JP2002078374A - Motor rotation speed controller and static pressure gas bearing spindle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a motor rotation speed controller which does not require the use of special hardware and realizes high-speed error compensation by controlling rise of cost, and to provide a static pressure gas bearing spindle utilizing the same controller. SOLUTION: The compensation value of the error element of a rotating angle detection sensor 9 is stored in a memory 5; a compensation value corresponding to the rotating position of the rotating angle detection sensor 9 is read with a read circuit 6; such a compensation value is applied to a phase difference signal of a phase comparator 1 for subtraction with a subtraction circuit 7; and the signal is then converted, after the subtraction, into a deviation signal which is proportional to the angle by a deviation detection circuit 2, in order to drive the motor 8 via a compensation circuit 3 and a motor drive circuit 4.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a motor rotation speed control device and a hydrostatic gas bearing spindle using the same, and more particularly, to controlling the rotation speed of a motor used in a spindle of a precision machine or a precision inspection device. The present invention relates to a rotational speed control device and a hydrostatic gas bearing spindle using the same.

[0002]

2. Description of the Related Art Spindles such as precision processing machines and precision inspection devices require high-precision rotation speed control. For this reason,
Conventionally, a PLL control circuit has been used for spindle control.

FIG. 6 is a block diagram showing an example of such a PLL control circuit, and FIG. 7 is a waveform diagram of each part.

In FIG. 6, a rotation angle detection sensor 9 is attached to a rotation shaft of a motor 8, and a plurality of angle detection signals b are provided from the rotation angle detection sensor 9 at equal intervals within one rotation of the rotation shaft. The signal is output with a waveform as shown in FIG. The reference signal a shown in FIG. 7A is input to the phase comparator 1, and the phase comparator 1 converts the phase difference signal c shown in FIG. 7C according to the phase difference between the two input signals. Output. This phase difference signal c is applied to the low-pass filter 10 to extract a low-frequency component, and is applied to the compensation circuit 3 as a deviation signal f shown in FIG. The compensation circuit 3 inputs the output signal g shown in FIG. 7 (g) to the motor drive circuit 4 as a current command value, and the motor drive circuit 4 drives the motor 8 to control the rotation of the spindle. When the compensation circuit 3 is composed of a proportional element and a differential element, control is performed so as to maintain a phase difference for generating a torque of the motor 8 according to the mechanical loss.

If the phase difference is within one cycle of the reference signal, the spindle rotates at a frequency obtained by dividing the reference signal frequency by the number of detection signals of the rotation angle detection sensor 9 output during one rotation. Further, the fluctuation of the rotation cycle is within ± 1 cycle of the reference signal. Therefore, a combination of a spindle supported by a static pressure gas bearing, a brushless AC servomotor, and a non-contact rotation angle detection sensor, which makes the resistance to rotation such as friction almost zero, uses a crystal oscillator or the like to achieve frequency accuracy and stability. If a high reference signal is generated and the PLL control is used, the fluctuation of the rotational speed is reduced, and the rotational speed can be controlled with high accuracy.

However, a scale disk 91 and a scanning unit 92 as shown in FIG.
A built-in optical rotary encoder and the like separated from each other are used. A graduation grid 93 is formed on the graduation disk 91, and is fixed to the shaft by a set bolt with a clearance fit. For this reason, since the slit center and the rotation center of the rotary encoder do not coincide with each other, when the scanning unit 92 scans the graduation grid 93, the interval between the graduation grids 93 becomes larger or smaller, and the output signal of the rotary encoder becomes , And errors due to eccentricity and slit pitch errors. Since the motor 8 is controlled by the output signal including these errors, the rotation speed becomes uneven.
As a countermeasure, there is a method of removing an error component of a deviation signal by performing error correction, thereby reducing speed unevenness.

FIG. 9 shows another example of the conventional example,
FIG. 10 is a waveform diagram of each part shown in FIG. 10, a deviation detection circuit 2, a memory 5, a read circuit 6, and a subtractor 7 are provided instead of the low-pass filter 10 shown in FIG. The deviation detection circuit 2 converts the phase difference signal into a deviation signal proportional to the angle, and the memory 5 stores a table for correcting a rotation synchronization component. The read circuit 6 reads the value of the memory 5 according to the rotational position. The subtracter 7 subtracts the memory data from the deviation signal.

Next, the operation of the motor rotation speed control device shown in FIG. 9 will be described. The phase comparator 1 is shown in FIG.
The angle detection signal b shown in FIG. 10B is compared with the reference signal a input as a rectangular wave shown in FIG. As a result, the phase difference signal c shown in FIG.
In order to use a constant error correction signal, the apparatus shown in FIG. 9 uses the deviation detection circuit 2 in which the output phase does not change even when the rotation speed changes. In the memory 5, the value of the correction table estimated from the rotation synchronization component of the deviation signal is stored at an address corresponding to the rotation position. The readout circuit 6 detects the rotation angle by counting the number of outputs of the angle detection signal based on the origin signal of the rotation angle detection sensor 9, reads out the memory data of the address corresponding to the rotation angle from the memory 5, and corresponds to the rotation angle. The correction value d shown in FIG.

The subtractor 7 subtracts the correction value d from the pre-correction phase difference signal h shown in FIG. 10 (h) to correct and remove the error component of the rotation angle detection sensor 9 as shown in FIG. 10 (i). The corrected deviation signal i is output. The corrected deviation signal i is input to the compensation circuit 3 and is the output of the compensation circuit 3 shown in FIG.
The fluctuation component of the current command value g due to the error of the rotation angle detection sensor 9 shown in (g) can be corrected and removed. This current command value g
Is input to the motor drive circuit 4 to drive the motor 8, so that the motor current has no fluctuation component due to the error of the rotation angle detection sensor 9. Speed control can be realized.

The correction table stored in the memory 5 approximates the rotation synchronization component of the deviation signal appearing in a non-corrected state by a periodic function, and prepares a table by changing the amplitude, offset, phase, and the like. The current command value g having the minimum rotation synchronization component is selected. This is because if the approximation of the rotation synchronization component of the deviation signal in the uncorrected state is used as the correction table as it is, the amplitude, offset, phase, etc. are pure eccentric components due to the influence of other elements in the control loop. This is because the value may not always be the optimum value. As another method of creating the correction table, a method of measuring and determining an error of the rotation angle detection sensor 9 in a built-in state, or the like can be considered.

[0011]

In the case of the prior art shown in FIG. 6, control with high rotation cycle accuracy can be obtained with a simple circuit, but the speed unevenness within one rotation is caused by the error of the rotation angle detection sensor 9 itself. And the angle detection error caused by the mounting error.

Further, in order to reduce the speed unevenness, FIG.
In the case of performing error correction as in the conventional example shown in (1), when the phase difference signal is smoothed by a low-pass filter to obtain a deviation signal, the phase changes according to the rotation speed due to the characteristics of the low-pass filter. It is necessary to change according to the number of rotations. For this reason, it is necessary to prepare a huge error correction signal table. To avoid this,
A circuit for digitally generating a deviation signal is required.

Therefore, in order to add a correction function to the conventional control system, it is necessary to add a significant change to the control circuit, and the circuit scale becomes large as compared with the case where no correction is performed, resulting in an increase in cost. The substrate area increases.

If a CPU is mounted and processing is performed by software, the circuit scale and cost can be reduced as compared with the case where processing is performed only by hardware, but if the sampling frequency is not set to be higher than the maximum frequency of the reference signal. ,
The accuracy of the rotation cycle may be inferior to the conventional example of FIG. The maximum frequency of the reference signal is determined by the resolution of the rotation angle detection sensor 9 and the maximum number of rotations.
As described above, when a higher-speed and higher-resolution sensor is used in the future, the maximum frequency of the reference signal may be 1 MHz or more. To deal with this, a fast C
A PU and a peripheral circuit corresponding to the PU are required, which causes a cost increase.

SUMMARY OF THE INVENTION It is, therefore, a primary object of the present invention to provide a motor rotation speed control device and a hydrostatic gas bearing spindle using the same, which can reduce the error correction of the rotation angle detection sensor at a lower cost and at a higher speed than before. It is.

[0016]

SUMMARY OF THE INVENTION The present invention is a rotation speed control device for controlling the number of rotations of a motor, wherein the rotation speed of the motor is one.
Rotation angle detection means for outputting a plurality of detection signals at equal angular intervals each time the motor rotates, and phase comparison means for comparing the phase of the detection signal from the rotation angle detection means with the reference signal and outputting a phase difference signal Storage means for storing a correction value for correcting an error component of the rotation angle detection means at an address corresponding to the rotation angle, and reading means for reading and outputting the stored correction value from the address corresponding to the rotation angle. Phase difference signal correction means for correcting the output of the phase comparison means with the read correction value, deviation detection means for converting the output signal of the phase difference signal correction means into a deviation signal proportional to the angle, and deviation detection means And a driving means for controlling the current of the motor based on the output signal of the compensating means.

Therefore, according to the present invention, the rotation speed of the motor can be controlled with a relatively simple circuit configuration and without performing complicated correction processing.

Further, the phase difference signal correction means is an arithmetic unit for adding or subtracting the output signal of the phase comparison means and the correction value read from the storage means.

Further, the storage means stores a value proportional to the angle error of the rotation angle detection means measured in advance as the error component correction value.

Further, the storage means stores a value obtained from a function approximating an angle error of the rotation angle detection means measured in advance as an error component correction value.

Another invention is a hydrostatic gas bearing spindle in which a rotating shaft on which a rotor of a motor is mounted is supported by a static pressure gas bearing in a non-contact manner, and the motor is controlled by a rotation speed control device. A rotation angle detection unit that is attached and outputs a plurality of detection signals at equal angular intervals each time the motor rotates, compares the phase of the detection signal from the rotation angle detection unit with a reference signal, and outputs a phase difference signal. A phase comparing means for outputting, a storage means for storing a correction value for correcting an error component of the rotation angle detection means at an address corresponding to the rotation angle, and a correction value stored in the storage means corresponding to the rotation angle. Reading means for reading and outputting from the address, phase difference signal correcting means for correcting the output of the phase comparing means based on the correction value read by the reading means, and output of the phase difference signal correcting means. Deviation detection means for converting a signal into a deviation signal proportional to the angle, compensation means for applying phase compensation to the deviation signal from the deviation detection means to increase control stability, and a motor based on an output signal of the compensation means. And driving means for controlling the current.

Therefore, by driving the hydrostatic gas bearing spindle with such a rotational speed control device, the rotational speed unevenness can be greatly improved, and a high-precision spindle device can be realized.

Further, the phase difference signal correction means is an arithmetic unit for adding or subtracting the output signal of the phase comparison means and the correction value read from the storage means.

Further, the storage means stores a value proportional to the angle error of the rotation angle detection means, which is measured in advance, as the error component correction value.

Further, the storage means stores a value proportional to a value obtained from a function obtained by approximating an angle error of the rotation angle detection means measured in advance as an error component correction value.

The phase comparing means, the storing means, the reading means, the phase difference signal correcting means, the deviation detecting means, the compensating means and the driving means are provided separately from the hydrostatic gas bearing spindle body. And

[0027]

FIG. 1 is a block diagram showing the configuration of a motor speed control device according to an embodiment of the present invention. 1, the motor rotation speed control device includes a phase comparator 1, a deviation detection circuit 2, a compensation circuit 3, a motor drive circuit 4, a memory 5, a read circuit 6, a subtractor 7, and a rotation angle detection sensor 9. . The rotation angle detection sensor 9 has an origin signal and detects the rotation angle of the motor 8 and supplies the detection signal to the phase comparator 1 and the readout circuit 6. The phase comparator 1 compares the output signal of the rotation angle detection sensor 9 with the reference signal and outputs a phase difference signal to the subtractor 7. The memory 5 stores a table for correcting the rotation synchronization component, and the readout circuit 6 reads out memory data corresponding to the rotation position from the memory 5 based on the detection signal of the rotation angle detection sensor 9.
The subtracter 7 subtracts the memory data read by the reading circuit 6 from the phase difference signal from the phase comparator 1.
The deviation detection circuit 2 converts the output signal of the subtracter 7 into a deviation signal proportional to the angle, and the compensation circuit 3 performs phase compensation on the deviation signal and outputs a current command value to the motor drive circuit 4. The motor drive circuit 4 drives the motor 8 according to the current command value. The motor 8 drives, for example, a hydrostatic gas bearing spindle.

FIG. 2 is a waveform diagram of each part shown in FIG.
Next, a specific operation of the embodiment of the present invention will be described with reference to FIGS. The phase comparator 1 has a reference signal a input as a rectangular wave shown in FIG.
A pulse signal c having a width equal to the phase difference between the two is output as shown in FIG. 2C by comparing the angle detection signal b from the rotation angle detection sensor 9 shown in FIG. Since the value of the correction table is stored in the memory 5 at an address corresponding to the rotation position, the readout circuit 6 detects the rotation angle from the output of the angle detection signal of the rotation angle detection sensor 9 and stores the corresponding memory data. It is read out and output to the subtractor 7 as a correction signal d shown in FIG.

The subtractor 7 subtracts the correction value d from the phase difference signal c, so that the reference level of the pulse of the phase difference signal c is shifted in the opposite direction to the fluctuation due to the error component of the rotation angle detection sensor 9. The phase difference signal e is output.
The deviation detection circuit 2 removes the high-frequency component and smoothes it, thereby correcting and removing the error component of the deviation signal f of the rotation angle detection sensor 9. Therefore, since there is no rotation synchronous component in the motor current, the fluctuation of the angular velocity during one rotation is reduced, and more accurate rotation speed control can be realized. Note that the correction value may be added to the phase difference signal after sign inversion.

In the correction table, it is assumed that the error data of the rotation angle detection sensor 9 measured after being mounted on the spindle or the sign thereof is inverted. Further, instead of the error data itself, a value approximated by a periodic function or the like may be used. Further, not only is the error of the rotation angle sensor 9 corrected, but also with respect to the repetitive speed fluctuation due to other error factors, the fluctuation of the output signal of the rotation angle sensor 9 due to the error factor is measured in advance and the correction value is calculated. Can be similarly corrected by calculating

In the embodiment shown in FIG. 1, the deviation detection circuit 2 may be constituted by the conventional low-pass filter 10 shown in FIG. In addition, error correction can be performed with a simple configuration in which only the memory 5, the readout circuit 6, and the subtractor 7 are added to the configuration of the conventional example shown in FIG. 6, and a CPU and special hardware are used. Since there is no need to perform this operation, it is possible to suppress the increase in cost and achieve high-speed operation.

FIG. 3 is a more specific block diagram of the embodiment shown in FIG. 1, in which the present invention is applied to a motor rotation speed control device for a hydrostatic gas bearing spindle 15.

In FIG. 3, the motor rotation speed control device is provided separately from the static pressure expectation bearing spindle main body and is connected by a cable. The rotating shaft 16 of the hydrostatic gas bearing spindle 15 is supported in the radial direction and the axial direction by a journal bearing 17 and a thrust bearing 18. These journal bearing 17 and thrust bearing 18
Supports the rotating shaft 16 in a non-contact manner by supplying compressed air from the outside. The rotating shaft 16 is driven to rotate by a three-phase brushless AC servomotor 8, and the number of rotations is detected by an optical non-contact rotary encoder 19.
It comprises an A converter 12 and an inverting amplifier 13.
A rotary encoder 19 of a hydrostatic gas bearing spindle 15 is used as the rotation angle detection sensor 9 shown in FIG. 1, and a low-pass filter 10 is used instead of the deviation detection circuit 2.
Is used. The counter circuit 11 counts an output signal from the rotary encoder 19 and detects a rotation position. D
The A converter 12 converts the correction value from the memory 5 into an analog signal. The inverting amplifier 13 inverts the sign of the output of the DA converter 12.

The phase comparator 1 outputs a pulse signal having a width equal to the time between the output signal b of the rotary encoder 19 and the rising edge of the reference signal a as a phase difference signal c. The sign of the phase difference signal c is-if the output signal of the rotary encoder 19 is ahead of the reference signal in phase, and + if it is behind the reference signal.
It becomes. The counter circuit 11 counts the feedback pulse of the rotary encoder 19 with reference to the origin signal, the count value is input as an address signal of the memory 5, and the data output according to the address is input to the DA converter 12. Is converted to an analog signal to obtain a correction signal. The corrected phase difference signal e obtained by adding the signal d obtained by inverting the correction signal by the inverting amplifier 13 and the phase difference signal c by the adder 15 is input to the low-pass filter 10. As a result, a deviation signal from which a rotation synchronization component due to an angle error of the rotary encoder 19 has been removed can be obtained. By driving the motor 8 via the compensating circuit 3 and the motor driving circuit 4 at the subsequent stage, fluctuations in the rotation cycle and the speed unevenness within one rotation can be reduced.

The correction table stored in the memory 5 is generated as a value proportional to the accumulated angle error based on the origin signal position in a state where the rotary encoder 19 is incorporated. This is because when the angular resolution of the rotary encoder 19 is θ, the full scale value of the deviation signal when the phase difference becomes 360 ° is Emax, and the angular error at the rotational position n is An, the DA at the rotational position n is obtained. The correction signal Dn output from the converter 12 is obtained by the following equation to generate correction data.

Dn = Emax · An / θ Alternatively, the angle error at the rotational position n is An, the maximum absolute value of the angle error is Amax, and the DA converter 12
Assuming that the maximum value of the absolute value of the output is Dmax, the correction table may be generated so that the output Dn of the DA converter 12 at the rotational position n becomes a value represented by the following equation.

Dn = Dmax.An / Amax In this case, an amplifier may be provided at the subsequent stage, the gain G thereof may be set to a value represented by the following equation, and the output may be used as a correction signal.

G = (Emax / Dmax) · (Amax / θ) The waveforms of the corrected phase difference signal e, the deviation signal f, and the correction signal d are shown in FIG. 4 as a state with correction, and FIG. 5 is a state without correction. Shown as

In the state without correction shown in FIG. 5, the correction signal is always 0V. The deviation signal f is in a state close to a sine wave of the rotation frequency. On the other hand, in the state where the correction shown in FIG.
The effect of the correction is clear. This configuration requires only a counter circuit 11, a memory 5, a DA converter 12, an inverting amplifier 13 and a subtractor 14 to be added to the conventional example shown in FIG. As a result, compactness and low cost can be realized. In addition, since it can be configured only with hardware, high-speed operation is possible.

As described above, the hydrostatic gas bearing spindle 15 driven by the three-phase brushless AC servomotor 8 shown in FIG. 3 causes rotation speed unevenness because the main shaft 16 is supported in a non-contact manner. Since the number of components is small and the error of the rotary encoder 19 has a relatively large effect on the rotational speed unevenness of the main shaft 16, the rotational speed unevenness is greatly improved by combining with the rotational speed control device according to the present invention. An accurate spindle device can be configured.

The embodiments disclosed this time are to be considered in all respects as illustrative and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

[0042]

As described above, according to the present invention, the correction value of the error component of the rotation angle detecting means is stored, the correction value is read out in accordance with the rotation angle, and the correction value is stored in the phase difference signal. In addition, since the signal is converted into a deviation signal proportional to the angle, the rotation speed of the motor can be controlled with a relatively simple circuit configuration without performing complicated correction processing.

Further, by driving the hydrostatic gas bearing spindle with such a rotational speed control device, the rotational speed unevenness can be greatly improved, and a high-precision spindle device can be realized.

[Brief description of the drawings]

FIG. 1 is a block diagram of a motor rotation speed control device according to an embodiment of the present invention.

FIG. 2 is a waveform diagram of each unit shown in FIG.

FIG. 3 is a more specific block diagram of the embodiment shown in FIG. 1;

FIG. 4 is a waveform diagram when a corrected phase difference signal, a deviation signal, and a correction signal are corrected.

FIG. 5 is a diagram illustrating waveforms of a corrected phase difference signal, a deviation signal, and a correction signal without correction.

FIG. 6 is a block diagram showing a conventional example of a motor rotation speed control device.

7 is a waveform chart of each part in FIG. 6;

FIG. 8 is a view for explaining a scale grid of a scale disk included in the rotary encoder.

FIG. 9 is a block diagram showing another example of the motor rotation speed control device.

FIG. 10 is a waveform chart of each part in FIG. 9;

[Explanation of symbols]

1 phase comparator, 2 deviation detection circuit, 3 compensation circuit, 4
Motor drive circuit, 5 memories, 6 readout circuits, 7
Subtractor, 8 motor, 9 rotation angle detection sensor, 11
Counter circuit, 12 DA converter, 13 inverting amplifier, 15 hydrostatic gas bearing spindle, 16 rotating shaft, 1
7 journal bearings, 18 thrust bearings, 19 rotary encoders.

Claims (9)

[Claims] 1. A rotation speed control device for controlling the number of rotations of a motor, comprising: rotation angle detection means for outputting a plurality of detection signals at equal angular intervals each time the motor makes one rotation; Phase comparison means for comparing the phase of the detection signal from the means with the reference signal and outputting a phase difference signal; and a correction value for correcting an error component of the rotation angle detection means stored at an address corresponding to the rotation angle. A reading unit that reads and outputs a correction value stored in the storage unit from an address corresponding to a rotation angle, and corrects an output of the phase comparison unit based on the correction value read by the reading unit. Phase difference signal correction means, a deviation detection means for converting an output signal of the phase difference signal correction means into a deviation signal proportional to an angle, and a deviation signal from the deviation detection means. And compensating means for applying phase compensation to increase the stability of the above, and a drive means for controlling a current of the motor based on an output signal of the compensation means, rotation speed control device of the motor. 2. The apparatus according to claim 1, wherein said phase difference signal correcting means is an arithmetic unit for adding or subtracting an output signal of said phase comparing means and a correction value read from said storage means. A rotational speed control device for a motor according to claim 1. 3. The storage device according to claim 1, wherein the storage unit stores a value proportional to an angle error of the rotation angle detection unit measured in advance as the error component correction value.
Or the rotational speed control device for a motor according to 2. 4. The storage means stores a value proportional to a value obtained from a function approximating an angle error of the rotation angle detection means measured in advance as the error component correction value. The motor speed control device according to claim 1 or 2. 5. A hydrostatic gas bearing spindle in which a rotating shaft to which a rotor of a motor is attached is supported in a non-contact manner by a static pressure gas bearing, and the motor is controlled by a rotation speed control device, wherein the spindle is attached to the rotating shaft. A rotation angle detection unit that outputs a plurality of detection signals at equal angular intervals each time the motor makes one rotation; and a phase difference signal comparing the detection signal from the rotation angle detection unit with a reference signal. Phase comparison means for outputting a correction value for correcting an error component of the rotation angle detection means at an address corresponding to a rotation angle; and a correction value stored in the storage means for a rotation angle. Reading means for reading and outputting from an address corresponding to, and a phase difference signal correcting means for correcting the output of the phase comparing means with a correction value read by the reading means. Deviation detection means for converting an output signal of the phase difference signal correction means into a deviation signal proportional to an angle; andcompensation means for adding phase compensation to the deviation signal from the deviation detection means to increase control stability. A hydrostatic gas bearing spindle, comprising: driving means for controlling a current of the motor based on an output signal of the compensating means. 6. The apparatus according to claim 5, wherein said phase difference signal correction means is an arithmetic unit for adding or subtracting an output signal of said phase comparison means and a correction value read from said storage means. A hydrostatic gas bearing spindle as described. 7. The storage unit according to claim 5, wherein the storage unit stores a value proportional to an angle error of the rotation angle detection unit measured in advance as the error component correction value.
Or a hydrostatic gas bearing spindle according to 6. 8. The storage means stores a value proportional to a value obtained from a function obtained by approximating an angle error of the rotation angle detection means measured in advance as the error component correction value. The hydrostatic gas bearing spindle according to claim 5 or 6. 9. The method according to claim 1, wherein the phase comparing means, the storage means,
9. The device according to claim 5, wherein the reading unit, the phase difference signal correcting unit, the deviation detecting unit, the compensating unit, and the driving unit are provided separately from the hydrostatic gas bearing spindle main body. 2. A hydrostatic gas bearing spindle according to claim 1.