Method of balancing the output of two lines of a packing system

A method of balancing the output of two lines of a packing system, wherein the two lines extend through at least two machines, at least one of which is a two-line machine, along two respective paths to produce and form respective articles into groups, and to pack the groups; the method including slowing down the articles, on each line, at at least one control station to form a continuous queue of contiguous articles; measuring the length of each queue; and maintaining the lengths of both queues and the difference between the lengths of the two queues within a first and a second given variation range respectively.

BACKGROUND OF THE INVENTION 
The present invention relates to a method of balancing the output of two 
lines of a packing system. 
The present invention may be used to advantage in the tobacco industry, 
particularly for forming and wrapping cartons of cigarettes, to which the 
following description refers purely by way of example. 
The tobacco industry is known to employ packing systems featuring two 
packing lines, and which comprise a two-line or dual cigarette packing 
machine, a cartoning machine, and a two-line or dual cellophaning machine 
interposed between the dual packing machine and the cartoning machine. 
In normal operating conditions, the three machines of packing systems of 
the above type are driven synchronously so that each operates in time with 
the other two. 
For any of various reasons, however, the operating speed of one of the 
machines may fall below the common speed at which the three machines are 
timed to operate. For example, if the packing machine slows down, even 
temporarily, with respect to the cellophaning and cartoning machines, each 
packing machine line produces one or more packets short of the number 
required to form a carton in at least one operating cycle of the system, 
i.e. in at least one cycle of operations performed simultaneously on the 
two lines by the three machines in the system to form and wrap two 
respective cartons of cigarettes, so that the cartoning machine produces 
at least two cartons with one or more packets missing. 
Moreover, at least one reject station for rejecting faulty packets is 
normally provided along each of the two lines in the system. 
Rejections obviously have the effect of unbalancing the lines. For example, 
in the event the packing machine produces a faulty packet on one line, the 
faulty packet is later rejected at the reject station, so that the number 
of packets supplied to the cellophaning machine on that particular line is 
one packet short, and, in the corresponding operating cycle, the cartoning 
machine produces two cartons, one of which with one packet short. 
The above drawbacks could be eliminated by compensating the output of the 
two lines in the packing system by means of compensating stores 
interposed, along each of the two lines, between the packing and 
cellophaning machines, and between the cellophaning and cartoning 
machines. Such a solution, however, though valid, is fairly expensive. 
SUMMARY OF THE INVENTION 
It is an object of the present invention to provide a method of 
automatically balancing the output of two lines of a packing system, to 
eliminate the aforementioned drawbacks. 
According to the present invention, there is provided a method of balancing 
the output of two lines of a packing system, wherein the two lines are 
operated in time with each other and extend through at least two machines, 
at least one of which is a two-line machine, along two respective given 
paths; the method being characterized by comprising the steps of feeding a 
succession of articles along said paths at a first given frequency, at a 
first given speed and in a given direction; slowing down the articles, on 
each line, at at least one control station to form a continuous queue of 
contiguous articles; measuring the length of each queue; and automatically 
maintaining the lengths of both queues and the difference between the 
lengths of the two queues within a first and a second given variation 
range respectively.

DETAILED DESCRIPTION OF THE INVENTION 
Number 1 in the accompanying drawing indicates as a whole a packing system 
comprising two packing lines 2, which are operated in time with each 
other, and extend, along respective substantially parallel packing paths 
3, through a cigarette packing machine 4 with two wrapping lines, a 
cartoning machine 5, and a cellophaning machine 6 having two wrapping 
lines and interposed between packing machine 4 and cartoning machine 5. 
Machines 4, 5, 6--which are known and therefore shown schematically in 
block form--are driven in known manner (not shown) by respective drive 
devices 4a, 5a, 6a, and cooperate with one another to produce, at each 
operating cycle of system 1, two cartons 7 of cigarettes, each comprising 
a predetermined number of cellophaned packets 8 of cigarettes. 
Drive devices 4a, 5a, 6a are all connected to a single central control unit 
9, which controls device 4a to operate machine 4 at a frequency equal to a 
first given frequency, and devices 5a and 6a to operate respective 
machines 5 and 6 at a frequency equal to a second given frequency. 
Packing machine 4 comprises, for each line 2, a reject station 10 for 
rejecting any faulty packets 8; and an output station 11 connected to a 
corresponding input station 12 of cellophaning machine 6 by a conveying 
device 13 extending along respective path 3, and which is powered to feed 
an orderly succession of packets 8 of cigarettes along path 3 from packing 
machine 4 to cellophaning machine 6. 
Each conveying device 13 comprises two conveyors 13a and 13b, which extend 
from respective stations 11 and 12, extend along respective 
portions--perpendicular to each other in the example shown--of respective 
path 3, and converge at a transfer station 14. 
Each conveyor 13a is a belt conveyor driven in time with packing machine 4 
to feed respective packets 8 to respective station 14 at a given speed and 
at a frequency equal to said first given frequency. 
In each of the two stations 14, there are provided, crosswise to conveyor 
13a, a plate 15 for arresting packets 8 on conveyor 13a; and a pusher 16, 
which, by means of a respective actuator 17 controlled by central control 
unit 9, is moved back and forth, at a frequency equal to the second given 
frequency, between a withdrawn rest position, in which pusher 16 is 
located on the opposite side of transfer station to conveyor 13b, and a 
work position, in which pusher 16 extends along plate 15 in the direction 
of conveyor 13b to transfer from conveyor 13a to conveyor 13b the packets 
8 fed successively onto plate 15. Each pusher 16 carries an integral plate 
18 substantially parallel to respective plate 15, and which provides for 
arresting packets 8 on the corresponding conveyor 13a when pusher 16 is in 
the work position. 
Along each path 3, upstream from transfer station 14, there is provided a 
control station 19 where two moving endless belts 20 on either side of and 
crosswise to conveyor 13a define a movable gripping device 21. Belts 20 
are moved (by drive devices not shown) in the traveling direction of, but 
at a slower speed than, conveyor 13a, adhere by friction to packets 8 fed 
towards station 19, and push packets 8 towards plate 15 to form, on plate 
15, a continuous queue 22 of contiguous packets 8. 
A measuring device 23 is provided at each control station 19, between 
machine 4 and respective gripping device 21, to measure the length of 
respective queue 22 and supply a corresponding signal to central control 
unit 9. 
Each conveyor 13b is a pocket conveyor defined by two endless belts 24 
fitted to two pulleys (not shown), one of which is powered to feed belts 
24 in steps and at said second frequency towards cellophaning machine 6. 
Each conveyor 13b is connected to a transfer device defined by a pusher 
25, an arm 26 of which is movable between the two belts 24 and carries an 
integral push plate 27 over and crosswise to belts 24. Pusher 25 is 
activated by a respective actuator 28 connected to central control unit 9, 
and is controlled by central control unit 9 to feed, in time with belts 24 
and at a frequency equal to said second frequency, each packet 8 into a 
respective pocket of conveyor 13b, which feeds respective packets 8 to 
input station 12 of machine 6. 
Each pocket of conveyor 13b cooperates at input station 12 with a 
respective counter-pusher 29 of cellophaning machine 6 to load each packet 
8, together with a respective sheet 31 of overwrapping material, into a 
pocket of a wrapping wheel 30 of machine 6. 
Once loaded into the respective pocket on wheel 30, each packet 8 is fed 
along a wrapping path, along which respective sheet 31 is folded in known 
manner about packet 8 to form a tubular wrapping 8a open at each end. At 
an output station 32 of the wrapping path, each packet 8 and respective 
wrapping 8a are transferred by respective counter-pusher 29 to the input 
of a further belt conveyor 33, which is operated in steps at said second 
frequency to transfer each packet 8 to the input station 34 of cartoning 
machine 5 via a folding station 35 where a known helical folding device 36 
closes the opposite ends of each tubular wrapping 8a to complete the 
overwrapping of each packet 8. 
Along each path 3, immediately upstream from input station 34 of cartoning 
machine 5, there is provided a grouping station 37 for grouping the 
cellophaned packets 8, and where two moving endless belts 38 on either 
side of and crosswise to conveyor 33 define a movable gripping device 39. 
Belts 38 are moved (by drive devices not shown) in the traveling direction 
of, but at a slower speed than, conveyor 33, adhere by friction to 
cellophaned packets 8 fed towards station 37, and push cellophaned packets 
8 towards station 34 in groups, each comprising a number of cellophaned 
packets 8 equal to that required to form a carton 7. 
In actual use, the packets 8 of cigarettes produced simultaneously by the 
two wrapping lines of packing machine 4 are fed simultaneously by 
respective conveyors 13a along respective paths 3 to respective control 
stations 19. 
At each of the two control stations 19, packets 8 are slowed down by 
respective gripping device 21, and continue traveling, in contact with one 
another, towards respective stop plate 15 on which a queue 22 is formed. 
Pusher 16 of each line 2 then loads packets 8 onto respective conveyor 13b, 
which feeds them to input station 12 of cellophaning machine 6, where they 
undergo a known overwrapping process as described above. 
The cellophaned packets 8 from machine 6 are then fed by the two conveyors 
33 to respective grouping stations 37, at each of which the cellophaned 
packets 8 are slowed down by respective gripping device 39, and continue 
traveling, in contact with one another, towards respective input station 
34 of cartoning machine 5, to form a group of cellophaned packets 8 
corresponding to to a carton 7 of cigarettes. 
In normal operating conditions, machines 4, 5 and 6, pushers 16 and 25, and 
conveyors 13a, 13b and 33 all operate in time with one another at the same 
frequency, i.e. said first and second frequencies are equal, so that both 
queues 22 are maintained at predetermined constant lengths, which, in the 
absence of any rejects on machine 4, are also equal or generally differ by 
a relatively small constant amount. 
If, for any reason, the output of machine 4 varies and machine 4 is 
operated at other than the common sync frequency, measuring device 23 of 
each line 2 detects a variation in the length of respective queue 22. If, 
as a result of said variation, the length of queue 22 is outside a given 
variation range, central control unit 9 causes machines 5 and 6, pushers 
16 and 25, and conveyors 13b and 33 to also operate at other than the sync 
frequency to restore the length of queue 22 within the variation range, 
and further varies the frequency to keep queue 22 within the variation 
range. In other words, alongside a variation in the output of one of the 
machines of system 1 resulting in a similar variation in the lengths of 
both queues 22, central control unit 9 responds by acting on the motors of 
the other machines, on the motors (not shown) of the conveyors connecting 
the machines, and on the actuators of the transfer devices to vary the 
respective operating frequencies. 
If, on the other hand, a condition of unbalance arises between the two 
lines 2, as a result of a different number of reject operations being 
performed at the two reject stations 10, the length of one queue 22 
differs from that of the other. If the difference between the lengths of 
the two queues 22 is outside a respective given variation range, normally 
equal to the queue formed by packets 8 defining a carton 7, central 
control unit 9 disables, for an entire operating cycle of system 1, the 
actuator 17 of line 2 with the shorter queue 22. 
Via delay means (not shown), the same central control unit 9 transmits a 
command to machines 5 and 6 to cut off the supply of wrapping material 
corresponding to the operating cycles in which the supply of packets 8 has 
been suspended. 
In the variation shown by the dash lines in the accompanying drawing, any 
difference in the lengths of queues 22 is compensated by an automatic 
compensating station 40 common to both lines 2 and located between packing 
machine 4 and the two control stations 19. 
Station 40 comprises, along each of first conveyors 13a, an unloading 
station 41 where conveyor 13a communicates with the input end of a guide 
42 extending crosswise to conveyor 13a and for feeding packets 8 from 
unloading station 41 to a loading station 43 located along the opposite 
conveyor 13a and facing unloading station 41. A pusher 44 is provided at 
each unloading station 41, and is moved, by a respective actuator 45 
controlled by central control unit 9, between a withdrawn rest position, 
in which pusher 44 is located on the opposite side of unloading station 41 
to guide 42, and a work position, in which pusher 44 extends along guide 
42 to feed a packet 8 to the corresponding loading station 43. 
In actual use, if the difference between the lengths of the two queues is 
outside the respective given variation range, central control unit 9 
operates actuator 45 of line 2 with the longer queue 22 to transfer a 
packet 8 to the loading station 43 of line 2 with the shorter queue 22, 
when central control unit 9 detects, by means of sensors (not shown), a 
missing packet 8 in station 43. The above transfer operation is repeated 
until the difference between the lengths of the two queues 22 is restored 
within the respective given variation range. 
Finally, the balancing method described being of general application, 
cellophaning machine 6 and cartoning machine 5 may of course be interfaced 
in exactly the same way as machines 4 and 6, should machine 6 comprise a 
reject station (not shown) for each line 2.