US2725508A

US2725508A - Electronic dancer roll control

Info

Publication number: US2725508A
Application number: US275540A
Authority: US
Inventors: Francis T Bailey; Frederick D Snyder
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1952-03-08
Filing date: 1952-03-08
Publication date: 1955-11-29
Anticipated expiration: 1972-11-29

Description

1955 F. T. BAILEY ETAL ELECTRONIC DANCER ROLL CONTROL Filed March 8, 1952 aw mun v os E N B N E D R VT k m B C T C H A 8 VI HB WITNESSES: i 2 flaw ELECTRONIC DANCER ROLL CONTROL Francis T. Bailey, East Aurora, N. Y., and Frederick D.

Snyder, Milton, Mass, assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application March 8, 1952, Serial No. 275,540

13 Claims. (Cl. 318-6) Our invention relates to electric systems of control and more particularly to electric control systems for controlling the speed of operation of an electric motor in a selected relation to the speed of operation of a machine.

In many industrial processes a plurality of machines successively operate on a material being processed. For example, in a variable speed direct current range drive operating on a web of cloth such as Orlon, rayon, cotton, nylon, wool, etc., it is a recognized problem to obtain satisfactory tension control between individual sections of the drive.

By means of prior art devices the tension control is obtained by employing dancer roll rheostats. Such rheostat operation always requires a relatively large minimum amount of tension for moving the mechanical linkages between the dancer roll and the rheostat shaft. Consequently, it has been extremely-difiicult to obtain satisfactory results in those many applications where very light tension control is required.

One broad object of our invention is the provision of a system of control for a motor operating a machine in a sectional drive so that very minute changes in tension, in the material being processed, suflice to control the speed of the motor.

Another broad object of our invention is the provision of an inexpensive, reliable system of control that responds to extremely small variations in tension in the material passing from one machine to another machine in a continuous process drive.

A further object of our invention is the provision o a tension regulating system for a web of material in a continuous process drive operating on a wcbi of material.

A still further object of our invention is the provision of a system of control for a direct-current motor which effects very rapid speed of response to a change in tension or intelligence signal.

Other objects and advantages will become moreapparent from a study of the following specification and the accompanying drawing, in which:

Figure 1 is a diagrammatic showing of a preferred embodiment of our invention;

Fig. 2 is a diagrammatic showing of a modification of our invention; and v Fig. 3 shows a modification of the contact arrangement forming part of our invention.

In Fig. 1 the rolls 1, 2, 3, etc, represent sections of a drive in which each machine is drivenby its own motor (not shown) and the material hangs in a loose loop between successive machines.

In an actual installation, a nine-section woolen-cloth washer, the loose loop is about six feet long with the two elements of the loop fairly close together, some- What like the showing in Fig. 3. The requirement was that there be substantially zero tension in the material between the sections. It is apparent that if sucha loop can be maintained at a substantially constant length, the tension in the material, except for the weight of the 1 ited States Patent C "ice 2 loop, is extremely low and the variations are small so long as but small changes in loop length sufiice to actuate the control.

The loops shown in Figs. 1 and 2 are shown rather wide merely so as not to crowd the showing of the circuits.

In Fig. 1, the motors for driving the rolls 1 and 3 are not shown and need not be shown because our electric control system does not involve a complicated interconnected control as is often used in sectional drives. The motor M is coupled to drive the machine 2. The armature 10 of the motor is energized from a suitable constant potential direct-current source indicated by the terminals shown. The speed changes of motor M are eifected entirely by means of field excitation control.

In this control the field winding 11 is connected to the direct-current terminals of the full-wave rectifier 12. The alternating current to the rectifier 12 is supplied by the transformer T having the secondary winding 17 and the primary winding 18 connected to alternatingcurrent supply buses of the mill.

Our invention is not limited to field control only. Our invention is equally eifective if the armature were connected to the rectifier 12 and the motor field be energized from constant potential direct current terminals, as the terminals shown.

The transformer secondary 17 and rectifier 12 are connected in a loop circuit that may be traced from the right-hand terminal of the rectifier through the adjustable resistor 13, the primary winding 14 of the transformer 15 connected in parallel with the adjustable resistor 16, the secondary winding 17, to the left-hand terminal of the rectifier 12.

The transformer 15 has its secondary winding 19 connected in a loop circuit with the anode 20 and cathode 21 of the thyratron tube 22. When tube 22 is not conducting, the transformer iron of the transformer 15 is unsaturated and, in consequence, the reactance of the primary winding 14 is very high. The result is that the voltage supplied to the rectifier 12 is very low and the resulting field current in field 11 is also very low. The motor thus speeds up. However, when the tube 22 is conducting, the transformer 15 is loaded, its magnetic circuit becomes saturated, and, as a result, the reactance of the primary winding 14 is very low. The voltage supplied to the rectifier 12 is high, and the field current in field 11 is high with the result that the motor speed is low.

To prevent excessive motor speeds, we provide the adjustable resistor 16 in parallel to the primary 14. The minimum field current and, thus, the maximum motor speed may, therefore, be readily adjusted by adjusting the effective resistance of resistor 16. To prevent the motor speed from dropping too low, we provide the adjustable resistor 13 in the loop circuit including the rectifier 12. The motor thus operates either at some low speed when the tube 22 is conducting or some higher speed when the tube 22 is not conducting. These two motor speeds need not necessarily be widely difierent, but the two speeds do have to be alternately above and below the reference speed, which reference speed may be either the speed of roll 1 or the speed of roll 3. The purpose of this will become more readily apparent fromthe descripthe secondary through the common lead 33. The capacitor 34 is connected between the junction 27 and lead 33 and the

resistors

35 and 36, connected in series in the order recited, are connected between the junction 27 and the lead 33. The electric characteristics of the elements 23 to 36 inclusive are so chosen for the circuit arrangement just discussed that tube 22 is normally non-conducting.

With the switch S in the position shown, the machine section to the right of the section to which motor M is connected is considered as the machine operating at the reference speed. Further, since tube 22 is non-conducting, the motor M operates at its higher speed. The higher speed of motor M is so selected that roll 2 operates at a slightly higher speed than the speed of roll 3. The result is that the web W, assuming web movement from left to right, is so moved between roll 2 and roll 3 that the lax loop becomes longer and longer.

The instant the web touches the contacts 41. and 42 a circuit is established from the positive, or right-hand side, of the capacitor 34 through switch contacts 37, conductor 38, switch contacts 39, conductor 4%

contacts

41 and 42 bridged by the bight portion of the loop 1L2 of the conducting strip W, conductor 43, contacts 44, and resistor 24 to the grid 45, making the grid less negative, thus causing the tube to become conducting. As soon as tube 22 becomes conducting, the excitation of field 11 is increased and the motor slows down. As soon as the motor has slowed down suficiently to raise the loop 1L2 off the

contacts

41 and 42, the tube comes non-conducting and the motor goes back to its higher speed to thus repeat the cycle. The motor M thus runs at an average speed equal to the reference speed.

In view of the extreme simplicity and the very rapid response of our control, the loop length for a six-foot loop varies no more than a half an inch for each cycle of operation, and the time length of each cycle is in the neighborhood of two to three seconds.

Of course, our systems of control are not limited to the particular circuit arrangement and function discussed. If the web is assumed to move from left to right and the speed of roll 1 is the reference speed, then the switch S may be thrown to the right. Now, if roll 2 runs slower than roll 1, then the loop 1L1 will sooner or later bridge the contacts 47 and 48. When this takes place, a circuit is established from the negative, or right-hand, side of capacitor 34, through contacts 26, conductor 33, contacts 39, conductor 46, contacts 47 and 48 bridged by the loop 1L1, conductor 49, contacts 44, and resistor 24 to the grid 45. The grid 45 thus becomes more negative to thus stop the conduction of tube 22. In consequence, the excitation of field 11 is decreased and the motor M speeds up to raise the loop 1L1 off the contacts 47 and 4-3. As soon as the circuit at contacts 47 and 43 is broken, the grid 45 becomes less negative and the tube 22 becomes conducting to thus decrease the speed of motor M to thus efifect a repetition of the cycle.

In the showing in Fig. 2, the elements designated by

reference characters

102, 103, 111 to 122 inclusive, and 128, 129, 130, 145, M and 10T correspond in structure and function to the elements in Fig. 1 designated by reference characters 2, 3, 11 to 22 inclusive, and 28, 29, 30, 45, M and T, respectively.

The secondary winding 128 is connected to the fullwave rectifier 131. The direct-current terminals of this rectifier are connected across the capacitor 134 with the positive terminal being grounded. The negative terminal is connected to the grid 145 through the

resistors

125 and 124 connected in series. A conductor 140 has its lower end connected to the junction between the

resistors

125 and 124 and has its upper, or other, end connected to a contact 141 disposed below the bight of the loop 2L2 between the

rolls

102 and 103.

In many Processes, as in the washing and dyeing of materials, the web is quite conductive so that grounding l of the machine grounds the web, and when the loop 2L2 touches contact 141, both the contact 141 and conductor are grounded.

If the arrangement is such, for the circuit conditions shown in Fig. 2, that tube 122 is non-conducting, then the speed of motor 10M is at its higher value, with the result that loop 2L2 is being lowered, because the speed selection is such that the speed of roll 102 is higher than the speed of roll 103. As soon as the loop 2L2 engages the contact 141, the grid becomes less negative and tube 122 becomes conducting. The speed of motor 16M is thus decreased until the loop 2L2 moves to the position shown to again increase the motor speed and thus repeat the cycle.

In some industrial processes, the web is nonconductive. In such case, a very light spring-biased grounded roller R rides in the bight of the loop 3L2 and alternately causes the contact 342 to engage the contact 341 to ground the conductor 34% to thus alternately cause the grid 14-5 to become less negative and more negative to cause the tube to alternately conduct and not conduct and, in consesequence, alternately cause the motor ltiM to slow down and to speed up. The spring preferably lifts on the roller by a force just a trifie less than the weight of the roller.

While We are aware that many attempts have heretofore been made to solve the problem before us but such prior attempts have resulted in apparatus much more involved, considerably more expensive, and, worst of all, less reliable and less expeditious in response than our apparatus.

While our invention is made in a crowded art, We, nevertheless, believe that our invention is capable of various adaptations and that changes and modifications may be made or substitutions resorted to which come within the spirit of our invention as set forth in the claims hereto appended.

We claim as our invention:

1. In a system of control for a motor operating a machine for moving a web of material with reference to a second machine also coacting with the Web and operating a reference speed, in combination, a direct-current motor having an armature winding energized by a constant direct-current potential and coupled to the first machine, said motor having a field winding, a full-wave rectifier, said field winding being connected to the direct current terminals of the rectifier, a loop circuit including a transformer secondary winding energized at a suitable fixed voltage and frequency from an energized primary winding, the alternating-current terminals of the full-wave rectifier, and a reactor, means for changing the reactance value of the reactor from one value to a different value, the electrical characteristics of the elements associated with the field winding being so chosen that the motor runs at a speed somewhat higher than the reference speed for one value of reactance of the reactor and runs at a speed somewhat lower than the reference speed for another value of reactance of the reactor, and means responsive to selected speed changes of the motor for alternately altering the reactance value of the reactor to cause said motor to alternately operate at a speed higher than the reference speed and a speed lower than the reference speed.

2. In a system of control for a motor, in combination, a direct-current motor having an armature winding energized at a substantially constant potential from a suitable source, and having a field winding the excitation of which is to be varied to control the speed of the motor, a rectifier, circuit means for connecting the motor field to the directcurrent terminals of the rectifier, a loop circuit including the rectifier, a reactor, and a pair of terminals energized with alternating current, whereby the motor field winding is energized as a function of the reactance value of the reactor, a shaft coupled to be driven by the motor, control means for alternately changing the reactance value of the reactor from a first value to a second value, to the first value, and so on, so as to alternately alter the motor speed between two values, and means responsive to the difference between the actual speed of the motor and its average speed to control the operation of said'control means.

3. In a system of control for a motor, in combination, a direct-current motor having an armature winding energized at a substantially constant value from a suitable source and having a field winding the excitation of which is to be varied to alter the speed of the motor, a full-wave rectifier, field excitation circuit means including connections of the field to the direct-current terminals of the rectifier, current control meansfor selectively limiting to any selected value the maximum current to be carried by the field winding, and a loop circuit including a pair of terminals energized with alternating current, a reactor, and the alternating-current terminals of the rectifier, whereby the motor field winding is energized as a function of the reactance value of the reactor and the setting of the current control means, reactive control means for alternately changing the reactance value of the reactor between two selected values to thus alternately alter the motor speed between two values, and means responsive to the difference between the actual speed of the motor and its average speed to control the operation of said reactance control means. i

4. In a system of control for a motor, in combination, a direct-current motor having an armature winding energized at a substantially constant value from a suitable source and having a field winding the excitation of which is to be varied to alter the speed of the motor, a full-wave rectifier, field excitation circuit means including connections of the field to the direct-current terminals of the rectifier, current control means for selectively limiting to any selected value the maximum current to be carried by the field winding, and a loop circuit including a pair of terminals energized with alternating current, the alternating-current terminals of the rectifier, and an impedance circuit adjusted to have a selected maximum impedance sufficiently low to cause no less than a selected minimum of field current to traverse the field winding, whereby the motor field winding is energized as a function of any impedance change of the impedance circuit and the setting of the current control means, impedance control means for alternately changing the impedance value of the impedance circuit between said maximum impedance value and some selected lower impedance value to thus alternately alter the motor speed between a selected maximum speed and a selected lower speed, and means responsive to the difference between the actual speedof the motor and its average speed to control the operation of said impedance control means.

5. In a system of control for a motor, in combination, a direct-current motor having an armature winding energized at a substantially constant value from a suitable source and having a field windingthe excitation of which is to be controlled to alter the speed of the motor, a fullwave rectifier, field excitation circuit means including connections of the field winding to the direct-current terminals of the rectifier, and a loop circuit including a pair of terminals energized with alternating current, the alternating-current terminals of the rectifier, and an impedance circuit adjusted to have a selected maximum impedance sufiiciently low to cause no less than a selected minimum of field current to traverse the field winding, whereby the motor field winding is energized as a function of any impedance change of the impedance circuit, impedance control means for alternately changing the impedance value of the impedance circuit between said maximum impedance value and some selected lower impedance value to thus alternately alter the motor speed between a selected maximum speed and a selected lower speed, and means responsive to the difference between the actual speed of the motor and its average speed to control the operation of said impedance control means.

6. In a system of control, in combination, a direct-current motor having an armature winding in use energized 6 at a substantially constant value, and having a field winding, a full-wave rectifier having its direct-current terminals connected to the field winding, a loop circuit infor eifecting a certain bias on the control grid, and means responsive to a difference between the actual speed of the motor and the average speed of the motor for so altering the grid bias as to affect the magnitude of the current conducted by the tube in such a sense that the reactance of the secondary is so changed as to alter the motor speed to bring it back toward its average speed.

7. In a system of control, in combination, a direct-current motor having an armature winding in use energized at a substantially constant value, and having a field winding, a full-Wave rectifier having its direct current terminals connected to the field winding, a loop circuit including the alternating-current terminals of the rectifier, an adjustable resistor, the primary winding of a transformer, and a pair of terminals energized vwith alternating current, a secondary winding for the primary winding in the loop circuit, a thyratron tube having an anode and. a cathode connected in a loop circuit with the secondary winding, a control grid for thethyratron, energizing circuit means for effecting a certain bias on the control grid, and means responsive to a difference between the actual speed of the motor and the average speed of the motor for so altering the grid bias as to affect the magnitude of the current conducted by the tube in such a sense that the reactance of the secondary is so'changed as to alter the motor speed to bring it back toward its average speed.

8. In a system of control, in combination, a direct-current motor having an armature winding in use energized at a substantially constant value, and having a field winding, a full-wave rectifier having its direct-current terminals connected to the field winding, a loop circuit including the alternatingcurrent terminals of the rectifier, the primary winding of a transformer connected in parallel to an adjustable resistor, and a pair of terminals energized with alternating current, a secondary winding for the primary winding in the loop circuit, a thyratron tube having an anode and a cathode connected in a loop circuit with the secondary winding, a control grid for the thyratron, energizing circuit means for effecting a certain bias on the control grid, and means responsive to a difference between the actual speed of the motor and the average speed of the motor for so altering the grid bias as to afiect the magnitude of the current conducted by the tube in such a sense that the reactance of the secondary is so changed as to alter the motor speed to bring it back toward its average speed.

9. In a system of control, in combination, a direct-current'motor having an armature Winding in use energized at a substantially constant value and having a field winding, a full-wave rectifier having its direct-current terminals connected to the field winding, a loop circuit including the alternating-current terminals of the rectifier, the primary windings of a transformer and a pair of terminals energized with alternating current, a secondary winding for the primary winding in the loop circuit, an electronic tube of the thyratron type having an anode and a cathode connected respectively to the terminals of the secondary winding, a control grid for the tube, means for placing a selected bias on the grid so that the tube is non-conducting, whereby the reactance of the primary Winding in the loop circuit is a maximum and in conse' quence the field winding of the motor is excited at a minimum to cause the motor to run at a speed higher than a certain selected constant reference speed, a second motor operating at said constant selected reference speed, and means responsive to a certain accumulated positive speed difference between said motors for altering the grid bias to make the tube conducting to thus cause the motor to run at a speed lower than said selected reference speed, said last-named means being operable in response to a certain accumulated negative speed difference between the motors to establish the original bias on the grid.

10. In a system of control, in combination, a directcurrent motor having an armature Winding in use energized at a substantially constant value and having a field winding, a full-wave rectifier having its direct-current terminals connected to the field winding, a loop circuit including the alternating-current terminals of the rectifier, an adjustable resistor for limiting the maximum current to flow in the loop circuit, the primary windings of a transformer, and a pair of terminals energized with alternating current, a secondary winding for the primary winding in the loop circuit, an electronic tube of the thyratron type having an anode and a cathode connected respectively to the terminals of the secondary winding, a control grid for the tube, means for placing a selected bias on the grid so that the tube is non-conducting, whereby the reactance of the primary winding in the loop circuit is a maximum and in consequence the field winding of the motor is excited at a minimum to cause the motor to run at a speed higher than a certain selected constant reference speed, a second motor operating at said constant selected reference speed, and means responsive to a certain accumulated positive speed difference between said motors for altering the grid bias to make the tube conducting to thus cause the motor to run at a speed lower than said selected reference speed, said lastnamed means being operable in response to a certain accumulated negative speed difference between the motors to establish the original bias on the grid.

11. In a system of control, in combination, a directcurrent motor having an armature winding in use energized at a substantially constant value and having a field winding, a full-wave rectifier having its direct-current terminals connected to the field winding, a loop circuit including the alternating current terminals of the rectifier, the primary windings of a transformer connected in parallel to an adjustable resistor to limit the minimum current to flow in the loop circuit, and a pair of terminals energized with alternating current, a secondary winding for the primary Winding in the loop circuit, an electronic tube of the thyratron type having an anode and a cathode connected respectively to the terminals of the secondary winding, a control grid for the tube, means for placing a selected bias on the grid so that the tube is non-conducting, whereby the reactance of the primary winding in the loop circuit is a maximum and in consequence the field winding of the motor is excited at a minimum to cause the motor to run at a speed higher than a certain selected constant reference speed, a second motor operating at said constant selected reference speed, and means responsive to a certain accumulated positive speed difference between said motors for altering the grid bias to make the tube conducting to thus cause the motor to run at a speed lower than said selected reference speed, said lastnamed means being operable in response to a certam accumulated negative speed difference between the motors to establish the original bias on the grid.

12. in a system of control, in combination, a directcurrcnt motor having an armature winding in use energized at a substantially constant value and having a field winding, a full-wave rectifier having its direct-current terminals connected to the field winding, a loop circuit including the alternating-current terminals of the rectifier, an adjustable resistor for limiting the maximum cur rent to flow in the loop circuit, the primary windings of a transformer connected in parallel to an adjustable resistor to limit the minimum current to flow in the loop circuit, and a pair of terminals energized with alternating current, a secondary winding for the primary winding in the loop circuit, an electronic tube of the thyratron type having an anode and a cathode connected respectively to the terminals of the secondary winding, a control grid for the tube, means for placing a selected bias on the grid so that the tube is non-conducting, whereby the reactance of the primary winding in the loop circuit is a maximum and in consequence the field winding of the motor is excited at a minimum to cause the motor to run at a speed higher than a certain selected constant reference speed, a second motor operating at said constant selected reference speed, and means responsive to a certain accumulated positive speed difference between said motors for altering the grid bias to make the tube conducting to thus cause the motor to run at a speed lower than said selected reference speed, said last-named means being operable in response to a certain accumulated negative speed difference between the motors to establish the original bias on the grid.

13. A system of control for a direct-current motor comprising one motor operating at a selected fixed reference speed, a second motor having an armature winding and having a field winding, one of said windings being excited at a fixed value and the other alternately excited by two values of excitation to cause the second motor first to run at a speed that is higher than the speed of the first motor and second to run at a speed that is lower than the speed of the second motor, and means responsive to a certain accumulated speed difference of one sense between the motors to increase the excitation of the second motor to its lower value and responsive, after the second motor operates at its lower speed, to a certain accumulated speed difference of an opposite between the motors to decrease the excitation of the second motor and so on, whereby the second motor is caused to have an average speed equal to the speed of the first motor.

References Cited in the file of this patent UNITED STATES PATENTS 1,426,123 Stoekle Aug. 15, 1922 2,597,136 Snyder May 20, 1952 FOREIGN PATENTS 389,801 Great Britain June 18, 1931