JP4228325B2 - Magnetic bearing control device for machine tool and control method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a control device for a magnetic bearing device used for a spindle of a machine tool.
[0002]
[Prior art]
Attraction control type magnetic bearings using magnetic attraction force are being widely used in the industry because they have high bearing rigidity and can support relatively large loads with high accuracy. In particular, application to spindles has been attempted for machine tools that require machining accuracy and productivity. Control-type magnetic bearings have advantages such as non-contact support and low support friction, so that high-speed rotation is possible, bearing loss is small, and the service life is very long. Has a problem that it easily enters the control loop and vibrates. However, it has been reported that the resonance can be suppressed by inserting a filter in the control loop, and the problem is reduced. Various configurations are used for the filter, but a typical one is a notch filter. When the notch filter is used, the signal at the resonance frequency of the mechanical system is greatly attenuated when circulating through the control loop, and signals at other frequencies are not affected.
[0003]
[Problems to be solved by the invention]
However, even if a filter that sufficiently reduces the resonance frequency of the machine is provided, the machining frequency when the cutter attached to the machine tool spindle is in contact with the workpiece is compared with the resonance frequency of the mechanical system when the cutter is not in contact with the workpiece. Since the resonance frequency of the mechanical system is lowered, the preset filter frequency and the resonance frequency of the actual mechanical system are not matched, and there is a problem that the control system loses stability and is likely to oscillate.
In order to avoid oscillation during machining, an attempt was also made to set the filter by measuring the resonance frequency in advance when the cutter is in contact with the workpiece, but in that case, the stability when not machining is insufficient. As a result, there is a problem that oscillation tends to occur.
An object of the present invention is to stabilize the control system of the magnetic bearing that supports the main shaft and improve the performance of the machine tool main shaft, both when it is not being processed and when it is being processed.
[0004]
[Means for Solving the Problems]
Therefore, a magnetic bearing device for a machine tool according to the present invention includes a rotor, a motor that applies torque to the rotor, a stator including an electromagnet, a sensor that detects the position of the rotor with respect to the stator, and a fixed An amplifier that supplies current to the child, a controller that sends a command to the amplifier by controlling the difference from the difference between the command position and the position of the stator detected by the sensor, and the controller or A filter provided at the front and rear and having a specific frequency set so as to remove the natural frequency component of the mechanical system including the rotor from the passing signal, and a filter controller for controlling the specific frequency. The controller includes a fi calculator that calculates a natural vibration component of the mechanical system from the signal of the controller or the signal of the sensor, and a signal of a torque sensor that detects a driving torque of the motor, Or, when collecting data by receiving a machining command from the NC device and a processing command of the NC device from a current of the stator and a load w applied to the rotor, the natural frequency fij calculated by the fi calculator And the load w calculated by the W calculator are respectively stored in the memory, and when obtaining the specific frequency in response to the machining command of the NC device, the machining command of the NC device and the information stored in the memory are used. The controller comprises a controller that calculates a frequency corresponding to the natural frequency of the mechanical system, and a commander that receives the information of the controller and sets the specific frequency of the filter.
Further, the control method of the magnetic bearing control device for machine tool according to the present invention is such that when the machining command of the NC device is received and the filter controller performs a compensation operation, the load w recorded in advance and the natural frequency of the mechanical system are recorded. From the relationship, the natural frequency fi corresponding to the machining command is obtained, the natural frequency is set to the specific frequency of the filter when machining is started, and the original setting is restored when machining is completed. It is characterized by operating according to procedures. Further, when the filter controller performs a data collection operation in response to a machining command from the NC device, when detecting that machining has started, the load w applied to the rotor and the natural frequency fi of the mechanical system are obtained. Sampling at a predetermined sampling period, summing the sampling values, dividing the total value by the number of samplings to obtain an average value, and detecting the completion of machining, the obtained load w and the natural frequency of the mechanical system It is characterized by operating in the procedure of storing the average value of fi.
As a result, even if the resonance frequency of the mechanical system changes due to machining, the specific frequency of the filter changes accordingly, so that a stable bearing can be maintained without impairing the stability of the control system. .
[0005]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram of a magnetic bearing control device for a machine tool showing the configuration of the present invention. In the figure, reference numeral 10 denotes a machine tool magnetic bearing control device according to the present invention, and 30 denotes a bearing which is controlled by the machine tool magnetic bearing control device 10 and supports a machine tool main shaft. The machine tool magnetic bearing control device 10 includes a controller 11, a filter 12, a distributor 13, amplifiers 14 and 15, a sensor amplifier 16, and a filter controller 20, and the bearing 30 includes a rotor 34 and an upper stator. 32, a lower stator 33, and a sensor 31. The upper stator 32 and the lower stator 33 are fixed above and below the rotor 34 via an air gap to a frame (not shown) of the machine tool spindle, and the sensor 31 detects the flying position of the rotor 34 in the same manner. It is fixed to the frame. When a current is supplied to the upper and lower stators 32 and 33, a magnetic attractive force is generated between the stator 34 and the rotor 34 so as to approach each other. The sensor 31 for detecting the relative positions of the upper and lower stators 32 and 33 and the rotor 34 is detected in a non-contact manner. Therefore, it is preferable to use eddy current, static electricity, light, or the like. A shape sensor is desirable. The sensor 31 is operated by the sensor amplifier 16, and the detection signal is also amplified by the sensor amplifier 16. The output of the sensor amplifier 16 is a signal representing the floating position of the rotor 34. When the controller 11 receives a position command xs for instructing the flying position of the rotor 34 and a signal indicating the difference between the sensor amplifier 16, the controller 11 controls the phase and gain and outputs the result. A PID controller is often used as this controller, but the controller is not limited to this as long as it can function in the same manner. The filter 12 is a circuit that filters and outputs an input signal, and includes a notch filter and a phase advance filter, and the center frequency can be controlled by the external signal c. The distributor 13 performs a predetermined calculation on the input signal and outputs two signals. The calculation includes a calculation for compensating the non-linear characteristic of the magnetic attraction force and apparently linearizing the entire magnetic bearing control system, and is described in Japanese Patent Publication Nos. 3-43766 and 63-19734. Technology is used. Therefore, although the signal of the sensor amplifier is inputted and used for the calculation, it is omitted for simplifying the drawing and because the gist of the present invention is not there. The amplifiers 14 and 15 output a current proportional to the input signal and supply power to the upper and lower stators 32 and 33.
[0006]
The filter controller 20 includes a fi computing unit 21, a W computing unit 22, a memory 23, a command unit 24, and a control unit 25. The fi calculator 21 has an FFT calculation function, and receives either the position signal x of the rotor 34 detected by the sensor 31 and output from the sensor amplifier 16 or the command signal of the controller 11 to analyze the frequency. do. Then, the resonance frequency of the mechanical system including the rotor is obtained and a signal fij is output. Here, i is the order of the resonance frequency, and j is a number corresponding to the magnitude of the load.
[0007]
The W calculator 22 receives a drive torque signal applied to the rotor 34 or a current applied to the bearing 30, calculates the load size of the rotor 34, and outputs a corresponding signal W. A motor is connected to the rotor 34, and a torque applied to the rotor 34 is detected by a torque sensor provided between the rotor 34 and the motor. In addition, the torque sensor may be one that is electrically detected, and the configuration is not limited as long as the torque applied to the rotor 34 can be detected. When the torque T is detected, the radial load W is obtained by the following equation using the cutter diameter D included in the NC machining information.
W = T / (D / 2) (1)
[0008]
When the load is obtained from the current of the bearing 30, since the attractive force of the electromagnet is proportional to the square of the current, the force W 1 in the supporting direction from the current I 1 of the upper stator 32 and the current I 2 of the lower stator 33 is the next. It is obtained by the formula.
W1 = k (I1 ² + I2 ² ) k: constant (2)
Strictly speaking, the magnetic attractive force is inversely proportional to the square of the air gap, and may be calculated using an equation that incorporates this property.
The support force W2 in a direction orthogonal to the direction of the support force W1 can be obtained in the same manner, and the support force of the bearing 30, that is, the load magnitude W is obtained by the following equation.
W = √ (W1 ² + W2 ² ) (3)
[0009]
In the data collection stage, when receiving the machining command included in the NC machining information of the NC device, the controller 25 inputs the signal fij of the fi computing unit 21 and the signal W of the W computing unit 22 and samples them at a predetermined cycle. And add. At the same time, the addition value is divided by the number of additions to obtain an average value. When sampling is completed, data f1j, f2j, f3j,... Corresponding to the jth load wj are stored in the memory 23. On the other hand, in the compensation stage, when a machining command for the NC device is received, the resonance frequency of the mechanical system corresponding to the command is calculated. The calculation is performed as follows. Since the data stored in the memory 23 stores data corresponding to discrete loads wj (= w1, w2, w3,...), When processing information is input, the load magnitude W is obtained therefrom. The machining information includes a rotational speed, a cutter diameter, a cutting depth, a workpiece material coefficient, a correction coefficient based on the cutter and the bearing current, and the load W is obtained from an empirical rule. Next, the resonance frequency fij of the mechanical system corresponding to the load W is interpolated from the data stored in the memory. Data of W1 and W2 that are closest to the load W and have a relationship of W1 <W <W2 are known, and corresponding mechanical resonance frequencies f1j (= f11, f12, f13,...) And f2j (= f21, f22). , F23,...), The mechanical resonance frequency fj corresponding to the load W is obtained by the following equation.
fj = f1j + a · (f2j−f1j)
a = (W−W1) / (W2−W1) (4)
When the mechanical resonance frequency is thus obtained, it is output to the command unit 24.
[0010]
The command device 24 includes a conversion circuit for adjusting a specific frequency of the filter 12 corresponding to the frequency. When the variable frequency type filter 12 is configured by an analog circuit and is configured by a state variable type filter that adjusts a specific frequency by the size of a resistor externally connected to the operational amplifier, a large number of parallel frequency or series connected A specific frequency can be determined by short-circuiting a part of the resistor with an analog switch and using a resistor that is not short-circuited. In this case, the command unit 24 includes a decoder and an analog switch, and the obtained frequency can be decoded to function the analog switch, and a predetermined resistor can be short-circuited to set a specific frequency. Since the decoding method is known in the technical field of the filter, detailed description thereof is omitted. According to the gist of the present invention, the command unit 24 may have any configuration as long as the above function can be performed, and is not limited to a circuit configuration corresponding to only the state variable filter.
[0011]
When the magnetic bearing control device 10 for machine tool having such a configuration controls the levitation, it operates as follows. When the sensor 31 is driven by the sensor amplifier 16 and the position of the rotor 34 with respect to the stators 31 and 32 is detected, the sensor amplifier 16 converts the position into a signal. The signal is compared with the position command xs and input to the controller 11. If the rotor 34 is positioned below the command position, a signal to move up is output, and if it is positioned above, a signal to move down is output. When the signal passes through the filter 12, the natural frequency component of the mechanical system including the rotor 34 is removed. Then, the signal is divided into two signals, a current command is given to the amplifiers 14 and 15, and current is supplied to the upper stator 32 and the lower stator 33. This current causes a magnetic attractive force between the rotor 34 and the rotor 34 in a desired position. The above is the same operation as a conventional bearing.
[0012]
Next, the process by which the machine tool magnetic bearing control device 10 collects the resonance frequency of the mechanical system will be described with reference to the flowchart of FIG. When machining is started by the NC device, the spindle starts to move from the standby position and approaches the workpiece (S1). When the cutter comes into contact with the workpiece, the load applied to the spindle changes, so the output signal of the W calculator 22 changes, and the start of machining is detected (S2). While the spindle is approaching the workpiece, the output signal of the W calculator 22 does not change, so it is waited until a change appears. After the start of machining is detected, the output of the fi calculator 21, that is, the output of the fi calculator 22 and the output of the W calculator 22 are sampled and added together to obtain a total value, and simultaneously divided by the number of samples. The average value is obtained (S3). Next, when it is detected that the output of the W computing unit 22 has returned to the initial state, it is determined that the machining has been completed (S4), and the average values of the obtained fi and w are stored in the memory 23 (S5). The above data collection is performed by changing the magnitude of the load in various ways, and the collected data is recorded in the order of the magnitude of the load w as shown in FIG.
[0013]
Next, a compensation process for compensating for the mechanical resonance frequency during the processing for stabilization will be described with reference to the flowchart of FIG. When machining is started by the NC device, the controller 25 first calculates the load w and the machine resonance frequency fi corresponding to the load w from the machining command (S12). The load w is determined empirically from the number of rotations, cutter diameter, depth of cut, workpiece material coefficient, correction coefficient by cutter and bearing current, and is associated in advance, and is obtained as soon as a processing command is given. . Since the data stored in the memory 23 is discrete data as shown in FIG. 3, the mechanical resonance frequency corresponding to the load w is obtained by interpolation calculation using the equation (4). Next, when the output of the w calculator 22 is changed and the start of machining is detected (S13), the mechanical resonance frequency obtained by the controller 25 is output to the command unit 24, and the specific frequency of the filter 12 is changed (S14). ). This state is maintained because machining is in progress until the end of machining is detected. When the processing is completed, the output of the W computing unit 22 is restored to the original value, so that the completion of the processing is detected (S15), the command of the command unit 24 is restored, and the specific frequency of the filter 12 is restored (S16).
Since it operates as described above, even if the cutter contacts the workpiece during machining and the mechanical resonance frequency changes, the specific frequency of the filter is changed in accordance with the change, so the bearing control system becomes unstable. Therefore, a stable main shaft state is maintained.
[0014]
【The invention's effect】
As described above, according to the present invention, even if the cutter attached to the spindle contacts the workpiece and the natural frequency of the machine changes, it can be stably supported without impairing the performance of the spindle that has been speeded up. Practical effects can be obtained in that stable machining can be maintained and higher performance of machine tools can be promoted.
[Brief description of the drawings]
FIG. 1 is a block diagram showing the configuration of a magnetic bearing control device of the present invention. FIG. 2 is a block diagram showing the configuration of a filter. FIG. 3 is a table explaining the contents of a memory. FIG. 5 is a flowchart showing an operation procedure during machining.
DESCRIPTION OF SYMBOLS 10 Magnetic bearing control apparatus 11 Controller 12 Filter 13 Distributor 14, 15 Amplifier 16 Sensor amplifier 20 Filter controller 21 fi calculator 22 W calculator 23 Memory 24 Commander 25 Controller 30 Bearing 31 Sensor 32 Upper stator 33 Below Stator 34 Rotor

Claims (3)

A rotor, a motor for applying torque to the rotor, a stator including an electromagnet, a sensor for detecting the position of the rotor with respect to the stator, an amplifier for supplying current to the stator, and a command position; A controller for controlling the difference from the difference in the position of the stator detected by the sensor to send the command to the amplifier, and a controller provided in or before and after the controller, from the signal passing through the rotor In a magnetic bearing device for a machine tool comprising a filter in which a specific frequency is set so as to remove a natural frequency component of a mechanical system including a filter controller that controls the specific frequency,
The filter controller is
A fi calculator for calculating a natural frequency component of the mechanical system from the signal of the controller or the signal of the sensor;
A W calculator for detecting a load w applied to the rotor from a signal of a torque sensor for detecting a driving torque of the motor or a current of the stator;
When collecting data in response to the machining command of the NC device, the natural frequency fij calculated by the fi calculator and the load w calculated by the W calculator are received and stored in memory, respectively, and control of the NC device is performed. When obtaining the specific frequency in response to a command, a controller that calculates a frequency corresponding to the natural frequency of the mechanical system from the machining command of the NC device and the information stored in the memory,
A command device for receiving the information of the control device and setting the specific frequency of the filter;
A magnetic bearing device for machine tools, comprising: A rotor, a motor for applying torque to the rotor, a stator including an electromagnet, a sensor for detecting the position of the rotor with respect to the stator, an amplifier for supplying current to the stator, and a command position; A controller for controlling the difference from the difference in position of the stator detected by the sensor, and a natural vibration of a mechanical system provided in or around the controller and including the rotor from a signal passing therethrough In a magnetic bearing device for a machine tool comprising a filter in which a specific frequency is set so as to remove several components, and a filter controller for controlling the specific frequency,
When the filter controller performs a compensation operation in response to the machining command of the NC device,
From the relationship between the load w recorded in advance and the natural frequency of the mechanical system, the natural frequency fi corresponding to the machining command is obtained,
When processing is started, its natural frequency is set to the specific frequency of the filter,
When processing is complete, restore the original settings.
The control method of the magnetic bearing control apparatus for machine tools characterized by operating according to the procedure. A rotor, a motor for applying torque to the rotor, a stator including an electromagnet, a sensor for detecting the position of the rotor with respect to the stator, an amplifier for supplying current to the stator, and a command position; A controller for controlling the difference from the difference in position of the stator detected by the sensor, and a natural vibration of a mechanical system provided in or around the controller and including the rotor from a signal passing therethrough In a magnetic bearing device for a machine tool comprising a filter in which a specific frequency is set so as to remove several components, and a filter controller for controlling the specific frequency,
When the filter controller receives a machining command from the NC unit and performs data collection,
When it is detected that machining has started, the load w applied to the rotor and the natural frequency fi of the mechanical system are obtained, sampled at a predetermined sampling period, the sampled values are summed, and the total value is divided by the number of samples. To find the average value,
When it is detected that the machining is completed, the average value of the obtained load w and the natural frequency fi of the mechanical system is stored.
The control method of the magnetic bearing control apparatus for machine tools characterized by operating according to the procedure.

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