Abstract:
A method of checking cigarettes, whereby cigarettes are fed in steps along a gravity channel in the outlet of a hopper, and are successively arrested substantially at a checking station where a checking device determines the density of the open ends of the cigarettes and emits at least one control signal indicating the density; and the control signal is optimized by determining the position of the cigarette in the checking station with respect to the checking device.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a method of checking cigarettes. 
     The present invention may be used to advantage on the input unit of a cigarette packing machine, to which the following description refers purely by way of example. 
     Known packing machines normally comprise an input unit featuring an input hopper, the outlet of which is defined by a number of side by side channels for successively feeding superimposed, parallel, horizontal layers of cigarettes to an extracting device moving back and forth through the outlet of the hopper to feed the layers to a device for forming groups of cigarettes. 
     On some known packing machines, the cigarettes are not checked until after the groups are formed, and any groups comprising even only one faulty cigarette are rejected. 
     To save economically on the number of cigarettes rejected, U.S. Pat. No. 4,592,470, for example, proposes checking the cigarettes inside the hopper, and rejecting any faulty cigarettes before the groups are formed. 
     The above method, however, involves several drawbacks, mainly on account of the cigarettes not always being arrested in the same position in front of the checking device. That is, as the cigarettes must be checked and possibly rejected before reaching the extracting device, the checking and extracting devices must be located a given distance apart, so that a column of cigarettes is formed between the two devices, and which varies in height according to humidity, any minor differences in diameter, and the traveling speed of the cigarettes (the faster the cigarettes travel, the more the cigarettes in the column are compressed when arrested). As a result, the cigarettes are not always arrested in the same position in front of the checking device, thus resulting in possible reading errors, and in full cigarettes being rejected or, worse still, partly empty cigarettes being passed. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a cigarette checking method designed to overcome the aforementioned drawbacks. 
     According to the present invention, there is provided a method of checking cigarettes, the method comprising the steps of feeding cigarettes, arranged transversely side by side in a column, in a given transverse feed direction and substantially in steps along a gravity channel; successively arresting the cigarettes substantially at a checking station; measuring, at the checking station and by means of a checking device, the density of the open ends of the cigarettes, and emitting at least one control signal indicating the presence or absence of material in front of the checking device; and expelling any faulty cigarettes at a reject station downstream from said checking station; the method being characterized by comprising a detecting step for obtaining position information relative to a position assumed, at the checking station and during the measuring step, by each cigarette with respect to the checking device; and an optimizing step for optimizing said control signal by means of said position information to obtain an optimum signal; a reject signal only being emitted when the optimum signal is below a given threshold value. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A non-limiting embodiment of the present invention will be described by way of example with reference to the accompanying drawings, in which: 
     FIG. 1 shows a section of a preferred embodiment of a cigarette supply unit implementing the method according to the present invention; 
     FIG. 2 shows a detail of FIG. 1 in three possible operating configurations; 
     FIG. 3 shows a variation of FIG. 1; 
     FIG. 4 shows a detail of FIG. 3. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Numeral 1 in FIG. 1 indicates as a whole a packing machine comprising an input unit 2, in turn comprising an input hopper 3 for a mass (not shown) of cigarettes 4 arranged horizontally and each comprising a filter 5. Unit 2 also comprises a device 6 for forming and conveying groups 7 of cigarettes 4 (only one shown partly in FIGS. 1 and 3), each group 7 comprising a number of cigarettes 4 equal to the number of cigarettes in a packet (not shown); and an extracting device 8 for feeding cigarettes 4 from hopper 3 to device 6. 
     Hopper 3 comprises at least one outlet 9 defined by a rear wall 10 facing filters 5, and by a vertical front wall 11 parallel to wall 10 and defining, with wall 10, a cavity of a width approximately equal to but no smaller than the length of cigarettes 4. The cavity is divided into a number of elementary channels 12 (only one shown) by partitions or dividing walls 13 (only one shown in FIGS. 1 and 3) separated by a distance approximately equal to but no less than the diameter of cigarettes 4. 
     Channels 12 are defined at the bottom by a horizontal plate 14 for supporting cigarettes 4, which are arranged in columns along respective channels 12 to define a number of superimposed horizontal layers 15, each of which, on contacting plate 14, is engaged by a pusher 16 forming part of extracting device 8, and is expelled from hopper 3, in a direction parallel to the longitudinal axis of cigarettes 4, into a respective cavity 17 of device 6. 
     As shown in FIGS. 1 and 3, pusher 16 comprises an expulsion element defined by a flat plate 18 fitted contacting the top surface of plate 14, and which is slid along plate 14 by an actuating member 19 forming part of extracting device 8. Plate 18 is of a width approximately equal to but no smaller than the width of a layer 15, is of a thickness substantially equal to the radius of cigarettes 4, and is movable back and forth, through walls 10 and 11, between a forward work position and a withdrawn rest position. In the work position, plate 18 engages two through openings 20 and 21 in walls 10 and 11 to feed cigarettes 4 of a layer 15 into a cavity 17; and, in the rest position, plate 18 rests on plate 14, outside hopper 3 and behind rear wall 10 of the hopper. Accordingly, the cigarettes 4 in the layer 15 descend in steps as the extracting device undergoes reciprocal movement back and forth. 
     Detailed descriptions of the structure of hopper 3, extracting device 8, and device 6 are to be found in British Patents n. 1,298,785 and 2,023,994. 
     A checking device 22 is mounted along each channel 12, to the front of wall 11 at a checking station 23, to check each of cigarettes 4 traveling in steps along channel 12, to determine the substantially exact position of the cigarette 4-- hereinafter indicated 4a-- facing device 22, and to emit a signal 24 indicating the position and density of cigarette 4a. More specifically, device 22 emits a number of signals indicating the density of cigarette 4a arrested at station 23, and, as a function of the position of cigarette 4a at station 23, selects an optimum signal 24 best indicating the density of cigarette 4a. 
     The optimum signal 24 is supplied to a central unit 25 controlling a known reject device 26 for pneumatically extracting any faulty cigarettes 4 from hopper 3 through a hole 27 formed in wall 10 of outlet 9 at a reject station 28 downstream from checking station 23 in the traveling direction 29 of cigarettes 4 towards plate 14. 
     In the embodiment in FIG. 1 example, device 22 comprises two optical sensors 30a, 30b, which are housed inside respective holes 31, 32 in wall 11, are positioned facing the free ends of cigarettes 4, are aligned with each other in direction 29, and are arranged at a distance 33 from each other, measured in direction 29, at most equal to the diameter &#34;D&#34; of cigarettes 4. 
     Each sensor 30a, 30b emits a cyclic signal 24a, 24b timed by the travel of cigarettes 4, i.e. by extracting device 8; and the value of signal 24a, 24b, which depends on the mass facing sensor 30a, 30b, varies according to whether sensor 30a, 30b directly faces a peripheral edge 34 or a central portion 35 of the free end of cigarette 4a, and according to the density of the free end of cigarette 4a. Central portion 35 is a free end portion close to the longitudinal axis 36 of cigarette 4a, and edge 34 is defined by a free end portion at the cylindrical surface 37 of cigarette 4a. 
     In FIG. 2a, both sensors 30a, 30b face central portion 35 of the free end of the same cigarette 4a of sufficient density, so that signals 24a, 24b emitted by respective sensors 30a, 30b assume respective maximum values 38a, 38b above a given threshold value 39 by which to accurately select said optimum signal 24. In the FIG. 2a case, either of signals 24a, 24b may therefore be selected as optimum signal 24. 
     In FIG. 2b, sensor 30a faces central portion 35 of a cigarette 4a of sufficient density, and sensor 30b faces edge 34 of the same cigarette 4a, where cigarette 4a substantially rests on the downstream cigarette 4 in channel 12. Sensor 30a therefore emits a signal 24a of a maximum value 38a above threshold value 39, and sensor 30b a signal 24b of a maximum value 38b below threshold value 39, so that, in this case, only signal 24a may be selected as optimum signal 24. 
     In FIG. 2c, sensor 30a faces central portion 35 of a cigarette 4a of insufficient density, and sensor 30b faces edge 34 of the same cigarette 4a. The maximum values 38a, 38b of signals 24a, 24b are therefore both below threshold value 39, so that, in this case, either of signals 24a, 24b may be selected as optimum signal 24. 
     In actual use, and with reference to one channel 12, cigarettes 4 are fed in a column and substantially in steps along channel 12 as each cigarette 4 on plate 14 is expelled by extracting device 8, so that each cigarette 4 is fed through and arrested for a short time at checking station 23. Sensors 30a, 30b, which are activated in time with each step of cigarettes 4, emit respective cyclic signals 24a, 24b, each indicating the mass facing respective sensor 30a, 30b; and signals 24a, 24b are supplied to central unit 25, which performs an optimizing operation whereby the maximum values 38a, 38b of signals 24a, 24b are compared with threshold value 39. 
     When both values 38a, 38b are above threshold value 39, as in FIG. 2a, this means the cigarette 4a at the checking station is positioned correctly with respect to both sensors 30a, 30b and is of sufficient density, so that, as stated, either of signals 24a, 24b may be selected as optimum signal 24, which, being above threshold value 39, does not activate reject device 26. 
     When, as in FIG. 2b, either one of signals 24a, 24b assumes a value (in this case 38a) above threshold value 39, this means the cigarette 4a at checking station 23 is only positioned correctly with respect to sensor 30a, the signal 24a of which is therefore selected as optimum signal 24 and does not activate reject device 26. 
     When the maximum values 38a, 38b of both signals 24a, 24b are below threshold value 39, as in FIG. 2c, the position of cigarette 4a may be interpreted in two ways: both sensors 30a, 30b may be positioned facing central portion 35 of the free end of a cigarette 4a of insufficient density; or, as in FIG. 2c, only sensor 30a is positioned facing central portion 35 of a cigarette 4a of insufficient density, and sensor 30b is positioned facing edge 34 of the same cigarette 4a. Whichever the case, when maximum values 38a, 38b are both below threshold value 39, either of signals 24a, 24b may be selected as optimum signal 24, which causes central unit 25 to emit a signal activating reject device 26 to expel the faulty cigarette 4 on reaching reject station 28. 
     In the FIGS. 3 and 4 variation, checking device 22 comprises three optical sensors 40a, 40b, 40c for detecting the density of the free ends of cigarettes 4, and three sensors 41a, 41b, 41c for detecting the position of the cigarettes with respect to sensors 40a, 40b, 40c at a checking station 42. Sensors 40a, 40b, 40c are housed inside respective holes 43, 44, 45 in wall 11, are positioned facing the free ends of cigarettes 4, are aligned with one another in direction 29, and are equally spaced over a distance 46 less than the diameter &#34;D&#34; of cigarettes 4. The projection of distance 46 in a direction perpendicular to direction 29 defines the extension of checking station 42 through which cigarettes 4 are fed one at a time. Each position sensor 41a, 41b, 41c is fitted to a plate 47 in turn fitted to partition 13 (not shown), and is aligned with a respective sensor 40a, 40b, 40c in a direction perpendicular to direction 29. 
     In actual use, and with reference to FIG. 4, when a cigarette 4a is arrested in checking station 42, position sensors 41a, 41b, 41c emit respective signals 48a, 48b, 48c indicating the presence of a cigarette in station 42, and the value of each of which increases in proportion to how close the axis 36 of cigarette 4a is to the respective sensor 41a, 41b, 41c. As sensors 41a, 41b, 41c are equally spaced over distance 46, one of them emits a higher signal than the other two--in FIG. 4, the highest signal is signal 48b emitted by sensor 41b. 
     At the same time, sensors 40a, 40b, 40c emit respective signals 49a, 49b, 49c indicating the mass of material in the respective portions of station 23 facing the sensors. 
     Central unit 25 performs an optimizing operation by selecting an optimum signal 49 among the signals emitted by sensors 40a, 40b and 40c. The optimum signal 49 is emitted by whichever of sensors 40a, 40b, 40c is aligned with the sensor 41a, 41b, 41c emitting the highest of signals 48a, 48b and 48c. This may be done by central unit 25 either activating all three sensors 40a, 40b, 40c and only using the signal 49a, 49b, 49c corresponding to the highest of signals 48a, 48b, 48c, or by only activating the sensor 40a, 40b, 40c aligned with the sensor 41a, 41b, 41c emitting the highest of signals 48a, 48b, 48c. The selected optimum signal 49 is compared by central unit 25 with threshold value 39, and, if the signal value is below threshold value 39, central unit 25 emits a reject signal to expel the faulty cigarette 4 on reaching reject station 28.