Electrical warp thread-monitoring apparatus for a loom

An electrical warp thread-monitoring apparatus for a loom wherein a multiplicity of warp threads each carry a drop wire which, in the presence of thread rupture, connects a pair of current rails which are mutually electrically insulated from one another, and thus, closes an alternating-current circuit. The alternating-current circuit possesses at its input side an alternating-current voltage source which can be connected by means of a bridge rectifier with the current rails. This bridge rectifier or rectifier circuit forms the input of a voltage-dependent pulse converter following which there is connected in circuit a RC-integration stage and a threshold value-switching stage, which also then produce a shutdown or stop signal when the contact locations are contaminated and prevent generation of a shutdown or stop signal when contaminants, leakage currents and dancing drop wires produce short pulses.

BACKGROUND OF THE INVENTION 
The present invention broadly relates to stop motions for looms and, in 
particular, concerns a new and improved construction of an electrical warp 
thread-monitoring apparatus for a loom. 
The warp thread-monitoring apparatus of the present development is of the 
type comprising a multiplicity and drop wires each carried by a warp 
thread and current rails which extend over the entire width of the warp 
threads. In the presence of rupture of a warp thread the current rails can 
be electrically connected with one another by the related drop wire which 
has dropped. The current rails are located conjointly in an 
alternating-current circuit in order to produce a stop or shutdown signal 
for the loom in the presence of warp thread rupture. 
An entire host of requirements are placed upon equipment of this type, 
which for reasons of safety also must be maintained and which particularly 
arise by virtue of the varying surounding conditions at the region of the 
drop wires and the current rails during the weaving operation. Such 
conditions require, among other things, a spark-free contact to be made 
between the drop wires and the current rails. Additionally, there is 
required a positive functioning of the current circuit, and thus, a 
positive generation of a stop or shutdown signal even in the presence of 
increasing contamination during operation of the loom. Additionally, there 
must be prevented faulty functioning due to leakage currents, for instance 
arising in the presence of increased humidity, and finally, there must be 
avoided faulty response of the monitoring apparatus due to vibrating 
(dancing) drop wires. 
None of the heretofore known electrical warp thread-monitoring apparatuses 
is however capable of satisfying all of the aforementioned requirements. 
In particular, the heretofore known warp thread-monitoring apparatuses are 
neither capable of preventing spark formation nor faulty operation in the 
presence of increasing fluff formation and/or increasing air humidity. 
Thus, in Swiss Pat. No. 555,914 there has only been proposed connecting 
into the current circuit of an electrical warp thread-monitoring apparatus 
a time-delay relay, in order to enable response of the stop motion device 
at the loom only then when a current pulse of the warp thread-monitoring 
apparatus lasts beyond a predetermined period of time. 
Furthermore, in British Pat. No. 1,054,559 there is taught to the art an 
arrangement wherein for increasing the contact between the drop wires and 
the contact rails there is employed a cold cathode tube. The employed 
circuit responds in the presence of the most brief pulses, as soon as such 
correspond to the ignition or firing potential. This is disadvantageous in 
as much as the cold cathode tubes also can be fired in the presence of 
leakage currents which, in practice, can flow between the contact rails 
due to the presence of contaminants (formation of snarls or fluff and 
moisture). Additionally, the circuit can respond in the presence of pulses 
which are formed due to vibration or dancing of the drop wires. 
In British Pat. No. 1,209,728 there is taught a circuit arrangement wherein 
an integrator stage prevents response of the circuit to short pulses. Here 
however the response time is influenced so extensively by the transfer 
resistance at the warp thread monitor-drop wire-contact, which can 
fluctuate in practice between 0 and 30 Kilohms that there is precluded any 
positive switching operation. 
SUMMARY OF THE INVENTION 
Therefore, with the foregoing in mind it is a primary object of the present 
invention to provide a new and improved construction of an electrical warp 
thread-monitoring apparatus for a loom which is not associated with the 
aforementioned drawbacks and limitations of the prior art constructions. 
Another and more specific object of the present invention aims at providing 
a new and improved construction of an electrical warp thread-monitoring 
apparatus of the previously mentioned type, which is capable of satisfying 
all of the requirements imposed thereon, even when operating over a longer 
period of time, and, in particular, insuring for a constantly positive 
function also in the presence of pronounced fluctuations of the operating 
conditions and suppressing faulty signals caused by leakage currents or 
dancing drop wires. 
Now in order to implement these and still further objects of the invention, 
which will become more readily apparent as the description proceeds, the 
warp thread-monitoring apparatus of the present development is manifested 
by the features that the alternating-current voltage source which is 
connected at the input side by means of the current rails at the 
alternating-current circuit, is operatively connected by means of a bridge 
rectifier with the input of a voltage-dependent pulse converter, whose 
output signal constitutes a base signal for the shutdown signal. 
It is preferred if a RC-integration stage is connected after the 
voltage-dependent pulse converter. Furthermore, it is advantageous if 
there is connected at the output of the RC-integration stage the input of 
a threshold value-switching stage which delivers the shutdown or stop 
signal for the loom. 
By virtue of these measures it is now possible, apart from avoiding the 
formation of any type of sparks, to maintain an approximately linear 
output voltage even with varying contact transfer resistances between the 
drop wires and the current rails, by virtue of the voltage-dependent pulse 
converter which operates with the full operating current in the saturation 
region. Hence, there is possible a response even in the presence of 
pronounced formation of snarls or fluff at the contact locations. 
Additionally, upon falling below the lower operating current threshold the 
subsequently connected integrator and the threshold value-switching stage 
can suppress at the pulse converter an output signal which is produced for 
instance by a leakage current, so that also in this case there is 
prevented any faulty response. The same current circuit, integrator and 
threshold value-switching stage additionally prevent, by virtue of their 
time-delay characteristic, the generation of a shutdown or stop signal due 
to current pulses because of dancing of the drop wires.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Describing now the drawing, reference character 10 designates the warp of a 
loom, this warp 10 being formed by a large number of mutually parallel 
warp threads 11. Each warp thread 11 carries a drop wire 12 or equivalent 
structure formed of at least partially electrically conductive material. 
Each drop wire 12 is seated by means of a web 13 upon the related warp 
thread 11. Now if a warp thread 11 ruptures, then the corresponding drop 
wire 12 drops downwards. 
All of the drop wires 12 are threaded on to a contact rail arrangement 50, 
which as a rule extends transversely across the entire loom. This contact 
rail arrangement 50 piercingly extends in a contact-free manner through 
each related window or opening 14 of each drop wire 12. In the embodiment 
under discussion, this contact rail arrangement 50 comprises a first 
current rail 15, an insulating layer 16 and a second current rail 17. The 
current rails 15 and 17 are formed of any suitable electrically conductive 
material, and the first current rail 15 extends in an upright fashion 
through the drop wires 12 and carries at its upper edge, separated by the 
insulation layer 16, the second current rail 17. 
Thus if in the presence of rupture of one of the warp threads 11 the 
related drop wire 12 drops downwards, then such drop wire comes into 
contact with the edge of its opening or window 14 both with the upper 
current rail 17 and also with one side or face of the contact rail 15. 
This produces an electrical connection between the current rails 15 and 
17, and as a result there is closed the current circuit 20 which will be 
more fully described hereinafter. 
At its input side the current circuit 20 contains an alternating-current 
voltage source 21, the one output 22 of which is electrically connected 
with the first current rail 15 and the other output 23 of which is 
connected by means of a Graetz or bridge rectifier 24 with the second 
current rail 17. 
This rectifier circuit 24 forms at its direct-current side the input of a 
voltage-dependent pulse converter 25. This pulse converter 25 can be, for 
instance, an optocoupler having a normally controlled phototransistor or a 
special transformer or a Schmitt-trigger and which converts the input-side 
half wave signals into square or topped pulses which are applied to the 
input of a RC-integration stage 26. This RC-integration or integrator 
stage 26 has connected thereafter a threshold value-switching stage 28 
which, on the one hand, operates as a time-delay element and, on the other 
hand, as a threshold value switch. Connected at the output side of the 
threshold value-switching stage 28 is an output signal amplifier 29 which, 
in the presence of warp thread rupture, delivers the shutdown or stop 
signal 30 for the loom. 
The alternating-current voltage source 21 advantageously only delivers a 
comparatively small voltage, wherein also in the presence of the greatest 
possible current, governed by the resistor or resistance R, there is 
ensured that sparks cannot form at the contact locations between a drop 
wire 12 and the current rails 15 and 17. 
Since the voltage-dependent pulse converter 25 operates at the full 
operating current in the saturation region, the square wave pulses formed 
during contact making by a drop wire 12 and appearing at the output of the 
pulse converter 25 produce an approximately linear voltage at the 
capacitor 27 of the RC-integration stage 26 even with markedly fluctuating 
current I.sub.L in the input circuit owing to different contact transfer 
resistances between the drop wires 12 and the current rails 15 and 17. 
This ensures that also then there will be reliably produced a shutdown or 
stop signal for the loom, if the contact locations between the drop wires 
12 and the current rails 15 and 17 with time are heavily covered with 
fluff or snarls. 
Upon exceeding the lower operating current limit the voltage at the 
capacitor 27 of the RC-integration stage 26 can steeply drop. In this way 
there is ensured that possible input-side leakage currents caused by 
pronounced contamination and/or high air humidity at the region of the 
current rails 15 and 17 cannot produce any undesired shutdown or stop 
signal 30. 
Furthermore, due to a preselected time-delay characteristic of the 
RC-integration stage 26 and the threshold value-switching stage 28 there 
is ensured that the previously described circuit arrangement responds with 
such a time-delay that brief current pulses caused by dancing or jumping 
around of the drop wires 12 cannot produce any shutdown or stop signal 30 
at the output side of the amplifier stage 29. 
Therefore, with the described electrical warp thread-monitoring apparatus 
it is possible to completely fulfill all of the previously mentioned 
conditions or requirements. 
While there are shown and described present preferred embodiments 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