U.S. patent number 3,908,920 [Application Number 05/380,034] was granted by the patent office on 1975-09-30 for process and apparatus for maintaining constant thread tension.
This patent grant is currently assigned to FMN Schuster & Co.. Invention is credited to Peter Hermanns.
United States Patent |
3,908,920 |
Hermanns |
September 30, 1975 |
Process and apparatus for maintaining constant thread tension
Abstract
The process and an apparatus for maintaining a constant thread
tension is disclosed for feeding a thread to a processing textile
machine. A constant air stream is blown against the thread to form
a thread loop having an apex. The displacement of the loop apex
resulting from thread speed fluctuations is monitored. The amount
of displacement of the loop apex is used as an adjusting value for
the regulation of the thread supply. The blowing operation is
effected within an open ended elongated channel. Means providing at
least two light barriers which extend in a direction across the
path of movement for the apex of the thread loop within the air
channel are used to effectuate the monitoring step. Means
associated with the light barriers are used to regulate the supply
of thread along its path of movement through the air channel to the
processing textile machine.
Inventors: |
Hermanns; Peter (Stommeln,
DT) |
Assignee: |
FMN Schuster & Co.
(Efferen, DT)
|
Family
ID: |
23499645 |
Appl.
No.: |
05/380,034 |
Filed: |
July 17, 1973 |
Current U.S.
Class: |
242/413.1;
242/147A; 242/413.3; 242/414.1; 242/417.1 |
Current CPC
Class: |
B65H
59/105 (20130101); B65H 59/385 (20130101); B65H
2701/31 (20130101) |
Current International
Class: |
B65H
59/00 (20060101); B65H 59/38 (20060101); B65H
59/10 (20060101); B65h 059/38 () |
Field of
Search: |
;242/147A,147R,45,75.51,75.52,182-185 ;250/209,561 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
1,133,810 |
|
Nov 1956 |
|
FR |
|
37-9751 |
|
Jul 1962 |
|
JA |
|
Primary Examiner: Gilreath; Stanley N.
Attorney, Agent or Firm: Markva; Neil F.
Claims
Having thus set forth and disclosed the nature of this invention,
what is claimed is:
1. An apparatus for maintaining a constant thread tension while
feeding a thread to a processing textile machine comprising:
a. housing means forming an open ended, elongated air channel,
b. means for moving a thread along a path transversely across the
air channel at one end thereof,
c. means adjacent the channel for blowing a fluid stream against
the thread to form a thread loop having an apex which moves within
the air channel,
d. at least two light barrier means disposed at laterally spaced
locations with respect to each other and extending in a direction
across the path of movement for the apex of the thread loop within
the air channel,
e. each light barrier means defining a signal point within the air
channel where an electrical signal is generated by the thread loop
as it passes by a signal point,
f. the electrical pulse signals generated by the thread loop at
both signal points being transmitted to separate inputs of a
bistable element that stores in each case the last pulse signal up
to the receipt of the next signal,
g. the output of the bistable element being connected with a
circuit and at the output of said circuit there is generated a
voltage change dictated by the pulse sequence at the bistable
element due to the pulse scanning ratio, and
h. means responsive to the electrical signals generated at the
light barriers for regulating the supply of thread along its path
of movement.
2. An apparatus as defined in claim 1 wherein
means is provided for oscillating the light barrier means.
3. An apparatus as defined in claim 1 wherein
the circuit comprises an integration step with a condenser
changeable via a first transistor and a resistance and
dischargeable by a second transistor and a resistance,
both said transistors being controlled by the output of the
bistable element.
4. An apparatus as defined in claim 1 wherein
the processing textile machine has a take-up means driven by an
electrical drive motor for taking up the thread moving along said
path and means providing a signal corresponding to the speed of the
take-up means,
the output signal of the integration step and the signal
corresponding to the speed of the take-up means are provided at the
entries of a differential amplifier which, if necessary through a
power amplifer, controls the drive motor of the take-up means.
5. An apparatus as defined in claim 1 wherein
the charging time constant and the discharging time constant of the
integration step is great relative to a cycle of movement of a
setting device.
6. An apparatus as defined in claim 5 wherein
the charging time constant and the discharging time constant of the
integration step are equal.
7. An apparatus as defined in claim 1 wherein
means are provided to effect oscillating movement of the light
barrier means, and
the charging time constant and the discharging time constant of the
integration step is great relative to a cycle of movement of the
oscillating movement of the light barriers.
8. An apparatus as defined in claim 7 wherein
the charging time constant and the discharging time constant of the
integration step are equal.
9. An apparatus as defined in claim 1 wherein
said two light barrier means constitute primary light barriers
and
there are supplemental light barriers disposed outside the region
of the primary light barriers,
the supplemental light barriers are electrically connected in the
control circuit to generate supplemental electrical signals when
the length of the thread loop passes by a signal point established
by the supplemental light barriers, and
second means responsive to said supplemental electrical signals are
provided for regulating the supply of thread along its path of
movement.
10. An apparatus for maintaining a constant thread tension while
feeding a thread to a processing textile machine comprising:
a. housing means forming an open ended, elongated air channel,
b. means for moving a thread along a path transversely across the
air channel at one end thereof,
c. means adjacent the air channel for blowing a fluid stream
against the thread to form a thread loop having an apex which moves
within the air channel,
d. at least two light barrier means disposed at laterally spaced
locations with respect to each other along the air channel and
extending in a direction across the path of movement for the apex
of the thread loop within the air channels,
e. means for oscillating the light barrier means, and
f. means responsive to the electrical signals generated at the
light barrier means for regulating the supply of thread along its
path of movement.
11. An apparatus for maintaining a constant thread tension while
feeding a thread to a processing textile machine comprising:
a. housing means forming an open ended, elongated air channel,
b. means for moving a thread along a path transversely across the
air channel at one end thereof,
c. means adjacent the air channel for blowing a fluid stream
against the thread to form a thread loop having an apex which moves
within the air channel,
d. at least two light barrier means disposed at laterally spaced
locations with respect to each other along the air channel and
extending in a direction across the path of movement for the apex
of the thread loop within the air channel,
e. each light barrier means defining a signal point within the air
channel where an electrical signal is generated by the thread loop
as it passes by a signal point,
f. the electrical pulse signals generated by the thread loop at
both signal points are being transmitted to separate inputs of a
trigger step means storing in each case the last pulse signal up to
the receipt of the next signal,
g. the output of the trigger step being connected with a circuit
and the output of the said circuit there is generated a voltage
change dictated by the pulse sequence at the trigger step due to
the pulse scanning ratio, and
h. means responsive to the electrical signals generated at the
light barrier means for regulating the supply of thread along its
path of movement.
12. An apparatus as defined in claim 11 wherein
the circuit comprises an integration step with a condenser
chargeable via a first electronic switch and a resistance and is
dischargable via a second electronic switch and a resistance,
both said electronic switches being controlled by the output of the
trigger step means.
Description
SUMMARY OF THE INVENTION
The invention relates to a process and an apparatus for maintaining
constant thread tension while the thread is being fed to a textile
processing machine such as a winding machine and the like.
It is extremely important that the thread tension of thread being
fed into a textile machine remain constant during the operation of
the textile machine. This is particularly true with textile
machines where one of several threads are being fed at the same
time such as in winding machines for the production of thread
windings of different types. Constant thread tension is applicable
to transverse spool machines and the like in which fluctuations of
the thread tension of the thread being fed occur due to the working
process. It is also important to maintain constant thread tension
in machines actually working under a constant thread speed in
which, however, due to other influences such as friction,
differences during the rerouting of the individual threads and the
like, the thread may change speed.
To permit a constant thread speed during such an operation, it is
known to use the thread tension of a thread guided in a loop as a
measured variable for the actuation of the control and adjusting
device of a thread feeding assembly. Such a prior art apparatus is
known as a dancing lever unit. In the dancing lever unit, the
thread is guided at the outer end of the dancing lever about a
guide pin or a guide roller with a looping angle of about
180.degree.. A counter force is used to retain the thread loop
resulting from a predetermined thread tension. Weights or
adjustable tension springs are used as a counter force. However,
the restoring moment may be effected electromagnetically or the
like. The actual value of the thread tension is covered by the
dancing lever. Fluctuations resulting from the dancing lever are
corrective values for the control system so that the ratio of the
thread speed at the supply point of the processing machine to the
thread feeding speed may be kept constant subject to the thread
tension adjusted at the dancing lever.
The dancing arm is a guide element with mass and its dynamic
inertia is so great that it cannot cover short-time thread tension
fluctuations. The guide roller provided at the end of the dancing
lever is a body rotating with a high speed and due to its moment of
inertia, it cannot react on short-time changes of the thread speed.
Moreover, friction at the guide rollers or at the guide pin of the
dancing lever do not permit small thread tensions with high thread
speeds. Above all, with transverse spool machines, short-time
thread speed variations occur at the turning points of the winding
assembly so that considerable thread tension peaks may be caused
while the inert dancing lever does not react.
In other winding machines, the thread is guided to and fro in an
oscillating motion from a stationary supply point to the spool.
With these machines it is necessary to compensate for a large
distance existing between the stationary supply point and the
spool. In other words, there must be established a considerable
length for the so-called thread triangle in order to reduce thread
tension peak at the turning points. As a result thereof, the
building height of the machine is considerable. It is extremely
important to keep the thread tension constant during the feeding of
the filament to the processing machine because changes of the
thread tension will adversely influence the final product being
produced.
PURPOSE OF THE INVENTION
The primary object of the invention is to provide a method and an
apparatus for maintaining a constant thread tension during the
feeding of a thread to a processing machine with a high sensitivity
for the control of the adjustment.
Another object of this invention is to provide a method and
apparatus which easily and safely covers short time fluctuations of
the thread speed having an effect on the thread tension.
A further object of this invention is to use a thread guided in a
loop wherein the change of the loop length is a major variable for
operation of a control or adjusting device of the thread supply
assembly.
A further object of this invention is to provide a mechanism for
maintaining constant thread tension through the use of a
substantially massless operation.
SUMMARY OF THE INVENTION
These objects and other advantages are accomplished through the use
of the process and apparatus as disclosed herein. The thread loop
is formed by blowing the thread being fed with a constant air
stream. Contactless scanning elements providing light barriers are
used to monitor the displacement of the loop apex resulting from
thread tension fluctuations. The displacement of the loop apex is
used as corrective value for the adjustment of the thread supply
assembly.
An apparatus made in accordance with this invention includes an
open-ended channel housing forming a channel having a long
extension. An inlet aperture and an outlet aperture are provided at
the end of the channel housing opposite the open end. The thread
passes into the inlet aperture through the open-ended channel and
out of the outlet aperture. Means is provided for establishing an
air stream between the inlet and outlet apertures and against the
thread so that a loop is formed in the thread. The apex of the loop
is located within the channel. At least two consecutive light
barriers or the like are provided within the area of the loop apex
of the thread. The light barriers are connected with a control
device for a supply assembly which supplies the thread to the
processing machines. The channel housing or walls may consist of
transparent material thus permitting observation at any time of the
loop and the position of the reversing arc or apex of the loop.
A thread delivery unit to be controlled may be provided before the
blowing device so that it feeds a thread at a constant speed. It is
also possible to have the control assembly act on a thread delivery
unit located behind the blowing device.
Another feature of the invention is directed to the manner in which
the desired supply control is effectuated. Each time the reversing
arc of the loop apex passes through the light barriers, an
electrical signal is applied to separate inputs of a trigger step
circuit which always stores the last signal up to the receipt of
the next signal. The outlet end of the trigger step circuit may be
connected with a circuit at the output of which a voltage or
voltage change subject to the impulse scanning ratio of the impulse
signal sequence generated at the trigger step circuit is
caused.
It is necessary for such a control that the reversing arc of the
thread loop constantly moves to and fro between the two light
barriers. The adjustment is made in such a way that the thread
tension differences caused due to the movement of the setting
device, will allow the signal points to pass about a reversing arc
of the loop so that during one working cycle of the setting device,
both signal points are normally surpassed. As a consequence
thereof, there is created a constant impulse sequence, the scanning
ratio of which, i.e. the ratio impulse: impulse interval, may be
used to control a thread delivery unit. The evaluation of the
scanning ratio is carried out with the integration step generating
a direct voltage in accordance with the effective value of the
impulse sequence.
In cases where the thread tension in the processing machine is
constant from the beginning, the blowing device for the control and
adjustment of the constant thread tension may be used in such a way
that the light barriers commonly oscillate to and fro. The change
of length of the thread loop otherwise achieved is replaced by the
oscillation or swing of the light barriers within a predetermined
area to permit operation with the control device. It is also
possible to generate artificial thread fluctuations which are
constant, e.g.
The control circuit may be designed as an integration step with a
condenser chargable via a first electronic switch and a resistance
dischargable via a second electronic switch and a resistance. Both
of the electronic switches are controlled from the output end of
the trigger step circuit. In other words, the condenser is charged
during the time when the pulses are generated by the trigger step
while it is discharged for the remaining time or vice versa. The
charging time constant and the discharging time constant are large
relative to a period of movement of the setting device and,
consequently, large with respect to the pulse frequency expected
normally. This is necessary to ensure that no complete discharge of
the condenser takes place between two pulses.
The output signal of the integration step and a signal
corresponding to the speed of the delivery unit or to the spool
respectively are connected to the inputs of a differential
amplifier which, optionally via a power amplifier, controls the
drive motor of the spool or the like. The output voltage of the
integration step, the change of which is a measure for the
mechanical thread tension, is compared to the output voltage of the
tacho-generator. The differential signal controls the drive
motor.
BRIEF DESCRIPTION OF DRAWINGS
Other objects of this invention will appear in the following
description and appended claims, reference being made to the
accompanying drawings forming a part of the specification wherein
like reference characters designate corresponding parts in the
several views.
FIG. 1 is a schematic sectional view of the thread travel through a
blowing device to a winding device in accordance with this
invention,
FIG. 2 is a sectional view along line II--II of the blow device of
FIG. 1,
FIG. 3 is a schematic circuit diagram of the controller used with a
device made in accordance with this invention,
FIG. 4 is a plan view of a further application of the invention,
and
FIG. 5 is a schematic cross-sectional view of another embodiment of
a blowing device made in accordance with this invention.
DESCRIPTION OF SPECIFIC EMBODIMENTS
More specifically, referring to the drawings, a constant tension
blowing apparatus, generally designated 12, is used to determine
and adjust the tension of the thread 10 being supplied at a
constant speed from a motor driven pulley 11. The thread 10 passes
through the constant tension device 12 over the guide pin 13 and
thread guide 14 and is wound up on spool 15. Spool 15 is driven by
the motor 16 by way of the gear 17 which also drives the thread
roller 18 causing the control of the thread guide 14 which has an
oscillating to and fro movement. The direction of the oscillating
movement of thread guide 14 is transverse to the direction in which
the axis of the spool 15 extends. The speed of movement for the
thread guide 14 is subject to the speed of the spool 15 due to the
coupling via the gear 17.
In this specific embodiment, the assembly 12 includes a housing 20
forming a channel with a rectangular cross-section and having an
opening 21 at the front side thereof. At the other end of the
channel housing 20 is an aperture 22 into which is blown an air
stream from an air supply 23 by a nozzle-shaped outlet aperture 24.
Openings 25 and 26 are disposed at the narrow sides of the channel
housing 20 to feed and remove thread 10 as shown in FIG. 1.
The thread 10 enters directly into the channel 20 near the outlet
apertures 24. A loop is formed in the thread 10 by making a reverse
arc 27 of 180.degree.. Thread 10 runs out of the channel housing 20
through the opening 26 at the other narrow side thereof near the
outlet apertures 24. The thread 10 then goes to a subsequent
processing machine, e.g. a winding machine, by way of guide pin 13.
If desired, a brake mechanism can be intercalated.
Two light barriers 28 and 29 are disposed on the middle axis of the
broad sides of the channel housing 20 approximately in the center
of the length of the channel 20. The light barriers 28 and 29 scan
the inside of the channel 27 and are interrupted by the reversing
arc 27 of the thread 10 when the thread loop moves across the path
of either of the light barriers 28 and 29 if the thread 10 has the
corresponding length. Additional light barriers 30 and 31 are
disposed on opposing opposite sides of the light barriers 28 and 29
and are in alignment therewith as shown in FIGS. 1 and 2 for
effecting a quick and momentary change of the speed of the motor 16
when there are large changes of length in the thread loop.
Air is blown through the outlet apertures 24 into the inside space
of the channel housing 20 which has a slot shaped cross-section.
Due to the air current, the thread loop is tensioned so that the
reversible arc 27 takes its greatest distance possible from the
lower channel end 22. Means may be provided for adjustably varying
the force of the blown air stream.
The reversing arc 27 in the thread loop moves along the length of
the channel housing 20 during the operation of the processing
meachine which is disposed down steram of the assembly 12. For
example, the processing machine may require a periodic change in
the thread speed during its operation. It is during this operation
of this processing machine that the reversing arc 27 is movably
displaced by the air stream blown into the channel housing 20. A
channel housing 20 may be disposed vertically or obliquely as
desired.
The location of the light barriers 28 and 29 along the channel
housing 20 and their spacing therebetween is dimensioned so that
the reversing arc 27 may exceed the light barriers 28 and 29 in a
predetermined area. The sensitivity of the light barriers 28, 29,
30 and 31 may be adjusted such as to cover the finest titers up to
15 den., and, if desired, below that value. The effective area of
the light barriers 28, 29, 30 and 31 is very small against the
total area covered by the reversing arc 27 so that the light
barrier signals are short pulses.
The wiring diagram of FIG. 3 is for the controller which performs
the evaluation of the signals from the assembly 12. The light
barrier 28 consists of a light 33 and phototransistor 35 provided
in series with a resistance 35 at the supply direct voltage. The
light barrier 29 is composed of light 36 and phototransistor 38
provided in series with a resistance 37 at the supply direct
voltate. The collector of phototransistor 34 is connected at input
40 of a bistable trigger step 36a. The input 43 of trigger step 36a
is connected to the collector of phototransistor 38 via a coupling
condenser 37a. The trigger step 36a has a storage function and it
keeps its switch position with a pulse trigger as long as the
trigger pulse appears at the other input concerned.
The output 39 of trigger step 26a is connected to a current
constant step or counter-contact step, generally designated 44. The
current constant step consists of two series connected
complementary transistors 45 and 46 and the resistances 47, 48, 49,
47a, 48a, and 49a are necessary for the adjustment of the
operational points. The connectors of the transistors 45 and 46 are
placed at different supply potentials via resistances 49 and 49a,
respectively, and are interconnected and connected with the
condenser 50. The other connection of the condenser 50 is placed at
the minus potential.
The voltage of condenser 50 is compared to the output voltage of a
tacho-generator 19 in the differential amplifier 51. The
differential amplifier 51 is connected via a control unit 52 with a
thyristor power amplifier 53 connected in series with drive motor
16 and the output of which is determinative for the speed of drive
motor 16.
The operation of the controller is as follows:
First, it is assumed that the supply speed of the thread 10 is
equal to the minimum winding speed on the spool 15. As explained
hereinabove, the reversing arc 27 then moves between a minimum and
maximum point which are both outside the area of the light barriers
28 and 29. Therefore, there are generated pulses at the light
barriers which trigger the trigger step 36a each time that the
thread passes through the light barriers 28 and 29.
If the reversing arc 27 of the thread 10 passes through the upper
light barrier 29, the output 39 of the trigger step 36a is turned
on. When the arc 27 passes through the lower light barrier 28, the
output 39 is turned off. Due to the quick change between the upper
and lower reversible point of the reversing arc 27, there is caused
a square voltage of the output of the trigger step 36a. The pulse
scanning ratio of the trigger step 36a is subject to the medium
position of the reversing arc 27 within the channel housing 20.
The square signals are transmitted to the current constant step 44
and there the signals alternatively cause the opening of
transistors 45 and 46 constituting electronic switches. If the
transistor 46 is conductive, condenser 50 is charged via transistor
46 and its emitter resistance 46a. If, however, transistor 46 is
blocked, transistor 45 is conductive and the condenser 50 is
discharged by the transistor 45 and its emitter resistance 49. The
time constant of the condenser charging is dimensioned so as to be
great against the time of an impulse ensuring the formation of a
direct voltage at condenser 50 which is only constant in case of a
pulse ratio of 1:1 while it either constantly increases or
decreases otherwise. This direct voltage is at the input of the
differential amplifier 51 at the other end of which the voltage of
the tacho-generator 19 is located. The differential voltage is at
the input of the control device 52.
When the thread supply is equal to the medium speed at the
processing machine, e.g. winding up speed, the pulse scanning ratio
at the trigger step output 39 is first 1. In other words, there is
a constant voltage at condenser 50 corresponding to the voltage of
the tacho-generator 19. Thus, the drive motor 16 keeps its speed.
If the diameter of the spool 15 is greater, the winding speed
increases. As a result thereof, the central position of the
reversing arc 27 is shifted in direction toward the nozzle 24. The
influence on the two light barriers 28 and 29 is no longer
symmetric and thus causes an asymmetric square voltage at the
trigger step output 39. Therefore, the average value of the voltage
at the condenser 50 constantly decreases so that the voltage at the
output of the differential amplifier 51 also decreases. The speed
of the motor 16 and the winding speed of the spool 15 are lowered
accordingly.
In other words, the control always becomes effective with the aim
of establishing a pulse scanning ratio of 1:1. If this ratio is
established, the voltage at the condenser 50 is constant. The
absolute height of said voltage does not play a primary part. It
decreases with increasing spool size because the equilibrium
between the condenser voltage and the voltage of the
tacho-generator 19 changes to smaller voltage values with an
increasing spool 15.
The device of this invention permits the quick and exact control of
the winding speed. In order to keep the amount of air necessary for
the operation of switch system 12 as small as possible, it should
be possibly avoided to deviate threads 10 between the supply pulley
11 and the thread intrance into the air channel. This is especially
important if small tractions of up to 0.5g with high speeds shall
be obtained for processing fine deniers.
The different yarn types require different thread winding forces.
The traction upon discharge from the air channel may be influenced
by changing the amount of air injected per unit of time.
Preferably, one will operate with air amounts as small as possible
in order to obtain a low discharge traction. This small discharge
traction may be realized by a brake (not shown) on the desired
winding traction. The brake may be connected with the winding unit
so that the thread winding traction decreases with increasing
diameter.
It has been found that the distance between the assembly 12 and the
thread guide 14 should be kept very small because the speed change,
in case of small thread triangles, does not cause difficulties in
the edge build-up of the spool 15 to be formed.
In the embodiment of FIGS. 4 and 5, the filament or filaments 56a,
56b, 56c and 56d are moved under a constant speed while no regular
or irregular fluctuations, due to the processing machine, impair
the thread tension of the thread being delivered. In such a case,
the apparatus for the control of the retention of the thread
tension may be used within predetermined limits. Threads 56a, 56b,
56c and 56d are removed from stationary spools 57a, 57b, 57c and
57d, respectively, and are wound up on spool body 55 while
maintaining the same thread speed. Blowing devices 12a, 12b, and
12c and 12d are provided to control the thread tension so that it
is always the same or so that it remains within a predetermined,
limited range during the winding process. Each of the blowing
devices 12a, 12b, 12c and 12d include two light barriers 28a and
29a between which the apex of the thread loop 27a is kept. FIG. 5
is a cross-sectional view of the blowing device 12a which is
representative of all the other blowing devices of this
embodiment.
Two light barriers 28a and 29a are in an extension arm 58 which is
pivotal about the pivot point 59. The arm 58 swings constantly with
predetermined movements according to arrow 60 in cross-direction
relative to the apex of the loop 27a. Supply units 61a, 61b, 61c
and 61d are provided for each thread 56a, 56b, 56c and 56d,
respectively. As long as the apex of the thread loop 27a remains
within the provided swing area with predetermined sizes, the
fluctuations of the thread tension are as small as to be within the
admissible tolerance area. This is controlled by the light barrier
pair 28a and 29a which are kept swinging.
The apex of the thread loop 27a causes pulses on the swinging light
barriers 28a and 29a. These pulses control the trigger step 36a and
they generate a pulse sequence with a pulse scanning ratio
corresponding to the position of the apex in the air channel. It is
possible to perform the control electronically such as described
with the circuitry of FIG. 3. By means of the control unit, the
supply unit of the spool body 55 may be controlled. It is also
possible to use a pneumatic flip-flop control.
With a device in which the thread speed of the moving thread
essentially unchanged, the thread tension may be controlled by the
blowing device 12a to have an adjusted medium value.
ADVANTAGES OF THE INVENTION
With the process and apparatus of this invention, only the mass of
the thread is subjected to a movement concerning a longer or
shorter loop following the change of the thread speed. The thread
itself has only an extremely small mass on the loop length. The
movement of the prior art jumping arm itself additionally caused
relatively high tension flucutations on the thread. This type of
fluctuation is completely eliminated with the apparatus of this
invention.
According to the invention, the thread is not affected by any
means. Changes in the length of the thread loop, i.e. increasing or
decreasing of the loop, do not bring about shocks in the thread.
Thread loop modifications are due to variations of the thread speed
resulting from the processing machine. Consequently, a high
sensitivity and accuracy is possible for the control of maintaining
a constant thread tension.
The change of the thread loop length occurs smoothly against the
counter force, i.e. against the air stream without the occurrence
of additional losses by friction or the like. Therefore, a
frictionless thread buffer is provided particularly in the case of
a sudden speed change of the processing machine. Only this massless
reverse with the retention of the constant thread speed is used for
the control. It is possible to re-establish the thread reserve with
the thread loop within a short period of time in accordance with a
predetermined thread tension by using the contactless scanning
elements according to the invention. Due to these phenomenon, the
retention of the constant thread tension may be realized much more
accurately and with lesser tolerances than heretofore.
Above all, the reaction times may be essentially reduced so that a
highly sensitive response is ensured for short-time thread tension
fluctuations. It is possible to adjust finest titer down to 5 den.
to a constant thread tension. Moreover, only partially stretched
threads may be processed without the risk of causing titer
fluctuations within the thread due to the control. It is guaranteed
that the processing machine is always fed with threads having a
constant thread tension.
The intensity of the air stream may be adapted to the thickness of
the thread being processed. When processing thin threads, it is
possible to operate with a correspondingly low air stream, thus
considerably increasing the sensitivity of control.
The assembly made in accordance with this invention contains
elements which are stationary. It is extremely handy. It does not
offer any difficulty to use it for the control of maintaining a
constant thread tension for filaments fed to the processing
machine. Finally, the apparatus is adaptable to many different
process parameters. That is, the strength of the blown air stream
may be variably adjusted. As a result thereof, the same blowing
device may be used for different thread thicknesses and titers and
for the adjustment of different predetermined thread tensions.
While the process and apparatus for maintaining constant thread
tension has been shown and described in detail, it is obvious that
this invention is not to be considered as being limited to the
exact form disclosed, and that changes in detail and construction
may be made therein within the scope of the invention, without
departing from the spirit thereof.
* * * * *