US 3593006 A
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Description (OCR text may contain errors)
0 United States Patent 11113,593,006
 Inventors Arthur L. McGee  References Cited Jose; UNITED STATES PATENTS 3,420,989 1/1969 Sapp 235/92 Jepsen, San Jose, all of, Calif.
2,208,270 7/1940 Grout.... 200/52  AppLNo. 762,087 3 450 897 6/969 H enn..... 307/223 [221 med 2 s 12 137 11/1951 Curtis 235/98 patented y 13,19." I  Assignee FMC Corporation Primary ExaminerThomas A. Robinson San Jose, Calif. Assistant Examiner-Robert F. Gnuse Attorneys-F. W. Anderson and C. E. Tripp ABSTRACT: A layer of fruit in random arrangement is passed beneath a row of switch-actuating arms. Each switch serves as an input to a two-stage set-reset flip-flop circuit. A detectable  g sg s s pulse is created by the flip-flop circuit arrangement as a fruit 8 leaves its associated switch-actuating arm providing that the  U.S.Cl 235/92 PK, adjacent arms are unactuated, and, consequently, only one 235/92 LG, 235/92 L, 235/98 R pulse will be created for each fruit that passes beneath the row  Int. Cl ..G06m 7/04, of arms as the last arm thereof drops off of it. The pulse out- 606m 3/12 puts from the various flip-flop circuits are all directed to con-  Field of Search 235/92, 98; ventional pulse counting means to give a count of the total number of fruit passing beneath the row of arms.
OUTPUT 2 L COUNTER PATENTEU JUL 1 315m SHEET 1 OF 5 I'ENRY N. ESTERLY DAVID B. JEPSEN ATTORNEYS PATENTED JUL] 319m 3,593 Q 006 sum 2 0F s Illlllllllllllllllllll]Illlllllll F'IE IEI AT TORNE YS PATENTEU JUL] 3 l97l 593; 006
SHEET 3 OF 5 7 11" FIE-L 1 RI 1 OUTPUT COUNTER IN V IZNTOR. ARTHU L. MCGEE HENR ESTERLY jw DAVID B. JEPSEN ATTORNEYS PATENTED JUL] 31971 SHEET Q [1F 5 h. ll m- H-HHI RE mmmm m m s. m VL .1. ma n mmm A TNAVA r Ma J6 V.. B o o o o o N x PATENTEB Jun 3 19m 3 593 005 sum 5 nr 5 ESTERLY ARTHUR L. mos: 3:? 5" JEPSEN BY 7 m* ll UZ-P m. mu m m M r m: T 2 S 3 3 2 Z J p umJam .SPPDO V l .r M r J I H o IL 2 I F o w J o f 1 r J n O I 2 p F J O I a .F P I o F Ill! Cam. 02 I tam. IIIII'I Cam. Oz
COUNTING MECHANISM BACKGROUND OF THEINVENTION l. Field ofthe Invention In general, this invention pertains to that field of art concerned with counting mechanisms, and more particularly, it pertains to counting mechanisms which are operable to count articles, such as fruit, of a generally rounded or spherical shape which may be randomly arranged in a single layer upon conventional conveying apparatus.
2. Description of the Prior Art The counting of bulk supplies of articles such as fruit has long presented problems particularly for the fruit-packing industry due to variations of the individual .fruit in both size and shape. Up to the present time, when it was desired to count a bulk supply of even a generally spherical (and therefore easily handled) fruit such as oranges which can bemoved by stan-.
dard conveyor belts, it has been the practice to provide diverting means or other obstructions to form the fruit into a single lane or into a plurality of parallel lanes where they can be individually fed past a switch-actuating arm.
The problems encountered with-the aforedescribed apparatus are considerable. First, a relatively large amountof time is required to arrange the fruit into the single lineformations, and the resulting delays in the feeding of the fruit are frequently the primary factor in extending the length of time necessary tor a particular fruit packing or processing operation. Secondly, the irregularities in size and shape thatarenor-r mally encountered in any given run of fruit make the design considerations for the lane-feeding apparatus extremely difficult and frequently result in the, introduction of costly and complex mechanisms which require frequent maintenance and repair. Finally, the efficiency of the prior art singulating fruit feeding devices is relatively low, and most of these devices are subject to jamming or erratic operation necessitating work stoppages and resultant loss of profits.
SUMMARY OF THE INVENTION The counting mechanism of the present invention may be installed over a typical conveyor assembly arranged to carry a plurality of fruit which are randomly received in sporadic groupings. Each individual fruit will be counted as it passes the counting mechanism regardless of its relative positioning with regard to the other fruit with but few exceptions.
Basically, the structure of the present invention includes a I series of sensing devices spaced in a row across the path of fruit travel. The sensing devices are positioned and spaced so that each fruit will contact at least one sensing device as it moves down the conveyor path. Furthermore, the spacing of the sensing devices is small enough so that at least one sensing device will remain unactuated between a pair of fruit which are in close engagement travellingdown the conveyor.
The sensing devices operate to feed a signal into a switching circuit when they are activated and deactivated. As a fruit passes a sensing device a signal pulse is generated in the associated switching circuit if and only if the pulse generating means has not been inhibited because of the activation of the adjacent sensing devices, That is to say, a counting pulse will be generated if a fruit deactivates a sensing device while neither of the adjacent sensing devices are activated or if an adjacent group of sensing devices are simultaneously deactivated while the adjacent sensing devices are unactivated.
The pulse which is generated by each fruit is counted by means of a conventional electronic pulse counter in order to provide a running total of the number of fruit passing the counting mechanism.
The only limitations upon the counting mechanism of the present invention are that the fruit be generally rounded .or spherical in shape so that there will be a detectable space between adjacent fruit even when they are in engagement; that the individual fruit do not reverse direction upon the conveyor so as to activate a sensing device more than one time; that only a single layer of fruit is passed to the counting mechanism; and that two fruit do not leave the system within the period of time of a counting pulse. In regard to the latter limitation, however, since the pulse created by the circuitry of the present invention is in the order of to 200 nanoseconds, such an occurrence is extremely unlikely and, for allpractical purposes, can be neglected.
One feature of the preferred embodiment of the present invention is that the activation of the pulse-producing means is obtained as the travelling fruit moves past the counting mechanism, i.e., as the trailing edge of the fruit deactivates the sensing device. This'arrangement provides a better control for counting the individual fruit.
While the mechanism of the present invention is particularly designed to count fruit, it will be apparent that other articles could be counted without necessitating any basic changes in the structureor operation of the mechanism.
BRIEF'DESCRIPTION OF THE DRAWINGS FIG. 1 is an isometric of the counting mechanism of the present invention positioned above a belt conveyor with portions of the mechanism being broken away to illustrate the construction of the switch mounting arms.
FIG. 2 is a front elevation of the counting mechanism show in Figure I particularly illustrating the'action of the switch mounting arms when contacted by fruit travelling upon the underlying conveyor.
FIG. 3 is a side elevation of the counting mechanism shown in Figure I further illustrating the movement of the switchmounting arms when contacted by fruit.
FIG. -4 is a schematic representation of the switching circuitry of the present invention.
FIG. 5 is a detailed schematic representation of one of the switching circuits disclosed in FIG. 4.
FIG. 6 is a table illustrating the logic of the components of the circuitry shown in FIG. 5.
FIG. 7 is a graph illustrating the relative voltage condition at each of the designated points in the circuitry of FIG. 5 during various time intervals as a fruit is passed beneath the associated switch.
DESCRIPTION OF THE PREFERRED EMBODIMENT The fruit-counting mechanism 10 of the present invention is shown in a position to be used for counting fruit F FIGS. 2 and 3) travelling along a belt conveyor 12 between a pair of side rails 14. A pair of side frame members 16 support the counting mechanism and are mounted above the conveyor by means of threaded bolts I8 adjustably secured to the outwardly extending flanges 14a of the conveyor side rails. A shaft 20 is mounted to extend between the side frame members and a plurality of switch mounting arms 22 are freely pivotably received upon the shaft.
Each of the mounting arms 22 comprises a pair of brackets 24 and 24a (FIG. 3) spaced apart to carry therebetween a conventional snap-action mechanical switch SW. Each of the brackets 24 and 24a include an inclined edge 26 facing in the direction of the oncoming fruit and being adapted to intercept the fruit so that the entire arm can be pivoted upwardly about the shaft 20, as shown for example in FIG. 3. The switches SW include actuating arms 30 which extend parallel to the fruit contacting edges 26 and, in their unactuated position (as shown in the dashed line representation of FIG. 3), extend downwardly to a location below the lowermost edges 27 of the brackets. Each of the mounting arms is supported in its unengaged position by a rigid bar 32 (FIG. 3) extending transversely across the structure of the counting mechanism just upstream of the fruit-contacting edges 26.
It will be apparent that the fruit F moving along the conveyor 12 may strike one or more of the mounting arms and push the mounting arms upwardly as is shown in FIGS. 2 and 3. The apparatusmay. be adjusted by adjustment of the mounting of the supporting bolts 18 so that all of the fruit withina particular run will range in diameter between a maximum sized fruit capable of moving under the structure of the counting mechanism and a minimum sized fruit capable of striking at least one switch actuating arm 30 as it moves beneath the structure. In handling fruit, the range of shapes and sizes must be taken into consideration and the apparatus is usually adjusted so that the minimum diameter of fruit will just pass under the lowermost edges 27 of the switch-mounting arms 22; thus, contact of at least one switch-actuating arm by such fruit is assured.
All of the mounting arms are loosely received upon the shaft 20 in abutting engagement with wear strips 34 of Teflon or similar material being provided on the outer front faces of the bracket members 24. The spacing between the adjacent mounting arms is critically determined so that at least one switch will be unactuated between two fruit moving in engagement down the conveyor 12, i.e., at least one switch must be unactuated while the switches adjacent to it are actuated by different fruit, the unactuated switch thereby serving to recognize the interface between the fruit. In a structure designed for the counting of oranges having an average diameter of approximately 2.2 inches, switches were set on spacings of five/eighth inches across the conveyor in order to provide satisfactory operation.
The signal from each of the switches is transmitted into the control portion 35 of the apparatus positioned above the switch mounting arms 22 which control portion comprises the counting device and the switching circuitry that will be described in detail hereinafter.
As shown in FIG. 4, each of the switches SW provides a signal to a switching circuit comprised of logic gates G1, G2, G3 and G4 which circuit, in turn, provides a signal to a fourinput logic gate G5 capable of providing a pulsed output along a common line 40 to a counter. The counter may be any of many commercially available electronic counters for detecting and counting pulsed inputs. A positive voltage supply +v is provided for each of the switching networks through load resistors R1 and R2 as shown. As indicated by the phantom line representations in FIG. 4, a plurality of switching circuits including gates GlGS (one for each switch SW) may be provided with each of the switching circuits being interconnected with the adjacent switching circuits in the manner indicated.
The operation of each of the switching circuits associated with one of the fruit contacting switches SW will be explained with particular reference to the switching circuit shown in the schematic diagram of FIG. 5. Each of the two-input gates G1, G2, G3 and G4 are in the NAND/NOR configuration the logic of which is shown in the table of FIG. 6. As can be seen, a (i.e., ground potential) output Z will only be obtained if both inputs X and Y are (i.e., a positive voltage value). If either one or both of the inputs are 0 then the output 2: will be The gates GlG4 are connected in a two-stage set-reset flip-flop circuit arrangement whereby one of the inputs of each of the parallel gates G1 and G2 is tied to the output of the opposite gate and whereby one of the inputs of each of the parallel gates G3 and G4 is tied to the output of the opposite gate. The four-input gate G5 is also in the NAND configuration whereby its output will be 0 if and only ifall of the four inputs are During its unactuated state, i.e., with no fruit in contact with the switch-actuating arm 30, the switch SW will be in the position shown in full line inFlG. 5 wherein point a is grounded at 0 and point b is provided with the positive potential +v. Since point a is at 0, the output of gate GI will be at point 0. Since point 0 serves as an input to the gate G2, both of the inputsto G2 are and its output at point d, therefore, is 0. Since one of the inputs to gate G4 is 0 at point d, the output at pointfmust be This makes both inputs from c and f+ to gate G3 therefore making the output at point e 0 into the gate G5. With at least one input to the gate G5 being zero, the output thereof at point g will remain The aforestated conditions will remain so long as the switch SW is not actuated by a passing fruit. At the left side of the time chart of FIG. 7, the states of each of the aforementioned contact points a-g of the circuit of FIG. 5 are depicted during the time that no fruit is received upon the associated switch actuating arm 30. Assuming that at some time t, the leading edge of a fruit comes into contact with the switch-actuating arm and moves it out of electrical contact with point a, the state of point a will change to This change of state will have no effect upon the remainder of the circuit since the 0 input to G1 from point d will keep point 0 at Depending upon the design of the mechanical snap-action switch, point b will be contacted (as shown in dashed lines in FIG. 5) and grounded through the switch at some later time t: to place b in the 0 state. Although the time interval between t, and 2 might be typically from 3 to 5 milliseconds with most of the generally available mechanical snap-action switches, it is one of the important features of the present invention that the time necessary to shift the position of this switch is immaterial and the relatively long duration of this time interval will not affect the operation or response of the switching circuitry of the present invention. Furthermore, the noise or transient currents generated by the opening and closing of the switch are not transmitted to the pulsed output of the circuit so as to affect it.
Once the point b is moved to 0 at time t point d will change to due to the logic of gate G2, this change taking place after an interval of time between t and t as determined by the internal components of the gate circuitry. When d changes to at time t;,, both inputs to the gate G1 will be and the output at 0 will therefore change to 0 at time t, after a time interval similar to that between 1 and With c at 0 the output of gate G3 will change to at time after another similar time interval. Finally, with both of the inputs from e and d to gate G4 now being the output 'atf will change to 0 at a subsequent time As indicated in FIG. 7, the foregoing states of the circuit contact points will remain throughout the contact of the fruit with the switch. It will be noted that one of the inputs to the gate G5 is from the point c between the two flip-flop arrangements. Since this point went to 0 before any change in state of the G5 input at point e, the output of gate G5 remains unaffected during the transition of the switch SW from the unactuated to the actuated state.
We next consider the condition of the switching circuitry at some considerably later time I, when the switch-actuating arm 30 has moved over the face of the fruit and down the trailing edge thereof to drop off the fruit and thereby move the switch out of the dashed-line position of FIG. 5 to again place point b at a positive potential +v. At some later time t,,, after a time interval similar to the interval between time t, and time t switch SW will close into the full line position of FIG. 5 to place point a at 0. Now a new sequence of switching state changes is initiated whereby point 0 first goes to at time since both inputs to gate G1 will then be 0. At a subsequent time 2, as determined by the components making up the gate G2, the point d will go to 0 since both inputs to G2 will then be With d again at 0, the gate G4 provides a output atfat a subsequent time 1 Finally, at time t point e will return to 0 since both inputs to gate G3 will be It is important to note that both the input from e and the input from c to the gate G5 will be between the time t and the time I If we assume that the other two inputs (i.e., the outermost pair of inputs) to gate G5 are also during this time interval, then the output at g from G5 will be 0 and an inverted signal pulse will be transmitted to the counter as illustrated in FIG. 7.
It will be noted, from the circuit diagram of FIG. 4, that the outer two inputs to each of the logic gates G5 are received from the points 0 on the adjacent two switching circuits. From the foregoing description it will be remembered that the point 0 on a switching circuit will be at only when the switch associated with this circuit is not actuated by a fruit. It will be appreciated, therefore, that each switching circuit, when actuated, serves as an inhibitor of the pulse output from the adjacent switching circuits since every input to the logic gate G5 must be in order to get the pulse output. Consequently, a pulse output to count one fruit can only be achieved when the last switch-actuating arm drops off the trailing edge of the fruit even though the fruit may have actuated several switches as it passed beneath the structure of the counting mechanism. As shown in the circuit diagram of FIG. 4, the switching circuits for the outermost two switches (i.e., those nearest to the conveyor side rails 14) have one of their inputs to the logic gate G5 tied directly to the +V line so that it will always be at and, hence, these'switching circuits can only be inhibited by an adjacent switch rather than by two adjacent switches.
It should be pointed out that it is possible to have simultaneous pulses generated from two adjacent switchactuating arms at the exact same time or within the time interval of a pulse. However, since each pulse will be directed into a common input to the electronic counter, such an occurrence would only be counted as a single pulse so that the accuracy of the mechanism could not be affected. Since it was specified that at least one switch must be unactuated between a pair of fruit on the conveyor, separate pulses will be provided for each fruit since the unactuated middle switch will not-inhibit the count of either of the two fruit. Another limitation to the switching apparatus of the present invention is that the switch actuating arm must be permitted to fully deactuate its switch between two fruit moving one behindthe other down the conveyor.
it will be appreciated that there is a chance for errorin the system if the switch actuating arms drop off two fruit at the same time or within an interval of time defined by the pulse width from time 1 to I Since thispulse width is typically in the order f 100 nanoseconds when using commercially available solid-state gate circuitry, it can be seen that the possibility of such an occurrence is extremely remote and that the relatively few instances of a simultaneous" discharge of fruit will not significantly affect the accuracy of the counting mechanism.
It is further pointed out that a two-stage flip-flop switching arrangement is used so that the noise generated by the opening and closing of the switch SW will not be transmitted through the circuitry to the four-input gate G5. That is to say, the first flip-flop stage isolates the switch'from'the input to the logic gate G5 and provides for a clean signal to this gate. However, if the noise level generated by the switch can be tolerated in certain applications, it is possible toachieve the same results as with the disclosed circuitry if points and-d are tied directly to two of the inputs to gate G and the second flip-flop stage, comprising gates G3 and G4, is eliminated.
The pulse width, as determined bythe time interval between and r is fixed by the internal components of the various switching gates and is in the order of 50 nanoseconds when using generally available solid-state circuitry, as .previously pointed out. Although the short pulse width is desirable from the accuracy standpoint, it is possible to extend thispulse width slightly without unduly affecting theaccuracy of the circuit. For this purpose, small capacitors Cl may be tied into the output circuitry to the logic gate G5, as shown in FIG. 4, to slow down the action of the switching circuitry.
it will be recognized that the count for each fruit isnot achieved until the last switch-actuating arm drops off the trailing edge of the fruit. However, it will be appreciated that a reverse type of operation is possible by reversing the normal unactuated position of the switch SW from the full line to the dashed line position indicated in FIG. 5. With this type of arrangement, the counting mechanism can be made to function so that a counting pulse will be created when the first switch actuating arm contacts the leading edge of the fruit prior to the contact of the fruit by the switch actuating arm on either side thereof. While it is preferable to use the trailing edge of the fruit to achieve a count, the indicated reverse arrangement of the switching circuitry would be within the scope of the present invention.
It is also pointed out that other types of sensing devices might be substituted for the pivotably mounted mechanical switches herein disclosed. For example, an arrangement of spaced photoelectric cells could be utilized. Also, underlying probes might be utilized which would sense the conductivity of the travelling fruit, i.e., the fruit might close a circuit through each of the contacted probes so as to change the state of a bistable element in the same manner as the switch SW. It will be recognized that other variations of the sensing means might be utilized by one skilled in the art.
From the foregoing description, it can be seen that a counting mechanism has been provided which is capable of operation on random arrangements of articles moving rapidly down a conveyor. There are no special lane dividers or feeding apparatus necessary to prearrange the articles, and, therefore, the simple counting mechanism of the present invention can be placed directly over a conventional conveyor as disclosed herein; thus, the present invention is readily adaptable to commercial fruit packing house conditions. The counting mechanism can also be readily adjusted for handling different sizes or varieties of fruit or for handling other articles which are generally rounded in shape so that an interface will be provided between adjacent articles which can be detected by the sensing devices of the present invention.
Although the best mode contemplated for carrying out the present invention has been herein shown and described, it will be apparent that modification and variation may be made without departing from what is regarded to be the subject matter of the invention as set forth in the appended claims.
Having completed a detailed description of the invention so that those skilled in the art could practice the same, we claim:
1. A counting .mechanism for detecting rounded articles such as fruit arranged at random along a conveying path, said mechanism comprising a plurality of sensing means aligned across said path in spaced relationship and in positions so as to be actuated by said articles as they are moved along said conveying path and with the spacing between adjacent sensing means being such that at least one sensing means will be unactuated between each pair of articles moving along said conveying path, means associated with each of said sensing means for producing and transmitting a pulse signal to a counter in direct response to a certain change in the state of actuation of the sensing means, and means associated with each sensing means and operable during the actuation thereof for inhibiting the pulse producing means of each adjacent sensing means whereby said pulse signal will never be produced or transmitted to said counter in response to the. actuation of one of the sensing means if said certain change in the state of actuation of said one sensing means occurs while an adjacent sensing means thereto is actuated.
2. A countingmechanism as set forth in claim 1 wherein said pulse signal will be transmitted to said counter only when said certain change in the state of actuation of said one sensing means occurs while said adjacent sensing means are unactuated or when said certain change in the state of actuation of a group of adjacent sensing means simultaneously occurs while the adjacent sensing means thereto are unactuated.
3. A counting mechanism as set forth in claim 2 wherein said pulse producing means comprises a switching circuit and an output gate operable to produce an output pulse in response to a unidirectional change in the state of actuation of said sensing means.
4. A counting mechanism as set forth in claim 3 wherein said pulse producing means comprises a set-reset flip-flop circuit having a plural input connected to said sensing means and a plural output connected to a four-input gate, said gate also having inputs from the flip-flop circuits associated with each of the adjacent sensing means, and said gate being conditioned to produce a pulse output in response to one of the changes in the state of its associated flip-flop circuit during actuation or deactuation ofits associated sensing means.
5. A counting mechanism as set forth in claim 3 wherein said pulse producing means comprises a pair of cascaded setreset flip-flop circuits having a plural input connected to said sensing means and an output connected to a four-input gate,-a second input to said gate being obtained from a point between said pair of flip flop circuits, said gate also having inputs from the circuitry associated with each of the adjacent sensing means, and said gate being conditioned to produce a pulse output in response to one of the changes in the state of its associated flip-flop circuitry due to actuation or deactuation of said sensing means.
6. A counting mechanism as set forth in claim 3 wherein said pulse producing means is conditioned to produce a pulse only in response to the deactuation of said sensing means.
7. A counting mechanism as set forth in claim 1 wherein each of said sensing means comprises a switch having an actuating arm extending into the conveying path of said articles.
8. A counting mechanism as set forth in claim 7 wherein each of said switches is carried upon a pivotally mounted carrier extending above and generally parallel to said conveying path, and means for vertically adjusting the height of said carriers to accommodate various size ranges of articles.
9. A counting mechanism as set forth in claim 8 wherein said pulse producing means is conditioned to produce said pulse signal at the time when the last switch actuating arm drops off of the trailing edge of the article to be counted as it moves along said conveying path.
10. A counting mechanism for detecting rounded articles such as fruit arranged at random along a conveying path, said conveying path being of a width whereby a plurality of articles may be moved abreast along said path, said mechanism comprising a plurality of switches mounted in alignment across said entire conveying path in spaced relationship, each of said switches having an actuating arm positioned so as to be engaged by said articles moving along said conveying path, pulse producing means associated with each of said switches for transmitting a signal pulse to a counter in response to actuation of its associated switch, and means associated with each of said switches and operable during the entire period of actuation of each switch for inhibiting the pulse-producing means associated with each of the adjacent switches so that said pulse-producing means of said adjacent switches cannot respond to the actuation of their associated switches.
11. A counting mechanism as set forth in claim 10 wherein each of said switches is adjustably mounted above said conveying path with the mounting means for said switches being such that the actuating arm for each switch will be permitted to return to its unactuated position between every pair of articles moving along said conveying path, said spacing between said switches being such that at least one switch will be unactuated between each pair of articles moving along said conveying path. I
12. A counting mechanism including a detecting circuit comprising sensing means arranged for activation by an article moving along a conveyor path, a gate having at least two-in puts and a single output conditioned to transmit a pulse signal to a counting device in response to a predetermined input pattern, and a logic circuit connected between said sensing means and said two inputs to said gate, both of said inputs being connected to said logic circuit but at different points whereby the condition of one input is at least partially dependent upon the condition of the other input, said circuit logic being such that said two inputs will create a pulsed output of relatively short duration in response to the deactivation of said sensing means as the trailing edge of an article on the conveyor path moves past said sensing means.
13. A counting mechanism as set forth in claim 12 wherein said logic circuit comprises a cascaded pair of set-reset flipflop circuits with said sensing means providing the inputs to the first flip-flop stage and with the inputs to said gate being provided from an output of the first stage and an output of the second stage of said flip-flop circuits.
14. A counting circuit for providing an output pulse of short duration in response to the passage of an article along a conveying path; said circuit including sensing means arranged for activation by said article for a relatively long duration as compared with the duration of said output pulse; a pair of terminals connected to said sensing means with the condition at each of said terminals corresponding to the state of said sensing means; and a lo ic circuit comprising first, second and third gate means each avlng two inputs and a single output,
one input of said first gate means being connected to one of said terminals and one input of said second gate means being connected to the other of said terminals, the other input of said first gate means being connected to the output of said second gate means and the other input of said second gate means being connected to the output of said first gate means, and the inputs of said third gate means being connected to the input and the output of one of said first or second gate means whereby a short duration pulse is produced during one of the changes of state of said sensing means.
15. A counting circuit for providing an output pulse of short duration in response to the passage of an article along a conveying path, said circuit including sensing means arranged for activation by said article for a relatively long duration as compared with the duration of said output pulse, a pair of terminals connected to said sensing means with the condition at each of said terminals corresponding to the state of said sensing means, an output gate having at least two inputs and a single output conditioned to transmit said output pulse in response to a predetermined input pattern, and a logic circuit connected between said terminals and said output gate with each of said inputs to said output gate being derived from said logic circuit, said logic circuit comprising a plurality of interconnected gates arranged to change state in a predetermined sequence in response to the change of state of said sensing means whereby a short duration pulse is produced on the output of said output gate in response to one of the changes of state of said sensing means.