Spindle of a tool grinding machine

Abstract

The positioning of a cylindrical workpiece (that has to be machined by grinding) can be performed particularly precisely if the workpiece abuts to at least one, preferably two, static supporting elements and is fixed in a collet of a spindle, which allows a wobble compensation as well as a radial displacement of the spindle axis relative to the longitudinal axis of the workpiece.

Claims

1. A spindle for a machine tool comprising at least: a spindle head, having a first longitudinal axis and being configured to receive a clamping means, and a rear spindle portion, having a second longitudinal axis and configured to be received in a bearing block and as a drive shaft for the spindle head, at least one bearing arranged between the spindle head and the rear spindle portion and connecting them, wherein the at least one bearing: is sized to allow, in operation of the spindle, a wobbling movement between the spindle head and the rear spindle portion, and is configured to transmit at least one of compression and tensile forces in a longitudinal direction from the spindle head to the drive shaft, and is bridged by at least one coupling configured to transmit torques between the rear spindle portion and the spindle head.

2. The spindle according to claim 1, wherein the spindle head and the rear spindle portion have respective centering surfaces that are opposite to one another, between which a tapered centering slider is slideably movable between at least a first position and a second position, wherein in the first position the at least one bearing is bridged in a locking manner, whereby the spindle head and the rear spindle portion are mutually centered.

3. The spindle according to claim 1, wherein the at least one bearing has at least one of first and second partial bearings, wherein the first partial bearing has two complementary first bearing blocks with spherical-segment-shaped bearing surfaces and wherein the second partial bearing has two complementary bearing blocks with planar bearing surfaces, said planar bearing surfaces having respectively-corresponding surface normals, said surface normals being parallel to either the first longitudinal axis or the second longitudinal axis.

4. The spindle according to claim 3, wherein the at least one bearing has an intermediate portion formed as a ring or a ring segment, the at least one bearing having a first bearing surface that is either a spherical-segment-shaped surface or a cylinder-segment-shaped surface, the at least one bearing having a second bearing surface that is either a planar surface or a cylinder-segment-shaped surface, the second bearing surface located on a side of the at least one bearing that is facing away from the first bearing surface.

5. The spindle according to claim 3, wherein at least one of the first and second partial bearings is a hydrostatic bearing with a fluid gap between at least two of bearing surfaces.

6. The spindle according to claim 5, wherein bearing blocks of at least one of the first and second partial bearings are preloaded against each other by a magnetic force.

7. The spindle according to claim 6, wherein at least one permanent magnet is arranged in at least a first of two complementary bearing blocks, wherein magnetic flux of the at least one permanent magnet is guided from a magnetic north pole thereof to a magnetic south pole thereof such as to bridge at least once an air gap between the bearing surfaces, to thereby pre-load the bearing blocks by a magnetic force.

8. The spindle according to claim 1, wherein the at least one bearing has at least one of first and second partial bearings, wherein the first partial bearing has two mutually complementary first bearing blocks with first cylinder-segment-shaped bearing surfaces, and the second partial bearing has two mutually complementary second bearing blocks with second cylinder-segment-shaped bearing surfaces.

9. The spindle according to claim 8, wherein the at least one bearing has a ring-shaped or ring-segment-shaped intermediate portion having at least one first bearing surface that is a spherical-segment-shaped surface or a cylinder-segment-shaped surface and having, on a side of said intermediate portion that faces facing away from the at least one first bearing surface, at least one second bearing surface that is either a planar surface or a cylinder-segment-shaped surface.

10. The spindle according to claim 8, wherein at least one of the first and second partial bearings is a hydrostatic bearing with a fluid gap between at least two of bearing surfaces.

11. The spindle according to claim 10, wherein bearing blocks of at least one of the first and second partial bearings are preloaded against each other by a magnetic force.

12. The spindle according to claim 11, wherein at least one permanent magnet is arranged in at least a first of two complementary bearing blocks, wherein the magnetic flux of the at least one permanent magnet is guided from a magnetic north pole thereof to a magnetic south pole thereof such as to bridge at least once an air gap between the bearing surfaces, to thereby pre-load the bearing blocks by a magnetic force.

13. The spindle according to claim 1, wherein the spindle head has a continuous recess, in one side of which at least one clamping means is located, which is connected to a tension element being arranged in the recess and being preloaded against the spindle head.

14. The spindle according to claim 1, wherein the at least one coupling has elastically deformable struts including an elastically deformable strut on each of two sides of at least one of the first and second longitudinal axes, which elastically deformable struts connect the spindle head and the spindle portion at least indirectly torsion-proof to each other.

15. The spindle according to claim 1, wherein the at least one bearing is configured to effectuate a radial displacement of the spindle head and the first longitudinal axis relative to the rear spindle portion and relative to the second longitudinal axis.

16. The spindle according to claim 1, wherein the at least one bearing is sized to compensate, as a result of said wobbling movement, for errors in alignment of a workpiece, which is clamped in said machine tool during the operation, with respect to the second longitudinal axis.

17. A spindle for a machine tool comprising at least: a spindle head, having a first longitudinal axis and configured to receive a clamping means, and a rear spindle portion, having a second longitudinal axis and configured to be received in a bearing block and as a drive shaft for the spindle head, at least one bearing arranged between the spindle head and the rear spindle portion and connecting them, wherein the at least one bearing: is configured to allow at least one of tilting and pivoting of the spindle head and the of first longitudinal axis relative to the rear spindle portion and relative to the second longitudinal axis, and Is configured to transmit at least one of compression and tensile forces in a longitudinal direction from the spindle head to the drive shaft, and is bridged by at least one coupling configured to transmit torques between the rear spindle portion and the spindle head; wherein the spindle head and the rear spindle portion have respective centering surfaces that are opposite to one another, between which a tapered centering slider is slideably movable between at least a first position and a second position, wherein in the first position the at least one bearing is bridged in a locking manner, whereby the spindle head and the rear spindle portion are mutually centered.

18. The spindle according to claim 17, wherein the at least one bearing has at least one of first and second partial bearings, wherein the first partial bearing has two mutually complementary first bearing blocks with first cylinder-segment-shaped bearing surfaces, and the second partial bearing has two mutually complementary second bearing blocks with second cylinder-segment-shaped bearing surfaces.

19. The spindle according to claim 17, wherein the spindle head has a continuous recess, in one side of which at least one clamping means is located, which is connected to a tension element being arranged in the recess and being preloaded against the spindle head.

20. The spindle according to claim 17, wherein the at least one coupling has elastically deformable struts including an elastically deformable strut on each of two sides of at least one of the first and second longitudinal axes, which elastically deformable struts connect the spindle head and the spindle portion at least indirectly torsion-proof to each other.

21. The spindle according to claim 17, wherein the at least one bearing is configured to effectuate a radial displacement of the spindle head and the first longitudinal axis relative to the rear spindle portion and relative to the second longitudinal axis.

22. A spindle for a machine tool comprising at least: a spindle head, having a first longitudinal axis and being configured to receive a clamping means, and a rear spindle portion, having a second longitudinal axis and configured to be received in a bearing block and as a drive shaft for the spindle head, at least one bearing arranged between the spindle head and the rear spindle portion and connecting them, wherein the at least one bearing: is configured to allow at least one of tilting and pivoting of the spindle head and of the first longitudinal axis relative to the rear spindle portion and relative to the second longitudinal axis, and is configured to transmit at least one of compression and tensile forces in a longitudinal direction from the spindle head to the drive shaft, and is bridged by at least one coupling configured to transmit torques between the rear spindle portion and the spindle head; wherein the at least one bearing has at least one of first and second partial bearings, and the first partial bearing has two complementary first bearing blocks with spherical-segment-shaped bearing surfaces and the second partial bearing has two complementary bearing blocks with planar bearing surfaces, said planar bearing surfaces having respectively-corresponding surface normals, said surface normals being parallel to either the first longitudinal axis or the second longitudinal axis.

23. The spindle according to claim 22, wherein the at least one bearing has at least one of first and second partial bearings, wherein the first partial bearing has two mutually complementary first bearing blocks with first cylinder-segment-shaped bearing surfaces, and the second partial bearing has two mutually complementary second bearing blocks with second cylinder-segment-shaped bearing surfaces.

24. The spindle according to claim 23, wherein at least one of the first and second partial bearings is a hydrostatic bearing with a fluid gap between at least two of bearing surfaces.

25. The spindle according to claim 24, wherein bearing blocks of at least one of the first and second partial bearings are preloaded against each other by a magnetic force.

26. The spindle according to claim 25, wherein at least one permanent magnet is arranged in at least a first of two complementary bearing blocks, wherein the magnetic flux of the at least one permanent magnet is guided from a magnetic north pole thereof to a magnetic south pole thereof such as to bridge at least once an air gap between the bearing surfaces, to thereby pre-load the bearing blocks by a magnetic force.

27. The spindle according to claim 22, wherein the at least one bearing has a ring-shaped or ring-segment-shaped intermediate portion having at least one first bearing surface that is a spherical-segment-shaped surface or a cylinder-segment-shaped surface and having, on a side of said intermediate portion that faces facing away from the at least one first bearing surface, at least one second bearing surface that is either a planar surface or a cylinder-segment-shaped surface.

28. The spindle according to claim 22, wherein at least one of the first and second partial bearings is a hydrostatic bearing with a fluid gap between at least two of bearing surfaces.

29. The spindle according to claim 28, wherein bearing blocks of at least one of the first and second partial bearings are preloaded against each other by a magnetic force.

30. The spindle according to claim 29, wherein at least one permanent magnet is arranged in at least a first one of two complementary bearing blocks, wherein magnetic flux of the at least one permanent magnet is guided from a magnetic north pole thereof to a magnetic south pole thereof such as to bridge at least once an air gap between the bearing surfaces, to thereby pre-load the bearing blocks by a magnetic force.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, the invention will be described by way of example, without limitation of the general inventive concept, on examples of embodiment and with reference to the drawings.

(2) FIG. 1 shows an isometric view of a spindle.

(3) FIG. 2 shows a first side view of a spindle,

(4) FIG. 3 shows a second side view of the spindle.

(5) FIG. 4 shows a top view of the spindle.

(6) FIG. 5 shows a side view of the spindle with mounted cover.

(7) FIG. 6 shows a longitudinal section of the spindle along the plane A-A of FIG. 5.

(8) FIG. 7 shows a longitudinal section of the spindle along the plane B-B of FIG. 6.

(9) FIG. 8 shows a spindle in a partially assembled tool grinder machine.

(10) While the invention is susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents and alternatives falling within the spirit and scope of the present invention as defined by the appended claims.

DETAILED DESCRIPTION

(11) The spindle 1 in FIG. 1 has a spindle head 10 with a collet receptacle 41 being located in a collet 42. The spindle head 1 has a bearing block 11 whose rear part may be protected by a cover 50 (see FIG. 6 and FIG. 7). In the illustrated embodiment, the collet receptacle 42 is a component being connected to the bearing block 11; alternatively, the bearing block 11 may also have a recess formed as a collet receptacle.

(12) To the rear, i.e. on the side facing away from the collet 42, the spindle 1 has a drive shaft 20, which is also referred to as a rear spindle portion 20. An air supply and actuating device 60 is attached to the drive shaft 20. The spindle 1 can be connected to a machine tool via the drive shaft 20, i.e. the drive shaft can be connected to a drive and can be received by a bearing block of the machine tool (not shown). The bearing block thereby allows, as usual, only a rotation of the drive shaft about its longitudinal axis, i.e. about the second axis.

(13) As can be seen best in FIGS. 6 and 7, the spindle 1 has a bearing which allows a radial displacement of the drive shaft 20 and the spindle head 10, as well as a mutual tilting of the drive shaft 20 and spindle head 10. The bearing consists of two partial bearings, which form a front partial bearing and a rear partial bearing. The rear partial bearing has two opposite and mutually displaceable bearing surfaces 24, 34. For this purpose, the drive shaft 20 can have a planar annular rear bearing surface 24, which is cut preferably orthogonally by the longitudinal axis of the drive shaft 20, i.e. of the rear spindle portion 20. In this sense, the rear spindle portion 20 is or has a bearing block. Opposite to the first bearing surface 24 of the rear bearing lies a second bearing surface 34 of the intermediate block, which second bearing surface is complementary, conforming in shape to the first bearing surface. Preferably, a thin air gap is between the two bearing surfaces 24, 34, which air gap may be fed with compressed air, for example via an air duct 46. Also alternative fluids may be used as lubricants. The rear spindle portion 20 and the intermediate block 30 thus form a linear bearing with two degrees of freedom; in other words, the intermediate block is radially slideable relative to the rear spindle portion 20. The intermediate part 30 would also be rotatable against the drive shaft 20 without the coupling described further below, therefore the rear partial bearing has, strictly speaking, three degrees of freedom.

(14) The front partial bearing is also formed by first and second bearing surfaces 33, 13, which are complementary in shape and each of which preferably has a shape conforming to a shape of a surface of a spherical segment. For this purpose, a first spherical-segment-shaped bearing surface 33 may be located on the side of the intermediate block 30 being opposite to the annular bearing surface 34. A bearing surface 13 of the spindle head 10 lies opposite to this bearing surface 33. Again, the gap between the bearing surfaces 33, 13 may be fed with compressed air or another fluid. Consequently, the front partial bearing allows tilting of the spindle head 10 relative to the rear spindle portion 20 around a center point common to these spherical-segment-shaped surfaces (2 degrees of freedom). Without the coupling described further below, the spindle head 10 would also be rotatable against the intermediate part 30; thus, also the front partial bearing has, strictly speaking, three degrees of freedom. In the illustrated example, the center point of the spherical surface segments is in the zone of the not shown workpiece. This has the advantage that a radial displacement in wobble compensation remains very small, and that the center of gravity of the spindle head lies below the rotation point in tilting; the spindle head therefore does not tip over, but is self-centering to the vertical in a spindle with an upright spindle axis.

(15) The first partial bearing and also the second partial bearing are preloaded against each other by permanent magnets. These are, however, outside the both sectional planes being offset from one another by 90, and are therefore not visible. The magnets are arranged annularly around the longitudinal axes of the corresponding components in recesses of the bearing blocks.

(16) Other than illustrated, also the front partial bearing could be a linear bearing and the rear partial bearing a ball joint. For the invention, it is only important that the partial bearings together preferably allow both, tilting with two degrees of freedom as well as a radial offset (also with 2 degrees of freedom) of the longitudinal axes of the spindle head 10 and the rear spindle portion 20, and are as torsionally rigid as possible, wherefore a coupling may be provided.

(17) To make the bearing torsionally rigid, it is bridged by a rotating coupling in the illustrated example. Their elements are best shown in FIGS. 1 to 4: The rear spindle portion 20 is connected with a coupling element 53 via two mutually parallel first struts 51 (FIG. 1 to FIG. 4 and FIG. 5 with FIG. 6). The coupling element is composed of two ring halves and surrounds the intermediate block 30 in a ring-like manner, however it does not abut to the intermediate block at least in its rest position. The coupling element is held in its position by first struts 51 and second struts 52.

(18) For fastening the first struts 51, the rear spindle portion 20 has fastening elements 55 on two sides lying mutually diametrically opposite with respect to the longitudinal axis of the drive shaft, e.g. the illustrated elbows 55, to which one respective end of a first strut 51 is fastened. The other end of the first strut 52 is force-fittingly connected to the coupling element 53. As illustrated, the longitudinal axes of the first struts 51 run preferably at least approximately parallel (15, particularly preferred 5, even more preferred 1) to each other, in a plane orthogonally intersecting the longitudinal axis of the intermediate plane. Further two (second) struts 52 may be arranged in the same plane. The further struts 52 are connected to the coupling element 53 at two diametrally opposing sides in the same manner, but offset by 90 with respect to the first struts 51. The other end of the second struts 52 is force-fittingly connected to the spindle head 10 via second fastening elements 56 (e.g. elbows 56). Thus, the struts 51, 52 form a rotating coupling together with the coupling element 53 (see FIG. 5). A radial displacement of the spindle head 10 to the rear spindle portion 20 is only affected by low restoring forces of the struts 51, 52. The same holds true for the wobble movement of the spindle head 10 to the rear spindle portion 20.

(19) As can be clearly seen in FIG. 6 and FIG. 7, the spindle has a centering device with which the spindle head 10 can be centered with the rear spindle portion 20 e.g. when inserting and/or removing a workpiece into and/or out of the collet 42, i.e. the bearing is locked. For this purpose, the rear spindle portion 20 has at least one first ring-shaped or ring-segment-shaped centering surface 44 which, in the example shown, tapers conically toward the spindle head 10. A ring-shaped or alternatively ring-segment-shaped piston with a shell surface section 45 tapering toward the spindle head 10 lies at the first centering surface 44 as a centering slide 43. The centering slide 43 is axially displaceable on a preferably cylindrical contact surface 141 of an axial pin 14 of the spindle head 10, which forms the second centering surface. The centering slide 43 is preloaded toward the spindle head 10 by means of elastic elements 47 (can only be seen in FIG. 7), such that the centering slide 43 is clamped with its shell surface section 45 against the first centering surface, whereby the spindle head 10 is centered relative to the rear spindle portion. To unlock the centering and thereby release the bearing, the piston may be charged with a fluid, e.g. compressed air, on the spindle head side, in order to displace it against the elastic elements, such that the shell surface section does no more contact at the first centering surface.

(20) At its rear end, the collet is connected to a pulling member 48, herein a rod (cf. FIG. 6 and FIG. 7). The rod 48 is located in a continuous recess 16 of the spindle head 10 and is tensionally preloaded by a clamping element 49 supported by the spindle head 10 (a plate spring package is illustrated) toward the rear spindle portion 10. For this purpose, a clamping ring 59 is located on the rod, to which clamping ring a clamping element 49 engages. The clamping element is in a chamber 40 of the spindle head 10. To open the collet 42, the rod 48 is moved axially toward the collet.

(21) The rod 48 has an axial recess 46, which serves as an air duct 46 for supplying compressed air (or other fluid) for the bearing and at the same time for opening the centering device. For this purpose the air duct 46 is connected via holes 461, or punctures 462 with the gaps between the bearing surfaces 13, 33 and 24, 34 as well as with the sealed annular gap 431 in which the centering slide is located. If the air duct 46 is charged with compressed air, the centering device is first displaced and the bearing is released. Once the pressure is large enough, such that the magnetic preload is compensated, the bearing is freely moveable.

(22) To open the collet 42, a piston rod 61 of the air duct and actuating unit 60 is located in the axial extension of the rear spindle portion 20, which piston rod is connected to (at least one) piston 62. The piston 62 is located in a recess 63 of the housing 64 of the air duct and actuating unit 60, which recess 63 serves as a cylinder for the piston 62, and the piston 62 is pressure-chargeable against the restoring force of a restoring element 65, whereby the piston 62 and thus also the piston rod 61 are displaced toward the collet, and thus the tension element, i.e. the rod 48 is relieved. Also the piston rod 61 and the piston 62 have an axial channel 66, which is connected in communication with the air duct 46. To connect the axial channel 66 and the air duct 46, the rod 48 has a radial protrusion at its distal end, which can be inserted into a complementary recess of the piston rod and then be locked in the recess by a rotation of 90.

(23) In FIG. 8, the spindle is illustrated together with some elements of a machine tool grinder. The spindle head, the optional cabin, the grinding head along with drive and slide unit are not shown for the sake of clarity. Preferably, the spindle is arranged standing, as shown, i.e. its longitudinal axis corresponds at least approximately (15) to the vertical. At a support unit 80, which is force-fittingly connected to the machine frame only partially shown, a prism 70 with a clamping finger 71 and a steady rest 75 are arranged. The guiding prism 70 has a groove 711 in which a workpiece can be fixed with the clamping finger. The position and orientation of the guiding prism 70 relative to the support unit 80 and thus to the spindle can be varied by means of a setting unit 73, until a desired position is reached. In the desired position, the same of the guiding prism 70 as well as of the clamping finger 71 can be set. In the same way, the steady rest 75 is adjustable in a desired position and orientation by means of a further adjustment unit 76, and can be fixed there.

(24) For grinding a workpiece, a workpiece or preferably a calibration mandrel is first inserted into the collet, while the bearing between the spindle head 10 and the rear spindle portion is preferably locked by means of the centering device. Now, the guiding prism and the steady rest can be attached to the calibrating mandrel or the workpiece, respectively, and can be fixed in the corresponding position. Before fixing the position and orientation of the guiding prism 70, the clamping finger 71 is preferably charged towards the guiding prism 70, whereby the latter is properly attached to the workpiece. In other words, the workpiece now lies in the corresponding grooves 711, 751 of the guide prism or the steady rest, respectively. Now, the calibration mandrel can be replaced by a workpiece, if necessary. Subsequently, the centering device is opened, i.e. the bearing is released, and the machining of the workpiece can start. The machining forces, as far as they act in the workpiece in radial direction, are exclusively absorbed by the guide prism 70 and the steady rest 75, respectively. Even when rotating the workpiece in the V-grooves 711, 751, the position of the workpiece is determined only (at least in radial direction) by the guide prism 70 and the steady rest 75. Even when rotating the workpiece, no radial forces are transmitted from the rear portion 20 to the workpiece due to the bearing between the spindle head 10 and the rear spindle portion 20, wherein the precision in positioning the work-piece in machining is improved.

(25) It will be appreciated to those skilled in the art having the benefit of this disclosure that this invention is believed to provide a spindle for a machine tool. Further modifications and alternative embodiments of various aspects of the invention will be apparent to those skilled in the art in view of this description. Accordingly, this description is to be construed as illustrative only and is for the purpose of teaching those skilled in the art the general manner of carrying out the invention. It is to be understood that the forms of the invention shown and described herein are to be taken as the presently preferred embodiments. Elements and materials may be substituted for those illustrated and described herein, parts and processes may be reversed, and certain features of the invention may be utilized independently, all as would be apparent to one skilled in the art after having the benefit of this description of the invention. Changes may be made in the elements described herein without departing from the spirit and scope of the invention as described in the following claims.

LIST OF REFERENCE NUMERALS

(26) 10 spindle head (briefly: head) 11 bearing block of the spindle head (briefly: head block) 13 bearing surface 14 axial pin 141 contact surface for centering ring/centering surface 16 continuous recess 20 rear spindle portion/drive shaft 24 bearing surface 30 intermediate portion/intermediate block 33 bearing surface 34 bearing surface 40 chamber for clamping element 41 collet receptacle, more general: clamping element receptacle 42 collet, more general: clamping means 43 centering slide/tapering slide 431 ring gap 44 conical shell surface section 45 conical contact surface for centering slide 46 air duct 461 hole 462 puncture 47 elastic elements 48 tension element, here rod 49 clamping element, e.g. plate spring 50 cover 51 first struts (from drive shaft 20 to intermediate block 30) 52 second struts (from intermediate block 30 to spindle head 10) 53 coupling element 55 first fastening elements for struts 51 (e.g. elbows) 56 second fastening elements for struts 52 (e.g. elbows) 60 air duct und actuating unit 61 piston rod 62 piston 63 recess/cylinder 64 housing 66 channel 70 prism/guiding prism/support prism 71 clamping finger 75 steady rest 73 adjustment unit for support prism 76 adjustment unit for steady rest 80 support unit