JPH0354285B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a capacitance type displacement detector, and particularly to a capacitive displacement detector that detects the displacement of a moving body by using both a moving electrode that moves with the moving body and a fixed electrode that is fixed to the main body. The present invention relates to a capacitive displacement detector that detects based on changes in capacitance between electrodes.

BACKGROUND ART Displacement detectors that electrically convert the mechanical displacement of a probe or the displacement of a moving base to detect the amount of displacement have been well known, and this type of device is usually movably installed in the main body of the device. a moving object, and an encoder that detects the amount of movement of the moving object, converts it into electrical signal pulses, and counts the electrical signal pulses output by the encoder in a counting circuit, and displays the counted value on a digital display. Digitally displayed above.

Incidentally, photoelectric encoders, contact encoders, electrostatic encoders, and the like are conventionally known as encoders used in this type of apparatus.

A photoelectric encoder includes slits provided at equal intervals on the surface of a scale or a rotating disk, and a light emitter and a light receiver that form an optical path through the slits in the scale or rotating disk. The scale or disk is moved or rotated according to the amount of displacement to turn on and off the optical path formed between the light emitters,
The amount of displacement of a moving object is detected.

However, this photoelectric encoder has disadvantages in that the power consumption of the light emitter is large, the number of replacements of batteries increases, and when a large capacity battery is used, the entire device becomes large. Furthermore, in order to improve measurement accuracy, it is necessary to provide slits at intervals of several microns on a scale or rotating disk, which is difficult to manufacture and also causes problems such as miscounts due to clearance changes during operation. It was hot.

Furthermore, since contact type encoders use slits, brushes, etc. to detect the amount of displacement of a moving object, there are problems in that these slits and brushes are subject to rapid wear and noise is likely to be mixed into the measurement signal.

On the other hand, electrostatic encoders do not consume as much power as photoelectric encoders, and do not have the problems of wear of brushes, slits, etc. and noise contamination like contact encoders. Widely used in equipment.

Conventional technology Conventionally, in an electrostatic encoder used in such a displacement detector, a capacitor is formed by arranging multiple pairs of electrode plates facing each other, and both electrode plates are moved relative to each other in accordance with the amount of displacement of a moving object. The amount of mechanical displacement at this time was electrically detected as a change in capacitance of the capacitor.

For example, one electrode plate is arranged on the main scale at regular intervals, and the other electrode plate is arranged on the index which is placed facing the main scale at a certain interval. is slid parallel to the plate surface according to the displacement of the moving body, and at this time, the amount of displacement of the moving body is detected by the change in capacitance of the capacitor formed by both electrode plates.

However, in the electrostatic encoder in the conventional device, a voltage dividing circuit is formed using a capacitor made of the moving electrode plate, and the displacement amount of the moving object is detected by detecting the voltage dividing ratio that changes according to the capacitance of the capacitor. was detected. For this reason, in conventional devices, when the capacitance of the capacitor changes due to a change in the distance between the surfaces of the movable electrode plates forming the capacitor for some reason, or when the power supply voltage applied to the voltage divider circuit changes, In some cases, the partial pressure output no longer corresponds accurately to the amount of displacement of the moving body, resulting in a drawback that accurate measurement cannot be performed.

Establishment process of the present invention In order to eliminate the above-mentioned conventional drawbacks, AC voltages of different phases are applied to one electrode of the plurality of electrode pairs, and a voltage signal induced in the other electrode is detected, A capacitive displacement detector has been proposed that determines the amount of relative movement by detecting a phase change with respect to a reference phase of an output signal that changes based on the relative movement of both electrodes.

FIG. 1 is a sectional view showing the electrode structure of this capacitance type displacement detector, FIG. 2 is a developed view showing the electrode structure of this capacitance type displacement detector, and FIG.
The figure is an explanatory diagram showing the wiring state of a connection pattern for applying an alternating current signal to the transmitting electrode, and FIG. 4 is a sectional view of FIG. 3.

As shown in FIG. 1, there is a fixed plate 10 made of a stator or scale plate fixed to the main body of the device, and a movable plate 16 that is movable at a predetermined distance from the fixed plate 10 is arranged opposite to the fixed plate 10. has been done. As shown in FIG. 2, on the surface of the fixed plate 10, a plurality of transmitting electrodes 12 are arranged at equal intervals along the moving direction of the movable plate 16. Band-shaped receiving electrodes 14 are arranged on the front side of the fixed plate 10 along a direction parallel to the alignment direction at regular intervals.

On the other hand, the movable plate 16 disposed opposite to the fixed plate 10 is provided on a rotor or a movable scale plate that moves in conjunction with the movable body. This moving plate 16 is
Coupling electrodes 18 and ground electrodes 20, which are disposed facing each other across the transmitting electrode 12 and the receiving electrode 14, and which capacitively couple the two, are alternately arranged at regular intervals.

Further, as shown in FIGS. 3 and 4, on the back side of the fixed plate 10, there is provided a wiring pattern 22 consisting of a plurality of electrical circuits that apply alternating current signals of different phases to each transmitting electrode 12. It is being AC signals having different phases are supplied from this wiring pattern 22 to the transmitting electrodes 12 through leads 24 passing through the fixed plate 10.

Further, as shown in FIG. 4, each of the transmitting electrodes 1
The alternating current signal from 2 is induced by the coupling electrode 18 into the receiving electrode 14 by capacitive coupling. Therefore, as described above, when the movable plate 16 is displaced in the moving direction with alternating current signals having different phases applied to each of the transmitting electrodes 12, an output corresponding to the amount of displacement of the movable plate 16 is generated from the receiving electrode 14. I get a signal. This output signal is counted by an integrator 15 shown in FIG. 1, and further compared with a predetermined reference phase, making it possible to accurately measure the amount of displacement of the moving body.

That is, as shown in FIG.
The signal is then sent to a capacitor composed of a coupling electrode 18 and a receiving electrode 14. In this case, the signal detected by the receiving electrode 12 is S, and the phase is Φ _j ,
If the capacitance value of the capacitor composed of the transmitting electrode 12 and the coupling electrode 18 is C _j and the angular frequency of the alternating current signal is ω, then the detection signal S can be expressed by the following equation.

S= ₄ 〓 ^j=1 C _j cos (ωt + Φ _j ) Note that the capacitance of the capacitor composed of the coupling electrode 18 and the receiving electrode 14 does not change even when the moving plate 16 moves, so the above formula is is not expressed.

As understood from the above equation, the moving plate 1
Since the capacitance value C _j of the capacitor changes according to the amount of displacement of the capacitor 6, the detection signal S also changes accordingly. Therefore, by obtaining this detection signal S, the amount of displacement of the moving plate 16 can be obtained.

To give a specific example, if the moving plate 16 shown in FIG. 5 moves the distance (this is called the array period length) to the transmitting electrodes 12-1 to 12-5,
As a result, the phase of the signal S changes by 360 degrees.

Note that if the amount of displacement of the moving plate 14 exceeds the arrangement period length of the transmitting electrodes 12, the amount of displacement cannot be specified, so the period of the signal S is counted by an integrator 15.

In recent years, in order to improve the portability and operability of devices,
There is a demand for miniaturization of devices, and when the proposed device described above is miniaturized, the electrode area of each electrode becomes smaller, and the distance between the electrodes becomes narrower. For this reason, the signal output voltage of the receiving electrode 14 decreases, and a phenomenon in which the SN ratio decreases due to so-called noise mixture occurs. Due to the narrow distance between the electrodes, the particles enter the receiving electrode 14 from the input part of the transmitting electrode 12 without passing through the coupling electrode 18, which causes a problem in that the detection accuracy of the device deteriorates.

In particular, as the distance between the electrodes becomes shorter due to miniaturization of the device, there is a problem in that noise that goes around the surface of the fixed plate 10 and mixes into other electrodes increases.

Purpose of the Invention The present invention has been made in view of the conventional problems described above, and its purpose is to provide a capacitive displacement device that can miniaturize the device and accurately detect the amount of displacement of a moving body. The purpose is to provide a detector.

Structure of the Invention In order to achieve the above object, the present invention includes a fixed plate, a movable plate disposed opposite to the fixed plate and movable in a predetermined direction, and a movable plate arranged on the surface of the fixed plate along the moving direction of the movable plate. A plurality of arranged transmitting electrodes, a receiving electrode arranged on the front side of the fixed plate at regular intervals from the transmitting electrodes, and a receiving electrode arranged on the movable plate and electrostatically coupled to both the transmitting electrodes and the receiving electrode. In a capacitive displacement detector including a coupling electrode,
A wiring pattern including at least a pair of electrical paths arranged on the back side of the fixed plate along the alignment direction of the transmitting electrodes and supplying alternating current signals of mutually opposite phases to predetermined transmitting electrodes, and of the pair of electrical paths, The present invention is characterized in that it includes an auxiliary electrode that is provided on the back side of the transmitting electrode connected to the electric circuit with the longer loop noise path through the fixed plate and is electrically connected to the receiving electrode.

Embodiments Hereinafter, preferred embodiments of the present invention will be described based on the drawings.

As mentioned above, FIG. 3 shows a plurality of transmitting electrodes 12 and receiving electrodes 14 arranged on the surface side of the fixed plate 10.
The arrangement relationship with is shown. Here, on the back side of the fixing plate there is a wiring pattern 22 which will be described in detail later.
is installed. This wiring pattern 22 applies a predetermined voltage signal to each transmitting electrode 12.

Further, FIG. 4 shows a cross section of the configuration shown in FIG. 3, and this FIG.
Noise that enters the receiving electrode 14 from the electrical circuit 2 is schematically shown.

Further, FIG. 5 shows a top view of the fixing plate 10.

As shown in FIG. 5, alternating current voltages having mutually different phases are applied to each transmitting electrode 12 in a predetermined order.

Here, the wiring pattern 22 includes two pairs of electric paths having mutually different phases, and AC signals having a phase difference of 180 degrees are sent to the electric paths in each pair. As a result, as shown in FIGS. 1 and 2, when the movable plate 16 moves relatively, the coupling electrode 18 and the
The phase of the AC voltage signal generated in the capacitor constituted by the two transmitting electrodes 12 changes. That is, this is because the contribution from each transmitting electrode 12 that is in an electrostatic coupling relationship with one coupling electrode 18 changes as the movable plate 16 moves.

To explain specifically about the phase of the AC voltage signal supplied to each transmitting electrode 12, the four phases are 0 degrees, 90 degrees, 180 degrees, and 270 degrees.
Two pairs of phase difference pairs having an opposite phase relationship of 180 degrees, 90 degrees, and 270 degrees are constructed. For example, in the case of 8 phases, 0 degrees and 180 degrees, 45 degrees and 225 degrees, 90 degrees and 270 degrees,
Four pairs of phase difference pairs having an opposite phase relationship of 135 degrees and 315 degrees are constructed. A more specific wiring structure will be described below using FIG. 5.

In FIG. 5 of this embodiment, a wiring pattern 22 is provided on the back surface of the fixed plate 10 corresponding to each transmitting electrode 12 to supply a common phase voltage to each common phase electrode of each of the transmitting electrodes 12-1 to 12-8. is formed, and this wiring pattern and each transmitting electrode 12-1~
12-8 is electrically connected by a lead 24. In the device shown in FIG. 5, each transmitting electrode 12
-1 to 12-8 sequentially 0 degrees, 90 degrees, 180 degrees, 270
Voltages with different phases of 180 degrees are applied to the transmitting electrode 12-5, where a signal with a phase of 0 degrees is input, and a signal with an opposite phase, that is, 180 degrees, is applied to the transmitting electrode 12-5.
Transmitting electrode 12-7 to which a voltage signal with a degree deviation is applied
A pair of phase difference sets are formed by , and similarly,
The transmitting electrode 12-2 and the transmitting electrode 12-4 and the transmitting electrode 12-1 and the transmitting electrode 12-3 form a phase difference pair, respectively.

Here, as shown in FIG. 4, the receiving electrode 1
There are mainly two types of noise mixed into the antenna 4: noise D that wraps around the end of the fixed plate 10 opposite to the receiving electrode 14, and transmitted noise a and b shown by broken lines in the figure.

The transmitted noise, that is, the noise that enters from the wiring pattern 22 through the inside of the fixing plate 10 is removed by means described later.

On the other hand, in the present invention, the feedback noise is eliminated by the auxiliary electrode 26'.

Here, the auxiliary electrode 26' provides the reception electrode 14 with an AC signal having a phase opposite to that of the wraparound noise, and cancels out the wraparound noise by mixing the two signals. The arrangement position of the auxiliary electrode 26' will be explained below.

As described above, the wiring pattern 22 is arranged on the back side of the fixed plate 10, and this wiring pattern 22 is composed of two pairs of electric circuits in this embodiment. Here, alternating current signals having mutually opposite phases are supplied to one and the other of the pair of electrical circuits. As is clear from FIG. 4, among the roundabout noises generated from each of the electric lines 22a to 22b, the noise coming from the electric line 22b has the highest noise level. In other words, this electric circuit 22b is likely to run around the fixed plate 10.
It is placed near the end of the

Therefore, as described above, if an AC signal having an opposite phase to the noise emitted from the electric line 22b is applied to the receiving electrode 14, the wrap-around noise can be canceled out.

Therefore, in this embodiment, the electric line 22 on which the AC signal having the opposite phase to the AC signal on the electric line 22b is carried.
An auxiliary electrode 26' is provided at a position on the back side of the transmitting electrode 22-7, to which d is connected, with the fixing plate 10 interposed therebetween.
Here, the auxiliary electrode 26' is electrically connected to the receiving electrode 14.

According to such a configuration, a capacitor is formed by the transmitting electrode 12-7 and the auxiliary electrode 26', and more AC signals having a phase difference of 180 degrees are transmitted to the receiving electrode 1.
4, and thereby the wraparound noise is relaxed and cancelled.

That is, in the present invention, attention is paid to noise coming from the electric circuit arranged near the end of the fixed plate 10, and an auxiliary electrode is provided to eliminate this noise.

The area related to the electrostatic coupling of the auxiliary electrode 26' is:
It is preferable to set it appropriately depending on the magnitude of the wraparound noise.

Next, a means for removing noise transmitted through the fixing plate 10 will be explained.

In other words, the amount of transmitted noise that enters from the wiring pattern 22 through the inside of the fixed plate 10 is determined by the amount of transmitted noise that enters from the wiring pattern 22 through the inside of the fixed plate 10. It has been confirmed through experience that the amount of contamination from the patterned circuit 22a on the electrode side is the largest, and the amount of contamination from other patterned circuits is extremely small.
Therefore, in this embodiment, the back surface position of the transmitting electrode is applied with an AC voltage having a phase opposite to the voltage phase guided by the patterned conductor 22a closest to the receiving electrode 14, which is 270° in FIG. That is, in FIG. 5, the auxiliary electrode 26 is provided at the back surface position of the transmitting electrode 12-2 to which a 90 degree phase voltage is applied.

Therefore, the transmitted noise that enters the receiving electrode 14 from the patterned electrical path 22a closest to the receiving electrode 14 is a signal with the opposite phase of this transmitted noise, that is, the supplementary noise induced by the transmitting electrode 12-2 in FIG. This is canceled out by the correction signal from the electrode 26, and almost the total amount of transmitted noise that enters the receiving electrode 14 from the wiring pattern 22 can be canceled out.

As described above, by providing the auxiliary electrodes 26' and 26, it is possible to remove both wrap-around noise and transmitted noise, thereby further improving the accuracy of detecting the amount of displacement of the moving body.

In this way, it is possible to focus on the pattern circuit with a large amount of noise mixed in among the circuits of the wiring pattern 22 and provide an auxiliary electrode to cancel out the noise from this pattern circuit to improve the detection accuracy, but in this case, In order to cancel out noise mixed in from other patterned circuits, it is also possible to provide a corresponding auxiliary electrode for each patterned circuit to achieve even more thorough noise cancellation.

In order to effectively remove noise (c shown in FIG. 4) that directly enters the receiving electrode 14 from the transmitting electrode along the front surface of the fixing plate 10, a filter is installed between the transmitting electrode 12 and the receiving electrode 14 as an auxiliary means. Figure 7 shows
As shown in FIG. 8, an isolation ground electrode 28 is provided to electrically isolate the two.

In addition, as shown in FIGS. 6 to 8, the fixing plate 1
0, an auxiliary earth electrode 30 is provided at a position outside the wiring pattern 22 of the transmitting electrode 12, and the fixing plate 10 is connected to the electric path that supplies the voltage signal to each transmitting electrode.
It is possible to prevent noise from entering the receiving electrode 14 by detouring along the plane.

Furthermore, as shown in FIG. 8, by providing a ground layer 32 inside the fixed plate 10, it is possible to prevent noise from entering the receiving electrode 14 from the electric path of the transmitting electrode 12 through the inside of the fixed plate 10. This is possible, and by appropriately providing the isolated earth electrode 28, the auxiliary earth electrode 30, and the earth layer 32, the effect of preventing noise from entering the receiving electrode 14 is further enhanced in conjunction with the effect of the auxiliary electrode 26.
The amount of movement of a moving object can be detected with extremely high accuracy.

Specific Example Next, a specific example in which the device of the present invention is applied to a micrometer will be described.

Device configuration (1) Arrangement of fixed plate and moving plate The moving plate is placed on the spindle side and the fixed plate is placed on the main body side.

(2) Arrangement of electrodes and their driving method Eight transmitting electrodes were made into a set, and five sets were arranged at equal intervals on the circumference of the stator. Then, sequentially apply 0 degrees, 45 degrees, 90 degrees, 135 degrees, and 180 degrees to each set of transmitting electrodes.
AC voltages having phases of 225 degrees, 225 degrees, and 270 degrees were applied, creating a so-called three-phase drive system.

Further, the auxiliary electrode was provided at a position on the back surface of the transmitting electrode to which an AC voltage having an opposite phase to the voltage phase led by the patterned electrical path closest to the receiving electrode was applied.

(3) Outline of the micrometer to which this device is applied In this specific example, the electrical angle changes in phase by 360° x 5 = 1800° per rotor rotation.
When applied to a micrometer with a 1 μm reading, a signal of 500 pulses per rotation of the rotor is output, and in this case, the phase of 360 degrees mechanical angle is 360 degrees / 500 ÷ 5 = 360 degrees / 100, that is, 1μ by dividing the 360° phase by 100
The reading of m is realized.

(4) Specific design values for the detection section Distance between the transmitting electrode and coupling electrode: 1 mm or less Distance between the receiving electrode and the closest wiring pattern circuit: 2 mm Electrode area of 1 transmitting electrode 6 mm Voltage applied to ² transmitting electrodes :3 Distance between transmitting electrode and auxiliary electrode: 1mm Electrode area of auxiliary electrode: 6mm ² Results In this specific example, as a result of the provision of an auxiliary electrode that cancels out the mixed noise, compared to the previously mentioned proposed device that does not have an auxiliary electrode. As a result, it was possible to effectively eliminate the adverse effects caused by noise intrusion into the receiving electrode.

In other words, according to the proposed device that does not have an auxiliary electrode, the noise that enters the receiving electrode from the wiring pattern is approximately 200 mv (S/N22d _B ), and the maximum phase error is 11 degrees, which is less than the 1 μm reading of the above configuration. For micrometers, the maximum nonlinear error is approximately
It becomes 3μm.

On the other hand, according to a specific example in which an auxiliary electrode was provided, the noise entering the receiving electrode from the wiring pattern was reduced to 40 mv (S/N 36d _B ), and the maximum phase error at this time was 2.2 degrees. The maximum non-linear error of the above micrometer is 0.6μm.
We were able to keep the error to an extremely small level.

Effects of the Invention As explained above, according to the present invention, since the auxiliary electrode is provided on the back surface of the transmitting electrode connected to the electric path with the longer path through the fixed plate, the noise generated from the electric path is The wrap-around noise can be canceled out by providing an AC signal with an opposite phase.

Thereby, a capacitive displacement detection device capable of detecting the amount of phase displacement with high accuracy can be constructed.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing the electrode structure of a capacitive displacement detector to which the present invention is applied, FIG. 2 is an explanatory diagram of each electrode provided on the fixed plate and the movable plate in FIG. The figure is an explanatory diagram showing the wiring pattern for applying AC voltage to each transmitting electrode and its input connection part, FIG. 4 is a side view of FIG. 3, and FIG. 5 is an illustration of the capacitive displacement detector according to the present invention. An explanatory diagram showing the electrode structure provided on the fixed plate side, FIG. 6 is a sectional view taken along line AA in FIG.
8 are views of other embodiments showing the electrode structure provided on the fixed plate of the device of the present invention. DESCRIPTION OF SYMBOLS 10... Fixed plate, 12... Transmitting electrode, 14... Receiving electrode, 16... Moving plate, 18... Coupling electrode, 22... Connection pattern, 26... Auxiliary electrode, 28... Isolated earth electrode, 30... Auxiliary earth electrode.

Claims (1)

[Scope of Claims] 1. A fixed plate, a movable plate disposed opposite to the fixed plate and movable in a predetermined direction, and a plurality of transmitters arranged in alignment along the moving direction of the movable plate on the front side of the fixed plate. an electrode, a receiving electrode arranged on the front side of the fixed plate at a constant interval from the transmitting electrode, and a coupling electrode arranged on the movable plate and electrostatically coupled to both the transmitting electrode and the receiving electrode. A capacitive displacement detector including at least a pair of electrical paths that are wired on the back side of the fixed plate along the alignment direction of the transmitting electrodes and supply mutually opposite phase AC signals to respective predetermined transmitting electrodes. and a loop noise path that goes around the transmitting electrode side side of the fixed plate, which is the side farthest from the receiving electrode, from the back side of the fixed plate and reaches the receiving electrode on the front side is longer than the pair of electric paths. an auxiliary electrode connected to one electric path, provided on the back side of the transmitting electrode via the fixed plate, and electrically connected to the receiving electrode. 2. In the device according to claim 1, an isolation ground electrode is provided on the front side of the fixed plate to electrically isolate the transmitting electrode and the receiving electrode, which are arranged at a constant interval. A capacitive displacement detector characterized by: 3. The capacitive displacement detector according to claim 1 or 2, wherein an auxiliary ground electrode is provided on the back side of the fixed plate adjacent to the wiring pattern.