US2982403A

US2982403A - Long-short separator for serially conveyed units

Info

Publication number: US2982403A
Application number: US508069A
Authority: US
Inventors: Gregory J Harmon
Original assignee: REED RES Inc
Current assignee: REED RES Inc; REED RESEARCH Inc
Priority date: 1955-05-13
Filing date: 1955-05-13
Publication date: 1961-05-02
Anticipated expiration: 1978-05-02

Description

Wired 4 Stat Paw O" LONG-SHORT SEPARATOR FOR SERIALLY CONVEYED UNITS Gregory J. Harmon, Bethesda, Md., assignor to Reed Research, Inc., Washington, D.'C., a corporation of Delaware Filed May13, 1 955,Ser.No. 508,069 l 4 Claims. Cl. 209-82) sensing. machine of the typedescribed in;copending applications, Serial Number 460,385, filed October 5, 1954, for Stamp Sensing Letter Sorter, now Patent No. 2,93 6,- 886, issued May 17, 1960, and Serial Number 478,694, filed December 30, 1954, for Article Handling andSorting Apparatus. t

It is a primary object of the invention to sort'all pieces Patented May 2, 1961 ice tion A, the path of the letter, indicated by arrow, I

crossed by a narrow beam of light from lamp 4 which is directed into a photocell 2. A similar lamp 5 and photocell 3 at station B provide a second sensing device. It is preferable that the light sources furnish light beams of constant intensity such that the beams do not cause the output currents of 2 and 3 to be modulated appreciably.

The sequence of events when aletter progresses through 1 in the direction shown in Fig. 1 is then as follows: ConsideringphotocellZ only, a steep voltage rise occurs in the output circuit 'of 2just.as the leadingedge 8 of letter '6. interrupts the light beam from lamp 4 at time t The increased voltage is sustained until trailing edge 7 of the letter emerges from theflight -beamat time t The output circuit of 2 then registers an abrupt voltage drop to the initial starting voltage. Since S and 5 are identical with 2 and 4 in all respects, including associated load circuits, etc., a second voltage excursion, identicalin polarity andmagnitude to that obtained in the load circuit of 2, occurs in the output circuit of.3 as letter 6 passes through the light beamfrom lamp 5. In Fig. 1, times t and 1 represent, respectively, the instants at which letter edges 8 bearnB. v y

Now, while t always marks a later point in timethan t t;, or 1 and t5 is always later than t t is not necesof mail which are not greater than a permissible maximum length into one conveyer channel, hereafter called the short channel, for further'treat-ment and to sort all items which are greaterthan said permissible length into another channel which may be termed the long, channel. Another object is to provide a sorting-device of the above type which is substantially independent of the gap between successive units, although 'it will be apparent'that a certain minimum gap must exist between units so that they can be distinguished at all by their length.

Another object is to provide electrical means for sorting serially conveyed spaced units, such as pieces of mail, according to length directly without the use of reference time-basis or markers such as electronically generated gates contained within the circuitry. 4

Another object is to provide a simple and fool-proof length sorter which is positive and definite in its action under all practical conditions.

According to the invention, passage of a conveyed unit past two spaced sensing stations causes a beam of light shining into a photocell at each station to be successively interrupted and reestablished, to produce at each station a voltage pulse having a leading and a trailing edge. The

circuit is so arranged that the time of the leading edge at the forward station is compared with the time of the trailing edge at the rearward station and the latter of these two times determines which channel will be selected.

The specific nature of the invention, as well as other objects and advantages thereof, will clearly appear from a description of a preferred embodiment as shown in the accompanying drawing, in which:

Fig. l is a schematic drawing showing the principle of the invention; and

Fig. 2 is a circuit diagram of a practical circuit for carrying out the invention of Fig l.

Referring to Fig. 1, the distance gage 1 contains two stations A and B separated by a distance corresponding to the desired critical length. Letters greater than this length are to be directed into onefchannel and shorter.

letters are to be directed into another channel. At stasarily later than Assume .thecase in which the length of letter, 6 measured fromedge'7 to edge 8 is sufficiently great to intercept the light beams at both stations A and B simultaneously. Then, it is apparent from Fig. 1 that as the letter travels in the direction indicated, edge 8 will enter the light beam at station E before edge 7 leaves the light beam at station A. In this-case t occurs earlier in time than t and the letter is designated as a long. Conversely, if the letter has insufficient length to interrupt the light beams at both stations Aand B simultaneously and, travels as shown, t will be delayed in time be'yond t and the letter is designated as a short. 1

By making use of the fact that t and t are interchangeable in time, depending on the lengths of the letters passed, a two-channel circuit may be arranged to cause polarities in Which they are delivered from the difierentiator of 9.

Elements

12 and 13 of Fig. 1 are thyratrons and form the two symmetrical halves of a bistable trigger circuit. That is, 12 will remain in a stable state, conducting current, with 13 rendered non-conducting, or vice versa. The circuitry is so arranged that only positive voltage pulses such as those at t or t will cause I triggering, 12 and 13 remaining unresponsive to negative pulses such as those-at t or 1 At the instant when a pulse at t causes 12 to conduct, an energizing current flows through the coil of relay 14 from the output circuit of 12 releasing an escapement or latch attached to the relay armature. The unlatching action permits pivoted and spring-retained gate door 16 to open under the impact of moving letter 6.

Channel II functions in entirely the same manner as channel I with the exception that 10, which is the exact counterpart of 9, is followed by a pulse-inverting circuit, 11. This is essential since the desired measurement pulse at 1' is delivered from 10 with negative polarity and and 7 enter, and emerge from,

must be positive when applied as a trigger at the input of 13. Because of the bistable action of 12 and 13, it is impossible for gate 17 to swing open when 12 is conducting or for gate 16 to open when 13 is conducting. In other words, gate 16, only, is open for a long letter with 17 closed, the reverse condition obtaining for a short letter.

It is clear then, that the sole determining factor in the routing of letters through

paths

18 or 19 is the priority of occurrence of pulses at t or t Any letter passed through 1 in Fig. 1 will cause both 12 and 13 to be triggered by pulses at t and t respectively. If the letter is a long, the determining pulse occurs at t since t in that case causes the last positive pulse set off by that letter to reach the trigger circuit. If the letter is a short, the determining pulse is at t since 12 then becomes the last positive pulse in the train. Thus, all longs are routed through path 18 and all shorts through 19.

Fig. 2 shows the details of a practical circuit in accordance with Fig. 1. Corresponding elements are given the same reference character as in Fig. l with a prime added. The plate voltage level of amplifier tube 9' is normally low since the tube is biased to conduct when the light beam at station A reaches photocell 2. Upon interruption of the beam by the leading edge 8' of letter 6', the grid bias of tube 9' goes negative and cuts off the tube, causing the plate voltage of tube 9 to rise and passing a positive pulse to the primary of pulse transformer 20 through the resistance of potentiometer 26, which is adjustable so that the amplitude can be varied, and thence through condenser 22 to the primary of pulse transformer 20. The condenser, together with the inductance and inherent resistance of the transformer, act as a conventional differentiating circuit to produce a sharp positive pulse in the primary of the transformer. The transformer secondary winding is so connected to the grid of thyratron 12' that a positive pulse in the primary produces a negative pulse in the secondary circuit which is applied to the grid. Similarly, when the letter passes station A, its trailing edge 7' produces the opposite effect throughout the foregoing circuit, resulting in a positive pulse at the grid of thyratron 12' at time t Damping resistor 56 is connected across the secondary of transformer 20 to prevent a large overshoot or oscillation in the opposite direction from the initial pulse, which might cause improper operation, it being desirable to have a single strong positive pulse occur only when the trailing edge passes station A. The magnitude of the pulse can, of course, be controlled by the setting of potentiometer 26.

At station B, the same effects occur, except that the opposite terminal of the secondary of transformer 11 is applied to the control grid of thyratron 13', so that the leading edge, rather than the trailing edge, produces the positive pulse to trigger thynatron 13'. Thus the action described in connection with Fig. 1 is produced. The plate circuits of thyratrons 12' and 13' are coupled through condenser 30 to produce the well-known bistable trigger circuit action whereby the last energized thyratron remains conducting until a sufliciently positive voltage is applied, which may be in the form of a brief pulse, to the grid of the other thyratron, which reverses the condition. Each thyratronactuates its associated

gate magnet

14 and 16 respectively to control the routing of the mail.

The power supply for the foregoing circuit is preferably regulated and may comprise transformers 36 and 38, the latter furnishing the filament supply for the rectifier tube (5690) and the grid bias for the thyratrons through a suitable ballast (7T1H) to insure that the correct bias values will be maintained under all ordinary conditions of line voltage. Similarly, transformer 36 furnishes the remaining filament supplies and the plate voltage supplies through filter circuit 40 and gas diode 42 (type 0D3W). In normal operation the gas tube fires and draws a bleeder current through 7500 ohms resistor 44 as a ballast current. If the current through the load tends to change so as to draw more or less current, the gas tube tends to compensate so that it draws less current as the circuit draws more, and vice-versa.

It will be apparent that instead of interrupting a beam of light by the passage of the letter, the reflection of a beam of light from the letter could be used to operate the photocells at stations A and B. Likewise, it will be apparent that the polarities shown are given by way of example only, and that the operative polarities could be reversed by the use of suitable circuitry. Similarly, other types of bistable triggers could be used than the one shown.

In order to clarify the operation of applicants apparatus and claim the combinations thereof in terms of the functional relationships disclosed above, the following terms are defined: the bistable trigger means comprises elements 12', 13', 30, and their associated connections as shown in Figure 2; the gate control means comprises

elements

12', 13', 30, 32, 34, 14', 15', and their associated connections as shown in Figure 2; the condition ing circuit means comprises

elements

9', 10', 20, 11, 22, 24, 26, and their associated connections as shown in Figure 2; and the gate operating circuits comprise (l) elements 32, 14', and their associated power supply as shown in Figure 2 and (2) elements 34, 15, and their associated power supply as shown in Figure 2.

It will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement within the scope of my invention is defined in the appended claims.

I claim:

1. In apparatus for sorting serially conveyed units according to length, the combination comprising; means for conveying a series of separate units in a predetermined path of motion, said path of motion having a direction, said units spaced by a predetermined minimum gap in the direction of said path of motion, each of said units having a leading edge and a trailing edge, said units oriented so that their leading edges traverse said path in advance of their trailing edges, a first sensing station positioned adjacent to said conveying means, said first sensing station comprising means for producing one electrical signal initiated by the passage of the trailing edge of a unit past said first station, a second sensing station positioned adjacent to said conveying means and spaced from said first sensing station forwardly along the direction of motion of said units by a predetermined distance corresponding to a critical length of said units, said second sensing station comprising means for producing another electrical signal initiated by the passage of the leading edge of a unit past said second station, two channels positioned adjacent to said conveying means and spaced forwardly of both of said first and second stations with respect to said direction of motion of said units, selector gate means positioned adjacent to said conveying means and operatively associated with said means for producing said one electrical signal and said another electrical signal at said first and second stations and said two channels, said gate means having two positions for directing said units to one of said two channels after said units have traversed both of said stations, bistable trigger means connected to each of said signal producing means, said trigger means having two alternative stable positions, electrical differentiating circuit means connected to each of said signal producing means for difierentiating said electrical signals and thereby producing sharp electrical pulses of one polarity corresponding to a leading edge signal from each of said signal producing means and sharp electrical pulses of the polarity opposite to said one polarity corresponding to a trailing edge signal from each of said signal producing means, means for inverting the polarity of the electrical signals a from one of said signal producing means connected to one of said differentiating circuit means so that the leading edge signal from said signal producing means of said second station is of the same polarity as the trailing edge signal from said signal producing means of said first station, and means for connecting said means for inverting of the one circuit, and said diiferentiating circuit means of the other circuit to said bistable trigger means for triggering said bistable means to one of said two stable positions with either said secondstation leading edge pulse signal or said firststation trailing edge pulse signal, whereby the latest in time of said last two signals determines the position of said selector gate means.

2. The invention according ,to' claim 1, said bistable trigger means comprising two thyratron trigger tubes electrically connected to have opposite and mutually excl-n sive conduction states.

3. The invention according to claim 2, said polarity inverting means comprising at least one pulse transformer having windings oriented to produce pulse polarity inversion.

4. In apparatus for sorting serially conveyed units according to length, the combination comprising; means for conveying a series of separate units in a fixed path of motion, said path of motion having a direction, said units spaced by a predetermined minimum gap in the direction of said path of motion, only two sensing stations spaced along said means for conveying and consisting of a first station and a second station spaced from said first station forwardly along the direction of motion of said units by a predetermined distance corresponding to a critical lengthof said units, two channels positioned adjacent to said means for conveying and spaced forwardly of both said first and second stations with respect to the direction of motion of said units, selector gate means operative to allow communication between said path and one of said two channels, each of said first and second stations comprising an electrical sensing means connected in an electrical signal circuit and operable during the time of passage of any of said units past said station to produce an electrical signal in its associated signal circuit, selector gate control means operatively associated with said electrical sensing means of the signal circuits of said first and second stations to condition one of said two gate operating circuits for operation in the absence of a signal from said electrical sensing means of said first station caused by'a trailing edge of a unit at the time when the leading edge of the same unit reaches said electrical sensing means of said second station and causes a signal, and for later conditioning the other of said two gate operating circuits for operation and returning said first conditioned circuit back to a non-conditioned state when the signal caused by the trailing edge of the same unit passes said electrical sensing means of said first station, whereby only the conditioned one of said two gate operating circuits is actuated upon the leading edge of a unit reaching said electrical sensing means of said second station.

References Cited in the file of this patent UNITED STATES PATENTS 1,998,950 Cockn'll ..Apr. 23, 1935 2,033,645 Parkhill Mar. 10, 1936 2,085,671 1 Powers June 29, 1937 2,162,508 Knowles June 13, 1939 2,415,176 Hurley Feb. 4, 1947 2,415,177 Hurley Feb. 4, 1947 2,602,847 Larew July 8, 1952 2,630,043 Kolisch Mar. 3, 1953 2,740,521 Calvin Apr. 3, 1956 2,933,185 Coleman et a1. Apr. 19, 1960 FOREIGN PATENTS 682,303 Great Britain Nov. 5, 1952 OTHER REFERENCES Circuit Theory of Electron Devices, pages 178 to 186, John Wiley and Sons, Inc., copyright 1953.. (Copy in Patent Ofiice Library).