Control means for controlling the warp let-off of a weaving machine

The pulse transmitter is synchronized with the weaving cycle of the machine drive and carries at least one sensing surface of variable shape. A detector is secured to the tension beam and is responsive to changes in warp tension. The detector carries a sensing element in the form of a proximity switch which is disposed over the sensing surface of the pulse transmitter. Depending upon the position of the proximity switch relative to the sensing surface, a pulse is emitted to the warp beam drive for stepping of the warp beam as the pulse transmitter rotates past the sensing element. This pulse is variable in the time-of-occurrence as well as in duration.

This invention relates to a control means for a warp let-off of a weaving 
machine. 
As is known, weaving machines have been provided with various types of 
controls for controlling the warp let-off during weaving. In a 
conventional case wherein a motor is used to step the warp beam in a 
periodic manner, the position of a spring-biased tension bar or beam is 
used to control the motor. In this case, a proximity switch has been used 
which is responsive to the positions of the tension beam so as to switch 
on and off. Depending upon the position of the proximity switch, the motor 
for the warp beam is switched on and off. However, one of the 
disadvantages of this device is that the inertia of the tension beam 
frequently causes the proximity switch to remain "on" for longer than 
necessary in relation to the warp length actually required. For example, 
the "on" time may extend over a number of weaving cycles or picks with 
the result that the structure of the produced cloth contains 
irregularities. 
Accordingly, it is an object of the invention to provide a control means 
for controlling a warp beam drive so as to avoid irregularities in a woven 
cloth. 
It is another object of the invention to provide a control means for 
controlling the warp let-off of a weaving machine which is of relatively 
simple construction. 
Briefly, the invention provides a weaving machine which has a machine drive 
and a warp beam drive for rotating a warp beam in an incremental motion 
with a control means for controlling the warp beam drive. The control 
means includes a movably mounted detector which is responsive to a change 
in warp tension, a pulse transmitter which is adapted to move in 
synchronism with a weaving cycle of the machine drive and in relative 
relation with the detector, at least one sensing surface of variable shape 
on one of the detector and transmitter and a sensing element on the other 
of the detector and transmitter. The sensing element is disposed to travel 
over the sensing surface in order to emit a pulse to the warp beam drive 
for stepping the warp beam. This pulse corresponds to the operative 
distance which the sensing element travels over the sensing surface such 
that the pulse is variable in time-of-occurrence and in duration. 
The warp beam drive is thus adapted to be acted upon by a pulsating 
electrical signal which is dependent upon the warp tension and/or warp 
length as well as upon the weaving cycle. 
The control means coordinates the pacing or stepping of the warp with the 
picking frequency. Stepping of the warp can occur, for example, at every 
pick or at every other pick or at every fourth pick. 
In one embodiment, the pulse transmitter is in the form of a disc while the 
sensing surface extends radially on the disc and is bounded either by a 
cardioid curve or an involute curve. In this case, the sensing element 
which may be in the form of a proximity switch is able to pass over the 
sensing surface along selected circular arcs of different arcuate extent 
depending upon the position of the sensing element relative to the sensing 
surface. 
In another embodiment, the pulse transmitter is in the form of a cylinder 
while the sensing surface is disposed on the generated surface of the 
cylinder. In this case, the sensing surface may be substantially 
triangular such that the sensing element travels across circular arcs of 
varying circumferential extent.

Referring to FIG. 1, the weaving machine for weaving terry cloth employs a 
ground warp beam 1 from which ground warps 2 are supplied over a 
deflecting beam 3 and a tension bar or beam 4. In addition, a pile warp 
beam 5 is rotatably mounted within the machine to supply pile warps 6 
which pass over a temple 7 to a resiliently mounted tension bar or beam 8. 
The tension beam 8 is secured to a pair of levers 9 which are pivotable 
about a pivot 10 in known fashion. In addition, a spring 11 is secured to 
a lever 9 at one end as well as to a fixed part of the frame at an 
opposite end in order to restore the levers 9 and, thus, the tension beam 
8 to a neutral position. 
As shown, the warps 2, 6 extend in a conventional manner to a warp stop 
motion 12, shafts 13 and a reed 14 for weaving with a weft yarn (not 
shown) into a terry cloth. The cloth which is produced runs over a slider 
15 associated with a temple 16, a moving breast beam 17, a needle-clothed 
stepping beam 18, a pressing beam 19, a temple 20 and, finally, a cloth 
beam 21 on which the cloth is wound. As indicated, the breast beam 17 is 
connected via links 22, 23 with a cam follower lever 24. The cam follower 
lever 24, in turn, coacts with a rotatable cam 25 for controlling the 
cloth movement from the machine. This cam 25 is actuated by a machine 
drive (not shown). 
The warp beam 5 is driven via a motor 32. To this end, the motor 32 has a 
worm gear 33 which drives a tooth ring 34 on the warp beam 5. 
A control means for controlling the warp beam drive includes a movably 
mounted detector 29 which is responsive to a change in warp tension and a 
pulse transmitter 27 which is adapted to move in synchronism with the 
weaving cycle of the machine drive and in relative relation with the 
detector 29. As shown in FIG. 1, the detector 29 is connected to the 
levers 9 and is pivotable about the pivot 10. The pulse transmitter 27 is 
in the form of a rotatable disc which is mounted on a shaft 52 and is 
connected via a chain drive 26 to the cam 25 and thus to the machine drive 
so as to move in synchronism therewith. In addition, the control means has 
a sensing surface 28 of variable shape which extends radially on the pulse 
transmitting disc 27 (FIG. 1a) and encompasses a non-active area 53 around 
the shaft 52. The control means also has a sensing element in the form of 
a proximity switch 30 disposed on the detector 29 in order to travel over 
the sensing surface 28. As indicated, the proximity switch has a 
substantially punctate switching zone 31. The switching zone 31 moves in 
the manner of a pick-up needle of a record player over the sensing surface 
28 without necessarily touching the surface 28, as is well known in the 
art with respect to proximity switches. 
In operation, as the length of warp extending around the tension beam 8 
varies in accordance with the requirements for pile warp 6 near the 
weaving shed, the lever pairs 9 pivot about the pivot 10. This results in 
a simultaneous pivoting of the detector 29 so that the proximity switch 30 
moves radially of the rotating disc 27. When the rotating sensing surface 
28 coincides with the zone 31 of the proximity switch 30, a pulse is 
emitted from the switch 30 via a suitable line 39 motor 32 for stepping 
the warp beam 5. When the motor 32 is energized, the warp beam 5 rotates 
in the direction indicated by the arrow 5a to let off warp. 
The "on" time of the beam 5 is determined by the movement path of the 
proximity switch 30 along the sensing surface 28. To this end, as shown in 
FIG. 3, the sensing surface 28 is bounded by a cardioid curve. Further, 
since the sensing surface 28 rotates with the disc 27 about a fixed axis, 
the proximity switch 30 on the detector 29 travels along a circular arc 
49. As shown, depending upon the position of the proximity switch relative 
to the axis of rotation of the disc 27, the circular arc 49 may be of 
different arcuate extents. The direction of rotation of the sensing 
surface 28 is indicated by the arrow 48. The sensing surface 28 can be an 
electrically conductive and/or dielectric exciting zone which cooperates 
with the proximity switch 30 to energize the warp beam drive (i.e. motor 
32). Alternatively, the sensing surface 28 can be a magnetic and/or 
optical exciting zone for cooperation with the proximity switch to 
energize the motor 32. 
Referring to FIG. 4, wherein like reference characters indicate like parts 
as above, the sensing surface 38 may be bounded by an involute curve. 
Referring to FIG. 2, wherein like reference characters indicate like parts 
as above the weaving machine may be of the plain weaving type which 
includes a rotating tension bar or beam 35 over which warps 6 are supplied 
from a warp beam 5. As above, the warp beam 5 is driven by a drive which 
constitutes a motor 32. As shown, the motor 32 drives the warp beam 5 via 
a worm gear 33 and the toothed ring on the warp beam 5. The tension beam 
35 is carried on a pair of bell crank levers 36 which are pivoted about a 
pivot 10 and which are spring biased by a spring 11 to the weaving machine 
frame. 
The control means for controlling the warp beam drive includes a detector 
38 which is connected via a link 37 to the bell crank levers 36 and a 
rotating pulse transmitting disc 41 which is coupled via a reduction 
transmission 46 to a shaft 47 of the machine drive. In addition, the 
detector 38 carries a proximity switch 30 which is positioned over a 
sensing surface on the pulse transmitting disc 41 (FIG. 2a). As shown in 
FIG. 2, the switch 30 is connected via a line 39 to a motor switch 40 for 
selectively energizing the motor 32. In addition, the sensing surface on 
the disc 41 is formed of four surfaces 42 - 45, each of which is of 
variable shape. 
The operation of the control means of FIG. 2 is similar to that as 
described above with respect to FIG. 1 and no further description is 
believed to be necessary. 
Referring to FIG. 5, the pulse transmitter may alternatively be in the form 
of a cylinder 51 with at least one substantially triangular sensing 
surface 50 which extends along the generated surface of the cylinder. This 
cylinder 51 cooperates with a switch (not shown) which moves axially of 
the cylinder 51. Alternatively, the pulse transmitter may be linear, for 
example, in strip or band or similar form. 
In each of the above described embodiments, the sensing element 30 is 
disposed to travel over the sensing surface 28 in order to emit a pulse to 
the warp beam drive for stepping the warp beam in an incremental fashion. 
The pulse corresponds to the operative distance which the sensing element 
30 travels over the sensing surface 28 whereby the pulse is variable in 
time-of-occurrence and in duration. As shown in FIGS. 3 and 4, the length 
of the circular arcs 49 and, therefore, the "on" time increases towards 
the center of the rotating disc 28. The shape, adjustment and peripheral 
velocity of the sensing surface 28 can be chosen to give the optimum 
instant of switch-on for weaving. Where the pulse transmitter is in the 
form of a cylinder 51 as shown in FIG. 5, the circular arcs are disposed 
about the axis of the cylinder 51 and are of decreasing circumferential 
extent towards one end of the cylinder. 
The frequency with which the sensing element 30 cooperates with the sensing 
surface 28 is variable relative to the picking frequency. As a rule, the 
sensing surface 28 passes by the proximity switch 30, at most, once per 
weaving cycle or pick. Consequently, depending upon the number of sensing 
surfaces, the warp can be stepped at every pick, at every other pick or at 
every fourth pick. In the case of the weaving machine for terry cloth as 
shown in FIG. 1, the disc 27 may run at the same speed as the cam 25 for 
moving the cloth, i.e. at one revolution per group of picks or per row of 
loops. In the case of the plain weaving machine as shown in FIG. 2, the 
rotating disc 41 runs at 1/4 the speed of the machine. 
It is to be noted that the proximity switch 30 can be disposed on the 
rotating disc 27 so that the switching zone 31 is arranged for rotation 
while the sensing surface is disposed on the detector 29. In this case, 
the sensing surface 28 would be movable in a linear manner.