RING SPINNING MACHINE

Abstract: A ring spinning machine has a direct drive spindle (1) rotatably supported by an upper bearing (2) in a bolster (11) and connected to a rotor (3) of a spindle motor (20) having an upper structure including upper coil end (5) of a stator (4) thereof. A ring (7) is movable up and down along the spindle (1) to guide a yarn (10) to be wound on a bobbin (7) carried by the spindle (1). The inside diameter of the ring (7) is determined in relation to the size of the upper structure of the spindle motor (20) such that the upper structure can be received at least partially in the ring (7) when the ring (7) is moved to the lower end of its vertical stroke. The length of the unsupported portion of the spindle (1) is reduced to increase the critical or resonance speed of the spindle (1), thus enabling the spindle (1) to operate at an increased speed.

Description: BACKGROUND OF THE INVENTION The present invention relates to a ring spinning machine and, more particularly, to an improvement in the construction of a ring spinning machine of the type which is suited to high-speed operation has a direct drive spindle which is driven directly by an electric motor. A ring spinning machine has been known which has a direct drive spindle (referred to simply as "spindle" hereinafter) which is driven directly by an electric motor. The spindle has a ring for guiding a yarn to be wound on the spindle and a ring rail for supporting the ring and is constructed such that the lower end of the range through which the ring and the ring rail move is positioned above the motor structure of the spindle. This type of spindle is disclosed, for example, in Japanese Patent Examined Publication No. 54-32864 and Japanese Patent Unexamined Publication Nos. 49-20445 and 58-109633. Such spindles are required to operate at a high speed to comply with a demand for higher production efficiency in yarn spinning process. Unfortunately, however, the spindle of the conventional construction could not sufficiently meet this requirement because the rotation speed of the spindle is limited due to the presence of a resonance speed in primary flexural mode which appears between the upper free end of the spindle and the portion of the spindle held by an upper bearing in a bolster which supports the spindle. SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a ring spinning machine incorporating a direct drive spindle which has a high resonance speed and, hence, can operate at a high speed. To this end, according to the present invention, there is provided a ring spinning machine comprising: a bolster having an upper bearing provided in an upper portion thereof and a foot step bearing provided in a lower portion thereof; a spindle rotatably supported by the bolster and carrying a bobbin for winding yarn thereon; a substantially cylindrical ring having an upper end provided with a traveler for guiding the yarn to the bobbin; a ring rail connected with a base portion of the ring and capable of moving the ring up and down in the direction of the axis of the spindle; and a spindle motor having a motor rotor including a motor core fixed to the spindle and secondary windings on the rotor core and a motor stator including a cylindrical stator core surrounding the rotor core leaving an annular gap therebetween and a stator winding on the stator core; wherein the ring has an inside diameter greater than at least a part of the spindle motor so that the ring can be lowered to a position where it accommodates at least the part of the spindle motor. In general, referring to Fig. 4, the resonance rotation speed of a cantilevered rotational member in primary flexural mode is determined by various factors such as the distance ℓ ₁ between the supporting point P and the centroid G of the member, the distance ℓ ₂ between the supporting point P and the free end of the member, the diameter d of the member and elastic modulus of the member. It is clear from the knowledge of dynamics of rotational member that the resonance speed in the primary flexural mode becomes higher as the lengths ℓ ₁ and ℓ ₂ become smaller provided that other factors are unchanged. According to the invention, the ring or the ring rail and the motor structure are so constructed that the inside diameter of the ring or the ring rail is greater than the outside diameter of at least a part of the motor structure, thereby reducing the distance between the upper bearing in the bolster and the bobbin mounted on the spindle. This makes it possible to reduce the above-mentioned lengths ℓ ₁ and ℓ ₂, so that the resonance speed of the spindle in the primary flexural mode can be increased as compared with conventional spindle made of the same material and having the same diameter. Consequently, the spindle according to the invention can rotate at a speed higher than that of the conventional spindle without any risk of breakdown due to response. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a partially sectioned elevational view of a spindle used in an embodiment of a ring spinning machine of the present invention; Figs. 2 and 3 are fragmentary sectional elevational views of different embodiments of the present invention; Fig. 4 is a diagrammatic illustration of vibration mode of a cantilevered rotary member; and Figs. 5, 6, 7, 8 and 9 are fragmentary sectional views of essential portions of modified embodiments. DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described hereinunder with reference to the accompanying drawings and, particularly, to Fig. 1. A ring spinning machine of the present invention has a spindle 1 which has an integral structure composed of an upper blade 1a, a cylindrical wharve 1b and a lower blade 1c. A bobbin 9 on which a yarn is to be wound is mounted on the upper blade 1a. The lower end of the wharve is connected to a motor rotor 3 which is a part of the spindle motor 20 for driving the spindle 1. The lower blade 1c is rotatably supported by an upper bearing 2. The spindle motor 20 has a motor stator 4 which coaxially surrounds the motor rotor 3. The motor stator 4 is supported by a stator frame 6 which has an open-type structure with its upper end extended to the same level as the upper axial end of a stator core 4b of the motor stator 4. Thus, the stator frame 6 supports the motor stator 4 such that an upper coil end portion 5 of the motor stator 4 is exposed upwardly. The lower end of the stator frame 6 is connected to a bolster 11 which has the above-mentioned upper bearing 2 for supporting the spindle 1. Details of the bolster 11 are not shown because the bolster is constructed in a manner known per se. Briefly, the bolster has a lower foot step bearing which supports the lower end of the lower blade 1c of the spindle and a spiral leaf spring which supports the upper bearing 2 mentioned above so that the lower blade 1c of the spindle is resiliently restricted in the radial direction with a suitable level of spring constant and damping coefficient. The ring spinning machine further has a ring 7 and a ring rail 8 which are adapted to be moved up and down along the spindle 1 while they are guided in a manner known per se. The ring 7 has a cylindrical form and has a construction suitable for mounting a traveler on the upper end thereof, while the lower end thereof is fixed to the ring rail 8. The spindle motor 20 is a 3-phase induction motor which is well known. More specifically, the motor 20 essentially has the motor rotor 3 and the motor stator 4 mentioned before. The motor rotor 3 has a rotor core 3b which fits in a thin cylindrical wall constituted by a downward extension of the wharve 1b of the spindle 1 and a secondary winding 3a, e.g., squirrel-cage winding, on the rotor core. The motor stator 4 has a tubular or cylindrical core 4b which surrounds the rotor core 3b leaving an annular space therebetween, and stator windings 4a formed on the stator core 4b. The stator windings 4a project above the upper end surface of the stator core 4b. The upper end of the stator windings 4a constitutes the upper coil end 5 mentioned before. The inner peripheral surface of the upper coil end 5 defines a cylindrical plane of a diameter greater than that of the cylindrical plane defined by the inner peripheral surface of the stator core 4b. The diameter of the cylindrical plane defined by the outer peripheral surface of the upper coil end 5 is smaller than that of the cylindrical plane defined by the outer peripheral surface of the stator core 4b. The inside diameter of the ring 7 and the outside diameter of the upper coil end 5 are determined in relation to each other such that, when the ring rail 8 has been moved to the lower end F of its stroke, the upper coil end 5 of the rotor stator 4 of the spindle motor 20 is positioned within the inner peripheral surface of the ring 7. More specifically, in order to prevent mutual interference between the upper coil end 5 and the ring 7, the inside diameter of the ring 7 as well as the size of the ring rail 8 to which the base of the ring 7 is secured are determined to be slightly greater than the outside diameter of the upper coil end 5. In addition, the axial length of the ring 7 is so determined that the traveler is located at a position which is sufficiently spaced away from the upper coil end 5 in the axial direction of the spindle. In operation of the ring spinning machine, the spindle is rotationally driven by the spindle motor 20 and the ring rail 8 is driven up and down along the bobbin 9 by a mechanism which is not shown. In consequence, the yarn is wound on the bobbin 9 through the traveler provided on the upper end of the ring 7. In the described embodiment, the direct drive spindle and the spindle motor 20 are so designed that the upper portion of the spindle motor 20 and, particularly, the upper coil end 5 are received in the ring 7 when the ring rail 8 and, hence, the ring 7 are moved to the lower end of their stroke. This arrangement makes it possible to reduce the distance between the upper bearing 2 and the bobbin 9, that is to say, the length of the portion of the spindle 1 projecting above the upper bearing 2. In consequence, it is possible to reduce, as compared with the known spindle, the distance between the supporting point P (see Fig. 4) provided by the upper bearing 2 and the centroid G which can be regarded as being positioned at the center of the bobbin 9. As a result, the resonance speed is increased so as to allow the spindle to be operated at a higher rotation speed. Fig. 2 shows another embodiment of the invention. This embodiment has an end cover 61 which is secured to the upper end of the stator frame 6 in such a manner as to cover the upper coil end 5 of the motor stator 4. More specifically, the end cover 61 has a thin-walled cylindrical central portion which surrounds the outer peripheral surface of the upper coil end 5, an annular top covering portion 61a extending radially inwardly from the upper end of the central portion and defining a central opening through which the spindle 1 extends and a lower collar portion 61b which extends radially outwardly from the lower end of the central portion along the top surface of the stator core 4b and the top of the stator frame 6 and is fixed to the stator frame 6. Thus, the embodiment shown in Fig. 2 is of a substantially hermetic construction. Fig. 3 shows still another embodiment in which the diameter of the upper end portion of the ring 7 is progressively decreased from the base portion of the ring 7. This embodiment is suitable for use in a case where the winding diameter of the yarn 10 on the bobbin 9 is comparatively small. In this embodiment, since the base portion of the ring 7 has an inside diameter large enough to accommodate the upper coil end 5 of the spindle motor 20, the length of the portion of the spindle 1 projected above the upper bearing 2 can be reduced as compared with known spindles, as in the cases of the preceding embodiments. In the embodiments described hereinbefore, the inside diameter of the ring 7 and, hence, the diameter of an aperture in the ring rail 8 receiving and supporting the ring 7 are so determined that the ring 7 can accommodate at least a part of the structure of the spindle motor 20, e.g., the upper coil end 5, the end cover 61 or the stator frame 6. With this arrangement, it is possible to lower the ring 7 and the ring rail 8 beyond the upper end of the upper coil end 5 to a position close to the upper end of the stator frame 6. A description will be made hereinunder as to a further embodiment with reference to Figs. 5 to 9. A major point of improvement proposed by this embodiment resides in that the lower end portion of the wharve constituting the spindle 1 is extended to form a thin-walled cylindrical portion and a thick-walled ring portion connected to the lower end of the thin-walled cylindrical portion. Fig. 5 shows a first form of this embodiment. The wharve 1b is fixed to the lower blade 1c. The lower end portion (right end as viewed in Fig. 5) of the wharve 1b is extended downward, i.e., to the right as viewed in Fig. 5, so as to form a thin-walled cylindrical portion 1f. At the lower end of the thin-walled cylindrical portion 1f, the thickness is increased again so as to form a thick-walled ring portion 1d constituting the free lower end of the wharve 1b. The rotor core 3b of the motor rotor 3 is fixed to the outer peripheral surface of the thin-walled cylindrical portion 1f such that the upper end portion of the rotor core 3b partially overlie the thick-walled portion of the wharve 1b. The motor rotor 3 has an end ring 3a′. The thick-walled ring 1d is placed inside the end ring 3a′. The upper end surface of the thick-walled ring 1d contacts the lower end surface of the rotor core 3b. A motor rotor having an inside diameter which is large relative to the outside diameter, like the motor rotor 3, is regarded as being an annular member having a comparatively low rigidity and, hence, being easily deformable. In the spindle shown in Fig. 5, however, the motor rotor 3 is stiffened by the wharve of the spindle because the upper end of the motor rotor 3 fits on the outer peripheral surface of the upper thick-walled portion of the wharve 1b while the lower end portion of the motor rotor 3 is held by the thick-walled ring 1d integral with the wharve 1b. In consequence, the rigidity of the tubular structure including the motor rotor 3 is increased to provide a greater resistance to any deforming force caused during operation by higher harmonic electromagnetic force components, whereby the tendency of the tubular structure to be deformed is remarkably suppressed, with the result that the vibration and noise of the spindle are greatly reduced during operation of the spinning machine. The arrangement described in connection with Fig. 5 increases the rigidity of the tubular structure also in the axial direction, so that the tubular structure also exhibits an increased resistance to any force which acts to bend the tubular structure along the axis thereof. In consequence, any tendency of the tubular structure to vibrate due to unbalanced mass or to be radially offset by magnetic attracting force is suppressed to reduce vibration, thus preventing the critical or resonance speed from being lowered. The ring 1d provided on the free end of the thin-walled cylindrical portion 1f may be made of a ferromagnetic material. In such a case, the reactance component of the spindle motor 20 is so increased that the higher harmonic components of the driving electric power can be suppressed, whereby the driving characteristics can be improved. This feature is advantageous particularly when the spindle motor 20 is driven by a switching power supply such as an inverter. It is also possible to make use of the thick-walled ring 1d as a balancing ring. Namely, it is possible to correct any unbalance of mass of the spindle 1 by making use of the thick-walled ring 1d without difficulty. Obviously, well-balanced spindle 1 can be rotated at a higher speed. During high speed operation of the spindle, the motor rotor 3 tends to expand radially outwardly. In order to prevent such a radial expansion of the motor rotor 3, therefore, it is necessary that the motor rotor 3 fits on the spindle 1 with a sufficient tightening margin. A too large tightening margin, i.e., a too large contracting force applied by the motor rotor 3 on the spindle 1, causes a risk that the tubular structure, particularly the thin-walled cylindrical portion 1f, is collapsed due to buckling. This problem, however, is overcome by the arrangement shown in Fig. 5 because the upper end portion of the rotor core 3b rests on the thick-walled portion of the wharve 1b while the lower end portion of the same is formed as the thick-walled ring 1d so that the tightening contracting force can be borne by the thick-walled portion of the wharve 1b and the thick-walled ring 1d thereof. The features offered by the arrangement shown in Fig. 5 is advantageous particularly in a spindle 1 incorporating a motor rotor 3 having a diameter ratio (inside diameter/outside diameter) not smaller than 0.5. Fig. 6 shows another form of the further embodiment in which the end ring 3a′ of the motor rotor 3 is extended radially inwardly and the thick-walled ring 1d is placed underneath and in the vicinity of the end ring 3a′. In addition, an annular balance ring 1e is provided on the wharve 1b of the motor rotor 3. In this case, the thick-walled ring 1d is made of a ferromagnetic material so that the reactance is increased in the region where this ring 1d exists, thereby reducing the influence of the higher harmonics of the driving electric power. Figs. 7 and 8 show different forms of the further embodiment. In these forms, a thickened portion 1g of a certain thickness is provided between the upper end portion of the thin-walled cylindrical portion 1f and the upper thick-walled portion of the wharve 1b and the upper portion of the rotor core 3b is placed over the thickened portion 1g. This arrangement also increases the rigidity of the rotational portion of the spindle motor 20. Fig. 9 shows an arrangement in which a thin-walled cylindrical portion 1f with an integral thick-walled ring 1d at the lower end is formed separately from the wharve 1b and is suitably connected to the wharve 1b. As has been described, the invention provides a ring spinning machine having a direct drive spindle and so constructed that the length of the unsupported portion of the spindle is decreased to increase the resonance or critical rotation speed so as to enable the spindle to rotate at higher speed than known spindles, thus improving the spinning efficiency of the spinning apparatus.

Claims: A ring spinning machine including: a bolster (11) having an upper bearing (2) provided in an upper portion thereof and a foot step bearing provided in a lower portion thereof; a spindle (1) rotatably supported by the bolster (11) and carrying a bobbin (9) for winding yarn thereon; a substantially cylindrical ring (7) having an upper end provided with a traveler for guiding the yarn (10) to said bobbin (9); a ring rail (8) connected with a base portion of said ring (7) and capable of moving said ring (7) up and down in the direction of the axis of said spindle (1); and a spindle motor (20) having a motor rotor (3) including a rotor core (3b) fixed to said spindle (1) and secondary windings (3a) on said rotor core (3b) and a motor stator (4) including a cylindrical stator core (4b) surrounding said rotor core (3b) leaving an annular gap therebetween and a stator winding (4a) on said stator core (4b); characterised in that said ring (7) has an inside diameter greater than at least a part of said spindle motor (20) so that said ring (7) can be lowered to a position where it accommodates at least said part of said spindle motor (20). A ring spinning machine according to claim 1, wherein said spindle motor (20) has a stator frame (6) which fits on the outer peripheral surface of said stator core (4b) and which has a lower end connected to said bolster (11), and wherein said ring (7) has an inside diameter greater than the outside diameter of said stator frame (6). A ring spinning machine according to claim 2, further including an end cover (61) which covers the upper end of said stator frame (6). A ring spinning machine according to claim 1, wherein said stator winding (4a) of said motor stator (4) has an upper coil end (5) which projects above the upper end surface of said stator core (4b), while said motor stator (4) is supported by a stator frame (6) extended from said bolster (11) such that said upper coil end (5) is exposed at least partially, and wherein said ring (7) has an inside diameter greater than the outside diameter of said upper coil end (5) so that said ring (7) together with said ring rail (8) can be lowered to a level where it accommodates said upper coil end (5) at least partially. A ring spinning machine according to claim 4, wherein said stator frame (6) is fitted on the outer peripheral surface of said stator core (4b) and has a lower end connected to said bolster (11) and an open upper end. A ring spinning motor according to either one of claims 4 and 5, wherein said upper coil end (5) has a cylindrical inner peripheral surface of a diameter greater than the diameter of the cylindrical inner peripheral surface of said stator core (4b), and a cylindrical outer peripheral surface of a diameter smaller than the cylindrical outer peripheral surface of said stator core (4b). A ring spinning machine according to anyone of claims 4, 5 and 6, wherein said ring (7) has a base end portion having an inside diameter greater than the outside diameter of said upper coil end (5) and fixed to said ring rail (8), and an upper end portion the diameter of which is progressively decreased towards the upper end of said ring (7). A ring spinning machine according to either one of claims 6 and 7, wherein said ring rail (8) is movable downwardly to a level close to the open upper end of said stator frame (6). A ring spinning machine according to anyone of claims 4, 5, 6 and 7, wherein said rotor core (3b) of said spindle motor (20) is fixed at its upper end to said spindle (1) and a thin-walled cylindrical member (1f) provided at its lower end with a thick-walled portion (1d) is fitted in said rotor core (3b). A ring spinning machine according to claim 1, wherein said stator winding (4a) of said motor stator (4) has an upper coil end (5) projecting above the upper end surface of said stator core (4b), while said stator core (4b) is supported by a stator frame (6) extended from said bolster (11) and provided on the upper end thereof with an end cover (61) which covers said upper coil end (5) of said stator winding (4a), said ring (7) having an inside diameter greater than the outside diameter of said end cover (61) so that said ring (7) and said ring rail (8) can be lowered to a level where it receives said end cover (61) at least partially. A ring spinning machine according to claim 10, wherein said stator frame (6) is fitted on the outer peripheral surface of said stator core (4b) and is fixed at its lower end to said bolster (11) while its upper end is extended to the same level as the upper end surface of said stator core (4b). A ring spinning machine according to either one of claims 10 and 11, wherein said upper coil end (5) has a cylindrical outer peripheral surface of a diameter smaller than the diameter of the cylindrical outer peripheral surface of said stator core (4b), and wherein said end cover (61) comprises a thin-walled cylindrical central portion and an upper portion (61a) the diameter of which is progressively decreased and a lower end (61b) expanded to fit the cylindrical outer peripheral surface of said stator frame (6). A ring spinning machine according to claim 12, wherein the base end of said cylindrical member of said ring (7) is radially expanded to provide an inside diameter greater than the outside diameter of the cylindrical surface of said end cover (61) and said ring (7) is fixed to said ring rail (8) at said base end of said cylindrical member. A ring spinning machine according to claim 13, wherein said ring rail (8) is movable downwardly to a level close to the upper end of said stator frame (6). A ring spinning machine according to claim 14, wherein said cylindrical member of said ring (7) has an upper end portion the diameter of which is progressively decreased towards the upper end of said ring (7). A ring spinning machine according to anyone of claims 14 and 15, further including a thin-walled cylindrical member (1f) fitted in said rotor core (3b) of said spindle motor (20), said thin-walled cylindrical member (1f) having an upper end (1b) connected to said spindle (1) and provided at its lower end thereof with a thick-walled portion (1d).

Inventors: KOBAYASHI, HIDEAKI, OBATA, TAKESHI
Applicants: HITACHI, LTD.
Application year: 1988
Main classification: D01H1
IPC codes: D01H1