US2169016A

US2169016A - Synchro-tie control

Info

Publication number: US2169016A
Application number: US180395A
Authority: US
Inventors: Rest R Baker
Original assignee: Westinghouse Electric and Manufacturing Co
Current assignee: CBS Corp
Priority date: 1937-12-17
Filing date: 1937-12-17
Publication date: 1939-08-08
Anticipated expiration: 1956-08-08

Description

Aug. 8, 1939. R. R. BAKER SYNCHRO-TIE CONTROL Filed Dec. 17, 1957 INVENTOR Rest R. Baker:

Patented Aug. 8, 1939 SYNCHBO-TIE CONTROL Rest R. Baker, Swissvale, 2a., udgnor to Westinghouse Electric A: Manufacturing Company, East Pittsburgh, Pa., a corporation of Pennsylvania Application December 1'1, 193?, Serial No. 180,395

'1 Claims. (CL 3-15) My invention relates, generally, to speed control systems and, more particularly, to a synchrotie system for maintaining a substantially constant speed ratio between two rotating elements.

In certain industrial operations such, for instance, as paper making, a web of material is passed from one roll to another and is subjected to a tension as it passes between the rolls. It willbe apparent that if the web were of some material that could not be easily stretched, it would only be necessary to maintain equal peripheral speeds on the rolls in order to properly pass the web from one roll to the next. If, however, the web were of a material having a tendency to shrink or lengthen while passing between the rolls, the peripheral speeds of the rolls would have to be different by an amount-depending upon the amount of shrinking or lengthening of the web. In some of such processes, slippage or creepage exists between the processing rolls and the material being processed, necessitating different peripheral speed ratios of the cooperating rolls depending upon the amount of this slippage or creepage.

The rolls cannot be rigidly mechanically connected together so as to maintain a fixed ratio of peripheral speeds determined by the amount of lengthening or shrinking of the web or by slippage or creeping for the reason that the amount of the lengthening or shrinking of the webor the degree of slippage or creeping may vary as between different parts of the web, thus requiring that the ratio of the peripheral speeds of the rolls vary.

It is common practice, in carrying out such industrial processes, to drive one of such rolls directly from the other by means of a drive belt and to provide for slippage of the belt on the driven roll to compensate for variations in the ratio of the required peripheral speeds of the rolls. Thus, with the ratio of the peripheral speeds of the rolls adjusted for a given amount of lengthening of the web between the rolls, and an amount of belt slippage to produce this ratio of speeds, in the event that such lengthening increases or decreases, the amount of slippage will automatically vary because of the variation of tension on the web between the rolls thus tending to keep approximately the proper tension on the web regardless of variations in the amount of lengthening of the web between the rolls. It will be apparent that this method of speed control by belt slippage is wasteful of power and causes excessive wear on the operating machinery.

An object of my invention is to provide an electrical drive for associated rotating elements which shall function to provide ratios between the speeds of the rotating elements equivalent to the functioning of a slip belt drive between the rotating elements.

Another object of the invention is to provide an electrical drive connection between roll members which cooperate to move a web member which shall function to vary the ratio of the speeds of the-rolls in accordance with variations of the tension on the web member between the rolls. a

A further object of the invention is to provide an electrical drive connection between roll members which cooperate to move a web member, which shall function to vary the ratio of the speeds of the rolls in accordance with variations in the amount of change in length of the web member as it is passing between the rolls and which may be selectively adjusted for predetermined normal speed ratios.

A still further object of the invention is to provide an electrical drive connection between roll members which cooperate to move a web member which shall function to vary the ratio of the speeds of the rolls in accordance with the variations in the amount of slippage or creepage of the web member as it is passing between' the rolls, and which may be selectively adjusted for predetermined normal speed ratios.

These and other objects and advantages of my invention will be apparent'from' the following detailed description taken in connection with the accompanying drawing, in which:

Figure 1 is a diagrammatic illustration of a preferred embodiment of my invention as applied to the calender and winding reel of a paper machine, and

Fig. 2 is a graph of the speed-torque characteristics of an auxiliary motor employed in carrying out my invention.

In practicing a preferred embodiment of my invention, a variable speed motor is provided for driving the rolls of a paper calender. A wound rotor polyphase induction generator of the type generally designated as a'syncbro-tie or selsyn unit in synchro-tie systems having its stator connected to a polyphase source of constant frequency, is driven by the calender driving motor in such a direction with respect to the direction of phase rotation of the flux of the stator of the induction generator, as to produce a frequency which is the sum of the frequencies produced by rotation of the generator rotor and the rotation of the generator stator flux.

- its speed torque characteristics may be varied.

This auxiliary motor may be a wound 'rotor induction motor as herein described, or it maybe any motor with a suitable drooping speed-load characteristic similar to that of the wound rotor induction motor, such as a direct current'series' wound motor of suitable design. The auxiliary motor is geared to drive the rotor of the second induction generator at a comparatively low speed in such -a direction with respect to the direction of phase rotation of the flux of the second induction generator as to produce a frequency which is the sum of the frequencies produced by--rotation of the generator rotor and the rotation-of the generator stator flux.

The speed of the winder driving motor will? be proportional to the resultant oithe frequencies applied to its rotor and stator and will vary with the speed of the auxiliary motor. Since the speed of-the auxiliary induction motor will decrease with increased torque,-the'winder speed will be automatically decreased. with increased torque on the web to thus automatlcally main-" tain the desired speed relation to produce' thedesired substantially constant tension on'the web, as it passes from the calender to the winder.

Referring now to Fig. 1 of thedrawing, a-paper calender 4 driven by a variable speed motor 6 delivers the strip of paper 8 which'is wound bywinder'lO driven by a wound rotor induction motor l2. A polyphase-induction generator --l4, which may be such a generator as is'commonly used as the sending unit-in synchro-tiesystems,

f is connected on the shaft of the motor 6 or--by any other common mechanical means to be drivenby motor 6 and to thus have its speed varied withthe variations of the speed of 'motor 6. .-The: stator l6 of the induction: generator sis-cons nected to be energized from a standard source of alternating current X, Y, Z and-to have.the:- direction of rotation of the field flux produced by the stator opposite to the direction of rotation-0t; the motor l8 of the induction generator l4.-

A second induction generator 28 has its stator winding 22 connected .to be energized by the po-; tential generated by induction generator l 4."- The. rotor 24 of induction generator .28 ,is :driven through suitable gearing at a relatively. low;

speed by the wound rotor induction motor-- 26.. The stator 28 of induction motor 2 6-is connected to be energized by the outputpote'ntialbfithe: induction generator l4. The rotor. 38: or .the induction motor 26 has its-windings connected incircuit with variable resistance elements"32,--84

and 36. The direction of rotation of therotor; '24 of induction generator-28 is opposite tp-the. direction of rotation of the flux produced by the\ stator winding 22 of induction generator".

The induction motor l2 which-drives'thewinder 10 has the circuit'of its rotor? 38 connectedato be.

energized by the output potential from the rotor- 24 of induction generator 28. The stator 4010finduction motor I2 is connected'tO be ene g ed from the standard source of alternating current X, Y, Z above referred to. The windings of the rotor 38 and the stator 48 of induction motor [2 are so connected that the rotation of the field flux'produced by each of these windings is in the same direction.

It will be seen in the operation of the device that the induction motor I2 is driven by the output of the induction generator l4 modified by the output of induction generator '20 which is under control of the induction motor 26. Assuming that the field flux produced by the polyphase stator winding I6 of induction generator I4 is rotating at a speed equivalent to 60 cycle frequency and that the rotor i8 of induction generator i4 is rotating in the opposite direction at a speed equivalent to the 60 cycle frequency, then a'potential of cycles frequency will be induced in the rotor winding of induction gen- Y erator l4 and will be applied to the stator windings of induction generator 28 and induction motor 26. Assume also that the speed of motor 28 is such as to drive the rotor 24 of induction generator 28- at a speed equivalent to a'frequency of 10 cycles. This will cause a potential of a frequency-of cycles to be generated in the'rotor winding of induction generator 28 and to be applied to the winding of the rotor 88 of induction motor [2. Further, assume that the winding 48 of the induction motor I2 is such as to provide a flux rotation at a speed of the equivalent frequency of 60 cycles. With the rotation of the flux produced by the stator winding 48 of induction motor l2 in the same direction as the rotation of the flux produced by winding of the rotor-38 of motor l2, it will be seen that the resultantfrequency acting to drivethe rotor 38 will be the diiference between 130 and 60, or-70 cycles. Thus the speed of rotation of motor 6 and the speed of rotation of motor l2 will bear the ratio of 60 to '70.

The induction motor 26 having the

resistance elements

32, 34 and 86 connected in its rotor circuit will have a speed torque characteristic similar to that shown in Fig. 2, that is, its speed will decrease in direction proportional to the torque required .to be furnished by it. 'Let us assume that the induction motor 26 is operating under the conditions represented by the point A on the graph of. speed torque of Fig, 2. Under these conditions the motor 28 will be supplying some of the-power for driving the induction motor l2 which, in'.turn,-drives the winder 18. If new the tension on the strip of paper 8 should increase for some reason, such as decreased stretching of the strip or increased shrinkage of the strip, 9."

88', since'there will be a resultant decrease in thefrequency of the potential applied to the rotor 38 of induction motor (2. As a result, the speed of rotation of the winding l8 will be decreased, thus preventing too. great an increase in tension on the \paper strip 8. v

In a like manner, should the tension on the strip 8 decrease-for any reason, such as increased stretching or decreased shrinking of the paper' strip; less torque'will be required of the motor 26 and it will operate under the conditions represented by th' point B on the'graph of Fig. 2. This decrease in the torque requirements of induction motor 26 will cause it to increase its speed thus increasing the speed of rotation of the motor 24 of induction generator 20 which, in turn, will cause an ncrease in the speed of rotation of the induction motor i 2 through the increased frequency applied to the rotor of induction motor i 2 from the rotor of induction generator 20. 'This increase in the speed of motor l2 will cause the winder ID to increase its speed to, in turn, increase the tension on the paper strip 8. Thus it is seen that a substantially constant tension is automatically maintained on the paper strip I.

If now it is desired to maintain a different tension onthe paper strip 8, the

resistance elements

32, 34 and 3G in the rotor circuit of induction motor 2-6 may be so varied as to change the speed torque characteristics oi motor I! and to thus provide a greater torque of motor 26 for a given speed.

It will be seen that the speed of rotation of the motor 28 will vary with the speed of motor 6. since the stator 28 of motor 28 will be excited at a frequency which varies with the speed of motor 6 and for this reason the motor 26 will act to maintain a nearly constant tension upon the paper strip 8 regardless of the speed of operation of the calender and winder.

It will be seen that I have provided a simple and eiilcientelectrical drive connection between va calender and a winder of a paper mill which will function 'to maintain a substantially con-- stant tension on the paper strip between the calender and winder regardless oi the change in stretching or shrinking of the strip between the calender and winder and regardless of the speed of operation of the calender and winder.

In compliance with the-requirements of the patent statutes, I have shown and described herein a preferred embodiment of my invention. It is understood, howeverfthat the invention is not limited to the precise construction shown and described but is capable of modification by one skilled in the art, the embodiment herein shown being merely illustrative of the principles of my invention.

I claim as my invention:

-1. In a speed control system for automatically maintaining a predetermlnedtension on a web.

as it is moved by and passes between spaced roller members, variable speed means for rotating'one of said roller members, frequency responsive variable speed means for rotating the other of said roller members, and means [or producing a potential which is variable in frequency in accordance with the load on said frequency responsive means; and the speed of said first variable speed rotating means for energizing saidfrequency responsive means.

2. In a speed control system for automatically maintaining a predetermined tension on a web as it is moved by and passes between spaced roller members, variable speed means for driving one of said roller members, generator means driven by said variable speed means for gener ating a potential having a frequency proportionate to the speed of said variable speed driving means, a variable speed frequency responsive driving means for the other of said roller members, and means responsive to the load on said frequency responsive driving means and the frequency of said generator means for generating a potential ofvariable frequency for energizing said frequency responsive driving means. I

3. In a speed control system for rotating elements cooperatively engaging a traveling element, rotating means for driving one of the rotating elements, a first polyphase induction generator driven by said rotating means. a polyphase source of excitation for said first induction generator, the rotor of said first induction generator being rotated in such a direction as to generate a potential at a frequency of the sum of the frequencies produced by rotation of the rotor and the rotation of the generator stator fiux, a first wound rotor induction motor having its stator connected to be energized by the output poten-. tialof said first generator, selectively variable resistance means connected in circuit with the rotor winding of said first induction motor, a second induction generator driven by said first induction'motor, the stator of said second inductiongenerator being energized by the output of said first induction generator, the rotor of said second induction generator. being driven in such a direction as to generate a potential at a frequency which is the sum of the frequencies produced by the rotation of the rotor and the rotation of the generator stator flux. and a second wound rotor induction motor connected to drive the other rotating element and having its rotor excited by the output potential of said second induction generator and having its stator excited by said polyphase source of excitation.

4. In a speed control system for automatically maintaining a predetermined tension on a web as it is moved by and passes between spaced roller members, variable speed means for rotating one of said roller members, frequency responsive vari-- able speed means for rotating the other of said roller members, means for producing a potential variable in frequency in accordance with the load on said frequency responsive means and the speed of said first variable speed rotating means for energizing said frequency responsive means, and means for selectively varying the rate of variation'of said frequency which varies in accordance with the load on said frequency responsive means and the speed of said first variable speed rotating means.

5. In a speed control system for rotating elements cooperatively engaging a traveling element, variable speed driving means for one of said rotating elements. a frequency responsive variable speed means for driving the other oi said rotating elements, means for generating a potential for energizing said frequency responsive means variable in accordance with the speed of rotation of said first rotating element and the load on said frequency responsive means, said generating means comprising an induction generator having its stator energized in accordance with the speed of said first-mentioned variable speed driving means, a wound rotor induction motor for driving the rotor of said induction generator, and means for energizing said induction motor stator at a frequency varying with the speed of said first-mentioned variable speed driving means.

6. In a speed control system for rotating elements cooperatively engaging a traveling element, variable speed driving means for one of said rotating elements, a frequency responsive variable speed means for driving the other of said rotating elements, means for generating a potential for energizing said frequency responsive means variable in accordance with the speed ofrotation of said first rotating element and the load on said frequency responsive means, said generating means comprising an induction generator having its stator energized in accordance with the speed of said first-mentioned variable speed driving means, a wound rotor induction motor for driving the rotor of said induction generator, means for energizing said induction motor stator at a frequency varying with the speed of said first-mentioned variable speed driving means, and variable resistance means in the rotor circuit of said induction motor for selectively varying the speed-torque characteristics of said motor.

7. In a system for maintaining the proper speed relation between a paper calender and a winder cooperating therewith, a variable speed motor for driving the calender, a frequency responsive means for driving the winder, a polyphase generator driven by said calender motor, an induction generator having its stator connected to be energized by said polyphase generator and its rotor connected to energize said frequency responsive means, and an induction motor connected to drive said induction generator, said induction motor comprising a wound rotor, a selectively variable resistance means connected in said rotor circuit-and a polyphase stator winding energized by said polyphase generator.

REST R. BAKER.