US2233647A - Preset speed operation of motors - Google Patents

Description

March 4, 1941. F. D. SNYDER PRESET SPEED OPERATION OF uowons Filed Dec. 7, 1938 2 Sheets-Sheet 1 INVENTOR Frederick D. Snyder. M5.

WITNESSES:

ATTORNEY March 4, 1941.

Filed Dec. 7, 1938 2 Sheets-Sheet 2 Fig. 2

Load 61 87 56 -60 stop 92k Start 74% 90 /55 Fast I O W!TNESSES INVENTOR WW FkedericA-D Snyder ATTORNEY Patented Mar. 4, 1941 UNITED STATES PATENT OFFICE PRESET' SPEED OPERATION OF MOTORS Pennsylvania Application December 7, 1938, Serial No. 244,403

9 Claims.

My invention relates to systems of control for electric motors, that is, more particularly to a control which affords preset speed operation for wound rotor alternating-current or direct-current motors.

An object of my invention is to provide for automatically bringing an alternating current wound rotor motor or a direct-current motor (with armature resistance) to a preset speed with standard push button control.

A further object of my invention is to provide a speed control system for a motor which is simple and inexpensive.

A still further object of my invention is to provide a speed control system for a motor which embodies protective features.

Other objects and advantages will become more readily apparent from the study of the following specification when considered in conjunction with the accompanying drawings, in which:

Figure 1 is a diagrammatic showing of my invention as applied to a direct-current motor; and

Fig. 2 is a diagrammatic showing of a modification of my invention as applied to an alternating-current wound rotor motor; and

Fig. 3 is a view of a portion of the device shown in Fig. 1 taken along line III--III of Fig. 1.

Referring to Fig. 1 of the drawings, i designates a direct current, reversible motor which is the source of power to operate a rheostat 2B.

This motor drives a standard gear reduction unit 2 and a sprocket 3 on the slow-speed shaft of the gear reduction unit, and through chain 4 and sprocket 5 drives a rheo'stat operating shaft 6, which is keyed thereto, together with a gear 1 which is also keyed to shaft 6. Gear meshes with a gear 8, the latter gear being loosely pivoted on a shaft l0 disposed on a speed selecting arm 9. Speed selecting arm 9 is loosely pivoted on rheostat operating shaft 6.

On arm 9 is yieldingly mounted a catch 20 which is adapted to engage any one of a plurality of notches on speed indicating rack II. A

a double-pole mercury switch I2 is rigidly mounted on gear 8, which has a neutral position and which closes one circuit when tilted to the-left, and closes another circuit when tilted to the right." A limit switch l3, which is normally closed by a spring i3, is disposed to be opened mechanically by an arm 22. The arm 22 is rigidly mounted on and insulated from the rheostat contact arm 23. The switch I3 is opened when the rheostat arm 23 is in the all resistance "in position and at the same time, limit switch l5,

which is normally open, is closed. A normally closed limit switch !4 is disposed to be opened mechanically by arm 22 when the resistance is in the all out position.

A relay actuating coil 41 when energized, opens contact members i6 and closes contact members H, and when deenergized allows contact members IE to close and contact members I! to open. A relay actuating coil 24 when energized closes cont-act members 25. The stop button or switch 43 is normally held closed by a spring 26 While the start button or switch 40 is normally held open by a spring 21. A direct-current motor 28, as for example, a series motor, and the speed of which it is desired to control, is coupied to drive any suitable load 29, as for ex ample, a spinning frame.

The operation of the control system is as follows. Assume the motor 28 is at rest but the incoming power lines or buses l8-i9 are energized. Since the start pushbutton 40 is not actuated, actuating coil 4! of relay 42 will not be energized and contact members i6 will thus be closed whereas contact members i7 will be open. An energizing circuit for the rheostat motor i will nevertheless be established. The circuit for motor i may be traced from bus 18 through conductor 35, motor l, conductor 38, contact members i6, conductor 3!), limit switch i3 and conductor 3| to bus H. The rotation of motor i will cause gear 1 to rot-ate in a counter-clockwise direction. Gear 8 will rotate in a clockwise direction, closing right-hand contact members 46 of mercury switch i2, but no current can flow through conductors 33 and 34 because of the open position of the normally open contact members i1. Motor i will continue to operate until limit switch !3 is opened, which is .the slow or all resistance in position of the rheostat.

Now assume that the start pushbutton 40 is actuated when the resistance is in the all in position. A circuit will be established from bus 48 through conductor 35, motor 28, conductor 36, rheostat arm 23, r-heostat 2|, actuating coils 4| and 24 of relays 42 and 44, stop switch 43, starting switch 40, conductor 45, limit switch 15, and conductor 3|, to the bus 19.

Operation of relay 44 causes the closing of contact members 25 to thus establish a holding circuit for both coils 24 and 41 for the relays 44 and 42, respectively. The starting switch, or pushbutton 40, may thus be released.

Operation of relay 42 causes the closing of contact members l1 and the opening of contact members l6. Opening of contact members It has no effect at this time because the circuit for motor I is already open at limit switch It. Closure of contact members II, however, since contact members ll of the switch I2 are closed, establishes a circuit for motor I for reverse operation. The motor circuit may be traced from bus I8 through conductor 85, motor I, conductor 33, contact members I, conductor 84, contact members II, conductor ll, limit switch I4 to bus ll. Motor I is now energised to rotate ear I in the clockwise direction, and gear 8 in the counter-clockwise direction, and will continue rotating the gears until the gear 8 is brought to a position so that mercury switch I2 is moved to its neutral position, as shown in the drawings.

Assume now that arm 5 is moved up or down to increase or decrease the" speed respectively. This will cause gear 8 to rotate around gear 1 and close the right or left contacts respectively, to operate motor I and gear 8 until mercury switch I2 is again in the neutral position, it being noted that conductor I8 is a lead-in for the windin: in motor I, which causes rotation in one direction, while conductor 32 is a lead-in to the winding in motor I, which causes rotation in a reverse direction.

Assume that the motor 28 is running at some given speed and it is desired to run it at a faster speed. Arm 8 is moved upwardly, thereby causing closure of the contact members 48 of the mercury switch and the following circuit will be established, from bus I8 through conductor 35, motor I, conductor 83, contact members 48, conductor 34, contact members l'l, conductor 31, limit switch It to the bus I. Motor I will rotate gear I in a clockwise direction and continue doing so until mercury switch is again moved to its neutral position, and while it is rotating in such clockwise direction, it also rotates'rheostat contact arm 23 in the clockwise direction, cutting out part of the resistance in the rheostat, thereby allowing faster operation of the direct-current motor 25, which is in circuit therewith. The clockwiserotation of gear I will also cause gear 8 to rotate counterclockwise, thereby tilting switch I2 to its neutral position at which position contact elements 46 thereof are opened thus interrupting the abovedescribed circuit through the motor winding thereby causing stoppage of the motor I. It will be apparent that the greater the degree of upward movement of speed selecting arm 9, the greater will be the angular movement of gear 8 in a clockwise direction, hence the greater will be the necessary angular movement of gear 6 in a counter-clockwise direction for restoring mercury switch I2 to its neutral position and the greater will be the clockwise movement of contact arm 23, the eiifect of which is to cut out more resistance and allow motor 28 to run faster.

Assume now that it is desired to decrease the speed. Speed selecting arm 9 is moved downwardly toward the slow position and in doing so causes gear 8 to rotate around gear I and cause mercury switch I2 to tilt to the left so as to close contact members 41. A circuit is thus completed from bus I8 through conductor 35, a different field winding of motor I than the one recited in the previous paragraph, conductor 38, contact members 41, conductor l8, switch I5, conductor II, to bus I. Thus the energization of the winding in motor I will cause motor I to rotate in a reverse direction from that recited in the previous paragraph, thereby causing gear I and contact arm 23 to move counter-clockwise, the effect of which will be to cut in more resistance in resistor 2| thus slowing down motor 22 and at the same time elfecting clockwise movement of gear 8. This operation will continue until gear 8 has moved suiiiciently in a clockwise direction so as to open contact.v members 41 of the mercury switch thereby interrupting the circuit through motor I thereby effecting stoppage thereof. If the motor is once stopped, it cannot be started again until the rheostat has reached the all resistance "in" position, because limit switch I5 will not close until then.

Fig. 2 shows schematically a modification of my invention as applied to a three-phase alternatingcurrent, wound rotor motor. The alternating current source is designated by power lines or buses 50, 5| and 52. The main line contact member I9 is provided with contact members 53, 5| and 55 which, when closed by the energization of an operating coil 58, energize an alternatingcurrent wound rotor motor 51, which motor drives a load 58, as, for example, a spinning frame. A primary coil 59 of a transformer is connected across one of the phases of the incoming alterhating-current source through buses 50 and 52, while the secondary 60 isconnected to a control circuit which will be hereinafter described. A reversible two-phase induction motor 6| drives a member 65 having three contact arms which vary the resistance of a resistor 86. The reversible motor BI has reversing windings 62 and 53 which are 90 apart and across which is connected a motor starting capacitor 54. The purpose of capacitor is to make the current and vo1tage relation of winding 62 different from the current and voltage relation of winding 63 so as to effect a rotating field and give a starting torque to motor BI in the nature of a split phase. Motor BI also drives a face plate interlock G1, which has slidable contact members 68 and 69 and a contact arm 10. Motor 5| also drives a gear II. It should be noted that while the motor drive to the various units above described is shown in Fig. 2, as being through worm gears II, 12 and I3, such showing is merely schematic and only for the purpose of simplifying the drawings. Actually, members 65, I0 and II are directly connected to a shaft which is driven by motor shaft I4 in a manner similar to that illustrated in Fig. 1. Numbers 6 to I2, inclusive, 2!! and 46 indicate the same control mechanism described in connection with Fig. 1 of the drawings, hence, further description thereof is deemed unnecessary.

A switch actuating arm I5 is insulated from and directly connected to one of the arms of member 65 and has a roller it which is adapted to engage a switch arm 11 to open contact members I8, said contact members being normally closed by a spring means. Operating coil 55, when energized, also closes contact members 19. Operating coil 80* when energized, opens contact members 8| and closes contact members 82, and when deenergized, permits closing of contact members 8| and opening of contact members 82. A stop" button or switch 83 is normally held closed by a spring, while 84 designates a "start button or switch which is normally held open by a spring.

The operation of the device is as follows.

Assume the motor 51 is at rest but the incoming power lines 50, 5I and 52 are energized. Power will be transmitted through the windings 59 and 60 of the transformer and a circuit in the sec ondary circuit will be as follows: from conductors 85 through conductor 86; motor 6| through its winding 62; conductor 81; contact members II conductor 88; contact member 68; contact arm 18; contact member 68; to conductor 88. From conductor 81 there will also be a parallel circuit through condenser 64 and winding 63. in order to cause a phase split in motor 6|.

Actuating coils 56 and 88 remain deenergized. Motor 6| will be now operated and will rotate gear I in a counter-clockwise direction. Gear 8 will operate in a clockwise direction, closing mercury switch contactmembers 46 but no current can flow therethrough because contact members 82 are open. Motor 6| will continue to operate until the contact arm 18 of the face plate interlock 61 moves from contact member 68 to contact member 81, which corresponds to the resistance all in position of the resistor 66.

Now assume the start button or switch 84 is pressed. The motor 51 will be started with all resistance in the secondary which effects slow speed operation of the motor. The circuit will be as follows: from conductor 85 through actuating coils 56 and 88; stop switch 83; start switch 84, contact members 91, 18 and 68 to condctors 96 and 88. The moment the actuating coils 56 and 88 are energized, contact members 19 and 82 will close; therefore, even though the start button is immediately released, the circuit will still be completed through contact members "l9 and 82 and conductors 88 and 88. Energization of actuating coil 56 will effect upward movement of its armature and closure of contact members 53, 54 and 55. Energization of actuating coil 88 will cause contact members 8| to open and contact members 82 to close. Mercury switch is already tilted to close its right-hand contact members 46. Thus motor 6| is now energized to rotate gear 1 in a clockwise direction, thereby rotating gear 8 ma counter-clockwise direction, and will continue to do so until gear 8 has been brought to a position such that the mercury switch I2 is in a neutral position.

Assume now that speed adjusting arm 8 is moved upwardly in order to increase the speed of motor 51. Such upward movement will cause gear 6 to rotate clockwise thereby tilting mercury switch l2 to the right and effecting closing of contact member 46 thereof which will complete a circuit as follows: from conductor 85, through conductor 86, winding 63 of motor 6|, conductor 6i, contact members 46, conductor 92, contact members 18, conductor 93, contact members 82, conductor 69 to conductor 88. Motor 6| is thus started and will rotate in such direction as to drive switch arms 65, contact arm 10 and gear 1 clockwise. The clockwise rotation of contact arm 65 will cut out part of the resistance of resistors 66 and effect speeding up of the motor 51; the clockwise rotation of contact member 18 will have no effect other than merely sliding along contact members 68 and 69 to maintain contact therewith; and the clockwise rotation of gear 1 will effect counter-clockwise rotation of gear 8, hence will restore mercury switch 2 to its neutral position, opening contact members 46. As contact members 46 are opened; the above-described circuit through motor 6| is interrupted hence motor 6| stops and ceases to move contact arms 65 and 18, and gear 1. It will be obvious that the degree of upward movement of speed selecting arm 8 will determine the degree of angular movement of gear 1 to restore mercury switch to its neutral position, hence the degree of movement of contact arm 65 and the degree of speed change of motor 51.

Assume now that speed adjusting arm 9 is moved downwardly in order to decrease the speed of motor 61. Such downward movement will cause gear 8 to rotate counter-clockwise thereby tilting mercury switch l2 to the left, closing contact. members 41 which will complete a circuit as follows: from conductor 85, through conductor 86, winding 62, conductor 81, conductor 85, contact members 41, conductors 84 and 88, contact member 68, contact arm 18, contact member 68, conductor 86 to conductor 88. Motor 6| is thus started in a direction opposite to that described in the previous paragraph therefore motor 6| drives switch arms 65, contact drum 16 and gear 1 counter-clockwise (as indicated by arrows in the drawings). Such counter-clockwise movement of contact arms 65, effects cutting in the resistance of resistors 66 hence effects slowing down of motor 51; the counter-clockwise movement of contact member 18 will have no effect than merely sliding along contact members 68 and 68 to maintain contact therewith and the counter-clockwise movement of gear 1 will effect clockwise rotation of gear 8, hence will restore mercury switch l2 to its neutral position, opening contact members 41, hence interrupting the circuit through winding 62 of motor 6| and effecting stoppage of motor 6| and stoppage of the movement of contact arms 65 and 18 and gear 1. If the motor is once stopped it cannot be started again until the contact arm of the variable resistor has reached the resistance all in position, that is until contact arm 18 bridges contact members 91 and 68.

I am, of course, aware that others, particularly after having had the benefit of the teachings of my invention, may devise, other control circuits within the spirit of my invention and I, therefore, do not wish to be limited to the specific showing made in the drawings and the descriptive disclosure hereinbefore made, but wish to be limited only by the scope of the appended claims and such prior art that may be pertinent.

I claim as my invention:

1. In a system of control for an electric motor, in combination, a reversible electric motor including a plurality of reversing windings, a source of potential therefor, a rotatable member driven by said motor, a second rotatable member in contact engagement with and directly driven by said first rotatable member, a double pole mercury switch rigidly mounted on said second rotatable member, an electric circuit including one of the windings of said motor and one of the pairs of contact members of the mercury switch to effect rotation of said motor in one direction, a second electric circuit including another winding of said motor and the other pair of contact members of the mercury switch to' effect rotation of said motor in an opposite direction, an arm which is loosely pivoted on said first rotatable means and upon which is loosely pivoted said second rotatable means to effect rotation of the second rotatable means about the first rotatable means, thereby tilting the mercury switch in either direction so as to close either pair of contact members thereof, thus selectively effecting rotation of said motor in either direction.

2. In a system of control for an electric motor, in combination, a reversible electric motor including a plurality of reversing windings, a source of potential therefor, a rotatable member driven by said motor, a second rotatable member driven by said first rotatable member, a double pole mercury switch rigidly mounted on said second rotatable member, an electric circuit including Lil one of the windings of said motor and one of the pairs of contact members of the mercury switch to effect rotation of said motor in one direction, a second electric circuit including another winding of said motor and the other pair of contact members of the mercury switch to eifect rotation of said motor in an opposite direction, an arm which is loosely pivoted on said first rotatable means and upon which is loosely pivoted said second rotatable means to effect rotation of the second rotatable means about the first rotatable means, thereby tilting the mercury switch in either direction so as to close either pair of contact members thereof, thus selectively effecting rotation of said motor in either direction, a second electric motor, a variable resistor in circuit with said second motor to regulate the speed thereof, said resistor having a contact arm which is directly connected to said first rotatable member which contact arm varies the resistance of said resistor in accordance with movements of said first rotatable member thereby varying the speed of said second motor.

3. In a system of control for an electric motor, in combination, a reversible electric motor including a plurality of reversing windings, a source of potential therefor, a rotatable member driven by said motor, a second rotatable member driven by said first rotatable member, a double pole mercury switch rigidly mounted on said second rotatable member, an electric circuit including one of the windings of said motor and one of the pairs of contact members of the mercury switch to effect rotation of said motor in one direction, a second electric circuit including another winding of said motor and the other pair of contact members of the mercury switch to effect rotation of said motor in an opposite direction, an arm which is loosely pivoted 'on said first rotatable means and upon which is loosely pivoted said second rotatable means to eifect rotation of the second rotatable means about the first rotatable means, thereby tilting the mercury switch in either direction so as to close either pair of contact members thereof, thus selectively effecting rotation ofsaid motor in either direction, a second electric motor, a variable resistor in circuit with said second motor to regulate the speed thereof, said resistor having a contact arm which is directly connected to said first rotatable member which contact arm varies the resistance of said resistor in accordance with movements of said first rotatable mem ber, thereby varying the speed of said second motor, a switch operating member which is directly connected to but insulated from said contact arm of the rheostat, a normally closed limit switch connected in circuit relation to one of the windings of the reversible motor and which is positioned so as to be opened by said switch operating member when the said contact arm has reached the resistance all in position, thereby opening the circuit through said winding, thus stopping the rotation of the reversible motor, a second normally closed limit switch connected in circuit relation to another of the windings of the reversible motor and which is positioned so as to be opened by said switch operating member when said contact arm has reached the resistance all out" position, thereby opening the circuit through the last-mentioned winding, thus stopping rotation of the reversible motor.

4. In a system of control for an electric motor, in combination, a reversible electric motor including a plurality oi reversing windings, a source or potential thereior, a rotatable member driven by said motor, a second,rotatab1e member driven by said first rotatable member, a double pole mercury switch rigidly mounted on said second rotatabie member, an electric circuit including one of the windings of said motor and one of the pairs of contact members of the mercury switch to effect rotation of said motor in one direction, a second electric circuit including another winding of said motor and the other pair of contact members of the mercury switch to eifect rotation of said motor in an opposite direction, an arm which is loosely pivoted on said first rotatable means and upon which is loosely pivoted said second rotatable means to eifect rotation of the second rotatable means about the first rotatable means. thereby tilting the mercury switch in either direction so as to close either pair of contact members thereof, thus selectively effecting rotation oi said motor in either direction, a second electric motor, a variable resistor in circuit with said second motor to regulate the speed thereof, said resistor having a contact arm which is directly connected to said first rotatable member, which contact arm varies the resistance of said resistor in accordance with movements of said first rotatable member, thereby varying the'lpeed of said second motor, a switch operating member which is directly connected to but insulated from said contact arm of the rheostat, a normally closed limit switch connected in circuit relation to one of the windings of the reversible motor and which is positioned so as to be opened by said switch operating member when the said contact arm has reached the resistance all in" position, thereby opening the circuit through said winding, thus stopping the rotation of the reversible motor, a second normally closed limit switch connected in circuit relation to another of the windings of the reversible motor and which is positioned so as to be opened by said switch operating member when said contact arm has reached the "resistance all out" position, thereby opening the circuit through the last-mentioned winding, thus stopping rotation of the reversible motor, means responsive to energization by said potential source to effect movement of said contact arm to the "resistance all in" position, a start" switch which has a spring holding it normally opened, a stop" switch which has a spring holding it normally closed, means responsive to the closure of said start" switch for efi'ecting rotation of said second motor at a speed which is preset in accordance with the positioning of said second rotatable member,

5. In a system of control for an electric motor, in combination, a reversible electric motor including a plurality of reversing windings, a source of potential therefor. a rotatable member driven by said motor, a second rotatable member driven by said first rotatable member, a double pole mercury switch rigidly mounted on said second rotatable member, an electric circuit including one of the windings of said motor and one of the pairs of contact members of the mercury switch to eiIect rotation of said motor in one direction, a second electric circuit including another winding of said motor and the other pair of contact members of the mercury switch to eifect rotation of said motor in an opposite direction, an arm which is loosely pivoted on said first rotatable means and upon which is loosely pivoted said second rotatable means to effect rotation of the second rotatable means about the first rotatable means, thereby tilting the mercury switch in either direction so as to close either pair of contact members thereof, thus selectively effecting rotation of said motor in either direction, a second electric motor, a'variable resistor in circuit with said second motor to regulate the speed thereof, said resistor having a contact arm which is directly connected to said first rotatable member, which contact arm varies the resistance of said resistor in accordance with movements of said first rotatable member, thereby varying the speed of said second motor, a switch operating member which is directly connected to but insulated from said contact arm of the rheostat, a normally closed limit switch connected in circuit relation to one of the windings of the reversible motor and which is positioned so as to be opened by said switch operating member when the said contact arm has reached the resistance all in position, thereby opening the circuit through said winding, thus stopping the rotation of the reversible motor, a second normally closed limit switch connected in circuit relation to another of the windings of the reversible motor and which is positioned so as to be opened by said switch operating member when said-contact arm has reached the resistance all out position, thereby opening the circuit through the last-mentioned winding, thus'stoppin'g rotation of the reversible motor, means responsive to energization by said potential source to effect movement of said contact arm to the resistance all in position, a start" switch which has a spring holding it normally opened, a stop switch which has a spring holding it normally closed, means responsive to the closure of said .start switch for effecting rotation of said second motor at a speed which is preset in accordance with the positioning of said second rotatable member, means responsive to the opening of said stop switch for efiecting movement of said contact arm to the resistance all in position, and a normally open switch which is positioned so as to be closed when said contact arm has reached the resistance all in position, thereby closing a circuit through the start contactor and which when open, breaks the circuit through the start switch and making it impossible to restart said second motor after it has once stopped until said normally open switch has been closed and said contact arm of the variable resistor is in the "resistanceall in position.

6. A device for controlling a reversible electric motor including, in combination, a reversible electric motor including a plurality of reversing windings, a source of potential therefor. a switch actuating means comprising a rotatable means driven by said motor, a second rotatable means in direct driving engagement with said first rotatable means, a double pole mercury switch rigidly mounted on said second rotatable means, an arm which is loosely pivoted on said first rotatable means and upon which is loosely pivoted said second rotatable means, the contact elements of said double pole mercury switch being so arranged that movement of said arm in one direction closes one pair of contact elements only so as to complete a circuit through one of said reversing windings and movement in an opposite direction closes the other pair of contact elements only so as to complete a circuit through another of said reversing windings, said motor being effective for rotating said first rotatable means for restoring said mercury switch to a neutral position in which all the contact members are open.

7. A device for controlling a reversible electric motor including, in combination, a reversible electric motor including a plurality of reversing windings, a source of potential therefor, a switch actuating means comprising rotatable means driven by-said motor, a second rotatable means in direct driving engagement with said first rotatable means, a double pole mercury switch rigidly mounted on said second rotatable means, an arm which is loosely pivoted on said first rotatable means and upon which is loosely pivoted said second rotatable means, the contact elements of said double pole mercury switch being so arranged that movement of said arm in one direction closes one pair of contact elements bnly so as to complete a circuit through one of said reversing windings and movement in an opposite direction closes the other pair of contact elements only so as to complete a circuit through another of said reversing windings, said motor being effective for rotating said first rotatable means for restoring said mercury switch to a neutral position in'which all the contact members ar open, and means for holding said arm in any one of a plurality of positions. 1 I

8. A device for controlling a reversible electric motor including, in combination, a reversible electric motor including a plurality of reversing windings, a source of potential therefor, a switch actuating means comprising a gear driven by said motor, a second gear in driving engagement with said first gear, an elongated double pole mercury switcn having a pair of contact members at both of its ends, which mercury switch is rigidly mounted on said second gear, an arm which is loosely pivoted on said first gear and upon which is loosely pivoted said second gear, said mercury switch being so arranged that movement of said arm in one direction effects closing one ofthe pairs 01 contact elements only so as to complete a circuit through one of said reversing windings and movement in an opposite direction eilects closing of the other pair of contact elements only so as to complete a circuit through another of said reversing windings, said motor being effective for driving said first gear for restoring said mercury switch to a neutral position in which all thecontact members are open.

9. A device for controlling a reversible electric motor including, in combination, a reversible electric motor including a plurality of reversing windings, a source of potential therefor, a switch actuating means comprising a gear driven by said motor, a second gear in driving engagement with said first gear, an elongated double pole mercury switch having a pair or contact members at both or its ends, which mercury switch is rigidly mounted on said second gear, an arm which is loosely pivoted on said first gear and upon which is loosely pivoted said second gear, said mercury switch being so arranged that movement oi. said arm in one direction efiects closing one 01' the pairs of contact elements only so as to complete a circuit through one of said reversing windings and movement in an opposite direction eflects closing or the other pair 01' contact elements only so as to complete a circuit through another of said reversing windings, and means for driving said first gear for restoring said mercury switch to a neutral position in which all the contact members are open, and means for holding said arm in any one or a plurality of positions.

FREDERICK D. SNYDER.

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