Multi coloured flexographic printing machine with an automatic throw-off device

Abstract

 An automatic printing cut-out device for a colour flexographic printing machine having at least one colour group comprising a block-holding cylinder and a screen cylinder rotatably mounted on suitable supports, a control system for monitoring movement of the supports (2, 3) comprising an end cross shaft (4) arranged on its respective colour group (1), a reversible electric motor (5) for the said end cross shaft, a helical gear (6, 7) at each side of the keyed flexographic printing machine keyed on the said end cross shaft (4) and at least one ball screw (8, 9) to transmit motion to a respective cylinder bearing support (2, 3) arranged on one side of the machine. Lead-nut means (12) is provided on each ball screw (8, 9) for displacing the cylinder supports, and reversable driving means for the said lead-nut means (12) designed to cause a limited angular movement to its respective ball screw (8, 9) thereby obtaining a desired linear movement of the respective support and thus of the respective cylinder thereof.

Description

[0001] The present invention relates to a multi coloured flexographic printing machine either of drum or stack-type having an automatic printing cut-out device.

[0002] As is well known, multi-colored flexographic printing machines require a device for printing cut-out for each colour group. In other words, it is necessary to displace apart by approximately 1mm a moving unit comprising at least one block-holding cylinder and one screen cylinder in each colour group and the offset cylinder or drum or backpressure cylinders in the case of stack-type flexographic printing machines. Traditionally, such a device in general comprises only one motor or two pairs of electric motors (one at each side of the machine), a train of gear wheels and a threaded shaft for transmitting motion from each motor to the block-holding and screen cylinders. Thus, one is dealing with a relatively complex machine that affects heavily on the total cost of construction of the flexographic printing machine and requires a high number of components.

[0003] The main object of this invention is to provide an automatic device for the automatic printing cut-out in a flexographic printing machine which device is designed to ensure quick and precise execution of the printing cut-out and comprises a small number of components, thereby being competitive with respect to the traditional printing cut-out devices.

[0004] Another object of the present invention is to provide a printing cut-out device which is also suitable for performing micrometric adjustment before printing setting.

[0005] Another object of the present invention is that the said printing cut-out device is simple in structure and suitable for being applied also to existing flexographic printing machines.

[0006] These and still other objects which will be further understood hereinbelow are attained by a device for printing cut-out in multi-colour flexographic printing machines comprising at least one colour group compising a block-holding and screend cylinder or roller rotatably mounted on suitable supports which can be slidingly moved towards or away from the printing offset drum or a respective back-pressure roller cylinder, a control system for monitoring movements of the supports comprising an end transverse or cross shaft arranged at the head of its respective colour group, a reversible electric motor for the cross shaft, a helical gear at each side of the flexographic printing machine keyed on the said end cross shaft, at least one ball screw which is rigid in rotation with a respective helical gear to trasmit motion to a respective cylinder bearing support arranged on one side of the machine, lead-nut means on each ball srew for displacing the cylinder supports of the cilinders and reversable driving means for the said lead-nut means designed to cause a limited angular movement to the respective ball screw, thereby obtaing a desired linear movement of the respective support and thus of the respective cylinder thereof.

[0007] Advantagiously, said lead-nut means comprises both a linear actuator for causing printing cut-out and a low electric power motor for micrometric setting of the cylinders.

[0008] Further aspects and advantages of the present invention will be better understood from the following detailed description with reference to the accompaning drawings, in which

FIGURE 1 is a partial side elevation view partly in section of a colour group equipped with an automatic printing cut-out device according to the present device;

FIGURE 2 shows a front cross-sectional view taken along the line II-II of Fig.1;

FIGURE 3 is a cross-section view taken along the line III-III of Fig.1;

FIGURE 4 illustrates a view similar to that of Fig.3, but relating to lead-nut means on another ball screw and in a different operative position; and

FIGURES 5 and 6 are each a diagrammatic view showing a different angular positioning of a ball screw under the drive of lead-nut means.

[0009] With reference to the Figures listed above, it will be noted that a flexographic colour printing machine either of offset drum or stack-type has two or more colour groups, generally indicated at 1, each of which comprises, as is known in the state of the art, a block-holding cylinder or roller and a screen cylinder or roller (not shown in the drawings) mounted for rotation on suitable supports (also not shown in the drawings and of any suitable type), which can slide on a couple of substantially radial brackets or guides 2 and 3, i.e. a guide on each side and more precisly one on the operator side and one on the rear side of the machine, so that they can be moved towards or away from the offset drum or a respective back pressure roller cylinder. The cylinder bearing supports comprise a control system for their movements, which has a trasverse or cross end shaft 4 arranged at the head of the brackets 2 and 3, an electric reversible motor 5 for driving the end cross shaft 4, two helical gears 6 and 7 keyed on the end cross shaft 4 at each side of the flexographic printing machine and a couple of ball screws, 8,9 and 10,11 respectively(a couple for each side), which are rigid in rotation with a respective helical gear 6, 7 by means of a respective helical gear 8a-11a for motion transmission to a respective cylinder bearing support.

[0010] Each ball screw 8, 9 on both sides, has a lead-nut group 12, which comprises a receiving case 13 arranged around a respective ball screw. The receiving case 13 preferably comprises a portion 13a, which almost completely locates its respective ball screw and a closing portion 13b delimitating therin a receiving seat 14 (Figures 3 and 4) for a helical screw 15 keyed by means of a key 16 on a shaft 17 extending trasversally to the ball screw, along which it may axially slide.

[0011] At one of its ends the shaft 17 is rotatably supported cantileverwise by a closing flange 18 for the seat 14, through which the shaft extends and projects outwards and it supports either a manual control handwheel 19 (Fig.3) or the output shaft of a reduction unit 20 controlled by an electric reversible low-power motor 21 (Fig.4). Against the other end of the shaft 17 one can abut an enlarged head 22 of a piston rod 23 of a linear actuator, e.g. a fluid operated cylinder, such as a pneumatic cylinder 24 disposed in axial allingment with the shaft 17. The head 22 is fixed to an end of the helical screw 15, so that for each movement of the piston rod 23 the helical screw 15 must slide along the shaft 17, thereby causing a corresponding light movement in one direction or the other of the relative ball screw. Should instead, the shaft 17 be rotated by the handwheel 19 or by the motor 21, a microscopic movement forwards or backwards of its respective ball screw is caused.

[0012] Actuation of the fluid-operated cyilinder 24 or the motor 21 is performed by an electronic control unit (not shown in the drawings) of a kind usually provided in a flexographic printing machine.

[0013] The movement transmitted to the ball srews owing to the movement of the piston rod 23 can be advantagiously used for printing cutout in a simple, quick and precise way, e.g. by causing a rotation of a predetermined angle a, for example 48°, between the initial position x and the final position y (Figs. 5 and 6) of the respective ball screw.

[0014] Partial micrometric angular movement x-y due to the action of either the handwheel 19 or the motor 21 is suitably used for micrometric setting before starting or during the printing.

[0015] The above described printing cut-out device can be subject to numerous modifications and variationswithin the scope of the claims.

Claims

1. An automatic printing cut-out device for a colour flexographic printing machine having at least one colour group (1) comprising

a block-holding cylinder and a screen cylinder rotatably mounted on suitable supports (2) slidingly movable towards or away from a printing offset drum or a respective back-pressure (2, 3) roller cylinder,

a control system for monitoring movement of the supports comprising

an end cross shaft (4) arranged on its respective colour group, a reversible electric motor (5) for driving said end cross shaft (4), a helical gear (6, 7) at each side of the keyed flexographic printing machine keyed on the said end cross shaft (4), at least one ball screw (8, 9) which is rigid in rotation with a respective helical gear (6, 7) to transmit motion to a respective cylinder bearing support (2, 3) arranged on one side of the machine

lead-nut means (12) on each ball screw (8, 9) for displacing the cylinder supports, and reversable driving means for said lead-nut means (12) designed to cause a limited angular movement to its respective ball screw (8, 9) thereby obtaining a desired linear movement of the respective support (2, 3) and thus of the respective cylinder thereof.

2. A device according to claim 1, wherein said driving means comprise a fluid operated linear actuator (23).

3. A device according to claim 2, wherein said driving means comprise a low power electric motor (21) for micrometric setting of the cylinder.

4. A device according to any previous claim, wherein each lead-nut group (12) comprises a receiving case (13) which completely locates a respective ball screw (8, 9) and delimits a traverse receiving seat (14) and a helical screw (15) rotatably and slidably mounted on said transversal receiving seat in meshing engagement with its respective ball screw.

5. A device according to claim 4, wherein said case (13) comprises a wrapping portion (13a) for its respective ball screw and a closing portion (13b) which delimits the said receiving seat (14) for the helical screw.

6. A device according to claim 5, wherein said helical screw (8, 9) in said receiving seat (14) is keyed on a rotatable shaft (17) which at one end thereof is canterleverwise supported by a closure flange (22) for said receiving seat.

7. A device according to claim 6, wherein said shaft (17) at one end thereof is operatively connected to said actuating means (23).

8. A device according to claim 7, wherein said driving means comprises a handwheel (19) for said shaft.

9. A device according to claim 7, wherein said driving means comprise a reduction unit (20).

10. A device according to any of the claims 6 to 9, wherein said helical screw (8, 9) is operatively connected to said linear actuator (23).

11. A device according to claim 10, wherein said linear actuator comprises a fluid-operated cylinder (24) aranged in axial alignment with said shaft (17).

Drawing