US2829266A - High speed counting apparatus - Google Patents

Description

W 1958 l. l. BESSEN 2,829,266

HIGH SPEED COUNTING APPARATUS Filed May 10, 1954 7 g5 g0 30 2.9 36 3g v M M M Z. INVENTOR. lRWlNl BESSEZV AGEN 1".

l-HGH SPEED COUNTHNG APPARATUS Irwin I. essen, New Rochelie, N. Y., assignor to North American Philips Company Application May 10, 1954, Serial No. 428,469

5 Claims. (Cl. 250-833) This invention relates to apparatus for counting articles, and, in particular, to apparatus for counting opaque articles conveyed at high speeds.

A particularly vexing problem which has confronted the steel industry for some time involves accurately and reliably counting plated and unplated steel sheets while being conveyed along by a conveyor mechanism at extremely high speeds, e. g., up to a maximum velocity of 2500 feet per minute. Such sheets, which subsequently may be fabricated into the so-called tin cans," actually tin-coated steel containers, are generally about 30 inches long and of the order of 0.010 inch thick. The conventional counting method employs alight source and a photoelectric cell together with associated amplifying circuits and indicating devices, and depends upon the presence of a gap between adjacent sheets to permit the passage of light therethrough to obtain an indication. However, at the high speeds at which the sheets are conveyed, adjacent sheets frequently overlap, with the con sequence that two sheets are recorded as. one.

The chief object of the present invention is to provide apparatus capable of accurately and reliably counting sheet members travelling at high speeds which frequently overlap at their edges.

A further object of the invention is to provide apparatus capable of responding to and thereby accurately counting sheet members travelling at speeds of up to 25-00 feet per minute.

These and other objects of the invention will be best understood from the following description.

According to the invention, I employ a source of penetrating radiation located on one side of the moving sheets together with a detector responsive to penetrating radiation located on the other. side of the sheets for counting the sheets. The source of penetrating radiation may be a natural radioactive source or an artificial radioactive source producing radiation of sufi'icient energy to penetrate the sheet members and actuate the detector. Alternatively, a high energy X-ray source may be utilized.

As the detector, any form of high speed device capable of responding to the penetrating radiation is suitable, such as conventional Geiger counters, proportional counters or scintillation detectors. The detector employed should exhibit a su'tliciently low response time so as to be able to respond to the rapid changes of intensity of radiation occurring as the steel sheets pass between it potentiometer 28.

counting register or the like, capable of summing up and transforming current pulses into a visual record.

The invention will now be described in connection with the accompanying drawing in which:

Fig. 1 illustrates one form of counting apparatus in accordance with the invention; and

Fig. 2 is a cross-sectional view along lines 2-2 of Fig. l.

Referring now to the drawing, the steel sheets 10 to be counted are conveyed along at high speeds by any one of various types of conventional conveyors 11, a roller type being illustrated in the drawing. Above the sheets and in close proximity thereto is located a source of penetrating radiation 12. I prefer to use a radioactive source, either natural or artificial, rather than an X-ray source, as the former is considerably less bulky and requires no external source of power. Suitable for this purpose would be any betaor gamma-emitting radioactive source producing radiation of suflicient intensity to penetrate the steel sheets and actuate a detector. Examples of those would be beta-particle emitting sources such as strontium-90 and cobalt-60, two by-products of nuclearfission processes. The energy of the source is preferably chosen so that the sensitivity of the detector to a thickness change is large, which would depend upon the density of the sheets, i. e., the application for which the apparatus is intended. About ten millicuries of strontium-90 has been found adequate for steel sheets of about l0-20 thousandths thickness. Of course, where space limitations are not critical, a high energy X-ray source, of about -100 k. e. v. capacity, will serve the sam purpose. 1

When a natural or artificial radio-active source is employed, it will generally consist of a substantially thick lead container 13, in which theradio-active material 14 is positioned, provided with a small aperture facing the sheets through which the radiation is transmitted, as shown at 15 in the drawing. The radiation naturally diverges from its source, and this has been indicated by the diverging dotted lines.

Directly beneath the steel sheets is located the detec tor it; which, in this case, is shown as a plurality or group of adjacent Geiger or proportional counters 1'9 arrayed in a line or row. Each of the counters 19 com-- prises a generally cylindrical metal shell having a radiation transparent window 20 at one end and containing a central anode wire. The interior of the tube is generally filled with a rare gas, such as argon, and an organic or halogen quench, such as ethylene or chlorine, and a suitable potential is applied between the cathode shell and the anode wire. region within the detector of suflicient energy content causes discharges to occur therewithin, which manifests itself as an electrical current at the output of the counter. The magnitude of the totality of discharge currents depend upon the intensity of the radiation received by the counter.

The output terminal of the counter is coupled to a circuit responsive only to current or voltage pulses of one polarity, i. e., either negative or positive. Subsequent to this circuit, there is provided suitable means for counting and recording the number of pulses of that one polarity which are transmitted by the circuit. In the embodiment counter is shown in the drawing. It comprises an integrating circuit 25 composed of a capacitor 26 connected in parallel with a series-connected fixed resistor 27 and The parameters of that integrating Passage of radiation into the gas circuit are chosen to produce approximately rectangular current pulses, of a duration equal to the length of time of passage of a single steel sheet beneath the radiation source, from the extremely-short-duration pulses produced by the counter in response to each quanta of radiation impinging thereon. The resultant signal appearing at the variable tap or output terminal of the potentiometer 28 is shown at 29 in the drawing. The upper portion of that signal represents the absence of a sheet between the radiation source 12 and the detector 18; whereas, the lower portion of the signal, denoting re duced radiation intensity, represents the presence of a sheet therebetween. The ripple or hash 34 on the horizontal portions of the signal denotes the effect of the short pulses of the counter itself, which have been integrated by the circuit 25 to the form shown. The magnitude of that ripple 30 can be controlled by adjustment of the parameters of the integrating circuit 25 and by the intensity measured.

The signal 29 is then amplified by a conventional amplifier 32 and passed through a differentiating circuit 35 to produce sharp positive and negative current pulses therefrom corresponding to the leading and trailing edges, respectively, of the rectangular pulses shown at 29. The dilferentiating circuit 35 is shown as constituted by a capacitor 36 and a resistor 3'7 in the grid circuit of a thyratron-type, gas-filled, discharge tube 40. The signal appearing at the output of the differentiating circuit 35 is shown at 39 in the drawing.

The control grid of the thyratron 40 is biased negatively by being connected through the resistor 37 to a source of negative potential C. This potential is chosen such that the positive pulses of the signal 39, exclusive of the random variations or ripple appearing in the horizontal portions of that waveform, is just suficient to cause the tube 40 to fire. The thyratron 40 is operative as a one shot pulser by suitable selection of the parameters of its associated circuit, a resistor 41 and capacitor 42. Values for the latter are chosen so as to cause the thyratron to extinguish automatically after firing in a time suited to the subsequent scalar circuits 45.

Since only the positive pulses of the signal 39 actuate the thyratron 40, the negative pulses merely increasing the bias thereon, the signal appearing at the output of the thyratron, which is shown at 43 in the drawing, is constituted by a series of pulses of only one polarity, in this case, negative. The negative pulses can then be counted by conventional scaler circuits 45, and the sum thereof recorded by a conventional indicator 50.

The apparatus shown in the drawing operates in the following manner. Assuming a steel sheet 10 interposed between the radioactive source 12 and the detector 18, the radiation from the source will penetrate the sheet and enter the detector thereby producing a substantially constant current output from the integrating circuit 25 depending upon the intensity of the incident radiation. No change in current will appear at the output of the integrator 25 as long as the sheet remains between the radiation source and the detector; consequently, the thyratron circuit will remain inoperative. As soon as the trailing edge of the first sheet passes from beneath the source, assuming no overlap of the succeeding sheet, the intensity of the radiation incident upon the detector will sharply increase, resulting in an increase in current at the output of the integrator 25. The leading edge of the current increase, after amplification and differentiation, will trigger the thyratron 40 and cause the indicator to register the passage of a single sheet.

When the leading edge of the succeeding sheet interposes itself in the path of the radiation from the source 12, the output current of the detector will decrease, resulting in the generation of a negative pulse, after amplification and differentiation. However, the thyratron circuit is not responsive to negative pulses and, consequently, will not fire. Similarly, the trailing edge of this sheet will produce a positive pulse which will actuate the thyratron and cause the indicator to record the passage of a sheet. Accordingly, the trailing edge of each steel sheet will elfect an indication of the passage of a sheet.

For the case of the edges of adjacent sheets overlapping, the following will occur. When the overlapped leading edge 51 of the second sheet passes beneath the source, inasmuch as a double thickness of steel sheet will be present between the radiation source and the detector, the intensity of the radiation incident upon the detector 18 will be further reduced, resulting in a negative pulse after ditferentiation which will not actuate the thyratron circuit. Similarly, the trailing edge 52 of the first sheet will produce a positive pulse, and the trailing edge of the second sheet also a positive pulse, since both will cause an increase in counter current. As will be readily appreciated from the foregoing, whether the sheets are separated or overlapped, the trailing edeg of each sheet will always result in the production of a positive pulse capable of actuating the one-shot pulser 40 and the indicator 50. Consequently, the sheets will be accurately counted by the apparatus of the invention whether separated, or overlapped at their edges.

I prefer to use a plurality of parallel-connected, Geiger counters 19 disposed in a row or line perpendicular to the direction in which the sheets are conveyed as the detector for the reason that they afford collectively a much higher counting rate enabling a reduction in response time. For this purpose, as shown in the drawing, the aperture 12 in the lead container for the radiation source 14 may have the form of a slit with its long axis in the same direction as the row of counters 19, thereby producing a ribbon or fan-shaped radiation beam corresponding in shape to the window area 20 of the grouped counters 19. A further advantage of this arrangement is the generation of a higher level signal. The number of counters 19 employed in this arrangement will depend upon the rate at which the sheets are travelling, and in general, upon the response required. That is to say, the variation or ripple 30 in the horizontal portion of the wave form 29 is limited by a higher counting rate the counter 19 and a larger capacitance of the integrating condenser 26. However, increasing the size of the capacitor 26 affords the disadvantage of a reduction in the circuit response which would tend to reduce the amplitude of the signal pulses of the wave form 39. Consequently, I prefer to employ a larger number of counters 19 in the array described and reduce the capacitance of the capacitor 26 to obtain the minimal variation in the wave form 29.

While we have described our invention in connection with specific embodiments and applications, other modifications thereof will be readily apparent to those skilled in this art without departing from the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

1. Apparatus for counting a succession of articles each having forward and rear edges and moving in a given direction along a given path comprising a beam source of radiation capable of penetrating said articles with re duced intensity disposed on one side of the path, radiation detection means disposed on the other side of the path and positioned to intercept the radiation from said source, said detection means producing electrical signals in response to the radiation from said source having variations therein corresponding to the passage of said articles between said source and said detection means, means coupled to said detection means for differentiating between pulses produced when said forward and rear edges intercept said beam, and means responsive only to pulses produced by one of said edges.

2. Apparatus for counting a succession of articles each having forward and rear edges and moving a given direction along a given path comprising a beam source of radiation capable of penetrating said articles with reduced intensity disposed on one side of the path, radiation detection means disposed on the other side of the path and positioned to intercept the radiation from said source, said detection means producing electrical signals in response to the radiation from said source having variations therein corresponding to the passage of said articles between said source and said detection means, pulseshaping means coupled to said detection means for producing a substantially square-shape wave of duration corresponding approximately to the passage of one of said articles, differentiating means coupled to said pulse-shaping means for producing pulses corresponding to the leading and trailing edges of said square'shape wave, and means responsive only to pulses produced by one of said edges of said square-shape wave.

3. Apparatus for counting a succession of articles each having forward and rear edges and moving in a given direction along a given path comprising a source of radioactive emanations disposed on one side of the path, radiation detection means disposed on the other side of the path and positioned to intercept the radiation from said source, said detection means producing electrical signals in response to the radiation from said source having variations therein corresponding to the passage of said articles between said source and said detection means, pulse-shaping means coupled to said detection means for producing a substantially square-shape wave of duration corresponding approximately to the passage of one of said articles, differentiating means coupled to said pulseshaping means for producing pulses corresponding to the leading and trailing edges of said square-shape wave, and means responsive only to pulses produced by one of said edges of said square-shape wave.

4. Apparatus for counting a succession of articles each having forward and rear edges and moving in a given direction along a given path comprising a source artificial radioactive emanation disposed on one side of the path, radiation detection means disposed on the other side of the path and positioned to intercept the radiation from said source, said detection means producing electrical signals in response to the radiation from said source having variations therein corresponding to the passage of said articles between said source and said detection means, pulse-shaping means coupled to said detection means for producing a substantially square-shape wave of duration corresponding approximately to the passage of one of said articles, diflerentiating means coupled to said detection means for producing pulses corresponding to the leading and trailing edges of said square-shape wave, and means responsive only to pulses produced by one of said edges of said square-shape wave.

5. Apparatus for counting a succession of: articles each having forward and rear edges and moving in a given direction along a given path comprising a beam source of radiation capable of penetrating said articles with reduced intensity disposed on one side of the path, radiation detection means comprising a plurality of series-connected radiation detectors disposed on the other side of the path and positioned to intercept the radiation from said source, said detection means producing electrical signals in response to the radiation from said source having variations therein corresponding to the passage of said articles between said source and said detection means, pulse-shaping means coupled to said detection means for producing a substantially square-shape Wave of duration corresponding approximately to the passage of one of said articles, differentiating means coupled to said detection means for producing pulses corresponding to the leading and trailing edges of said square-shape wave, and means responsive only to pulses produced by one of said edges of said square-shape wave.

References Cited in the file of this patent UNITED STATES PATENTS 2,049,376 Hertwig et a1 July 28, 1936 2,316,361 Piety Apr. 13, 1943 2,349,429 Herzog et al. May 23, 1944 2,523,517 Potter Sept. 26, 1950 2,566,868 Allia Sept. 4, 1951 2,605,332 Parsons July 29, 1952 OTHER REFERENCES Theory and Operation of G-M Counters, Brown, Nucleonics, October 1948, pp. 46-61.

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