US2677081A - Plural motor control system with load control - Google Patents

Description

mi -L la! April 27, 1954 J. P. MONTGOMERY, JR ,677,081

PLURAL MOTOR CONTROL SYSTEM WITH LOAD CONTROL Filed Feb. 6, 1952 2 Sheets-Sheet l WITNESSES: INVENTOR James PMonrgomery,Jr.

BY W f-ITORNEY April 27, 1 4 J. P. MONTGOMERY, JR

PLURAL MOTOR CONTROL SYSTEM WITH LOAD CONTROL Filed Feb. 6, 1952 2 Sheets-She et 2 INVENTOR James P.'Montgome ry,Jr.

To Couch WITNESSES: 477/14 20'? ATTORNEY Patented Apr. 27, 1954 UNITED STATES ATENT OFFICE PLURAL MOTOR CONTROL SYSTEM WITH LOAD CONTROL Application February 6, 1952, Serial No. 270,127

11 Claims. 1

This invention relates generally to systems ofmotor control and more in particular to such systems involving the control of a pair of motors.

In certain applications of electric motor drives, it is frequently necessary to drive a pair of mechanically inter-connected loads by means of separate motors. An application of this type is found in certain classes of paper-making machinery in that section of the machine which delivers the paper pulp to the paper press. This section is known to the trade as the couch section.

In general, a load of this type may comprise a pair of rolls which are in contact with an endless wire mesh or screen. The paper pulp is carried on the wire mesh or screen which functions essentially as a conveyor and carries the paper pulp across suitable sets of suction boxes. These suction boxes are utilized to reduce the moisture content of the pulp as it approaches the end of the couch section of the machine where it is picked off the wire and delivered to the press.

This end of the couch section in some commercial equipments is provided with a pair of rollers in contact with the wire. These are respectively known to the trade as the couch roll and the wire roll. Due to the geometry of the system the arc of contact between the couch roll and the wire is small compared to that of the wire roll about which the direction of linear motion of the wire reverses. Consequently, for a given wire tension the power transmitting capacity at the wire roll is considerably greater than at the couch roll.

To increase this capacity at the couch rolls, the couch roll is provided with a suction box internally thereof which rides against the inner periphery of the roll, the shell of which is perforated to pass moisture therethrough, and the degree of vacuum in this suction box determines the force of engagement of the wire with the couch roll. This force of engagement determines the amount of torque which may be delivered to the couch roll in driving the wire without the couch roll slipping with respect to the wire, and is of sufficient magnitude to increase the usable power at the couch roll to at least the level of that at the wire roll.

In practice, separate motors are utilized to drive the respective rolls. Accordingly, it is necessary that a degree of regulation be afiected on the motors under some operating conditions that each will tend to share the load up to substantially the maximum capacity of the connection between the couch roll and the wire, and that thereafter suitable control be aiiorded at least on the motor driving the couch roll to avoid delivering power to the couch roll in excess of the load capacity.

Accordingly it is a general object of this invention to provide a system of the character generally referred to embodying two motors wherein said motors are regulated in such a way as to prevent the delivery of excess power to a selected one of the two motors.

A further object of this invention is to provide a system of control for a pair of electric motors wherein equal load sharing over a predetermined load range is available.

A more specific object of this invention is to provide a drive for a pair of motors wherein both motors are substantially simultaneously speed regulated and one of the motors is controlled in dependence of a given operating characteristic of the load driven by the motors.

It is also an object of this invention to provide a drive of the character referred to in the preceding object wherein each motor is additionally regulated in dependence of a predetermined electrical characteristic thereof.

The foregoing statements are merely illustrative of the various aims and objects of this in vention. Other objects and advantages will become apparent upon a study or the following disclosure when considered in conjunction with the accompanying drawings, in which:

Figure 1 is a schematic illustration of an electric drive including two motors and embodying the principles of this invention; and

Fig. 2 is a schematic illustration of a second embodiment of this invention.

This invention as illustrated in each of Figs. 1 and 2 is applied to a paper-making machine of the type generally referred to in the opening statements of this specification. The paper-making machinery is only fragmentarily illustrated in the interest of simplicity. That portion of this machinery which is fragmentarily illustrated is the couch section and includes a couch roll CR and a wire roll WE which are mechanically interconnected by the wire screen or mesh W which functions as the conveyor for the paper-pulp P which is being processed. The wire W passes over the couch roll CR and then drops downwardly at an angle where it passes about the wire roll WR and returns to the other end of the machine.

The paper pulp P is carried along the upper surface of the screen in a direction from left to right as viewed and in its path of travel towards the couch roll CR passes over a plurality of suction boxes (not shown) which in practice are positioned directly beneath the wire W. These suction boxes, as explained, are utilized to draw the moisture from the pulp as it passes towards the discharge end of the couch section. The screen drags across the perforated covers of the suction boxes. The resulting frictional restraint constitutes a major portion of the couch section load. The pulp passes over the couch roll CR and is engaged by a felt belt, designate F, which passes about a pick-up roller PR located in the transfer section. The pulp adheres to the felt and is carried along the bottom side thereof from left to right as viewed towards the paper press (not shown), where final processing of the paper through the press rollers is done.

The couch roll CR is provided with a suction box, designated I, connected to a source of couch vacuum (not shown) which is independent of the vacuum source for the suction boxes over which the wire mesh passes. The couch suction box is located internally thereof, and the shell of the couch roll is suitably perforated to permit the passage of air therethrough into the suction box I. The suction box is stationarily mounted within the couch roll by suitable means (not shown) in a position with the outer perforated arcuate face thereof in sliding engagement with the inner face of the couch roll to effect a partial vacuum seal therewith.

The degree of vacuum in this chamber or suction box, as earlier explained, controls the pres-- sure of engagement of the wire W with the surface of the couch roll and hence determines the magnitude of the torque which may be delivered to the couch roll in driving the wire W without slippage of the couch roll with respect to the wire. In the present arrangement, the couch vacuum is utilized as the intelligence for controlling the motor MC which is mechanically connected to the couch roll.

In accomplishing this, the couch motor MC and a wire motor MW are each mechanically connected to the respective rolls CR and WR. The armature windings of these motors are connected in parallel to a suitable supply of constant direct current represented by the conductors designated G-land G--. Each of these motors is provided with a pair of field windings. The field windings for the couch motor MC are desig nated MC! and MCZ and the windings for the wire motor MW are designated MW! and MWZ. These respective pairs of windings are connected in opposite legs of respective bridge circuits, each of which includes resistors Bi and R2 in the remaining opposite legs. These respective bridge circuits are respectively connected, across a first pair of diagonal terminals, Ti and T2, in each, in parallel with a supply of direct current excita tion represented by the conductors designated E+ and E and the current supplied to the parallel circuits is controlled by a speed regu lating rotating contaotor, illustrated in block form only, designated SC which driven by the couch motor MC through a suitable variable speed drive generally designated VD.

The speed regulating contactor SC may be of any suitable type and by way of example may include a resistor in series in the line, the resistor being controlled by a suitable speed responsive device so that the resistance is maximum at minimum speed and minimum at maximum speed so that field current increases with speed. A device such as this if the current levels are above its rating may be utilized to control one of a pair of differentially related fields of an exalter, the other field of which is constantly excited and the armature winding of which is connected in series in the common branch suppiying the motor field generator bridge circuits, so that the exciter armature winding voltage due to the constant field excitation is opposed to the motor field supply voltage. The resistance of the speed regulating contactor again being maxi-- mum at minimum speed and minimum at maximum speed now regulates the other differential exciter field to strengthen this field as speed increases reducing th net exciter excitation and output voltage to increase motor field current as motor speed increases. As a further alternative, a tachometer generator driven by the couch motor and augmented by a small constant D. C. voltage to provide a minimum motor field at zero motor speed may be utilized as the speed intelligence for motor field excitation. With such conventional arrangements the value of current which flows in the parallel connected motor field circuits therefore depends upon the speed at which the speed regulating device or contactor is rotated, the current value increasing as the speed of rotation increases.

Each bridge circuit is provided with a rotating amplifier or regulator which is utilized to additionally control the excitation of the respective field windings in dependence of certain system derived intelligences which are utilized to control the amplifier. The amplifiers which are utilized for this application may be of any suitable type including static types such as electronic amplifiers, saturable reactors, magnetic amplifiers, etc.

The type herein illustrated involves a rotating regulating generator, that which is utilized in the bridge circuit associated with the windings of the motor MC is generally designated and that utilized in the bridge circuit associated with the field windings of motor MW is designated RW. These rotating regulators which are each driven at constant speed by motors (not shown), are similar in nature and have special operating characteristics which will be presently described.

Each rotating regulator as illustrated is a series self-energizing generator. Such mach are also available shunt connected and the tional aspects hereinafter described for the .30 machines are also obtainable with the shunt connected type. Each generator is provided with a plurality of field windings to which the spective system intelligences are applied to con trol the output thereof. Specifically referri the generator RC, this generator is provided 2 i a series field winding ROI, a differential connected field winding RC2, which is uti'. as an antihunt winding, a separately excited control field winding RC3, and a separately excited pattern field winding RC4 which is differentially related to winding RC3. These windings cor respond respectively to the windings RW l, RW3 and RW4 of the rotating regulator RW. The armature circuit of each generator, including the series field winding and a blocking recti fier 5 in series in the armature circuit, is connected across the two remaining diagonal termi nals T3 and T4 of the respective bridge circuits, the other two terminals TI and T2 of each bridge circuit being connected in the parallel excitation circuit controlled by the speed regulating contactor SC aforesaid.

These generators are arranged to operate on their air gap line, that is, the resistance line of the load circuit of each generator is adjusted to coincide with the initial straight-line portion of the no-load saturation curve by suitable resistance calibration of the load circuit, so that unstable operation of the generator obtains. Such a generator will therefore have an ouput anywhere along the tangent portions of the curves, depending upon the residual of the machine with respect to the direction of rotation. The output of the generator is then controlled, for instance by the net or differential excitation of the control field and the pattern field. These fields receiving excitation in dependence of intelligence from selected points in the system therefore urge the output voltage of the generator in the proper direction along the tangent curves, and when the required degree of control of the system is achieved, the net excitation drops to zero. At this point, assuming system conditions remain unchanged, such a self-exciting generator tends to maintain its output independently of external excitation. Should the generator output tend to wander from that condition required, one or the other of the respective controlling fields will predominate in excitation and will tend to urge the output of the generator in the proper direction to maintain the required magnitude of output. The function of the control field and the pattern field therefore becomes that of selecting the direction and magnitude of output of the generator and maintaining that point constant for a given or instant system condition. An arrangement such as this is highly desirable. Since the regulator requires no external excitation for maintaining a given magnitude of output, it is possible to regulate for zero error.

The control field of each regulating generator is excited in dependence of load current. This is accomplished in the case of control field E03 by connecting this field across a resistor R3 which is in series in the armature circuit of the motor MC and in the case of the control field RW3 by similarly connecting this field across a resistor R4 in series with the armature circuit of the motor MW. This current cue is provided in each case to prevent loading of the motors beyond their rated capacity.

Additionally in the case of the generator RC to the variable excitation of the pattern field RC4 this current cue serves to limit the output torque of motor MC at any value of speed determined by the pattern excitation at field RCA to prevent power delivery to couch roll CR in excess of the force transmitting capacity between the couch roll and the wire as determined by instant values of couch vacuum. In achieving this latter control function, the pattern field winding for regulating generator RC is excited in dependence of a voltage derived from a potentiometer PC which is connected directly across the supply conductors E+ and E--. The position of the tap of potentiometer PC determines the magnitude of excitation of the pattern field RCA and hence determines the magnitude of the output of the regulating generator RC. The pattern winding RW l of regulating generator RW is similarly connected to a potentiometer PW to be excited in dependence of the voltage tapped therefrom, this potentiometer also being excited in a circuit across supply conductors E-land E.

Potentiometer PW in practice is manually adjusted to a predetermined level and may, for example, be adjusted to provide maximum output of the motor MW. The potentiometer PC, however, has the tap thereof connected to the moving element of a vacuum-operated controller C. This controller, for illustrative purposes only, is represented as a conventional cylinder and piston arrangement in which the side of the piston, remote from the tap, is connected through a suitable line to the couch roll vacuum source (not shown). With this arrangement, the excitation of the pattern field winding RC4 is automatically varied in dependence of the couch roll vacuum which correspondingly controls the output of motor MC.

As earlier noted in this description, the capacity of the couch roll to drive the wire W is a function of the couch vacuum. Thus, this control of the potentiometer PC results in a base excitation of regulating generator RC which is a function of the couch vacuum and hence determines the magnitude of the output of the couch motor MC.

Before proceeding with the description of op eration of the system, it may be well to set forth some of the general requirements of a drive for a paper machine of the character herein generally referred to. These requirements are listed below as follows:

(1) The couch roll must be speed regulated.

(2) The ability of the couch roll to carry load is a function of the couch roll vacuum.

(3) The wire roll and couch roll must share load within the ability of the couch roll to carry load up to the full load on the wire roll.

(4) The couch roll must take all load above full load on the wire roll within the ability of the couch roll to carry load as determined by the vacuum in the couch roll. Under these conditions, the wire roll load should remain constant when the total load exceeds 200% of the wire roll motor rating.

(5) The couch section suction boxes (not shown) have a different vacuum source from that which supplies the couch roll vacuum, and therefore the ability of the couch roll to carry load varies independently of the total load on the couch section of the machine. A variation of zero to vacuum in the couch roll creates only about a 10% variation in the total load of the couch section, but will vary the ability of the couch roll to take load without slip between the wire and the couch roll over the range of zero to 100% vacuum.

(6) In connection with a specific embodiment employing, for example, a 100 horsepower wire motor, a drive of this character should;

(a) hold constant load on the wire roll above horsepower, that is, the drive must limit the load on the wire roll to 100 hp. when the total load exceeds 200 hp.;

(22) regulate the speed of the couch roll with an overriding control of current limit as a function of couch vacuum;

(0) regulate the speed of the wire roll by means of the speed cue from the couch roll with an overriding current limit above 100 hp.;

(d) prevent slipping of the couch roll with substantially no couch roll vacuum.

Further in regard to the aforesaid specific example, under certain operating conditions, the couch roll may require no more than a maximum of 12 hp. This condition, for example, could exist if the couch roll vacuum were zero. When this situation exists, it is entirely satisfactory for the couch section to slow down, in which case by suitablecircuit interconnections with the press section of the machine, the press section would also be caused to operate at a correspondingly lower speed or, alternatively, the pickup roll may be lifted from contact with the wire W.

In practice the system is started with the pickup roll temporarily displaced from the position shown so that the pickup felt is disengaged ii; iii

the wire. The entire machine is regulated from a master speed reference which synchronizes drive. The various starting controls including pushbuttons, contactors and other control devices commonly used in such a system have not seen illustrated in the interest of simplicity since such details are not necessary in understanding this invention.

Assuming that direct current power is applied to the respective supply buses or conductors, G+, G- and E+, E, suitable circuit connections exist for energizing the several components of the system illustrated in Fig. l. The armature winding circuit extends from supply conduct G+ through the armature winding of the couch motor MC, a starting resistor SR and resistor Pt to the negative conductor (3-. A second Sli circuit is established through the armature v ing or the wire motor MW and resistor series therewith between the supply conductors (3+ and G-.

The field windings for the respective motors are energized in parallel circuits across the supply conductors E+ and E- from which the citation voltages are obtained. The respective parallel motor field circuits being connected in series with the speed regulating rotating contactor SC, receive excitation in dependence of the speed of operation of the couch motor MC which *es the speed contactor SC.

Since the pattern fields of the respective regulatlng generators RC and RW are differently controlled, the function of the respective ge in controlling the respective motors difieis gree and it may be well to specifically cot-c the respective functional aspects.

couch motor regulating generator BC by reason of the variable pattern field exci functions to control the couch motor torque, any speed the drive happens to be operating, in dependence of the couch vacuum. The ampere turns of the current limit field RC3 are function of motor torque. With the regulating generator connected in the bridge circuit as shown, it is possible for the regulating generator to culate a current in the legs of the motor field bridge circuit which is essentially independent of no external circuit, that is, the supply circuit controlled by the speed regulating contactor SC. .sfherefore the current in the couch motor field bridge circuit is simultaneously a function or two things:

(a) The current from the constant voltage conductors E+ and E as determined by speed regulating contactor SC.

(b) The current produced by the regulating generator as a function of vacuum pressure at the couch roll.

The regulating generator RC operates as a current regulator working through the motor fields MCI and MC2 to control the current or load limit. on the motor through the control afforded by the pattern field RC4. The blocking rectifier 5 limits the flow of output current of generator EC to one direction only which is opposite to that produced by the pattern field RC4 and in the proper direction for that current resulting from the current limit field RC3. This current is cumulative with respect to current controlled by the speed respon sive contactor SC and therefore strengthens the motor fields MCI and MC2 when armature current exceeds the limit indicated by the pattern field ampere turns. If at any time the regulating generator output voltage drops below the voltage across the bridge circuit terminals to which it is applied, the current flowing through fields MCi and MC2 is then due only to the external supply 13+ and E-.

The wire motor regulating generator RW differs in function from the generator RC only in the degree of excitation of its pattern field RW'Z. This pattern field is excited by the tapped voltage of potentiometer PW which is normally adjusted to a pattern voltage level corresponding to substantially full power output of wire motor MW. Thus the level of current for which regulation is obtained corresponds to that existing at maximum horsepower which current level can also exist during periods of acceleration.

From the foregoing it will be appreciated that the couch regulator regulates for maximum usable horsepower within the capacity of the couch motor and the wire motor regulator regulates for maximum horsepower output or" the wire motor for an instant operating speed in dependence of load current limit.

With the circuit connections thus generally described, both of the motors MC and MW begin to accelerate. Initial acceleration of the couch motor is controlled by starting resistor SR which is shunted in steps by respective contacts felt! and SR2. These contacts are closed in sequence by any suitable conventional control means (not shown) to limit starting torque to obviate slipping of the couch roll with respect to the wire. The use of this starting resistor will depend on the specific system of application. Ccnceivably, current limit control of regulating generator winding RC3 may be adequate.

-t zero speed the starting currents in the arma tures of the respective motors are quite high. Consequently, the ampere turns of the respective current limit fields RC3 and RWS override the ampere turns of the respective pattern fields and EW-l. The resulting generator output currents fiow through the blocking rectifiers applying substantially full field to respective motor fields MCI, MC2 and MW!, MW 2. The machine characteristics and circuit calibration such that the accelerating torque load is shared by the motors. The starting current decreases as the motor speed increases and as a consequence the outputs of the respective regulating generators decrease. However, as rotational speed increases excitation due to the speed responsive contactor is introduced in increasing amounts. When the load current drops below the critical value, the pattern field ampere turns predominate and further decrease the generator outputs.

In view of the fact that the two motors are simultaneously speed regulated through field control obtained by the use of the speed regulating rotating contactor SC, it will be appreciated that these motors, assuming that they have substan' tially identical characteristics, will tend to the driven load. If the wire motor is con oiled for maximum horsepower output by the setting of the tap on potentiometer PW and if couch vacuum is sufficiently high, current limited load sharing will exist up to the time the full load the wire motor is reached. At this time the wire motor armature current rises to the critical mag nitude and tends to remain high. The drop across resistor R4 suniciently excites the current limit winding RW3 of regulating generator RW so that its ampere turns which are opposed to those of the ampere turns of pattern winding RW4 will predominate the ampere turns of the latter winding. At this point, the output of generator RW adds to that of the speed responsive contactor SC, strengthening the motor field and tending to slow the motor down. This condition is maintained due to the interaction of the windings RWS and RW i, the net ampere turns always being in a direction to maintain the output of the regulating generator at this upper current limit substantially constant.

If at this point the couch vacuum is sufiiciently high that the maximum usable horsepower at the couch roll has not yet been reached, the setting of the tap of potentiometer PC is governed by the vacuum operated controller C will be such that the ampere turns of pattern winding RC i of regulating generator RC will yet tend to predominate the opposed ampere turns of the current limit winding RC3 also associated therewith. The output of the couch motor MC will therefore continue to rise until such time as the ampere turns of winding RC3 exceed or at least balance those of the winding RC4. Regulation of couch motor horsepower at this upper limit will obtain at this point in the same manner as dcscribed in connection with the regulating generator RW.

If at this point the couch vacuum should diminish, the tap on the potentiometer PC will be moved to the right as viewed, reducing the effective ampere turns of pattern winding RC4. The net excitation of the regulating generator is now due to the current limit field and the output of the generator RC is added to the output of the speed responsive contactor SC to increase the excitation of fields MCI and M02 and decrease the speed of motor MC. As the motor current drops the ampere turns of the pattern field RC4 may again balance those of the field RC3. Regulating generator R at this point will circulate just the required current to maintain the new condition until a further system disturbance occurs. The horsepower output of the couch motor is thus maintained at this new operating level for the instant conditions.

If the total horsepower delivery to the drive under this condition has been such that the wire motor MW has not been loaded up to full rated horsepower, the load which has been dropped by the couch motor is in effect transferred to the wire motor MW. The diminishing vacuum of the couch roll which results in the resetting of the potentiometer PC to a position which weakens or reduces the ampere turns of the pattern field RC4, as described above, results in an increase in the excitation of the field windings MC! and M02 of the couch motor MC. This increase in field excitation tends to reduce the operating speed of the couch motor. As the operating speed drops, the average current passed by the speed regulating contactor SC decreases. As a consequence, the average excitation of the wire motor fields MW! and MWZ decreases, since there has been no change at this time in the control of the fields of the regulating generator RW which also controls the wire motor fields. The speed of the wire motor therefore tends to increase, increasing the horsepower input to the wire roll WR until system equilibrium i again attained. This new condition of load distribution will be maintained 10 until a further change in the vacuum condition of the couch roll CR takes place.

If the vacuum should drop to a point in which the load current of the wire motor exceeds a predetermined upper limit, the ampere turns of the current limit winding RWKi exceed the ampere turns of the pattern winding RWfil. At this point, the output of the regulating generator RW is in a direction corresponding to that for which the locking rectifier a will pass current, and the output of this regulating generator is added to the speed regulated excitation of the windings MW! and MW 2 to strengthen these fields, thereby tending to hold the speed of the wire motor at this level, and limiting the output thereof to the maximum rating.

If at the time the system is started the couch vacuum is some intermediate value tending, for example, to limit couch motor output to 50 horsepower, during acceleration, the couch and wire motors. tend to share the power delivery to the load up to the 50 horsepower level. The wire motor then tries to carry the load and further increase the speed of the drive. The rate of change of speed and the upper limit of speed of the wire motor under this condition is limited by the current limit sense of the wire motor regulator.

It will be appreciated from the foregoing considerations concerning the operation of this system that the various requirements of the system as hereinbefore enumerated are fulfilled in the control ai fordeol by this system, and that all of the several control functions are achieved without the need for manual manipulation of any of the control components of the system.

In the embodiment of the invention illustrated in Fig. 2, the arrangement of the several system components correspond essentially to that illustrated in Fig. 1. As a consequence, parts in this figure corresponding to those illustrated in Fig. 1 bear like reference characters. The principles of operation of. this system are essentially the same as those embodied in Fig. 1. The diiferences between these two systems reside in the manner in which the regulating generators for the couch motor and the wire motor are utilized to control excitation of the motor field system.

In Fig. 2, the couch motor and the wire motor are each provided with series field windings respectively designated MC3 and MW3. The respective motor armature windings together with their series field windings and respective series resistors R3 and RA are connected in parallel and the parallel circuit is connected across the supply conductors G+ and G- by means of the series connected switch S1 and adjustable rheostat ARI on the side of the parallel circuit adjacent the conductor G+ and by a switch S2 on the side of the parallel circuit adjacent the conductor G-.

The control fields for the respective motors are designated M02 and MWZ respectively. These are connected in respective branches of a parallel circuit, the couch motor field branch including in series therein, a resistor R5, the couch motor field MCZ, and the series field winding RCI oi the regulating generator RC. The wire motor field branch including a resistor R6, the field winding MW2 of the wire motor, and the series field winding RW! of the regulating generator RW. This parallel circuit is connected across the field excitation supply conductors E+ and E- by means of the speed regulating rotating contactor SC which is arranged in series with the parallel cirsuit.

The armature winding of the regulating generator RC is connected across the motor field winding M02 in a circuit including a tapped portion of the resistor R5 and a blocking rectifier 5. This blocking rectifier as in the case of regulating generator RC of Fig. l is disposed to prevent reversal of the output of the regulating generator when the ampere turns of pattern winding RC4 persistently predominate the am pere turns of current limit winding RC3. Similarly, the armature winding of regulating generator RW is connected across a tapped portion of the resistor R5 and the field winding MWZ of the wire motor, the circuit including in series the blocking rectifier 5, which prevents reversal of the output of regulating generator RW when the ampere turns of pattern winding RW i persistently predominate the ampere turns of current limit winding RW3.

For the system thus described, when the wire motor MW is operating below its load limit, the speed of the motor MW is essentially the same as the speed of the motor MC because the respec tive field windings MC2 and MWZ are again under the control of the speed regulating rotating contactor SC which is driven by the couch motor MC.

As in the preceding embodiment of this invention, when the supply conductors G+, G- and 151+, E- are energized, and the switches Si and S2 are closed, completing the connection of the armature circuits of the two motors across the motor armature supply conductors, the motors accelerate under the influence of the respective current limit controls to that speed determined by the setting of potentiometer PC under the infiuence of the couch vacuum.

Assuming the horsepower delivery by the respective motors in driving the load is below the upper limit of each and assuming further that the vacuum of the couch roll should increase, the setting of the potentiometer PC will change in a direction to increase the ampere turns of the pattern field RC4. Under this condition, the net excitation of the regulating generator RC will increase in favor of the pattern field. This decreases the output of regulating generator RC weakening the motor field MCZ tending to increase the speed of the drive.

Since the drive up to this point has not been operating at rated speed, the wire motor which has been attempting to carry the larger share of the load also increases in speed and substantial load sharing continues. As rated speed at normal load is approached the field excitation of both motors is increased by the speed responsive contactor SC and the motor speed tends to level off. Increases in speed at this point due to load variations, increases the motor field excitation to hold the speed down while decreases in speed are countered by field weakening which increases motor speed.

However, if this increase in couch vacuum is sufficiently high that the horsepower rating of the wire motor MW is exceeded, the ampere turns of the winding RW3 overbalance the am pere turns of the pattern winding RW l, and the output of the regulating generator is now of a polarity corresponding to that of blocking rectifier 5 with the result that the winding MW2 is strengthened sufiiciently in excitation to limit the wire motor current and torque. The couch motor MC will now carry the load within its capacity up to the limit of the couch vacuum as determined by the setting of potentiometer PC by the vacuum-operated controller C, at which time the current limit winding RC3 takes over the control of the regulating generator, increasing the excitation of couch motor winding MC2 to prevent overloading the couch motor. These considerations, it will be appreciated, while possibly stated a little differently, correspond to those made with regard to the system of Fig. 1.

Again as in the case of Fig. 1, if the couch vacuum should drop to a sufliciently low level, the ampere turns of winding RC3 predominate those of winding RC4, resulting in a regulating generator output which increases the excitation oi field MC2 to reduce the speed of the couch motor, thereby reducing the horsepower delivered to the couch roll CR to prevent slipping of the drive at that point. This reduction in couch motor speed reduces the excitation of the field MWZ, tending to increase the speed of the wire motor. Thus, a transfer of the load from the couch motor to the wire motor is achieved in this simple regulating connection and the wire motor assumes the newly added load up to its rated capacity as determined by the load current from which the excitation of the current limit winding RWS is derived.

Although the application of this drive has been demonstrated in connection with the couch section of a paper machine, it will be understood that similar problems are involved in the transfer and press sections of such a machine to which this invention may also be applied. In a general sense this drive is applicable to numerous other equipments requiring driving power from separate motors.

While but two embodiments of this invention have been illustrated, it will be appreciatde that variations in the electrical relationship of the ci'cuit elements together with Variations in the details or" these elements may be made without departing from the spirit and scope of this invention. It is therefore intended that the foregoing disclosure and the showings made in the drawings shall be considered only as illustrative of the principles of this invention and not interpreted in a limiting sense.

I claim as my invention:

1. In a control for operating a pair of motors parallel wherein one motor is to be controlled in dependence of a given operating characteristic of a load driven thereby, the combination of, a pair of motors, each having field winding means and an armature winding, circuit connections ;3. applying direct current excitation to s id armature windings in parallel, a regulating device responsive to the speed of operation of one motor for controlling the excitation of the field winding means of each motor, a first amplifier for applying excitation to said field winding means of said one motor, a second amplifier for applying excitation to said i'leld winding means of the other of said motors, adjustable impedance means for each amplifier for controlling the operation thereof, means for adjusting the impedance of the adjustable impedance means as sociatod with said first amplifier in dependence of said given operating characteristic of said load, and respective current responsive means connected. with the respective motors for controllin said respective amplifiers.

2. In a control for operating av pair of motors in parallel wherein one motor is to be controlled in dependence of a given operating characteristic of a load driven thereby, the combination of, a pair of motors, each having field winding means and an armature winding, circuit connections for applying direct current excitation to said arma=- ture windings in parallel, a regulating device responsive to the speed of operation of one motor for controlling the excitation of the field winding means of each motor, a first amplifier for applying excitation to said field winding means of said one motor, a second amplifier for applying excitation to said field winding means of the other of said motors, adjustable impedance means for each amplifier for controlling the operation thereof, control means connected with each amplifier and responsive to an electrical condition of the respective motors for controlling the respective amplifiers, and means for adjusting the impedance of the adjustable impedance means associated with said first amplifier in dependence of said given operating characteristic of said load.

3. In a control for operating a pair of motors in parallel wherein one motor is to be controlled in dependence of a given operating characteristic of a load driven thereby, the combination of, a pair of motors, each having field winding means and an armature winding, circuit connections for applying direct current excitation to said armature windings in parallel, a regulating device responsive to the speed of operation of one motor for controlling the excitation of the field winding means of each motor, a first amplifier for applying excitation to said field winding means of said one motor, a second amplifier for applying excitation to said field winding means of the other of said motors, adjustable impedance means for each amplifier for controlling the operation thereof, impedance means connected with each motor to respond to the load current of the motor, circuit means connecting the respective impedance means to the respective amplifiers to control the respective amplifiers, and control means responsive to said given operating characteristic of said load for adjusting the impedance of said adjustable impedance means associated with said first amplifier.

i. In a control for operating a pair of motors connected in different ways to drive a common load wherein load division between said motors is controllable in dependence of a given operating characteristic of one motor, each of said motors having an armature winding and at least one field winding, the combination of, electrical means responsive to the speed of operation of one motor for energizing the field winding of each motor, a regulator for each field winding for controlling the excitation thereof, means responsive to said given operating characteristic of said load for controlling the regulator associated with said one motor, and current responsive means connected with each motor for controlling the respective regulators.

5. In a control for operating a pair of motors connected in different ways to drive a common load wherein load division between said motors is controllable in dependence of a given operatin characteristic of one motor, each of said motors having an armature winding and at least one field winding, the combination of, electrical means responsive to the speed of operation of one motor for energizing the field winding of each motor, a regulator for each field winding for controlling the excitation thereof, an electrical device for each motor responsive to an elec trical condition of the respective motors for controlling the respective regulators, and means re- 14 sponsive to said given operating characteristic of said load for controlling the regulator associated with said one motor.

6. In a control for operating a pair of motors connected in different Ways to drive a common load wherein load division between said motors is controllable in dependence of a given operating characteristic of one motor, each of said motors having an armature winding and at least one field winding, the combination of, electrical means responsive to the speed of operation of one motor for energizing the field winding of each motor, a regulator for each field winding for controlling the excitation thereof, an impedance device for connection in series with the armature winding of each motor, circuit means con necting the respective impedance devices to the respective regulators to control the respective egulators, and means responsive to said given operating characteristic of said load for controlling the regulator associated with said one motor.

7. In a control for controlling a pair of motors connected in different ways to drive a common load, the combination of, a pair of motors each having an armature winding and a field winding, electrical means responsive to the speed of operation of one motor for controlling the excitation of each field winding, increasing the excitation with increasing speed and decreasing the excitation with decreasing speed, a device responsive to a coupling characteristic between said one motor and said lead, and circuit means responsive to said device for increasing the excitation of the field winding connected with said one motor upon a decrease in said coupling characteristic.

8. In a control for controlling a pair of motors connected in difierent Ways to drive a common load, the combination of, a pair of motor each having an armature winding and a field winding, electrical means responsive to the speed of operation of one motor for controlling the excitation of each field winding, increasing the excitation with increasing speed and decreasing the excitation with decreasing speed, a device responsive to a coupling characteristic between said one motor and said load, circuit means for each motor responsive to the electrical load of each motor for controlling the respective field windings, and circuit means responsive to said device for increasing the excitation of the field winding connected with said one motor upon a decrease in said coupling characteristic.

9. In a control for controlling a pair of motors connected in different ways to drive a common load, the combination of, a pair of motors each having an armature winding and a field winding, electrical means responsive to the speed of operation of one motor for controlling the excitation of each field winding, increasing the excitation with increasing speed and decreasing the excitation with decreasing speed, a device responsive to a coupling characteristic between said one motor and said load, an impedance device connected in series in each armature Winding circuit, circuit means connecting the respective impedance devices with the respective field windings, and circuit means responsive to said device for increasing the excitation of the field Winding connected with said one motor upon a decrease in said coupling characteristic.

10. In a load distributing control for a pair of motors connected to a common load, one motor having a variable friction connection with said load, the combination of, a pair if motors each having a field winding and an armature winding, speed responsive means responsive to the speed of operation of said one motor having a variable friction connection with the load for simultaneously controlling the excitation of both field "windings, increasing the excitation of each field with increasing speed, an amplifying device connected with each field winding, means for controlling the respective amplifiers in dependence of electrical conditions of the respective motors, and electrical means responsive to a given condition of the load indicative of a variation in the frictional connection of said one motor with said load for controlling the amplifier connected to the field of said one motor to increase the excitation of that field when said frictional connection decreases.

11. In a control for controlling load distribution between apair of motors connected to a common load, one having a connection in which the load transmitting capacity varies in direct relation with an operation condition of said load, the combination of, a pair of motors each having an armature winding and a field Winding, circuit connections for supplying direct current excitation in parallel to said armature windings, speed responsive means responsive to the speed of operation of the one motor having the variable load connection for supplying unidirectional excita tion to both said field windings, a regulator connected with each field Winding, a rectifier connected in the output of each regulator to polarize the output cumulatively with respect to the excitation supplied to each field Winding by said speed responsive means, a current responsive device connected in each armature Winding and connected with the associated regulator ior effecting regulator output corresponding to the polarity of said rectifier, an adjustable control for each regulator for opposing the current responsive control, and means responsive to said operating condition of said load for operating the adjustable control of the regulator associated with said one motor.

References Cited in the file of this patent UNITED STATES PATENTS Number

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