US1393404A - Safety device for electrically-operated systems - Google Patents

Description

W. S. SMITH. SAFETY DEVICE FOR ELECTRICALLY OPERATED SYSTEMS.

APPLICATION FILED AUG-3,1918.

Patented Oct. 11, 1921.

wit y have? UNITED STATESP'AT'ENT OFFICE.-

WILLIAM S. SMITH, OF CAMBRIDGE, MASSACHUSETTS.

SAFETY DEVICE FOR ELEcTnIcArLY-ornRATEn SYSTEMS.

Application filed August 3, 1918. Serial No.

To all whom it may concern.

' Be it known that LWILLIAM S. SMITH, a citizen of the United States, residing at Cambridge, in the county of Middlesex and State of Massachusetts, have invented a new and useful Improvement in Safety Devices for Electrically-Operated Systems, of which the following is a specification, reference be ing had therein to the accompanying drawm s; a

My invention relates to electrically operated systems in which a motor is utilized as the source of .power and more specifically to a safety'device for such systems.

\Vhere an electrical system comprising a motor is'used for driving machinery of various kinds including elevators, manually operated means are provided for controlling the operation of the motor. These means are of various types, such as a lever or a wheel, and sometimes, in the case of elevators, a rope, is utilized for this purpose. In the operation of these systems, a failure of currentfrom one cause or another is apt to be a frequent occurrence and at suchtimes, if the manually operated control means is not returned to a neutral position, a sudden reestablishment of the current will start the machinery without warning. Such conditions areprolific in accidents because of the failure of the operator to return the control means toavneutral position when the current in the system stops. This liability to accident is especially true in the case of elevators because of the proximity of passengers ignorant of therisks.

The principal object of my invention is to provide a safety device for electrical systems having manually operated control means to the end that when there is a failure of current and the manually operated control means is out of neutral position, the system remains lnoperatlve even after the current has been reestablished, until the manually operated control means has been first returned to a neutral position .Another object of the invention is to provide a safetyv device which is simple and positive in operation and of low cost of installation and maintenance.

Other objects of the invention will be more specifically set forth and described hereinafter.

Briefly statedmy invention contemplates the provision of means in the electrical sys- Specification of Letters Patent.

Patented Oct. 11, 1921. 248,176.

tem whereby'when there is a failure of current and the control means are out of neutral position, the system remains inoperative, even after the current is reestablished, until the manually operated control means are first returned to a neutral position from which it can be moved by the operator in the usual manner. Preferably, I accomplish these objects by placing in the motor circuit or, some other circuit necessary to the operation of the motor, a switch which is normally open. The. motor, therefore, cannot be started until this switch is closed. Means is provided for operating said switch electricallyto close the motor circuit and after being operated the means remain operable so long as current is furnished to the system.

In the accompanying drawings showing my invention applied to'an electrical system for operating elevators, Figure 1 is a diagrammatic view of a safety device constructed and operated in accordance therewith; Fig. 2 is a diagrammatic view of a modified form wherein a less amount of current is used inmaintain'ing the switch in the motor circuit in a closed position and Fig. 3 is a diagrammatic view of another modification. 1

In the drawings the arrangement of elements and circuits is shown as adapted for a direct current but my invention is capable of use" with an alternating current by making certain necessary modifications in the circuits, all of which would be apparent to one. versed in the art.

I have shown in elements and circuits of an electrical system which are necessary for a proper understanding of my invention. Passing to a description'of the electrical system, 5 and 6 indicate the positive and negative supply the drawings only those shown as a compound motor, having a shunt field coil 8 connected by a conductor 9 to supply lines 5 and 6. The motor circuit for operating the motor is shown in heavy lines as comprising conductors 10, 1 1, 12 and 13. In the motor circuit is included a series field coil 15 and a starting resistance coil 16. The former is generally used on this class of apparatus although not absolutely required and the latter is intended to prevent a too rapid rush of current when the motor is starting. Suitable means are provided for CII cutting out this resistance as the motor accelerates in speed; these means, however, not being shown because not essential to my invention.

For controlling the motor, that is, for starting, stopping and reversing the motor, a manually operated switch or control means is shown generally at 20 as being developed from the well known drum type. The drum carries a series of contacts adapted when revolved to engage or disengage certain fixed contacts on the various conductors and thereby close or break. the motor circuit. For rotating the drum various manually operated means are provided such as a lever,

a wheel or a rope.

Upon the periphery of the drum 20 are arranged two pairs of contacts, 22 and 23 and 24 and 25, the two former being electrically connected by a conductor 26 and the two latter by a conductor 27. These contacts are extended in order to engage the fixed contacts for a considerable arc of rotation of the drum. Fixed in position to be engaged by the drum contacts are six contacts as follows, 30 on conductor 11, 31 on conductor 12, 32 and 33 on conductor 10, and 34 and 35 on conductor 13. v The operation of the control 20 is as follows. When the drum is rotated from right to left, referring to the drawings, the contacts 22 and 23 on the drum move into engagement with the fixed contacts 30 and 34 and the contacts 24 and 25 on the drum engage the fixed contacts 31 and 33. The motor circuit is then closed and current flows from the positive supply line v5 through conductor 13, contact 34, contact 23, conductor 26, contacts 22 and 30, conductor 11, armature 7, conductor 12, contacts 31 and 24, conductor 27, contacts 25 and 33, conductor 10 to the negative side of the line. If, however, the drum be rotated in the opposite direction, that is, from left to right, then the contacts 22 23, 24 and 25 onthe drum engage the fixed contacts 31, 35,30 and 32 respectively and the circuit is closed and the .current passes through the armature in the opposite direction causing it to be reversed to its former direction. In this case, the current flows from the positive supply line 5, through conductor 13, contacts 35 and 23, conductor 26, contacts 22 and 31, conductor :2, armature 7, conductor 11, contacts 30 and 2t, conductor 27, contacts 25 and 32, con ductor 1.0 to the negative supply line 6.

T he foregoing construction and mode of operation is all old and well known in the art. As hereinbefore stated, myv invention consists in providing means in such a system for keeping the motor circuit open when there has been a failure of current and the control means have been left out of neutral position so that after the reestablishment of the current, the control means must be reafter a failure of current followed by a reestablishment of the current while the control means is out of a neutral and is in an operative position, the electrical system remains inoperative until the manually operated control means has been returned to a neutral position by the operator.

In Fig. 1 of the drawings, I have shown the preferred form of means for operating the switch 40 as above stated. A magnet 42 is provided for operating the switch 40 to engage contacts 41, 41 to close the motor circuit, the magnet being energized by a circuit across the line established whenever the control means are operated in either direction from neutral. For this purpose the drum of the control 20 is provided on its periphery with .an extended contact 43 electrically connected with the contacts 22 and 23 by the conductor 26 and the contact 43 cooperates with fixed contacts 44 and 45 which are in the circuit for energizing the magnet 42. hen the control 20 is operated in either direction, a circuit is established from the positive wire 5 through the conductor 13, and through either contact 34 or 35, contact 23, through conductor 26 through contact 43 and then through either contact 100 44 or 45, conductor 48 around the magnet 42, energizing the same, and then to the negative main 6. In this circuit is placed a switch 50 which is normally held open by gravity, and before this circuit can be closed to ener- 105 gize the magnet 42 the switch 50 must be closed against contacts 51, 51. To this end I provide .a magnet 52 which is energized by a circuit across the line so that the switch 50, after having been operated, remains 110 closed so long as current is continuously supplied to the system. This circuit is made up of the conductor 54 running from the positive main. and serving to energize the magnet 52 and the conductor 48 to the negative main. A resistance 55 is included in this circuit and the magnet 52 with all the resistance in is of sufficient strength to hold the switch 50 in closed position after it has been operated but is not of sufficient strength 120 to operate the switch. To accomplish this latter result a portion. of the resistance 55 is short cricuited by a conductor 56 running from a fixed contact 57 to. the resistance.

the controller 20 is in a neutral position. A portion of the resistance is therefore cut out when the control is in neutral position, with the result that the magnet 52 is strengthened sufficiently to operate the switch to close the operating circuit for the motor circuit switch 40. I

In the latter circuit may be placed door contacts 60 if the system isused for operating elevators or other elements, depend ing upon the purpose for which the system is used, which elements should be in a certain specified position before the system is operative.

The operation of the device is simple. So long as the manually operated control means is in a neutral position, the switch 50 is closed provided elements are closed. If the controller 20 then be moved in one direction or the other, theshort circuit removed but the circuit 54 with all the resistance in is still sufliciently strong to hold the switch 50 'in a closed position. The movement of the control first causes the con-. tacts on the drum to engage the fixed con tacts in the motor circuit and then establishes the circuit for energizing the magnet 42 which operates the switch 40 to close the motor circuit and admit current to the armature of the motor.

After the circuit through the line 54 has been closed to operate the switch 50, the movement ofthe control 20 has no effect upon it so long as the door contacts or simi lar elements are ,in their proper position for the operation of the system. The circuit for energizingthe magnet 42 to close the switch 40 in the motor circuit is made and broken by the movement of the controller 20. To prevent arcing in the controller, the 0011- tacts 44 and 45 are so arranged that the movement of the controller closes the circuit to operate the switch 40 just after the motor circuit is closed by it.

If for any reasonthere is a failure of current in the system, through a short circuit or otherwise, the switches 40 and are returned to an open position by the force of gravity. If the control means happens to be out of neutral position when this occurs and remains so when the current in'the system is reestablished, then the circuit through the wire 54 and wire 48 is weakened because the contact 58 on the, drum is with the contacts 57 and 59. Before the system can again be operated, the circuit through the line 54 and 48 must be strength- Y ened and this can be done only by returning the control means to'a neutral position in order to bring the contact 58 inengagement with the two contacts 57 and 59. With these provisions it becomes immaterialin what position the operator leaves the manually operated control means after the system has been rendered.inoperative'byfailure of current, because the system cannot again be the door contacts or other through the conductor56 is out of-engagement 70 is droppedwith the stem made operative until the control means are first returned to a neutral position.

In Fig. 2 there is shown a modified form of my invention designed to save current. In this form of the invention, instead of having the short circuit established by the contact 58 on the drum engaging the fixed contacts 57 and 59 for the purpose of operating the magnet 52, whereby the short circuit is cut out by the operation of the magnet itself so that the strength of current sufiicient to operate the magnet flowing through that circuit is of short duration. In the form of the inven tion shown in Fig. 1 the strength of the current .suflicient to operate the magnet 50 remains constant so long as the control means are held in a neutral position. To accomplish the cutting out of the short circuit by the operation of the switch 50, I pro-' vide a contact-piece 72 loosely mounted on the stem of the switch, adapted to engage two contacts 73 and 74 for the purpose of closing a circuit when the switch 50 is in an open position,through the following conductors The current flows from the positive main through conductor 80, resistance coil 81, around the magnet 52, contacts 74, 72, 73, conductor 82, contacts 57, 58, 59, conductor 83, conductor 48 tothe'negative side -ofthe line. This short circuits the resistance 78 in. conductor 7 and operates the magnet52 closing the switch 50. As soon as the switch 50 is closed, the contact 58 on the drum and fixed contacts 57 and 59 are cut out and a circuit is established acrossthe line through conductor 80, resistance coil81, magnetv 52 to contact 74, conductor 77, resistance coil 78 and conductor 48. This throws an added resistance 78.1mm the circuit, thereby reducing the amount of current flowing therethrough the two resistances 81 and 7 8, reducing the current just sufiiciently to hold the magnet in operative position and not being strong enough to operate it. j "The sum of the two resistances 81 and 78 is approximately the same as resistance in Fig. 1. In the operation of the switch 50 it is necessary that it he closed before the contact-piece 72 is separated from contacts 73 and 74 and any suit able means may be provided for this purpose. One form is shown. as consisting of a collar 'secured'to the stem of the switch .and a spring 71 underneath the switch 50' to push it upwardly against contacts 51, 51. When the switch is in an open position the collar and pushes the switch downwardly. to an open position. In the operation of clos'ng the switch, the stem is moved upwardly d the spring 71 there upon (closes the switch 50. The further movement of the collar then forces the contact 72 upwardly and away from the contacts 73'and 74 thereby cutting out the short manually operated circuit. The operation of the modified form oi apparatus, other than has just been described, is the same as in Fig. 1, the only difference in result being that the arrangement in Fig. 2 economizes in the amount of current employed for retaining the switch 5() in an operative position.

In Fig. 3 is shown another arrangement of circuits for accomplishing the same result in which a portion of the coil on the magnet is cut out after the magnet has been operated. in this arrangement a circuit is established across the line for energizing the magnet for maerating the switch 50, said circuit being at its full strength whenever the controlling means are in a neutral position. I then provide a contact in the drum cooperating with the fixed contacts so that when the controlling means are moved out of position a portion of the coil on the magnet which operates the switch 50. is short circuited, leaving the remaining portion of the coil of sufficient strength only to hold the magnet in operative position. It thereafter there is a failure of current in the system, the magnet 50 will drop by force of gravity to an open position, and if the control means is out of neutral position, that portion of the coil on the magnet 52 which is necessary to.operate it. is short circuited and is not thrown into the circuit to operate the magnet 50 until the control means are returned to a neutral position. The circuit across the line above referred to is through the conductor 90, around the magnet 52, through conductor 48 to the negative side of the system. So long as current is supplied to the system this circuit is in operation and is sufficient to operate the switch 50 to close it, provided the controlling means are in a neutral position. As soon as the control means is moved either tothe right or left out of a neutral position, a contact 43 on the drum engages contacts 93 and. 44 or contacts 95 and 45 and. thereby establishes two circuit-s, one ofwhich is the circuit just above described with a part of the actuating coil on the magnet 52 cut out, and the other is the actuating circuit for the magnet 42. The latter of these circuits runs from the positive line through conductor 13, contact 34 or 35, contact 23, conductor 26, contact 43. contact 44 or 45, conductor 48 through switch 50 to the negative side of the line. The other circuit is established through conductor 13, contact 34 or 35, contact 23, conductor 26, contact 43, contact 93 or 95, conductor 96 through a part of the actuating coil 52 to conductor 48. On account of the high resistance of the entire coil on the magnet 52 no current flows through the conductor after the contact 43 has engagedwith the fixed contact 93 or 95 through the movement of the control means out of neutral position. This movement practically short circuits a part of the operated coil tor magnet 50 and operates the switch 40 at the same time.- If there is a failure of current in this instance and the current is reestablished while the ,control means are out of neutral position, the amount of current flowing through the actuating coil on the magnet 5.2v through conductor 96 is not sullieient to operate it and therefore the system remains inoperative until the controlmeans are thrown back to neutral position and the entire actuating coil 52 is thrown into the circuit. The plan illustrated in Fig. 3 of the drawings requires a greater amount of current than the arrangement of Fig. 2 but requires practically the same amount of current as the arrangement in Fig. 1. It is, however, somewhat simpler than the plan of Fig. 1. The contacts 58, 57 and 59 of Fig. 1 are eliminated in Fig. 3 and the contact 43 is enlarged.

it will be observed that my safety device, as herein described, is extremely simple both in construction and mode of operation and yet is absolutely positive. Although it is designed for general use in electrical systems its value is more apparent in the use of electrical systems for operating elevators because the lack of a safety device is more productive of accidents in such vsystems than in those which are used for manufacturing purposes. The simplicity of my device permits it to be installed at a very low cost and the expense of maintenance adds no appreciable amount to the ordinary cost of maintaining an electrical system.

It is to be understood that my invention is not to be limited to the embodiments herein shown and described since it is susceptible of use in other forms all within the purview of the invention.

\Vhatl claim is 1- 1. The combination with an electrical sys tem comprising a motor and manually operated means for controlling said motor, of a magnet operated switch for closing the mo torcircuit, said switch being normally open and means operated by said manually operated controlling means for operating said magnet operated switch to close the motor circuit, said means including a second normally open magnet operated switch in the operating circuit of the first mentioned magnet operated switch and being so arranged that whenever there is a failure of current. 1

in the system and said magnet operated switch has returned to an open position in consequence thereof, the manually operated means must first be returned to a neutral position before the said magnet operated switch can again be operated to close the motor circuit.

2. The combination with an electrical system comprising a motor and manually operated means for controlling said motor, of a switch in the motor circuit normally open,

means including a second normally open magnet operated switch in the operatingcircuit of the first mentioned magnet operated switch and for closing said switch to close the motor circuit, said means being operated by said controlling means and being so arranged that whenever there is a failure of current in the system and said switch has returned to open position the said means remains inoperative until the manually operated controlling means has been re turned to a neutral position.

3. The combination with an electrical system comprising a motor and manually operated means for controlling said motor, of a switch in the motor circuit, said switch being normally open, means for closing said switch to close the motorcircuit, said means including a second normally open magnet operated switch in the operating circuit of the first mentioned magnet operated switch and being operated by said controlling means and being so arranged that a failure of current in the system will require the return of the manually operated controlling means to a neutral position before the said closingmeans can again be made operative.

I at. The combination with an electrical system comprising a motor, a motor circuit and manually operated means for controlling said motor, of a switch in said motor circuit,

said switch being normally open, a ma'gnet for closing said switch to close the motor circuit, means for energizing saidmagnet, said means including asecond normally open magnet operated switch in the operating circuit ofthe first mentioned magnet operated switch and being controlled by said manually operated means and being so arranged that aftera failure ofcurrent said energizing means remains inoperative until said manually operatedmeans is returned to a neutral position. i i d 5. The combination with an electrical system comprising a motor, a motor circuit and manuall operated means for controlling said motor, of a switch in said motor circuit, said switch being normally open, a magnet when energized for closing said switch,

means independent of said electrical system for energizing said magnet, said means including a second normally open magnet operated switch in the operating circuit of the first mentioned magnet operated switch and being so arranged that after a failure of current, it. re1nains inoperative on the re establishment of the current until the manually operated means has first been returned to'a neutral position. i

6. The combination with an electrical system comprising a motor and manually operated means for controlling said motor, of a magnet operated switch fpr closing the motor circuit, said switch beingnormally open and electrical means operated by sai manually operated controlling means for operating said magnet operated switch to close the motor circuit, said means including a second normally open magnet operated switch in the operating circuit of the first mentioned magnet operated switch and being so arranged that whenever there is a failure of current in the system and said magnet operated switch has returned to an open position in consequence thereof, the manually operated means must first be returned to a neutral position before the said magnet operated switch can again be oper* ated to close the motor circuit;

7. The combination with an electrical system comprising a motor and manually operated means for controlling said motor, of a switch in the motor circuit normally open, electrical means for closing said switch to close the motor circuit, said means including a second normally open magnet operated switch in the operating circuitof the first mentioned magnet operated switch and being operated by said controlling means and being so arranged that whenever there is a failure of current in the system and said switchhas returned to open position the said means remain inoperative until the manually operated controlling means has been returnedto a neutral position.

'8. The combination with an electrical system comprising a motor and manually operated means for controlling said motor, of a switch in the motor circuit, said switch being normally open, electrical means for closing said switch to close the motor circuit, said means including a second normally open magnet operated switch in the operatingcircuit of the first mentioned magnet operated switch and being operated by said controlling means and being so arranged thata failure of current in the system will require the return of the manually operated controlling means to a neutral position before the said closingmeans can again be made operative.

9. The combination with an. electrical system comprising a motor, a motor circuit and manually operated means for controlling said motor, of a switch in said motor circuit, said switch'bei'ng normally open, a magnet for closing said switch toclose the motor circuit, a circuit for energizing said magnet to close said switch, a second magnet operated switch in said energizing circuit, said switch being normally open, and means for closing said and for holding it in closed position; said means being of suflicient strength to hold said second magnet operated switch in a closed position irrespective of the movement or position of the said manually operated controlling means so long as current is second magnet operated switch when the controlling means are in a neutral position.

10. The combination with an electrical system comprising a motor, a motor circuit and manually operated means for controlling said motor, of a switch in said motor circuit, said switch being normally open, a magnet for closing said switch to close the motor circuit, a circuit for energizing said magnet, a normally open switch in said energizing circuit, and means for operating said last mentioned switch to close said energizing circuit and to hold said switch closed so long as current is furnished to the system; said means being capable of operating said switch only when the manually operated controlling means is in a neutral position.

11. The combination with an electrical system comprising a motor, a motor circuit and manually operated means for controlling said motor, of a switch in said motor circuit, said switch being normally open, a magnet for closing said switch to close the motor circuit, a circuit for energizing said magnet, a normally open switch in said energizing circuit and electrical means for operating said last mentioned switch to close sa'id energizing circuit and to hold said switch closed so long as current is furnished to the system; said means being capable of operating said switch only when the manually operated controlling means is in a neutral position.

12. The combination with an electrical system comprising a motor, a motor circuit and manually operated means for controlling said motor, of a switch in said motor circuit, said switch being normally open, a magnet for closing said switch to close the motor circuit, a circuit for energizingsaid magnet to close said'switch, a magnet operated switch in said last mentioned circuit, said switch being normally open, a circuit for energizing said'magnet operated switch to close the same, said circuit being so arranged as to be closed only when the manually operated controlling means is in a neutral position and means whereby after said last mentioned circuit has been closed a resistance is thrown into said circuit whenever said manually operated controlling means is moved out of neutral position, said resistance being sufficient to reduce the current in said last mentioned circuit so that while sufficient to hold said magnet operated switch in a closed position, it is not suflicient to close said magnet operated switch if at any time it returns 'to' an open position while said manually operated control means is out of neutral position.

'13. The ';combination with an electrical system comprising a motor, a motor circuit and manually operated means for controlling said motor, of a normally open switch in said motor circuit, a magnet foroperating said switch, a circuit for energizing said magnet, a second normally open switch in said energizing circuit, a magnet for closlng said switch and an actuating circuit for energizing said magnet suiliciently to close said second switch when said manually operated controlling means is in a neutral position and to hold said magnet in a closed position but not to operate it when said controlling means is out of neutral position.

14. The combination with an electrical system comprising a motor, a motor circuit and manually operated means for controlling said motor, of a normally open switch in said motor circuit, a magnet for closing said switch, a circuit for energizing said magnet to close said switch, a normally open switch in said energizing circuit, a second magnet for closing said switch in said energizing circuit and means when said controlling. means is in a neutral position for closing said switch and when said controlling means is out of neutral position for holding said switch in a closed position so long as current is furnished to the system, but not to close it.

15. The combination with an electrical system comprising a motor, a motor circuit and manually operated means for controlling said motor, of electrical means for 010s ing said motor circuit and means for setting said electrical means in operation; said last mentioned means including a magnet-operated switch and means for energizing said magnet, said last mentioned means being so arranged that said magnet is of sufiicient strength to operate said switch only when said manually operated controlling means is in a neutral position and at all other times is of a strength sufiicient to hold said switch in an operated or closed position so long as current is furnished to the system but not to operate it.

' 16. The combination with an electrical system comprising a motor, a mortor circuit and manually operated means for controlling said motor, of a switch in the motor circuit normally open, a magnet r'or operating said switch, a circuit for energizing said magnet to close said switch, a second normally open switch in said energizingcircuit, a magnet for closing said switch and means for energizing said magnet sufficiently to close said switch when said manually controlling means are in neutral position, said energizing means being so arranged as to be of sufiicient strength to hold said'switch in a closed position, but not to operate it, when said manually controlled means is out of neutral position.

117. The combination with an electrical system comprising a motor, a motor circuit and manually operated means for controlling s aid circuit, of a normally open magnetsaid controlling means is moved out of a neutral position whereby, so long as said controlling means is out of neutral position the said last mentioned magnet is of sufficient strength to hold said switch closed, but not to operate it. i

In witness whereof, I hereunto set In hand this twenty-first day of June, 1918.

WILLIAM S. SMITH.

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