US2922688A - Apparatus for recording electrically on heat-sensitive material - Google Patents

Description

Jan. 26, 1960 E. A. BOYAN 2,922,688

APPARATUS FOR RECORDING ELECTRICALLY ON HEAT-SENSITIVE MATERIAL Original Filed June 28, 1952 3 Sheets-Sheet 1 A.C. SUPPLY INVEN TOR. EDWIN A. BOYAN TO MACHINE BY 7 Wm MOTOR CIRCUIT W ATTORNEYS Jan. 26, 1960 E. A. BOYAN 2,922,688

APPARATUS FOR RECORDING ELECTRICALLY ON HEAT-SENSITIVE MATERIAL Original Filed June 28, 1952 5 Sheets-Sheet 2 INVENTOR. EDWIN A. BOYAN ATTORNEYS APPARATUS FOR RECORDING ELECTRICALL'Y N HEAT-SENSITIVE MATERIAL Edwin A. Boyan, Dayton, Ohio Original application June 28, 1952, Serial No. 296,200, now Patent No. 2,776,867, 'dated January 8, 1957. Divided and this application November 1, 1956, Serial No. 619,889

3 Claims. (Cl. 346-76) The present invention relates to recording apparatus, and more particularly although by no means exclusively to apparatus for recording the operation and production of machines and processes, for purposes of production control. In its application to production analysis apparatus, the invention is concerned with improvements in apparatus of the general type disclosed in my prior Patent No. 2,591,124, granted April 1, 1952. This application is a division of my copending application Serial No. 296,200, filed June 28, 1952, now Patent No. 2,776,867, issued Jan. 8, 1957. I

There are many applications where it is desirable to provide recording means by which information may readily be transcribed for subsequent use, with time intervals or duration concurrently entered as part of the record. Thus, for the effective analysis and control of production costs and machine productivity in industrial management, it is necessary to have accurate and comprehensive' information concerning the operation of the machines, particularly as to the variations or interruptions.

in normal operation. Upon proper analysis of the nature and significance of the various types of interruptions, it will generally be possible to eliminate or minimize at least some of the recurring interruptions.

In carrying out such an analysis of machine operation it is necessary to provide means for readily identifying on the recording medium the particular causes for interruptions as well as the durations thereof. It is essential, however, that the operation of such recording equipment not interfere with the normal production of the machine, so that the operator is burdened and his productivity decreased. On the other hand, the recordmg apparatus must not appear to the operator as a monitor by which the operator is kept under constant surveillance.

It is therefore an object of the present invention to provide apparatus which will permit pertinent information to be derived concerning the operation of a machine or other equipment, including particularly the nature and magnitude of delays or interruptions beyond his direct control, and wherein the actuation of the recording apparatus is in part automatic and in part dependent on the operator, which such actuation of the recording mechanism as the operator must perform being readily carried out without adding to the work of operating the machine,

More particularly, it is an object of the invention to provide production analysis apparatus wherein the operator may designate, by selection of a push button or analogous control means, the cause of an interruption in machine operation, the designation of the particular cause being accomplished at the end of a period of interruption and in the course of restarting the machine, with special supplementary control means provided for actuation by the operator at the commencement of a period of interruption whenever 'the operator decides on his own part to interrupt the operation of the machine without specific cause, to permit resumption of machine operation thereafter without requiring the actuation of 2,922,688 Patented Jan. 26, 1960 cause-recording means and automatic designation of the interval involved.

It is likewise an object of the invention to provide a novel and eflFective means for substantially instantaneously recording data, particularly suited to recording on a moving web or the like.

These and other objects, and the several features of the invention, will become apparent from the following description, taken in conjunction with the accompanying drawings in which Fig. 1 is a view illustrating one form of my recording apparatus as embodied in production analysis apparatus installed on a lathe-type machine;

Fig. 2 is a schematic wiring diagram of one'form of recording apparatus for production analysis;

Fig. 3 is an oblique view illustrating the data-recording mechanism of the invention;

Fig. 4 is a view, partly in section, showing the recording element or head for transcribing data on the record web;

Fig. 5 is an end view of the recording head;

Fig. 6 is a top plan view of the same;

Fig. 7 is a detail view, partly in section, showing the construction of a special control switch for use with the recording apparatus, and

Fig. 8 is a schematic wiring diagram of an alternative embodiment of the recording apparatus for production analysis. The recording apparatus of my invention is illustrated as embodied in units which may be attached to or mounted in the vicinity of the machine, with suitable connections made to the existingmachine control circuit by means of electrical cables or conduit. Fig. 1 illustrates the use of the recording apparatus in conjunction with a lathe, only so much of the machine being shown as is necessary to indicate the relationship of the recording apparatus to the machine itself. In this schematic showing of the machine, the work 12 is driven by a motor 14 associated with the head-stock ofthe lathe, the power to the motor being handled by the usual relay, not shown, contained in housing 16. In the absence of the recording apparatus of the invention, the motor relay is under the control of start and stop buttons mounted in box 18 in a location convenient to the machine operator.

The recording apparatus is preferably arranged in two units. One unit, containing the pushbuttons for the control of the recording apparatus, is mounted on the machine. In the illustrative embodiment, the pushbutton panel 20, shown on a somewhat enlarged scale relative to the machine itself for purposes of clarity, is mounted on the head-stock. The recording unit 22, which comprises the record-receiving web with its feeding and recording mechanism, may be mounted wherever convenient in the vicinity of the machine, or even at some remote point if desired. A cable 23 connects the recorder unit to the control panel, and a connection is made by cable 24 to the control circuit for the motor relay in housing 16. q

The control panel 20 is provided with a number of pushbuttons adapted to be marked with legends designating specific causes for interruption in machine production, the buttons when actuated being arranged to produce on the record-receiving web of the recorder unit 22 appropriate marks identifying the particular cause designated by that button. Actuation of the buttons likewise provides control of the operation of the machine,

not only to simplify the operation of the recording equipment but also to insure that the operator will utilize the recorder.

The recording unit 22 includes driving means for advancing the web at a timed rate of advance, the driving mechanism being illustrated in schematic fashion in Fig. 3; As shown in this figure, the web of margina1ly-per forated paper is drawn from its supply roll 26 over the recording head .28, to be described, the web take-up is at roll 32 which is driven by a slippahle belt 34 sprocket shaft 36 In the illustrative emhodirn ,a,tvsgo'- speed driveis'provided through "the useiof 'tw synchronous-type drive motors'38'and'4ill" These motors any be 6f "standard type employing built-in o'verrnnnihg clutch mechanism in the geart'rains sothat wheriiojne motor' i'sf energized to drive the web, the other is "automatical disengaged; Thus, when theweb is to be ad: vancedat 's'lo'w'speed, the motor 40 is energized, while during periods when intervals are to be tinted greater accuracy; the motor :zanneenemaea and motor "38 activatedto'advance the web at tne'faster'ofthe two; speeds. I

"Themarking' of theweb with appropriate data is arranged to be' carr'ied butelect'ricallyj by 'rn'a'rkingi meians moiinted in thereco'rding head28 illustrated in Figs. 4, and 6. Thepaper employed in the web islofa type sensitive to heat, the paper having been treated seas V .to' 'turn dark or black in the immediate vicinity 'of-the region where heat is applied. To mark the paper with appropriate data; there'cording head is providedwith a plurality of heating elements in the form of resista nce unitsha'ving sections 50 exposed in alignedfashion across the'ridge' portion '52 at theapeir of the head. i

The heating elements are madeof thin wires or rib bons 'of metal of composition eustomarily' employed for resistance "and heating'iunits operating at high teni perature To secure the resistance elements in placeand' "to 'make eneenve' electricalcontact without soldering or welding, the resistance elements are bent into'the form of -'U-shaped members, the legs of the U- being inserted' in holes Iformedin the-material of the head, which material isof suitable insulating nature; The resi'stanceielements are secured-in place by means of lockingmembe'rs 54 having a portion of theirleng ths c'rimpedas indicated at 56 so that when the smooth end of the connectors is inse'rted at the top of the head and drawn down into the passages in the space between the legs "ofadjac'ent heating' elements, the crimped portions 56' bear 'against the heating. elements and provideQg'o'od electrical contact while at the sameltime mechanically lockingthe heating elements in place. The portions 54 ofthe connectors expose below the head, serveas taps for connection to the source of electricity by which one or more of the heaters may be energized to markonthe moving web lines whose width transversely of "the web isfdetermined by the number of heating units ener gized at that moment. v v i Y The energization of the heating elements under the control of the pushbuttons, and the interrelation-ofthe. machine and the recording apparatus, are accomplished by means of the circuiearrangement shown in Fig} '2;- In'this-diag'ram, the cause-recording pushbuttons are indi catd at 60 .and for purposes of explanation the different buttons are designated by the letters A; B, C, D and E;

representing particular causes apt to be encountered by the machine with which the equipment is associated. The main heating unit of therecorder head is indicated by the resistance sections 50, the different sectionsxbeing connec'tedto their respective]pushbuttonsa so :that the number -of sections energized depends on which button, is, actuated by the operator. The various sectionsof the.

heater strip-are .norr'nallyde-energized while. thelpaper web is drawn over the recordinghead.

To insure'that the; heating units will be properly ener; gizedwhen a mark is. tobe placed onthe wehnmeans, are'provided by; which the heating and therefOre,. the:in-; tensity of the mark on the paper mayber'nadewholly; independent of themanner in, which the operato actur.

. a '4- to one or more of the heater sections, depending on whichpushbutton is'pressed, so as to provide practically instantaneous marking of the web and thereby leave a clean mark even though the web may. be advancing at a relatively rapid'rate. Furthermore, such automatic control of the heaters insuresthat the heaters may not inadvertently becomeburned out through holding the heating current. on an unnecessarily long time, as might be the case if the pushbuttons were in direct control of the application ofheating cnrrent to, the resistance elements. At thesarne time that the pushbuttons are actuated to Inark'the' record web and thereby identify the. nature. of the interruption, the machine is automati- 'c'ally restarted, this coordination of machine restart :and cause recording being in accordance with the teachings of my prior Patent No. 2,591,124 above referred to.

To time the pulse applied to the heaters when a pushbntton is actuated a relay .64 having one set of contacts 66 Y} n 'series with the AJC; supply to the heater unit is prov as shown inflFi'gi 2'. The solenoid- 6301; the relay is lllgewiseconnectediso that a portion of: the-current to the heater goes through the solenoid winding to energiz e the relay and"open contactsfiti; thereby inter rupting the supply OfClJl'Ifent llOjlhQ.h62ttf$ 50. The actuation of th'e' relay 64 is delayed a predetermined. amount Off time after; a pushbuttonis, pressed, by the plrovision of a condenser 70. connected across, therelay solenoid 68. A rectifier 72;an dfixedand variable resistors JAand 7 6 are likewise included in the delay circuit to control thechargingg'time of*the condenser andfltherefore the time when'the"rel;ay operates to open contacts lndescribing the operationoi the delaycircuit, assume that pnshbutton' C' is pressed; by the operator to indicate a'particular causefor' an 'interrnption. Current flows through the clos'ed contact"oithrougha dropping resistor 78 to the heater unit in the recordinghead, the

first three sections of'the heater receivingthe current flow. At the same time current fiow's-fintoihe condenser 70-,to build up a: charge. thereon, the rectifier 72*serving to convert the alternating current to direct current so as to charge the condenser with unidirectional cur-j of a second, so as to mark the paperalrnost instantaneously uponactuatipnof thepushbuttone; Thecontrol of the.heating current by I the time delay'bircuitj is sufli ciently precise. so that a relatively heavy heatingcurrent maybe'p-assed through the resistance wire of the records h i ub an allx ce s. of W a t e i c l carry without burning-out, if ,the,jcurrent wereflto be maintainedmore than thejbrief interval ofthe timed 1 p s ecau e. te... mingc r nit; the. h atin rent is .notefiected. hy-the length oftirne. thehoperator. holds the .pushbutton..down; once. the.. button has been pressed and theflsolenoid, actuated,l the,-solenoid remains energized; with contacts. 66..,held. open Upomrelease of thepushhntton, then heater circuit is broken,.the;.con-

ates the pushbutton. To this end, the pushbuttonsn-ae arranged to control. a circuit by which a pulse of cur.-

denserjt) dischargesithrough the solenoid fisandlcon- In t ll s rative e bo imen t e e .-i .c.1 a -:Pa ena ts, Hermann-g w whi h re p d t b l onns ssli Aha-s art; r u e thamas h e .p sw t rt.- buttqn ig nta e u e nt S t in raal;mot r:c n ro led-circu ts- Asjya u tnthe nonnalrs rt-z bu ton sabled t mi one a iq en e het ae a r iisirfleaen .v 7:... f Qne.=0

another ofitlie cause recording buttons in order to restart the machine following a stoppage.

To provide further information concerning'the operation of the machine being monitored, means are provided for indicating when the machine is operating normally and the duration of the periods when the operation is interrupted. Such indications are provided by supplementary marking heaters mounted at each end of the cause recording heater sections. One heater unit, indicated at 82 is energized whenever the machine is operating normally, while the other heater 84 is energized dur ing idleness periods of the machine.

The energization of one or the other of these marking heaters, as well as the control of the two-speed drive for the web advance, is under the control of a relay 90, the solenoid of which is connected in parallel with the machine motor circuit so that the relay is energized whenever the machine motor is in operation and de-energized when the machine stops. One set of double pole contacts of the relay serves to select the drive motor for the web, the lower speed drive motor 40 being energized during normal operation of the machine while the higher speed drive 38 is energized during idleness periads in order that the delay time may be more accurately computed from the web record.

The other set of contacts of the relay 90 is arranged to cause current to be applied either to the idleness marking unit 84 or the operate unit 82 depending on the machine status. Since one or the other of these heating units may be energized for appreciable periods of time,

the current must not exceed that within the capability of Y the resistance wire to handle continuously. Accordingly, the power supply for these two heaters is provided by a step-down transformer 96 with a suitable value of series resistance 98 to provide the right amount of heat for legible marking of the heat sensitive paper.

The data-recording means, as actuated by the interconnected restart circuit for the machine, serves to record the usual types of interruptions and their causes and duration, the push buttons bearing legendsv appropriate to the types of delays encountered by the particular machine with which the equipment is associated. Thus, whatever be the reason for stopping the machine, the record immediately begins to designate idle time, and continues to do so until the machine is restarted upon pushing a cause recording button to designate the reason for that particular interruption.

There may, however, be times when the operator prefers to cease operation for a period without the necessity for designating a reason upon resuming operation, or without indicating that there has been a break in this operation. This requires that he must be able to restart the machine without recourse to the combined causerecording and restart pushbutton switches. The ability to do this, without affecting the utilization of the apparatus to record delays and interruptions to which attention should be directed, and particularly those for which management may be responsible, is helpful in taking the apparatus out of the watchdog or constant surveillance category that is apt to be resented by the operators.

To permit this mode of operation when the operator deems it desirable, the apparatus is provided with special control means. This control, termed the Time Out control, is provided by supplemental push buttons 102, 104, the button 102 bearing the designation Time Out, while the button 104 is the Restart control for terminating a time-out period. These special control buttons are provided with a mechanical interlock, such interlock being shown schematically in Fig. 2 and a particular embodiment, for purposes of illustration only, being shown in detailed view Fig. 7.

The function of the Time-Out button is to permit the machine to be stopped without energizing the idle-marking heater element 84 to show idle time. Accordingly, the time-out switch is provided with contacts which, when the i 6 Time-Out button is pressed by the operator after stopping the machineby the regular Stop button at control box 18, take over the function of relay to maintain marking current through the operate marker coil 82 just as if the machine were continuing in normal operation. Once the Time-Out button has been pressed for this purpose,

the switch remains closed so long as the operator elects to continue this unaccounted-for time out period. At

the end of such period, to restartthe machine he pushes the Restart button associated with the Time-Out switch, thereby energizing solenoid 64 in control of the machine start circuit. At the same time, the Time-Out button is released by the mechanical interlock to permit that switch -to return to its normal position in which its upper set are bridged by washer 106 when the push button is in inactive or raised position, and having three contact that are bridged by washer 108 when the push button is depressed. The washers are carried by the switch actuator 110 which is mounted in insulating support 112. The Start switch is similarly mounted, but employs only the single set of contacts engaged by washer 114 when the button 104 is depressed by the operator.

To provide the requisite interlock above referred to, the actuator 110 of the Time-Out switch is provided with a circumferential recess or slot 118, while the actuator of the restart switch is provided with a recess shaped to define a sloping cam surface 122. Intermediate the two actuators 110 and 120 the body of the support 112 is recessed to receive an interlock member 124 pivotally mounted on screw 126. A torsion spring 128 is arranged to urge the interlock member against the actuator 110.

By this arrangement, when the Time-Out push button 102 is depressed by the operator at the commencement of an inoperative period that is not to be accounted for, the circuit included by the upper set of contacts is opened and the lower set of contacts is closed. As the switch reaches its lowermost poistion, the interlock member is I caused under the urging of the torsion spring to enter the slot 118, thereby preventing the switch from releasing. At the same time, the other end of the interlock member rotates into the recess in the Restart switch actuator 120. The interlock member holds the Time-Out switch in its down position throughout the time the operator is inactive, with the circuits represented by the lower set of contacts serving to maintain the operate marking coil energized and the timer drive motor 40 running, just as if the machine were in normal operation.

Upon the expiration of the operators voluntary time out period, the machine is restored to operation by pressing the restart button 104. Unlike the other push buttons of the apparatus, actuation of the button 104 does not place on the record medium any information concerning the period of no production. Instead, the switch 104, when pressed, serves to release the interlock member from locking engagement with the slot 118 in the Time Out actuator 110. Also, the contacts of the restart switch are closed momentarily, thereby serving to thel'ess it will be recognized'that use of the Time-Out mechanism cannot'be carriedto'an extreme, without being 'r'eflected in the operators-production record. As a result, the Time-Out mechanism will in the majority of cases be used relatively sparingly, with the'Cause- Recording mechanism primarily relied uponto indicate the various types (if-interruptions which the particular machine encounters during the Working period.

While the above-described embodiment, incorporating the Time-Out feature, provides a highly flexible-system wensuited to most inthistrial applications, nevertheless there may be types of operations where -th'esame general principles of cause recording may be u-tilized in-a slightly difierent manner. Such an embodiment is illustrated in Fig. '8. In this embodiment, the push-button "actuation of the cause recording mechanism is employed, with electrical pulses automatically generated to produce substantially instantaneous marking of the record-receiving web. 7

As distinguished from the prior embodiment, both the start and stop buttons of the main motor-control circuit are retained for controlling the operation of the machine. These switches, indicated at 140 and 142, control a relay 144 having the usual holding contacts in addition to the main contacts in the motor circuit. In this'embodiment, the relay 150 which controls the application of the pulse of marking currrent to the coils 152 is provided with an additional set of contacts that are normally closed when the relay solenoid is deenergized. These additional contacts are connected in series With'the circuitthrough motor stop switch 142 so that actuation of stopswitch 142 or the energization of the relay 150 will break the holding circuit for relay 144 and stop the machine.

The marking circuit for indicating particular causes for interruption 'ofmachine operation comprises the series-connected heater units 152 similar to those "already described, with push button switches 154. When a push button is depressed, current is supplied to the coil or coils included by the selected switch, the current flowing through resistor 156 via the upper set of contactsof relay 150. Upon the charging of solenoid-shuntingcondenser 158 by the rectified current through resistors 160 and 162 and rectifier 164,'the relay 150 is energized to open the contacts and terminate the pulse of marking current, all 'as previously described.

In this embodiment, however, the actuation of a push button switch to indicate the reason for a delay serves to stop the machine.

Accordingly, if an operator is to designate an interruption and the cause therefor, it must be done at the commencement of the period of interruption, if the full extent of the delay is to appear on the record. Otherwise, the record will continue to indicate normal operation of the machine, a situation which may not find support in the overall production record.

To bring about thismode of operation, the apparatus embodies a relay 170 the solenoid of which is connected in parallel with the solenoid of motor control relay 144 so as 'to be energized during operation of the machine.

'This relay forms a portion of the control circuit for relay 174 by which the energization of the idle and operate marking heaters 176 and 178, respectively, is determined. The heaters 176, 178 are supplied from astep-down transformer 180 through resistor 182, with the upper set of contacts of relay 174 arranged to energize the .idle

marker 176 when the relay is deenergized, and to supply current to the operate coil 178 when the'relay solenoid is energized.

As has been indicated, the operation of this form of production analysis apparatus is arranged so that the operator may designate the cause of an interruption at 'the commencementof a delay period. Assuming that the machine has been in normal operation, with relays 144 and 1'70 energized, the operate coil 178 will be supplied. with current to provide a-continuous operate? mark on the web as it is advancedby' drive motor 182.

Theoper'ator, in fact, may start and stop 'themachine at wilL'utilizing the start and stop switches 140, 142 inthe u'sual manne'r, without affecting the indication of snormal operation and without requiring the utilization of acauserecording push button;

.llf,'iho wever,,there occurs an interruption or stoppage be- I 'yon'd that normally encountered, the operator will advantageously have recourse to. one. of the push button switches 154, in order that the cause of the stoppagemay be set forth on thev record :for the benefit oftheman- :a'gement. If the'machine has already stopped, the actu- "ation of a cause=recording button will serve to place .a mark indicative of the particular nature ofthe delay, .as well as to indicate the time of commencement of the delay period. At the same time-the relay .174 is energized by the brief closing of relay 150 to transfer from the operate to-the idle marking coilsof'the continu- 'ousmarginal marking means. Relay 174 remains energized throughout the idle period by reason of the holdiin'g circuit provided by relay 170 in its deenergized condition.

Upon the termination of the period of interruption, the operator restarts the machine by actuating start button 140, which closes the motor circuit and relay. holding circuit, and at the same time actuates relay 170 to deenergizev relay .174 and transfer the steady marking current from idle coil 176 to operate coil 178, thus: indicating the'endof the idle period.

It will be observed that the operator may, if desired, utilize a cause recording button to stop the machine at the'beginning of a delay period, while at the same time indicating the particular reason for the delay. Thus, if the forthcoming delay is to be attributed to lackof. materials, the operator may, upon the completion of the final operation, select and actuate the button marked with a legend or designation indicative of that reason.

Such actuation will energize briefly the marking relay 150, thereby breaking the holding circuit for the main motor relay 144 and stopping the machine simultaneously withthe indication on the recording web of the. com- "rnencement of a delay period attributable to that cause.

From the foregoing description, it is apparent that what has been provided is a novel form of recording apparatus wherein the operator of a machine is enabled readily to indicate the nature and causes of interruptions and delays in machine operatiomso that, in particular,

is under rigid and critical supervision as to his own actions and performance.

a It will be evident that "the embodiments herein described represent'specific but by no means exclusiveforms of the invention, and the invention is to be understood as comprehending other forms and arrangementswithin the scope of the appended claims. a

I claim:

1. Recording apparatus for thermal recording on-he'a'tsensitive paper comprising a recording head, means for advancing a web of said paper over the head, electrically conductive heater elements disposed in said head for continuous contact with the web of paper, and means for supplyingfpulses of current to selected heater elements comprising switching means selectable by the operator to energize, Selectedheater elements, and a circuit for cont-rolling the duration of application or heating eurrent to said selected heater elements, said circuit comprising a relay having normally closed contacts, a circuit including said contacts for supplying current to the switching means and heater elements, and a second circuit connected to the switching circuit for energizing the relay solenoid a predetermined time interval after the actuation of the switching means by the operator, to terminate the interval of application of heating current to the selected marking elements.

2. Recording apparatus for thermal recording on heatsensitive paper comprising a recording head, means for advancing a web of said paper over the head, electrically conductive heater elements disposed in said head for continuous contact with the web of paper, and means for supplying pulses of current to selected heater elements comprising switching means selectable by the operator to energize selected heater elements, and a circuit for controlling the duration of application of heating current to said selected heater elements, said circuit comprising a relay having normally closed contacts, a circuit including said contacts for supplying current to the switching means and heater elements, and a second circuit in parallel with circuit including the relay contacts, said second circuit including the relay solenoid and a capacitor in shunt therewith to delay the energization of the relay solenoid, upon actuation of the switching means, until the capacitor becomes charged, thereby to time the duration of the pulse of heating current applied to the heating elements.

3. Recording apparatus for thermal recording on heatsensitive paper comprising a recording head, means for advancing a web of said paper over the head, electrically conductive heater elements disposed in said head for continuous con-tact with the web of paper, and means for supplying pulses of current to selected heater elements comprising switching means selectable by the operator to energize selected heater elements, and a circuit for controlling the duration of application of heating current to said selected heater elements, said circuit comprising a relay having normally closed contacts, a circuit including said contacts for supplying current to the Switching means and heater elements, and a second circuit connected to the switching circuit and energized upon actuation of the switching means, said second circuit including the relay solenoid, a capacitor in shunt therewith to bypass, until the capacitor becomes charged, current applied to said second circuit upon actuation of the switching means, a rectifier for supplying unidirectional current to the solenoid and shunting capacitor, and an adjustable resistor for controlling the charging cur rent to the capacitor to vary the time interval between the actuation of the switching means by the operator and the opening of the relay contacts.

References Cited in the file of this patent UNITED STATES PATENTS 1,114,612 Hibbard Oct. 20, 1914 1,306,631 Rogers June 10, 1919 1,904,261 Bedford Apr. 18, 1933 2,644,738 Gardner July 7, 1953 2,647,033 Faus July 28, 1953

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