JPS5819483Y2 - Rotation state detection device - Google Patents

Description

[Detailed Description of the Invention] The present invention comprises: a variable capacitance body that rotates together with a rotating body; and at least two fixed electrodes disposed close to and facing each other on the outer periphery of the variable capacitance body. Equipped with
The capacitance between the at least two fixed electrodes is changed according to the rotational state of the capacitance variable body that rotates with the rotation of the rotary body, and the capacitance is rotated according to the change in the capacitance. Regarding rotational state detection devices that obtain speed detection signals, rotational phase detection signals, etc., it is particularly applicable to motors used in devices that require speed control, or brushless motors that require armature coil current switching. It is ideal for intensive use.

Generally, in motors that need to rotate at a constant speed (for example, tape recorder capstan drive motors, VTR head drive motors, etc.), the rotation speed of the motor is detected by a rotation speed detection device, and this detection signal is , a reference frequency signal corresponding to a specified rotational speed is compared to form an error signal, and the rotational speed is controlled based on this error signal so that the motor rotates at a constant speed.

As such a rotational speed detection device, for example, a reluctance change type AC tacho generator is used.

This AC tachogenerator is composed of, for example, a disc-shaped rotor with a large number of magnetic poles formed over its entire outer circumferential surface, and an annular stator with a substantially rectangular cross section and in which an annular detection coil is housed. ing.

In a part of the magnetic path formed by the rectangular cross section, the annular stator is provided with a comb-shaped gap portion facing the outer peripheral surface of the rotor.

As the rotor rotates, the magnetic resistance of the comb-shaped gap portions is sequentially changed, so that a rotational speed detection signal of a predetermined frequency can be obtained.

Such a variable reluctance type AC tacho generator has a complicated structure and has a drawback that the frequency of the detection signal is low because there is a limit to the number of magnetic poles formed on the rotor.

Furthermore, since the comb-shaped gaps formed in the magnetic path are structurally difficult to achieve precision, the frequency of the detection signal is uneven, making it difficult to detect the true rotational speed.

For this reason, a capacitance change type rotation speed detection device has been proposed.

FIG. 1 is an axial longitudinal cross-sectional view showing the principle of a detection device based on this method.

As shown in FIG. 1, a rotating shaft 1 of a rotating body is attached with a disc-shaped rotating electrode 2 made of a conductive material and having tooth shapes formed on its outer periphery.

An annular fixed electrode 3 having substantially the same tooth profile formed on its inner circumferential surface is provided opposite to the outer circumference of the rotating electrode 2.

Therefore, as the rotating shaft 1 rotates, the tooth profile of the rotating electrode 2 sequentially faces the peaks and valleys of the tooth profile of the fixed electrode, and the capacitance between these electrodes changes.

As a result, a detection signal proportional to the rotational speed of the rotating shaft 1 can be obtained from between the rotating electrode 2 and the fixed electrode 3.

If the area of the crest of the tooth profile is Sl, the number of teeth is n, and the gap between the rotating electrode 2 and the fixed electrode 3 is g, then the rotation of the rotating shaft 1 (angular velocity ω) causes the crest of the tooth profile of the rotating electrode 2 to The difference between the capacitance when the tooth profile of the fixed electrode 3 faces the peak and the capacitance when the tooth profile of the rotating electrode 2 faces the valley of the tooth profile of the fixed electrode 3, that is, the amount of change in capacitance, (C Then, the difference between the maximum value and the minimum value of C becomes JC, and the frequency f of this capacitance change becomes.

Such a capacitance change type rotational speed detection device has a simple structure, so it is easy to achieve accuracy, and it is easy to accurately detect the rotational speed.

Furthermore, since the pitch of the tooth profile can be narrowed, the frequency of the detection signal can be increased, and therefore the servo band can be widened.

However, since the detection signal is obtained from the rotating electrode 2 and the fixed electrode 3, the signal from the rotating electrode is transmitted through the rotating shaft 1, a bearing, a motor case (not shown), or a slip specially provided on the rotating shaft 1. It must be removed via a ring and a brush (not shown).

FIG. 2 is an equivalent circuit of the rotational speed detection device shown in FIG. 1, in which a contact resistance r is formed between the bearing and the rotating shaft or the slip ring and the brush in series with the variable capacitance IC to be detected. .

Since this contact resistance r changes as the rotating shaft 1 rotates, the level of the detection signal changes and noise occurs.

Therefore, there are disadvantages in that an accurate detection signal cannot be obtained or that extra components such as slip rings and brushes are required.

In order to compensate for these drawbacks, an improved capacitance variable type rotational speed detection device has been proposed.

FIG. 3 is a vertical cross-sectional view in the axial direction showing the principle of the improved capacitance variable type rotational speed detection device.

In FIG. 3, a rotating ring 5 made of an electrically conductive material and having tooth shapes formed on its outer periphery is fitted around the outer periphery of a rotating disk 4 made of an insulator that rotates together with a rotating shaft 1 of a rotating body.

The outer circumferential surface (
First and second electrically conductive annular fixed electrodes 6.7 each having a tooth profile having substantially the same shape as the rotary ring 5 formed on their inner periphery are provided opposite to the tooth profile surface.

These fixed electrodes 6.7 are arranged one above the other with an insulating spacer 8 in between.

According to such a configuration, the capacitance C1 between the rotating ring 5 and the first fixed electrode 6 and the capacitance C2 between the rotating ring 5 and the second fixed electrode 7 are the same as that of the rotating ring 5 and the capacitance C2 between the rotating ring 5 and the second fixed electrode 7. It changes depending on the opposing state of the peaks and troughs of the respective tooth shapes with the electrodes 6 and 7.

FIG. 4 is an equivalent circuit of the detection system shown in FIG.
Detection signals proportional to the rotational speed can be obtained from the first and second fixed electrodes 6, 7, and as a result, noise generation, which is a problem with the method of extracting signals as in the method shown in FIG. 1, can be obtained. and structural complexity can be resolved.

However, according to such a configuration, the pair of fixed electrodes 6.7
must be mounted coaxially through a spacer 8 so that the tooth profile pitches of both the fixed electrodes 6 and 7 perfectly match vertically, which makes assembly complicated and increases the number of assembly steps. The problem is that it increases.

Further, since the fixed electrodes 6.7 are vertically opposed to each other with the relatively thin spacer 8 in between, a stray capacitance is generated between these electrodes 6.7.

Since the spacing between the electrodes 6 and 7 is very narrow, this stray capacitance is larger than the capacitance change (C) to be detected, which makes it more difficult to detect the rotation signal.

Therefore, for example, it is conceivable to increase the thickness of the spacer 8, but in that case, the thickness of the fixed electrodes 6 and 7 must be reduced by that amount. becomes smaller, and the amount of capacitance change JC to be detected becomes smaller.

It is also conceivable to increase the thickness of the spacer 8 without reducing the thickness of the fixed electrodes 6 and 7, but this would result in an increase in the size of the motor.

In particular, for motors of the axial air-gap type, whose main design goal is to flatten the thickness in the direction of the rotational axis, the spacer required for the component parts of the rotational speed detection device This is not preferable because the thickness in the axial direction must be increased.

This invention was made in view of the above-mentioned problems, and
A capacitance variable body that rotates together with the rotating body and has a large number of conductive uneven teeth formed on its outer periphery; a rotating state of the capacitance variable body, comprising at least one pair of fixed electrodes having a plurality of concave and convex teeth facing the concave and convex teeth of the capacitance variable body formed on a peripheral portion thereof, and rotating with the rotation of the rotary body; In the rotational state detection device in which the capacitance between the at least one pair of fixed electrodes is changed according to The present invention relates to a rotation state detection device characterized in that:

Therefore, according to the present invention, assembly is easy, and two
It becomes possible to reduce the capacitance between the two fixed electrodes.

The present invention will be explained in detail below with reference to examples.

First, the first embodiment will be explained with reference to FIGS. 5 to 9. As shown in FIGS. 5 and 6, a rotation detection device 12 is attached to the upper part of the casing 11 of the motor.

That is, the circular hole 14 provided in the center of the case 13 on the lower side of the rotation detection device 12 is connected to the outer periphery of the oil-less metal 16 that is attached to the casing 11 of the motor and rotatably supports the output shaft 15 of the motor. It is positioned in a state where it is fitted to the surface.

As will be explained in detail later, on the inner peripheral surface of the ring-shaped rib 17 integrally provided on the outer peripheral part of the lower case 13, a pair of electrodes, namely a first fixed electrode 21 and a second fixed electrode 21, are provided. A fixed electrode 22 is fitted.

A rotating electrode 20 is disposed inside these fixed electrodes 21 and 22, and is fixed to the output shaft 15 with screws 19.

This rotating electrode 20 is constructed by fitting a conductor 20 on which a tooth profile 18 is formed onto the outer periphery of an insulating disc 23 .

An upper case 24 is attached above the rotating electrode 20 and fixed electrodes 21 and 22.

A ring-shaped rib 25 formed on the outer periphery of the case 24 is fitted and positioned on the outer periphery of the pair of fixed electrodes 21 and 22.

The case 24, the pair of fixed electrodes 21 and 22, and the lower case 13 are attached to the motor casing 11 by screws 26 passing through them.

The output shaft 15 passes through a circular hole 27 formed in the center of the upper case 24, and the rotation detection device 1
It protrudes above 2.

Next, the fixed electrodes 21.22 will be described in particular with reference to FIGS. 6 and 7. Each of the fixed electrodes 21.22 is composed of a segment having an arc shape of about 170°, and is connected to the rotating output shaft 15. are arranged symmetrically with respect to

Each of these fixed electrodes 21 and 22 has teeth 28 and 29 formed on its inner peripheral surface like an internal gear.

These tooth profiles 28 and 29 are formed so that their peaks and valleys exactly match the peaks and valleys of the tooth profile 18 of the rotating electrode 20.

Furthermore, these fixed electrodes 21 and 22 are made of an electrically conductive material, so that the gap between the peaks of the tooth profile 28 of the first fixed electrode 21 and the peak of the tooth profile 18 of the rotating electrode 20 and the second fixed electrode Containers C1 and C2 (see FIG. 8) are formed between the peaks of the tooth profile 29 of the rotary electrode 22 and the peak of the tooth profile 18 of the rotating electrode 20, respectively.

In order to prevent these fixed electrodes 21.22 from being electrically connected to each other, the case 13.24 of the rotation detection device 12 is made of an insulating material, and the insertion hole for the screw 26 of the fixed electrode 21.22 is made of an insulating material. A bushing made of solid material is press-fitted.

In this way, since the fixed electrodes 21, 22 are composed of a pair of segments, assembly is facilitated.

Furthermore, since these electrodes 21 and 22 are disposed along the outer peripheral surface of the rotating electrode 20 symmetrically with respect to the output shaft 15 and on the same plane, the output shaft 15 of the rotation detection device 12 is The thickness in the axial direction can be made thinner.

Further, these electrodes 21 and 22 are mutually connected to the end surface 30 in the circumferential direction.
They only face each other at the edges, and the area in which they face each other becomes very small.

Therefore, the stray capacitance between these two medium electrodes 21 and 22 can be made very small, and an accurate rotational speed detection signal can be obtained in response to changes in rotation.

As described above, a pair of capacitors C□ are constituted by a rotating electrode 20 and a pair of fixed electrodes 21 and 22.

C2 can be represented by the equivalent circuit shown in FIG. 8, and signals corresponding to the rotational speed can be taken out from terminals 21 and 22.

Next, an example of a motor speed servo system using this rotation detection device 12 will be explained with reference to the block diagram shown in FIG.

Note that the pair of capacitors described above is shown as a single capacitor 31 in this block diagram.

Changes in the capacitance value of the capacitor 31 as the motor rotates are converted into electrical signals by a capacitance change detector 32.

Such a capacitance change detector 32 converts a carrier wave current of a predetermined frequency from a carrier wave oscillator 33 into a capacitor 31, for example.
It may be an AM modulator that converts the change in capacitance (that is, the change in impedance) of the capacitor 31 into a voltage to obtain a detection signal.

That is, the capacitance change detector 32 obtains a rotation speed detection signal obtained by AM modulating the carrier wave of the carrier wave oscillator 33.

This speed detection signal is supplied to an AM demodulator 34.

The AM demodulator 34 may be composed of, for example, a rectifier circuit and a low-pass filter, and the AM demodulator 34 is a signal obtained by removing a carrier component from an AM-modulated rotational speed detection signal.
obtained from the demodulator.

This signal is a frequency signal that corresponds to the capacitance change of the capacitor 31 and is proportional to the rotation speed.

This signal is then fed to a frequency-to-voltage converter 35,
Here, variations in rotational speed, ie, frequency variations, are converted into voltage.

Such a frequency-voltage converter 35 is configured to, for example, form a triangular wave signal with a predetermined slope from the frequency signal, sample the slope portion of this triangular wave with a predetermined reference sampling pulse, and perform frequency-voltage conversion. It may be configured.

The output voltage of the frequency-voltage converter 35 is compared with a reference voltage supplied from a reference voltage generation circuit 37 in a comparator circuit 36, and an error signal obtained by the comparator circuit 36 is supplied to a rotation control circuit 38.

Therefore, the motor 39 is controlled by the control circuit 38 so that its rotational speed is constant.

Next, a second embodiment of the present invention will be described with reference to FIGS. 10 and 11.

In the first embodiment, the first fixed electrode 21 and the second fixed electrode 22 are formed by a pair of segments cut from a conductive material and arranged symmetrically with respect to the output shaft 15. However, in this embodiment, these two electrodes 2
1.22 are integrally constructed.

That is, as shown in FIG. 10, synthetic resins such as AB
A tooth profile 41 is formed like an internal gear on the inner peripheral surface of a ring-shaped body 40 made of S resin.

Next, this ring-shaped body 40 is coated with, for example, Zn/Co so that a plating layer is formed on the entire surface of the ring-shaped body 40.
A conductive layer having a thickness of, for example, 5 to 8 μm is formed on the entire outer surface of the ring-shaped body 40 by electroless plating.

Next, as shown in FIG. 11, a pair of grooves 42 are formed at two approximately symmetrical locations in the circumferential direction of this ring-shaped body 40, and the conductive layer formed by plating is spread around the circle of this ring-shaped body 40. Divide into two in the circumferential direction.

As a result, a pair of fixed electrodes 21 and 22 are formed symmetrically on the surface of the ring-shaped body 40.

By configuring the pair of fixed electrodes 21, 22 in this manner, since both electrodes are made from one component, assembly becomes easier, and mutual alignment between the electrodes 21, 22 becomes unnecessary.

Furthermore, since both electrodes 21 and 22 are separated from the thin conductive layer formed on the ring-shaped body 40, the areas of the mutually opposing end surfaces 30 of both electrodes 21 and 22 are extremely small. The stray capacitance between them also becomes very small.

In this embodiment, a conductive layer is formed by plating on the ring-shaped body 40 on which the tooth profile 41 is formed, but the entire surface of the ring-shaped body on which the tooth profile 41 is not formed is first coated with a conductive layer. A layer may be formed and then a pair of grooves and teeth may be formed in the ring-shaped body.

In this way, since no conductive layer is formed in the valley portions of the tooth profile, a clearer rotational speed detection signal can be obtained.

Next, a third embodiment of the present invention will be described with reference to FIG.

In the above two embodiments, the pair of first electrode 21 and second electrode
The electrode 22 is fixedly arranged on the outer periphery of the rotating electrode 20. According to such a configuration, one rotation of the rotating electrode 20 is caused by the eccentricity of the pair of first and second electrodes 21 and 22 and the rotating electrode 20. This causes fluctuations or fluctuations in the capacitance change every time, and this is superimposed on the rotational speed detection signal.

In order to reduce such fluctuations, a plurality of pairs of the first electrode 21 and the second electrode 22 may be used.

In this embodiment, the rotating electrode 20 is
Two sets of first electrodes 21 and second electrodes 22 are alternately arranged on the outer periphery of the electrode.

Note that instead of the two pairs of first electrodes 21 and second electrodes 22, three or more pairs of first electrodes 21 and second electrodes 22 may be used.

Next, a fourth embodiment of the present invention will be described with reference to FIGS. 13 to 15.

In the third embodiment, in order to prevent fluctuations in the rotation speed detection signal due to eccentricity between the fixed electrode and the rotating electrode, two
Pairs of fixed electrodes are used, and in this embodiment, these two pairs of fixed electrodes are formed on the ring-shaped body 40 using a conductive layer.

That is, first, the ring-shaped body 40 on which the gear 41 is formed
is plated to form a conductive layer on the entire outer peripheral surface of the ring-shaped body 40.

Next, on the inner peripheral surface of the ring-shaped body 40, 4
Two grooves 43 are formed, and these grooves 43 are connected by grooves 44 formed in the upper and lower end surfaces of the ring-shaped body 40 at approximately every 90° in the circumferential direction.

Further, grooves 45 are formed on the ring-shaped body 40 and its outer circumferential surface so as to overlap each other around the entire circumference at approximately the center in the width direction thereof.

As a result, two pairs of first electrodes 21 and second electrodes 22 are formed on the ring-shaped body 40 in a state where they are separated from each other, and the two pairs of first electrodes 21 and second electrodes 22 facing each other are Each is connected to each other by a conductive layer.

Therefore, in this embodiment, there is no need to connect the two first electrodes 21 and the two second electrodes 22 with respective lead wires.

Furthermore, since the two pairs of fixed electrodes are formed on the ring-shaped body 40, there is no need to align the two pairs of first electrodes 21 and second electrodes 22 with each other.

Although the present invention has been described above with reference to embodiments, the above-mentioned embodiments are not intended to limit the present invention, and the present invention can be modified in various ways within the scope of its technical idea.

For example, in the above embodiments, one or two pairs of fixed electrodes are used, but the present invention is not limited to this, and it is also possible to use three or more pairs of fixed electrodes.

Furthermore, in the second and fourth embodiments, the ring-shaped body 40 is plated to form the conductive layer, but the formation of the conductive layer on the ring-shaped body 40 is not necessarily limited to plating. Other methods may be used, such as vapor deposition, and instead of forming grooves to separate the deposited conductive layer, the conductive layer may be etched.

As described above, in the present invention, at least one pair of fixed electrodes is arranged facing each other in the diametrical direction of the variable capacitance body that rotates integrally with the fixed body. The thickness of the rotor in the axial direction can be reduced, and mutual alignment of the two fixed electrode pairs in the axial direction of the rotating body is no longer necessary.

Furthermore, the areas where the two pairs of fixed electrodes face each other become extremely small, and the floating electrodes between them can be made small.

[Brief explanation of drawings]

1 to 4 show conventional rotation detection devices, FIG.
The figure is an equivalent circuit diagram, FIG. 3 is a vertical cross-sectional view of an improved capacitance variation type rotation speed detection device, and FIG. 4 is an equivalent circuit diagram. 5 to 9 show a rotation detecting device according to a first embodiment of the present invention, FIGS. 8 is a perspective view of the same essential parts, FIG. 8 is an equivalent circuit diagram of this rotation detection device, and FIG. 9 is a block diagram of a motor speed servo system. 10 and 11 show a second embodiment of the present invention, and FIG. 10 shows the ring-shaped body 4 before forming the groove 42.
0 and 11 are ring-shaped bodies 4 with grooves 42 formed therein.
FIG. FIG. 12 is a plan view of main parts of a third embodiment of the present invention. 13 to 15 show a fourth embodiment of the present invention, in which FIG. 13 is a perspective view of a ring-shaped body 40, FIG. 14 is a sectional view taken along the line W-■ in FIG. 13, and FIG. 14 is a sectional view taken along the line XV-XV in FIG. 13. FIG. In the reference numerals used in the drawings, 15 is an output shaft, 20 is a rotating electrode, 21 is a first fixed electrode, and 22 is a second fixed electrode.

Claims (1)

[Scope of utility model registration request] A capacitance variable body that rotates together with the rotating body and has a large number of conductive uneven teeth formed on its outer periphery; a rotating state of the capacitance variable body, comprising at least one pair of fixed electrodes having a plurality of concave and convex teeth facing the concave and convex teeth of the capacitance variable body formed on a peripheral portion thereof, and rotating with the rotation of the rotary body; In the rotational state detection device in which the capacitance between the at least one pair of fixed electrodes is changed according to A rotation state detection device characterized by: