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(11) | EP 1 048 762 A2 |
| (12) | EUROPEAN PATENT APPLICATION |
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| (54) | Drive device for driving draft rollers in spinning machine |
| (57) Spinning machine includes draft rollers 3, 4 and 5 and a drive device for driving
the draft rollers. The drive device has a drive unit 6 for driving the front draft
roller 5, and a drive unit 7 for driving the back and middle draft rollers 3 and 4.
Each drive unit has a variable speed motor M2 or M3 and a transmission mechanism,
and the variable speed motor of the drive unit 6 for driving the front draft roller
5 is a synchronous AC motor having permanent magnets. A reverse rotation preventing
device including a ratchet wheel and a pawl is arranged in the drive unit 6 for preventing
a reverse rotation of the front draft roller 5, occurring with a reverse rotation
of the synchronous motor M2, caused by the action of the permanent magnets in the
synchronous motor upon starting the synchronous motor. |
BACKGROUND OF THE INVENTION
1. Field of the Invention
[0001] The present invention relates to a drive device for driving draft rollers in a draft part of a spinning machine such as a spinning frame and, more particularly, the present invention relates to a drive device including a plurality of drive units for driving the draft rollers, at least one of the drive units having synchronous motor as a variable speed motor for driving the draft roller.
[0002] A drive device for driving draft rollers of the above-mentioned type has been known, for example, from Japanese Unexamined Patent Publication (Kokai) No. 55-128024. In this known technique, three elongated draft rollers in the draft part of the spinning machine are connected to synchronous motors, respectively, and each of the synchronous motors is imparted with an output signal from a frequency generator via a frequency regulator and a frequency converter so that each draft roller is independently rotated synchronously with the signal.
[0003] The above arrangement is advantageous in that the change of a rotational speed ratio between the draft rollers (the change of a draft ratio) can be very easily carried by using the frequency converter or the frequency regulator for controlling the former, and therefore, the operator is free from the troublesome operation for replacing gears for changing the draft ratio.
[0004] There is a permanent magnet type synchronous AC motor, as a synchronous motor, which includes a stator and a rotor having permanent magnets and cage conductors. when the motor starts, the rotor is started to move by the torque derived as an induction motor from the cage conductors, and as the rotational speed rises and approaches a synchronous speed, a so-called "synchronous pull-in" occurs to pull the magnetic field of the rotor generated by the permanent magnet into step with the revolving field of the stator. This motor is advantageous in that heat loss and energy consumption are minimized since no current flows through the cage conductors of the rotor after the synchronous pull-in occurs.
[0005] However, in the case where the synchronous motor of this type is adopted as a motor for driving draft rollers of a spinning machine, the following phenomenon occurs. A stop position of the rotor of the motor in the rotational direction (stop position of poles of the permanent magnets of the rotor) varies every time it stops, as shown in Figs. 7A and 7B in the attached drawings. In Figs. 7A and 7B, the arrow 21A shows a field of the permanent magnet of the rotor, and the arrow 22A shows a revolving field of the stator; the arrow X shows the normal rotating direction of the rotor, and the arrow Y shows the reverse rotating direction of the rotor. Upon a start of the machine, if polarity of the revolving field 22A of the stator is opposite to that of the field 21A of the permanent magnet of the rotor and the revolving field 22A of the stator is in front of the field 21A of the permanent magnet the rotor in the normal rotational direction X, the rotor may be pulled in the normal rotational direction (see Fig. 7A), but if the positional relationship is reversed to that of Fig. 7A, the rotor is pulled in the reverse rotational direction to slightly rotate in reverse (see Fig. 7B). As a result, the draft roller driven by the reversely rotated synchronous motor also rotates in reverse whereby a fiber bundle is slackened or is pulled between that draft roller and another draft roller driven by the normally rotated synchronous motor, causing an undesirable or erroneous draft, leading to yarn breakage or a yarn fault.
[0006] Japanese Unexamined Patent Publication (Kokai) No. 7-3539 and Japanese Unexamined Utility Model Publication (Kokai) No. 59-113362, for example, discloses a drive device for driving draft rollers, which includes a ratchet mechanism for preventing a reverse rotation of a draft roller. The purpose of the ratchet mechanism in the above described documents is to prevent the reverse rotation of the draft roller caused by a torsional movement of the draft roller in the case where the draft roller is driven from one end thereof. These publications are not aimed at preventing a reverse rotation of the draft shaft, occurring with a reverse rotation of the synchronous motor upon starting the synchronous motor.
SUMMARY OF THE INVENTION
[0007] An object of the present invention is to provide a drive device for driving draft rollers which includes a permanent magnet type synchronous AC motor, which is simple in construction, and which can minimize an undesirable draft which may occur upon starting the synchronous motor.
[0008] The present invention provides a drive device for driving a plurality of draft rollers in a spinning machine, the drive device comprising a plurality of drive units for driving the draft rollers, each of the drive units having a variable speed motor and a transmission mechanism operatively connected to the variable speed motor for driving at least one draft roller, one of the variable speed motors comprising a synchronous AC motor having permanent magnets arranged therein. The drive device also comprises a reverse rotation preventing device arranged in the transmission mechanism operatively connected to the synchronous motor for preventing a reverse rotation of the associated draft roller, occurring with a reverse rotation of the synchronous motor caused by the action of the permanent magnets in the synchronous motor upon starting of the synchronous motor.
[0009] In another feature of the present invention, the drive device also comprises a reverse rotation preventing device arranged in the transmission mechanism operatively connected to the synchronous motor for preventing a reverse rotation of the associated draft roller, occurring with a reverse rotation of the synchronous motor caused by the action of the permanent magnets in the synchronous motor upon a start of the synchronous motor, the transmission mechanism operatively connected to the synchronous motor having such a reduction ratio that the associated draft roller may otherwise be rotated in reverse to the extent to cause an undesirable draft.
[0010] In the above arrangements, since the reverse rotation preventing device prevents the draft roller associated with the drive unit including the synchronous motor from rotating in reverse upon starting thereof due to the permanent magnets arranged in the motor, the degree of slackening and/or stretching of a fiber bundle becomes less between the draft roller and the normally rotating draft roller to reduce an occurrence of an undesirable draft, compared with the case where a reverse rotation preventing device is not provided.
[0011] Preferably, the transmission mechanism operatively connected to the synchronous AC motor includes a gear attached to one end of the associated draft roller, and the other end of the associated draft roller is freely rotatable.
[0012] Preferably, the reverse rotation preventing device comprises a ratchet wheel rotatable with the associated draft roller and a pawl engageable with the ratchet wheel.
[0013] Preferably, the transmission mechanism operatively connected to the synchronous AC motor includes a shaft, and the ratchet wheel is attached to the shaft.
[0014] Preferably, the pawl is swingeably supported by a machine frame and the reverse rotation preventing device further comprises an actuator to swingeably move the pawl, so that the pawl is maintained at a waiting position in which it is disengaged from the ratchet wheel when the draft roller is normally rotating and is brought into an operating position in which it is engaged with the ratchet wheel when the draft roller is stopped.
[0015] Since the pawl is disengaged from the ratchet wheel during the operation of the spinning machine, a level of noise is lower than that in the case where the pawl is always engaged with the ratchet wheel and repeatedly touches the latter.
[0016] Preferably, the draft rollers comprise a back draft roller, a middle draft roller and a front draft roller, and the drive units comprise a first drive unit for driving the back and middle draft rollers and a second drive unit for driving the front draft roller.
[0017] Preferably, the reverse rotation preventing device is arranged in the transmission mechanism of the drive unit having the front draft roller.
[0018] Preferably, the reverse rotation preventing device comprises a one-way clutch allowing only the normal rotation of the draft roller.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] The present invention will become more apparent from the following description of the preferred embodiments with reference to the accompanying drawings in which:
Fig. 1 is a perspective view of a drive device for driving draft rollers according to the embodiment of the present invention;
Fig. 2 is a front view of the reverse rotation preventing device including a ratchet wheel and a pawl;
Fig. 3 is a side cross-sectional view of the permanent magnet type synchronous AC motor;
Fig. 4 is a cross-sectional view of the motor of Fig. 3, taken along the line IV-IV in Fig. 3;
Fig. 5 is a schematic view of a part of the spinning machine, including a control system;
Fig. 6 is a side cross-sectional view of the draft part; and
Figs. 7A and 7B are views showing the relationship between the magnetic poles of the rotor and the revolving field of the stator.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0020] Fig. 1 illustrates a draft part 2 of a spinning frame 1 (Fig. 5) which is a representative spinning machine. Here, the draft part 2 includes two sets of back draft rollers 3, middle draft rollers 4 and front draft rollers 5. A drive device for driving the draft rollers 3, 4 and 5 in the draft part 2 includes two drive units; one being a front roller drive unit 6 and the other being a back and middle roller drive unit 7. Each drive unit 6 or 7 has a synchronous motor M2 or M3, and a transmission mechanism operatively connected to the synchronous motor M2 or M3.
[0021] In the front roller drive unit 6, the rotation of the synchronous motor M2 having no speed reducing device is transmitted from an output shaft 14 of the synchronous motor M2 to the front draft rollers 5 via the transmission mechanism including belt drive devices 8 and a drive shaft 9. In the back and middle roller drive unit 7, the synchronous motor M3 is coupled to a speed reducing device 10, and the rotation of the synchronous motor M3 is transmitted to the speed reducing device 10, and from the speed reducing device 10 to the back draft rollers 3 via the transmission mechanism, including belt drive devices 11 and a gear train 12, and then to the middle draft rollers 4 via gear trains 13.
[0022] Assuming that a draft ratio of the draft part 2 is 40, the ratio of the rotational speed of the back draft roller 3 to the rotational speed of the front draft roller 5 is 1:40, so the front draft roller 5 rotates significantly faster. Accordingly, assuming that the synchronous motors M2 and M3 rotate at the same rotational speed, the ratio of the reduction ratio of the transmission mechanism of the back and middle roller drive unit 7 from the synchronous motor M3 to the back draft rollers 3 to the reduction ratio of the transmission mechanism of the front roller drive unit 6 from the synchronous motor M2 to the front draft roller 5 is 1/40:1. Since the draft ratio between the back draft roller 3 and the middle draft roller 4 is small and approximately 1.3, the reduction ratio of the front roller drive unit 6 is far smaller than that of the back and middle roller drive unit 7.
[0023] Therefore, in the back and middle roller drive unit 7, the back and middle draft rollers 3 and 4 are hardly rotated in reverse, even if the synchronous motor M3 is slightly rotated in reverse. In the front roller drive unit, however, a slight reverse rotation of the synchronous motor M2 causes a reverse rotation of the front draft roller 5, which may causes an undesirable or erroneous draft between the front draft roller 5 and the middle draft roller 4.
[0024] In the front roller drive unit 6, a ratchet wheel 15 is keyed to the drive shaft 9 at an intermediate portion thereof, to constitute a reverse rotation preventing device T. As shown in Fig. 2, a pawl 17 is pivotally supported at one end thereof by a machine frame F so that the pawl 17 is swingeable up and down to engage with teeth 16 of the ratchet wheel 15. An intermediate portion of the ratchet wheel 15 is connected to a tip end of a piston rod 19 of a pneumatic cylinder 18 as an actuator for a rocking motion of the pawl 17. The piston rod 19 is biased by a spring 20 arranged in the cylinder 18 in the outwardly projecting direction. When the machine is operating (when the draft rollers are rotating), pressurized air is not supplied to the cylinder chamber 18a so that the pawl 17 is maintained at a waiting position A in which the pawl 17 is released from the ratchet wheel 15. On the other hand, when the draft rollers are stopped, the pressurized air is supplied to the cylinder chamber 18a and the pawl 17 is brought into an operating position B in which the tip end of the pawl 17 is engaged with the teeth 16 of the ratchet wheel 15. The engagement of the teeth 16 with the pawl 17 allows only the normal rotation of the drive shaft 9 and the front draft roller 5.
[0025] As shown in Figs. 3 and 4, the synchronous motors M2 and M3 comprise permanent magnet type synchronous AC motors. In each of the motors M2 and M3, a stator 22 is provided integrally with the inner wall of a housing 30. The stator 22 has a core 22a formed of laminated steel sheets, and coils 22b arranged through the core 22a in the up-down (axial) direction, to generate a revolving field by supplying an alternate current with a frequency thereof equal to that of the AC current.
[0026] The output shaft 14 is rotatably supported by bearings 31 in the front and rear ends of the housing 30. A rotor 21 is provided integrally with the output shaft 13 at a position radially opposite to the inside of the stator 22. The rotor 21 includes a core 21a formed of laminated thin steel sheets, aluminum cage conductors 21b surrounding the rotational axis of the motor at a circumferentially constant pitch and extending through the core 21a in the form of a trapezoidal cross-section, and a pair of permanent magnets 21c embedded in the rotor 21 inside the cage conductors 21b. The pair of permanent magnets 21c have N and S poles on the side facing the stator 22, respectively. There is a predetermined radial gap between the rotor 21 and the stator 22 for facilitating the rotation of motor.
[0027] Fig. 5 shows the spinning frame 1 having spindles 40, a ring rail 41, the above-mentioned draft part 2, and a controller 50 for controlling them. A spindle drive system 43 for driving the spindles 40 includes a spindle drive motor M1 comprising an induction motor. The spindle drive system 43 from the spindle drive motor M1 to the spindles 40 includes a reference pulse generator 44. Also, a ring rail lifting device 45 includes a ring rail drive motor M4 comprising an induction motor.
[0028] Motors M1 to M4 are connected to inverters INV1 to INV4, respectively. The inverters INV1 to INV4 are controlled by commands issued from the controller 50. The controller 50 is imparted from outside with spinning conditions such as a rotational speed of the spindles, a draft ratio, a twist number and a layer pitch. When the spindle drive motor M1 is rotated via the inverter INV1 to establish a given spindle rotational speed, the reference pulse generator 44 detects the rotation thereof and issues a reference pulse "a" corresponding to the spindle rotational speed to the controller 50. The controller 50 calculates rotation commands to be input to the remaining inverters INV2 to INV4 to satisfy the spinning conditions, based on the reference pulse "a" and the spinning conditions, and issues rotation control commands to the inverters INV2 to INV4, respectively.
[0029] The inverters INV2 to INV4 supply frequency-controlled alternating electric power to the corresponding drive motors M2 to M4, according to these control commands. The rotational speeds of the drive motors M2 to M4 are controlled in accordance with the given frequencies to satisfy the above spinning conditions. In this regard, reference numerals 51 to 53 denote rotational speed detecting means for detecting the rotational speeds of the ring rail lifting device 45, the front roller drive unit 6, and the back and middle roller drive unit 7, respectively, for inputting the detected values to the controller 50 which in turn monitors the occurrence of operational abnormality of the machine by determining whether or not the detected values coincide with the rotation commands issued from the controller 50.
[0030] When the machine is stopped, the pressurized air is supplied into the cylinder chamber 18a to bring the pawl 17 into the operating position B in which the pawl 17 engages with the teeth 16 of the ratchet wheel 15. when the machine is started and the spindle drive motor M1 begins to rotate by the command from the controller 50, the reference pulse generator 44 generates the reference pulse "a", as stated before, and the speed control commands are issued from the controller 50 based on this reference pulse and the spinning conditions given in advance, so that frequency-controlled alternate electric power is supplied to the remaining motors M2 to M4 via the inverters INV2 to INV4. The motors M2 to M4 are thus rotated.
[0031] In the two synchronous motors M2 and M3, alternate electric power, the frequency of which is controlled, is supplied to the coil 22b of the stator 22 by the inverters INV2 and INV3. Therefore, a revolving field is generated in the coil 22b of the stator 22. An induced current flows through the cage conductors 21b of the rotor 21, based on the revolving field, to generate a field which generates, with the revolving field, a motor starting torque, whereby the rotor 21 or the output shaft 14 begins to rotate in the normal direction, causing the front draft roller 5, the back draft roller 3 and the middle draft roller 4 to rotate in the normal direction. At this time, the pawl 17 in the operating position B repeatedly disengages relative to the teeth 16 of the ratchet wheel 15 while compressing the pressurized air in the cylinder chamber 18a. After a time period preset by a timer (not shown) has lapsed from start-up of the rotation, the pressurized air supplied to the cylinder 18 is removed whereby the pawl 17 is displaced to the waiting position A by the bias of the spring 20 to disengage from the teeth 16 of the ratchet wheel 15. Thus, no engagement occurs between the pawl 17 and the teeth 16 and no noise is generated during the rotation of the draft rollers. When the rotor 21 is accelerated closer to the synchronous speed, the difference between the speed of the revolving field and the rotational speed of the permanent magnets 21c becomes extremely small, and the magnetic field of the permanent magnets 21c is pulled into the revolving field (the synchronous pull-in phenomenon), resulting in the synchronous rotation. By supplying an alternate electric power of a low frequency through the inverters INV2 and INV3 at a starting stage, the synchronous pull-in occurs while the speed of the revolving field of the stator 22 is at a low level. When the synchronous rotation has been established, no induced current flows through the cage conductors 21b of the rotor 21, whereby no heat is generated to attain energy saving, unlike the conventional induction motor in which an induced current always flows through the rotor to generate heat.
[0032] In this way, the draft rollers 3 to 5 rotate so as to realize the given draft ratio, the ring rail 41 repeats the lifting motion to realize the given layer pitch, and the spindles 40 rotate to realize the given twist.
[0033] When the synchronous motors M2 and M3 start to rotate, the rotor 21 may rotate reverse to the normal rotational direction due to magnetic attraction of the permanent magnets 21c of the rotor 21 toward the revolving field of the stator 22, if a polarity of the revolving field is different from that of the permanent magnets 21c of the rotor 21 and the revolving field 22A of the stator 22 is in front of the field 21A of the permanent magnets 21c of the rotor 21 in the rotational direction Y which is reverse to the normal rotational direction X (see Fig. 7B). The reverse rotation of the motor is not so serious in the back and middle roller drive unit 7 because the reduction ratio thereof is large and the back and draft rollers 3 and 4 are not substantially rotated in reverse. On the other hand, the reverse rotation of the motor is serious in the front roller drive unit 6, because the reduction ratio thereof is small, as described above, and the front draft roller 5 is rotated in reverse to such an extent that an undesirable or erroneous draft would occur between the front draft roller 5 and the middle draft roller 4.
[0034] However, according to the present invention, the ratchet wheel 15 is engaged with the pawl 17 and the drive shaft 9 is unable to rotate in reverse, so the front draft roller 5 is prevented from rotating in reverse and a risk of slack in the fiber bundle caused by the reverse rotation of the front draft roller 5 is avoided. Upon the start of the machine, the middle draft roller 4 begins to rotate in the normal direction, while the front draft roller 5 is stopped, slack in the fiber bundle (see P2 in Fig. 6) may occur between the front draft roller 5 and the middle draft roller 4. However, the amount of such a slack P2 in the fiber bundle will be smaller than that slack in the fiber bundle (see P1 in Fig. 6) in the prior art in which the middle draft roller 4 normally rotates and the front draft roller 5 reversely rotates. The synchronous motor M2 in the front roller drive unit 6 is subsequently rotated in the normal direction to thereby drive the front draft roller 5 to rotate in the normal direction. Thus, the drafting operation is carried out in the draft part 2. Since the slack in the fiber bundle is small, as described above, the risk of undesirable or erroneous drafting due to the slack is small. Needless to say, the pawl 17 is returned to the waiting position A, after a predetermined time period has lapsed from the time in which the synchronous motor M2 is rotated in the normal direction.
[0035] In the above embodiment, a mechanism including the ratchet wheel 15 and the pawl 17 engageable therewith is used as a reverse rotation preventing device, but it is possible to modify the reverse rotation preventing device from the illustrated example. For example, it is possible to use a one-way clutch of a well-known type between the drive shaft and the machine frame, allowing the drive shaft to rotate only in the normal direction.
[0036] Also, in the above mentioned embodiment, in the spinning frame, a reverse rotation preventing device is not provided in the back and middle roller drive unit 7 since the back and middle roller drive unit 7 has a greater reduction ratio, but it is possible to provide a reverse rotation preventing device in the back and middle roller drive unit 7 if the reduction ratio of the drive unit 7 from the synchronous motor M3 to the back and middle draft rollers 3 and 4 is small and the reverse rotation of the synchronous motor M2 derived from the above-mentioned permanent magnets 21a causes the back and middle draft rollers 3 and 4 to rotate in reverse to such an extent that an undesirable or erroneous draft occurs. In this case, there might be a possibility that the front draft roller 5 rotates in the normal direction and the middle draft roller 4 is prevented from rotating in reverse. Even in such a case, the fiber bundle present between the middle and front draft rollers 4 and 5 would be less pulled than in the case where a reverse rotation preventing device is not provided so that the front draft roller 5 normally rotates and the middle draft roller 4 reversely rotates. Thus, in this case too, an undesirable or erroneous draft is also mitigated. While both of the front roller drive unit 6 and the back and middle roller drive unit 7 are provided with synchronous motors, respectively, as a drive source in this embodiment, a servo-motor may be used as a drive motor for the back and middle roller drive unit 7.
[0037] As described above, according to the present invention, a draft roller drive device employs a synchronous AC motor having permanent magnets which is advantageous in having a lower energy consumption and less heat loss. While the motor of this type may reversely rotate at a start thereof due to the permanent magnets arranged therein, a reverse rotation preventing device provided in the drive device for driving draft rollers including the synchronous motor prevents the draft roller from reversely rotating, whereby the fiber bundle present between that draft roller and another draft roller which normally rotates is less pulled or slackened than in the case where no reverse rotation preventing device is provided, to reduce an undesirable or erroneous draft.
1. A drive device for driving a plurality of draft rollers in a spinning machine, said
drive device comprising:
a plurality of drive units for driving the draft rollers, each of said drive units having a variable speed motor and a transmission mechanism operatively connected to said variable speed motor for driving at least one draft roller;
one of the variable speed motors comprising a synchronous AC motor having permanent magnets arranged therein; and
a reverse rotation preventing device arranged in the transmission mechanism operatively connected to said synchronous motor for preventing a reverse rotation, of the associated draft roller, occurring with a reverse rotation of said synchronous motor caused by the action of the permanent magnets in the synchronous motor upon starting the synchronous motor.
2. A drive device for driving a plurality of draft rollers in a spinning machine, said
drive device comprising:
a plurality of drive units for driving the draft rollers, each of said drive units having a variable speed motor and a transmission mechanism operatively connected to said variable speed motor for driving at least one draft roller;
one of the variable speed motors comprising a synchronous AC motor having permanent magnets arranged therein; and
a reverse rotation preventing device arranged in the transmission mechanism operatively connected to said synchronous motor for preventing a reverse rotation, of the associated draft roller, occurring with a reverse rotation of said synchronous motor caused by the action of the permanent magnets in the synchronous motor upon starting the synchronous motor, said transmission mechanism operatively connected to said synchronous motor having such a reduction ratio that said associated draft roller may otherwise be rotated in reverse to an extent to cause an undesirable draft.
3. A drive device according to claim 1 or 2, wherein said transmission mechanism operatively
connected to said synchronous AC motor includes a gear attached to one end of the
associated draft roller, and the other end of said associated draft roller is freely
rotatable.
4. A drive device according to claim 1 or 2, wherein said reverse rotation preventing
device comprises a ratchet wheel rotatable with the associated draft roller and a
pawl engageable with the ratchet wheel.
5. A drive device according to claim 4, wherein said transmission mechanism operatively
connected to said synchronous AC motor includes a shaft, and said ratchet wheel is
attached to said shaft.
6. A drive device according to claim 5, wherein the pawl is swingeably supported by a
machine frame and said reverse rotation preventing device further comprises an actuator
to swingeably move the pawl, so that the pawl is maintained at a waiting position
in which it is disengaged from the ratchet wheel when the draft roller is normally
rotating and is brought into an operating position, in which it is engaged with the
ratchet wheel, when the draft roller is stopped.
7. A drive device according to claim 1 or 2, wherein said draft rollers comprise a back
draft roller, a middle draft roller and a front draft roller, and said drive units
comprise a first drive unit for driving the back and middle draft rollers and a second
drive unit for driving the front draft roller.
8. A drive device according to claim 7, wherein said reverse rotation preventing device
is arranged in the transmission mechanism of the drive unit driving the front draft
roller.
9. A drive device according to claim 1 or 2, wherein said reverse rotation preventing
device comprises a one-way clutch allowing only the normal rotation of the draft roller.