Note: Descriptions are shown in the official language in which they were submitted.
The present invention relates to a warp tension controller
for a weaving l.oom, with a comparing means Eor a measuring quantity
rela~ed to the warp tension and a reference quantity, which
through an operational amplifier connected as a PI-controller,
witn in the feedback circuit a resistor parallel to an integra-ti.ng
capacitor, controls an adjusting means for the warp tension.
Since in a weaving loom,the warp tension varies not only
at short term ~y the shaft movements, bu~ al.so varies at long term
by the nature of the warp yarn which is handled, the decreasing
diamet.er of the warp beam and other circumstances, whereas for
a goc~ quality of the fabric, the warp tension must be maintained
as ccnstant ns possible, modern looms make use of automatic
warp Jtension controllers, comprising a servo loop in which a
senso for the warp tension, a reference adjusting means, a
com~aring means for the output signals of these two, an operational
amplifier and a control means are connected The control means
usually aLfects the drive speed of the warp beam, and ~or obtaining
a smooth and stable control, the controller is usuall.y designed
aa a PI controller, i.e. a con-trol.leY w.ith proportional as well
as integratins action/ for which purpose tlle feedback clrcuit of
the operational amplifier compr.ises a resistor as well as a
capa-itor. The integrating part oE the operation of the operational
am~lifier ensures that the warp tension control hardly responds
at all to the rapid Eluctuations of the warp tension, caused by
the shaft movements, which fluctua-tions are too fast for
succesful mechanical compensation by the warp tension control.
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During operation, the integrating capacitor in the Eeedback
circuit carries a D ~C. voltage corresponding to the average-
output sigrlal of the operational ~mplifier with is required.
If tne loom is stopped, an entirely different condition of
the warp yarn is ob-tained mechanically, dependent upon the
arbitrary position in which the loom comes to a standstill,
50 that the D.C. voltage across the integrating capacitor
assumes a totally differen-t value than during operation.
Nevertheless, as soon as possible, àfter starting up, the
original D.~. voltage across the integrating capacitor should
again be reached, in order that Ihe condition of normal operation
be regained as soon as possible.
The invention aims at providing a solution for this problem.
For that purpose, a warp tension controller according to the
invention is characteri~ed by a voltage memory t the input of
which is connected to the output of the operational amplif.ier,
as w~ll as an automatically operated switch which upon disconnecting
the com drive, switches the integrating capaci.tor from the output
of the operat onal amplifier to the output of the voltage memory.
The voltage memory stores the output vol~age of the operational
amplifier whi.ch existed just prior -to swi.tching the lcom off~ By
connecting the integrating capacitor to the ou-tput of the voltage
memory during standstill, rather than to the output of t-he
o~erational amplifier, the D.C. voltage across the in-tegratin~
capacitor, after standstill oE the loom is no ].onger ef:Eected by
the voltage prevailing at the output of the operational ampliEier,
which is determined by the condition during standstil:L, rather
than by the normal operating condition, but by the output voltage
memory, whicn represents the normal. operation condition.
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When upon restarting the loom, the integrating capacitor is
switched bac~ from -the outpu-~ of the -voltage memory -to the
output of the operational amplifier, it from the very start
carries the correct D.C~ voltage, so that the stable condition
of the control is reached very fast.
Tha voltage memory can exist e.g. of an adjustable vol-tage
divider which is operated by a servo motor or oE a reference
voltage, the servo loop being so designed that the voltage
derived at the tap of the adjustablè voltage divider due to
the action of the servo motor always equals the output voltage
of the operationale amplifier, the position of the adjustable
voltaga divider being locked as soon as the loom is switched off.
The invention is further elucidated below with reference
to .he drawing, which represents a circuit diagram of an
ernbodiment of a warp tension Fontroller according to the invention.
In the figure, the output signal of a warp tension sensor
through the input 1 and the output signal of a reference source
through an input ~ are applied to a comparing means 3, the output
of which is connected to the inverting input of an operational
amplifier 4 of the warp tension control loop, which provides its
output signal at the tenninal 5. The operational amp:lifier ~ is
provided with a feedback network comprising the resistors 6 and
7 and the capacitor 8. The resistors 6 and 7 together determine
tha gain of the operational arnplifier at very low frequencies
and from a first change-over frequ~ncy, the gain falls due to
the integrating capacitor 8, again becoming constant at a lower
value at a second change-over frequency, due to the presence of
the resistor 7.
The output side of the integrating capacitor through a terminal
9 is connec-ted with the input oE the voltage memory (not shown),
the out~ut of which is connected to the terminal 10. As soon
as the loom is switched off, the ganged switches 11 and 12 are
operated automatically, whereby the integrating capacitor 8 is
disconnec-ted from -the feedback circuit (so that the operational
amplifier 4 now operates as a pure proportional controller,
rather than a proportional and integrating controllerl and its
output side through the resistor 13 is connec-ted to the output
1~ of the voltage memory. Since at the output 10 of the voltage
memory the voltage remains which immediately prior to the
cwitching-off of the loom exis-ted at the input 9 of the voltage
memoxy, the ~ntegrating capacitor 8 inde~initely xemains charged :~.. ..
to the voltage which existed immediately prior to switching-off
of the loom. As long as the loom remains switched-off, the
switcr. 12 connects a resistor 1~ parallel to the resistor 6
from th feedback ^ircuit, whereby the gain of the operational
ampl.Lier 4 is lower than during operation~
As soon ag the loom is again swi.tched on, the switches 11
and 12 are automatically returned to the position shown, which
res.oxes the feedback cixcuit to the initial condition, the
integrating capacitor 8 from the very beginning carrying the
correct voltage, so that the control starts with the correct
ir.itial conditions.
The ganged switches 15 and 16 and the resistor 17 serve
exclusively for slowly turning the loom, e.g. after a new warp
beam has been put on and the ends of the warp yarns of that new
warp beam have been knotted to the warp yarns of the woven fabric.
Under all other circumstances, the swi-tches 15 and 16 remain
in the position shown.
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