US3659437A - Knitting machine defective needle detector - Google Patents

Abstract

A circular knitting machine, comprising a device for detecting defective needles by detecting the absence of a needle hook from its proper place. The device is placed at a locality adjacent the circular path of needle travel, and the needles are raised by a cam so that the hook of every good and properly positioned needle intercepts a collimated bead of radiant energy. The beam is not intercepted properly by a needle which has a broken, bent or otherwise defective hook or which, because of broken butt or other causes, has not been raised properly. The detector is connected to an alarm and may also be connected to a conventional stop motion device. Alternatively, a small magnet mounted on a piezoelectric crystal or magnetic pickup is positioned in the proximity of the hooks of the needles which have been raised by the cam referred to above. The magnet will be deflected by each passing needle of proper constitution and attitude in substantially the same manner, but will be deflected differently by a defective needle.

Description

United States Patent McArthur et a1.

[ 51 May 2, 1972 [72] Inventors: Colln S. McArthur; Benny L. Hester, both of Winston-Salem, NC.

[73] Assignee: R. J. Reynolds Tobacco Company, Winston-Salem, NC.

[22] Filed: July 25, 1969 [21] Appl. No.: 844,808

[52] U.S. Cl. ..66/l57 [51] Int. Cl. ..D04b 35/18 [58] Field otSearch ..66/157, 163, 165

[56] References Cited UNITED STATES PATENTS 3,496,739 2/1970 Motin et a1. ..66/163 3,065,615 11/1962 Abrams ....66/l66 3,529,445 9/1970 Brose ....66/l57 2,165,975 7/1939 Lawson et a1 ....66/157 2,760,363 8/1956 Van Alen et al.... ...66/l57 2,963,890 12/1960 Hoots ..66/l57 OTHER PUBLICATIONS Schwabe, C., Photoelektrische Warenkontrolle An Doppelzylinder-Antomaten, Wirkerel-und Strickerel-Technik,

Coburg, October 1964, No. 10; Pages 478- 482 Fault Detection On Circular Knitting Machines," Peter Brose; The Hosiery Trade Journal, June 1969; Vol. 76, No. 906, Pages 89- 92.

Primary Examiner-Mervin Stein Attorney-Cooper, Dunham, Henninger & Clark [57] ABSTRACT A circular knitting machine, comprising a device for detecting defective needles by detecting the absence of a needle hook from its proper place, The device is placed at a locality adjacent the circular path of needle travel, and the needles are raised by a cam so that the hook of every good and properly positioned needle intercepts a collimated bead of radiant energy. The beam is not intercepted properly by a needle which has a broken, bent or otherwise defective hook or which, because of broken butt or other causes, has not been raised properly. The detector is connected to an alarm and may also be connected to a conventional stop motion device.

11 Claims, 10 Drawing F igurcs PATENTEDMAY 2 I972 SHEET 1 CF 3 ATTOPA/EV KNITTING MACHINE DEFECTIVE NEEDLE DETECTOR BACKGROUND OF THE INVENTION In the course of operating circular knitting machines, the needles are raised and lowered by cams and are also acted upon by sinkers, yarn, and the completed fabric. The needles are thus subjected to substantial stresses and to friction, as a result of which the needles are sometimes damaged. When such damage occurs, proper knitting is interrupted, wastage of knitted fabric takes place, and further damage to other needles or other parts of the knitting machine may result.

There are several weak points in the needles, one of which is the butt. As the butt is acted upon by lowering and raising cams in the course of knitting, it may break ofi, it may bend, or it may wear excessively. The needle then will not be raised and lowered properly and will not properly engage the yarn being fed to it. Another weak point is the upper end of a knitting needle and particularly the hook. The hook may be bent or broken off and thus fail to engage yarn being fed to it.

Since it is important to detect defective needles as early as possible, so as to minimize subsequent damages and wastage, there are various prior art devices for detecting defective needles. At least one device is known in the prior art for detecting the absence of a part of a needle. Such a device is described in the U.S. Pat. No. 2,760,363 to Van Alen et al., and provides a magnetic circuit having a gap through which the hook ends of the needles are passed as the needle cylinder rotates during knitting. Good needles affect the magnetic circuit in an identical manner, but a needle with a broken hook introduces less magnetic material in the gap and thus affects the magnetic circuit differently. However, it has been found that such an arrangement is of limited sensitivity in detecting many of the more common forms of needle deformations. For example, the device may fail to detect a needle which is merely bent such that its hook does not face in the proper direction.

Other known prior art devices are designed to detect the presence of a needle or a part thereof at a place where no part of a needle should be. For example, the device described in the U.S. patent to Hoots, U.S. Pat. No. 2,963,890 is designed to detect needles which have failed to retract due to broken butts or other causes. The device has a detecting element positioned above the normal circular path of the retracted needles. A non-retracted needle will-physically contact the detecting element and will deflect it.

Another type device for detecting defective needles, again by detecting the presence of a needle part at a place where it should not be, is described in the French Patent No. 1,007,430 to Antoine (copy in Class 66-157). The device is designed to detect broken hooks or latches by establishing electrical contact with only the defective needles.

One common disadvantage with the latter two prior art detectors is that physical contact between the detecting device and the defective needles is necessarily involved. Another disadvantage is that they detect not the primary defect, that is the absence of a critical part of a needle from its proper place, but a secondary effect, namely, the presence of a needle or a part thereof in an improper place. By looking only for secondary effects of a needle defect, these prior art devices may fail to detect certain defects.

SUMMARY OF THE INVENTION The invention is in the field of knitting machines and particularly circular knitting machines and is directed to detecting defective needles as early as practicable so as to avoid excessive subsequent damage and wastage due to defective needles.

One embodiment of the detecting device includes a source of radiant energy for producing a thin collimated beam and a detector, both of which may be mounted outside the circle defined by the hooks of the circularly arranged needles, so that the beam is substantially tangent to the circle of needles. Preferably at a locality spaced from the point where knitting takes place, the needles may be raised by a special cam such that when a needle is at the raised position, its hook intercepts and blocks off the beam of radiant energy. If all needles are good and have their hooks oriented in the proper fashion, the beam is continually intercepted and at least partly blocked, and is never allowed to impinge on the detector in full force. If, however, a hook is defective in that its butt is broken, bent or excessively worn, or its hook is broken, bent out of alignment or otherwise damaged, or if for any other reason the needle is not raised properly or its hook is not oriented properly, the beam is not intercepted and impinges on the detector in substantially full force. Upon impingement of the beam, the detector generates an electrical signal which is appropriately amplified and shaped to be used to activate an alarm indicating that a defective needle is present, and to activate a stopmotion device of conventional design to stop the knitting machine.

Should the beam of radiant energy be somewhat wider than the hooks at the point where the hooks intercept the beam, or should the beam be somewhat misaligned, relatively small amount of radiant energy will reach the detector with each passing hook which is in the proper position, but a relatively large amount of radiant energy will reach the detector upon the presence of a defective needle, especially where needle profile at the point of inspection is optimized by use of such as the previously mentioned cam. Threshold discriminating means is provided in the electrical circuit connected to the detector for discriminating between, on the one hand, the small amounts of radiant energy associated with good and properly positioned needles and, on the other hand, the larger amount of radiant energy associated with defective needles.

An alternative device for detecting defective needles includes a small magnet positioned near the hook of a nondefective needle when raised, preferably by the special cam referred to above. The magnet is mounted on a stationary transducer for converting mechanical stresses to electrical energy. Since the needles are usually of steel or other magnetic material; the magnet will be deflected in substantially the same fashion by each nondefective needle and the electrical signals generated by the transducer will be substantially identical. Should a needle be defective, however, its hook will not be in the proper position when the needle is raised by the special cam, and the magnet will not be deflected or will be deflected difi'erently, resulting in a difi'erent electrical signal generated by the transducer.

The transducer is connected to an electrical network which discriminates between the periodic electrical signals produced by the transducer as nondefective needles are passed by the magnet, and electrical signals produced by the transducer when a needle whose hook is absent from its proper place is passed by the magnet. The electrical network operates an alarm and a conventional stop-motion device.

As another alternative, in any of the embodiments discussed above, the special cam may be omitted and the detector may be associated with the conventional cam which raises and lowers the needles to do the knitting.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a simplified side elevational view of a portion of a circular knitting machine showing an apparatus for detecting defective needles constructed in accordance with the invention.

FIG. 2 is a simplified plan view of the apparatus shown in FIG. 1.

FIG. 3 is an enlarged fragmentary vertical section taken along lines 3-3 of FIG. 2.

FIG. 4 is an enlarged simplified fragmentary view of a portion of FIG. 2 showing schematically radiant energy generating and detecting devices and several needles in plan view.

FIG. 5 is a fragmentary perspective view showing a good needle intercepting a beam of a radiant energy and the positions of a set of radiant energy generating and detecting devices.

FIG. 6 is an enlarged fragmentary perspective view similar to that of FIG. 5, but showing a needle with broken hook.

FIG. 7 shows schematically an electrical circuit used in connection with a radiant energy detecting device for activating an alarm and a stop-motion device.

FIG. 8 is a timing diagram of signals generated by defective needle detecting devices.

FIG. 9 is a simplified plan view, similar to that of FIG. 4, of an embodiment of a defective needle detecting device.

FIG. 10 shows schematically an electrical circuit used in connection with the detecting device shown in FIG. 9.

DETAILED DESCRIPTION FIGURES 1 THROUGH 3 A conventional circular knitting machine normally has a stationary bed plate 10 and a needle cylinder 12 guiding a circular row of vertically disposed needles 16. An annular sinker cap 14 coaxial with the needle cylinder 12 is disposed around the periphery of the circle defined by the needles 16 adjacent but below the top ends thereof. The sinker cap 14 supports a number of individual sinkers (not shown) which cooperate with the needles 16 to form the fabric.

Each of the needles 16 normally includes a butt 18 (best seen in FIG. 3) which extends outwardly radially from the lower end of the needle, a stem 20 extending upwardly from the butt 18, and a hook 22 formed at the top end of the needle 16 and extending outwardly radially therefrom. Each needle may also have near its upper end a latch 26 pivoted at an axis 28 for movement up toward the hook 22 and downward away from the hook 22. Although the needles 16 are shown as flat in the radial dimension, they may be of other configurations. For example, the needles may be round, or may have square crosssection in the horizontal plane. Commonly, they are made of a suitable grade of steel.

In the course of knitting, the butts 18 of the needles 16 are acted upon by cams to raise the needle or to lower them so as to engage yarn fed to them. Knitting may take place in the general area indicated at 30 in FIG. 2, but will not be described here in any detail since it is conventional and well known in the art.

In co-acting with the knitting cams, the sinkers, the yarn and the completed fabric, the needles 16 are subjected to various stresses and frictional forces. There are at least two weak points in a needle: the butt 18 and the hook 22. lfthe butt 18 is bent, broken, or otherwise damaged, the needles 16 will not be raised and lowered properly during knitting and will not properly engage yarn at the hook ends. If, on the other hand, the hook 22 is bent, broken or otherwise damaged, the needles 16 may be properly raised, but will not properly engage yarn. Thus, if either or both the butt l8 and the hook 22 of a needle or needles are damaged or defective, proper knitting will be prevented and the result will be knitting of defective fabric or possibly damage to other needles or other parts of the knitting machine.

It is important therefor to detect defective or damaged needles as early as possible, and thus the present invention is in a device, indicated generally at 32 in FIG. 2, for detecting defective needles. The device 32 uses a thin collimated beam of radiant energy which is intercepted by every needle hook which is in its proper position as the needle cylinder 12 is rotated during knitting and as the needles 16 are raised by a special cam 64.

It is possible to position the device 32 so that its beam is aligned with the needle hooks at the point where they are raised by the conventional knitting cam. However, it is preferred to raise the needles for inspection purposes at a point peripherally spaced from the knitting point, so as to avoid interference of the yarn or fabric with the beam of radiant energy, as well as to present an optimum profile of the passing needles to the radiant energy beam.

The detecting device 32 includes a source of radiant energy 50 which may, for example, be a light, and a radiant energy detector 52 which may correspondingly be a photocell. The source 50 and the detector 52 are each attached to one of the shoulders of a T-shaped arm 42 by means of a bracket 54. Each of the brackets 54 is a rectangular metal strip partially superimposed on the arm 42, then extending around either the source 50 or the detector 52, and then terminating after extending partially along the bottom end surface of the arm 42.

A vertical bolt 56 passes through appropriate apertures in each of the brackets 54 and through opening 60 in the arm 42. Each of the openings 60 is considerably larger in vertical cross-section then the thickness of the stem of the bolt 56 so as to allow adjustment of the bracket 54 and thus of the source 50 or the detector 52 with respect to the arm 42 for the purposes of aiming the beam of radiant energy. The bolt 56 is secured by means of a nut 58 positioned below the bracket 54. For aiming in the vertical plane, the bracket 54 may be bent or 'shimmed appropriately.

The source of radiant energy 50, generating a beam 68, and the detector 52 are thus in a horizontal plane which is some distance above the sinker cap 14, and the beam 68 travels along a path tangential to a circle 69 defined, in plan view, by the needles 16. As seen in FIG. 3, the width of the beam 68 is somewhat less than the width of the hook 22 which intercepts it. A typical beam width may be about twenty-five thousandths of an inch, while the typical width of the hook at the place where it intercepts the beam may be about thirty-two thousandths of an inch. As seen in FIG. 4, the beam 68 is substantially tangent to the circle defined by the hooks 22 of the needles 16, and is positioned such that most of it, if not all of it, is obstructed by a hook 22 of a good needle 16 where the needle is in the beams path. It is possible, however, to position the arm 42 such that the source 50 and the detector 52 will be in a plane inclined from the horizontal, so long as a substantial portion of the beam generated by the source 50 is traversed by the hook 22 of nondefective needles 16.

The arm 42 extends radially from the needle cylinder 12 horizontally and is pivoted by means of a pivot shaft 62 and a hinge plate 44 such that it may be raised up and away from the needle cylinder 12. The hinge plate 44 is attached by means of appropriate screws 44-a and 44-h to a vertically disposed stand 34 which is secured at its bottom end to the stationary bed plate 10 by means of a vertical bolt 36. The bolt 36 passes through an appropriately sized and countersunk bore 38 in the bed plate 10 and threads into appropriately sized and threaded opening 40 at the bottom end of the stand 34.

As best seen in FIG. 1, the source 50 and the detector 52 are positioned at a convenient height above the top end of the sinker cap 14, and the retracted needles 16 have their books substantially at the level of the sinker cap 14. A special cam 64, restrained by a cam retainer ring 66, is provided for the purpose of raising the needles such that their hooks come up to the level of the beam of radiant energy between the source 50 and the detector 52. The purpose of raising the needles 16 is to insure that the effect of a broken needle butt 18 will be demonstrated. If a butt 18 is broken or otherwise damaged, its needle 16 will not be raised by the special cam 64 in the same manner as the good needles, and this fact will be detected.

FIGURES 4 THROUGH 8 As best seen in FIG. 4, the beam of radiant energy indicated at 68 is substantially tangential in plan view to the circle defined by the hooks 22 of the needles 16. As seen in even greater detail in FIGS. 5 and 6, the beam 68 is collimated and is narrower than the dimension of the hooks 22 perpendicular to it. If a book 22 is properly in its position, the beam 68 is blocked off and does not reach the detector 52. If a hook 22 is broken, however, as shown in FIG. 6 the path of the beam 68 is not interrupted and it reaches the detector 52.

Any suitable combination of a radiant energy source and a radiant energy detector may be used. One example is a light to be used as the source 50 and a photocell to be used as a detector 52. The light beam 68 may be collimated and made sufficiently narrow by conventional means such as by the use of fiber optics.

Ifall needles 16 have their hooks in the proper position, the beam 68 will be substantially blocked off at all times and will never reach the detector 52 in full force. A part of the beam 68 may however, impinge on the detector 52 for any number of reasons: the beam may not be perfectly collimated or aimed, the beam may be somewhat wider than the hook area that intercepts it, there may be vibration which disturbs the perfection of alignment between needles and the beam. However, only a small portion of the beam 68 should reach the detector 52 for as long as every needle 16 is good and is in its proper position. The effects of this small portion of radiant energy can be compensated by use of proper electrical circuitry, as will be explained later in connection with FIGS. 7, 8 and 10. As the needle cylinder 12 is rotated, the needle 16 which is in the path of the beam 68 will start moving out of that path, but the next needle 16 will interpose itself between the source 50 and the detector 52 before the preceding needle has moved out of the path of the beam 68.

Should one of the hooks 22 not be in its proper position, however, the beam 68 will no longer be blocked, and it will reach the detector 52 in full force. A hook 22 may be absent from its proper position due to any number of causes. Any absence, however, is a defect which ought to be detected as early as possible.

The source of radiant energy 50 is supplied with power by appropriate wiring (not shown), and the detector 52 is connected by appropriate wiring (again not shown) to an electrical circuit such as the circuit diagrammatically illustrated in FIG. 7 for the purpose of utilizing the signals produced by the radiant energy detector 52. If, for example, a photocell is used as a radiant energy detector 52, it will produce different electrical signals depending on the amount and intensity of the light that reaches it. The electrical signals produced by the detector 52 are amplified by an amplifier 70, of conventional design, and are then fed into a threshold gate 72, also of conventional design, which cuts out electrical signals below a certain voltage level and passes only electrical signals over a certain voltage level.

If a photocell is used as a radiant energy detector 52, the threshold gate 72 is adjusted such that it cuts out electrical signals generated by the photocell in response to ambient lighting or to the incidence of a small portion of the beam 68 as well as electrical signals due to noise, and passes only electrical signals generated by the photocell in response to its being impinged squarely by the light beam 68.

The output'of the threshold gate 72 is delivered to the Set input of a Set-Reset (RS) flip-flop 74, also of standard design. The flip-flop 74 is normally at its zero state, that is, there is a steady voltage signal at its output labeled 0 and there is no voltage signal at its output labeled 1". When a signal appears at its Set input, that is the input labeled S, the I output of the flip-flop 74 will be energized and the voltage signal therefrom will be delivered to an alarm 76 and to a stop-motion control 78.

The alarm 76 may be a light, a bell or any other device for calling the attention of a machine operator to the fact that a needle hook is absent from its proper place and a defect is indicated. The stop motion control 78 may be any standard device for stopping the motor operating the knitting machine and causing the needle cylinder 12 to stop rotating.

Once the attention of the operator has been obtained, he may then, by means of manual reset switch 80 reset the flipflop 74 to its zero state. The alarm 76 may be deactivated by the operator in a conventional manner and, after the defect has been repaired, the motor operating the knitting machine may be restarted by appropriate manual means.

The electrical signal produced by the detector 52 is illustrated in FIG. 8, Graph 82, which is a plot of the voltage output of the detector 52 vs. time. The time instances labelled t correspond to the interception of the beam 68 by a maximum area of the hooks 22. As one hook begins moving out of the beam 68 but prior to the time of another hook coming squarely in the beam, there may be a small amount of radiant energy reaching the detector 52 and resulting in a small voltage peak at the time instances indicated at Ifa needle hook is not at its proper place, however, the voltage pealc produced by the detector 52 will be of much greater magnitude, as indicated at t, at graph 82. The threshold level of the threshold gate 72 may be adjusted such that the small voltage peaks as those indicated at times I, will be cut off and only voltage peaks such as the one indicated at t will produce output signals at the output of the threshold gate 72.

Should the beam 68 be made so narrow, and aimed so perfectly, that it is blocked at all times by passing good needles, then the output of the detector 52 will be of the shape illustrated in graph of FIG. 8. Up to the point indicated at 80-a, the graph 80 shows that the path of the beam 68 is at all times blocked off by a needle hook and the output of the detector 52 is only in response to ambient lighting and possibly includes some noise.

If a hook 22, however, is absent from its proper place, the beam 68 will not be blocked and the beam will strike the detector 52. At that time, the voltage output of the detector 52 will have the general shape of the peak indicated at 804:. When the next good needle moves in the path of the beam 68 the beam will again be blocked, and the voltage output of the detector 52 will again drop as indicated at 80-0.

The broken line parallel to the time axis indicates the voltage level to which the threshold gate 72 of FIG. 7 is adjusted in order to cut ofi any signals from the detector 52 resulting from noise or ambient lighting effects. Any voltage above the threshold level results in an output signal at the threshold gate 72.

FIGURES 9 AND 10 An alternative device for detecting the absence of needle hooks from their proper places is illustrated schematically in FIG. 9. The device includes a magnet 90, which may for example be a pennanent magnet of very small mass as to minimize the efl'ects of its inertia. The magnet is aflixed to a transducer 92 for converting variations in mechanical stresses to variations in electrical signals and may, for example, be a piezoelectric crystal or a magnetic pick-up. The transducer 92 is mounted on a housing 94 which may also serve as a housing for associated electrical circuitry such as the circuitry shown in block schematic form in FIG. 10. The housing 94 may in turn be appropriately mounted onto a supporting structure similar to the one used for mounting the radiant energy detecting device discussed above.

As the needles 16, which are normally of steel or other magnetic material, pass by the magnet 90 as they are raised by the special cam 64, the magnet is deflected by each passing needle from its original position at which the crystal 92 is unstressed. If all needles are substantially of the same configuration and in substantially the same position with respect to the magnet 90 as they pass by it, the magnet 90 will be deflected in substantially the same manner by each passing needle 16. The mechanical stresses on the piezoelectric crystal 92 will then be substantially the same for each properly positioned and properly constituted needle, and the crystal will produce voltage peaks such as the peaks 84-a, 84-h and 84-c of graph 84 in FIG. 9.

Should a needle hook be absent from its proper place, however, such as schematically illusu'ated at needle l6-a at FIG. 9, the magnet 90 will be deflected less and the voltage peak produced by the piezoelectric crystal 92 will be of lesser magnitude as shown at 84-dof graph 84 in FIG. 8.

A conventional demagnetizer 91 energized by a power source 93 may be spaced peripherally from the housing 94 and adjacent to the path of the needles 16 to remove from the needles any residual magnetization which may cause a latch 26 to stick improperly to a hook 22 or a stem 18. The demagnetizer 91 and the power source 93 may be appropriately supported on the bed plate 10.

The electrical circuitry associated with the crystal 92 is shown in FIG. 10 where the crystal is shown as block 92 labeled DETECTOR. The voltage output of the crystal 92 which is of the shape illustrated at graph 84 of FIG. 8 is delivered to a conventional amplifier 93 and the output of the amplifier is delivered to the input of a one-shot multivibrator 96 which has adjustable time constant.

The multivibrator 96 is of standard design, with complementary and l outputs and a pulse input, and its characteristics are such that when pulsed at its input by a voltage pulse of sutficient magnitude, it produces a voltage level at its output labeled l for a time interval defined by its time constant. The amplifier 93 is adjusted such that voltage peaks such as 84-a, 84-b and 84-c of FIG. 8 correspond to voltage signals at the output of the amplifier 93 whose magnitude is just sufficient to trigger the multivibrator 96, but voltage peaks of lesser magnitude do not result in signals able to trigger the multivibrator 96.

If the multivibrator 96 is pulsed by a sufliciently strong voltage signal during the time interval defined by its adjustable time constant, a new time interval begins. If it is not pulsed during that time interval, the voltage level at its 1 output drops to 0 and a voltage signal appears at its output labeled 0". The 0 output of the multivibrator 96 is connected to an alarm 76 and to a stop-motion control 78 which are similar to and operate similarly as the alarm and the stop-motion device shown in FIG. 7 and discussed in connection thereto.

Thus, if every needle passing by the magnet 90 has its hook in the proper position, the transducer 92 will keep producing voltage pulses such as those illustrated at 84-a, 84-h and 84-c in FIG. 8 and the multivibrator 96 will be pulsed before its time interval ever gets a chance to run out. But, if there is a dcfective needle which does not have its hook at the proper place, the signal produced by the transducer 92 will be of the general shape illustrated at 84-41 in FIG. 8 (i.e., insufficient to trigger the multivibrator 96) and the time constant of the multivibrator 96 will run out before the next adequate pulse 84-e comes about.

When the time interval of the multivibrator 96 runs out before it receives an adequate triggering pulse, a voltage signal appears at its 0 output and the alann 76 and the stop-motion control 78 are activated in the same manner as described in connection with FIG. 7.

An electrical circuit such as the one shown in FIG. 10 may also be used in conjunction with a radiant energy device for detecting defective needles, if the radiant energy beam 68 is not tangential to the circle of needle hooks but is in a different plane. For example, if the beam 68 is in a plane perpendicular to the plane defined by the circle of needle hooks then, provided an inverter is connected to the output of the detector 52, the signals at the output of the inverter will be of the shape illustrated in graph 84 of FIG. 8 and defective needles can be detected by operating the circuit of FIG. 10 similarly to its operation in conjunction with the detecting device of FIG. 9.

When a knitting machine equipped with a defective needle detector as described above is turned on after having been stopped, the operation of the detector may be delayed until the needles reach their steady state speed so as to avoid undesirable transient efiects. To this end, the machine operator may turn on the detector manually several seconds after the knitting machine motor has been turned on. Preferably, however, the power line to the detector is connected to a conventional time delay relay (not shown) which is energizable upon turning on the knitting machine motor to connect power to the detector for a predetermined time delay allowing the needles to reach steady state speed.

We claim:

1. Apparatus for detecting defective needles in a knitting machine having a regular array of needles, comprising:

a. means for generating a beam of radiant energy;

b. means for producing relative motion between the beam and the needles so that the needles successively intersect and at least partially block the beam;

c. means for detecting the beam, said means located on the opposite side of the intersecting needles from the generating means, said detecting means producing a signal varying as a function of the radiant energy impinging thereon; and

d. means responsive to an irregular variation in said signal for indicating that a needle is defective.

2. Apparatus as in claim 1 including:

d. means for discriminating between, on the one hand, a first signal produced by the detecting means while said beam is intersected by a needle which is in its proper position, and, on the other hand, a second signal produced by the detecting means while said beam is directed toward the proper position of a needle which is not in its proper position; and

e. an alarm and a stop-motion device, each energizable by said discriminating means upon the detection by said discriminating means of said second signal.

3. Apparatus as in claim 1 wherein said generating and said detecting means are positioned for directing the beam of radiant energy along a path intersected by the needle hoods, said detecting means producing a first type signal to correspond to a needle which has its hook in the normal position while intersecting the beam and producing a second type signal to correspond to a needle whose hook is absent from its normal position.

4. Apparatus as in claim 1 wherein said needles are in a circular arrayof needles, and includin g:

a. means for rotating the needle array with respect to the beam and means for raising needles successively as the circular array of needles is rotated; and wherein b. the generating and the detecting means are positioned for directing the beam of radiant energy along a path intersected by the hooks of the needles as they are raised successively by said raising means.

5. Apparatus as in claim 1 wherein means is provided for collirnating the beam of radiant energy to a width less than the width of a needle at the point where the beam is intersected by the needles.

6. Apparatus as in claim 1 wherein said array of needles is a circular array and including means for supporting said generating means and said detecting means entirely outside the space defined by said circular array of needles.

7. Apparatus as in claim 6 wherein said beam is parallel to a tangent of said circular array of needles.

8. Circular knitting apparatus, including a stationary support, a circularly disposed array of vertically movable needles of magnetic material, each needle having a hook at its top end, and means for rotating said array of needles; the improvement comprising:

a. magnet means for generating a magnetic field intercepting the array of needles, said magnet means positioned near the normal path of travel of the needles as they are rotated;

b. a transducer for converting mechanical stresses to electrical energy, said transducer being rigidly connected to said magnet means; and

c. means connected to said stationary support for supporting the transducer,

whereby said magnet means is affected in substantially the same manner by each passing needle which is in its proper position and is affected in a different manner by a passing needle which is not in its proper position, and whereby said transducer produces a first electrical signal in response to passing needles which are in their proper positions and a second, distinctively different electrical signal in response to needles which are not in their proper positions.

9. Apparatus as in claim 8 wherein said magnet means is positioned adjacent the normal path of travel of the needle b. means for positioning said magnet means adjacent the normal path of the hooks of the raised needles,

whereby needle defects afi'ecting the ability of a hook to be properly raised are detected.

11. Apparatus as in claim 8, including demagnetizing means positioned along the path of the needles past said magnet for removing residual magnetism from the needles.

l l i

Claims (11)

1. Apparatus for detecting defective needles in a knitting machine having a regular array of needles, comprising: a. means for generating a beam of radiant energy; b. means for producing relative motion between the beam and the needles so that the needles successively intersect and at least partially block the beam; c. means for detecting the beam, said means located on the opposite side of the intersecting needles from the generating means, said detecting means producing a signal varying as a function of the radiant energy impinging thereon; and d. means responsive to an irregular variation in said signal for indicating that a needle is defective.

2. Apparatus as in claim 1 including: d. means for discriminating between, on the one hand, a first signal prodUced by the detecting means while said beam is intersected by a needle which is in its proper position, and, on the other hand, a second signal produced by the detecting means while said beam is directed toward the proper position of a needle which is not in its proper position; and e. an alarm and a stop-motion device, each energizable by said discriminating means upon the detection by said discriminating means of said second signal.

3. Apparatus as in claim 1 wherein said generating and said detecting means are positioned for directing the beam of radiant energy along a path intersected by the needle hoods, said detecting means producing a first type signal to correspond to a needle which has its hook in the normal position while intersecting the beam and producing a second type signal to correspond to a needle whose hook is absent from its normal position.

4. Apparatus as in claim 1 wherein said needles are in a circular array of needles, and including: a. means for rotating the needle array with respect to the beam and means for raising needles successively as the circular array of needles is rotated; and wherein b. the generating and the detecting means are positioned for directing the beam of radiant energy along a path intersected by the hooks of the needles as they are raised successively by said raising means.

5. Apparatus as in claim 1 wherein means is provided for collimating the beam of radiant energy to a width less than the width of a needle at the point where the beam is intersected by the needles.

6. Apparatus as in claim 1 wherein said array of needles is a circular array and including means for supporting said generating means and said detecting means entirely outside the space defined by said circular array of needles.

7. Apparatus as in claim 6 wherein said beam is parallel to a tangent of said circular array of needles.

8. Circular knitting apparatus, including a stationary support, a circularly disposed array of vertically movable needles of magnetic material, each needle having a hook at its top end, and means for rotating said array of needles; the improvement comprising: a. magnet means for generating a magnetic field intercepting the array of needles, said magnet means positioned near the normal path of travel of the needles as they are rotated; b. a transducer for converting mechanical stresses to electrical energy, said transducer being rigidly connected to said magnet means; and c. means connected to said stationary support for supporting the transducer, whereby said magnet means is affected in substantially the same manner by each passing needle which is in its proper position and is affected in a different manner by a passing needle which is not in its proper position, and whereby said transducer produces a first electrical signal in response to passing needles which are in their proper positions and a second, distinctively different electrical signal in response to needles which are not in their proper positions.

9. Apparatus as in claim 8 wherein said magnet means is positioned adjacent the normal path of travel of the needle hooks, whereby said transducer produces a first electrical signal to correspond to needles which have their hooks in the proper position, and a second electrical signal to correspond to needles whose hooks are absent from their normal positions.

10. Apparatus as in claim 8 including: a. means for raising the needles as they approach the magnetic means; and b. means for positioning said magnet means adjacent the normal path of the hooks of the raised needles, whereby needle defects affecting the ability of a hook to be properly raised are detected.

11. Apparatus as in claim 8, including demagnetizing means positioned along the path of the needles past said magnet for removing residual magnetism from the needles.

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