JPH06147812A - Position detector for rotary body - Google Patents

Abstract

(57) [Abstract] [Purpose] In detecting the position of a rotating body based on a change in electrostatic capacitance, the influence of noise is greatly reduced and position detection accuracy is improved. [Structure] A high-frequency voltage having a frequency sufficiently higher than that of a noise source is obtained by a high-frequency oscillation source 1, and the high-frequency voltage is applied to a variable capacitor 4 via a coaxial cable 3 so that the coaxial cable 3 has a high-frequency oscillation source side end portion The standing wave voltage is detected by the wave detector 6 to obtain a position detection signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rotor position detecting device, and more particularly to a rotor position detecting device suitable for a magnetic bearing mechanism that magnetically supports a rotor in a non-contact manner.

[0002]

2. Description of the Related Art Magnetic bearings have been conventionally used as bearings for ultra-high speed motors and the like. In this magnetic bearing, for example, at least one pair, preferably two pairs of electromagnets are arranged at a target position with a rotating shaft made of a magnetic material sandwiched therebetween, and each pair of electromagnets is excited to generate an attractive force. If the electromagnets of each pair are alternately excited, the excitation cycle is shortened to equivalently obtain a state in which the electromagnets of each pair simultaneously exert an attractive force on the rotating body. Can be firmly supported. Further, in the case of exciting each pair of electromagnets with direct current, it is possible to generate an attractive force in a desired direction by changing the level of direct current to be excited.

Even when the rotating body is held by the magnetic bearing, the position of the rotating body may be displaced for some reason. In this case, the direction of displacement of the rotating body and The position shift can be eliminated by controlling the electromagnets so that the attraction force of one of the electromagnets of each pair becomes larger than the vibration attraction force of the other in accordance with the amount. Further, as is clear from the above description, in order to control the electromagnet, it is essential to detect the position of the rotating body. Therefore, even in the conventional magnetic bearing, a device for detecting the position of the rotating body has been added. Since such a position detecting device is required to detect the position of the rotating body in a non-contact manner, does a sensor using a coil like an eddy current sensor be used (see Japanese Patent Laid-Open No. 63-214519). ) Or using a sensor using a capacitor (see Japanese Patent Application Laid-Open No. 2-201101). However, if the former sensor is adopted, the magnetic field is likely to be affected by the magnetic flux leaked from the motor, so that the position detection accuracy inevitably decreases, or a magnetic shield or the like is required to suppress the decrease in position detection accuracy. Therefore, there is an inconvenience that the structure becomes complicated and the size becomes large. On the other hand, the latter sensor is essentially unaffected by the magnetic flux, so that the above-mentioned inconvenience of the former sensor can be eliminated.

[0004]

However, in a sensor using a capacitor, a DC voltage is applied to the capacitor, and an impedance change caused by a position change of the rotating body is based on the divided voltage of the DC voltage. Since the electrodes constituting the capacitor cannot be made too large, the signal cable or the like connecting the capacitor and the detection circuit section is easily affected by noise.

As a result, although the capacitor itself is hardly affected by noise, the accuracy of the position detection signal obtained is deteriorated because the signal cable receives noise.

[0006]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and in detecting the position of the rotating body based on the impedance change of the capacitor, the position of the rotating body capable of sufficiently eliminating the influence of noise. The purpose is to provide a detection device.

[0007]

In order to achieve the above object, a position detecting device for a rotating body according to a first aspect of the present invention includes a capacitor whose impedance changes according to the displacement of the rotating body,
It includes a high frequency oscillation source and a coaxial cable connected between the high frequency oscillation source and the capacitor. According to another aspect of the present invention, in the position detecting device for a rotating body, the length of the coaxial cable is increased in order to increase the rate of change of the standing wave voltage level at the end of the coaxial cable on the high frequency oscillation source side with respect to the change in the distance between the rotating body and the electrode. Is set.

According to a third aspect of the present invention, there is provided a position detecting device for a rotating body, which has two capacitors and coaxial cables respectively connected to the capacitors with the conductive rotating body as a reference. A voltage is applied. The position detecting device for a rotating body according to claim 4 is
It further includes a difference output means for obtaining a difference between the standing wave signals at the ends of both coaxial cables on the high frequency oscillation source side.

[0009]

According to the position detecting device of the rotating body of the present invention, a high frequency voltage is applied to the capacitor whose impedance changes in accordance with the displacement of the rotating body from the high frequency oscillation source through the coaxial cable. Therefore, a standing wave voltage is generated in the coaxial cable. Here, the standing wave voltage changes depending on whether the end of the coaxial cable is short-circuited, open, or an intermediate state between these, and the capacitor connected to the end of the coaxial cable is the position of the rotating body. Since the impedance changes in accordance with the change, it is possible to easily detect the impedance of the capacitor, and thus the relative position of the rotating body, based on the standing wave voltage at a predetermined position of the coaxial cable. In addition, the coaxial cable itself is less susceptible to noise, and by setting the frequency of the applied voltage sufficiently high, it can be less affected by low frequency noise, and the impedance of the coaxial cable is stable regardless of the placement position, etc. The degree of freedom in arranging the coaxial cable and the like can be increased, and stable position detection can be achieved.

According to the position detecting device of the rotating body of the second aspect, the rate of change of the standing wave voltage level at the end of the coaxial cable on the high frequency oscillation source side with respect to the change in the distance between the rotating body and the electrode is increased. Since the length of the coaxial cable is set accordingly, a sufficiently large change in the standing wave voltage level can be detected even by a minute displacement of the rotating body, which in turn greatly reduces the position detection accuracy due to measurement errors. Can be suppressed.

According to a third aspect of the present invention, there is provided a rotary body position detecting device, which has a plurality of capacitors and coaxial cables respectively connected to the respective capacitors with the conductive rotary body as a reference. Since the high frequency voltage is applied to the capacitors, the configuration of the position detection device as a whole can be simplified as compared with the case where a high frequency oscillation source is provided for each capacitor. Further, the frequencies of the voltages applied to all the capacitors can be completely matched.

According to another aspect of the present invention, in the position detecting device for a rotating body, at least one pair of capacitors is arranged at a target position with the conductive rotating body as a reference, and both coaxials connected to the capacitors of each pair. Since it further includes a difference output means for obtaining the difference between the standing wave signals at the end portion of the high frequency oscillation source side of the cable, the standing wave voltage level at the predetermined position of each coaxial cable is relative to the displacement of the rotating body. Despite not having very high linearity, it is possible to obtain a difference that has high linearity with respect to the displacement of the rotating body, and due to the high linearity, it is possible to control the electromagnet of the magnetic bearing. Can be simplified.

[0013]

Embodiments will be described in detail below with reference to the accompanying drawings showing embodiments. FIG. 1 is an electric circuit diagram showing an embodiment of a position detecting device for a rotating body of the present invention. A high frequency voltage from a high frequency oscillator 1 is connected in series with a matching circuit 2 composed of resistors and a coaxial cable 3 of a predetermined length. It is applied to the variable capacitor 4 via the. Then, the voltage at the connection point between the matching circuit 2 and the coaxial cable 3 is taken out through the matching circuit 5 and supplied to the detector 6 to obtain a position detection signal. The variable capacitor 4 is
One of the electrodes facing each other is composed of a rotating body, and the other electrode is arranged so as to be close to the rotating body. Therefore, the capacity changes due to the displacement of the position of the rotating body. The oscillation frequency of the high frequency oscillator 1 is
The frequency is set to a sufficiently high frequency so that the impedance can be made sufficiently small even if the capacitance of the variable capacitor 4 is extremely small.

The operation of the position detecting device having the above structure is as follows. A coaxial cable 3 having a variable capacitor 4 as a load connected to the end through a matching circuit 2.
When a high frequency voltage is applied to the coaxial cable 3, a standing wave voltage is generated in the coaxial cable 3. Then, when the capacitance of the variable capacitor 4 changes due to the positional displacement of the rotating body, the phase of the standing wave voltage changes within a quarter wavelength range. Therefore, if the extraction position of the standing wave voltage is determined in advance, the value of the extracted standing wave voltage changes according to the phase change. By extracting the value of this standing wave voltage through the matching circuit 5 and detecting it by the wave detector 6, the impedance of the variable capacitor 4, that is, the position detection signal indicating the relative position of the rotating body can be obtained.

Although the length of the coaxial cable 3 can be freely set, the variable capacitor 4 can be set based on the upper and lower limits of the positional displacement limit amount of the rotating body which is allowed in the magnetic bearing and the like. Since the variable capacity range is predetermined, the rotation by the coaxial cable 3 (rotation on the Smith chart) should be performed so that the value of the standing wave voltage changes the most corresponding to the variable capacity range. The detection sensitivity can be improved by changing the length of the cable 3.

[0016]

[Embodiment 2] FIG. 2 is an electric circuit diagram showing another embodiment of the position detecting device of the present invention, which has two matching circuits 2 and 5, a coaxial cable 3, a variable capacitor 4 and a detector 6. And one high-frequency oscillator 1
The high-frequency voltage output from the respective circuits is supplied to each of the above series via the buffer circuit 7. The configuration of each of the above series is the same as that of the above-mentioned embodiment, and the description thereof will be omitted. However, both of the variable capacitors 4 have the rotating body as one electrode, and the other electrode is arranged at a 180 ° rotation target position with respect to the rotating body.

Therefore, in the case of this embodiment, the high-frequency oscillator 1 can be shared even though the position detection circuits of two systems are provided, and the structure can be simplified. In addition, when it is detected that the distance to the rotating body has increased in one system, it is detected that the distance to the rotating body has decreased in the other system. By detecting the position of the rotating body by using the above-mentioned method, it is possible to suppress a decrease in accuracy due to an error or the like and achieve highly accurate position detection.

[0018]

[Embodiment 3] FIG. 3 is an electric circuit diagram showing still another embodiment of the position detecting apparatus of the present invention. The difference from the embodiment of FIG. 2 is that the detector 6 of one system and the detector 6 of the other system are different. Detector 6
And 8 are set to perform detection of opposite phases to each other, and an addition circuit 8 for adding output signals from both detectors 6
It is only the point that is provided.

Therefore, in the case of this embodiment, the difference between the standing wave voltages of both systems is obtained and output.
The linearity of the output signal of the adder circuit 8 with respect to the positional displacement of the rotating body can be remarkably improved, and post-processing such as control of the electromagnet can be simplified. More specifically, FIG. 4 (A1) (B
When the capacitances of both variable capacitors 4 are equal at the standing wave voltage level shown in 1), that is, when the rotating body is located at the center of both electrodes, broken line arrows in FIGS. 4A1 and 4B1. Since the standing wave voltage of the same phase is taken out as shown by, the addition of both results in 0. Further, when the rotating body is displaced from the center of both electrodes, the impedances of both variable capacitors 4 are different from each other, so that the phase of the standing wave voltage to be extracted is as shown in FIG. 4 (A1) (B1). They will shift in opposite directions based on the state {Fig. 4
(See (A2) and (B2)}. Therefore, by adding both, even if the standing wave voltage is significantly different from the straight line, the addition result can be in a state of extremely high linearity.

[0020]

As described above, according to the first aspect of the present invention, the impedance of the capacitor and the relative position of the rotating body can be easily detected based on the standing wave voltage at the predetermined position of the coaxial cable. In addition, the coaxial cable itself is less susceptible to noise, and by setting the frequency of the applied voltage sufficiently high, it is less susceptible to low frequency noise, and the impedance of the coaxial cable is stable regardless of the placement position. Therefore, it is possible to increase the degree of freedom in arranging the coaxial cable and the like, and to achieve a unique effect that stable position detection can be achieved.

According to the invention of claim 2, in addition to the effect of claim 1, a sufficiently large change in the standing wave voltage level can be detected even by a minute displacement of the rotating body, and thus the position detection accuracy resulting from a measurement error or the like. It is possible to significantly suppress the decrease of In addition to the effect of claim 1 or claim 2, the invention of claim 3 can simplify the configuration of the position detecting device as a whole as compared with the case where a high-frequency oscillation source is provided for each capacitor, and can be applied to both capacitors. There is a unique effect that the frequencies of the voltages to be applied can be perfectly matched.

According to the invention of claim 4, in addition to the effect of claim 3, the standing wave voltage level at a predetermined position of each coaxial cable does not have a very high linearity with respect to the displacement of the rotating body. Regardless, it is possible to obtain a difference having a high linearity with respect to the displacement of the rotating body, and due to the high linearity, it is possible to simplify the control and the like of the electromagnet of the magnetic bearing.

[Brief description of drawings]

FIG. 1 is an electric circuit diagram showing an embodiment of a position detecting device for a rotating body of the present invention.

FIG. 2 is an electric circuit diagram showing another embodiment of the position detecting device of the present invention.

FIG. 3 is an electric circuit diagram showing still another embodiment of the position detecting device of the present invention.

FIG. 4 is a diagram schematically showing improvement in linearity.

[Explanation of symbols]

 1 High Frequency Oscillation Source 3 Coaxial Cable 4 Variable Capacitor 6 Detector 8 Adder Circuit 91 Rotating Body 93 Electrode

Claims (4)

[Claims] 1. A capacitor (4) whose impedance changes according to the displacement of a rotating body (91), a high frequency oscillation source (1), and a connection between the high frequency oscillation source (1) and the capacitor (4). Position detecting device for a rotating body, comprising: the coaxial cable (3). 2. The rate of change of the standing wave voltage level at the end of the coaxial cable (3) on the high frequency oscillation source (1) side with respect to changes in the distance between the rotating body (91) and the electrode (93) is increased. The position detecting device for a rotating body according to claim 1, wherein the length of the coaxial cable (3) is set accordingly. 3. A high frequency oscillation source (1) having a plurality of capacitors (4) with a conductive rotating body (91) as a reference and coaxial cables (3) respectively connected to the capacitors (4). The position detecting device for a rotating body according to claim 1 or 2, wherein a high frequency voltage is applied to all the capacitors (4). 4. At least one pair of capacitors (4) is arranged at a target position on the basis of the conductive rotating body (91), and both coaxial cables (3) are respectively connected to the capacitors (4) of each pair. Difference output means (6) for obtaining the difference between the standing wave signals at the end on the high frequency oscillation source (1) side of FIG.
The position detecting device for a rotating body according to claim 3, further comprising (8).