US3467149A - Electronic device for surveying the presence of weft thread in weaving looms - Google Patents

Description

Sept. 16, 1969 Pp DOSCH ET AL 3,467,14

ELECTRONIC DEVICE FOR SURVEYING THE PRESENCE OF WEFT THREAD IN WEAVING LOOMS Filed May 26, 1967 4 Sheets-Sheet l HH! Wm 44 54 42 I ."JVENTORS P5 Dose/v 5 4 E/VZ 40 BY /@91/z la /W /477 O NEYS Sept. 16,1969 P. DOSCH ET AL ELECTRONlC DEVICE FOR SURVEYING THE PRESENCE OF WEFT THREAD IN WEAVING LOOMS 4 Sheets-Sheet 2 Filed May 26, 1967 m m0 MW Sept. 16, 1969 Filed May 26, 1967 P. DOSCH ETAL ELECTRONIC DEVICE FOR SURVEYING THE PRESENCE OF WEFT THREAD IN WEAVING LOOMS 4 Sheets-$heet INVENTORS Para 006M fM/t. 560 2 BY RAUL 5?U %gw%%u S p 6. 1969v P. DOSCH ET AL 3,467,149

ELECTRONIC DEVICE FOR SURVEYING THE PRESENCE OF WEFT THREAD IN WEAVING LOOMS Filed May 26, 1967 4 Sheets-Sheet l {10 3 :5 4 iwgvfcRj a W 0050/ l y fM/l. 5.50 2 7 7 R414. 89%? United States Patent Office 346 7, 1 Patented Sept. 16, 1 969 3,467,149 ELECTRONIC DEVICE FOR SURVEYING THE PRESENCE OF WEFT THREAD IN WEAVING LOOMS Peter Dosch, Jona, and Emil Benz and Paul Brulnn, Wattwil, Switzerland, assignors to Heberlein & Co. A.G., Wattwil, St. Gall, Switzerland, a corporation of Switzerland Filed May 26, 1967, Ser. No. 641,559 Int. Cl. D03d 51/34 U.S. Cl. 139-371 15 Claims ABSTRACT OF THE DISCLOSURE Detection device for indicating passage of thread out of a moving shuttle in which the moving thread rubs against a wire-like element causing it to vibrate and shift the electrical parameters of a circuit in the shuttle, in such manner that the circuit interacts variably with a fixed circuit.

This invention relates to detection and signalling and more particularly it concerns a novel method and apparatus for indicating thread movements from the shuttles on weaving looms.

It is necessary in weaving looms to stop the loom immediately when the weft thread carried by the shuttle breaks. If the loom is not stopped the shuttle will move back and forth without supplying weft threads. Also the end of the broken weft thread can become jammed in among the warp threads if the shuttle continues to operate. In both cases, defects are produced in the finished woven fabric. Such defects can be avoided only if the breakage of the weft thread is detected and the weaving loom is stopped immediately.

In the past, attempts have been made to solve this problem by providing mechanical weft feelers which check the weft thread for its tension while it is introduced between the warp threads. Because of the high mechanical speeds which occur in loom operation and because of the difficulty of adjusting these feeling devices to various thread tensions, especially when thin and thick threads are worked into the same fabric, these mechanical weft feelers are very diflicult to operate. This is also true for all known electromechanical devices which use the tension of the weft thread or the movement of the weft thread during the insertion as a criterion for the generation of weft thread intact or weft thread broken signals. Thus, it is always necessary to carefully adjust the thread monitoring device with respect to the thread being used and its properties. This is true whether the monitoring device is fixed on the loom or whether it is positioned in the moving shuttle itself.

In order to avoid the above disadvantages, the present invention uses as an indication of the movement or nonmovement of the Weft thread, the friction of the weft thread itself on a guide or support member. According to the present invention, the friction energy between the thread and guide produces a signal which is transferred without contact to a receiver placed in the loom itself. The present invention makes advantageous use of the fact that the difference between the friction energy when the thread stands still and the friction energy when the thread is moving is so great in all cases, irrespective of variations in yarn tension, yarn materials and yarn running speeds, that it is not necessary to adjust the device to each individual set of operating conditions. 7

According to one aspect of the present invention, shuttle thread movement is detected by causing the shuttle to pass closely adjacent a first, fixed electrical circuit, and during this passage using the thread movement within the shuttle to vary the electrical characteristics of a second electrical circuit which is located within the shuttle. These elecrical characteristics are varied in such a manner that a corresponding variation in electromagnetic field interaction takes place between the two electrical circuits. By noting the effects of this interaction on the fixed circuit, an indication of thread movement can be obtained.

There has thus been outlined rather broadly the more important features of the invention in order that the detailed description thereof that follows may be better undersood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described hereinafter and which will form the subject of the claims appended hereto. Those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures for carrying out the several purposes of the invention. It is important, therefore, that the claims be regarded as including such equivalent constructions as do not depart from the spirit and scope of the invention.

Specific embodiments of the invention have been chosen for purposes of illustration and description, and are shown in the accompanying drawings forming a part of the specification, wherein:

FIG. 1 is a perspective view of a portion of a loom arrangement incorporating the present invention;

FIG. 2 is a section view taken in side elevation, of a shuttle incorporating a signal generating device forming a portion of the present invention;

FIG. 3 is an enlarged fragmentary view of the front portion of the shuttle shown in FIG. 2;

FIG. 4 is a further enlarged fragmentary view illustrating a portion of a signal generator used in the shuttle of FIGS. 2 and 3;

FIG. 5 is an enlarged fragmentary view illustrating a portion of the loom arrangement of FIG. 1;

FIG. 6 is a circuit diagram illustrating the wiring arrangement for the signal generator utilized in the shuttle of FIGS. 2 and 3;

FIG. 7 is a circuit diagram illustrating the wiring arrangement utilized in the loom of FIG. 1;

FIG. 8 is a set of wave forms illustrating the operational characteristics of the present invention according to a first mode of operation;

FIG. 9 is a set of wave forms illustrating the operational characteristics of the present invention according to a second mode of operation;

FIG. 10 illustrates an alternate signal generator arrangement usable in connection with the present invention;

FIG. 11 is a circuit diagram illustrating a Wiring arrangement for use in conjunction with the signal generator illustrated in FIG. 10;

FIG. 12 is a circuit diagram illustrating a modification of the circuit represented in FIG. 11;

FIG. 13 is a schematic illustration of another signal generator arrangement usable in connection with the present invention; and

FIG. 14 is a schematic wiring arrangement of an alternate signal generator according to the present invention.

FIG. 1 illustrates in general outline, a portion of a loom 20. On the loom 20 there is provided a reed 22 which serves to guide first and second groups, 24 and 26, of warp threads as they move along in the direction of an arrow A.

It will be noted that the threads of the first warp thread group 24 are interspersed with those of the second shed 26. Heddles (not shown) move the sheds up and down with respect to each other; and after each such movement a shuttle 28 is thrown transversely across the loom 20 through the space between the first and second groups.

24 and 26. During this movement the shuttle 28 feeds out a weft thread 30 and lays it crossways of the warp threads. Means not forming a part of this invention are provided to push the weft thread 30 snugly up against the interaction of the sheds. Thus as the sheds are moved up and down and weft thread 30 is played back and forth, there is generated a woven fabric construction 32 which is drawn olf around a beam 34.

The reed 22 as well as various other elements making up the loom 20 are mounted on a base or sley 36. These other elements include a signal receiver 38 positioned flush with the surface of the sley 36 about midway across it. As will be explained more fully hereinafter, the signal receiver 38 responds to movements of the shuttle 28 across the loom 20, and at the same time detects movements of the weft thread 30 out of the shuttle during this time.

Turning now to FIG. 2, it will be seen that the shuttle 28 is formed with a hollow central chamber 40', within which is mounted a bobbin 42. The weft thread 30 to be supplied by the shuttle 28 is wound about the bobbin 42 and is played out from the front end of the bobbin. The thread passes over a signal generator 44 near the front of the shuttle; and then it leaves the shuttle via an output guide 46. The bobbin 42 is supported at the rear thereof by means of a bobbin support 48 within the hollow chamber 40.

As shown in FIG. 3, the signal generator 44 is mounted within the hollow chamber 40 toward the front thereof by means of rubber bearings 50 which serve to isolate the signal generator from Vibratory effects within the shuttle. The signal generator 44 itself includes a base member 52 mounted between the rubber bearings 50. A wire-like thread feeler element 54 is mounted on the base member 52 and extends to a position such that the weft thread 30 must rub across the feeler element 54 as it is drawn off from the bobbin 42 and moves toward the output guide 46.

The positional relationship of the mechanical portions of the signal generator 44 are best seen in the enlarged fragmentary view of FIG. 4. As can be seen in FIG. 4, the wire-like thread feeler element 54 is mounted in cantilever fashion at one end to extend upwardly from the base member 52. The thread feeler element then bends over to extend transversely across and above the base member 52. Referring now to FIG. 5, it will be seen that the base member 52, the bobbin 42, and the output guide 46 are all positionally related such that the weft thread 30 presses slightly downwardly upon the thread feeler element 54 toward its free end and rubs across the element 54 during its movement from the bobbin 42 toward the output guide 46. As shown in FIGS. 4 and 5, an elongated piezoelectric crystal 56 is supported at each end thereof by means of mounting elements 58 to extend horizontally above the base member 52 just under the thread feeler element 54. A vibration coupling member 60 interconnects the thread feeler element 54 and the piezoelectric crystal 56 at a point midway between the two mounting elements 58.

As shown in FIG. a signal generator coil 62 is wound about the periphery of the base member 52. This coil acts as an antenna for controlling electromagnetic field interaction between the moving signal generator 44 and the stationary signal receiver 38 as the shuttle passes close- 1y over the signal receiver. Various other electrical ocmponents (not shown in FIG. 5) are embedded within the base member 52 and are electrically connected with the signal generator coil 62 and the piezoelectric crystal 56 in a manner shown in the wiring diagram of FIG. 6.

As shown in FIG. 6, there is provided a variable capacitance diode 64 connected across the piezoelectric crystal 56. A load resistor 66 is also connected across the variable capacitance diode 64 and the crystal 56. The signal generator coil 62 is connected in series with a balance capacitor 68 and the coil 62 and capacitor 68 are together con- 4 nected across the variable capacitance diode 64. The variable capacitance diode 64, the load resistor 66 and the balance capacitor 68 are all embedded within the base member 52. Essentially, the circuit arrangement of FIG. 6 is a resonant LC circuit made up of the inductance of the signal generator coil 62 and the combined capacitances of the balance capacitor 68 and the variable capacitance diode 64.

The variable capacitance diode 64 is characterized in that at certain frequencies it exhibits a capacitive elfect. Moreover, by changing the voltage applied across the anode and cathode of the variable capacitance diode 64, the degree of its capacitive effect can be altered. Thus voltage variations supplied to the diode 64 by the piezoelectric crystal 56 will serve to change the capacitive effect of the diode 64 and thereby change the resonant frequency of the LC circuit. It can also be seen that as the weft thread 30 rubs across the thread feeler element 54 and causes the thread feeler element to vibrate, its vibratory movements will be transmitted via the coupling member 60 to the piezoelectric crystal 56 causing it to produce corresponding voltage variations. These voltage variations in turn serve to change the capacitive characteristic of the variable capacitance diode 64, thereby causing the resonant circuit, including the signal generator coil 62, to experience different resonant frequencies.

Reverting to FIG. 5, it will be seen that the shuttle 28 during its transversal movement across the loom, passes very closely adjacent to the signal receiver 38. The signal receiver 38 itself contains a signal receiver coil 70 which is embedded in the surface of the sley 36. Also mounted on the sley 36 are various other electrical components which are interconnected with the signal receiver coil 70 in the manner shown in FIG. 7.

As can be seen in FIG. 7 there is provided an electrical oscillator 72 which is connected via a coupling resistance 74 across a resonant circuit 76. The resonant circuit 76 itself is made up of a fixed capacitor 78 and the signal receiver coil 70 connected in parallel. A demodulating diode 80 is connected to one side of the resonant circuit 76, and the output of the demodulating diode 80 is supplied to a signal detector 82.

Operation of the above described system will noW be discussed. As indicated, the shuttle 28 is cause to be thrown across the loom 20 between the warp thread groups 24 and 26 each time the relative position of the sheds is reversed. During such transverse movement of the shuttle 28, the weft thread 30 is pulled off from its bobbin 42. As the weft thread 30 moves out from the shuttle 28, it rubs across the thread feeler element 54. This causes the thread feeler element 54 to vibrate.

It is important to note at this point that the vibrations of the thread feeler element 54 which are produced by the rubbing action of the weft thread 30 are frequency independent of the thread itself. In other words, the thread feeler element 54 will vibrate at a fixed frequency established by its own mechanical characteristics and is in no way affected by incidental variations in roughness, thickness or other surface irregularities of the weft thread 30. Actually, the only characteristic of the weft thread 30 that the thread feeler element 54 depends upon is the movement or non-movement of the weft thread. If there is no movement of the weft thread 30, then the thread feeler element 54 will not vibrate. On the other hand, if there is any movement of the weft thread 30, then the thread feeler element 54 will vibrate at its own natural frequency irrespective of the speed of movement of the weft thread or of any other incidental physical characteristics of the weft thread. This phenomenon is analogous to the effect of a bow on a violin string, where the movement of the bow will cause the string to vibrate at its own natural frequency, which is essentially independent of the roughness or surface irregularities of the bow.

The vibratory movements of the thread feeler element 54 are communicated via the vibratory coupling member 60 to the piezoelectric crystal 56, causing this crystal to vibrate at the natural frequency of the thread feeler element 54. These vibrations are converted by the crystal 56 into corresponding voltage variations which are imposed across the terminals of the variable capacitance diode 64. This in turn changes the the capacitance characteristic of the diode at a rate corresponding to the vibrationed frequency of the thread feeler element 54. As a result, the resonant frequency of the LC circuit made up of the coil 62 and the capacitance of the capacitor 68 and the diode 64, shifts at the vibratory rate.

As the shuttle 28 passes closely adjacent to the signal receiver 38 as shown in FIG. 5 the LC circuit in the shuttle will interact electromagnetically with the signal receiver by an amount corresponding to the closeness of its resonant frequency to the frequency at which the signal receiver is being driven. The amount of this interaction manifests itself in a variation in the voltage across the receiver resonant circuit 76. This voltage variation is extracted from the driving frequency by the demodulating diode 80 and the output of the demodulator is detected by the signal detector 82.

FIG. 8 illustrates the manner in which the voltage output from the demodulating diode 80 varies for the situation where the electrical parameters of the signal generator 44 are such that the normal resonant frequency of its LC circuit portion is displaced from the driving frequency of the receiver circuit 38; but are also such that the vibratory movements of the piezoelectric crystal 56 cause the resonant frequency of the signal generator LC circuit portion to shift into and out of the driving frequency of the receiver circuit 38. This, of course, produces a change in the electromagnetic field interaction between the signal generator and receiver circuits so that a voltage variation appears at the output of the demodulator diode 80 at the natural vibratory frequency of the thread feeler element 54.

In FIG. 8, curve a represents the demodulator output voltage for the case where the Weft thread 30 is not moving and therefore is not causing the thread feeler element 54 to vibrate and change the LC resonant frequency. In this case, as the shuttle 28 moves past the signal receiver 38 a certain amount of interaction takes .place between the receiver and generator circuits. However, because there is no change in the electrical characteristics of the generator circuit during this time, the amount of electromagnetic field interaction between the generator and receiver circuits remains substantially constant over the duration of shuttle movement past the signal receiver. As a result, the voltage level output from the demodulating diode 80 decreases and then remains constant during the time that the shuttle is passing over the receiver, as illustrated at a.

Curve b in FIG. 8 represents the demodulator output voltage for the case when the weft thread does move out of the shuttle 28. In this case, when the shuttle 28 passes over the signal receiver 38 while the weft thread 30 is being fed out through the output guide 46 of the shuttle, the thread will rub against the thread feeler element 54 causing it to vibrate at its natural frequency; and this in turn will induce corresponding vibrations in the piezoelectric element 56 causing the resonant frequency of the LC circuit to shift over into and back from the driving frequency of the receiver circuit. As a result, in addition to the above described electromagnetic field interaction between the signal generator and receiver circuits, an additional and far greater interaction will take place each time the resonant frequency of the signal generator circuit shifts to equal the driving frequency of the signal receiver. As a result of these greater field interactions, the voltage at the output of the demodulator will dip likewise at the same rate, which, of course is the vibratory rate of the thread feeler element 54. The pattern of this voltage variation is illustrated at b in FIG. 8.

FIG. 9 illustrates the manner in which the voltage output from the demodulator diode 80 varies for the situation where the electrical parameters of the signal generator 44 are such that the normal resonant frequency of its LC circuit is equal to the driving frequency of the signal receiver circuit. Curve a in FIG. 9 represents the demodulator output when the weft thread is not causing the thread feeler element 54 to vibrate a very great electromagnetic field interaction occurs between the signal generator and receiver circuits as the shuttle moves over the signal receiver. This produces a rather large although steady decease in output from the demodulator diode 80, as shown at a.

FIG. 9b represents the demodulator output when the weft thread 30 moves across the thread feeler element 54 and out from the shuttle 28 as the shuttle is thrown across the loom 20. In this case the movement of the thread 30 will cause the thread feeler element 54 to vibrate at its natural frequency. As previously explained, this vibratory action is transmitted to the piezoelectric crystal 56 which generates corresponding voltages to change the capacitive characteristics of the diode 64 so that the resonant frequency of the LC portion of the signal generator circuit is caused to shift out from and back across the driving frequency of the signal receiver. In this case, since the signal receiver driving frequency corresponds with the centerposition of the thread feeler element 54, it is crossed twice for each vibratory cycle of the thread feeler element. Thus in this case, the output of the demodulator diode is twice that for the situation represented in FIG. 8, as shown by curve b in FIG. 9.

The detector 82 is set to respond to the voltage variations which occur as in either FIG. 812' or FIG. 9b; and to operate mechanisms (not shown) for controlling loom operation.

FIGS. 10 and 11 show another form of signal generator whereby an electrodynamic arrangement is substituted for the piezoelectric crystal 56 of the preceding embodiment. As shown in FIG. 10, a thread feeler element 54' is mounted in cantilever fashion from the base member 52 to extend upwardly therefrom and then to extend over the base member 52 in a horizontal direction, as in the preceding embodiment. However, in the arrangement of FIG. 10, there is no coupling member, nor is there provided any piezoelectric element. Instead, in the arrangement of FIG. 10, a permanent magnet is suspended downwardly at one end from the thread feeler element 54. The permanent magnet 90 enters into the core of an electrical coil 92 mounted on the base member 52. As the thread feeler element 54 vibrates, it causes the permanent magnet 90 to move with respect to the coil 92 in such a manner that the magnetic lines of flux from the magnet 90 cut across the turns of the coil 92 and thereby generate varying voltages across the ends of the coil.

As shown in FIG. 11, the coil 92 is connected across the variable capacitance diode 64 in the same manner that the piezoelectric crystal 56 of the previous embodiment was connected. Otherwise, the circuit of FIG. 11 is identical to that of FIG. 6. Thus, it can be seen that a signal generator may be provided utilizing either a piezoelectric member or an electromagnetic member to produce the voltages which change the resonant characteristics of the capacitor-inductor portion of the circuit. For certain situations, it may be desired to dampen the half Waves of the signal generator. This may be accomplished by the circuit arrangement of FIG. 12 which employs a plurality of diodes 94 connected in bridge fashion with a moving magnet coil 96 and a signal generator coil 98. The signal generator coil 98 may itself be part of a resonant LC circuit.

FIG. 13 illustrates a somewhat different form of the signal generator usable in connection with the present in vention. As shown in FIG. 13, there is provided an elongated wire-like vibratory thread feeler element 100 which is mounted in cantiliver fashion to a base member 102. The feeler element 100 is positioned such that as the weft thread 30 is pulled out from the shuttle, it rubs across the surface of the thread feeler element and causes it to vibrate at its own natural frequency. In the arrangement of FIG. 13, the thread feeler element 100 itself is connected to one side of a signal generator coil 104. The other side of the signal generator coil is connected to a fixed contact 106 mounted within the shuttle itself. The signal generator coil 104 is bridged by a damping resistor 102.

During operation of the arrangement shown in FIG. 13, the movement of the weft thread 30 across the thread feeler element 94 produces vibratory oscillations of the thread feeler element 100 to a degree such that the thread feeler element 100 touches the fixed contact 106 and short circuits the signal generator coil 98. When this occurs while the shuttle is passing over the receiver coil 70, the alternate making and breaking of the coil short circuit will cause the coil to interact electromagnetically by different amounts with the signal receiver on the loom. Thus, an indication of thread movement is produced at the signal receiver.

FIG. 14 shows an alternate arrangement for the signal receiver. In the arrangement of FIG. 14, the oscillating circuit is integrated with the signal receiver coil. As shown in FIG. 14, there is provided a signal receiver coil 110 which is partially coupled to an amplifier 112. A portion of the energy of the receiver coil is thus amplified in the amplifier. A portion of the amplifier output is fed back to the coil 110, while the remainder passes through a demodulator diode 114. In normal operation this system operates as a free running oscillator which transmits electromagnetic energy continuously at a fixed frequency. When the shuttle passes by and interacts with the signal generator different amounts of electromagnetic energy are driven from the coil 110. As a result, the amount of energy fed to the amplifier 112 changes; and this is manifested in a voltage variation at the output of the demodulator diode 114.

Having thus described my invention with particular reference to the preferred forms thereof, it will be obvious to those skilled in the art to which the invention pertains, after understanding my invention, that various changes and modifications may be made therein Without depart ing from the spirit and scope of my invention, as defined by the claims appended thereto.

What is claimed as new and desired to be secured by Letters Patent is:

1. Apparatus for the production of a signal to indicate the movement of a weft thread out from the shuttle of a weaving loom, such signal being produced without physical contact with said moving shuttle, said apparatus comprising a passive electrical circuit within said shuttle, said circuit including a coil and a variable impedance means arranged to be influenced by weft thread movements from said shuttle to change the frequency response characteristic of said electrical circuit in a cyclical manner, and a detection circuit including a further coil arranged along the path of shuttle movement, means for electrically energizing said further coil continuously at a given frequency, and means responsive to the occurrence of cyclical changes in the electromagnetic interaction between said coils.

2. Apparatus as in claim 1 wherein said means for electrically energizing said further coil comprises an electrical oscillator loosely coupled to a resonant circuit which includes said further coil.

3. Apparatus as in claim 1 wherein said coil in said passive electrical circuit is connected in series with resistance means, arranged to have its resistance varied by movements of said weft thread.

4. Apparatus according to claim 1 wherein said means for electrically energizing said further coil comprises a resonant circuit including said further coil and amplifier means coupled with said resonant circuit in a manner to produce self-sustained oscillation.

5. Apparatus according to claim 1 wherein said variable impedance means comprises a mechanical member mounted to vibrate at a predetermined frequency upon the rubbing movement of thread thereon and means converting such vibratory movements to electrical impedance changes in said passive electrical circuit to shift its frequency response characteristic in accordance with the vibrations of said mechanical member.

6. Apparatus as in claim 5 wherein said passive electrical circuit includes a coil and electrical means connected to said mechanical member for varying the reaction of said coil.

7. Apparatus as in claim 5 wherein said passive electrical circuit comprises a resonant electrical circuit including a variable capacitor and means converting the vibrations of said mechanical member to variations in the capacitance of said capacitor.

8. Apparatus as in claim 7 wherein said variable capacitor is a variable capacitance diode having a capacitance characteristic which varies with an applied voltage, means for converting vibratory movements of said mechanical member to corresponding voltages and means applying said voltages across said diode.

9. Apparatus as in claim 8 wherein said means for converting said vibratory movements to corresponding voltages includes piezoelectric crystal mechanically connected to be stressed by movements of said mechanical member;

10. Apparatus as in claim 8 wherein said means'for converting said vibratory movements to corresponding voltages comprises a magnet and a coil and means mounting said magnet and coil to undergo relative movement in response to vibratory movements of said mechanical member.

11. Apparatus as in claim 5 wherein said mechanical member is a wire-like element mounted to be rubbed against by said weft thread as it moves out of said shuttle and to vibrate at its own natural frequency in response to such rubbing.

12. Apparatus as in claim 5 wherein said passive electrical circuit includes a wire-like element mounted to extend in cantilever fashion from a base member and to be rubbed against by said weft thread moving out of said shuttle, said passive electrical circuit further including an antenna coil and switch means connected across said coil and mounted to open and close in response to vibratory movements of said wire-like element.

. 13. A method of detecting the movement of thread inside a moving shuttle, said method comprising the steps of causing said shuttle to pass closely adjacent a first, fixed electrical circuit and during said passage using thread movement within said shuttle to vary the electrical impedance characteristic of an element forming a portion of a passive electrical circuit in said shuttle to vary its frequency response characteristic in a cyclical manner, continuously energizing said fixed electrical circuit at a given frequency and monitoring the electrical interaction between said fixed and passive electrical circuits.

14. A method as in claim 13 wherein said resonant frequency is varied at a predetermined rate by thread movement within said shuttle and remains constant in the absence of such thread movement.

15. A method as in claim 13 wherein said electrical rea'ctance is varied by directing said thread to move across a mechanical element induced thereby to vibrate at a predetermined natural frequency and converting such vibrations into corresponding changes in electrical characteristics.

References Cited UNITED STATES PATENTS 2,524,579 10/1950 Taylor 19.25 2,535,369 12/1950 Pelce 139-371 3,140,604 7/1964 Bernet 28---64 X (Other references on following page) 9 10 3,298,401 1/1967 Stutz 139-371 508,875 2/1952 Belgium. 3,322,162 5/1967 Rydborn 139371 861,829 1/ 1953 Germany.

FOREIGN PATENTS 1,003,875 9/1965 Great Britain.

1,47 ,899 2/ 1967 France. 5 JAMES KEE CHI, Primary Examiner

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