DRIVE DEVICE FOR THE CYLINDER OF A HOSIERY MACHINE AND ROTOR ASSEMBLY FOR A BRUSHLESS SYNCHRONOUS MOTOR

Abstract: A permanent magnet rotor assembly is formed directly on the outer cylindrical surface of a cylinder-spindle (4) of a hosiery machine (1) by fastening on the outer cylindrical surface of the cylinder one or more pair of permanent magnets and polar expansion pieces of ferromagnetic material functionally coupled with the permanent magnets. The stator winding of the drive motor is housed in a flanged tubular casing (6) which is inserted over the rotor assembly and fastened in a functionally disposed position underneath the machine's bench, onto which is rotatably mounted the knitting head (2). The drive eliminates the customary belt transmission, permitting a saving and reducing the encumbrance underneath the machine's bench.

Description: DRIVE DEVICE FOR THE CYLINDER OF A HOSIERY MACHINE AND ROTOR ASSEMBLY FOR A BRUSHLESS SYNCHRONOUS MOTOR The present invention relates to a device for driving the . cylinder of a hosiery machine, i.e. a ma¬ chine for manufacturing tubular fabrics, notably stockings and panty-hoses (collants) and to a particu¬ larly suited brushless motor, rotor assembly. Knitting machines for producing tubular- fabrics are commonly provided with a hollow cylinder, open at both ends, connected to a cylindrical knitting needle-head which is rotatably mounted on bearings on the machine's bench. Numerous mechanical organs which are sequential¬ ly controlled in function of the speed of rotation of the knitting head cooperate with the latter and produce the desired knitting of the various textile threads which are customarily fed to the knitting head from a plurality of coils held in an aerial structure of the machine. The tubular fabric, the stocking or panty hose which is produced hangs down passing through a hollow cylinder connected to the knitting needle head and rotating together with the latter and is recovered through the bottom end of the rotating cylinder. The cylinder acts as a rotating spindle of the knit- ting head and is rotated by means of a driving electric motor, which is housed under the machine's bench. Trans¬ mission of rotation to the spindle-cylinder of the ma¬ chine is customarily made by means of a belt transmis¬ sion between a motor's pulley and a pulley mounted on the machine's cylinder-spindle. These traditional trans¬ missions have a nonnegligeable cost and exert a flex- ural force on the cylinder which on the other hand is often connected in a cantilever manner to the base of the knitting head, moreover they encumber the cabinet space underneath the machine's bench and are often cause of stoppages for the periodic substitution of worn out belts, etc.. The present invention obviates to all these draw¬ backs by providing a device for rotating a cylinder- spindle of a hosiery machine which is less cumbersome and expensive, more reliable and which does not require in practice any maintenance as compared with the known drive arrangements. Basically the device of the invention is character¬ ized by the fact that a rotor assembly comprising at least a pair of permanent magnets and a pair of polar expansions of a ferromagnetic material, is directly mounted on the outer cylindrical surface of the ma¬ chine's cylinder and the assembly constitutes the rotor of a collector-less, asynchronous motor, cooperating with a stator winding which is held in a tubular stator casing operatively fixed to the underside of the machine's bench supporting said rotating knitting head. According to a preferred embodiment, the cylinder is made of an amagnetic material and the rotor assembly utilizes permanent magnets having a rectilinear, flat- bar shape, held in radially disposed cavities defined between radially oriented opposing coupling faces of two adjacent ferromagnetic polar expansion pieces whose shape determines the realization of a functionally effective magnetic semicircuit. The peculiar aspects and related advantages of the drive device of the present invention will be recog¬ nized more easily through the following description of preferred embodiments and reference to the attached drawings, wherein: Figure 1 is a partial schematic illustration of a hosiery machine, equipped with a drive in accordance with the present invention; Figure 2 is a simplified schematic cross-sectional view of an electric drive motor which utilizes the hosiery machine cylinder as a motor's shaft; Figure 3 is a partially sectioned prospective view of a rotor assembly in accordance with a preferred embodiment of the present invention; Figure 4 is an enlarged detail of the rotor assembly depicted in Fig. 3; Figure 5 depicts a die-stamped ferromagnetic lamina used for making a rotor's magnetic pack, in accordance with a preferred embodiment of the present invention; Figure 6 is a partial prospectic view of an amagnet- ic cylindrical sleeve onto which the ferromagnetic die- stamped laminae of Fig. 5 may be assembled. As shown in Fig. 1, a hosiery machine 1 for produc¬ ing tubular fabrics, such as stockings and panty-hoses, essentially comprises a rotating knitting head 2, which is rotatably mounted on bearings on a bench 3 of the machine. A hollow cylinder 4, open at both extremities, is rigidly connected to the rotating knitting head 2 and the tubular fabric produced 5 passes through the cylinder 4. Beside that of a "keeper" of the produced fabric, the cylinder 4 has also the function of a spindle for rotating the knitting needle head 2. As schematically shown in Fig. 1, in accordance with the present invention, the driving element for rotating the cylinder-spindle 4 of the machine is an electric motor 6, the rotor of which is formed directly on the outer cylindrical surface of the cylinder 4. Preferably the motor 6 is a brushless type, permanent magnet motor whose rotor consists of at least a pair of excitation permanent magnets and at least a pair of polar expan- sions of a ferromagnetic material, direclty mounted over the cylinder 4 of the hosiery machine. The stator winding of the motor is housed in a substantially tu¬ bular stator casing which is supported concentrically about the rotor formed on the cylinder-spindle 4 of the machine by fixing the casing by means of a plurality of bolts to the lower face of the bench 3 of the machine or to a stationary basement 6h of the turning needle head 2 of the knitting machine and which is in turn fixed to the bench of the machine. The polar expansions, among which or on which the excitation permanent magnets are fixed, may be directly mounted on the outer cylindrical surface of the cylin¬ der 4 or on a sleeve which may be inserted over and me¬ chanically keyed to the cylinder 4. A preferred embodiment of the drive of the cylinder 4 of the hosiery machine is depicted in Fig. 2. A rotor which may be mechanically connected to the cylinder 4 may be formed by a cylindrical sleeve 7, having key way 7a, of aluminum or of another amagnetic material, onto which polar expansions 8 made of a ferro- magnetic material are fastened. Elongated permanent mag¬ nets (not shown in the figure) are functionally dis¬ posed between radially oriented lateral faces opposing each other of adjacent polar expansions. The stator winding 9, i.e. the stator armature formed by the wind- ing and by the pack 10 of ferromagnetic laminae, is con¬ tained within a tubular casing 6a, which is provided with a flange 11 for fastening to a similar flange of a stationary basement of the knitting cylindrical needle head of the machine. The relatively concentric position between opposing revolution surfaces of the rotor and of the stator may be ensured by means of a spacing flange 12, which may be screwed into a threaded open end of the tubular cas¬ ing 6a and provided with three or more circumferential- iy spaced adjustable spacers 13, which are provided with a contrasting surface for restraining the external cylindrical surface of a ring 14 of an antifriction ma¬ terial mounted at the extremity of the sleeve 7. Of course the spacing feelers 13 may be provided with con- trasting cylinders mounted on rollers or ball bearings for reducing friction. The driving device of the cylinder of hosiery ma¬ chine object of the present invention does not require any transmission and the construction of the drive mo¬ tor itself is simplified and less costly then in known machines. In fact the motor is virtually without a shaft, shaft's bearings and external pulley. Also the motor casing may be formed in an extremely economic way. Moreover it is evident the greatly reduced encum¬ brance that a drive made in accordance with the present invention has as compared to a known belt drive system. Advantageously the configuration of the rotor as¬ sembly installed directly over the hosiery machine cylinder-spindle is shown in the Figures 3 to 6. In the embodiment depicted in Figures 3 and 4, the rotor of the brushless electric motor has two pairs of permanent magnets (i.e a four-pole configuration as depicted by the magnetic flux arrows drawn in Fig. 4) . The excitation magnetic circuit of the rotor il¬ lustrated in Figures 1 and 2, utilizes four straight, parallelepiped-shaped magnets 15, e.g. of Neodimium- Iron-Boron or of Cobalt-Samarium, radially disposed at regular intervals inside respective cavities which are defined by radially oriented lateral faces of polar ex¬ pansions pieces 16 of a ferromagnetic material having the shape of channeled sectors of an hollow cylinder, having a longitudinal channel 17 with a substantially triangular cross-section, the base of which is open to¬ ward the inner circumference of the sectors and the ver¬ tex of which extends toward the outer circumference of the sectors. The longitudinal channel being cut in a middle position in respect to the two radially oriented terminal faces of each sector constituting a polar ex¬ tension piece or more simply a polar expansion. As may be observed in Fig. 3, each magnetic semi- circuit of the rotor comprises a permanent magnet 15 and two halves of the two ferromagnetic polar expansion pieces 16, coupled with the permanent magnet. The substantially cylindrical, magnetic circuit por¬ tion of the rotor which is formed by the magnets 15 and by the polar expansions 16, may be mounted, as shown, on a sleeve 18 of an amagnetic material, such as for example aluminum. The sleeve 18 may have a key way- channel or other similar means for mechanically coup¬ ling with a motor spindle, which, in accordance with the main objective of the present invention, consists of the hollow cylinder of a hosiery machine. The amag¬ netic nature of the sleeve 18 onto which the ferromag¬ netic parts of the rotor are assembled prevents an un- desired closing of the magnetic circuit through a ferro¬ magnetic cylinder-spindle. Of course the cylinder of the hosiery machine itself may be advantageously made with an amagnetic material and in this case the magnetic parts of the rotor may be directly assembled on the outer cylindrical surface of the machine's cylinder. As shown in Figures 3 and 4, the polar expansions 16 may be of machined low-carbon steel and may be individu¬ ally fastened to the amagnetic sleeve 18 (or to the ma¬ chine ' s hollow cylinder) by one or more retaining screws 19. Each polar expansion piece 16 has two radial- ly oriented lateral faces 16a and 16b, respectively, which magnetically couple with the opposite faces of a respective permanent magnet 15. The terminal coupling faces of each polar expansion may be provided with a tangentially protruding lip-portion 16c having the func- tion of retaining the permanent magnet 15. The perma¬ nent magnets 15 are positively retained in the respec¬ tive housings, even if the adhesive which is normally used for assemblying the parts together should fail. Also the assembly operations of the rotor are greatly simplified by the special configuration of the inven¬ tion. The polar expansions, shaped as cylindrical sec- tors, may be mounted on the sleeve 18 without complete¬ ly tightening the retaining screws 19. At this point a certain amount of adhesive paste may be applied inside the permanent magnet housings before inserting the per- manent magnets strips 15 and finally tightening the screws 19 to complete the assembly. The rotor assembly may then be machined and dinamically balanced before completing the motor assembly. Of course the polar expansions may also be customa- rily formed by a pack of die-stamped ferromagnetic laminae. One of these die-stamped ferromagnetic laminae for an eight-pole motor is depicted in Fig. 5. So as die-stamped, the various sectors of the relative polar expansion lamina are held together by metal bridges 20 which connect the two outer ends of the protruding lip- portions 16c of the die-stamped aperture which will constitute the cavity into which the permanent magnets will be housed. Also in this case, because of the fact that the permanent magnets are entirely contained with- in the outer cylindrical surface of the rotor, the ro¬ tor assembly once completed may be machined at a lathe for eliminating the metal bridges 20 as well as for rec¬ tifying the outer cylindrical surface of the rotor it¬ self. In order to make assemblying easier, each cylin- drical sector of the die-stamped laminae has a trape- zoidally shaped extension 21, which fits into purposely made longitudinal channels 22, having an inverted trape¬ zoidal cross-section on the outer cylindrical surface of a sleeve 18 or, as the case may be, of the cylinder- spindle of the hosiery machine, as schematically shown in Fig. 6.

Claims: C L A I M S 1. A device for driving into rotation a cylinder- spindle of a hosiery machine having a knitting head ro- tatably mounted on a machine's bench and connected to said cylinder-spindle which is rotated by means of an electric motor mounted underneath said machine's bench, wherein at least a pair of permanent magnets and polar expansions of a ferromagnetic material are mounted on the outer cylindrical surface of said machine's cylinder-spindle forming a rotor of a brushless-type, asynchronous motor, cooperating with a stator winding housed in a tubular stator casing functionally disposed over said rotor assembled on the outer cylindrical sur¬ face of said cylinder-spindle and fastened underneath said bench. 2. The rotating device as defined in claim 1, where- in said polar expansions of ferromagnetic material and said permanent magnets are assembled on the outer cylin¬ drical surface of a sleeve of an amagnetic material, said sleeve being inserted over and connected to said cylinder-spindle of the hosiery machine. 3. A rotating device as defined in claim 2, wherein said permanent magnets are in the form of a straight parallelepiped flat bar having a magnetization axis nor¬ mal to the major faces thereof and oriented tangential- ly in respect to a rotor's circumference and said polar expansions having terminal radially oriented faces func¬ tionally coupling with said major surfaces of said per¬ manent magnets and a longitudinal channel with a sub¬ stantially triangular cross section, the base of which widens toward the internal circumference of the polar expansion and the vertex of which extends near the outer circumference of the polar expansion. 4. A hosiery machine having a knitting head ro- tatably mounted on a machine's bench and connected to said cylinder-spindle which is rotated by means of an electric motor mounted underneath said machine's bench, wherein at least a pair of permanent magnets and polar expansions of a ferromagnetic material are mounted on the outer cylindrical surface of said machine's cylinder-spindle forming the rotor of a brushless-type asynchronous motor, cooperating with a stator winding housed in a tubular stator casing functionally disposed over said rotor assembled on the outer cylindrical sur- face of said cylinder-spindle and fastened to the under¬ side of said machine's bench. 5. The hosiery machine as defined in claim 1, where¬ in said polar expansions of ferromagnetic material and said permanent magnets are assembled on the outer cy¬ lindrical surface of a sleeve of an amagnetic material, said sleeve being inserted over and connected to said cylinder-spindle of the hosiery machine.

Inventors: VIGILI GIANLUIGI, VIGILI, GIANLUIGI
Applicants: ACM AZIENDA COST MOTORI, A.C.M. AZIENDA COSTRUZIONE MOTORI S.A.S. DI RACCA
Application year: 1992
Main classification: D04B15
IPC codes: D04B15, H02K1