US3742795A

US3742795A - Cigarette dense end monitoring and controlling apparatus

Info

Publication number: US3742795A
Application number: US00234767A
Authority: US
Inventors: J Lipcon; J Horn
Original assignee: Industrial Nucleonics Corp
Current assignee: Industrial Nucleonics Corp; ABB Automation Inc
Priority date: 1972-03-15
Filing date: 1972-03-15
Publication date: 1973-07-03
Anticipated expiration: 1990-07-03
Also published as: DE2313025A1; CA988805A; AU5328073A; JPS49500A; GB1432231A; FR2176453A5; IT983563B

Abstract

A dense-end monitor and controller is provided for a cigarettemaking machine of the dense-ending type. In a preferred embodiment, a density gauge is positioned adjacent to the moving cigarette rod for providing a first signal varying with the occurrences of dense portions in the tobacco rod. Another signal is supplied for each cutting action of the rod cutter by means synchronized to the rod cutter. Correlation waveform generators generate sawtooth and triangular-shaped waveforms which are phase-synchronized with the dense portion pulses in the density gauge signal. Two output signals, one representing deviation of the dense portions from their proper position at the ends of the cut cigarettes, and the other representing the relative increase in the amount of tobacco in the dense portions, are provided for visual display and machine control purposes. The signals are obtained by correlating the density signal with the triangularshaped waveform and by sampling the sawtooth-shaped waveform at the instant the cutter signal is generated. The output signals are free of any interdependence of information content.

Description

United States Patent [191 Lipcon et al. July 3, 1973 1 CIGARETTE DENSE END MONITORING AND CONTROLLING APPARATUS [57] ABSTRACT Primary ExaminerFrank T. Yost Attorney-William T. Fryer et al.

[75] Inventors: Jesse B. Lipcon; James N. Horn, both of Columbus, Ohio [73] Assignee: Industrial Nucleonics Corporation, Columbus, Ohio [22] Filed: Mar. 15, 1972 [21] Appl. No.: 234,767

[52] US. Cl 83/13, 83/72, 83/76, 83/360, 83/361, 83/522, 13l/21 R, 131/21 B '[51] Int. Cl. A24c 5/32 [58] Field of Search 83/13, 72, 74, 76, 83/360, 361, 370, 522; 131/21 B, 21 R, 22 R, 63, 65, 46

[56] References Cited UNITED STATES PATENTS 3,066,562 12/1962 Barnett et al. 8 3/74 3,604,429 9/1971 DeWitt 131/21 B 3,604,430 Norwich et al 131/21 B A dense-end monitor and controller is provided for a cigarette-making machine of the dense-ending type. In a preferred embodiment, a density gauge is positioned adjacent to the moving cigarette rod for providing a first signal varying with the occurrences of dense portions in the tobacco rod. Another signal is supplied for each cutting action of the rod cutter by means synchronized to the rod cutter. Correlation waveform generators generate sawtooth and triangular-shaped waveforms which are phase-synchronized with the dense portion pulses in the density gauge signal. Two output signals, one representing deviation of the dense portions from their proper position at the ends of the cut cigarettes, and the other representing the relative increase in the amount of tobacco in the dense portions, are provided for visual display and machine control purposes. The signals are obtained by correlating the density signal with the triangular-shaped waveform and by sampling the sawtooth-shaped waveform at the instant the cutter signal is generated. The output signals are free of any interdependence of information content.

21 Claims, 5 Drawing Figures A I 22 FORMER O DENSITY MEASURE RE E 3 SIGNAL PEAKS s2 PULSE GENERATOR 4 PHASE ERROR SIGNAL $3 I as FIRST 63 SIGNAL e ifi g' i MULTIPLIER A E A 66\ GENERATOR MEANS PHASE- FREQUENCY so SYNCHRONIZER SECOND 62 R CUTTER ggkggfi' MULTIPLIER PBIEgIASLSI GENERATOR %DENSE-ENDING PHASE ANGLE PATENTED JUL 3 I975 SHEU 0F 3 TRIANGULAR CORRELATING WAVE FORM PEAK S2 I DENSITY SIGNAL: I

FIG. 3a

I DENSITY I SIGNAL PEAK 52 k-ZERO-CROSSING POINT T SAWTOOTH 3b CORRELATING WAVEFORM CUTTING SIGNAL PULSE g zERo-cRoss|NG I POINT T SAWTOOTH I .3 CORRELATING FG C WAVEFORM CIGARETTE DENSE END MONITORING AND CONTROLLING APPARATUS BACKGROUND It is well known in the cigarette-making art to manufacture cigarettes having increased amounts of tobacco in the regions adjacent to the cut ends. The purpose of this process, known as dense ending, is to give the cigarette a superior appearance, a firm feel to the touch, and to prevent loosely-packed tobacco from falling out of the cigarette ends.

Dense-ending devices are a part of many contemporary cigarette makers and they may take on various forms. For example, compacting members may be used to periodically compress the tobacco stream ahead of atrimmer, extra charges of tobacco may be placed at intervals in the tobacco stream, a special rotating trimmer wheel having peripheral indentations may be used to trim off more tobacco in certain spaced regions of the tobacco rod than in others, or a tobacco-conveying belt may be provided with perforations corresponding to the desired density pattern to enable air to be drawn therethrough, arranging the tobacco filler in the desired dense-end pattern. U.S. Pat. Nos. 1,920,708, issued Aug. 1, 1933, and 3,306,305, issued Feb. 28, 1967, both to D. W. Molins, 1,968,018, issued July 31, 1934 to C. Arelt, and 3,032,041, issued May 1, 1962, to R. Lanore, are representative of the state of the art.

In cigarette-making machines utilizing dense enders, serious problems arise when the occurrences of the dense ends in the tobacco stream get out of synchronization with the cigarette cutter. Normally, the denseending device is synchronized with the cutter so that the cut occurs approximately in the center of the dense regions. However, it is sometimes desired to offset the dense-end regions from the location of the cut end, as for example where the leading ends of non-filter cigarettes are densed for the purpose of compensating for weight losses due to deceleration forces. The cutter is often located several feet downstream from the denseending device, so that unpredictable compression or stretching of the tobacco stream which forms the cigarette rod may occur, sometimes as a function of machined speed, causing an out-of-synchronization condition such that dense regions can appear in portions of the cigarette other than the desired portions.

Modern cigarette makers have a production rate of between 1,000 and 4,000 cigarettes per minute, so that careful and accurate monitoring of cigarette quality is necessary to prevent wasted tobacco, or wasted time where low-quality cigarettes have to be reprocessed. Manual inspection is impractical because of the need to sample a large number of cigarettes, and because it is virtually impossible to discriminate between a lowquality condition resulting from loss of denseend/cutter synchronization and one resulting from a decrease in the density of the dense regions. Likewise, manual inspection may overlook cigarettes in anoverdensed condition, which are not free on the draw" and are expensive to make.

Two prior dense-end measuring and controlling devices are described in U.S. Pat. No. 3,604,429, issued Sept. 14, 1971, to John E. DeWitt and U.S. Pat. No. 3,604,430, issued Sept. 14, 1971, to Alan Norwich et al., both assigned to the same assignee as the present invention. According to these patents, in general, information is obtained as to the relative position of the dense-end region and the cigarette end. In one embodiment, a gauge is positioned adjacent to the moving cigarette rod for measuring the weight per unit length or density of the dense-end regions, and a reference signal synchronized to the operation of the cutter is generated for comparison with the output of the density gauge. In one approach these signals are utilized to provide an oscilloscope display. However, the oscilloscope display, in the embodiment disclosed, is somewhat difficult to set up and interpret by cigarette-making machine operating personnel without extensive training. In another form, these signals are utilized to produce continuous electrical output signals for indicating, as by the deflection on one or two meters, the position and relative density of the dense ends. Where separate output signals are provided according to the prior embodiments, there may be an interdependence of the signals such that, unless the dense ends occur in proper phase with the cutter, the signal which indicates the position of the dense ends is affected by their relative density, and the signal which indicates their relative density is affected by their position. Also, the use of a simple square waveform for the reference signal has caused difficulty in obtaining the desired degree of accuracy, since, if the reference signal pulse length is not the same as the length of the dense-end pulse, the denseend position output signal has a dead signal range around the point of perfect synchronization.

The present invention solves the problem of how to prevent phase angle information from intruding into the percent density signal and vice versa, as will be apparent from a reading of the description which follows.

SUMMARY OF THE INVENTION regions ascompared with the non-dense regions, thus offering a reliable real-time check on the desired relative density of the dense regions, which may be, for example, 10 percent, 15 percent, or 20 percent over the density of the remainder of the tobacco rod. Moreover, the apparatus according to the invention provides outputs which may in addition be used to exert feedback control over the cigarette-maker to correct maladjustments in the process automatically.

According to one specific embodiment, a gauge is positioned adjacent to the moving cigarette rod. This gauge provides an output signal indicative of the weight per unit length of the cigarette rod. The signal includes recurrent component peaks representative of the dense regions in the cigarette rod. A reference pulse generator synchronized to the action of the cutter produces another periodically varying signal. Two correlating waveform generators are provided to produce two different correlating waveforms in response to timing pulses from a phase-frequency synchronizing means. One correlating waveform is symmetrical, or even, about the periodically occuring peak which represents the location of the dense region. The other correlating waveform is asymmetrical, or odd, about the location of the density peak. The phase-frequency synchronizer causes these correlating waveforms to be generated at the frequency of the cutter signal pulse.

The even correlating waveform is correlated with the density signal by a multiplying means, and the product is averaged and read into a visual display means to provide a percent dense-ending indication. The odd correlating waveform is correlated with the density signal in another multiplying means. The product is averaged, and the average is fed back as a phase error signal to the phase-frequency synchronizer. This phase error signal will be zero if the phase of the correlating waveforms is identical to the phase of the dense region peaks in the density signal. Should the correlating waveforms be out of phase with the peaks in the density signal, the phase error signal will have a polarity dependent on the direction of the phase displacement and a magnitude directly proportional to the amount of phase displacement. The phase error signal causes the phasefrequency synchronizer to adjust its timing pulses so that the correlating waveforms are again in phase with the density signal peaks, reducing the phase error signal to zero. Thus the phase-frequency synchronizer means delivers a timing pulse to the correlating waveform generators at the frequency of the cutter pulse and at a phase which causes the correlating waveforms to be in phase with the density signal peaks. A phase angle signal suitable for operating a visual display device is derived by a sample-and-hold circuit which is responsive to the same correlating waveform that generates the phase error signal. The sample-and-hold circuit is gated by the cutter signal.

The present invention solves the problem of how to prevent phase angle information from intruding into the percent density signal and vice versa. It accomplishes this, in a preferred embodiment, by generating one or more reference correlating waveforms, having a frequency identical with that of the cutter signal, while being in exact phase-synchronization with the dense-end peaks in the density gauge signal. In this manner, with the phase error between the correlating waveforms and dense-end peak maintained at zero, the output signal representing percent dense-ending is directly proportional to the average amount of the increase in the cigarette weight per unit length caused by the extra tobacco in the dense ends and is independent of the displacement of the dense regions from the cut ends of the cigarettes. To obtain the displacement or phase angle output, the appropriate reference correlation waveform is sampled at the instant of cutting, giving either a positive or negative signal representative of the position of the cut ends with respect to the average position of the dense regions.

OBJECTS OF THE INVENTION Accordingly, it is an object of the present invention to provide an improved dense-end monitor which generates output signals indicative of cutter/dense-end synchronization and of the relative increase in density of the tobacco in the dense regions of the tobacco rod, which signals are free of any mutual dependence.

It is another object of the present invention to provide an improved dense-end monitor in which, by a proper choice of correlating waveforms, the output signals are linear with respect to changes in cutter/denseend synchronization and percent dense-ending, and do not have dead signal" portions.

Further objects and advantages will become apparent from the following detailed description of preferred apparatus according to the invention, taken in conjunction with the appended drawings.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a schematic showing of a cigarette-making machine in combination with an improved dense-end monitoring and control system according to the invention.

FIG. 2 is a more detailed schematic drawing of the improved dense-end monitoring and control system of FIG. 1.

FIG. 3a is a graph showing waveforms depicting the condition of perfect phase synchronization between one preferred correlating waveform and the density signal.

FIG. 3b is another graph depicting the condition of perfect phase synchronization between the other preferred correlating waveform and the density signal.

FIG. 3c is another graph depicting the condition of perfect phase synchronization between the other preferred correlating waveform and the cutting signal pulse.

CIGARETTE DENSE-ENDING PROCESS With reference now to the drawings and particularly to FIG. 1, a typical cigarette-making machine includes a tobacco stream former l0 delivering a stream of tobacco 12 to a rod former 14. Here, a paper strip 16 is wrapped around the tobacco stream 12, and the seam is glued to form a cigarette rod 18. The cigarette rod 18 passes on to a cutter 20 which periodically cuts a cigarette 22 of length L from the continuous rod 18. Conventionally, the cigarette rod is measured and the machine is controlled to provide cigarettes having a desired weight per unit length.

A dense-ending device 24 may be built onto the cigarette-making machine to provide regions of higher relative density in the tobacco stream. These devices may take on various forms as stated above. As seen in FIG. 1, a rotating trimmer disc 24 trims off some tobacco 12a which is returned upstream leaving an excess amount of tobacco in dense regions R of the tobacco stream fed to rod former 14. The dense regions are spaced one cigarette length L apart from one another for non-filter cigarettes and a distance 2L for filter cigarettes. Where the tobacco stream has been wrapped to form the rod 18, which is of relatively constant diameter, the density of the tobacco in the dense regions of the cigarette rod may be up to 30 percent greater than the density in the remainder of the rod. As a typical example, the length of the dense region R may be 10 to 20 millimeters for a cigarette millimeters in overall length.

A main drive motor 26 provides motive power for simultaneously conveying the cigarette rod 18 toward the cutter 20 and actuating the cutter 20 to cut cigarettes of substantially equal length from the rod 18. The dense-ending device 24 is also coupled via differential drive unit 48 to the main drive motor 26 as indicated by the dotted line 28. The purpose of the differential drive unit 48 is to time the dense-ending device 24 with the cutter 20, so that the cutter cuts the tobacco rod 18 substantially in the center of each dense region R.

If, clue to the longitudinal dimensional changes of the tobacco stream 12 or rod 18 or slippage of the drive to either the cutter 20 or the dense-ending device 24, the cutter and dense regions R are not in synchronism, the cigarettes 22 will either have an excessive or an insufficient amount of tobacco at one end or the other, or they may lack dense ends entirely.

For non-filter cigarettes, when the rod 18 is properly cut substantially in the center of each dense region, one end of the cigarette 22 contains approximately the same amount of extra tobacco as the other end. To accomplish this result, one must know the position of the dense regions with reference to the cut ends of the cigarettes to determine whether the cutter is properly synchronized, and, if it is not synchronized, the amount and direction in which it is out of synchronization. For filter cigarettes, in which only the open end is densed, the tobacco rod 18 is cut both through the center of each dense region R (a distance 2L apart) and through the midpoint between adjacent dense regions R. In this case, the occurrence of each dense region R is compared with every other cutting stroke, as explained in more detail below.

DENSE-END MONITOR AND CONTROL The dense-end monitor includes a gauge 30 located upstream from the cutter 20 to measure the density of the rod 18. It may be of any well known type which measures the weight per unit length or density of the cigarette rod. A cutter reference pulse generator 32 is synchronized to the action of the cutter through mechanical, electrical, photoelectric, magnetic, or other equivalent means well known to those skilled in the art. In addition to generating cutter pulses Sl, generator 32 provides a fixed number of segment pulses S1 per cigarette, for purposes to be explained below. According to the preferred embodiment, six segment pulses are generated per cigarette in essentially the same manner as the cutter pulses. Both types of pulses are amplified and shaped by appropriate circuitry in pulse generator 32. In a simpler form, reference pulse generator 32 may consist of one or more switch contacts which close every time a cigarette 22 is cut from the rod 18.

Two correlating

waveform generators

60 and 61 are provided for generating correlating waveforms of differing types to be compared with the density signal peaks S2 and the cutter signal pulses S1 to give a percentage dense-end reading and a phase-angle reading, respectively. The correlating waveforms are preferably triangular and sawtooth waveforms generated by conventional waveform generators, although other waveforms can be used. Correlating waveform generator 61 generates the sawtooth waveform, and correlating waveform generator 60 generates the triangular waveform. These waveform generators are set up to be triggered at the frequency of the cutter signal pulses Sl by means of a phase-frequency synchronizer 66. Phasefrequency synchronizer 66 also maintains the phase of the correlating waveforms in synchronism with the phase of the density signal.

' Referring to FIG. 1, the density signal and the even correlating waveform output of generator 60 are correlated in multiplier 62, yielding a signal which is averaged in an averaging circuit 64 and fed into a visual display means, such as a meter 40. A cigarette-making machine operator monitoring the visual display 40 is thus provided with a continuous reading representative of the relative increase in tobacco in the dense regions R. The instantaneous value of the odd correlating waveform output of generator 6] is sampled at the in stant the cutter signal pulse S] is generated, by means of a sample-and-hold circuit 67, whose output is fed into a visual display means comprising a meter 41 to indicate to the operator whether the dense region R is being positioned in the rod 18 such that the cutter 20 will pass through the center of the dense region R, and if not, the amount and direction of the deviation of the dense regions R from the cut ends.

The operator can thereby make appropriate adjustments to the machine to correct the faulty dense-end condition. Alternatively, automatic control can be exerted by means of a suitable controller device 46 operating directly from the phase angle signal T1, as described below.

Multipliers

62 and 63, which perform the correlation functions, may assume various forms, the proper selection of which will be apparent to one skilled in the art. For example, each multiplier may be a true analog multiplier (Hall effect, transistor or integrated-circuit transconductance, Field effect, duty-cycle, etc.). It may be a digital-to-analog type of hybrid multiplier, if the correlation waveform is in digital form. Or it may be a pseudomultiplier or multiplier-like circuit, such as an analog gate, synchronous demodulator, or the like. In the preferred embodiment,

multipliers

62 and 63 are of the true analog multiplier type.

CORRELATING WAVEFORMS The proper choice of correlating waveform is dependent upon the desired form of output signal to be obtained from the multiplication process. Because a zero phase angle signal is desired for the condition of perfect cutter/dense-end synchronization, with positive-going and negative-going signals representing lead or lag, a correlation waveform having essentially a constant slope from l to is preferred. It is to be understood that each l80 to +l80 cycle corresponds to the time required for one cigarette length to pass a given point, for example the location of gauge 30. See FIG. 3c. Such a waveform may be described as an asymmetrical or odd waveform and defined by the equation f(t)-f(-t), with the origin of the time t and f(t) reference axes being positioned midway along the slope between the lowest and highest points of the waveform. See FIG. 3b. The odd correlation waveform is normally phase-synchronized to the density signal peak S2, such that itsf(t) reference axis eoincideswith the center of the density peak S2. In other words, this correlation waveform is odd with respect to the density peak S2. The point midway along the waveform slope is arranged to be at zero or ground potential, and it is from this point, the so-called zero-crossing point," that deviations of the positions of the density signal peak and the cutting signal pulse are measured. When the zero-crossing point of the sawtooth correlating waveform is exactly in phase with the density signal peak S2, a zero-valued phase error feedback signal S3 will result. Similarly, when the zero-crossing point of the sawtooth waveform is exactly in phase with the cutting signal pulse 81, a zero-valued phase angle output signal T1 will result.

With respect to density information, an output signal having a magnitude directly proportional to the amplitude of the density signal peak is desired. Thus a correlation waveform which is symmetrical about a reference axisf(t) drawn through the average position of the positive peak is preferred. Such a waveform may be described as a symmetrical or even waveform and defined by the equation f(t)=+f(t), with the f(t) reference axis passing through the positive peak and the t reference axis passing through points midway along the slopes between the highest and lowest points of the waveform. See FIG. 30. When the even correlation waveform is in phase with the density signal peak S2, its f(t) reference axis coincides with the center of the density peak S2, and the correlation waveform is said to be even about the density peak S2. The even waveform generator is arranged so that the t reference axis is at ground potential and passes through the points midway along the waveform slope. When a correlation waveform of this approximate shape is multiplied with a non-zero density signal, the resulting product will be a positive, non-zero output signal directly proportional to the magnitude of the percent dense-ending factor. Thus, when the positive peak of the triangular correlating waveform is exactly in phase with the peak S2 in the density signal, their product will yield an output signal directly proportional to the percent dense-ending.

While the preferred correlating waveforms may be described rather precisely by the above equations in terms of functionsf(t) and f(t) about a selected reference axis, waveforms having only the general characteristics of the above-described correlating waveforms may be used as equivalents. That is, a waveform fitting neither of the equations f(t)=f(t) or flt)=f(t) precisely may nevertheless be equivalent in general shape and in function to one or the other preferred correlating waveforms. The appearance of the correlating waveforms can be described either by smooth, continuous curves or by discrete levels or steps. Examples of the former are ramp, sawtooth, triangular, sinusoidal, and similar waveforms. In the latter category, waveforms consisting of one or more discrete levels may be generated by any well known on/off, stepping, counting, or other digital circuit. By way of illustration, a digital up/down counter may be used to provide an incrementally increasing and decreasing periodic signal resembling a triangular-shaped waveform.

PHASE-FREQUENCY SYNCHRONIZER The phase-frequency synchronizer 66 performs a dual function, in that it triggers the

correlation waveform generators

60 and 61 at the frequency of the cutter signal pulses S1, while maintaining the phase of the correlation waveforms in exact synchronization with the phase of the density signal peaks S2. As to the latter function, the phase-frequency synchronizer 66 acts in the capacity of a variable phase delay, by either advancing or retarding the phase of the correlation waveforms with respect to the phase of the density signal peaks S2.

Referring now to FIG. 2, a more detailed schematic of the structure comprising the phase-frequency synchronizer 66 as it appears in the preferred embodiment is shown. An up/down counter 102 is provided for storing an arbitrary eight-bit number C to C The up/- down counter 102 is an eight-bit register, whose input lines are driven by voltage-controlled oscillators 101 and 103. Cycling counter 104 is an eight-bit counter, whose outputs are A to A Cycling counter 104 is driven by a voltage-controlled oscillator (VCO) 106, which is responsive to the cutter signal pulse S1, such that cycling counter 104 makes one complete 00000000 through 1 ll 1 l 1 ll cycle during the time each cigarette passes the gauge 30. A digital comparator is provided for delivering a synchronizing pulse exactly once per cigarette when the eight-bit number A generated by cycling counter 104 coincides with the eight-bit number C stored in up/down counter 102. The A=C output pulse of comparator 100, occurring once per cigarette, is the basic timing reference for the

correlation waveform generators

60 and 61.

A phase detector 108 and VCO 106, cooperate with cycling counter 104 to form a phase-locked loop, such that the cycling counter 104 completes a full 00000000 through 11111111 counting cycle between successive cutter signal pulses. The most significant bit A in cycling counter 104 is fed back as one input to the phase detector 108. Phase detector 108 may supply a positive or negative output, corresponding to a lag or lead condition of A with respect to the cutter signal pulse, to integrator 107 whose output in turn drives the VCO 106. For example, if the occurrence of the most significant bit A lags the cutter signal pulse, a positive output is supplied to integrator 107 for an amount of time dependent upon the amount of lag, causing the integrator 107 output to go more negative, thereby causing a higher frequency output from VCO 106. Likewise, if the A Comparison pulse occurs too soon, phase detector 108 supplies a negative output for an amount of time dependent upon the amount of lead, causing the VCO 106 output to go less negative, thereby commanding a lower frequency. These positive and negative-going signals control the output frequency of VCO 106 in such a manner as to maintain the A 1 to 0 transition coincident with the cutting signal pulse.

In normal operation, with the phase-locked loop in the locked condition, the A 1 to 0 transition occurs very close to the time of the cutting signal pulse. How ever, phase errors can occur because of electronic noise, integrator input leakage currents, and speed changes in the cigarette-making machinery. The combined effect of these errors is to cause very small corrections to occur in either direction. Thus, at the instant of the cutting signal reference pulse, there will be a very short positive or negative-going correction output pulse from phase detector 108.

The variable eight-bit number C to C in up/down counter 102 is compared with all the eight-bit numbers generated during the 00000000 to l l l 11 1 l 1 transition of cycling counter 104, by means of the digital comparator 100 to provide a coincidence pulse A=C exactly once during each cigarette period. For a relatively lower number in up/down counter 102, the A=C coincidence pulse will occur relatively sooner during the transition cycle of cycling counter 104. Conversely, a relatively higher reference number in up/down counter 102 will occasion a relatively later A=C coincidence pulse.

In order to advance or retard the occurrence of the A=C correlation waveform triggering pulse, a phase error signal S3, representative of any phase difference between the correlating waveforms and the dense end peaks S2, is applied to the phase-frequency synchronizer 66. Because the correlating waveform generators are triggered simultaneously, their respective waveforms are automatically in phase-synchronization with each other. It is necessary, therefore, to compare the phase of only one selected correlating waveform with the phase of the dense end peaks S2. In the preferred embodiment, the sawtooth correlating waveform is selected for this phase comparison process, since the phase error signal S3 will be zero when the density signal peak S2 coincides with the zero-crossing of the sawtooth waveform, as seen in FIG. 3b. Thus, with reference to FIG. 2, the sawtooth correlating waveform is compared with the phase of the dense end peaks S2 by means of the multiplying circuit 63, and theresultant signal is averaged in the averaging means 65. Phase error signal S3 brings about either an increase or a decrease in the variable number C in up/down counter 102, by means of the voltage-controlled oscillators 101 and 103. Voltage-controlled oscillators 101 and 103, as well as 106, are well-known electronic circuits for generating output signals at a frequency directly proportional to the magnitude of the voltage input. For an input of positive polarity or for no input at all, VCO 101 and VCO 103 generate no output. For a negative voltage input, they generate pulses at a frequency which is directly proportional to the magnitude of the input signal.

When the zero-crossing point T of the sawtooth correlating waveform (FIG. coincides with the center of the density peak S2, the average value of their product is zero, and no change is effected in the reference number C stored in up/down counter 102. Should the zero-crossing point T stray from the center of the density peak, either a positive or negative DC voltage results, in the form of the phase error signal S3, thereby causing either VCO 103 or VCD 101, respectively, to generate pulses which step up or step down the reference number stored in up/down counter 102. For example, if the zero-crossing point T leads the center of the density peak S2, the average value of the product of the two waveforms is a positive DC phase error voltage. The positive voltage prevents VCO 101 from operating. However, the positive input to inverter 105 results in a negative output therefrom, causing VCO 103 to put out pulses at a repetition rate proportional to the magnitude of the error. These pulses cause the up/- down counter 102 to count up, gradually bringing the sawtooth correlation waveform into phase equilibrium with the density signal, at which point the phase error voltage is again zero. If the zeroecrossing point T lags the occurrence of the density signal peak, a negative DC phase error voltage appears at the output of averaging means 65, causing VCO 101 to step down the reference number in up/down counter 102 until phase equilibrium is reached. The inverter 105 at this time applies a positive voltage to VCD 103, keeping it turned off.

CORRELATION AND OUTPUT Because of the synchronizing action of the phase error control loop, the zero-crossing point T of the sawtooth correlating waveform tracks the position of the dense end peak S2. The triangular correlating waveform is also synchronized with the sawtooth correlating waveform, so that the positive peak of the triangular waveform coincides with the zero-crossing point T of the sawtooth waveform. In one embodiment of the dense end monitor which has been constructed, this was done by using the sawtooth waveform to generate the triangular waveform. The sawtooth voltage, taken with reference to ground, was applied to a conventional absolute value circuit having a gain of 2, with the absolute value of the sawtooth voltage effectively subtracted from a fixed constant voltage to yield the corresponding value of the triangular waveform. The sawtooth waveform can also be generated by using, say, a conventional eight-bit digital up counter responsive to VCO 106 and being reset by the A=C pulse. The triangular waveform is again generated from the sawtooth waveform by using the 00000000 through 0] l l l I ll portion of the counting cycle to generate the up" slope of the triangular waveform and the l0000000 through 111111 11 portion to generate the down slope. A conventional digital-to-analog arrangement is used for generating a voltage proportional to the pulse counts. Thus, with the zero-crossing T of the sawtooth correlating waveform tracking the dense-end pulse $2, the positive peak of the triangular waveform also tracks the dense-end pulse. Therefore, when the triangular correlating waveform is multiplied in the multiplying circuit 62 by the density signal, and averaged over time in the averaging circuit 64, the resulting voltage is directly proportional to the magnitude of the percent dense-end signal. This signal will always be independent of phase angle due to the fact that the positive peak of the triangular correlating waveform has been synchronized to coincide with the dense-end peak.

The output voltage representative of the degree of dense-ending is applied to meter 40 to give a reading representing percent dense-end or quality. In addition, the percent dense-ending output voltage is compared with an adjustable limit 112, which can be preset by the machine operator to the desired degree of percent dense-eriding, by means of limit comparing means 113. A green light 114 is held on by means 113 so long as the percent dense-end signal equals or exceeds the desired limit, while a red light 116, representing low quality, is switched on if the percent dense-ending output goes below the desired limit.

Referring now to FIG. 30, if the sawtooth correlating waveform is subjected to a sample-and-hold operation at the time of the cutting signal pulse, a voltage is obtained which is proportional to the phase angle difference between the cutting signal pulse and the denseend pulse. This output voltage will be zero when the occurrence of the dense-end regions is synchronized with the cutter. A positive phase angle voltage results when the cutting pulse lags the dense-end pulse, and a negative phase angle voltage results when it leads the denseend pulse. The magnitude of the positive or negative signal is proportional to the amount of phase angle difference alone, independent of the magnitude of the dense-end pulse. The phase angle voltage is applied to a suitable readout device such as a meter 41. According to one embodiment of the invention which has been constructed and tested, the phase angle voltage is amplified, inverted, and filtered with a 6-second time constant before it is applied to visual display meter 41, providing the machine operator with a true average indication of the phase relationship between the cutter and the dense-end regions.

Output signal Tl, representing the direction and magnitude of any phase error between the cutter 20 and the dense regions R, is especially useful in controlling the cigarette-making process to maintain proper synchronization. For example, phase angle meter 41 may be a center-zero meter, calibrated in degrees or in millimeters, for the purposes of showing immediately to operating personnel the amount and direction by which the occurrences of the dense regions R must be shifted relative to the operation of the cutter 20. Such corrections may be made manually by retiming the denseending means to achieve perfect synchronization. Alternatively, automatic control can be exerted by means of a suitable controller 46 operating from the phase angle output signal Tl. A differential gearing unit 48 couples the main drive motor 26 simultaneously to the cutter 20 and the dense-ending device 24. Differential 48 is provided with a pair of

output shafts

50 and 52, whose relative angular position can be adjusted by means of the controller 46. Controller 46 is coupled to the control shaft of differential unit 48 by the heavy dotted line 54. U.S. Pat. No. 3,306,305, supra, discloses a dense-ending device employing differential gearing to maintain dense-end/cutter synchronization. Other mechanisms for effecting automatic control of dense-end/cutter synchronization will be apparent to those skilled in the art.

Output signal T2, representing the percentage of increased tobacco density in the dense regions R, may similarly be applied to a meter 40, calibrated in percent increase in tobacco density or in milligrams. Alternatively, the quality signal T2 may be used as part of an automatic control over the percent increase in tobacco density in the dense regions R, where the nature of the cigarette-making machinery would allow it.

The above description of the invention is equally applicable to the dense-ending of filter or non-filter cigarettes. Reference pulse generator 32 supplies the cutter signal reference pulse S1 for each cutting of the cigarette rod, such cuttings normally occurring a distance L apart. In the case of non-filter cigarettes, each cut is made in the center of a dense region R. in the case of filter cigarettes having only one end densed, but both ends cut, cutter signal pulses are generated at both the densed and undensed cut ends, and it is necessary to select the cutter signal corresponding to the densed end as the reference pulse S1.

FREQUENCY FEED-FORWARD CIRCUIT To insure that the phase-locked loop circuit 109 will respond to changes in the cutter signal frequency resulting .from substantial changes in cigarette maker speed as well as from slight speed fluctuations, a frequency feed-forward circuit 111 is included as part of the phase-locked loop. This circuit assumes the larger share of the burden of providing the DC command voltage to VCO 106, thereby requiring the phase-locked loop circuit 109 to provide only a much smaller correction voltage needed in order to maintain perfect phase-synchronization between the A 1 to 0 transition from cycling counter 104 and the cutter signal pulse S1. The frequency feed-forward circuit reduces considerably the amount of the required to achieve a phaselocked condition and in tracking the small frequency fluctuations in the cutter signal pulse train. However, it may be omitted at the option of one practicing the invention, with-out destroying the function or utility of the device.

The frequency feed-forward circuit 11'] comprises a frequency-to-voltage converter 110, whose output to.-

gether with the command voltage of integrator 107, is applied to VCO 106, which includes conventional circuit means for algebraically summing the two voltages. Although converter must have a fast response, no great accuracy is required since reasonable errors in frequency to voltage conversion are corrected by the phase-locking circuit. The input to the frequency-tovoltage converter 110 consists of a segment pulse train, as described above, synchronized with the reference pulse train and having a frequency six or [2 times as high. There are six segment pulses per cutter reference pulse for non-filter cigarettes, while there are 12 segment pulses per cutter reference pulse for filter cigarettes.

Because there are either six or 12 segment pulses per cutter signal pulse, depending upon whether filter or non-filter cigarettes are being made, and since the frequency feed-forward circuit 111 delivers a command voltage proportional to the frequency of the pulses in the segment pulse train S1, provision must be made to allow for a scaling difference in VCO 106. This function is performed by a scaling circuit 123, including a switch 121 which may be connected to ground as indicated by the dotted line. For non-filter cigarettes, having both ends densed, there are six segment pulses per cutter signal pulse, and switch 121 is connected to the output voltage V of the frequency-to-voltage converter 110. For filter cigarettes, with only one end densed, but both ends cut, there are 12 segment pulses generated "between the occurrences of the dense regions R. In order to maintain the cycling rate of cycling counter 104 at one complete cycle between the occurrence of consecutive dense regions R, the oscillation rate of VCO 106 must be halved. This is accomplished by connecting switch member 121 to ground, thereby halving the voltage applied to VCO 106 from the frequency-feed-forward circuit 111.

While one specific embodiment of the invention has been illustrated and described, with a number of modifications suggested, many other modifications may be made thereto, as will be apparent to those skilled in the art, without departing from the true spirit and scope of the invention as set forth in the appended claims. Thus, for example, while the preferred embodiment of the invention provides separate outputs for both percent dense-ending and for dense-end/cutter synchronization, the invention may be practiced by providing only one or the other form of output signal. Thus, the even waveform generator 60, multiplier 62, averaging means 64, and display means 40, including the limitcomparison circuitry associated with the present denseend signal T2 may be omitted, should one desire only the display and control signal relating to denseend/cutter synchronization. Likewise, the sample-andhold circuit 67 and display means 41, associated with the dense-end/cutter synchronization output signal T1 may be omitted, should be desire only the display and control signal relating to percent dense-ending.

We claim:

1. The method of producing an improved output response from a cigarette dense-end monitor, said monitor having means for measuring the variations in density along the length of a rod of tobacco having locally dense regions spaced along said length for providing a density signal having recurrently varying portions corresponding to said dense regions in said rod, means for generating a recurrent signal waveform responsive to the operation of a cutter which periodically cuts said rod to form individual cigarettes, and means responsive to said recurrent waveform and to said density signal for providing said output response which is indicative of a characteristic of said dense regions,vsaid method comprising adjusting the phase of one of said recurrent waveform and density signals in response to the recurrent waveform and density signals so that said signals will have a predetermined phase relationship irrespective of the position of said dense regions with respect to said cutter at the instant the rod is cut.

2 The method of monitoring the operation of a machine for producing cigarettes with dense ends, said machine having means for forming a tobacco rod with locally dense regions spaced along its length and means for conveying said rod past a cutter for severing said rod into a plurality of cigarettes, said method comprising the steps of measuring the variations in density of said rod along its length to produce a density signal having recurrently varying portions thereof corresponding to said dense regions,

generating a recurrent reference signal in response to the operation of the cutter,

generating a recurrent waveform having a predetermined frequency relationship to said reference signal,

synchronizing the phase of.said recurrent waveform with the phase of said varying portions of said density signal, irrespective of the relationship between said cutter and said dense regions at the instants of severing the rod, and

correlating said recurrent waveform with one of said recurrent reference and density signals to provide an output signal indicative of a characteristic of said dense ends -in said plurality of cigarettes.

3. Apparatus for monitoring the operation of a cigarette-making machine having a cutter providing a plurality of cigarettes cut from a continuous rod of tobacco moving along a path relative to said cutter and having locally dense regions spaced along said tobacco rod, said apparatus having means for measuring the density of said tobacco rod as it passes a point along said path to generate a density signal having a recurrently varying portions corresponding to the said dense regions in said moving rod, means responsive to the action of said cutter for generating a cutting signal, means for generating a recurrent waveform, and means for correlating said recurrent waveform with one of said density and cutting signals to provide an output signal indicative of a characteristic of said dense regions,

wherein said apparatus includes means for synchronizing the phases of said density signal and said recurrent waveform, irrespective of the positions of said dense regions with respect to said cutter at the instant the rod is cut.

4. Apparatus for monitoring the operation of a cigarette-making machine having a cutter providing a plurality of cigarettes cut from a continuous rod of tobacco moving along a path relative to said cutter and having locally dense regions spaced along said tobacco rod, said apparatus comprising:

means for measuring the density of said tobacco rod as it passes a point along said path to generate a density signal having recurrently varying portions corresponding to said dense regions in said moving rod,

means responsive to the action of said cutter for generating a cutting signal,

waveform generating means responsive to said cutting signal for generating a recurrent waveform in synchronized phase relationship with said varying portions of said density signal, and

means for correlating said recurrent waveform with said cutting signal to provide an output signal indicative of any displacement between the dense regions and the cut ends of the cigarettes.

5. Apparatus as set forth in claim 4, including means responsive to said cutting signal for generating an additional recurrent waveform in synchronized phase relationship with said density signal, and

means for correlating said additional recurrent waveform with said density signal to provide an additional output signal indicative of the relative density of said dense regions.

6. Apparatus as set forth in claim 4, including phase comparison means for correlating said recurrent waveform with said density signal to provide a control signal indicative of the phase relationship between said waveform and said density signal, and control means responsive to said control signal for maintaining said recurrent waveform in exact phase synchronization with said density signal.

7. Apparatus as set forth in claim 6, in which said control means includes means for triggering the operation of said waveform generating means, and variable delay means responsive to said control signal and connected to said triggering means, so that said waveform is triggered in exact phase synchronization with said density signal.

8. Apparatus as set forth in claim 7, in which said variable delay means comprises a first information storage means for storing information relating to said control signal, a second information storage means responsive to said cutting signal and cycling through a plurality of informational states for each cigarette cut from the tobacco rod, and a comparison means responsive to both information storage means for causing said triggering means to trigger said waveform generator to generate said waveform at the frequency of said cutting signal and in exact phase synchronization with said density signal.

9. Apparatus as set forth in claim 8, in which said first and second information storage means are digital registers and said comparison means is adigital comparator.

10. Apparatus as set forth in claim 8, including an additional phase comparison means for comparing the phase of said cutter signal with respect to one of the informational states occurring during each cycle of. said second informational storage means, said additional phase comparison means delivering an additional control signal indicative of the phase relationship betweensaid cutter signal and said reoccurring informational state, said additional control signal controlling the rate at which said second informational storage means cycles through its plurality of informational states.

11. Apparatus as set forth in claim 4, including output means responsive to said output signal for providing said relationship between the dense regions and the cut ends of the cigarettes in the form of a visual indication.

12. Apparatus as set forth in claim 5, including output means responsive to said additional output for providing a visual indication of the relative density of said dense regions.

13. Apparatus as set forth in claim 4, including a controller means responsive to said output signal for controlling the physical relationship between said cutter and said locally dense regions.

14. Apparatus as set forth in claim 4, in which said recurrent waveform is defined approximately by the equation f(l) =-f(t), with the origins of the time axis, t, and f(l) axis positioned so as to pass through the point midway between the lowest and highest values of a waveform period.

15. Apparatus as set forth in claim 14, in which said recurrent waveform is a sawtooth waveform.

16. Apparatus as set forth in claim 5, in which said additional recurrent waveform is defined approximately by the equation f(t) =f(t), with the f(t) axis positioned to coincide with the positive peak occurring within a waveform period and the time axis, 1, positioned to coincide with points midway along the slopes between the highest and lowest points of the waveform.

17. Apparatus as set forth in claim 16, in which said additional recurrent waveform is a triangular waveform.

18. Apparatus as set forth in claim 4, in which said correlating means comprises a sample-and-hold circuit.

19. Apparatus as set forth in claim 5, in which said correlating means comprises an analog multiplying circuit.

20. Apparatus as set forth in claim 6, in which said phase comparison means comprises an analog multiplying circuit.

21. Apparatus for monitoring the operation of a cigarette-making machine having a cutter providing a plurality of cigarettes cut from a continuous rod of tobacco moving along a path relative to said cutter and having locally dense regions spaced along said tobacco, said apparatus comprising:

means for measuring the density of said tobacco rod as it passes a point along said path to generate a density signal having recurrent portions corresponding to the said dense regions in said moving rod,

means responsive to the action of said cutter for generating a cutting signal,

first waveform generating means for generating a sawtooth-shaped recurrent waveform,

means for sampling said sawtooth waveform with said cutting signal to provide an output signal indicative of the phase relationship between the dense regions and the cut ends of the cigarettes,

second waveform generating means for generating a triangular-shaped recurrent waveform,

means for correlating said triangular waveform with said density signal to provide an output signal indicative of the percent density increase in tobacco in said dense regions,

phase comparison means for correlating said sawtooth waveform with said density signal to provide a control signal indicative of the phase relationship between said sawtooth waveform and said density signal,

an up/down counter responsive to said control signal for storing a number representative of the phase relationship between said sawtooth waveform and said density signal,

a cycling counter responsive to said cutting signal and cycling through a plurality of numbers for each cigarette cut from the tobacco rod,

a digital comparator responsive to said up/down counter and to said cycling counter for generating an output pulse when one of the plurality of numbers stored in said cycling counter equals the number stored in said up/down counter,

means for triggering the operation of both said waveform generating means, said means being responsive to the output pulse of said digital comparator,

additional phase comparison means for comparing the phase of said cutter signal with respect to a particular one of the plurality of numbers stored in said cycling counter during each cycle, said additional phase comparison means delivering an additional control signal indicative of the phase relationship between said cutter signal and said reoccurring particular number, said additional control signal controlling the rate at which said cycling counter cycles through its plurality of numbers, and

output means responsive to said output signals for providing visual indications of said phase relationship and said percent density increase, respectively.

Claims

1. The method of producing an improved output response from a cigarette dense-end monitor, said monitor having means for measuring the variations in density along the length of a rod of tobacco having locally dense regions spaced along said length for providing a density signal having recurrently varying portions corresponding to said dense regions in said rod, means for generating a recurrent signal waveform responsive To the operation of a cutter which periodically cuts said rod to form individual cigarettes, and means responsive to said recurrent waveform and to said density signal for providing said output response which is indicative of a characteristic of said dense regions, said method comprising adjusting the phase of one of said recurrent waveform and density signals in response to the recurrent waveform and density signals so that said signals will have a predetermined phase relationship irrespective of the position of said dense regions with respect to said cutter at the instant the rod is cut.

2. The method of monitoring the operation of a machine for producing cigarettes with dense ends, said machine having means for forming a tobacco rod with locally dense regions spaced along its length and means for conveying said rod past a cutter for severing said rod into a plurality of cigarettes, said method comprising the steps of measuring the variations in density of said rod along its length to produce a density signal having recurrently varying portions thereof corresponding to said dense regions, generating a recurrent reference signal in response to the operation of the cutter, generating a recurrent waveform having a predetermined frequency relationship to said reference signal, synchronizing the phase of said recurrent waveform with the phase of said varying portions of said density signal, irrespective of the relationship between said cutter and said dense regions at the instants of severing the rod, and correlating said recurrent waveform with one of said recurrent reference and density signals to provide an output signal indicative of a characteristic of said dense ends in said plurality of cigarettes.

3. Apparatus for monitoring the operation of a cigarette-making machine having a cutter providing a plurality of cigarettes cut from a continuous rod of tobacco moving along a path relative to said cutter and having locally dense regions spaced along said tobacco rod, said apparatus having means for measuring the density of said tobacco rod as it passes a point along said path to generate a density signal having a recurrently varying portions corresponding to the said dense regions in said moving rod, means responsive to the action of said cutter for generating a cutting signal, means for generating a recurrent waveform, and means for correlating said recurrent waveform with one of said density and cutting signals to provide an output signal indicative of a characteristic of said dense regions, wherein said apparatus includes means for synchronizing the phases of said density signal and said recurrent waveform, irrespective of the positions of said dense regions with respect to said cutter at the instant the rod is cut.

4. Apparatus for monitoring the operation of a cigarette-making machine having a cutter providing a plurality of cigarettes cut from a continuous rod of tobacco moving along a path relative to said cutter and having locally dense regions spaced along said tobacco rod, said apparatus comprising: means for measuring the density of said tobacco rod as it passes a point along said path to generate a density signal having recurrently varying portions corresponding to said dense regions in said moving rod, means responsive to the action of said cutter for generating a cutting signal, waveform generating means responsive to said cutting signal for generating a recurrent waveform in synchronized phase relationship with said varying portions of said density signal, and means for correlating said recurrent waveform with said cutting signal to provide an output signal indicative of any displacement between the dense regions and the cut ends of the cigarettes.

5. Apparatus as set forth in claim 4, including means responsive to said cutting signal for generating an additional recurrent waveform in synchronized phase relationship with said density signal, and means for correlating said additional recurRent waveform with said density signal to provide an additional output signal indicative of the relative density of said dense regions.

9. Apparatus as set forth in claim 8, in which said first and second information storage means are digital registers and said comparison means is a digital comparator.

10. Apparatus as set forth in claim 8, including an additional phase comparison means for comparing the phase of said cutter signal with respect to one of the informational states occurring during each cycle of said second informational storage means, said additional phase comparison means delivering an additional control signal indicative of the phase relationship between said cutter signal and said re-occurring informational state, said additional control signal controlling the rate at which said second informational storage means cycles through its plurality of informational states.

14. Apparatus as set forth in claim 4, in which said recurrent waveform is defined approximately by the equation f(t) -f(-t), with the origins of the time axis, t, and f(t) axis positioned so as to pass through the point midway between the lowest and highest values of a waveform period.

16. Apparatus as set forth in claim 5, in which said additional recurrent waveform is defined approximately by the equation f(t) f(-t), with the f(t) axis positioned to coincide with the positive peak occurring within a waveform period and the time axis, t, positioned to coincide with points midway along the slopes between the highest and lowest points of the waveform.

21. Apparatus for monitoring the operation of a cigarette-making machine having a cutter providing a plurality of cigarettes cut from a continuous rod of tobacco moving along a path relative to said cutter and having locally dense regions spaced along said tobacco, said apparatus comprising: means for measuring the density of said tobacco rod as it passes a point along said path to generate a density signal having recurrent portions corresponding to the said dense regions in said moving rod, means responsive to the action of said cutter for generating a cutting signal, first waveform generating means for generating a sawtooth-shaped recurrent waveform, means for sampling said sawtooth waveform with said cutting signal to provide an output signal indicative of the phase relationship between the dense regions and the cut ends of the cigarettes, second waveform generating means for generating a triangular-shaped recurrent waveform, means for correlating said triangular waveform with said density signal to provide an output signal indicative of the percent density increase in tobacco in said dense regions, phase comparison means for correlating said sawtooth waveform with said density signal to provide a control signal indicative of the phase relationship between said sawtooth waveform and said density signal, an up/down counter responsive to said control signal for storing a number representative of the phase relationship between said sawtooth waveform and said density signal, a cycling counter responsive to said cutting signal and cycling through a plurality of numbers for each cigarette cut from the tobacco rod, a digital comparator responsive to said up/down counter and to said cycling counter for generating an output pulse when one of the plurality of numbers stored in said cycling counter equals the number stored in said up/down counter, means for triggering the operation of both said waveform generating means, said means being responsive to the output pulse of said digital comparator, additional phase comparison means for comparing the phase of said cutter signal with respect to a particular one of the plurality of numbers stored in said cycling counter during each cycle, said additional phase comparison means delivering an additional control signal indicative of the phase relationship between said cutter signal and said re-occurring particular number, said additional control signal controlling the rate at which said cycling counter cycles through its plurality of numbers, and output means responsive to said output signals for providing visual indications of said phase relationship and said percent density increase, respectively.