Device for detecting knot-like thick places in travelling textile threads

Novel device for detecting knot-like thick places in travelling textile threads, comprising a plate-shaped or rectangular vibratory member which is fixed at one end and has a straight edge at its other end. A plate-shaped piezoelectrical transducer element is fixed at one of the major surfaces of said vibratory member. A thread guiding member having a straight edge is arranged in essentially parallel relationship to the straight edge of the vibratory member such as to form a thread passage gap between said straight edges. Means adjust the width of said thread passage gap, and a case or support structure is provided for receiving the vibratory member, electromechanical transducer element and thread guiding member.

BACKGROUND OF THE INVENTION 
The present invention relates to a new and improved construction of a 
device for detecting knot-like thick places in travelling textile threads 
or the like. It is known to use capacitive or optoelectrical transducers 
for detecting thick places in textile threads travelling at textile 
machines or through a testing device, and to process the electrical 
signals generated by the transducers in an electronic circuitry which 
produces output signals indicative of the presence of such thick places. 
Moreover, from German patent No. 1,101,018 there is known a 
mechanoelectrical device for detecting thick places and knots in threads 
or rovings and twisted yarns, where the thread material to be tested 
travels through a slot of a guage which is set to the nominal thickness 
value of the thread material, and where an electrical contact system is 
actuated, by means of resilient feeler members, when said nominal 
thickness value is exceeded, causing the thread travel to be stopped 
and/or a counting device to be tripped. 
Capacitive or optoelectrical transducers or sensing devices which operate 
without touching the thread work accurately and without inertia even at 
high yarn speeds, however, they are expensive to manufacture. On the other 
hand, mechanoelectrical sensing devices exhibit a certain amount of 
sluggishness or inertia owing to the relatively great mass of the feeler 
member touching the thread. Thus, such mechanoelectrical sensing devices 
do not work in a satisfactory manner at high yarn travel speeds. 
SUMMARY OF THE INVENTION 
It is a primary object of the invention to provide a mechanoelectrical 
sensing device for detecting knot-like thick places in travelling yarns 
which has low inertia and operates accurately even at high yarn speeds. 
It is a further objective of the invention to supply a sensing device which 
is simple and may be manufactured with low expenditure. 
These and other objects will be apparent as the description proceeds may be 
realized by the inventive sensing or detecting device comprising a support 
structure, a vibratable plate-shaped or cantilever member whose free end 
is formed with a first straight edge, a mechanoelectrical transducer 
element supported by said cantilever member and responsive to vibration 
thereof, a thread guide member having a second straight edge arranged in 
opposite relationship to said first straight edge, such that a thread 
passage gap is formed between said first and second straight edges, and 
means for adjusting the width of said thread passage gap.

DETAILED DESCRIPTION OF THE INVENTION 
With reference to FIGS. 1 and 2, a casing 1 which serves as a support 
structure for the other components of the sensing device is designed as an 
oblong rectangular receptacle. A substantially rectangular resilient 
tongue or cantilever member 2 is clamped at one of its ends in a bearing 
block 8, by means of a cover plate 9. The other free end 4 of tongue 2 is 
bent over such as to form a rounded first straight edge 7. Free end 4 is 
laterally extended over both of the longitudinal edges of tongue 2, as 
shown in FIG. 1. Beneath free end 4, there is arranged in casing 1 a 
damping material 10 which embraces tongue 2 and at the same time prevents 
dust and dirt from penetrating into the lower part of casing 1. The 
damping material 10 preferably consists of porous soft elastic material, 
such as foam or sponge rubber. At one of the major faces of tongue 2 
between bearing block 8 and damping material 10, there is attached a 
rectangular plate-shaped piezoelectrical transducer element 3, e.g. by 
soldering or cementing. 
The electrodes and electrical connections of transducer element 3 which are 
not shown may be formed in conventional manner. 
In the upper part of casing 1 there is placed a rod-shaped thread guide 5 
of semicircular cross-section, forming a second straight edge 6 which is 
arranged in parallel and opposite relationship to the first straight edge 
7 of resilient tongue 2 such as to form a thread passage gap between said 
straight edges 6, 7. Thread guide 5 is made of a hard material, such as 
ceramic oxide. Thread guide 5 is mounted in casing 1 movable in the 
longitudinal dimension of tongue 2, so that the distance d or width of the 
gap between the first and second straight edges 6 and 7, respectively, may 
be changed continually. For this purpose, thread guide 5 is fixed to a 
block-shaped slide member or slider 11 provided with an internal thread 
12. A set screw 13 whose non-referenced shank passes through an equally 
non-referenced bore in the upper wall of casing 1 engages with the 
internal thread 12 of slider 11. At the shank of set screw 13 there is 
fixed a collar 14 sunk into the upper wall of casing 1 and covered by a 
counter flange 15 fixed to the outer face of casing 1, in such a manner 
that set screw 13 is prevented from axial displacement. Slider 11 is 
slidably guided in a recess 16 of casing 1 such as to be secured against 
rotational motion. 
The open side of casing 1 is covered by a plate-shaped cover plate 17 which 
may be fixed to casing 1 by screws (not shown) or equivalent fastening 
means. As may be seen in particular from FIG. 2, there are provided, on 
both sides of the gap between the first and second straight edges 6 and 7, 
respectively, a first window 18 in the bottom of casing 1, and a second 
window 19 in lid 17 in covering relationship with first window 18. The 
width of the windows 18, 19 in the longitudinal direction of casing 1 may 
be dimensioned such that a thread F can be guided over thread guide 5 at 
an obtuse angle without contacting the edges of windows 18, 19 as shown in 
FIG. 2. Alternatively, guide members (not shown) made of ceramic oxide may 
be used and inserted in windows 18, 19, which, in this event, as well as 
the guide members, should be shaped circular. 
Tongue 2 is preferably made of a thin resilient material, such as steel, 
bronze or brass, in order to present as little inertia as possible when 
tongue 2 is deflected by a knot appearing in the travelling thread. By way 
of example, the mechanical vibratory system comprising tongue 2 and 
transducer element 3 may have a fundamental frequency far below 100 Hz 
when the thickness of tongue 2 is about 0.1 mm and the free length thereof 
is 20 mm. However, with the applications which will still be described, it 
is also possible to make use of the overtone vibrations of said vibratory 
system. 
FIG. 3 shows an electronic circuitry 21-26 adapted for evaluating the 
output signal of the sensing device illustrated by FIGS. 1 and 2, when 
such sensing device is used on textile machines which produce spurious 
noise or sound conducted through solids, and for producing switching and 
indicating signals. Input stage 21 comprises an impedance converter 
connected to the piezoelectrical transducer element 3 shown in FIGS. 1 and 
2, which impedance converter may be fitted with a fieldeffect transistor. 
Input stage 21 is followed by a narrow band amplifier 22 comprising, by way 
of example, two stages and tuned to a relatively narrow range of 
frequencies in order to preclude spurious frequencies. Said narrow range 
includes one of the natural frequencies of the mechanical vibratory system 
comprising tongue 2 and transducer element 3. The amplification factor or 
gain of said narrow band amplifier 22 may be, by way of example, about 
100. A stage 23 having controllable threshold response, e.g. a 
Schmitt-trigger, follows narrow band amplifier 22. The threshold value of 
stage 23 is controllable by a setting device 24, such as an adjustable 
resistor, in a range from some millivolts to some volts. A pulse circuit 
25, e.g. a monoflop or oneshot, is connected to the output of threshold 
responsive stage 23. 
An amplifier 26 comprising two output terminals is connected to the output 
of pulse circuit 25 and forms an output stage of electronic circuitry 
21-26. One of said output terminals is connected to a switching device 27, 
e.g. a relay 27, and the other output terminal is connected to an 
indicating or counting device 28, e.g. a lamp or a light emitting diode. 
The switching device may be used for stopping the textile machine when a 
knot appears in the travelling thread. 
When the sensing device shown in FIGS. 1 and 2 is going to be used, the 
distance d is adjusted, depending upon the cross-sectional dimension of 
thread F, such that the travelling knot-free thread has no contact with 
the edge 7 of tongue 2, however, all knots whose diameter is greater than 
a certain threshold value will touch tongue 2 and cause vibration of same, 
inducing an output signal of transducer element 3 shaped as a damped 
electrical vibration. The component thereof filtered out and amplified in 
narrow band amplifier 22 gives rise to a short trigger pulse in threshold 
responsive stage 23, or a series of such pulses, the first of which trips 
pulse circuit 25 so that the latter generates a switching pulse of 
definite duration, e.g. 25 milliseconds. This switching pulse is further 
processed in output stage 26 in order to actuate switching device 27 
and/or indicating device 28. 
The inventive sensing device may be used for assessing knots in weft 
threads on weaving machines, e.g. gripper weaving machines, such as rapier 
looms, gripper shuttle looms and jet looms, where high speeds occur when 
the weft thread is being inserted. With this application it is important 
that any knot in the weft thread is detected early enough for stopping the 
loom before the knot enters the weaving shed, or at least that the loom is 
stopped in a position where the knot may be found in the open shed such as 
to be easily removed. 
Moreover, the sensing device may be used on spinning and winding machines 
for assessing or counting knot-like thick places or knots. 
While there is shown and described a present preferred embodiment of the 
invention, it is to be distinctly understood that the invention is not 
limited thereto, but may be otherwise variously embodied and practiced 
within the scope of the following claims. ACCORDINGLY,