WO1995022458A1 - A device for screen printing discrete objects, in particular containers of substantially elliptical or polycentric cross section - Google Patents

Abstract

The device is designed for use in a screen process printing machine, and more especially a machine able to accommodate containers (14) of elliptical cross section. The single container (14) is secured between a pair of end restraints (7, 8) arranged in such a way as to remain permanently associated with a movable structure (15) forming part of the device and invested with movement in a plane perpendicular to the planes in which the squeegee carriage (1) and the stencil carriage (3) of the print station are reciprocated. In operation, the containers (14) are handled by an infeed-outfeed system employing cradles (38) supported and translated toward and away from the print station by respective linear actuators (39, 40) which are interconnected through an articulated structure (42) set in motion by the main drive system of the machine.

Description

A device for screen printing discrete objects, in particular containers of substantially elliptical or polycentric cross section

The present invention relates to a screen process printing device for discrete objects. More exactly, the device is suitable for printing containers, and in particular containers exhibiting a substantially elliptical or polycentric type of cross section, including those with a mouth offset from the longitudinal axis of the container itself. In conventional screen process printing machines, the objects to be printed are directed by conveyor systems of various types into a print station where a squeegee is drawn across a mesh stencil of silk, nylon or polyester, coated with the printing ink; those areas of the printed surface not destined to receive ink are left blank by stopping the holes in the corresponding areas of the mesh.

The ink is thus forced by the squeegee through the open holes of the mesh stencil and deposited on the surface beneath. The prior art embraces screen process machines of which certain are suitable for printing cylindrical containers and others are able to print containers of substantially elliptical cross section. In the latter instance, the method is effectively one of printing a virtual cylindrical container having a radius of curvature equivalent to that of the elliptical surface.

One such screen process printing machine suitable for containers of elliptical section is disclosed in European Patent 0 063 390, which illustrates a device comprising a squeegee carriage set in motion by a rocking lever and translatable horizontally along slide ways.

The device in question also comprises a similarly translatable screen or stencil carriage coupled to a sector gear and caused thus to traverse beneath and parallel with the squeegee carriage, in the opposite direction; the sector gear is adjustable for height (mounted slidably in a relative slot afforded by an element rigidly associated with the squeegee carriage) , and meshes with a rack afforded by the underside of the stencil carriage. Such a device will use a variety of interchangeable sector gears, each designed to match a particular curvature presented by the surface of an object to be printed. The individual objects for printing are restrained longitudinally by means comprising a pivotable base clamp and a freely rotatable or dead centre clamp, between which the object is secured. The restraining means are rotatable about their own longitudinal axis, which coincides with the axis of the clamping action, in such a way as to follow the profile of the sector gear. The device further comprises a flat frame occupying a position beneath the two carriages and associated pivotably with the machine in such a manner that it can oscillate in a vertical plane parallel with the stroke axes of the squeegee and stencil carriages. It is to the free end of the flat frame that the restraining means are mounted: thus, the object to be printed is carried by a clamping or chucking mechanism anchored to a fixed point of the machine by way of the flat pivotable frame, to which both the squeegee carriage and the stencil carriage are also connected mechanically.

A first drawback betrayed by the device outlined above is attributable to the fact that the squeegee and stencil carriages move in mutually opposite directions: this results in a notably high print velocity (the sum of the absolute values reflecting the rate of displacement of the screen and of the squeegee, respectively) during the printing stroke, leading to difficulty in controlling the operation and possible smudges due to the lack of precision. A further drawback of the device in question stems from the fact that a container with a mouth offset in relation to its own longitudinal axis cannot be printed, since this requires a live centre clamp. The object of the present invention is to provide a device for screen printing discrete objects, and in particular containers of circular, elliptical or polycentric cross section, which is able also to print containers embodied with a mouth offset from the longitudinal axis of the relative body. A further object of the invention is to allow of reducing the print velocity at any given output of the printing machine, thus obtaining a more precise printed image and avoiding smudges. The stated objects are realized, according to the present invention, in a screen process printing device as characterized by the appended claims, and principally in that the means by which objects are restrained during printing are arranged in such a way as to remain rigidly associated with a movable structure of the device, the movable structure in its turn being equipped with means by which it is rendered capable of movement in a plane orthogonal to the planes of movement of the squeegee carriage and the stencil carriage. Moreover, the restraining means are disposed in a manner such that their axis of rotation is offset from and parallel with the longitudinal axis along which the object for printing is secured. An additional object of the invention is to provide a screen process printing machine equipped with a container feed system that will allow of printing cylindrical containers of circular cross section, as well as containers of substantially elliptical, polycentric, square or rectangular cross section, both in an extremely simple manner and without the need for complex adjustments typical of machines embraced by the prior art, for example as disclosed in Italian Patent IT 1242401. Yet another object of the invention is to simplify those operations made necessary by a change in the dimensions and/or in the shape of the containers. These further objects are fully realized, according to the present invention, in feed means comprising cradles by which single containers are supplied to the print station, then taken up after printing and transferred to an outfeed station; the cradles are supported by and translatable toward and away from the print station through the agency of respective means interconnected mechanically by an articulated structure and set in motion by the drive system of the printing machine.

A preferred embodiment of the invention will now be described in detail, by way of example, with the aid of the accompanying drawings, in which: -fig 1 illustrates the device disclosed, in its entirety, viewed in perspective from the front; -fig 2 illustrates a detail of the device, viewed in perspective from above; -figs 3 and 4 are views from the rear, illustrating the configuration of the device in two different operating steps;

-fig 5 is a schematic illustration of restraining means by which objects are clamped during printing; -figs 6, 7, 8 and 9 illustrate feed means by which the objects are directed through the print station, seen in perspective and in four different operating configurations;

-figs 10 and 11 show details of the feed means, viewed respectively in elevation and in perspective from the rear; -fig 12 is a diagram illustrating the operation of the elements shown in fig 11.

With reference to the drawings, 1 denotes a first carriage, in its entirety, of which the function is to support a squeegee 2 mounted to the bottom of a head 13 rigidly associated with the carriage 1. The carriage 1 is translatable horizontally along a pair of cylindrical ways 5. 3 denotes a second carriage serving to support a mesh stencil 4 as used in screen process printing, which is indicated by phantom lines. Fig 2 provides a detailed illustration of means, linked mechanically to the squeegee carriage 1 in a manner to be described more fully in due course, by which a single object, namely a container 14, can be restrained longitudinally during the printing step and released thereafter.

Such restraining means comprise a mutually coaxial base clamp 7 and centre clamp 8, both of which are power driven; the two components are interconnected mechanically and disposed in such a way that their common axis of rotation 30 extends offset from and parallel with the longitudinal axis 31 along which the container or object to be printed is secured, as illustrated in fig 5. With reference to figs 3 and 4 of the drawings, 17 denotes a rocking lever rotatable about a pivot 18 through the agency of the drive means (conventional in embodiment and therefore not illustrated) with which the printing machine is equipped.

The top end of the rocking lever 17 is connected mechanically to the squeegee carriage 1 by way of a rod 19. Still observing figs 3 and 4, the rear part of the squeegee carriage 1 carries a block 20 associated slidably with a slot 21 and adjustable thus for height. The block 20 rotatably supports a sector gear 10 constituting a first toothed member of which the profile coincides with the profile of the surface presented by the object 14 to be printed, and meshes uppermost with a second toothed member consisting in a rack 11 afforded by the underside of the stencil carriage 3. The sector gear 10 is connected rigidly by way of a bracket 12 to a movable structure 15 carrying the restraining means, in such a way that movement is transmitted from the gear to the structure. The restraining means, the movable structure 15 and the two carriages 1 and 3 are thus interconnected mechanically. The movable structure 15, a carriage type assembly capable of vertical movement in a plane orthogonal to the planes of movement of the carriages 1 and 3, is permanently associated with a pair of rods 16 (one only of which can be seen in the drawings) axially slidable within relative sleeves 22. The orthogonal plane aforementioned is one and the same as the plane occupied by the axes of the rods 16. The rods 16 are interconnected at the bottom ends by a bridging member 24 which is connected in its turn through linkages 23, consisting in a pair of rods and a torsion bar, to a pneumatic cylinder 25. The function of the cylinder 25 is to balance the force generated by the weight of associated moving parts during the operating cycle of the machine, when the movable structure 15 is reciprocated in the vertical direction. In this way, the precision of movements and timing mechanisms is guaranteed, and vibrations are neutralized. 26 denotes transmission components associated with the restraining means, by which the base clamp 7 and centre clamp 8 are drawn toward and distanced from one another along the relative longitudinal axis 31. These comprise a shaft 27, attached to a structure 28 supporting the centre clamp 8, which is axially slidable inside a sleeve 32 associated with the structure supporting the base clamp 7. As discernible from figs 2 and 5, the base clamp 7 and centre clamp 8 are interconnected mechanically by a shaft 29, pulleys 34 and timing belts 33.

More exactly, rotation is transmitted by way of a first belt 33a from a first pulley 34a, keyed onto a shaft supporting the base clamp 7, to a second pulley 34b keyed to the interconnecting shaft 29. A third pulley 34c, a further belt 33b and a fourth pulley 34d combine to complete the transmission to to the shaft supporting the centre clamp 8. A shaft 29 of telescopic type is adopted, so that the distance between the base and centre clamps can be varied in the event that containers of different size are to be printed.

The present invention also relates to feed means, denoted 9 in fig 1 and illustrated in more detail in figs 6 to 12, by which the single containers 14 are conveyed into the print station beneath the stencil 4 and the squeegee 2. The single container is secured initially by the restraining means with the longer axis of the base clamp 7 angled at 40° from a plane normal to the planes occupied by the two carriages 1 and 3, and released subsequently, on completion of an angular movement by the base and centre clamps during the printing step, with the base clamp positioned as in fig 1, i.e. angled at 40° but in the opposite direction to that of the initial restraining position.

In the course of the oscillating movement described by the container and the sector gear 10 (which is substantially less than the corresponding angular distances described by conventional devices) , the translational movement of the squeegee carriage and the squeegee is unidirectional, from left to right in the example of fig 1, whilst the translational movement of the stencil carriage and the stencil is bidirectional and significantly less in terms of absolute distance.

More exactly, as the squeegee traverses from left to right during the printing stroke (and from right to left on the return stroke) , the stencil carriage completes one portion of its travel in the same direction as the squeegee (during which the print velocity is given by the difference between the absolute values of the speeds of the squeegee and the stencil) and another in the opposite direction. It is therefore evident that the print velocity, at a given output tempo, is reduced in comparison to conventional solutions where the two carriages 1 and 3 traverse in opposite directions during the printing step. The precision of the printed image is also enhanced by the reduced angular travel.

Further advantage is gained by virtue of the fact that the limited travel of the stencil carriage, between 0 and 6 mm approximately, helps to reduce inertia and obtain greater print accuracy, avoiding ink smudges.

The vertical motion of the movable structure 15 is induced by way of the bracket 12 which, in contrast to conventional solutions, remains permanently associated with a moving part of the machine and thus allows the movable structure 15 to describe a faultlessly vertical trajectory.

Moreover, given the particular arrangement of the container during the printing step, i.e. offset from the axis of rotation of the restraining means, it is a simple matter to print a container having the mouth disposed eccentrically in relation to the longitudinal median axis of the container body. When printing cylindrical containers with a machine of the type to which the present invention relates, it suffices simply to replace the offset base and centre clamps with others identical in design, but of geometry such that the axis of the restraining action coincides with the axis of rotation. Similarly, the sector gear 10 will be replaced with another of circular profile.

Referring to figs 6...12, which illustrate the feed means aforementioned, blank containers 14 are taken up from a conveyor system 36 of conventional type along which the container advances retained between two side fences, one invested with movement, and transferred subsequently, after being printed, to a runout conveyor 37 of identical embodiment. The area coinciding with the print station, that is to say directly beneath the squeegee 2, is occupied by a pair of mutually opposed cradles 38: an infeed cradle 38a by which the blank container is taken up from the incoming conveyor 36 and positioned in the print station, and an outfeed cradle 38b by which the printed container is removed from the station and transferred to the runout.

Each cradle 38 is supported by a rod 39, which can be disposed either substantially perpendicular to the plane occupied by the cradle (as in figs 6...9) or at an angle to the cradle (as in fig 10) . Each rod 39 is capable of movement along its own axis, generated by a relative pneumatic cylinder 40. The cylinders 40 and their rods 39 thus constitute means by which the cradles 38 are supported and invested with rectilinear movement. Each cradle 38 also affords an opening to allow the insertion of a suction duct 41 through which a partial vacuum is generated in the cradle to the end of retaining the container more easily. In practice, the duct 41 will be connected by way of small bore pipelines to means of generating suction, neither of which are illustrated in the drawings, being conventional in embodiment.

The two cradles 38 and their respective pneumatic cylinders are connected to the opposite ends of an articulated structure, denoted 42 in its entirety, comprising a lever 44 associated with the single drive system of the machine via a cam and invested thus with oscillating motion which is transmitted to a rod and crank denoted 45 and 46, as indicated by the arrows 54 in fig 9.

Movement is transmitted from the resulting linkage 44, 45 and 46 to the cradles 38 through a further mechanism 47 composed of two parallelogram linkages arranged in crossed formation and positioned behind a supporting plate 43. This mechanism, illustrated to advantage in figs 11 and 12, comprises four hinged joints 48a, 48b, 48c and 48d coinciding with the ends of two contoured rods or bars 49. The joints are interconnected in pairs by two triangular levers 56, one of which one denoted 56a is rotatable about a relative pivot 55 and set in motion by the crank arm 46. The two cylinders 40 aforementioned are rigidly associated with the two contoured bars 49, the one at a point on one bar in the neighbourhood of the joint denoted 48d, the other with the opposite end of the remaining bar.

It is to the free ends 50 of the cylinders 40 that the cradles 38 are attached. With the device in operation, a blank container 14 reaching the end of the incoming conveyor 36 (as in fig 6) will be taken up by the infeed cradle 38a and transferred, correctly aligned, to a position of readiness for printing (see fig 7) , where it is held fast between the base clamp 7 and the centre clamp 8. At this point, the linkage components 44, 45 and 46 and the parallelogram mechnism 47 are at their top dead centre. The passage of the mechanism beyond its top dead centre triggers the start of the print step proper, during which the infeed cradle 38a descends and returns gradually to the take-up position, whilst the outfeed cradle 38b will ascend in readiness to receive the container 14 from the print station following completion of the printing step (fig 8) . During the next step (fig 9) , the printed container is released onto the runout conveyor 37 and another blank container is transferred to the print station by the infeed cradle 38a. In the case of containers exhibiting an essentially elliptical or polycentric cross section, a change from one size of container to another is effected quite simply by adjusting the stroke length of the rods 39 of the pneumatic cylinders 40, since this will adapt the parallelogram mechanism 47 to the new operating situation.

The adjustment is effected by loosening a pair of screws 53 to free a relative stroke limit block 57, then repositioning the block, which is accommodated slidably by a relative support 58, and retightening the screws.

The screws 53 and the sliding block 57, together with its support 58, thus combine to provide means for adjusting the stroke of the rods 39. Clearly, the solution disclosed is much simplified in comparison to the complicated and laborious adjustments required in traditional machines. When operating with containers of circular, square or rectangular cross section, moreover, the above adjustment is not even necessary when changing over to a new size since the rods 39 remain set at the maximum travel limit and the cylinders 40 are not activated during the operating steps, the movement of the cradles 38 being produced exclusively by the parallelogram mechanism 47.

Similarly, when effecting frequent changes from containers of circular cross section to containers of square or rectangular section, and viceversa, there is no need to alter the travel limit of the rods 39, which remain set at the maximum extension. Thus, the feed means disclosed allow containers of any given cross section (whether circular, square, rectangular, elliptical, polycentric) to be printed with ease, whilst the changeover from one shape to another requires only a few simple adjustments.

Claims

Claims

1) A device for screen printing discrete objects (14) , in particular containers exhibiting a substantially elliptical, polycentric or circular cross section, comprising:

-a first carriage (1) supporting a squeegee (2) and invested with reciprocating movement; -a second carriage (3) supporting a mesh stencil of the type used in screen printing and invested with reciprocating movement beneath and parallel to the squeegee carriage (1) ;

-restraining means (7, 8) , connected mechanically to the squeegee carriage (1) , by which objects (14) for printing are secured longitudinally, characterized in that the restraining means (7, 8) are arranged in such a way as to remain permanently associated with a movable structure (15) forming part of the printing device and invested with movement in a plane orthogonal to the planes of movement of the squeegee carriage (1) and stencil carriage (3) . 2) A device as in claim 1, wherein the restraining means (7, 8) are arranged in such a manner that their axis of rotation (30) extends offset from and parallel with the longitudinal axis (31) along which an object (14) for printing is restrained.

3) A device as in claim 1, wherein the restraining means (7, 8) comprise a live oscillating clamp (7) serving to accommodate the base of an object (14) for printing, and a live centre clamp (8) connected mechanically to the base clamp (7) .

4) A device as in claim 3, wherein the centre clamp

(8) is connected mechanically to the base clamp (7) by way of timing belts (33) looped around pulleys (34) keyed to a transmission shaft (29) .

5) A device as in claim 1, further comprising:

-a first toothed member (10) connected mechanically to the squeegee carriage (1) in such a way that one is driven by the other, and exhibiting a profile of which the pitch line matches the curvature of the surface presented by the object (14) for printing; -a second toothed member (11) associated with the stencil carriage (3) and engaged in meshing contact with the first toothed member (10) in such a way that the squeegee and stencil carriages are coupled mechanically;

-an element (12) rigidly interconnecting the first toothed member (10) and the movable structure (15) .

6) A device as in claim 1 or claim 5, wherein the movable structure (15) is invested with movement in a plane orthogonal to the planes of movement of the squeegee carriage (1) and the stencil carriage (3) by means of a transmission component (17) , coupled to the squeegee carriage (1) , which is connected by way of the squeegee carriage to a first toothed member (10) engaged in meshing contact with a second toothed member (11) associated with the stencil carriage (3) , and connected by way of the first toothed member to an element (12) rigidly interconnecting the first toothed member (10) and the movable structure (15) .

7) A device as in claim 1, wherein the squeegee carriage (1) and the stencil carriage (3) are interconnected mechanically in such a manner that each traverse effected by the squeegee (2) in one direction during the printing step coincides with a shorter and bidirectional traverse effected by the stencil (4) .

8) A device as in claim 1, wherein the movement of the movable structure (15) is governed by a pair of rods (1) axially slidable in relative sleeves (22) , and the orthogonal plane of movement is the plane occupied by the axes of the rods (16) .

9) A device as in claim 1, wherein the movable structure (15) consists essentially in a carriage and is associated, via mechanical linkages (23) , with a cylinder (25) serving to balance the forces generated by the weight of the movable structure itself when in movement .

10) A device as in claim 9, wherein the cylinder (25) is a pneumatic cylinder.

11) A device as in claim 1, further comprising at least two cradles (38) including a cradle (38a) by which blank containers (14) are transferred singly to a print station and a cradle (38b) by which printed containers are transferred to an outfeed station, wherein the cradles (38) are carried by respective support means (39, 40) and translatable thus toward and away from the print station through the agency of the selfsame support means (39, 40) , which are interconnected mechanically through an articulated structure (42) set in motion by the drive system of the printing machine.

12) A device as in claim 11, wherein each cradle (38) is supported by relative means (39, 40) comprising a pneumatic cylinder (40) of which the rod (39) is anchored to the base of the cradle, thus rendering the cradle translatable along the axis of the rod.

13) A device as in claim 11, wherein the articulated structure comprises linkage elements (44, 45, 46) by which motion is transmitted to a mechanism (47) consisting in two parallelogram linkages created with rods (49) arranged in a crossed formation.

14) A device as in claim 13, wherein the mechanism (47) comprises two contoured rods or bars (49) , of which the respective ends are connected by way of hinged joints (48) to respective levers (56) including one lever (56a) mounted pivotably to a fulcrum (55) and set in motion by a linkage element (46) , also two cylinders (40) associated one with each contoured rod or bar (49) .

15) A device as in claim 12, comprising means (53, 57, 58) by which to adjust the length of stroke allowed to the rods (39) of the cylinders (40) .

16) A device as in claim 11, wherein each cradle (38) affords an opening for the connection of a suction duct (41) through which a partial vacuum is created to the end of retaining the container (14) stably positioned in the cradle.

17) A device as in claim 15, wherein each cylinder (40) is furnished with adjustment means comprising a pair of screws (53) which are loosened to release a block (57) mounted slidably along a corresponding support (58) and functioning as a stroke limiter for the relative rod (39) .