Locking device for the releasable coupling of the rotor of an electric spindle

Abstract: A locking device for the releasable coupling of a rotatable member (3-7) of an electric spindle to the stator (1,2,8-10) thereof, the rotatable member comprising a spindle shaft (10) housed within the stator and rotatably mounted thereto by means of bearing means (5,6), comprises an axial holding means (15) for the spindle shaft, said axial holding means being housed in a respective sliding seat provided in said stator and being capable of being moved transversally to the spindle shaft between a locking position in which said axial holding means engages respective hooking means (17) provided on said spindle shaft, and an unlocked position in which said axial holding means is disengaged from said hooking means, thereby the rotatable member can be decoupled from said stator.

Description: The present invention concerns an electric spindle with a rotatable member axially extractable from a static member. Conventionally, for example as disclosed in EP-A-0 525 405, electric spindles for machine tools comprise a rotatable member, which comprises a spindle shaft provided with means for coupling a tool thereto. The rotatable member is coupled to the static member by means of bearings. A problem affecting conventional electric spindles is due to seizure of the bearings. When this occurs, the bearings are to be replaced. This operation must be carried out by skilled technicians, and involves disassembly of the electric spindle, so as to separate the rotatable member, bearings included, and replacement of the seized bearings. This naturally requires to keep the machine tool unoperable for possibly long times, causing a significant reduction in productivity. In view of the state of the art described, it is an object of the present invention that of providing a locking device for the releasable coupling of the rotatable member of the electric spindle to the stator thereof, allowing for overcoming the above-mentioned problem, making thus easy a prompt replacement of the rotatable member. According to the present invention, such an object is achieved by means of an electric spindle as defined in claim 1. Thanks to the present invention, the substitution of the rotatable member of the electric spindle is extremely easy and fast to carry out, and can be performed directly by the user. Advantageously, it is possible to sell of a set comprising a static member and a plurality of rotatable member interchangeably couplable to the static member by means of a locking device according to the invention. In case of seizure of the bearings, the user can immediately and easily replace the rotatable member, without having to leave the machine tool inoperable for long times. These and other features and advantages of the present invention will be made apparent by the following detailed description of a particular embodiment thereof, illustrated as a non-limiting example in the annexed drawings, wherein: Figure 1 shows in axial cross-section section along a longitudinal plane an electric spindle equipped with a locking device according to the present invention, in a locking position; Figure 2 is similar to Figure 1, but shows the locking device in an unlocked position with a rotatable assembly of the electric spindle partially extracted; Figure 3 is a cross-section along line III-III in Figure 1; Figure 4 is a cross-section along line IV-IV in Figure 2; and Figure 5 shows, in a view similar to that of Figure 1, the electric spindle during an unlocking procedure of a tool. With reference to the drawings, there is shown an electric spindle comprising a static member made up of an internally hollow casing 1, within which a stator 2 of an electric motor is fixedly mounted, and a rotatable member rotatably housed within the static member and comprising a spindle shaft 3 with a rotor 4 of the electric motor fixedly mounted externally to the spindle shaft; two bearings 5 and 6 are further keyed onto the spindle shaft 3 for the rotatable coupling of the latter to the static member. The rotatable member further comprises a rod 7 slideably housed within the spindle shaft 3 for unlocking a (not shown) tool mounted on the spindle shaft. On the back of the casing 1 a cylinder-piston assembly is mounted comprising a cylinder 8 slideably housing a piston 9 activatable by means of a pressurized fluid. The cylinder-piston assembly is mounted to the casing 1 by means of a reaction flange. At the back of the cylinder-piston assembly a cooling fan 11 is mounted to a box-like frame 12 enclosing the cylinder-piston assembly and the reaction flange 10. The box-like frame is attached to the casing 1 by means of vibration-dumping clamping members comprised in the shown example of screws 13 inserted in expansion rubber bushes 14, housed in respective holes provided in the casing; when the screws are fastened, the bushes expand within the respective holes and assure the clamping of the frame 12 to the casing 1. The rubber bushes 14 absorb the high-frequency vibrations of the casing 1 when the electric spindle is in operation, and prevent said vibrations from being transmitted to the cooling fan 11, which could otherwise be damaged. Inside the reaction flange 10 there is provided a seat for slideably housing a sliding drawer 15, slidable transversally to the axis of the spindle shaft 3. Through a driving rod 16, ending with a threaded end screwed into the drawer 15 and extending to the outside of the reaction flange 10, the drawer 15 can be activated so as to be moved from a lowered position, shown in Figure 1, wherein the drawer engages a circumferential slot 17 provided on the spindle shaft 3 so as to axially lock the spindle shaft, to a risen position, shown in Figure 2, wherein the drawer 15 clears the slot 17 so as to allow the axial movement of extraction of the rotatable member (spindle shaft, rotor, bearings, tool unlocking rod) from the static member of the electric spindle. The operation of the drawer 15 is clearly visible in detail in the cross-sections of Figures 3 and 4. In Figure 3, referring to the condition in which the axial movement of the spindle shaft 3 is locked and thus prevented, the drawer 15 is in the lowered position and engages with the slot 17 of the spindle shaft 3. It is further visible a locking screw 18 screwed into the reaction flange 10 so to lock, through a washer 19, the drive rod 16 of the drawer 15. Figure 4 refers instead to the condition wherein the drawer is risen so as to clear the slot 17 of the spindle shaft 3; to this purpose, the locking screw 18 has been removed, and the drive rod 16 has been risen to draw the drawer 15 from the lowered position of Figure 3 to the risen position of Figure 4. In Figure 5 there is shown the operation of the reaction flange 10. During an unlocking operation of a tool (not shown) that is attached frontally to the spindle shaft 3, a compressed fluid is introduced in the cylinder 8 so as to determine the sliding ahead of piston 9. Piston 9, beating against a head 20 of the unlocking rod 7, causes the latter to slide ahead; the front end 21 of the unlocking rod 7, acting on the tool attached to the spindle shaft 3, will cause the tool be unlocked. The width of the slot 17 is made larger than the thickness of the drawer 15, so that when piston 9 moves ahead under the action of the compressed fluid, the force acting on the cylinder due to the action-reaction principle makes the cylinder and the reaction flange fixed thereto move rearwardly; such a dynamic reaction transmits, through the drawer 15, to the spindle shaft 3, and compensates the axial thrust exerted on piston 9 so as to cancel the thrust. In this way it is possible to prevent the thrust from discharging onto the bearings 5 and 6, negatively affecting the life thereof. The invention has been so far described making reference to one possible embodiment thereof. However, as clearly appears to any one skilled in the art, other embodiments are possible, all falling in the scope of the invention as defined in the annexed claims.

Claims: Electric spindle comprising a static member (1,2,8-10), a rotatable member (3-7) axially extractable from the static member (1,2,8-10) and a locking device for the releasable coupling of the rotatable member (3-7) of an electric spindle to the static member (1,2,8-10) thereof, the rotatable member comprising a spindle shaft (3) housed within the static member and rotatably mounted thereto by means of bearing means (5,6), characterized in that said locking device comprise an axial holding means (15) for the spindle shaft, said axial holding means being housed in a respective sliding seat provided in said static member and being capable of being moved transversally to the spindle shaft between a locking position in which said axial holding means engages respective hooking means (17) provided on said spindle shaft, and an unlocked position in which said axial holding means is disengaged from said hooking means, thereby the rotatable member can be decoupled from said static member. Electric spindle according to claim 1, characterized in that said axial holding means comprises a drawer (15) slidable transversally to the axis of the spindle shaft (3), and said hooking means are comprised of a circumferential slot (17) provided on an external surface of the spindle shaft. Electric spindle according to claim 2, characterized by comprising drive means (16) for driving the sliding of said axial holding means (15). Electric spindle according to claim 3, characterized in that said driving means comprises a drive rod (16) fixed at one end thereof to the drawer (15) and having the other end protruding externally from the static member (1,2,8-10). Electric spindle according to claim 4, characterized in that means (18,19) are provide for the releasable locking of the drive rod (16). Electric spindle according to any one of the preceding claims, characterized in that said rotatable member (3-7) comprises an unlocking rod (7) for unlocking a tool mounted to the spindle shaft (3), the unlocking rod (7) slideably housed in the spindle shaft, and in that said static member (1,2,8-10) comprises a cylinder-piston assembly (8,9) for causing the displacement of the unlocking rod to determine unlocking of the tool. Electric spindle according to claim 6, characterized in that said cylinder-piston assembly (8,9) is coupled to a casing (1) of the electric spindle by means of a reaction flange (10). Electric spindle according to claim 7, characterized in that said sliding seat of the axial holding means (15) is formed in said reaction flange (10). Electric spindle according to claim 8, characterized in that said axial holding means (15) and said hooking means (17) cooperates so as to guarantee at least a limited axial clearance, so as to compensate by way of reaction an axial thrust of said piston (9). Electric spindle according to any one of the preceding claims, characterized in that a ventilation assembly (11) of the electric spindle is provided, said ventilation assembly being fixed to the static member (1,2,8-10) by means of vibration dumping elements (13,14). Electric spindle according to claim 10, characterized in that said vibration dumping elements comprises screws (13) inserted in expansion bushes (14) of a material suitable for absorbing vibrations. Set for electric spindle, characterized by comprising a static member and a plurality of rotatable members which can be interchangeably associated to said static member by means of a locking device according to any one of claims 1 to 11.

Inventors: ANNONI GIORGIO, MARELLI FLAVIO, ZAPPA FLAVIO, ANNONI, GIORGIO, MARELLI, FLAVIO, ZAPPA, FLAVIO
Applicants: F M ELETTROMECCANICA S R L, F.M. ELETTROMECCANICA S.R.L.
Application year: 1997
Main classification: H02K7
IPC codes: H02K5, H02K9, H02K7