US2311406A - Measuring lengths and correcting skew and bow in woven material - Google Patents

Description

1943- A. P. MANSFIELD ETAL 2,311,406

MEASURING LENGTH AND CORRECTING SKEW AND BOW IN WOVEN MATERIAL file March 24, 1942 2 Sheets-Sheet 1 Inventors: Albert F? Mansfield, Cremer La Pierre,

MHton-S. Mead J William t-Ljanssen, x m ff J M The'l Attorney F 1943- A. P. MANSFIELD ETAL 1 40 MEASURING LENGTH AND CORRECTING SKEW AND BOW "IN WOVEN MATERIAL;

Filed March 24, 1942 2 Sheets-Sheet 2 Fig.3. I Fig.4.

Inventors. Albert E- .Mansfield, Crammer La Pierre,

Milton S. Mead JT,

' William H. anssen,

by flawyfiwim Their- Attorney.

to compensate for wear.

Patented Feb. 16, 1943 IVIEASURING LENGTHS AND CORRECTING SKEW AND BOW IN WOVEN Albert P. Mansfield, Lynnfield, Mass., and C'ramer W. La Pierre and William H. Janssen, Schenectady, and Milton S. Mead, Jr., Hempstead, N. Y., assignors to General Electric Company, a corporation of New York.

Application March 24, 1942, Serial No. 435,958

15 Claims.

Our invention relates to the manufacture of woven material, the weave of which is of an irregular character by which a design or pattern is produced, as for example lace curtains, and it relates particularly to such manufacture when the material comprises successive similar unit sections or lengths. One object of our invention is to provide improved apparatus to be employed in such manufacture for detecting faults in the woven material such as skew, bow and variations in length that may occur in the similar unit sections from a predetermined standard length. Another object is to provide apparatus for correcting the detected skew, bow and length variation.

Our invention will be better understood from the following description taken in connection with the accompanying drawings and its scope will be pointed out in the appended claims.

Referring to the drawings, Fig. 1 is a plan view of a form of apparatus embodying our invention; Fig. 2 is a simplified side view of the apparatus shown in Fig. 1; Fig. 3 shows a fragment of the strip of woven material forming a part of Fig. 1 but drawn to a larger scale; Fig. 4 shows a form of scanning head used in the apparatus; Fig. 5 shows a modification thereof,

and Fig. 6 is a circuit diagram.

Referring now to Figs. 1 and 2, where the strip of woven material is represented at I and as moving from right to left as shown by the arrow, that part of the apparatus last to receive the strip is that commonly employed in the manufacture of woven material of the character described, such as lace curtains, and comprises the tenter 2 and the calender rolls 3, one of which, namely the roll 4, is a driven roll. Inasmuch as the aforementioned tenter and calender rolls are old and Well known in the art no detailed description need be given herein. The tenter 2 is driven through the speed reduction gearing 5 from the main driving motor 6 and the calender rolls likewise are driven from the same motor 6 through the gearing 5 and I which latter gearing is usually constructed to permit small speed variations for the purpose of making necessary adjustments in the relative speeds of the tenter and the calender rolls Arranged between the two opposed chains of the tenter are the two scanning heads 8 and 8', the one being shown arranged near one edge of the woven strip I and the other in the central portion thereof. As so arranged the scanning heads together with the apparatus controlled thereby,

to be described later, are for the purpose of detecting and correcting any bow that may be present in the material at this point.

For engaging the strip I prior to its reaching the tenter 2, we have provided a second tenter denoted by H! which may be much shorter than the tenter 2 and is provided for the purpose of enabling the detection of any skew that maybe present in the material. The two sides of the tenter It which may be similar to that represented by Fig. l of the La Pierre Patent 2,106,611 are driven by the receiver of angular motion II which is electrically connected with the transmitter of angular motion I2 shown directly connected with the main driving motor 6. After leaving the ten-ter Iii, the strip passes under the polished roll I3, up over the polished roll I3, and between the nip rolls I4 and I5 beyond which it is supported by the endless carrier I 6 which is shown as comprising the two endless belts I'i'. From the carrier I6 the strip passes between the nip rolls I8 and I9 and then is taken up by the tenter 2. Ihe roll I8 is driven through the speed reduction gearing 20 by the receiver of angular motion 2| which is connected to be driven from the transmitter of angular motion I2. The roll I4 is driven from the same receiver II as the tenter III and hence the strip normally is moved at the same speed by the roll I8, the roll M, and the tenter I0, which speed is also the same as that at which the strip is moved by the tenter 2 and the calender rolls 3. Between the chains of the tenter III are the scanning heads 22 and 22' which may be identical with the scanning heads 8 and 8 and which are arranged adjacent the opposite edges of the strip. These scanning heads in cooperation with the apparatus controlled thereby, to be described later, serve to detect and to correct any skew that may be present in the strip. Arranged between the belts I! are the scanning heads 23 and 23' which are spaced a distance approximately equal to the desired length of each unit section of the strip, or, in other words, approximately equal to the desired length of each curtain. These scanning heads which may be identical with the scanning heads 8 and 8 in cooperation with the apparatus controlled thereby to be described later, serve to detect any variation in the length of the successive unit sections of the strip from a predetermined standard length. r

If, with the apparatus briefly described above, a definite amount of Askew is detected by the scanning heads 22 and 22' and apparatus con- 23 and 23' and the apparatus controlled thereby 1O detects a material variation in the length of the successive unit sections of the strip as, for example, successive curtain lengths from a "predetermined standard length then the speed of the roll i l and the tenterltl is changed with respect to thespeed of theroll l8, the'tenter 2 and the calender rolls 3 in such a manner as to correct that variation, that is, if the sections of the strip I, such as the individual curtains, are found to be too short then the speed of the roll i4 and the tenter ill is decreased slightly with respect to the speed of the roll 18, the tenter 2 and the rolls 3 so as to further stretch the material comprising the strip at that part thereof which is supported by the carrier l6.

If, on the other hand, the sections of the strip are found to be too long then the speed of the roll l4 and the tenter It is increased relative to the speed of the roll 18, the tenter 2 and the of scanning heads and the apparatus controlled thereby for producing an indication and for operating the several correcting motors will now be described. As mentioned above, the strip l is woven to form successive unit sections having the same design or pattern. In the manufacture of lace curtains it is customary to provide what is commonly termed a cutting mark between adjacent unit sections or curtains which mark comprises a narrow transverse open portion which usually has only warp threads and may have a width of substantially one-half inch, the material at each side of these transverse portions containing closely woven weft threads with the result that the strip has two dense transverse portions separated by a portion having very slight density, the two dense portions being at least as wide as the intermediate portion of low density. We take advantage of these transverse portions of large difference in density between the sections of the strip for controlling photoelectric apparatus forming a part of the means which we have devised for detecting skew, bow and length variations in the sections of the 5 strip.

calender rolls 3 to allow the strip to shrink slightly. 7

A change in the speed of the roll i4 and the tenter ill with respect to the speed of the roll 18, the tenter 2 and the calender rolls 3 is efinterposed in the drive connection between the receiver H and the roll l4 and tenter it, this differential being controlled by means of the motor 3|.

fected by means of the differential 39 which is g' If. with the apparatus a definite amount of bow is detected by the scanning heads 8 and 8 and apparatus controlled thereby the speed of the tenter I0 is varied with respect to the speed of the roll M. This variation is accomplished by the use of the difierential 32 which is arranged in the drive connection between the chains of the tenter i9 and the drive shaft of the roll i l, the differential 32 being controlled by the motor 33.

We have found that it is essential to arrange the apparatus for detecting and correcting skew and bow in the strip and variations in the length of the sections thereof in a definite order in the path of travel of the strip. In order that skew may be corrected, the ends of the strip where the correction is to be made must be essentially ,free to enable the desired corrections to be made, hence the straightening tenter it] where the skew correction is made must precede the nip rolls, [4 and i5. In order that the machine may deliver corrected unit sections or curtains inde pendent of corrections made for bow and skew it is necessary that the length adjustment be made independently of those corrections and after the tenter l0 and the nip rolls l4 and I5 must be adjusted with respect to the speed of the nip rolls l8 and i9 and this done independently of The construction and operation of the pairs 75 Each of the two scanning heads of a pair, for example, the heads 22 and 22, may be of the form shown in Fig. 4 where the projector 36 projects three narrow light beams represented by the dot and dash lines 31 through the strip I each into a separate photoelectric device 38 in the housing 39. In cross section these light beams may, for example, be 1 /2 inches long by of an inch wide. The spacing of the three light beams 37 lengthwise of the strip is substantially the same as the width of the cutting mark shown at 40 in Fig. 3, which mark separates the two dense portions 4i. Instead of using a projector 36 which will project the three light beams 31, we may employ a projector such as shown at 42 in Fig. 5 which will project a single broad beam of light 43 on the strip l and provide the casing 39 for the photoelectric devices with the mask 44 on the under side provided with, the slots 45 having the dimensions of the beams 31 thereby limiting the light received by each photoelectric device to that which passes through an area of the strip having the same cross sectional dimensions as the beams 31.

To avoid the giving of wrong indications by the detecting apparatus due, for example, to possible combinations in the strip of thin and dense portions in the wide variety of patterns in which lace curtains may be made, we have devised a scanning head employing the three light beams spaced as described above and have provided cooperating apparatus which will operate togive an indication and to produce a correction only when the light of the beam affecting 0 the middle photoelectric device is less than the they have been completed; hence the speed of combined light of the beams affecting the other two photoelectric devices. A further requirement is that this condition must prevail for a length of time sufiicient for the middle beam to move relatively to the strip a material distance across the cutting mark, preferably half way or more across it. This apparatus is represented by the circuit diagram comprising Fig. 6. As shown in this figure the two outer photoelectric devices 38 of a single scanning head are connected together in parallel, and in cooperation with the middle photoelectric device thereof operate to control the impedance of the electric discharge'device 46. This device is energized by direct current and has its anode-cathode circuit connected through the resistor 41 between the positive end of the divider 48 and the tap 49 thereof. The two outer photoelectric devices are connected in parallel between the grid and the positive end of the divider and the middle photoelectric device is connected in a reverse manner between the grid and the negative end of the divider, the divider being shown supplied from the source 50 of direct current. The capacitor connected between the anode and cathode of the device 46, will begin to receive a charge the instant that the impedance of the device 46 reaches a high value; it also discharges through the device 453 when the impedance thereof drops to a low value. Connected between the positive plate of the capacitor 5! and the tap 52 of the divider is the output or signal circuit 53 of: the scanning head 22. The circuit of the scanning head 22' is identical with that of 22, its output or signaling circuit being represented at 5d.

The signal circuit 53 connects with the grid circuit of the gas electric discharge device 55 which device is arranged in a series circuit including the winding of the relay A, the resistor 51 and the high resistance winding of the relay C connected across the resistor 58 of the voltage divider 59. nects with the grid circuit of the gas electric discharge device 56 which device is arranged in a series circuit including the winding of the relay C, the winding of the relay B, and the resistor 58 connected across the resistor 6| of the voltage divider This divider is supplied by direct current obtained from the secondary winding 62 of the transformer 563 through the grid controlled rectifier E4 and the filter 65. A rectifier having grid control is necessary in this case in order that the direct current supply to the devices and 58 may be interrupted to restore them to a high impedance condition after each operation. Connected in the grid circuit of the rectifier 64 is the small capacitor 68, a secondary winding 5'? of the transformer 63 and the contacts of the relay C and the lower contacts of the relays A and B whereby when the relay C operates or if the relays A and B operate at the same time the grid current during the n gative half cycles of the voltage supplied to the rectifier charges the capacitor in such a manner that the plate connected with the grid is negative and because of this negative charge the rectifier is shut 0.1T and continues so until the charge on the capacitor is dischargedthrough the resistors 68 and 69. By the interruption of the direct current supply by this means the several relays are given ample time to move to their release positions. The charge on the capacitor 66 having leaked off and the relays being all in released position the rectifier is restored to its original condition.

The capacitor To which may have a capacitance of 80 m. f. is bridged across the winding 01 the relay C through the upper contact arms of the relays A and B so that it becomes charged in accordance with the potential difference across the winding of C when current flows therethrough and with a polarity in accordance with the direction of current flow. When the relays A and B open simultaneously they close a local circuit including the winding of the relay D and the battery 7 l. The contacts of the relay D by closing allow the capacitor '52 which may have a capacitance of one m. f. to become charged from the capacitor 10. The capacitor 12 connects across the grid circuit of the electric Likewise, the signal circuit 54 con-' light beam has progressed at least 3 discharge device 14, the anode-cathode circuit of which is supplied with direct current through the resistors '15 and 16. Connected across those resistors and the device are the resistors 71 and 18 forming therewith a Wheatstone bridge arrangement and connected across this bridge are the indicator whose pointer swings in either direction from an intermediate zero point and the field winding 8| of the reversible motor '26.

This motor, it will be remembered, is the motor which controls the differential 25 by which skew is corrected in the strip l. Apparatus in exact duplicate to that just described above is used for giving indications and for the control of each of the motors SI and 33 by which variations in length or" the strip sections are corrected and bow in the strip is corrected respectively.

The operation of the above-described apparatus will now be described. 'If a small amount of skew is present in the material the middle beam of one of the scanning heads will reach the cutting mark before the middle beam on the other scanning head, the dense portions 4| of the strip being in the paths of the outer beams. Assuming that the skew is in such a direction that the middle beam of the scanning head 22 is the first to reach the cutting mark the output of the photoelectric devices or" that head will cause theimpedance of the device 4% associated therewith to be reduced to an amount sufficient to cause the capacitor El to take on a predetermined charge. The charging of this capacitor begins at the instant that the light beam enters the cutting mark but the capacitor charge does not build up to the full value, that is, to a suiiicient value to cause the gas electric discharge device 55 to begin passing current, until the half way across the cutting mark. With the device 55 passing current the windings of the relays A and C are energized. As the relay B has not yet been energized a charging circuit for the capacitor E6 is established through the upper switch arm of the relay B and connected across the Winding of relay C; hence the capacitor 10 takes on a charge in accordance with the potential difference across the winding of the relay C and has a polarity such that the upper plate of the capacitor, as shown in Fig. 6, is positive.

At a brief time later, depending upon the amount of skew, the middle light beam of the other scanning head 22' in like manner operates to cause the gas electric discharge device 56 to begin passing current. This device closes the circuit through the winding of the relay C and the winding of the relay B. The energization of the relay B opens the charging circuit of the capacitor 70 by the shifting of the upper switch arm thereof; hence, the amount of charge left on the capacitor ii) is proportional to the angle of the skew. By the operation of both relays A and B the local circuit including the relay D and the battery II is closed. The resulting operation of the relay D allows the capacitor '52 to receive a charge from the capacitor l8. Inasmuch as both of the relays A and B have operated and thereby have closed the grid circuit of the rectifier 64 through their lower switch arms, the rectifier shuts 0d the supply of direct current to the voltage divider 59 and holds it off until the relays which are energized have had ample time to return to their released position. It will be understood, however, that before the supply of rectified current will have been interrupted the relay D will have operated and the capacitor 12 will have received its charge. The charge given to the capacitor '12, which having been received from the capacitorwll) will also be proportional to the'amount of the skew, operates through the discharge device 14included in one arm of the Wheatstone bridge to cause the pointer of the indicating device 80 to swing to the right or to'the left in accordance with the amount and the character of the skew. The current which actuates the indicating device also energizes the field winding 8! of the reversible motor 26 in such a manner that the motor is caused to turn in the proper direction and amoimt to cause a correction of the skew through the operation of the diiferential device 25.

Should the material be made in a pattern which includes an opening which is nearly as wide or which is wider than the cutting strip the apparatus will not function in the manner above described for in that case the capacitor would not become charged a suflicient amount to operate the device 55. Moreover should the material have an opening therein which is equal in width to the cutting strip but has one or more weft elements extending therethrough then at the passage of such an element through the middle beam 31 the impedance of the device 46 would suddenly drop to a low value permitting whatever'charge had been received by the capacitor 5| quickly to discharge through that device. After the passage of such a weft element the capacitor begins again to recharge but its charge would not reach a high enough value to operate the device 55 before the opening would have passed the middle beam.

Had the skew been of the opposite character to that assumed above whereby the scanning head 22' operated prior to the scanning head 22, then the charge on the capacitor 10 and likewise on the capacitor 12 would have been in the opposite sense. Accordingly, the pointer of the indicator 80 would have swung in the other direction and the motor would have been caused to turn in the opposite direction.

If there is no skew present in the material the middle beam of the two scanning heads will reach the cutting mark simultaneously. In that case the two relays A and B will be operated simultaneously but since the current supplied to the windings of those relays tends to flow in opposite directions through the winding of the relay C, little or no current actually flows therethrough and there will be no appreciable potential difference across it; hence the capacitor 10 will receive no appreciable charge. The relays A and B by their simultaneous operation close the grid circuit of the rectifier as before to interrupt the supply of rectified current to the divider in order that they may be ready for operation at the approach of the next cutting mark.

Inasmuch as the capacitor 10 is bridged across the winding of the relay C that relay does not operate to cause the rectifier to shut off the supply of rectifiedcurrent to the divider until the capacitor 10 has received nearly its full charge which corresponds with the maximum amount of skew which th apparatus is designed to indicate and for which it is designed to make correction. The relay C thus has a protective function in that should the amount of skew be eX- cessive, that is, beyond that for which the apparatus is capable of making correction, the apparatus will refuse to attempt to correct it. Also.

should one of the relays A and B make a false operation or, in the event that one has operated in response to the presence of skew and by reason of some defect the other one should fail to operate when it should, the operation of the relay C would restore all the operated relays to their released positions thereby preventing the correcting motor from doing possible injury to the material of the strip in responding to a false operation of its control mechanism. 7

The construction and operation of the scanning heads 23 and 23' and the apparatus controlled thereby for giving an indication as to whether the successive unit sections of the material or the separate curtains are either longer or shorter than the standard length and if so for making the necessary correction are identical with that described above for detecting and correcting skew. Also, the construction and operation of the scanning heads 8 and 8 and the apparatus controlled thereby for giving an indication as to whether bow is present in the material and if so for making the necessary correction are also identical with that described above for the detection and correction of skew. It will, of course, be understood that for the correction of inaccuracies in length of the unit sections the apparatus controlled by the scanning heads 23 and 23' will cause the motor 3| to turn in one direction or the other to adjust the differential 3i! and that for the correction of bow in the material the apparatus controlled by the scanning heads 8 and 8 will cause the motor 33 to turn in one direction or the other to adjust the differential 32.

While we speak of the material throughout the description and claims as being woven, We do not wish to be limited by that term since our invention is applicable to the manufacture of any strip material having transverse elements susceptible to a condition of skew or. bow or having transverse demarkations for dividing the strip into uniform lengths.

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

1. In apparatus employed in the manufacture of material woven as a continuous strip comprising a series of similar sections separated by transverse portions of predetermined length having a light characteristic which is materially different from that of those portions of the strip at opposite sides thereof, means for detecting variations in length of said sections from a predetermined standard length comprising means for moving said strip longitudinally, means for causing a plurality of light beams to emanate from said strip at fixed points spaced apart longitudinally thereof a distance equal to said standard length and means operative to give an indication in response to a time difference in the occurrence of corresponding variations in said light beams.

2. In apparatus employed in the manufacture of material woven as a continuous strip comprising a series of similar sections separated by transverse portions in which the density of the weave is materially different from that of those portions of the strip at opposite sides thereof, means for detecting variations in length of said :sections from a predetermined standard length comprising means for moving said strip longitudinally, means for producing light beams controlled by said weave density and spaced apart longitudinally of the strip a distance equal to said standard length and means operative to give an indication in response to a time difference in the occurrence of corresponding variations in said light beams.

3. In apparatus employed in the manufacture of material woven as a continuous strip comprising a series of equally spaced sections separated by bands extending substantially perpendicular to the strip and having a different light transmission from that of the adjacent portions of said sections, means for detecting variations'in length of said sections from a predetermined standard comprising means for moving said strip longitudinally, means for projecting light beams therethrough spaced longitudinally thereof a distance equal to said standard length, photoelectric devices arranged to receive said light beams respectively, and means operative to give an indication in response to a time difierence in the output impulses of said photoelectric devices.

4. In apparatus employed in the manufacture of material woven as a continuous strip comprising a series of similar sections separated by transverse portions in which the density of the Weave is materially different from that of'those portions of the strip at opposite sides thereof,'means for adjusting the lengths of the successive sections of the strip equal to a predetermined amount comprising means engagingsaid strip at two longitudinally spaced points for moving the same, means for moving said strip longitudinally, means for producing light beams controlled by said weave density and spaced apart longitudinally of the strip a distance equal to a predetermined standard, photoelectric devices arranged to receive said light beams, and means responsive to a time difference in the output impules of said photoelectric devices for varying the relative speeds of the strip moving means at said two points.

5. In apparatus employed in the manufacture of material woven as a continuous strip comprising a series of similar sections separated by bands extending substantially perpendicular to the strip in which bands the density of the weave is materially diiferent from that of those portions of the strip at opposite sides thereof, means for detecting a departure from perpendicularity of said bands comprising means for moving said strip longitudinally, means for producing light beams controlled by said weave density and arranged on a line perpendicular to said strip and means operative to give an indication in response to a time difference in the occurrence of corresponding variations in said light beams.

6. In apparatus employed in the manufacture 1 of material woven as a continuous strip comprising a series of like sections separated by bands extending substantially perpendicular to the strip and having a difierent light transmission from that of the adjacent portions of said sections, means for detecting a departure from perpendicularity of said bands comprising means for moving said strip longitudinally, means for pro- J'ecting therethrough spaced light beams arranged on a line perpendicular to said strip, photoelectric devices arranged to receive said light beams, and means operative to give an indication in response to a time difference in the output impulses of said photoelectric devices.

'7. In apparatus employed in the manufacture of material woven as a continuous strip comprising a series of similar sections separated by bands extending substantially perpendicular to the strip in which bands the density of the weave is materially different from that of those portions of the strip at opposite sides thereof, means for correcting a departure fromperpendicularity of said bands comprising means engaging each side of the strip for moving it longitudinally, means for producing light beams controlled by said weave density and arranged on a line perpendicular to saidstrip and means responsive to a time difference in the occurrence of corresponding variations in said light beams for varying the relative speeds at which the two sides of the strip are moved by the moving means. v 7- r 8. In apparatus employed in themanufacture of material woven as a continuous strip comprising a series of similar sections separated, by transverse portions in which the density of the weave is materially different from that of those portions of the strip at opposite sides thereof, apparatus for producing continuous longitudinal movement of said strip, means for removing skew in said sections, means for adjusting the length of said sections in accordance with a predetermined standard length and means for removing bow in said sections, said several means being arranged to operate on said strip successively and in the order named.

9'. In apparatus employed in the manufacture of material woven as a continuous strip comprising -a series-of like sections separated by bands extending substantiallyperpendicular to the strip and having a different light transmission from that of the adjacent portions of said sections, a first tenter having parts arranged to engage the opposite edges of said strip for advancing and expanding the same, means for detecting skew in said sections including means arranged between said tenter parts at spaced points on a line perpendicular to said strip for producing impulses inresponse to the passage past said points of said strip portions having said difference in light transmission as the strip is advanced, means for detecting variations in length of said sections from a standard length after they leave said tenter comprising means for producing impulses in response to the passage of said portions past points in the path of movement of the strip separated a distance equal to said standard length, a second tenter having parts arranged toengage'the opposite edges of said strip for advancing and expanding the same after it leaves said means for detecting, variations. in the length of the sections and means for detecting bow in said sections including means arranged between said tenter parts at spaced points on a line perpendicular to said strip for producing impulses in response to the passage past said points of said strip portions having said difference in light transmission as the strip is advanced.

10. Apparatus constructed and arranged to move longitudinally a strip of woven material having at spaced intervals therein similar transverse portions having a light characteristic which is materially different from that of those portions of the strip at opposite sides thereof, and means operative to detect the passage of said transverse portions comprising means for causing three narrow light beams to emanate from said strip, said beams being controlled by the light characteristios of said portions and being spaced apart a distance approximately equal to the width of said transverse portions, and means for producing an indication when the difference between the amount of light of the middle beam and the sum of the amounts of light of the other two beams is greater than a predetermined quantity.

lllfApparatus constructed and arranged to meve'longitudinally a stripof woven material havingat spaced intervals therein similar transverse'portions in which the density of the weave is materially different from that of those portions of the strip at opposite sides thereof, and means operative to detect the passage of said transverse portions comprising means for producing three narrow light beams controlled by said weave density and spaced apart a distance approximately equal to the width of 'said transverse portions,

and means for producing an indication when the difference between the amount of light of the middle beam and the'sum of the amounts of light of the other two beams is greater than a predetermined quantity. v

1 2. Apparatus constructed and arranged to move longitudinally a strip of woven material having at spaced intervals therein similar transverse bands whose light transmission is materially different from that of those portions of the strip on opposite sides thereof and means operative to detect the passage of said transverse portions comprising means for producing three narrow light beams controlled by the light transmission of said portions and spaced apart a distance approximately equal to the Width of said transverse bands, and means'for producing an indication when the difference between the amount of light of the middle beam and the sum of the amounts of light of the other two beams is greater than a predetermined'quantity.

13; Apparatus constructed and arranged to movelongitudinally a strip of woven material having at spaced intervals therein similar transverse bands whose light transmission is materially different from that of those portions of the strip on opposite sides thereof and -means operative to detect the passage of said transverse portions comprising means for projecting three narrow light beams through said strip, said beams being spaced apart a distance approximately equal to the width of said transverse bands, and means for producing an indication when the difference between the amount of light of the middle beam transmitted by the strip and the sum of the amounts of light of the other two beams transmitted by thestrip is greater than a predetermined quantity. 7

'14 Apparatus constructed and arranged to move longitudinally a strip of woven material having at spaced intervals therein similar transverse bands whose light transmission is materially different from that of those portions of the strip on opposite sides thereof and means operative to detect the passage of said transverse portions comprising means for projecting three narrow light beams through said strip, said beams being spaced apart a distance approiiimately equal to the width of the transverse bands, a photoelectric device arranged to receive the light of each beam transmitted by said strip, means for amplifying the output of said devices, means operative to give an indication when the amplified output of the device. receiving light from the middle beam is different by a predetermined amount from the amplified output of the two other devices taken together, and means for delaying the giving f said indication until the leading edge of said transverse band has advanced materially beyond said middle light beam.

15. Apparatus constructed and arranged to move longitudinally a strip of woven material having at spaced intervals therein similar transverse bands whose light transmission is materially different from that of those portions of the strip on opposite sides thereof and means operative to detect the passage of said transverse portions comprising means for projecting three narrow light beams through said strip, said beams being spaced apart a distance approximately equal to the width of the transverse bands, a photoelectric device arranged to receive the light of reach beam transmitted by said strip, means for amplifying the output of said devices,

7 means operative to give an indication when the ALBERT P. MANSFIELD. CRAMER W. LA PIERRE. WILLIAM H. JANSSEN. MILTON S. MEAD, JR.

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