JP2537158Y2 - Variable preload spindle device - Google Patents

Description

[Detailed description of the invention]

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improved preload variable spindle device having a preload adjusting means for adjusting a preload applied to a rolling bearing for supporting a spindle shaft.

[0002]

2. Description of the Related Art The preload of a bearing that supports a main shaft of a machine tool is usually set to be high in rigidity at the time of low-speed rotation for performing heavy cutting. In such a spindle device, the bearing generates heat due to the rotational friction of the bearing during high-speed rotation, and the shaft expands.As a result, the preload of the bearing is excessively large, and the bearing is liable to seize at an early stage. A variable preload type spindle device has been proposed in which a preload applied to a bearing is adjusted so as not to be disturbed. Conventionally, it has been proposed to use hydraulic pressure to make the preload variable.However, this requires a hydraulic unit, which increases the size of the spindle device, raises the temperature of the spindle device due to the oil temperature, and increases the precision. There is a disadvantage that it is difficult to control the hydraulic pressure. As a preload variable spindle device that solves such a disadvantage, both ends of a main shaft are supported by rolling bearings fitted in a housing, and one of a pair of rolling bearings that support the main shaft is fitted to a movable sleeve. Are movable relative to the housing in the axial direction. An internal thread groove is formed on the inner surface of the housing, and a movable sleeve provided with an external thread groove that engages with the internal thread groove and engages with a sliding screw is screwed into the housing. Is engaged with the teeth of a pinion driven by a motor, the movable sleeve is rotated by driving the motor, and the outer ring of one of the rolling bearings to which the movable sleeve is fitted is axially urged to preload the preload. Is provided. This pressing is performed by moving the movable sleeve in the axial direction by rotating the movable sleeve. (See, for example, JP-A-61-223324 and JP-A-64
No. -40203. )

[0003] Further, as a conventional preload variable spindle device, a thread groove of a ball screw is formed on the outer periphery of a movable sleeve, and a thread groove facing the thread groove is formed on an inner periphery of a nut. There is also known a spindle device in which a preload of a bearing can be varied by fitting a ball into a nut and directly driving a nut by a motor. (For example, see JP-A-3-79.
No. 205 publication. )

[0004]

However, in a conventional preload variable spindle device in which a movable sleeve is moved by a slide screw to apply a preload to a bearing,
Since the contact of the thread is surface contact and the friction of the thread is large,
When adjusting the preload, fine adjustment of the movable sleeve cannot be obtained due to stick slip of the movable sleeve, and when adjusting to increase the preload of the bearing, the movable sleeve moves too much when rotating the movable sleeve, and the preload tends to be excessive and the preload tends to be too large Excessive ones have the problem of bearing seizure occurring at an early stage.When adjusting to reduce the preload of the bearing, too, when the movable sleeve is rotated too much, the preload becomes too small and the rigidity of the spindle device becomes a predetermined value. In this case, there is a problem in that the cutting becomes extremely extreme and heavy cutting cannot be performed, and chatter occurs. JP-A-3-7920
In the variable preload spindle device as disclosed in Japanese Patent Application Publication No. 5 (1993) -1995, a ball screw is used instead of a sliding screw as means for moving the movable sleeve in the axial direction, and the driving of the nut is directly driven by a driving motor. In addition to the fact that the pitch of the ball screw is large, the rotation angle of the motor is directly the rotation angle of the nut, so a large motor output is required and a fine resolution motor is required for fine adjustment of the preload. As a result, there is a problem that the motor becomes large and the motor becomes expensive. The outer ring of the bearing that supports the shaft is fitted in the inner hole formed in the rear lid fitted in the rear housing, and is not fitted to the inner surface of the housing processed by the same set. ,
Misalignment is likely to occur between the main shaft housing and the rear lid, and it is not easy to manufacture an accurate spindle device.
There is a problem that the cost increases.

Accordingly, an object of the present invention is to provide a compact and inexpensive preload variable spindle device which can precisely adjust the preload of a bearing.

[0006]

According to the preload variable spindle device of the present invention, both ends of the main shaft are supported by a rolling bearing fitted in an inner hole of a housing, and a race of the rolling bearing is capable of adjusting a pressing force. In the preload variable spindle device, which is pressed in the axial direction by means, the pressing means has a ball screw groove, and one end face is in contact with a race of one of the rolling bearings. And a ball screw groove having a slightly different pitch in the same direction as the ball screw groove of the first bearing spacer and having one end face abutting on the race of the other rolling bearing. A cylindrical preload adjusting spacer having a second bearing spacer, a ball screw groove of the second bearing spacer, and a ball screw groove respectively opposed to the ball screw groove of the first bearing spacer; Bore of first bearing spacer A plurality of balls rotatably fitted between each of the ball screw grooves of the preload adjusting spacer facing the screw thread grooves and the ball screw grooves of the second bearing spacer; The object has been achieved by providing a preload adjusting spacer driving means for rotating the preload adjusting spacer relative to the bearing spacer and the second bearing spacer.

[0007]

According to the preload variable spindle device of the present invention, the first bearing spacer and the second bearing spacer are formed with ball screw grooves of ball screws having slightly different pitches from each other in the same torsion direction. The differential screw portion is constituted by a preload adjusting spacer which is screwed to both bearing spacers via a ball having a ball screw groove opposed to each groove via a ball, and is rotatable. Preload adjusting spacer driving means for rotating the bearing to change the relative position between the bearing spacers is provided. When the preload adjusting spacer is rotated, the ball moves while rolling between the ball screw grooves of the both bearing spacers and the ball screw groove of the preload adjusting spacer. In response to the movement, the first bearing spacer moves axially relative to the second bearing spacer. The length dimension between both end surfaces of the first bearing spacer and the second bearing spacer abutting on the bearing race changes in accordance with the amount of rotation of the preload adjustment spacer. In the case of the present invention, the pitch of both ball screw grooves is slightly different.Because the differential screw part is not a slide screw but a ball screw, there is very little friction, and this occurs when a slide screw is used. Since easy stick-slip does not occur, the dimensional change between the end faces of both bearing spacers per unit rotation angle of the preload adjusting spacer can be made extremely small and precise.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a longitudinal sectional view of an embodiment of a variable preload spindle according to the present invention. Rolling bearings 3 and 4 are interposed in the inner hole of a rectangular block-shaped housing 2 at axial intervals. . The main shaft 1 is inserted through the bearings 3 and 4, and the main shaft 1 is rotatably supported by the bearings 3 and 4. Bearing 3,
Numerals 4 denote angular ball bearings, respectively. The front end face of the inner ring 3A of the bearing 3 at the front (left side in FIG. 1) is in contact with the step 1A of the main shaft 1. The bearing 4 is fitted from behind to the main shaft 1 through the spacer 5, and is axially tightened through the spacer 7 by a nut 35 screwed to the main shaft 1, and the bearing 3 and the bearing 4 are fixed to the main shaft 1. Have been. The front end face of the outer ring 3B of the bearing 3 is in contact with a front lid 6 attached to the end face of the housing 2 with bolts B1. The outer diameter portion of the spacer 7 has a very small gap with the small diameter portion 2A formed in the housing 2 to prevent foreign matter from entering the bearing 4 from outside. Outer ring 4B of bearing 4
Is in contact with a step 8 provided in the housing 2.

The first bearing spacer 10 is a stepped cylindrical member, and an end face 45 of the large diameter portion 44 is in contact with a rear end face of the outer ring 3B of the bearing 3. The outer peripheral surface 46 of the large-diameter portion is slidably fitted on the inner peripheral surface of the housing 2 as a guide surface when the first bearing spacer 10 moves in the axial direction. The outer peripheral surface 46 is provided with a concave portion. , A sensor 11 (strain gauge) is attached. A first ball screw groove 12 having a Gothic arch-shaped cross section is provided on the outer peripheral surface of the small diameter portion 47 of the first bearing spacer 10. Second bearing spacer 13
Is a stepped cylindrical member similar to the first bearing spacer 10, and the end surface of the small diameter portion is arranged so as to face the end surface of the small diameter portion of the first bearing spacer 10, and the end surface 49 of the large diameter portion 48. Is in contact with the front end surface of the outer ring 4B of the bearing 4.

The outer peripheral surface 50 of the large diameter portion of the second bearing spacer 13
Is fitted on the inner peripheral surface of the housing 2, and on the outer peripheral surface thereof, a number of concave grooves 17 are provided in equal divisions, and a detent pin 15 fitted in a through hole 14 provided in the housing 2 is fixed to a predetermined position. The second bearing spacer 13 is made non-rotatable by engaging with the groove 17 at the position to form a detent means. Although not shown, the first bearing spacer is also provided with a similar detent means. A second ball screw groove 16 whose cross section is a gothic arch groove is provided on the outer peripheral surface of the small-diameter portion of the second bearing spacer 13, and the ball screw groove 16 is formed of a first ball screw groove.
The pitch is different in the same screw direction as the ball screw groove 12.

The preload adjusting spacer 20 is a ring-shaped member and has ball screw grooves 36 and 37 on its inner peripheral surface facing the first ball screw groove 12 and the second ball screw groove 16.
A nut drive lever 21 is fixed to the outer peripheral surface by a bolt B2. The ball screw groove 36 of the preload adjustment spacer and the first
Ball screw groove 12 and ball screw groove 3 of preload adjustment spacer
A ball 23 is rotatably fitted between 7 and the second ball screw groove 16. A square opening is formed in the upper part of the housing 2, and a nut drive lever 21 is located at the center of the opening. The support unit housing 25 is attached at a position close to the opening.

The lever driving ball screw shaft 26 is a stepped screw shaft. A lever driving ball screw nut 27 is screwed into the large diameter screw portion, and the intermediate stepped portion is fitted into the support unit housing 25. Is inserted through the rolling bearing 28,
It is fixed by a lock nut 33 and is axially immovable and rotatably supported. The shaft end of the small diameter portion of the ball screw shaft 26 for lever driving is connected to a drive motor 3 fixed to the support unit housing 25 via a coupling 29.
0 (for example, a servo motor). Two lever driving pins 31 are fixed to both opposing side surfaces of the ball screw nut 27 for lever driving, at right angles to the axis and having the same axis. Lever drive pin 3
Numerals 1 and 31 respectively engage with U-shaped cutouts 32 formed at the upper portion of the nut drive lever 21 and open at the top. The nut drive lever 21 is pushed by the linear movement of the lever drive ball screw nut 27, and the preload adjustment spacer is provided. 20 is rotated. At this time, since the lever drive pin 31 is in contact with the plane of the U groove of the nut drive lever 21, the linear movement of the lever drive ball screw nut 27 is not hindered.

A preload is formed by engaging a lever drive ball screw nut 27 screwed to a lever drive ball screw shaft 26 rotated by a drive motor 30 with a nut drive lever 21 fixed to the preload adjustment spacer 20. Preload adjustment spacer driving means for rotating the adjustment spacer 20 is configured.
The differential screw portion is formed by screwing the first bearing spacer 10 and the second bearing spacer 13 and the preload adjustment spacer 20 via the ball 23, and the preload adjustment spacer 20 is connected to the preload adjustment spacer. The first bearing spacer 10 is axially moved by a predetermined amount with respect to the second bearing spacer 13 by being rotated by the driving means to adjust the axial pressing force of the outer ring 3B. It is configured to apply a predetermined preload. The ball screw portion composed of the first bearing spacer 10, the preload adjustment spacer 20 and the ball 23 has a right-hand thread and a pitch of 10 mm, and the second bearing spacer 13, the preload adjustment spacer 20 and the ball 23 have the same pitch. The formed ball screw portion has a right-hand thread and a pitch of 7 mm.
When the nut drive lever 21 is turned to the near side of the paper surface in FIG. 1, that is, when the spindle is viewed from the right, the preload adjustment spacer 20 is turned counterclockwise, for example, by 1 ° counterclockwise. Of the first bearing spacer 1 through the rolling of
0 is 10 mm to the left in FIG. 1 with respect to the preload adjustment spacer 20.
× 1 ° ÷ 360 ° = 0.0278 mm, and the preload adjustment spacer 20 moves to the right with respect to the second bearing spacer 13 by 7 mm × 1
° ÷ 360 ° = 0.0194 mm. Therefore, the length dimension between the end faces of the first bearing spacer and the second bearing spacer is 0.0278 mm−0.0194 mm = 0.0084 m.
m. As a result, each of the bearings 3 and 4 has 4.2
A preload amount corresponding to μm is applied. Conversely, when the preload adjustment spacer 20 is rotated to the right by 1 °, the first bearing spacer 10 moves 0.0278 mm to the right with respect to the preload adjustment spacer 20, and the preload adjustment spacer 20 becomes the second bearing spacer. 0.0 for 13
After moving 194 mm, the dimension between both end surfaces of the first bearing spacer and the second bearing spacer is reduced by 0.0084 mm. As a result, the preload amount corresponding to each of the bearings 3 and 4 is reduced by 4.2 μm. Incidentally, when appropriately adjusting the above-mentioned bearing preload in the range from light cutting to heavy cutting, the total axial movement amount applied to the bearing outer rings 3B, 4B is in the range of about 20 to 50 μm, and the accuracy of the movement amount is as follows. About 2 μm is required. This positioning accuracy of 2 μm corresponds to a rotation angle of the preload adjustment spacer of 0.24 °,
In particular, it is an accuracy that can be sufficiently secured without using a drive motor having high positioning accuracy. In the case of this embodiment, the preload adjusting spacer 20 is driven by a ball screw on the nut drive lever 21 attached to the preload adjusting spacer 20, so that the first bearing spacer 10 is moved by 2 μm. The rotation angle of the drive motor 30 required for the
1 may be rotated by 0.24 °, which is 0.38 mm in terms of the amount of movement of the ball screw nut 27 for driving the lever, and the pitch of the ball screw for driving the lever is 4 mm. Is 0.38mm ÷ 4
mm × 360 ° = 34.2 °, for example, when a 500-split drive motor is used, the bearing spacer can be positioned with an accuracy of 0.042 μm.

Next, the required drive torque of the drive motor 30 for obtaining the preload to be applied to the bearings 3 and 4 will be examined.
In the spindle device of this embodiment, the preload of the bearing in the range from light cutting to heavy cutting is in the range of about 30 to 300 kgf. In order to obtain a preload of 300 kgf by axial movement of the first bearing spacer 10 and the second bearing spacer 13, assuming that the conversion efficiency is 0.9, the preload adjusting spacer 20 is rotated at a rotational torque Tb = 300 kgf × 0.3 cm. × 0.9 ÷ 2π = 1
It is necessary to rotate at 2.9 kgfcm or more. In order to rotate the preload adjustment spacer 20 at 12.9 kgfcm or more, the lever drive pin 31 acts on the nut drive lever 21 at a position having a radius of 90 mm from the axis of the main shaft 1.
From 9 cm = 12.9 kgfcm, a force of F = 1.43 kgf is applied to the nut driving lever 21 by the lever driving pin 31.
Should be added to The rotation torque of the lever driving ball screw shaft 26 required to obtain an axial force of 1.43 kgf is Tb '=
1.43 kgf × 0.4 cm × 0.9 ÷ 2π = 0.08
It becomes 19 kgfcm. It is sufficient for the servo motor that generates such a starting torque to have an outer diameter of about 60 mm and an overall length of about 40 mm. Therefore, the preload variable spindle device itself can be made compact and inexpensive.

Further, since the bearings 3 and 4 are fitted on the inner diameter surface of the housing 2 machined by the same set, the bearings 3 and 4 are different from conventional spindles of this kind.
Can be secured very easily, and a spindle device with low cost and high accuracy can be provided. Further, the axial movement of the first bearing spacer and the second bearing spacer is performed through the rolling of the ball 23, and the ball is preloaded and the rolling friction is very small. Unlike the case of using a conventional slide screw, there is no problem due to stick-slip, and the preload can be precisely adjusted by moving the bearing spacer.

The front cover 6 is a ring-shaped member and has a small diameter portion that fits on the inner diameter surface of the housing 2 and a flange portion that contacts the end surface of the housing 2. A radial slit 38 is formed in the outer surface of the small diameter portion in the circumferential direction.
A radial slit is formed in the inner surface portion adjacent to the axial direction from 8 in the circumferential direction. These radial slits are provided deeper than the center of the thickness of the small diameter portion of the front lid 6. The inner diameter of the front lid 6 has a very small gap with the large diameter portion following the step 1A of the main shaft 1 so that foreign matter does not enter the bearing 3. The end face of the small diameter portion of the front lid 6 fixed to the housing 2 is in contact with the outer ring 3B of the bearing. Front lid 6
The end on the side in contact with the bearing 3 has a predetermined spring effect in the axial direction by alternately formed slits 38, 38, and presses the bearing 3 in the depth direction by a predetermined spring force. When a preload is applied to the bearing 3, the outer ring 3B can be moved in the axial direction by pressing the outer ring 3B with a force greater than the force applied to the front lid by the preload adjustment spacer 20. The outer peripheral surface of the outer race 3B and the inner peripheral surface of the housing 2 are fitted with a small gap so that the outer race of the rolling bearing can move during the preload adjustment. As a result, the movement of the outer ring 3B in the radial direction is restrained, so that the support rigidity of the bearing 3 is increased.

When the bearing spacer 10 is moved away from the bearing 3 to reduce the preload, the front ring 6B is attached to the outer ring 3B.
, The movement of the outer ring 3B is not hindered by the frictional force between the outer ring 3B and the housing 2, the outer ring 3 can move smoothly, and the preload adjustment of the bearing can be precisely performed.

A pulley (not shown) is attached to the rear end of the main shaft 1, and rotation is transmitted to the main shaft 1 by driving the pulley to rotate by a main shaft motor (not shown). Generally, when low-speed heavy cutting is performed, a large preload is applied to the bearings 3 and 4 to obtain a necessary high rigidity.
On the other hand, when light cutting is performed at high speed, switching to a small preload is performed to suppress heat generation of the bearing. When the preload changes due to heat generation of the bearing during use of the spindle, a preload adjustment command predetermined according to a signal from the pressure sensor 11 is input from the control means 41 to the drive unit 40 as a target position command. In response to this, the motor drive current is output from the current control unit of the drive unit 40 to the drive motor 30 via the power amplifier circuit, and the rotation angle of the output shaft of the drive motor 30 is controlled.
Thus, the lever driving ball screw shaft 26 connected to the output shaft of the driving motor 30 via the coupling 29 rotates by a predetermined amount, and the lever driving ball screw nut 27 moves in the axial direction according to the rotation amount. Nut drive lever 2
1, the preload adjustment spacer 20 is rotated by a predetermined angle.
When the preload adjustment spacer 20 rotates, the first bearing spacer 10 moves a predetermined amount in the axial direction with respect to the second bearing spacer 13 through the rolling of the ball 23, and the outer ring 3B of the bearing is moved in the aforementioned manner. As described above, the bearing is pressed in the axial direction by the first bearing spacer 10 and is positioned at a predetermined position. As a result, the bearing preload is adjusted to a predetermined value. At this time, the preload adjustment result is detected by the pressure sensor 11, and the detected value is input to the control means 41. If the input value does not correspond to the preload adjustment command value, the target position command is input to the drive unit 40 again by the necessary correction value to adjust the preload, and the preload control is performed with high accuracy by repeating this adjustment.

According to the present invention, in a variable preload spindle device, a first bearing spacer and a second bearing spacer are formed with thread grooves of a ball screw having a slightly different pitch from each other in the same thread direction. A preload adjusting spacer which has a ball screw groove corresponding to each of the screw grooves and is screwed to both bearing spacers via balls, and is rotatable, and the preload adjusting spacer is rotated. A preload adjusting spacer driving means for adjusting the preload of the bearing by moving both bearing spacers in the axial direction is provided. As a result, there is an effect that the preload adjustment of the bearing can be easily and precisely performed even during the rotation of the spindle, and a compact and inexpensive preload variable spindle device with high spindle rotation accuracy can be obtained.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a variable preload spindle device according to the present invention.

FIG. 2 is a cross-sectional view taken along the line CC of FIG. 1, and an upper right portion is a cross-section along a center line of a ball screw shaft for lever driving.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main shaft 2 Housing 3 Rolling bearing 4 Rolling bearing 6 Front lid 10 First bearing spacer 13 Second bearing spacer 20 Preload adjustment spacer 23 Ball 30 Drive motor 40 Drive unit 41 Control means

Claims (1)

(57) [Scope of request for utility model registration] 1. A preload variable spindle device in which both ends of a main shaft are supported by a rolling bearing fitted into an inner hole of a housing, and a race of the rolling bearing is pressed in an axial direction by a pressing means capable of adjusting a pressing force. The pressing means has a ball screw groove, one end face of which is in contact with a race of one of the rolling bearings; a cylindrical first bearing spacer; and a ball screw groove of the first bearing spacer. A cylindrical second bearing spacer having a ball screw groove having the same torsion direction and a slightly different pitch and having one end face abutting against the race of the other rolling bearing; and the second bearing. A cylindrical preload adjusting spacer having a ball screw groove opposed to the ball screw groove of the spacer and the ball screw groove of the first bearing spacer; a ball screw groove of the first bearing spacer; Opposed to the ball screw groove of the bearing spacer of No. 2 A plurality of balls rotatably fitted between each of the ball screw grooves of the preload adjustment spacer, and the preload adjustment spacer with respect to the first bearing spacer and the second bearing spacer. A preload variable spindle device comprising: a preload adjusting spacer driving means for relatively rotating a seat.