US2081977A - Acceleration control system - Google Patents

Description

W. l. BENDZ `lune l, 1937.

ACCELERATION CONTEOL SYSTEM Filed Aug. 5l, 1936 77m@ fa Acce/erafe.

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Patented June 1, 1937 PATENT OFI-ICE ACCELERATION CONTROL SYSTEM Waldemar I. Benda, Arlington, Mass., assignor to Westinghouse Electric s; Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application August 31, 1936, Serial No. 98,757

7Claims.

LU invention relates to control systems for adjustable-speedelectric motors, and it has particu- .lar relation to systems incorporating automatic accelerating means which, during the starting '5 cycle, progressively increase the speed of the motor in a plurality of time-spaced steps.

Generally stated, the object of my invention is to improve the starting perfomance of adinstable-speed electric motors, particularly those l intended for use in cloth finishing and other ap plications whereV closely controlled acceleration is important.

A more specific object is to maintain the rate of startlngpacceleration substantially uniform for 15 differing settings of the field rheostat or other device which selects the motor operating speed. My invention itself, together with additional objects and advantages, will best be understood through the following description of a specific 20 embodiment thereof when taken in conjunction with the accompanying drawing in which:

Figure 1 is a diagrammatic view of apparatus and circuits representing one preferred form of my invention applied to an automatic accelerat- 25 ing system for a direct-current motor, and

Fig. 2 is a diagram of curves illustrating the performance of the complete system of Fig. 1 for two different settings of the speed-selecting rheostat.

In Fig. 1 of the drawing, the motor to be controlled is represented at I0 as being of a wellknown direct-current type adapted to derive energizing current from a power circuit |2-.i4. The circuit through which the armature winding 35 I6 is energized includes one or more starting resistor sections I8. and the contact member 20 of a main control contactor 22. The energizing circuit for the eld winding 24 includes a plurality of accelerating resistor sections 26 and a speed- 40 setting rheostat 28.

Contactar 22 controls the operation of motor Ill by completing its armature energizing circuit. It is actuated by a winding 38 energized through a push button 32 and deenergized by a 45 second push button 33. Once actuated, contactor 22 locks itself in through an auxiliary member 35 thereby maintaining the armature circuit closed until this actuating circuit is interrupted atl push button 33. i

Resistors I8 limit the initial starting current to a safe value. A short time after the armature is energized a relay 34 is actuated through a circuit which includes a delayed closing member 3| of contactor 22. This bypasses one of the sections .55 of resistor I8. The resulting increase in current further raises the motor speed. After a further short delay, a second relay 36 is similarly actuated by action of an auxiliary contact member 31 of relay 34. This bypasses the remaining resistor section I8, thereby impressing the full power circuit voltage upon the motor armature.

In the system disclosed, field circuit resistors 26 are then progressively bypassed by the associated accelerating relay devices 38, 40, 42, 44 and 46 which are arranged automatically to actuate oneafter the other in time-spaced succession. The range of this automatic field acceleration control begins at what may be designated as full ield speed. This is indicated at 48 in Fig. 2. It ends at the value of motor operating speed which the setting of rheostat 28 determines.

When the arm 50 of this rheostat is rotatedcounter-clockwise to insert all of the resistor 52 into the lield winding circuit, this operating speed of the motor will be maximum. Such a value is indicated at 54 in Fig. 2 and may be designated as a maximum weak eld speed. When, as represented in Fig. 1, the rheostat arm occupies an intermediate position in its range of adjustment, this nal operating speed will be of some lower value such as indicated at 56, in Fig. 2.

Systems of the general type thus far described are well known, and have for some time been extensively utilized with adjustable-speed directcurrent motors. Such motors are excellently suited for use in driving cloth finishing machines and in other applications, where a large range of adjustment in driving speed is essential. A range of adjustment of 3 to 1 or 4 to 1 by field control is readily attained.

All such prior art control systems with which I am familiar are, however, subject to a serious disadvantage. In the past the accelerating relays (devices 38, 40, 42, 44 and 46 of Fig. 1) have been designed to introduce the same time delay between successive actuations under all conditions of motor operation. This uniform time spacing of successive decreases in the motor excitation means that the total time required to accelerate the motor from its full-field speed `48 to its nal operating speed is always the same.

When the iield rheostat 28 is set for maximum operating speed, the rate of acceleration will be determined by the slope of curve 56 of Fig. 2. When, however, the setting is for a lower speed 56, the rate of acceleration will be decreased to the much lower value represented by the slope of curve 60. The average rate of acceleration cannot therefore be the same for two different settings of the speed determining device 28.

l For many applications this variation is highly objectionable. In cloth flushing machines for example, the operating speed of the driving motor must be adjusted in accordance with the cloth being processed. A fine open material such as-surgical gauze usually runs at a speed approximately four times as fast as a heavy shirting material. Particularly when a comparatively weak material is to be run at high speed, the driving motor must be accelerated with caution. In order thatV the material may not be injured during the starting cycle, it is necessary that the acceleration be uniform from si indstill up to the full operating speed.

In accordance with my invention, I so arrange the automatic accelerating apparatus that the rate of acceleration of the motor speed will be maintained substantially uniform regardless of the setting of the field rheostat 28 or other speed stantially coincides with the curve 58 according towhich` the motor accelerates to the high speed 54. As examination of these curves will reveal, the total accelerating time is much less for the slower iinal speed 56 than for the high operating speed 54. 'Ihe time for each individual step of acceleration, determined by the spacing between successive actions of devices 38 to 46, is correv spondingly'reduced for the slower speed.

'Ihe curves of Fig. 2 apply to the control system of Fig. 1 which provides three steps of armature control and ve steps of ileld control. The curve 58` represents how the motor I8 accelerates to a maximum speed of 1600 R. P. M. while the curve 62 applies to the same motor accelerating,

' to 800 R. P. M. Up to the full-field speed of 400 R. P. M. the two curves exactly coincide. From this point on, however, or within the range of field acceleration, the increment per step is three times as great for curve 56 as for curve 62.

In the embodiment of my invention represented in Fig. 1, the timing between the successive steps of armature acceleration may be determined by any suitable form of delaying device associated with control devices 22 and 34 and represented in the form of dash pots 64. The proper timing for these steps of acceleration will in general remain constant for a given application 'and-when once determined may remain fixed thereafter.

As previously explained, the timing relays 38 to146 which control the eld acceleration are of a type capable of adjustment in response to the setting of motor field rheostat 28. In the system of Fig. 1, the relays chosen for this purpose are of the inductive type, the time of operation of I which is readily adjusted by varying the current flow through a demagnetizing or timing winding 66. The magnitude of this current, in turn, is adjusted by means of an auxiliary element 68 ofthe speed-setting rheostat 28. This element is included in the circuit through which the several relay timing windings `66 are energized.

In addition to the timing windings, each of the eld accelerating relays comprises a U-shaped or 'other equivalent core 1l which, when magnetized by a main winding 12, biases a plvoted a'rmature 14 into the downwardly illustrated position against the upward pull of a spring`16. The

,core also carries a heavy damping conductor 'I8 the circuits of which they form a part. Deen;

ergization of the main winding allows neutralizing winding 66 slowly to reduce the core ilux. After a time delay, this reduction is carried to a point where spring 16 biases the armature 14 upwardly, thereby opening the relay contact members.

The operation of these ield accelerating relays in the system represented is as follows:

Upon closure of armature accelerating relay 36, which impresses full line voltage upon the motor armature winding i6, an auxiliary contact deenergizes the main winding of eld accelerating relay 38. After a time delay this relay biases its contact members upwardly, inserting the rst resistor section 26 into the motor eld winding circuit.

In so actuating, an auxiliary contact member 82 of the relay interrupts the energizing circuit for the main winding of field accelerating relay 46. After \a time delay it similarly inserted a second resistor section 26 into the eld winding circuit and by an auxiliary contact 84, places relay 42 in a condition for actuation. In delayedly actuating this relay introduces a third resistor section 26 and places relay 44 in condition for actuation. This, in turn, causes relay 46 to insert the last resistor section 26 into the eld winding circuit.

In this manner the motor speed is increased from the full-held value 48 to the iinal operating value in a plurality of time spaced steps. The spacing of these steps varies with the position of speed setting rheostat 28. When the arm 58 is rotated counter-clockwise to a high speed position, the portion of auxiliary resistor 66 in active circuit with the relay timing winding 66 is maximum. The comparatively weak current supplied p to these windings causes the delay in the relay actuation to be prolonged, as is required to produce an acceleration of the type shown by curve yWhen, however, the rheostat arm SII is rotated clockwise to a low speed position, only a small portion of auxiliary element 6l is in the relay timing circuit and the current traversing windings 66 is correspondingly larger. In consequence the delay in the actuation of the iield accelerating relays is correspondingly reduced to the smaller value required to produce an acceleration curve of the type shown at 62 in Fig. 2.

It will thus be seen that I have provided a very simple and effective method for maintaining the rate of acceleration uniform regardless of they setting of the speed determining rheostat associated with the controlled motor. My invention is not restricted to the particular arrangement illustrated, but is capable of broad application to all situations in which operation of the type above discussed is desired.

In representing it as applied to the eld controlled direct current motor of Fig. l, I have included only those portions oi a conventional n control circuit which are essential to a proper explanation of my invention. No attempt, for example, has been made to show the system of dynamic braking which is commonly applied to motorsoi this type, nor have I represented various other control renements such as under voltage protection, means for stopping the accelerating cycle at full-field speed, means 4for applying maximum exciting current to the eld winding during the initial starting, and the like.

Although I have shown and described a certain specific embodiment of my invention, I am fully aware that many modifications thereof are possible. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the scope of the appended claims.

I claim as my invention:-

1. In a system comprising an electric motor, a device for adjusting the operating speed thereof, and starting means including apparatus adapted progressively to increase the speed of the motor in a plurality of time-spaced steps, the combination of means for maintaining the rate of motor-speed acceleration substantially uniform for differing spe'ed settings of said device.

2. In a system comprising an electric motor, a device for adjusting theoperating speed thereof. and starting means including apparatus adapted progressively to increase the speed of the motor in a plurality of time-spaced steps, the combination of means for varying the time-spacing of said steps in accordance with the speed setting of said device.

3. In a system comprising an electric motor, a device for adjusting the operating speed thereof, and starting means including apparatus adapted progressively to increase the speed of the motor in a plurality of time-spaced steps, the combination of means for causing the time-spacing of said steps so to vary with the speed setting of said device that the rate of motor-speed acceleration is maintained substantially uniform regardless of the magnitude of said setting.

4. In a system comprising an electric motor having a speed-determining winding, a speedings in accordance with the speed-setting or said.v

rheostat.

5. In a system comprising an electric motor having a speed-determining winding, a speedadjusting rheostat associated therewith and motor starting means including a plurality of "i speed-raising relays adapted to actuate in delayed time-spaced succession, the combination of means for causing the length of said time spacings so to vary with the speed setting of said rheostat that the rate of motor-speed acceleration is maintained substantially uniform reardless of the magnitude of said setting.

6. In a system comprising a direct-current motor having a speed-determining eld winding, a speed-adjusting rheostat connected in circuit therewith and motor-starting means including a plurality of speed-raising relays adapted to actuate in delayed or time-spaced succession and each of which is provided with a timing-adjusting winding, the combination of means actuated by said rheostat for adjusting the energization of said delay-adjusting windings whereby to vary the length of time spacings in accordance with the speed setting of the rheostat.

'7. In a system comprising a direct-current motor having a speed-determining ileld winding, a speed-adjusting rheostat connected in circuit therewith and motor-starting means including a plurality of speed-raising relays adapted to actuate in delayed or time-spaced succession and each of which is provided with a timing-adjust-V ing winding, the combination of an energizing circuit for said timing-adjusting windings and an auxiliary section of said rheostat included inr saidcircuit to cause the relay timings to vary with the speed setting of the rheostat.

WALDEMAR I. BENDZ.

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