US3351820A - Pulse stretcher electric circuit - Google Patents

Description

NOV. 7, 1967 N 3,351,820

PULSE STRETCHER ELECTRIC CIRCUIT Filed April 21, 1964 I NVENTOR.

United States Patent 3,351,820 PULSE STRETCHER ELECTRIC CIRCUIT Andrew Balint, Park Ridge, Ill., assignor to Bell & Howell Company, Chicago, 111., a corporation of Illinois Filed Apr. 21, 1964, Ser. No. 361,499 6 Claims. (Cl. 317-1485) ABSTRACT OF THE DISCLOSURE responsive to the pulses. The switching means is connected to the pulse stretching circuit by meansof an input circuit having first and secondresistors and a capacitor so that closure of the normally open switch contacts will cause the capacitor to' discharge through one of the resistors and the gate of the SCR. The charge time of the capacitor and the closure time of the'co-ntacts are such as to protect the contacts. against arcingand to insure that only a single pulse for each closure. of the contacts will be produced.

At present, the use of solenoid devices, such as relays, counter-actuators, and the like is greatly limited due to the time required to fully actuate such devicesQOne approach to decreasing the time required to operate a solenoid actuating device is to decrease'the' mass of the relay armature, solenoid plunger, or the like which is to be moved by energization of the device. A reduction in the massof such a movable component will decrease the time required to accelerate .or actuate the component; however, a point is reached where the mass can no longer be decreased and still maintain the usefulness of, thedevice.

A further object of this invention is to provide means to increase the usable life of switching devices which are successively actuated at a high'rate.

, moving document makes contact with switching means Another approach to decreasing the time required to actuate a solenoid device is to increase the power applied thereto. However, increasing the actuating power may require relatively expensive components and may lead to a design which is not economically acceptable. Also, a point is reached where an increase in power applied to the solenoid device'has little or no effect on the timerequired to actuate the solenoid plunger or relay armature. It can be seen therefore, that this approach not only has characteristiclimitations, but is very costly because the cor responding components must be of a higher quality.

It is therefore an object of this invention to provide a means whereby conventional" solenoid devices can be actuated byshort time duration pulses which would otherwise have no effect on the solenoid device.

Another object of this invention is to provide a pulse stretching device which will respond to an input pulse of short time duration and provide an output pulse of substantially longer time duration capable of actuating an electromechanical load.

and will deenergize the counter while the document is still in contact with the switching means, thereby enabling the counter to'count overlapping documents as well as docu ments which successively follow each other.

A highly advantageous application of the invention resides in the counting of rapidly moving documentsand a specific embodiment of the invention for this purpose has been disclosed herein. However, it will be apparent that the invention has a wide field of utility.

' On the drawings: T

The single figure of drawings shows a schematic diagram of a pulse stretching circuit, which is constructed in accordance with'this invention, and illustrates by way of example a switch means with which the invention may be employed.

As shown on the drawings: g

The present invention has particular utility when combined with document-handling apparatus utilizing a document-actuated switching means comprising normally open switch contacts which are actuated in response to movement of sheet-like articles to develop short make-break time intervals which are so short as to preclude actuation of an electromechanical device by using such pulses directly. Thus, handling apparatus a pulse stretching circuit having an SCR with a gate electrode and which is responsive to the pulses of short time duration to actuate the electromechanical device. The switching means is connected to the pulse stretching circuit by means of an input circuit having first and second resistors and'a capacitor so that closure of the switch contacts will cause the capacitor to discharge through one of the resistors and the gate of the SCR. The charge timeof the capacitor and the closure time of the contacts is such as to protect the contacts against arcing and to insure that only a single pulse for each closure of the contacts will be produced. The life of such a switch will be. so extended that it will last as long as the apparatus with which it is associated.

The pulse stretching circuitgenerally designated by reference numeral 10, is rendered operative by actuation of a counting switch 11, which has a pair Of'bltiCtllCElllY conductive contacts 13 and 14. The contacts 13 and 14 are connected through a' pair of conductors 15 and 16 respectively to an input circuit 18 of a silicon controlled rectifier 19. The silicon controlled rectifier 19 has connected to the anode thereof an indicating lamp 20.

In the illustrated embodiment, the actuating coil 21 of one electromechanical counter device is coupled to the anode of control rectifier 19'via a diode 22. A second counter device is shown having its actuating coil 23 connected with control rectifier 19 through a diode 24. A com- Another object of this invention is to provide a means.

for counting short time duration pulses in a simple and inexpensive manner using conventional electromechanical counters instead of using relativelycomplex and expensive electronic counting devices.

mutating capacitor 27 also has one terminal thereof connected to the anode of the control rectifier 19. A diode 28 is connected in parallel with the counter 21 and in series, but of opposite conduction, with the diode 22. Adiode 29 is connected in parallel with the'counter 23 and in series, but of opposite conduction, with the diode 24. The cathode of control rectifier 19 is connected with line731. A four layer Shockley diode 30 has the cathode thereof connected to the, line 31, and the anode thereof there is combined with such documents connected to a resistor 32 and to the other terminal of the capacitor 27.

The silicon controlled rectifier 19 and the four layer Shockley diode 30 have similar characteristics in that they are both controlled rectifiers, the main difierence being that the silicon controlled rectifier 19 has two main electrodes and a control electrode connected thereto and the four layer Shockley diode 30 has only two main electrodes connected thereto. With the anode and cathode of the silicon controlled rectifier 19' forward biased, a signal is required at the gate electrode to switch on the silicon controlled rectifier 19. However, all that is required to switch on the four layer Shockley diode is to have the forward bias applied thereto exceed the breakover voltage, which is slightly less than the supply voltage.

In operation, with no counting signal from the switch 11, the four layer Shockley diode 30 is conductive through resistor 32. A charging circuit for capacitor 27 is present through the indicating lamp 20. When a counting signal, generated by the closure of contacts 13 and 14, is applied to the input circuit 18 of the silicon controlled rectifier 19, the silicon controlled rectifier 19 is rendered conductive. Energizing current then flows in parallel through the indicating lamp 20, through the counter 21 and diode 22, and through the counter 23 and the diode 24. This current is of Sufiicient magnitude and duration to actuate the counters represented by coils 21 and 23. The capacitor 27 applies a reverse polarity voltage across the four layer Shockley diode 30 which is thereby commutated into the non-conductive state. The capacitor 27 discharges through a circuit including control rectifier 19 and resistor 32 and then receives a charge of opposite polarity under the control of resistor 32. After a predetermined time, determined by the values of resistor 32 and capacitor 27, the capacitor 27 will become charged to a voltage nearly equal to that of the supply voltage and of polarity to tend to produce conduction by the four layer Shockley diode. The capacitor 27 will continue to charge through resistor 32 until such time that the voltage applied to the anode of the four layer Shockley diode 30 reaches the breakover voltage thereof. At this time, the four layer Shockley diode 30 is rendered conductive and the silicon controlled rectifier 19 is rendered non-conductive through the commutating capacitor 27 The indicating lamp 20, the counter 21 and the counter 23 will then remain deenergized until the next counting signal from the counting switch 11.

The input circuit 18, which is coupled to the gate circuit of the silicon controlled rectifier 19, includes a resistor 35 connected between the line 31 and the gate electrode of the silicon controlled rectifier 19. Also connected to the gate electrode is electrically conductive contact 13 of switch 11. Capacitor 37 has one terminal thereof thereof connected to the line 31, and the other terminal connected to switch contact 14 and to a resistor 39.

A transformer 40 having a primary Winding 41 and a secondary winding 42 is used to decrease alternating voltage from a conventional source of power to the desired value for the pulse stretching circuit 10. A bridge rectifier circuit 44 has the AC terminals thereof connected to the secondary winding 42 of the transformer 40. The DC terminals of the bridge rectifier 44 have connected thereacross a filter capacitor 46 and a bleeder resistor 47.

The counting switch 11, by way of example and not by way of limitation is of the type used in counting overlapping sheet-like articles such as cardboard cards and has three sensing arms 50, 51 and 52 fixedly secured to a triangular rotating cam 54. The sensing arms 50, 51 and 52 are arranged to extend through a panel member 55 for engagement with the cards such as indicated at 57 which move in the direction of arrow 58. The counting switch 11 may also be a snap-action switch for actuation by documents that successively follow each other in spaced relation.

The cards 57 each rotate the cam 54 through 120 to momentarily actuate the contacts 13 and 14. The amount the documents can overlap is proportional to the number of sensing arms on the switch 11 and inversely proportional to the length of the sensing arms 50-52. The time interval between make and break of contacts 13 and 14 is very short, too short, in fact, to actuate the counters 21 and 23 without the use of the pulse stretching circuit. When the contacts 13 and 14 are closed by passage of a card 57, the capacitor 37 will discharge through the gate resistor 35 of the silicon controlled rectifier 19 thereby rendering the silicon controlled rectifier 19 conductive. Even though the contacts 13 and 14 reopen after actuation thereof by the triangular rotating cam 54, the silicon controlled rectifier 19 remains conductive for a predetermined time interval such that the counters 21 and 23 are effectively actuated. After a predetermined time, depending upon the time constant of the capacitor 27 and resistor 32, the four layer Shockley diode 30 will be rendered conductive and the silicon controlled rectifier 19 will be commutated to a non-conductive state through the commutating capacitor 27. The diodes 28 and 29, which are connected across the counters 21 and 23, respectively, will act to maintain the counters in the energized state for a period of time, for example, approximately 5 milliseconds, after the control rectifier 19 becomes non-conductive.

By way of example only and not of limitation, a circuit as illustrated in the drawing may utilize the following components.

Part reference numeral: Illustrative component 19 Type 2N2323.

30 Type 4E208.

21, 23 IVOF108 type counters.

40 TRIAD F45X, 117 volt R.M.S. primary, 24 volt R.M.S secondary.

20 1829 lamp.

44 Type 1N537 rectifiers.

22, 23, 2 8, 29 Type 1N537 rectifiers.

47 100 ohms.

39 270,000 ohms.

35 27 ohms.

32 1500 ohms.

37 .01 microfarad.

27 6 microfarads.

46 4500 microfarads.

With a circuit having the specific illustrative components given above, the power supply provides an output of 30 volts D.C. Since the contacts 13 and 14 of the switch 11 are normally open, the capacitor 37 is charged to 30 volts through resistor 39. The four layer diode 30 is turned on and conducts through resistor 32, and the voltage across the four layer diode at this time is about one volt. The capacitor 27 is charged positive on the left and negative on the right, through the lamp 20 and the counters 21 and 23. When the contacts 13 and 14 close, capacitor 37 discharges through the gate of the silicon controlled rectifier 19 to render the control rectifier conductive, thereby energizing the lamp 20 and the counters 21 and 23. While the silicon controlled rectifier 19 is conductive, the voltage thereacross is about one volt which essentially grounds the left side of capacitor 27. The charged capacitor 27 appears briefly as a battery Whose voltage opposes the potential through resistor 32. The

four layer diode is then turned off until the capacitor 27 discharges through resistor 32 and recharges to the opposite polarity of about 20 volts. At this time the four layer diode is again rendered conductive and the charge on capacitor 27 positive on the right and negative on the left, now opposes the voltage across the lamp 20 and the counters 21 and 23. Therefore, the silicon controlled rectifier 19 is commutated off and is ready for a subsequent pulse from the sensing switch 11.

The values of resistor 32 and capacitor 27 determine the length of time the silicon controlled rectifier is conis introduced by the shunt diodes 28 and 29. The control rectifier 19 will be triggered on by each pulse and remain conductive for about '15 milliseconds after which it will be off until the next pulse isreceivedAt theend of such a train of pulses, the counters will be deactuated after a time interval of about milliseconds.

Summary of operation In operation each successive card 57 actuates the paddle I Wheel sensing device 11 momentarilyrto close contacts 13 and 14. This produces. a pulse across resistor 35 which triggers silicon control rectifier 19jto a conducting state. Current then flows through the actuating coils 21 and 23 a said contacts against arcing and producing only a single pulse for each closure of the contacts. 2. The invention ofclaim 1 wherein said pulse stretching circuit more specifically comprises direct current power supply means for'delivering a predetermined direct cur- I rent voltage and having'resistance means in series thereof the electromechanical counters for a suflicient time interval to actuate the counters. The time interval is determined by'the time constant of'the circuit including resistor 32 and capacitor 27. At the expiration 'of the selected time interval, capacitor 27 has been charged to such a value that the four layer shockley diode 301becomes'conductive; Conduction of diod'e 30 applies the voltage of capacitor 27 across control rectifier 19 so as to shut off the control rectifier and thus return the circuit to its initial state in readiness for a further pulse.

A circuit such as specifically illustrated thus comprises an electronic switch (provided by silicon control rectifier 19) capable of responding to pulses of a few microseconds in duration, a circuit controlled by the switch for generating a standardized actuating pulse having a duration of the order of 15,000 microseconds, and a means (including capacitor 27 and Shockley diode 30) for automatically resetting the circuit to its initial condition after the desired actuating time interval.

It will be understood that modifications and variations may be made without departing from the spirit and scope of the novel concepts of this invention.

I claim as my invention:

1. In combination With document handling apparatus having document-actuated switching means comprising normally open switch contacts and actuating means responsive to movement of sheet-like articles such as documents to develop short make-break time intervals, the improvement of:

a pulse stretching circuit having a silicon controlled rectifier with a gate electrode and being responsive to pulses of short time duration to actuate an electromechanical device which could not be actuated of said resistors and having the other terminal thereof connected to a line, whereupon closure of said switch contacts said capacitor will discharge through said one of said resistors and the .gate of said silicon controlled rectifier,

the charge time of the capacitor and the closure time of the contacts being such as to protect with, a four layer Shockley diode connected in series circuit with said direct current power supply means and said resistance means, I i

. saidfour layer Shockley diode havinga breakover voltage slightly less than said predetermined direct current voltage, a capacitor connected between said silicon cont-rolled rectifier and said four layer Shockley diode for placing said Shockley diode in its conductive state a predetermined time] after said controlled rectifier becomes conductive and for concurrently commutating said controlled rectifier to its non-conductive state in preparation for receipt of a further input pulse,

" and means for connecting an electromechanical device in said pulse stretching circuit.

3;.The invention of claim 1 whereinsaid' actuating means comprises V arotatablecam operatively connected to said switch contacts and having plural cam surfacesifor actuating said switch contacts and v a a corresponding plurality of sensing armsdrivingly connected tosaidcam. I 4. The invention of claim 3 wherein the number of said plural sensing arms is proportional to the amount the documents can overlap and the length of each of said I sensing arms is inversely proportional to the amount th documents can overlap.

5. A pulse actuated circuit comprising: an electromechanical device having first and second terminals, 7 a silicon controlled rectifier having anode, cathode and gate electrodes, r saidanode being connected to said first terminal, a source of direct current voltage having a positive terminal connected to said second terminal and a negative terminal connected to said cathode, a first resistor, switch means having one end thereof connected to one end of said first resistor forming a first circuit point, the other end of said first resistor being connected to the positive terminal of said source and the other end of said switch means being connected to the negative terminal of said source, a first capacitor connected between said anode'of said silicon controlled rectifier and the circuit point formed by said first resistor and said switch means,

a second resistor,

to one end of said second resistor thereby forming a second circuit-point,

the other end of said second resistor being con nected to the positive terminal of said source and the other end of said second capacitor being connected to the negative terminal of said source thereby charging said second capacitor, a thirdresistor having one end thereof connected to said gate electrode and the other end thereof connected to the negative terminal of said source,

and document-actuated meansincluding normally open contact members connected electrically between said second circuit point and'said gate electrode and being operable upon closure by a document for substantially discharging said second capacitor through said third resistor to render said silicon controlled rectifier conductive to energize said electromechanical device,

= the closure time of said contacts and the charging time of said second capacitor being such that the contacts are protected against arcing,

second capacitor having one end thereof connected 3,351,820 r I? 8 6. A pulse actuated circuit as defined in claim 5 and OTHER REFERENCES further characterized by the charge time of said second Survey of some Circuit Application of the Silicon capacitor through said second resistor being in the order Controlled Switch and silicon Controlled Rectifier, of 9 at least abopt loooo dlschtrge tune Applications and Circuit Design Notes, Solid State Prodof said second capacitor through said third resistor. 5 ucts Inc Bulletin D December 1959 pp References Cited 4, 8, 27.

UNITED STATES PATENTS MILTON o. HIRSHFIELD, Primary Examiner. 1/1966 Fel'check 317148-5 L. T. HIX, Assistant Examinen 3,243,665 3/1966 Fayer et a1. 3l7148.5 10

Claims (1)

1. IN COMBINATION WITH DOCUMENT HANDLING APPARATUS HAVING DOCUMENT-ACTUATED SWITCHING MEANS COMPRISING NORMALLY OPEN SWITCH CONTACTS AND ACTUATING MEANS RESPONSIVE TO MOVEMENT OF SHEET-LIKE ARTICLES SUCH AS DOCUMENTS TO DEVELOP SHORT MAKE-BREAK TIME INTERVALS, THE IMPROVEMENT OF: A PULSE STRETCHING CIRCUIT HAVING A SILICON CONTROLLED RECTIFIER WITH A GATE ELECTRODE AND BEING RESPONSIVE TO PULSES OF SHORT TIME DURATION TO ACTUATE AN ELECTROMECHANICAL DEVICE WHICH COULD NOT BE ACTUATED BY SAID PULSES DIRECTLY. AND AN INPUT CITCUIT CONNECTING SAID SWITCHING MEANS TO SAID PULSE STRETCHING CIRCUIT AND MORE SPECIFICALLY COMPRISING: FIRST AND SECOND RESISTORS, ONE OF SAID RESISTORS BEING CONNECTED BETWEEN SAID GATE ELECTRODE OF SAID SILICON CONTROLLED RECTIFIER AND A LINE, ONE OF SAID SWITCH CONTACTS BEING CONDUCTIVE AND BEING CONNECTED TO SAID GATE ELECTRODE, AND A CAPACITOR HAVING ONE TERMINAL CONNECTED TO THE OTHER OF SAID SWITCH CONTACTS AND TO THE OTHER OF SAID RESISTORS AND HAVING THE OTHER TERMINAL THEREOF CONNECTED TO A LINE,

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