JPH039116A - Automatic preload adjustment device for rolling bearings - Google Patents

Abstract

PURPOSE:To perform optimum adjustments of the amount of preload by arranging electrostriction elements between a housing and a rolling bearing, and detecting the amount of preload to control voltages applied to the electrostriction elements. CONSTITUTION:A spacer sleeve 27 is inserted into a housing 11 against the end face of the front side of an outer ring 17a of a rear angular ball bearing 17 so that it can move in the axial direction. Plural cylindrical piezoelectric elements 29 are mounted between the other end face of the spacer sleeve 27 and the housing 11 in laminated state so as to generate an axial thrust. Lead wires 31 of the piezoelectric elements 29 are drawn out to the outside and connected to a DC amplifier 35. Further, a strain gage 37 is attached to the sleeve 27 in the direction where axial forces can be detected. Preload is given to the bearing 17 by extension of the piezoelectric element 29, and the strain gage 37 detects the amount of the preload to send a signal to an NC device 43. The NC device adjusts voltage applied to the piezoelectric elements 29 so that the preload reaches a specified amount of preload.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an automatic preload adjustment device for a rolling bearing used in the main spindle of a machine tool, for example, the internal grinding shaft of a grinding machine, the main spindle of a machining center, or a lathe. be.

[Prior art] Bearings used for the main spindle of machine tools generally receive radial loads and thrust loads, so angular ball bearings or tapered roller bearings are used, and a preload is applied to them to improve the rotational accuracy and rigidity of the main spindle. Improving. However, it is difficult to set the amount of preload, and if the amount of preload is too large, the bearing will generate significant heat during high-speed rotation, and as the rotational speed of the main shaft increases, a lot of frictional heat will be generated in the bearing, and this frictional heat will affect the main shaft and other components. , the bearing expands. This causes strong pressure to be applied to the spindle bearing, which in turn generates even more frictional heat, creating a vicious cycle, causing complex thermal distortions in various parts of the machine tool, and reducing overall accuracy. . In addition, vibration may occur in the main shaft, or in the worst case, the bearing may seize.

Until now, preload adjustment devices using hydraulic pressure or spring pressure have been used to solve this problem.

[Problems to be Solved by the Invention] However, these methods have a difficulty in controlling the amount of preload. Therefore, as shown in JP-A-61-127922, a method has been proposed in which an electrostrictive element is used as the preload means and the preload is adjusted by detecting temperature changes in the bearing. However, it is not only difficult to determine whether the temperature rise in the bearing is due to preload or other causes, but also difficult to control the bearing to provide an appropriate amount of preload depending on the operating conditions. Further, since there are variations in the relationship between the electric power applied to the electrostrictive element and the amount of expansion and contraction of the electrostrictive element, there have been problems such as difficulty in applying an accurate preload.

The present invention has been made to solve the above-mentioned problems, and an object of the present invention is to provide an automatic preload adjustment device for a rolling bearing that can apply an appropriate amount of preload to the bearing.

[Means for Solving the Problems] In order to achieve this object, the automatic preload adjustment device for a rolling bearing of the present invention includes an electrostrictive element disposed between the housing and the rolling bearing, and an electrostrictive element provided by the electrostrictive element. The electrostrictive element includes a preload amount detection means for detecting the preload amount detected by the preload amount detection means, and a control means for controlling the voltage or current applied to the electrostrictive element based on the preload amount detected by the preload amount detection means.

[Function] In the automatic preload adjustment device for a rolling bearing of the present invention having the above configuration, when a predetermined voltage or current is applied to the electrostrictive element, a predetermined amount of preload is applied to the rolling bearing, and the amount of preload is is detected by the preload amount detection means. Based on the preload amount detected by the preload amount detection means, the voltage or current applied to the electrostrictive element is controlled by the control means, and the preload amount is optimally adjusted.

[Example] Hereinafter, an example embodying the present invention will be described with reference to the drawings.

In FIG. 1, outer rings 3a of front angular contact ball bearings 3 and 5 that support the main shaft 1 of a machine tool.

5a is pressed against the front cover 9 and fixed to the housing 11 in the axial direction with a spacer sleeve 7 in between. Inner rings 3b and 5b are axially fixed to main shaft 1 with a lock nut 15 with a spacer sleeve 13 in between.

Also, a rear angular contact ball bearing 17 supporting the main shaft 1.
The outer rings 17a and 19a of the 19 are inserted into the housing 11 so as to be movable in the axial direction with a spacer sleeve 21 in between, and the inner rings 17b and 19b are connected to the main shaft 1 with a lock nut 25 with a spacer sleeve 23 in between. Fixed in the axial direction. Furthermore, a spacer sleeve 27 is attached movably in the axial direction within the housing 11 in contact with the front end surface of the outer ring 17a of the rear angular contact ball bearing 17, and between the other end surface of the spacer sleeve 27 and the housing 11. A plurality of cylindrical piezo elements 29 are stacked and attached in the axial direction, and are configured to generate thrust in the axial direction. Piezo element 29
The lead wires 31 are connected in parallel and taken out from a wiring hole 33 provided in the housing 11, and connected to a driving DC amplifier 35. Further, a strain gauge 37 is attached to the spacer sleeve 27 in a direction that can detect the force applied in the axial direction as shown in FIG. 2, and its lead wire 39 is taken out from the wiring hole 33 and connected to the amplifier 41. has been done. The amplifier 35.41 is N
It is connected to the C device 43, and each command or input is made.

The present embodiment is constructed as described above, and its operation will be explained next.

The axial force generated by the expansion of the piezo element 29 is
The pressure is transmitted to the outer rings 17a and f9g of the rear angular contact ball bearings 17.19 via the spacer sleeve 27, and preload is applied to the bearings. The amount of preload is detected by the strain gauge 37 attached to the spacer sleeve 27, and its signal is sent to the amplifier 41, and the signal from the amplifier 41 is sent to the NC device 4.
Sent to 3. NC if the specified preload amount has not been reached.
A signal to increase the applied voltage is sent from the device 43 to the DC amplifier 35, and a corresponding applied voltage is applied from the DC amplifier 35 to the piezo element 29, causing the piezo element 29 to expand and increase the amount of preload. Conversely, if the preload amount is large, the NC device 4
3 sends a signal to lower the applied voltage to the DC amplifier 35, and the applied voltage applied from the DC amplifier 35 to the piezo element 29 is lowered.

Furthermore, the temperature sensor 45 is mounted on the rear angular ball bearing 17.
The temperature signal of the bearing is N
It is sent to C device 43. Therefore, it is also possible to control the amount of preload according to the machining situation while monitoring the temperature rise of the bearing, and to reduce the amount of preload when the bearing temperature rises.

In this embodiment, since the electrostrictive element 29 has a cylindrical shape, it is possible to uniformly apply preload to the bearing.

Furthermore, since the strain gauge for detecting the amount of preload is attached to the spacer sleeve, the amount of preload can be detected without affecting the accuracy and rigidity of the bearing.

[Effects of the Invention] As is clear from the detailed description above, according to the present invention, a predetermined amount of preload is applied to the bearing using the expansion and contraction action of the electrostrictive element, and the amount of preload is detected and the electrostrictive element Since the applied voltage is feedback-controlled, the predetermined amount of preload can be accurately controlled.

[Brief explanation of the drawing]

Figures 1 and 2 show an embodiment embodying the present invention. Figure 1 is a sectional view of the main shaft bearing, and Figure 2 is an enlarged view of how the strain gauge is attached to the spacer sleeve. FIG. In the figure, 3 and 5 are front angular contact ball bearings, 17°19 is a rear angular contact ball bearing, 27 is a spacer sleeve, 29
is a piezo element, and 37 is a strain gauge.

Claims (1)

[Claims] 1. An automatic preload adjustment device for a rolling bearing that applies preload to a rolling bearing that supports a rotating shaft (1) rotatable about one axis and automatically adjusts the amount of preload, comprising: a housing; (11) and an electrostrictive element (29) disposed between the rolling bearing and displaced in accordance with applied voltage or current to provide a predetermined amount of preload; A preload amount detection means (37) for detecting the given preload amount, and a voltage or current applied to the electrostrictive element (29) based on the preload amount detected by the preload amount detection means (37). An automatic preload adjustment device for a rolling bearing, characterized in that it is equipped with a control means (43) for controlling.