US2972268A

US2972268A - Automatic strip thickness control apparatus

Info

Publication number: US2972268A
Application number: US651387A
Authority: US
Inventors: John W Wallace; Robert E Hull; Raymond W Moore
Original assignee: Westinghouse Electric Corp
Current assignee: CBS Corp
Priority date: 1957-04-08
Filing date: 1957-04-08
Publication date: 1961-02-21
Anticipated expiration: 1978-02-21
Also published as: GB841503A; BE566576A; FR1205344A; JPS364059B1

Description

Feb. 21, 1961 J. w. WALLACE ET AL 2,972,268

AUTOMATIC STRIP THICKNESS CONTROL APPARATUS Filed April 8, 1957 3 Sheets-Sheet 2 350m muuto 0 o :00 250 z mu m tcoo 8 2 mm! 6: 0 czouamcum mm 350w ww h m mm 8 mm 12 N L .0.Q 0 4 Feb. 21, 1961 w WALLACE ETAL 2,972,268

AUTOMATIC STRIP THICKNESS CONTROL APPARATUS Filed April 8, 1957 3 Sheets-Sheet 3 D. 0. Voltage I Source A. 0. Voltage Source D. C. Voltage Source A.g.Voltoqe ource Input VD Output Fig. 4

B F lg. 5.

Under Gouge Slow Down 5 Initial Threading T and stopping c z and Sfurf-Up W0, ucce Ive 0| -4+- 4% .C 0 On Gouge w I a :8 Length of Strip Over Gauge 0 0 Fig.3.

United States Patent AUTOMATIC STRIP THICKNESS CONTROL APPARATUS John W. Wallace, Orchard Park, and Robert E. Hull, Amherst, N.Y., and Raymond W. Moore, Whitehall, Pa., assignors to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Filed Apr. 8, 1957, Ser. No. 651,387 14 Claims. (Cl. 80-32) The present invention relates, in general, to control apparatus for automatically controlling the operation of one or more motor devices, and more particularly, relates to automatic control apparatus for controlling the gauge or thickness of a strip of material by controlling the operation of one or more motor devices of a rolling mill operative to determine the gauge or thickness of a continuous strip of metal or other material.

It is an object of the present invention to provide improved motor control apparatus, and more particularly, to provide improved apparatus for controlling the operation of one or more motor devices of a strip rolling mill or the like, to thereby better control the final gauge or thickness of the strip over a greater portion or length of said strip. a

It is another object of the present invention to provide improved control apparatus for a strip rolling mill, which apparatus is more rapidly responsive to any deviation in the operation of said rolling mill away from a predetermined operation or a reference operation, such as a strip thickness determination, and further, to provide improved apparatus which is capable of more rapidly correcting for and removing any such deviation in the operation of said rolling mill to thereby improve the operating efliciency regarding the on-gauge or desired thickness of strip as the final product.

It is a different object of the present invention to provide improved control apparatus for a strip rolling mill, which apparatus is operative to better control the strip thickness by varying the tension of the strip relative to one or more stands of the rolling mill, and further, to provide improved apparatus operative to vary the spacing between the roller members of one or more stands of the rolling mill as necessary to better control said strip thickness for errors in thickness greater than a predetermined magnitude, and to thereby prevent strip breakage or strip sagging due to the otherwise required excessive strip tension variation.

It is a further object of the present invention to provide improved control apparatus operative with a strip rolling mill for better holding substantially constant or as may be desired the pressure between the cooperating roller members of one or more stands of the rolling mill to thereby better control the spacing between said roller members substantially constant or as may be desired.

It is an additional object of the present invention to provide improved control apparatus for better controlling the output strip thickness or gauge from a strip rolling mill which apparatus is operative to automatically reset the control apparatus from a first screw-down setting condition to a second screw-down setting condition should an operator change to said second screw-down setting condition of operation.

The use of well known X-ray or radiation type of thickness gauges as a thickness error detection device presents two major problems. Firstly, a transport time delay is introduced, consisting of the time required for a given section of the strip to pass from the roller members to the thickness sensing gauge. The latter gauge must be positioned about 6 or 7 feet from the roller members, and thusly an immediate sensing of thickness errors cannot be made in this manner. Also stability problems are introduced into the strip thickness control apparatus by this device. Secondly, radiation type gauges are relatively complex and sensitive instruments that are difiicult to adjust, have rather low power output signals, and generally have an inherent time delay provided by the gauge itself. Thusly, only a limited strip thickness control accuracy is obtainable as a result of this time delay and the noise level of the thickness gauge.

These and other objects and advantages of the present invention will become apparent in view of the following description taken in conjunction with the drawings, wherein:

Figure 1 is a diagrammatic showing of one form of the control apparatus in accordance with the teachings of the present invention;

Fig. 2 is a schematic showing of the subject control apparatus;

Fig. 3 is a curve chart illustrating the operation of the subject control apparatus;

Fig. 4 is a schematic showing of magnetic amplifier devices connected in a push-pull circuit arrangement suitable for use with the present control apparatus;

Fig. 5 is a schematic showing of a well known limiter circuit arrangement suitable for use with the present apparatus; and

Fig. 6 is a schematic showing of a well known deadzone circuit arrangement suitable for use with the screwdown control device if desired.

In Fig. 1 there is shown control apparatus for a ro ling mill including a mill stand 10 having an upper roller member 12 and a lower roller member 14 between which a strip of material 16 may be positioned, such that the spacing between the upper roller member 12 and the lower roller member 14 is effective to determine the thickness or the gauge of the strip of material 16 after it has passed from the previous mill stand through the stand 10 to a successive stand or the delivery reel 20. A screw-down control device 22 is operated by a suitable motor 24 controlled by a screw-down control device 25 for determining said spacing between the upper roller member 12 and the lower roller member 14.

The operative speed of the stand 10 is determined by a motor 26 operated by a motor control device 28 which, in turn, is responsive to a control signal from a strain gauge device 30 mounted on the mill stand 10 and responsive to the pressure between the upper roller member 12 and the lower roller member 14, as reflected by strain induced in the housing of the mill stand 10, and thereby the spacing between said roller members. The strain gauge device 30 provides a control signal to a first amplifier device 32 which, in turn, provides this amplified control signal to a second amplifier device 34, and to an integration device 36 which, in turn, provides a control signal to the amplifier device 34. The resultant output signal from the amplifier device 34 is supplied to the motor control device 28 for controlling the operation of the mill motor 26 in accordance with a control signal received from the strain gauge 30. If this resultant control signal has a value greater than a predetermined value, a control signal is supplied to the screw-down control device 25.

In Fig. 2 the rolling mill stand 10 is shown including the upper roller member 12 and the lower roller member 14'. A first strain gauge 31 is mounted on one side of the mill stand housing 10 and a second strain gauge 33 is mounted on the opposite side of the mill stand housing 10. Differential type transformer strain gauges may also be used. The strain gauges are mounted in diametrically opposite posts of the mill housing. Any well known type 3 of strain gauge, such as a resistance element gauge, may be used. The first strain gauge 31 is operative with a control winding which has an inductance value varied as a function of the strain within the mill stand housing as sensed by the strain gauge 31. The second strain gauge 33 is operative with a control winding 42 which-has an inductance value which varies as a function of the strain in the mill stand housing as sensed by the strain gauge 33;

The control windings 40 and 42 are connected in a bridge circuit with reference windings 43 and 46 and energized by a suitable alternating current voltage source 48, such that any unbalance of the latter bridge resulting from physical strain in the housing of the mill stand 10 as sensed by either or both of the strain gauge devices 31 or 33 is operative to provide to the alternating current terminals of a rectifier bridge device 50 a control signal which varies in accordance with said strain in the mill stand housing. The direct current terminals of the rectifier bridge 5i} are connected through

conductors

52 and 54 to the

control windings

56 and 58 of a magnetic am-' plifier device to thereby energize said

control windings

56 and 58 with a direct current signal which varies as a function of the spacing between the upper roller member 12 and the lower roller member 14 which, in turn, is a function of the roll pressure or roll force as applied to the strip 16.

A second pair of

control windings

60 and 62 are energized from a signal from across a pressure reference setting potentiometer 64 as determined by the setting of a movable contact arm on said potentiometer 64 as will be later explained. The pressure reference setting potentiometer 64 is part of a bridge circuit including a direct current voltage source 66 which energizes a potentiometer 68 operative to vary the range segment of the pressure reference potentiometer, in other words, operative as a coarse setting for the pressure reference setting potentiometer 64. A vernier setting potentiometer 70 is connected in series with the potentiometer 64.

The output load windings of the magnetic amplifier device 81) are connected in a push-pull arrangement across the impedance devices 82 and 84 toprovide a voltage drop across said impedance devices 82 and 84 having a magnitude which varies as a function of the magnitude of the roll force or pressure between the roller members 12 and 14 and which has a polarity determined by the actual pressure between the roller members 12 and 14 being either above or below a predetermined reference pressure as determined by the pressure reference setting potentiometer 64. The control voltage signal across the impedance devices 82 and 84 is applied to the control windings 36 and 88 of a second magnetic amplifier device 90. This same control voltage is applied through conductors 92 and 4 to the control windings 96 and 98 of a third amplifier device 100, of the integration device 36. A sec- 0nd pair of control windings 102 and 104 of the amplifier device )6 is energized by a control signal received from the integration device 36 as will be'later described.

The output or load windings of the amplifier device are connected in a push-pull arrangement across the

impedance devices

108 and 110, with the output. control signal across the latter said impedance devices 108 and 111 being applied to the

control windings

112 and 114 of a magnetic amplifier device 116 within the motor control device 28.

The output control voltage from across the impedance devices 108 and is also applied across a first pair of

control windings

118 and 120 of the amplifier device 169. A second pair of

control windings

122 and 124 as well as a third pair of

control windings

126 and 128 are energized as feedback stabilization windings by the voltage difference between the contact arms of the respective potentiometers 130 and. 132 of a bridge circuit energized by a suitable direct current voltage source 134, as shown in Fig. 2. A servo or reset motor 136 having a forward field winding 138 and a reversecontrol field winding 140 is energized by the output or load windings of the amplifier device 100, with the reset motor 136 being operatively connected through the clutch device 146 to the contact arm of the potentiometer 132.

The control windings 1412 and 104 of the amplifier device 90 are energized through the conductors 148 and 150 by a signal determined by the settings of the respective contact arms of the

potentiometer devices

130 and 132.

The output or load windings of the amplifier device 116 of the motor control device 28 shown in Fig. l, energizes the impedance devices 152 and 154 which, in turn, energize impedance devices 156 and 158 connected in a series reference circuit. The latter series reference circuit further includes the

impedance devices

160 and 162 which receive through the operation of the amplifier device 164 and the impedance device 166 an IR compensating feedback control signal. Also a reference excitation generator 168 is provided having a control field 170 energized by a suitable direct current voltage source 172. A supply generator 174 is provided for controlling the energization of the mill motor 26 and, in turn, i11- eludes control field windings 176 and 177 energized by an amplifier device 178. The

control windings

180 and 182 of the latter amplifier device 178 are connected in the above series reference circuit along with the first pair of impedance devices 156 and 158 provided with a thickness error correction signal and the second pair of

impedance devices

166 and 162 provided with an IR compensating feedback signal and the reference excitation generator 168 and the energy supply generator 174. Thusly, the control windings 181 and 182 are operative through the amplifier device 178 to control the energization of the control field windings 176 and 177 of the supply generator 174 to thereby control the operating speed of the mill motor 26 and thusly, the speed of the mill stand 10 to thereby vary the tension of the strip 16 as may be desired to correct for any errors in the thick ness or gauge of the strip 16, as compared to a predetermined desired gauge or thickness for the strip 16.

In Fig. 3 there is shown a curve chart illustrating the operation of the control apparatus in accordance with the present invention. In Fig. 3 there is a plot of delivery strip thickness or gauge deviation as a function of the length of the strip of material. The initial threading of the strip through the rolling mill and the start-up operation normally causes an initial length or portion of the strip which is not on gauge as shown by the dotted portion of the curve, then the remaining portion of a particular coil of the strip may be on gauge up to a portion between coils where the ends of the successive coils are welded or fastened together which may not be on gauge as shown by the dotted curve portion, then a second potrion of the total length of the strip is on gauge until the end of the last coil where the mill operation must slow down and stop.

With the control apparatus of the present invention, this initial threading and start-up portion of the strip or at least a considerable portion of this initial part of the strip may be made to be on gauge as shown by the solid curve portion, as is asubstantial portion of the in-between or welded segment of the strip and the final segment of the strip.

In Fig. 4 there is shown a schematic showing of a push-pull circuit arrangement using magnetic amplifier devices, and suitable for-use in the subject control apparatus. In the schematic circuit of Fig. 3, the output terminals of the load windings of the magnetic amplifier devices have been shown, and not the load winding as such, in an effort to simplify the illustration of the drawing. However, it should be understood that the load winding circuits including the unidirectional conductive devices as shown in Fig. 4 are intended to be used.

In Fig. 5 there is illustrated a well known limiter device,

operative such that when the voltage applied across the input terminals A and B is greater than the voltage provided by the adjustable DC. voltage source across the bridge terminals C and D, a low impedance path for any difference voltage is provided in parallel with any output or load device connected to the output terminals.

In Fig. 6 there is shown a well known dead zone or dead-band device, operative such that when the voltage across the input or terminals A and B of the bridge is less than the voltage provided by the adjustable DC voltage source across the terminals C and D of the bridge device, no current will flow to a load device connected across the output terminals.

In accordance with the operation of the subject control apparatus the zero setting of the potentiometer device 132 within the integration device 36 may be initially made by closing the clutch device 65 connecting the movable contact arm of the pressure reference setting potentiometer 64 with the reset motor 136 and opening the clutch device 146 to disconnect the contact arm of the potentiometer device 132 from the reset motor 136. For the initial reset or zero error setting operation, the

conductor members

92 and 94 are operative to sense any thickness error control signal received from the strain sensing device 31 and strain sensing device 33 when the roller members 12 and 14 are spaced in accordance with the predetermined and desired strip thickness, and is operative to control the operation of the reset motor 136 through the clutch device 65 to move the contact arm of the potentiometer 64 to balance out any such error voltage by suitably energizing the

control windings

60 and 62 such that a zero control voltage or signal is there by provided across the impedance devices 82 and 84. In this regard, the contact 95 is initially closed for the zero control reset operation and the

contacts

97, 99 and 101 are initially open. Now, the clutch member 65 is opened and the clutch member 146 is closed to thereby disconnect the contact arm of the potentiometer 64 from the reset motor 136 and to connect the contact arm of the potentiometer 132 to the reset or servo motor 136. Additionally, the contact member 95 is opened and the

contact members

97, 99 and 101 are closed such that now the control apparatus is readied for the normal operation of the mill stand relative to controlling the thickness or gauge of the strip 16.

The initial zero setting should be made with the strip 16 between the roller members 12 and 14 at the predetermined desired thickness of the strip 16 or with the predetermined desired spacing between the upper roller member 12 and the lower roller member 14.

Now with the mill stand ready for normal operation with the strip 16 passing between the upper roller member 12 and the lower roller member 14, the strain gauges 31 and 33 are operative to sense the pressure between the roller members and to provide an output signal across the

impedance members

108 and 110 in the output of amplifier device 90 in the form of an error correction signal. This error correction signal is supplied through the now closed contactor 101 to the

control windings

118 and 120 of the amplifier device 100 to control the energization of the load windings to suitably control the operation of the servo motor 136 through the now closed clutch 146 to move the position of the contact arm of the potentiometer 132, such that a difference vo'ztage having a magnitude corresponding to the difference between the actual roll pressure as sensed by the strain gauges 31 and 32 and the predetermined desired roll pressure as provided by the potentiometer 64 through the

control windings

60 and 62 of the amplifier device 80, and a polarity determined by the actual roll pressure being greater or smaller than said predetermined reference is provided, which error or difference signal in the form of an integrated signal is applied through the conductors 148 and 150 to the control windings 102 and 104.

The error control voltage is thusly reduced to zero by the operation of the latter integration signal applied to the integration control windings 102 and 104.

In this respect the control by the present apparatus of the operating speed of the mill stand motor 26 or the control of the screw-down motor 24 is intended to be an initial and very rapid correction with the correction subsequently being handled by the radiation gauge 190 in accordance with the teachings of copending application Serial No. 651,512, filed April 8, 1957, by the same inventors as the present application and assigned to the same assignee, and further, in accordance with the teachings of copending application Serial No. 651,386, filed April 8, 1957, by the same inventors and assigned to the same assignee.

The operation of the strain gauges 31 and 32 is to sense the actual pressure or force between the upper roller member 12 and the lower roller member 14 and to thereby vary the impedance relationship of the bridge circuit including the variable impedance members 40 and 42 to energize the

control windings

56 and 58 of the amplifier device with a control signal in accordance with the actual roll pressure or force between the roller members of the mill stand 10. The

control windings

60 and 62 receive a predetermined energization in accordance with a predetermined desired roll pressure corresponding to a predetermined spacing between the roller lmernbers, and thereby a predetermined thickness or gauge of the strip 16. Any difference between the energization of the

reference control windings

60 and 62 and the actual pressure energization of the

control windings

56 and 58 results in a difference control signal or error correction control signal being applied across the impedance members 82 and 84 and, in turn, passes through the

control windings

86 and 88 of the succeeding amplifier device 90 to result in an error correction control signal appearing across the impedance devices and 108. The error correction control signal from across the

latter impedance members

108 and 110 is applied to the

control windings

112 and 114 of the output amplifier device 116 for varying the operative speed of mill motor 26 and is secondly applied to the

control windings

118 and 120 of the reset amplifier device 100 to cause the reset motor 136 to operate in a direction in accordance with the polarity of the error correction control signal and to operate an amount or to reset the control arm of the potentiometer device 132 an amount corresponding to the integral of the error correction control signal, to thereby provide a feedback or integration control signal to the control windings 102 and 104 to balance out or bring to zero the error correction control signal resulting from the difference between the actual roll pressure and the predetermined desired roll pressure.

In this respect the operation of the integrator device 36 is slow acting and thereby, is operative to correct for a major portion of the initial errors in strip thickness and allows the radiation gauge after a predetermined transmit time from the mill stand 10 to detect the gauge or thickness error and provide the desired subsequent and more accurate correction to either the mill motor 26 or the screw-down motor 24 in accordance with the above-described copending applications.

In the operation of the control apparatus in accordance with the present invention, it is desirable to hold the gauge or thickness of the strip 16 to within one-tenth of a mil accuracy, in other words to within one ten-thousandths of an inch accuracy. The output signal from the strain gauge devices 31 and 33, including their respective variable inductance control windings 40 and 42, is a voltage proportional to the actual rolling pressure between the roller members 12 and 14, which control voltage is applied to the

control windings

56 and 58. This actual rolling pressure is equal to the predetermined desired pressure corresponding to the predetermined desired thickness or gauge of the strip 16 plus or minus any change in the rolling pressure due to any error in the gauge'or thickness of the strip. Thusly, the pressure reference potentiometer 64 is operative to energize the control windings 6t and 62 to balance out the voltage re ceived from the strain gauge devices corresponding to the desired rolling pressure, such than any output signal from the amplifier device 80 as applied to the impedance members 82 and 84 corresponds to the change in roll pressure due to any error in the gauge or thickness. When the impedance members 82 and 84 have no voltage drop across them, this corresponds to an operating condition of the mill stand with the actual gauge or thickness of the strip 16 corresponding to the predetermined desired gauge or thickness.

Thusly, any error correction control signal across the impedance members 82 and 84 is applied through the impedance members res and 110 to the control windings 112 to 114 to vary the output voltage of the generator device 174, and to thereby vary the tension of the strip 16 relative to the mill stand 10 by correspondingly varying the operating speed of the mill motor 26 and thereby the operating speed of the mill stand 10.

The control apparatus in accordance with the present invention must have a strip thickness error condition to provide an output signal across the impedance members .108 and lit The amplifier device 1% senses any error output voltage across the output of the amplifier device 90 and moves the reset motor 136 to supply to the control windings 102 and iii -5- of the amplifier device 9% an integrated signal to cancel out the error correction signal received from the amplifier device 89, thusly, causing the output of the amplifier device 96 to go to zero slowly. In this respect, the integration device 36 is operative to cancel out the error correction signal in the output of the amplifier device 90 in a time period of from 1 to 2 seconds. This allows the radiation gauge 1% and its associated control apparatus in accordance vwith the teachings of the above-copending applications to follow with the needed subsequent gauge or thickness corrections to thereby replace the error correcting action of the strain gauge control system in accordance with the present application.

If the operator of the rolling mill, including the mill stand 10, should decide to jog the screw-down device 22 to thereby jog or vary the spacing between the roller members 12 and 214, for example, between successive rolls or coils of strip, the screw-down device 22 is operatively connected, by relay devices not shown but well known to persons skilled in this art, with the

clutch members

65 and 146 and with the

contact members

95, 97 and 101 to close the clutch 65 and open the clutch 146 and to close the contact 95 and to open the

contacts

97, 99 and 101, such that the reset motor 136 operates to fast calibrate the position of the contact arm of the potentiometer 64 through the clutch member 65 to provide a new reference control signal to the control windings 6t) and 62 of the amplifier device 86 to balance out the error signal received from the strain gauges 3i and 33 to thereby provide the amplifier device 55% with the desired zero output voltage signal and thereby recalibrate the control apparatus to the new roll pressure as-sensed by the strain gauges 31 and 33 and corresponding to the new predetermined desired roll pressure.

if the end of a particular coil of strip material occurs with an error in the strip gauge present as sensed by the strain gauges 3i and 33, and thusly, providing an error corrective control signal across the impedance members 158 and 110, this same corrective control signal may not be needed for the next succeeding coil. Thusly, the bridge including the

potentiometer devices

130 and 132 has its output voltage measured through the contactor 97 to reset the potentiometer 132 and to thereby cancel any prior corrective action. in this respect, the contactor 97 closes at the end of the coil, by relay devices not shown, and the contactors 9 and 1191 open at the end of a coil to cancel any prior corrective actionby resetting the contact arm 132 of the potentiometer device by suitably con trolling the resetmotor 136 to a zero or balanced ,condition.

The slow integration operation is desirable because of temperature changes, in the mill housing or oil film thickness on the mill roller bearings. Otherwise, a gauge error may be indicated falsely clue to these conditions which would not be detected until the radiation gauge 190 was operative after, the time lag due to the passage of the particular section of strip from the mill stand it) to the radiation gauge 1%. In this respect, the strain gauge control apparatus in accordance with the teachings of the present application is intended to be operative relative to the predetermined and desired strip thickness and to correct for changes in strip gauge or thickness, whereas the radiation gauge control apparatus in accordance with the teachings of the copending application Serial No. 651,386, filed April 8, 1957, is intended to be operative relative to the actual gauge or thickness of the strip,

Further, it, should be noted that any time that the screw-down device 22 is jogged by the control motor 24, whether the mill stand Ill is operating or not, the clutch device 65 will close and the contact member 95 will close to sense the output of the amplifier device 86 and operate the reset motor 136 to recalibrate the position of the contact arm on the potentiometer 64 as may be desired to zero the output signal from the amplifier device 80.

The operation of the subject strain gauge apparatus is such that it receives an immediate indication of gauge or thickness error by measuring the rolling pressure of the mill stand ltl between the upper roller member 12 and the lower roller member 14 and thusly, the roll gap opening. The strain gauge system is fundamentally operative to hold substantially constant the rolling pressure in a predetermined mill stand such as the fifth mill stand. Holding a substantially constant rolling pressure is operative according to Hookes law, such that the stretch of the mill stand is substantially proportional to the strain or roll pressure up to the elastic limit of the mill stand and the elastic constant of the mill housing rolls, and in this manner a constant roll gap may thereby be efiected. As there is little or no elastic recovery of the strip in a cold mill, the roll gap opening is also a measure of the delivery gauge or thickness.

In the operation of the subject strain gauge control system, a magnetic strain gauge 30 is mounted on one or more of the fifth stand columns and a signal proportional to the actual rolling pressure is continuously and immediately obtained. The amplifier device 84 is operative to build up the power level and the voltage level of this actual rolling pressure signal and the output of the amplifier device is fed into a second amplifier device fit) which is operative to further increase the signal level.

The output of the latter amplifier device 90 is fed into the fifth stand amplifier device 116 in exactly the same manner as, and additive to, the error correction control signal from the radiation gauge control system as described in the above copending application Serial No. 651,386, filed April 8, 1957.

To provide an error correction control signal from the output signal received from the strain gauge 30, which may include the two strain gauges 31 and 33 shown in Fig. 3, a reference signal is provided and supplied to one set of control windings of the amplifier device 80. The difference between the strain gauge output signal and this latter reference signal represents the error correction signal and appears at the output of the amplifier device 80.

According to Hookes law whenever the screw-down device 22 is operated to change the screw-down or specing between the roller members and it is desired to roll the same strip gauge or thickness as was being rolled prior to said screw-down change, a new rolling pressure must be used. Therefore, the reference voltage received from the potentiometer member 64 must be re- 9. calibrated and is so recalibrated automatically by the operation of the screw-down control device 25 whether the screw-down jogging is done automatically or manually.

The integration device 36 is operative as a slow integrate device during normal running of the mill stand above threading speed with the unit being responsive to the output error correction signal of the second amplifier device 90 and slowly causes this output error correction signal to go to zero by inserting a differential control signal into the control windings 1G2 and 104 of the amplifier device 90. The latter action is provided mainly to guarantee that any possible drift or unwanted change in roll gap due to temperature changes or oil film thickness on the bearings for the roller members 12 and 14, rather than due to changes in incoming strip variations, Will be cancelled out and the reference will be recalibrated for these former changes. In this regard, the radiation gauge 190 is operative as the ultimate standard of measurement of delivery gauge or thickness under all conditions of mill stand operation.

At the finish of a roll or coil of strip and previous to running the successive coil, the integrator bridge including the

potentiometer members

130 and 132 is zeroed so that it cannot insert an unwanted signal when starting the next run on a successive strip of material. Also, during this change-over period or if the screws are jogged during normal running operation, the pressure reference is reset to the value desired by the operator.

It should be understood that the subject control apparatus senses the actual rolling pressure between the roller members. If, for example, the actual strip thickness at the roller members is too thick, this increases the actual rolling pressure, and causes thesubject control apparatus to provide an error correction signal having a polarity, for example positive, for increasing the speed of the roller members to thereby increase the strip tension relative to the roller members and thereby effecting an increased strip thickness reduction by the roller members and in this manner return to the desired rolling pressure. In this regard it should be understood that either entry strip tension or delivery strip tension relative to the roller members may be varied as desired for strip thickness error correction. However, relative to particularly the final stand of the rolling mill, it may be preferable to vary entry strip tension and not interfere with the desired strip coiling operation by the delivery winding reel. 7 It should be further understood that the teachings of the present application, as well as the teachings of the referenced copending applications, are readily adaptable to single or multiple stand mills, either tandem or reversible mills. Also it should be understood that the subject strip thickness control apparatus is intended to be added to or combined with the presently well known rolling mill control apparatus for the mill stands and winding reels as well known to persons skilled in this art.

Although the present invention has been described with a certain degree of particularity, it should be understood that the present disclosure has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts may be resorted to without departing from the scope and the spirit of the present invention.

We claim as our invention:

1. In control apparatus for a rolling mill including a first device having a pair of roller members between which a strip of material may be positioned for performing a predetermined operation relative to said strip of material, withsaid rolling mill including a second device for pulling on the strip relative to said first device, the combination of a roller pressure sensing device for providing a first control signal that varies as a predetermined function of the roll pressure between said pair of roller members, a motor member operative with one of said first and second devices for controlling the tension in said strip between said first and second devices, a first motor control device responsive to said first control signal and operatively connected to said motor member for controlling the tension of s'aid strip between said first device and said second device in accordance with the variations of said first control signal, and a second motor control device responsive to said first control signal for providing a second control signal that varies as a predetermined function of the variations of said first control signal, with said first motor control device being responsive to said second control signal for controlling the tension of said strip between said first device and said second device in accordance with the variations of said second control signal.

2. In control apparatus for a first device having a pair of cooperating members between which a strip of material may be positioned for performing a predetermined operation relative to said strip of material and a second device operative with said strip to provide a predetermined tension in said strip between said first and second devices, the combination of a motor member operatively connected to one of said first and second devices for controlling the tension of said strip between the first and second devices to thereby control the thickness of said strip, a pressure control device for providing a first control signal that varies as a predetermined function of the pressure between said pair of cooperating members, a first motor control device responsive to said first control signal and operative with said motor member for controlling the tension of said strip between said first and second devices as a predetermined function of the variations of said first control signal, and a second motor control device responsive to said first control signal for providing a second control signal which varies as a function of the magnitude of said first control signal, with said second motor control device being operative with said motor member for controlling the tension of said strip between said first and second devices as a predetermined function of the variations of said second control signal.

3. In control apparatus for a rolling mill including a first device having a pair of roller members operative with a strip of material positioned between said roller members, with said rolling mill including a second device for pulling on the strip in a direction away from said first device, the combination of a motor member operatively connected to one of said first devices and said second devices for controlling the tension of said strip between the first device and the second device, a strain measuring device operative with said first device for measuring a predetermined strain of said first device resulting from the operation of said roller members relative to said strip of material, with said strain measuring device providing a first control signal which varies as a predetermined function of said strain of said first device, a first motor control device responsive to said first control signal and operatively connected to said motor member for controlling the tension of said strip between said first device and said second device in accordance with the variations of said first control signal, a second motor control device responsive to said first control signal for providing a second control signal which varies as a pre determined function of the variations of said first con trol signal, with said first motor control device being responsive to said second control signal for controlling the tension of said strip between said first device and said second device in accordance with the variations of said second control signal.

4. In control apparatus for a first device having a pair of cooperating members between which a strip of material may be positioned for performing a predetermined operation relative to said strip of material and a second device operative with said strip to provide tension in said strip between said first and second devices, the combination of a motor member operatively connected to one of said first and second device for controlling the operation of said one device relative to said strip of material, a deformation sensing device operative with said first device for providing a first control signal that varies as a predetermined function of' the deformation of said first device resulting from the operation of said pair of cooperating members relative to said strip of material, a first motor control device responsive to said first control signal and operative with said motor member for controlling the operation of said first device relative to said strip of material, and a second motor control de vice responsive to said first control signal for providing a second control signal which varies as a function of the magnitude of said first control signal, with said second motor control device being operative with said motor member for controlling the operation of said first device relative to said strip of material as a predetermined function of the variations of said second control signal.

5. In control apparatus for a first device having a pair of cooperating members between which a strip of material may be positioned for performing a predetermined operation relative to said strip of material and a second de vice operative with said strip of material to provide a tension in said strip between said first and second devices, the combination of a pressure control device operative with said first device for providing a first control signal that varies as a predetermined function of the pressure between said pair of cooperating members, a reference control device for providing a second control. signal as a function of a predetermined desired pressure between said pair of cooperating members, a first control device responsive to said first control signal and responsive to said second control signal for controlling the operation of said first device in accordance with a predetermined comparison between said first control signal and said second control signal for controlling the operation of said first device relative to said strip of material, and a second control device responsive to said first control signal for providing a third control signal that varies as a predetermined function of said first control signal, with said second control device being operative with said first device for controlling the operation of said first device relative to said strip of material as a predetermined function of the variations of said third control signal.

6. In control apparatus for a rolling mill including a first device having a pair of roller members between which a strip of material may be positioned for performing a predetermined operation relative to said strip of material, said rolling mill including a second device for pulling on the strip relative to said first device, the combination of a roller pressure sensing device operative with said first device for providing a first control signal that varies as a predetermined function of the pressure between said pair of roller members, a motor operative with one of said first and second devices, a first motor control device responsive to said control signal and operatively connected to said motor for controlling the tension of said strip between said first device andtsaid second device in accordance with the variations of said first control signal, and a second motor control device responsive to said first control signal for providing a second control signal that varies .as a predetermined function of the variations of said first control signal, with said first motor control device being responsive to said second control signal for controlling the tension of said strip between said first device and said second device in accordance with the variations of said second control signal.

7. In control apparatus for a first device having a pair of cooperating members between which a strip of material may be positioned for performing a predetermined operation relative to said strip of material, with said control apparatus being operative with a second device to provide a predetermined tension in said strip between said first and second devices, the combination of, a motor member operatively connected to said first device for controlling the tension of said strip between the first and second devices, a pressure control device operative with said first device for providing a first control signal that varies as a predetermined function of the pressure between said pair of cooperating members, a first motor control device responsive to said first control signal and operative with said motor member for controlling the tension of said strip between said first and second devices as a predetermined function of the pressure between said pair of cooperating members, and a second motor control device responsive to said first control signal for providing a second control signal which varies as a function of said first control signal, with said second motor control device being operative with said motor member for controlling the tension of said strip between said first and second devices as a predetermined function of the pressure between said pair of cooperating members.

8. In control apparatus for a rolling mill including a first device having a pair of roller members between which a strip of material may be positioned for performing a predetermined operation relative to said strip of material, said rolling mill including a second device for pulling on the strip relative to said first device, the combination of a roller pressure sensing device for providing a first control signal that varies as a predetermined function of the pressure between said pair of roller members, a motor operative with one of said first and second devices, a first motor control device responsive to said control signal and operatively connected to said motor for controlling the tension of said strip between said first device and said second device in accordance with the variations of said first control signal, a second motor control device responsive to said first control signal for providing a second control signal that varies as a predetermined function of the variations of said first control signal, with said first motor control device being responsive to said second control signal for controlling the tension of said strip between said first device and said second device in accordance with the variations of said second control signal, and a strip tension limiting device operative with one of said motor control devices for limiting the strip tension between said first and second devices to a predetermined maximum tension value.

9. In control apparatus for a first device having a pair of cooperating members between which a strip of material may be positioned for performing a predetermined operation relative to said strip of material and a second device operative with said strip to control the tension in said strip between said first and second devices, the combination of a motor member operatively connected to one of said first device and said second device for controlling the tension of said strip between the first and second devices, a pressure control device operative with said first device for providing a first control signal that varies as a predetermined function of the pressure between said pair of cooperating members, a first motor control device responsive to said first control signal and operative with said motor member for controlling the tension of said strip between said first and second devices as a predetermined function of said first control signal, a second motor control device responsive to said first control signal for providing a second control signal which varies as a predetermined function of said first control signal, with said second motor control device being operative with said motor member for controlling the tension of said strip between said first and second devices as a predetermined function of said second control signal, and a strip tension limiting device operative with said motor member for limiting to a predetermined maximum value the tension of said strip between said first device and said second device.

10. In control apparatus for a first device having a pair of roller members and operative with a strip of ma- 13 terial for determining the thickness of said strip and a second device operative with said strip to control the tension'in said strip between said first and second devices, the combination of a motor member operative with at least one of said first and second devices for controlling the tension of said strip between said first and second devices, a roller pressure sensing device for providing a first control signal that varies as a predetermined function of the pressure between said pair of roller members, with said first control signal having one polarity when the pressure between said pair of roller members is greater than a predetermined pressure and with said first control signal having an opposite polarity when the pressure between said pair of roller members is less than a predetermined pressure, a first motor control device operative with said motor member for controlling the operating speed of said motor member, with said first motor control device being responsive to said first control signal for increasing the motor member speed when the first control signal has said one polarity and for decreasing the motor member speed when the first control signal has said opposite polarity, and a second motor control device responsive to said first control signal for providing a second control signal that has a first polarity when said first control signal has said one polarity and has a second polarity when said second control signal has said opposite polarity, with said second motor control device being operative with said motor member to increase the motor member speed when said second control signal has said first polarity and being operative to decrease the motor member speed when said second control signal has said second polarity.

11. In control apparatus for a first device having a pair of roller members and operative with a strip of material for determining the thickness of said strip and a second-device operative with said strip to control the tension in said strip between said first and second devices, thecombination of a motor member operative with at least one of said first and second devices for controlling the tension of said strip between said first and second devices, a roller pressure sensing device for providing a first control signal that varies as a predetermined function of the pressure between said pair of roller members, with said first control signal having a first polarity when the pressure between said pair of roller members is greater than a predetermined pressure and with said first control signal having a second polarity when the pressure between said pair of roller members is less than a predetermined pressure, a first motor control device operative with said motor member for controlling the tension of said strip between said first and second devices, with said first motor control device being responsive to said first control signal for increasing said strip tension when the first control signal has said first polarity and for decreasing said strip tension when the first control signal has said second polarity, and a second motor control device responsive to said first control signal for providing a second control signal that has a first polarity when said first control signal has said first polarity and has a second polarity when said second control signal has said second polarity, with said second motor control device being operative with said motor member to increase said strip tension when said second control signal has said first polarity and being operative to decrease said strip tension when said second control signal has said second polarity.

12. In control apparatus for a first device having a pair of roller members and operative with a strip of material for determining the thickness of said strip and a second device operative with said strip to control the tension in said strip between said first and second de vices, the combination of a motor member operative with at least one of said first and second devices for controlling the tension of said strip between said first and second devices, a roller pressure sensing device for providing a first control signal that varies as a predetermined function of the pressure between said pair of roller members, with said first control signal having a first polarity when the pressure between said pair of roller members is greater than a predetermined reference pressure and with said first control signal having a second polarity when the pressure between said pair of roller members is less than a predetermined reference pressure, a first motor control device operative with said motor member for controlling the operating speed of said motor member, with said first motor control device being responsive to said first control signal for increasing the motor member speed when the first control signal has one of said first polarity and said second polarity and for decreasing the motor member speed when the first control signal has the other of said first polarity and said second polarity, and a second motor control device responsive to said first control signal for providing a second control signal that has a first polarity when said first control signal has said first polarity and ha a second polarity when said second control signal has said second polarity, with said second motor control device being operative with said motor member to increase the motor member speed when said second control signal has one of said first polarity and said second. polarity and being operative to decrease the motor member speed when said second control signal has the other of said first polarity and said second polarity.

13. In control apparatus for a first device having a pair of cooperating members between which a strip of material may be positioned for performing a predetermined operation relative to said strip of material and a second device operative with said strip of material to provide a tension in said strip between said first and second devices, the combination of a pressure control device operative with said first device for providing a first control signal that varies as a predetermined function of the pressure between said pair of cooperating members, a reference control device for providing a sewnd control signal as a function of a predetermined desired pressure between said pair of cooperating members, a first control device operative with one of said first device and said second device and being responsive to said first control signal and responsive to said second control signal for controlling the operation of said one of said first and second devices in accordance with a predetermined comparison between said first control signal and said second control signal for controlling the tension of said strip between said first device and said second device, a second control device responsive to said first control signal for providing a third control signal that varies as a predetermined function of said first control signal, with said second control device being operative with one of said first device and said second device for controlling the tension of said strip of said first device relative to said strip of material as a predetermined function of said first control signal, with said first control signal being greater than said second control signal when the actual pressure between said pair of cooperating members is greater than said predetermined desired pressure and with said first control signal being less than said second control signal when said actual pressure between said pair of cooperating members is less than said predetermined desired pressure.

14. In control apparatus for a first device having a pair of cooperating members between which a strip of material may be positioned for performing a predetermined operation relative to said strip of material and a second device operative with said strip of material to provide a tension in said strip between said first and second devices, the combination of a pressure control device operative with said first device for providing a first control signal that varies as a function of the pressure between said pair of cooperating members, a refer- 15 ence control device. for providing a second control signal as a function of a predetermined desired pressure between said pair of cooperating members, a first control device operative with one of said first and second devices and responsive to said first control signal and responsive to said second control signal for controlling the operation of said one of said first device and second device relative to said strip in accordance with a predetermined comparison between said first control signal and said second control signal, a second control device responsive to said first control signal for providing a third control signal that varies as a predetermined function of said first control signal, with said second control device being operaative with said first device for controlling the operation 16 of said first device relative to said strip of material as a function of said third control signal, and a strip tension limiting device operative with one of said control devices for limiting the magnitude of the total control signal applied to said first device.

References Cited in the file of this patent UNITED STATES PATENTS 2,264,096 Mohler Nov. 25, 1941 2,281,083 Stoltz Apr. 28, 1942 2,322,418 Crawford June 22, 1943 2,410,283 Gar Oct. 29, 1946 2,544,467 Michel Mar. 6, 1951 2,659,154 Rendel Nov. 17, 1953