Machine for the offset printing of flat objects, in particular for compact discs

Abstract: A printing machine of offset type for compact discs comprises at least one printing cylinder for at least one colour driven with uniform rotary motion and a chain conveyor driven with intermittent motion for feeding the objects to be printed.

Description: The purpose of the present invention is to confront the problem of the offset printing of flat objects, such as compact discs. The ever increasing distribution of this type of object has made it essential in practice to subject them directly to the multicolour printing of the brand name and other information required to identify their contents. Such articles are currently offset printed on machines comprising an object conveyor which advances at constant speed below at least one printing station, the printing cylinder of which carries a series of equidistant cylindrical segment-shaped printing plates which have collected the image inked in the various inking stations positioned peripherally to the printing cylinder, and deposit it on the objects as they pass below them, The circumferential distance apart of said printing plates equals the linear distance between the objects to be printed which advance on the underlying conveyor, the peripheral speed of the printing plates being exactly equal to the rectilinear speed of the underlying conveyor. With this type of machine, which has proved suitable for printing large flat objects, problems arise when used for printing particularly delicate objects. In this respect, it is virtually impossible to accurately position a delicate object such as a compact disc on a moving conveyor feeding it below a printing station without subjecting the object to impacts and jolting which could damage it. Again, on offset printing machine could not be operated intermittently because the cyclic stoppage of the printing cylinder could compromise the proper operation of the inking rollers. A printing offset system is described in US-A-4271757 in which the conveyor feeding the objects below the printing cylinder advances with intermittent movement wherein a cycle has one halt period, one acceleration period and one deceleration period. An object to be printed is conveyed to a temporary rest determined by the photoelectric detection of a perforation in the conveyor commanding a vacuum actuated clutch and brake unit; then the sensing of the angular displacement of the offset wheel accomplished by means of switches restarts the conveyor and the offset roll surface rolls over the moving object. While this system does not compromise the proper operation of the inking rollers as the printing cylinder rotate continuously, however, it subjects the objects to impacts and jolting. Moreover it is very complex, costly and functionally weak because of the several and complex means necessary for imparting the intermittent motion to the conveyor. Said drawbacks are obviated by the machine as described in the claims. The linear speed during the period of uniform movement is equal to the peripheral speed of the printing plates located on the printing cylinder, which instead rotates with uniform movement. The halt periods are sufficiently long to enable the objects to be loaded onto and discharged from the conveyor. The printing plates carried peripherally by the printing cylinder are spaced apart by a distance depending on the halt and movement periods of the underlying conveyor, so that the printing cylinder can continue to rotate with uniform movement to hence allow correct inking of the printing plates, even when the underlying conveyor cyclically stops. The merits and operational and constructional characteristics of the invention will be more apparent from the detailed description given hereinafter with reference to the figures of the accompanying drawings, which illustrate a preferred embodiment of the invention by way of non-limiting example. Figure 1 is a schematic side view of the invention; Figure 2 is a section on the line II-II of Figure 1; Figure 3 is a schematic plan view of the invention; Figure 4 is a front view of the device which transmits intermittent movement to the conveyor; Figure 5 is a view in the direction V of Figure 4; Figure 6 is a diagram showing the conveyor speeds during one working cycle, as imposed by the devices shown in Figure 4 and Figure 5; Figure 7 is a plan view of one of the constituent plates of the object feed conveyor; Figure 8 is a section on the line VIII-VIII of Figure 7. The figures show a conveyor 1 positioned between a device 2 for loading the objects 3 to be printed and a device 4 for collecting the printed objects 3. Sucker means 5 are provided between the devices 2 and 4 and the conveyor 1 to withdraw the objects from the device 2 and place them on the conveyor 1, and to withdraw the objects from the conveyor 1 and place them in the device 4 after printing. In the illustrated embodiment two printing units 6 and 7 respectively are positioned above the upper portion of the conveyor 1. The device 6 is a single-colour device comprising a printing cylinder 66 which is brought into contact with the underlying object 3 moving along the conveyor 1. In the illustrated embodiment the printing device 7 is a six-colour device in which the inking stations have been omitted for clarity of drawing, only one of them being indicated schematically. Four equidistant printing plates 71 of suitable material are positioned on the printing cylinder 77 to receive the image inked in its various colours by the six inking rollers and transfer it onto the object 3, which is carried below the cylinder 77 by the conveyor 1. The conveyor 1 consists of a strong central tubular frame 8 (Figure 2) carrying slide guides 9 on its upper side and lower side. Two mutually facing slide guides 9 are provided on each of the upper and lower sides and are each composed of three parts 91, 92 and 93, so that overall they create slide tracks for wheels of vertical axis and horizontal axis as described hereinafter. The conveyor 1 slides on the frame 8 after passing about two end toothed wheels, not shown, and is composed of a series of links in the form of plates 10, better seen in Figures 7 and 8, which externally carry wheels 12 on their mutual hinging axes 11, and lowerly carry a centering wheel 13 with its axis perpendicular to the hinging axis 11. The wheels 12 and 13 slide in the tracks created by the guides 9 as stated, and as can be seen in Figure 2. On the opposite side to that comprising the wheel 13 each constituent plate 10 of the chain supports a slab 14 of treated steel, projecting laterally from the guides 9. A seat 15 for receiving one of the objects to be printed is fixed at regular intervals on each slab 14. The seats 15 centrally comprise a projecting pin 16 to be inserted into the central hole in a compact disc 3, which is thus maintained in a fixed position during the printing operations. During the operation of the machine the pin 16 is received in a cavity, not shown, provided in the cylinder 66 and in the printing plates 71. Two series of aligned support rollers 89 are fixed by brackets 88 to the sides of the central frame 8 on those portions below the printing stations 6 and 7 to act as a sliding support for the slabs 14, hence providing rigidity to the system during printing. With particular reference to Figure 3 it can be seen that the machine comprises a single motor 18 which via a first step-down gear 20 operates a programmer mechanism 21 responsible for the intermittent movement of the conveyor 1. The programmer mechanism 21 is shown in Figures 4 and 5, and consists of a bush 22 carrying two facing parallel flat cams 23 and 24 of antisymmetrical development. The bush is keyed onto the output shaft 25 of the step-down gear 20 and is rotatably supported by an external structure, not shown, which supports a second bush 26 which receives and is coupled to the exit shaft 27 of the device. The bush 26 connects together three parallel plates 28, 29 and 30, between which there are positioned two groups each of three equidistant idle rollers 31. The two groups of three rollers positioned between the plates 28 and 29 and between the plates 29 and 30 are arranged to interact with the described cams 23 and 24 respectively, and are displaced by sixty degrees from each other. The exit shaft 27 is connected to one of the toothed wheels about which the conveyor 1 passes and is driven. Because of the aforedescribed configuration, as can be seen from Figure 6 the exit shaft 27 and hence the conveyor 1 are driven with intermittent movement comprising a first stage corresponding to 270 degrees of rotation of the output shaft 25 of the step-down gear 20 during which the speed of the shaft 27 increases, then remains constant and finally decreases to zero, and a second stage corresponding to one quarter of a revolution of the shaft 25 during which the speed of the shaft 27 remains at zero. By virtue of the described device the conveyor 1 which receives the objects to be printed and feeds them below the printing cylinders is driven with an intermittent movement comprising halt stages during which the object to be printed can be easily loaded onto the seat 15 provided on the conveyor 1, and printing stages during which the conveyor moves at a constant speed exactly equal to the peripheral speed of the printing plates 71 provided on the printing cylinder 77 and at the peripheral speed of the cylinder 66. The printing cylinders 66 and 77 are rotated by independent mechanical transmissions connected to the motor 18 at a constant speed such that the respective peripheral speeds are exactly equal to the linear speed of advancement of the conveyor 1 during the periods in which it moves at constant speed. In the illustrated embodiment, relating to the printing of compact discs, the conveyor 1 is composed of 72 plates 10, has a distance between the axes of the toothed wheels of 3600 mm, and supports 36 seats 15 for receiving compact discs 3. If the peripheral speed of the printing means is 40 m/min, 100 objects can be printed per minute.

Claims: A printing machine of offset type for flat objects, in particular for compact discs, comprising: at least one printing station (6, 7) comprising a printing cylinder (66, 77) of offset type driven with rotary uniform movement by a single motor (18); an endless chain conveyor (1) having a rectilinear upper portion for feeding the objects (3) to be printed below said printing cylinder (66, 77); means (15, 16) positioned at regular intervals along said conveyor (1) to receive the objects (3) to be printed and maintain them in position; a step-down gear (20), driven by said single motor (18), which operates a programmer mechanism (21); the programmer mechanism (21) driving the conveyor (1) with intermittent movement in which halt periods alternate with periods during which the speed increases, then remains constant and then decreases; means (2, 4) for loading and discharging the objects (3) onto and from the conveyor (1), and operated in synchronism with its halt periods; characterized by that the programmer mechanism (21) for driving the conveyor (1) comprises: two antisymmetrical parallel cams (23, 24) driven with uniform movement, each interfering with one of two identical circumferential series of rollers (31) supported by a shaft (27) connected to the shaft of the toothed wheel driving the chain conveyor (1). A machine as claimed in claim 1, characterised in that at least the rectilinear upper portion of the chain conveyor (1) is guided within suitable slide tracks (91, 92, 93) which receive idle lateral wheels (12) mounted on the hinging axes of the chain links, and idle central wheels (13) mounted on the chain links with their axis perpendicular to the hinging axes of the chain links. A machine as claimed in claim 1, characterised in that a slab (14), which at those portions thereof concerned with the operation is laterally supported by idle aligned wheels (89), is fixed to those chain links which are intended to support the objects (3) to be printed. A machine as claimed in claim 1, characterised in that the conveyor links are plates (10) which at their mutual hinging points are guided to undergo a circumferential trajectory tangential to a rectilinear trajectory.

Inventors: TERZI FERMO, VERONA MASSIMO, TERZI, FERMO, VERONA, MASSIMO
Applicants: OMSO SPA, O.M.S.O. S.P.A.
Application year: 1993
Main classification: B41F17
IPC codes: G11B23, G11B7, B41F17