JPH0735683Y2 - Magnetic bearing control circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to a magnetic bearing control circuit, and more particularly to controlling a magnetic bearing for magnetically levitating a grinding spindle for grinding a workpiece with a grindstone attached to the tip thereof. The present invention relates to a magnetic bearing control circuit.

[Problems to be Solved by Conventional Techniques and Inventions] FIG. 5 is a diagram showing an outline of a conventional ultra-high speed grinding spindle.

In FIG. 5, the spindle 1 is magnetically levitated in the radial direction by magnetic bearings 2 and 3, and is axially supported by a thrust magnetic bearing (not shown), while being driven by a motor (not shown) to rotate. A grindstone 6 is attached to the tip of the spindle 1, and the work 7 is ground by the grindstone 6.

In the ultra-high speed grinding spindle configured as described above, when the grindstone 6 comes into contact with the work 7, an equivalent spring acts on this part. By the action of this spring,
The rigidity of the specific frequency of the spring-mass system determined by the contact rigidity generated by the contact between the grindstone 6 and the workpiece 7 and the mass of the spindle 1 and the moment of inertia decreases, and as a result, the dynamic rigidity of the spindle 1 decreases. Therefore, when the inner peripheral surface of the work 7 is ground by the ultra-high speed grinding spindle as shown in FIG. 5, there is a problem that the roundness is deteriorated.

Therefore, a main object of the present invention is to provide a magnetic bearing control circuit capable of preventing a decrease in rigidity that occurs when a work and a grindstone come into contact with each other.

[Specific Means for Solving the Problem] The present invention is a magnetic bearing control circuit for controlling a magnetic bearing for magnetically levitating a grinding spindle for grinding a workpiece by a grindstone attached to the tip thereof. Comparing means for comparing a signal indicating the reference position of the spindle and a signal indicating the displacement with respect to the reference position, a PID adjusting circuit for performing a proportional-integral-derivative operation based on the output signal of the comparing means,
Its center frequency is lower than the normal rotation speed of the grinding spindle and is selected as a frequency higher than the rigidity reduction frequency caused by the contact between the work and the grindstone, and the bandpass filter to which the output signal of the comparison means is given, and the PID adjustment circuit An adder circuit for adding the output and the output of the bandpass filter, and in response to the rotation speed of the grinding spindle exceeding the center frequency of the bandpass filter, the output of the bandpass filter is given to the adder circuit to set the phase and And a switch for increasing the gain.

[Operation] In the magnetic bearing control circuit according to the present invention, the switch is closed when the rotational speed of the spindle exceeds the center frequency of the bandpass filter, and the output of the bandpass filter is output by the addition circuit to the output of the PID adjustment circuit. To increase the phase and gain to compensate for the decrease in rigidity that occurs when the work and the grindstone come into contact with each other.

[Embodiment of the Invention] FIG. 1 is a block diagram of an embodiment of the invention.
The drawing is a gain characteristic diagram of the second-order bandpass filter shown in FIG. 1, and FIG. 3 is a diagram similarly showing a phase characteristic.

Next, the configuration of an embodiment of the present invention will be described with reference to FIG. A reference signal and a displacement signal are given to the comparison circuit 8. The reference signal is a signal indicating the reference position of the spindle shaft 1 shown in FIG. 5, and is given from, for example, a reference position signal generating circuit (not shown). The displacement signal is a signal indicating the displacement of the spindle shaft 1 with respect to the reference position, and is provided from a sensor (not shown) provided in association with the magnetic bearings 2 and 3. The comparison circuit 8 outputs the difference voltage between the reference signal and the displacement signal and supplies it to the PID adjustment circuit 9 and the secondary bandpass filter 11. The PID adjusting circuit 9 performs a proportional-integral-derivative operation, and the secondary bandpass filter 11 is for compensating for a decrease in rigidity when the grindstone 6 contacts the work 7.

As shown in FIG. 2, the transfer function of the second-order bandpass filter 11 has a maximum gain at a frequency f ₀ and a phase of the third-order bandpass filter 11.
As shown in the figure, the frequency f ₀ changes ± 90 °. The output of this bandpass filter 11 is added via a switch 12 to an adder circuit.
Given to 10. The output of the PID adjustment circuit 9 is given to the adder circuit 10, and the adder circuit 10 adds both of them and gives them to the current amplifier circuit 13. The current amplifier circuit 13 drives the magnetic bearing 2.

FIG. 4 is a diagram showing the characteristics of the disturbance frequency vs. rigidity of the ultra-high speed grinding spindle.

Next, the specific operation of the embodiment of the present invention will be described with reference to FIGS. When the switch 12 shown in FIG. 1 is opened, the comparison circuit 8 outputs the difference voltage between the reference signal and the displacement signal, and the PID adjustment circuit 9 performs the proportional-integral-derivative operation based on the difference voltage. The output is given to the current amplification circuit 13 via the addition circuit 10, and the current amplification circuit 13 controls the magnetic bearing 2. The rigidity of the ultra-high speed grinding spindle is normally as shown by the solid line in FIG. 4, but when the grindstone 6 and the workpiece 7 come into contact with each other, the rigidity decreases at the frequency f ₁ as shown by the dotted line in FIG.

When the rotation speed of the ultra-high speed grinding spindle becomes higher than the frequency f ₁ and approaches the normal rotation speed, the switch 12 is closed. As shown in FIGS. 2 and 3, the bandpass filter 11 has a high gain and a phase advance of 90 ° at the frequency f ₁ . Therefore, the bandpass filter 11
When the output of the PID adjusting circuit 9 is added to the output of the PID adjusting circuit 9 by the adding circuit 10, compared with the case where the magnetic bearing 2 is controlled only by the output of the PID adjusting circuit 9 in the frequency range near and lower than the frequency f _0. , The phase and gain are increased, and good damping can be given. That is, the rigidity at the frequency f ₁ can be increased. As a result, the decrease in rigidity in the frequency f ₁ range shown by the dotted line in FIG. 4 can be compensated as shown by the solid line in FIG.

[Advantage of Invention] As described above, according to this invention, the center frequency of the bandpass filter selected is lower than the normal rotation speed of the grinding spindle and higher than the rigidity reduction frequency caused by the contact between the work and the grindstone. By adding the output to the output of the PID adjustment circuit, it is possible to prevent the decrease in rigidity that occurs when the grindstone and the workpiece come into contact with each other.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment of the present invention. Second
The figure is a characteristic diagram of the gain of the second-order bandpass filter shown in FIG. FIG. 3 is a diagram similarly showing the phase characteristics. FIG. 4 is a diagram showing the characteristic of disturbance frequency vs. rigidity of the ultra-high speed grinding spindle. FIG. 5 is a diagram showing an outline of a conventional ultra-high speed grinding spindle. In the figure, 2 is a magnetic bearing, 8 is a comparison circuit, 9 is a PID adjustment circuit, 10 is an addition circuit, 11 is a bandpass filter, 12 is a switch, and 13 is a current amplification circuit.

Claims (1)

[Scope of utility model registration request] 1. A magnetic bearing control circuit for controlling a magnetic bearing for magnetically levitating a grinding spindle for grinding a work by means of a grindstone attached to its tip, said signal being indicative of a reference position of said grinding spindle and said Comparing means for comparing a signal indicating a displacement of the grinding spindle with respect to the reference position, a PID adjusting circuit for performing a proportional-integral-derivative operation based on an output signal of the comparing means, and a center frequency of which is a normal rotation speed of the grinding spindle. Lower than, a bandpass filter selected to a frequency higher than the rigidity lowering frequency caused by the contact between the work and the grindstone, the output signal of the comparison means is given, the output of the PID adjustment circuit and the bandpass filter An adder circuit for adding the output of the grinding spindle and the rotation speed of the grinding spindle to the center of the bandpass filter. In response to exceeding the wave number, a switch for giving the output of the bandpass filter to the adding circuit to increase the phase and the gain is provided, and the rigidity generated when the work and the grindstone come into contact with each other. A control circuit for a magnetic bearing, characterized by compensating for a decrease.