JPS6361527B2 - - Google Patents

Abstract

PURPOSE:To always keep the center of rotation at a specified position by a method wherein displacement sensors are arranged at one of a pair of magnets and another pair of magnets and a mean value of sensed values of the displacement sensors arranged at a pair of magnets is compared with each of the sensed values as a displacement reference value. CONSTITUTION:Displacement sensors 3y and 3y' are arranged at a pair of magnets 2c and 2d, and a displacement sensor 3x is arranged at a magnet 2b, the sensed values deltay1, deltay2 of the displacement sensors 3y, 3y' are applied to an adder 9 and a multiplier 10 to get a mean value deltam, and the mean value deltam and the sensed value deltay1 of the displacement sensor 3y are compared with the sensed value deltax of the displacement sensor 3x by the comparators 11 and 12 and then an exciting current is controlled by the control devices 14y and 14x in such a way as each of the sensed values deltay1, deltax is equal to the reference value deltam. Thereby, it is possible to correct a clearance standard in response to an expansion caused by an increased temperature of the rotating shaft 1, so that it is possible to keep always the center of rotation at a specified position with a rapid response to the operating condition.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a magnetic bearing device that corrects a displacement reference value in response to dimensional changes in a rotating shaft due to temperature or centrifugal force.

Magnetic bearings that support the rotating shaft in a non-contact manner are used in high-speed rotating electric machines used to drive the spindle of high-speed, high-precision numerically controlled machine tools. Precise and responsive control is required.

The magnetic bearing device has a rotating shaft 1 as shown in FIG.
Two pairs of electromagnets 2a, 2b, 2c, 2d are placed on the outer peripheral surface of
A pair of electromagnets 2a and 2b are arranged symmetrically on the X-axis, and another pair of electromagnets 2c and 2d are arranged symmetrically on the Y-axis that is perpendicular to the X-axis. Electromagnets 2b and 2d on each side of the Y axis
Displacement detectors 3x and 3y are provided at positions close to
The excitation of each electromagnet is adjusted so that the detected value of the displacement detector becomes equal to the displacement reference value.

However, the displacement reference value is determined by the reference value of the air gap between the rotating body and each electromagnet, and even if the rotating shaft and electromagnet expand due to heat or centrifugal force, and the amount of air gap changes, the displacement cannot be detected. Since the detected amounts of the magnets 3x and 3y are controlled to match the displacement reference values, the gap between the other electromagnet 2a and 2c of each pair and the rotating shaft 1 becomes smaller, causing the rotating shaft center to become eccentric and impairing the accuracy of the machine tool. lower.

For this reason, one pair of displacement detectors may be provided on each of the X and Y axes so that the detected values of the pair of displacement detectors for each axis are equal, but displacement detectors are expensive and Since the number of interfaces increases, the control device becomes complicated, which is undesirable.

The present invention provides a device in which one displacement detector is added opposite to one of the displacement detectors 3x or 3y and can perform the same function.

An embodiment of the present invention will be described below with reference to FIG.

The same symbols as in Figure 1 indicate the same parts,
3y' is a displacement detector arranged symmetrically on the Y-axis with the rotating shaft 1 in between, facing the displacement detector 3y, and these displacement detectors 3x, 3y, 3y' are arranged on a concentric circle. 8 is a low-pass filter that removes periodic fluctuations caused by the inertial circle of the rotating shaft 1, scratches, unbalanced mass, etc. included in the detected value of the displacement detector, and 9 is a low-pass filter for removing the periodic fluctuations caused by the inertial circle of the rotating shaft 1, scratches, unbalanced mass, etc., which are included in the detected value of the displacement detector, and 9 is the opposed displacement detector 3y, 3y'. Detected value δy ₁ ,
₁₀ is a multiplier that multiplies the output of adder 9 by 1/2; 11 is the output δy ₁ of the displacement detector 3y and the output δm of the multiplier 10; 12 is a comparator that compares the output δx of the displacement detector 3x and the output δm of the multiplier 10. 14x is an excitation device 15a, 15b for the electromagnets 2a, 2b using the output of the comparator 12.
A control device 14y adjusts the command voltage of the electromagnets 2c and 2d using the output of the comparator 11.
This is a control device that adjusts the command voltages of 5c and 15d.

When the rotating body starts operating and the temperature of each part rises, the rotating shaft 1 expands due to the temperature rise and centrifugal force, and the detected values δx, 3y' of each displacement detector 3x, 3y, 3y'
δy ₁ and δy ₂ decrease.

The detection values δy ₁ and δy ₂ of the displacement detectors 3y and 3y' are inputted to an adder 9 after removing periodic fluctuation components due to shaft inertia, scratches, and unbalanced masses by a low-pass filter 8. In this adder 9, (δy ₁ + δy ₂ )
is calculated, multiplied by 1/2 in the multiplier 10, and the average value δm is output. The comparator 11 compares this output δm with the detected value δy ₁ of the displacement detector 3y as a reference value for the gap corrected in the Y-axis direction, and the control device 14y makes the detected value δy ₁ equal to the reference value δm. 2
Control the excitation current to c and 2d.

Furthermore, since the expansion of the rotating shaft 1 is uniform and the displacement detectors 3x, 3y, and 3y' are arranged on a concentric circle, the output δm of the multiplier 10 is used as the corrected reference value in the X-axis direction. The detected value δx of the displacement detector 3x and the output δm are compared by a comparator 12,
The controller 14x controls the excitation currents 2a and 2b so that the detector δx becomes equal to the reference value δm.

As described above, the present invention can prevent expansion due to temperature rise of the rotating shaft by simply adding one displacement detector to either the The gap reference value can be corrected on the fly, and the center of rotation can be kept constant at all times with a quick response that adapts to the operating conditions, which has the effect of maintaining high machining accuracy for CNC machine tools, etc.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of a conventional example, and FIG. 2 is a control block diagram showing an embodiment of the present invention. 1 is a rotating shaft, 2a, 2b, 2c, 2d are electromagnets, 3x, 3y, 3y' are displacement detectors, 8 is a low-pass filter, 9 is an adder, 10 is a multiplier, 1
1 and 12 are comparators, 14x and 14y are control devices,
15a, 15b, 15c, and 15d are excitation devices.

Claims (1)

[Claims] 1. Equipped with multiple pairs of electromagnets surrounding the rotating shaft, each pairing with the rotating shaft in between, detecting the displacement of the rotating shaft relative to each electromagnet, and excitation of each electromagnet so that the detected value is equal to the displacement reference value. In a magnetic bearing that adjusts the displacement, displacement detectors are provided on one of the electromagnets in one pair and one of the electromagnets in the other pair, and the average value of the two displacement detection values provided on the pair of electromagnets is used as the displacement standard. A control device for a magnetic bearing, characterized in that the value is compared with a value detected by each displacement detector.