US3000243A

US3000243A - Sheet length controller

Info

Publication number: US3000243A
Application number: US533478A
Authority: US
Inventors: Loren F Stringer
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1955-09-09
Filing date: 1955-09-09
Publication date: 1961-09-19
Anticipated expiration: 1978-09-19

Description

Sept. 19, 1961 F, s R 3,000,243

SHEET LENGTH CONTROLLER Filed Sept. 9, 1955 5 Sheets-Sheet 1 Fig. I A

WITNESSES PTl \NVENTOR Loren F. Stringer 57 W BY QUJJAZZMA ai/5W ATTORNEY Sept. 19, 1961 L. F. STRINGER 3,000,243

SHEET LENGTH CONTROLLER Filed Sept. 9, 1955 5 Sheets-Sheet 2 Fig. IB

444:; I :i7v44 1-{42 39 5 Sheets-Sheet 3 Filed Sept. 9, 1955 Fig. IC

MT i -Riki United States Patent 3,000,243 SHEET LENGTH CONIROLLER Loren F. Stringer, Monroeville, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Sept. 9, 1955, Ser. No. 533,478 9 Claims. (Cl. 80-56) My invention relates generally to motor control systems, and it has reference in particular to a control system for the screwdown motor of a rolling mill for controlling the length of a sheet of material being rolled.

Generally stated, it is an object of my invention to provide for controlling the length of sheets or strips of material being rolled by controlling the separation of the rolls in a rolling mill.

More specifically, it is an object of my invention to provide for automatically operating the screwdown motor of a rolling mill to adjust the separation of the rolls in accordance with the length of a sheet which is to be rolled, so as to produce a rolled sheet of a predetermined length.

Another object of my invention is to provide in a control system for a rolling mill for adjusting the separation of the rolls in accordance with the length of a piece of material which is to be rolled and for checking the length of the piece after it is rolled, in order to make adjustments in the roll separation to correct for variations from the desired length.

It is also an object of my invention to provide for using a servo system to produce a signal in accordance with the length of a sheet which is to be rolled, controlling the roll separation in accordance with such signal and then using the signal to reset the servo system.

Another object of my invention is to provide in a screwdown control system for a rolling mill, for using a voltage proportional to the speed of a sheet of material entering the rolling mill for operating a servo system to effect adjustment of the roll separation so as to produce a rolled sheet having a predetermined length.

Yet another object of my invention is to provide in a control system for a rolling mill, for controlling the roll separation by means of a velocity matching servo system in accordance with the length of a sheet entering the mill, and for resetting the servo system by utilizing the output thereof to return it to an initial position.

It is an important object of my invention to provide in a control system for a rolling mill, for operating the mill screwdown to maintain the quotient of initial sheet length over final sheet thickness a constant value.

Other objects will in part be obvious and will in part be explained hereinafter.

In practicing my invention in accordance with one of its embodiments, sheets of a predetermined length are to be produced from sheets of substantially uniform thickness and variable length. For this purpose a magnetic amplifier is used to control the screwdown motor of a rolling mill by utilizing a servo system which is responsive to the speed of approach of a sheet of material of finite length which is to be rolled to a predetermined length, for applying to the magnetic amplifier a voltage proportional to the initial length of the sheet. This voltage is multiplied by a voltage proportional to the initial sheet thickness and the product is matched against the product of voltage proportional to the roll separation as determined by a synchro system driven by the screwdown motor, and a voltage portional to the final sheet length. The length of the rolled sheet is then checked by a light responsive length checking system, and a correction factor is applied to the final sheet length voltage for correcting any deviation from the predetermined length. The servo system is reset after the screwdown motor is operated by feeding its output back into the system to restore it to an initial setting.

For a more complete understanding of the nature and scope of my invention, reference may be made to the following detailed description which may be read in connection with the accompanying drawings, in which FIG- URES 1A, 1B and 1C taken together are a schematic diagram of a screwdown system embodying the principal features of the invention.

Referring to FIG. IE, it will be seen that a rolling mill 10 having work rolls 11 and 12 provided with backup rolls 13 and 14, respectively, is provided with screwdown means 15 represented by a threaded shaft for moving the upper roll 11 relative to the lower roll 12 for varying the roll separation. The work rolls 11 and 12 may be driven in a well known manner by means of a main mill motor MM which may be provided with suitable controls of a type well known in the art. Conveyor rolls 17 are provided in conjunction with the rolling mill 10 for feeding a sheet of material which is to be rolled toward the rolling mill and carrying it away therefrom after it had been rolled. The conveyor rolls 17 may be driven in any suitable manner, and since their speed should be matched with that of the work rolls 11 and 12, they are shown schematically as connected in driving relation with the mill motor MM for purposes of simplicity.

The screwdown means 15 is provided with a screwdown motor SDM having an armature 20 connected in driving relation with the screwdown means, a series field winding 21, and a main separately excited field winding 22 which is connected to a suitable source of direct current. Electrical energy is supplied to the armature 20 of the motor SDM from a screwdown generator SDG having an armature 24 which may be driven by any suitable prime mover, a series field winding 25 connected in circuit with the armature 24, series field winding 21 and armature 20, and oppositely disposed

main field windings

26 and 27 for reversibly controlling the output of the generator.

Energization of the

field windings

26 and 27 is selectively efiected in opposite senses under the control of a magnetic amplifier 30 which comprises a plurality of

magnetic cores

31 and 31 arranged in pairs and having load windings 32 thereon for selectively connecting the

field windings

26 and 27 through rectifier bridges circuits 34 and 35 to alternating current sources represented by the transformers 36. The load windings 32 of each pair of cores are connected in parallel circuit relation, in series with oppositely disposed rectifier devices 38 so as to provide for unidirectional magnetization of the cores. The cores are also provided with jog windings 39 and 39' which are reversibly energizable so as to be cumulative with respect to the respective load windings and are connected to a source of direct current through a manual reversing control switch 40 in opposition with the voltage of the armature 24 of the generator so as to provide for manual control of the screwdown motor SDM.

Feedback windings

42 and 42 are provided on the cores and are connected to a pilot generator PG driven by the screwdown motor. These windings are difierential with respect to control windings 44. Control windings 44 are energized in a manner which will be hereinafter described.

Because of the conservation of volume involved in the rolling process, V =L W S V =L W XS where V equals the sheet volume, L equals the sheet length, W equals the sheet width and S equals the sheet thickness, the subscript 1 referring to initial conditions and subscript 0 referring to final conditions. if

and hence Since initial thickness '8 remains substantially fixed, it is only necessary to measure the initial length of each sheet and vary the screwdown setting of the rolling mill and hence vary the final thickness of the rolled sheet to maintain the quotient constant.

The sheet length can be measured by measuring the length of time it takes for the sheet which is being transported to the finishing mill on the conveyor rolls to pass a specified position. A means for doing this is shown in FIG. 1A. A pair of germanium diode phototransistors PTl and PT2 of the NPN junction type are spaced a distance L which is less than the initial length of the sheet, longitudinally of the conveyor rolls 17 ahead of the rolling mill on the entry side, in conjunction with light sources LS1 and LS2, respectively. These transistors are connected in parallel circuit relation, in series with the operating winding of a control relay CRL which is normally energized and is deenergized when an approaching sheet of material 48 moving toward the rolling mill on rolls 17 interrupts both of the light sources. A velocity matching servo system 50 is used in conjunction with a relay CRL to operate the movable contact Pla of a potentiomettr P1, for providing a voltage c in accordance with the length of the sheet.

The servo system 50 comprises a two-phase servo motor SM which drives the moving contact Fla. The motor SM is provided with one phase winding 51 which is energized from an alternating current source represented by a transformer 52 through a capacitor 53, and a second phase winding 55 which is energized with a reversible phase relation through the

load windings

56 and 56 of a magnetic amplifier 58. The

load windings

56 and 56 are disposed on magnetic cores 59 and connect the winding 55 to the transformer 52 through oppositely disposed

rectifier devices

60 and 61. The cores 59 are provided with opposing flux resetting windings 63,

and opposing pattern windings 65 which are energized from apilot generator G2 driven by the conveyor rolls 17 whenever the control relay CRL is deenergized.

Resetting of the servo motor system after passage of a sheet is provided for by reset windings 66 which are connected between the moving contact Fla and the intermediate point of a voltage divider comprising resistors *68 and 69 which are connected to a control source repre-' sented by the conductors 70. Feedback control windings 72 on the cores are connected across a pilot generator G1 driven by the servo motor under the control of a reset relay LR, and oppose pattern windings 65. The relay LR is used in conjunction with a timing relay LRT to give a predetermined reset period following operation of a screwdown control relay RL which is utilized to connect the control windings 44 of the screwdown magnetic amplifier 30 to the moving contact P3a of a potentiometer P3 which is energized through a rectifier bridge circuit 75 in accordance with the output voltage of a 'synchro receiver 76 which is electrically connected to a synchro transmitter 77 driven by the screwdown motor SDM.

The stator of the screwdown receiver 76 is manually ad justable to change the phase relation relative to the transmitter 77, so that the output voltage of the receiver 76 is proportional to the separation of the rolls 11 and 12.

The other end of the control windings '44 is connected to' the moving contact PM of a potentiometer P2 which is adjusted in accordance with the initial thicknessSl of the sheet. The operation of the screwdown control relay R1. is determined by a timing relay RLT and the control relay CRL. A timing relay TL and a sequence relay PL are used to set up the operating circuit for the timing relay RLT so as to provide a single timing interval as each sheet approaches the mill.

In order to provide for correcting for deviations due to an error in the initial thickness S a length checking system 80 is provided for checking the length of the rolled sheet and correcting the position of the contact arm P2a of the potentiometer P2 in accordance therewith. This checking is accomplished by utilizing control relays CR1, CR2 and CR3 disposed along the conveyor on the exit or delivery side of the rolling mill and operated by phototransistors PT3, PT4, PTS respectively in combination with light sources LS3, LS4 and LS5, respectively. The light sources LS4 and LS5 are set a distance on either side of an intermediate point indicated by dotted line 1 which is a predetermined sheet length from the light source LS3, which distance is slightly less than the negative and positive tolerances respectively in the sheet length. The following sequence of events can occur:

(A) Relays CR1 and CR2 are not deenergized during a common interval of time.

(B) Relays CR1 and CR2 are deenergized during a common interval of time.

(C) Relays CR1 and CR3 are not deenergized during a COHIIIIOIJ. interval of time.

(D) Relays CR1 and CR3 are deenergized during a common interval of time.

Occurence of event A indicates off-length sheets on the short side, occurence of events B and C indicate on-length sheet and occurence of event D indicates off-length sheet on the long side. A scheme based on the above sequences for determining whether a sheet is long or short is shown in FIG. 1C. A time delay relay T is used in conjunction with a program relay P and a coincidence relay C to permit relays S and L to be controlled by the relays CR1, CR2 and CR3 to determine short and long sheet conditions. These relays in turn energize relays S and L respectively, for a timed interval determined by a timing relay DT for operating a motor M in opposite directions to adjust the moving contact P2a to correct for the variation in sheet length.

If the light sources LS1 and LS2 are separated by a distance L and the origin of time (i=0) is taken as the instant the sheet interrupts the first light source and I is the time as measured from this origin at which the first light source is restored, the length of the sheet is given by,

13 L1: f v dt For later convenience let t represent the instant the second light source is interrupted and the operation of the servo controller initiated. Then t t; L f ll dt l f 111dt The first integral is, of course, given by,

f v dt=L L, wit

and if the servo system is linear and its response to a umt step function input is represented by It T, then L; f v dt As previously noted, however,

Thus,

and hence,

r =L1 m The output voltage of the servo system, as seen from FIG. 1A, is given by,

The maximum length that can be measured by the system is given by,

LID: oi- 121+ 2 and hence,

The output voltage is consequently directly proportional to sheet length.

Normally, relays CRL and TL are energized and relays PL, RLT, RL, LR and LRT are deenergized. When the sheet 48 interrupts both of the light sources LS1 and LS2, the resistance of both of the phototransistors PTI and PT2 are increased and the relay CRL returns to the deenergized position. This connects the pattern winding 65 of the magnetic amplifier 58'to the pilot generator G2 driven by the rolls through contact e of relay CRL applying thereto a voltage responsive to the speed of the sheet. This causes the magnetic amplifier 58 to operate the servo motor SM and position moving contact Pla in accordancewith the length of the sheet. Deenergization of relay CRL interrupts the energizing circuit for the timing relay TL at contact member a of relay CRL, and completes an energizing circuit for the operating winding of relay PL at contact member b and sets up energizing circuits for relays RLT and RL at contacts 0 and d respectively. Relay PL is picked up until such time as the timing relay TL times out. Energization of relay PL completes an energizing circuit for the timing relay RLT at contact member c of relay PL. The timing relay RLT operates to the energized position and completes an operating circuit for the screwdown control relay RL at contact b. Operation of control relay RL connects the control winding 44 of the screwdown magnetic amplifier 30 between the moving contact P311 of potentiometer P3 and the moving contact P2a of potentiometer P2 through contact a, so that the voltage e which is equal to e XL X kn, and is therefore proportional to the product of roll separation times final length, or L XS is matched against the voltage e of potentiometer P2, which is proportional to the product of L XS Accordingly, the control winding is energized in accordance with a differential between the product of measured roll separation times final length and the product of initial length times initial thickness. This provides for energization of the

field windings

26 and 27 selectively, so as to energize the screwdown motor SDM to raise or lower the rolls to the proper position to make the quotient of constant.

When the timing relay RLT times out, the control relay RL is deenergized and disconnects the control windings 44 from the potentiometers. A circuit is provided at contact member c of relay RL for a reset relay LR under the control of a timing relay LRT. The relay LR provides a shunt about a portion of a resistor 82 in circuit with the control winding 72, and connects the reset windings 66 to be energized in accordance with the displacement of the potentiometer contact Fla. The magnetic amplifier 58 thereupon functions to operate'the servo motor SM to return the contact arm Pla to its initial or its zero position.

When the rolled sheet passes through the mill, it then passes through the length checking system 80. In the absence of a sheet, relays CR1, CR2 and CR3 are energized. Program relay P is energized through contact a of relay T and contact member b of relay CR1. The relay P remains energized until the timing relay T, which is normally energized, times out, at which time it returns to the deenergized position and remains there until the arrival of the next sheet. The momentary closure of relay P energises relay C and DT through contacts d and a thereof, both of which provide holding circuits for themselves. If relay CR1 is energized before relay CR2 is deenergized, as will be the case if the sheet is short, relay S will be energized momentarily through contact d of relay CR1 and contact a of relay CR2. An energizing circuit is thereby provided for control relay S through contact a of relay S until the timing relay DT times out. If relay CR3 is deenergized before relay CR1 is deenergized, as will be the case if the sheet is long, relay L will be energized momentarily through contact a of relay CR3 and contact c of relay CR1. This provides an enerigizing circuit for the control relay L which will seal in until the timing relay DT is deenergized and opens the circuit at contact a. Relays S and L thus selectively apply voltages of opposite polarity to the motor M for a fixed interval of time as determined by the timing relay DT, depending on whether the sheet is short or long. The motor changes the setting of potentiometer P2 to adjust the voltage e and hence the product L S E by a fixed amount in a direction for the ofi-length condition. The potentiometer P2 may also be adjusted manually and remote indication of its position should be provided where it is available to the operator.

From the above description and the accompanying drawings, it will be apparent that I have provided in a simple and effective manner for controlling the length of rolled sheet. The roll separation is automatically adjusted in accordance with the length of the sheet entering the mill and correction of the mill setting is antomatically made subsequent to rolling of the sheet in accordance with the measured length of the rolled sheet to compensate for errors including error due to variation in thickness of the sheet. A sheet length controller embodying the features of my invention provides for accurately rolling sheets, which, for example, may vary in.

7 thickness from .486 inch to .510 inch and in length from 29.953 inches to 30.047 inches, to a predetermined length of 120.48 inches with a tolerance of i2% Without incurring delays in the rolling process.

Since certain changes may be made in the above described construction and difierent embodiments of the invention may be made Without departing from the spirit and scope thereof, it is intended that all the matter contained in the above description and shown in the accompanying drawings shall be considered as illustrative and not in a limiting sense.

I claim as my invention:

1. In a control system for a rolling mill having a pair of rolls With driving means therefor and having a screwdown motor operable to vary the spacing of the rolls, the combination of regulating means operable to effect operation of the screwdown motor, first signal producing means actuated by the screwdown motor to produce a first signal in accordance with the roll spacing, second signal producing means actuated by the passage of a sheet of material toward the rolls for measuring the length of a sheet of material to be rolled and for producing a second signal in accordance-therewith, and circuit means connecting the regulating means and saidfirst and second signal producing means for applying a control signal to the regulating means in accordance with a differential between said first and second signals.

2. A control system for a screwdown motor operable to vary the spacing of the rolls in a rolling mill having driving means therefor, control means reversibly energizing said motor, sheet length responsive means actuated by the passage of a piece of material of finite length to be rolled for producing a first signal responsive to the length of said piece of material to be rolled, roll separation responsive means responsive to the position of the rolls for producing a second signal in accordance with the separation of the rolls, and circuit means connecting the sheet length responsive means and the roll separation responsive means to said control means for producing a signal responsive to said first and second signals and applying it to thecontrol means for effecting operation of the control means to energize said motor to position said rolls.

3. Screwdown apparatus comprising, a motor reversibly operable and connected to vary the spacing of the rolls of a rolling mill which have'driving means connected therewith, means operating said motor including a generator having a field winding and regulating means therefor having input and output circuits, sheet length sensing means actuated by the passage of a piece of material of finite length for producing a first signal in accordance with the initial length of a piece of material approaching the rolling mill, roll spacing sensing means actuated in accordance Withthe position of one of the rolls for producing a second signal in accordance with the spacing of the rolls, first circuit means connecting said sheet length and roll spacing means to said input circuit for applying said first and second signals to the input circuit of the regulating means in opposed relation, and second circuit means connecting said output circuit and the generator field for effecting operation of the motor to adjust the roll spacing to maintain the quotient of initial length final thickness substantially constant.

4. screwdown control apparatus for a rolling mill having a pair of rolls with driving means for at least one of 'said rolls comprising, a motor connected in operating relation with one of the rolls of the rolling mill for vary-.

a signal in accordance with the length of said sheet, first circuit means including a voltage divider connected to multiply said signal by a quantity proportional to the initial thickness of the sheet, second circuit means including means actuated by one of the rolls to produce a signal proportional to the roll separation and a second voltage divider connected to produce a signal in accordance with the product of the length and thickness of the rolled sheet, third circuit means connecting said first and second circuit means and the regulator for applying the signals produced by said first and second circuit means to the regulator in opposed relation for operating the motor in accordance with a differential therebetween, and additional circuit means connecting the servo systems for operating the servo system in accordance with the length responsive signal for resetting the servo system after the passage of a sheet.

5. In a sheet length control for a rolling mill having a pair of rolls with driving means therefor and screwdown means operable to vary the separation of the rolls, a screwdown motor operable to operate the screwdown means, sheet length responsive means actuated by the passage of a sheet approaching the mill to produce a first signal responsive to the length of a sheet approaching the mill in response to passage of the sheet, roll separation responsive means actuated by one of the rolls for producing a second signal in accordance with the roll separation, regulating means connected to control the operation of the screwdown motor, circuit means connecting the roll separation and sheet length responsive means to the regulating means to make the regulating means selectively responsive to a differential between said first and second signals for reversibly operating the screwdown motor to maintain a predetermined relation of the initial sheet length and the roll separation, second circuit means including means actuated by the passage of a sheet leaving the mill operable to produce a third signal in accordance with the length of a sheet departing from the rolling mill, and control means operated by the last mentioned third signal and connected to modify a predetermined one of said first and second signals in response to the variation of length of the rolled sheet fiom a predetermined value.

6. In a sheet length controller for a rolling mill having a pair of rolls with driving means therefor and screwdown means for varying the roll separation, a screwdown motor operable to actuate. the screwdown means, sheet length sensing means including a speed matching servo system actuated by a sheet entering the mill to produce a first voltage proportional to the length of a sheet of material entering the mill, roll separation sensing means including a selsyn device operated by the position of the screwdown motor for producing a second voltage proportional to the separation of the rolls, regulating means having a winding connected to be energized by the difference between said first and second voltages and connected to eifect energization of the screwdown motor to adjust the roll separation, means operated by the servo system producing a signal in response to operation of the servo system, circuit means applying said signal to reset the servo system, sheet length checking means actuated by the passage of a sheet leaving the mill to check the length of a sheet leaving the rolling mill, and means including apotentiometer connected in circuit with the servo system and operated by the checking means to modify said voltage signal applied to the regulating means from the servo system. a

7. In sheet length control apparatus for a rolling mill having a pair of rolls with driving means therefor and screwdown means for varying the roll separation, a screwdown motor connected in driving operation with the screwdown means, a regulator connected to control .the operation of the screwdown motor, circuit means connected to produce and apply to the regulator a first voltage in accordance with the speed of the screwdown motor, circuit means connected to produce a second voltage in accordance with the separation of the rolls, means including a voltage divider connected to apply a predetermined portion of said second voltage to the regulator, means including a servo system operated by the passage of a sheet approaching the mill for producing a third voltage in accordance with the length of a sheet of material to be rolled, and circuit means for multiplying said second and third voltages including a voltage divider connecting the regulator and the servo system to apply a predetermined portion of the third sheet length voltage to the regulator in opposition to the second roll separation voltage.

8. Control apparatus for a rolling mill having a pair of rolls with driving means therefor and screwdown means for varying their separation and comprising, a screwdown motor connected in driving relation with the screwdown means, a regulator connected to control the operation of said motor, circuit means including a pilot generator driven by the screwdown motor connected to apply to the regulator a first voltage in accordance with the speed of the screwdown motor, means including a synchro system operated by the screwdown means to pro duce and apply to the regulator a second voltage in accordance with the separation of the rolls for operating the motor to reduce the separation of the rolls, means including a servo system operated by the passage of and responsive to the speed of a sheet of material entering the mill to produce a third voltage in accordance with the length of the sheet, circuit means producing a fourth voltage proportional to the thickness of a sheet entering the mill, and additional circuit means comprising a voltage divider connected to the servo system and the regulator to apply to the regulator a predetermined portion of the sheet length third voltage so as to multiply the length third voltage and the thickness fourth voltage and to apply the resultant to the regulator in opposition to the roll separation second voltage.

9. Sheet length control apparatus for a rolling mill having a pair of rolls with driving means therefor and screwdown means operable to vary the separation of the rolls and comprising, a screwdown motor connected in driving relation with the screwdown means, a regulator connected to vary the energization of the motor for controlling the operation of the screwdown motor, circuit means including a pilot generator driven by the screwdown motor and connected to apply to the regulator a voltage in accordance with the speed of the screwdown motor, means including a synchro transmitter and receiver operated by the screwdown motor to apply to the regulator a first voltage in accordance with the roll separation, means including a servo system having a motor responsive to the speed of a sheet of material entering the mill for operating a sheet length potentiometer connected to a source of control voltage to produce a second voltage in accordance with the length of a sheet of material entering the mill, a thickness potentiometer connected in cascade with said sheet length potentiometer for applying a predetermined portion of the second volt age to the regulator in opposition to the roll separation first voltage, sheet length checking means operated by a sheet leaving the mill to check the length of the sheet leaving the mill, and means operated by the length checking means and operable to adjust the thickness potentiometer in accordance with variations in the final sheet length of a sheet already rolled to correct the length of the next sheet to be rolled.

References Cited in the file of this patent UNITED STATES PATENTS 2,051,018 Umansky Aug. 11, 1936 2,297,812 Stoltz Oct. 6, 1942 2,332,573 Hibschman Oct. 26, 1943 2,476,839 Cook July 19, 1949 2,687,052 Zeitlin Aug. 24, 1954 2,851,911 Hessenberg Sept. 16, 1958 FOREIGN PATENTS 627,000 Great Britain July 25, 1949