JP2816596B2 - Bearing preload device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a preloading device for a bearing mounted on a main shaft of a machine tool such as a milling machine or a grinding machine, and more particularly, to a preloading device using a piezoelectric element. It concerns the device.

(Prior art) In recent machine tools, the productivity and finishing accuracy have been greatly improved by increasing the speed of the spindle, as the performance of components including drive motors and cutting tools has increased. High precision is also required for setting the preload of the bearing that supports the main shaft.

However, with the conventional preload setting method, there are problems such as seizure due to heat generation of the bearing due to high speed rotation of the spindle and insufficient rigidity in the low speed range for bearings for high speed rotation, and complicated structure due to installation of special preload device. There were new problems, such as the emergence of

In this regard, a preloading device using a piezoelectric element as a member for applying a preload to a bearing has been developed. In the preloading device, a plurality of piezoelectric elements are arranged in a circumferential direction and incorporated between bearings. . Then, by applying a voltage corresponding to the detected temperature or the detected rotation speed of the bearing to these piezoelectric elements, the piezoelectric element is displaced in the axial direction, and a required preload is applied to the bearing. Thus, the preload of the bearing is maintained at an appropriate value regardless of whether the rotation speed is low or high.

(Problems to be Solved by the Invention) However, such a preloading device using a piezoelectric element is not perfect due to the following problems, and further improvement has been demanded.

That is, the plurality of piezoelectric elements arranged in the circumferential direction
Due to the manufacturing conditions and the like, these dimensional differences and displacement amounts cannot be avoided, which makes it difficult to apply a uniform displacement (preload) to the bearing.

In addition, since the bearings on both sides are fixed in the axial direction, the thermal expansion of the main shaft and the housing to which these are fixed directly affects the preload setting. For this reason, the voltage control of the piezoelectric element requires complicated control in consideration of these external factors, and there is room for further improvement in order to realize more accurate control.

The present invention has been made in view of such a conventional problem, and provides a bearing preload device capable of controlling uniform and highly accurate preload control by adjusting a dimensional difference and a displacement amount difference of each piezoelectric element. The purpose is to do.

(Means for Solving the Problems) To achieve the above object, a bearing preloading device of the present invention includes a piezoelectric actuator provided adjacent to an axial side of the bearing, and the piezoelectric actuator has On one axial side, a pair of first protrusions are provided to abut against the axial side of the outer race of the bearing, and on the other axial side, the first protrusion and the circumferentially alternate And a pair of second protrusions arranged in the piezoelectric actuator, whereby the piezoelectric actuator is swingably disposed about the protrusions as a fulcrum.

A specific structure of the piezoelectric actuator includes an annular main body and a pair of piezoelectric elements provided on the annular main body. The piezoelectric element is provided on one side of the annular main body in the axial direction. Disposed on the diameter line, the tip is the first protrusion, a second protrusion is provided on the other axial side of the annular body, and the second protrusion is provided with the piezoelectric element. Are arranged on one diameter line orthogonal to the one diameter line. Also, the inner ring of the bearing is fixed to the shaft portion, and the outer ring is movable in the axial direction with respect to the housing portion, and the first protrusion of the piezoelectric element abuts on the axial side portion of the outer ring. Have been. On the other hand, a cylinder having a strain gauge is supported on a fixed portion of the housing, and the second protrusion is in contact with an axial side of the cylinder.

(Operation) Since the piezoelectric actuator performs the seesaw motion with the first and second protrusions as fulcrums, the dimensional difference and the displacement amount difference between the pair of piezoelectric elements are effectively balanced.

Further, since the outer ring pressed by the first protrusion of the piezoelectric actuator is movable in the axial direction with respect to the housing portion, the axial displacement of the piezoelectric element is reliably and smoothly transmitted to the outer ring. , High-precision preload control is performed.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 shows a main shaft portion of a machine tool provided with a bearing preloading device according to the present invention. The main shaft portion is specifically a milling machine, and a main shaft 1 is a pair of front and rear double-row angular ball bearings. It is rotatably supported in the support hole 5 of the main shaft case 4 via 2 and 3. The tip 1a of the main shaft 1 is a tapered cutting tool mounting hole, and a cutting tool such as a face mill (not shown) is detachably mounted in the cutting tool mounting hole 1a. A rear end portion 1b of the main shaft 1 projects rearward of the main shaft case 4, and a belt wheel 6 is fixedly attached thereto. Although not shown, the belt wheel 6
Are linked to a drive motor, which is a drive source, via a conduction belt. A preloading device 7 for applying a preload to the rear bearing 3 is provided between the pair of bearings 2 and 3.

The front bearing 2 has an inner ring 2 a, 2 a fixed to the outer peripheral surface of the spindle 1, and an outer ring 2 b, 2 b
Is fixed to the front end 5a of the
c, 2c ... are loaded so as to be able to roll. 8 is the outer ring 2b, 2
It is a fixing member for fixing b.

On the other hand, in the rear bearing 3, the inner rings 3a, 3a are fixed to the outer peripheral surface of the main shaft 1, and the outer rings 3b, 3b are fixed to the bearing case 9, and a number of steel balls 3c, 3c, 3c… is loaded so that it can roll. The bearing case 9 has a rear end 5b of the support hole 5 of the spindle case 4 as described later.
Are accommodated so as to be movable in the axial direction. Front and rear bearings 2,3
Spacings 10, 11 are interposed between the inner rings 2a, 3a of the
The preload device 7 is interposed between the outer peripheral surface of the main shaft case 4 and an intermediate portion 5c of the support hole 5 of the spindle case 4. Reference numeral 12 denotes a fixing member for fixing the inner rings 3a, 3a.

The bearing case 9 is for holding the outer races 3b, 3b of the bearing 3 movably in the axial direction with respect to the main shaft case 4.
At the front and rear ends of the outer peripheral surface 9a, annular grooves 13, 13 are provided in parallel in the circumferential direction over the entire circumference, and a number of steel balls 14, 14,. ing.
Are rollable between the annular groove 13 and the rear end 5b of the support hole 5 of the spindle case 4, whereby the bearing case 9, that is, the outer ring 3b, 3b
Is supported movably in the axial direction with respect to the spindle case 4. That is, the outer races 3b, 3b are provided with a contact end face 4c of the spindle case 4 and a fixing member attached to the spindle case 4.
It can be moved in the axial direction within the range of the interval set between 30 and.

The preloading device 7 mainly includes a piezoelectric actuator 15 and a control device (not shown) for controlling the operation thereof. The piezoelectric actuator 15 is adjacent to the front side (axial side) of the rear bearing 3. In addition, it is provided integrally with the cylinder 16 having the strain gauge 31.

As shown in FIGS. 2 and 3, the piezoelectric actuator 15 includes an annular main body 17 and a pair of piezoelectric elements 18 provided on the main body.

The annular body 17 is provided between the intermediate portion 5 c of the support hole 5 and the spacer 10.
And a cylindrical shape having an inner and outer diameter dimension that can be accommodated between them, and an engaging step portion 17b is provided on the entire outer periphery of the front side surface 17a. Further, a pair of second protrusions 17d, 17d are provided on one diameter line of the front side surface 17a so as to project from the front surface 17a. It is adapted to cooperate with children 18a, 18a.

The piezoelectric element 18 is connected to the control device via a lead wire 19, and is applied by an applied voltage corresponding to a preset preload value, or by the rotation speed and axial displacement of the main shaft 1 or the bearings 2, 3 It is configured to be displaced in the axial direction by a predetermined amount by an applied voltage corresponding to various operating conditions such as a change in temperature of the motor. Further, the pair of piezoelectric elements 18, 18
As shown in FIG. 2, the rear surface 17c of the annular main body 17 is disposed on a diameter line orthogonal to a diameter line connecting the second protrusions 17d. The tip 18a of the piezoelectric element 18 has a tapered wedge shape.
It is considered to be the first projectile that cooperates with d and 17d.

That is, these first projections 18a, 18a abut on the front side surface 21a of the spacer 21 integrated with the bearing case 9;
The second protrusions 17d, 17d are in contact with the rear side surface 16a of the tubular body 16, whereby the piezoelectric actuator 15 swings around these protrusions. Due to the so-called seesaw movement of the piezoelectric actuator 15, the dimensional difference and the displacement amount difference between the piezoelectric elements 18, 18 are kept in balance.

The annular main body 17 also includes a displacement sensor 22 on the rear side surface 17c. The displacement sensor 22 faces the front side surface 21a of the spacer 21 and constantly detects the distance therebetween, and the detection result is sent to the control device, whereby the axial displacement of the spindle 1 is indirectly controlled. Is to be measured.

The strain gauge 31 detects an axial displacement amount of the piezoelectric actuator 15 and feeds it back to the control device.The strain gauge 31 is provided on the outer periphery of the cylinder 16 and is connected to the control device via the lead wire 20. Are linked. The cylindrical body 16 has a cylindrical shape concentric with the piezoelectric actuator 15, and an engaging projection 16 b is provided on an outer peripheral portion of a rear side surface 16 a over the entire circumference, and the engaging projection 16 b is It is designed to engage with 15 engagement steps 17b. On the other hand, the front side surface 16c of the cylindrical body 16 is in contact with a fixed portion of the main shaft case 4, that is, a boundary step 5d between the front end portion 5a of the support hole 5 and the intermediate portion 5c.

In the preloading device 7 configured as described above, a voltage corresponding to a preset preload value is applied to the piezoelectric elements 18 of the piezoelectric actuator 15 in the initial stage. Then, these piezoelectric elements expand in the axial direction,
Appropriate initial preload is applied to the outer rings 3b, 3b of the bearing 3 integrated with the bearing case 9. On the other hand, during operation, the spindle 1
Correction of the preload of the bearing 3 is appropriately performed by an applied voltage according to various conditions such as the rotation speed, axial displacement, or change in the temperature of the bearings 2 and 3.

In this case, the outer races 3b of the bearing 3 can move in the axial direction with respect to the main shaft case 4 together with the bearing case 9, so that the axial displacement of the piezoelectric elements 18 can be surely and smoothly. The preload is transmitted to the outer races 3b, 3b, and highly accurate preload setting is performed.

In addition, the piezoelectric elements 18 may have a characteristic value difference such as a dimensional difference and an expansion coefficient due to the manufacturing accuracy thereof.These differences are caused by the protrusions 18a and 17d. Are corrected as appropriate by the seesaw motion of the piezoelectric actuator 15 with the fulcrum as a fulcrum, so that adverse effects on the preload setting are effectively prevented.

(Effects of the Invention) As described in detail above, according to the present invention, various excellent effects listed below can be obtained.

(1) The piezoelectric actuator provided adjacent to the bearing in the axial direction has, on one axial side thereof, a pair of first protrusions which abut on the axial side of the outer race of the bearing. The other axial side portion is provided with a first protrusion and a pair of second protrusions alternately arranged in the circumferential direction, whereby the piezoelectric actuator swings around the protrusion as a fulcrum. Since it is provided as possible, uniform and high-precision preload control becomes possible.

In other words, the piezoelectric actuator performs a seesaw motion with the first and second protrusions as fulcrums, so that even if there is a dimensional difference or a displacement amount difference between the pair of piezoelectric elements, these differences are reduced. Correction is appropriately made, and the balance between the two is kept effective. As a result, uniform axial displacement is given to the bearing outer ring, and uniform and high-precision preload control can be performed.

(2) Further, since the outer ring of the bearing pressed by the first protrusion of the piezoelectric actuator is movable in the axial direction with respect to the housing portion, the axial displacement of the piezoelectric element can be surely and smoothly performed. And the synergistic effect with the seesaw motion realizes extremely high-precision preload control.

(3) In addition, by adopting such a configuration, the bearing is not directly affected by the thermal expansion of the housing or the main shaft to which the bearing is attached, and these external factors are taken into account in controlling the piezoelectric element. No complicated control method is required.

[Brief description of the drawings]

FIG. 1 is a side view partially showing a main shaft portion of a machine tool provided with a bearing preload device according to an embodiment of the present invention, and FIG.
FIG. 3 is a front view showing a piezoelectric actuator of the preloading device, and FIG. 3 is a cross-sectional view of the piezoelectric actuator taken along line III-III in FIG. 1 ... Main shaft (shaft), 3 ... Double row angular contact ball bearing, 3a
…… Inner ring, 3b …… Outer ring, 3c …… Steel ball (rolling element), 4…
Main shaft case (housing part), 5: Support hole, 7: Preload device, 9: Bearing case, 15: Piezoelectric actuator, 15d: Boundary step (fixed part of housing part), 16
…… Strain gauge, 16a …… Back side (axial side), 17 ……
Annular body, 17a Front side (axial side), 17c Rear side (axial side), 17d Second protrusion, 18 Piezoelectric element, 18a Front end (first Projection), 21 ... Spacing (axial side of outer ring)

Claims (4)

(57) [Claims] The present invention further comprises a piezoelectric actuator provided adjacent to an axial side of a bearing, wherein the piezoelectric actuator has a pair of abutting one axial side and an axial side of an outer ring of the bearing. And a pair of second protrusions alternately arranged in the circumferential direction on the other axial side portion, whereby the piezoelectric actuator has A preloading device for a bearing, wherein the preloading device is provided so as to be swingable with the protrusion as a fulcrum. 2. The piezoelectric actuator according to claim 1, further comprising: an annular body;
A pair of piezoelectric elements provided on the annular main body, wherein the piezoelectric element is disposed on one diameter line of the annular main body at one axial side of the annular main body, and a tip end of the piezoelectric element is the first piezoelectric element. A second protrusion is provided on the other axial side of the annular main body, and the second protrusion is arranged on a diameter line orthogonal to the diameter line on which the piezoelectric element is arranged. The bearing preloading device according to claim 1. 3. An inner ring of the bearing is fixed to a shaft portion, and an outer ring is movable in an axial direction with respect to a housing portion. A first protrusion of the piezoelectric element is provided on an axial side portion of the outer ring. 3. The preloading device for a bearing according to claim 2, wherein 4. A cylinder provided with a strain gauge is supported on a fixed portion of the housing, and the second protrusion is in contact with an axial side of the cylinder. Bearing preload device.