JPH1113754A - Bearing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To rotate the main spindle of a machine tool and the like from rotation at high speed to rotation at low speed while maintaining high rigidity by providing a dynamic pressure bearing supporting a rotor and a rolling bearing concentrically arranged putting side by side with the dynamic pressure bearing for a bearing device rotatably supporting the rotor in a housing. SOLUTION: In a bearing device rotatably supporting a rotor such as the main spindle of a machine tool, a dynamic pressure bearing 3 fitted to a spindle stock 2 and rotatably supporting a main spindle 1, a cylindrical roller bearing rotatably supporting the main spindle 1 is provided, and the inner ring 6 is fitted to the end face of the spindle stock 2 concentrically with the main spindle 1. Meanwhile, the outer ring 7 of the cylindrical roller bearing rotatably supporting the main spindle 1 is fitted to the tapered cylindrical part of the main spindle concentrically with the main spindle 1. Rollers 8 as rolling elements are interposed between the inner ring 6 and the outer ring 7. Hereby, at low speed rotation, the cylindrical roller bearing has large rigidity, at high speed rotation rigidity of the dynamic pressure bearing 3 is raised, and hence the main spindle 1 can be held strongly and surely.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bearing for rotatably supporting a rotating body such as a main shaft of a machine tool, and more particularly to a bearing device using both a rolling bearing and a sliding bearing.

[0002]

2. Description of the Related Art As a main shaft bearing of a machine tool, a slide bearing is used for high precision machining, and a rolling bearing is generally used for high speed and heavy cutting. As a plain bearing, a hydrostatic bearing is often used as shown in FIG. This has good damping properties against vibration and can obtain a very smooth finished surface. Then, the hydrostatic bearing sends pressure oil into the bearing pocket 21 to cause the main shaft 1 to float by static pressure and firmly restrain it at a fixed position. However, the effect of the oil film pressure due to the rotation of the main shaft 1 is small, and it cannot be expected that the holding rigidity increases as the main shaft 1 rotates at a high speed, which is not suitable for high-speed rotation or heavy cutting.

As a plain bearing, a dynamic pressure bearing is also used as shown in FIG. With this structure, as the rotation of the main shaft 1 increases, the oil film pressure of the oil that has entered the wedge-shaped gap between the main shaft 1 and the bearing surfaces 26 provided at a plurality of inner peripheral portions of the bearing main body 25 increases, thereby obtaining high holding rigidity. And high holding rigidity can be obtained during high-speed rotation. However, at the time of low-speed rotation, there was a problem that sufficient holding rigidity was not obtained.

One-sided rolling bearings, particularly cylindrical roller bearings as shown in FIG.
Can be fixed to the main shaft 1 without any gap. The clearance between the roller 32 and the inner ring 31 and the clearance between the roller 32 and the outer ring 33 are also reduced, and the allowable radial load becomes extremely large. Therefore, the roller is suitable for high-speed and heavy cutting, and is often used as a main shaft bearing of a machine tool. . However, since the rotational accuracy is inferior to the plain bearing and the damping property against vibration is small, chattering easily occurs during cutting, and a beautiful finished surface cannot be desired.

Further, as a modification of the rolling bearing shown in FIG. 7, an inner ring 35 is attached to a bearing housing 36 and an outer ring 37 is attached to the main shaft 1, that is, the inner ring 35 and the outer ring 3 are mounted.
No. 7 is reversely assembled and is known as Japanese Patent Application Laid-Open No. 2-35216. This is to prevent the seizure accident caused by the phenomenon that the inner ring expands due to the centrifugal force at the time of high-speed rotation and the inner ring becomes hotter than the outer ring when the temperature of the bearing rises in a general ordinary rolling bearing. It is. However, there is still a problem that the rotational accuracy is inferior to the plain bearing as the above-mentioned drawbacks peculiar to the rolling bearing, and the vibration is easily generated due to a small damping property against vibration.

Therefore, as shown in FIG. 8, a hybrid bearing technology in which a static pressure bearing and a plain bearing are used in a double structure as shown in FIG. 8 has been proposed in Japanese Patent Laid-Open No. 3-111103. This allows the hydrostatic bearing 41 to move at high precision and low speed,
The rolling bearing 42 is used by switching between high speed and heavy cutting depending on the application. That is, when used as the rolling bearing 42, the rolling bearing housing 43 is clamped to the headstock body 40 by the disk brake 44 so that only the rolling bearing 42 operates. When used as the hydrostatic bearing 41, the rolling bearing 42
Is configured not to rotate much due to preload, and a rolling bearing housing 43 is supported by a hydrostatic bearing 41. The rolling bearing 42 in the housing 43 also rotates together with the main shaft 1.

[0007]

Recently, there has been a demand for a higher speed than ever before, and it has become impossible to cope with JP-A-3-111103 described in the prior art. That is, when the rolling bearing 42 is used as the hydrostatic bearing 41 in JP-A-3-111103, the inner ring, the rollers, and the outer ring maintain the integrated state only by the force of the preload, and no other clamping mechanism is used. . Therefore, when the number of revolutions of high-speed rotation increases, the above-mentioned integrated state collapses, and a difference in rotation occurs between the inner ring and the outer ring, which results in a striped surface due to the roller interval peculiar to the rolling bearing. Had.

When the housing 43 is used as a rolling bearing in JP-A-3-111103, the action of the hydrostatic bearing 41 is completely eliminated because the housing 43 is clamped to the headstock 40 by the disc brake 44. The lubricating oil for the hydrostatic bearing acts as cooling oil, and cools the housing 43 from outside. At this time, the inner ring, the outer ring, and the rollers tend to be displaced outward due to thermal expansion due to heat generated by the bearing portion acting as the rolling bearing 42. However, there has been a problem that seizure occurs in the bearing portion because thermal displacement is prevented by cooling from the outside.

[0009] Further, generally, in a rolling bearing, the centrifugal force increases as the rotational speed increases, and the inner ring, the roller and the outer ring tend to expand outward. However, since the outer ring 33 is normally prevented from being expanded by the housing 34 as shown in FIG. 6, there is also a problem that there is no gap between the inner ring 31 and the roller 32 and the outer ring 33, so that rotation becomes difficult and seizure occurs. ing. The present invention has been made in view of the above problems, and rotates a main spindle of a machine tool while maintaining high rigidity from high-speed rotation to low-speed rotation, does not cause seizure even at high-speed rotation, and is resistant to vibration. An object of the present invention is to provide a bearing device with high damping.

[0010]

SUMMARY OF THE INVENTION In order to achieve the above object, a bearing device of the present invention is a bearing device for rotatably supporting a rotating body in a housing. A pressure bearing, and a rolling bearing disposed concentrically and concentrically with the dynamic pressure bearing to support a rotating body, wherein the rolling bearing is directly mounted concentrically to the rotating body and has an outer peripheral surface opened; An outer ring having a large diameter rolling surface on the inner diameter side, an inner ring supported concentrically with the rotating body in the housing and having a small diameter rolling surface on the outer diameter side, the small diameter rolling surface and the large diameter And a rolling element interposed between the side rolling surface. As described above, since the dynamic pressure bearing and the point bearing are juxtaposed, the main shaft can always be supported with high rigidity even at high speed rotation and at low speed rotation.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described with reference to FIG. 1 is a spindle of a machine tool, 2 is a headstock, 3 is a dynamic pressure bearing mounted on the headstock 2 and rotatably supporting the spindle 1, and 4 is a lubricating oil supplied to the dynamic pressure bearing 3. The cap 3 is fastened to the headstock 2 with a bolt (not shown) to prevent the pressure bearing 3 from flowing out of the end face to the outside. Reference numeral 5 denotes an oil seal housed in the cap 4 for preventing lubricating oil supplied to the dynamic pressure bearing 3 from flowing out of the cylindrical surface of the main shaft 1. Reference numeral 6 denotes an inner ring of a cylindrical roller bearing rotatably supporting the main shaft 1, which is attached to an end surface of the headstock 2 concentrically with the main shaft 1 by a bolt (not shown). Reference numeral 7 denotes an outer ring of a cylindrical roller bearing for rotatably supporting the main shaft 1, which is fitted concentrically with the main shaft 1 on a tapered cylindrical portion of the main shaft 1. Reference numeral 8 denotes a roller serving as a rolling element interposed between the inner ring 6 and the outer ring 7 and rotating. The inner ring 6, the outer ring 7, and the rollers 8 constitute a cylindrical roller bearing. Reference numeral 9 denotes a nut which is screwed to the end thread portion of the main shaft 1 and presses the outer ring 7 so as to be securely attached to the main shaft. 1
Numeral 0 denotes a large-diameter-side roller rolling surface of the outer ring 7 which is located on the inner diameter surface.
The roller 8 rolls on this surface when rotating. Reference numeral 11 denotes a small-diameter-side roller rolling surface of the inner ring 6, which is on the outer diameter surface. The roller 8 rolls when the main shaft 1 rotates. That is, the two rolling surfaces 10, 11
Rollers 8 roll between the rollers.

Next, the operation will be described. While the main shaft 1 is rotating at low speed, the rigidity of the dynamic pressure bearing 3 is small, but the cylindrical roller bearing has a large rigidity and holds the main shaft 1 strongly and securely. When the main shaft 1 rotates at a high speed, the rigidity of the dynamic pressure bearing 3 increases as the number of rotations increases, and the dynamic pressure bearing 3 strongly and securely holds the main shaft 1. At this time, in the cylindrical roller bearing, the portion of the rolling surface 10 of the outer race 7 directly fitted to the main shaft 1, particularly the side end near the headstock 2, expands in the outer peripheral direction due to centrifugal force. Therefore, the outer shape of the outer ring 7 is slightly deformed into a truncated cone. On the other hand, no centrifugal force acts on the inner ring 6 directly attached to the headstock 2, and therefore, no deformation occurs due to the centrifugal force. That is, the outer ring 7 is deformed into a truncated conical shape having a large diameter on the headstock 2 side due to centrifugal force, and the rollers are in a single contact state on the side farther from the headstock 2 with respect to the outer ring 7, so that large rigidity cannot be exhibited. After all, at low speed rotation, the cylindrical roller bearing supports the main shaft 1 with high rigidity,
During high-speed rotation, the dynamic pressure bearing 3 supports the main shaft 1 with high rigidity, so that the holding rigidity of the entire bearing can always be maintained high.

[0013]

FIG. 2 shows another embodiment of the present invention, in which the initial preload can be adjusted with respect to the cylindrical roller bearing in FIG. That is, the inner diameter of the inner ring 6 is formed in a tapered hole shape, and a tapered bush 12 that fits into the tapered hole is mounted and screwed with the cap 4.
At the outer end of the tapered bush 12, hook grooves 14 are provided at a plurality of positions on the circumference, and the grooves 14 are operated from a hole 13 formed on the side surface of the outer ring 7 with a dedicated wrench (not shown). By this operation, the taper bush 12 is turned to make a slight movement in the axial direction of the main shaft 1 to adjust the preload of the cylindrical roller bearing.

[0014]

In FIG. 1, the inner race 6 is fixed to the headstock 2 with bolts. However, the inner ring 6 may be press-fitted to the headstock 2 as shown in FIG.

[0015]

According to the present invention, during low-speed / heavy cutting, a cylindrical roller bearing supports the main shaft with high rigidity, and the outer ring directly attached to the main shaft becomes hot due to heat generation and deforms in the outer peripheral direction. It has a structure that can be freely deformed without any obstructing members. However, the outer peripheral surface of the outer ring is open and air-cooled during rotation, so the amount of deformation is small, and the centrifugal force is relatively small at low speed and heavy cutting.
Rotation can be performed smoothly because deformation due to centrifugal force is small. During high-speed precision cutting, the spindle is supported with high rigidity by dynamic pressure bearings. That is, since the dynamic pressure bearing is a slide bearing, the rotation is smooth and precision finishing is possible.
At this time, since the outer ring of the cylindrical roller bearing is deformed into a truncated conical shape due to centrifugal force, the rollers become one-sided, do not directly participate in rotation, and do not adversely affect rotation, and smoothly rotate at high speed. Becomes possible.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a hybrid bearing device of the present invention.

FIG. 2 is an explanatory view showing another embodiment of the hybrid bearing device of the present invention.

FIG. 3 is an explanatory view showing another embodiment of the hybrid bearing device of the present invention.

FIG. 4 is an explanatory view of a conventional dynamic pressure bearing.

FIG. 5 is an explanatory view of a conventional dynamic pressure bearing.

FIG. 6 is an explanatory view showing a use state of a conventional cylindrical roller bearing.

FIG. 7 is an explanatory view of a conventional angular ball bearing in which an inner ring and an outer ring are mounted in a state opposite to a normal state.

FIG. 8 is an explanatory diagram of a conventional hybrid bearing device using both a rolling bearing and a hydrostatic bearing.

[Explanation of symbols]

 Reference Signs List 1 spindle 2 headstock 3 dynamic bearing 6 inner ring 7 outer ring 8 roller

Claims (1)

[Claims] 1. A bearing device for rotatably supporting a rotating body within a housing, comprising: a dynamic pressure bearing housed in the housing for supporting the rotating body; and a rotating body disposed concentrically with the dynamic pressure bearing. A rolling bearing, which is directly attached concentrically to the rotating body, has an outer peripheral surface that is open, and has a large-diameter rolling surface on the inner diameter side; and the housing has the above-mentioned rolling bearing. An inner ring supported concentrically with the rotating body and having a small-diameter side rolling surface on an outer diameter side, and a rolling element interposed between the small-diameter rolling surface and the large-diameter rolling surface are provided. A bearing device characterized by the above-mentioned.