System for controlling warp take up and let off rates

A take-up rate and a let-off rate in warp feed on a loom are controlled while a displacement (.DELTA.L) of a cloth fell position C is taken into account. The system comprises a cloth fell position compensation circuit (2, 16, 21) which outputs a cloth fell compensation signal (.DELTA..omega..sub.c) to compenate a displacement (.DELTA.L) of the cloth fell position (C) when a weaving condition such as a target weft density (D*), a target warp tension (T*) or the kinds of weft and warp yarns is changed. The cloth fell compensation signal is added to a basic warp feed rate (.omega..sub.f) obtained from D*, so that the displacement motion of the cloth fell is completed in a shorter time. According to this compensation, a weft density of a resultant fabric rapidly coincides with the target weft density.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to a system for controlling a warp feed in a 
loom in response to changes of weaving conditions. 
2. Description of the Related Art 
In the prior art, a weft density of a fabric is adjusted by cooperatively 
controlling take-up and let-off rates of a warp on a loom in accordance 
with a target weft density, as disclosed in Japanese Unexamined Patent 
Publication No. 62-263347. In the above document, the take-up rate and the 
let-off rate are taken as functions solely of the target weft density, and 
other weaving conditions are not taken into account. This is because it 
has been considered in the prior art that the weft density is merely an 
inverse proportional factor to the take-up or let-off rate of warp feed. 
According to experiments conducted by the present inventors, it has been 
proved that the actual weft density in a fabric portion immediately after 
a change of the weaving condition has occurred is different from the 
target weft density. Namely, even if the target weft density is changed in 
a stepwise manner, the actual density varies gradually, whereby a 
considerably large area is formed in which the weft density is different 
from the target value. 
This is because a position of a cloth fell, i.e., a boundary line between a 
warp region in which a weft has not been inserted and a fabric now being 
formed on a loom, moves by a certain distance until a steady state is 
reestablished corresponding to the change of the target weft density. Such 
a displacement of cloth fell position may be caused not only by the change 
of the target weft density but also by changes of other weaving 
conditions, such as the kind of weft or warp yarns or a warp tension. 
Namely, as shown in FIG. 2(a), when a change of the weaving condition 
occurs, the cloth fell C is displaced from an original position L to a 
position L' or L" shown in chain lines, at which a new steady state of the 
cloth fell C is reestablished in accordance with a tension balance between 
warp and fabric in the vicinity of the cloth fell. 
The above phenomenon will be explained in more detail with reference to 
FIG. 2(b). Assuming a displacement of the cloth fell position C per weft 
pick is .DELTA.L, then this value can be equivalent to a displacement rate 
.DELTA.V.sub.c of the cloth fell position, because the weft is picked at a 
constant period. The displacement rate .DELTA.V.sub.c may have either a 
positive value or a negative value, in accordance with the direction in 
which the cloth fell position C is moved. Accordingly, as shown in FIG. 
2(b), a warp feed rate V is influenced by this .DELTA.V.sub.c as if the 
apparent warp feed rate V' becomes larger or smaller corresponding to the 
direction in which the cloth fell position C is moved. Note, the 
.DELTA.V.sub.c converges to zero as the steady state is reestablished 
under the new weaving conditions, but the disturbance of the weft density 
continues while the displacement of the cloth fell position continues. 
Even if it is desired to change the weft density in a stepwise manner, as 
illustrated in FIG. 2(c), the actual weft density gradually varies in 
accordance with the displacement of cloth fell position over a fabric 
length corresponding to about ten through twenty picks until the new cloth 
fell position is established. 
Accordingly, in the prior art, a transition of the weft density cannot be 
avoided when the weaving condition has changed. 
SUMMARY OF THE INVENTION 
An object of the present invention is to eliminate the above drawbacks of 
the prior art. 
Another object of the present invention is to provide a system for 
obtaining a desired weft density in a fabric when a weaving condition, 
such as a target weft density, kinds of weft and warp yarns, warp tension, 
or woven structure such as a plain or twill weave, has been changed, by a 
cooperative optimum control of take-up and let-off rates of warp feed, 
which take the displacement of the cloth fell position into full account. 
The above objects are achieved by a system illustrated in FIG. 1, according 
to the present invention, for controlling take-up and let-off rates of a 
warp feed on a loom by taking the displacement of a cloth fell position 
into account when the weaving condition has changed; comprising a device 1 
for setting weaving conditions; a cloth fell position compensation circuit 
2 for outputting a cloth fell compensation signal .DELTA..omega..sub.c 
corresponding to a displacement of the cloth fell position caused by the 
variation of the weaving conditions; a take-up control circuit 3 for 
outputting a take-up rate control signal .omega..sub.1 * for controlling a 
rotational rate of a take-up motor for driving a take-up roller of the 
loom, which signal is modified by the weaving conditions and the cloth 
fell position compensation signal .DELTA..omega..sub.c ; a tension 
detector 4 for detecting a warp tension T; an arithmetic circuit 5 for 
comparing the detected warp tension T with a target warp tension T* and 
outputting a deviation therebetween (T*-T); a gain compensation circuit 6 
for outputting a gain compensation signal G.sub.1 .multidot..omega..sub.1 
* obtained by multiplication of the take-up rate control signal 
.omega..sub.1 * modified by the displacement of the cloth fell position by 
a gain corresponding to the deviation (T*-T) between the detected warp 
tension and the target warp tension; and a let-off control circuit 7 for 
outputting a let-off rate control signal .omega..sub.2 * for controlling a 
rotational rate of a let-off motor for driving a let-off beam, comprising 
an adder for adding a signal proportional to the tension deviation (T*-T) 
to the take-up rate control signal G.sub.1 .multidot..omega..sub.1 * 
modified by the gain compensation circuit 6. 
If a weaving condition such as a target weft density D* is changed through 
the weaving condition setting device 1, a signal .omega..sub.f * 
inversely-proportional to the weft density D* is output therefrom, and the 
cloth fell position compensating circuit 2 in turn outputs the cloth fell 
position compensating signal .DELTA..omega..sub.c corresponding to the 
displacement of the cloth fell position. The take-up control circuit 3 
outputs the take-up rate control signal .omega..sub.1 * in accordance with 
the signal .omega..sub.f * from the weaving condition setting means 1 and 
the cloth fell position compensation signal .DELTA..omega..sub.c from the 
cloth fell position compensation circuit 2. This signal .omega..sub.1 * is 
input to a take-up motor driving circuit 8, so that the rotational rate of 
the take-up motor can be controlled while the displacement of the cloth 
fell position is taken into account. On the other hand, the tension 
detector 4 outputs a tension signal T detected thereby, and the arithmetic 
circuit 5 operates to output the tension deviation signal (T*-T) by a 
comparison of the detected tension T relative to the target tension T*. 
The gain compensation circuit 6 outputs the gain compensation signal 
G.sub.1 .multidot..omega..sub.1 * obtained by the multiplication of the 
take-up rate control signal .omega..sub.1 * with a gain G.sub.1 
corresponding to the tension deviation signal (T*-T). The let-off control 
circuit 7 adds the tension deviation signal (T*-T) to the gain 
compensation signal G.sub.1 .multidot..omega..sub.1 * and outputs the 
result as the let-off rate control signal .omega..sub.2 * modified by the 
displacement of the cloth fell position. This signal .omega..sub.2 * is 
input to a let-off motor driving circuit 9, so that the rotational rate of 
the let-off motor can be controlled while the displacement of the cloth 
fell position is taken into account. 
As stated above, according to the system of the present invention, since 
the rotational rates of both the take-up and let-off motors are 
cooperatively controlled so that the cloth fell displacement can be 
rapidly completed, the transition state of a weft density does not last 
for a long period as in the prior art, and therefore, an undesirable 
gradual change of a weft density on the woven fabric, having often 
observed in the prior art, can be eliminated.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
A principle of a cloth fell position compensation circuit according to the 
present invention will be described with reference to a case in which the 
target weft density is changed. 
As stated hereinbefore, even when a weaving condition, such as a weft 
density, is stepwisely changed as shown in FIG. 2(c), the cloth fell 
position cannot be instantly displaced to a new steady position in 
response thereto, but is gradually moved to this new position, and wefts 
picked during this gradual displacement of the cloth fell position cause a 
density unevenness in a resultant fabric. Accordingly, the cloth fell 
position compensation circuit of the present invention is intended to 
obtain a signal to shorten the period of the displacement of the cloth 
fell position. 
When the target density is changed, the cloth fell is displaced in 
synchronization with the weft picking, although the displacement per pick 
is very small. According to an experiment conducted by the present 
inventors, a reestablished cloth fell position is represented as a linear 
function of a weft density, although the inclination varies with the yarn 
thickness, as shown in a graph of FIG. 3(a), and with the warp tension as 
shown in a graph of FIG. 3(b). 
The cloth fell position compensation circuit controls at least either one 
of a compensation value .DELTA..omega..sub.c for modifying a basic warp 
feed rate with reference to a displacement .DELTA.L of cloth fell position 
varying in accordance with the change of the target weft density, or a 
time duration .DELTA.t during which .DELTA..omega..sub.c is output. A 
magnitude of .DELTA..omega..sub.c and the time duration .DELTA.t must be 
selected with reference to a fabric quality, motor characteristic, etc., 
and for this purpose, a command for changing a weaving condition, such as 
a weft density, may be differentiated, relative to a passing of time, in a 
real time manner and the obtained data used for controlling the magnitude 
or the .DELTA.t of the .DELTA..omega..sub.c. Alternatively, many pairs of 
.DELTA..omega..sub.c and times .DELTA.t may be prepared by preliminary 
experiments corresponding to the changes of the respective weaving 
conditions, and an optimum pair selected when a change of the weaving 
condition occurs. According to a feed-forward control based on such a 
compensation signal, the time necessary for the displacement of the cloth 
fell position accompanied by the change of the weaving condition can be 
shortened, whereby the disturbance of the weft density is minimized. 
The cloth fell position compensation circuit according to the present 
invention outputs a compensation value .omega..sub.c, for a take-up rate, 
corresponding to a displacement .DELTA.L of the cloth fell position 
accompanied by the change of a target weft density D* when a command 
signal shown in FIG. 4(a) is received from the weaving condition setting 
device. The magnitude of .DELTA..omega..sub.c is decided by taking a 
fabric quality and a motor characteristic into account. That is, if a 
steep change in the resultant weft density is necessary, the compensation 
period .DELTA.t shown in FIG. 4(b) should be short and a magnitude of 
.DELTA..omega..sub.c should be large. Hatched areas in FIG. 4(b) represent 
a total size of the cloth fell position compensation signal, which is 
combined in a take-up control circuit with a basic warp feed rate command 
output from the weaving condition setting device. This modified speed 
command is illustrated in FIG. 4(b). If a motor to be controlled has a 
poor responsitivity and cannot follow this pulsed signal, the magnitude of 
.DELTA..omega..sub.c value should be made smaller and the .DELTA.t made 
longer. In this case, the resultant weft density D does not change so 
steeply. In any case, the magnitude of .DELTA..omega..sub.c and the 
.DELTA.t are selected so that the following equation is satisfied. 
##EQU1## 
wherein .DELTA.L is a displacement of a cloth fell position. 
Note, these values may be obtained without regard to the above equation, 
but by taking the fabric quality into account. 
In the conventional method, in which the warp feed is controlled merely by 
a basic warp feed rate command defined as a function 
inversely-proportional to a target weft density, as shown in FIG. 5(a), 
there is a considerable time lag until the actual weft density coincides 
with the target density, when the target weft density is changed, as shown 
in FIG. 5(b). 
Conversely, if a compensation signal proportional to a differential value 
of the basic warp feed rate command of FIG. 5(a) is added to the basic 
warp feed rate command by the cloth fell position compensating circuit 
according to the present invention, a modified warp feed rate command 
shown in FIG. 5(c) is obtained, whereby the time lag of the actual weft 
density relative to the target weft density is considerably shortened, as 
shown in FIG. 5(d). Namely, the time lag in the conventional method 
hatched in FIG. 5(b) is preliminarily added as a compensation signal 
hatched in FIG. 5(c) to the basic feed rate command, so that the 
feed-forward control is conducted. If a motor to be controlled has upper 
and lower rotational limits, the compensation signal also should have 
upper and lower limits corresponding thereto. In such a case, a time 
.DELTA.t for outputting the compensation signal is preferably prolonged 
accordingly. 
If the basic command has a trapezoidal form as shown in FIG. 5(e), the 
compensation signal is added as shown by the hatching in the drawing, 
whereby a more improved control of the weft density can be achieved. 
The cloth fell position compensation according to the present invention can 
be conducted in various ways. For example, (1) a density change command is 
processed in a real time manner and the obtained data is added to a basic 
speed command for the rotation of a motor output by a weaving condition 
setting device, and (2) a possible density change command is preliminarily 
processed and the obtained data is stored in a memory, which data is 
temporarily read therefrom when needed and added to a basic warp feed rate 
command for the rotation of a motor output by a weaving condition setting 
device. 
Various circuits may be used when practicing the first method (1), but 
preferably a cloth fell position compensation circuit comprising a 
differentiating circuit for differentiating a command for the change of a 
weft density and an amplifier for multiplying the differentiated signal by 
a certain constant is used. These circuits may be formed by analog or 
digital arithmetric circuit. The advantages of this method reside in the 
simplicity of the data processing, but the data must be processed in a 
very short period because a real time processing is necessary. Therefore, 
this method is not suitable when a precise control is required. 
The second method (2) requires the use of a microcomputer in which process 
programs and data tables, prepared by the preparatory experiments, are 
stored for obtaining a cloth fell position compensation. The compensation 
signal is obtained by sequentially referring to these tables and programs. 
According to this method, a precise control is possible even when a 
plurality of factors of the weaving conditions are simultaneously changed, 
such as a weft density and a thickness of a weft yarn, or a weft density 
and a weaving structure. 
FIRST EMBODIMENT 
A first embodiment of a system, according to the present invention, as 
shown in FIG. 6, is intended to control the change of a target weft 
density D* at two levels during the weaving operation. 
A weaving condition setting device 10 outputs a weft density command D* 
corresponding to a target weft density pattern on a fabric and a 
rotational rate N (rpm) for a loom motor. In addition to these commands, 
the device 10 also outputs a basic take-up rate command .omega..sub.f * in 
accordance with equation (1), with reference to the weft density D 
(/inch); 
EQU .omega..sub.f *=[(25.4/D)/D.sub.f ].multidot.(N/60) (rad/sec) (1) 
for controlling a rotational rate .omega..sub.1 of a take-up motor M.sub.1. 
In this connection, D.sub.f is a constant corresponding to a diameter of a 
take-up roller and a reduction ratio thereof. 
The cloth fell compensation circuit 16 consists of a take-up rate variation 
detecting circuit 161 and a variable gain amplifier 162. The take-up rate 
variation detecting circuit 161 comprises a differentiator for detecting a 
time dependent variation of the basic take-up rate command .omega..sub.f * 
output from the weaving condition setting device 10, and outputs, for a 
unit of time, a reference signal informing the variable gain amplifier 162 
whether or not such a variation has occurred. The variable gain amplifier 
162 amplifies the reference signal and outputs a cloth fell compensation 
signal .DELTA..omega..sub.c modifying the basic take-up rate command 
.omega..sub.f *. 
According to this embodiment, a weft density is changed between two levels, 
i.e., from a higher level to a lower level or vice versa. If a more 
precise change of the weft density is necessary, a gain of the variable 
gain amplifier 162 may be varied in accordance with a value of the basic 
take-up rate command .omega..sub.f *, as illustrated by a dotted arrow in 
FIG. 6. 
The take-up control circuit 11 comprises an adder 111 for adding the basic 
take-up rate command .omega..sub.f * output from the weaving condition 
setting device 10 to the cloth fell compensation signal 
.DELTA..omega..sub.c, and outputs the resultant value as a modified 
command .omega..sub.1 *. 
The tension detector 12 detects a warp tension T by a load cell or the like 
and outputs a corresponding signal. The signal is input to a tension 
deviation calculating circuit 13. 
The take-up control circuit 11 further comprises a switch 112 which is 
either "on" or "off" in association with a starting switch S for a loom 
motor LM, and in the "on" position, transmits the modified take-up rate 
.omega..sub.1 * to a take-up motor driving circuit 17 for driving the 
take-up motor M.sub.1. The .omega..sub.1 * is also output to a gain 
compensator 14 connected to the circuit 11. 
The tension deviation calculating circuit 13 comprises a variable resistor 
131 for setting a target warp tension T* as an electric signal, and a 
difference amplifier 132 for obtaining a difference between the signal 
corresponding to the detected warp tension T output from the tension 
detector 12 and the signal corresponding to the target warp tension T* set 
by the variable resistor 131, and outputs this difference to a let-off 
control circuit 15 and the gain compensator 14. 
The gain compensator 14 comprises a pair of variable resistors 141 and 142 
for setting predetermined positive and negative direct-current voltage 
values, respectively, a sign selector 143 for selecting either of the 
variable resistor 141 or 142 in accordance with a polarity sign of the 
electric signal output from the difference amplifier 132, and connecting 
the selected resistor to a integrator 144 which amplifies the preset 
voltage output from the resistor 141 or 142. More specifically, if the 
signal from the difference amplifier 132 has a positive sign, the positive 
voltage resistor 142 is selected, and if the signal has a negative sign, 
the negative voltage resistor 141 is selected. The gain compensator 14 
further comprises an integrator 144 for integrating the selected preset 
voltage output through the sign selector 143, and outputs the integral 
value to a variable gain amplifier 145 which amplifies the take-up rate 
command .omega..sub.1 * from the take-up control circuit 11 with a 
suitable gain determined in accordance with this integral value; i.e., if 
this value is positive, a smaller gain is selected, and if this value is 
negative, a larger gain is selected. Finally, the obtained signal is 
transmitted to a let-off control circuit 15. 
The let-off control circuit 15 comprises an amplifier 151 and an adder 152. 
The amplifier 151 proportionally amplifies the electric signal from the 
tension deviation determining circuit 13 and transmits the result to the 
adder 152. The adder 152 adds the signal output from the amplifier 151 to 
the take-up rate command .omega..sub.1 * output from the gain compensation 
circuit 14, and transmits the resultant value .omega..sub.2 *, as a 
let-off rate command, to a let-off motor driving circuit 18. 
The take-up and let-off motor driving circuits 17, 18 carry out a feedback 
control of a take-up motor M.sub.1 and a let-off motor M.sub.2 in 
accordance with the take-up and let-off rate commands .omega..sub.1 * and 
.omega..sub.2 *, while carrying out a feed-forward control for 
compensating a displacement of a cloth fell position. 
Prior to starting this system, the operator sets the weaving conditions, 
such as a target weft density D* or a rotational speed N of a loom, in the 
weaving condition setting device 10, and the weaving condition setting 
device 10 then outputs a basic signal .omega..sub.f * based on the 
equation (1). 
By taking the weaving conditions into account, the operator sets a target 
warp tension T* in the tension deviation calculating circuit 13 through 
the variable resistor 131. 
Further, from a preliminarily obtained relationship between the weaving 
condition and the cloth fell position as shown in FIGS. 3(a) and 3(b), a 
gain of the amplifier 162 is determined by the variable resistor 163 in 
the cloth fell position compensation circuit 16, and a magnitude of the 
cloth fell compensation signal .DELTA..omega..sub.c is determined by this 
gain of the amplifier 162. A unit of time during which the reference 
signal is delivered from the take-up rate variation detecting circuit 161 
corresponds to .DELTA.t described before. Also, as stated before, the 
following relationship exists among the displacement .DELTA.L of the cloth 
fell position to be compensated, .DELTA..omega..sub.c and .DELTA.t; 
##EQU2## 
According to this embodiment, .DELTA.t is always constant, and therefore, a 
large magnitude .DELTA..omega..sub.c is selected when the .DELTA.L is 
large, by setting a large gain value in the amplifier 162, and a small 
magnitude .DELTA..omega..sub.c is selected when the .DELTA.L is small, by 
setting a small gain value in the amplifier 162. 
When the operator turns on a starting switch S for the loom motor LM, the 
switch 112 in the take-up control circuit 11 is made "on" in association 
therewith. Then the take-up rate command .omega..sub.1 * is delivered to 
the take-up motor driving circuit 17, the .omega..sub.1 * being formed by 
adding the basic take-up rate command .omega..sub.f * for the take-up 
motor M.sub.1 output from the weaving condition setting device 10 to the 
cloth fell position compensating signal .DELTA..omega..sub.c output from 
the cloth fell position compensating circuit 16, so that the weaving 
operation is carried out while the rotation of the take-up motor M.sub.1 
is controlled by the take-up rate command .omega..sub.1 *. 
In the let-off control circuit 15, an electric signal representing a 
tension deviation (T*-T), corresponding to the difference between the 
target warp tension T* set in the variable resistor 131 and the actual 
warp tension T detected by the tension detector 12 is proportionally 
amplified by a gain G.sub.2 in the amplifier 151. This signal is added to 
the result delivered from the gain compensator 14, obtained by the 
multiplication of the variable gain G.sub.1 determined by the polarity 
sign of the tension deviation (T*-T) with the take-up rate command 
.omega..sub.1 * output from the take-up control circuit 11, and the 
resultant signal is delivered to the let-off motor driving circuit 18 as a 
let-off rate command .omega..sub.2 *. The rotational rate of the let-off 
motor M.sub.2 is controlled to coincide with the .omega..sub.2 *. If the 
tension deviation (T*-T) is positive, i.e., the detected warp tension is 
larger than the target tension T* or the warp is in a slack condition, the 
smaller G.sub.1 is selected so that the rotational rate .omega..sub.2 for 
the let-off motor is smaller than the rotational rate .omega..sub.1 of the 
take-up motor. Conversely, if the tension deviation (T*-T) is negative, 
i.e., the detected warp tension is smaller than the target tension T* or 
the warp is in a tense condition, the larger G.sub.1 is selected so that 
the rotational rate .omega..sub.2 for the let-off motor M.sub.2 is larger 
than the rotational rate .omega..sub.1 for the take-up motor M.sub.1. When 
the tension deviation has been eliminated as a result of the control, the 
take-up rate .omega..sub.1 and the let-off rate .omega..sub.2 coincide 
with each other. Strictly speaking, .omega..sub.1 is smaller than 
.omega..sub.2 due to a crimp shrinkage of warp. As this crimp shrinkage, 
however, is negligibly samll, .omega..sub.1 is substantially equal to 
.omega..sub.2. 
When this system is disturbed, for example, when the diameter of a warp 
beam is reduced with the progress of the weaving operation or when the 
friction of a warp path is varied, this system also controls the let-off 
rate and the take-up rate so as to coincide with each other. 
According to the repetition of the above control of the take-up and let-off 
rates of the warp, a fabric with the desired weft density can be obtained. 
When the target weft density is changed, the cloth fell position C is 
displaced, as shown in FIG. 2. This displacement of the cloth fell 
position causes a disturbance of an apparent warp feed rate, due to a 
displacement rate .DELTA..omega..sub.c, and therefore, the weft density D 
is in error while the displacement of the cloth fell position lasts. 
According to this embodiment, however, the basic take-up rate command 
.omega..sub.f * corresponding to the target density D* is modified with 
reference to the .DELTA..omega..sub.c value, so that the displacement of 
the cloth fell position is compensated. 
The effect of the first embodiment of the present invention is as follows: 
Since the increment or decrement of the take-up and let-off rates of warp 
feed is adjusted to coincide with the displacement of the cloth fell 
position .DELTA.L when the target weft density D* has changed, the time 
lag of the resultant weft density D can be shortened. 
The cloth fell compensating circuit 16 according to the first embodiment, 
has a simple structure, and can be easily introduced into the existing 
weft density control system without a great modification thereof. 
SECOND EMBODIMENT 
FIG. 7 is a block diagram illustrating a structure of a system of a second 
embodiment according to the present invention. 
In this embodiment, the relationship between a loom LM and the warp take-up 
and left-off motor driving devices is the same as that of the first 
embodiment, and thus only the difference between the two embodiments will 
be explained hereinafter. 
In FIG. 7, the warp feed rate control system according to the second 
embodiment comprises a keyboard KB for setting the weaving conditions, a 
tension detector 22 for detecting a warp tension T, a system control 
computer 21, a take-up control computer 23, and a let-off control computer 
24; the respective computers being provided with an interface circuit, a 
microprocessor (referred to as CPU hereinafter), and a memory. 
The system control computer 21 supervises the entire warp feed rate control 
system and takes in, through the interface circuit 211, the weaving 
conditions such as a weft density D*, a rotational rate N of the loom, a 
target warp tension T*, kinds of weft and warp yarns, and a start command 
St or a stop command Sp input from the keyboard KB. 
The system control computer 21 also outputs, through an interface circuit 
211, a basic take-up rate command .omega..sub.f * to the take-up control 
computer 23; and the start and stop commands St, Sp to a loom control 
computer CM, the take-up control computer 23, and the let-off control 
computer 24. The memory 212 consists of a RAM 2121 and ROM 2122. The RAM 
2121 stores data related to the weaving conditions input from the 
interface circuit 211 and data to be processed in the CPU 213. A system 
control program based on a preset sequence is written, in the ROM 2122, by 
which the CPU 213 executes sequential processes. An example of such a 
program is illustrated in FIG. 8. 
The system control computer 21 determines a command .omega..sub.1 * for a 
take-up motor M.sub.1 from the target weft density D* and the rotational 
rate N of the loom in accordance with equation (1). The .omega..sub.f * is 
a basic warp feed rate command for obtaining a fabric with the desired 
weft density D*. 
The system control computer 21 sequentially checks whether or not the 
weaving condition, such as a weft density D*, kinds of weft and warp yarns 
or a target warp tension T* is to be changed. The object of this check is 
to obtain information on whether or not a displacement of the cloth fell 
position will occur. If the check shows that the weaving condition has 
changed, the basic warp feed rate command .omega..sub.f * is modified by a 
value .DELTA..omega. obtained from the following equation (2); 
EQU .DELTA.L=A.multidot.(D1-D2)+B.multidot.(T1-T2) 
EQU .DELTA..omega.=K.multidot..DELTA.L (2) 
This equation is a linear approximation of the relationship among the weft 
density D, warp tension T and the cloth fell position C illustrated in 
FIGS. 3(a) and 3(b), and coefficients A, B in the above equation have been 
preliminarily determined from the inclination of a curve illustrating the 
above relationship. D1, D2 are old and new target weft densities, 
respectively, and T1, T2 are old and new target warp tensions, 
respectively. 
Accordingly, if the target weft density or the target warp tension is 
changed during the weaving operation, the displacement of the cloth fell 
position C is forecast by the equation (2), and thus is compensated by the 
control system. The .DELTA..omega. value in the equation (2) corresponds 
to a compensation signal, and the magnitude thereof can be adjusted by a 
value of K. 
The displacement .DELTA.L of the cloth fell position is expressed as 
follows, by a compensation value .DELTA..omega..sub.c and a compensation 
period .DELTA.t: 
##EQU3## 
In the second embodiment, .DELTA.t is equivalent to the number of weft 
picks, because the weft is inserted at a constant period and the take-up 
rate command .omega..sub.1 * is changed in synchronization with the weft 
pick, as stated later. The coefficients A, B should be varied when the 
kind of weft and warp yarns or a warp tension T is changed to suit newly 
set weaving conditions. It can be considered that the total influence on 
the displacement of the cloth fell position due to the change of the 
weaving conditions is a mere addition of the respective changes of the 
individual weaving conditions, and thus the displacements due to the 
change of the individual weaving conditions are summed up to produce a 
total displacement as represented in equation (2). 
In the above example, the cloth fell position compensation value 
.DELTA..omega..sub.c is obtained by the equation (2). This value, however, 
may be obtained by a data table stored in the memory. Alternatively, this 
value may be obtained by an assumption of the displacement of the cloth 
fell position from the detectable changes of the take-up and let-off rates 
.omega..sub.1, .omega..sub.2 and/or from the detectable change of a warp 
tension T during the weaving operation. 
One example of a pattern of a take-up rate .omega..sub.1 * thus obtained is 
shown in FIG. 4(b) relative to the passing of time, i.e., relative to the 
number of weft picks in this embodiment. 
The .omega..sub.1 * is stored in the RAM 2121 of the memory 212, and 
simultaneously, transmitted to the take-up control computer 23 and is 
stored in the RAM 2321. 
The take-up control computer 23 corresponds to the take-up control circuit 
3 shown in FIG. 1. The interface circuit 231 takes in the take-up rate 
command .omega..sub.1 * for the take-up motor M.sub.1, the start command 
St and the stop command Sp from the system control computer 21, and a zero 
phase rectangular pulse output by a rotary encoder RE fixed on a loom 
crank shaft; this pulse being output at each rotation of the loom crank 
shaft. 
The interface circuit 231 outputs the take-up rate command .omega..sub.1 * 
for the take-up motor M.sub.1 to the take-up motor driving circuit 7 and 
the let-off control computer 24. 
The memory 232 comprises a RAM 2321 in which a series of the take-up rate 
commands .omega..sub.1 * and data to be processed by CPU 233 are stored, 
and a ROM 2322, on which a take-up control program for operating CPU 233 
is written. An example of the program is illustrated in FIGS. 9(a) and 
9(b). 
The take-up control computer 23, while allowing an interruption, 
sequentially reads the take-up rate commands .omega..sub.1 * stored in the 
RAM 2321 in synchronization with the zero phase pulse output by the 
encoder RE. The read .omega..sub.1 * is transmitted to the take-up motor 
driving circuit 27 and the let-off control computer 24. This operation, 
however, starts only after several pulses have been output during the 
initial stage of a loom start. Namely, a warp take-up or let-off operation 
is not carried out during this period. The reason therefor is as follows: 
As shown in FIG. 10(a), the weft arrangement on a fabric in the vicinity of 
the cloth fell becomes nonuniform while the loom is stationary, and when 
the loom starts as usual, causes a light filling bar in the area close to 
the cloth fell. This filling bar can be remedied, as shown in FIG. 10(b), 
by suppressing the warp feed for a while so that the wefts picked after 
the loom starts push the wefts picked before the loom starts toward the 
take-up side. 
The take-up rate commands .omega..sub.1 * stored in the take-up control 
computer 23 may be preliminarily transferred to the let-off control 
computer 24 and stored in the RAM 2421 thereof. In this case, a 
synchronizing signal, such as the zero phase pulse, is also transferred to 
the let-off control computer 24. 
The let-off control computer 24 corresponds to a combination of the 
arithmetic circuit 5, the gain compensator 6, and the let-off control 
circuit 7 shown in FIG. 1. 
The interface circuit 241 thereof takes in into the let-off computer 24 the 
take-up rate command .omega..sub.1 * from the take-up control computer 23, 
the detected value T of a warp tension from the tension detector 22 and 
the target value T* of a warp tension, and the start command St and the 
stop command Sp from the system control computer 21, and further, outputs 
a let-off rate command for the let-off motor M.sub.2 to a let-off motor 
driving circuit 28. 
The memory 242 comprises a RAM 2421 in which the target value T* of a warp 
tension and data to be processed by CPU 243 are stored, and a ROM 2422, in 
which a let-off control program for operating CPU 243 is written. An 
example of the program is illustrated in FIG. 11. 
The let-off control computer 24, when the start command St is input, 
carries out a warp tension control in accordance with the tension 
deviation (T*-T). Also, a let-off rate command .omega..sub.2 * modified so 
that the influence by the warp take-up rate .omega..sub.1 is compensated 
is output to a let-off motor driving circuit 28. 
To obtain the let-off rate command .omega..sub.2 *, the take-up rate 
command .omega..sub.1 * output by the take-up control computer 23 is 
multiplied in the let-off control computer 24 with a variable gain G.sub.1 
preliminarily stored in the RAM 2421, which gain is selected in accordance 
with the tension deviation (T*-T). The resultant value is added to a basic 
let-off rate command obtained by the multiplication of the tension 
deviation (T*-T) and a fixed gain G.sub.1, and the final result is output 
as a modified let-off command .omega..sub.2 *. 
The variable gain G.sub.1 on RAM 2421 becomes smaller with the passing of 
time if the tension deviation (T*-T) has a positive value, i.e., when the 
warp is in a slack state, so that a suitable let-off rate .omega..sub.2 
smaller than the take-up rate .omega..sub.1 is obtained. Conversely, if 
the tension deviation (T*-T) has a negative value, i.e., when the warp is 
in a tense state, the variable gain G.sub.1 in the RAM 2421 becomes larger 
with the passing of time, so that a suitable let-off rate .omega..sub.2 
larger than the take-up rate .omega..sub.1 is obtained. According to these 
operations, the warp feed is always controlled so that the tension 
deviation (T*-T) becomes zero, i.e., the take-up rate .omega..sub.1 and 
the let-off rate .omega..sub.2 of a warp coincide with each other. 
Through the take-up and let-off motor driving circuits 27, 28, as described 
in the first embodiment, the rotational rates of the take-up and let-off 
motors are controlled so as to coincide with the .omega..sub.2 *. 
The operation of the second embodiment according to the present invention 
will be described below. 
The operator inputs data representing the weaving conditions, such as kinds 
of weft and warp yarns, a target weft density D*, a rotational rate of a 
loom N, or a target warp tension T*, through the keyboard KB. For the 
target weft density D*, more than one value can be input so that various 
weft density patterns are obtained. Also, for the target value T* of the 
warp tension, more than one value can be input so that a smooth weaving 
operation and a favorable fabric quality are obtained, although the target 
tension is usually set at one level during the weaving operation. 
After the completion of the data input from the keyboard KB, an initial 
step for conducting the weaving operation is commenced, as follows: 
In the system control computer 21, a take-up rate command .omega..sub.f * 
is determined by referring to the input data. Also, the modification of 
the .omega..sub.f * is carried out by taking the displacement of the cloth 
fell position into account. These results and the target value of a warp 
tension are transmitted to the take-up control computer 23 and the let-off 
control computer 24. On the other hand, the let-off control computer 24 
controls the warp tension to coincide with the target value T* transmitted 
from the system control computer 21, prior to the commencement of the 
weaving operation, so that a sudden change of the warp tension does not 
occur immediately after the loom start. Such a tension change would cause 
an undesirable displacement of the cloth fell position. 
After the above initial step, the operator inputs a start command St 
through the keyboard KB, which command is transmitted by the system 
control computer 21 to the take-up control computer 23, the let-off 
control computer 24, and the loom control computer CM. 
The picking and shedding motions of the loom are started under the 
supervision of the loom control computer CM. 
The take-up control computer 23 sequentially reads the take-up rate 
commands .omega..sub.1 * stored in the RAM 2321, in synchronization with 
the zero phase pulses output from the rotary encoder RE as the crankshaft 
of the loom is rotated, and transmits the same to the take-up motor 
driving circuit 27 and the let-off computer 24. 
The let-off control computer 24 carries out a warp tension control in 
accordance with the tension deviation (T*-T) between the detected warp 
tension T issued from the tension detector 22 and the target tension T*. 
Also, the computer 24 outputs a let-off rate command .omega..sub.2 * for 
the let-off motor M.sub.2, modified so that the influence by the warp 
take-up rate .omega..sub.1 is compensated. The command .omega..sub.2 * is 
transmitted to a let-off motor driving circuit 28. 
The weaving operation is smoothly carried out by the repetition of the 
above sequential operations. 
When the operator inputs the stop signal Sp through the keyboard KB, this 
command is transmitted by the system control computer 21 to the take-up 
control computer 23, let-off control computer 24, and the loom control 
computer CM, and thus the loom control computer CM stops the picking and 
shedding motions of the loom, and the take-up control computer 23 and the 
let-off control computer 24 output zero warp feed rate commands to stop 
the take-up and let-off motors. 
The effects of the second embodiment are as follows: 
A warp take-up speed always optimally controlled to match a warp let-off 
speed, even when a weaving condition such as the weft density is changed. 
Further, since the displacement of the cloth fell position due to the 
change of the weaving condition can be compensated by the present 
invention, a high quality fabric free from an uneven weft density is 
obtainable. 
Further, since the sequential control operations are conducted by software, 
the hardware of the system can be simplified. 
Also, since the compensation value for the displacement of the cloth fell 
position may be optionally obtained from an equation or a data table, a 
precise control for a warp feed rate can be achieved in response to the 
various weaving conditions. Further, the control constants are easily 
changed by observing the weft density in the resultant fabric. 
Since the influence on the displacement of the cloth fell position due to 
the change of the respective weaving condition is linearly approximated, 
the compensation therefor is flexibly and precisely carried out. 
Finally, even if the weaving conditions are complicated, such conditions 
can be easily and precisely set in the control system.