JP7327243B2 - Displacement sensor for bearing - Google Patents

Description

The present invention relates to a displacement sensor for bearings.

Patent Literature 1 discloses a magnetic bearing. A magnetic bearing rotatably supports a rotating shaft in a non-contact manner by floating the rotating shaft by magnetic force. A magnetic bearing has an actuator that generates a magnetic force. The actuator controls the magnetic force provided to the rotating shaft by controlling the current provided to the coil wound around the core. In addition, the magnetic bearing has a bearing displacement sensor for obtaining information about the position of the axis of rotation. The bearing displacement sensor acquires a change in inductance according to the distance from the core around which the coil is wound to the rotating shaft as a change in voltage output from the coil.

Patent No. 6244734

It is desired to increase the output of rotary machines using magnetic bearings. In order to increase the output, it is necessary to further increase the rotational speed of the rotating shaft. In order to increase the number of rotations, it is necessary to suppress the positional fluctuation of the rotating shaft that accompanies the rotation. Therefore, it was necessary to further improve the detection accuracy of the position of the rotating shaft.

SUMMARY OF THE INVENTION Accordingly, the present invention provides a bearing displacement sensor capable of enhancing the detection accuracy of the position of a rotating shaft.

One aspect of the present invention is a bearing displacement sensor that obtains the position of a rotating shaft. The bearing displacement sensor controls the distance from the rotating shaft to the core by moving the core with respect to the rotating shaft based on a core made of a magnetic material, a coil wound around the core, and temperature. and a core position control unit.

The bearing displacement sensor obtains the amount of change in the position of the rotating shaft as the amount of change in the inductance generated in the core. The amount of change in inductance may include the amount of change due to the temperature change of the displacement sensor in addition to the amount of change in the distance from the core to the rotation axis. Therefore, the core position control unit controls the distance from the core to the rotating shaft so as to cancel the amount of change in inductance caused by temperature change. Therefore, it is possible to eliminate the influence caused by temperature change. As a result, it is possible to improve the detection accuracy of the position of the rotating shaft.

In one form, the core position control unit may reduce the distance from the core to the rotation axis as the temperature rises and expand the distance from the core to the rotation axis as the temperature drops. As the temperature increases, the inductance of the core decreases. Therefore, the core is moved closer to the rotating shaft so as to offset the decrease in inductance. On the other hand, as the temperature decreases, the inductance of the core increases. Therefore, the core is moved away from the rotating shaft so as to offset the increase in inductance. Therefore, it is possible to preferably eliminate the influence of inductance fluctuations caused by temperature changes.

In one aspect, the core position control unit generates a first spring that generates a first biasing force along the radial direction of the rotating shaft and a second biasing force that extends along the radial direction of the rotating shaft. and a second spring arranged in series, wherein the first spring temperature coefficient indicating the relationship between the spring constant of the first spring and temperature is the second spring indicating the relationship between the spring constant of the second spring and temperature. It may be different from the temperature coefficient. According to this configuration, it is possible to provide the core with an urging force that brings the core closer to the rotating shaft when the temperature rises. Additionally, a biasing force can be provided to the core that moves the core away from the axis of rotation as the temperature drops.

One form of the bearing displacement sensor further comprises a housing arranged to surround the rotating shaft, the first spring being arranged between the core and the second spring, the second spring and the housing. According to this configuration, it is possible to generate an urging force for controlling the position of the core according to the temperature with a simple configuration.

In one form, the first spring temperature coefficient may be less than the second spring temperature coefficient. According to this configuration, it is possible to suitably provide the core with an urging force that brings the core closer to the rotating shaft when the temperature rises and separates the core from the rotating shaft when the temperature drops.

According to the present invention, there is provided a bearing displacement sensor capable of increasing the detection accuracy of the position of the rotating shaft.

FIG. 1 is a perspective view showing the configuration of a rotating machine that employs a magnetic bearing having a bearing displacement sensor according to an embodiment. FIG. 2 is a functional block diagram showing the configuration of the magnetic bearing. FIG. 3 is a front view showing the arrangement of the bearing displacement sensor. FIG. 4 is a diagram showing the operation of the bearing displacement sensor at room temperature. FIG. 5 is a graph conceptually showing temperature characteristics of a variable spring constant and temperature characteristics of a fixed spring constant. FIG. 6 is a diagram showing the operation of the bearing displacement sensor at the operating temperature. FIG. 7A is a schematic diagram for explaining the displacement of the variable spring and the displacement of the fixed spring at room temperature. FIG. 7(b) is a schematic diagram for explaining the displacement of the variable spring and the displacement of the fixed spring at the operating temperature. FIG. 8A is a graph showing temperature characteristics of a spring included in the bearing displacement sensor according to Modification 1. FIG. FIG. 8(b) is a graph showing temperature characteristics of a spring included in the bearing displacement sensor according to Modification 2. FIG. FIG. 9 is a front view showing a bearing displacement sensor according to a comparative example.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the accompanying drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and overlapping descriptions are omitted.

As shown in FIG. 1, magnetic bearing 1 is used in motor 100 . A motor 100 is used in a rotary machine 200 such as a compressor. The rotary machine 200 includes, for example, an impeller (not shown), and the impeller is fixed to the end of a motor shaft 101 that is the rotating shaft of the motor 100 . A motor 100 has a rotor 102 fixed to a motor shaft 101 and a stator 103 surrounding the rotor 102 . This motor 100 has a large capacity and can rotate at high speed. The magnetic bearing 1 can be suitably used for such a large-capacity, high-speed motor 100 .

A motor shaft 101 is rotatably supported by a pair of magnetic bearings 1 in a non-contact manner. The magnetic bearings 1 are arranged so as to sandwich the motor 100 . In other words, the magnetic bearing 1 is arranged between the motor 100 and the impeller. A ball bearing 104 may be arranged between the motor 100 and the impeller. The ball bearing 104 rotatably supports the motor shaft 101 when the magnetic bearing 1 fails to support the motor shaft 101 .

The magnetic bearing 1 noncontactly and rotatably supports the motor shaft 101 . Furthermore, the magnetic bearing 1 controls the position of the motor shaft 101 to stop at a predetermined position. This control is performed by applying magnetic forces to the motor shaft 101 from a plurality of different directions so as to surround the motor shaft 101 . The magnetic bearing 1 has a controller 10 (see FIG. 2), an actuator 20 that generates magnetic force, and a bearing displacement sensor (hereinafter referred to as "displacement sensor 30") that obtains information on the position of the motor shaft 101. In addition, in FIG. 1, the actuator 20 and the displacement sensor 30 are illustrated simply as a simple rectangular parallelepiped.

Actuator 20 generates a magnetic force by providing current to a wire wound around a magnetic member. Further, the displacement sensor 30 obtains information regarding the position of the motor shaft 101 by using changes in inductance according to changes in the distance between the motor shaft 101 and the displacement sensor 30 .

The magnetic bearing 1 further has a housing 2 in addition to the actuator 20 and the displacement sensor 30 . The housing 2 is an annular member surrounding the motor shaft 101 . The housing 2 may be made of a magnetic material. The housing 2 holds the actuator 20 and the displacement sensor 30 in place. The actuators 20 are arranged around the motor shaft 101 at every 90 degrees. The displacement sensors 30 are also arranged around the motor shaft 101 at every 90 degrees.

As shown in FIG. 2, the magnetic bearing 1 has a controller 10. As shown in FIG. The controller 10 uses the voltage obtained from the displacement sensor 30 to obtain information regarding the position of the motor shaft 101 . Using this information, controller 10 controls actuator 20 .

More specifically, the magnetic bearing 1 has four displacement sensors 30A, 30B, 30C and 30D. In the following description, when the four displacement sensors need to be distinguished from each other, reference numerals "displacement sensors 30A, 30B, 30C, and 30D" are attached. When it is not necessary to distinguish between the four displacement sensors, they are simply referred to as "displacement sensor 30".

The displacement sensors 30A and 30B output voltages to the controller 10 for obtaining the displacement of the motor shaft 101 along the X-axis direction. The controller 10 then provides current to the actuator 20A that generates the holding force in the X-axis direction. The magnetic bearing 1 also has a similar configuration in the Y-axis direction. That is, the displacement sensors 30C and 30D output voltages to the controller 10 for obtaining the displacement of the motor shaft 101 along the Y-axis direction. The controller 10 then provides current to the actuator 20B that generates the holding force in the Y-axis direction.

The controller 10 has differential amplifiers 11A and 11B, PID controllers 12A and 12B, and power amplifiers 13A and 13B. A differential amplifier 11A, a PID controller 12A, and a power amplifier 13A are used for control in the X-axis direction. A differential amplifier 11B, a PID controller 12B, and a power amplifier 13B are used for control in the Y-axis direction.

The differential amplifier 11A receives voltages from the displacement sensors 30A and 30B and outputs a voltage difference. For example, in the output of the differential amplifier 11A, the sign of the output signal may be inverted. The output of the differential amplifier 11A is added to the signal indicating the target position and then input to the PID controller 12A. 12 A of PID controllers generate|occur|produce a control signal according to an input value. The PID controller 12A outputs a control signal to the power amplifier 13A. The power amplifier 13A outputs current corresponding to the control signal to the actuator 20A.

The differential amplifier 11B, the PID controller 12B, and the power amplifier 13B for controlling in the Y-axis direction differ only in the direction to be controlled, so detailed description thereof will be omitted.

The displacement sensor 30 will be described in detail with reference to FIG. The displacement sensor 30 has a core unit 40 and a core position control unit 50 (core position control section). Core unit 40 obtains a voltage corresponding to the distance from core unit 40 to motor shaft 101 . The core position control unit 50 controls the distance from the core unit 40 to the motor shaft 101 according to temperature.

A proximal end of the core position control unit 50 is fixed to the inner peripheral surface 2 a of the housing 2 . Core position control unit 50 may be integrated with housing 2 . Also, the core position control unit 50 may be separate from the housing 2 . In FIG. 3 , the core position control unit 50 is illustrated as being integrated with the housing 2 . A core unit 40 is arranged on the distal end side of the core position control unit 50 . That is, the core unit 40 is arranged between the core position control unit 50 and the motor shaft 101 . The core position control unit 50 movably holds the core unit 40 . Specifically, the core unit 40 can move relative to the core position control unit 50 in a direction perpendicular to the rotation axis RL. In other words, the core unit 40 can move toward the motor shaft 101 and move away from the motor shaft 101 .

FIG. 4 shows an enlarged view of the displacement sensor 30 shown in FIG.

The core unit 40 has a core 41 and a coil 42 . The core 41 defines the orientation of the magnetic path caused by the current flowing through the coil 42 . The core 41 is an integral part and includes a core body 41a and a coil winding portion 41b. The core body 41a extends in a tangential direction of an imaginary circle centered on the motor shaft 101, and coil winding portions 41b are provided at both ends thereof. A core position control unit 50 is connected to the center of the core body 41a. A conductor wire is wound around the coil winding portion 41 b , and the wound conductor wire forms the coil 42 . That is, the coil winding portion 41 b and the coil 42 constitute the winding portion 43 . According to this configuration, a magnetic path is formed from one winding portion 43 to the other winding portion 43 via the core body 41a.

The core position control unit 50 has a case 51, a shaft 52, a variable spring 53 (first spring), and a fixed spring 54 (second spring). The term "variable" as used herein means that the spring constant varies with temperature. Also, "fixed" means that the spring constant is constant regardless of temperature.

Case 51 accommodates shaft 52 , variable spring 53 and fixed spring 54 . A proximal end of the case 51 is fixed to the inner peripheral surface 2 a of the housing 2 . Case 51 extends from housing 2 toward motor shaft 101 . In other words, the case 51 extends from the inner peripheral surface 2 a of the housing 2 toward the center of the housing 2 . An isolation wall 51a is provided inside the case 51, and the isolation wall 51a forms an outer chamber 51S and an inner chamber 51T. A proximal end of the shaft 52 is arranged in the outer chamber 51S. A portion of the shaft body 52, the variable spring 53 and the fixed spring 54 are accommodated in the inner chamber 51T. The isolation wall 51a and the tip wall 51b of the case 51 are provided with coaxial through holes. A shaft 52 is arranged in this through hole.

The shaft body 52 is disposed in the inner chamber 51T between the shaft distal end projecting from the distal end wall 51b of the case 51, the shaft base end disposed in the outer chamber 51S of the case 51, and the shaft distal end and the shaft base end. and an axial portion.

A core unit 40 is connected to the tip of the shaft. Specifically, the tip of the shaft is connected to the core body 41 a of the core unit 40 . The shaft base end is arranged in the outer chamber 51</b>S, and more specifically, the end of the shaft base end is separated from the bottom surface of the case 51 .

A flange 56 is fixed to the shaft-to-shaft portion. That is, the flange 56 is arranged in the inner chamber 51T. The flange 56 divides the inner chamber 51T into a variable spring region 51Ta and a fixed spring region 51Tb. A variable spring region 51Ta is between the isolation wall 51a and the flange 56 . A variable spring 53 is arranged in the variable spring region 51Ta. On the other hand, the fixed spring region 51Tb is between the flange 56 and the tip wall 51b. A fixed spring 54 is arranged in the fixed spring region 51Tb.

The variable spring 53 generates a variable biasing force (first biasing force) in a direction that separates the flange 56 from the isolation wall 51a. This variable biasing force Fa is determined by the variable spring constant ka of the variable spring 53 and the displacement xa of the variable spring 53 from the natural length La according to Hooke's law.

The fixed spring 54 generates a fixed urging force Fm (second urging force) directed to move the flange 56 away from the tip wall 51b. This fixing biasing force Fm is determined by the fixing spring constant km of the fixing spring 54 and the displacement xm from the natural length Lm of the fixing spring 54 according to Hooke's law.

The isolation wall 51 a and the tip wall 51 b are part of the case 51 . Therefore, the distance from the isolation wall 51a to the tip wall 51b remains unchanged. On the other hand, the flange 56 is fixed to the shaft 52 . The shaft 52 is movable with respect to the case 51 . That is, the distance from the isolation wall 51a to the case 51 and the distance from the tip wall 51b to the case 51 are variable.

The operation of the core position control unit 50 will be described in detail below with reference to FIGS. 4 to 7 as appropriate.

As shown in FIG. 7(a), the position of the flange 56 is determined by the relationship between the variable spring constant ka and the fixed spring constant km. When the flange 56 is stationary, the variable biasing force Fa1 and the fixed biasing force Fm1 are balanced. At this time, the displacement xa1 of the variable spring 53 is determined by the variable biasing force Fa1 and the variable spring constant ka1. When the displacement xa1 of the variable spring 53 is determined, the length La1 of the variable spring 53 is determined. As a result, the distance from the isolation wall 51a to the flange 56, which is equivalent to the length La1 of the variable spring 53, is determined.

Similarly, the displacement xm1 of the fixed spring 54 is determined by the fixed biasing force Fm1 and the fixed spring constant km1. Once the displacement xm1 of the fixed spring 54 is determined, the length Lm1 of the fixed spring 54 is determined. As a result, the distance from the flange 56 to the tip wall 51b, which is equivalent to the length Lm1 of the fixed spring 54, is determined.

Then, if the magnitude relationship between the variable spring constant ka and the fixed spring constant km can be adjusted, the position of the flange 56 can be controlled. That is, the position of the shaft 52 to which the flange 56 is fixed can be controlled. As a result, since the length of projection of the shaft 52 from the case 51 can be controlled, the position of the core unit 40 fixed to the tip of the shaft 52 can be controlled. That is, the distance L1 from the core unit 40 to the motor shaft 101 can be controlled.

In this embodiment, the magnitude relationship between the variable spring constant ka and the fixed spring constant km is determined based on the temperature. That is, at least one of the variable spring constant ka and the fixed spring constant km is a function of temperature, and the spring constant changes as the temperature changes. This temperature is the temperature of the variable spring 53 . In the following description, it is assumed that the variable spring constant ka changes according to temperature changes. On the other hand, it is assumed that the fixed spring constant km is unchanged (constant) according to temperature changes.

FIG. 5 shows an example of the relationship between the variable spring constant ka and the fixed spring constant km. The horizontal axis indicates temperature. The vertical axis indicates the spring constant. Graph G5a shows the variable spring constant ka and graph G5b shows the fixed spring constant km. Graphs G5a and G5b are for explaining the operation of the core position control unit 50 of the present embodiment, and the tendencies shown by the graphs G5a and G5b are examples.

A graph G5a showing the variable spring constant ka shows that the magnitude of the spring constant increases as the temperature rises. As the variable spring 53 having such characteristics, for example, a spring using a shape memory alloy can be used. On the other hand, the graph G5b showing the fixed spring constant km indicates that the spring constant is constant regardless of the temperature. Examples of the variable spring 53 having such characteristics include springs using general spring materials such as piano wire and stainless steel wire for springs.

<At room temperature>
First, attention is paid to the room temperature T1. It can be said that the room temperature is a state in which the motor 100 is not operating. As shown in the graphs G5a and G5b of FIG. 5, the variable spring constant ka1 is smaller than the fixed spring constant km1 at room temperature T1.

In this state, as shown in FIG. 7A, the variable spring 53, which is a compression spring, is in a state of being compressed by a displacement xa1 from its natural length La. That is, the variable spring 53 produces a large displacement xa1 from its natural length La. On the other hand, the fixed spring 54 is in a state of substantially the natural length Lm. That is, the fixed spring 54 may have a slight displacement xm1 from the natural length Lm, and may have a substantial displacement xm1 of zero. As a result, the variable spring 53 produces a variable biasing force Fa1 based on a relatively large displacement xa1 and a relatively small variable spring constant ka1. On the other hand, the fixed spring 54 generates a fixed biasing force Fm1 due to a relatively small displacement xm1 and a fixed spring constant km1 larger than the variable spring constant ka1. The variable biasing force Fa1 is balanced with the fixed biasing force Fm1. In this state, since the flange 56 is closer to the housing 2 side, the distance from the core 41 to the motor shaft 101 is kept at the predetermined distance L1.

For example, if the variable spring 53 is compressed by a displacement xa1, the variable biasing force Fa1 generated by the variable spring 53 is expressed by the following equation according to Hooke's law.
Fa1=ka1×xa1 (1)
This variable biasing force Fa1 acts on the fixed spring 54 . The displacement xm1 of the fixing spring 54 is represented by the following formula.
xm1=Fa1/km1=xa1×(ka1/km1) (2)
In the above equation (2), if ka1 is much smaller than km1 (ka1<<km1), it can be seen that ka1/km1 is almost zero. As a result, the fixed spring 54 does not substantially expand and contract, and maintains its natural length Lm. That is, the distance L1 from the core unit 40 to the motor shaft 101 does not change from the initial state. At the room temperature T1, changes in inductance due to temperature changes are almost negligible. Therefore, the original position of the core unit 40 should be maintained. The core position control unit 50 of this embodiment can meet that requirement.

<At operating temperature>
Next, attention is paid to the operating temperature T2. It can be said that this operating temperature T2 is the state when the motor 100 is in operation. As shown in graph G5b of FIG. 5, operating temperature T2 is higher than room temperature T1. At the operating temperature T2, the variable spring constant ka2 is greater than the fixed spring constant km2. That is, there exists a temperature between the room temperature T1 and the operating temperature T2 at which the magnitude relationship between the variable spring constant ka and the fixed spring constant km is reversed.

Such a relationship may be defined by the relationship between the variable spring temperature coefficient (first spring temperature coefficient) of the variable spring constant ka and the fixed spring temperature coefficient (second spring temperature coefficient) of the fixed spring constant km. These spring temperature coefficients show the relationship between spring constant and temperature. The relationship between the spring constant and temperature may be a linear function or a higher-order function, as shown in the graph G5a of FIG. In this embodiment, the relationship between spring constant and temperature is represented by a linear function. In this case, the spring temperature coefficient is the slope of the graphs G5a and G5b.

As described above, the fixed spring constant km is assumed to be constant regardless of the temperature. Therefore, the fixed spring constant km maintains a substantially constant value from the room temperature T1 to the operating temperature T2. In this case, the fixed spring temperature coefficient, which is the slope of the graph G5b, is one. On the other hand, the variable spring constant ka was assumed to be a function of temperature. The variable spring 53 has a variable spring constant ka that increases as the temperature rises. In this case, the variable spring temperature coefficient, which is the slope of the graph G5a, is a positive value larger than one.

As shown in FIGS. 6 and 7B, at the operating temperature T2, the variable spring 53 has a substantially natural length La. That is, the variable spring 53 is slightly displaced xa2 from its natural length La. On the other hand, the fixed spring 54 is in a state of being compressed by a displacement xm2 from its natural length Lm. That is, the fixed spring 54 has a large displacement xm2 from its natural length Lm. As a result, the variable spring 53 generates a variable biasing force Fa2 with a relatively small displacement xa2 and a relatively large variable spring constant ka2. On the other hand, the fixed spring 54 generates a fixed biasing force Fm2 due to a relatively large displacement xm2 and a fixed spring constant km2 smaller than the variable spring constant ka2. Variable biasing force Fa2 is balanced with fixed biasing force Fm2. In this state, the flange 56 is closer to the motor shaft 101 side, so the distance from the core 41 to the motor shaft 101 is kept at a distance L2 shorter than the predetermined distance L1. That is, as the temperature rises, the distance from the core unit 40 to the motor shaft 101 decreases.

Equations (1) and (2) hold at the operating temperature. At the operating temperature T2, the variable spring constant ka2 of the variable spring 53 becomes larger than the fixed spring constant km2. As a result, according to equation (1), the fixing spring 54 contracts. At this time, the shaft body 52 and the flange 56 that are integral with each other come close to the motor shaft 101 . The core unit 40 of the displacement sensor 30 also approaches the motor shaft 101 . Generally, the magnetic properties of the core unit 40 change as the temperature rises. More specifically, inductance is reduced. The core position control unit 50 shortens the distance between the motor shaft 101 and the core unit 40 when the temperature rises. As a result, the inductance increases. That is, changes in inductance caused by temperature changes can be canceled out.

By the way, the correction target by the core position control unit 50 is the change in the inductance caused by the temperature change of the core 41 . Therefore, strictly speaking, it is desirable that the position control of the core unit 40 is based on the temperature of the core 41 . On the other hand, in this embodiment, the position control of the core unit 40 utilizes the temperature, which is based on the temperature of the variable spring 53 . That is, in the present embodiment, the temperature of the variable spring 53 is regarded as the temperature of the core 41 and the position of the core unit 40 is controlled. For example, the temperature fluctuation width of the core 41 may be considered equivalent to the temperature fluctuation width of the variable spring 53 . Therefore, without directly using the temperature change of the core 41, control can be performed to cancel out the change in inductance caused by the temperature change of the core 41. FIG.

<Effect>
A displacement sensor 30 for obtaining the position of the motor shaft 101 includes a core 41 made of a magnetic material, a coil 42 wound around the core 41, and moving the core 41 relative to the motor shaft 101 based on temperature. , and a core position control unit 50 that controls the distance from the motor shaft 101 to the core 41 .

For example, in a displacement sensor 300 of a comparative example shown in FIG. 9, a core 341 around which a coil 342 is wound is fixed to a housing 302 . That is, core 341 cannot move with respect to motor shaft 101 . In this configuration, the voltage output from the core 341 includes the influence of the inductance that occurs when the temperature of the core 341 changes, in addition to the influence of the inductance based on the distance from the core 341 to the motor shaft 101. . The influence of the inductance caused by the temperature change of the core 341 becomes a noise component.

The displacement sensor 30 obtains the amount of change in the position of the motor shaft 101 as the amount of change in the inductance generated in the core 41 . The change in inductance may include the change in inductance caused by the temperature change of the displacement sensor 30 in addition to the change in the distance from the core 41 to the motor shaft 101 . Therefore, the core position control unit 50 of the displacement sensor 30 adjusts the distance from the core unit 40 to the motor shaft 101 so as to cancel the change in inductance caused by the temperature change. Therefore, it is possible to eliminate the influence due to the temperature change from the change in the distance from the core unit 40 to the motor shaft 101 . As a result, the detection accuracy of the position of the motor shaft 101 can be improved.

That is, even if the magnetic characteristics of the displacement sensor 30 change due to temperature changes of the core unit 40 , the core position control unit 50 moves the core unit 40 so as to cancel out the change in the magnetic characteristics. As a result, the magnetic bearing 1 including the displacement sensor 30 can exhibit stable bearing functions in a wide temperature range.

The core position control unit 50 reduces the distance between the core unit 40 and the motor shaft 101 as the temperature rises, and expands the distance between the core unit 40 and the motor shaft 101 as the temperature drops. Inductance decreases as temperature increases. Therefore, the core unit 40 is moved closer to the motor shaft 101 so as to offset the decrease in inductance. On the other hand, the inductance increases as the temperature decreases. Therefore, the core unit 40 is moved away from the motor shaft 101 so as to offset the increase in inductance. Therefore, it is possible to preferably eliminate the influence of inductance fluctuations caused by temperature changes.

The core position control unit 50 generates a variable spring 53 that generates a variable biasing force Fa along the radial direction of the motor shaft 101 and a fixed biasing force Fm along the radial direction of the motor shaft 101 . and a fixed spring 54 positioned at the . The variable spring temperature coefficient indicating the relationship between the variable spring constant ka and the temperature of the variable spring 53 is different from the fixed spring temperature coefficient indicating the relationship between the fixed spring constant km and the temperature of the fixed spring 54 . According to this configuration, it is possible to provide the core unit 40 with an urging force that brings the core unit 40 closer to the motor shaft 101 when the temperature rises. Further, it is possible to provide the core unit 40 with a biasing force that moves the core unit 40 away from the motor shaft 101 when the temperature drops.

Displacement sensor 30 further includes a housing 2 arranged to surround motor shaft 101 . The variable spring 53 is arranged between the core unit 40 and the fixed spring 54 . The fixed spring 54 is arranged between the variable spring 53 and the housing 2 . According to this configuration, it is possible to generate an urging force for controlling the position of the core unit 40 according to the temperature with a simple configuration.

The variable spring temperature coefficient is less than the fixed spring temperature coefficient. According to this configuration, it is possible to provide the core unit 40 with an urging force that brings the core unit 40 closer to the motor shaft 101 when the temperature rises. In addition, it is possible to provide the core unit 40 with an urging force that moves the core unit 40 away from the motor shaft 101 when the temperature drops.

<Modification>
The present invention has been described in detail based on its embodiments. However, the present invention is not limited to the above embodiments. Various modifications are possible for the present invention without departing from the gist thereof.

In the operation of the core position control unit 50, the variable spring constant ka at room temperature should be smaller than the fixed spring constant km, and the fixed spring constant km at the operating temperature should be larger than the fixed spring constant km. Therefore, there is no particular limitation as long as the temperature characteristic of the spring constant can realize such a relationship.

For example, the first variable spring constant ka of the first spring shown in the graph G8a of FIG. 8A has a positive sign and a slope of a predetermined value. The second variable spring constant km of the second spring shown in graph G8b also has a positive sign and a slope of a predetermined value. In this case, the first variable spring temperature coefficient is greater than the second spring temperature coefficient. Even with such temperature characteristics, the first variable spring constant ka1 is smaller than the second spring constant km1 at the room temperature T1, and the first variable spring constant ka2 is smaller than the second variable spring constant km2 at the operating temperature T2. The condition of being large is satisfied.

For example, the first variable spring temperature coefficient of the first spring shown in graph G8c of FIG. 8B has a positive sign and a slope of a predetermined value. The second variable spring temperature coefficient of the second spring shown in graph G8d has a negative sign and a slope of a predetermined value. Even with such temperature characteristics, the first variable spring constant ka1 is smaller than the second spring constant km1 at the room temperature T1, and the first variable spring constant ka2 is smaller than the second variable spring constant km2 at the operating temperature T2. The condition of being large is satisfied.

1 magnetic bearing 2 housing 10 controller 11A, 11B differential amplifier 12A, 12B PID controller 13A, 13B power amplifier 20, 20A, 20B actuator 30, 30A, 30B, 30C, 30D displacement sensor (displacement sensor for bearing)
40 core unit 41 core 41b coil winding section 42 coil 43 winding section 50 core position control unit (core position control section)
51 case 52 shaft 53 variable spring (first spring)
54 fixed spring (second spring)
56 flange 100 motor 101 motor shaft 102 rotor 103 stator 104 ball bearing 200 rotary machine

Claims (5)

A bearing displacement sensor for obtaining the position of a rotating shaft,
a core made of a magnetic material;
a coil wound around the core;
A displacement sensor for bearings, comprising: a core position control section that controls a distance from the rotating shaft to the core by moving the core with respect to the rotating shaft based on temperature. The core position control unit is
reducing the distance from the core to the rotating shaft as the temperature rises;
2. The displacement sensor for a bearing according to claim 1, wherein the distance from said core to said rotating shaft is increased as said temperature decreases. The core position control unit is
a first spring that produces a first biasing force along the radial direction of the rotating shaft;
a second spring that generates a second biasing force along the radial direction of the rotating shaft and is arranged in series with the first spring;
3. The method according to claim 1, wherein a first spring temperature coefficient indicating the relationship between the spring constant and temperature of the first spring is different from a second spring temperature coefficient indicating the relationship between the spring constant and temperature of the second spring. Displacement sensor for bearings. further comprising a housing arranged to surround the rotating shaft;
The first spring is arranged between the core and the second spring,
4. The bearing displacement sensor according to claim 3, wherein the second spring is arranged between the first spring and the housing. 5. The bearing displacement sensor according to claim 3, wherein said first spring temperature coefficient is smaller than said second spring temperature coefficient.

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