JPH0617798B2 - Displacement detection device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a displacement detection device including a phase discrimination type capacitance sensor, and more particularly, to one electrode plate and the other electrode plate forming the same sensor. The parallelism adjusting mechanism is provided with a parallelism detecting means for speedily and easily.

It is used for electronic dial gauges, calipers and linear length measuring instruments.

[Prior Art] A displacement detection device including a phase discrimination type capacitance sensor has advantages of high accuracy and low power consumption as compared with a device including other sensors such as a photoelectric type. Further, since the dimension between the facing surfaces of the relative moving counter electrode and the like can be made large, it is widely used in various length measuring instruments and the like.

A conventional structure of such a phase discrimination type capacitance sensor is shown in FIG.

In FIG. 2, 20 is a plurality of transmitting electrode elements 21a to 2a.
This is a one-sided electrode plate in which a transmission electrode 21 and a reception electrode 23 each composed of 1 h are arranged in alignment. Reference numeral 30 is the other electrode plate in which the coupling electrodes 31 and the ground electrodes 33 are alternately arranged.
The coupling electrode 31 and the ground electrode 33 have a polar area sufficient to face the transmitting electrode 21 and the receiving electrode 23. Reference numeral 40 is a phase discrimination type detection circuit connected to the reception electrode 23.

Therefore, if voltages having different phases are applied to the plurality (eight in the example of FIG. 2) of the transmitting electrode elements 21a to 21h forming the unit, the two electrode plates 20 and 30 are relatively moved in the arrow Y direction. By the two-stage capacitive coupling, the detection circuit 40 can detect the relative movement displacement amount of the both 20 and 30.

By the way, in order to guarantee the desired detection accuracy, both electrode plates 2
The relative positional relationship between 0 and 30 must be accurate. That is, the transmitting electrode 21, the receiving electrode 23, and the coupling electrode 31 face each other in parallel, they must not be positioned in the width direction, and the inclination in the yawing direction shown by the angle θ in FIG. 2 must be within the allowable range.

For this reason, the conventional displacement detection device, for example, in the case of an electronic dial gauge type, is generally configured as shown in FIGS. 4 and 5.

In the figure, the displacement detection device is roughly composed of a dial gauge type main body, a phase discrimination type capacitance sensor, a positioning mechanism 70 and a parallel adjustment mechanism 60.

The dial gauge type main body has a structure in which a spindle 11 is slidably mounted on an annular case main body 1. 5
Is a stem and 12 is a probe.

A support 13 is provided on the spindle 11. The spindle 11 is urged downward by a spring (not shown) having one end locked to the spring hook 15 and the other end locked to the case body 1. 4 is a shock absorber. On the other hand, the case body 1 is provided with a plurality of mounting holes 3.

The phase discrimination type capacitance sensor is formed of the one electrode plate 20, the other electrode plate 30, and the detection circuit 40. For convenience of wiring processing, the other electrode plate 30 is attached to the spindle 11 (support 13) which is a movable body, and the other electrode plate 30
0 is attached to the case body 1 as a stationary body via the adjusting plate 71 and the fixed frame 9.

The adjusting plate 71 adjusts the position of the fixing frame 9 fitted to the inner peripheral edge 2 of the case body 1 by the positioning mechanism 70, and then sets the set screw 7
It is fixed at 5.

Here, the alignment mechanism 70 is a means for attaching the one electrode plate 20 to the fixed frame 9 (case body 1) so that there is no inclination in the yawing direction with respect to the other electrode plate 30 (the angle θ = 0). Is.

Specifically, it is formed of four holes 72 provided in the adjusting plate 71 and four eccentric pins 73 corresponding thereto. The three eccentric pins 73 are loosely inserted into the corresponding mounting holes 3, and the other one eccentric pin 73 is inserted.

Therefore, when the fixed frame 9 is used as a reference, the tilt of the one electrode plate 20 can be adjusted by rotationally adjusting the three eccentric pins 73. Together with both electrode plates 20,
The relative position in the width direction of 30 is also adjusted at the same time. After the adjustment, the set screw 75 is tightened to prevent the eccentric pin 73 from freely rotating, and is fixed to the fixed frame 9. The eccentric pin 73 is adhered to the case body 1 as needed.

For this reason, the flexible printed wirings 22 and 24 are used to electrically connect the one electrode plate 20, the power source (not shown) provided on the fixed frame 9 side, the detection circuit 40, and the like.

The arc-shaped flexible printed wiring 19 of the fixed frame 9
As shown in FIG. 5, the outer frame 6 fitted to the case body 1 is rotatable with respect to the case body 1.

Therefore, it is possible to change the direction of the display means 7 attached to the outer frame 6 to a direction convenient for visual observation. Measurement values are input to the display means 7 from the detection circuit 40 via the flexible printed wiring 19. The measured value is displayed in analog or digital.

Next, the parallel adjustment mechanism 60 is means for adjusting the attitude of the other electrode plate 30 with respect to the one electrode plate 20 to adjust and establish the face-to-face parallelism of the two electrode plates 20, 30. Further, it also serves as a rotation stopping function of the spindle 11.

The parallel adjusting mechanism 60 includes a guide member 61 having a guide groove 62 extending parallel to the axis C of the spindle 11, a plurality of adjusting screws 63 for adjusting the posture of the guide member 61 with respect to the case body 1, and a base end portion. Is fixed to the support body 13 and has a tip end portion formed with an engaging member 64 fitted in the guide groove 62. The engagement member 64 is formed so as to be slidable in the guide groove 62 in the longitudinal direction thereof.

Therefore, the adjusting screw 63 is appropriately rotated to rotate the guide member 6
When the posture of No. 1 is changed, the other electrode plate 30 is rolled around the axis C of the spindle 11. As a result, the other electrode plate 30 can be parallel to the one electrode plate 20.

In the conventional displacement detection device having such a configuration, the other electrode plate 30 is attached to the support 13. On the other hand, the electrode plate 30 is attached parallel to a plane including the axis C of the spindle 11. Next, with respect to the fixed frame 9 fitted in the case main body 1, the position adjusting mechanism 70 is operated to finely adjust the one electrode plate 20, and the attitude of the other electrode plate 30 is adjusted. The angle θ is adjusted to be zero.

Then, the parallel adjustment mechanism 60 is operated to operate the one electrode plate 20.
Adjusting the attitude of the other electrode plate 30 with respect to the both electrode plates 2
Adjust the parallelism of 0 and 30 within the allowable range. Here, the relative positional relationship between the two electrode plates 20 and 30 is established to a predetermined one.

Therefore, the vertical displacement amount of the spindle 11 is detected with high accuracy by the phase discrimination type capacitance sensor, and the value can be read by the display means 7.

[Problems to be Solved by the Invention] However, the conventional displacement detection device described above has the following problems.

At the time of design, the parallel adjustment mechanism 60 includes both electrode plates 20,
The parallelism of 30 can be adjusted almost perfectly. However, as shown in FIG. 6, the adjustment confirming means is one in which at least two contact type measuring devices 69, 69 are brought into contact with the other electrode plate 30 and read by the meter 79. Therefore, both measuring devices 6
It is extremely difficult to perfectly adjust the parallelism from the relationship of the consistency of 9, 69 and the contact pressure.

In addition, both measuring devices 69, 69 must be set by removing the outer frame 6 from the case body 1, and disassembling and assembling them requires complicated work and requires a lot of time and labor.

On the other hand, also in the adjustment of the alignment mechanism 70, the relative inclination of both electrode plates 20 and 30 is set to zero (θ =
It is very difficult to set 0).

In this way, no matter how the components are processed with high precision, due to the practical difficulty of assembly and adjustment, both electrode plates 20,
The parallelism and the inclination of 30 cannot be perfectly adjusted.
Therefore, these adjustments are actually compromised to the extent that they do not affect the final detection accuracy.

By the way, such a compromise is devised separately for the inclination and detection accuracy of both electrode plates 20 and 30, and the parallelism and the inspection accuracy. In particular, it is general that the parallelism has a very small influence on the detection accuracy if the opposing pole surface ratio is constant.

However, according to many tests and studies of the applicant,
It was found that the parallelism and the tilt subtly interact with each other, and that even a small tilt has a great influence on the detection accuracy depending on the degree and direction of the parallelism. In other words, if it is possible to adjust the parallelism easily and completely, it is possible to further simplify and speed up the tilt adjustment.

The reason for this is devised as follows.

As shown in FIG. 3A, if there is no inclination (θ = 0), the coupling capacitance between the transmission electrode 21 and the coupling electrode 31 and between the coupling electrode 31 and the reception electrode 23 is constant even if the parallelism is poor to some extent. There is little influence from.

On the other hand, even if there is some inclination, if the parallelism is completely close, the influence on the detection accuracy is slight.

On the other hand, as shown in (B), there is a slight inclination and the parallelism is incomplete [(B) causes the coupling electrode 31 to approach the transmitting electrode 21 side and be isolated to the receiving electrode 23 side. On the other hand, the case where the electrode plate 30 is inclined in the rolling direction is shown. ], The transmitting electrode element 21a lacks the portion closest to the coupling electrode 31, and the transmitting electrode 21 (21a-
21d) and the coupling capacitance between the coupling electrode 31 are reduced.

Here, in the phase discrimination capacitance sensor, units are formed, power supplies having different phase vectors are applied to the respective units, the phases of the composite vector electric signals of the plurality (eight) of the transmission electrodes 21a to 21h are discriminated, and the transmission electrodes 21 are separated. The relative displacement between the coupling electrode 31 and the coupling electrode 31 is detected.

Therefore, if there is some inclination and the parallelism is incomplete, the detection accuracy will be greatly affected. That is,
The relationship between the unit U2 (21a to 21h) and the coupling electrode 31 shown in FIG. 3 and the relationship between the unit U1 (21a to 21h) and the coupling electrode 31 do not change. But unit U
1 (U2) and the coupling electrode 31 move relative to each other in the Y direction, that is, when the rolling direction tilt occurs when the minimum resolution is obtained, the transmission electrode 21 and the coupling electrode 3
It has been found that a capacitance change other than that caused by relative movement occurs between 1 and 1 and the detection accuracy is unstable and deteriorates.

The present invention has been made in view of the above circumstances, and an object thereof is to provide a displacement detection device including parallelism detection means capable of quickly and easily adjusting parallelism and establishing an accurate parallelism. To do.

[Means for Solving the Problem] According to the present invention, the capacitance coupling state is constant unless the facing area ratio of the coupling electrode and the transmission electrode / reception electrode changes.
That is, the detection accuracy in the detection circuit can be maintained, and when the one electrode plate and the other electrode plate are in an incomplete parallelism state, it is inevitable that the one electrode plate and the other electrode plate in the width direction are between the two electrode plates. As the distance differs, the coupling electrode and the transmission electrode
Paying attention to the fact that the coupling capacitance with the receiving electrode changes, the receiving electrode is formed from a pair of receiving electrode elements sandwiching the transmitting electrode, and the electrical signal cancels based on the capacitance change induced in each receiving electrode element. It is formed so that the degree of parallelism can be detected from the balance.

That is, a phase discrimination type capacitance sensor including one electrode plate having a transmitting electrode and a receiving electrode, the other electrode plate having a coupling electrode, and a detection circuit connected to the receiving electrode, and one electrode plate and the other electrode. In a displacement detecting device having a parallel adjustment mechanism for adjusting the parallelism between two electrodes, which is involved in any one of the plates, the receiving electrodes are arranged so as to oppose each other in the width direction of the one electrode plate while sandwiching the transmitting electrode. Formed of a pair of receiving electrode elements, the coupling electrode is formed to have a size capable of facing the transmitting electrode and both receiving electrode elements, and the electric signals generated in the respective receiving electrode elements are compared with each other. It is characterized in that a parallel degree detecting means for detecting the parallel degree of the plates facing each other is provided.

[Operation] In the present invention having the above configuration, when the parallelism between the one electrode plate and the other electrode plate is not perfect, the distance between the one receiving electrode element and the coupling electrode and the distance between the other receiving electrode element and the coupling electrode are It is different from the distance across the space. Further, when the one electrode plate and the other electrode plate are relatively tilted in the yawing direction, the coupling capacitances between the transmission electrode and the coupling electrode and between the coupling electrode and the reception electrode vary.

Therefore, a difference occurs between the electric signal induced in the one receiving electrode plate element and the electric signal induced in the other receiving electrode element, so that the parallel degree of both electrode plates can be detected by comparing these signals.

Therefore, if the parallelism adjusting mechanism is operated so that the parallelism detected by the parallelism detecting mechanism becomes zero or in the vicinity thereof, the parallelism can be adjusted quickly and accurately. So,
It is possible to guarantee stable and highly accurate displacement detection.

[Embodiment] An embodiment of the displacement detecting device according to the present invention will be described below in detail with reference to the drawings.

The displacement detecting device includes a dial gauge type body, a phase discrimination type capacitance sensor, a parallel adjusting mechanism 60, and a positioning mechanism 70.
The characteristic feature is that the phase discrimination type capacitance sensor has a novel structure and the parallelism detecting means 50 is provided.

Incidentally, the dial gauge type main body (case main body 1, spindle 11, etc.), parallel adjustment mechanism 60, and alignment mechanism 70.
Since the above is the same as the conventional structure shown in FIG. 4 and FIG. 5, the description of those structures will be simplified or omitted.

The phase discrimination type capacitance sensor is roughly composed of one electrode plate 20, the other electrode plate 30, and a detection circuit 40.

On the other hand, the electrode plate 20 is fixed to the adjusting plate 71 which is a stationary body and the fixed frame 9 (main body case 1), and the other electrode plate 30 is fixed to the support body 13 (spindle 11) which is a movable body. Further, the detection circuit 40 is housed in the case body 1.

Therefore, the displacement amount of the spindle 11 is detected by the detection circuit 4
0 is detected and can be read by the display means 7 attached to the outer frame 6.

Here, the one electrode plate 20 includes transmitting electrode elements 21a to 21a forming units (eight) arranged in the central portion.
a plurality of sets of the transmitting electrodes 21 and the transmitting electrodes 21
A pair of receiving electrode elements 23 that are arranged to face each other across the width
and a receiving electrode 23 composed of a and 23b.

The pole area of the receiving electrode 23 is equal to those of the receiving electrode elements 23a, 23
This is the sum of the polar areas of b and is the same as the polar area of the conventional receiving electrode (23) shown in FIG. Power supplies of different phases are supplied from the connection pattern 27 to the transmission electrode elements 21a to 21h of each unit. In this example,
The connection pattern 27 is connected to the electrodes 21 a to 21 h and 23 a, 2 via the step 29 provided at the end of the one electrode plate 20.
It is connected to the flexible printed wiring 22 that is fixed flush with the surface of 3b. Receiving electrode elements 23a on both sides,
This is for providing 23b. Similarly, each receiving electrode element 23
The a (23b) is connected to the detection circuit 40 by the flexible printed wiring 24a (24b) via the connection patterns 26a (26b) spaced apart from both ends of the one electrode plate 20.

The other electrode plate 30 has a coupling electrode 3 extending in the longitudinal direction.
1 and the ground electrode 33 are alternately arranged at a predetermined pitch. The ground electrodes 33 are connected in series by the short circuit pattern 32.

Here, each coupling electrode 31 has the same length (dimension in the vertical direction in FIG. 1) that straddles the eight transmitting electrode elements 21a to 21d forming the unit. Further, the width dimension thereof is large enough to face both the receiving electrode elements 23a and 23b. Each ground electrode 33 is for improving the S / N ratio, and the facing area thereof is almost the same as that of each coupling electrode 31. Each ground electrode 3
3 is a conductive layer (not shown) applied to the peripheral surface of the other electrode plate 30 through the short-circuit pattern 32 and a conductive adhesive 36.
It is grounded to the spindle 11 via (see FIG. 4).

The center line L of the other electrode plate 30 is the spindle 1
It is fixed to the support 13 so as to match the axis C of 1. Therefore, the one electrode plate 20 is fixed to the adjusting plate 71 (fixing frame 9) so that the transmitting electrode 21 coincides with the center line L.

Next, the detection circuit 40 includes an adder 41, an integrator 42, and a discrimination circuit 43. The basic configuration and operation are the same as those of the conventional detection circuit 40, but in the present embodiment, a pair of receiving electrode elements 23 in which the receiving electrodes 23 are distributed and arranged.
Since it is composed of a and 23b, the adder 41 is formed so as to converge and integrate the entire electric signal induced in each of the receiving electrode elements 23a and 23b. Therefore, even if the receiving electrode 23 is divided into two, high detection accuracy can be guaranteed.

Here, the parallelism detecting means 50, which is one of the characteristic technical matters of the present invention, electrically detects the parallelism between the one electrode plate 20 and the other electrode plate 30, and the receiving electrode element 24.
The degree of parallelism is known from the unbalance of electric signals between a and 24b.

That is, the output voltages of the pair of chargers 51a, 51b connected to the receiving electrode elements 23a, 23b are compared with the output voltages of the chargers 51a, 52b to compare the two electrode plates 20,
Completely parallel (zero) with the comparison circuit 52 for obtaining the degree of parallelism of 30.
A parallel degree detecting means 50 is formed by a display device 55 indicating the parallel degree oriented around the center. Both of the chargers 51a and 51b are formed of an integrating circuit, and are for amplifying an electric signal to improve comparison convenience and resolution.

The charger 51a is connected to the receiving electrode element 23a via the flexible printed wiring 24a, and the charger 51b is connected to the receiving electrode element 23b via the flexible printed wiring 24b.

In this embodiment, the parallelism detecting means 50 is connected to the terminals 57a and 57 for the purpose of downsizing the displacement detecting device itself and convenience of handling.
It is formed so as to be connectable and separable to the detection circuit 40 (main body case 1) via b. That is, the parallelism detecting means 50
Both receiving electrode elements 23 through the detection circuit 40 only when in use
a, 23b can be connected. Of course, in the present invention, the installation location of the parallelism detecting means 50 is not limited, and thus the parallelism detecting means 50 may be housed in the case body 1 while being connected to the receiving electrode elements 23a and 23b.

Next, the operation will be described.

On the other hand, it is assumed that the electrode plate 20 is fixed to a predetermined position of the case body 1 via the adjusting plate 71 and the fixing frame 9 by the operation of the alignment mechanism 70.

Here, each of the transmitting electrode elements 21a to 21h of the transmitting electrode 21.
When power supplies having different phases are applied to the respective receiving electrode elements 23a and 23b via the coupling electrode 31, electric signals based on the relative positional relationship between the one electrode plate 20 and the other electrode plate 30 in the longitudinal direction (Y direction). Is induced.

Here, if the parallelism between the one electrode plate 20 and the other electrode plate 30 is imperfect, the magnitudes of the electric signals generated in the receiving electrode elements 23a and 23b are different from each other. Therefore, the comparison circuit 52 obtains the parallel degree according to the difference between the electric signals. In this embodiment, the receiving electrode element 23a and the coupling electrode 3 are
When the other electrode plate 30 is inclined in a direction in which the distance between the other electrode plate 1 and the receiving electrode element 23b becomes smaller than the distance between the receiving electrode element 23b and the coupling electrode 31 (the other electrode plate 30 rotates clockwise around the axis L in FIG. 1). The pointer 56 of the display 55 is formed so as to be inclined in the counterclockwise rotation direction.

Now, it is assumed that the pointer 56 of the display 55 is tilted to the left and the parallelism is incomplete.

In this case, each adjustment screw 63 forming the parallel adjustment mechanism 60 is rotated and adjusted. That is, in the state shown in FIG. 4, when the adjusting screw 63 is rotated in the direction in which it is projected into the main body case 1, the spindle 11 causes the guide member 61,
It is rotated counterclockwise via the engaging member 64. With the rotation, the pointer 56 rotates clockwise. Therefore,
When the pointer 56 points to the zero scale, the adjustment screw operation ends.

Here, the parallelism of both electrode plates 20 and 30 is the best that can be adjusted. When the pointer 56 is tilted in the right rotation direction, the reverse operation to the above may be performed.

After the adjustment is completed, the terminals 47, 47 are pulled out.

Therefore, according to this embodiment, the pair of receiving electrode elements 23 are arranged so that the receiving electrodes 23 are opposed to each other with the transmitting electrode 21 interposed therebetween.
a, 23b, each receiving electrode element 23a, 23b
The parallel adjustment mechanism 60 can be operated quantitatively because the parallel degree detection means 50 for detecting the degree of parallelism between the two electrode plates 20 and 30 by comparing the electric signals induced in the parallel adjustment mechanism 60 can be operated quantitatively. The parallelism between the two electrode plates 20 and 30 can be adjusted quickly and easily.

In addition, the parallelism degree detecting means 50 is configured to detect both the receiving electrode elements 23.
Since the degree of parallelism is automatically detected from the electrical difference between a and 23b, the degree of parallelism can be detected with high accuracy, and the degree of parallelism can be visually read by the display 55, which facilitates handling. Since the parallelism detecting means 50 can be detached from the main body by pulling out the terminals 57, 57, the miniaturization of the entire apparatus can be maintained.

Further, the parallelism detecting means 50 is connected to an electric path connecting the one electrode plate 20 and the detection circuit 40 to electrically detect, and therefore, as in the conventional case, the outer frame 6, the fixed frame 9, and the adjusting plate. It is possible to eliminate complicated work such as disassembling and assembling 71 and the like, and positioning and setting the contact type measuring devices 69, 69. From this point as well, quick and accurate parallel adjustment can be achieved.

Furthermore, since the parallelism between the two electrode plates 20 and 30 can be perfected, even if there is a slight inclination in the yawing direction with the two electrode plates 20 and 30 [see FIG. Will not be adversely affected. Therefore, it is not necessary to excessively enhance the precision of processing and assembling of the alignment mechanism 70, and excessive alignment work is not required. Then, the assembly of the entire device is facilitated and the cost can be reduced.

Furthermore, since the perfect degree of parallelism can be adjusted, the facing distance between the electrode plates 20 and 30 can be further reduced, and the detection efficiency and detection accuracy can be further improved.

In the above embodiment, the dial gauge type main body was constructed by incorporating the phase discrimination type capacitance sensor into the main body.
The form is not limited to that. For example, the main body may be a caliper, a linear measuring machine, or the like. Therefore, the parallel adjusting mechanism 60 is not limited to the one including the guide member 61 with the guide groove 62, the engaging member 64, etc., and can be arbitrarily selected. The point is that one or the other of the positions can be changed so that the parallelism between the one electrode plate 20 and the other electrode plate 30 can be adjusted. For example, in the case of a linear measuring machine, one electrode plate attached to a flat plate stationary body is adjusted to the other electrode plate attached to a similar flat plate movable body by adjusting the taper rod. It may be configured to do so.

[Effects of the Invention] As is clear from the above description, the present invention forms the receiving electrode from a pair of receiving electrode elements, and the difference between the electric signals generated between the receiving electrode elements causes the one electrode plate and the other electrode plate to differ from each other. Since the parallelism detecting means for detecting the parallelism is provided, the parallelism of both electrode plates can be established easily, quickly and accurately. As a result, the cost of the apparatus can be reduced, and there is an excellent effect that stable displacement detection can be guaranteed with high accuracy.

[Brief description of drawings]

FIG. 1 is a circuit diagram showing an essential part of an embodiment of the present invention, and FIG.
FIGS. 6 to 6 show a conventional displacement detecting device, FIG. 2 is a circuit diagram of a main part, and FIG. 3 is a diagram for explaining presence / absence of relative inclination between both electrode plates and a change in polar area. ) Is for no tilt,
(B) shows the case with inclination. FIG. 4 is an exploded perspective view of the entire apparatus, FIG. 5 is a front view of the same, and FIG. 6 is a view for explaining the parallelism confirmation work. DESCRIPTION OF SYMBOLS 1 ... Case main body, 6 ... Outer frame, 11 ... Spindle, 20 ... One electrode plate, 21 ... Transmission electrode, 21a-21h ... Transmission electrode element, 23 ... Reception electrode, 23a, 23b. Receiving electrode element, 30 ... Other electrode plate, 31 ... Coupling electrode, 40 ... Detection circuit, 50 ... Parallelism detecting means, 60 ... Parallel adjustment mechanism, 70 ... Positioning mechanism.

Claims (1)

[Claims] 1. A phase discrimination type capacitance sensor including one electrode plate having a transmitting electrode and a receiving electrode, another electrode plate having a coupling electrode, and a detection circuit connected to the receiving electrode, and one electrode plate. And a parallel adjustment mechanism for directly or indirectly participating in one of the other electrode plates to adjust the face-to-face parallelism of the two electrode plates, wherein the receiving electrode sandwiches the transmitting electrode and one electrode The receiving electrode element is formed of a pair of receiving electrode elements arranged to face each other in the width direction of the plate, and the coupling electrode is formed in a size capable of facing the transmitting electrode and both receiving electrode elements, and is induced in each receiving electrode element. A displacement detecting device comprising parallel degree detecting means for comparing face-to-face parallelism of both electrode plates by comparing electric signals.