JPH0835520A - Preload adjusting device for main shaft bearing - Google Patents

Abstract

PURPOSE:To provide a correct actual preload value without affected by thermal displacement in an axial direction due to the temperature rise of a bearing by providing a preload detection device for detecting an actual preload value on an axis same as that of the preload giving device for pressing the bearing through the side surface of an outer wheel body to give a preload. CONSTITUTION:In a preload giving device 5 such as a piezo actuator, an outer wheel body 4a is pushed from a side surface against the energizing force of an energizing means 9 to give a preload. An actual preload value, given by the preload giving device 5, is determined by arithmetically processing a detected signal from a preload detection device 6 such as a pressure sensor provided coaxially with the preload giving device 5. The optimum preload value in accordance with a main shaft rotation frequency is read out in a comparison circuit from a memory in a control device to be compared with an actual preload value. When both the sides do not conform, the drive of the preload giving device 5 is controlled by a compared result to increasingly/decreasingly adjust a preload value given to the outer wheel body 4a to make the actual preload value optimum in accordance with the rotation frequency of a main shaft 2.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a spindle bearing pre-adjustment capable of adjusting the preload applied to the spindle bearing to an optimum value corresponding to the spindle rotation speed in accordance with a change in the spindle rotation speed of a machine tool. The present invention relates to a load adjusting device.

[0002]

Rolling bearings (hereinafter referred to as bearings) for rotatably supporting a main shaft of a machine tool are used to increase the rigidity of the main shaft and to achieve accurate positioning in the axial direction and radial direction of the main shaft, and to improve rotational accuracy. It is common practice to preload the bearings in order to increase And
In order to prevent seizure and temperature rise of the bearing during high-speed rotation, a preload adjusting device that reduces the preload with an increase in main shaft rotation speed is disclosed in, for example, Japanese Utility Model Laid-Open No. 64-31.
It is disclosed in Japanese Patent Laid-Open No. 19 and Japanese Patent Laid-Open No. 3-9116. The preload adjusting devices disclosed in these publications press the outer ring body of the bearing from the side surface with an actuator formed of an electrostrictive element having a property of extending in the axial direction when a voltage is applied, and the preload adjusting device is applied by the actuator. In order to detect the preload value, the strain gauge is attached to the outer peripheral surface of the outer ring body or the surface of the spacer sleeve fitted on the outer ring body so as to detect the axial displacement, and the detection signal of this strain gauge is calculated. The drive of the actuator is controlled based on the actual preload value (actual preload value) obtained by processing so that the preload value can be corrected to the optimum preload value according to the spindle rotation speed.

[0003]

However, in the above-mentioned conventional preload adjusting device, since the preload value is obtained based on the axial displacement of the outer ring body and the spacer sleeve, the main shaft rotation speed increases. When the temperature of the bearing rises, the thermal displacement in the axial direction that occurs in the outer ring body and the spacer sleeve is also detected, which makes it difficult to obtain an accurate actual preload value. Further, since the strain gauge is attached to the outer peripheral surface of the outer ring body or the spacer sleeve, the strain gauge may be peeled off or broken, which makes it unsuitable for long-term use and has poor reliability.
Further, there is also a problem that a special technique is required at the time of assembling work by replacing the bearing. The present invention has been made in view of the above problems, and an object thereof is to obtain an accurate actual preload value that is unlikely to be affected by thermal strain of an outer ring body or a spacer sleeve, and for a long period of time. Another object of the present invention is to provide a highly reliable preload adjusting device for a main shaft bearing, which can withstand even the use of.

[0004]

In order to solve the above problems, a preload adjusting device for a spindle bearing of a machine tool according to the present invention applies a preload to an outer ring body of a rolling bearing that rotatably supports a spindle of a machine tool. A preload adjusting device for a main shaft bearing capable of increasing and decreasing the preload according to a change in the number of revolutions of the main shaft, in which a biasing force is constantly applied from one side surface of the outer ring body to one direction side. Biasing means for applying, and pressing the other side surface of the outer ring body in the other direction against the biasing means,
A preload applying device for applying a predetermined preload to the rolling bearing through the outer ring body, and an actual preload device provided on the same axis as the preload applying device and applied to the outer ring body by the preload applying device. A preload detection device for detecting a load value, a storage unit for storing an optimum preload value for the spindle speed, an optimum preload value and the preload value read from the storage unit according to the spindle speed. Comparing means for comparing the actual preload value detected by the load detecting means, and drive control means for controlling the drive of the preload applying device based on the actual preload value when the comparison results do not match. And a control device. Further, the preload applying device may be an electrostrictive element that extends in the axial direction by applying a voltage or injecting a charge amount. Further, the preload detection device may be an electrostrictive element that generates charges between electrodes by applying pressure.

[0005]

Since the present invention is constructed as described above, it operates as follows. A preload applying device such as a piezo actuator or a fluid pressure cylinder applies a preload by pushing the outer ring body from the side against the urging force of the urging means. The actual preload value given by the preload applying device is obtained by arithmetically processing a detection signal from a preload detecting device such as a pressure sensor provided coaxially with the preload applying device. The optimum preload value according to the spindle rotational speed is read out from the storage means in the control device to the comparison means, and this comparison means compares it with the actual preload value. When the two do not match, the comparison means outputs the comparison result to the drive control means, and the drive control means controls the drive of the preload applying device to increase / decrease the preload value applied to the outer race. By repeating the above operation, the actual preload value applied to the outer ring body of the bearing can be optimized according to the rotation speed of the main shaft.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a sectional view of a main part of a spindle head provided with a preload adjusting device of the present invention. The spindle 2 having a tool T removably attached to its tip is rotatably supported in the housing 1 by bearings 3 and 4. As the bearings 3 and 4, ball bearings (angular ball bearings or groove balls) in which a rotatable roller or rolling element 4c which is a ball are interposed between an inner ring body 4b and an outer ring body 4a which are fitted onto the main shaft 2 are provided. Bearings) and roller bearings (cylindrical roller bearings, tapered roller bearings, etc.) are common. The outer ring body 4a is urged by a biasing means 9 formed of an elastic body such as a return spring or rubber provided in the housing 1.
Through an engaging member 9a that engages with one side surface of the outer race 4a,
It is always urged from one side toward the tip of the spindle. The biasing means 9 are provided at a plurality of locations (three locations in this embodiment) at equal intervals along one side surface of the outer ring body 4a. Further, the outer ring body 4a of the bearing 4 has an annular retainer 7 having a collar portion 7a that can be engaged with the other side surface of the outer ring body 4a.
Is fitted concentrically with the bearing 4.

On the opposite side of the urging means 9 with the bearing 4 interposed,
A preload applying device 5 is provided which presses the other side surface of the outer ring body 4a via the collar portion 7a of the retainer 7 and applies a predetermined preload to the outer ring body 4a against the urging force of the urging means 9. There is. The preload applying device 5 is fitted to the insertion portion 1a formed in the housing 1 on the tip side of the main shaft with respect to the bearing 4, and along the other side surface of the outer ring body 4 like the biasing means 9. Are evenly spaced at three locations. FIG.
In FIG. 8, reference numeral 8 a is a lead wire for driving the preload applying device 5 or a supply pipe for pressurized fluid.

The above-mentioned preload applying device 5 may be a known piezo actuator composed of an electrostrictive element having a property of being stretched in the axial direction by applying a voltage or injecting a charge amount, or it may be provided outside the housing 1. It may be a fluid pressure cylinder such as an air cylinder or a hydraulic cylinder that is driven by being supplied with the pressure fluid by generating a pressure fluid of a predetermined pressure by a fluid supply device (not shown) such as a provided compressor or hydraulic pump. In the case of using such a piezo actuator, the preload value applied to the outer ring body 4a can be finely adjusted by changing the applied voltage or the injected charge amount, and the preload value can be changed in accordance with the change in the spindle rotational speed. There is an advantage that the value can be adjusted precisely.

One end of the preload applying device 5 comes into contact with the inner wall of the housing 1 in the insertion portion 1a, and the other end comes into contact with the flange portion 7a of the retainer 7 with the preload detecting device 6 such as a pressure sensor interposed therebetween. There is. As the preload detection device 6, a pressure sensor (piezosensor) in which electrodes are arranged between substances having a piezoelectric effect such as ceramics or crystal can be used. When a pressing force is applied to the preload detecting device 6 by the preload applying device 5, electric charges are generated between the electrodes. A voltage is generated by this electric charge, and this voltage is proportional to the pressing force. An actual preload value (actual preload value) applied to the outer ring body 4a can be obtained by sending out a voltage signal or electric charge through the lead wire 8b and performing arithmetic processing. The preload detection device 6 includes a retainer 7 and a preload application device 5.
The preloading device 5 may be provided between the inner wall of the housing 1 and the preloading device 5.

When the preload detecting device 6 is a piezo sensor as described above, the preload applying device 5 and the preload detecting device 6 are integrated with each other by combining with the piezo actuator composed of the same electrostrictive element. Be able to configure. FIG. 2 is a longitudinal sectional view of an explanatory view of a preload applying device integrally incorporating a preload detecting device. A case in which electrostrictive elements 12, 12, ..., which are formed by sandwiching both sides of a substance having a piezo effect between thin film electrodes 11, 11, .. A plurality of layers are stacked along the axis of the body 10. One end of the laminated electrostrictive elements 12, 12, ... Is fixed to the bottom of the case body 10 by a bolt 15 via an insulating plate 13, and the other end is fixed to a support member 17 fitted in the case body 10 by a bolt 16. Is fixed by. A cap 18 is screwed into the opening 10a of the case body 10 that opens toward the outer ring body 4a and is in contact with the support member 17.
That is, the electrostrictive elements 12, 12, ... Are enclosed in the case body 10 with both ends being restrained.

A plurality of laminated electrostrictive elements 12, 12, ...
Of the actuator part A extending in the axial direction by applying a voltage or injecting a charge amount, and the remaining part on the other end side is the actuator part A.
The sensor unit B generates a voltage or an electric charge in proportion to the pressing force applied by the stretching. Actuator part A
The sensor section B is separated from the sensor section B by an insulating plate 13.
Further, lead wires 18a, 18b are connected to the electrodes 11, 11 of the electrostrictive elements 12, 12, ... Constituting the actuator section A and the sensor section B, respectively. When a voltage is applied or an electric charge is injected from one of the lead wires 18a to the electrostrictive elements 12, 12, ... Constituting the actuator section A, the actuator section A extends in the axial direction and the case body 10 moves in the axial direction. While inflating, the other side surface of the outer ring body 4a is pressed via the retainer 7. As a result, a pressing force is applied to the sensor section B, so that a voltage or electric charge is generated between the electrodes 11, 11 of the electrostrictive elements 12, 12 ,. This voltage or charge signal is sent to the amplifier or the like via the other lead wire 18b. Since the magnitude of the generated voltage and the actual preload value are in a proportional relationship, the actual preload value can be obtained by calculating the voltage signal. As described above, according to the preload applying device 5 in which the preload detecting device 6 is integrally incorporated, the preload adjusting device can be easily attached at the time of assembling the machine tool, and the preload adjusting device 5 can be installed even when a failure occurs. Since the load applying device 5 and the preload detecting device 6 may be replaced as a unit, there is a feature that maintenance and inspection are extremely easy.

Next, a control procedure for controlling the operation of the preload applying device based on the actual preload value detected by the preload detecting device 6 will be described with reference to the control block diagram of FIG.
In FIG. 3, (a) is an example of a control block diagram when the preload applying device is the piezo actuator 5a.
(B) is an example of a control block diagram when the preloading device is the fluid pressure cylinder 5b. First, the case of the piezoelectric actuator 5a shown in FIG. 3A will be described. An optimum preload value according to the spindle speed is stored in advance in a memory 21 as a storage means provided in the control device 20. The spindle speed and the optimum preload value are in inverse proportion to each other, and the optimum preload value corresponding to the spindle speed can be easily obtained from the data showing the relationship between the spindle speed and the optimum preload value. When the spindle rotation speed is input to the control device 20, the control device 20 reads the optimum preload value corresponding to the spindle rotation speed from the memory 21 and sends it to the comparison circuit 22. On the other hand, the voltage signal output from the preload detection device 6 is amplified by the amplifier 24, and the actual preload value is obtained by the arithmetic processing unit 25. When the output from the preload detection device 6 is electric charge, the electric charge is converted and amplified by the charge amplifier (charge amplifier), and the actual preload is obtained by the arithmetic processing unit 25.

The comparison circuit 22 compares the actual preload value with the optimum preload value. When the comparison result shows that the actual preload value is less than the optimum preload value, the charge injection circuit 23a injects the charge amount into the piezo actuator 5a, and the piezo actuator 5a presses the outer ring body 4a (see FIG. 1). Increase. On the other hand, when the actual preload value> the optimum preload value, the charge discharging circuit 23b reduces the injected charge amount of the piezo actuator 5a to reduce the pressing force. In the figure, reference numeral 23c is a high voltage power supply for the charge injection circuit 23a and the charge discharge circuit 23b. The result of the increase / decrease adjustment of the pressing force by driving the piezo actuator 5a is the preload detection device 6
And is fed back to the comparison circuit 22 via the arithmetic processing unit 25. Then, the above-described operation is repeated until the actual preload value and the optimum preload value match.

Next, the fluid pressure cylinder 5 shown in FIG. 3 (b).
The case of b will be described. In this case, the portion that drives the fluid pressure cylinder 5b (reference numeral 23 in the figure)
Except for the portions a ', 23c'), there is no difference from the case of the piezo actuator 5a of FIG.
The same parts as those in FIG. 3A are designated by the same reference numerals, and detailed description thereof will be omitted. When the comparison result by the comparison circuit 22 shows that the actual preload value is less than the optimum preload value, the proportional solenoid pressure control valve 23a 'including a proportional solenoid relief valve, a proportional solenoid pressure reducing valve, etc. is connected to the fluid pressure cylinder 5b. The outer ring body 4a is supplied by a fluid pressure cylinder 5b by supplying a pressure fluid such as air or pressure oil.
The pressing force (see FIG. 1) is increased. On the other hand, when the actual preload value> the optimum preload value, the proportional electromagnetic pressure regulating valve 23
a'reduces the pressure of the fluid supplied to the fluid pressure cylinder 5b to reduce the pressing force. In the figure, reference numeral 23
Reference numeral c'denotes a pressure fluid supply device for supplying pressure fluid to the fluid pressure cylinder. The above-described operation is repeated until the actual preload value and the optimum preload value match, as in the case of FIG.

Having described the preferred embodiment of the invention,
The invention is not limited to this example. For example, the preload applying device 5 and the urging means 9 are provided at three positions along the side surface of the outer ring body 4a at equal intervals, but if the preload can be evenly applied to the outer ring body 4a, it is 2 It may be provided in four places or more.

[0016]

Since the present invention is configured as described above, it has the following effects. Since the preload detection device for detecting the actual preload value is installed on the same axis as the preload application device that applies the preload by pressing the bearing through the side surface of the outer ring body, it is possible to increase the spindle speed. Accurate actual preload value can be obtained without being affected by axial thermal displacement due to bearing temperature rise, and optimum preload according to spindle speed is applied to outer ring body for high accuracy. Can be processed. Further, by using the pressure sensor, the life of the preload detecting device is extended, and a highly reliable preload adjusting device for the main shaft bearing can be obtained. Moreover, the preload adjusting device can be easily assembled. Also, by using a piezo actuator or piezo sensor made of electrostrictive elements, it is possible to obtain an integrated preloading device with a built-in preload detection device. The load can be adjusted.

[Brief description of drawings]

FIG. 1 is a cross-sectional side view of a main portion of a main shaft provided with a preload adjusting device according to an embodiment of the present invention.

FIG. 2 is a vertical cross-sectional view of an embodiment of a preload applying device integrally incorporating a preload detecting device including an electrostrictive element.

3A and 3B are control block diagrams for controlling the drive of the preload applying device. FIG. 3A is a case where the preload applying device is a piezo actuator, and FIG. 3B is a case where the preload applying device is a fluid pressure cylinder.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Housing 2 Spindle 3,4 Rolling bearing 4a Outer ring body 5 Preload application device 6 Preload detection device 7 Retainer 9 Energizing means 10 Case body 11 Electrode 12 Electrostrictive element 20 Control device 21 Memory (memory means) 22 Comparison circuit ( Comparing means) 23a Charge injection circuit 23a 'Proportional electromagnetic pressure control valve 23b Charge discharge circuit 23c High-voltage power supply 23c' Pressure fluid supply device 24 Amplifier 25 Operation processing unit

Claims (3)

[Claims] 1. A spindle bearing capable of applying a preload to an outer ring body of a rolling bearing that rotatably supports a spindle of a machine tool, and increasing or decreasing the preload in accordance with a change in the rotational speed of the spindle. Of the outer ring body, and a biasing means for constantly applying a biasing force from one side surface of the outer ring body to one direction side, and the other side surface of the outer ring body to the other direction side against the biasing means. A preload applying device that presses and applies a predetermined preload to the rolling bearing through the outer ring body, is provided on the same axis as the preload applying device, and is applied to the outer ring body by the preload applying device. Preload detection device for detecting the actual preload value, storage means for storing the optimum preload value for the spindle speed, and the optimum preload value read from the storage means according to the spindle speed. And the actual load detected by the preload detection means A control device comprising a comparison means for comparing the load value and a drive control means for controlling the drive of the preload applying device based on the actual preload value when the comparison result does not match. A preload adjusting device for the main spindle bearings. 2. The preload adjusting device for a main shaft bearing according to claim 1, wherein the preload applying device is an electrostrictive element that extends in the axial direction by applying a voltage or injecting a charge amount. apparatus. 3. The preload adjusting device for a main shaft bearing according to claim 1, wherein the preload detecting device is an electrostrictive element that generates an electric charge between electrodes by applying pressure. .