US2411763A - Control system - Google Patents

Description

Nov. 26, 1946- A. w. SWINGLE EI'AL 2,411,763

CONTROL SYSTEM 0' 1 Filed Feb. 2,-- 1944 Lon 5pm 851,6 aw

I lnven'tohsz /z AP'LTTO W.' Swingie,

George H. ettibone, Joseph E. Dill,

Their Attorney Patented Nov. 26, 1946 CONTROL SYSTEM Artro W. Swingle, Schenectady, George H. Pettibone, Scotia, and Josep N. Y., assignors to Gen h E. Dill, Schenectady, eral Electric Company, a

corporation of New York Application February 2, 1944, Serial No. 520,728

4 Claims.

This invention relates to control systems, more particularly to systems for controlling the operation of an electric motor, and it has for an object the provision of a simple, reliable, improved, and inexpensive control system of this character.

A more specific object of the invention is the provision of a control circuit arrangement which minimizes heat losses resulting from circulating currents.

In carrying the invention into efiect in one form thereof, a split series field motor is utilized, together with a directional resistor connected across the terminals of the field winding and a speed controlling resistor connected between an intermediate tap of the directional resistor and one side of the source. These resistors are controlled by banks of spring contacts which in turn are selectively actuated by high and low speed Selsyns.

In illustrating the invention in one form thereof, it is shown as embodied in the drive portion of a follow-up control system.

For a better and more complete understanding of the invention, reference should now be had to the following specification and to the accompanying drawing of which the single figure is a simple, diagrammatical sketch, partly in perspective, of an embodiment of the invention.

Referring now to the drawing, an electric motor III is connected to drive an object H into positional agreement with a remote controlling object (not shown).

The motor III is a split series field type motor;

i. e., its field winding is divided into two field coils Ilia and Ilb of opposite polarity to eflect rotation of the motor in either direction when the excitation of one field coil predominates over that of the other. The lower brush Iiic of the motor is connected to one side I 2 of an A.-C. supply source I2, H. The upper brush I M of the motor is connected to the common point of the two field coils Ito and llib.

A resistor I4 and a capacitor I! are connected in parallel across the opposite terminals of the field coils Ilia and lb by means of conductors l8 and II. This resistor is referred to as the directional control resistor. A second resistor II is connected between the center tap Ha of resistor I4 and the side I2 of the A.-C. supply source. This resistor is provided with a plurality of taps Ito, I8b, lie, Ild, and I88 to provide for short cireuiting portions of the resistor, thereby to vary the speed of the motor I0. Consequently, resistor I 8 is referred to as the speed varying resistor.

To provide for short circuiting the portions of the resistor which are defined by the taps "a to lie, inclusive, a plurality of spring contacts are provided. These contacts are arranged in two groups or banks It and 20. As shown, the group I9 comprises contacts Illa to I9), inclusive, and the group 20 comprises contacts 20a to 20), inclusive. Both groups of contacts are mounted on a supporting member 2|, with the individual contacts separated from each other. The member 2| is preferably made of a suitable insulating material.

The innermost contacts I91: and 20a of the two groups are connected to the opposite terminals Ilb and I40, respectively, of the speed varying resistor I4, and the contacts lab and 2017 are connected together to the terminal I8a of the speed varying resistor l8 and thus to the center tap Ha of the directional resistor. The taps lab, I80, I8d, and the terminal I88 of the speed varyin resistor it are connected to the contacts lsc, ISd, I9e, and I9], respectively, of the group I9, and also to corresponding contacts Zilc, 20d, 20c, and 20! of the group 20. Capacitors 22 and 23 are connected across the taps I and ltd and between midtap I8d and the terminal lie.

The actuation of the contacts to control the speed of the motor I 0 is controlled by a high speed or "fine Selsyn receiver 24 and by a low speed or "c0arse Selsyn receiver 2!. These Selsyn receivers 24 and 25 are electrically connected to high and low speed Selsyn transmitters, respectively, (not shown). The high speed Selsyn receiver 24 comprises a rotor member 24a and a stator member 241) which, in this application, is mounted in ball bearings and is free to rotate. It is connected through spur gearing 28 and worm gearing 28a to the shaft of the drive motor I II. The ratio of the gearing is such that the ratio between the revolutions of the stator 24b and the driven object I I is a suitable number such as 36:1; i. e., the stator 2417 will rotate 36 times for each revolution of the driven object I I.

The low speed Selsyn receiver 25 has a rotor member 25a and a rotatably mounted stator member 26b. The rotatably mounted stator 24!: of the high speed Selsyn receiver is connected with the rotatably mounted stator 25b of the low speed receiver by means of gearing 21 having a ratio such that the low speed stator 25?) rotates at a very low speed with respect to stator 24b; e. g., one revolution for each 36 revolutions of the high speed stator 24b.

For directly actuating the contacts of'the banks It and 20, a member 28:: located in the space between the two banks and mounted on a lever 28 is provided. The lever 28 is mounted in a suitable bearing 29 for rotation about the bearing Y axis. Rotation of the lever 28 is effected by means of a heart cam assembly comprising a heartshaped cam 30 which is secured to the shaft of rotor 24a and a cam follower 2| mounted on a yoke 22 which is pivotally connected to lever 28.

To provide for transferring the control of the contacts from the high speed Selsyn receiver to aria-tee in one direction or the other by means of two electromagnets 3d and 35. The selective energization of the operating coils 3M and 35a of these electromagnets is controlled by means of a heart cam assembly 36 which is operated by the low speed receiver 25, together with a pair of'directional contacts 31 and 38.

The operation is as follows: At any instant cur rents flow from one side of the source through the armature ID of the follow-up motor, field coils Ida and lob in parallel, upper and lower halves of the directional control resistor i l in parallel to the center tap Ma, speed varying resistor it to the opposite side of the source. Since the upper and lower halves of the directional control resistor it are equal, the currents circulating through these halves to the field winding coils Ma and liib are also equal. Consequently, the torques produced by these currents are opposite so that the net torque acting on the armature I is zero and the motor is at rest. When the motor is at rest, the circulating currents are reduced to a very low value, owing to the high ohmic resistance of the directional resistor, and thus the standby losses of the motor are reduced to a minimum.

Rotation of the rotors of the transmitters causes the rotors-Eda and 25a to rotate to follow the rotors of the transmitters. If the rotation of the rotor 29a is in a clockwise direction, the cam follower ill will have a component of movement toward the right, thereby to rotate the lever 28 in a clockwise direction about the axis of bearing 29. The clockwise rotation of lever 28 moves the member 280. into engagement with contact i9q. As the clockwise rotation of the rotor 23a continues; contact i9a is moved into engagement with contact lsb, thereby short circuiting the half of the directional control reill the rotor 26a will rotate the heart cam do in a counterclockwise direction, thereby to move the member 26a downward. The downward movement of member 28a relieves the pressure on the contacts of bank it, thereby successively inserting the sections of the speed controlling resistor i t in the armature circuit and reducing the speed of motor it. The separation of contacts the and lab interrupts the short circuit about the upper half of the directional resistor it. This results in reducing theexcitation of the split field coil Ida to equalize the excitation of both split field coils ltd. and, iEb and restore the standby zero torque condition of the motor ill.

The rotors'25a and 25b rotate simultaneously with the rotor 26a and stator 2th and in the same directions, respectively. Owing to the 36:1 reducthrough the split field coil iila than flows through coil Iflb, and a net torque is developed which causes the motor ill to rotate in a direction which drives the stator 24b in a counterclockwise direction. Owing to the full amount of resistor l8 in the armature circuit of the motor, the rotation is at a slow speed. The rotor 24b continues to rotate in the clockwise direction and at a speed which is equal to the difierence between the speed of the transmitter rotor and the speed of the stator 26b. A continued clockwise rotation of the rotor 24a acting on the heart cam assembly causes the member 28a to continue its upward movement to close the contacts I90, i901, lee, and lQf in succession. With the successive closing of these contacts, successive sections of the speed varying resistor l8 are short circuited, thereby increasin the voltage applied across the armature and field coil Ilia. As a result, the speed of the motor Ill increases until the speed of the counterclockwise rotation of the stator 25b is equal to the speed of the rotor of the transmitter. When this condition is reached, the rotor Zea is at standstill with the result that the speed of the motor i0 is not further increased.

If, now, the speed of the transmitter is decreased, the speed of the stator 24b does not decrease at first because it cannot change until the speed of motor ill changes. Consequently,

tion of gearing 27, the amount of rotation of the rotor 25a and the stator 25b is only one-thirty sixth th corresponding rotations "of the rotor 24a and the stator 24b of the high speed Selsyn receiver. l a

If the rotation of rotor 25a in a clockwise direction exceeds a predetermined amount, e. g., two and one-half degrees, the heart cam 30 will have rotated to the -degree position, at which position it is desirable to transfer control to the low speed Selsyn 25. The rotation of the heart cam assembly 36 closes contacts 37, thereby to energize operatin coil Ma. The armature 33 is attracted toward core member 36, thereby rotating lever 28 in a clockwise direction to close all the contacts of bank is which may not have been closed by rotation of rotor Eda. The speed of motor i0 is rapidly accelerated to its maximum value. As a result, the driven object ii is driven in the desired direction at maximum speed and the stators 26b and 251) are driven in a counter. clockwise direction. When the counterclockwise speed of the stators exceeds the speeds of the rotors of the transmitters to which they are respectively connected, the rotors 2 5a and 25a will rotate in a counterclockwise direction. When the rotor 25a returns to within two and one-half degrees of its initial position with respect to the rotor of the low speed transmitter, the heart cam assembly 36 will open the contacts 37, thereby to deenergize the operating coil Sta. As a result of the deenergization of coil Sta, the armature 33 is no longer attracted by the core member 34 and, consequently, the control of the contacts I9a to WI, inclusive, is restored to the high speed Selsyn 26.

If the initial rotation of the rotor Eda is in a counterclockwise direction, in response to a rotation of the rotor of the transmitter in a direction opposite to that described in the foregoing, the operation will be the same as that described except that the rotation of the heart cam 30 and lever 28 will be in a counterclockwise direction and the contacts 20a to 20f, inclusive, of the lower bank 20 will be actuated. The closing of contacts 2M and 28b short circuits the lower half of the directional resistor I ti, thereby efiecting rotation of the motor ii! in the reverse direction. contacts 201), 20c, 29d, we, and 20 short circuits successive portions of the speed varying resistor E8 to accelerate the motor H3 in the manner described in the foregoing.

Although in accordance with the provisions of the patent statutes, this invention is described as embodied in concrete form and the principle thereof has been explained, together with the best mode in which it is now contemplated apply- The subsequent successive closing of ing that principle, it will be understood that the apparatus shown and described is merely illustrative and that the invention is not limited thereto, since alterations and modifications will readily suggest themselves to persons skilled in the art without departing from the true spirit of this invention or from the scope of the annexed claims.

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

1. A control system comprising in combination, a split series field motor having one armature terminal connected to an intermediate tap of the series field winding and a connection from the opposite armature terminal leading to one side of a supply source, a resistor connected across said series fielding winding, a second resistor connected-from an intermediate tap of said first resistor to the opposite side of said source and having a plurality of taps, a plurality of spaced apart contacts arranged in two banks, a contact of one of said banks being connected to one terminal of said first resistor and a corresponding contact of the other bank being connectedto the opposite terminal of said first resistor and each of the taps of said second resistor being connected to a different one o1 the contacts of one bank and to a correspondin contact of the second bank, and means for selectively engaging the contacts of one of said banks to close in succession thereby to short circuit a selected portion of said first resistor to effect rotation of said motor in a, corresponding direction and successively to short circuit portions of said second resistor to vary the speed of said motor. I

2. A control system comprising in combination, a split series field motor having one armature terminal connected to an intermediate tap of the series field winding anda connection from,

the opposite armature terminal to one side of a supply source, a first resistor connected across said series field winding, a second resistor connected from the midpoint of said first resistor to the other side of said source and having a plurality of taps, a supporting member, a plurality of contacts mounted on said supporting member in cooperative spaced apart relationship and in two groups separated from each other to provide a centrally disposed space,-the end contacts of said groups adjacent said centrally disposed spacebeing connected to opposite terminals of said first resistor, and a member mounted within said space for movement in opposite directions to selectively actuate said groups of contacts and to close the contacts of the selected group in succession thereby to short circuit a selected half of said first resistor to efiect rotation of said motor in a selected direction and successively to short circuit'portions of said second resistor to vary the speed of said motor.

3. A control system comprising in combination, a split series field motor having one armature terminal connected to an intermediate tap of the series field winding and a connection from the opposite armature terminal to one side of a supply source, a resistor connected across said series field winding, a second resistor connected from an intermediate tap of said first resistor to the opposite side of said source and having a plurality of taps, a pair of banks of spring contacts separated from each other to provide a centrally posltely disposed electromagnets disposed space, each of said banks comprising a plurality of spring contacts mounted in spaced apart relationship, a contact of one of said banks being connected to one terminal of said first re=- sistor and a corresponding contact of the other bank being connected to the opposite terminal oi said first resistor and each of the taps of said sec- 0nd resistor bein connected to a different one oi. the contacts of one of said banks and a corresponding contact of the second bank, an actuating member mounted in said centrally disposed space for movement in opposite direction, a relatively high speed Selsyn receiver for movin said member in a selected direction to initiate the successive closing of the contacts of the selected bank thereby to short circuit a selected portion of said first resistor to effect rotation of said motor in a selected direction and to increase its speed, a relatively low speed Selsyn receiver, speed reducing gearing connecting said Selsyns, and means responsive to a predetermined amount of rotation of said low speed Selsyn receiver for moving said actuating member to an extreme position to close all of said contacts 01' said selected bank thereby to effect rotation of said motor at maximum speed.

4. A control system comprising in combination, a split series field motor having one armature terminal connected to an intermediate tap of the series field winding and a connection from the opposite armature terminal to one side of a supply source, a resistor connected across said series field winding, a second resistor connected from an intermediate tap of said first resistor to the opposite side of said source and having a plurality of taps, a pair of banks of spring contacts separated from each other to provide a centrally disposed space, each of said banks comprising a plurality of sprin contacts mounted in spaced apart relationship, a contact of one of said banks being connected to one terminal of said first resistor and a corresponding contact of the other bank being connected to the opposite terminal of said first resistor and each of the taps of said second resistor being connected to a difierent one of the contacts of one of said banks and a corre-- sponding contact of the second bank, a pivotally mounted lever provided with an actuating menuber in said, centrally disposed space and also provided with an armature member, a pair of oparranged in cooperative relationship with said armature for eifecting pivotal movement of said lever in opposite directions, a relatively high speed Selsyn receiver for moving said lever in a selected direction to initiate successive closing of the contacts of one of said banks thereby to short circuit a portion of said first resistor to effect rotation of said motor in a selected direction, a relatively low speed Selsyn receiver, speed reducing gearing connecting said Selsyn receivers, and means responsive to a predetermined amount of rotation of said low speed Selsyn receiver for selectively energizing said electromagnets to move said lever to an extreme position to close all of said contacts of said selected bank to efiect rotation of said motor at maximum speed.

ARTRO W. SWINGLE. GEORGE H. PETTIBQNE. JOSEPH E. DILL.

Images