JPH0742730A - Pre-load variable spindle device - Google Patents

Abstract

PURPOSE:To provide a pre-load variable spindle device which can secure rotational accuracy at any rotational speed of a shaft by detecting oscillations or displacement of the shaft, varying characteristic frequency of the shaft according thereto, and eliminating resonance to the oscillations of a rolling bearing. CONSTITUTION:A hydraulic piston mechanism is operated for applying axial force to an outer ring of a bearing which is installed between a shaft 7 and a housing 10, and for varying pre-load amount of the bearing. An oscillation or displacement sensor 24 is arranged on the sensor 24. A controller 26 adjusts hydraulic force of the hydraulic piston mechanism according to a detected value of the sensor 24. The controller 26 alsoadjusts the hydraulic force of the hydraulic piston mechanism so as to vary characteristic frequency causing resonance to the oscillations of the shaft 7 due to its rotation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a preload variable spindle device, and particularly to a preload which is used for a work spindle of a precision lathe having a machining accuracy of submicron and which eliminates the vibration generated by the bearing and the resonance of the shaft. The present invention relates to a variable spindle device.

[0002]

2. Description of the Related Art In a spindle device in which a shaft portion is supported by a housing through a plurality of rolling bearings, it has been conventionally practiced to change the preload of the rolling bearing according to the rotational speed of the shaft portion. The preload of the rolling bearing is performed by axially pressing the outer ring of the rolling bearing by, for example, tightening the outer ring pressing member screwed into the inner peripheral surface of the housing. Generally, in a spindle unit of a machine tool for cutting, when it is configured for low speed rotation, the axial pressing force of the bearing outer ring is strengthened to a high preload, and conversely for high speed rotation, the axial pressing force of the bearing outer ring is reversed. Is weakened to a low preload.

The preload amount of the rolling bearing of the spindle device affects not only the bearing rigidity but also the natural frequency of the shaft supported by the bearing. As described later, the rolling bearing generates vibrations of various frequencies related to the rotation frequency by rotating. When the vibration frequency based on the rotation of the bearing and the natural frequency of the shaft match, the shaft generates large vibration in the radial direction and the axial direction. Conventionally, when operating a machine incorporating a spindle device, the spindle device is used at a rotation speed that avoids the rotation frequency that causes resonance with respect to the natural frequency of the shaft.

[0004]

As described above, the rolling bearing, when rotated, generates vibrations of various frequencies related to its rotation speed. It has been confirmed that among these generated vibrations, a vibration having a frequency of about 10 times the number of rotations occurs considerably. When the vibration frequency of about 10 times this rotation frequency and the natural frequency of the shaft portion of the spindle device match, the shaft portion vibrates in the axial or radial direction with an amplitude of 1 μm at maximum. Such vibrations adversely affect the flatness and roundness of the end surface of the work, and deteriorate the finish accuracy of the work. It may not be desired to change the rotation frequency that causes resonance with respect to the natural frequency because the required work peripheral speed cannot be changed depending on the machining content.

According to the present invention, there are factors that affect the rotation accuracy,
For example, the radial or axial displacement or vibration of the shaft is detected, and based on this, the preload of the bearing is automatically adjusted so as to change the natural frequency of the shaft, thereby ensuring rotation accuracy and use. It is an object of the present invention to provide a preload variable spindle device that is not restricted by the rotation speed.

[0006]

According to the present invention, there is provided a hydraulic piston mechanism for changing the preload of the bearing by applying an axial force to the outer ring of the bearing mounted between the shaft portion and the housing, and provided on the housing side. And a controller for detecting the rotational accuracy of the shaft portion and a controller for adjusting the hydraulic pressure of the hydraulic piston mechanism based on the detection value of the sensor, the controller having a vibration frequency dependent on the rotational speed of the bearing. There is provided a preload variable spindle device that adjusts the hydraulic pressure of the hydraulic piston mechanism so as to change the natural frequency of the shaft portion that causes resonance.

[0007]

When the variable preload spindle device according to the present invention is used for the work spindle of a precision lathe, a hydraulic piston mechanism is provided in the outer ring retainer of the rolling bearing at the end of the housing near the work chuck, and the cylinder chamber is hydraulically operated from the outside. The outer ring of the rolling bearing is pressed in the axial direction by applying. By pushing the outer ring of the rolling bearing in the axial direction, the outer ring spacer, which determines the preload amount of the rolling bearing, is bent in the radial direction, and the preload amount applied to the rolling bearing is reduced. Due to the decrease in the bearing preload amount, the axial rigidity and the radial rigidity of the rolling bearing decrease, and the natural frequency of the shaft portion changes to the lower side. When the device is operated, the number of revolutions to be used is determined in advance, the rotational accuracy in the rotational operation is actually checked, and if vibration or displacement occurs, the preload amount is automatically adjusted so that the vibration is reduced.

[0008]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a vertical sectional view of a preload variable spindle device for a precision lathe according to an embodiment of the present invention. The housing 10 has a cylindrical inner surface into which a bearing is fitted. A hollow shaft portion 7 is provided in the housing 10 via a pair of front side rolling bearings 3 and 5 and a pair of rear side rolling bearings 11 and 13.
Is rotatably supported and extends through the housing 7. A work chuck (not shown) is attached to the front end of the shaft portion 7, and a drive pulley 16 is fixed to the rear end of the shaft portion 7 with a key 14 and a tightening nut 17. The source causes the shaft 7 to rotate.

One of the front rolling bearings 3 has an inner ring 3A.
Of the outer ring 5 </ b> B of the outer ring 5 </ b> B of the housing 10 is in contact with the front step surface of the shaft 7.
The rearward movement is restrained by contacting the stepped portion of the bearing, and a large amount of preload is preliminarily applied by the outer ring spacer 4 and the inner ring spacer 6 arranged between the bearings 3 and 5 to assemble the rear combination. ing. The outer ring spacer 4 has a concave peripheral groove 4 in the center of the outer peripheral portion.
It is an annular member formed with a and having a substantially U-shaped cross section, whereby it is easily deformed in the axial direction by an axial load and a desired spring constant is given. In the embodiment, the outer ring spacer 4 has an axial rigidity value of about 250 kgf / μm. Inner rings 3A, 5 of front side rolling bearings 3, 5
A is fixed to the shaft portion 7 via a collar 8 by a nut 9 screwed to the shaft portion 7. A ring-shaped outer ring pressing piston 2 is axially fitted to the inner end surface of the outer ring pressing member 1 fixed to the front end of the housing 10 by bolting or the like. The outer ring pushing piston 2 is the front rolling bearing 3
The outer ring 3B is inserted into the front end of the housing 10 so as to press the outer ring 3B in the axial direction. A hydraulic pocket 21 is formed between the base end of the outer ring pressing piston 2 and the outer ring pressing member 1, and the hydraulic pocket 21 includes a hydraulic pressure supply portion through a hydraulic pressure supply hole 19 formed in the outer ring pressing member 1. A force that is in communication with the device 23 and is proportional to the magnitude of the hydraulic pressure introduced by the hydraulic pressure supply unit is applied to the outer ring pressing piston 2 so that the preload amount of the front side rolling bearings 3 and 5 is adjusted. Has become. The hydraulic pocket 21 is sealed by O-rings 20 mounted on the outer circumference and the inner circumference of the piston 2.

A displacement sensor 24 is attached to the outer ring pressing member 1 close to the outer peripheral surface of the shaft portion 7. The displacement sensor 24 detects the displacement of the shaft portion 7 in a non-contact manner, and the detection signal is input to the controller 26 via the detection circuit 25. The controller 26 controls the hydraulic control device 23 so as to adjust the pressing force of the outer ring pressing piston 2 based on the detection signal of the displacement sensor 24 and change the natural frequency of the shaft portion 7 according to the change in the preload amount. A temperature sensor 27 is provided in the vicinity of the rolling bearing 3. The detected value of the temperature sensor 27 is detected by the temperature detection circuit 28 and input to the controller 26. When the temperature of the rolling bearing changes due to the rotation of the shaft portion 7, the preload changes accordingly. Therefore, in order to prevent the bearing preload or the natural frequency from shifting due to the relationship between the temperature and the preload, a correction value is input in advance. As a result, the fluctuation that occurs during use can be minimized.

The pair of rear side rolling bearings 11 and 13 are combined as a rear face by an inner ring spacer 18 and an outer ring spacer 12 disposed between them to provide a proper preload, and the inner rings of these bearings 11 and 13 have a shaft portion. 7 is fitted with a tightening allowance and is fixed by the stepped portion on the rear side of the shaft 7 and the nut 15, and the outer ring is installed in the housing 10 with an appropriate clearance and moves in the axial direction with respect to the housing 10. It is possible.

In this embodiment, in the state before the operation in which the hydraulic pressure is not applied to the hydraulic pocket 21, the pistons 2 are attached to the outer rings 3B and 5B of the front and rear rolling bearings 3 and 5 by the outer ring pressing member 1.
The press allowance is set so as to be pressed with an axial force of about 50 kgf via the. When a hydraulic pressure is applied to the hydraulic pocket 21, an axial force of up to about 3000 kgf proportional to this hydraulic pressure is applied to the outer rings 3B, 5B via the outer ring pressing piston 2 in a direction to reduce the bearing preload amount, and as a result, the outer ring spacer 4 Deforms up to 12 μm in the axial direction, and the amount of preload applied to the rolling bearings 3 and 5 changes (decreases).
Along with this, the bearing rigidity and the natural frequency of the shaft portion 7 also change. Specifically, the displacement sensor 24 detects the displacement of the shaft portion 7 at the number of revolutions set in accordance with the processing conditions, and when this value exceeds a preset value, the controller 26 controls the hydraulic control device 23. By controlling, the hydraulic pressure applied to the outer ring pressing piston 2 is adjusted to avoid the peak value. In this way, resonance is avoided by shifting the natural frequency of the shaft portion 7 from the frequency generated by the rotation of the bearings 3, 5.
Excessive vibration is prevented.

In the above-mentioned embodiment, the displacement of the shaft portion with respect to the housing is detected as a determination element of the rotation accuracy, but the rotation accuracy may be determined by the vibration of the device generated during the rotation operation. For example, a vibration measuring element is directly attached to the housing 10 at an appropriate position, and the data of the detected vibration value and the number of rotations used are loaded into the controller 26,
The vibration value at the time of non-resonance with the natural frequency is constantly compared with the detected vibration value, and when the occurrence of resonance vibration is detected, a signal is output from the controller 26 to the hydraulic control device 23 so that the vibration value becomes smaller than the set level. The hydraulic pressure supplied to the outer ring pressing piston 2 is adjusted. When the number of revolutions used is changed, the preload amount is once returned to the original reference value and the occurrence of resonance is rechecked.

When used as a work spindle of an actual precision lathe, an appropriate preload is applied by hydraulic pressure before starting machining. A large disturbance often enters the sensor during processing, but control feedback should not be applied at this time. When a value (vibration, displacement, etc.) above a certain set value is detected by the sensor (abnormal machining), the bearing preload is further changed (secondary correction) before the next work machining. If the value detected by the sensor is excessive and the workpiece becomes defective, an alarm is issued and the machine is stopped.

[0015]

As described above, according to the present invention, the radial or axial displacement or vibration of the shaft portion related to the rotation accuracy is detected by the sensor, and the external hydraulic pressure supply source is detected according to the detected value. Since the preload of the rolling bearing that supports the shaft is changed by adding the hydraulic pressure from the shaft to change the natural frequency of the shaft by changing the bearing rigidity, the vibration generated from the rolling bearing and the natural vibration of the shaft can be changed. It is possible to avoid resonance with the number of revolutions, and it is possible to perform precise machining at any number of revolutions without being restricted by the number of revolutions used.

[Brief description of drawings]

FIG. 1 is a partial vertical sectional view of a preload variable spindle device for a precision lathe according to an embodiment of the present invention.

[Explanation of symbols]

 1 Outer ring pressing member 2 Outer ring pressing piston 3,5 Front side rolling bearing 4,12 Outer ring spacer 6,18 Inner ring spacer 7 Shaft part 10 Housing 11,13 Rear side rolling bearing 21 Hydraulic pocket 23 Hydraulic control device 24 Displacement sensor 25 Detection Circuit 26 Controller 27 Temperature Sensor 28 Temperature Detection Circuit

Claims (1)

[Claims] 1. A hydraulic piston mechanism for changing the preload of the rolling bearing by applying an axial force to an outer ring of the rolling bearing mounted between the shaft portion and the housing, and displacement or vibration of the shaft portion provided on the housing side. And a controller that adjusts the hydraulic pressure of the hydraulic piston mechanism based on the detection value of the sensor, and the controller causes a vibration frequency dependent on the rotation speed of the shaft portion and a shaft portion that resonates. A preload variable spindle device, characterized in that the hydraulic pressure of the hydraulic piston mechanism is adjusted so as to change the natural frequency of the.