JPH0335118A - Structure of electrostatic capacity type detection head permitting accurate extension - Google Patents

Abstract

PURPOSE:To reduce errors by divided areas by dividing the core electrode part of a measuring common electrode which moves according to displacement by length which is nearly a half as long as its measurement range and providing movable electrodes and reference ring electrodes corresponding to the two core electrode parts. CONSTITUTION:When the length from a start point to a switching origin P near a mid-point is measured, a movable electrode A1 and a reference ring electrode C1 are applied with opposite-phase voltages of the same frequency. Consequently, capacity Cm is formed between the electrode A1 and a core electrode part B1 and capacity Cr is formed between the electrode C1 and a reference core electrode D. A current (i) is induced at a common electrode B by those capacity Cm and capacity Cr. This current is proportional to the displacement of the electrode B and the quantity of the displacement can be measured from this current. Further, when subsequent measurements are taken from an origin P, a movable electrode A2 and a reference ring electrode C2 are applied with opposite-phase voltages of the same frequency. At this time, the current (i) induced at the electrode B is obtained by the capacity Cm formed between the electrode A2 and a core electrode part B2 and the capacity Cr formed between the electrode C2 and electrode D.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to the structure of a capacitive detection head that converts an amount of mechanical displacement into an electrical signal as a change in capacitance. The present invention relates to a structure capable of accurately extending the measured displacement amount of a detection head having a reference capacitance and a variable capacitance, and obtaining mechanical displacement by comparing the variable capacitance value with the reference capacitance value.

<Prior Art> A conventional capacitive detection head of this type has a structure as shown in FIG. 4.

This includes a fixed adjustment capacitor for adjusting the measurement starting point and a variable measurement capacitor.

That is, this detection head includes a cylindrical variable electrode 1, a core electrode 2 movable on the center line within the variable electrode 1, and an adjustment electrode electrically connected to the core electrode 2 by, for example, a flexible cable 4. It is composed of a core electrode 3 and a ring electrode 5 centrally arranged around the outer periphery of the adjustment core electrode 3.

In this detection head, with the tip of the core electrode 2 slightly inserted into the variable electrode 1 as shown in FIG. 4, the capacitance C formed by the variable electrode 1 and the core electrode 2
It is set or adjusted so that the sum of the currents induced on the core electrode 2 from the capacitance Cr formed by the adjustment core electrode 3 and the ring electrode 5 becomes zero.

As a result, the tip of the core electrode 2 at this time is located at the 8
This point is the zero starting point for measurement.

When the core electrode 2 is further inserted into the variable electrode 1 beyond 8 points, a current i that changes in proportion to the displacement X from the 8 points is obtained on the core electrode 2, and from this current value the displacement Measure.

<Problems to be Solved by the Invention> In the capacitive detection head having the above configuration, in order to set the measurement range to a long stroke such as 40 mm, 50 mm or more, the length of the core electrode 2,
It is also necessary to make the length L2 of the variable electrode 1 at least longer than the measurement range. For example, if the measurement range is 40mm, it is necessary to set L2≧40mm and LL≧40mm.If the measurement range is several tens of mm or more, the accuracy can be measured on the order of 1μm or 0.1μm or more. In order to ensure this over the entire range, it is necessary to keep the geometrical tolerances such as cylindricity and surface roughness extremely small over the entire length of the core electrode and variable electrode, that is, to keep the machining errors to an extremely small level. be.

This not only immediately leads to an increase in costs, but also poses the problem of being forced to limit the accuracy of the processing machine itself that processes the electrodes and the like.

The purpose of the present invention is to avoid increasing processing costs,
Another object of the present invention is to provide a structure of a capacitive detection head that can extend the measurement range with high precision without being limited by the precision of processing machines.

Means for Solving the Problems> The capacitive detection head of the present invention includes first and second variable electrodes A, A2, which are cylindrical and arranged in parallel on the same center line.
and first and second core electrode portions B3. B2, a measurement common electrode B movable on the center line; a reference core electrode electrically connected to the measurement common electrode and fixed;
First and second reference ring electrodes C, C2 are provided concentrically around the outer periphery of this reference core electrode. A voltage is applied to the reference ring electrode C1, and at the latter stage of the force measurement range, the second variable electrode A2 and the second reference ring are connected to the gummy electrode C1.
A voltage is applied to each, and the displacement is measured from the current i induced in the common electrode B at this time.

In the capacitive detection head of the present invention, measurement from the starting point to the switching origin P near the midpoint is performed using the first variable type f! A
Voltages having the same frequency and opposite phases are applied to the reference ring electrode C1 and the first reference ring electrode C1.

As a result, the first variable electrode AI and the first core electrode part B
A capacitance Cm is formed between the first reference ring electrode wlCI and the reference core electrode wlCI, and a capacitance C! - is formed.

A current i is induced in the common electrode B by these capacitances Cm and Cr. This current i is a current that is proportional to the displacement of the common electrode B, and the amount of displacement can be measured from this current.

Further, for measurements after the switching origin P, voltages having the same frequency and opposite phases are applied to the second variable electrode A2 and the second reference ring electrode C2, respectively. At this time, a capacitance Cm formed between the second variable electrode A2 and the second core electrode portion B2, and a capacitance Cm formed between the second reference ring electrode C2 and the reference core electrode portion A current i induced in the common electrode B by Cr is obtained.

<Example> The present invention will be described in detail below based on the drawings.

FIG. 1 is a schematic explanatory diagram showing the structure of a capacitive detection head according to an embodiment of the present invention.

A1 is a cylindrical first variable electrode, and A2 is a cylindrical second variable electrode.

The first and second variable electrodes AI and A2 are arranged at a constant interval so that their centers are located on the same center line.

10 is the first and second variable type t? jIt is an insulating member for keeping the interval between A1 and A2 constant, and is interposed between the first and second variable electrodes A1 and A2.

B is a measurement common electrode movable on the center line within the first and second variable electrodes A, , A2.

This measurement common electrode B includes a first core electrode part B1 and a second core electrode part B1.
A core electrode portion B2 is provided.

The first and second core electrode portions B, B2 are attached to the measurement tool conducting electrode B at a constant interval, and their outer peripheral surfaces and the first and second variable electrodes A I, A 2
are arranged so that the inner circumferential surface thereof is at a predetermined interval.

A shield ring 20 is arranged between the first and second core electrode portions Bl and B2 via ring-shaped insulating spacers 21, 23 and cylindrical insulating spacers 22. This shield ring 20 and insulating spacers 21, 22, 23
Therefore, the distance between the first and second core electrode portions B1 and B2 is kept constant.

Note that this shield ring 20 is grounded in this embodiment.

D is a reference core electrode that is electrically connected to and fixed to the measurement common electrode B by a coil spring 30 or the like.

cl and C2 are cylindrical reference ring electrodes, which are arranged concentrically so that their inner peripheral surfaces and the outer peripheral surface of the reference core electrode are spaced apart from each other by a predetermined distance.

Next, the operation and function of the capacitive detection head having the above structure will be explained using FIGS. 1 to 3.

As shown in FIG. 1, when the tip of the first core electrode part B is inserted up to point a near the opening in the first variable electrode AI, the second core electrode part B2 is inserted into the insulating member. It is located within 10.

In this state, a constant AC voltage VI is applied to the first variable electrode A, and at the same time, the first reference ring electrode C1
An AC voltage V2 having the same frequency and opposite phase as the AC voltage V8 is applied to the AC voltage V8. Also, at this time, the second variable current A2 and the second
Both reference ring electrodes C2 are grounded.

At this time, a capacitance Cm is established between the first variable type [t A l and the first core electrode portion B1 and between the first reference ring voltage P i c 1 and the reference core electrode D, respectively.

Cr is formed. Currents are induced in the measuring device current ff1iB by these capacitances Cm and Cr, and the voltage V2 is set so that the sum i of the currents becomes zero. The value of the current i may be set to zero by adjusting the distance between the first reference ring electrode CI and the reference core electrode using the adjustment screw 41 provided at C1.

When set in this way, point a becomes the starting point of the first stage of measurement.

Next, in the process of displacing the measurement common electrode B from the state shown in FIG. 1 to just before the state shown in FIG. The third variable electrode A1 and the first reference ring electrode C
Voltages V I and V 2 are applied to I, respectively,
Common measurement type [! The capacitance Cm is varied in accordance with the displacement of B, thereby making it possible to obtain a current i that is proportional to the displacement.

Thereafter, as shown in FIG. 2, the tip of the first core electrode part B reaches the switching origin P, and the tip of the second core electrode part B2 reaches the Q within the vicinity of the end of the second variable electrode A2. When you reach the point,
A constant alternating current voltage V is applied by switching from the first variable electrode A1 to the second variable electrode A2, and the first variable electrode A1 is grounded.

Also, at this time, an AC voltage V2 having the same frequency and opposite phase as the voltage Vl is applied by switching from the first reference ring electrode C1 to the second reference ring electrode C2, and the first reference ring electrode C1 is grounded. Ru.

In this case, the second variable electrode A2 and the second core electrode part B2
A capacitance Cm is formed between the second reference ring electrode C2 and the reference core electrode C2, and a capacitance Cr is formed between the second reference ring electrode C2 and the reference core electrode C2.

This time, a current is induced in the measurement common electrode B by these capacitances Cm and Cr, and the voltage V2 is increased again so that the sum i becomes zero.
Set.

Note that, without changing the voltage V2, the current i may be adjusted to zero using the adjustment screw 42 provided on the second reference ring electrode C2. Further, the voltage applied to the second reference ring electrode C2 does not necessarily have to be the voltage V2;
It is sufficient if the voltage value is set so that the current i obtained from the measurement common type fiB becomes zero when the core electrode portion B2 of is at the position of the Q point.

By setting in this way, the Q point becomes the starting point of the latter part of the measurement.

Here, in the process of displacing the measurement common electrode B from the state shown in FIG. 2 to the state shown in FIG. Voltage V on C2 respectively 4. V 2 is applied, and the capacitance Cm is varied by the displacement of the measurement common electrode B from the point Q, so that a current i proportional to the displacement is induced on the measurement common electrode B.

As described above, in this embodiment, displacement is measured using currents induced by capacitances formed between different electrodes at the front and rear stages of the measurement range, respectively.

In this embodiment, it is preferable that the position of point P in FIG. 2, that is, the position of the switching origin, be set accurately at approximately half of the measurement range.

For example, the position of the switching origin P when the measurement range is 40 mm is determined by actually displacing the measurement common electrode B accurately by 20 mm using a high-precision length measuring device or block gauge capable of measuring on the order of 1Q nm. The current value (or the value converted to a voltage value) obtained from the measurement common electrode B at that time is set in advance by storing it in an electronic device (not shown) or the like.

The capacitive detection head in this embodiment measures the current induced by the first core electrode part B up to this switching origin P, and at this switching origin P, this current is forcibly set to zero, and the switching is started. After the origin P, the measurement is performed using the current induced by the second core electrode portion B2.

Therefore, by accurately setting the position of this switching origin P, displacement can be precisely measured before and after this switching origin P, and as a result, the measurement range can be extended.

In addition, when the first core electrode part B1 reaches the switching origin P, the measured displacement amount is displayed as 20 mm from the value stored in the electronic device, and after this switching origin P, the second core A value based on the current induced by the electrode portion B2 is added to the 20 mm display at point P and displayed.

Further, in the above embodiments, edge effects and stray capacitances occurring between each electrode are not taken into account.

However, in actual products, the dimensional relationships of each component are set after taking these into consideration.

Furthermore, although only one switching origin P is provided in this embodiment, by providing multiple switching origins within the measurement range, it is possible to adjust the positional accuracy of the parts in front and behind each switching origin, respectively. This makes it possible to obtain a detection head with higher accuracy.

<Effects of the Invention> According to the present invention, the core electrode portion of the measurement common electrode that moves according to displacement is divided into approximately half the length of the measurement range, and each of the two core electrode portions is divided into two parts. Since corresponding variable electrodes and reference ring electrodes are provided, errors can be reduced for each divided range. Therefore, it is no longer necessary to apply continuous geometric tolerances over the entire length of the measurement range as in the past, so processing costs can be significantly reduced compared to the past, and the limitations of the processing machine are not excessive. It disappears.

Furthermore, since the switching origin is provided within the measurement range, measurement errors occurring before the switching origin are not accumulated in subsequent measurement values, and accuracy can be improved.

Furthermore, according to the present invention, there is no need to consider geometrical tolerances over the entire length of the measurement range, so the gap between the variable electrode and the core electrode can be made smaller than in the conventional method. The capacitance change of the variable capacitor per unit measurement length can be increased while maintaining geometric tolerance and measurement accuracy, and the sensitivity and stability of measurement can be improved accordingly.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the structure of a capacitive detection head according to an embodiment of the present invention, and FIGS. 2 and 3 are diagrams showing a state of displacement measurement by the capacitive detection head shown in FIG. 1. , FIG. 4 is a diagram showing the structure of a conventional capacitive detection head. a first variable electrode, a second variable electrode, a measurement common electrode, a first core electrode section, a second core electrode section, a first reference ring electrode, a second reference ring electrode, and a reference core electrode.

Claims (2)

[Claims] (1) Cylindrical first and second variable electrodes (A_1, A_2) arranged in parallel at a constant interval on the same center line
and the first and second core electrode parts (B_
1, B_2), and the first and second variable electrodes (A
The measurement common electrode (
B), a reference core electrode (D) electrically connected to and fixed to the measurement common electrode (B), and first and second electrodes provided concentrically around the outer periphery of the reference core electrode (D). The first variable electrode (A_1) is equipped with two reference ring electrodes (C_1, C_2), and a constant AC voltage is applied to the first variable electrode (A_1) in the first stage of measurement up to the switching origin (P), which is preset near the midpoint of the measurement range. (V_1) and the first reference ring electrode (C_
1) A measurement AC voltage (V_2) of the same frequency and opposite phase as the AC voltage (V_1) is applied to the first variable electrode (A_1).
Capacitive coupling (Cm) between and the first core electrode part (B_1) and the reference core electrode (D) and the first reference ring electrode (C_1
) and capacitive coupling (Cr) to the measurement common electrode (B
) is measured in proportion to the current (i) induced on the common electrode (
B), and in the subsequent measurement stages including the switching origin (P), the AC voltage (V_1) is switched and applied from the first variable electrode (A_1) to the second variable electrode (A_2). At the same time, the measured AC voltage (V_2) is transferred from the first reference ring electrode (C_1) to the second reference ring electrode (C
_2) and apply the capacitive coupling (Cm) between the second movable electrode (A_2) and the second core electrode part (B_2) and the reference core electrode (D) and the second reference ring electrode (C_2).
Measurement common electrode (B) by capacitive coupling (Cr) with
Precisely extendable capacitive sensing head structure, characterized in that it measures the displacement of the measuring common electrode (B) from the switching origin (P) in proportion to the current induced thereon. (2) The first and second variable electrodes (A_1, A_2)
and the first and second reference ring electrodes (C_1, C
_2) The structure of the precisely extendable capacitive detection head according to claim 1, wherein when a voltage is applied to one of each, the other is grounded.