Print unit

Information

  • Patent Grant
  • 6250218
  • Patent Number
    6,250,218
  • Date Filed
    Wednesday, June 30, 1999
    24 years ago
  • Date Issued
    Tuesday, June 26, 2001
    23 years ago
Abstract
The invention relates to a print unit for a packaging machine, in which a cavity, equipped with an armature made of ferromagnetic material and supporting, in operation, a blank to be printed, is mobile in front of a fixed electromagnet, which can be activated so as to attract the armature against a fixed print head, thus clamping the blank between the armature and the print head.
Description




BACKGROUND OF THE INVENTION




The present invention relates to a print unit. In particular, the invention relates to a print unit suitable for use in cigarette packaging machines, to which the following text refers, although without limiting the scope of the invention, for printing a code on wrapping material blanks used in the packaging machine.




Known cigarette packaging machines normally comprise a print unit for printing a code on the blanks, allowing identification, for example, of the date and/or place of production of the relative packet.




In the above-mentioned packaging machines, the print unit in turn comprises a seat designed to hold a blank and mounted on a rotary wheel which moves the blank forward along a path which passes through a print station. The print station houses an actuator which moves a print head away from and towards the seat, so as to print the above-mentioned code on a blank held in the seat.




The above-described print unit is normally equipped with a deformable elastic element, which is inserted between the above-mentioned actuator and the print head, or between the seat and the wheel, and can be adjusted to calibrate the force with which the print head acts upon the blank.




In operation, the above-described print unit subjects the wheel shaft supports to relatively high levels of stress, particularly in modern packaging machines, which have very high operating speeds (over 500 packets per minute). Since they must stand such stress, the shaft supports and corresponding seats must be very strong and are, therefore, expensive.




Moreover, in the above-mentioned print unit, it is very difficult to precisely calibrate the force with which the print head acts upon the blank, since said force depends on the elastic characteristics of the deformable element, on the reciprocal position of the print head and the seat, and on the actuator travel.




The aim of the present invention is to provide a print unit which has none of the above-mentioned disadvantages and, at the same time, is simple and economical to produce.




SUMMARY OF THE INVENTION




Accordingly, the invention provides a print head comprising a print head housed in a print station for printing a graphic symbol on a sheet; an electromagnet housed in the print station; an armature made of a ferromagnetic material which moves away from and towards the print head due to the action of a magnetic field produced by the electromagnet; feed means for feeding the sheet to the print station in a position between the armature and the print head; and control means designed to activate the electromagnet, so as to attract the armature against the print head.











BRIEF DESCRIPTION OF THE DRAWINGS




The invention will now be described with reference to the accompanying drawings, which illustrate an embodiment of the invention, without limiting the scope of its application; and in which:





FIG. 1

is a side elevation view, with some parts cut away to better illustrate others, of a preferred embodiment of the unit according to the present invention;





FIG. 2

is a scaled-up detail from

FIG. 1

, in cross-section according to line II—II in

FIG. 1

; and





FIG. 3

is a scaled-up detail from FIG.


2


.











DESCRIPTION OF THE PREFERRED EMBODIMENTS




With reference to the accompanying drawings, in

FIG. 1

the numeral


1


indicates as a whole a continuous packaging machine comprising a motor-driven wrapping wheel


2


, designed to turn with continuous motion (counterclockwise in

FIG. 1

) about its axis (not illustrated) perpendicular to the plane in FIG.


1


. The wheel


2


has a plurality of evenly distributed peripheral seats


3


(only one of which is illustrated), designed to receive a succession of ready-folded blanks


4


made of cardboard or a similar material. The machine


1


also comprises a magazine


5


for a stack


6


of blanks


4


, and a suction pick-up unit


7


, located between a pick-up station S


1


which is positioned at an open base


8


of the magazine


5


, and a feed station S


2


which is positioned at the wrapping wheel


2


, to take the blanks


4


from the open base


8


and feed them in succession to the seats


3


.




The pick-up unit


7


comprises a motor-driven wheel


9


which turns continuously, and clockwise in

FIG. 1

, about its fixed central axis


10


, parallel with the axis (not illustrated) of the wheel


2


, and perpendicular to a longitudinal axis


11


of the magazine


5


. The wheel


9


has an inner chamber


12


(only partially illustrated), pneumatically connected by a pipe


13


to a suction pump


14


designed to create a vacuum in the inner chamber


12


, so that the pressure in the inner chamber is lower than the outside atmospheric pressure.




The chamber


12


is connected (in a known way, not illustrated) to a plurality of pneumatic pick-up heads


15


supported by the wheel


9


and evenly distributed about the axis


10


. The pick-up heads


15


are connected to the wheel


9


by arms


16


, each hinged to the wheel


9


by a pin


17


(illustrated in

FIG. 2

) in such a way that it oscillates, relative to the wheel


9


, about an axis


18


parallel with the axis


10


. Each pick-up head


15


is, in turn, hinged to the relative arm


16


in such a way that it oscillates, relative to the arm


16


, about an axis


19


parallel with the axis


10


.




The angle of each arm


16


about the axis


18


is controlled by a cam control device (of the known type and not illustrated) housed in the wheel


9


.




The angle of each pick-up head


15


about the axis


19


is controlled by another cam control device (of the known type and not illustrated) housed in the wheel


9


and mechanically connected to the pick-up head


15


by a lever mechanism


20


comprising a lever


21


hinged to the wheel


9


in such a way that it oscillates about the axis


18


by a hollow pin


22


(illustrated in

FIG. 2

) which houses the relative pin


17


, and a connecting rod


23


, one end of which is hinged to the lever


21


, the other end being hinged to the pick-up head


15


in such a way that it oscillates, relative to the pick-up head


15


, about an axis


24


parallel with the axis


10


.




As is better illustrated in

FIG. 2

, each head


15


substantially has the shape of a plate, one side of which is connected to the relative arm


16


, and the other side of which is limited by a pick-up surface


25


, in which a cavity


26


is defined, delimited by a ring-shaped edge


27


and connected to the chamber


12


by a pipe


28


made along the arm


16


.




In the embodiment illustrated, the pick-up surface


25


is substantially defined by the upper surface of the edge


27


.




Inside each pipe


28


, at the joint


29


connecting the pipe


28


to the relative head


15


, there is a valve


30


, designed to open and close the pipe


28


, so that it is communication with or cut off from the cavity


26


. Each head


15


also has a through-hole


31


, which provides permanent communication between the cavity


26


and the outside.




Each valve


30


is of the known type with mechanical control, and is controlled by a rod


32


designed so that it can be moved axially in a direction that is radial to the axis


10


by a cam driver device (of the known type and not illustrated) housed in the wheel


9


, between an open position (illustrated in

FIG. 2

) in which the cavity


26


is pneumatically connected to the pipe


28


and, therefore, to the chamber


12


, and a closed position (not illustrated) in which the cavity


26


is pneumatically isolated from the pipe


28


and, therefore, the chamber


12


.




In order to hold a blank


4


in contact with the pick-up surface


25


of a head


15


, the surface


25


is substantially brought into contact with the blank


4


, which seals the cavity


26


and, together with the cavity


26


, forms a vacuum chamber, in which a vacuum is created (relative to the atmospheric pressure), by opening the corresponding valve


30


and, therefore, putting the vacuum chamber in communication with the chamber


12


, in which the pump


14


constantly maintains a vacuum.




The head loss caused by the presence of the through-hole


31


permanently connected to the outside does not create particular problems, since the pump


14


is able to compensate even high levels of head loss, such as those induced by the through-hole


31


.




In order to release the blank


4


, the atmospheric pressure in the vacuum chamber is automatically restored, thanks to the presence of the hole


31


, by simply closing the valve


30


.




As illustrated in

FIG. 1

, each seat


3


is made on an outer surface


33


of a head


34


opposite an inner portion of the head


34


connected to the wheel


2


in such a way that it oscillates, relative to the wheel


2


, about an axis


35


parallel with the axis


10


, controlled by a cam-rocker switch control device (of the known type and not illustrated). Each seat


3


has two lateral surfaces


36


, which are angled towards one another and towards a lower surface


37


, in which there are holes


38


for communication with a known type of suction device, not illustrated.




The continuous rotation of the wheel


9


about the axis


10


causes each head


15


to move forwards along a closed path P, substantially circular and extending about the axis


10


, and through the pick-up station S


1


, in which the head


15


picks up a blank


4


from the open base


8


of the magazine


5


, through a print station S


3


, in which a print unit


39


prints a code (not illustrated) on the blank


4


, and through the feed station S


2


, in which the head


15


feeds the blank


4


to a corresponding seat


3


of the wrapping wheel


2


.




The above-mentioned code (not illustrated) is normally alphanumeric, or a bar code, and usually indicates the date and/or place of production of the packet.




As illustrated in

FIG. 2

, the print unit


39


comprises a support pin


40


, mounted on the machine


1


in such a way that it oscillates about an axis


41


parallel with the axis


10


, under the thrust of a cam actuator device (of the known type and not illustrated), and rigidly supporting an electromagnet


42


, which has a core


43


made of ferromagnetic material with a pair of opposite pole shoes


44


, between which there is a chamber


45


through which the pin


40


passes.




In the chamber


45


and, therefore, between the pole shoes


44


, is a print device


46


which is rigidly supported by the pin


40


and has a print head


47


designed to print the code on a blank


4


.




The electromagnet


42


also comprises a coil


48


designed to produce a magnetic field along the core


43


when an electric current with adjustable intensity is passed through it, said current generated by a control device


49


of the known type electrically connected to the coil


48


.




As illustrated in

FIG. 3

, each pick-up head


15


comprises an armature


50


made of ferromagnetic material, which has a flat outer surface


51


designed to support a blank


4


and is mounted in such a way that it is mobile in the cavity


26


, moving along a direction


52


perpendicular to the axis


19


against the action of a pair of springs


53


, each of which is wrapped around a fixed pin


54


, along which the armature


50


can slide.




Each spring


53


is compressed between the armature


50


and an upper head


55


of the relative pin


54


, so that the armature


50


is normally held in a home position (illustrated in

FIG. 3



a


), in which the surface


51


is at a given distance other than zero from a relative blank


4


. An upper surface


56


of each head


55


constitutes a base upon which a blank


4


rests, the blank held by the corresponding pick-up head


15


.




The operation of the machine


1


is described below with reference to a single pick-up head


15


and starting from a moment in which the pick-up head


15


has released a blank


4


into a seat


3


at the feed station S


2


and moves, under the thrust of the wheel


9


and along the path P, towards the pick-up station S


1


, to pick up another blank


4


.




During the transit between the feed station S


2


and the pick-up station S


1


, the valve


30


of the head


15


is kept in the closed position and the cam control devices (of the known type and not illustrated) impart to the arm


16


an early oscillation (clockwise in

FIG. 1

) about the axis


18


, which continues until the head


15


, moving along the path P, reaches a position close to the feed station S


1


.




When the head


15


moves close to the station S


1


, the cam control devices (of the known type and not illustrated) impart to the arm


16


a delay oscillation (counterclockwise in

FIG. 1

) about the axis


18


and a simultaneous oscillation (clockwise in

FIG. 1

) of the head


15


about the axis


19


, so that the head


15


is substantially stopped in a position opposite the base


8


of the magazine


5


and, at the same time, the head


15


is pushed outwards in a radial direction until it adheres to the blank


4


which is in contact with the base


8


, and the head


15


is, therefore, pushed in the direction of the axis


11


towards the inside of the magazine


5


, exerting a given pressure on the blank


4


.




As the head


15


moves forwards inside the magazine


5


in the direction of the axis


11


, suction is activated through the cavity


26


, bringing the valve


30


into the open position, to hold the blank


4


in contact with the surface


25


.




When the blank


4


adheres to the surface


25


, an oscillation (clockwise in

FIG. 1

) about the axis


19


is imparted to the head


15


, allowing a first edge of the blank


4


, the lower edge in

FIG. 1

, to be deformed and clear a tooth


5


a delimiting the base


8


, then removal of a second edge (the upper edge in

FIG. 1

) of the blank


4


from under a tooth


5




b


delimiting the base


8


, thus completing extraction of the blank


4


from the base


8


.




At this point, the cam control devices (of the known type and not illustrated) interrupt the delay oscillation of the arm


16


about the axis


18


and, due to the rotation of the wheel


9


, the head


15


leaves the pick-up station S


1


, in which it picked up the blank


4


, and goes to the print station S


3


.




During the transit between the pick-up station S


1


and the print station S


3


, the cam control devices (of the known type and not illustrated) impart to the arm


16


an early oscillation (clockwise in

FIG. 1

) about the axis


18


, which continues until the head


15


, moving along the path P, reaches a position close to the print station S


3


.




When the head


15


moves close to the print station S


3


, the cam control devices (of the known type and not illustrated) impart to the arm


16


a delay oscillation (counterclockwise in

FIG. 1

) about the axis


18


and a simultaneous oscillation (clockwise in

FIG. 1

) of the head


15


about the axis


19


, so that the head


15


is substantially stopped, for a given interval, in a position opposite the print unit


39


(as illustrated in

FIG. 2

) which, in turn, and for the same purpose, completes a corresponding oscillation about the axis


41


.




In accordance with another embodiment, not illustrated, the pin


40


is a fixed pin and the unit


39


does not oscillate about the axis


41


.




In the print station S


3


and during the above-mentioned interval, the blank


4


is in a position (illustrated in

FIG. 2

) between the armature


50


and the print head


47


. The control device


49


then supplies the coil


48


with a current with preset intensity, to generate at the core


43


a magnetic field which attracts the armature


50


towards the pole shoes


44


against the action of the springs


53


; the consequent movement of the armature


50


towards the pole shoes


44


brings the surface


51


of the armature


50


into contact with a corresponding inner surface


57


of the blank


4


, bringing an outer surface


58


of the blank


4


into contact with the print head


47


with a preset force, depending on the elastic force generated by the springs


53


and the intensity of the magnetic field, which, in turn, depends on the intensity of the electrical current circulating in the coil


48


.




Then, when the magnetic field is interrupted by interrupting the current passing through the coil


48


, the armature


50


returns, due to the action of the springs


53


, to the home position (illustrated in

FIG. 3



a


) and the cam control devices (of the known type and not illustrated) interrupt the delay oscillation of the arm


16


about the axis


18


and, due to the rotation of the wheel


9


, the head


15


leaves the print station S


3


and goes to the feed station S


2


.




During the transit between the print station S


3


and the feed station S


2


, the cam control devices (of the known type and not illustrated) impart to the arm


16


an early oscillation (clockwise in

FIG. 1

) about the axis


18


, which continues until the head


15


, moving along the path P, reaches a position close to the feed station S


2


.




When the head


15


moves close to the station S


2


, the cam control devices (of the known type and not illustrated) impart to the arm


16


a delay oscillation (counterclockwise in

FIG. 1

) about the axis


18


and a simultaneous oscillation (clockwise in

FIG. 1

) of the head


15


about the axis


19


, so that the head


15


is substantially stopped in a position opposite the corresponding seat


3


of the wrapping wheel


2


and, at the same time, the head


15


is pushed outwards until the pick-up surface


25


substantially adheres to the lower surface


37


of the seat


3


.




When the pick-up head


15


is in the feed station S


2


, the head


34


in which the seat


3


is made also oscillates about the axis


35


, to keep the pick-up surface


25


and the lower surface


37


opposite one another and substantially parallel.




During the substantially radial movement of the surface


25


towards the lower surface


37


, the suction through the cavity


26


is interrupted, bringing the valve


30


into the closed position and, at the same time, suction through the holes


38


is activated, so that the blank


4


is left in the seat


3


and is pneumatically held in the seat


3


.




At this point, the cam control devices (of the known type and not illustrated) interrupt the delay oscillation of the arm


16


about the axis


18


and, due to the rotation of the wheel


9


, the head


15


leaves the feed station S


2


and goes to the pick-up station S


1


. The above-mentioned operations are repeated cyclically.




Obviously, the above-mentioned oscillations (clockwise in

FIG. 1

) of the head


15


about the axis


19


during the steps in which the head


15


moves towards the stations S


1


, S


2


, S


3


, are followed by return oscillations (counterclockwise in

FIG. 1

) about the axis


19


during the subsequent steps in which the head moves away from the stations S


1


, S


2


, S


3


.




As illustrated in

FIG. 1

, insertion of the head


15


in the seat


3


allows the blank


4


to be folded into a U-shape along its pre-folded lines (of the known type and not illustrated) as the blank


4


is fed to the seat


3


.




The above description clearly indicates that, during the printing operations, the shaft (not illustrated) of the wheel


9


, the pins


17


and hinges at


19


are not subjected to any impact generated by the contact between the armature


50


and the print head


47


, since such impacts are absorbed by the pin


40


. Moreover, the force with which each blank


4


makes contact with the print head


47


can be regulated, even during operation, in a simple, rapid, precise fashion, by simply adjusting the intensity of the current supplied to the coil


48


.



Claims
  • 1. A print unit comprising:a print head housed in a print station for printing a graphic symbol on a sheet, including an electromagnet in the print station; an armature made of ferromagnetic material and mobile away from and towards the print head under the action of a magnetic field produced by the electromagnet; feed means for feeding the sheet from a pick-up station to the print station in a position between the armature and the print head, said armature being supported by said feed means; and control means, being designed to activate the electromagnet so as to attract the armature against the print head.
  • 2. The unit according to claim 1, wherein the print head is integral with the electromagnet.
  • 3. The unit according to claim 1, wherein the electromagnet comprises a pair of pole shoes, said shoes, in operation, being opposite the armature; the print head being positioned between the pole shoes.
  • 4. The unit according to claim 1, wherein the electromagnet comprises a coil; the control means comprising a generator designed to cause an electrical current with adjustable intensity to circulate in the coil.
  • 5. The unit according to claim 1, comprising elastic means, the armature being mobile towards the print head against the action of the elastic means, and the print head being mounted in a fixed position.
  • 6. The unit according to claim 5, wherein the elastic means comprise a pair of springs.
  • 7. The unit according to claim 1, wherein the feed means comprising conveyor extending through the print station and, in turn, comprising a pick-up head which picks up a sheet; the armature being mounted on the pick-up head in such a way that it is mobile.
  • 8. The unit according to claim 7, wherein the feed means comprise at least one cavity made in the pick-up head, and suction means for creating a vacuum inside the cavity; the suction means comprising a pipe communicating with the cavity, a control valve positioned along the pipe, and a suction pump connected to the pipe; the valve being located between the pump and the cavity and close to the cavity; and at least one through-hole, being made in the head so that the cavity is permanently in communication with the outside.
  • 9. The unit according to claim 8, wherein the armature is mounted in the cavity in such a way that it is mobile.
  • 10. The unit according to claim 7, wherein the conveyor comprises a wheel which rotates about a first, fixed, central axis; there being jointed connecting means between the pick-up head and the wheel.
  • 11. The unit according to claim 10, wherein the jointed connecting means comprise an arm, being hinged to the wheel in such a way that it oscillates, relative to the wheel, about a second axis, the latter being parallel with the first axis; the pick-up head being hinged to the arm in such a way that it oscillates, relative to the arm, about a third axis, the latter being parallel with the first axis.
  • 12. The unit according to claim 11, wherein the print head and the electromagnet are designed to oscillate about a fourth axis, the latter being parallel with the first axis.
Priority Claims (1)
Number Date Country Kind
BO98A0421 Jul 1998 IT
US Referenced Citations (4)
Number Name Date Kind
3995730 Kwan et al. Dec 1976
4098389 Kwan Jul 1978
5002267 Brecy Mar 1991
5048986 Czesnik et al. Sep 1991
Foreign Referenced Citations (1)
Number Date Country
961245 May 1950 FR