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Publication numberUS3775653 A
Publication typeGrant
Publication dateNov 27, 1973
Filing dateJan 16, 1973
Priority dateJan 16, 1973
Publication numberUS 3775653 A, US 3775653A, US-A-3775653, US3775653 A, US3775653A
InventorsR Peterson, M Hensleigh
Original AssigneeWestinghouse Electric Corp
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Proportional integrator squared (pi) 2 speed controller for utilization in a speed regulator system
US 3775653 A
Abstract
A speed controller for utilization in a speed regulator system for a d.c. motor. An operational amplifier receives a voltage V1 through a first resistor R1, the voltage V1 being a function of the instantaneous speed of the d.c. motor. A second input to the operational amplifier is a speed reference signal. A feedback path connects the first input resistor R1 with an adjustable portion alpha of the amplifier output Vo. The feedback path includes a second resistor R2 serially with capacitors C1 and C2; a third resistor R3 is connected between the union of capacitors C1 and C2 and ground. The speed controller is a proportional integrator squared (PI)2 having the Laplace transfer function:
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Description  (OCR text may contain errors)

United States Patent 1 Peterson et al.

[111 3,775,653 Nov. 27, 1973 [75] Inventors: Robert S. Peterson; Melvin A.

Hensleigh, both of Williamsville, N.Y. 14221 [73] Assigneez Westinghouse Electric Corporation;

Pittsburgh, Pa.

22 Filed: Jan.16,1973 21 App1.No.:324,054

[52] US. Cl 318/326, 318/332, 318/331 [51] Int. Cl. 1102p 5/16 [58] Field of Search 318/326, 327, 332,

[56] References Cited UNITED STATES PATENTS 12/1971 OCallaghan ..3l8/326 9/1972 Nakajima 318/327 SIGNAL Primary Examiner-Bernard A. Gilheany Assistant Examiner-Thomas Langer Att0rneyF. Shapoe et a1.

[ 5 7] ABSTRACT A speed controller for utilization in a speed regulator system for a d.c. motor. An operational amplifier receives a voltage V through a first resistor R the voltage V being a function of the instantaneous speed of the do motor. A second input to the operational amplifier is a speed reference signaL, A feedback path connects the first input resistor R, with an adjustable portion a of the amplifier output V0. The feedback path includes a second resistor R serially with capacitors C, and C a third resistor R is connected between the union of capacitors C and C and ground. The speed controller is a proportional integrator squared (Pl) having the Laplace transfer function:

PATENTEDNBV271975 v N 3775.653

' sum 2 OF 3 I 1 v Wv (VOLT-S) (VOLTS) SPEED {R4 REFERENCE FIG. 2. SIGNAL 7 (PI) SPEED CONTROLLER C (PI) SPEED CONTROLLER FREQUENCY 0L) FIG.4A

PATENTEDNOvz? 191s 3.775.653

SHEET 3 [IF 3 STAN D SPEED ERROR O\fi "-05 SEC- TIME DRIVE ARM. CURR TIME IMPACT LOAD RESPONSE OF PI SPEED CONTROLLER STAND SPEED ERROR A c o M s .05 SEC. (H TIME DRIVE 7 TlME- IMPACT LOAD RESPONSE OF P1 SPEED CONTROLLER .PROPORTIONALINTEGRATOR SQUARED (PI) 2 SPEED CONTROLLER FORUTILIZATION IN A SPEED REGULATOR SYSTEM BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a speed regulator system for a d.c. motor, and more'specitically to a speed controller for utilization with such a system.

'2. Description of the Prior Art:

In bar, roll and stretch mills when the material being processed leaves one roller stand and proceeds to the next stand, there is aresulting speed drop due to the impact of the material upon entry into the succeeding stand. In somesituations the loss'in speed is of sufficient magnitude to develop a loop sufficiently large so as to rub on the adjacent structure thereby damaging the material.

in tension, itis customary to anticipate the change by displacing the mill screws ahead of the interstand tension zone. The change in screw displacement is always such as toworsen the gauge error. This is brought about by the necessary trade off between roll force and tension.

As an example, considerthe case where the processed material has been reduced in gauge and thick I (unprocessed) material iswelded to the thinnerIprocessed) material. As the welded joint goes'through the stand there is a lower load on the mill motor, and it responds by speeding up, thus buildingtension. in the material. In order to bring the material back to apreset magnitude, it is necessary to displace the screws in a downward direction in the process of trading off roll force for tension. As the screws come down, the roll gauge is narrowed, thus making the gauge smaller, possibly allowing off-gauge material to pass through; If no adjustment is made in the screws, the gauge in the vicinity of the weld will be better, but there is always the possibility of having too little tension or too much tension. It is therefore necessary to establish some maximum and minimum tension standards. If the tension is too low, the roll force may become high enough to cause a pinch in the material. (A pinchis a momentary pause in the moving strip which can cause serious 7 SUMMARY OF THE INVENTION This invention relates to a speed regulator system for a d.c. motor having a unique speed controller means.

An operational amplifier means has a first input, a second input and an output with a feedback path connected between the first input and an adjustable portion of the output. The first input receives a signal which is a function of the" instantaneous speed of the motor while the second inputreceives a speed reference signal. First and second resistance means and first and second capacitance means are in said feedback path, the first resistance means and said first and second capacitance means being serially connected, the second resistance means being connected between the union of the first and second capacitance means and ground. The speedcontroller means acts as a proportional integrator squared.

; BRIEF DESCRIPTION or TI-IEDRAWINGS FIG. 1 is a block diagram disclosing a speed regulator system for a d.c. motor, the speed controller of the invention being a component part of the speed regulator system; I

FIG. 2 is an electrical schematic of the proportional integrator squared (PI) speed controller of the instant invention;

FIGJS is an open loop Bode plot for comparing the (PI) speed controller of the invention, with the PI speed controller of the .prior art;

FIG. 4A depicts the impact load response of the prior art PI speed controller, and 7 FIG. 4B depicts the impact load response of the (PI) speed controller of the instant invention.

DESCRIPTION OF AN EXEMPLARY EMBODIMENT Referringnow to FIG. 1 there is shown a speed regulator systemfor one or more d.c. mill motors. For simplicity, a single drive, single converter speed regulator system. is depicted, although it will be appreciated that the invention is equally applicable with dual converters as well as duplex or multi-motor drives.

A single converter drive is one in which thereare no regenerative capabilities available in the thyristor source for the thyristor is indicated at 14. The thyristor converter 12 converts the a.c. power to controllable d.c. power. The regulator system incorporates two cascaded minor loops namely: the voltage and current loops. The minor voltage-loopcomprises a voltage controller 16, a gate pulse generator and amplifier 18, a voltage sensor 20 and a reverse current simulator 22. The current loop comprises a current-controller 24, the minor voltage loop, and a current sensor 26. A set of three currenttransformersindicated'syrnbolically at 28 supply a-feedback voltage signal-(ia) to the current sensor 26 whichdelivers'a signal i,, to thecurrent controller 24. The current loop controls the motor current by controlling the bus voltage signal 'Vb* to the voltage controller 16. The voltage loop controls the thyristor converter l2-output busvoltage+Vb as a function of the voltage signal -Vb* andthe feedback voltage signal+Vb supplied by the voltage sensor 20. The voltage controller 16 controls the gating angle of the thyristor The main'speed regulator loop includes a speed controller 30 and a tachometer generator 32 connected to the shaft of the d.c. motor 10. This loop regulates the motor speed, by comparing in the speed controller-30, the reference voltageto a voltage V, from the tachometer generator 32 which is proportional to motor speed. The output of the speed controller 30 provides the reference l,,* to the current controller 24.

Completing the description of FIG. 1, the reverse current simulator 22 prevents the current controller 24 from going into reverse saturation should .the speed controller 30 so demand on slowdown, sincethe drive system is not capable of regeneration or reverse current.

Finally, if for some reason the armature currentexceeds the current limit value, a systems fault is indicated. When this happens, a pulse signal is released from thecurrent sensor 26 which instantaneously suppresses all further pulsing in the gate pulse generator 18. Thus, the fault currentis confined to the last conducting thyristors in' the thyristor converter 12.

The speed controller of the invention is shown in FIG. 2, and comprises an operational amplifier indicated generally at 34 having input resistors R and R amplifier 36 and output potentiometer 38, having an adjustable gain a, the slide of the potentiometer 38 being connected in a feedback path indicated generally at 40 to the input of amplifier 36. The feedback path 40 includes serially connected resistor R and capacitors C, and C resistor R connected between the union of capacitorsC and C and ground.

v The Laplace transfer function of the speed controller is:

2 1 s(C1+C2)Sl-1 V1 0 3 8 CzRaS (1) When the transfer function is broken down there obtains: I i

The prior art has provided a speed controller having proportional integration (PI) properties. In the Laplace transfer function of equations (2) and (3), within each the first term in the bracket provides'the proportional part, and the second term within each bracket provides the integrating part as indicatedfby the 1/8 operator. The speed controller is'therefore identified as a (PI) operational amplifier..

Open loop Bode plots of the respective speed loops for PI and (PI) speed controllers are depicted in FIG.

3. As maybe observed for a study of these plots, the

crossover frequency w is the same for both PI and (PI) speed controllers. Thus the transient stability for bothcontrollers is substantially the same.

Performance" characteristics for the (PI) and (PI) controllers are empirically demonstrated in FIGS. 4A and 4B. In FIG. 4A there is shown the input and .4 response of a PI speed controller. The stand speed error A1 is finite and substantial. In FIG. 48 there is shown the impact load response of a (PI)- speed controller. The error is substantially zero sincethe areas A =areaB+area C.

Using the final value theorem, it can be demonstrated that the i (which is the speed error with respect to time) is 0.002 per unit seconds for the prior art speed controller (PI) and 0 per unit seconds (no strip storage) for the (PI) speed controller.

What we claim is: 1. In a speed regulator system for a d.c. motor, a speed controller means comprising:

a. operational amplifier means controlling said motor and having a first input, a second input, an output, and a feedback path'connected between said first input and an adjustable portion of said output; said 7 first input receiving a signal which is a function of the instantaneous speed of said motor, said second input receiving a speed reference signal;

b. first and second resistance means in said feedback path;

c. first and second capacitance means in said feedback path, said first resistance means and said first and second capacitance means being serially connected, said second resistance means being connected between the union of the first and second capacitance means and ground, said speed controller having the characteristics of a proportional integrator squared.

2. Speed controller means according to claim 1 wherein said second capacitance means is very much greater than said first capacitance means.

3. Speed controller means according to claim 1 wherein said output includes a potentiometer having a sliding member, the position of said sliding member defining said adjustable portion.

4. In a speed regulator system for a d.c. motor, a speed controller means comprising:

a. operational amplifier means controlling said motor and having a first input resistor (R a second input, an output having an output voltage (V,) and a feedback path connected between said first input resistor and and adjustable portion (a) of said output, said first input resistor receiving an input signal (Vo) which is a function of the instantaneous speed of said d.c. motor, said second input receiving a speed reference'signal;

b. second and third resistors (R 3 insaid feedback path;

c. first and second capacitors in said feedback path,

said second resistor R and said first and second capacitors (C C being serially connected, said third resistor (R being connected between the union of the first and second capacitors and ground, whereby the speed controller has the Laplace transform:

w wa

than the first capacitor C

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US3629633 *Oct 26, 1970Dec 21, 1971Eaton Yale & TowneControlled-velocity drive control
US3694720 *Nov 13, 1970Sep 26, 1972Yaskawa Denki Seisakusho KkSpeed control for d.c. motor
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3935520 *Jul 24, 1974Jan 27, 1976General Electric CompanyDC motor regulator
US4527101 *Nov 23, 1983Jul 2, 1985Black & Decker Inc.Universal electric motor speed sensing by using Fourier transform method
US4675584 *May 29, 1985Jun 23, 1987Kabushiki Kaisha ToshibaControl system
US4691150 *Jun 20, 1986Sep 1, 1987Ncr CorporationMotor speed controller
US5355060 *Oct 24, 1990Oct 11, 1994Aeg Automation Systems CorporationLoad impact controller for a speed regulator system
US5586444 *Apr 25, 1995Dec 24, 1996Tyler RefrigerationControl for commercial refrigeration system
Classifications
U.S. Classification388/821, 388/906, 318/610
International ClassificationB21B37/46, H02P7/292, H02P7/06
Cooperative ClassificationB21B37/46, H02P7/2925, Y10S388/906
European ClassificationB21B37/46, H02P7/292A
Legal Events
DateCodeEventDescription
Sep 4, 1990ASAssignment
Owner name: AEG WESTINGHOUSE INDUSTRIAL AUTOMATION CORPORATION
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST.;ASSIGNOR:WESTINGHOUSE ELECTRIC CORPORATION;REEL/FRAME:005424/0551
Effective date: 19900313