US 3573444 A
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Description (OCR text may contain errors)
United States Patent Inventors James S. Kawabata Niles;
James E. Tudor, Jr., Des Plaines, 111. 830,418
June 4, 1969 Apr. 6, 1971 Contour Saws, Inc.
Des Plaines, Ill.
Appl. No. Filed Patented Assignee GAGING CAMBER OF LENGTIIWISE MOVING STRIP MATERIAL 9 Claims, 6 Drawing Figs.
U.S. Cl 235/1513, 33/174, 73/105 Int. Cl. G05d 5/00 Field ofSearch 33/1, 174; 235/151.3;73/73,105,159
References Cited UNITED STATES PATENTS 3,056,209 10/1962 Oliver 33/174 3/1965 Lowy 33/142 LVDTZ /9 3,377,828 4/1968 Harmon 73/105X 3,470,739 10/1969 Takafujiet al...... 73/105X 3,502,968 3/1970 Tobin Jr. et a1 33/147X OTHER REFERENCES Lateral Edge Web Guide" Boni and Overacker; IBM Technical Disclosure Bulletin; Vol. 12 No. 8, January 1970, Page 1309 Primary Examiner-Malcolm Morrison Assistant Examiner-Edward .1. Wise Attorney-Ira Milton Jones 22-3 DEMODULATOR /2Z/ DEMODULATOR fzzz DEMODULATOR D.C.OUTPUT DCOUTPUT 3-52 D.C.OUTPUT 3% 4 r39 42-- 4/ 47 4/ I43 LVDT. LVDT (7 AMPLIFIER INDICATOR -----1 OR CONTROLLER Patented April 6, 1971 3,573,444
+ AMOUNT OF CAMBER (EXAGGEQATED) amps 51f awabafa Patented April 6, 19m 1% 4 Shets-Sheet 2 GAGING (IAMBER F LENGTI'IWISE MOVING STRIP MATERIAL This invention relates to a method and means for gauging the straightness of strips of steel and the like, such as strip stock to be formed into bandsaw blades and finished bandsaw blades; and the invention is more particularly concerned with a method and means i for detecting departures from straightness in such a strip while it is moving lengthwise, and for producing a signal that corresponds in sign and magnitude to departures from straightness, which signal can be used, for example, in determining whether straightness of the strip is within acceptable tolerance limits, or for purposes of control in effecting straightening of the strip.
It is particularly important that a bandsaw blade have its cutting edge as nearly perfectly straight as possible. Any departure from straightness, measured in directions edgewise of the blade and transverse to its length, will cause variations in the feed force that the blade exerts against a workpiece as it cuts through it, and can cause vibration, poor quality cuts, decreased blade life and other undesirable consequences. Such departures from straightness in the cutting edge of a saw band are known as camber.
Camber in a finished bandsaw blade may be the result of camber in the raw strip stock from which the band was manufactured, or may be induced in the band by stresses developed in the course of forming the teeth in it, hardening it or tempermg it.
However caused, it is important that camber in a bandsaw blade be detected before the blade reaches the user, and that the blade either be rejected or straightened if the camber exceeds prescribed limits.
As a rule, the manufacture of bandsaw blade is a continuous process in which the strip and/or blade moves linearly along a defined path; and there are locations along the path at which inspection for camber can be conveniently and profitable conducted. It is, of course, possible to detect camber by direct visual inspection, looking edgewise along the length of the blade, and heretofore this has been the prevailing manner of inspecting bandsaw blade for camber. But such visual inspection is unreliable because it is dependent not only upon the inspectors subjective judgment as to whether or not such camber as exists is within acceptable tolerance limits, but also depends upon the inspectors unremitting attention to a monotonous task.
While bandsaw blade is a type of strip in which camber is particularly objectionable, there are other types of strip materials in which certain amounts of departure from true straightness are objectionable or intolerable, and it will therefore be understood that bandsaw blade has been cited herein solely by way of example, the invention having general application and utility in gauging and/or straightening all sorts of strip materials.
With the foregoing in mind, it is a general object of this invention to provide a dependable method and means for gauging the camber in strip material as it moves lengthwise through a defined zone, and more particularly to provide a method and means for producing an output or signal which accurately reflects the magnitude and direction of departures from true straightness in a strip, and which can therefore be used either for purposes of inspection or for the control of an operation that effects straightening of the strip.
Another and more specific object of this invention relates to the tendency of strip material moving linearly through an inspection zone to shift bodily in the directions of the departures from straightness that are to be gauged; and with that in mind the invention provides a method and means for compensating for such shifting of the strip while producing a signal or output corresponding to departures from straightness in the strip in the same directions that it tends to shift.
A further specific object of this invention is to provide gauging apparatus of the character described that has a high inherent accuracy, has no tendency to accumulate dirt in its moving parts that might diminish its sensitivity or useful life,
and has no tendency to impose a substantial load upon a strip being gauged whereby a camber might be imparted to the strip by the gauging instrumentality itself.
It is also an object of this invention to provide a method and means for detecting the straightness of strip material, and for producing a signal or output that corresponds to departures from straightness and signifies not only the magnitude of such departures but also their direction or sign.
With these observations and objects in mind, the manner in which the invention achieves its purpose will be appreciated from the following description and the accompanying drawings. This disclosure is intended merely to exemplify the invention. The invention is not limited to the particular structure and method disclosed, and changes can be made therein which lie within the scope of the appended claims without departing from the invention.
The drawings illustrate one complete example of the physical embodiment of the invention constructed according to the best mode so far devised for the practical application of the principles thereof, and in which:
FIG. 1 is a plan view of a length of flat strip material having in it an edgewise departure from straightness, or so-called camber, illustrating the nature of the undesirable quality that is gauged by the method and means of this invention;
HO. 2 is a perspective view of the exterior of the apparatus employed in the practice of this invention and illustrating a strip being gauged thereby;
FIG. 3 is a more or less diagrammatic perspective view of an essential part of the apparatus in operative relationship to a strip being gauged;
FIG. 4 is a cross-sectional view through FIG. 2 on the plane of the line 4-4;
FIG. 5 is a plan view of a portion of the apparatus, and particularly illustrating in section, part of the structure shown in FIG. 3;
FIG. 6 illustrates the theoretical basis of the invention; and
FIG. 7 is a circuit diagram of an embodiment of the invention in which electrical transducers are employed to produce a signal or output indicative of departures from straightness in a strip being gauged.
Referring now more particularly to the accompanying drawings, the numeral 5 designates a relatively thin, narrow strip of steel or the like, which, for example may be a length of bandsaw blade, although the cutting edge that characterizes a finished saw blade is not shown. Such a strip is acceptable only when camber in it lies within specified tolerance limits. In other words its departures from true straightness in edgewise directions transverse to its length must not exceed certain prescribed values. While the present invention is concerned with detection of the magnitude and sign of camber, it will be apparent that the principles of the invention are also applicable to detecting departures from flatness, should this be desirable for any reason.
According to the invention, camber :is gauged in the strip 5 while it is moving lengthwise through a defined elongated zone 6 that can be located in any suitable portion of the path that the strip travels in the course of the processes that are performed in manufacturing or finishing it. Those skilled in the art will be aware that a continuous linearly moving strip of steel or the like has a tendency, to shift bodily in an edgewise or side-to-side direction, as it travels through an elongated zone; and since such bodily shifting is in the same directions as the departures from straightness that are to be gauged, it greatly aggravates the difficulty of making the desired measurement. Any attempt to constrain the: strip against edgewise displacement merely compounds the difficulty. If increased tension on the strip is employed in an effort to keep it from floating back and forth, the camber present in the strip may be reduced in an acceptable minimum and hence not detected, only to reappear when the tension on the strip is relaxed. And if the strip is forced to travel along a fixed path by guides engaging an edge thereof, the resulting stresses introduced into the strip will produce false camber.
Accordingly, if true and accurate measurement of existing camber is to be obtained, the gauging means must accommodate itself to the inevitability of bodily edgewise shifting of the strip as it travels through the zone 6. The present invention proceeds upon that premise.
In the implementation of the invention, three fixed points 8, 9 and 10 are established that are equidistant from one another and on a line 7 which is parallel to the length of the zone 6 and spaced from the strip passing through the zone, regardless of any possible edgewise displacement of the strip. Three continuous primary outputs are produced, one for each point. Each primary output at all times corresponds to a function of the distance between its point and the adjacent edge of the strip, said distances being measured in the direction of the departures from straightness that are to be gauged.
As further explained hereinafter, there is a transducer 14 for each of the three points 8, 9 and 10, and each of those points can be defined by the axis of a fulcrum or pivot 11 for a lever or feeler 12 that comprises a part of the movable element 13 of its transducer. Preferably the three transducers are identical electrical instrumentalities, each adapted to produce a primary output having a characteristic value, such as voltage, that corresponds to the distance being measured.
Since each distance measurement is taken along a perpendicular to the line 7 through the fixed points 8, 9 and 10, there will always be three points 8', 9' and 10 on the edge of the strip that respectively correspond to those fixed points (see FIG. 6).
For the purposes of this invention it is assumed that any camber that is detected will have a uniform radius, that is, that a cambered edge of the strip will lie along the arc of a true circle. (While this assumption may not always be strictly accurate, its inaccuracies will be negligible for practical purposes.) On the basis of that assumption, camber is measured in terms of the distance from the middle point 9' on the edge of the strip to a straight line 15 connecting the two outermost points 8' and 10' on the edge of the strip. The line 15 is of interest only for its midpoint 16, the location of which can be defined in relation to the line 7 through the fixed points 8, 9 and 10 as the average of the distance measurements from point 8 to point 8' and from point 10 to point 10'. Since camber is measured in terms of the distance from midpoint 16 to point 9' the value of camber can be expressed as the distance from point 9 to point 9 minus the average just mentioned.
Desirably the sign or sense of any detected camber should also be known, and to this end the distance measurements that are constantly made from the points 8, 9 and 10 to the strip are preferably compared to a fixed reference distance that is the same for each of the three fixed points 8, 9 and 10 and which thus defines a fixed reference baseline 17 which is parallel to baseline line 7. The reference distance is so chosen that the reference baseline 17 lies within the zone 6, intermediate the expected limits of edgewise shifting of the strip, and is in practice the normal or nominal projected length of the levers or feelers 12 in the measurement direction. Thus the output from each of the transducers 14 has a value which baseline to the distance between its respective point 8', 9' or 10' on the strip and the reference baseline 17 and that output has a sign which depends upon the direction baseline said point on the strip is spaced from the reference baseline.
Referring to the situation depicted in FIG. 6, the portion of the strip occupying the zone 6 is assumed to have a camber represented by the Actual Curve line, and the reference base line 17 is at an arbitrarily selected reference distance of 6 units from the line 7 through the fixed points 8, 9 and 10. The point 8' on the edge of the strip is at an absolute distance of 4 units from fixed point 8, but it is at -2 units from the reference base line 17. The point 10' on the edge of the strip is at a distance of 10 units from line 7 but is +4 units from the reference base line 17. The location of the midpoint 16 can be given as 4+l0/2, or 7 units from point 9, or can be given as 2+4/2, or at +1 relative to line 17. The distancefrorn point 9 units) from point 9 to midpoint 16. Similarly, point 9' is at 3 units from reference baseline 17, or at +2 units relative to midpoint 16. By either reckoning, therefore, the strip portion illustrated in H6. 6 has a camber of +2.
Obviously if mathematical signs are properly taken into account, it makes no difference whether distances are measured from the actual line 7 through the fixed points 8, 9 and 10 or from the theoretical reference baseline 17.
However, for practical purposes, owing to the nature of the preferred transducers, it is deemed more expedient to measure distances from the theoretical base line 17.
Each of the transducers 14 can be a so-called linear variable differential transformer, comprising (as best seen in FIGS. 5 and 7), a fixed medial primary winding 19 that is adapted to be energized from a constant-voltage AC source, a pair of secondaries 20 that are fixed coaxially with respect to the primary at axially opposite sides of it, and a magnetically penneable core 21 couples the primary winding with the two secondary windings, and comprises a part of the movable element 13 of the transducer. The two secondaries of each transducer are connected with a demodulator 22 of known type by which the alternating currents induced in the secondaries are converted to a single DC output.
When the core 21 of a transducer is in a null position, centered between its secondaries 20, it provides equal coupling between the two secondaries and the primary, and the alternating currents induced in the secondaries are of equal voltage but opposite sign so that upon being fed through the demodulator they cancel each other and yield a zero voltage DC output. When the core is shifted out of its centered position, the secondaries are unequally coupled with the primary, and the output of the demodulator is a DC having a sign dependent upon the direction of displacement of the core and a voltage depending upon the amount by which the core is offset from its centered position.
The core 21 of each transducer has a motion transmitting connection, comprising a link 23, with the feeler 12 associated with the transducer, whereby swinging motion of the feeler in either of the directions of measurement is translated into a corresponding linear motion of the core.
Although each feeler and the core of its transducer must be thus connected, it is important that dust and dirt be kept out of the transducer and the bearings for the pivot 11 upon which the feeler is fulcrumed. To this end the transducers can be housed in an elongated boxlike enclosure 25 that extends lengthwise parallel to the zone 6. As shown, each transducer is secured to the front wall of the enclosure (i.e., the wall that faces the strip) by means of a pair of screws 26 that are threaded into the body of the transducer through lengthwise elongated slots 27 in said enclosure wall. The slots 27 provide for bodily adjustment of the transducer in the directions of travel of its core to enable the core to be centered when its feeler is engaged with a straight strip and the strip is at the middle of its range of edgewise shifting motion. Obviously, any other suitable means may be employed to effect such zeroing adjustment of the transducers.
The enclosure 25 has a small forwardly projecting rectangular bay 29 in front of each transducer to house axially spacedapart bearings 30 for the pivot 11 associated with the transducer. Each pivot-has its axis upright, perpendicular to the surfaces of the strip. Only its top and bottom end portions project out of the enclosure, and hence the bores through which the pivots project are the only openings in the enclosure. These can be readily sealed against the entry of foreign matter by the choice of suitable pivot bearings 30 that closely underlie the top and bottom walls of the bay, as best seen in FIG. 2.
Each of the feelers 12 is a bifurcated lever that has its branches straddling its bay and nonrotatably connected to the projecting end portions of its pivot 11. As shown, the feeler is H-shaped, so that its free end is likewise bifurcated, to carry an upright rodlike anvil or shoe 31 that bridges its branches and is attes e f9! in snsssqmsm w t s? of e to point 9' is 9 units, or 2 units greater than the distance (7 strip. The shoe has a height substantially greater than the thickness of the strip to accommodate any up or down motion the strip may have due to departures from true flatness or bodily up or down drift.
Inside each bay 29 is a short lever arm 32 that is nonrotatably secured to the medial portion of the pivot 11, between its bearings 34 and to which the link 23 is pivotally connected. The arm 32 extends into the interior of the enclosure 25 through a large slot 33 in the front wall thereof, but of course the bay 29 provides a cover over this slot and the short lever arm to prevent dirt from getting into the mechanism. It will be observed that the feeler 12 and the lever arm 32, together with the pivot 1111 to which they are attached, comprise a bellcranlt.
The illustrated structure minimizes friction in the moving parts of the mechanism, to insure utmost accuracy of the transducers. The bifurcated configuration of each feeler imposes a balanced load upon opposite ends of its pivot ill, to avoid the imposition of lateral force couples upon the bearings 30. To further insure low lateral forces upon the pivots, each feeler extends toward the strip at a relatively small acute angle thereto, inclined in the direction of strip motion, to minimize friction between the strip and the shoe 3ll on the feeler. ln addition, the short lever arm 32 of each bellcrank extends nearly at right angles to the axis of motion of the core 21 and swings through a relatively short arc, thus having only a negligible component of motion transverse to the stroke of the core so as to impose only negligible lateral forces upon it.
The movable element of each transducer is lightly biased in the direction to swingthe feeler toward the strip, as by means of a tension spring 35 connected between a seat member 36 on the interior of the housing and a coaxial rod 37 on the core 211, opposite the link 23. The spring seat member 36 can be made adjustable in the directions of core motion for regulation of the biasing force exerted by the spring.
FIG. 7 illustrates the circuit connections by which an output signal having a sign and magnitude corresponding to detected camber is derived from the primary outputs of the three transducers. The transducer having an output corresponding to fixed point 3 in FIG. 6 is designated LVDTll, that corresponding to point 9 is LVDT2 and that corresponding to point 110 is LVDT3.
Across the output terminals 38, 39 of the demodulator 22-11 connected with LVDTll there are a pair of resistors 4 0, connected in series. Since the two resistors 40 have the same value, the voltage across either of them will be equal to onehalf the voltage across the terminals 34 and 39. A pair of series-connected equal-value resistors 41 is likewise connected across the terminals 42, 43 of the demodulator 22-3 connected with LVDT3. By means of a conductor 45, the junction 46 of resistors 40 is connected with terminal 42 of demodulator 22-3. From the junction 47 of the resistors 41 across the terminals of demodulator 22-3, a lead 44 is connected with one input terminal of a DC amplifier. The two terminals 46 and 42 that are connected by conductor are of opposite polarity, so that said conductor establishes a series connection, hence the voltage between terminal 34 of demodulator 22-1l and the junction point 47 associated with demodulator 22-3 equals the algebraic sum of one-half of the output of each of those demodulators, and is thus a secondary output corresponding to the midpoint 16 in FIG. 6.
However, by means of a conductor 50, terminal 34 of demodulator 22-1 is connected with the terminal 511 of like polarity of demodulator 22-2 for LVDT2. The other terminal 52 of demodulator 22-2 is connected, by means of lead 53, with the other input terminal of the DC amplifier. it will be seen that the output of demodulator 22-2 is a bucking arrangement with the averaged outputs of demodulators 22-11 and 22-3, so that the input to the amplifier represents the output of LVDTZ minus the sum of one-half of the outputs of LVDTll and LVDT3, which is to say that input to the amplifier corresponds to the amount and sign of detected camber.
As illustrated in FIG. 7, the output signal from the amplifier can be fed either to an indicator which provides a visual indication of camber, for inspection purposes, or to a control apparatus associated with means for effecting straightening of the strip.
From the foregoing description taken with the accompanying drawings it will be apparent that this invention provides an accurate and efficient method and apparatus for gauging the amount and direction of camber in a strip of steel or the like as the strip moves lengthwise along a defined course.
l. The method of producing a signal which represents the magnitude of departures from straightness in one transverse dimension of a strip of steel or the like as the strip moves lengthwise through a defined zone, said method comprising:
A. establishing three aligned points at fixed locations adjacent to said zone, spaced apart lengthwise of the strip;
B. continuously producing three separate primary outputs, one for each of said points, each a function of the distance, measured in said dimension, between its point and the strip;
C. producing a secondary output which is a function of onehalf the sum of the primary outputs for the two outer ones of said points; and
D. obtaining said signal as a function of the algebraic difference between the primary output corresponding to the medial one of said points and said secondary output.
2. The method of producing a signal having a value which corresponds to the magnitude and direction of departures in straightness in one transverse dimension of a strip of steel or the like as the strip moves lengthwise through a defined elongated zone in which the strip tends to shift bodily in the directions of said departures, said method comprising:
A. establishing three points at fixed locations adjacent to said zone, spaced apart lengthwise of said zone; B. continuously producing three separate primary outputs, one for each of said points, each a function of the amount and sing of the difference between 1. a predetermined normative distance between the point and the strip, and
2. the instantaneous actual distance between the point and the strip, said distances being measured in the directions of said departures;
C. producing a secondary output which is a function of the average of the outputs corresponding to the two outer ones of said points; and
D. obtaining said signal from the difference between the primary output corresponding to the medial one of said points and said secondary output.
3. Means for detecting departures from straightness of a strip of steel or the like in a pair of opposite directions transverse to the length of the strip as the strip moves lengthwise through a defined elongated zone in which the strip tends to shift bodily in said directions, and for producing an output that corresponds to the magnitude and direction of such departures, said means comprising:
A. three transducers, each comprising:
1. an element constrained to back and forth motion, and
2. means for producing an output having a value that varies in correspondence with changes of position of said element;
B. means mounting said transducers at fixed locations that are adjacent to said zone and spaced apart lengthwise of it, and with the transducers so oriented that their movable elements can be at all times engaged with the strip and move in said directions;
C. averaging means connected with the two outer ones of said transducers and responsive to their outputs to produce a secondary output having a value that corresponds to one-half the sum of said values of the outputs of said two transducers, and
D. summations means 1. connected with said averaging means to receive said secondary output therefrom, and
2. connected with the medial one of said three transducers to receive its output, said summation means being constructed and arranged to produce a signal having a value corresponding in sign and magnitude to the difference between the value of the output from the medial transducer and the value of said secondary output.
4 The apparatus of claim 3, further characterized by:
A. each of the transducers comprising:
1. a primary winding adapted to be energized by alternating current,
2. a magnetically permeable member coupled with the primary winding and movable relative thereto in opposite directions, and i 3. a pair of secondary windings coupled with the primary winding through the permeable member and in which currents are respectively induced that have values dependent upon the position of the permeable member;
B. each of said movable elements comprising 1. a lever fulcrumed to swing toward and from a strip in said zone about a fixed pivot and having a strip engaging shoe at its free end, and
2. linkage means connecting the lever with said permeable member; and
C. means biasing the movable element of each transducer in the direction to maintain its shoe engaged with the strip.
5. Apparatus for detecting departures from straightness of a strip of steel or the like in a pair of opposite directions transverse to the length of the strip as the strip moves lengthwise through a defined elongated zone in which the strip tends to shift bodily in said directions, and for producing an output that represents the magnitude and direction, of such departures, said apparatus comprising:
A. three transducers, each comprising:
1. an element constrained to opposite motions along a defined path, and
2. means for producing an output having a value that varies in dependence upon the position of said element in its path; I
B. an elongated supporting member fixed adjacent to said zone and extending parallel thereto, said supporting member comprising housing means enclosing and mounting said transducers at fixed locations spaced lengthwise of the supporting member;
C. means providing three pivots, one for each transducer,
each of said pivots 1. being rotatable on an axis transverse to said directions and to the length of the supporting member,
2. having its medial portion within the housing means,
near its transducer, and
3. having opposite end portions projecting from the housing means, said pivots having their axes spaced apart and along a line that extends lengthwise of the supporting member;
D. a first lever arm outside the housing means for each of said pivots, each of said first lever arms having;
I. a bifurcated end portion secured to the projecting end portions of its pivot, and
2. an opposite end portion comprising a shoe adapted for sliding engagement with a strip in said zone;
E. a second lever arm for each pivot that is inside the housing means, each of said second lever arms;
1. being secured to the medial portion of its pivot to be swung thereby in unison with swinging of the first lever arm, and
2. having a motion transmitting connection with said element of its transducer whereby swinging motion of its first lever arm is translated into motion of said element;
and I v F. means biasing each of the first lever arms in the direction to swing its free end toward a strip in said zone. 6. The apparatus of claim 5, further characterized by: G. averaging means connected with the two transducers associated with the outer ones of said pivots and responsive to the outputs of said transducers, to produce a secondary output having a value that corresponds to one-half the sum of said values of their outputs; and
H. summation means 1. connected with the averaging means to receive said secondary output therefrom, and
2. connected with the third transducer to receive its output, said summation means being constructed and arranged to produce a signal having a value corresponding in sign and magnitude to the difference between the value of the output from said third transducer and said value of the secondary output.
7. Apparatus for detecting departures from straightness of a strip of steel or the like in a pair of opposite directions transverse to the length of the strip as the strip moves lengthwise through a defined elongated zone in which the strip tends to shift bodily in said directions, and for producing an output that represents the magnitude and direction of such departures, said apparatus comprising:
A. three transducers, each comprising;
1. an element constrained to opposite motions along a defined path, and
2. means for producing an output having a value that valies in dependence upon the position of said element in its path;
B. an elongated supporting member fixed adjacent to said zone and extending parallel thereto, said supporting member comprising housing means enclosing and mount ing said transducers at fixed locations spaced lengthwise of the supporting member;
C. means providing three pivots, one for each transducer,
each of said pivots comprising;
l. bearing means inside the housing means, the axis of which is perpendicular to said directions and transverse to the length of the supporting member, and
2. a shaft journaled in said bearing means, said shaft having a part thereof inside the housing means and a part thereof projecting through a wall of the housing means to the exterior thereof;
D. a bellcrank fixed to each of said shafts, one of the arms of the bellcrank being inside the housing means and the other being outside the housing means, the arm that is outside the housing means having a part thereof positioned to engage a strip in said zone;
E. means providing a motion transmittigg connection between the arm that is inside the housing means and the movable element of its associated transducer; and
F means independently biasing each of the bellcranks in the direction to maintain its outer arm in engagement with a strip in said zone.
8. The apparatus of claim 7, wherein the transducers are identical to one another, and wherein all of the bellcranks are of the same size, so that equal displacements of the outer arms in response to detected departures from straightness of a strip passing through said zone, produce equal displacements of the movable elements of the transducers.
9. The apparatus of claim 8, wherein the outer arms of the bellcranks are considerably longer than the inner arms.
UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 573 ,444 Dated April 6 1971 James S Kawabata -et a1 Inventor(s) It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:
Column 3, line 53 cancel "baseline"; same line 53, afte1 "to" insert the line 59, "baseline" should read corresponds line 61 "baseline" should read in which Column 6 line 38 "sing" should read sign Signed and sealed this 17th day of August 1971 (SEAL) Attest:
EDWARD M.FLETCHER,JR. WILLIAM E. SCHUYLER, J Attesting Officer Commissioner of Patent FORM PO-IOSO (IO-69)