Lock-up Mechanism For Flexible Printing Plates Providing Improved Reference Adjustment

Abstract

A plate lock-up mechanism which includes a longitudinally extending mounting bar for securing the end of a printing plate and recessed, for limited circumferential and axial movement, in a groove formed in the plate cylinder. Adjustment in the two directions is obtained by circumferentially extending and axially extending screws engaging the walls of the groove. Seated in the groove at each end of the bar is a reference member having flat, circumferentially facing and axially facing surfaces. Mounted on the ends of the bar and overlying the reference members are index member having corresponding circumferentially and axially facing surfaces. The members are adjusted to such position that when the bar and plate occupy a reference position with respect to the cylinder, the circumferentially facing and axially facing surfaces on the members are in precise coplanar alinement, the surfaces being spaced closely edge-to-edge and sufficiently extensive so that the coplanar relationship may be detected by sight or touch. During subsequent adjustment to achieve registration of the printed impressions, the amount of offset of the index surfaces with respect to the reference surfaces provides constant and exact indication of the degree of circumferential offset, axial offset and skew of the plate. In a preferred form of the invention a series of mounting bars are spaced end to end in the groove with axial adjusting screws interposed between them, and in the end positions, for independent axial adjustment of the bars. The adjusting screws are free to shift laterally so that the adjustments in the two directions may be made independently. Pins on the mounting bar engage registering notches at the end of the plate. A clamping rail extending along the mounting bar serves to clamp the plate to the mounting bar, the clamping rail being relieved in the region of the pins to provide constant visual indication that the plate is fully inserted and registered with the mounting bar. In lithographic multi-color printing the different colors of ink are applied successively to the sheet by successive printing units using flexible printing plates. For precise, superimposed register of the printed impressions provisions must be made in the lock-up mechanism for slightly adjusting the position of the plate on the plate cylinder in circumferential position, axial position and, in some cases, skew. The amount of offset from the reference position is usually extremely small and must be susceptible to precise control. One of the problems faced by a pressman during setup is to establish a precise initial reference condition for each of the plates which may be employed as a basis, or starting point, for the subsequent, minute adjustment necessary to produce exact register. In conventional lock-ups for flexible printing plates it is difficult for the pressman to know when the lock-up, and printing plate, are in the desired reference condition. It is, accordingly, an object of the present invention to provide a lock-up and adjusting mechanism for flexible printing plates having immproved means for indicating to the pressman that each printing plate in the press is in a precise reference position on its plate cylinder, and hence that all of the plates are referenced to one another, in readiness for the making of the final adjustment. It is a related object to provide means giving a constant and exact indication of the amount of offset, or incremental adjustment, necessary for precise register of the impressions made by a number of differently inked plates. It is a more specific object to provide a lock-up mechanism which includes a mounting bar for registrably engaging the end of a flexible printing plate and which is provided with index members at the end of the bar which cooperate with similarly shaped reference members, the members having respective circumferentially facing and axially facing surfaces in close proximity, edge to edge, and which may be brought into visual alinement by turning of the respective adjusting screws to bring the mounting bar and plate into a precise reference position with respect to the printing cylinder as a starting point for the making of register adjustments. It is an object of the invention to provide an index which may be felt or "sighted" to establish the plate in an initial condition and which may be observed, either sensibly or by a gauge, in order to determine the direction and degree of offset of the plate from the reference condition. It is an object of the invention in another of its aspects to provide register-indicating and adjusting means which is not only simple and inexpensive but which is durable and which retains an accurate reference setting even in the face of hard and continuous usage. It is a related object of the present invention to provide a plate lock-up and adjusting mechanism which not only provides visual indication of the initial condition and subsequent condition of registered adjustment but in which the adjustments themselves, circumferentially, axially, and in skew, may be made quickly and easily substantially independently of one another, and in which adjustment, once made, is preserved during the running of the press. In one of the aspects of the present invention it is an object to provide means for securely clamping the end of the plate to the mounting bar, with the clamping rail being so constructed that the relationship between the plate and locator pins may be verified at a glance without necessity for disturbing the clamped condition.

Description

Other objects and advantages of the invention will become apparent upon reading the attached detailed description and upon reference to the drawings in which:

FIG. 1 is a fragmentary cross sectional view of the adjusting and indicating mechanism taken along the line 1--1 in FIG. 2.

FIG. 2 is a fragmentary plan view corresponding to FIG. 1.

FIG. 2a shows cooperating index and reference members in the alined condition.

FIG. 3 is a fragmentary elevation looking along the line 3--3 in FIG. 2.

FIG. 4 is a more complete plan view showing a series of plate mounting bars spaced end to end in the plate cylinder.

While the invention has been described in connection with a preferred embodiment, it will be understood that I do not intend to limit the invention to the embodiment shown but intend on the contrary to cover the various alternative and equivalent constructions included within the spirit and scope of the appended claims.

Turning now to the drawings there is shown a portion of a printing cylinder 10. This cylinder will be understood to form a part of a conventional lithographic printing unit consisting of a printing cylinder, blanket cylinder and impression cylinder, which latter have not been illustrated. Formed in the printing cylinder is a longitudinally extending groove 11 having parallel side walls 12 and end walls 13. The lock-up and adjusting mechanism to be described, generally indicated at 15, is nested within the groove 11. The mechanism serves to hold captive, in tension, and positionally adjust, a flexible lithographic printing plate 16. The printing plate has ends 17, only one of which is shown in FIG. 2, with the ends being formed with C-shaped cut-outs or notches 18.

For the purpose of registrably engaging the plate, a plate mounting bar 20 is provided having lateral edges 21, 22 and ends 23, the bar being coextensive with, and extending somewhat beyond, the edges of the printing plate. To clamp the end of the plate, the mounting bar is fitted with a clamping rail 25 having a clamping lip 26 and which is engaged by a series of socket head screws 27. Locator pins 28 respectively register with the notches 18 in the plate so that when the plate is fully inserted as shown the plate occupies a predetermined reference position with respect to the bar. In order that the pressman might at all times be able to confirm that the plate has been fully inserted into engagement with the locator pins, the lip of the clamping rail is relieved, or scalloped out, at the pin locations as indicated at 29.

For the purpose of guiding the mounting bar 20 for limited circumferential and axial movement, including, where necessary, a certain amount of skew, the bar is mounted upon a pair of circumferentially extending supporting rails 30 (only one of which is shown, FIGS. 2 and 3) which are secured to the bottom of the groove by one or more cap screws 31 and which present to the bar a flat bearing surface 32, the underside of the bar being cut out as indicated at 33 to accommodate the rail, and the bar, in addition, presenting an overlapping portion 34 which retains the bar 20 secure on the rail 30 even in the face of centrifugal force as the plate cylinder rotates.

In order to adjust the position of the bar 20 in the circumferential direction, a pair of adjusting screws 40 are threaded into the bar each having a head 41 and a tip 42 which abuts a land 43 formed on the wall of the groove. Following adjustment, each adjusting screw 40 is locked in position by a locking nut 44.

To adjust the mounting bar 20 endwise, that is, in the axial direction, adjusting screws are provided at the ends of the bar. Referring to the upper end 23 of the bar, as viewed in FIG. 2, an adjusting screw 50 is provided having a head 51 which bears against a land surface 53 located at the end of the groove, the screw being held in its adjusted position by a lock nut 54. The axial adjusting screw at the other end of the bar will be discussed later in connection with FIG. 4.

It may be noted that since the adjusting screws are in abutting engagement with flat lands on the groove wall, lands which are arranged at 90.degree., the circumferential adjustment of the plate may be accomplished independently of the axial adjustment. To maintain the tips of the circumferential adjusting screws continuously in contact with the wall of the groove, even in absence of a printing plate, one or more coil springs 60 may be provided pressing in the direction of the plate. As shown in FIG. 2 the spring 60 encircles a pin or plunger 61 which is freely slidable in a circumferential bore 62. The head of the pin 60 reacts against a fixed bracket 63.

In accordance with the present invention index members, preferably in the form of angle brackets, are provided at the respective ends of the mounting bar and closely spaced with respect to similarly shaped reference members which are secured to the bottom of the groove. Further in accordance with the invention the index member and reference members both include flat circumferentially facing surfaces which are located closely edge-to-edge and which are relatively movable, in and out of, an alined, coplanar condition, and with the members being so positioned that alinement corresponds to a reference condition for the mounting bar and the plate which is secured to it.

To understand the details of the index and reference members, reference is made to FIGS. 1 and 2 which shows the members at one end of the bar. Thus a reference member 70 is provided in the form of a small L-shaped "angle bracket" having a seating surface 71, an upper surface 72 and a circumferentially facing flat reference surface 73. The angle bracket is clamped securely to the floor of the groove by a machine screw 74.

Overlying the reference member 70, and in general radial alinement with it, is an index member in the form of an angle bracket 80 having a seating surface 81, an "under " surface 82 and a flat circumferentially facing index surface 83. The angle bracket is clamped into engagement with the side wall 22 of the mounting bar by means of a machine screw 84.

It will be understood that a substantially identical set of reference and index members are provided at the other end of the bar as shown in FIG. 4 where corresponding reference numerals have been used.

In accordance with one of the further aspects of the invention at least one of the sets of reference and index members are provided with corresponding flat alinement surfaces which are faced in the axial direction, that is, at 90.degree. to the surfaces 73, 83. Such axially facing surfaces are indicated, in FIG. 2, at 75, 85, respectively. The members 70, 80 have the same profile to the extent that the surfaces 73, 83 and 75, 85 thereon are respectively alineable with one another.

In accordance with a still further aspect of the invention the reference and index members have provision for relative adjustment so that, in the adjusted position, alinement of the surfaces 73, 83 and 75, 85 occurs when the mounting bar 20 occupies a precise reference position with respect to the plate cylinder in which it is mounted and, hence, with respect to the plates on the other plate cylinders in the printing press. Preferably the members 70 and 80 are, for purposes of adjustment, provided with slots which accommodate the clamping screws and which extend at right angles to one another. Thus the clamping screw 74 cooperates with a slot 76 to provide circumferential adjustment while the clamping screw 84 has a clearance slot 86 to provide relative axial adjustment.

In making this adjustment the screws are first slacked off slightly and the bar 20 is adjusted, by means of the adjusting screws 40, 50 so that it occupies reference position with respect to the cylinder both circumferentially and axially. (This adjustment in the case of the "first" or master, plate cylinder on the printing press may be arbitrary, but the bars in the succeeding plate cylinders are each adjusted with reference to the corresponding bar in the first cylinder.) The reference member is then moved in the circumferential direction until the surfaces 73, 83 are in perfect coplanar alinement with one another, as shown in FIG. 2a, following which the clamping screw 74 is tightened. This is done at each end of the bar. Next the index member 80 is moved in the axial direction until the axially facing surfaces 75, 85 are also in perfect coplanar alinement. Following this the clamping screw 84 is tightened to complete the initial reference adjustment which need not be thereafter disturbed.

While the second set of members 70, 80 may also be provided with alineable axially facing flat surfaces corresponding to the surfaces 75, 85, this is considered optional. Moreover, while the index and reference members may have the same width thereby to provide alineable surfaces facing in opposite axial directions, this, too, is considered an optional feature not possessed by the structure as actually illustrated. To facilitate establishing the initial condition of "factory" alinement, a suitable mechanical gauge may be used. Such gauge may, for example, be of the type that has a flat seating surface and an adjacent dial indicator. In use the seating surface may be seated upon the reference surface 73, for example, while the plunger of the dial indicator engages the index surface 83, with the reference member 70 being adjusted slightly back and forth until a zero reading is obtained along the entire axial length of the surfaces.

However, it is one of the features of the present construction that the reference surface 73 and index surface 83 are spaced closely edge-to-edge in the radial direction. This makes it possible for the eye to sight along the surfaces, making it easy to pick up any departure from the alined condition.

As stated in the introduction, it is necessary in a printing press having a plurality of plate cylinders carrying plates printing in different colors for a new set of plates, upon installation in the press, to be adjusted to an initial reference condition which forms the starting point for any subsequent minor adjustment which may be necessary, in the skill and judgment of the pressman, to achieve precise superposition of the printed images. In conventional presses achieving this initial, and nominal, reference condition is extremely difficult. However, in the present construction, which makes use of the alined or coplanar surfaces arranged 90.degree. to one another, installation of the plate may be accomplished quickly and easily as follows:

Assuming the clamping screws 27 are backed off to release the clamping rail 25, the end 17 of the plate is inserted under the clamping rail with the notches 18 in register with the locator pins 28, with the plate being fully inserted until the notches "bottom" upon the pins. This condition of full insertion or bottoming is easily confirmed via the clearance openings 29 in the clamping lip, following which the clamping screws 27 are turned tight.

Next the circumferential adjusting screws 40 may be released by backing off the locking nuts 44, following which the screws are turned in one direction or the other in order to bring the index surfaces 83, at each end of the mounting bar, into precise alinement with the cooperating reference surfaces 73. This can be done visually with a high order of accuracy or, as stated, a gauge may be used. Since the adjusting screws 40 work against the spring, or springs, 60, turning the screw slightly in opposite directions causes corresponding circumferential movement of the bar 20 in opposite directions without lost motion or play. When the desired coplanar relationship is obtained the lock nuts 44 may be turned tight.

To adjust the bar 20, and the plate which is connected to it, to the reference condition in the axial direction, the screw 50 is turned until the surfaces 75, 85 are in perfect alinement.

In the event that ink or other foreign matter should collect on the alineable surfaces, the surfaces are fully exposed so that they may be cleaned by the wipe of a cloth. Moreover, since the surfaces are spaced so closely edge to edge, the reference condition of alinement may be achieved by the sense of touch as well as the sense of sight.

With one of the ends of the plate in its nominal registered condition, tension is applied to the other end of the plate (see FIG. 4) where the plate is gripped by a mounting bar 90 which is constructed similarly to the mounting bar 20 and which is provided with circumferential screws 91 and an axial adjusting screw 92. If desired, the mounting bar 90 may be fitted with index members having cooperating reference members, just as in the case of the mounting bar 20 at the other end of the plate, but in a practical case this may not be necessary. The adjusting screws 91 are tightened just sufficiently to apply tension to the plate so that it is held securely on the surface of the cylinder.

After the plates on the different printing cylinders within the press have all been adjusted to the reference, or starting, condition as discussed above, the press may be started and allowed to print a number of proof sheets in full color. It is then necessary for the pressman to decide the amount that the adjusting screws should be turned from the initial reference condition to bring about exact register between the inked impressions. Because of the high degree of precision attainable in establishing the reference condition it will be found that only a slight touch-up adjustment will be necessary.

While the invention has been described in connection with the mounting of a single plate on a given plate cylinder, it is one of the features of the present construction that the invention may be extended to a plurality of flexible plates secured to mounting bars which are spaced end to end in the cylinder groove. Referring to FIG. 4 which shows three plates mounted side by side, corresponding reference numerals have been employed with the addition of subscripts a and b respectively for elements associated with the second and third plates.

It is one of the features of the present invention that double ended axial adjusting screws are interposed between the presented ends of adjacent bars. Thus between the mounting bars 20, 20a there is a screw 100 which is threaded at one end, 101, into the bar 20 and which has a second end 102 which is cylindrical and which is fitted into an axially extending bore formed in the end of the bar 20a. At the middle of the screw 100 is a knurled knob 103 for convenient manual adjustment. A similar adjusting screw 100 is provided between the bars 20a, 20b as shown. Corresponding axial adjusting screws 110 are used between the spaced bars 90 at the other ends of the plates.

While the adjustment of the plate has been described in connection with movement in the circumferential and axial directions, it will be understood that a small amount of skew may be imparted, if necessary, to the bar 20 by differential adjustment of the screws 40. As a practical matter the axial adjusting screws 100 between the bars may be constructed with sufficient lateral play so as to accommodate slight differential displacement in the circumferential direction.

The terms "similarly shaped" and "of corresponding shape" are used herein in referring to the reference and index members. This has only to do with the fact that the members have generally coextensive alineable surfaces.

While it is preferred to employ separate index members and reference members at the respective ends of the plate mounting bar it will be understood that the members may, if desired, be extensive in the longitudinal dimension of the bar so that only one of each member may suffice.

The term "sensible observation" includes the senses of both sight and touch.

Also while it is preferred to have both axially facing and circumferentially facing alinement surfaces on the same members, arranged at 90.degree. to one another, the two surfaces may, if desired, be located upon different members; for example, the flat end surface 23 of the bar 20 may be employed as an axial index.

The securing and adjusting arrangement has been found to fulfill all practical requirements and is inherently durable so that its accuracy and convenience is preserved is spite of extended rough usage. It is one of the features of the construction that it is not limited to the particular environment shown, and angle brackets, carrying the alineable surfaces, may be incorporated in existing designs of printing cylinders already in the field.

Claims

What I claim is:

1. A plate lock-up mechanism for securing and adjusting a flexible printing plate on a plate cylinder having a longitudinal groove formed therein, comprising, in combination, a plate mounting bar extending longitudinally in the groove and having means for registerably engaging the end of the plate, means for supporting the bar for limited circumferential and axial movement, means including adjusting screws spaced along the bar and extending in a circumferential direction for adjusting the circumferential position of the bar and plate, means engaging the bar in the axial direction for adjusting the axial position of the bar and plate, reference members seated in the groove adjacent the ends of the bar, index members of corresponding profile secured to the bar and closely overlying the respective reference members, the index members and reference members having cooperating circumferentially facing flat surfaces and axially facing flat surfaces and so positioned that when the flat surfaces are respectively in visual coplanar alinement the mounting bar and plate occupy a precise reference position on the cylinder, with any slight departure from reference position by reason of subsequent adjustment being indicated in direction and amount by the offset between the surfaces.

2. The combination as claimed in claim 1 in which the cooperating index and reference members are in the form of small angle brackets and in which at least one of the cooperating brackets is seated for relative adjusting movement thereby to establish a precise reference condition between plate and cylinder.

3. The combination as claimed in claim 1 in which the adjusting screws are positioned to engage and react against the walls of the groove with provision for relative lateral movement so that the two adjustments may be made substantially independently of one another.

4. The combination as claimed in claim 3 in which means are provided for biasing the clamping bar in the circumferential direction to maintain the circumferential adjusting screws in bottomed condition against the engaged wall of the groove.

5. A plate lock-up mechanism for securing and adjusting a flexible printing plate on a plate cylinder having a longitudinal groove formed therein, comprising, in combination, a plate mounting bar extending longitudinally in the groove having means for registerably engaging the end of the plate, means for supporting the bar for limited circumferential and axial movement thereby to position the plate, first screw means extending circumferentially of the bar and reacting against the cylinder for adjusting the circumferential position of the bar and plate, second screw means extending radially of the bar and reacting against the cylinder for adjusting the axial position of the bar and plate, an index member in the form of a bracket secured to the bar presenting flat circumferentially facing, longitudinally extending surfaces as well as axially facing surfaces, a reference member on the cylinder and secured in the groove and presenting respectively cooperating circumferentially facing and axially facing surfaces, the cooperating surfaces being closely spaced to one another edge-to-edge to permit adjusting movement into and out of coplanar relationship, all of said circumferentially and axially facing surfaces being extensive as to enable direct sensible observation of the condition of coplanar alinement, the reference member being so relatively positioned on the cylinder that the said condition of alinement provides direct indication that the plate is in an accurate reference position on the cylinder in readiness for final adjustment of register.

6. The combination as claimed in claim 5 in which at least one of the cooperating index and reference members is adjustably mounted to permit adjustment of the reference position of the bar and plate in both the circumferential and axial directions.

7. In a plate lock-up mechanism for securing and adjusting a flexible printing plate, having notched ends, on a plate cylinder having a longitudinal groove formed therein comprising, in combination, a plate mounting bar extending longitudinally in the groove, means for supporting the bar for limited circumferential and axial movement, means including circumferentially and axially arranged screws engaging the bar and reacting against the cylinder for adjusting the bar in circumferential and axial directions, rectangularly shaped reference members secured in the groove adjacent the ends of the bar, correspondingly shaped index members secured to the ends of the bar and overlying the reference members, pins on the mounting bar for registering with the notches in the plate, a clamping rail extending along the top of the mounting bar and having means for clamping the same to the mounting bar for tightly holding the plate, the clamping rail being relieved along its edge to clear the pins and thereby to provide constant visual indication that the plate is seated intimately against the pins in registered condition with the bar, the reference and index members each having flat cooperating circumferentially facing and axially facing surfaces spaced closely edge-to-edge and so positioned as to indicate by respective coplanar alinement that the mounting bar and plate are in reference position with respect to the cylinder and with any offset between the surfaces indicating the direction and degree of offset of the plate with respect to the cylinder in the circumferential and axial directions.

8. The combination as claimed in claim 7 in which the cooperating alined surfaces are extensive in the radial direction as to permit visual sighting, across them, to verify the condition of alinement.

9. A plate lock-up mechanism for securing and adjusting flexible printing plates on a plate cylinder having a longitudinal groove formed therein, comprising in combination, a series of plate mounting bars spaced longitudinally in the groove end-to-end and having means for registerably engaging the ends of respective plates, means for mounting the bars for circumferential and axial movement thereby to position the plates, means including adjusting screws for individual circumferential adjustment of each bar and associated plate, index members secured to the respective ends of each bar and having flat circumferentially facing surfaces, reference members seated in the groove in radial alinement with the respective index members and having cooperating flat circumferentially facing surfaces, the reference members being so related to the index members that when the bars and their associated plates are in reference positions on the cylinder the respective circumferentially facing surfaces are in coplanar visual alinement, axial adjusting screws interposed between the spaced ends of adjacent bars and in the end positions for adjusting the respective axial positions of the bars, and means including index members on each bar for indicating when each bar is in a reference axial position.

10. A plate lock-up mechanism for securing and adjusting a flexible printing plate on a plate cylinder having a longitudinal groove formed therein, comprising in combination, a plate mounting bar extending longitudinally in the groove and having means for registerably engaging the end of the plate, means for mounting the bar for limited circumferential and axial movement thereby to position the plate, means for adjusting the circumferential position of the bar and plate, means for independently adjusting the axial position of the bar and plate, means including an index on the bar and a cooperating reference on the cylinder for indicating the axial position of the bar, a pair of reference members secured in the groove adjacent the ends of the bar, and a pair of index members in the form of brackets on the bar overlying the reference members and spaced closely thereto in the radial direction, said reference and index members each having flat circumferentially facing surfaces, the reference members being so adjustably positioned with respect to the cooperating index members that when the bar is in a reference position with respect to the cylinder the circumferentially facing surfaces are in coplanar visual alinement.

11. A plate lock-up mechanism for securing and adjusting a flexible printing plate on a plate cylinder having a longitudinal groove formed therein, comprising, in combination, a plate mounting bar extending longitudinally in the groove having means for registerably engaging the end of the plate, means for supporting the bar for limited circumferential and axial movement thereby to position the plate, first screw means extending circumferentially in the bar and reacting against the cylinder for adjusting the circumferential position of the bar and plate, second screw means extending axially with respect to the bar and reacting against the cylinder for adjusting the axial position of the bar and plate, index means on the bar presenting flat circumferentially facing and axially facing index surfaces, reference means on the cylinder and secured in the groove presenting fixed circumferentially facing and axially facing reference surfaces cooperating with the respective index surfaces, the cooperating surfaces being closely spaced to one another edge-to-edge to permit direct sensible observation of an alined coplanar condition, the reference surfaces being so positioned with respect to the cylinder that alinement of the circumferentially facing surfaces signifies a reference circumferential condition of the plate on the cylinder and the condition of alinement of the axially facing surfaces signifies a reference axial condition of the plate on the cylinder, with any offset of the cooperating surfaces providing direct indicating of the direction and degree of circumferential and axial offset of the bar and plate with respect to the cylinder.