US2264873A - Control system - Google Patents

Description

1941- r w. D. COCKRELL 2,264,873

CONTROLSYSTEM Filed July 13, 1940 Fig I.

SCANNING UNIT vInventor"- William D. Cockr'ell,

b jg 6. Himtor'neg.

; Patented Z 1841 m3 OONTIOLSYB'III WiIIsnnm,N.!.a-Ignor m serpentine! Ge-calm New! mun-momma. Sari-($845,421

Thisinventionrelatestoqntrolsystmmm'e afteraintervllottime.

More the inventim relates to a timedelaydevlceoi'thecharacterdescribedin whichthetimeintervalhmvenely tothespeedotamoviimelementminusaflxed time.

Oneapplicaflonotadeviceoithischaracteris iisuseinwithaphotoelectricdevice fordetectlngandmarkingflielocationof inholesinasteelstrip. Inthispinholedetector applicatiomthesheetismarkedbyamagnetimbin whichTrepresentsthetimedelay,Srepresenisthespeedandxandaareconstants.

Incarryingtheinventionintoeflectinone form thereof, the time inversely proportional to speedminustheflxedtimeisobtainedby charging a capacitor with a constant current the value of which is proportional to the speed of amoving element and adding to the voltage of the capacitor a voltage produced by this charging current flowing through a resistor. The circuit is arrangedsothatwhenthesumoithese twovoltages attains a predetermined value, a controlling operation is initiated.

Inillustratingtheinventioninonetormthereof, it is shown as anhodied in a photoelectric pinhole detecting and marking device. It will he understood, however, that the invention has other applicatimn.

For a better and more complete oftheinvenflcn,reterence shouldnowbehad to the foilowim speciiicatim md to the accommnyinsdrawiminwhichl'lg.lisaslnmle,diagrammaflcal sketch 0! an t of the inventIm,andHg.2 isadisgrammaflcviewin perspective illustrating an' application at the invention.

lightsource lamps ll andlens system. 'lhelower box contains the photoelectric cells, amplifier tubesandassociatedcircuitsmountedonapanel. Alenssystemsimilartothatintheupper boxis alsoprovided. Thescanneris q inpcdwitha pair of shutters (not shown) which provide for operation with any width of strip within predetermined limits. The structural details 01 the scanner do not constitute any part of the present invention. Scanning units of this character are well \mderstood devices. They are procurable upon the market and are described in printed publications and patents. For example, a scanningunitoithischaracterisdescribedinUnited States Patent No. 2,193,590 Gulliksen. It is sutflcient to understand that when a pinhole in the strip passu through the scanner, an impulse of positive voltage is applied to the conductor It,

i. e. the potential of conductor It becomes positive with respect to the negative side ll of the direct-current source l5, I for a few thousandths of a second. This signal voltage sets the device in operation.

A magnetic marking device I1 is mounted a short distance away from the scanner in the direction of the travel of the strip and near the edge of the strip. This marking device serves to place a mark on the edge of the strip when a pinhole hasbeen detected. Normally, the'solethecathodeisconnectedtothenegaflvesideli oithesource. Thescreengridli-isconnected totheposiflvesideoithesourceandisthmgivenapositivebiaaandgrldlhisconnectedthrough resistor litothenegativeside ltofthesource.

I6 Thuatbeccntmlgridllsisatthecathodepo tential and consequently the tube is normally conducting and solenoid i1 is normally energised.

Atwin triode electric valve II isalsoconnected across the source II, It. This valve is normally biasedthroughtheanode resistorllandthegridvoltage divider resistors I2 and 23 so that the gridbias as measured between points 22. and 24 is approximately zero. and therefore the total tube current flows through the left-hand path of the triode and throughits cathode resistor 25. A resistor 21 and a capacitor 2h are connected ter generator 3|, resistors 32 and It and capacitor 34. Other types of tubes with high transconductance would be. equally as satisfactory as electric valve 2'. Tachometer generator ii is driven from the rolls II and consequently it generates a voltage proportional to the speed of the strip which is applied to the grid of valve 2. The positive terminal of the generator is connected to the grid.

A current. that is very closely proportional to the strip speed is caused to flow in the circuit of electric valve 26. The current is maintained constant for any given tachometer generatorv voltage because any tendency for the current to change such as caused by a variation in anode voltage is accompanied by a change in the volt-' age drop across resistors 28 and 20. This change in the voltage drop across these resistors is applied to the grid and produces a current change in the opposite direction. The overall result is that the current is maintained substantially consteady state condition,

-is approximately at; cathode potential which across source I, It to filter the voltage supplied causes the valve to conduct. This results in practically short circuiting the timing capacitor 34 andin maintaining the voltage across the capacitor at'a very low value.

A thyratron tube a is also connected across conductors. ii, I. Resistor I! is connected between the anode and the side it of the source,

and the cathode is connected through resistors 40, ll and'voltage divider resistor 42 to the negative side It of the source. Normally, the thyraunderstood from the following description.

When a pinhole in the strip passes through the photoelectric cell-detecting unit If, light falls for a brief instant of time on one of thephotoelectric cells. This produces an electrical impulse, i. e. a sudden positive variation in the voltage between it and the negative side It of the source which is applied to the grid of the thyratron II and as a result'thethyratron becomes conducting. 'From'the time the light falls on the photoelectric cell until the thyratron becomes conducting is so brief that the two events occur practically simultaneously. When current passes through the voltage dropping resistor It, the voltage of the junction point lti'drops from its normal steady state value to a very low value. For example, the steady state potential of this point may be 300 volts and I when the current is flowing, the potential may stant for" a wide range of anode voltages and across resistors II and It, and this has the effect.

of extendingv the linear variation of the tube current to low values of tachometer voltage.

Capacitor 36 and resistor 30 act as a filter to smooth out any ripple in the voltage of the tachometer generator such as might be produced by its commutator.

' Capacitor I4 is the timing capacitor which is charged by the constant current supplied by electric valve 28. This same charging current also flows through the fixed resistor 33 and the adjustable resistor 32 to provide the voltage which is added 'to thevoltage of the capacitor to compensate for the fixed time of the operation of the marker; Since the actual operating speeds of different markers vary, the adjustable resistor 32 is provided to adjust the circuit accurately when the installation is completed.

An electric valve 31 is connected in parallel with capacitor 34; i. e. its anode is connected to one terminal of the capacitor and the cathode to the other. -This valve is preferably of the "beam" or pento'de type in which the anode may operate successfully at a minimum voltage posidrop to a value of less than 20 volts.

This resultant potential change is transferred to the timing circuit through the capacitor 48. More specifically, the decrease in voltage of point It allows capacitor I! to discharge with the As the capacitor 34 becomes charged, the voltage across the capacitor increases and as this voltage increases, the voltage of the junction point 32a also increases. After an interval of time which is inversely proportional to the speed oftachometer generator 3| minus a fixed time, the voltage of the grid II. to which the point 32. is connected attains a'value at which the right-hand path of the valve 2| begins to conduct and causes current to flow through the resistor 2|. As a result of this the voltage of point 2i. which is connected to grid 20 is decreased to such an extent that the left-hand. path of valve II ceases to conductcurrent. and the current of the left-hand path is transferred to the right-hand path. Asa result of the large j current which now flows through resistor 2|, the

' voltage of point Ilsis suddenly decreasedto a 'thegrid'lta of. valve II. As a voltage of grid lls becomes so negativewith man its cathode that valve; ll ceases to conduct curtive with respect to the cathode. In the normal 78 rentv and the solenoid II of-the marker is deenergized. After the fixed time required for the marker element l1 to drop to the strip, the surface of the strip is suitably marked as by hiuriing at the edge oi! the strip. 11 all the adjustments. have been properly made, the mark will be made at a distance from the detector equal to the distance of the pinhole from the detector so that the pinhole may be readii located.

That the time interval interposed by the timing circuit between the signal voltage and the deenergimtion of valve It to release the marker is inversely proportional to the speed of the strip minus a fixed time may be demonstrated mathematically as follows:

Let

e=the voltage across resistors 32 and 33 an capacitor 3,

E=the tripping voltage, i. e. the grid voltage required to render the right-hand path of valve II conducting,

S=speed of the tachometer generator Si or the speed of the strip ll,

R=ohmic resistance of resistors 32 and 33,

C=capacitance oi capacitor II.

Then,

(l) 1:115 in which i is the constant current from valve 26 which charges capacitor 34 and N is a constant.

Consequently for the time T to trip at a fixed limit voltage E,

E R ""c1 and substituting from (i) E R cNs fi Since E,R,CandNareconstants is also a constant==K and Thus K In other words, T is a time which is inversely proportionaltothespeedofthestrlpminusa fixed time.

At the instant of the removal of voltage from marker solenoid I'l, voltage is also removed from the coil of "rese relay 5. Relay I5, however, does not drop out instantly because of the capacitor 46 which is connected across its coil. The brief interval during which the reset relay is held picked up is suiiicient to permit the plunger of the marker solenoid to drop out completely before the reapplication of power.

When the contacts a oi relay do open, and

39. regains the positive potential of the side l5 oi the source. As a result, capacitor 43 is subjected to a greatly increased voltage and charges rapidly. This causes the voltage of the grid 81. of valve 31 to become more positive, thereby to render the valve 31 conducting so that capacitor ll is again short circuited and thereby rapidly discharged. The resulting decrease in voltage across the capacitor 34 causes the potentials of the point 32. and of the grid 20. of valve 2| to become increasingly negative with the result that the right-hand path 01' valve 2| becomes nonconducting.- The interruption of current in the right-hand path of valve 2| causes the IR drop acrossresistorsfl and todisappearsothat the potential of point'll. attains a high positive value, thereby increasing the voltage across capacitor 4|. As capacitor 44 charges, the grid b of valve ll becomes increasingly positive so that the left-hand path 01 valve 2| again becomes conducting. Simultaneously, the voltage of grid Ila becomes more positive and causes interrupt the anode circuit of the thyratron 3 8,

the thyratron becomes non-conducting. Resistor l1 and capacitor 48 form a highly damped oscillatory circuit to insure the positive circuit break and minimum surge on remake. In responsetotheinterruptionotcm'rentinthe anode-cathode circuit of thyratron a, the m drop'acros resistor it disappears, and point the valve ll to become conducting, thereby to energize the marker operating solenoid l! to retract the marker and also to energize solenoid 45 of the reset switch which thereupon recloses its contacts 45-. This terminates one complete timing cycle, and the system is now in its steady state condition and is thus reset for a subsequent operation.

Resistor 29 is made adjustable to provide a means for varying the charging current for a given tachometer voltage. The resultant variation in the time delay in the operation of the marker mam it possible to use this control for adjusting the distance that the pinhole will move forward beiorethestripm marked. Thisisdesirablebecauseitpermitsthemarkertobeinstalledatvarious distancesi'rmnthescanner.

Although in accordance with the provision of the Patent statuts th'm invention '3 as embodied in concrete form and the principle thereothasbeendescribedtogetherwiththebest mode in which it is now contemplated applying thatm'lnciplaitwillbeunderstoodthattheapare merely illustrative and that the invention is not limited thereto, since alterations and modifications will readily suggest themselves to persons skilled in the art without departing from the true spirit of this invention or from the scope of the annexed claims.

What I claim as new and desire to secure by letters Patent of the United States is:

1. A device for producinga time delay inversely proportional to the speed of a movin element minus a fixed time comprising an electrical energy storage device, means responsive to a signal for initiating the supply of current to said energy storage device, means for maintaining said current substantially constant at a value proportional to said speed, means for supplying a voltage pr p rtional to said fixed time to the circuit of said energy storage device, and means responsive to the sum of said voltage and the voltage across said energy storage device for initiating a controlling operation when the sum of said voltages attains a predetermined value.

2. A device for producing a time delay inverselyproportionaitothespeedoiamovingelement minusafixedtimecomprisingasubstantially discharged capacitm', means mponsiye to a sigml for initiating the supply of current to said capacitor to increase the voltage acres said capacitor, means for maintainin said current conspacers stant at a value proportional to said speed.

said capacitor thereby to increase the voltage across said capacitor. means for maintaining said current constant at a value proportional to said speed, means for supplying a voltage .proportionaltosaidfixedtimetothecircuitoi'said capacitor, and means responsive to the sum of said voltages for initiating a controlling operation when the sum of said voltages attains a predetermined value.

4. A device for initiating a controlling operationinresponsetoasignalanintervalottime' after said signal that is inversely proportional tothespeed ot amovingelementminusafixed timecomprisingacontrolcircuitanelectrical energy storage device connected in said circuit, means for short circuiting said energy storage device prior to said signal, means-tor introducing avoltageinsaid circuitproportionaltosaidfixed time. means for causing a current to fiow in said circuit proportional to the speed of said element,

means responsive to said signal for interrupting the shortcircuit about said energy storage device thereby to cause said current to store electrical energy in said storage device and to produce an increasing voltage across said storage device, and means responsive to the sum of said voltages for initiating said controlling operation when said sum equals a predetermined value.

5. A device for initiating a controlling opera-' tion in response to asignal an interval of time after said Si nal Prop rtional to the speed of a moving element minus a fixed time comprising a.

control circuit, a capacitor connected in said circuit, means for causing a current to fiow in said circuit, means for short circuiting said capacitor.

prior to said signal, means for introducing a voltage in said circuit proportional to said fixed time, means responsive to said signal for rendering said short circuiting means ineiiective, means for maintainnig the current in said circuit substantially constant at a value proportional to the speed of said element so that the voltage across said capacitor is caused to increase, and means ing a controlling operation when said sum equals a predetermined value.

7. A control system for initiating a controlling operation in response, toa signal a time interval 'aitersaldsignalthatisllroportionaltothespe'ed,

of a moving element minus afixedtime comprising a control circuit, a capacitor and an adjus able resistor connected in series. relationship in said circuit. means for causing a current to now: in said circuit. means for short circuiting said.

capacitor prior to said sig means for maintaining the current in said circuit substantially constant at a fixed value proportionalto the speed oi said element, said resistor being ad- Justed so that the voltage drop across said resistor is proportional to said fixed time, means responsive to said signal for rendering said short circuiting means inefiective whereby said capacitor is charged and the voltage across said capacitor is increased. and means for initiating a controlling operation when the sum oi said voltages attains a predetermined value comprising a second control circuit including an electric valve having its grid circuit connected acrosssaid cspacitor and said resistor.

' 8. A time delay device comprisingvin tion a control circuit, a capacitor and a resttor included in said circuit, means for causing a current to fiow in said circuit, an electric valve connected across said capacitor, control means for rendering said valve conducting thereby tosh'ort circuit said capacitor, means including a tachometer generator connected in said circuit for maintaining the current in said circuit substantially constant at a value proportional to the speed or said generator, means responsive to asignal for rendering said short circuiting means ineflective whereb said capacitor is charged and the voltage 7 across said capacitor is increased, and means mined value.

means responsive to a signal for rendering said responsive to the sum of said voltages for initiating a controlling operation when said sum attains a predetermined value.

6. A' control system for initiating a controlling operation in response to a signal an interval of time alter said signal proportional to the speed oi a moving element minus a fixed time comprising a control circuits capacitor in said circuit. a resistor connected in series with said capacitor, means for causing a current to fiow in said circuit, means for short circuiting said capacitor v prior to said signal, means responsive to said signal for rendering said short circuiting means ineii'ective, means for maintaining the current oi said circuitsubstantially constant at a value proportlonal to the speed of saidelement whereby the voltage across said capacitor is increased, and meansresponsive to the sum of the voltages across said capacitor and said resistor tor initiatresponsive to the sum of the voltages across said capacitor and resistor for initiating a controlling operation after an interval oi time required tor the sum of said voltages to attain a predeter- 9. A time delay device comprising in com tion a control circuit, a capacitor and an adiust- V able resistor included in said circuit, means for ing an electric valve and'a tachometer generator included in said circuit for maintaining the current in said circuit substantially constant at a value proportionalto the speed of said generator,

short circuitingmeans inefiective -so that. said capacitor is charged and the voltage across said capacitor is increased, and means responsive to the sum of the voltages acrosssaid capacitor and resistor for initiating a controlling operation after an interval of time required for the sum of said voltages to attain a predetermined-value.

10. A time delay device comprising in combina-' tion a control circuit. a capacitor and a resistor included in said circuit, means for causing a current to flow in said circuit, a first electric valve connected in parallel with said capacitor and connected to be conducting i'orshort circuiting said capacitor, means for maintaining the current in said circuit substantially constant at a value proportional to the speed oi a moving element, a second electric valve connected to be non-conducting, means for applying .a signal,

voltage to the grid oi said non-conducting valve to render said valve conducting, means including a connection from the anode-cathode circuit of said second valve to the grid circuitofsaidfirst 2,264,873 valve for rendering said first valve non-conducting so that said capacitor is charged and the voltage across said capacitor is increased, means responsive to the sum of the voltages across said capacitor and resistor for initiating a controlling operation after a time interval required for the sum or said voltages to attain a predetermined value, and means responsive to said controlling operation for rendering said second valve nonconducting thereby to reset said time delay device for a subsequent operation.

11. A time delay device comprising in combination a control circuit, a capacitor and a resistor connected in said circuit, a first electric valve connected in parallel with said capacitor, means for applying voltage to the grid of said valve to render it conducting thereby to short circuit said capacitor, a second electric valve, means for applying a voltage to the grid oi! said second valve to render said second valve non-conducting, means for applying a signal voltage to the grid 01' said second valve to render said second valve conducting, a connection from the anode-cathode circuit of said second valve to the grid circuit of said first valve for rendering said first valve nonconducting in response to current in the anode cathode circuit oi said second valve thereby to cause said capacitor to be charged and the voltage across said capacitor to increase. and electric valve means responsive to the sum of the voltages across said capacitor and resistor for initiating a controlling operation after an interval oi time. I

requiredtorth'esumotsaidvoltagestoattaina predetermined value.

12. A control system for initiating a controlling operation in response to a signal an interval of time after said signal proportional to the speed of a moving element minus a fixed time comprising a control circuit, a capacitor and a first adjustable resistor included in said circuit, means including a first electric valve included in said circuit for controlling the current in said circuit, means comprising a tachometer generator driven by said element and a second adjustable resistor connected in the anode-cathode circuit oi said valve and a connection from said anode-cathode circuit to the grid of said valve for maintaining the current in said control circuit substantially constant at a value proportional to the speed of said element, said first resistor being adjusted to a value such that its voltage drop is proportional to said fixed time, a second electric valve having its anode-cathode circuit connected in parallel with said capacitor, means for applying a voltage to the grid circuit of said second valve to render said second valve conducting thereby to short circuit said capacitor, means for applying a signal voltage to the grid circuit or said second valve thereby to render said second valve non-conducting so that said capacitor is charged and the voltage across said capacitor is increased. and means responsive to the sum or the voltages across said capacitor and first resistor for initiating a controlling operation when the sum of said voltages attains a predetermined value.

WHLIAMD.COCKRE[L.

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