US2320896A - Motor control system - Google Patents

Description

June 1, 1943. SNYDER 2,3205896 MOTOR CONTROL SYSTEM Filed Jan. 30, 1942 WITNESSES: INVENTOR W lqedemclr D. Snyder.

ATTORNEY- Patented June 1, 1943 MOTOR CONTROL SYSTEM Frederick- D. Snyder, East Milton, Mass., assignor to Westinghouse Electric 8; Manufacturing Company, East Pittsburgh, Pa., a corporation oi Pennsylvania Application January 30,1942, Serial No. 428,902

4 Claims.

My invention relates to systems of control for electric motors, that is, more particularly, to a control which provides a selectable preset speed of operation of a motor and provides for superimposing a speed variation on the speed selected for the motor.

An object of my invention is to provide for automatically bringing an alternating current wound rotor motor, or any other type of electric motor, to a preset speed with standard pushbutton control, and superimposing a speed variatiori of a definite character on said motor.

Another object of my invention is to provide a speed control system which automatically alternately increases and decreases the speed of a motor equal amounts.

A further object of my invention is to provide a speed control for an electric motor that is simple and inexpensive.

The foregoing objects are merely illustrative of many other objects and advantages of my invention, which other objects will readily become apparent from a study of the following specification andthe accompanying drawings, in which, the single figure is a diagrammatic showing of my invention as applied to alternating current motors utilized in a spinning machine.

The motors may, of course, be direct current motors and I do not wish to be limited to the particular type of motors shown.

Referring to the drawing, I designates a single-phase alternating current capacitor type reversible motor for operating the speed control rheostat 2 for the main motor M. The main motor M drives a suitable load at a selected speed and for the particular load coupled to it is required to vary its speed from a preselected speed, that is, cyclicly increase its speed first above and then below the preselected speed,

This type of operation is required in spinning mills where the main motor is coupled to operate the spinning machine at a given speed but which speed must alternately increase and decrease as the builder arm guides the spun thread up and down on the bobbin to build the thread up to fill the bobbin.

Main motor M is suitably coupled to drive a spinning machine and. among many elements. drives the spindle 3 through suitable mecha- -nisms. The bobbin core 4 is mounted on spindle 3, and the builder arm 5 is actuated through suitable mechanisms, as 6. Builder arm 5 moves in synchronism with the motor so that its displacement, as it moves up and down, is prothe builder arm is adjacent the top and should be less when it is adjacent the bottom. With my control I accomplish exact correspondence of spindle speed to bui-lder arm position without any lag or displacement. I further provide for gradually and slowly starting and accelerating the motor up to the speed at which it is desired, to spin at the moment and this I can do regardless of where the machine is stopped. during spinning, with reference to the bobbin diameter.

A better understanding of my contribution to the art can, no doublt, be had from a more detailed study of my control and its operation. Assuming the spinning machine had been in operation and then was stopped 50 that all parts had come to rest. All the circuits and elements shown in the figure will have the position shown. It will be noted that all the resistance is in the secondary circuit of the wound rotor motor.

If the attendant now wishes to again start the spinning machine, he depresses the starting switch I0 thereby establishing a circuit from bus I, which bus I is suitably energized from control transformer T connected to the source of alternating current, through coil 8 of contactor 8, starting switch it, stop switch ii to the bus II. The motor M, with all the resistor sections of the secondary in circuit, will thus start gradually and slowly.

The contactor 9 will establish its own holding circuit at contact members i3 and will close a circuit at contact members it. Closure of contact members it will complete a circuit from bus I. through contact members H. coil ii of relay ii to bus l2. Operation of relay i6 establishes a circuit from bus 1 through contact members '1, limit switch 48, field winding I! connected in parallel with the series circuit including the capacitor 20 and field Winding 2i, to bus i1.

Motor i is thus caused to operate in such a direction as to operate sprocket wheel 22 counterclockwise. Pulley 23 thus moves up and pulley 24 moves down. Since pulleys 25 and 26 are fixed, this operation of motor I will cause the clockwise operation of the double groove sheave 21 coupled to shalt 29. Sheave 21 is double spindle 3 should rise.

clockwise movement produced by such upward grooved and thus has cable 28 wrapped about it twice so that there is not relative slippage between cable and sheave.

- This clockwise operation of sheave 21 operates the rheostat arms of rheostat 2 clockwise to thus accelerate the motor M to higher and higher speeds. Immediately after sheave 21 has moved clockwise through a small angle, switch 30 is closed. The purpose of this switch 30 will appear later, because at this stage no circuits are established by the closure of switch 30.

The speed of the motor increases until pulley 24 has moved low enough so that dog 3I operates switch III to open position. Motor I immediately stops and motor M thus operates at some preselect speed, at least so far as any speed change produced by motor I is concerned.

Switch I8 is mounted on a support 32, and is arranged, as shown, to be vertically adjustable. The support 32 is provided with graduations so that by suitablypositioning bracket 33 relative to the graduations indicating speedany desired top speed may be selected for motor M.

- The lever 34 is loosely pivoted on shaft 29 and is pivotally connected to a connecting rod 35 which in turn is coupled through the length adjusting turn-buckle 36 to the builder rod.

After the motor I stops pulleys 23 and 24 have become fixed in space. The movementof builder arm thus moves the cable connecting'points 31 and 38 up. and down with the movement or the builder arm. The sheave 21 is thus alternately rotated clockwise and counterclockwise. When the builder arm 5 moves upwardly the speed of This is exactly what the movement of the builder arm 5 will do. Again when the builder arm moves down the sheave 21 is moved counterclockwise and the speed of spindle 3 is decreased. Motor M thus alternately increases and decreases its speed, the motor speed 'being at one time somewhat above the speed determined by the speed'presetting limit switch I8 and then somewhat below the speed set by this'switch I8.

Normally lever 34 will be so adjusted or connected to the builder arm that lever 34 will be horizontal when lever 3| engages switch I8 when this switch isv adjustedto a preset speed position corresponding to the usual expected speed of operation of the spinning machine. This increases the operating range and accuracy of my control.

It should be noted that the speed control effect of the builder arm movements and the eflect of motor I are not necessarily successive as above described, but may, and as long as motor M'is not up to the preset speed, always do occur simultaneously. When the effects are produced simultaneously, as while motor M is still accelerating, then the pulley, cable, and sheave system merely acts as a special diilerential. That is, as pulley 24 moves down or builder arm 5 moves down, the motor acceleration will be slower than for an upward movement of builder arm 5 and a downward movement of pulley 24. r

Now, if for any desirable reason, the stop switch II is operated then contactor 9 moves to the position shown and relay I5 moves to the posi tion shown. Motor M is thus stopped but motor 1 is set in operation in a reverse direction. The circuit for motor I now is from bus I through contact members 39, limit switch 30, now closed, field winding 2I connected in parallel to the series circuit including the capacitor and field winding I9, to bus i2. The motor I now operates in such a direction that sprocket wheel 22 now turns clockwise thus causing pulley 24 to move up and pulley 23 to move down. At the initial upward movement of pulley 24, switch I8 is reclosed, but this does not at this stage eil'ectany operations. sheave 21 is moved counterclockwise until dog 40 opens the limit switch 30. Dog 40 is so positioned on, sheave 21 that all the resistor sections of the rheostat 2 are in the secondary circuit when limit switch 30 opens. All the parts are thus back to the positions shown in the figure for the respective parts. Other starting and stopping operations just repeat the same operations heretofore described.

From the foregoing, it will be apparent that I obtain the desirable operation of varying the speed of the spindle 3 in cycles as the yarn is alternately wound on the small and large diameter of the bobbin.- Also, regardless of where the machine is stopped, that is, while spinning on the large or small diameter of the bobbin, I obtain the desirable result of starting the motor slowly and oi accelerating it gradually up to the preset speed at which it is at the moment desired to spin. Essentially, my. control scheme allows the spinning machine to move the builder arm 5, that is, lever 34, and to move the arms of the rheostat with it mechanically at exactly the same speed as the builder arm 5 is moved. Further, when the main drive motor M is stopped the motor operated portion of the rheostat mecha nism will put all resistor sections of the rheostat in the motor secondary without moving the speed presetting means, and when the motor M is again started the resistance will be gradually shunted by the mechanism operated by motor I until the preset speed point is reached, that is, until switch I3 is.opened.

My invention isnot limited to a combination including only alternating current motors, since those skilled in the art, after having had the benefit of my disclosure can readily devise direct current systems of control, and still other control circuits within the spirit 'of my invention. I, therefore, 'wish to be limited only by the scope of the appended claims and such prior art as may.

be pertinent.

I claim asmy invention:

1. In a control system for an electric motor, in combination, an electric motor, speed control means for said motor, a load element coupled to the motor to operate in a reciprocating manner,

motor means, means for connecting the motor means to operate a preselected number of revolutions, said motor means and load element'being coupled 'to said speed control means to alter the speed of said motor in accordance with the combined function of the number of revolutions made by the motor means and the position of said load element.

2. In a control system for an electric motor, a

and further control means, also set in operationat the starting of said motor, for also operating on said speed control means to superimpose a I cycliceilect on said speed control means, whereby the actual speed of themotor at any time after start will be determined by the combined efl'ect of said control means.

3. In a system of control for an electric motor, in combination, a wound rotor induction motor having an adjustable resistor in its secondary winding, a load element coupled to be driven in a reciprocating manner by said motor, motor means set in operation at the starting of said wound rotor induction motor, an adjustable limit switch disposed to stop said motor means after having made any selected number of revolutions, a differential mechanism, certain elements coupied to the motor means, certain other elements coupled to the load element and the elements of the diflerentlal mechanism responsive to the algebraic sum of the number of revolutions made by the motor means and the position of the load element being connected to the adjustable resistor, whereby the speed of the induction motor at any given instant after starting will be determined by the position of the load element and the number of revolutions having been made by the motor means at the particular instant after starting.

4. In a speed control for a wound rotor induction motor having a shii'table rheostat arm for adjusting the resistance value of the secondary winding of the wound rotor induction motor, in combination, a machine element operated to move first in one direction and then in another direction, a second machine element adapted to move from a starting position to a selected final position, a differential device having two of its units connected respectively to the machine elements and having a third of its units, that is, the unit responsive to the algebraic sum oi the movements of the two machine elements, connected to the shiftable rheostat arm.

FREDERICK D. SNYDER.

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