Apparatus for printing a curved surface of an object

An apparatus for printing a curved surface of an object, for example a ball includes a stationary printing unit for printing the object, the printing unit including an inkjet print head producing a print on the object surface in an active region of the print head, a curing unit for curing the print, the curing unit including a radiant heater curing the print in an active region of the radiant heater, a movable holding unit for receiving the object in a receiving region, moving the object from the receiving region into the active region of the print head, moving the object in the active region of the print head during production of the print and moving the object into the active region of the curing unit, and a control unit for controlling the movements of the holding unit, the production of the print and the curing of the print.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority, under 35 U.S.C. §119, of German Patent Application DE 10 2014 004 507.2, filed Mar. 27, 2014; the prior application is herewith incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an apparatus for printing on a curved surface of an object.

The invention lies in the technical field of inkjet printing of spatially extended, three-dimensional objects or bodies or their surfaces.

It is already known to print on such objects in special apparatuses. For example, golf balls can be printed individually by inkjet in specially configured printing apparatuses. An apparatus of that type is disclosed in Japanese Patent Application JP 11320863 A. Golf balls are very small objects and their handling is therefore not very problematic. In the case of larger objects, for example soccer balls, the handling becomes more difficult. The width of a print head is then no longer sufficient, for example, to print one half of the ball in one pass. In addition, due to the size and curvature of the ball, edge nozzles of the print head are at too great a spacing from the surface of the ball and therefore print imprecisely. The ball therefore has to be moved under the print head, in particular has to be rotated and the print head has to be controlled correspondingly. A holding apparatus is required for the movement of the ball. Similar problems occur in differently shaped, large objects, for example bags, vehicle trimmed parts or the like. Collisions can also occur and are to be avoided. German Patent Application DE 10 2009 058 212 A1 has also already disclosed using a robot to move the object.

SUMMARY OF THE INVENTION

It is accordingly an object of the invention to provide an improved apparatus for printing a curved surface of an object, which overcomes the hereinafore-mentioned disadvantages of the heretofore-known apparatuses of this general type and which makes it possible to provide3D objects with an imprint on their surface.

With the foregoing and other objects in view there is provided, in accordance with the invention, an apparatus for printing a curved surface of an object, comprising a stationary printing unit for printing the object, the printing unit including an inkjet print head, and the print head producing a print on the surface of the object in an active region of the print head, a curing unit for curing the print, the curing unit including a radiant heater, and the radiant heater curing the print in an active region of the radiant heater, a movable holding unit for receiving the object in a receiving region, for moving the object from the receiving region into the active region of the print head, for moving the object in the active region of the print head during the production of the print and for moving the object into the active region of the curing unit, and at least one control unit for controlling the movements of the holding unit, the production of the print and the curing of the print.

One preferred development of the apparatus according to the invention can be distinguished by the fact that the holding unit includes a plurality of movement units, each movement unit generating a linear or rotational movement, and only one movement unit being active for the linear or rotational movement of the object from the receiving region into the active region of the print head and from there into the active region of a further print head or into the active region of the radiant heater.

Another preferred development of the apparatus according to the invention can be distinguished by the fact that the printing unit includes a plurality of print heads, the print heads being disposed substantially on a horizontally oriented circle and spaced apart from one another in such a way that nozzle rows of the print heads are oriented substantially radially with respect to the circle.

A further preferred development of the apparatus according to the invention can be distinguished by the fact that the curing unit is disposed substantially on the horizontally oriented circle and spaced apart from the print heads.

An added preferred development of the apparatus according to the invention can be distinguished by the fact that the printing unit includes a plurality of print heads, the print heads being disposed substantially on a horizontally oriented straight line and spaced apart from one another in such a way that nozzle rows of the print heads are oriented substantially perpendicularly with respect to the straight line.

An additional preferred development of the apparatus according to the invention can be distinguished by the fact that the curing unit is disposed substantially on the horizontally oriented straight line and spaced apart from the print heads.

Yet another preferred development of the apparatus according to the invention can be distinguished by the fact that the holding unit includes a plurality of movement units, a first movement unit being disposed substantially on a vertical axis and substantially perpendicularly below the center point of the circle and making a linear movement of the object vertically possible.

Yet a further preferred development of the apparatus according to the invention can be distinguished by the fact that a second movement unit is disposed on the first movement unit and is disposed substantially on the vertical axis and makes a rotational movement of the object about the vertical axis possible.

Yet an added preferred development of the apparatus according to the invention can be distinguished by the fact that a third movement unit is disposed on the second movement unit and makes a rotational movement of the object about a radial axis possible.

Yet an additional preferred development of the apparatus according to the invention can be distinguished by the fact that a fourth movement unit is disposed on the second movement unit and makes a linear movement of the object in the radial direction possible, and that a third movement unit is disposed on the fourth movement unit and makes a rotational movement of the object about a radial axis possible.

Again another preferred development of the apparatus according to the invention can be distinguished by the fact that the holding unit includes an articulated arm robot, in particular with 5 or 6 rotational axes.

Again a further preferred development of the apparatus according to the invention can be distinguished by the fact that the holding unit includes a suction gripper.

Again an added preferred development of the apparatus according to the invention can be distinguished by the fact that the print heads include in each case one closure which, in the closed state, protects the print head nozzles against radiation of the radiant heater.

Again an additional preferred development of the apparatus according to the invention can be distinguished by the fact that the print heads are received in each case in an aligning unit which makes an alignment of the print head possible linearly in the radial and tangential direction and axially about a print head axis which lies perpendicularly with respect to the plane of the circle.

Still another preferred development of the apparatus according to the invention can be distinguished by a projection unit which projects a marking onto the object in the receiving region.

Still a further preferred development of the apparatus according to the invention can be distinguished by a measuring unit which contactlessly measures at least one section of the surface of the object and makes the measured data which are obtained in the process available, in particular for correcting the spacing between the object and the print head or radiant heater.

Still an added preferred development of the apparatus according to the invention can be distinguished by a precuring unit which includes a radiant heater and precures the print.

A concomitant preferred development of the apparatus according to the invention can be distinguished by a delivery region, the holding unit moving the object from the active region of the curing unit to the delivery region, and the at least one control unit controlling the movement.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the figures of the drawings in detail and first, particularly, toFIG. 1thereof, there is seen a side view of a preferred embodiment of an apparatus1according to the invention for individually printing a surface3of a three-dimensional moving object2, in which the surface3is curved in any desired directions. The object can be a ball, for example.FIG. 2shows a plan view of the same preferred embodiment of the apparatus1according to the invention. In the two drawings, elements which correspond to one another are provided with the same designations in each case.

The apparatus1includes a printing unit4. The printing unit is disposed in a stationary manner in the upper region of the apparatus. The printing unit includes an inkjet print head5. The print head is received in an aligning unit26of the printing unit. The aligning unit is disposed in an opening of a horizontally disposed plate35of a frame34of the apparatus1. The plate has a plurality of openings, so that a configuration of a plurality of print heads is therefore possible. The openings and the plurality of print heads lie on a circle14about a center point18. The openings can be provided in terms of their position, orientation and size in dependence on the size of the print heads and the size of the objects to be printed. Each print head prints one color in the form of ink droplets by using nozzles in nozzle rows15. If a multiple-color print6is to be produced on the object2a plurality of print heads are provided, for example in accordance with known CMYK printing. However, even more print heads, for example up to seven, can be provided if special colors, white pigment or varnish are used. The print heads are connected through a non-illustrated ink supply to one or more ink supply vessels33in the lower region of the apparatus1. The ink supply can also be provided outside the apparatus.

The print heads5can be adjusted in three directions by using their respective aligning unit26or print head receptacle, namely linearly in radial and tangential direction26a,26bwith regard to the circle14and axially about a print head axis26cwhich lies perpendicularly with respect to the plane of the circle. An alignment of this type is usually required only during setting up of the apparatus or in the case of maintenance. During printing, the print heads remain fixedly in their position. It is also possible to tilt the print heads in the direction of the center axis of the apparatus1. This can be advantageous, in particular, in the case of elongate objects2, in order to prevent them from colliding with the inactive print heads during printing.

The print heads5can be configured as two-color heads, with only one color being printed, however. In this case, the nozzles for the second color are used as reserve nozzles which are employed in the case of a nozzle failure for the first color.

A curing unit8including a radiant heater9is provided in a further opening on the same plate35. The radiant heater is preferably a UV radiant heater if UV ink is used, but can also be an IR radiant heater. The radiant heater can be configured as an LED radiant heater. The radiant heater is also disposed on the circle14. The print heads5are disposed on the circle so as to follow one another in one direction. The radiant heater is disposed so as to follow the print heads in this direction. The curing unit or the radiant heater has an active region10. In addition to the curing unit, a precuring unit30(a so-called pinning module) with a radiant heater31can also be provided. A plurality of pinning modules can also be provided, in each case one behind each print head4.

In order to protect the print heads5against radiation of the curing unit8, respective closures25(so-called shutters) are provided on the print heads. Inactive heads are closed in the case of an active curing unit, as a result of which curing of ink on or even in the nozzles can be avoided. Each closure can have two pivotable shutters.

A modular holding unit11is disposed on the frame34below the plate35, that is to say in the central region of the apparatus1. The holding unit has a vertical axis17which runs substantially through the center point18of the circle14. The holding unit serves to receive and transport and rotate the object2, that is to say it holds the object during printing, with the object being moved. The object is received in a receiving region12and, for example, is transferred by hand or in an automated manner to a suction gripper24. The latter can have a metallic suction plate with three or more suction openings (see the suction gripper24inFIG. 3).

In the receiving region, an optical marking28can optionally be projected onto the surface3of the object2by a projection unit27, for example by using a laser or a so-called beamer or projector. By acting as a positioning aid, the marking facilitates the introduction of the object in a desired orientation for the operator. For example, the printable region on a ball2can be indicated by way of a marking frame, with the result that the operator can orient the ball with the region to be printed in the printable region.

As an alternative, a positioning cross can be projected onto the object by using laser light. The alignment of a ball can then preferably take place in such a way that a seam of the ball is oriented on the cross. Two crosses can also be projected onto the object at different locations (preferably at locations which lie opposite one another, for instance).

At least one section of the surface3of the object2can likewise be measured contactlessly in the receiving region, optionally by a measuring unit29. The measuring unit can include a camera or a distance sensor. It serves to detect the shape of the object. In the case of a ball, measurements can be carried out, for example, as to whether the ball corresponds exactly to the ideal spherical shape or whether there are local or even global deviations. Deviations of this type can be calculated from the measured data, for example distance data, and can be stored. Later, the data can be used during the production of the print and the curing, by correcting the spacing of the units from the surface by way of a spacing correction of the object. The measured data can also be used to displace the image to be printed within the printable region in an automated manner. This can be necessary, for example, if the object has locations which cannot be printed, such as the seams of a sewn ball which are depressed and can therefore be detected satisfactorily.

It can optionally also be provided to pretreat the surface region to be printed of the object2with a primer, in order to improve the adhesion of the ink. To this end, a primer unit40can be provided, for example, in the receiving region12. The primer unit40can have, for example, a transfer belt for the primer application. The belt can also be used to remove a (sample) print again which has been carried out and has not yet cured. The belt can also be used to clean the object before the primer application, in particular to clean it of dust.

The holding unit11preferably includes at least three modular movement units. A first movement unit16is disposed substantially on the vertical axis17. The first movement unit includes a first (linear) drive36which makes a linear movement19of the object2in the vertical direction possible. This movement serves primarily to vertically align the object, in particular with regard to the respective spacing from the print heads4and from the radiant heater9during printing and irradiation.

The holding unit11includes a second movement unit20. The latter is disposed on the first movement unit16and makes a rotational movement21of the object2about the vertical axis17possible, with the result that the object passes during its transport movement sequentially into the active region7of the print head5and the active region10of the radiant heater. To this end, the second movement unit includes a second (rotational) drive37. The drive serves primarily for the transport movement of the object.

The holding unit11includes a third movement unit22with a third (rotational) drive38. The unit is disposed on the second movement unit20and makes a rotational movement21of the object2about a radial axis23possible. In the case of a ball, the radial axis can preferably coincide with an axis of symmetry of the ball itself. The drive serves primarily for the rotational movement of the object during printing or curing. The third movement unit can also be disposed on an adjusting unit39and the latter in turn can be disposed on the second movement unit. The adjusting unit then preferably allows the radial adjustment of the third movement unit, for example for manual or automated presetting in the case of a defined ball size.

The holding unit11receives the object and conveys or cycles it from the receiving region12into the active region7of the print head4or sequentially into the active regions7of the plurality of print heads4. After printing, the holding unit conveys or cycles the object into the active region of the curing unit8. From there, it conveys or cycles the object into a delivery region32. There, the ball is removed by hand or in an automated manner. The delivery region is preferably identical to the receiving region and is situated behind a lateral opening in the frame, which opening can be closed by way of a door. However, the delivery region and receiving region can also be different from one another.

If a pinning module30is provided, the holding unit11can convey the object from a print head to the pinning module and then to the next print head and from the last print head to the curing unit8. A movement of this type can also include forward and reverse movements (in the circular direction).

The movement of the object2is controlled by a control unit13in the lower region of the apparatus1. The control unit13controls at least the holding unit11or its drives36,37and38. The same control unit can also actuate the print heads2and the radiant heater9, or at least their switch-on and switch-off times. The printing data for the print heads are fed directly or through the control unit13to the print heads from a non-illustrated unit of the so-called prepress stage.

When printing identical objects, such as balls2, the holding unit11can advantageously always perform identical (preset and stored) movements, both for the transport of the ball and for the rotation during printing. The following is generally true (without being restricted to the embodiment which is shown): the holding unit11has a plurality of movement units, each movement unit generating a linear or rotational movement, only one movement unit being active for the linear or rotational movement of the object2from the receiving region12into the active region7of the print head5and from there into the active region7of a further print head or into the active region10of the radiant heater9. In this way, positional errors of the object during printing and curing can be kept small in an advantageous way. If, nevertheless, substantial positional errors occur, they are reproducible and can therefore be taken into consideration, for example, during printing by way of correspondingly compensating printing data.

Balls are preferably printed with one or with two image strips by way of the apparatus1according to the invention. In this case, an individual image strip can span the entire ball circumference and can be at most as wide as the participating print head4can print in a single pass. It can be provided in the user interface of the apparatus to print any desired image in one of the strips and, for example, to complete a text or pattern.

However, it is also possible to print the entire ball, that is to say its surface3apart from the holding region. To this end, the holding unit11can have, for example, a further drive which allows the ball to be pivoted with regard to the print head5or its active region7.

The modular holding unit11can also have up to six movement units or modules. These can be linear drives and rotational drives in any desired combination, depending on the shape of the object2which is to be imprinted. For example, the use of an articulated arm robot with up to six degrees of freedom is also preferred.

As an alternative to the circular configuration of the print heads5and the radiant heater9, a linear configuration can be provided on a straight line, preferably a horizontally running straight line. In this case, the object2is moved by the holding unit11linearly from an active region7of a print head to the next active region7of a following print head or to the active region10of the radiant heater. A forward and reverse movement is also possible, for example if a single pinning module30is used.

FIG. 3shows a perspective view of a further embodiment of the invention. The apparatus1includes a first movement unit16with a linear drive36, a second movement unit20with a rotational drive37, and a third movement unit22with a rotational drive38. In addition, the apparatus includes a fourth movement unit41with a linear drive42(servomotor). The fourth movement unit is disposed between the second and third movement units. The third movement unit is disposed on a carriage43. The carriage allows a movement44in the radial direction (parallel to the radial axis23). The rotational movement of the third movement unit and of the gripper24preferably takes place about a rotational axis which is parallel to the axis23or the thrust direction of the linear drive42. The fourth movement unit41serves for adaptation/adjustment during printing of objects2of different sizes, for example balls of different diameter.

Printing by way of the apparatus1according toFIG. 3takes place as follows:

The movement unit16serves for a compensation movement, if the object2deviates from its ideal shape (sphere, cylinder, etc.) or is clamped-in imprecisely. In this way, the spacing of the object from the print head5can be kept constant. The actual shape and clamping of the object are measured to this end and are transmitted to the control unit13.

The movement unit20serves to cycle or cyclically move the object2from station to station (priming, printing, curing).

As has already been described above, the movement unit41serves for size adaptation. Balls and spherical objects2can be positioned in the radial direction in such a way that, for example, their equator comes to lie under the print head5. The ball can thus preferably be printed with a printing track along the equator. Cylindrical objects are held with their cylinder axis parallel to the radial axis and are rotated about their cylinder axis. In the case of cylinders (for example, bottles, cans, etc.), the movement unit41serves for advancing in the radial direction, with the result that the objects can be provided with a plurality of adjacent circumferential printing tracks by one print head5.

The movement unit22serves to rotate the object2, in order to produce one or more printing tracks in the circumferential direction by way of the print head5. This printing movement and the compensation movement (of the movement unit16) proceed in a superimposed or simultaneous manner, if compensation is required.