Screen-printing machine with a device for transferring objects to be printed

The present invention relates to a screen-printing machine of the type comprising:a print station comprising a squeegee and a screen support for supporting a screen-printing screen, and an object holder for holding an object to be printed, the screen support and the squeegee being mounted to move relative to each other;at least one support surface for supporting the objects away from the print station; andat least one transfer device for transferring an object between a support surface and the object holder, which transfer device comprises:a manipulator arm equipped with an end clamp, the arm being hinged relative to the support surface about a pivot axis and the clamp being hinged relative to the arm about a tilt axis that is offset angularly from the pivot axis; andsynchronization means for synchronizing the movement of the arm and the movement of the clamp for moving the transfer device between a position in opposition to the support surface and a position in opposition to the print station.

BACKGROUND OF THE INVENTION

As is known per se, circularly symmetrical objects are printed in a screen-printing machine by turning the object about its own longitudinal axis and by concomitantly moving a screen in a plane tangential to the object, with ink being transferred through the screen by a squeegee being pressed against said screen, the screen being squeezed between the object and the squeegee.

Flat objects such as compact disks can also be printed by screen-printing. They are then held stationary under the screen which is also stationary, and the squeegee is moved over the length of the-screen to transfer the ink progressively to the flat object.

Such machines are used for repetitively printing identical objects.

Solutions have been proposed in order to automate putting the objects in place in the print station and removing them therefrom. In such machines, the objects to be printed are brought into the vicinity of the print station by a feed conveyor, and they are then transferred from the conveyor to the print station by a transfer device. In addition, a symmetrical other transfer device transfers the printed objects from the print station to a removal conveyor.

On the conveyors, the objects to be printed are generally disposed with an orientation different from the orientation of the objects in the print station.

More precisely, when the objects to be printed are flasks, they are placed vertically on the surface of the conveyor with their longitudinal axes disposed perpendicularly to the surface of the conveyor. Whereas, in the print station, the objects must be disposed with their longitudinal axes disposed generally horizontally, i.e. perpendicularly to the initial orientation direction of the objects on the conveyor.

Therefore, the transfer device interposed between the feed conveyor and the print station is suitable for moving the object all the way between the outlet end of the conveyor and the print station while also simultaneously turning the object over.

The opposite movement must be provided by the other transfer device in order to transfer the printed object from the print station to the removal conveyor.

In those documents, the transfer device comprises a manipulator arm equipped with an end clamp. The arm is hinged relative to the frame of the print station to pivot about an axis extending exactly perpendicularly to or parallel to the support surface for supporting the objects on the feed conveyor. The clamp is hinged relative to the arm so that the arm and the clamp are moved concomitantly.

With such a device, it is observed that, for objects whose bases are relatively wide, the periphery of the base hits the surface of the conveyor during the initial stage in which the object is moved towards the print station. Tilting the object by turning the clamp starts while the object is still in contact with the conveyor. Thus, the periphery of the base of the object exerts a pressure on the conveyor, thereby generating large forces in the transfer device and in the conveyor, reducing their lives.

Likewise, it is observed that such forces exist while the objects are being put in place in the print station. In addition, excessive forces are also encountered by the transfer device for removing the printed objects and transferring them to the removal conveyor.

OBJECTS AND SUMMARY OF THE INVENTION

An object of the invention is to propose a printing machine in which the transfer device is not subjected to large forces during the initial and final stages of moving the object to or from the print station.

To this end, the invention provides a printing machine of the above-mentioned type, wherein the pivot axis of the arm defines with the normal to the support surface a non-zero angle of inclination that is less than 45°.

According to particular embodiments, the machine has one or more of the following characteristics:the pivot axis is offset relative to the segment connecting the support-surface to the print station, and the pivot axis extends away from the normal to the support surface in the same direction as said normal;said angle of inclination lies in the range 1° to 20°;the pivot axis and the tilt axis of the clamp are non-perpendicular;the tilt axis extends in a plane parallel to the plane of the screen-printing screen that is defined by the screen support when the transfer device is in its position in opposition to the print station;said synchronization means comprise a reference bevel gear disposed on the pivot axis and a drive bevel gear for driving the clamp carried by the arm as the arm pivots about the pivot axis, which drive bevel gear is movable in rotation about its own axis relative to the arm and is meshed with the reference bevel gear so that it turns when the arm pivots;the axis of the drive bevel gear of the clamp is perpendicular to the pivot axis and defines a non-zero angle with the tilt axis about which the clamp tilts, the clamp and said drive bevel gear being coupled together so that they are constrained to rotate with each other by a universal joint;the machine further comprises means for moving the reference bevel gear in rotation relative to the arm independently of the movement of the arm; andin the print station, the screen support is movable in translation between a position away from the object holder for holding an object to be printed and a position close to the object holder, and said machine further comprises a control unit suitable for sequencing the movement of the screen support between its away and close positions and for transferring an object between a support surface and the object holder by means of the transfer device.

MORE DETAILED DESCRIPTION

For example, the printing machine10of the invention is designed for printing flasks. It essentially comprises a screen-printing print station12, a feed conveyor14for feeding in objects to be printed and a removal conveyor16for removing printed objects, and, between each conveyor14,16and the print station,12, a respective transfer device referenced18,20, one transfer device being suitable for loading objects onto the print station, and the other being suitable for unloading objects therefrom.

The machine further comprises a control unit for controlling the print station12, the two conveyors14,16, and the transfer devices18,20so that operation of them is synchronized, as is known per se.

The print station12, shown in a front view inFIG. 2, has a frame22that extends generally vertically and a cradle24for supporting a screen-printing screen26. The cradle is mounted to move in translation along a side face of the frame in a horizontal plane in a direction a—a.

A stationary squeegee28is disposed opposite to the cradle24and bearing against the top surface of the screen26. In addition, the print station includes means30for retaining an object to be printed and for driving it in rotation. Said means comprise a rotary socket32defining a cavity of shape matching the shape the bottom of the object to be printed. The socket is mounted to turn about an axis A—A that is perpendicular to the direction of movement of the screen. Means for driving the socket in rotation about its axis are disposed in the frame22. Facing the cavity and along the axis of rotation A—A of the socket, a spike34is disposed for retaining the object to be printed, as shown inFIG. 1. The spike is mounted to slide towards and away from the socket in order to squeeze the object to be printed axially between the socket32and the spike34.

The means30for retaining and driving the object to be printed, which means are constituted by the socket and by the spike, are prevented from moving in translation relative to the frame22in the plane perpendicular to the axis A—A. Conversely, the squeegee28and the cradle24carrying the screen26are mounted to move in translation relative to the frame22between a position away from the axis A—A as shown in continuous lines inFIG. 2and a position close to the axis as shown in dashed lines. This movement takes place in a direction b—b in a plane that is perpendicular to the plane of the screen and that contains the axis of rotation A—A.

The conveyors14,16are identical, and each of them comprises a looped conveyor belt40held between two parallel deflector rollers42, one of which is motor-driven. The conveyors14,16define respective support surfaces40A,40B for supporting the objects, which surfaces extend in a common plane which is preferably horizontal.

The objects to be printed are disposed one behind the other on the conveyor. An abutment43for stopping the objects is disposed at the downstream end of the feed conveyor14so as to retain the objects until they are removed by the transfer device18.

The transfer devices18and20are mutually symmetrical about a vertical midplane. Thus, only the device18is described in detail, in particular with reference toFIGS. 3 and 4.

Said transfer device18essentially comprises a support plate50, a base52secured to the plate, an arm54mounted to pivot relative to the base52about an axis Z1-Z1and a clamp56for grasping the objects, which clamp extends the arm54. The clamp is mounted to pivot relative to the arm54about an axis R1-R1.

The plate50is constituted by a plane rigid sheet. It is secured relative to the conveyor14and to the frame22in a position such that said plate extends parallel to the support surface40A for supporting the objects at the outlet-end of the conveyor14.

The pivot axis Z1-Z1of the arm54defines an angle with the base50and thus with the support surface40A for supporting the objects at the outlet of the conveyor, said angle being a non-zero angle smaller than 45° and preferably lying in the range 1° to 20°.

As shown inFIG. 1, the pivot axis Z1-Z1of the arm54is offset relative to the print station and to the conveyor outside the segment connecting the outlet end of the conveyor14to the print station12, and said pivot axis extends substantially on the mean perpendicular of said segment.

Thus, the axis Z1-Z1is equidistant from the outlet end of the conveyor14and from the print station12. It is inclined so that it extends away from the segment connecting the outlet end of the conveyor14to the print station12in the same direction as the normal to the support surface40A, i.e. in the upward direction extending away from said surface.

For this purpose, the base52supporting the arm54is carried by two wedge-shaped chocks58interposed between the plate and the base52as shown inFIG. 3.

The base52comprises a casing60associated with a motor and gearbox unit62for driving the arm54which is secured to the casing60on a side face thereof. A drive shaft64that is visible inFIG. 4and that comes from the motor and gearbox unit62projects into the casing. A gearwheel66for driving the arm54is mounted to turn inside the casing60. The gearwheel extends along the axis Z1-Z1. It is provided with peripheral fluting adapted to co-operate with complementary fluting provided on the drive shaft64.

In the embodiment in question, the gearwheel66is guided by two ball bearings68retained in the casing on either side of the gearwheel.

The arm54is provided with a turret70extending the gearwheel66coaxially on one side and extending generally along the axis Z1-Z1. The gearwheel66and the turret70are constrained to rotate with each other.

The arm54is also provided with a radial extension72secured to the turret70and extending along an axis X1-X1that is perpendicular to and that intersects the axis Z1-Z1.

The clamp56is carried at the end of the radial extension72.

As shown inFIG. 3, the clamp56comprises two jaws78and mechanism80for supporting and actuating the jaws. Said support is secured to the end of a shaft82mounted to turn about the axis R1-R1via bearings83at the free end of the extension72.

The support and control mechanism80comprises pneumatic actuators for actuating the two jaws78which are hinged about axes extending perpendicularly to the axis R1-R1. The mechanism80is suitable for moving the jaws apart on either side of the axis R1-R1, making it possible to release an object, and for moving the two jaws towards said axis in order to hold an object between them.

The transfer device includes mechanical means for synchronizing the turning of the clamp56about the axis R1-R1and the turning of the arm54about the axis Z1-Z1, so that they move angularly in corresponding and concomitant manner.

The shaft82of axis R1-R1is connected to a primary drive rotary shaft84extending inside the extension72along the axis X1-X1via a universal joint86. The axes R1-R1and X1-X1define a non-zero angle that is preferably equal to the angle defined by the axis Z1-Z1with the normal to the bearing surface40A for the objects at the outlet of the conveyor14.

At its end, the shaft84is provided with a bevel gear88projecting into the turret70. The bevel gear88is in engagement with a complementary bevel gear90carried by a shaft92extending along the axis Z1-Z1and passing through the turret70, through the base52, and through the plate50. In particular, said shaft extends through a bore provided axially through the gearwheel66.

Thus, the bevel gears88and90form an angle deflector, the bevel gear88being mounted to rotate about its own axis relative to the arm54and in particular relative to the turret70about the axis X1-X1.

At its bottom end projecting from the casing60and beyond the plate50, the shaft92is provided with a control crank94constrained to rotate with the shaft. At its free end, the crank94is secured to the drive rod of an actuator96whose other end is secured to the plate50. For example, the actuator96comprises a pneumatic actuator or an incremental motor. The motor and gearbox unit62and the actuator96are connected to the control unit of the machine, which control unit also causes the movement of the conveyors14,16to be synchronized, causes the spike34to move, causes the socket32to be moved in rotation, causes the screen26and the squeegee28to be moved upwards and downwards along the direction b—b, causes the cradle24for supporting the screen to move along the direction a—a, and causes the clamp56to open and to close via the pneumatic mechanism80.

The printing machine operates as follows under the control of the control unit which ensures that operation of the various drive elements takes place in sequence.

For objects of cylindrical shape, regardless of whether they are circular or oblong in cross-section, the axis of rotation of the socket32extends parallel to the support surface40A for supporting the objects at the outlet of the conveyor14. In which case, the actuator96is inactive throughout the operating cycle of the machine, so that the bevel gear90is held stationary relative to the base52. The turret70is mounted to turn relative to the bevel gear90about the axis Z1-Z1under the action of the motor and gearbox unit62.

Initially, the screen is assumed to be spaced apart from the object-holder and the grasping device is in its collection position in which it collects an object from the conveyor14. In this position, in opposition to the support plate40A, the two jaws78are spaced apart from each other on either side of an object. Firstly, the object is clamped between the two jaws by operating the mechanism80. The motor and gearbox unit62is then actuated. The turret70turns about the axis Z1-Z1towards the print station by operating the motor and gearbox unit62driving the shaft64, and the gearwheel66. While the turret is turning, since the bevel gear90is held stationary and since the complementary bevel gear88is driven in rotation with the turret70about the axis Z1-Z1, the bevel gear88turns about its own axis, i.e. about the X1-X1, thereby causing the clamp56to turn about the axis R1-R1, the movement in rotation being transmitted by the universal joint86. Thus, the object retained by the clamp is moved from the conveyor14towards the print station12, and is tilted concomitantly under the action of the clamp56turning until it reaches the print station12where the transfer device is in its loading position, in opposition to the print station. In this position, the axis R1-R1is parallel to the plane of the screen26. The screen and the squeegee are then lowered to the object holder in order to perform the printing under the control of the control unit.

Insofar as the axis Z1-Z1is offset angularly relative to the plane of the conveyor14, the object is moved in a plane that is not parallel to the support surface40A and that is disposed above the plane containing said support surface.

Thus, during this initial stage in which the object is being moved and tilted, said object is driven upwards away from the initial bearing surface40A, thereby preventing the periphery of the bottom of the object from hitting the conveyor as it is being initially tilted.

Similarly, the inclination of the axis Z1-Z1facilitates engaging the bottom of the object into the cavity of the socket32.

Simultaneously with the movement of the transfer device18, the transfer device20moves and tilts an object that has been printed in the print station12in the opposite direction towards the removal conveyor16. The printed object moving in an inclined plane facilitates disengaging it from the cavity and depositing it on the conveyor without the periphery of its bottom acting on the cavity or on the conveyor.

Between the simultaneous transfer stages, an object is printed in the station12in a manner known per se by turning the object and by tangentially moving the screen.

When the object to be printed referenced0is frustoconical in shape (tapered), as shown inFIG. 5, the axis of rotation A—A of the socket32is offset angularly relative to the plane E—E of the screen when said screen is lowered, so that the peripheral surface of the object extends tangentially to the screen.

In particular, in such a case, the axis of rotation of the object during printing is offset angularly relative to the support surface for supporting the objects at the outlet of the conveyor14. In this particular case, and in order to bring the objects into the print station12in a satisfactory angular position, the actuator96is activated when the motor and gearbox unit62is activated or at the end of activation thereof. Thus, when the turret70turns, the bevel gear90is moved slightly angularly under the action of the actuator96, so that the turning of shaft86, and thus of the clamp56is reduced in view of the angular movement of the bevel gear90.

This particular arrangement makes it possible for the same machine to be used to print cylindrical objects and frustoconical objects, without the bevel gears88and90being changed in order to modify-the gearing ratio.

In a variant, the installation is equipped with a non-rotary object carrier suitable for receiving flat objects to be printed. In this embodiment, the screen is fixed relative to the object during printing whereas the squeegee is movable in translation along the length of the screen so as to transfer the ink to the object.