JP2807827B2 - Capacitance type distance meter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance-type distance meter, and more particularly, to a distance meter that measures an approaching state of a moving object.

[Prior art] In a distance meter using a capacitance-type sensor, a resonance frequency has been conventionally changed by utilizing a characteristic in which a capacitance of a capacitor changes according to a distance to an object, and the change is detected by detecting the change. The distance was being measured. However, such conventional rangefinders have drawbacks in terms of detection accuracy and temperature compensation. In order to solve this problem, the present applicant has used two capacitors for measurement and comparison, and while supplying an AC signal to both,
A method for detecting a change in capacitance as a phase difference was developed prior to the present invention and a patent application has been filed (Japanese Patent Laid-Open No. 63-59018,
JP-A-63-59019).

[Problems to be Solved by the Invention] In the systems disclosed in the above patent applications, in addition to the problem that the temperature compensation is not sufficient, there is a problem in the method of setting the detection distance. That is, in order to set the phase difference to 0 or a predetermined value, a DC voltage is applied to one of the capacitors, and this is performed by manually adjusting the potentiometer. However, the relationship between the voltage set by the potentiometer and the corresponding detection distance is non-linear, and has a hysteresis characteristic that the corresponding value differs depending on the change direction of the set distance. FIG. 7 is a graph showing this situation, and there is a difference in voltage for obtaining a desired set distance when the set distance is changed from a short distance to a long distance and vice versa. Therefore, there is a problem that the set distance may have an error with respect to the actual distance.

Accordingly, it is an object of the present invention to provide a capacitance type distance meter that has sufficient temperature compensation and has a small error between a set distance and an actual distance.

[Means for Solving the Problems] In order to achieve the above object, the present invention does not connect two capacitors for measurement and comparison in series as a capacitor of a sensor unit, but rather uses a simple three-layer structure with a single capacitor. The voltage at that time is detected by detecting the time point of the output reversal due to the change in the stray capacitance of one electrode of the capacitor due to the approach of a moving object, while continuously increasing and decreasing the voltage for setting the distance. The distance is measured by reading. Further, in order to prevent the influence of hysteresis on the rise and fall of the voltage, the distance can be measured only when the voltage is rising or falling.

That is, according to the present invention, the first electrode arranged close to the device under test and the second electrode arranged close to the first electrode
An electrode, a plate-like dielectric disposed between the first and second electrodes, a first resistor having one end connected to the first electrode, and a second resistor having one end connected to the second electrode. A pulse generator or an AC generator connected between the other end of the first resistor and the second resistor and the ground, and one of the first electrode and the second electrode repeatedly rising and falling with time A static voltage generator comprising: a means for applying a DC voltage; a phase difference detecting means connected to the first electrode and the second electrode; and a means for reading the DC voltage when receiving an output signal from the phase difference detecting means. A capacitance type distance meter is provided.

Embodiment An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a first embodiment of the capacitance type distance meter of the present invention.

C is a capacitor having a three-layer structure constituting a sensor unit, and the details of the structure will be described with reference to FIGS. 2 and 3. 20 is a detection electrode, 22 is a compensation electrode, and 26 is a dielectric. Detection electrode 20 is connected to a pulse generator 14 via the resistor R ₁ is connected to one input terminal of the D flip-flop 16 through an inverter 10. On the other hand, the compensation electrode 22 is connected to the pulse generator 14 via the resistor R ₂ is connected to the other input terminal of the D flip-flop 16 through an inverter 12. 18 is a variation DC voltage generating circuit to produce a triangular wave or a sawtooth wave, the output of which is connected to the compensation electrode 22 via the resistor R ₃ is grounded via a capacitor 24.

FIG. 2 is a side sectional view of a sensor section of the capacitance type distance meter according to the present invention, and FIG. 3 is a sectional view taken along line II-II of FIG. The sensor unit has a three-layer capacitor C housed in a case 30 made of synthetic resin or the like, and a support member 34 is used for fixing the capacitor C. The capacitor C is a three-layer sandwich laminated structure of two metal foils 20 and 22 such as copper foil and one glass or epoxy substrate, or a plate-like or film-like dielectric substrate 26 such as Teflon or polyimide. is there. The metal foils 20 and 22 are attached to the substrate 26 or provided by chemical treatment, vacuum deposition, sputtering, or the like. The metal foils 20 and 22 constitute the detection electrode (first electrode) and the compensation electrode (second electrode) shown in FIG. 1, respectively. Is arranged close to the object to be measured. Each electrode 20,
A lead wire 32 is attached to one end of each 22. As a material of the dielectric substrate 26, a thin plate such as another synthetic resin, ceramic, or glass can be used. However, when the dielectric substrate 26 is not a flat plate but is curved, a flexible substrate such as polyimide is preferable. In this case, the thickness is 50μm ~
100 μm is optimal. Note that, for example, from the viewpoint of capacity and heat conduction, the thickness of the dielectric substrate 26 is preferably about 1 to 2 mm even when it is not curved. In the example of FIG.
The thickness of 6 is 1.6mm.

As shown in FIG. 3, the capacitor C has a circular shape and is housed in the cylindrical case 30. However, the shape is not limited to a circle, but may be a desired shape such as a polygon or an ellipse. If the shape is circular and the diameter is 3 cm, a capacitor C having a capacitance of several pf to several tens pf is obtained depending on the thickness of the dielectric substrate 26. The periphery of the capacitor C is fixed by a support member 34 without using a filler, and has a structure resistant to external impact. When a filler is used, the filler may peel off from the capacitor surface due to thermal expansion depending on the type and use conditions.

First, the circuit of FIG. 1 will be described.
A pulse having a frequency of, for example, 3 kHz from 14 is applied to the detection electrode 20 and the compensation electrode 22 of the capacitor C via the resistors R ₁ and R ₂ , respectively. As the resistors R ₁ and R ₂ , a thermistor, a metal coating resistor, a carbon resistor, or a combination thereof can be used as necessary. In this case the resistors R ₁ , R ₂
Is preferably arranged near the capacitor C from the viewpoint of temperature compensation.

Assuming that the detection electrode 20 is not close to the device under test and that the variable DC voltage generation circuit 18 is not connected, the stray capacitances of the detection electrode 20 and the compensation electrode 22 are substantially equal. The phase of the voltage applied to both the electrodes 20 and 22 is set so that the detection electrode 20 is advanced and applied to two inputs of the D flip-flop 16. When an object to be detected approaches the detection electrode 20, the stray capacitance of the detection electrode 20 increases, and the symmetry of the capacitor C is lost. Therefore, the rise of the voltage of the detection electrode 20 is delayed, and the phase is delayed from the phase of the voltage applied to the compensation electrode 22. Accordingly, the phase relationship between the two input signals of the D flip-flop 16 is reversed, and as a result, the output state of the D flip-flop 16 is inverted.

The DC voltage output from the variable DC voltage generation circuit 18 is
The frequency repeatedly rises and falls between 3 V and 9 V at a frequency of about Hz to several hundred Hz. FIG. 4 shows how the voltage changes. Since the phase of the compensation electrode 22 with respect to the detection electrode 20 changes due to a change in the DC voltage applied to the compensation electrode 22, the set distance to be detected changes as a result. When the object to be detected is a moving object, the voltage change speed must be sufficiently fast in consideration of the moving speed.

Thus, the voltage applied to the input of the inverter 12 continuously increases due to the output voltage of the variable DC voltage generation circuit 18,
Since the output falls, the condition that the output of the D flip-flop 16 is inverted requires that the input voltage on the detection electrode 20 side be delayed due to an increase in the stray capacitance. As described above, this state is caused by the approach of the object to be measured, and the output of the D flip-flop 16 is inverted. This inverted output is used as a hold control signal of the voltage hold circuit 28, and holds the output voltage of the variable DC voltage generation circuit 18. The DC voltage value thus held is supplied to the display circuit 36 and displayed in a form that the user can see. This display circuit
As 36, a voltmeter having a rotating needle, a digital display, or the like can be used. Note that a reset circuit 38 is connected to the voltage hold circuit 8 so that the voltage hold circuit 28 is reset at a constant cycle, so that the approaching state of the device under test can be continuously monitored. Note that this reset circuit
38 can be a manual circuit depending on the purpose of use.

In order to measure the distance to the object to be measured approaching using the capacitance type distance meter of FIG. 1, the fluctuating DC voltage at the time of inversion of the output of the D flip-flop 16 is read as described above.
The distance to the object can be known by looking at the prepared voltage-distance comparison table. Also, if the voltage value changes one after another, the change in distance, speed, acceleration, and movement amount can be known.

Since this voltage and distance have a non-linear relationship, it is desirable to make a voltage proportional to the distance through a predetermined linearization circuit in order to directly read the distance from the detected voltage.

In the circuit shown in FIG. 1, the voltage is held both when the variable DC voltage from the variable DC voltage generating circuit 18 rises and when the variable DC voltage falls, and as described with reference to FIG. As a result, a difference occurs in the detection distance between when the voltage is increased and when the voltage is decreased, and accurate measurement cannot be performed. Therefore, accurate measurement is possible by measuring only when this voltage is increasing or decreasing, and by grasping the exact relationship between voltage and distance at this time. For this purpose, the voltage hold operation can be performed only when the voltage rises, for example, or the display operation of the display circuit 36 can also be performed only when the voltage rises.

FIG. 5 is a block diagram showing an example of a configuration in which the hold operation is performed only when the voltage rises (or drops), and shows only the changed portions in FIG. Reference numeral 40 denotes a pulse generation circuit that controls the variable DC voltage generation circuit 18, and its output is also supplied to an AND gate 42. Assuming that the DC voltage rises when the output of the pulse generation circuit 40 is at the H level and falls when the output of the pulse generation circuit 40 is at the L level, the output of the D flip-flop 16 is output only when the DC voltage is rising.
Will be given to

FIG. 6 is a circuit diagram showing another embodiment. In this embodiment, a two-stage operational amplifier is used in place of the D flip-flop.
52 and 62 are used, and an AC generator 14 'is used instead of the pulse generator. The output voltage according to the phase difference between the two inputs of the operational amplifier 52 is obtained.
Then, the output voltage is compared with a predetermined voltage, and the output of the operational amplifier 62 is inverted depending on the magnitude of the output voltage. Therefore, the operational amplifier 62
Can be used in place of the output of the D flip-flop 16 of FIG. The same components as those in FIG. 1 are denoted by the same reference numerals, and a description thereof will be omitted. Note the variable resistor R ₄ to the inverting input and is connected between the output of the operational amplifier 62 is for fine adjustment of the inversion timing of the operational amplifier 62, for manual adjustment in order to perform accurate distance measurement as required.

Assuming that the ambient temperature of the sensor rises in each of the above embodiments, the volume of the dielectric 26 thermally expands, increasing its thickness. As a result, the capacitance of the capacitor C decreases. However, the capacitor C does not take the midpoint of the ground,
Since it is levitated from the ground and symmetrically connected by a resistor equal to the pulse generator 14 or the AC generator 14 ', no phase difference occurs due to the expansion of the dielectric 26. Therefore, temperature compensation can be easily achieved to prevent a detection error due to a change in capacitance due to an ambient temperature.

In addition, when the measurement was performed using the capacitance type distance meter of the present invention, the measurement error was 10% in a temperature change from 0 ° C. to 90 ° C.
It was below.

In addition to the above embodiment, the present invention can be used for measuring a distance to a large object. That is, in the case of a large object to be measured, the capacitor of the sensor unit may be a film having a width and a height of about several tens cm to several meters, and may be attached to a wall surface. In this case, the capacitance becomes considerably large, but a desired temperature compensation characteristic can be obtained regardless of the magnitude of the capacitance.

[Effects of the Invention] As is clear from the above description, the capacitance type distance meter of the present invention uses a simple three-layer capacitor as a sensor of the phase difference detection system, and provides two resistors without providing a grounded neutral point. Since a pulse or AC power supply is connected to both electrodes of the capacitor via, and phase difference detection means for detecting the phase difference between both electrodes is provided, it is possible to cancel out and compensate for the influence of the change in ambient temperature, In addition, since the variable DC voltage is applied to one of the electrodes and the variable DC voltage is read in response to the output of the phase difference detecting means, the distance measurement of the moving object can be easily performed.

Further, assuming that the capacitance of the capacitor C is C, due to its impedance 1 / ωc, it shows a large attenuation characteristic against unnecessary high frequency noise, and shows a few kHz signal from a pulse generator or an AC generator. Has a small amount of attenuation and a large common-mode rejection ratio to obtain a large gain. Furthermore, since a single capacitor is used, the same standard 2 for measurement and comparison is used.
This eliminates the need to maintain the accuracy required to prepare two capacitors, thus improving production problems. By adopting a phase difference detection method and performing temperature compensation, the size can be increased, and the shape and arrangement of the electrodes can be freely changed according to the measurement purpose and situation. Furthermore, since the sensor section also has a laminated structure, there is an advantage that mass production can be easily performed similarly to electronic parts such as semiconductors. In addition, since the supporting member for supporting the peripheral portion is used for fixing the capacitor in the sensor case without filling with the synthetic resin, there is no adverse effect due to the thermal expansion of the filler.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a first embodiment of a capacitance type distance meter according to the present invention, FIG. 2 is a side sectional view of an embodiment of a sensor unit in FIG. 1, and FIG. FIG. 4 is a cross-sectional view taken along line II-II of FIG. 4, FIG. 4 is an output voltage waveform diagram of the variable DC voltage generating circuit in FIG. 1, FIG. 5 is a block diagram showing a partial change mode in FIG. FIG. 6 is a block diagram showing another embodiment of the capacitance type distance meter of the present invention, and FIG. 7 is a graph showing hysteresis characteristics when the distance setting voltage is changed in the conventional device. 10, 12 …… Inverter, 14 …… Pulse generator, 14 '……
AC generator, 16 D flip-flop, 18 Fluctuating DC voltage generation circuit, 20 Detection electrode, 22 Compensation electrode, 26
... plate dielectric, 28 ... voltage hold circuit, C ... capacitor, 30 ... case, 32 ... lead wire, 34 ... support member, 36 ... display circuit, 38 ... reset circuit, 52, 62 ……
Operational amplifier, R ₁ , R ₂ …… Resistance.

Claims (7)

(57) [Claims] A first electrode disposed close to an object to be measured, a second electrode disposed close to the first electrode, and a plate disposed between the first and second electrodes. A dielectric, and the first
A first resistor having one end connected to the electrode, a second resistor having one end connected to the second electrode, the first resistor and the second resistor;
A pulse generator or an AC generator connected between the other end of the resistor and the ground; a means for applying a DC voltage that repeatedly rises and falls with time to one of the first electrode and the second electrode; An electrostatic capacitance type distance meter comprising: a phase difference detecting means connected to one electrode and the second electrode; and a means for reading the DC voltage when receiving an output signal from the phase difference detecting means. 2. The electrostatic capacitance type according to claim 1, wherein the means for reading the DC voltage has means for reading the DC voltage only when the DC voltage is rising or falling. Rangefinder. 3. The capacitance type distance meter according to claim 1, wherein a glass cloth / epoxy substrate, Teflon or polyimide is used as said plate-shaped dielectric. 4. The capacitance type distance meter according to claim 1, wherein the thickness of said plate-shaped dielectric is 2 mm or less. 5. The capacitance type distance meter according to claim 1, wherein the thickness of said plate-shaped dielectric is 50 μm to 100 μm. 6. The capacitance type distance meter according to claim 1, wherein said first and second electrodes are copper foils adhered to said plate-shaped dielectric. 7. The first electrode, the second electrode, and the plate-like dielectric are held in a hollow cylindrical case by a supporting member at their peripheral portions, and the first electrode is arranged near one end of the case. The capacitance type distance meter according to claim 1.