JP2000237902A - Main shaft device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an excessive stress applied to a bearing and to smoothly rotate a main shaft even at a surperhigh speed rotation in spite of an exothermic of the bearing caused by a rotation of the main shaft. SOLUTION: Of a bearing mechanism pivotally supporting a main shaft 1 in the main shaft device, an outer ring of a bearing part 6 permitting an axial elongation due to a heat expansion by an axial movement is fixed to a bearing case 44 and a sleeve 40 surrounds the bearing case 44 and clamps/ releases the bearing case 44 by an elastic deformation. A pressure chamber 43 into which a pressure fluid is flowable is formed in the sleeve 40. The pressure chamber 43 has a position relationship for mainly deforming an inner periphery side of the sleeve 40 toward a radial and inward direction in the sleeve 40 when the sleeve 40 is elastically deformed by a flowing the pressure fluid into the sleeve 40.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a machine tool such as a machining center, which avoids stress or excessive load applied to bearings irrespective of temperature change due to heat generated by rotation of a spindle, and rotates the spindle smoothly and stably. The present invention relates to a spindle device capable of machining.

[0002]

2. Description of the Related Art Generally, a bearing mechanism of a spindle device is configured to support two points, and a long spindle is configured to support three points. Each support point is constituted by a single bearing or a combination of a plurality of bearings. Further, the relationship between the axial relative position of the inner ring and the axial relative position of the outer ring between the bearings is determined so that a preload is applied to prevent slippage of the rolling elements of the bearings and increase the rigidity of the main shaft assembly. ing.

FIG. 5 shows an example of such a prior art.
This is the front bearing that bears the radial and axial loads,
The rear bearing receives only a radial load.
Depending on the type of machine tool, such as a lathe, the rear bearing receives an axial load on the rear bearing, but generally the front bearing receives an axial load on the front bearing as in the example of FIG. The description will be made on the assumption that the front bearing bears the load in the axial direction. In the rear bearing, the inner diameter of the inner ring of the bearing and the main shaft are combined by shrink fit, and the outer diameter of the outer ring and the inner diameter of the housing or the bearing case are combined by clearance fit. The degree of these fittings is determined by the type and size of the bearing, the maximum number of revolutions of the main shaft, and the like. In the following, the front portion is referred to as a load side as a side on which a tool or a workpiece is mounted, and the rear portion is referred to as a non-load side opposite thereto.

In FIG. 5, a main shaft 1 includes bearing cases 3 and 4 provided at the front and rear of a headstock housing 2.
It is supported by two load-side rolling bearings 5 and non-load-side rolling bearings 6 held therein. The load-side bearing case 3 is fixed to the headstock housing 2 together with the cover 7, and the non-load-side bearing case 4 also serving as a housing is fixed to the headstock housing 2.

[0005] The spindle 1 has a plurality of cylindrical portions 1b, 1 whose diameter gradually decreases toward the rear side of the flange portion 1a at the front end.
c, 1d, and the load-side rolling bearing 5
It is positioned and fixed by a front nut 8 which abuts on the flange portion 1a and is shrink-fitted to the cylindrical portion 1b.
The anti-load-side rolling bearing 6 has cylindrical portions 1c and 1d.
Is positioned and fixed by a rear nut 11 shrink-fitted to the cylindrical portion 1d in contact with the stepped portion between them. A rotor 10 having a rotor sleeve (not shown) is shrink-fitted and fixed to a cylindrical portion 1c between the front and rear rolling bearings 5, 6. The rotor 10 has a cylindrical fixed casing 1 forming a cooling oil passage 12 for cooling oil flow.
Stator 14 fixed to headstock housing 2 via 3
Together, they constitute a built-in motor that rotationally drives the main shaft. The cooling oil passage 12 defined by the fins 15 of the cylindrical fixed casing 13 is connected to an annular chamber 17 formed between the load-side bearing case 3 and the cover 7 via a front passage 16, and the cooling oil inflow passage 18 and the cooling oil Together with the oil outflow passage 19, a cooling oil circulation passage for cooling the motor and the tip of the spindle is configured.

When the main shaft rotates, the bearing generates heat and thermally expands, and the generated heat is transmitted to the main shaft.
A temperature rise also occurs in the main shaft, and thermal expansion also occurs. With respect to such thermal expansion, while the axial expansion is absorbed by the gap between the outer diameter of the bearing outer ring and the inner diameter of the bearing case, the bearing outer ring and the bearing case move relatively, and the axial expansion is absorbed. However, as the rotational speed of the spindle increases, the degree of thermal expansion of the bearing further increases, and further thermal expansion occurs in the spindle whose temperature increases due to heat conduction. As a result, due to the thermal expansion of the bearing in the radial direction, the fitting at the outer diameter of the outer ring is reduced and the axial movement is hindered, and a load is applied to the bearing itself. In the case of a spindle device with a built-in motor for driving the spindle, as in the above example, the rotor of the spindle-side motor also generates heat, and the temperature rise of the spindle becomes even greater, and in the worst case, bearing damage may occur. is there.

Therefore, it is conceivable to set a clearance between the outer diameter of the outer ring and the inner diameter of the bearing case so that the bearing on the non-load side can smoothly move in the axial direction when the main shaft is rotated at the maximum rotation speed. However, such a configuration has a disadvantage in that the clearance becomes excessive at the time of low-speed rotation and at the time of stop, and the rigidity of the main shaft is reduced. The fact that the non-load-side bearing moves in the axial direction means that there is a gap regardless of the size, and vibration occurs when the main shaft rotates, which adversely affects the machined surface. Further, fretting or fretting occurs on the outer diameter surface of the outer ring and the inner diameter surface of the bearing case due to the vibration, and rust is generated. When this rust enters the bearing, adverse effects such as shortening the life of the bearing occur.

Therefore, in order to smoothly absorb the thermal deformation of the main shaft, a part of the bearing outer ring (the bearing outer ring on the non-load side) is fixed to a moving flange or a bearing case movably mounted in the fixed housing in the axial direction. Spindle devices have been proposed. An example of such a spindle device is shown in FIG.

The configuration of FIG. 6 is basically the same as that of FIG. 5 except that the bearing case and the moving flange for housing the case and the bearing can move in the axial direction on the non-load side. . For the sake of simplicity, only the points described with reference to FIG. 5 will be denoted by reference numerals, and only the axial movement on the non-load side will be described.

[0010] Support tube 2 fixed to headstock housing 2
2, a ball gauge 20 is fitted on the inner periphery, and a bearing case 24 is fitted on the inner periphery. The ball gauge 20 is a thin cylindrical retainer in which a large number of balls are held so as to protrude from both sides in the radial direction. Bearing case 24
Does not rotate with respect to the support cylinder 22, but can move in the axial direction together with the moving flange 21 via the ball of the ball gauge.

That is, in the above-described configuration shown in FIG. 6, of the thermal expansion of the main shaft, the expansion in the axial direction expands with reference to the load-side bearing, and moves the non-load-side bearing. This absorbs the axial deformation of the main shaft. In such a configuration, since the rolling of the rolling element is used, the movement is smoother than that of only the fitting (FIG. 5), but there is still a problem. For example, if a gap is provided in the fitting of the ball gauge, Vibration occurs when the main shaft rotates, and fretting occurs at the contact point of the ball. For this reason, a preload is applied to use as a slight shrink fit. However, there is a disadvantage that the rolling resistance is increased by applying the preload. If the preload is set at the time of main shaft rotation stop, the bearing case will be hotter than the support cylinder due to heat generation of the bearing at high speed rotation, the clearance will be small and the preload will be excessive, the rolling resistance during shaft movement will increase, When the preload is set according to the high-speed rotation,
There is also a disadvantage similar to the example in FIG. 5 in that the clearance becomes large at low speed and the spindle rigidity becomes insufficient.

The degree of temperature rise of the spindle changes depending on the rotation speed. Particularly, the temperature rise of the spindle is large during high-speed rotation, but in a high-speed machining center or the like, stable operation is performed over a wide rotation range from low to high. It is required to be possible. However,
In the classical configuration as described above, the point that obstruction of movement in the axial direction at the time of high-speed rotation causes excessive preload cannot be solved.

[0013]

Therefore, in recent years, as disclosed in, for example, Japanese Patent Application Laid-Open No. 10-286701, a double structure in which a support cylinder or an inner portion of a housing member has a fluid pressure chamber in the middle in the radial direction. There has been proposed a configuration in which an inner peripheral portion of the fluid pressure chamber is elastically deformed by the fluid pressure of the fluid pressure chamber.

FIG. 7 shows the basic structure. The configuration in FIG. 7 is basically the same as that in FIG. 5 except that the bearing case and the moving flange for housing the case and the bearing can move in the axial direction on the non-load side. For the sake of simplicity, only the points described with reference to FIG. 5 will be denoted by reference numerals, and only the axial movement on the non-load side will be described.

In the case of this example, the support cylinder 22 outside the bearing case 34 which is movable in the axial direction together with the movable flange 21 is provided.
A shallow annular groove 33 is formed in a portion of the inner peripheral surface except for the front and rear ends. The thin bush 32 is fixed to the entire inner peripheral surface of the support cylinder 22, and the space between the inner peripheral surface of the support cylinder 22 and the outer peripheral surface of the bush 32 is sealed by O-rings 30 and 31 before and after the annular groove 33. . An annular hydraulic chamber 38 is formed by closing the annular groove 33 with the bush 32. The hydraulic chamber 38 communicates with the adjustment oil connection port 37 from the support cylinder 22 via a passage 36 formed in the headstock housing 2, and the connection port 37 is connected to an adjustment oil supply device (not shown). I have. The thin bush 32 on the inner peripheral side of the hydraulic chamber 38 is elastically deformed in the radial direction by the hydraulic pressure of the adjustment oil supplied to the hydraulic chamber 38. It has also been practiced to smooth the axial movement of the bearing case by combining the configurations of the ball gauges.

However, Japanese Patent Application Laid-Open No. 10-286701
In the configuration disclosed in Japanese Patent Application Laid-Open Publication No. H10-209, in which elastic deformation is performed in the radial direction using a thin bush, when hydraulic pressure is applied, an annular groove 33 on the inner periphery of the support cylinder 22 (an annular groove formed on the outer peripheral side of the thin bush in some cases). The hydraulic chamber 38 is widened, and a gap occurs between the outer peripheral surface of the bush and the inner peripheral surface of the supporting cylinder over the entire length of the bush, which is longer than the length of the annular groove. Would. With such a configuration, for example, a machining center having an ultra-high-speed main spindle that reaches 60,000 revolutions per minute is extremely unstable and cannot be put to practical use.

Accordingly, the present invention prevents the stress applied to the bearing from becoming excessive despite the fact that the bearing generates heat due to the rotation of the spindle, and ensures that the spindle rotates smoothly even at ultra-high speed rotation. An object is to provide a spindle device.

[0018]

The object of the present invention is to provide a bearing mechanism in which a main shaft, a headstock, each inner ring is fixed to the main shaft, each outer ring is supported by the headstock, and the main shaft is supported at at least two points on the main headstock. In the main shaft device, the outer ring of a bearing portion of the bearing mechanism that supports the shaft at at least two points and that allows axial expansion due to thermal expansion by axial movement is fixed to the bearing case, and surrounds the bearing case. There is a sleeve for clamping / unclamping the bearing case by deformation, and a pressure chamber through which a pressure fluid can flow is formed in the sleeve. The pressure chamber mainly serves to elastically deform the sleeve due to the flow of the pressure fluid. The problem is solved by having a positional relationship in the sleeve that deforms the inner circumferential side of the sleeve inward in the radial direction.

It is preferable that the pressure chamber has a positional relationship in the sleeve such that the pressure chamber is elastically deformed only in a central region in the longitudinal direction of the sleeve. Further, the pressure chamber has a shape formed by a combination of a rectangular portion and circular portions at both ends on the side near the inner periphery of the sleeve in a cross section along the axial direction,
It is more effective if the thickness of the inner circumferential side of the sleeve corresponding to the circular portion is smaller than the thickness of the inner circumferential side of the sleeve corresponding to the rectangular portion.

It is preferable to periodically pressurize the pressure chamber by the inflow of the pressure fluid, clamp the bearing case with the sleeve at the time of pressurization, and release the clamp at the time of pressurization release.
Further, the pressure chamber may be pressurized when the tool comes into contact with the workpiece to clamp the bearing case, and the clamp may be released when the tool and the workpiece are separated. Alternatively, the amount of axial displacement of the bearing case per unit time is detected when the clamp is released, and when the displacement is smaller than a predetermined displacement, the pressure chamber is pressurized to lengthen the time for clamping the bearing case, and when it is larger, the clamping time is increased. May be shortened. Further, a difference in the axial displacement per unit time of the inner and outer rings when the bearing portion is released from clamping, which allows the axial expansion due to the thermal expansion by the axial movement, is detected. It is also preferable to extend the time for clamping the bearing case by pressing, and to shorten the clamping time when it is large.

Advantageously, the rolling elements are arranged between the sleeve and the bearing case. It is also preferable that a coating layer of a wear-resistant material is formed on the inner peripheral surface of the sleeve and the outer peripheral surface of the bearing case.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described based on an example shown in the drawings. In FIG. 1, the main shaft 1 is supported by a two-point support mechanism. That is, each is supported by two load-side rolling bearings 5 and a non-load-side rolling bearing 6. The load-side rolling bearing 5 is held together with a cover 7 in a bearing case 3 fixed to the headstock housing 2. The non-load-side rolling bearing 6 is held in a bearing case 44 that can move in the axial direction together with the moving flange 21. Both the load-side rolling bearing 5 and the non-load-side rolling bearing 6 are back-to-back angular contact ball bearings, and are provided with the same value and opposite axial preloads at the same value. Bearings are also possible.

The main shaft 1 is formed of a front flange portion 1a and a plurality of cylindrical portions 1b, 1c, 1d. The plurality of cylindrical portions 1b, 1c, 1d are connected to the front end flange 1a.
There is a relationship that the diameter gradually becomes smaller toward the rear side.
The load-side rolling bearing 5 abutting on the front end flange portion 1a of the main shaft 1 is positioned and fixed by a front nut 8 shrink-fitted to the first cylindrical portion 1b. The non-load-side rolling bearing 6 that contacts the step between the cylindrical portions 1c and 1d is positioned and fixed by a rear nut 11 shrink-fitted to the third cylindrical portion 1d. A rotor 10 having a rotor sleeve (not shown) is shrink-fitted and fixed to the cylindrical portion 1c located between the front and rear rolling bearings 5, 6. The rotor 10 constitutes a built-in motor for rotating the main shaft together with the stator 14 located on the outer periphery thereof.

The stator 14 has a cylindrical fixed casing 13.
The fixed casing 13 is provided with fins 15 defining a cooling oil passage 12 on the outer peripheral surface of the fixed casing 13. The cooling oil passage 12 is connected to an annular chamber 17 formed between the load-side bearing case 3 and the cover 7 through a front passage 16 formed from the headstock housing 2 to the load-side bearing case 3, and is cooled. Together with the oil inflow path 18 and the cooling oil outflow path 19, a cooling oil circulation path for cooling the motor and the tip of the spindle is configured.

An annular sleeve 40 to be fixed to the headstock housing 2 is disposed on the outer periphery of the bearing case 44 that can move in the axial direction. The annular sleeve 40 made of steel (S45C) or the like is provided with two O-ring grooves 41 on the outer peripheral surface as shown in FIG. 2A, and has a cross section (a cross section along the axial direction as viewed in FIG. 1). Has an annular cutting portion 42 which is a combination of a rectangular portion and circular portions at both lower sides thereof. Then, the annular cutting portion 42 is closed, and the annular hydraulic chamber 4 is closed.
2b, the split spacers 45 shown in FIG. In the hydraulic chamber 43, the thickness of the inner peripheral side of the annular sleeve is extremely thin (0.5 mm in the test described below) due to the circular portions at both ends in cross section close to the bearing case side. However, the annular sleeve has such a positional relationship that the elastic sleeve is elastically deformed when the hydraulic pressure is turned on and has a rigidity enough to come into surface contact with the bearing case 44 (2.5 mm in the following test). As a result, a substantially trapezoidal shape is formed on the inner peripheral side of the cross section of the annular sleeve.

The spacer 45 has a groove 46 on its outer peripheral surface.
Oil supply hole 4 penetrating into the hydraulic chamber 43
7 are formed. An adjustment oil supply path is formed from the hydraulic chamber 43 to the passage 48 formed in the headstock housing 2 through the outer peripheral groove 46 via the supply hole 47 and an oil tank.
It is connected to a hydraulic pressure generating device (FIG. 3) as a hydraulic control means having a pump and the like.

Adjustment oil, which is a pressurized fluid, is supplied to the hydraulic chamber 43, and the oil pressure causes the inner peripheral surface of the annular sleeve 40 to be elastically deformed in the radial direction. The control thereof will be described below with reference to FIG. I do. In addition, rolling elements (rollers and balls) 50 are disposed in front and rear positions of the hydraulic chamber 43 on the outer peripheral surface of the bearing case 44, and the axial movement of the main shaft 1, the non-load-side bearing 6, and the bearing case 44 becomes smooth. The inner peripheral surface of the annular sleeve 40 and the outer peripheral surface of the bearing case 44 are coated with hard chrome plating or titanium coating to achieve abrasion resistance.

The outer sleeve side moving sleeve 2 of the non-load side bearing 6
A first position sensor 51 for detecting the axial movement of the first nut and a second position sensor 52 for detecting the axial movement of the rear nut 11 on the inner race are connected to a controller 5 connected to the NC device.
It is connected to 3. The controller 53 and the NC device are connected to a hydraulic pressure generator 54, and the hydraulic pressure generator 54 supplies the adjustment oil to the hydraulic chamber 43 from an oil supply path via an electromagnetic valve. For periodic hydraulic control, a timer 55 connected to the hydraulic pressure generating device 54 and the NC device is provided.

When the power of the machine tool is turned on and the machining operation is started, the adjusting oil is supplied from the hydraulic pressure generator 54 to the hydraulic chamber 43 to apply a predetermined hydraulic pressure, and the inner peripheral surface of the annular sleeve 40 is radially inward. To securely clamp the bearing case 44. Thereafter, the hydraulic pressure is turned off at an appropriate time, for example, at a stage when a sufficient margin is reached against the limit at which the bearing is damaged by the stress increased by thermal expansion. Thereafter, the oil pressure is periodically turned on and off to make the annular sleeve 4
0 is elastically deformed or released in the radial direction to repeat fitting fit and clearance, thereby balancing axial movement of the main shaft and rigidity.

In this on / off control, oil pressure may be applied while machining is being performed with the tool mounted on the spindle, and oil pressure may be released when the tool is away from the machining point. If the continuous processing time is long, adjustment may be made to turn off the hydraulic pressure when the tool is temporarily separated from the processing point by a program, and to turn on the hydraulic pressure while in contact with the processing point. . In the above on-off control, the hydraulic pressure off time is, for example, about several seconds.

When the hydraulic pressure is turned on, a hydraulic pressure is selected such that the bearing case 44 can be almost completely clamped by pushing the annular sleeve 40 inward in the radial direction, and the on / off control is performed. Even when the bearing case 44 gradually slides with respect to the annular sleeve 40 together with the main shaft 1 and the bearing 6 due to thermal expansion at the time of turning on, the axial movement and rigidity of the main shaft can be balanced by the same on / off control. it can.

When the machining operation is started, the hydraulic pressure is not turned on, and the displacement amount of the moving sleeve 21, that is, the bearing outer ring, within a predetermined time is detected by the first position sensor 51 and compared with a predetermined displacement amount. If it is small, turn on the hydraulic pressure,
If it is large, it is possible to control to keep it off. Further, the displacement of the rear nut 11, that is, the displacement of the bearing inner ring is detected by the second position sensor 52, and the first position sensor 51 is detected.
, The difference between the displacement and the displacement of the bearing outer ring may be calculated, and the difference may be compared with a predetermined displacement difference per time to turn on / off the hydraulic pressure.

In the on / off control, the selected hydraulic pressure is the only one. However, when the thermal expansion extends for a long time, the hydraulic pressure is changed stepwise, and the axial movement of the main shaft and the rigidity are stepwise changed. May be balanced.

Finally, the specifications of the prototype used in the test will be described. The most characteristic annular sleeve of the present invention is made of S45C and has an inner diameter of 80 mm and an outer diameter of 11 mm.
It has dimensions of 0 mm and a length of 46 mm. As shown in FIG. 4, the cutting portion 42 formed on the annular sleeve includes:
When viewed from the cross section, it is a combination of a rectangular portion having a length of 26 mm and a depth of 27.5 mm and circular portions having a diameter of 5 mm located at both ends on the inner diameter side of the sleeve. Due to the presence of the circular part,
The thinnest portion on the inner circumferential side of the sleeve is 0.5 mm thick, and the thinnest portion in the axial direction is 7 mm. The outer diameter of the bearing case 44 was set so as to have a clearance of 30 μm when the hydraulic pressure was turned off with respect to the inner diameter of the annular sleeve 40. Table 1 shows displacement amounts (corresponding to radii) at points a, b, c, d, and e (FIG. 4) when hydraulic pressure is applied to the hydraulic chamber.

[0035]

[Table 1]

Even when a hydraulic pressure of 50 kg / cm ² was applied, the spindle could be rotated at 60,000 revolutions / minute to perform a machining operation. At this time, the ON time was 2 minutes and the OFF time was 5 seconds. Therefore, the present invention can be applied to a machining center having a maximum rotation speed of 60000 rpm.
In order to be able to use even a higher rotation speed, the clearance between the inner diameter of the annular sleeve and the outer diameter of the bearing case when the machine is stopped should be increased, and the hydraulic pressure should be switched stepwise.

[0037]

According to the present invention, the outer race of the bearing portion of the bearing mechanism for supporting the main shaft, which permits axial expansion due to thermal expansion by axial movement, is fixed to the bearing case and surrounds the bearing case. There is a sleeve that clamps / unclamps the bearing case by elastic deformation, and a pressure chamber into which pressure fluid can flow is formed in the sleeve. The pressure chamber mainly operates when the sleeve elastically deforms due to the flow of pressure fluid. Since the sleeve has a positional relationship in the sleeve that deforms the inner circumferential side of the sleeve radially inward, when the main shaft is super-rotated and the bearing generates heat, the stress applied to the bearing does not become excessive, and the pressure chamber The support of the sleeve is not unstable due to the expansion, and the main shaft can be smoothly rotated while securing sufficient rigidity.

By arranging the rolling element between the sleeve and the bearing case, the generation of vibration can be suppressed even when the pressure is released.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional configuration diagram of a spindle device according to the present invention.

FIGS. 2A and 2B are perspective views of an annular sleeve and a spacer constituting a hydraulic chamber; FIG. 2A is a schematic view of the annular sleeve cut in half, and FIG. 2B is a schematic view of a split spacer;

FIG. 3 is a schematic diagram showing a configuration of hydraulic control.

FIG. 4 is a schematic view showing specifications of a cutting portion in the annular sleeve.

FIG. 5 is a cross-sectional configuration diagram showing a spindle device according to a conventionally known clearance fit.

FIG. 6 is a cross-sectional configuration diagram of a spindle device having a conventionally known ball gauge.

FIG. 7 is a cross-sectional configuration diagram of a spindle device including a fluid pressure chamber and an elastically deformable thin bush.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Main shaft 50 Rolling element 2 Headstock housing 51 1st position sensor 6 Non-load side bearing 52 2nd position sensor 11 Rear nut 53 Controller 21 Moving sleeve 54 Hydraulic pressure generator 40 Annular sleeve 55 Timer 43 Hydraulic chamber 44 Bearing case 45 Spacer

Claims (9)

[Claims] 1. A spindle device comprising: a spindle; a headstock; and a bearing mechanism in which each inner ring is fixed to the spindle and each outer ring is supported by the headstock and supports the spindle at at least two points on the spindle head. An outer ring of a bearing portion of the bearing mechanism that supports at least two points and that allows axial expansion due to thermal expansion by axial movement is fixed to the bearing case, surrounds the bearing case, and clamps the bearing case by elastic deformation. There is a sleeve for releasing the clamp, and a pressure chamber into which the pressure fluid can flow is formed in the sleeve. The pressure chamber mainly radially inwards the inner circumferential side of the sleeve when the sleeve is elastically deformed by the flow of the pressure fluid. A spindle device having a positional relationship within the sleeve for causing the sleeve to deform. 2. The spindle device according to claim 1, wherein the pressure chamber has a positional relationship in the sleeve such that the pressure chamber is elastically deformed only in a central region in a longitudinal direction of the sleeve. 3. The pressure chamber has a cross section along an axial direction,
It has a shape composed of a combination of a rectangular portion and circular portions at both ends on the side closer to the inner periphery of the sleeve, and the thickness of the inner peripheral side of the sleeve corresponding to the circular portion is greater than the thickness of the inner peripheral side of the sleeve corresponding to the rectangular portion. The spindle device according to claim 1, wherein the spindle device is thin. 4. The pressure chamber is periodically pressurized by inflow of a pressure fluid, the bearing case is clamped by a sleeve at the time of pressurization, and the clamp is released at the time of pressurization release. The spindle device according to claim 1. 5. The method according to claim 1, wherein the pressure chamber is pressurized when the tool comes into contact with the workpiece to clamp the bearing case, and the clamp is released when the tool and the workpiece are separated. 3. The spindle device according to 1. 6. An axial displacement of the bearing case per unit time is detected when the clamp is released, and when the displacement is smaller than a predetermined displacement, the pressure chamber is pressurized to increase the time for clamping the bearing case, and when the displacement is large, The spindle device according to any one of claims 1 to 3, wherein a clamping time is shortened. 7. A difference in the axial displacement per unit time of the inner and outer races at the time of unclamping of the bearing portion, which permits axial expansion due to thermal expansion by axial movement, is detected. The spindle device according to any one of claims 1 to 3, wherein a time for clamping the bearing case by pressurizing the chamber is lengthened, and when the pressure is large, the clamping time is shortened. 8. The spindle device according to claim 1, wherein a rolling element is disposed between the sleeve and the bearing case. 9. The spindle device according to claim 1, wherein a coating layer made of a wear-resistant material is formed on an inner peripheral surface of the sleeve and an outer peripheral surface of the bearing case.