Spinning units in an open end spinning machine

An open end spinning machine includes a plurality of spinning units. Each spinning unit includes a first yarn breakage sensing device assuming a yarn sensing, operative position, in which it contacts the yarn, when the spinning unit is in a normal spinning operation and an inoperative position, in which it is not in contact with the yarn, when the spinning unit is in a transient condition either from or to the normal spinning operation, and a second yarn breakage sensing device assuming a yarn sensing position at least when the spinning unit is in the transient condition. Upon occurrence of yarn breakage when the spinning unit is in the transient condition, such breakage is detected by the second yarn breakage sensing device and the supply of fibers to the associated spinning unit is interrupted by the second yarn breakage sensing device.

BACKGROUND OF THE INVENTION 
This invention relates to spinning units in an open end spinning machine, 
and more particularly to the prevention of the spinning rotor in each 
spinning unit from being clogged by fibers fed thereinto. 
Generally, in an open end spinning machine such as, for example, described 
in U.S. Pat. No. 3,354,626, each spinning unit includes means for feeding 
individually opened fibers into a spinning rotor, in which 
superatmospheric pressure is produced by rotation thereof. The opened 
fibers are formed into a yarn in the spinning rotor. The yarn is 
transported from the spinning rotor by a winding means. Also, in the above 
open end spinning machine, each of the fiber feeding means, yarn take-up 
means and yarn winding means is mounted on a separate driving shaft and a 
single motor drives these separate driving shafts through a rotation 
transmission mechanism including trains of gears. This motor also drives 
an endless belt, which is in frictional contact with spindles of the 
spinning rotors to rotate the same. 
When the spinning machine is stopped, the fiber feeding means is first 
stopped to discontinue the supply of fibers to the spinning rotor, the 
take-up roller and winding roller are then stopped at a time when the yarn 
end resulting from breakage of the yarn still remains in the yarn take-up 
tube, which undergoes the suction effect of the subatmospheric pressure in 
the spinning rotor, so as to facilitate the simultaneous connection of the 
yarn endings in all of the spinning rotors on subsequent starting of the 
spinning machine. Finally, all the spinning rotors are stopped. On 
starting, all the spinning rotors start to rotate simultaneously, the yarn 
take-up rollers and winding rollers are then rotated in a reverse 
direction to push the yarn ends from the take-up tubes into the spinning 
rotors, while the fiber feeding means are operated to supply opened fibers 
into the spinning rotors thereby to allow them to be twisted into the 
reversed yarn ends. Thereafter, the take-up rollers and winding rollers 
are rotated in a normal, yarn winding direction. 
In order to detect a possible yarn breakage during the normal spinning 
operation, each spinning unit is provided with a yarn breakage sensing 
device of the contact type allowing a yarn sensing lever thereof to be in 
contact the yarn to detect the breakage and to be maintained in this yarn 
sensing or detecting position by the yarn tension during the normal 
spinning operation. Typically, such a yarn breakage sensing device is 
illustrated in British Pat. No. 1,158,623. 
With the yarn breakage sensing device of the type described above, the yarn 
sensing lever may not be maintained in the yarn detecting position, i.e., 
moved into a yarn breakage position, under the transient condition either 
from or to the normal spinning operation during which the spinning machine 
is stopping or starting by pushing down a stop push-button or a start 
push-button, since the yarn tension during such a transient condition is 
lower than that during the normal spinning operation. In order to 
eliminate this disadvantage of the above-described yarn breakage sensing 
device, heretofore, the yarn sensing lever has been designed to be 
forcibly moved into an inoperative position, in which it is not in contact 
with the yarn, by using for example an electromagnet during the transient 
conditions. However, since such a forced movement of the yarn detecting 
lever has been effected simultaneously in all of the spinning units, 
fibers would be supplied into not only spinning rotors in which the yarn 
end connecting operation has been favourably carried out, but also a 
spinning rotor in which the yarn end connecting operation has failed. 
In the past, the number of rotations of spinning rotors was relatively low 
i.e. on the order of about 30,000 r.p.m., and therefore the fiber supply 
rate was low. Also, the spinning rotor had a relatively large inner 
diameter so as to apply a sufficient centrifugal force on the fibers in 
the low speed spinning rotor. However, recently, the rotation speed of 
spinning rotors has been increased to values of about two to three times 
30,000 r.p.m. and accordingly the inner diameter of the spinning rotor has 
been decreased (this results in a decreased volume of the spinning rotor) 
to restrict the centrifugal force within favourable limits. Moreover, the 
fibers have had to be supplied at an increased rate to spin the same 
amount of yarn. These recent spinning conditions cause the fibers to 
overflow if they are supplied into a spinning rotor in which the yarn end 
connecting operation failed, and the spinning rotor to be clogged by the 
supplied fibers. Thus, there is the danger of disadvantages such as a fire 
occurring in the clogged spinning rotor due to frictional heat. 
It is therefore a principal object of this invention to provide an open end 
spinning machine, in which a yarn breakage can be detected even during the 
transient conditions of the spinning machine and the supply of fibers into 
a spinning rotor can be stopped if a yarn end connecting operation has 
failed in the associated spinning rotor during the transient conditions. 
SUMMARY OF THE INVENTION 
In general, an open end spinning machine includes a plurality of spinning 
units according to this invention. With the above object in view, each 
spinning unit includes a first yarn breakage sensing device assuming a 
yarn sensing, operative position, in which it contacts the yarn when the 
spinning unit is in a normal spinning operation and an inoperative 
position, in which it is not in contact with the yarn, when the spinning 
units are in a transient condition either from or to the normal spinning 
operation, and a second yarn breakage sensing device assuming a yarn 
sensing position at least when the spinning unit is in the transient 
condition. Upon occurrence of the yarn breakage while the spinning unit is 
in the transient condition, the yarn breakage is detected by the second 
yarn breakage sensing device and the supply of fibers to the associated 
spinning unit is interrupted by the second yarn breakage sensing device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring to FIG. 1, there is shown a drive transmission mechanism of a 
prior open end spinning machine similar to that described in U.S. Pat. No. 
3,354,626 and this invention can be applied to such a spinning machine. 
Although only one spinning unit is shown in FIG. 1, the spinning machine 
normally comprises a number of spinning units along each side of the 
spinning machine, and yarn ending operations are simultaneously effected 
in all the spinning units on starting the machine. 
Each spinning unit comprises a spinning rotor 1 into which opened fibers 
are supplied and formed into a yarn 9, means for feeding a sliver or 
roving 35 from a can 34, means for opening the sliver 35 into individual 
fibers and supplying them into the spinning rotor 1, means for taking up 
the yarn 9, and a winding roller 4 for winding the yarn 9 onto a bobbin 
11. The feeding means comprises lower and upper feeding rollers 2 and 7 
forming a nip therebetween, through which the sliver 35 is fed. The fiber 
opening and supplying means comprises a combing roller 5 of the well known 
type. The take-up means 3 includes a lower take-up roller and an upper 
take-up roller driven by the lower roller. The spinning rotor 1 may be of 
either the self-discharge type, wherein air in the interior of the 
spinning rotor is discharged through openings provided in the bottom of 
the spinning rotor due to its rotation, or the forced-discharge type, 
wherein air in the interior of the spinning rotor is discharged through an 
intake system (not shown) disposed outside of the spinning rotor. In any 
case, a subatmospheric pressure is produced in the interior of the 
spinning rotor 1 during rotation and the individual fibers opened by the 
combing roller 5 are thereby drawn into the interior of the spinning rotor 
1. 
The take-up means further includes a yarn take-up tube 1' disposed between 
the take-up roller 3 and the spinning rotor 1 so as to be in air 
communication with the latter. As is well known, the individual fibers are 
twisted into the yarn end in the spinning rotor 1 and the resultant yarn 9 
is taken up from the spinning rotor 1 through the take-up tube 1' by the 
take-up rollers 3. Although only one pair of take-up rollers 3 is shown, 
all the lower take-up rollers equal in number to the number of spinning 
units, are mounted on a common driving shaft 10 mounted for rotation in 
the frame of the spinning machine. The winding roller 4, which has 
crossing grooves, is in driving relationship with the bobbin 11 to wind a 
package thereon in a cross winding manner. All the winding rollers 4 of 
the spinning units are attached to a driving shaft 12 rotatably mounted in 
the machine frame and controlled by an electromagnetic brake MB2 in a 
manner as discussed below. 
To detect a yarn breakage, a first and a second yarn breakage detecting 
device 6 and 6', both of which form part of this invention, are provided 
respectively adjacent the yarn outlet of the yarn take-up tube 1' and in a 
position between the take-up roller 3 and the winding roller 4. In this 
embodiment, the second yarn breakage detecting device 6' is of the 
non-contact type, for example, a phototube unit capable of detecting the 
yarn breakage without contacting the yarn. Such a non-contact type yarn 
breakage detector may be disposed at any position between the yarn outlet 
of the yarn take-up tube 1' and the winding roller 4. 
The driving shaft 12 is rotated through a train of gears 13, 14 and 15 by 
the driving shaft 10 in the same direction as the shaft 10. 
Also, all the sliver feed rollers 7 are mounted on a common driving shaft 8 
connected through a sliver feed electromagnetic clutch MC3 (hereinafter 
referred to as the "feed clutch") with a shaft 16' supporting a gear 16, 
which is driven through a train of gears 17, 18, 19 and 20 by an electric 
motor M and controlled by an electromagnetic brake MB1 as discussed below. 
The shaft 10 for driving the take-up rollers 3 is connected through an 
electromagnetic clutch MC1 with a shaft 17' supporting the gear 17. The 
clutch MC1 is hereinafter referred to as the "reverse clutch" because the 
yarn is fed in a reverse direction when the clutch MC1 is in engagement. 
To rotate the shaft 10 in a forward direction, the gear 18 supported by a 
shaft 18' is connected through an electromagnetic clutch MC2 and a train 
of gears 23, 24 and 25 with the shaft 10. The gear 23 is mounted on the 
shaft 10 so as to be positioned between the reverse clutch MC1 and the 
gear 15. The gear 23 meshes with the intermediate gear 24, which meshes in 
turn with the gear 25 supported by a shaft 26. The shaft 26 is connected 
to a driven member of the clutch MC2. The clutch MC2 is hereinafter 
referred to as the "forward clutch," because the yarn is fed in a forward 
direction when it is in engagement. 
Mounted around a pair of pulleys 30 and 31 is an endless belt 29, which is 
in driving relationship with all the spinning rotors 1 in a conventional 
manner so that all the spinning rotors 1 are simultaneously rotated in the 
same direction. The pulley 30 is driven through a train of gears 32, 32', 
33 and 20 by the motor M. 
Therefore, it will be understood that in this embodiment all the spinning 
units are driven by the single motor M and their operation is controlled 
by controlling the motor M, forward clutch MC2, reverse clutch MC1, feed 
clutch MC3, electromagnetic brakes MB1 and MB2, and yarn breakage sensing 
devices 6 and 6' by means of a control apparatus 21. 
Details of the yarn breakage sensing device 6 and the control apparatus 21 
are shown respectively in FIG. 2 and FIGS. 3A and 3B. In FIG. 2, there is 
shown a yarn breakage sensing device, which is similar to that disclosed 
in British Pat. No. 1,158,623. The sensing device includes a base plate 6a 
provided with a V-shaped guide notch 6b, adjacent to which the upper end 
of the take-up tube 1' extends upwardly, and a yarn sensing lever 6c 
pivotably connected with the base plate 6a. The yarn sensing lever 6c is 
provided with oppositely extending plate-like arms 6e and 6f made of 
suitable known ferromagnetic material and associated respectively with an 
electromagnet SOLe and a permanent magnet 6g. When the magnet SOLe is 
energized, it attracts the arm 6e and causes the lever 6c to turn from a 
yarn breakage position (shown in FIG. 2) into a righthandmost inoperative 
position (not shown). In the yarn breakage position, the lever 6c abuts at 
its upper end 6d against an elastic support block 6h to hold the yarn 9 
therebetween. When the lever 6c turns toward the yarn breakage position, 
the lower arm 6f is attracted by the permanent magnet 6g thereby to urge 
the lever 6c into the yarn breakage position. This ensures that the lever 
6c provides an increased pressure against the support block 6h to firmly 
hold the yarn 9. 
When the spinning machine is stopped, the fiber feeding means is first 
stopped to discontinue the supply of fibers to the spinning rotors. At 
that time, yarn breakage occurs in each of the spinning rotors or a 
lowering of tension of the yarn occurs due to the discontinuance of fiber 
supply and therefore the lever 6c is turned into the yarn breakage 
position in which its end 6d elastically holds the yarn end in cooperation 
with the support block 6h before the yarn end moves out of the take-up 
tube 1'. When the lever 6c is in this position, a magnet 6i mounted 
thereon causes a reed switch PRS to be closed thereby to energize the 
electromagnet SOLe under the control of the control apparatus 21 as 
described in detail hereinafter, whereupon the electromagnet SOLe attracts 
the upper arm 6e against the action of the permanent magnet 6g, this 
causing the lever 6c to be moved into the righthandmost position (in which 
it does not contact with the yarn) and the yarn end held by the lever 6c 
to be released. Such movements of the levers 6c to the righthandmost 
position occur simultaneously in all of the spinning units. Therefore, 
when the spinning machine is re-started with the levers 6c maintained in 
the righthandmost position, fibers will be supplied simultaneously into 
all the spinning rotors regardless of whether or not a particular yarn 
ending operation has been achieved successfully, if the second yarn 
breakage detecting device 6' according to this invention were not provided 
for each spinning unit. This results in the aforementioned disadvantages. 
A suitable form of the control apparatus 21 and its operation are described 
below in conjunction with FIGS. 3A and 3B. 
The vertical lines labelled respectively with a plus symbol (+) and a minus 
symbol (-) represent the positive and negative sides of a source of 
current, and the various elements constituting the control apparatus 21 in 
this embodiment of the invention are connected in the manner shown in 
FIGS. 3A and 3B. A power on-off switch SW.sub.1, stop pushbutton SW.sub.2 
and start pushbutton SW.sub.3 are in series with each other. These 
switches are in the on state, i.e., closed during spinning operation of 
the spinning machine. 
When the spinning machine is stopped, the stop pushbutton SW.sub.2 is 
turned off with the pushbuttons SW.sub.1 and SW.sub.3 maintained in the on 
state, whereupon a motor switch relay MS is deenergized to open its 
contacts MS-1 to MS-3 thereby causing the motor M to rotate by inertia. 
Simultaneously, contacts MS-4 are opened to deenergize a timer TR1, 
whereby its contacts TR1-1 are opened to deenergize a relay CR2. By the 
opening of normally open contacts CR2-3, a relay CR3 is deenergized to 
open the normally open contacts CR3-2 and close the normally closed 
contacts CR3-3, whereby the supply clutch MC3 and supply brake MB1 both 
connected to the shaft 8 (FIG. 1) are brought into the off state and on 
state respectively, stopping the supply of fibers. On the other hand, 
since the normally closed contacts MS-5 and CR2-2 are closed 
simultaneously with the deenergization of the relays MS and CR2, a timer 
or time counter TR13 for a delayed operation of the electromagnetic brake 
MB2 associated with the winding shaft 12 (FIG. 1) starts to count to a set 
time. When it counts up the set time, the normally closed contacts TR13-1 
cause a control relay CR4 to be deenergized, whereupon the normally open 
contacts CR4-3 are opened to bring the forward clutch MC2 into the off 
state and the normally closed contacts CR4-4 are closed to bring the 
winding shaft brake MB2 into the on state. Thus, the spinning machine is 
topped. 
Due to the afore-mentioned discontinuance of fiber supply, yarn breakage or 
reduction of yarn tension occurs before the stoppage of the spinning 
machine. At that time, the yarn sensing levers 6c of the first yarn 
breakage sensing devices 6 in all of the spinning units, which have been 
maintained in a yarn sensing position during normal spinning operation, 
are turned to the lefthandmost, yarn breakage position shown in FIG. 2 by 
the assistance of the permanent magnet 6g attracting the lower arm 6f 
thereto. This causes the reed switch PRS to be closed by the permanent 
magnet 6i mounted on each lever 6c, thereby energizng a solenoid SOL.sub.f 
to bring a known supply clutch (not shown) out of engagement, which is 
provided for each of the fiber supply means 2 and normally in engagement 
to allow the associated fiber supply means 2 to supply the fibers into the 
corresponding spinning rotor 1. Thus, the fiber supply is prevented in all 
of the spinning units, in which the levers 6c are in the yarn breakage 
position shown in FIG. 2. 
With respect to the second yarn breakage sensing device 6', it is apparent 
from FIG. 3B that the device 6' comprises a photoelectric cell PH capable 
of always sensing yarn breakage. Even if the yarn breakage occurs on 
stopping or starting the spinning machine, this photoelectric cell PH 
disposed above the take-up roller 3 is not responsive to yarn breakage so 
far as the yarn end resulting from the yarn breakage remains at least in 
the yarn take-up tube 1'. This allows a switch PH-1 of the photoelectric 
cell PH to be maintained closed. Therefore, the solenoid SOLe for 
attracting the lever 6c thereto can be energized to bring the lever 6c 
into the righthandmost, inoperative position, whereby the reed switch PRS 
is opened to deenergize the solenoid SOLf in each spinning unit, thus 
bringing the supply clutch (not shown), provided for each of the fiber 
supplying means 2, into engagement. However, in the case where the 
resultant yarn end in a specific spinning unit is wound up on the 
associated winding roller 4 for some reason, the second yarn breakage 
sensing device 6' can detect this condition and causes its switch PH-1 to 
be opened thereby to prevent the energization of the solenoid SOLe for 
attracting the lever 6c thereto. Therefore, the lever 6c only in the 
specific spinning unit can be maintained in the yarn breakage position 
shown in FIG. 2 and the solenoid SOLf only in such specific spinning unit 
is energized to bring the associated supply clutch out of engagement, 
preventing the fiber supply to the specific spinning unit. 
When the spinning machine is restarted from the above discussed stop 
condition, both the start and stop switches WS.sub.3 and SW.sub.2 are on 
to close the circuit. Because of this, the relay MS is energized to close 
the normally open contacts MS-1 to MS-4, whereupon the motor starts to 
rotate and the timer TR1 is picked up to count out the set time. 
When the timer TR1 counts up the set time, the contacts TR1-1 are closed to 
energize the relay CR2 thereby closing the contacts CR2-1, whereupon both 
the timers TR11 and TR12 count to the set times, respectively, while the 
contacts CR2-4 are closed to bring the reverse clutch MC1 into the on 
state and the contacts CR2-5 are opened to bring the winding shaft brake 
MB2 into the off state. Thus, the take-up rollers 3 and winding rollers 4 
are rotated in a reverse direction and the yarn ends can be pushed into 
the spinning rotors 1. When the timer TR11 counts up the set time, the 
contacts TR11-1 are closed to cause the relay CR3 to be energized through 
the closed contacts CR2-3 thereby to close the contacts CR3-2 and open the 
contacts CR3-3, whereupon the supply clutch MC3 common to all the spinning 
units is brought into engagement and the supply brake MB1 is brought out 
of engagement, thus allowing rotation of the fiber supply shaft 8. It is 
therefore understood that the fibers can be supplied into the spinning 
rotors 1 of all the spinning units, excepting a spinning unit in which the 
supply clutch provided for each fiber supply means 2 is out of engagement, 
and the yarn end connecting operations are carried out in the spinning 
rotors which have been supplied with the fibers. 
When the timer TR12 for setting a time, at which the taking up of the yarn 
is to begin in timed relation with the afore-mentioned yarn ending, counts 
up the set time, its normally open contacts TR12-1 close to energize the 
relay CR4 through the normally closed contacts TR13-1 of a timer TR13 and 
the timer TR3 starts to count to a set time. Upon energization of the 
relay CR4, the contacts CR4-3 close to energize the forward clutch MC2 
while the normally closed contacts CR4-2 and CR-4 open to deenergize both 
the reverse clutch MC1 and the winding shaft brake MB2. Thus, the take-up 
rollers 3 and winding rollers 4 are rotated in a forward direction so that 
the pulling out of the yarn 9 can be effected at a proper timing with 
respect to the connection of the yarn end with the fibers collected in the 
spinning rotor. 
When the set time of the timer TR3 elapses, its contacts TR3-1 close to 
energize the relay CR5 thereby opening the normally closed contacts CR5-1 
(FIG. 3B), whereupon the lever 6c, which has been attracted to the 
righthandmost, inoperative position by the solenoid SOLe energized through 
the closed contacts PH-1 due to the non-occurrence of the yarn breakage, 
is turned leftwardly in FIG. 2 by the deenergization of the solenoid SOLe 
and the action of the permanent magnet 6g and into the yarn sensing 
position in which the lever 6c contacts with the ended yarn 9 to detect 
yarn breakage. Moreover, since the normally open contacts CR5-2 close 
simultaneously with the opening of the contacts CR5-1, the reed switch PRS 
of the first yarn breakage sensing device 6 can detect the yarn breakage 
when it occurs. 
It is assumed that a yarn end connecting operation has failed in a specific 
spinning unit during the afore-mentioned starting operation of the 
spinning machine until the set time of the timer TR3 elapses. In this 
case, the relay CR5 is not yet energized and the normally closed contacts 
CR5-1 are maintained closed. However, the photoelectric cell PH of the 
always operative, second yarn breakage sensing device 6' can detect the 
failure of the yarn end connecting operation or the yarn breakage and 
causes the switch PH-1 to open, whereupon the solenoid SOLe only in the 
specific spinning unit is deenergized to allow the lever 6c to turn to the 
yarn breakage position shown in FIG. 2. This causes the reed switch PRS to 
be closed. Since the switch PH-2 is closed upon the yarn breakage, the 
solenoid SOL.sub.f in the specific spinning unit is energized to bring the 
supply clutch for the specific spinning unit out of engagement. Thus, the 
fiber supply to the specific spinning unit can be prevented. 
Furthermore, if a yarn breakage should occur in a specific spinning unit 
after the lapse of the set time of the timer TR3, i.e., during the normal 
spinning operation, the fiber supply to the specific spinning unit also 
can be stopped in the same manner as in the prior art upon the 
disengagement of the supply clutch for the specific spinning unit, which 
is caused by the closing of the reed switch PRS resulting from the turning 
of the lever 6c to the yarn breakage position shown in FIG. 2. 
Although the first embodiment of this invention hitherto described employs, 
as the second yarn breakage sensing device 6', the photoelectric cell PH 
which is not in contact with the yarn to sense the latter, the second yarn 
breakage sensing device 6' may be of the same type as the first yarn 
breakage sensing device 6 which contacts with the yarn for sensing. In 
this case, an electric circuit for a control apparatus 21 may be formed 
substantially in the same manner and the second yarn breakage sensing 
device 6' is preferably disposed between the take-up roller 3 and the 
winding roller 4. 
In an open end spinning machine including devices for regulating the 
winding tension of the yarn, each regulating device is available as a part 
of the second yarn breakage device 6'. For example, a regulating device of 
FIGS. 4 and 5 as disclosed in Japanese Laid-Open U.M. Specification No. 
53-19046 comprises a tension regulating swing arm 44 having a 
semi-cylindrical portion 42 loosely mounted onto a horizontally extending 
shaft 41, and a balance weight 46 mounted on part of the portion 42 
opposite to the arm 44 so that the balance weight 46 is positioned on the 
front side of a vertical plane including the center axis of the shaft 41 
when the arm 44 is moved to the lowermost position thereof and on the back 
side of the vertical plane when the arm is moved to the uppermost position 
due to changes in the yarn tension. The balance weight 46 is adapted to 
provide a counter moment smaller than that of the arm 44. To detect a yarn 
breakage by using such a regulating device, a microswitch 43 is arranged 
beyond the range of swing of the arm 44 during the normal spinning 
operation and within the range of swing of the arm 44 when the yarn 
breakage occurs. If the yarn breakage should occur, the arm 44 will swing 
to the position shown by the dot and dash line in FIG. 4 to operate the 
microswitch 43. Thus, the yarn breakage occurring under the transient 
conditions of the spinning machine, i.e., during a stopping and starting 
operation, can be detected. It will be obvious to those skilled in the art 
to connect contacts of the microswitch 43 in a similar manner to the 
contacts PH-1 and PH-2 of the photoelectric cell PH shown in FIG. 3B. 
FIGS. 6A and 6B show an electric circuit for another embodiment of this 
invention, which is different from the circuit of FIGS. 3A and 3B in that 
the yarn end is adapted to be held between the block 6h and the end 6d of 
the lever 6c to prevent the occurrence of snarls in the yarn end. In FIGS. 
6A and 6B, when the start switch SW.sub.3 is pushed down to start the 
spinning machine, a timer TR0 starts to count to a set time and then the 
set time elapses to close the contacts TR0-1. At that time, if the second 
yarn breakage sensing device 6' is sensing the presence of yarn (i.e., 
switch PH-1 is being closed), the solenoid SOLe will be energized thereby 
to cause the lever 6c to turn from the yarn breakage position shown in 
FIG. 2 to the righthandmost, inoperative position. After the lapse of the 
set time of the timer TR0, the timer TR3 counts up the set time to open 
the normally closed contacts TR3-1 thereof, whereupon the timer TR0 is 
re-set and the solenoid SOLe is deenergized to release the lever 6c. Thus, 
the lever 6c is turned to the yarn sensing position. On stopping, the stop 
switch SW.sub.2 is pushed down to stop the motor M. At the same time, the 
solenoid SOLe is energized to turn the lever 6c from the yarn breakage 
position to the righthandmost position. When the stopping operation is 
completed, the solenoid SOLe is deenergized to turn the lever 6c from the 
righthandmost position to the yarn breakage position to hold the yarn end 
between the block 6h and the end 6d of the lever 6c. 
Therefore, it will be apparent from the foregoing that since each spinning 
unit according to this invention is provided with the second yarn breakage 
sensing device capable of sensing the yarn breakage even during the 
stopping and starting operations of the spinning machine, it is possible 
to completely prevent the unnecessary supply of fibers into the spinning 
rotor during such operations. Thus, there will occur no clogging of the 
spinning rotor by the fibers and the spinning unit is free from the danger 
of a fire and the disadvantages of reduction of the useful life of the 
parts, especially a spindle for the spinning rotor, due to contamination, 
damage and over-heating thereof. 
Although preferred embodiments has been described above, it will be readily 
understood by those skilled in the art that this invention is equally 
applicable to other open end spinning machines having different 
constructions. For example, the spinning machine may employ a single 
electromagnetic clutch in lieu of the reverse and forward clutches MC1 and 
MC2. Also, the spinning rotors may be driven by a separate motor 
independent of the motor M, and the feeding of the yarn end in the reverse 
direction may be carried out by storing up an additional length of yarn 
between the take-up roller 3 and the take-up tube 1', when the spinning 
machine is stopped and releasing the stored yarn when it is necessary to 
feed the yarn end in the reverse direction, whereupon the released yarn is 
sucked into the spinning rotor by the subatmospheric pressure produced 
therein. Furthermore, the second yarn breakage sensing device 6' may 
utilize the principles employed in an Uster evenness tester, wherein a 
yarn is passed through a gap between capacitors forming a part of a high 
frequency circuit to determine changes in capacitance and the changes are 
detected by a resonance circuit.