Frequency control system

Abstract

To provide an improved technology that can appropriately control a frequency that is used for a magnetic bearing and the peripheral devices thereof.SOLUTION: A frequency control system 8 includes: a sensor current detector 30 for detecting a current I supplied to a displacement sensor 5 that detects a position of a floating body 2; a sensor frequency determination unit 31 for determining a sensor frequency F1 that is used for the displacement sensor 5 on the basis of the detected current I; and a control unit 33 for issuing a first warning when the sensor frequency F1 and a carrier frequency F2, F3 used for a magnetic bearing system 1 overlap on each other.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a frequency control system for use in a magnetic bearing system. [Background technology]

[0002] A magnetic bearing is a device that levitates and supports a rotating body using the magnetic force of an electromagnet. Rotating machines whose rotating shafts are supported by such magnetic bearings have no bearing wear and do not require lubricating oil, which offers significant advantages such as maintenance-free bearings, high-speed rotation, and reduced noise.

[0003] Magnetic bearings are also suitable for use in rotating equipment used in extremely clean environments, such as semiconductor manufacturing equipment. This is because magnetic bearings do not require lubricating oil and do not produce wear particles, preventing contamination of semiconductor wafers and other objects. For this reason, magnetic bearings are suitable for fields requiring clean spaces, vacuums, etc. In particular, magnetic bearings that enable contactless support are preferred because the coefficient of friction at the contact points of ordinary bearings becomes extremely large in a vacuum. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-230168 Summary of the Invention [Problem to be solved by the invention]

[0005] Magnetic bearings and their peripheral devices include electromagnets that levitate the rotating body to be levitated, motors that rotate the rotating body, and displacement sensors that detect the position of the rotating body. If the multiple frequencies used in these electromagnets, motors, displacement sensors, etc. interfere with each other, unexpected malfunctions can occur in each device. Therefore, the frequencies used in magnetic bearings and their peripheral devices must be appropriately controlled to prevent interference.

[0006] Therefore, the present invention provides an improved technique that can appropriately control the frequency used in a magnetic bearing and its peripheral devices. [Means for solving the problem]

[0007] In one aspect, a frequency control system is provided that controls the frequency used in a magnetic bearing system that supports and rotates a levitated object, the frequency control system comprising: a sensor current detection unit that detects the current supplied to a displacement sensor that detects the position of the levitated object; a sensor frequency determination unit that determines the sensor frequency used in the displacement sensor based on the detected current; and a control unit that issues a first alarm when the sensor frequency overlaps with the carrier frequency used in the magnetic bearing system. In one aspect, the displacement sensor includes a resonant circuit in which a coil and a capacitor are connected in parallel, and the sensor frequency determiner is configured to determine the current frequency input to the displacement sensor as the sensor frequency when the detected current is smaller than a predetermined current threshold, and to change the frequency input to the displacement sensor when the detected current is equal to or greater than the current threshold. In one aspect, the sensor current detection unit is configured to detect the current at predetermined time intervals.

[0008] In one aspect, the magnetic bearing system includes an electromagnet that levitates the levitated body and a motor that rotates the levitated body, and the carrier frequency includes a magnetic bearing carrier frequency used by the electromagnet and an inverter carrier frequency used by an inverter that drives the motor. In one aspect, the control unit is configured to issue a second alarm when at least one of the sensor frequency, the magnetic bearing carrier frequency, and the inverter carrier frequency is equal to or less than a breakpoint frequency used in the electromagnet. In one embodiment, the control unit is configured to issue a third alarm when the sensor frequency is less than 10 times the break frequency. In one aspect, the control unit is configured to issue a fourth alarm when any one of the sensor frequency, the magnetic bearing carrier frequency, and the inverter carrier frequency overlaps with an integer multiple of the other frequency. [Effects of the Invention]

[0009] According to the present invention, the control unit issues a first alarm when the sensor frequency used by the displacement sensor and the carrier frequency used in the magnetic bearing system overlap, thereby making it possible to appropriately control each frequency so that the frequencies used in the magnetic bearing system do not interfere with each other. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a schematic diagram illustrating an embodiment of a magnetic bearing system. [Figure 2] 10 is a graph showing an example of a control frequency characteristic. [Figure 3] 10 is a flowchart illustrating an embodiment in which a sensor frequency determiner determines a sensor frequency. [Figure 4] 1 is a flow chart illustrating one embodiment in which a frequency control system controls the frequency used in a magnetic bearing system. [Figure 5] 1 is a flow chart illustrating one embodiment in which a frequency control system controls the frequency used in a magnetic bearing system. [Figure 6] FIG. 10 is a diagram illustrating an embodiment in which the control unit controls the frequency used in the magnetic bearing system when the levitated body is changed from a first rotation axis to a second rotation axis. [Figure 7] FIG. 2 is a diagram illustrating an embodiment in which a control unit controls a frequency used in a magnetic bearing system when the operating environment of the magnetic bearing system changes from a first temperature to a second temperature. [Figure 8]FIG. 10 is a diagram illustrating an embodiment in which a controller controls the frequency used in a magnetic bearing system when the inverter carrier frequency is changed. [Figure 9] FIG. 10 is a diagram illustrating an embodiment in which a controller controls the frequency used in a magnetic bearing system when the magnetic bearing carrier frequency is changed. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Figure 1 is a schematic diagram showing one embodiment of a magnetic bearing system 1. The magnetic bearing system 1 of this embodiment is an active magnetic bearing system. The magnetic bearing system 1 includes an electromagnet 4 that levitates a rotating shaft 2 as a levitated object, a displacement sensor 5 that detects the position of the rotating shaft 2, and a motor 6 that rotates the rotating shaft 2.

[0012] The electromagnet 4 is arranged around the rotating shaft 2. The electromagnet 4 is a magnetic force generating source that functions as a magnetic bearing, and levitates the rotating shaft 2 by its magnetic force. The displacement sensor 5 is arranged around the rotating shaft 2. The displacement sensor 5 is configured to detect the radial position of the rotating shaft 2 levitated by the electromagnet 4. In this embodiment, the magnetic bearing system 1 includes a pair of electromagnets 4 and a pair of displacement sensors 5, but the numbers of electromagnets 4 and displacement sensors 5 are not particularly limited to this embodiment.

[0013] Each of the displacement sensors 5 includes a resonant circuit in which a coil 5a and a capacitor 5b are connected in parallel. The coil 5a has a core made of magnetic material. The rotating shaft 2 has a magnetic material as a target. The displacement sensors 5 are inductance-type displacement sensors that measure the displacement of the rotating shaft 2 by utilizing the fact that the inductance of the coil 5a changes in response to the displacement of the magnetic material of the rotating shaft 2. The displacement sensors 5 are connected to an AC signal generator 20 that supplies an AC signal to the displacement sensors 5. The AC signal generator 20 is configured to generate an AC signal based on a sensor frequency F1 input from a control unit 33, which will be described later. The displacement sensors 5 that receive the AC signal from the AC signal generator 20 detect the position of the rotating shaft 2.

[0014] The displacement sensor 5 is connected to the displacement detection unit 22, and the position of the rotating shaft 2 detected by the displacement sensor 5 is sent to the displacement detection unit 22. The displacement detection unit 22 is configured to compare the target position of the rotating shaft 2 with the position of the rotating shaft 2 detected by the displacement sensor 5, and output a differential signal that indicates the difference between the target position of the rotating shaft 2 and the position of the rotating shaft 2. The displacement detection unit 22 is connected to the compensator 11, and the differential signal output by the displacement detection unit 22 is input to the compensator 11.

[0015] Compensator 11 is a control circuit that generates a control signal for stably supporting rotating shaft 2 at a target position, and is configured with a PID (proportional-integral-differential) control circuit and the like. Compensator 11 is configured to generate a control signal based on a control frequency characteristic R input from control unit 33. FIG. 2 is a graph showing an example of control frequency characteristic R. As shown in FIG. 2, control frequency characteristic R includes a control frequency band B that is set according to the type of rotating shaft 2, and a break point frequency (cutoff frequency) F4.

[0016] Compensator 11 is connected to signal amplifier 12, and the control signal generated by compensator 11 is input to signal amplifier 12. Signal amplifier 12 is configured to amplify the control signal or limit the amplitude of the control signal by an amplitude limiter provided in signal amplifier 12. Signal amplifier 12 is connected to pulse width modulation unit 14, and the control signal amplified or amplitude-limited by signal amplifier 12 is input to pulse width modulation unit 14 as a control current.

[0017] The triangular wave signal generator 18 is configured to generate a triangular wave signal based on the magnetic bearing carrier frequency F2 input from the control unit 33. The triangular wave signal generator 18 is connected to the pulse width modulation unit 14, and the triangular wave signal generated by the triangular wave signal generator 18 is sent to the pulse width modulation unit 14.

[0018] Pulse width modulation unit 14 is configured to modulate the pulse width of the control current input from signal amplifier 12 and supply the pulse width modulated control current to electromagnet 4. Pulse width modulation unit 14 includes comparator 15 and amplifier 16. Comparator 15 is configured to generate a pulse width modulated signal by comparing the control signal sent from signal amplifier 12 with a triangular wave signal sent from triangular wave signal generator 18. Amplifier 16 is configured to power amplify and output the pulse width modulated signal generated by comparator 15. The output current from amplifier 16 is supplied to electromagnet 4 as a pulse width modulated control current.

[0019] The electromagnet 4, to which a control current is supplied from the pulse width modulation unit 14, exerts a magnetic attractive force corresponding to the control current on the rotating shaft 2, moving the position of the rotating shaft 2 closer to the target position. Due to this feedback control, even if an external force is applied to the rotating shaft 2, causing a disturbance, the rotating shaft 2 is stably levitated and supported at the target position.

[0020] The motor 6 is disposed around the rotating shaft 2. The motor 6 is connected to an inverter 25 that supplies a current (AC current) for driving the motor 6. The inverter 25 is configured to generate an AC current based on an inverter carrier frequency F3 input from the control unit 33. The motor 6 supplied with the AC current from the inverter 25 rotates the rotating shaft 2. In this embodiment, the magnetic bearing system 1 includes a pair of motors 6, but the number of motors 6 is not particularly limited to this embodiment.

[0021] The frequencies used in the magnetic bearing system 1 include the sensor frequency F1 used in the displacement sensor 5, the magnetic bearing carrier frequency F2 used as a carrier frequency in the electromagnet 4, the inverter carrier frequency F3 used in the inverter 25, and the control frequency characteristic R (including the control frequency band B and the break point frequency F4) used in the electromagnet 4. If the sensor frequency F1, magnetic bearing carrier frequency F2, inverter carrier frequency F3, and control frequency characteristic R interfere with each other, unexpected malfunctions may occur in the magnetic bearing system 1. Therefore, the magnetic bearing system 1 further includes a frequency control system 8 that controls the frequencies so that the frequencies used in the magnetic bearing system 1 do not interfere with each other.

[0022] The frequency control system 8 includes a sensor current detection unit 30 that detects the current I supplied to the displacement sensor 5, and a sensor frequency determination unit 31 that determines the sensor frequency F1 used in the displacement sensor 5. The sensor current detection unit 30 is configured to detect the current I of the AC signal supplied from the AC signal generator 20 to the displacement sensor 5. The sensor current detection unit 30 is connected to the sensor frequency determination unit 31.

[0023] As described above, the displacement sensor 5 has a resonant circuit including the coil 5a and the capacitor 5b. In order for the displacement sensor 5 to accurately detect the position of the rotating shaft 2, the sensor frequency F1 must be set to one that electrically resonates in the resonant circuit. When the sensor frequency F1 that electrically resonates in the resonant circuit is input to the AC signal generator 20, the current I supplied to the displacement sensor 5 becomes an extremely small value. Therefore, the sensor frequency determination unit 31 of this embodiment is configured to determine the sensor frequency F1 used by the displacement sensor 5 based on the current I detected by the sensor current detection unit 30.

[0024] Specifically, when the current I detected by the sensor current detection unit 30 is smaller than a predetermined current threshold, the sensor frequency determination unit 31 determines the current frequency input to the displacement sensor 5 as the sensor frequency F1. The determined sensor frequency F1 is sent to the control unit 33. The current threshold is determined in advance based on, for example, the value of the current supplied to the displacement sensor 5 when a frequency that electrically resonates in the resonant circuit is input to the AC signal generator 20, which is obtained through experiments. The current threshold is set to, for example, 1 nA (nanoampere) or 1 μA (microampere).

[0025] The sensor frequency determination unit 31 changes the frequency input to the displacement sensor 5 when the current I detected by the sensor current detection unit 30 is equal to or greater than a predetermined current threshold. More specifically, when the current I detected by the sensor current detection unit 30 is equal to or greater than a predetermined current threshold, the sensor frequency determination unit 31 sends a frequency change signal X to the control unit 33. The control unit 33 is configured to input a frequency different from the current frequency to the AC signal generator 20 based on the frequency change signal X.

[0026] FIG. 3 is a flowchart showing an embodiment in which the sensor frequency determination unit 31 determines the sensor frequency F1. In step S101, the control unit 33 inputs an arbitrary initial sensor frequency to the displacement sensor 5. The AC signal generator 20 generates an AC signal based on the initial sensor frequency and supplies the AC signal to the displacement sensor 5. In step S102, the sensor current detection unit 30 detects the current I supplied to the displacement sensor 5.

[0027] In step S103, the sensor frequency determination unit 31 determines whether the current I detected by the sensor current detection unit 30 is smaller than a predetermined current threshold value. If the current I is smaller than the current threshold value ("YES" in step S103), the sensor frequency determination unit 31 determines the current frequency input to the displacement sensor 5 (i.e., the initial sensor frequency) as the sensor frequency F1 (step S104). The determined sensor frequency F1 is sent to the control unit 33.

[0028] When the current I detected by the sensor current detection unit 30 is equal to or greater than the current threshold value ("NO" in step S103), the sensor frequency determination unit 31 changes the frequency input to the displacement sensor 5 (step S105). More specifically, when the current I detected by the sensor current detection unit 30 is equal to or greater than a predetermined current threshold value, the sensor frequency determination unit 31 sends a frequency change signal X to the control unit 33. Based on the frequency change signal X, the control unit 33 inputs a frequency different from the current frequency (i.e., the initial sensor frequency) to the AC signal generator 20. Thereafter, steps S102, S103, and S105 are repeated until the current I detected by the sensor current detection unit 30 becomes smaller than the current threshold value, and the sensor frequency F1 is determined.

[0029] The inductance of the coil 5a and the capacitance of the capacitor 5b of the displacement sensor 5 may change due to, for example, a temperature change of the displacement sensor 5. When the inductance of the coil 5a and the capacitance of the capacitor 5b of the displacement sensor 5 change, the frequency at which the resonant circuit of the displacement sensor 5 resonates changes. Therefore, in one embodiment, the sensor current detection unit 30 may be configured to detect the current I supplied to the displacement sensor 5 at predetermined time intervals. In this case, the sensor frequency determination unit 31 determines the sensor frequency F1 used by the displacement sensor 5 based on the current I each time the sensor current detection unit 30 detects the current I. This makes it possible to determine an appropriate sensor frequency F1 in response to, for example, a temperature change of the displacement sensor 5. As a result, the displacement sensor 5 can detect the position of the rotating shaft 2 with high accuracy.

[0030] The frequency control system 8 includes a control unit 33 that inputs command values ​​for the frequencies used in the magnetic bearing system 1 to each device. The control unit 33 is configured to input a command value for the control frequency characteristic R to the compensator 11, input a command value for the sensor frequency F1 to the AC signal generator 20, input a command value for the magnetic bearing carrier frequency F2 to the triangular wave signal generating unit 18, and input a command value for the inverter carrier frequency F3 to the inverter 25.

[0031] The control frequency characteristic R, the magnetic bearing carrier frequency F2, and the inverter carrier frequency F3 are input by a user to the control unit 33 via the input unit 38. In one embodiment, the input unit 38 may be provided outside the magnetic bearing system 1.

[0032] The control unit 33 is configured to compare the frequencies used in the magnetic bearing system 1 and issue an alarm under predetermined conditions, thereby controlling the frequencies used in the magnetic bearing system 1. The control unit 33 is configured to issue a first alarm when the sensor frequency F1 overlaps with the carrier frequencies (i.e., the magnetic bearing carrier frequency F2 and the inverter carrier frequency F3). The first alarm may be an electrical signal that displays an alarm on a display device (not shown), or a user-recognizable signal such as a color or sound. In one embodiment, the first alarm may include information about the overlapping frequencies (e.g., information that the sensor frequency F1 and the magnetic bearing carrier frequency F2 overlap).

[0033] When the first alarm is issued, at least one of the sensor frequency F1, the magnetic bearing carrier frequency F2, and the inverter carrier frequency F3 (at least one of the overlapping frequencies) is changed. In one embodiment, when one of the overlapping frequencies is the sensor frequency F1, the control unit 33 inputs a frequency different from the current frequency to the AC signal generator 20 based on the first alarm. Thereafter, as described with reference to FIG. 3, the sensor frequency determination unit 31 determines a sensor frequency F1 different from the current frequency.

[0034] In another embodiment, when one of the overlapping frequencies is the magnetic bearing carrier frequency F2 or the inverter carrier frequency F3, the user inputs a magnetic bearing carrier frequency F2 or an inverter carrier frequency F3 different from the current frequency into the control unit 33 through the input unit 38 based on the first alarm.

[0035] The control unit 33 is configured to issue a second alarm when at least one of the sensor frequency F1, the magnetic bearing carrier frequency F2, and the inverter carrier frequency F3 is equal to or less than a breakpoint frequency F4 of the control frequency characteristic R. The second alarm may be an electrical signal that displays an alarm on a display device (not shown), or a signal that can be recognized by a user, such as a color or sound. In one embodiment, the second alarm may include information about the frequency that is equal to or less than the breakpoint frequency F4 (e.g., information that the sensor frequency F1 is equal to or less than the breakpoint frequency F4).

[0036] In one embodiment, the control unit 33 may be configured to issue a second alarm when the lowest frequency among the sensor frequency F1, the magnetic bearing carrier frequency F2, and the inverter carrier frequency F3 is equal to or lower than the break point frequency F4 of the control frequency characteristic R.

[0037] When the second alarm is issued, the frequencies below the break point frequency F4 are changed. In one embodiment, when the sensor frequency F1 is below the break point frequency F4, the control unit 33 inputs a frequency higher than the break point frequency F4 to the AC signal generator 20 based on the second alarm. Thereafter, as described with reference to FIG. 3, the sensor frequency determination unit 31 determines a sensor frequency F1 that is different from the current frequency.

[0038] In another embodiment, when the magnetic bearing carrier frequency F2 or the inverter carrier frequency F3 is equal to or lower than the break point frequency F4, the user inputs a magnetic bearing carrier frequency F2 or an inverter carrier frequency F3 higher than the break point frequency F4 to the control unit 33 through the input unit 38 based on a second alarm.

[0039] The control unit 33 is configured to issue a third alarm when the sensor frequency F1 is lower than 10 times the break point frequency F4. The third alarm may be an electrical signal that displays an alarm on a display device (not shown), or a signal that can be recognized by the user, such as a color or sound.

[0040] When the third alarm is issued, the sensor frequency F1 is changed. In one embodiment, the control unit 33 inputs a sensor frequency F1 that is 10 times or more the break point frequency F4 to the AC signal generator 20 based on the third alarm.

[0041] The control unit 33 is configured to issue a fourth alarm when any of the sensor frequency F1, the magnetic bearing carrier frequency F2, and the inverter carrier frequency F3 overlaps with an integer multiple of another frequency. The fourth alarm may be an electrical signal that displays an alarm on a display device (not shown), or a user-recognizable signal such as a color or sound. In one embodiment, the fourth alarm may include information about the frequency that overlaps with an integer multiple of another frequency (e.g., information that the magnetic bearing carrier frequency F2 overlaps with an integer multiple of the sensor frequency F1).

[0042] When the fourth alarm is issued, at least one of the sensor frequency F1, the magnetic bearing carrier frequency F2, and the inverter carrier frequency F3 is changed. In one embodiment, when the sensor frequency F1 is one of the frequencies that overlaps with an integer multiple of the other frequencies, the control unit 33 inputs a frequency different from the current frequency to the AC signal generator 20 based on the fourth alarm. Thereafter, as described with reference to FIG. 3, the sensor frequency determination unit 31 determines a sensor frequency F1 that is different from the current frequency.

[0043] In another embodiment, when one of the frequencies overlapping with an integer multiple of another frequency is the magnetic bearing carrier frequency F2 or the inverter carrier frequency F3, based on the fourth alarm, the user inputs a magnetic bearing carrier frequency F2 or an inverter carrier frequency F3 different from the current frequency into the control unit 33 through the input unit 38.

[0044] When the first, second, third, and fourth alarms are not issued, the current sensor frequency F1, magnetic bearing carrier frequency F2, inverter carrier frequency F3, and control frequency characteristic R input to control unit 33 become their respective command values. The command values ​​for sensor frequency F1, magnetic bearing carrier frequency F2, inverter carrier frequency F3, and control frequency characteristic R are input to AC signal generator 20, triangular wave signal generator 18, inverter 25, and compensator 11, respectively, and are used in displacement sensor 5, electromagnet 4, and inverter 25.

[0045] The frequency control system 8 includes at least one computer. The frequency control system 8 includes a storage device 35 storing a program. The sensor frequency determination unit 31 is configured to determine the sensor frequency F1 in accordance with the program stored in the storage device 35. The control unit 33 is configured to compare the frequencies used in the magnetic bearing system 1 in accordance with the program stored in the storage device 35 and issue an alarm under predetermined conditions, as described above. The control unit 33 stores the sensor frequency F1 sent from the sensor frequency determination unit 31, and the magnetic bearing carrier frequency F2 and inverter carrier frequency F3 input from the input unit 38 in the storage device 35.

[0046] The storage device 35 includes a main storage device (e.g., random access memory) accessible by the sensor frequency determination unit 31 and the control unit 33, and an auxiliary storage device (e.g., a hard disk drive or solid state drive) that stores programs. The sensor frequency determination unit 31 and the control unit 33 include a CPU (central processing unit) or a GPU (graphic processing module) that performs calculations according to instructions included in the programs stored in the storage device 35. The specific configuration of the frequency control system 8 is not limited to these examples. The sensor frequency determination unit 31 and the control unit 33 may be configured as a single calculation device, or may be configured as calculation devices provided in separate computers.

[0047] 4 and 5 are flow charts illustrating one embodiment in which the frequency control system 8 controls the frequency used by the magnetic bearing system 1. FIG. In step S201, the sensor frequency determination unit 31 inputs the determined sensor frequency F1 to the control unit 33. In step S202, the control frequency characteristic R, the magnetic bearing carrier frequency F2, and the inverter carrier frequency F3 are input to the control unit 33 via the input unit . In step S203, the control unit 33 determines whether the sensor frequency F1, the magnetic bearing carrier frequency F2, and the inverter carrier frequency F3 overlap. When any of the sensor frequency F1, the magnetic bearing carrier frequency F2, and the inverter carrier frequency F3 overlap ("YES" in step S203), the control unit 33 issues a first warning (step S204). In one embodiment, the first warning may include information about the overlapping frequencies.

[0048] When the first alarm is issued, at least one of the sensor frequency F1, the magnetic bearing carrier frequency F2, and the inverter carrier frequency F3 (at least one of the overlapping frequencies) is changed (step S205). In one embodiment, the control unit 33 determines the sensor frequency F1 using the sensor frequency determination unit 31 based on the first alarm (step S206). The sensor frequency determination unit 31 inputs the determined sensor frequency F1 to the control unit 33 (return to step S201). In one embodiment, based on the first alarm, the user inputs the magnetic bearing carrier frequency F2 or the inverter carrier frequency F3, which is different from the current frequency, to the control unit 33 via the input unit 38 (return to step S202).

[0049] In step S203, when none of the sensor frequency F1, the magnetic bearing carrier frequency F2, and the inverter carrier frequency F3 overlaps ("NO" in step S203), the control unit 33 executes step S207. In step S207, the control unit 33 determines whether at least one of the sensor frequency F1, the magnetic bearing carrier frequency F2, and the inverter carrier frequency F3 is equal to or less than the break point frequency F4 of the control frequency characteristic R. When at least one of the sensor frequency F1, the magnetic bearing carrier frequency F2, and the inverter carrier frequency F3 is equal to or less than the break point frequency F4 ("YES" in step S207), the control unit 33 issues a second warning (step S208). In one embodiment, the second warning may include information about the frequency that is equal to or less than the break point frequency F4.

[0050] When the second alarm is issued, the frequencies equal to or lower than the break point frequency F4 are changed (step S209). In one embodiment, based on the second alarm, the control unit 33 inputs a sensor frequency higher than the break point frequency F4 to the AC signal generator 20, and the sensor frequency determination unit 31 determines the sensor frequency F1 (step S206). The sensor frequency determination unit 31 inputs the determined sensor frequency F1 to the control unit 33 (return to step S201). In one embodiment, based on the second alarm, the user inputs a magnetic bearing carrier frequency F2 or an inverter carrier frequency F3, which is different from the current frequency, to the control unit 33 via the input unit 38 (return to step S202).

[0051] In step S207, when the sensor frequency F1, the magnetic bearing carrier frequency F2, and the inverter carrier frequency F3 are all higher than the break point frequency F4 of the control frequency characteristic R ("NO" in step S207), the control unit 33 executes step S210.

[0052] In one embodiment, in step S207, the control unit 33 may be configured to issue a second alarm when the lowest frequency among the sensor frequency F1, the magnetic bearing carrier frequency F2, and the inverter carrier frequency F3 is equal to or lower than the break point frequency F4 of the control frequency characteristic R.

[0053] In step S210, the control unit 33 determines whether the sensor frequency F1 is lower than 10 times the break point frequency F4. If the sensor frequency F1 is lower than 10 times the break point frequency F4 ("YES" in step S210), the control unit 33 issues a third alarm (step S211).

[0054] When the third alarm is issued, the sensor frequency F1 is changed (step S212). In one embodiment, based on the third alarm, the control unit 33 inputs a sensor frequency F1 that is 10 times or more the break point frequency F4 to the AC signal generator 20, and the sensor frequency determination unit 31 determines the sensor frequency F1 (step S206). The sensor frequency determination unit 31 inputs the determined sensor frequency F1 to the control unit 33 (return to step S201). In step S210, when the sensor frequency F1 is equal to or greater than 10 times the break point frequency F4 ("NO" in step S210), the control unit 33 executes step S213 shown in FIG.

[0055] In step S213, the control unit 33 determines whether any of the sensor frequency F1, the magnetic bearing carrier frequency F2, and the inverter carrier frequency F3 overlaps with an integer multiple of another frequency. When any of the sensor frequency F1, the magnetic bearing carrier frequency F2, and the inverter carrier frequency F3 overlaps with an integer multiple of another frequency ("YES" in step S213), the control unit 33 issues a fourth alarm (step S214). In one embodiment, the fourth alarm may include information about the frequency that overlaps with an integer multiple of another frequency.

[0056] When the fourth alarm is issued, at least one of the sensor frequency F1, the magnetic bearing carrier frequency F2, and the inverter carrier frequency F3 is changed (step S215). In one embodiment, based on the fourth alarm, the control unit 33 inputs a frequency different from the current frequency to the AC signal generator 20, and determines the sensor frequency F1 using the sensor frequency determination unit 31 (step S206 in FIG. 4). The sensor frequency determination unit 31 inputs the determined sensor frequency F1 to the control unit 33 (return to step S201). In one embodiment, based on the fourth alarm, the user may input the magnetic bearing carrier frequency F2 or the inverter carrier frequency F3 different from the current frequency to the control unit 33 via the input unit 38 (return to step S202).

[0057] In step S213, when none of the sensor frequency F1, the magnetic bearing carrier frequency F2, and the inverter carrier frequency F3 overlaps with an integer multiple of another frequency ("NO" in step S213), the control unit 33 executes step S216. In step S216, the current sensor frequency F1, magnetic bearing carrier frequency F2, and inverter carrier frequency F3 input to the control unit 33 become command values ​​for each device. The command values ​​for the sensor frequency F1, magnetic bearing carrier frequency F2, inverter carrier frequency F3, and control frequency characteristic R are input to the AC signal generator 20, triangular wave signal generator 18, inverter 25, and compensator 11, respectively, and are used by the displacement sensor 5, electromagnet 4, and inverter 25.

[0058] In this way, the frequency control system 8 can appropriately control each frequency used in the magnetic bearing system 1, namely, the sensor frequency F1, the magnetic bearing carrier frequency F2, the inverter carrier frequency F3, and the corner frequency F4, so that they do not interfere with each other.

[0059] Furthermore, when the input value of the sensor frequency F1, the magnetic bearing carrier frequency F2, the inverter carrier frequency F3, or the control frequency characteristic R (including the break point frequency F4) is changed, the control unit 33 controls the sensor frequency F1, the magnetic bearing carrier frequency F2, the inverter carrier frequency F3, and the break point frequency F4 so that the conditions for issuing the first to fourth alarms are not met. Below, an embodiment will be described in which the control unit 33 controls the frequency when at least one of the sensor frequency F1, the magnetic bearing carrier frequency F2, the inverter carrier frequency F3, and the control frequency characteristic R (including the break point frequency F4) is changed.

[0060] FIG. 6 is a diagram illustrating an embodiment in which the control unit 33 controls the frequency used by the magnetic bearing system 1 when the levitated object is changed from the first rotating shaft 2A to the second rotating shaft 2B. In the magnetic bearing system 1, the type of rotating shaft used as the levitated object may be changed. When the type of rotating shaft is changed, the control frequency characteristic R corresponding to the rotating shaft and the inductance of the coil 5a of the displacement sensor 5 may change. The change in inductance in the displacement sensor 5 changes the frequency at which the resonant circuit of the displacement sensor 5 resonates. Therefore, the sensor frequency F1 determined by the sensor frequency determination unit 31 also changes. In this embodiment, the frequency control system 8 controls the frequency used by the magnetic bearing system 1 when the control frequency characteristic R and the sensor frequency F1 change in accordance with the change in the levitated object.

[0061] When the levitated body is the first rotating shaft 2A, the sensor frequency F1, the magnetic bearing carrier frequency F2, the inverter carrier frequency F3, and the break point frequency F4 included in the control frequency characteristic R corresponding to the first rotating shaft 2A are controlled by the control unit 33 so as not to interfere with each other. More specifically, as described with reference to Figures 3 to 5, the sensor frequency F1, the magnetic bearing carrier frequency F2, the inverter carrier frequency F3, and the break point frequency F4 of the control frequency characteristic R are controlled to frequencies that do not interfere with each other and do not satisfy the conditions for the control unit 33 to issue the first to fourth alarms.

[0062] In this embodiment, the control frequency characteristic R corresponding to the first rotation axis 2A is different from the control frequency characteristic R' corresponding to the second rotation axis 2B. The break point frequency F4' included in the control frequency characteristic R' corresponding to the second rotation axis 2B is higher than the break point frequency F4 included in the control frequency characteristic R corresponding to the first rotation axis 2A. When the levitated object is changed from the first rotation axis 2A to the second rotation axis 2B, the control frequency characteristic R' corresponding to the second rotation axis 2B is input by the user to the control unit 33 via the input unit 38.

[0063] In this embodiment, the sensor frequency F1 determined by the sensor frequency determiner 31 when the levitated object is on the first rotation axis 2A is different from the sensor frequency F1' determined by the sensor frequency determiner 31 when the levitated object is on the second rotation axis 2B. The sensor frequency F1' corresponding to the second rotation axis 2B is higher than the sensor frequency F1 corresponding to the first rotation axis 2A. When the levitated object is changed from the first rotation axis 2A to the second rotation axis 2B, the sensor frequency determiner 31 inputs the determined sensor frequency F1' corresponding to the second rotation axis 2B to the control unit 33.

[0064] As described with reference to FIGS. 3 to 5, the control unit 33 controls the input sensor frequency F1', magnetic bearing carrier frequency F2, inverter carrier frequency F3, and break point frequency F4' so as not to satisfy the conditions for issuing the first to fourth alarms. Therefore, the sensor frequency F1', magnetic bearing carrier frequency F2, and inverter carrier frequency F3 do not overlap. The sensor frequency F1', magnetic bearing carrier frequency F2, and inverter carrier frequency F3 are all higher than the break point frequency F4'. The sensor frequency F1' is at least 10 times the break point frequency F4'. The sensor frequency F1', magnetic bearing carrier frequency F2, and inverter carrier frequency F3 do not overlap with any integer multiple of the other frequencies. As a result, even if the type of rotating shaft is changed, the frequencies used in the magnetic bearing system 1 are controlled to frequencies that do not interfere with each other.

[0065] 7 is a diagram illustrating an embodiment in which the control unit 33 controls the frequency used by the magnetic bearing system 1 when the operating environment of the magnetic bearing system 1 changes from a first temperature TA to a second temperature TB. When the operating environment (e.g., temperature) of the magnetic bearing system 1 changes, the inductance of the coil 5a and the capacitance of the capacitor 5b of the displacement sensor 5 may change. The change in inductance in the displacement sensor 5 changes the frequency at which the resonant circuit of the displacement sensor 5 resonates. Therefore, the sensor frequency F1 determined by the sensor frequency determination unit 31 also changes. In this embodiment, the frequency control system 8 controls the frequency used by the magnetic bearing system 1 when the sensor frequency F1 changes in accordance with a change in the operating environment of the magnetic bearing system 1.

[0066] In one embodiment, the sensor current detection unit 30 may detect the current I supplied to the displacement sensor 5 at predetermined time intervals, and the sensor frequency determination unit 31 may determine the sensor frequency F1 used in the displacement sensor 5 based on the current I each time the current I is detected by the sensor current detection unit 30. In this way, the current I supplied to the displacement sensor 5 can be monitored at predetermined time intervals, and an appropriate sensor frequency F1 corresponding to changes in the driving environment can be determined.

[0067] When the operating environment of the magnetic bearing system 1 is at a first temperature TA, the sensor frequency F1, the magnetic bearing carrier frequency F2, the inverter carrier frequency F3, and the break point frequency F4 included in the control frequency characteristic R are controlled by the control unit 33 so as not to interfere with each other. More specifically, as explained with reference to Figures 3 to 5, the sensor frequency F1, the magnetic bearing carrier frequency F2, the inverter carrier frequency F3, and the break point frequency F4 of the control frequency characteristic R are controlled to frequencies that do not interfere with each other and do not satisfy the conditions for the control unit 33 to issue the first to fourth alarms.

[0068] In this embodiment, the sensor frequency F1 determined by the sensor frequency determination unit 31 when the operating environment of the magnetic bearing system 1 is at a first temperature TA is different from the sensor frequency F1' determined by the sensor frequency determination unit 31 when the operating environment is at a second temperature TB. The sensor frequency F1' corresponding to the second temperature TB is higher than the sensor frequency F1 corresponding to the first temperature TA. When the operating environment of the magnetic bearing system 1 changes from the first temperature TA to the second temperature TB, the sensor frequency determination unit 31 inputs the determined sensor frequency F1' corresponding to the second temperature TB to the control unit 33.

[0069] As explained with reference to FIGS. 3 to 5, the control unit 33 controls the input sensor frequency F1', magnetic bearing carrier frequency F2, inverter carrier frequency F3, and break point frequency F4 so as not to satisfy the conditions for issuing the first to fourth alarms. Therefore, the sensor frequency F1', magnetic bearing carrier frequency F2, and inverter carrier frequency F3 do not overlap. The sensor frequency F1', magnetic bearing carrier frequency F2, and inverter carrier frequency F3 are higher than the break point frequency F4. The sensor frequency F1' is 10 times or more the break point frequency F4. The sensor frequency F1', magnetic bearing carrier frequency F2, and inverter carrier frequency F3 do not overlap with any integer multiple of the other frequencies. As a result, even if the operating environment of the magnetic bearing system 1 changes, the frequencies used by the magnetic bearing system 1 are controlled to frequencies that do not interfere with each other.

[0070] 8 is a diagram illustrating an embodiment in which the control unit 33 controls the frequency used in the magnetic bearing system 1 when the inverter carrier frequency is changed from F3 to F3'. In the magnetic bearing system 1, the inverter carrier frequency F3 may be changed when the type of inverter 25 is changed or to suppress noise generated by the inverter 25. In this embodiment, the frequency control system 8 controls the frequency used in the magnetic bearing system 1 when the inverter carrier frequency F3 is changed.

[0071] Before the inverter carrier frequency F3 is changed, the sensor frequency F1, the magnetic bearing carrier frequency F2, the inverter carrier frequency F3, and the break point frequency F4 included in the control frequency characteristic R are controlled by the control unit 33 so as not to interfere with each other. More specifically, the sensor frequency F1, the magnetic bearing carrier frequency F2, the inverter carrier frequency F3, and the break point frequency F4 of the control frequency characteristic R are controlled to frequencies that do not interfere with each other and do not satisfy the conditions for the control unit 33 to issue the first to fourth alarms, as described with reference to Figures 3 to 5.

[0072] In this embodiment, the changed inverter carrier frequency F3' is lower than the original inverter carrier frequency F3 and overlaps with the sensor frequency F1. The changed inverter carrier frequency F3' is input to the control unit 33 via the input unit 38 by the user.

[0073] In this embodiment, because the sensor frequency F1 overlaps with the changed inverter carrier frequency F3', the control unit 33 issues a first warning. Based on the first warning, the control unit 33 inputs a frequency different from the current frequency to the AC signal generator 20. Thereafter, as described with reference to FIG. 3, the sensor frequency determination unit 31 determines a sensor frequency F1' different from the sensor frequency F1. The determined sensor frequency F1' is input to the control unit 33. In this embodiment, the changed sensor frequency F1' is higher than the sensor frequency F1 before the change.

[0074] In this way, as described with reference to FIGS. 3 to 5, the control unit 33 controls the sensor frequency F1', magnetic bearing carrier frequency F2, inverter carrier frequency F3', and break point frequency F4 so as not to satisfy the conditions for issuing the first to fourth alarms. Therefore, the sensor frequency F1', magnetic bearing carrier frequency F2, and inverter carrier frequency F3' do not overlap. The sensor frequency F1', magnetic bearing carrier frequency F2, and inverter carrier frequency F3' are higher than the break point frequency F4. The sensor frequency F1' is 10 times or more the break point frequency F4. The sensor frequency F1', magnetic bearing carrier frequency F2, and inverter carrier frequency F3' do not overlap with any integer multiple of the other frequencies. As a result, even when the inverter carrier frequency F3 is changed, the frequencies used in the magnetic bearing system 1 are controlled to frequencies that do not interfere with each other.

[0075] 9 is a diagram illustrating an embodiment in which the control unit 33 controls the frequency used in the magnetic bearing system 1 when the magnetic bearing carrier frequency is changed from F2 to F2'. In the magnetic bearing system 1, the magnetic bearing carrier frequency may be changed depending on the type of electromagnet 4. In this embodiment, the frequency control system 8 controls the frequency used in the magnetic bearing system 1 when the magnetic bearing carrier frequency F2 is changed.

[0076] The sensor frequency F1 before the magnetic bearing carrier frequency F2 is changed, the magnetic bearing carrier frequency F2, the inverter carrier frequency F3, and the break point frequency F4 included in the control frequency characteristic R are controlled by the control unit 33 so as not to interfere with each other. More specifically, the sensor frequency F1, the magnetic bearing carrier frequency F2, the inverter carrier frequency F3, and the break point frequency F4 of the control frequency characteristic R are controlled to frequencies that do not interfere with each other and do not satisfy the conditions for the control unit 33 to issue the first to fourth alarms, as described with reference to Figures 3 to 5.

[0077] In this embodiment, the changed magnetic bearing carrier frequency F2' is lower than the magnetic bearing carrier frequency F2 before the change and overlaps with the sensor frequency F1. The changed magnetic bearing carrier frequency F2' is input to the control unit 33 via the input unit 38 by the user.

[0078] In this embodiment, since the sensor frequency F1 overlaps with the changed magnetic bearing carrier frequency F2', the control unit 33 issues a first warning. Based on the first warning, the control unit 33 inputs a frequency different from the current frequency to the AC signal generator 20. Thereafter, as described with reference to FIG. 3, the sensor frequency determination unit 31 determines a sensor frequency F1' different from the sensor frequency F1. The determined sensor frequency F1' is input to the control unit 33. In this embodiment, the changed sensor frequency F1' is higher than the sensor frequency F1 before the change.

[0079] In this way, as described with reference to FIGS. 3 to 5, the control unit 33 controls the sensor frequency F1', magnetic bearing carrier frequency F2', inverter carrier frequency F3, and break point frequency F4 so as not to satisfy the conditions for issuing the first to fourth alarms. Therefore, the sensor frequency F1', magnetic bearing carrier frequency F2', and inverter carrier frequency F3 do not overlap. The sensor frequency F1', magnetic bearing carrier frequency F2', and inverter carrier frequency F3 are higher than the break point frequency F4. The sensor frequency F1' is 10 times or more the break point frequency F4. The sensor frequency F1', magnetic bearing carrier frequency F2', and inverter carrier frequency F3 do not overlap with any integer multiple of the other frequencies. As a result, even when the magnetic bearing carrier frequency F2 is changed, the frequencies used in the magnetic bearing system 1 are controlled to frequencies that do not interfere with each other.

[0080] The above-described embodiments have been described for the purpose of enabling a person of ordinary skill in the art to practice the present invention. Various modifications of the above-described embodiments would be obvious to a person skilled in the art, and the technical concept of the present invention may be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but is to be interpreted in the broadest scope in accordance with the technical concept defined by the claims. [Explanation of symbols]

[0081] 1. Magnetic bearing system 2. Floating object (rotating shaft) 4. Electromagnets 5. Displacement Sensor 5a coil 5b capacitor 6 motors 8 Frequency Control System 11 Compensator 12 Signal Amplifier 14 Pulse width modulation section 15 Comparator 16 Amplifier 18 Triangular Wave Signal Generator 20 AC signal generator 22 Displacement detection unit 25 inverter 30 Sensor current detection section 31 Sensor frequency determination unit 33 Control Unit 35 Storage section 38 Input section

Claims

1. A frequency control system for controlling a frequency used in a magnetic bearing system that supports and rotates a levitated object, a sensor current detection unit that detects a current supplied to a displacement sensor that detects the position of the levitated object; a sensor frequency determination unit that determines a sensor frequency to be used in the displacement sensor based on the detected current; a control unit that issues a first alarm when the sensor frequency overlaps with a carrier frequency used in the magnetic bearing system;

2. the displacement sensor includes a resonant circuit in which a coil and a capacitor are connected in parallel; The sensor frequency determination unit When the detected current is smaller than a predetermined current threshold, a current frequency input to the displacement sensor is determined as the sensor frequency; The frequency control system of claim 1 , configured to change a frequency input to the displacement sensor when the detected current is equal to or greater than the current threshold.

3. The frequency control system according to claim 1 , wherein the sensor current detection unit is configured to detect the current at predetermined time intervals.

4. The magnetic bearing system includes: an electromagnet that levitates the levitated object; a motor that rotates the levitated body, The frequency control system according to claim 1 , wherein the carrier frequencies include a magnetic bearing carrier frequency used in the electromagnet and an inverter carrier frequency used in an inverter that drives the motor.

5. 5. The frequency control system according to claim 4, wherein the control unit is configured to issue a second alarm when at least one of the sensor frequency, the magnetic bearing carrier frequency, and the inverter carrier frequency is equal to or lower than a breakpoint frequency used in the electromagnet.

6. The frequency control system according to claim 4 , wherein the control unit is configured to issue a third alarm when the sensor frequency is lower than 10 times the break point frequency.

7. 5. The frequency control system according to claim 4, wherein the control unit is configured to issue a fourth alarm when any one of the sensor frequency, the magnetic bearing carrier frequency, and the inverter carrier frequency overlaps with an integer multiple of another frequency.

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