US2945957A

US2945957A - Intermittent feed cut-off register control

Info

Publication number: US2945957A
Application number: US729627A
Authority: US
Inventors: Leroy U C Kelling
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1958-04-21
Filing date: 1958-04-21
Publication date: 1960-07-19
Anticipated expiration: 1977-07-19

Description

July 19, 1960 u. c. KELLING INTERMITTENT FEED CUT-OFF REGISTER CONTROL Filed April 21, 1958 INVENTOR LEROY U.C. KELLING,

HIS ATTORNEY.

United States Patent INTERMITTENT FEED CUT-OFF REGISTER CONTROL I Leroy U: C. Kelling, Waynesboro, Va., assignor to General Electric Company, a corporation of New York Filed Apr. 21, 1958, Ser. No. 729,627

12 Claims. (Cl. 2502'19)' The present invention relates generally to register control apparatus and more particularly to control apparatus for synchronizing the feed of web material to a blanking machine with the operation of a reciprocating blanking die which cuts blanks from theweb material.

Blanking machines of the type with which the control apparatus of the present invention is particularly concerned utilizes a reciprocating blanking die orblanking dies having other cyclic movements, for cutting blanks from web material supplied to the machine in the form of strip sheets. The blanking die is continuously reciprocating and after each cutting operation, the material must be advanced in order to present a new region of the material to the die, and brought to a complete stop before the die again contacts the material.

It is a broad object of the present invention to provide a control apparatus for blanking machines wherein movement of web material from which blanks are punched or cut is synchronized with the movement of a reciprocating blanking die which cuts the blanks from the material.

It is another object of the present invention to provide a control system for a blanking machine which provides for rapid acceleration and deceleration of material being presented to a reciprocating blanking die employed to cut appropriate cup blanks from the material.

(Ihe synchronization of the feed of the Web material with the movement of the reciprocating blanking die is quite critical, for instance, in consequence of printed information previously applied to paper stock. Specifically, while the paper stock is still in sheet form and prior to its presentation to the blank cutting machine, the paper stock is printed with appropriate designs, the name of the manufacturer and other pertinent information such as his trademark. The design and other imprinted information is intended to have a predetermined location in two dimensions on each finished article such as a cup or other container and, therefore, the positioning of the paper stock under the blanking die is quite critical. A photocell sensing approach to accurate positioning of the printed information on the stock with respect to the blanking die may be completely satisfactory when the printed information is located such that it does not become disposed in the path of light to the photocell.

However, in some operations the printed information may become disposed in the path of light reflected from the web to the photocell and might produce spurious operation of the brake if steps were not taken to prevent such operation.

Therefore, it is an object of this invention to provide a novel register control apparatus utilizing gaseous control tubes which are selectively energized in response to visible indicia to control feeding sheet material to a blank ing machine.

It is another object of this invention to provide a novel apparatus to maintain registration of sheet material from which blanks are formed and which includes means to prevent spurious signals from marks other than registra- 2,945,957 Patented Julyv 19, 19.60

It is still another object of this invention to. provide a novel apparatus for maintaining registration of sheet material with a machineperforming operations thereon which includes a circuit elfective to prevent the passage of control signals for a predetermined time so that spurious control signals developed in response to marks other than registration will not function to cause improper registration of the sheetmaterial.

It is another object of the present invention to provide a paper cup-making machine utilizing feeding-apparatus for presenting printed paper'stock to a reciprocating blanking die, and including an electric circuit for terminating the movement of the paper upon detection by a photoelectric system of visual index marks on thepaper web; and a time delay circuit for rendering the system non-responsive to detection of the visual marks on the paper stock for a predetermined time after initiating movement of the feeding apparatus.

It is yet another object of the presenttinvention to provide alternatively energizedtbrake and clutch mechanisms for stopping and starting, respectively, the operation' of feeding apparatus employed tov present paper stock to a reciprocating punching die and to provide electric circuits for energizing the clutch uponinitiationof movement of the reciprocating punching die away from the paper stock, for energizing the brake to terminate movement of the-apparatus .upon detection .by a photo: cell system-of an index markon the paper stock, and for rendering the electric circuits nonresponsive to printed material on the paper stock for a predeterminedftime after energization of the clutch mechanism;

The amount of power required to produce. rapid actuation of the brake and clutch is quite considerable and'it' has been found that where it is attempted to terminate conduction of the gas tubes too rapidly, there results a considerable amount of gas clean-up within the tube.

When the gas in a gas tube ionizes, there is produced positive ions and electrons with the electrons flowingtfrom' the cathode toward the anodeand the positivev ions flowing toward the cathode. If conduction through the tube is terminated toorapidly, the positive ions are nolonger drawn toward the cathodeand bombard the-metallic parts of the tubes and become imbedded therein. When suflicient quantities of the gas within the tube have become imbedded in the metallic parts, the pressure within the tube is reduced-to such an extent that the current handling capability thereof is considerably reduced. and the tube becomes substantially inoperativefor its intended purpose.

It is still another object of the present'inventionto provide a paper cup-making machinehaving a control system wherein gas tubes are utilized for alternately energizing a brake mechanism and a clutch mechanismand for preventing 'a too rapid terminationof conductionof each gas tube upon the other tube being renderedconductive.

Briefly, the objects of my invention are achieved in one embodiment by the provision of means for controlling the movement of. a web under a blanking die by controlling the energization of brake and clutch devices in response to signals received from a photoelectric de vice through a control circuit which is' ineffective to transmit any signals from the photoelectric device for a predetermined time to insure that signals developed by any mark other than a register mark will not be effective to energize the brake and stop the movement of the web. Also, my invention contemplates the provision of a time delay circuit in a circuit with a oommutating capacitor coupled between the anodes of. a pair of gas tubes se, lectively energizing the brake and clutch so that the current in the tube being shut off is relatively slowly decreased until conduction in that tube is terminated.

The above and still further objects, features and advantages of the present invention will become apparent upon consideration of the following detailed description of one specific embodiment thereof, especially when taken in conjunction with the accompanying drawings, wherein:

Figure 1 is a schematic illustration of a blanking machine incorporating an embodiment of my invention; and

Figure 2 is a schematic illustration of an electrical circuit for carrying out the objectives of my invention.

Referring specifically to Figure 1 of the accompanying drawing, there is schematically illustrated a machine generally designated by the reference numeral 1 for producing blanks from web or sheet material. The machine 1 may comprise a reciprocating blanking die 2 adapted to cut paper blanks from a continuous web of paper 3 by pressing the paper web 3 against an anvil portion 4. The paper web 3 is .presented to the reciprocating blanking die 2 by means of a conveyor mechanism generally designated by the reference numeral 6 and schematically illustrated in the figure of the drawing. The conveyor mechanism 6 must be capable of rapid starting and stoping and to this end there is provided a shaft 8 adapted to be coupled to a continuously rotating motor 7 through a clutch 9 or, alternatively, to a stationary surface by a brake 10. The shaft 8 is coupled to the conveyor mechanism 6 via a gear assembly 11.

The web of paper 3 is provided with markings, generally designated by the reference numeral 12, which are to have a predetermined location on each of the finished cups. Since the blanking die 2 is continuously reciprocating, the presentation of the paper web to the blanking die, which is controlled by the conveyor mechanism 6, must be synchronized with the cyclic operation of the blanking die. -In order to synchronize the presentation of the various portions of the web 3 to the reciproeating blanking die 2, there is provided a switch 13 for controlling energization of the clutch 9 and a photocell for controlling energization of the brake i0. Specifically, the switch 13 is adapted to sense movement of the blanking die 2 away from the anvil 4 so that movement of the conveyor 6 is initiated as soon as practical after each blank is stamped out. The web 3 has imprinted thereon a plurality of index marks 16 which are disposed on the web 3 so as to pass under a beam of light directed upon the Web by a light source 17 and transmitted as by transmission through or reflection from the web 3 to the photocell 14. The photocell 14 senses the appearance of each mark 16 under the beam of light and in response thereto energizes the brake so as to terminate movement of the conveyor 6. Each of the marks 16 are equally spaced from one another and bear a predetermined special relationship to the printed material 12 such that the movement of the web 3 is terminated with the material 12 centrally located under the die 2. Other specific terminal relationships between the material 12 and die 2 are equally obtainable and it is not intended to limit the invention to a specific arrangement of elements.

It is readily apparent from reference to Figure 1 of the accompanying drawing that the printed material 12 may extend between the index marks 16 and therefore the circuit of the present invention must prevent actuation of the brake mechanism 10 in response to the printed material 12.

Referring again to Figure l of the accompanying drawing, the clutch mechanism 9 is provided with a clutch actuating coil 19 while the brake mechanism 10 is provided with a brake actuating coil 21. Turning attention to Figure 2, it may be seen that the clutch coil 19 has one end connected to a current control device such as a gaseous discharge device 22, such as a thyratron,

having an anode 23, to which coil '19 is connected, and, in addition, a control grid 24 and cathode 26. The coil 19 and tube 22 are connected in series between a pair of

voltage buses

27 and 28 which are supplied with unidirectional voltage from a source (not shown). The voltage bus 27 is positive with respect to the voltage bus 28 and the cathode 26 of the tube 22 is connected to the voltage bus 28 while the upper end of coil 19, as illustrated in the accompanying drawing, is connected to the positive voltage bus 27.

The brake control winding 21 has one end connected to the voltage bus 27 and the other end connected to an anode 31 of a second gaseous discharge device 32 having a control grid 33 and a cathode 34 connected directly to the negative voltage bus 28. As will be explained subsequently, the

grids

24 and 33 of the

gas tubes

22 and 32 are adapted to receive positive pulses in order to produce firing of their respective tubes. From the nature of the system, it is apparent that when one of the tubes becomes conductive, the other of the tubes must be rendered non-conductive so that the clutch 9 and brake 10 are never energized simultaneously. In order to insure that one of the tubes is rendered non-conductive, when the other is rendered conductive, a commutating capacitor 36 is connected between two

equal value resistors

37 and 38 across the anodes 23 and 31 of the

tubes

22 and 32, respectively.

The operation of the commutating capacitor 36 is well-known in the art, but for the sake of completeness of description, a brief discussion of its operation is given. Assuming, for the purposes of example, that the tube 32 is initially conducting, the left-hand plate of the capacitor 36 is negative with respect to the right-hand plate, all as viewed in the figure of the drawing. Upon the application of a positive pulse to the grid 24 of the tube 22, the voltage on the anode 23 of the tube 22 suddenly de creases and since the left-hand plate of the capacitor 36 is negative with respect to the right-hand plate, the voltage on the anode 31 of the tube 32 is driven further negative to such an extent that a discharge sustaining potential no longer exists between the anode 31 and the cathode 34 of this tube. During the period of conduction of the tube 22, the capacitor 36 is charged in the opposite direction so that when the tube 32 is again rendered conductive, the anode 23 and the tube 22 is driven negative and this latter tube is rendered non-conductive.

Considerable difiiculty has been experienced, since the advent of the highpowered, gaseous discharge tubes, with clean-up of the gas Within the tube which gradually reduces the gas pressure therein and materially effects the operating characteristics of the tube. One of the basic reasons for gas clean-up in gas-filled tubes is the result of high speed positive ions striking metallic surfaces within the tube and becoming imbedded in the metal. It has been found that extreme bombardment of the metallic parts of the tube results when a large current through the tube is suddenly discontinued and in consequence the ions are no longer attracted to the cathode. Further, the intensity with which the positive ions bombard the metallic elements of the tube is a function of the rate of application of inverse voltage across the tube after cessation of conduction thereof. It has been found that in order to prevent severe gas clean-up within the tubes, the product of the rate of discontinuance of conduction of and the rate at which inverse voltage is applied across the tubes must be kept relatively low.

In accordance with the present invention both the rate at which conduction of the

gas tubes

22 and 32 is discontinued and the rate of application of inverse voltage across the tubes is limited by the

resistors

37 and 38 connected in series with the capacitor 36 and by means of a further capacitor 39 connected between the negative voltage bus 28 and the junction of the capacitor 36 and the resistor 37. The

resistors

37 and 33 and the capacitor 39 constitute a time delay circuit which limits the rate at which the anode of a previously conducting tube, 22 or 32, may be driven negative and therefore limits the rate at which current flow through the tube is reduced and the rate at which the inverse voltage across the anodes and the cathodes is applied. Specifically, the upper plate of the capacitor 39 assumes the same charge as the left plate of the capacitor 36 and, due to its own charging characteristics through the resistor 37 or the resistor 38, limits the rate of change of the voltage on this plate of the capacitor 36.

Referring again specifically to the control circuit of the present invention, the application of positive pulses to the

grids

24 and 33 of the

tubes

22 and 32 is controlled by a flip-flop circuit generally designated by the reference numeral 41. The flip-flop circuit 41 comprises a first triode section 42 having an anode 43, connected through a resistor 44 to the voltage bus 28, a control grid 46 and cathode 47 connected througha resistor 48 to a source of reference potential hereinafter referred to as the grounded voltage bus 49. A positive voltage is established between the voltage bus 28 and the voltage bus 49 by supplying a unidirectional voltage to the bus 28 so that the voltage on the bus 28 is positive with respect to the bus 49 while the voltage on the bus 27 is positive with respect to the bus 28. The flip-flop circuit 41 further comprises a second triode stage 52 having an anode 53, connected through a resistor 54 to the voltage bus 28, a control grid 56 and a cathode 57 connected through the resistor 48 to the voltage bus 49. The control grids 46 and 56 of the triode stages 42 and 52 are appropriately connected to the anodes of the opposite tubes in order to obtain a bi-stable, flip-flop circuit; these connections being completely conventional.

The anode 43 of the triode stage 42 is connected to the grid 33 of the gas tube 32 via a pulse-forming network comprising a capacitor 58 connected in series with a resistor 59 between the anode 43 of the triode section 42 and a junction 61 between resistors 62 and 63. The resistors 62 and 63 constitute two elements of a voltage divider connected between the

voltage buses

28 and 49 which further includes

resistors

64, 66 and 67 connected in that order between the

buses

28 and 49, respectively. The control grid 33 of the tube 32 is connected between the capacitor 58 and resistor 59 and when the tube section 42 is rendered non-conductive, the rise in voltage of the anode 43 produces a positive pulse across the resistor 59 which is applied to the grid 33 of the gas tube 32 and renders it conductive. The anode 53 of the triode section 52 is adapted to control firing of the gas tube 22 by applying a positive pulse to its grid 24 in response to the tube section 52 being rendered non-conductive. Specifically, the anode 53 is connected via a pulse-forming circuit comprising a capacitor 68 and resistor 69 to the junction 61 on the voltage divider and the junction between the capacitor 68 and resistor 69 is connected to the grid 24 of the gas tube 22. It is apparent that since the

gas tubes

22 and 32 are rendered conductive by positive pulses applied to their respective control grids, that the

tube sections

42 and 52 render their respective gas tubes conductive upon becoming non-conductive. It is apparent, therefore, that when the photocell 14 detects an index mark 16, the flip-flop 41 must be switched to a state wherein the tube section 52 is rendered conductive and when the switch 13 detects upward movement of the reciprocating blanking die 2 the tube section 42 must be rendered conductive in order to energize the clutch control winding 19 and initiate movement of the web 3.

In order to energize the clutch control winding 19, the switch 13 has one contact connected to the voltage bus 28' and the other contact coupled via a coupling capacitor 71 and a resistor 72to a grid 73 of a tube section 74. The tube section 74 includes a cathode 76, connected to the junction of resistors 66, 67 of the aforesaid voltage divider, and an anode 77 connected 'via a lead 78 to the anode of the tube section 42 of the flip-flop 41 and therefore through the appropriate flipflop coupling circuit to the control grid 56 of the tube section 52. The junction of the capacitor 71 and the resistor 72 is connected via a further resistor 79-to the grounded voltage bus 49. Also, the junction of the switch 13 and the capacitor 71 is connected to-the voltage bus 49 via a resistor 81 which provides a rapid discharge path for the capacitor 71.

Initially, with the switch :13 open, the grid '73 of the tube 74 is at ground potential and since the cathode'76 is connected to the aforesaid voltage divider the grid is negative with respect to cathode and the tube is nonconductive. Upon closing of'the switch 13, the capacitor 71 initially passes a large surge of current through the resistor 79 and the grid 73 of the tube 74 istemporarily driven in a positive direction with respect to its cathode to turn the tube on. Conduction through the tube is initiated and the anode 77 is instantaneously driven negative. The negative pulse appearing at the anode 77 and therefore on the lead 78 is applied to the control grid 56 of the tube section 52 causing this section to become non-conductive and thereby causing switching of the flip-flop 41 to'render the triode section 42 conductive. Upon the section 52 becoming non-conductive, a positive pulse is applied to the control grid 24 of the tube 22 and the clutch is energized so that the paper web 3 is advanced to present a new section to the reciprocating blanking die 2.

In order to stop the advance of the web 3 when an index mark 16 is detected by the photocell 14, the photocell fhas an anode 82 connected to a junction 83 between

resistors

84 and 86 which constitute two elements of a voltage divider having a further resistor '87, the "resistor 84- having one end connected to the voltage bus 28 and the resistor -87 having one end connected to the voltage bus 49. The phototube 14'is also provided with a photo emissive cathode .88 connected via a resistor 89 to the negative voltage bus 49;. the connections of the anode 82 and photo-emissive cathode 88 providing a positive voltage across the tube 14. The light from the lamp '17 which is reflected from the normally reflective surface of the paper web 3, maintains a predetermined current through the tube 14 and therefore establishes a predetermined voltage across the resistor '89.

Upon an index mark 16 being disposed in the path between the bulb 17 and the photocell 14, the degree of conduction of the cell 14 is reduced and the negative pulse produced thereby is coupled through a coupling capacitor 91 to a resistive element 92 of a potentiometer 93. The resistive element 92 of the potentiometer 93 has its other end connected to the bus'49 and is adapted to be engaged by a wiper arm 94 connected via'a resistor 96 to a grid 97 of a vacuum tube '98. The tube 'hasa cathode '99, connected between theresistors 86 'and'87, and an anode 101 connected via a resistor 102' to the voltage bus 28. The circuit connections of the elements of the tube .98 render it' normally conductive sqthat when there is a decrease in current through the photocell'14 and a negative pulse is applied across the resistiveelement 92 of the potentiometer 93, the conduction through the tube 98 is suddenly decreased and the voltage of the anode 101 of the tube 98 suddenly increases. The anode 101 is connected via a coupling capacitor 123 to a grid 103 of a driver tube '104. The junction of the grid 103 and the capacitor 123 is connected via a resistor 122 to the junction between

the'resistors

64 and 66 in order to pro- 104 further comprises an anode 108 connected via a-lead 109 to the anodeof thet-riode stage 52'of the flip-flop 41.-

Upon the anode 101 of the tube 98 becoming more positive, a positive voltage pulse appears on the grid 103 of the tube 104 to render the tube conductive. In consequence, the voltage of the anode 108 of the tube 104 is suddenly reduced and the reduced voltage is coupled to the grid 46 of the triode stage 42 and renders this tube non-conductive thereby rendering the tube section 52 conductive. Upon the tube 42 being rendered non-conductive, a positive pulse is applied to the control grid 33 of the tube 32 and the brake control winding 21 is energized to discontinue movement of the conveyor mechanism 6 and therefore of the paper Web 3.

As previously indicated, the printed information lying between the index markings 16 have substantially the same effect upon the photocell 14 as the index marks and if some provision were not made for distinguishing between the index marks 16 and the printed material 12, the machine would be subject to repeated erroneous operation. In accordance with the present invention, erroneous operation, resulting from detection by the photocell 14 of the printed information 12, is prevented by rendering the driver tube 104 inoperative for a predetermined period after energization of the clutch winding 19. The duration of this interval is determined by the spacing between the printed material 12 and the index 16 and the rate of travel of the Web 3, this information being known precisely prior to operation of the apparatus.

The mechanism for disabling the tube 104 for predetermined time intervals, comprises a vacuum tube 111 having a cathode 112 connected to the voltage bus 49 and anode 113 connected to the junction between the resistors 106 and 107 and therefore connected to the cathode 105 of the tube 104. The tube 111 is also pro vided with a grid 114 connected via a resistor 116 and a timing capacitor 117 to the lead 78. The junction of the capacitor 117 and resistor 116 is connected via a variable timing resistor 118 and a fixed resistor 119 to the junction of the resistors 66 and 67. The connections of the cathode 112 and the grid 114 render the tube 111 normally conductive and the connections of the capacitor 117 render its lower plate, as viewed in the figure of the accompanying drawing, negative with respect to its upper plate. When the switch 13 is closed and the lead 78 is driven negative as a result of the conduction through the tube 74, the capacitor 117, since its lower plate is negative with respect to its upper plate, drives the grid 114 of the tube 111 sutficiently negative to render the tube nonconductive.

Upon the tube 111 becoming non-conductive the effective resistance of the elements in series with the resistor 107 suddenly increases being now the resistance of resistor 106, thereby increasing the voltage on the cathode 105 of the tube 104. This increases the voltage on cathode 105 of the tube 104 to such an extent that the tube cannot be rendered conductive by the voltage pulse developed on its grid 103 in response to detection of a dark area on the web 3 by the photocell 14. The tube 111 is maintained non-conductive for a predetermined interval determined by the capacity of the capacitor 117, the value of the resistance 119 and the adjustable value of the variable resistor 11& As long-as the lower plate of the capacitor 117 remains sutficiently negative to render the tube 111 non-conductive, the tube 104 cannot respond to detection of marks by the phototube 14 and therefore printed material on the web of paper 3 cannot eifect the system. When the capacitor 117 becomes sufficiently discharged, the tube 111 becomes conductive and its anode 113 decreases to a potential which is limited by a rectifier 121 connected between the anode 113 and the junction of the resistors 63 and 64 of the aforesaid voltage divider. Conduction of the tube 111 reduces the resistance in series with the resistor 107 and the potential of the cathode 105 falls to a predetermined clamped potential such that the relative voltages of the cathode 105 and the anode 108 of the tube 104 permit conductionof the tube upon apdetection by the photoelectric cell 14 of an index mark 16 the tube 104 may now be rendered conductive and effect switching of the flip-flop 41 such that the brake winding 21 is energized and the clutch winding 19 is dcenergized.

The apparatus of the invention is described as applied to a paper cup-making machine but it is not intended to limit the scope of the invention to a specific machine or class of machines, since the concepts of the invention are applicable in many other fields. The control may be applied to any machine having a cyclically operating member adapted to perform an operation upon a con tinuous member or series of discrete members adapted to be fed to the machine in synchronism with the operation of the cyclically operating member. Indexing may be accomplished by sensing switches as well as photocells and with regard to photocells light index areas against a dark background may be employed by the addition of a phase inverter circuit.

While I have described and illustrated one specific embodiment of my invention, it will be clear that variations of the details of construction which are specifically illustrated and described may be resorted to without departing from the true spinit and scope of the invention as defined in the appended claims.

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

l. A control circuit comprising a first load control circuit, a second load control circuit, a bi-stable circuit means for energizing one of said load control circuits upon obtaining one of its stable states and for energizing the other of said load control circuits upon obtaining the other of its stable states, first sensing means for sensing a first condition, second sensing means for sensing a second condition, a first circuit means responsive to said first sensing means for causing said bi-stable circuit means to assume one of its stable states, a second circuit means for causing said bi-table circuit means to assume the other of its stable states, and further means responsive to said first sensing means for rendering said second circuit means non-responsive to said second sensing means for a predetermined time interval.

2. A control circuit comprising a first load control circuit, a second load control circuit, a bi-stable circuit means for energizing one of said load control circuits upon obtaining one of its stable states and for energizing the other of said load control circuits upon obtaining the other of its stable states, means for deenergizing each said load control circuit upon the other such circuit becoming energized, first sensing means for sensing a first condition, second sensing means forsensing a second condition, a first circuit means responsive to said first sensing means for causing said bi-stable circuit means to assume one of its stable states, a second circuit means responsive to said second sensing means for causing said bi-stable circuit means to assume its other stable state and further means responsive to said bi-stable circuit means obtaining said one of its stable states for rendering said second circuit means nonresponsive to said second sensing means.

3. A control system comprising a first load control circuit, a second load control circuit, a flip-flop circuit having two stable states of conduction, means for energizing said first load control circuit when said flip-flop circuit obtains one of its stable states of conduction-and for energizing said second load control circuit when said flipfiop obtains the other of its stable states of conduction, an operation sensing switch, an electro-optical system for detecting index markings, first circuit means responsive to a predetermined operation of said switch for causing said flip-flop circuit to assume a predetermined one of its stable states of conduction, second circuit means responsive to detection by said electro-optical system of an index mark for causing said flip-flop circuit to assume its other stable state of conduction and timing means responsive to said flipflop cirGuit Obtaining said one stable state for 9 rendering said second circuit means nonresponsive to said electro-optical system for a predetermined time interval.

4. A control system for alternately energizing an electrically controlled brake and an electrically controlled clutch comprising a brake control winding, a first load control circuit for selectively energizing said brake control winding, a clutch control Winding, a second load control circuit for selectively energizing said clutch control winding, a flip-flop circuit having two stable states of conduction, means for energizing said first load control circuit when said flip-flop circuit obtains one of its stable states of conduction and for energizing said second load control circuit when said flip-flop obtains the other of its stable states of conduction, an operation sensing switch, an electro-optical system for detecting index markings, first circuit means responsive to a predetermined operation of said switch for causing said flip-flop circuit to assume a predetermined one of its stable states of conduction, second circuit means responsive to detection by said electro-optical system of an index mark for causing said flip-flop circuit to assume its other stable state of conduction and timing means responsive to said flip-flop circuit obtaining said one stable state for rendering said second circuit means non-responsive to said electro-optical system for a predetermined time interval.

5. A control system for alternately energizing an electrically controlled brake and an electrically controlled clutch comprising a brake control winding, a first gaseous discharge device connected in series with said brake control winding, a clutch control winding, a second gaseous discharge device connected in series with said clutch control winding, a fiip-fiop circuit having first and second stable states of conduction, means for rendering said first and second devices conductive when said flip-flop circuit obtains its first and second stable states of conduction, respectively, transfer means for discontinuing conduction of each of said devices when the other is rendered conductive, a normally open switch, first circuit means for causing said flip-flop to assume its second stable state when said switch is closed, a photoelectric system, second circuit means responsive to generation of a predetermined signal by said photoelectric system for causing said flipflop to assume its first stable state and timing means responsive to said flip-flop circuit assuming its second stable state for rendering said second circuit means unresponsive to said photoelectric system for a predetermined length of time.

6. The control system according to claim 5, wherein said transfer means comprises means for generating a voltage pulse in response to one of said devices becoming conductive and for applying it to the other of said devices to render the latter tube non-conductive and further comprising means for preventing gas clean-up in said devices which includes means for limiting the rate of rise of said voltage pulse.

7. The control system according to claim 5, wherein said tubes each includes at least an anode and wherein said transfer means includes a capacitor connected between said devices for transferring a voltage pulse therebetween.

8. The control system according to claim 7, further comprising means for minimizing gas clean-up in said devices including a time delay circuit for limiting the rate of rise of said voltage pulse.

9. A gaseous discharge tube switching circuit comprising a pair of gaseous discharge devices each having at least an anode and a cathode, a pair of load circuits, a pair of series circuits each including a different one of said load circuits and a cathode and an anode of a dinerent one of said devices, means connected between said series circuits for applying a voltage pulse to either one of said circuits to render its associated tube non-conductive upon the other of said devices being rendered coriductive, and means for minimizing gas clean-up in said devices comprising timing means connected between said first mentioned means and said series circuits for limiting the rate of rise of said voltage pulse.

10. A gaseous discharge tube switching circuit comprising a pair of gaseous discharge devices each having at least an anode and a cathode, a pair of load circuits, a pair of series circuits each including a difierent one of said load circuits and a cathode and an anode of a difierout one of said devices, a capacitor connected between said anodes and efiective to render either one of said devices non-conductive upon the other of said devices being rendered conductive and means for preventing gas clean-up in the one of said devices rendered non-conductive, said last-mentioned means comprising time delay means connected to said anodes and said capacitor.

11. A gaseous discharge tube switching circuit comprising a pair of gaseous discharge devices each having at least an anode and a cathode, a pair of load circuits, a pair of series circuits each including a diflfere nt one of said load circuits and a cathode and an anode of a different one of said devices, a capacitor connected between said anodes and having a capacity suflicient to render one of said devices non-conductive upon the other of said devices being rendered conductive and means for preventing gas clean-up in the one of said devices rendered nonconductive, said last-mentioned means comprising a pair of resistors each connected between a different one of said anodes and said first capacitor and a second capacitor connected between said first capacitor and a common connection of said series circuits.

12. A control system for a blank cutting machine employing a cyclically operating blanking die and apparatus for supplying material having index marks thereon to said blanking die in synchronism therewith, said system comprising a clutch for selectively coupling a drive member for said apparatus'to a source of motive power, a brake for selectively coupling said drive member to a stationary member, said brake having an electrically energizable brake control winding, a first gaseous discharge device connected in series with said brake control winding, said clutch having an electrically energizable clutch control winding, a second gaseous discharge device connected in series with said clutch control winding, a flip-flop circuit having first and second stable states of conduction, means for rendering said first and second devices conductive when said flip-flop circuit obtains its first and second stable states of conduction, respectively, transfer means for discontinuing conduction of each of said devices when the other is rendered conductive, a normally open switch, means for closing said switch upon movement of said blanking die away from said material, first circuit means for causing said flip-flop to assume its second stable state when said switch is closed, a photoelectric system for producing a predetermined signal in responseto said index References Cited in the file of this patent UNITED STATES PATENTS 1,834,889 Bedford Dec. 1, 1931 2,050,316 Gulliksen Aug. 11, 1936 2,366,038 Livingston Dec. 26, 1944 2,401,396 Wolfner June 4, 1946 2,529,161 Kelling et a1 Nov. 7, 1950 2,874,333 Gray Feb. 17, 1959