US2982901A - Repositioning selective control system - Google Patents

Description

May 2, 1961 M. w. CANNON 2,982,901

REPOSITIONINGSELECTIVE CONTROL SYSTEM Filed April 1956 O/V-OFF T/ME Inventor: Maurice \N. Cannon is Attor n eg.

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May 2, 1961 M. w. CANNON REPOSITIONING SELECTIVE CONTROL SYSTEM Filed April 2?, 195a 4 Shee Inventor Maurice W. Cannon 135 W His Attorneg.

y 2, 1961 M. w. CANNON 2,982,901

REPOSITIONING SELECTIVE CONTROL SYSTEM Filed April 27, 1956 4 Sheets-Sheet 3 Inventor: Maurice W. Cann o1"!v FAQ/c.

His Attorney.

y 2, 1961 M. w. cANNoN 2,982,901

REPOSITIONING SELECTIVE CONTROL SYSTEM Filed April 27, 1956 4 Sheets-Sheet 4 1 a 93 I v A 9/ v v OFF I M 7; \!\\I n 7|- 40/70 I 97 88 I K96 J v 99 /00 I o/v A\A\ I 1 K; I .94 10/10 I Maurice \N. Cannon b W QWJML His A'b'borheg.

United States Patent ()ce 2,982,901 Patented May 2, 1961 REPOSITIONING SELECTIVE CONTRQL SYSTEM Maurice W. Cannon, Roanoke, Va., assignor to General Electric Company, a corporation of New York Filed Apr. 27, 1956, Ser. No. 581,103

3 Claims. (Cl. 318-466) The invention relates to positioning control systems, particularly reversible electric motor operated selective positioning control systems having alternative selective position control means such, for example, as may be suitable for selectively controlling either manually or automatically the roll spacing of a rolling mill or in any other similar working member selective positioning control service.

In such alternative selective positioning control service, a reset of the working member to some particular position that may be accurately set or selected by one selective positioning control means may become desirable only during or following subsequent positioning control of the member by the alternative selective positioning control means.

One of the principal objects of the present invention is the provision of an improved repositioning selective control system and apparatus capable of responding to the departure from any position of the member as set or selected by one selective positioning control means only when the departure is controlled by an alternative selective control means and of effecting an automatic reset to such set or preselected position.

The improved repositioning selective control system of the present invention, although not limited thereto, is particularly advantageous for resetting the roll spacing of a steel strip rolling mill to any value manually set or selected for the beginning of the rolling of any gage strip when each subsequent strip enters the mill to be rolled under automatic gage control.

In such rolling mill operation the largest part of the oil-gage material usually is located at the beginning of each strip. The remaining material normally may be rolled most accurately to the desired thickness or gage under automatic thickness gage control, since it does not deviate from the desired thickness by any large amount. Thus, in such service, the present invention can produce large savings, since the improved repositioning selective means can reset the rolls to the manually preselected or preadjusted spacing required to correct the entering oilgage material very quickly at the time the rolling of each subsequent strip under automatic gage control is started.

To operate the steel strip rolling mill in accordance with the present invention, the initial roll spacing is accurately set by manual reversing control of the roll positioning screwdown motor or motors so that the strip to be rolled can be threaded at a suitable low speed between the rolls with the initial spacing thereof at the proper value determined by experiment, calculation, judgment or experience to produce the necessary reduction of the particular size and quality material being rolled substantially to the desired thickness or gage. After the low speed threading operation is accomplished, the rolling speed increases and the automatic thickness gage control becomes effective to automatically control the further reversing operation of the roll screwdown motor so as to vary the spacing of the rolls at the proper time and in the proper direction and amount required to maintain the thickness of the rolled material at or as near to the desired predetermined value or gage as possible.

But concurrently with the low speed threading of each subsequent strip of material between the rolls preparatory to full speed rolling under automatic thickness gage control, the improved selective repositioning control system of the present invention functions automatically to reset the rolls quickly from any spacing to which they may have become adjusted under automatic control to their preselected initial setting in order to produce the proper roll spacing for the accurate reduction of the beginning of each subsequent strip which may be assumed to be off-gage in the same way as the preceding strip. Heretofore, the mill operator had to remember the particular rolling schedule and the proper initial roll spacing and then try to effect such roll spacing reset each time under manual control with attendant possibilities of error, inaccuracy, and unnecessary delay.

A more specific object of the present invention is to provide improved selective electrical interlocking and electrically operated clutch connections between a reversible electric motor operated positioning control systcm having alternative positioning control elements and an automatic electrical unbalancing responsive control ieans of an improved sensitive magnetic amplifier type whereby the positioning system can be automatically reset more accurately and quickly to any initial position preselected by one control element when a predetermined working or operating condition occurs during the positioning operation under the alernative control element.

A further object is to provide an improved form of electrically adjustable magnetic amplifier type selective limit control for the automatic selective repositioning control system capable of insuring, in the case of the rolling mill, that the rolls never can be operated in either direction under automatic control beyond fixed limits that are independently adjustable electrically to a relatively high degree of accuracy.

The novel features believed characteristic of the invention are set forth with particularity in the appended claims. The invention itself, however, together with further objects and advantages thereof may best be understood by referring to the following description taken in connection with the accompanying drawings in which Figs. 1a, lb and 10 on separate sheets when placed in adjacent relation constitute a schematic representation of a preferred embodiment of the invention in a positioning control system for the roll screwdown motor of a strip rolling mill.

Fig. 2 shows a typical form of magnetic amplifier suitable for use in the control system of Figs. la, lb and 10.

Fig. 3 shows a modification of the screwdown motor control system of Figs. la, lb and 1c.

Referring to Figs. la, lb and lo, I have shown my invention in one form as applied to the control of the screwdown motor ltl having a separately excited shunt field winding 10a and a commutating field winding 19b, and arranged to drive through the gears 11 the lowering and elevating mechal "sm of one roll 12a of a rolling mill 12 that is provided with a suitable roll driving motor, not shown. A strip of material 13 is passed through the rolls 12 to reduce the gage or thickness thereof an amount that depends upon the positioning of the roll 12a by the motor it The thickness of the rolled strip may be measured by any suitable form of thickness gage mechanism 14, preferably of the noncontacting X-ray type, such as described more fully in the Clapp Patent 2,467,812.

In the system shown, the reversing operation of motor 10 to position the roll 12a may be controlled either mana ually by means'of the manual reversing switch 24 and the armature reversing contactors 1D, 2D and 1U, 2U, or by means of suitable automatic thickness or gage control apparatus 21 (shown in Fig. lb) that is arranged to operate the reversing contactors 1D, 2D and 1U, 2U automatically under the control of the X-ray gage 14 to automatically maintain the roll spacing at the proper value required to produce a desired thickness of the rolled strip. A suitable transfer or selector switch 22 shown in Fig. 1b serves to selectively render either the manual or automatic control effective. In the ordinary procedure, the manual control 20 is used to selectively and accurately position the roll 12a when the leading end of the first strip of material 13 is initially threaded into the mill operating at suitable low threading speed, and the transfer switch 22 is then operated to enable further positioning of the roll to be controlled automatically by the Xray gage 14 at the full rolling speed of the mill.

Z'Janual positioning control With the transfer or selector switch 22 in position M, the manual reversing control switch 20 is rendered effective for reversibly controlling the screwdown motor 10 to select the initial position of roll 1L1 which may be indicated by a suitable roll spacing indicator, not shown. The selected initial position of roll 12a ordinarily will be in accordance with experimental data, calculation, judgment or experience of the operator to produce the necessary reduction of the particular size and quality material to be rolled substantially to the desired thickness or gage.

In order to raise roll-12a to increase the gage, the manual switch 2% is moved to the Up position marked U. As a result the contact 20a of the manual switch 20 energizes the relay BC to release the electromagnetically operated brake B. At the same time contact 20b energizes the Up contactors 1U and 2U through a circuit extending from the line L1, the disconnecting switch S in its closed position, conductor C1, contact 20b, conductor C2, interlocking contact 2D1 of the Down contactor 2D, interlocking contact BUl of the antiplugging relay BU and the operating windings of the Up contactors 1U and 2U in parallel to the line L2. The resulting closure of the armature circuit contacts 1U1 and 2U1 serves to energize the motor armature 10 for operation in the Up direction with the accelerating resistors R1, R2 in the circuit between lines L1, L2 provided the undervoltage and overload protective line switch L is closed, due to closure of the contact UV of a suitable undervoltage responsive relay and the contact L of a suitable overload responsive relay, which are not shown for the sake of simplicity.

Upon the opening of interlocking contact 1112 of the Up contactor 1U, the dynamic braking contactor D3 is deener gized to open the circuit through the braking resistor R3 by opening contact DB1. Also, the contact DB2 is closed. The opening of contact 2U2 of Up conin producing operation of the motor 10 in the opposite direction to reduce the roll spacing. In this way the roll 12a can be selectively set quite accurately under manual control to a particular position that is suitable for threading the entering end of the first strip of material 3.3 to be rolled into the mill.

Automatic positioning control As soon as the leading end of the first strip is properly threaded into the rolling mill while operating at the reduced threading speed, the speed of the rolls then may be increased to normal rolling speed and the selector switch 22 moved by the operator from position M to position A to obtain automatic gage positioning control of the screwdown motor 10. In the automatic position A switch 22 energizes the relay marked AUTO and shown in Fig. 1b. The closure of contact AUTO-1 enables the automatic gage control apparatus 21 and the magnetic amplifiers 23 and 24 of a suitable type, such as shown in Fig. 2, and having, respectively, the relays EU and ED energized thereby, to produce automatic reversing operation of motor 10 under the control of the X-ray gage 14 in the following manner:

When the rolled strip becomes oif-gage, the output of X-ray gage 14 will vary in polarity dependent upon whether the strip is light or heavy, and in magnitude dependent'upon the amount of the error. The automatic gage control apparatus 21 will therefore respond to the output of gage 14 to vary the energization of the amplitactor 2U similarly deenergizes the operating winding of accelerating control relay lAR to close contacts 1AR1. This produces energization of accelerating contactor 1A to short-circuit the accelerating resistor R1 through contact 1A1. Also contact 1A2 opens to deenergize the acceleration control contactor 2AR and thereby close contact 2AD1. This results in the subsequent energization of contactor 2A to close contact 2A1 and thereby short-circuit the second accelerating resistor R2 to produce full speed operation of motor 10.

The closure of contact 2U3 serves to connect the antiplugging relay B1) to be responsive to the voltage of the motor armature and thereby close its sealing contact EDI and open its antiplugging interlocking control contact 'BDZ.

Upon operating the manual control switch 20 in the opposite direction to position D, contacts 20a and 20b perform precisely the same functions as just described fier control windings 23a and 24a in accordance with both the polarity and magnitude of the output of X-ray gage 14. But the On-Otf time contact shown in Fig. 1a is cyclically closed by suitable means (not shown) for time intervals that vary only in accordance with the magnitude of the output of the X-ray gage 14. Since this general type of variable timing control is disclosed in the Mohler Patent 2,264,095, further description thereof is omitted for the sake of simplicity.

When the rolled strip 13 is running heavy, the polarity of the output of gage 14 will energize control winding 24:: in the On direction as indicated by the arrow. If the error is of suflicient magnitude, the heavy gage signal energization of winding 24:: relative to the magnitude of the energization of the amplifier OE biasing winding 24b as determined by the adjustment of potentiometer 26 will trigger the the amplifier 24 to pick up relay ED and contact EDI will be closed and contact EDZ opened.

As a result of the closure of contact EDl, relay AD will be energized to cyclically close contacts AD]; to release the brake B and AD2 to energize theDown contactors 1D and 2D in a time cycle dependent upon the closure interval of the On-Ofi time contact. As previously pointed out, this closure interval will vary as a function of the magnitude of the error signal from gage 14. In this way the screwdown motor 10 will be progressively operated in graduated steps to lower roll 12a and thereby decrease the deviation of the rolled strip thickness from the desired value. a When the error signal from gage 14 is of the opposite polarity due to the strip running light, the winding 23a of magnetic amplifier 23 may be energized in the direction to cause the amplifier 23 to energize the relay EU sufficiently to pick up and close the contact EU]. and open contact EU2. In this case the pickup signal magnitude of amplifier 23 is dependent upon the adjustment of potentiometer 25 which determines the biasing magnitude of the 01f biasing winding 23bv With contact EUI closed, the cyclical closure of the On-Otf time contact will produce cyclical energization of the relay AU. This in turn will result in cyclical closure of contact AU to release the brake B and of AU2 to energize the Up contactors 1U and 2U. This Will operate the screwdown motor 10 in steps of progressively decreasing length in the direction to raise the roll 12a and thereby decrease the light deviation of the rolled strip 13.

It will be observed that in the automatic operation of motor in both the Up and Down directions, the contact AUTO-2 serves to maintain the accelerating relay lAR energized continuously and thereby eliminates the short-circulating of the accelerating control resistors R1 and R2. In this way a more delicate and accurate automatic positioning of the roll 12a to precisely the position required to maintain the desired thickness of the roll strip '13 is obtained. Consequently, the automatic gage control apparatus will function to hold the strip thickness at or as near to the desired predetermined value or gage as possible during the rolling of the strip under automatic gage control.

As will be described more fully hereinafter, the adjustable resistor 28 and its short-circuiting contact ED2 function to recalibrate the decrease in signal magnitude in the control winding 24a required to drop out the relay ED. The purpose is to enable the dropout signal magnitude to be adjusted as close as may be desired to the variable pickup signal magnitude determined by adjustment of the potentiometer 26. Likewise, the adjustable resistor 27 and its short-circulating contact EU2 perform similar functions in cor-relating the dropout signal magnitudes of relay EU. Such improved pickup and dropout signal recalibrating control system is more fully described and claimed in my patent application, Ser. No. 581,179, filed concurrently herewith.

Automatic reset control The present invention provides improved electrical unbalance responsive means for eifecting a quick and accurate reset of the roll 12a to any particular position initially selected under manual control preparatory to the roiling of each succeeding strip under automatic gage control. For this purpose a selsyn transmitter 30 is driven through the gearing 31 in order to move the receiving selsyn 32, shown in Fig. 1b, proportionally to the movement of the roll 12a. The motion of receiving selsyn 32 may be transmitted through the electrically operated clutch 33 to rotate the sliding contact or balance control element 34 of the reset control potentiometer 35. But whenever clutch 33 is disengaged, the balance control element 34 may be moved to its balanced position in which it is shown by means of the separate reversible electric motor 36 operating through the electromagnetic clutch 37.

During the automatic gage positioning control of roll 12a, the departure of potentiometer control element 34 from its mid or balanced position serves to perform three functions: First, to automatically control the reversing operation of motor 10 to return the roll 12a to any position that was preselected under manual control when each succeeding strip is threaded into the mill; second, to provide an indication of such departure at the mill operators cabinet; and third, to provide a preselected upward travel limit and downward travel limit to the departure of the roll v12a from any position that was preselected by operation of the motor 10 under control of the manual controller 20.

To accomplish the first function, the balance control element 34 is arranged to control the energization of the control windings 4t) and 41, respectively, of the magnetic amplifiers 42 and 43 that may be of a suitable type such as shown in Fig. 2, and energize, respectively, the operating windings 44 and 45 of the electromagnetically operated relays or switches RU and RD. The magnetic amplifier illustrated in- Fig. 2 is of the type generally known as an amplistat. When the control element 34 is in its mid or balanced position as shown, the potentiometer 35 is balanced with respect to the midpoint between the equal resistors 46 and 47 shown in Fig. 1c. Therefore, the energization of control windings 40 and 41 is substantially zero under balanced conditions.

The biasing windings 48 and 49 of the magnetic amplifiers or amplistats 42 and 43 serve to predctermine the signal values in their respective control windings 40 and 41 required to pick up the corresponding switches RU and RD. The potentiometer 56 enables the biasing action of Winding 48 to be adjusted to produce a corresponding adjustment of the signal voltage of control Winding 40 required to pick up the electromagnetically operated switch RU. As shown, the potentiometer 56 has a variable portion of its resistance in shunt with the biasing winding 43. The adjustable resistor 57 which is normally short-circuited by contact 1RUX1 is connected in series with the variable resistance of potentiometer 56 in shunt with the biasing winding 48. When switch RU is picked up, the short-circuiting switch lRUXl is opened, due to energization of relay lRUX, thereby removing the short circuit from resistor 57. This enables the adjustment of resistor 57 to control the reduction in signal voltage value in control Winding 40 required to drop out relay RU.

The energization of the biasing winding 49 of the magnetic amplifier or amplistat 43 is controlled by the potentiometers 58 and the adjustable resistor 59 that is normally short-circuited by contact 1RDX1 of relay lRDX in a similar manner to correlate the pickup and dropout signal voltage values in control winding 41.

But before the automatic repositioning control can function, the balance control member 34 must be selectively positioned into its balanced position. This occurs automatically when the positioning operation of the motor 10 is under control of the manual controller 20. During this operation the balance control element 34 is automatically moved to its midposition or balanced position by energization of clutch 37 through contact AUTO-5 and selective reversing control of motor 36 through the agency of the unbalance responsive magnetic amplifiers 42, 43 and the electromagnetic switches RU and RD controlled thereby and which in turn selectively operate the reversing relays for motor 36. Thus, whenever the selector switch 22 is in its manual position and control element 34 is unbalanced in one direction, the pickup of switch RU by amplifier 42 will serve to energize relays lRUX and ZRUX. In turn, the contacts of these relays selectively control the energization of the reversing windings of motor 36 to operate the balance control member 34 towards its mid or balanced position. At this same time contact AUTO-5 will energize the clutch 37.

When control element 34 is unbalanced in the other direction, a similar operation will be produced when relays RD, lRDX and ZRDX are picked up by triggering amplifier 43, except that motor 36 will be operated in the reverse direction, to return element 34 to its balanced position. In this way whenever the roll 12a is being positioned to some selected position under control of the manual controller 22, the unbalance responsive control means always insures that the balance control element 34 is returned to its mid or balanced position.

When the selector switch 22 is operated to transfer the positioning of the roll 12a to automatic control by the X-ray gage 14, thereupon the clutch 33 is energized by contact AUTO-5. As a result the departure of the balance control element 34 from its mid or balanced position becomes proportional to any repositioning of roll 1241 that may occur under automatic control of the X-ray gage 14. This is accomplished by means of the sending selsyn 3b, the gearing 31 and the receiving selsyn 32.

After the rolling of each strip is completed, the mill is conditioned for threading in the succeeding strip. For this purpose a tensiometer or other suitable means (not shown) preferably is provided for suspending the opera tion of the automatic gage as soon as the tail end of the strip leaves the rolls. Then in order to guide the head end of the succeeding strip between the rolls, a suitable guide member 15 is moved by suitable hydraulic means 16 into working relationship with the rolls. Upon 7 establishment of such working conditions, the contact 17 of the hydraulic pressure responsive device 16 is automatically closed, thereby energizing the automatic reset control relay SR as soon as the contact RUN is closed. As a result a circuit is established through SR contact SR1 and contact AUTO1 of the automatic operation relay AUTO that is controlled by the selector switch 22. This establishes an energizing circuit for either relay AU or AD, depending upon whether the contacts 1RUX2 or lRDXZ of relay IRUX or IRDX are closed The closure of either relay lRUX or IRDX depends upon the pickup of either RU or RD by the unbalance responsive amplifiers 42 and 43 which, in turn, depends upon the direction of departure of control element 34 from its mid or balanced position as well as the amount of this departure which is further dependent upon the adjustment of the potentiometers 56 and 58 that control the biasing windings 48 and '49, respectively. The interlocking connections are such that when relay AU is energized, the brake B is released by contact AU]. and the reversing control switches 1U and 2U are energized by contact AU2' to operate the screwdown motor in the direction to return the roll 12a to the predetermined position selected under manual control when the departure therefrom due to automatic gage operation of roll 12a and balance control element 34 is in one direction.

In case the departure of control element 34 due to automatic gage operation is in the other direction, the pickup of relay R-D by the unbalance responsive amplifier '43 serves to energize the reversing switches 1D and 2D to effect a similar return of the roll 12a to the predetermined position. In each case the motor 10 operates to return the balance control element 34 to its mid or balanced position simultaneously with the reset of the roll 12a to the predetermined position selected under manual control.

Thus, it will be seen that the interlocking connections of the present invention are such that whenever the manual controller 22 is selected for positioning the roll 12a, the unbalance responsive control means including the balance control element 34 functions to reversely control the operation of motor 36 and clutch 37 automatically to position the balance control element 34 in its mid or balanced position. But when the X-ray gage 14 is selected to automatically position the roll 1211 so as to maintain the output thickness of strip 13 at a desired value, the departure of the balance control element 34 from its mid or balanced position is always proportional to the movement of roll 12a away from the manually selected position. But when a predetermined working condition occurs as when a succeeding strip is threaded into the rolls, the improved selective repositioning control system of the present invention functions automatically to control the motor '10 and the clutch 33 to return the balance control element 34 to its mid or balanced position and thereby reset the roll 12a to the manually preselected position.

As an additional function the balance control element 34 of potentiometer 35 operates to vary the energizing potential impressed upon the screw departure indicator 70, thereby indicating to the operator at all times the departure effected under automatic control from the manually preselected position of roll 12a.

The third function provided by the balance control element 34 is to establish any desired maximum limits for the departure of roll 12a from the manually preselected position under automatic control. Thisis accomplished by means of the magnetic amplifiers 72 and 73 having, respectively, the control windings 74 and 75 energized under control of the balance control element 34 for the purpose of controlling the pickup of the Up limit relay LU and the Down limit relay LD. These limit relays have contacts LU1 and LDl controlling the relays LUX and DUX and contacts LUZ and LD2 for rendering the X-ray gage 14 and its automaticcontrol apparatus 21 ineffective to energize the relays AU and AD whenever predetermined upper and lower limits of movement of roll 12a are produced under automatic control. These limits are readily adjustable by means of the potentiometers 76 and 77 that, respectively, control the energization of the biasing windings 78 and 79 of the magnetic amplifiers 72 and 73. The short-circuiting of adjustable resistors 80 and 81 is removed by relays that cooperate with the potentiometers 76 and 77 in controlling the energization of the biasing windings 78 and 79 so as to calibrate the dropout voltage of the limit relays LU and LD in exactly the same way as previously described in connection with the reset relays RU and RD.

In each case the potentiometer is adjustable to vary the pickup value of the relay, while the resistor is adjustable to control the decrease in the signal voltage energizing the control winding to produce dropout of the relay. In this way the adjustable resistors serve to produce dropout of the relays with a'minimum decrease in the control signal voltage energizing the control windings. Furthermore, when the potentiometers are adjusted to change the pickup value, substantially the same minimum decrease in signal voltage will result in dropout of the relay without any further adjustment of the resistor.

Each of the magnetic amplifiers referred to above may be of the well-known bridge type schematically shown in Fig. 2. Briefly, this type of magnetic amplifier comprises two separate magnetic cores 91 and 92 having the reactor windings 93 and 94 as well as the control winding 95, and reference or biasing winding 96 interlinked therewith as shown. The reactor windings 93, 94 are interconnected with the rectifiers 97, 98, 99, 100, as shown, to form a bridge circuit that is continuously energized from a suitable alternating current source connected between the rectifiers. A load circuit is interconnected with the bridge, as shown, to supply energization to the electromagnetic relays that are energized under control of the magnetic amplifier with direct current of a polarity as indicated.

The biasing winding 96 serves to establish a reference magnetization of the cores 91, 92 opposite to the magnetizations produced by the reactor windings 93 and 94, and also in opposition to the magnetization produced by the control winding 95. Consequently, the magnitude of the signal energizing the control winding 95 required to trigger the amplifier to produce load current can be varied by adjustment of the energization of the biasing winding 96 in the manner previously explained.

In the modification illustrated in Fig. 3, the screwdown mechanism of the rolling mill may be operated by the motor M having a separately excited field F1 the same as motor 10 shown in Fig. la. In this case the armature of motor M is shown connected in a loop circuit with the armature of the generator G having a field winding F2 excited by means of a so-called amplidyne type of dynamoelectric machine A. This a special dynamoelectric machine of the now well-known crossarmature reaction excited, direct-armature reaction compensated type. This type of dynamoelectric machine differs from a conventional direct current machine in that it has a pair of auxiliary brushes b-b arranged on an axis that is normally displaced substantially electrical degrees from the axis of the main load brushes aa. The auxiliary brushes b-b are'substantially short-circuited by an external conductor 0. The dynamoelectric machine A is shown provided with three control field windings; namely, the main control field winding F3, the diiferential control field winding'F4, and the rate control field winding F5. The main field winding F3 is shown schematically connected to be energized from the direct current supply lines L1, L2 under the reversing control of the contacts AUS and AU6 and ADS and AD6 that, it should be understood, are adapted'to be operated by the corresponding relays AU and AD shown in'Fig. 1a. It

will be further understood that these relays AU and AD may be operated under automatic thickness control and under automatic reset contrel in substantially the same way as previously described. In order to obtain manual control, the switches MU and MD may be provided and interlocked in substantially the same way as the manual controller 20 previously described with the automatic thickness control and the reset control, so as to permit manual control at any time desired.

As will occur to those skilled in the art, various different arrangements and combinations of the principles described above may be employed without departing from the true spirit and scope of the invention, and I therefore do not wish to limit my invention to the particular arrangement described. For example, the working condition under which the automatic repositioning becomes effective could be signalled by other means than the strip positioning element 15, such as photocell detection of the running out or the threading in of each strip, or by a similar signal obtained from a strain gage associated with the roll housing, or by a tensiometer responsive to the tension between the roll 12a and the next succeeding roll.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In an electrical positioning control system for a movable member, a first reversible motor for driving said member, a first control means comprising a reversing master switch for controlling said motor to drive said member to a predetermined position, a second control means for said motor, an electrical balancing network device having cooperating network and balance control elements, driving connections including a clutch between said motor and one of said elements, a second motor connected to one of said elements, a selector switch for selecting operation of said first motor by said first control means and controlling said clutch to interrupt said driving connection or for alternatively selecting operation by said second control means and controlling said clutch to establish said driving connection thereby to unbalance said network to produce a control signal related to the departure of said member from said predetermined position, and magnetic amplifier means responsive jointly to selection of said first control means and to said unbalance signal for controlling said second motor to balance said network and responsive jointly to said signal and selection of said second control means to control said second motor to restore said member to said predetermined position.

2. In an electrical positioning control system for a movable member, driving means for said member comprising a first reversible motor provided with reversing switching means and alternatively operable first and second directional control means therefor, the first for controlling said motor to drive said member to a preselected position and the second for controlling said motor to drive said member to various positions within a predetermined range, an electrical balancing network device having cooperating network and balance control elements, a second motor connected to one of said elements, magnetic amplifier means responsive jointly to unbalance of said network and actuation of said first directional control means and reversing relay means controlled thereby for efiecting relative movement of said elements to balance said network, a clutch responsive to actuation of said second reversing control means for connecting one of said network elements to said first motor for effecting an unbalance of said network representative of the departure of said member from said preselected position, and automatic reset means responsive to a predetermined working condition for transferring control of said reversing switching means to said magnetic amplifier and relay means to control said first motor to return said member to said preselected position.

3. In a system including means for positioning a member to a preselected position, automatic control means for controlling said positioning means to position said member at difierent positions within a predetermined range, said control means having periods of activity and inactivity, a resetting means efiective during periods of inactivity of said automatic control means to cause said positioning means to return said member to said preselected position, said resetting means comprising an electrical network provided with a network balancing device for producing a control signal, movable control elements for said device to effect network balance, a connection from said member to one of said elements for effecting an unbalance of said network in proportion to the departure of said member from said preselected position during said activity period, a switching device responsive to a predetermined working condition for rendering said network device active to produce a signal representative of said unbalance, and means responsive to said signal for actuating said positioning means to restore said member to said preselected position and to balance said network.

4. In a control system having a positionable member, means for positioning said member, manual means for controlling said positioning means to move said member to a predetermined position, automatic means for controlling said positioning means, switching means for selecting manual control or automatic control means, a resetting means for controlling said positioning means to return said member to said preselected position comprising a normally inactive electrical network provided with a network balancing device for producing a control signal, said device having relatively movable network and balance control elements for effecting network balance in response to actuation of said manual means, a connection between said positioning means and one of said relatively movable elements completed in response to selection of automatic control for efiecting unbalance of said network device an amount representative of the departure of said member from said predetermined position produced by said automatic means, switching means responsive to a predetermined condition for rendering said network balancing device active to produce a signal in response to said unbalance and representative of the amount thereof, and means responsive to said signal for controlling said positioning means to restore said member to said predetermined position and to balance said network device.

5. In an automatic positioning control system for a working member, driving means for said working member, manual control means for controlling said driving means to drive said member to a preselected position, automatic control means for controlling said driving means to drive said member to various positions within a predetermined range and having periods of activity and inactivity, selector switching means for selectively rendering effective said manual or said automatic control means, a resetting control means normally inactive during operation of said automatic control means and active during said periods of inactivity to return said working member to said preselected position comprising an electrical network provided with a network balancing device for producing a control signal, said device having relatively movable network and balance control elements for effecting network balance in response to actuation of said manual control means, a driving connection from said member to one of said elements for eifecting an unbalance of said network an amount representative of the departure of said member from said preselected position during said period of activity, an automatic switching device responsive to a predetermined working condition for rendering said network balancing device active to produce a signal representative of said unbalance, and means responsive to said signal for controlling said driving means to restore said member to said preselected position and to rebalance said network.

6. In an electrical positioning control system for a movable member, a first reversible driving means for said member, a first control means comprising a reversing master switch for controlling said driving means to drive said member to a predetermined position, an

electrical network balancing device for producing a control signal, said device having cooperating balance control elements and balanced in response to actuation of said master switch, a second control means for controlling said driving means to drive said member to various positions within a predetermined range, a driving connection including a clutch between said driving means and one of said elements, a second driving means connected to one of said elements, a selector switch for selecting operation of said first driving means under said first control means and controlling said clutch to interrupt said driving connection and for alternatively selecting operation of said first driving means under control of said second control means and controlling said clutch to establish said driving connection to effect unbalance of said network device in accordance with departure of said member from said predetermined position, and means responsive jointly to unbalance of said network and selection of said first control means for controlling said second driving means to balance said network and responsive jointly to unbalance of said network and selection of said second control means to control said first driving means to restore said member to said predetermined position.

7. In an electrical positioning control system for a movable Working member, a-reversible motor for driving said member, reversing switching means for said motor, manual and automatic electrical control means for said reversing switching means, a selector switch operable to a first position to render said manual control means eflective and operable to a second position to render said automatic control means effective, a resetting control system for said motor normally inactive during operation of said automatic control means for returning said working member to a preselected position comprising an electrical network balancing device for pro- 12 ducing a' control signal, said device having cooperating balance control elements and balanced in response to actuation of said manual control means, a driving con nection between said motor and one of'said elements established in response to operation of .said selector switch to said second position for unbalancing said network to produce a control signal related to the departure of said member from the last position selected by operation of the motor under the control of said manual con: trol means, an automatic circuit-controlling switch'responsive to a predetermined working condition, and means responsive jointly to operation of said automatic circuit-controlling switch and said signal when said se-' lector switch is in said second position for controlling said reversing switching means to return said member to said last position.

8. The invention set forth in claim 4 wherein the said connection actuates the network balancing device to pro duce an unbalance signal having a magnitude represent ative of the amount of departure of the positionable member from the predetermined position and in which means responsive to the magnitude of the said signal are provided for rendering the positioning means inactive for a selected maximum departure from the said preselected position.

References Cited in the file of this patent UNITED STATES PATENTS 1,832,400 Knight Nov. 17, 1931 1,969,536 Winne Aug. 7, 1934 2,114,603 McBain Apr. 19, 1938 2,264,095 Mohler Nov. 25, 1941 2,275,509 Dahlstrom Mar. 10, 1942 2,339,359 Shayne et al. Jan. 18, 1944 2,564,284 Schurr Aug. 14, 1951 2,687,052 Zeitlin Aug. 24,- 1954 2,708,254 Macauley et al. May 10, 1955

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