Flexographic colour assembly with central print registration and pressure adjustment

Abstract

 A flexographic colour assembly designed to be arranged at a print drum, comprising a screen roller and a plate-carrying roller, supported at its ends on skids that can be moved in parallel and independently between three positions: one rest position distant from the printing drum, one working or attachment position, where the screen roller is positioned in contact with the plate-carrying roller, and the plate-carrying roller is shifted into contact with the printing drum, and a detached position in which the plate-carrying roller is shifted a pre-established short distance from the contact with the printing drum, and the screen roller is shifted a short pre-established distance from contact with the plate-carrying roller, said plate-carrying roller having side and longitudinal rollers to adjust its positioning with respect to the printing drum. The colour assembly comprises a single drive motor (17) for its movement between said rest position and working position of said screen rollers (2) and plate-carrying rollers (3), and, for driving said plate-carrying roller side and longitudinal registers, motion transmission means between said motor (17) and said support slides (5a,5b) and longitudinal support skids and said side and longitudinal registers and a pair of actuators (50a,50b) to control a respective attachment-detachment movement of the screen roller (2) and plate-carrying roller (3) independently from the motor (17) and a control unit (54).

Description

[0001] The present invention regards a flexographic printer that enables print registering and pressure adjustment to be carried out from a single control unit.

[0002] As is well-known a flexographic colour assembly comprises a screen roller and a plate-carrying roller that are parallel one to the other and supported in such a way as to adjustably slide closer or further away with respect to each other and with respect to the much larger so-called printing drum around which can be arranged a number of colour assemblies for colour printing. Each colour assembly may traditionally require the presence of no less than six distinct motors to regulate the reciprocal print roller pressures and their longitudinal and sideways registration.

[0003] The main object of this invention is to provide a colour assembly with a much-reduced number of motors for the carrying out of all the movements and adjustments required for the printing positions

[0004] Another object of this invention is to provide a colour assembly that is more simply constructed and highly reliable while also able to favourably compete with traditional colour assemblies in terms of cost.

[0005] These and other objects, that will be appear in more detail below, are achieved by a flexographic colour assembly according to the present invention that is located at a print rotary drum, comprising a screen roller and a plate-carrying roller, supported at its ends on skids that can moved in parallel and independently between three positions: one rest position distant from the printing drum, one working or attachment position, where the screen roller is positioned in contact with the plate-carrier roller, and the plate-carrying roller is shifted into contact with the printing drum, and a detached position in which the plate-carrying roller is shifted a pre-established short distance from the contact with the printing drum, and the screen roller is shifted a short pre-established distance from contact with the plate-carrying roller,said plate-carrying roller having side and longitudinal rollers to adjust its positioning with respect to the printing drum, and is characterised in that it comprises a single drive motor for its movement between said rest position and said working position of said screen rollers and plate-carrying rollers, and, for driving said plate-carrying roller side and longitudinal registers, motion transmission means between said motor and said support side and longitudinal support skids and said side and longitudinal registers and a pair of linear actuators to control a respective attachment-detachment movement independently from said motor, and a control unit.

[0006] Advantageously, the said motor system comprises an electric motor and said linear actuators comprise two pneumatic jacks.

[0007] Further aspects and advantages of the present invention will better appear from the following detailed description of a currently preferred embodiment thereof with reference to the accompanying drawings, in which:

Figure 1 shows a diagrammatic general view of a flexographic printing machine;

Figure 2 is a plan view of a colour assembly in accordance with the present invention;

Figure 3 is side elevation view of the colour assembly in Figure 2;

Figures 4a and 4b each show a front view of the control, respectively, of the attachment and detachment of the colour assembly in Figure 2;

Figure 5 shows a view on an enlarged scale of the coupling for a lateral register and the attach-detach control for the colour assembly in Figure 4;

Figure 6 shows a cross-section view on an enlarged scale of the coupling for the longitudinal register and the attach-detach control and the motor and its motion transmission means for the colour assembly in Figure 4; and

Figure 7 illustrates a cross-section view taken along the line VII-VII of Figure 6.

[0008] With reference to the above listed Figures, it will be seen that a flexographic colour assembly in accordance with the present invention, generically indicated with 1, has a screen roller or cylinder 2 and a plate-carrying roller o cylinder 3 provided with bar holds 2a, 2b and 3a, 3b at their two ends, respectively. The bar holds of the screen roller are rotatably supported on a pair of skids 4a and 4b slidably mounted on respective skids 5a and 5b which rotatably support the plate-carrying roller 3 and are in their turn slidably mounted on a respective side of the supporting frame of a printing machine, generally indicated at 6. The skids 4a and 4b and 5a and 5b can thus be moved parallel to, and independently of, each other between a rest position distant from a drum 51, a work position, in which the screen cylinder is positioned in contact with the plate-carrying roller and the plate-carrying roller is in contact with the print drum, and a detached position in which the plate-carrying roller is shifted relative to the printing drum 51 (e.g. by some tenths of a millimetre) as the screen roller is shifted from the flexographic roller (e.g. by some tenths of a millimetre).

[0009] The skids can be moved back and forth along the respective machine side 6 by means of two pairs of ball screws 7a and 7b for skids 4a and 4b and 8a and 8b for skids 5a and 5b, respectively, - (Figures 4a, 4b) - a pair of screws 7a and 8a being provided at one side of the machine 6, whereas the pair of screws 7b and 8b are located on other side of the machine. One front end of each ball screw 7a, 7b and 8a, 8b is constrained (but can rotate) at the respective skid or skate and the other end, the rear end, is rotatably mounted by means of bearings 9 and 10, respectively, on a rear cross-member 11 (Figure.7), that is in its turn mounted on skid 5b.

[0010] At the rear end of each ball screw there are also keyed helical toothed wheels 12a, 12b and 13a, 13b, respectively. The toothed wheel pair 12a, 12b can take up the drive from a transmission shaft 14, while the toothed wheel pair 13a, 13b can take up the drive by means of a transmission shaft 15 extending parallel to the shaft 14 along the cross-member 11.

[0011] Between and parallel to the transmission shafts 14 and 15 the cross-member 11 rotatably supports, by means of the bearings 16a and 16b (Figure 2), a third transmission shaft 16, that in part acts as a transmission drive and in part as a support for components, as will be explained below.

[0012] There is a single electric motor 17 at one end of the cross-member 11, substantially at the head of the transmission shafts 14, 15 and 16 (Figure 6), which by means of a triple-output reduction unit 18 (two outputs of which have a respective internal gearing 18a, 18b that is free to move longwise) is operatively connected to the transmission shafts 14, 15 and 16. Transmission of the drive between each transmission shaft 14 and 15 and the corresponding toothed wheels 12a, 12b and 13a, 13b, respectively, occurs through an endless screw 19a, 19b and 20a, 20b (Figures 4a, 4b, 5 and 6).

[0013] By pneumatic control through the tubes 52a, 52b, 53a, 53b (or in some other suitable manner, e.g. by cogged transmission) of the attachment-detachments 57a, 57b, 58a, 58b, the ball screws 7a, 7b or 8a, 8b can be selectively actuated.

[0014] Each attachment-detachment 57a, 57b, 58a, 58b, as can be seen more clearly in Figures 4a, 4b and 7, consists of a flanged bush 141 slid onto a respective shaft 7a, 7b, 8a, 8b to abut against one of the bearings 9 or 10. The flanged bush 141 is keyed onto the corresponding shaft 7a, 7b, 8a, 8b, and thus it rigid in rotation with it by means of a key 142 and is fixed in place by a head ring nut 143. A flanged sleeve 144 with a conical peripheral surface on its own flange is mounted onto the flanged bush 141. The flanged sleeve 144 can slide on the bush 141 against one or more spiral springs 145 located in a respective seat formed in the bush 141 and is rigid in rotation with the bush 141 itself because it is connected to it by one or more longitudinal pins 146. The sliding movements of the flanged sleeve 144 are caused, against the action of spring or springs 145, by a flange 147 (that acts as a piston, as will be seen more clearly below) slidably mounted on the bush 141 and abutting against the sleeve 144.

[0015] The flange 147 is slidably housed in boring in the retaining body 148 that is fixed, e.g. by bolts, to the structure of the machine 6. Between the retaining body 148 and the flange 147 there is delimited a variable volume air chamber 149 that is sealed by seals 150, between the retaining body 148 and flange 147 and bush 141, and 151 between the retaining body 148 and the flange 147. The chamber 149 communicates through a duct 52a, 52b, 53a, 53b with a valve distributor (of any suitable kind) 156 controlled in its turn by a PC 54 and supplied by a compressed air source 155 (Figure 1).

[0016] Between the retaining body 148-flange 47 and flanged sleeve 144 there is a ring-shaped recess into which is mounted a toothed wheel 12a, 12b and 13a, 13b, whose end facing the flange 147 abuts against a rolling bearing 154 that rests on the opposite side against a fastening ring 154a, 154b bearing against the retaining body 148, whereas its other end rests against a brass bush 156 and ends with a female conical annular extension having a complementary inclination to that of the peripheral edge of the flanged sleeve 144.

[0017] With this arrangement, when air under pressure is supplied to the chamber 149, the flange 147, and thus the flanged sleeve 144, is shifted against the force of the spring or springs 145 in a direction that takes the flanged sleeve away from its toothed wheel 12a, 12b and 13a, 13b, so that the wheel no longer takes up the drive from the respective shaft 7a, 7b, 8a, 8b. When air under pressure is discharged from the chamber 149, the spring or springs 145 ensure meshing engagement between the flanged sleeve 144 and the respective toothed wheel.

[0018] As can easily be appreciated, forward and backward movement can thus be obtained according to the direction of rotation of the electric motor 17, for positioning the screen rollers 2 and plate-carrying roller 3 between the rest position and the working position, or rapid movements for fine adjustment of the printing pressure or the rapid longitudinal and transverse register control with the single motor 17.

[0019] For reasons of comfort and convenience, the drive to the screws 7a, 7b and 8a, 8b, 39a, 39b can also be manually transmitted by a hand wheel 21 mounted for rotation on the cross-member 11 with its rotation axis at right angles to the shaft 16 and arranged to turn a bevel gear 22 (Figure 2), that can engage with a bevel gear 23 slidably mounted on the shaft 16 and rigid in rotation therewith. The slide of the bevel gear 23 along the shaft 16 is controlled by a pneumatic jack 24 supported by the cross-member 11, so that it can be taken, upon control, to engage with the bevel gear 22 or detach itself therefrom.

[0020] The transmission shaft 16 supports at its two ends a pneumatic clutch device indicated by 25a, 25b, which substantially comprises following components: a conical male element 26a, 26b keyed on the shaft 16, but free to slide along it, a truncated-cone female bush 27a, 27b mounted for rotation by means of bearings 28a, 28b on the transmission shaft 16 and suitable for engaging at an inclined plane with the corresponding conical male element, a spring 29a, 29b between the male part 26a, 26b and its respective receiving bush 27a, 27b and designed to yield to keep the conical male element away from its respective bush, and a collar 30a, 30b mounted for rotation by means of bearings 31a, 31b on the transmission shaft 16 and delimiting a variable volume fluid-seal chamber 32a, 32b with its respective conical male element 26a, 26b. The chamber 32a, 32b communicates through a duct 25a, 25b and a control valve 156 with the source 155 of fluid under pressure (compressed air) to push, upon control, the corresponding conical male element 26a, 26b engaging with its respective receiving bush, thereby overcoming the force of its respective spring 29a, 29b.

[0021] The bush 27a, 27b has a toothed wheel 34a, 34b, respectively, keyed to it, whereby if the conical male element 26a, 26b is pneumatically energized, the motion is transmitted via the toothed wheels 35a, 35b to its respective registering screw 39a, 39b (Figure 2). The motion can be transmitted by the shaft 16, i.e. through the hand wheel 21, to any of the registering screws 39a, 39b.

[0022] The two toothed wheels 34a and 34b are keyed onto the transmission shaft 16 in order to carry out the function of longitudinal and transverse registering or setting, consisting in shifting the gearing of the plate-carrying roller, to correct the printing position in a direction parallel to the axis of the printing rotary drum and at right angles to the sliding direction of the material to be printed (e.g. a web of paper fed to the print drum 51 by any suitable manner) even during the printing operation (Figure. 2). On each toothed wheel 34a, 34b passes a respective chain 36a, 36b passing around a gearwheel 37a, 37b keyed onto a corresponding rotating shaft 38a, 38b parallel to the shaft 16 and projecting from its respective skid 5a, 5b. The projecting part of each rotating shaft 38a, 38b is provided with a threaded section 39a, 39b, the so-called registration screw, that in turn engages with a nut screw 40a, 40b that can move along a corresponding shaft 41a, 41b. In its movement along the shaft 41a, 41b the screw pulls with it a respective radial arm 42a, 42b, that engages with its free end a respective groove on the bar hold 3a, 3b of the plate-carrying roller 3. According to the direction of rotation of the electric motor 17, the registration can be shifted in the desired direction.

[0023] To carry out the attaching-detaching operations there are two linear actuators or double jacks 50a, 50b (Figures 4a, 4b and 5), that, by means of the respective bell joints 49a, 49b are mounted at the heads of the shafts 14 and 15, respectively. Each bell joint 49a, 49b supports a respective bearing 48a, 48b for rotatably supporting the adjacent end of its respective shaft 14, 15. At their other ends, the shafts 14 and 15 are rigid in rotation with the gears 18a and 18b of the reduction unit 18, that, as has been stated previously, can slide longitudinally on a motor gearing 18c.

[0024] The actuators 50a, 50b are designed to cause a controlled longwise shift of the respective shaft 14, 15, that in its turn causes a simultaneous angular movement β₁, β₂ of the ball screws 7a, 7b, 8a, 8b with a simultaneous movement of the skids 4a, 4b, 5a, 5b to move the screen roller 2 and the plate-carrying roller 3 by about 1 mm relative to the print drum 51 for the coupling-uncoupling operation. It will be noted how, due to the engaging of the gearing 12a, 12b, 13a, 13b with its respective endless screw 19a, 19b, 20a, 20b the coupling-uncoupling shifts are effected practically with no play between the various components in movement.

[0025] Advantageously, also the control signals for the various pneumatic control components (electro-valves) for the distribution system of compressed air fed by the source 155 are issued from the central electronic unit 54 controlled by a PC.

[0026] The above-described flexographic colour assembly may be subject to numerous modifications and variants within the scope of the claims.

[0027] Thus, for example, between the motor 17 and the transmission shafts 14, 15, 16 couplings of any suitable type can be provided to avoid breakages from torsion force peaks.

[0028] It will be noted that the above-described structure makes it possible to precisely carry out all the attaching-detaching functions and longitudinal and transverse registration, as well as the positioning of rollers 2 and 3 with a high degree of precision with just one electric motor 17 and one only pair of linear actuators 50a, 50b.

Claims

1. A flexographic colour assembly designed to be arranged at a print drum, comprising a screen roller and a plate-carrying roller, supported at its ends on skids that can moved in parallel and independently between three positions: one rest position distant from the printing drum, one working or attachment position, where the screen roller is positioned in contact with the plate-carrier roller, and the plate-carrying roller is shifted into contact with the printing drum, and a detached position in which the plate-carrying roller is shifted a pre-established short distance from the contact with the printing drum, and the screen roller is shifted a short pre-established distance from contact with the plate-carrying roller, said plate-carrying roller having side and longitudinal rollers to adjust its positioning with respect to the printing drum, and is characterised in that it comprises a single drive motor for its movement between said rest position and said working position of said screen rollers and plate-carrying rollers, and, for driving said plate-carrying roller side and longitudinal registers, motion transmission means between said motor and said support side and longitudinal support skids and said side and longitudinal registers and a pair of linear actuators to control a respective attachment-detachment movement independently from said motor, and a control unit.

2. A colour assembly in accordance with claim 1, characterised in that said motion transmission means comprises a pair of supporting skid members for the said screen roller and said plate-carrying roller, a ball screw whose end is constrained by a respective skid member and whose other end is rigid in rotation with its respective toothed wheel, and is characterised in that it comprises a first and a second transmission shaft that are operatively connected to said source of motion and have keyed thereto a pair of toothed wheels arranged to mesh engaging with a respective toothed wheel rigid in rotation with a ball screw and coupling-uncoupling means between each toothed wheel rigid in rotation with said ball screws and its respective toothed wheel rigid in rotation with one of the two said shafts, and control means for the said coupling-uncoupling means.

3. An assembly in accordance with claim 2, characterised in that said transmission means comprises a third transmission shaft parallel to said pair of transmission shafts and provided with end gears and a clutch device for each of its gearing mechanisms for controlled engagement with respective gears rigid in rotation with said pair of transmission shafts.

4. An assembly in accordance with claim 3, characterised in that said third transmission shaft comprises a bevel gear slidably mounted thereon but rigid in rotation therewith, a bevel gear that can be controlled by a hand wheel arranged to engage with said sliding bevel gear, and a linear actuator arranged to control the sliding movements of said sliding gear for engagement and disengagement, upon control, of said bevel gear controlled by said hand wheel.

5. An assembly in accordance with claim 3 or 4, characterised in that said motion transmission means of said third transmission shaft comprises a pair of toothed wheels keyed thereto and arranged to control a respective chain designed to transmit a longitudinal registration movement for said plate-carrying roller.

6. An assembly in accordance with claim 5, characterised in that it comprises at least one gear and an endless screw cooperating therewith to turn the rotary motion of said chains into a translation motion for a control element for longitudinal movements controlled by said plate-carrying roller.

7. A colour assembly according to any previous claim 1 to 6, characterised in that said motion source comprises an electrical motor

8. An assembly in accordance with any claim 2 to 7, characterised in that said attachment-detachment means includes a flanged sleeve slidably mounted on, and rigid in rotation with, a respective transmission shaft and having a conical edge surface at its flange, resilient means to act against sliding of said sleeve, a thrusting flange slidably mounted on said transmission shaft and abutting against said flanged sleeve, a restraining body for said thrusting flange, that delimits therewith a variable volume chamber in fluid communication with a source of fluid under pressure, and a toothed wheel slidably mounted on said flanged sleeve and designed to couple with, or detach itself from it on an inclined plane under the action of said thrusting flange and said resilient resisting means.

9. An assembly in accordance with any of the claims from 3 to 8 above, characterised in that said first and said second transmission shafts are mounted for rotation and have a toothed wheel rigid in rotation therewith and in motion transmission engagement with said motor means with the possibility of effecting longitudinal movements.

10. An assembly in accordance with claim 9, characterised in that the or each motor means comprises a linear actuator mounted at the head of the one of the said first and second transmission shaft, and a rotary support joint between each linear actuator and its respective transmission shaft, thereby causing controlled longitudinal movements to its transmission shaft without preventing it to rotate in order to effect attaching-detaching operations.

Drawing