JPH1177487A - Displacement correcting device for main spindle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely correct an axial direction displacement of a main spindle caused by centrifugal force, in the main spindle of a constant pressure and pre-load construction. SOLUTION: A main spindle 5 of a machining center is provided with a constant pressure and preload construction for applying always constant preload on a bearing using a spring member such as a coil spring and a coned disc spring. A correlation between main spindle rotating speed and an axial direction displacement rate is memorized in a memory unit 11 with a system of a relational expression or a correlation table. Using the relational expression and the correlation table, the axial direction displacement rate corresponding to command rotating speed is calculated in a calculating unit 12. The main shaft 5 is moved and controlled in a direction reverse to a displacement direction with a correction rate corresponding to the calculating value by a numerical control unit 13.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention corrects axial displacement of a main shaft caused by a change in the contact position of a bearing rolling element due to centrifugal force in a main shaft of a constant pressure preload structure in which a constant preload is always applied to a bearing by a spring member. It concerns the device.

[0002]

2. Description of the Related Art Conventionally, in a machine tool or the like, a technique of applying a preload to a bearing to increase rigidity and rotational accuracy of a main shaft has been widely adopted. In particular, in a high-speed machining center in which angular bearings are frequently used, a main shaft of a fixed position preload structure that applies a preload by hydraulic pressure at a fixed position and a main shaft of a constant pressure preload structure that always applies a constant preload by a spring member are known. .

[0003] The main shaft of the fixed position preload structure is provided with a means for switching the preload amount in accordance with the number of rotations, because the preload becomes excessive due to heat generation of the bearing during high-speed rotation and there is a danger of seizure. Also, in order to reduce the machining accuracy by displacing the spindle in the axial direction at the time of switching the preload, a method of recognizing the switching of the preload and correcting the displacement of the spindle by axial movement has been adopted (Japanese Patent Laid-Open No. 5-237704). Gazette, JP-A-6-262
485).

On the other hand, in a main shaft of a constant pressure preload structure, a constant preload is always applied to a bearing by a spring member such as a coil spring or a disc spring, so that even if the main shaft rotation speed changes, the preload amount hardly changes. Accordingly, there is no need to provide a preload switching means, and there is an advantage that the main shaft for high-speed rotation can be configured more simply.

[0005]

However, when the main shaft of the constant-pressure preload structure rotates at high speed, the contact position of the rolling element of the bearing changes due to centrifugal force. In this case, since the main shaft is urged in the axial direction by a spring member via a bearing, the main shaft is displaced in the axial direction with a change in the position of the rolling element, and the position of the tool edge changes, adversely affecting machining accuracy. Had the problem that

An object of the present invention is to provide an apparatus capable of accurately correcting axial displacement of a main shaft due to centrifugal force in a main shaft of a constant-pressure preload structure.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, a displacement compensating device according to the present invention comprises a contact member of a bearing having a constant pressure preload structure in which a constant preload is always applied to a bearing by a spring member. A device for correcting axial displacement of a main shaft associated with a position change, a storage unit for storing a correlation between a main shaft rotational speed and an axial displacement amount, and a displacement amount corresponding to a commanded rotational speed based on stored data. It comprises a calculation unit for calculating and a numerical control unit for controlling the movement of the main shaft in the direction opposite to the displacement direction with a correction amount corresponding to the calculated value.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a machining center will be described below with reference to the drawings. As shown in FIGS. 1 and 2, the machining center includes a bed 1, a column 2, a table 3, a spindle head 4, and a spindle 5. The main shaft 5 is rotatably supported by upper and lower angular bearings 7 and 8 inside the housing 6.
A constant preload is always applied to the upper angular bearing 7 by a coil spring 9.

The control system of the machining center is provided with a device for correcting axial displacement of the main shaft 5 due to centrifugal force. The displacement correction device includes a storage unit 11 that stores a correlation between the rotation speed of the main shaft 5 and an axial displacement amount, an operation unit 12 that calculates a displacement amount corresponding to a commanded rotation speed based on the storage data, The numerical control unit 13 controls the movement of the main shaft 5 in the direction opposite to the displacement direction with a correction amount corresponding to the calculated value. Although the machining center shown in FIG. 1 is of a vertical type, the same correction system can be adopted in the case of a horizontal type.

Here, the axial displacement is obtained in advance by actually rotating the main shaft 5 and measuring the end face position, or by analyzing and calculating the displacement of the rolling element of the angular bearing 7 due to centrifugal force. be able to. FIG. 4 illustrates the correlation between the spindle speed N and the axial displacement δ obtained by the analytical calculation. From this, it can be seen that the rotational speed N and the displacement amount δ match well by quadratic approximation. Therefore, the relational expression illustrated in the figure may be stored in the storage unit 11, or a correlation table between the rotation speed N and the displacement amount δ may be stored in the storage unit 11.

Next, a correction method by the above-described device will be described with reference to a flowchart of FIG. First, when a change in the rotation speed of the main shaft 5 is confirmed, the axial displacement amount of the main shaft 5 corresponding to the commanded rotation speed at this time is calculated using a relational expression or a correlation table stored in the storage unit 11. Here, when the displacement data corresponding to the command rotation speed does not exist in the correlation table, the axial displacement amount is estimated by interpolation from the neighboring values.

The displacement amount obtained by the calculation is retained during the operation period based on the rotation speed, a correction amount corresponding to the displacement amount is output from the numerical controller 13, and the main shaft 5 is controlled to move in the direction opposite to the displacement direction. You. This control is continued until the rotation speed changes, and the axial displacement of the main shaft 5 due to the centrifugal force is corrected. At this time, a correlation table between the spindle rotation speed and the correction amount is displayed on the NC operation screen as shown in FIG. Therefore, according to this machining center, the cutting edge position of the tool can be kept constant during high-speed rotation, and the machining accuracy can be improved.

The present invention is not limited to the above-described embodiment. For example, the present invention is applied to a spindle having a structure in which a preload is applied using a disc spring, or to various machine tools other than a machining center. However, it is also possible to appropriately change the shape and configuration of each part without departing from the spirit of the present invention.

[0014]

As described in detail above, according to the present invention,
In the main shaft of the constant-pressure preload structure, an excellent effect that the axial displacement of the main shaft due to centrifugal force can be accurately corrected is exhibited.

[Brief description of the drawings]

FIG. 1 is a system configuration diagram of a machining center according to an embodiment of the present invention.

FIG. 2 is a sectional view showing a main shaft of a constant-pressure preload structure.

FIG. 3 is a flowchart illustrating a method of correcting axial displacement of a main shaft due to centrifugal force.

FIG. 4 is a characteristic diagram showing a correlation between a spindle rotation speed and an axial displacement amount.

FIG. 5 is a correlation table between a spindle speed and a correction amount displayed on an NC operation screen.

[Explanation of symbols]

5, main shaft, 7, 8, angular contact bearing, 9, coil spring, 11 storage unit, 12 arithmetic unit, 13
-Numerical control unit.

Claims (1)

[Claims] An apparatus for correcting axial displacement of a main shaft caused by a change in a contact position of a bearing rolling element in a main shaft having a constant pressure preload structure in which a constant preload is always applied to a bearing by a spring member. A storage unit that stores the correlation with the axial displacement amount, a calculation unit that calculates the displacement amount corresponding to the commanded rotation speed based on the stored data, and a main shaft that is opposite to the displacement direction with a correction amount corresponding to the calculated value. A displacement compensating device comprising a numerical control unit for controlling movement of the displacement.