby the position and orientation of the form rolls of inking stations can be set quickly and with sufficient accuracy, ideally without any the need to conduct any wasteful and time consuming test printing run, and which can be easily explained and implemented such that it can be carried out by relatively low-skilled personnel. It is to these ends that the present invention is directed. Summary of the Invention According to the present invention there is provided a calibration roll or sleeve adapted to be temporarily rotationally mounted in printing or coating apparatus in place of, and in identical manner to, the primary inking or coating roll or sleeve mounted therein and to which, in use, is typically applied a layer of liquid ink or coating fluid by one or more applicator rolls also rotationally mounted within said apparatus, said one or more applicator rolls having a cylindrical exterior surface constituted of or covered with a resilient elastomeric material, said apparatus further comprising means whereby the relative position and orientation of the axes of rotation of the primary inking or coating roll or sleeve and the one or more applicator rolls can be adjusted, characterised in that said calibration roll or sleeve being has an exterior cylindrical surface of diameter D and is constituted of a first material which is rigid compared to the elastomeric material of the applicator roll in that it has a modulus of elasticity (Young's modulus, E) which is at least one order of magnitude greater than that of the elastomeric material, said calibration roll or sleeve further being provided, in and along substantially the entire axial length of the exterior cylindrical surface thereof, with a plurality of axially aligned parallel recesses which are circumferentially spaced apart by a circumferential arc having a length less than or equal to ttD / 72 and having width (w) and depth (d) dimensions which are both less than 1.5mm, said recesses being in precise alignment with the longitudinal axis of the calibration roll or sleeve, where dimension D of the calibration roll or sleeve is exactly the same as the corresponding exterior diametral dimension of that or those surfaces of the primary inking or coating roll or sleeve to which ink or coating fluid is applied by said applicator roll such that the calibration roll or sleeve exerts the same contact pressure on said applicator roll when temporarily installed in said apparatus as would the corresponding primary inking or coating roll during production, and whereby, when said applicator roll is brought into its conventional operative position against the calibration roll or sleeve when angularly positioned to ensure that at least a plurality of the axially aligned recesses in the exterior cylindrical surface thereof lie within the contact region betwixt the respective rolls or sleeves, said recesses leave an impression in the elastomeric material of the applicator roll which is not only immediately visible to the naked eye when the applicator roll or sleeve is retracted from its conventional operative position, but also immediately indicative of one or more of the following potential positional, orientational or surface characteristic deficiencies: - the extent to which the exterior surface of the applicator roll is, or is not perfectly cylindrical, - the relative degree of parallelism or axial misalignment of the axes of rotation of the calibration roll or sleeve and the applicator roll, and - the relative proximity of the axes of rotation of the of the calibration roll or sleeve and the applicator roll, and thus the degree to which said axes of rotation may be excessively or insufficiently distant, at one end or another, or along the entire length thereof. As previously alluded to, one of the primary difficulties faced by machine operatives during preliminary, pre-production set up procedures is both establishing whether and to what extent the form or applicator rolls of each inking station which is to be operative during the print run are misaligned relative to, or whether they are disposed too proximate or distant from, the primary printing plate cylinders associated with or forming part of those inking stations. Furthermore, there is, Applicant believes, currently no check performed on the form or applicator rolls themselves, other than by eye, to determine whether and to what extent the exterior surfaces of those rolls may be misshapen, deformed, or whether their surface profiles may have some other abnormality which could affect their operational efficacy. The use of a calibration sleeve as prescribed above solves all these issues, because the spaced apart impressions created on the form or applicator roll cylindrical surface by the narrow, shallow, and precisely parallel and perfectly axially aligned recesses provided in the exterior surface of the calibration sleeve are not only immediately readily visible to the naked eye, but also, when the impressions created in the form or applicator roll are not similarly aligned, parallel and straight, they provide an immediate indication of the extent to which there is relative misalignment in the position and orientation of the axes of rotation of the applicator roll and of the calibration roll or sleeve (which is of course that of the primary printing and coating roll or sleeve). Furthermore, the impressions created by the calibration roll can also provide a ready indication if the degree and nature of any non-uniformity in the surface profile of the elastomeric outer layer or coating provided on the applicator roll. To explain further, if two adjacent impressions created in the elastomeric outermost layer or coating provided on the applicator roll are parallel and straight, but lie at an angle relative to a notional perfectly axial line perpendicular between each end and extending along the surface of the roll from one end to the other, then this would immediately indicate not only a lack of parallelism between the axes of rotation of the applicator or form roll and calibration roll, but also the direction of that lack of parallelism, and this therefore provides a ready indication as to which end of the applicator or form roll needs adjustment, and by how much. Indeed, Applicant believes that a single impression created by a calibration roll as prescribed above and further described below against each applicator or form roll which is to be operative may be provide sufficient indication to enable operatives to perform all the required adjustments (or replacements) by firstly conducting some simple measurements of the impressions, for example their general and relative inclinations, their width and height, and the extent of any relative convergence or divergence, and then secondly converting these measurements, either by means of a simple conversion chart or, more likely a computer, to some corresponding actual physical adjustment that was to be applied to the mounting of the applicator or form roll. This would represent a major improvement as compared to the often multiple "trial and error" type adjustments that machine operatives currently carry out. Preferably, the recesses provided in the calibration sleeve or roll are created by precise and repeated machining carried out on the exterior cylindrical surface of said sleeve or roll, for example when mounted in computer numerical control (CNC) metal component machining apparatus. Although in its simplest form, the invention only requires at least two recesses be provided in the exterior cylindrical surface of the calibration roll, preferably the plurality of recesses numbers at least 4, more preferably at least 10, and most preferably 20, in any one circumferential region of the calibration sleeve or roll. Further preferably, the plurality of recesses are grouped together in at least one, and more preferably two, pairs of groups of recesses, with all the recesses forming part of any group being arcuately equidistantly spaced apart by the requisite arcuate separation distance, ttD / 72, or less. Further preferably, a first group in any pair of groups of recesses extends around an arc length of the exterior cylindrical surface of the roll or sleeve having a length of N(nD / 72+w) + w, where N is the number of recess provided in the group, and w is the width dimension of any single recess. As previously mentioned, preferably, 4<N<20, resulting in a total number of recesses, in two pairs of groups is provided of between 16 and 80. In further preferred embodiments, any first group in any pair of groups of recesses is provided in a position around the exterior cylindrical surface of the roll or sleeve which is exactly diametrically opposed to the position of the second group in that pair, and equally, most preferably, any single recess in any single group has a corresponding recess which lies in a similarly diametrically opposition position to that single recesses, that is to say the angular separation of the groups in a pair, and the recesses within those groups is 180°. Preferably, the invention provides a calibration sleeve (which is completely hollow, and as opposed to being in the form of a roll which is more typically takes the form of a solid cylinder and is thus significantly heavier), and the sleeve is preferably of a multi-laminar construction. Preferably the most exterior lamina of the calibration sleeve is essentially a simple metal or alloy tube, most preferably being constituted of aluminium or some alloy thereof, in the exterior surface of which it is relatively easy to precisely and accurately machine or otherwise create the narrow, shallow spaced apart recesses. Most preferably, inside this outer metal tube, there is provided a compressible liner, also of multi-laminar construction, which is most preferably bonded to the inside of the metal tube and which is, yet more preferably elastically radially deformable, for example when subjected to a source of pressurised air, so as to be radially compressible so that the sleeve as a whole can be "blown" on and off a suitable mounting mandrel provided on the plate cylinder or other primary printing or coating rotating support structure. Yet further preferably the sleeve is provided internally at either end with steel end rings which support the overall structure of the sleeve, particularly at each end thereof. Examples of the type of compressible liner which are considered as suitable for the interior of the calibration sleeve of the present invention, and of the overall construction of the calibration sleeve as a whole, can be found in Applicant's own prior patents and applications therefore, for example in WO2017 / 089221, WO2020 / 239843, WO2021 / 078648, among others. Although the proposed construction of the sleeve itself is of lesser importance to the present invention than the nature, position and orientation of the plurality of recesses which are provided in the perfectly cylindrical exterior surface of the sleeve, it is nevertheless important to mention that many advantages of the present invention arise directly as a result of the very lightweight yet robust construction of the sleeve. Indeed, the lightweight sleeves of the invention may, for example, weigh no more than 2-4kg, which means that they can be carried and otherwise manoeuvred by only a single human operative, and also very easily and quickly positioned, installed, and subsequently extracted from relevant print and coating machinery within which the sleeve is required to perform its calibration functions. At this stage, it should also be mentioned that while much of the foregoing and following description of the present invention is restricted to, and to the use of, a calibration sleeve within metal decoration apparatus, and specifically as regards the adjustment of, or identification of the need for replacement of one or more of the form rolls within or associated with the inking stations of such apparatus, the skilled reader will no doubt have already understood that a cylindrical calibration device such as is described herein, whether in roll or sleeve form, could be employed as a means of providing similar calibration of one or more of the applicator rolls within coating apparatus, wherein there is often a similar requirement for accuracy and precision in the application of coating liquids, and within which the applicator roll(s) are, like the applicator or form rolls within metal decoration apparatus, commonly covered or otherwise provided with elastomeric liquidbearing surfaces. Thus both the calibration device of the present invention, and its method of use as further described below, should not be considered as being specifically limited only to specific types of printing apparatus, such as metal decorators, alone. Preferably, end rings are provided at both ends of the sleeve and said end rings are preferably screwed in place end rings. Said end rings are thus preferably provided with screw threads over some portion of, if not all of their exterior cylindrical exterior surfaces such that each may be screwed in to the ends of the aluminium or other metal alloy tube of which primarily constitutes the calibration sleeve. In turn, said calibration is thus also preferably provided, on an inner circumferential surface thereof and extending axially some short distance equivalent to the axial depth of the end rings, with corresponding screw threads (i.e. corresponding in pitch, angle, depth, separation and of corresponding crest height and root depth) to allow the end rings to be fully screwed inside the aluminium tube ends, preferably up to a point where the annular end surfaces of the end rings lie flush with the annular end surfaces of the tube. As described in greater detail in Applicant's own earlier published patents and applications, in order that the calibration sleeve as a whole, and in particular the compressible liner bonded to the interior thereof can function properly, the inner diameter of the end rings much be greater than the inner diameter of the liner in its uncompressed, relaxed state, this configuration thus allowing a small (typically only very few mm, possibly even as little as 1 mm or less) increase in the inner diameter of the liner when subjected to air pressure from the inside, at until it adopts a position in which its inner diameter is the same as that of the inner diameter of the end rings disposed immediately adjacent the annular ends of the liner at either end thereof, and wherein the inner cylindrical surface of the liner lies flush with the inner cylindrical surfaces of the end rings at either end thereof. Preferably, in an outer annular end surface of one or both of the end rings, there is provided one or a pair of registration notches, being recesses, preferably having their exposed edges chamfered, and being machined out of the end ring to a depth less than the overall axial depth of the end ring such that the notch is blind-ended and provided wholly within the end ring itself. Most preferably, the registration notch is machined out from the innermost annular edge of the end ring, and extends radially towards the outermost annular edge of the end ring, terminating before reaching this outermost annular edge such that said registration notch is provided wholly and completely within, said end ring. This registration notch is provided to cooperate with a corresponding registration lug provided at the axially most deep end (often described as the machine side or machine end, as opposed to the more accessible operator side or operator end) of the mandrel that the calibration sleeve is adapted to be mounted on. In a second aspect of the present invention there is provided a method of calibrating one or more cylindrical rotary applicator rolls adapted, in use, to apply a uniformly thick layer of a liquid printing ink or coating fluid to a primary rotary cylindrical printing or coating roll or sleeve conventionally mounted within larger printing or coating apparatus, said applicator roll being constituted of, or being provided with an outermost layer of, a resilient elastomeric material, said method including the steps of: retracting said applicator roll from its conventional operative position in pressurised contact with said primary inking or coating roll or sleeve, dismounting and removing said primary inking or coating roll or sleeve and replacing with a calibration roll or sleeve according to the above first aspect of the present invention, ensuring that the angular position of the calibration sleeve or roll is such that at least a plurality of the axially aligned parallel recesses provided in the exterior cylindrical surface thereof are exposed such that their radial proximity to the adjacent applicator roll(s) is substantially minimised, securing the calibration sleeve or roll to its mounting in this position, returning the applicator roll(s) to their operative position so as to be in pressurised contact with a or multiple relevant portions of the exterior cylindrical surface of said calibration sleeve or roll, and maintaining this condition for a predetermined period of time, again retracting the applicator roll(s) from this conventional operative position and inspecting corresponding relevant portion(s) of their elastomeric exterior cylindrical surfaces for impressions made therein by the recesses of the calibration sleeve or roll, determining from the size, shape, position, orientation, and extent of convergence or divergence of said impressions (a) whether and to what extent the relative current positions and orientations of the axes of rotation of the applicator roll(s) and the calibration sleeve or roll are misaligned, or (b) whether and to what extent the elastomer provided on the applicator roll is misshapen, in the event of (a), effecting a suitable adjustment upon one or more of: the relative positions and orientations of the mounting axes of one or both of the applicator roll and the calibration sleeve or roll, and in the event of (b), replacing the deficient applicator roll, and optionally repeating the relevant calibration steps of this method again, dismounting and removing the calibration sleeve or roll, and returning and remounting the primary printing or coating roll or sleeve, and, returning the applicator roll(s) to their operative position so as to be in pressurised contact with the exterior cylindrical surface of the primary printing or coating roll. Preferably the step of determining whether and to what extent deficiencies (a) and / or (b) exist includes one or both of: visible inspection, and physical measurement, of one or more of the size, shape, position, orientation, and extent of convergence or divergence of said impressions. Most preferably, the method includes the further step of performing a conversion of the inspected and / or measured extent of the deficiencies into one or more required physical adjustment values, said one or more values being representative of one or more of: - a required linear axial adjustment (i.e. indicative of a linear offset amount, being that distance by which the axial position of the applicator roll is offset relative to the calibration roll) - a required radial separation adjustment (i.e. indicative of the adjustment required to move the axis of rotation of the applicator roll, and thus entire applicator roll itself more proximate or distant from the calibration roll or sleeve, which in turn increases or reduces the contact pressure betwixt them to a required level), - one or more required lateral (x-direction) and medial (y-direction) adjustments to the physical position of one end (e.g. the more accessible, operator end) of the axis of rotation (z-direction) of the applicator roll relative to the alternate end of that axis (e.g. the in-machine end), such being indicative of relative axial misalignment between the axis of rotation of the applicator roll and that of the calibration roll or sleeve. Preferably, the step of effecting one or more suitable adjustments is conducted solely on the applicator or form roll(s), and specifically further preferably on the mounting thereof within the printing or coating apparatus, which commonly includes both means to adjust most if not all of: - the axial position of the roll relative to the axial position of the calibration roll or sleeve (and thus the primary printing or coating roll or sleeve when installed), - the radial separation distance between the axes of rotation of applicator roll and calibration sleeve or roll, both unilaterally (i.e. when the applicator roll is moved in its entirety towards or away from the calibration roll or sleeve), and independently (when only one or other end of the applicator roll is moved towards or away from the calibration roll or sleeve, or both such ends are moved but by different amounts, and in one or both of the lateral (x-) and medial (y-) directions). Preferably the predetermined period of time that the applicator roll is maintained in operative pressurised contact with the calibration sleeve or roll is between 5s and 5minutes. A specific embodiment of the invention is now described by way of example and with reference to the accompanying drawings wherein. Brief Description of the Drawings Figure 1 (prior art) shows a schematic outline of the major components of a conventional metal decorator machine, Figure 2 (prior art) shows a perspective view of a single inking station adapted for use in a conventional metal decorator such as shown in Figure 1, Figure 2A (prior art) shows a schematic end elevation of a modified inking station including two form rolls in its conventional operative position adjacent a plate cylinder, which is shown adjacent a blanket wheel and in contact therewith, Figure 3A shows an end elevation of a calibration sleeve according to the present invention, Figure 3B shows an enlarged detail view of a small oval section within the circled area labelled 'B' of the sleeve of Figure 3A, specifically illustrating two adjacent recesses provided in the exterior cylindrical surface, Figure 3C shows a sectional elevation of the sleeve of Figure 3A on A-A as indicated in that Figure, Figure 3D shows an enlarged detailed view of the circled area D in Figure 3A, in which a registration notch provided in the end ring is shown in greater detail, Figure 3E shows a sectional view through the registration notch illustrated in Figure 3D on the line C-C indicated in that Figure, Figures 4A-D show, purely schematically and respectively, - a perspective view of a calibration sleeve according to the present invention and an immediately adjacent form roll in a state of misalignment, - an end elevation of the sleeve and form roll of Figure 4A, - a perspective view on of the form roll of Figure 4A in up-ended, vertical orientation, after having been in pressurised contact with the calibration sleeve for a predetermined time period, such that the resulting impression lines created by the calibration sleeve thereon as a result of that contact are clearly visible, - a perspective view on of the form roll of Figure 4A in up-ended, vertical orientation, after having been subjected to corrective adjustment, and then again brought into pressurised contact with the calibration sleeve for a predetermined time period, and Figures 5A, 5B show, purely schematically and respectively, - a perspective view of a form roll, a central region of which has become permanently expanded through use, - - a perspective view on of the form roll of Figure 5A in up-ended, vertical orientation, after having been in pressurised contact with the calibration sleeve for a predetermined time period, such that the resulting impression lines created by the calibration sleeve thereon as a result of that contact are clearly visible. Detailed Description Referring firstly to Figure 1, a conventional Concord™ metal decorator machine 2, of the type generally available from the Stolle Machinery Company is illustrated. Open topped can bodies 4, illustrated in the Figure simply as black dots given their end-on representation in the Figure, are fed individually (at usually very high infeed rates, e.g. many hundreds or even thousands of cans per minute "CPM") into a can infeed and transfer mechanism 6 whereby each can is transferred to one of the many individual mandrels provided around a mandrel wheel 8. Said mandrel wheel in this case is provided with 32 individual mandrels, each of which is capable of individual mechanical actuation (e.g. expansion and contraction to grip and release the interior of the can body), and each of which is individually resiliently mounted on the mandrel wheel, for example using some form of spring biased mounting mechanism such that each mandrel and thus the can body thereon is biased towards the outer reaches of the mandrel wheel and adopts a position such that a most radially remote portion of any can body lies approximately coincident the circular periphery of the mandrel wheel itself. In the machine shown, mandrel wheel 8 is configured to rotate in a clockwise direction as shown by arrow 9, progressively bringing each mandrel and can body thereon into direct contact with an ink blanket wheel 10, which is driven in the opposite anticlockwise direction, as shown at arrow 12. Around the outside of ink blanket wheel 12 are arranged 8 individual, distinct and separate inking stations 14, 16, 18, 20, 22, 24, 26, 28, each being provided with a respective printing plate cylinder 14A, 16A, 18A, 20A, 22A, 24A, 26A, 28A each of which, if operative, transfers a wet ink pattern of a particular colour ink consecutively to each of the (in this case) 12 areas of the exterior cylindrical surface of the blanket wheel designated to receive the wet ink patterns, so that what results on each of said areas after any one has been rotated under the ink transfer rolls of all the ink stations is a complete, composite wet ink image which, as a result of the further rotation of the blanket wheel is brought into contact with the exterior cylindrical surface of a can body, in the instant illustrated in the Figure, at nip point 30. As a result of the contact between the ink blanket wheel and the can body, the underlying mandrel supporting the can is deflected inwardly of the mandrel wheel against the spring bias, and while it is contact therewith, the can body naturally rotates on the mandrel as a result of both the contact pressure between can body and ink blanket wheel, and the relative and opposite motions of the ink blanket wheel and the mandrel wheel. After the wet ink composite image has been completely transferred in this manner, the can body emerges from the contact area in fully printed state, and in the instant depicted in the Figure, such a printed can is referenced at 32. Continued clockwise rotation of the mandrel wheel then causes each printed can body to enter a varnishing unit indicated generally at 34 which transfers a thin, uniform, unpatterned layer of varnish over the entirety of the printed exterior of the can body, thus effectively encapsulating the printed image beneath the varnish. Thereafter, subsequent transfer rolls 36, 38, lift the can bodies from the mandrel and transport them away to, for example, and oven or similar varnish curing facility (not shown) before the completed open-topped can bodies are then collected for packaging. As the skilled reader might may appreciate from the foregoing, there is an additional requirement, within the metal decorator itself, for extremely precise registration of the various component parts of the machinery - in short, all the various component parts of the machine must work completely in unison and in precise registration with one another for successful decoration and varnish coating of any one individual can. Therefore, not only are the various different rotary and reciprocating components within the decorator often mechanically geared or otherwise linked together, there are numerous static and dynamic operation characteristics of practically all of the major components of the machinery which can be minutely adjusted to ensure that each and every can received by and exiting from the machine is properly printed, coated, and otherwise decorated. Referring now to Figure 2, there is shown a perspective view of a known inking station assembly 200, and in this regard further reference should be had to US2012272846A1 to Stolle Machinery Company Inc. As illustrated and described in that document (salient portions of which are reproduced briefly here purely to aid understanding of the present invention), the ink station assembly 200 includes an ink fountain 202 structured to provide a supply of ink 400 (shown in phantom line drawing). A fountain roll 204 receives the ink 400 from the ink fountain 202. The ink station assembly 200 further includes a distributor roll 206 and a ductor roll 208 that cooperates with both the fountain roll 204 and the distributor roll 206 to transfer the ink 400 from the fountain roll 204 to the distributor roll 206. A number of oscillator rolls 210,212 (two are shown) each include a longitudinal axis 214,216, respectively. The oscillator rolls 210,212 are structured to oscillate back and along longitudinal axes 214,216, respectively, and thus oscillate laterally of and within the ink station. By way of example, and without limitation, it will be appreciated that oscillator roll 212 in the example oscillates back and forth along axis 216 in the directions generally indicated by arrow 217. Oscillator roll 210 (partially shown) oscillates back and forth along longitudinal axis 214 in a similar manner. It will further be appreciated that, although the example shown and described herein includes two oscillator rolls 210,212, that any known or suitable alternative number and / or configuration of oscillator rolls (not shown) could be employed. The example ink station assembly 200 also includes two transfer rolls 218, 220, each of which cooperates with at least one of the oscillator rolls 210,212. It will be appreciated, however, that any known or suitable alternative number and / or configuration of transfer rolls (not shown) other than that which is shown and described herein, could be employed. A printing plate cylinder 222 includes a printing plate (generally indicated by reference number 224), and cooperates with a single applicator or form roll 230 to apply the ink 400 to the printing plate cylinder 222, and more specifically to the one (or possibly two) printing plates 224 removably secured thereto, as will be described in greater detail hereinbelow. As can be understood from the above and the Figure, the exemplary ink station assembly 200 includes a total of nine rolls (e.g., fountain roll 204, distributor roll 206, ductor roll 208, first and second oscillator rolls 210,212, first and second transfer rolls 218,220, single form roll 230, and rider roll 240), and all these rolls together, with the possible exclusion of the terminal form roll 230, can be regarded as a collective "train" of rolls which are typically arranged one after another. The overall purpose of this train of rolls is ultimately to move ink progressively and increasingly uniformly, as regards the coating applied to successive rolls within the train, from the fountain to the terminal form roll 230. In order for a precisely even, consistent, and uniformly thick layer of ink to be repeatedly applied by said form rolls to respective adjacent plate cylinders throughout any print run, or at least to maximise the chances of achieving this desired optimum performance, it is usually always necessary, and certainly always advised, to perform some preliminary adjustments, particularly as regards the position and orientation of the terminal form rolls of each ink station which is to be operative during any print run. In this particular regard, further reference is to be had to Figure 2A which provides a schematic end elevation view of the relevant end of a modified inking station indicated generally at 250, and which is provided, in this particular case, with a pair of form rolls 252, 254 in contact with a plate cylinder 256 on which a pair of printing plates are mounted, each occupying the majority of each of notional two halves of the total circumferential area of the plate cylinder. To complete the conventional arrangement, the plate cylinder 256 is shown adjacent and in contact with a larger blanket wheel 258. This figure is provided by Stolle themselves as part of their own proprietary instructions on how the form rolls 252, 254 should be adjusted to ensure their position and orientation are correct, relative to the plate cylinder. A brief paraphrased version of these instructions is as follows: In order to set the parallel position and contact of the form rolls relative to the plate, the following steps are required: 1. loosening lockbolts (not shown) for both an inside adjusting lever (not shown) and the outside adjusting knob (not shown) for the upper form roll 252, 2. turning the inside adjusting lever until there is a clearance of 1 / 16 inch (1.5875mm) between the form roll 252 and the printing plate (not shown) on the plate cylinder 256, 3. Using a direct light source, such as a professional torch , directing a beam of light between the full length of the form roll and the printing plate to see a clearance between the two, 4. (a) If the form roll and printing plate are parallel, go to step (5) (b) If the form roll and printing plate are not parallel, rotate the outside adjustment knob until they are, 5. Re-tightening the lockbolt on the outside adjustment knob, 6. Rotating the inside adjustment lever until the roll contacts only the raised section ofthe printing plate. The amount of measurable contact is should be approximately .0005 inch (0.0127mm). If a "feel" method is used, then there should be only a light feeling of contact on the raised portion of the printing plate. Thus, as can immediately understood from the above, not only the current assessment of the alignment and position ofthe form roll(s) performed purely by eye, but there is practically no further guidance provided to an operative as to the actual physical extent of misalignment or the extent to which the form roll is too proximate or too remote from the plate cylinder. Indeed, these types of adjustment technique border on pure guesswork. In order to provide a ready means and method whereby the nature and extent of form roll adjustments required can be quickly, easily and accurately ascertained, the present invention provides a calibration sleeve, and method of using such a sleeve as further described below in reference to Figures 3A-3F. Referring firstly to Figure 3A there is shown an end elevation of a calibration sleeve according to the present invention and indicated generally at 300. The sleeve itself consists of an aluminium tube 302 having a radial thickness of between 5-10mm, ideally about 7-8mm, inside of which there is bonded a cylindrical annular compressible liner (not shown or referenced in this Figure, but see Fig. 3C and description thereof below) which in this particular embodiment (though not necessarily in all embodiments) is of similar thickness to the tube. The axial length of the compressible liner is less than that of the tube so that when disposed axially centrally within the tube and bonded to the inside thereof in this position, rebated end regions are effectively defined inside the tube by the annular end surfaces ofthe liner and the remaining exposed cylindrical interior surface ofthe tube, and it is into these regions that a pair of end rings, one of which is referenced at 304 in Figure 3A, are screwed to complete sleeve construction. Most preferably, in the completed sleeve, the annular end surfaces of the end rings 304 lie perfectly flush with the adjacent annular end surfaces of the tube, and the inner diameter of the end rings is marginally greater than the inner diameter of the immediately adjacent liner, for example by an amount in the range 0.5mm-4mm. Thus, in its uncompressed condition, the liner is effectively (radially) thicker than the end rings, and therefore an annular shoulder portion of the liner (of a thickness between 0.25mm-2mm) remains exposed immediately behind the end rings inside the sleeve (see Figure 3C and description thereof for further details). Applicant herefor has made significant recent advances in this type of sleeve construction, and particularly with regard to providing fluid-impregnable seals between the annular end surfaces of the liner and the immediately adjacent annular end surfaces of the end rings. In general however, it is known to provide sleeves having functional exterior surfaces adapted for printing or coating with interior compressible liners in order that they can be easily mounted and dismounted from a mandrel by means of pressurised air. As the present invention is not especially concerned with the specifics of the sleeve construction, except that any sleeve of the present invention should be capable of being mounted and dismounted equally quickly and easily as the printing or coating sleeve it temporarily replaces, further description of the sleeve construction is not provided in the interests of brevity. Returning to Figure 3A, there are shown in the Figure a first set of lines, some of which are referenced at 306, and a second set of lines, some of which are referenced at 308, and all these lines (20 lines 306, and 20 lines 308, so 40 altogether) extend diametrally through a centre point 310, which also defines the position of the central rotational axis of the sleeve. It is to be understood that these lines 306, 308 are notional and exist only in the illustration, and are provided as a means of indicating the 80 positions on and around the circumference of the exterior cylindrical surface of the sleeve whereat recesses are to be provided (as further described below), said recesses extending axially substantially or completely from one end of the sleeve to the other and being in perfect axial alignment with the central rotational axis of the sleeve, one end of which is indicated at 310. Thus, as the skilled reader will understand from the arrangement and number of lines in the figure, 80 axially extending recesses are to be provided in the exterior cylindrical surface of the aluminium tube, and these 80 recesses, being essentially grooves or so-called "scribe lines", are arranged circumferentially around the exterior cylindrical surface of the tube in two pairs of groups 320A, 320B and 322A, and 322B, with each group of any pair containing 20 recesses, and any single recess within any group being exactly diametrically opposite a corresponding recess in the alternate group in a particular pair. In the specific embodiment illustrated, the total angle subtended between any first and last line 306 (or 308) in any group, and thus between the circumferential midpoints of the first and last recess in any group is 28.604°, but of course the present invention covers a wide range of possible circumferential recess spacings. Indeed, it is not so much the exact circumferential spacing of the recesses themselves which is important, more that there are a plurality of recesses which are spaced apart from one another, circumferentially, by a relatively small amount, axially parallel to each other and all in perfect alignment with the central axis of the sleeve, very narrow and shallow, relative to the overall circumferential and thickness dimensions of the Aluminium tube in which they are provided, and thus the sleeve as a whole. There are good reasons for all of the above features, as will become apparent from the following description, but it is worth explaining here the reason why a relatively small circumferential spacing between any two adjacent recesses is advantageous. As previously mentioned above, the calibration roll or sleeve of the present invention is adapted to calibrate adjacent form or applicator rolls or sleeves which usually have elastomeric exterior surfaces which are thus resilient, and elastically deformable, for example under the typical slight contact pressure they exert against the primary printing or coating roll when in their conventional operative position. Likewise when a calibration roll or sleeve according to the present invention is used to temporarily replace the primary printing or coating roll or sleeve, and the form roll or sleeve is brought into position against it, the exterior surface of the applicator roll is identically elastically deformed, because the calibration roll or sleeve is specifically designed to have an identical exterior diameter dimension to that of the primary printing or coating roll it temporarily replaces for the purpose of calibration and preliminary set up. In any event, regardless of which roll or sleeve is mounted within the larger apparatus, the fact that the exterior surface of the applicator or form roll is of an elastomeric, resiliently deformable material means that, instead of a line of contact betwixt the two rolls or sleeves (as there would be if the contacting exterior surfaces of both rolls or sleeves were constituted of metal), there is an area of contact, said area being (at least) that area of the form or applicator roll which is deformed. Of course, this area will still be within a relatively small sector of the applicator roll or sleeve, one maybe only 2-3° wide or even less, and therefore if at least a pair of recesses provided in the exterior surface of the calibration sleeve or roll are to make an impression within this area, then not only must the calibration roll or sleeve be generally in the correct angular position so that the recesses (or group thereof) are exposed and proximate the applicator or form roll prior to engagement thereof with said calibration sleeve, but said recesses must also be disposed sufficiently closely together such that both said recesses (or at least two within a larger group of recesses) lie within the eventual contact area created on the applicator or form roll or sleeve when it is brought into its conventional operative position against the calibration sleeve or roll. Returning now again finally to Figure 3A, the end of the sleeve visible in the figure is provided with a registration notch 330, specifically machined out of and subsisting entirely within the end ring 304. Registration notch 330 is described in greater detail below with reference to Figures 3D, 3E. To provide some further specific dimensions and to give the reader some context as to the general size of the sleeves commonly in use in metal decoration apparatus, the sleeve illustrated and described herein has an external diameter of 228.36mm. Referring to Figure 3B, showing the enlarged detail of a portion of the exterior cylindrical surface of the sleeve of Figure 3A, a pair of adjacent recesses 312, 314 can be clearly seen. With the total angle that a group of recesses extends over being, as mentioned above, 28.604°, this means that for 20 recesses in a group, the angular separation is 1.5055° (28.604 / 19), equating to a physical arcuate separation distance of 3mm, for a sleeve having an external diameter as given above. As regards the width and depth of the recesses, as previously mentioned above, in order for any recess to make any good impression in the applicator or form roll when brought into pressurised contact against the calibration roll or sleeve, the recess is preferably be relatively narrow and sufficiently deep that the recess is more groove like than merely some imperceptible depression in the surface of the calibration roll or sleeve. In the specific embodiment shown, the recess width is 0.25mm and the depth is the same. These dimensions give the recess sufficient groove-like qualities, and indeed when the width and depth dimensions are the same, as is most preferred, then the recess cross-section is actually square, hence the commonly used term "square groove". In any event, it has been found by Applicant that these dimensions result in recesses which leave good, visible, and reasonably long-lasting (e.g. of the order of a few minutes at least, and certainly not permanent) impressions in the surface of most common applicator or form rolls or sleeves. In most preferred arrangements, one or both the recess width and depth may be between 1 / 5 and 1 / 20 of the circumferential distance between any two adjacent recess. In other preferred arrangements, the preferred depth of the recesses will be less than 1mm. Referring nowto Figure 3C, the calibration sleeve 300 of the present invention is shown in sectional elevation along its length, and all of the aluminium tube 302, the end rings 304, and now the interior compressible liner 310 can all be clearly seen. Again, to provide some further specific dimensions for the illustrated sleeve, the overall total length is 180.975mm, and interior diameter of the end rings is 197.47mm. The interior diameter of the liner in its uncompressed, relaxed condition (illustrated) will be marginally less than this, e.g. 195-196.75mm, so the liner will project into the interior of the sleeve beyond the end rings slightly, as previously mentioned above. Referring briefly to Figures 3D, 3E, registration notch 330 is shown in greater detail in these Figures, and it can be seen in Fig. 3D that the notch has a radial dimension which is less than the total annular thickness of the end ring 304, and thus the registration notch subsists and defined completely and only within the end ring. Furthermore, as can be seen from both Figures 3D and 3E together, the depth of the registration notch is less than the total depth (measured in the axial direction of the sleeve) of the end ring, and therefore the registration notch is blind ended and terminates within the end ring. Finally, the outermost edges of the registration notch, particularly those edges which are within, or at the inner most circular edge of, the annular end surface of the end ring, are chamfered, such chamfered surfaces 332 acting as guide means for guiding the machine-side lug, pin or other protrusion (not shown) into the notch when lug and notch are in approximate, but not exact registration. Naturally, when said lug and notch are in complete registration, the lug is received completely in the notch, and the calibration sleeve is then locked in position because the notch effectively prevents any angular displacement of the calibration sleeve relative to its mounting (and to the lug) when the lug is completely and most preferably also snugly received in said notch. Referring now to Figures 4A-4F, in Figure 4A a calibration sleeve 300 according to the present invention and a form roll or sleeve 400 are schematically shown in perspective and in mutually contacting relationship. As the skilled reader will understand, no other parts of the decorator machinery or inking station in which these rolls or sleeves are mounted are shown, but it is to be understood that the calibration sleeve 300 is fully and completely mounted with such decorator apparatus in an identical position, and in identical manner to the primary printing plate cylinder it temporarily replaces. As required by the present invention, the external diameter of the calibration sleeve is chosen so that it is identical to that of the primary printing plate cylinder, including the printing plate mounted therearound so that when the relevant inking station, of which the form roll forms a terminal part, is brought into its conventional operative position, the position and orientation of the form roll relative to the calibration sleeve, and thus the contact pressure exerted by the former on the latter, are exactly the same as would be the case when the primary printing plate cylinder were mounted within the decorator machine. As can also be seen from Figure 4A, respective axes of mounting 300A, 400A, and thus rotation, are shown for each of the calibration sleeve 300 and form roll 400 respectively, if these axes are considered to be, in Cartesian notation, the "z" direction axes for each of the said sleeve and roll, then (for the roll only), a pair of orthogonal x,y axes are also illustrated, one being at the front, operator end of the form roll, Xi, yi, and one being at the rear or machine-side end of the form roll, X2, y2. Again these references are provided only to aid understanding. Additionally, it will be immediately from the Figure that there is significant misalignment between axes 300A and 400A, by an angular amount 6°. Again, this extent of misalignment is significantly exaggerated in the Figure to ease understanding - in practice any relative misalignment there might be (and often is) between the respective mounting axes of the calibration sleeve (and thus plate cylinder) and the form roll is generally not perceptible, or is only barely perceptible, by the human eye, and this is one reason at least that the calibration sleeve of the present invention proves very useful, as will become apparent from the further description below. Finally, in the Figure, a large blanket wheel is shown in dotted outline and referenced generally at 402, with an area 404 thereon also shown in dotted being an area to which, during conventional operation of the decorator apparatus, that an inked printing plate provided on a plate cylinder would transfer a pattern of wet ink to as blanket wheel and plate cylinder mutually rotated in opposite directions, as indicated by arrows 406, 300B. The direction of rotation of the form roll 400 is of course the same as that of the blanket wheel, given the configuration of the various components, and is indicated at 400B. In the arrangement shown in Figure 4A, it is immediately obvious that some correction of the relative misalignment between the mounting axes of calibration sleeve and form roll is required. As the axis of mounting of the calibration sleeve (being one and same as that for the printing plate cylinder) cannot generally be adjusted, and indeed in practice is presumed fixed and perfectly aligned to that of the much larger adjacent blanket wheel, it is thus generally always the form roll itself, and in particular the lateral (herein referenced by the x-axes, Xi, X2) and medial (herein referenced by the y-axes, yi, y2) position of one or both ends of the form roll 400 which are adjusted in order to correct the position and orientation of that roll. For example, the skilled reader will immediately understand from Figure 4A that an adjustment of the position of the front end of the form roll 400 in the general direction of the dotted arrow 408 would achieve the required alignment of the respective mounting axes. Referring briefly to Figure 4B, which shows a schematic end elevation of the arrangement of Figure 4A, it can be seen that an adjustment in the position of the orthogonal axes Xi, yi by amounts -Ax, and +Ay, while the alternate end of the form roll remained fixed in place, would bring the respective mounting axes of form roll and calibration sleeve into axial alignment, but of both the physical x and y adjustment distances will be small, and furthermore must be very carefully chosen so as to achieve not only the required relative axial alignment with the plate cylinder, but also to ensure that the contact pressure that is exerted by the (relatively much harder) calibration sleeve on the form roll is uniform and consistent over the entire axial length of the form roll. To explain further, it is not only the relatively axial alignment between the form roll and calibration sleeve that is important - the contact pressure between the two is equally, if indeed not more important. Indeed it is regarded in some circumstances as critically important that this contact pressure is not only uniform over the entire axial length of the contact area between the form roll and calibration sleeve, but also that its scalar value is correct, that it is to say that the contact pressure is neither too great (in which case too significant a quantity of ink is transferred to the printing plate and which can result in blurring, loss of resolution, and / or unwanted spreading or expansion of details in the ultimately printed image) nor too little (in which case there is insufficient ink transferred to the printing plate, known as ink starvation, leading to unprinted areas, such as pinholes or larger ink-starved areas appearing within the ultimately printed image) Although the relative misalignment between the mounting axes is immediately apparent from Figure 4A, what is not at all apparent is the extent to which one, other or indeed both ends of the form roll too close to the calibration sleeve (meaning a contact pressure which is to great at the said one or other end, or entirely along the axial length of the form roll), or is too remote from said calibration sleeve (meaning insufficient contact pressure at the said one or other end, or entirely along the axial length of the form roll). Referring briefly to Figure 4C, the form roll is shown (schematically) in isolation and in a vertically upright position so that an area thereof is visible, said area being the contact area and against and on which the calibration sleeve exerts a contact pressure when the form roll and calibration sleeve are in their conventional operative positions, as illustrated in Figure 4A. As can be seen from Figure 4C, impression lines 410 are visible, these resulting from impressions made in the elastomeric resiliently deformable surface of the form roll by the closely spaced recesses provided in the exterior cylindrical surface of the calibration sleeve. It is important to note here that not only are impression lines 410 clearly forwardly inclined relative to the central axis (which of coincides with the axis of mounting 400B) of said form roll by an amount 0°, but also there is some change in the weight of the impressions over their length, for example the degree to which they are or become quite or very faint, or even entirely absent, or where they are or become quite or very pronounced, possibly to the point of merging together in places. In the Figure 4C, it can be seen that the lower (machine side) ends 410A of the impression lines 410 are more faint than the upper operator side) ends, and therefore it can immediately been seen by any operative that some additional adjustment is required in order to achieve the desired arrangement of impression lines 412 shown in Figure 4D, wherein the impression lines are not only axially aligned with the central axis 400B, but also of generally even and constant weight along their entire length. Thus the impression lines 410 not only provide a ready immediately visible indication of axial misalignment, but they also provide an equally ready and visible indication of the degree to which the contact pressure between form roll and calibration sleeve (and thus printing plate cylinder) is sub-optimal in some respect, both in terms of axial variation along the form roll and more generally in terms of a general excess or insufficiency. Finally these impression lines also provide a ready indication as to how the position and orientation deficiencies can be corrected so that the respective rolls are both aligned, and sufficiently proximate one another, at both ends, so that the contact pressure exerted by the calibration sleeve on the form rolls is approximately constant, uniform, and sufficient, and so that ultimately, post-adjustment, the impressions lines created on the on the form roll appear as illustrated in Figure 4D. As regards the benefit derived from using the calibration sleeve according to the present invention, Applicant has found not only that the time taken to perform the required preliminary set-up procedures can be substantially reduced, but also that the overall accuracy and precision of form roller setting in general is markedly improved. For example, conventional preliminary form roll adjustment and set-up procedures can often take as much as 20-30 minutes to perform, for each inking station which is to be operative in a print run, meaning that for complex print runs wherein all 8 inking stations are to be operative, individually adjusting each of the 8 form rolls can often take as much as 3-4 hours to perform, depending on the extent to which each of the form rolls is currently misaligned relative to their respective plate cylinders, or is disposed too proximate or too remotely therefrom. When it is considered that modern decorators when operating at full capacity, have throughputs in excess of 2000 CPM, such machine downtime represents a very significant loss in production - at this rate of production, in excess of 20 million cans could foreseeably be produced in a period of 3 hours, so the skilled reader will immediately understand that any means whereby machine downtime is substantially reduced can have immediate, real and very significant benefits. A further possible benefit of the calibration sleeve according to the present invention is that, by using the sleeve in the manner previously described, it is also possible to quickly identify when the exterior elastomeric surface of any form roll is already plastically deformed such that its usually generally perfectly cylindrical exterior surface is no longer so. This is a common problem, because over time, the often chemically aggressive printing inks (and for that matter, coatings such as lacquers and varnishes) that are used can impregnate the surfaces of the form rolls (and other coating and / or applicator rolls and sleeves). Naturally, this impregnation is or becomes most pronounced over that axial portion of the roll which contacts the printing plate cylinder (or other primary coating roll or sleeve), not least because the contact pressure that exists between the form roll and plate cylinder during conventional operation can actively promote irreversible fluid impregnation of the former. Referring briefly to Figures 5A, 5B, form roll 400 is again depicted, with it's exterior surface visibly misshapen and deformed into a condition wherein an axially central region of the form roll has become expanded relative to the end regions. In these Figures the deformity is significantly exaggerated so as to be visible, but it should be understood that in production form rolls it is often invisible to or imperceptible by the naked eye. A further advantage of the calibration sleeve or roll of the present invention is that utilising such a sleeve can immediately identify to an operative when any form roll is deformed in this manner, and thus should be replaced, because when the calibration sleeve is brought into pressurised contact with such a form roll, the impression lines 414 (see Figure 5B) created in the exterior surface of the roll are nonlinear and instead curved, often progressively increasingly, away from one another, and in opposite circumferential directions away from a central one of the impression lines 414, which may indeed be relatively straight. Thus these impression lines, and this particular arrangement and appearance thereof, immediately and visibly indicates to an operative that there is some pervasive deformity in the exterior cylindrical surface of the form roll. As this type of deformity is generally permanent, and cannot otherwise be cured by adjusting the position and orientation of the form roll relative to the calibration sleeve, the only correct solution to the problem is either to replace the deficient form roll in its entirety, or at least to remove the deficient elastomeric covering thereon, clean the relevant underlying surface of the form roll, and then dispose a new sleeve of elastomeric material therearound. Of course, the arrangement of impression lines 414 shown in Figure 5B, being axially aligned and of relatively uniform weight, is indicative of a form roll which is generally correctly positioned and orientated. It is certainly possible that in addition to the impression lines 414 being curved in the manner shown, they could additionally be inclined relative to the central axis of the form roll, and furthermore be off different and varying weights along their length. That is to say, the pattern of impression lines created in the form roll exterior surface could be a combination of the pattern shown in Figure 4C and 5B. In any event, again, the impression lines which are created in the form roll provide a ready, visible, and easily recognisable indication of both the extent to which the form roll is axially misaligned, too proximate or too remote from the calibration sleeve, at one, other or both ends thereof, and also whether there is any more pervasive and (often) 5 permanent deformity in the usually perfectly cylindrical exterior surface thereof.

Claims

1. A calibration roll or sleeve adapted to be temporarily rotationally mounted in printing or coating apparatus in place of, and in identical manner to, the primary inking or coating roll or sleeve conventionally mounted therein and to which, in use, is typically applied a layer of liquid ink or coating fluid by one or more applicator rolls also rotationally mounted within said apparatus, said one or more applicator rolls having a cylindrical exterior surface constituted of or covered with a resilient elastomeric material, said apparatus further comprising means whereby the relative position and orientation of the axes of rotation of the primary inking or coating roll or sleeve and the one or more applicator rolls can be adjusted, characterised in thatsaid calibration roll or sleeve being has an exterior cylindrical surface of diameter D and is constituted of a first material which is rigid compared to the elastomeric material of the applicator roll in that it has a modulus of elasticity (Young's modulus, E) which is at least one order of magnitude greater than that of the elastomeric material,said calibration roll or sleeve further being provided, in and along substantially the entire axial length of the exterior cylindrical surface thereof, with a plurality of axially aligned parallel recesses which are circumferentially spaced apart by a circumferential arc having a length less than or equal to ttD / 72 and having width (w) and depth (d) dimensions which are both less than 1.5mm, said recesses being in precise alignment with the longitudinal axis of the calibration roll or sleeve, where dimension D of the calibration roll or sleeve is exactly the same as the corresponding exterior diametral dimension of that or those surfaces of the primary inking or coating roll or sleeve to which ink or coating fluid is applied by said applicator roll such that the calibration roll or sleeve exerts the same contact pressure on said applicator roll when temporarily installed in said apparatus as would the corresponding primary inking or coating roll during production, and whereby, when said applicator roll is brought into its conventional operative position against the calibration roll or sleeve when angularly positioned to ensure that at least a plurality of the axially aligned recesses in the exterior cylindrical surface thereof lie within the contact region betwixt the respective rolls or sleeves, said recesses leave an impression in the elastomeric material of the applicator roll which is not only immediately visible to the naked eye when the applicator roll or sleeve is retracted from its conventional operative position, but also immediately indicative of one or more of the following potential positional, orientational or surface characteristic deficiencies:- the extent to which the exterior surface of the applicator roll is, or is not perfectly cylindrical, - the relative degree of parallelism or axial misalignment of the axes of rotation of the calibration roll or sleeve and the applicator roll, and- the relative proximity of the axes of rotation of the of the calibration roll or sleeve and the applicator roll, and thus the degree to which said axes of rotation may be excessively or insufficiently distant, at one end or another, or along the entire length thereof.

2. A calibration roll or sleeve according to claim 1 wherein the recesses provided in the calibration sleeve or roll are created by precise and repeated machining carried out on the exterior cylindrical surface of said sleeve or roll by means of computer numerical control (CNC) metal component machining apparatus.

3. A calibration roll or sleeve according to any preceding claim wherein the total actual number of recesses provided in any one circumferential region of the calibration sleeve or roll is one of:at least 2, at least 4, at least 10, at least 20.

4. A calibration roll or sleeve according to any preceding claim wherein the plurality of recesses are grouped together in pairs of groups of recesses, with the number of pairs of said groups being one of: at least one, at least two.

5. A calibration roll or sleeve according to claim 4 wherein the recesses forming part of any group are arcuately equidistantly spaced apart by a maximum arcuate separation distance of ttD / 72.

6. A calibration roll or sleeve according to 4 or 5 wherein a first group in any pair of groups of recesses extends around an arc length of the exterior cylindrical surface of the roll or sleeve having a length of N(nD / 72+w) + w, where N is the number of recess provided in the group, and w is the width dimension of any single recess, and 4<N<20.

7. A calibration roll or sleeve according to claim 4 or any claim dependent thereon whereinany first group in any pair of groups of recesses is provided in a position around the exterior cylindrical surface of the roll or sleeve which is exactly diametrically opposed to the position of the second group in that pair.

8. A calibration roll or sleeve according to claim 4 or any claim dependent thereon wherein any single recess in any single group has a corresponding recess which lies in a diametrically opposition position to that single recesses.

9. A calibration sleeve according to any preceding claim and which is of a multi-laminar construction, the first most exterior lamina of the sleeve being constituted of a simple metal or alloy thereof, and a second, innermost lamina being a compressible liner bonded to the inside of the first lamina and which is elastically radially deformable.

10. A calibration sleeve according to claim 9 provided internally at either end with steel end rings which support the overall structure of the sleeve, particularly at each end thereof.

11. A calibration sleeve according to claim 10 wherein, in an outer annular end surface of one or both of the end rings, there is provided at least one registration notch.

12. A method of calibrating one or more cylindrical rotary applicator rolls adapted, in use, to apply a uniformly thick layer of a liquid printing ink or coating fluid to a primary rotary cylindrical printing or coating roll or sleeve conventionally mounted within larger printing or coating apparatus, said applicator roll being constituted of, or being provided with an outermost layer of, a resilient elastomeric material, said method including the steps of:retracting said applicator roll from its conventional operative position in pressurised contact with said primary inking or coating roll or sleeve,dismounting and removing said primary inking or coating roll or sleeve and replacing with a calibration roll or sleeve according to the above first aspect of the present invention, ensuring that the angular position of the calibration sleeve or roll is such that at least a plurality of the axially aligned parallel recesses provided in the exterior cylindrical surface thereof are exposed such that their radial proximity to the adjacent applicator roll(s) is substantially minimised,securing the calibration sleeve or roll to its mounting in this position, returning the applicator roll(s) to their operative position so as to be in pressurised contact with a or multiple relevant portions of the exterior cylindrical surface of said calibration sleeve or roll, and maintaining this condition for a predetermined period of time, again retracting the applicator roll(s) from this conventional operative position and inspecting corresponding relevant portion(s) of their elastomeric exterior cylindrical surfaces for impressions made therein by the recesses of the calibration sleeve or roll, determining from the size, shape, position, orientation, and extent of convergence or divergence of said impressions (a) whether and to what extent the relative current positions and orientations of the axes of rotation of the applicator roll(s) and the calibration sleeveor roll are misaligned, or (b) whether and to what extent the elastomer provided on the applicator roll is misshapen,in the event of (a), effecting a suitable adjustment upon one or more of: the relative positions and orientations of the mounting axes of one or both of the applicator roll and the calibration sleeve or roll, and in the event of (b), replacing the deficient applicator roll, and optionally repeating the relevant calibration steps of this method again, dismounting and removing the calibration sleeve or roll, and returning and remounting the primary printing or coating roll or sleeve, and,returning the applicator roll(s) to their operative position so as to be in pressurised contact with the exterior cylindrical surface of the primary printing or coating roll.

13. A method according to claim 12 wherein the step of determining whether and to what extent deficiencies (a) and / or (b) exist includes one or more of:visible inspection, and physical measurement, of one or more of the size, shape, position, orientation, and extent of convergence or divergence of said impressions.

14. A method according to claim 12 or 13 wherein the method includes the further step of performing a conversion of the inspected and / or measured extent of the deficiencies into one or more required physical adjustment values, said one or more values being representative of one or more of:- a required linear axial adjustment (i.e. indicative of a linear offset amount, being that distance by which the axial position of the applicator roll is offset relative to the calibration roll)- a required radial separation adjustment (i.e. indicative of the adjustment required to move the axis of rotation of the applicator roll, and thus entire applicator roll itself more proximate or distant from the calibration roll or sleeve, which in turn increases or reduces the contact pressure betwixt them to a required level),- one or more required lateral (x-direction) and medial (y-direction) adjustments to the physical position of one end (e.g. the more accessible, operator end) of the axis of rotation (z-direction) of the applicator roll relative to the alternate end of that axis (e.g. the in-machine end), such being indicative of relative axial misalignment between the axis of rotation of the applicator roll and that of the calibration roll or sleeve.

15. A method according to any of claims 12-14 wherein the step of effecting one or more suitable adjustments is conducted solely on the applicator or form roll(s), and specifically on the mounting thereof within the printing or coating apparatus.5 16. A method according to any of claims 12-15 wherein the predetermined period of time thatthe applicator roll is maintained in operative pressurised contact with the calibration sleeve or roll is between 5 seconds and 5 minutes.

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