US3548197A

US3548197A - Light protection device with a movable opaque shield

Info

Publication number: US3548197A
Application number: US807386A
Authority: US
Inventors: Bernard C Nordmann
Original assignee: Megatronics Inc
Current assignee: Megatronics Inc
Priority date: 1969-03-14
Filing date: 1969-03-14
Publication date: 1970-12-15
Anticipated expiration: 1987-12-15

Description

\ B. c. NORDMANN 3,548,197

LIGHT PROTECTION DEVICE WITH A MOVABLE OPAQUE SHIELD van 10,19!

Filed March 14, 1969 3,548,197 LIGHT PROTECTION DEVICE WITH A MOVABLE OPAQUE SHIELD Bernard C. Nordmann, Kirkwood, Mo., assignor to Megatronics, Inc., St. Louis, Mo., a corporation of issouri Filed Mar. 14, 1969, Ser. No. 807,386 llnt. Cl. G01j 1/42; Gtlld 5/56; (202i 1/30 U.S. Cl. 250,-229 21 Claims ABSTRACT OF THE DISCLOSURE This invention relates to improvements in light-sensitive, optical, control systems. More particularly, this invention relates to improvements in light-sensitive, optical, control systems which control electromagnetic elements such as solenoids.

It is, therefore, an object of the present invention to provide an improved light-sensitive, optical, control system which controls an electromagnetic element such as a solenoid.

.As pointed out in George I. Fischer Pat. No. 3,377,427 for Light-Sensitive Optical Control System Fora Television Camera, which was granted April 9, 1968, it is important to protect the vidicon or other light sensitive tube of a television camera from injury due to-excessive amounts of light. That patent provides a light-sensitive element which acts, whenever the light directedi toward the vidicon or other light-sensitive tube of a ""le'vision camera exceeds a predetermined level, to cau rotary solenoid to interpose a light-intercepting ele ni''iit between that vidicon and the source of light. Thefcontrol system of that patent requires line voltage which is essentially constant; but, unfortunately, essentially donstant line voltage is not available at all locations. Consequently, it would be desirable to provide a light-sensitive, opftical, control system for an electromagnetic device, suclii as a solenoid, which could provide prompt and effective actuation of that electromagnetic device despite appreciable variations in line voltage. The present invention provides such a light-sensitive, optical, control system; and it is, therefore, an object of thd'present invention to provide a light-sensitive, optical, control system which provides prompt and effective actuation of an electromagnetic device, such as a solenoid, despite appreciable variations in line voltage.

The light-sensitive, optical, control system provided by the present invention assures prompt and elfective actuation of the electromagnetic device controlled thereby, by applying a relatively high voltage pulse to that electromagnetic device to actuate that electromagnetic device. That voltage pulse is so high that it will be able toassure prompt and effective actuation of that electromagnetic device, even if a sharp drop in line voltage shar'ply reduces the value of that voltage pulse. However, that voltage pulse is so high that it would cause excessive heating of that electromagnetic device, if that voltage pulse was of long duration. The light-sensitive, optical, control system provided by the present invention assures prompt and effective actuation of the electromagnetic device controlled thereby, by applying a relatively high voltage pulse to that electromagnetic device to actuate that 3,54%,BW Patented Dec. l5, l i'lll electromagnetic device; and it avoids excessive heating of that electromagnetic device during the ensuing energization of that electromagnetic device by making the duration of that voltage pulse short and by using a sub stantially lower voltage to keep that electromagnetic de-= vice energized. The substantially lower voltage not only minimizes the heating of the electromagnetic device, but it also reduces the amount of power that is consumed by that electromagnetic device. It is, therefore, an object of the present invention to provide a light-sensitive, optical, control system which uses a relatively high voltage pulse to actuate an electromagnetic device and which uses a substantially lower voltage to keep that electromagnetic device energized.

The light-sensitive, optical, control system provided by the present invention has a ramp-generating subcircuit which enables that control system to develop the relatively high voltage pulse which is needed to assure prompt and effective actuation of the electromagnetic element controlled by that control system; and that control systern develops a regulated voltage and applies that regulated voltage to the input of that ramp-generating subcircuit. The application of that regulated voltage to the input of that ramp-generating subcircuit enables that control system to develop the relatively high voltage pulse which is needed to promptly and effectively actuate the electromagnetic elementeven if the line voltage drops sharply. It is, therefore, an object of the present invention to provide a control system with a ramp-generating su=bcircuit which enables that'lcontrol system to develop a relatively high voltage pulse, and to develop a regulated voltage and to apply that regulated voltage to the input of that ramp-generating subcircuit.

The light-sensitive, optical, control system provided by the present invention uses direct current to energize the electromagnetic element controlled thereby, but it senses the amount of light received by the light-sensitive element thereof during every half-cycle of the alternating current supplied to that control system. As a result, that control system provides the quiet operation of that electromagnetic element which direct current makes possible, and yet that control system provides instantaneous sensing of the amount of light falling upon the light-sensitive element thereof. It is, therefore, an object of the present invention to provide a light-sensitive, optical, control system which utilizes direct current to actuate the electromagnetic element controlled thereby, but which senses the amount of light falling upon the light sensitive element thereof during each half-cycle of the alternating current supplied to that control system.

Other and further objects and advantages of the present invention should become apparent from an examination. of the drawing and accompanying description.

In the l-drawing and accompanying description a me ferred embodiment of the present invention is shown and described but it is to be understood that the drawing and accompanying description are for the purpose of illustration only and do not limit the invention and that the invention will be defined by the appended claims.

The drawing is a schematic diagram of one preferred embodiment of light-sensitive, optical, control system that is made in accordance with the principles and teachings of the present invention.

COMPONENTS OF CONTROL SYSTEM Referring to the drawing in detail, the numeral 1% denote'sa-maI plug which' has prongs that can be inserted into a socket connected to a suitable source of alternating currentln the preferredembodiment of light-sensitive, optical, control system shown by the drawing, the prongs of the plug 10 will be inserted into a socket connected toa source of one hundred and fifteen volts, sixty cycle, alternating current, The numeral 12 denotes a fullwave, bridge rectifier which includes diodes 14, 16, 1S and 2t and one of the input terminals of that full-wave, bridge rectifier is directly connected to one prong of the plug while the other input terminal of that full-wave,

bridge rectifier is connected to the lower prong of that plug by a fuse 22 and a resistor 24. The resistor 24 acts as a current limiting resistor to protect the diodes 14, 16, 18 and from injury due to excess flow of current through them.

A resistor 28 and two Zener

diodes

32 and 36 are connected in series with each other, and are connected across theoutput terminals of the full-wave, bridge rectifier 1 2 by junctions 26, and 34 and by a return conductor 38-. The Zener diode 36 will determine the maximum voltage which can be developed at the junction 34; and the Zener diode 32 will coact with the Zener diode 36 to determine the maximum voltage which can be developed at the junction 30.

A. junction 40 connects the upper terminal of a resistor 46 to the junction 30; and that resistor, a potentiometer 48,, and a light-sensitive element 50 are connected in series with each other between the junction 40 and the return conductor 38. Although different light-sensitive elements can be used as the light-sensitive element 50, a cadmium sulphide photocell has been found to be very useful. The numeral 32 denotes an NPN transistor; and a junction 42, a resistor 54, a junction 56, and. a resistor Sdconnect the collector of that transistor to the junction 40. A junction and a resistor 62 connect the emitter of that transistor to the return conductor 38. A resistor 64 and a junction 66 connect the movable contact of the potentiometer 48 to the base of the transistor 52. A resistor 63 has the lower terminal thereof connected to the resistor 62 by the junction 60; and it has the upper terminal thereof connectedto the junction 42 by a junction 44.

The numeral 70' denotes a PNP transistor; and the emitter of that transistor is directly connected to the junction 44, and the collector of that transistor is connected to the return conductor 38 by a junction 72 and a resistor 74. The base of the transistor 70 is directly connected to the junction 56; and a resistor 76 is connected between the junctions 66 and 72.

The numeral 78 denotes a diode which has the anode thereof directly connected to the junction 72;; and the cathode of that diode is connected to the upper terminal of a capacitor 81 by a junction 80. The lower terminal of that capacitor is directly connected to the return conductor 38. The numeral 86 denotes a potentiometer which has the upper terminal thereof connected to the junction i it by a junction 82; and the lower terminal of that potentiometer is connected to the return conductor 38 by a resistor 88. The numeral 90 denotes a PNP transistor; and a junction '84, a resistor 92, and a junction 98 connect the emitter of that transistor to the junction 82. A capacitor 94 and a resistor 96 are connected in series with each other; and the upper terminal of that capacitor is directly connected to the junction 84, while the lower terminal of that resistor is directly connected to the junction 98. A diode 101) has the anode thereof connected to the movable contact of the potentiometer 86, and it has the cathode thereof connected to the anode of a diode 162. The cathode of the diode 102 is connected to the base of the transistor 96 by a junction 194-; and a resistor 106 is connected between the junction 104 and the return conductor 33. The diodes 1% and. 1112 are provided to compensate for any changes in the temperature of the transistor 90.

A junction 1% connects the collector of the transistor 91 to the upper terminal of a capacitor 110; and the lower terminal of that capacitor is connected to the return conductor 38. A unijunction transistor 112 has the emitter thereof connected to the junction 108; and it has the base-one thereof connected to the return conductor 38 by a junction 116 and a resistor 118. The base-two of 4 that unijunction transistor is connected to the junction 34 by a resistor 114.

The lower terminal of the coil 120 of a rotary solenoid is connected to the upper terminal of a resistor 126 by a junction 124; and the lower terminal of that resistor is connected to the anode of a controlled rectifier 1.28. That controlled rectifier preferably is a silicon controlled rectifier, and the cathode of that controlled rectifier is directly connected to the return conductor 38. A junction 11? connects the upper terminal of the coil 120, and the upper terminal of a capacitor .122, to the junction 26; and the lower terminal of that capacitor is connected to the lower terminal of that coil by the junction 124.

The coil 120 of the rotary solenoid controls a lightintercepting element 132; and the returning spring, not: shown, of that rotary solenoid biases that light-intercepting element for movement into the path of light directed toward the vidicon or other light-sensitive tube, of the television camera with which the control system of the present invention is used. However, that light-intercept ing element will move out of the path of that light whenever the coil 120 is energized. The coil 120 and the lightsensitive element 50 are enclosed within a dashed line 130; and that dashed line is intended to indicate that the said coil and the said light-sensitive elementwill be mounted in one or two enclosures on the housing of the television camera. 7

The full-wave, bridge rectifier 12 acts as a source of direct current; and the

Zener diodes

32 and 36 set upper limits for the DC. voltages at the junctions Mind 34. The light-sensitive element 50, the potentiometer 48, the

resistors

46, 54, 5 8, 62, 64, 68, 74 and 76,'and the

transistors

52 and 70 constitute a light level detector 77. The

capacitors

81 and 94, the potentiometer 86, the re sist-o'rsSS, 92, 96 and 106, the transistor 90, 'and the

diodes

100 and 102 constitute a subcircuit 109 which acts as a ramp-generator and a current source.-The capacitor 110, the unijunction transistor 112, and the resistors 114 and 118 constitute a unijunction transistor relaxation oscillator 117.

OPERATION OF CONTROL SYSTEM When the prongs of the plug 10 are inserted into a suitable socket, current will flow from the upper prong of that plug via diode 14, junction 26, resistor 28, junction 313, Zener diode 32, junction 34, Zener diode 36, return conductor 38, diode 18, resistor 24, and fuse 22 to the lower prong of that plug, during those half-bycles of the alternating current when that upper prong is positive relative to that lower prong. During those half-cycles of that alternating current when the lower prong of the plug 10 is positive relative to the upper prong of that plug, current will flow from that lower prong via fuse 22, resistor 24;, diode 16, junction 26, resistor 28, junction 30, Zener'diode 32, junction 34, Zener diode 36, return conductor 38, and diode 20 to that upper prong. The resulting direct current which fiows through resistor 28 and Zener;

diodes

32 and 36 is not filtered; and hence the voltage across the output terminals of the full-wave, bridge rectifier 12 will start at zero, will rise to a maximum, and will then fall to zero during each half-cycle of the alternating current. Because the Zener diode 36 determines the maximum voltage which can be developed at the junction 34, the voltage at the junction will start at zero, will rise to a maximum, and will then fall to 2510 during each half-cycle of the alternating current. Because the Zener diode 32 contact with the Zener diode 36.to determine the maximum voltage which can be developed at the junction 30, the voltage at that junction will start at zero, Will rise to a maximum, and will then fall to zero during each half-cycle of the alternating current. In one preferred embodiment of the control system shown by the drawing, the voltage at the junction 34 will rise to ten volts and the voltage at the junction 30 will rise to twenty volts during each half-cycle of the alternating current.

The voltage at the junction 30 will be applied across series-connected resistor 46, potentiometer 48 and lightsensitive element 50; and the voltage at the movable contact of that potentiometer will be a function of the setting of that movable contact and of the effective resistance of that light-sensitive element.- Since the effective resistance of that light-sensitive element will vary with the amount of light impinging upon that light-sensitive element, the voltage at the movable contact of the potentiometer 48 will be a function of the light which impinges upon the light-sensitive element 58. The voltage at the junction 30 also will be applied across the voltage divider which consists of the resistor-s 68 and 62; and that voltage divider will develop a Voltage at the junction 60, and thus at the emitter of transistor 52-, which will rise to a predetermined value during the first part of each half-cycle of the alternating current, which will remain at that value during the middle portion of that half-cycle, and which will fall to zero at the end of that half-cycle. The voltage at the junction 30 also will be applied across series-connected

resistors

54 and 58, the collector-emitter circuit of transistor 52, and resistor 62; and that voltage also will be applied across the series-connected emittercollector circuit of transistor 70 and resistor 74.

The lower portion of the potentiometer 48 and the light-sensitive element 50 are connected in series with each other and in parallel with series-connected resistor 64, the base-emitter circuit of transistor 52, and resistor 62; and, whenever the total resistance of the series-connected lower portion of potentiometer 48 and the light sensitive element 58 is appreciably smaller than the total resistance of series-connected resistor 64, the base-emitter circuit of transistor 52 and resistor 62, insufficient current will flow through that base-emitter circuit to make that transistor conductive. Consequently, whenever the value of the light which impinges upon the light-sensitive element 50 is great enough to make the resistance of that light-sensitive element relatively small, the transistor 52 will become essentially non-conductive. As long as the transistor 52 is essentially non-conductive, the voltage at the junction 56, and thus at the base of transistor 70, will be essentially the same as the voltage at the emitter of the latter transistor; and the latter transistor will be essentially non-conductive. At, such time, the voltage at the junction 72 will be essentially zero.

Whenever the total resistance of the series-connected lower portion of potentiometer 48 and the light-sensitive element 50 exceeds the" total resistance of series-com nected resistor 64, the base-emitter circuit of transistor 52, and resistor 62, suificient current will flow through that baseemitter circuit to render that transistor conductive. Consequently, whenever the value of the light which impinges upon the light-sensitive element 58 is small enough to make the resistance of that light-sensitive element relatively large, the transistor 52 will be conductive. As the transistor 52 becmes conductive, the resulting voltage drop across the resistor 54 will make the base of transistor 70 less positive than the emitter of that transistor; and hence the transistor 70 will become conductive. The resulting increase in voltage drop across the resistor 74 will cause the voltage at the junction 72 to become more positive; and the resistor 76 will couple that more-positive voltage to the base of the transistor 52 via the junction 66, thereby further increasing the .conduc tivity of that transistor. That further increase in conductivity will make the voltage at the junction 56, and thus at the base of transistor 70, even less positive than the voltage at the emitter of that transistor, and will thereby make that transistor even more conductive. Very quickly, the positive feedback provided by the resistor 76 will cause both of the transistors 52 and '70 to saturate. Consequently, whenever the amount of light impinging upon the light-sensitive element 50 is below a predetermined value, the

transistors

52 and 78 will saturate during each half-cycle of the alternating current supplied to the plug 8 lil; and the voltage at the junction 72 will closely ap proach twenty volts during each of those half-cycles. Ali of this means that aslong as the valueof the light impinging upon the light-sensitive element 56 is below a predetermined level, the light level detector 77 will cause the voltage at the junction 72 to closely approach twenty volts during each half-cycle of the alternating current. Further, it means that whenever the value of the light irnpinging upon the light-sensitive element 5'8 exceeds that predetermined level, the light level detector 77 will cause the voltage at the junction 72 to drop essentially to zero.

Whenever the light level detector 77 causes the voltage at the junction 72, and thus at the anode of the diode 78, to exceed the voltage at the cathode of that diode, that diode will he become conductive and will permit current to flow from junction 72 via that diode, junction 80, and capacitor 811 to the common conductor 38. That current wilt quickly charge that capacitor to a value close to the pealc value of the voltage atthe junction 72. The capacitor will tend to discharge through series-connected poten tiometer 86 and resistor 88 during those portions of each half-cycle of the alternating current wherein the voltage at the junction 72 is less than the voltage at the upper terminal of that capacitor; but the values of potentiometer 86 and of resistor 88 will be selected to limit the rate of discharge of that capacitor to a value which will keep the voltage across thatcapacitor' essentially constant as long as the light level detector 77 renders the transistor 78 conductive during each half-cycle of the alternating current. As a result, the capacitor 81 will act as a source of steady DC. voltage for subcircuit 188.

When the light level detector 77 renders the diode 78 conductive, further current will flow from junction 72 via that diode, junctions' 8tl and 82, and the upper portion of potentiometer 86 to the movable contact of that potentiometer; and then one part of that further current will flow through the lower portion of that potentiometer and resistor 88 to the return conductor 38 while a second part of that further current will flow through diodes 168 and 102 and resistor 106 to that return conductor, The resulting voltage drop across the series-connected upper portion of potentiometer 86 and diodes 100 and 182 will make the base of transistor 90 less positive than the emitter of that transistor; and hence sufiicient current 'will flow, from junction 72 via diode 78, junctions 88, 82 and 84, parallelconnected resistor 92 and series capacitor 94 and resistor 96, junction 98, the emitter-base circuit of transistor 90, junction 104, and resistor 106 to the return capacitor 38, to render that transistor conductive, Consequently, current will flow from junction 72 via diode 78,

junctions

80, 82 and 84, parallel-connected resistor 92 and seriesed capacitor 94 and resistor 96, junction 98, the emitter-ooh lector circuit of transistor 96, and capacitor tlllti. The voltage at the junction 72, and thus at the anode of diode 78, will fall below the' voltage at the upper terminal of capacitor 81, and thu tt.,the cathode of that diode, at the end of each half-cycle of the alternating current; and hence that diode will become non-conductive. However, the capacitor 81 will act as a power supply when the diode 78 is non-conductive; and hence that capacitor will keep the transistor 90 conductive.

Prior to the time when the light level detector 77 first renders the transistor 70 conductive, the capacitor 94 will be discharged-that capacitor discharging through the path constituted by

resistors

92 and 96. Because the capacitor 94 is initially discharged, it will constitute a low irnpedance at the instant the light level detector 77 first renders the transistor 70 conductive; and, because that capacitor and resistor 96 are seriesed and are connected in paral lel with resistor 92, that capacitor will elfectively reduce the resistance in the emitter circuit of transistor .88, Con sequently, the latter transistor will supply a high value of current to the capacitor 11110 as that transistor becomes conductive. The high value of' current which the transistor 9t) initially supplies to the capacitor lllltl will quickly charge that capacitor; and it will cause the voltage at the junction 108 to exceed the emitter peak point voltage of the unijunction transistor 112 at an early point in the halfcycle of the alternating current.

The voltage at the junction 34 is applied across seriesconnected resistor 114, the base-two base-one circuit of the unijunction transistor 112, and resistor 118; and while that unijunction transistor will be non-conductive during the first part of each half-cycle of the alternating current, that unijunction transistor will be rendered conductive as soon as the charge on the capacitor 110 causes the voltage at the junction 1 08 to exceed the emitter peak point voltage of that unijunction transistor. When the unijunction transistor 112 becomes conductive, the charge within the capacitor 110 will cause current to flow from the upper terminal of that capacitor via junction 108, the emitter base-one circuit of that unijunction transistor, junction 116, resistor 118, and return conductor 38 to the lower terminal of that capacitor; and that flow of current will develop a voltage drop across the resistor 118 which will cause current to flow through the gate-to-cathode circuit of the controlled rectifier 128.

The junctions 26 and 119 and the return conductor 38 place series-connected coil 120, resistor 126 and controlled rectifier 128 across the output of the full-wave, bridge rectifier 12; and, whenever sufiicient current flows through the gate-to-cathode circuit of that controlled rectifier, that controlled rectifier will become conductive and energize the coil 120 of the rotary solenoid. The capacitor 122, which is connected in parallel with the coil 120 of the rotary solenoid, will coact with the resistor 126 to filter the sharp current pulse that is supplied to that coil as the controlled rectifier 128 becomes conductive; and hence the coil 120 will receive a longer-duration current pulse. That coil will respond to that current pulse to urge the armature of that rotary solenoid, and the light-intercepting element 132 connected to that armature, toward retracted position-and thus away from the path of the light directed toward the vidicon or other light-sensitive tube to be protected by that light-interceping element.

Because the capacitor 94 initially acts as a low impedance, the transistor 90 will permit the capacitor 110 to charge up to the emitter peak point voltage of unijunction transistor 112 during the early part of the first half-cycle of the alternating current; and the resulting relatively long on time of the controlled rectifier 128 will enable the coil 120 to receive a voltage pulse of about ninety volts. Inasmuch as that coil is rated at twenty-four volts, the ninety volt pulse is amply large enough to enable that coil to apply strong rotative forces to the armature of the rotary solenoid and to the light-intercepting element 132.

At the end of the first half-cycle of the alternating current, the voltages at the junctions 26, 3t) and 34 will fall to zero; and, as the voltage at the junction 30 falls to zero, the

transistors

52 and 70 of the light level detector 77 will again become non-conductive, and the voltage at the junction 72 will fall to zero. However, the capacitor 81 will act as a source of direct current; and it will keep enough current flowing through the series-connected upper portion of potentiometer 86,

diodes

100 and 102, and resistor 106 to keep the base of transistor 90 less positive than the emitter of that transistorand thus to keep that transistor conductive. Also, the capacitor 81 will cause current to flow through the emitter-collector circuit of transistor 90 and start i e-charging the capacitor 110.

As the voltage at the junction 34 falls to zero, at the end of the first half-cycle of the alternating current, the voltage at the base-two of the unijunction transistor 112 will fall to zero; and hence that unijunction transistor will be non-conductive. That unijunction transistor may become non-conductive even before the end of the first half-cycle of the alternating currentbecause that unijunction transistor will become non-conductive as soon as the capacitor 110 has discharged sufliciently to make the voltage at the junction 108 less than two volts-and, in that event, that unijunction transistor will remain nonconductive until it is rendered conductive during the second half-cycle of the alternating current.

Although the voltage at the junction 26, and hence at the junction 119, will fall to zero at the end of the first half-cycle of the alternating current, the capacity of the capacitor 122 is large enough so that capacitor could, if necessary, cause current to continue to flow through the coil 120 of the rotary solenoid for about fifteen milliseconds. As a result, current will continue to flow through the coil 120, and thus enable that coil to continue to sup-= ply rotative forces to the armature of the rotary solenoid and to the light-intercepting element 132, even after the controlled rectifier 128 becomes non-conductive-as it. will do at the end of the first half-cycle of the alternating current. This means that at the end of the first halfcycle of the alternating current, the light level detector 77 will permit the voltage at the junction 72 to drop to zero, but the capacitor 81 will keep the transistor conductive and will be charging the capacitor 110. The unijunction transistor 112 will be non-conductive, and the controlled rectifier 128 will be non-conductive; but the coil 120 will be applying rotative forces to the armature of the rotary solenoid and to the light-intercepting element 132, and that armature and that light-intercepting element will tend to continue to move toward retracted position.

During the second half-cycle of the alternating current, the light level detector 77 will again develop a voltage, which closely approaches twenty volts, at the junction 72; and a voltage of about ten volts will be applied across the series-connected resistor 114, the base-two base-one circuit of unijunction transistor 112, and resistor 118, and a voltage in excess of one hundred volts will be applied across the series-connected coil 120, resistor 126, and controlled rectifier 128.

The diode 78 Will respond to the voltage at the junction 72 to become conductive, thereby applying a further charge to the capacitor 81; and that diode and that capacitor will supply the current which is needed to cause the voltage across the capacitor to rise to the emitter peak point voltage of the unijunction transistor 112. As that unijunction transistor becomes conductive again, the capacitor 110 will develop a voltage drop across the resistor 118 which will render the controlled rectifier 128 conductive again; and hence the coil of the rotary solenoid will have another relatively high voltage pulse applied to it.

Because the capacitor 94 will have retained some of the charge that it received during the first half-cycle of the alternating current, the impedance of series-connected capacitor 94 and resistor 96 will be higher than it was at the beginning of the first half-cycle of the alternating current; and hence the total impedance of parallel-com nected resistor 92 and seriesed resistor 96 and capacitor 94 will be higher than it was at the start of that first half-cycle. However, that impedance will still be low enough to permit the capacitor 110 to render the transistor 112 conductive during the early part of the second half-cycle of the alternating current; and hence a voltage which is close to ninety volts will be developed across the coil 120. This is important, because the armature of the rotary solenoid and the light-intercepting element 132 will have appreciable massand hence appreciable inertia; and it is desirable that the voltage applied to the coil 120 remain at a relatively high level until that armature and that light-intercepting element have had sufiicient time to rotate into retracted position.

At the end of the second half-cycle of the alternating current, the voltages at the

junctions

26, 34 and 72 will again drop to Zero, and the unijunction transistor 112 and the controlled rectifier 128 will be non-conductive again. However, the capacitor 81 will again keep the transistor 90 conductive. Also, the capacitor 122 will again.

cause current to continue to fiow through the coil 120 after the controlled rectifier 128 becomes non-conductive.

During each succeeding half-cycle of the alternating current applied to the plug 10, the light level detector 77 will cause the diode 78 to supply a further charge to the capacitor 81; and the subcircuit 109 will cause the tran sistor 90 thereof to supply sufficient current to the ca pacitor 110 to render the unijur'iction transistor 1112 con ductive. During each succeeding half-cycle of the alternating current, the impedance of the capacitor 94 will be higher than it was at the beginning of the immediatelypreceding half cycle-because of the progressively-higher retained charge in that capacitor-until the charge in that capacitor stabilizes. Thereafter, during succeeding halfcycles of the alternating current, the additional charge which the capacitor 94 receives during any given halfcycle will equal the charge which that capacitor loses at the end of that half-cycle as it causes current to flow through the

resistors

92 and 96. In the said preferred embodiment of control system shown by the drawing, it takes a total of about sixteen half-cycles of the alternating current for the charge in the capacitor 94 to stabilize; and, during those sixteen half-cycles, the voltage pulses applied to the coil 120 of the rotary solenoid will decrease exponentially from about ninety volts to about fifteen volts. The initial voltage pulse, and the immediatelysucceeding voltage pulses, applied to the coil 120 will be so high that they will be able to cause that coil to effect prompt and efiective rotation of the light-intercept ing element 132 to retracted position, even if the voltage applied to the plug drops considerably below its normal value. -As a result, the control system provided by the present invention is able to apply amply strong rotative forces to the light-intercepting element 132-even in locations where considerable variations in line voltage are experienced.

As the charge in the capacitor 94 becomes stabilized, the impedance of that capacitor will become essentially fixed; and that impedance will be extremely large. At such time, the amount of current which can flow through the transistor 90 during a given half-cycle of the alternating current will be very much less than the amount of chrrent which fiowed through that transistor during the first halfcycle of the alternating current. The resulting longer charging time of the capacitor 110 will cause the unijunction transistor 112, and hence the controlled rectifier .128, to become conductive later during that given half-cycle; and hence the voltage pulse applied to the coil 120 will be only about fifteen volts. While the capacitor 94 is being charged and its impedance is low, the subcircuit 109 will act as a ramp-generating subcircuit; but once that capacitor has become charged and its impedance is very high, the subcircuit 109 will act as a current source.

The fifteen volt pulses whichare applied to the coil 126 are amply large to keep that coil energized; and this is important, because it means that the control system provided by the present invention will be able to keep the light-intercepting element 132 in retracted position, even if the voltage applied to the plug 10 drops considerably below its normal value. As a result, the control system provided by the present invention is able to keep the light-intercepting element 132 from prematurely intercepting the light passing to the vidicon or other light-sensitive tube-even in locations where considerable variations in line voltage are experienced.

The voltage pulses of about fifteen volts are amply large to keep the coil 120 energized; but they will permit that coil to develop far less heat than it would develop if it was supplied with its rated voltage of twenty-four volts. Further, the fifteen volt pulses reduce the total amount of power that is consumed by the coil 120.

As long as the value of the light impinging upon the light-sensitive element is below a predetermined level, the

transistors

52 and 70 of the light level detector 77 will be rendered conductive during each half-cycle of the alternating current applied to the plug 10; and the come quent re-charging of the capacitor 81 will enable the subcircuit 109 to render the unijunction transistor 112, and. hence the controlled rectifier 128, conductive during that half-cycle. Consequently, as long as the value of the light; impinging upon the light-sensitive element 50 is below that predetermined value, the coil 120 will hold the light-- intercepting element 132 in retracted position. However, as soon as the value of the light impinging upon the lightsensitive element 50 exceeds that predetermined value, the impedance of that light-sensitive element will decrease sutliciently to make the total impedance of the series-com nected lower section of potentiometer 48 and that lightsensitive element appreciably less than the impedance of series-connected resistor 64!, the base-emitter circuit of transistor 52, and resistor 62. Thereupon, the current flowing through the base-emitter circuit of that transistor will decrease to the point where that transistor becomes non-conductive; and, at such time, the voltage at the junction 56, and thus at the base of the transistor 70, will essentially rise to the value of the voltage at the

junctions

42 and 44, and thus at the emitter of transistor 70. Consequently, the transistor 70 will become non-conductive; and hence the voltage at the junction 72 will drop to essentially zero. This means that during the next half-cycle of the alternating current, and during all succeeding halt cycles wherein the value of the light falling upon the light sensitive element 50 exceeds the predetermined level, the light level detector 77 will not develop an appreciable voltage at the junction 72. As a result, the capacitor 81 will not receive any additional charges during any of those half-cycles of the alternating current.

The capacitor 81 of the subcircuit 109 will have suificient capacity to enable it to keep the transistor conductive for one and possibly two or three half-cycles of the alternating current after the voltage at the junction 72 drops to zero, and that capacitor will have sufficient capacity to raise the voltage at the upper;terminal of the capacitor 110 to the emitter peak point voltage of the unijunction transistor 112 once or possibly twice. However, very quickly, the chargejn the capacitor 81 will dis sipate to the point where the voltage at the upper terminal of the capacitor 110 will be unable to reach the emitter peak point voltage of the unijunction transistor 112. Con sequently, in less than three half-cycles after the value of the light impinging upon the light-sensitive element tl increases above the predetermined level, the 'unijunction transistor 112 will remain non-conductive, and hence the control rectifier 128 will remain non-conductive. While the capacitor 122 will be able to keep the coil of the rotary solenoid energized for about fifteen milliseconds after the controlled rectifier 128 becomes non-conductive, the restoring spring of that rotary solenoid will then start moving the armature of that rotary solenoid and the light-' intercepting element 132 toward the path of the light directed toward the vidicon or other light-sensitive tube. In the said preferred embodiment of control system shown by the drawing, it takes the returning spring of the rotary solenoid only about one hundred and twenty milliseconds to move the armature of that rotary solenoid and the light-intercepting element 132 into the path of the light directed toward the vidicon or other light-sensitive tube; and hence that control system permits the light-intercept-= ing element 132 to be moved into light-intercepting position in less than one-fifth of a second after the value of the light impinging upon the light-sensitive element 5% increases above the predetermined level.

The returning spring of the rotary solenoid will hold the armature of that solenoid and the light-intercepting element 132 in the light-intercepting position, as long as the value of the light impinging upon the light-sensitive element 50 is above the predetermined level. However, as soon as the value of that light falls below that predetermined level, the impedance of that light-sensitive element will increase sufliciently to cause the transistor 52 of the tight level detector 77 to become conductive again. Thereupon, that light level detector will cause the subcircuit 109 to charge the capacitor 110 of the unijunction relaxation oscillator 117with a consequent firing of unijunction transistor 112 and of controlled rectifier 128. Because the capacitor ?4 became fully discharged through

resistors

92 and 96, while the value of the light impinging upon the light-sensitive element 50 was above the predetermined level, that capacitor will again act as a low impedance, and thus will permit a large value of current to flow through the transistor 90. The resulting prompt charging of the capacitor 110 will cause the unijunction transistor 112 and the controlled rectifier 128 to be rendered conductive during the early part of the half-cycle of the alternating current. This means that the coil 120 of the rotary solenoid will again receive a voltage pulse of about ninety volts; and that voltage pulse will enable that coil to start rotating the armature of that rotary solenoid and the light-intercepting element 132. toward light-intercepting position. The coil 120 will receive further high voltage pulses during succeeding half-cycles of the alternating current, and those high voltage pulses will assure prompt and certain rotation of the light-intercepting element 132 into light-intercepting position even if the voltage applied to the plug drops considerably. After the charge in the capacitor 94 becomes stabilized, the voltage pulses applied to the coil 120 will be about fifteen volts; all as explained hereinbefore. Consequently, the coil 120 will be able to hold the light-intercepting element 132 in light-intercepting position without experiencing undue heating.

The relatively high voltage pulses which are applied to the coil 120, as that coil moves the light-intercepting ele- :ment 132 to retracted position, are very desirable; because they enable that coil to move that light-intercepting element to retracted position even when appreciable decreases in line voltage are experienced. The sharply lower voltage pulses which are applied to the coil 120, as that coil holds the light-intercepting element in retracted position, are very desirable; because they avoid undue heating of that coil, and because they reduce the amount of power consumed by that coil. The action .of the Zener diode 36 in providing a regulated voltage for the base-two baseone circuit of the unijunction transistor, and the action of the

Zener diode

32 and 36 in providing a regulated voltage for the light level detector 77, are important: in making the voltage at the base of the transistor 52 essentially dependent upon the amount of light impinging upon the light-sensitive element 50 and essentially independent of changes in line voltage. The action of the Zener diode 36 in providing a regulated voltage for the light level detector 77, is important in enabling the control system to apply properly-timed voltage pulses to coil 1% despite changes in the line voltage.

The positive feedback provided by the resistor 76 causes hoth of the

transistors

52 and 70 to become conductive at the saturation level as soon as the transistor 52 becomes conductive and that positive feedback causes both of those transistors to become non-conductive as soon as the transistor 52 becomes non-conductive. As a result, prompt development of about twenty volts at the junction 72 is assured when the plug 10 is inserted into a socket at a time when the amount of light impinging upon the lightsensitive element 50 is below the predetermined level. Further, and more importantly, the positive feedback provided by the resistor 76 assures prompt removal of the approximately twenty volts at the junction 72, as soon as the amount of light impinging upon the light-sensitive element 50 rises above the predetermined level, and thus assures prompt de-energization of the coil 120 of the rotary solenoid.

The position of the movable contact of the potentiometer 48 will determine the amount of light which must impinge upon the lightsensitive element 50 to cause the transistor 52 to become non-conductive; and that movable contact will usually be set to enable that light-sensitive element to cause that transistor to become non-conductive at light levels appreciably below potentially hurtful light levels. The position of the movable contact of the potentiometer as will determine the firing angle which the subcircuit 109 provides for the unijunction transistor 112 after the charge in the capacitor 94 has stabilized. While that movable contact has been set to cause the unijunction transistor 112 and the controlled rectifier 128 to apply voltage pulses of about fifteen volts to the coil 120, after the charge in the capacitor 94 has stabilized, that movable contact can be set to cause that unijunction transistor and that controlled rectifier to apply higher or lower voltage pulses to that coil or to another electromagnetic element which is used in lieu of that coil.

It thus should be apparent that the light-sensitive optical, control system provided by the present invention is largely insensitive to changes in line voltage. Also, it should be apparent that the said control system senses and responds to the amount of light which impinges upon the light-sensitive element 50 thereof during each halfcycle of the alternating current applied to the plug Iii, applies relatively high voltage pulses to the coil of the rotary solenoid during turn on and during a limited number of half-cycles after the light-intercepting element 132 has been in light-intercepting position, and promptly permits that light-intercepting element to move to light-intercepting position whenever the light impinging upon that light-sensitive element reaches a predetermined level.

Whereas the drawing and accompanying description have shown and described a preferred embodiment of the present invention, it should be apparent to those skilled in the art that various changes may be made in the form of the invention without affecting the scope thereof.

What I claim is:

1. A light-sensitive, optical, control system which comprises:

a light-sensitive element,

a light-intercepting element that is movable into and out of light-intercepting position,

an electromagnetic element to move said light-inter cepting element relative to said light-intercepting position, a subcircuit which acts as a ramp-generator, and a driving circuit for said electromagnetic element, said subcircuit responding to a given signal from said light-sensitive eleme't to cause said driving circuit to develop a relativ ly large voltage pulse for said electromagnetic element, to assure prompt and effective energization of said electromagnetic element,

whereby said driving circuit and said subcircuit assure prompt and effective energization of said electromagnetic element.

2. A light-sensitive, optical, control system as claimed in claim. 1 wherein said subcircuit has means therein causing said subcircuit to cause said driving circuit to progressively reduce the values of the voltage pulses for said electromagnetic element until said voltage pulses are substantially lower than said relatively high voltage pulse.

3. A light-sensitive, optical, control system as claimed ing claim 1 wherein said subcircuit has means therein causing said subcircuit to act as a current source after said subcircuit has caused said driving circuit to apply said relatively high voltage pulse to said electromagnetic element.

4. A light-sensitive, optical, control system as claimed in claim 1 wherein said subcircuit has means therein causing said subcircuit to cause said driving circuit to develop a lower voltage pulse for said electromagnetic element to keep said electromagnetic element energized, said lower voltage pulse minimizing the heating, and the power consumption, of said electromagnetic element.

5. A lightsensitive, optical, control system as claimed in claim 1 wherein said subcircuit includes a chargestoring element that initially has a low impedance but l3 that increases the impedance thereof as it stores charges.

a A light-sensitive, optical, control system as claimed in claim 1 wherein said subcircuit includes a transistor and a capacitor in the emitter-collector circuit of said transistor, said capacitor initially being discharged and thus initially permitting a high level of current flow through said emitter-collector circuit of said transistor to cause said driving circuit to develop said relatively high voltage pulse, said capacitor subsequently becoming charged and thus permitting only lower levels of current to flow through said emitter-collector circuit of said transistor to cause said driving circuit to develop a lower voltage pulse for said electromagnetic element.

7. A light-sensitive, optical, control system as claimed in claim llwherein said driving circuit includes a normally noncoriductive element that can be fired to render it conductive, and wherein pulsating current is supplied to said driving circuit, whereby said driving circuit recurrently supplies voltage pulses to said electromagnetic element.

8. A light-sensitive, optical, control system as claimed in claim lwherein said driving circuit includes a normally non-conductive element that can be fired to render it conductive, and wherein said subcircuit includes means thatautomatically reduces the firing angle of said normally non-conductive element after said driving circuit has applied said relatively high voltage pulse to said electromagnetic element.

9. A light-sensitive, optical, control system as claimed in claim 1 wherein said driving circuit includes a normally non-conductive element that can be fired to render it conductive, and wherein said subcircuit includes a capacitor that exponentially reduces the firing angle of said normally non-conductive element after said driving circuit has applied said relatively high voltage pulse to said electromagnetic element.

it A light-sensitive, optical, control system as claimed in claim 1 wherein a light level detector includes said light-sensitive element and responds to a predetermined change in the light impinging upon said light-sensitive element to apply a distinctively difierent signal to said subcircuit.

H. A light-sensitive, optical, control system as claimed in claim 1 wherein a light level detector includes said light-sensitive element and responds to a predetermined change in the light impinging upon said light-sensitive element to apply a distinctively different signal to said subcircuit, j'fsaid light level detector including a plurality of stages aiid means to provide positive feedback from a subsequeiritstage to an earlier stage to effect prompt development of said distinctively different signal.

12. A light-sensitive, optical, control system as claimed in ,claim 1 wherein a light level detector includes said light-sensitive element and responds to a predetermined change in the light impinging upon said light-sensitive element to. apply a distinctively different signal to said subcircuit and wherein a voltage regulator applies a regulated voltage to said light level detector, said voltage regulator making the operation of said light level detector essentially independent of variations in line voltage.

13. A light-sensitive, optical, control system as claimed in claim 1 wherein a light level detector includes said light-sensitive element and responds to a predetermined change in the light impinging upon said light-sensitive element to apply a distinctively different signal to said subcircuit, wherein a voltage-regulating means applies a regulated voltage to said light level detector, and where in a further voltage-regulating means applies a regulated voltage to a firing means for said driving circuit, the first said and said second voltage-regulating means making the operation of said light level detector and of said firing means essentially independent of variations in line voltage.

lid. A light-sensitive, optical, control system as claimed in claim 1 wherein a light level detector includes said light-sensitive element and responds to a predetermined. change in the light impinging upon said light-sensitive element to apply a distinctively different signal to said. subcircuit, and wherein a voltage regulator applies regulated voltage to said light level detector, said voltage regulator making the operation of said light level detector essentially independent of variations in line voltage, said voltage regulator supplying pulsating DC. voltage to said light level detector and thereby permitting the voltage applied to said light level detector to recurrently fall essentially to zero.

15. A light-sensitive, optical, control system as claimed in claim 1 wherein a light level detector includes said. light-sensitive element and responds to a predetermined change in the light-impinging upon said light-sensitive element to apply a distinctively different signal to said. subcircuit, wherein a voltage-regulating means applies a regulated voltage to said light level detector, and wherein. a further voltage-regulating means applies a regulated. voltage to a firing means for said driving circuit, the first said and said second voltage-regulating means main ing the operation of said light level detector and of said firing means essentially independent of variations in line voltage, said first said and said second voltage-- regulating means supplying pulsating voltage to said light level detector and to said firing means and thereby permitting the voltage applied to said light level detector and to said firing means to recurrently fall essentially, to zero. I

16. A light-sensitive, optical, control system as claimed in claim ll wherein said electromagnetic element is the coil of a solenoid, and wherein a capacitor is connected in parallel with said coil.

17. A light-sensitive, optical, control system which come prises:

a light-sensitive element,

an electromagnetic element to move said light-intercepting element relative to said light-intercepting position,

a light level detector which includes said light-sensitive element and which develops signals that vary when. the light impinging upon said light-sensitive element varies,

a driving circuit for said electromagnetic element,

said light level detector acting, whenever the amount 0t light impinging upon said light-sensitive element exceeds a predetermined value, to develop a signal which enables said driving circuit to cause said electromagnetic element to permit prompt and effective movement of said light-intercepting element into light-intercepting position, and I j a voltage-regulating means that supplies a regulated voltage to said light level detector,

whereby said predetermined value of light impinging upon said light-sensitive element is essentially independent of changes in line voltage.

18. A light-sensitive, optical, control system as claimed in claim 17 wherein said voltage-regulating means applies said regulated voltage across a voltage divider which includes said light-sensitive element.

19. A light-sensitive, optical, control system. which comprises:

a light-sensitive element,

an electromagnetic element to move said light-intercepting element relative to said. light-intercepting position,

a light level detector which includes said light-sensitive element and which develops signals that vary when the light impinging upon said light-sensitive element varies,

a driving circuit for said electromagnetic element,

said light level detector acting, whenever the amount of light impinging upon said light-sensitive element exceeds a predetermined value, to develop a signal which enables said driving circuit to cause said electromagnetic element to permit prompt and effective movement of said light-intercepting element into light-intercepting position, and

a voltage-supplying means that supplies a pulsating voltage to said light level detector,

whereby the voltage supplied to said light level detector recurrently drops essentially to zero.

2%. A light-sensitive, optical, control system which comprises:

a light-sensitive element,

a light-intercepting element that is movable into and out and of light-intercepting position,

a light level detector which includes said light-sensitive element and -which develops signals that vary when the light impinging upon said light-sensitive element varies,

a driving circuit for said electromagnetic element,

said light level detector acting, whenever the amount of light impinging upon said light-sensitive element ex ceeds a predetermined value, to develop a signal which enables said driving circuit to cause said electromag netic element to permit prompt and effective move ment of said light-intercepting element into lightintereepting position,

a plurality of stages in said light level detector, and

means to provide positive feedback from a subsequent stage to an earlier stage to effect prompt development of said signal by said light level detector whenever the amount of light impinging upon said light-sensitive element exceeds said predetermined value.

21. A light-sensitive, optical, control system which comprises:

a light-sensitive element,

a light level detector which includes said light-sensitive element and which develops signals thatvary when the light impinging upon said light-sensitive element varies,

a driving circuit for said electromagnetic element,

said light level detector acting, whenever the amount of light impinging upon said light-sensitive element exceeds a predetermined value, to develop a signal which enables said driving circuit to cause said electromagnetic element to permit prompt and effective movement of said light-intercepting element into light-intercepting position, and I avoltage-supplying' means that supplies a pulsating voltage to said driving circuit,

whereby the voltage supplied to said driving circuit recurrently drops essentially to zero,

References Cited UNITED STATES PATENTS 3,191,516 6/ 1965 Corcoran 350--269X 3,198,883 8/1965 Borberg et al 178-7.92X 3,377,427 4/l968 Fischer 178-7.2X

OTHER REFERENCES TV Camera Protection Circuit, by Vernon I. Poehls, RCA Technical notes, RCA TN No. 459, September 1961,

JAMES W. LAWRENCE, Primary Examiner C. R. CAMPBELL, Assistant Examiner US. Cl. X.R,