BALANCING DEVICE FOR ROTORS, IN PARTICULAR FOR ELECTRIC MOTOR ROTORS

Abstract: A balancing device for rotors, in particular for electric motor rotors, including at least two mills (4) with cutting directions opposite with one another, two counter-rotating spindles each (2, 3) suitable for supporting at least one said mill (4) with cutting direction corresponding to the rotation direction of the related spindle, a support (5) angularly oscillating around an oscillating axle (6) parallel to said spindles (2, 3) and suitable for supporting these last spindles eccentrically and in different angular positions, and rotation means (12) for said angularly oscillating support (5), suitable for positioning said spindles (2, 3).

Description: The present invention refers to a balancing device for rotors, in particular for electric motor rotors, defined in the preamble of the accompanying Claim 1. As it is known, the dynamic balancing of a rotor requires that the compensation of unbalances occurs in two different planes, named balancing planes, which are spaced with one another and transversal to the rotation axis of the same rotor. Generally the two balancing planes are located in conjuction with the opposite ends of the rotor. For getting this compensation, in particular in balancing automatic machines, it is generally used one or more milling units suitable for removing the exceeding material quantities precedently measured by proper measure devices. In particular, for balancing a rotor of an electric motor, the opposite ends of the rotor lamellar pack are milled. Further for getting mechanically perfect millings, without causing changes or breackages of sheets forming the lamellar pack, it is used the technique of milling in the two balancing planes with a cutting direction and relative progress movement of the mills from the external side towards the centre of the same rotor, for getting that the stresses caused by the same mills are always directed towards the centre of the lamellar pack. In this manner the stresses are taken up and the breackages of edges of laminae are avoided. For making these milling operations it is known a device, disclosed in DE-A- 3 005 423 and in DE-A-1 241 153, that uses two different milling machines or units spaced with one another and having the spindles or drive shafts of the mill tools parallel with one another. During the work phase the spindles are perpendicular to the rotor to be balanced. In detail, DE-A-3 005 423 discloses two milling units which are both moved in a direction parallel to the rotation axis of the rotor to be balanced, while DE-A-1 241 153 discloses a device where it is the same rotor that can be moved for being milled on both balancing planes. This device has a high price owing to the presence of two milling machines or units and does not allow a high production rate. Further it is known another device, described in DE-A-2 638 876, in which a milling unit foresees a sole spindle, on which at least two different milling units, that are named briefly mills in the following, are keyed reciprocally spaced with one another. In particular the sole spindle supports one or more first mills having a fixed cutting direction, and one or more second mills having a cutting direction opposite to the first mill cutting direction. Each mill or each homogeneous mill unit is used for milling a rotor end in conjuction with a first balancing plane. In practice, for being able to mill both ends, at first it is necessary to mill one end of the rotor by the first mills, then to move the spindle towards the other rotor end, and then to move axially the spindle for adjusting the second mills in right position, and finally to invert the rotation direction of the drive motor of the same spindle and to make the milling. The axial traverse of the spindle for allowing the replacement of mill located on the rotor and the inversion of the rotation direction of the spindle drive motor cause, in adddition to a great wear of remote control switches controlling the motor also time losses and then allow only a limited production rate. Further above all in the case in which more mills are used in each homogeneous unit, the mill holder has a protruding part having a rather high length and then it can cause no negligible vibrations during the milling and therefore a faulty machining. In this situation the technical object forming the basis of the present invention is to provide a balancing device for rotors, in particular for electric motor rotors suitable for obviating substantially to the above mentioned drawbacks. The technical object is substantially achieved by a balancing device for rotors, in particular for electric motor rotors, as claimed in Claim 1. Preferred embodiments of the invention are specified in Claims 2 to 9. Further particularities and the advantages of the invention will be more clearly understood from the detailed description of the balancing device according to the invention, shown in the annexed drawings, in which: Figures 1 and 2 show two front views of the device, corresponding to two different work positions; Figure 3 is a lateral view of the device; Figures 4 and 5 show a first embodiment of rotation and locking means used in the device; Figure 6 is a rear view of the device, shown in partial section; Figure 7 is a second embodiment of rotation and locking means, and Figure 8 shows in particular a start milling position according to the second embodiment of Figure 7. Making reference to the above mentioned figures, the balancing device according to the invention is indicated by the number 1 . It includes two counter-rotating spindles 2 and 3 supporting mills 4 with opposite cutting directions, corresponding to the rotation directions of the spindles. The spindles 2 and 3 are hold by a support 5 , formed by a cylindrical sleeve rotatable around a rotation axis 6 coinciding with the symmetry axis of said sleeve and parallel to spindles 2 and 3. The spindles are eccentric from the rotation axis 6 and angularly displaced with respect to each other about the rotation axis 6. The support or sleeve 5 is housed within a bearing structure 7 , to which it is joined a sole motor unit 8 for the drive of both spindles. The spindles 2 and 3 are driven in opposite rotation directions by movement transmission means 9 , including, for example, a belt 10 and a spur gearing 11 . The sleeve 5 is driven in rotation by rotation means 12 suitable for orienting selectively the spindles 2 and 3 into operative positions with respect to a rotor 13 to be balanced. This last rotor can be moved along its axial direction by means of mounting means 14 substantially realized by a slide, for bringing the balancing planes 13a in substantially vertical alignment with either of the spindles 2 and 3 in operative positions. The bearing structure 7 can be moved along a vertical direction, in a relative movement with respect to the mounting means or slide 14, or also fixed in a vertical position, as specified in the following. A first embodiment, shown in Figure 4, has rotation means 12 that includes at least a linear-type actuator 15 , for example a fluid-dynamic cylinder, whose rod is engaged to a rack element 16 meshing with a toothed gear krown 17 joined to the sleeve 5. The Figure 4 shows two single-acting fluid-dynamic cylinders moving the sleeve 5 in opposed directions. Further there is a locking means 18 , shown in Figure 5, suitable for locking the rotation of the sleeve 5 at exact operative positions of the spindles 2 and 3. The locking means 18 includes a couple of hooking elements 19 rotating around the pins 20 , and held against the sleeve 5 by an elastic force caused by springs 21 . The hooking elements 19 can be snap-joined into locking notches 22 provided into the sleeve 5 in areas suitable for locking this last sleeve in angular positions corresponding to the operative positions of the spindles 2 and 3. A releasing element 23 , formed by a linear fluid-dynamic actuator, acting selectively onto each hooking element 19, allows its releasing from the relevant locking notch 22. The just described first embodiment has the bearing structure 7 mobile in vertical direction in relative movement with respect to the slide 14, under the control of known means, for moving the mills 4 in vertical direction 4 and making the cuttings with the required cut depths. A second embodiment, shown in Figure 7, has rotating means 12 including a worm screw 24 , driven by a drive motor 25 with the meanly connected reduction unit 26 , and a gear 27 joined to the sleeve 5 and operatively meshed with the worm screw 24. Known control means, not shown in the drawings, allows the same worm screw 24 and sleeve 5 driven by this worm screw to be moved by prefixed rotations corresponding to the angular strokes required for the mills. The stop of the worm screw 24 in any position establishes also a locking position for the rotation of the sleeve 5, as the worm screw-gear transmission is not reversible. Finally it is provided a device 28 surveying the angular position of worm screw 24 and rotating sleeve 5. The bearing structure 7 is fixed in vertical direction, as the same rotation of the sleeve 5 can adjust the position of mills 4 in vertical direction. The running of the device 1 occurs as follows. The rotor 13 to be balanced is mounted on the mounting means or slide 14 and this slide is moved for adjusting a balancing plane 13a where the intervention of a mill 4 is foreseen. Considering the first embodiment of rotation means 12, the mill 4 is moved in operative position by fluid-dynamic cylinders 15 that turn the sleeve 5. Then a hooking element 19 is snap-inserted into the related notch 22 allowing an angular exact positioning of the sleeve 5 and spindles in its operative position. Then the bearing structure 7 moves vertically for allowing a milling according to the required cut depth. After having ended the milling, the releasing element 23, pressing against the hooking element 19, causes its output from the locking notch 22 and allows the rotation of the sleeve 5 for bringing the mill or mills of the other spindle to the operative position and carrying out the milling in the other balancing plane 13a. Considering the second embodiment of rotation means 12, the worm screw 24 allows the operative reciprocating adjusting of spindles 2 and 3 of the relevant mills, but establishing for any position in which it is stopped also a rotation locking position of sleeve 5. Further the worm screw allows the mill to be directly moved in relation to the required cut depth. In fact, as shown in Figure 8, each mill is positioned in an initial operative position angularly displaced with respect to the vertical direction. The following rotation of the worm screw 24 causes a further angular traverse of the mills, in particular of the working mill, that approaching to the radial vertical position is lowered until the calculated cut depth. Considering the second shown embodiment, the means for the vertical traverse of the bearing structure 7 is not necessary The invention achieves important advantages. In fact the use of two counter-rotating spindles makes unncessary the inversion operation of the rotation direction and therefore, in addition to the quick mill replacement obtained with circular movements instead of traverse movements, allows to get a high production rate. Further, being unnecessary to have at disposal many mills onto the same spindle, this spindle can have a reduced length and therefore it has very reduced vibration levels and running inaccuracies.

Claims: A balancing device for rotors, in particular for electric motor rotors, including: at least two mills (4) having cutting directions opposed to each other, each of said mills (4) being provided for removing an established material quantity from a rotor (13), two counter-rotating spindles (2, 3), each spindle (2,3) supporting one of said at least two mills (4) having a cutting direction corresponding to the rotation direction of said spindle (2, 3) on which it is fixed, and mounting means (14) for mounting said rotor (13) to be milled by said mills (4), said mills (4) and said mounting means (14) being arranged such that when mounted said rotor (13) is milled at each of its two ends in a balancing plane (13a) perpendicular to the rotor axis by a respective one of said mills (4), characterized in that it includes: a support (5), rotatable about a rotation axis (6) and supporting said spindles (2, 3) parallel to said rotation axis (6) in positions eccentric from said rotation axis (6) and angularly displaced with respect to each other about said rotation axis (6), and rotation means (12) for rotating said support (5) about said rotation axis (6) so as to selectively position either of said spindles (2, 3) in operative position with respect to said rotor (13). A balancing device according to Claim 1, wherein said support (5) is formed by a sleeve having a symmetry axis coinciding with said rotation axis (6). A balancing device according to Claim 1, wherein a sole motor unit (8) is provided for driving both said spindles (2, 3) and wherein movement transmission means (9) is provided for turning contemporaneously said two spindles (2, 3) in directions opposed to each other. A balancing device according to Claim 1, wherein said rotation means (12) of said support (5) includes: at least a linear-type actuator (15), a rack element (16) meshed with said linear-type actuator (15), and a toothed krown (17) joined to said support (5) and meshing with said rack element (16). A balancing device according to Claim 1, wherein locking means (18) suitable for locking the rotation of said support (5) at said operative positions of said spindles (2, 3) is provided. A balancing device according to Claim 5, wherein said locking means (18) includes at least one hooking element (19) suitable for snap-locking said support (5). A balancing device according to Claim 6, wherein locking notches (22) machined in said support (5) are provided, and wherein said at least one hooking element (19) can be inserted in said locking notches (22), further a releasing element (23) acting on said hooking element (19) and suitable for releasing said hooking element (19) from said locking notches (22) being provided. A balancing device according to Claim 1, wherein said rotation means (12) includes: a worm screw (24), a gear (27) joined to said support (5) and operatively meshed with said worm screw (24), and a drive motor (25) for said worm screw (24). A balancing device according to Claim 8, wherein control means is provided for said drive motor (25), known and suitable for causing prefixed rotations of said worm screw (24), and wherein a device (28) is provided for surveying the angular position of said worm screw (24) and said support (5).

Inventors: TRIONFETTI, GIANNI
Applicants: BALANCE SYSTEMS S.R.L.
Application year: 1991
Main classification: G01M1
IPC codes: H02K15, B23C1, G01M1, B27G19