JPH0455701A - Measuring method for displacement through impedance of coil - Google Patents

Abstract

PURPOSE:To make it possible to measure displacement highly accurately without contact by making an AC flow through three coils having the different distances with respect to a material to be measured, and operating the distance between the material to be measured and the coils based on the amounts of the changes in impedance of the coils. CONSTITUTION:AC is made to flow through three coils L1 - L3 having the different distances with respect to a material to be measured 1. Then, the impedance of the coils L1 - L3 are changed differently with changes in distances between the material to be measured 1 and the coils L1 - L3. The distance X between the coils L1 - L3 and the material to be measured 1 is operated and obtained by the specified expression based on the differences in changing amounts of the impedances.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) The present invention applies eddy currents generated in a conductor due to changes in a magnetic field. Generally, when an alternating current is passed through a coil, the magnetic field changes, and the fluctuations in the magnetic field generate eddy currents in conductors within the magnetic field. The impedance of the coil changes due to the eddy current.

When three coils are fixed at different distances from the conductor and an alternating current is passed through the coils, the impedance of the three coils changes differently as the distance between the conductor and the coil changes. From the difference in the amount of impedance change,
The distance between the coil and the object to be certified (hereinafter referred to as displacement) is calculated by the following equation.

X = Ln-” [E J LnY 1 + E2 Ln
Yl +Els LnY30E4 ] ■ Here, X is the displacement to be sought.

Ln-' means antilogarithm.

Yl, Yi, and Ys are the impedance changes of each of the three coils.

LnX is the natural logarithm of X. The meaning of Ln is the same below.

El, E, , E, and R4 are constants.

As is conventionally known, when measuring displacement using eddy currents, the impedance of the coil is affected by the material and shape of the object to be measured.

Therefore, when the material or shape of the object to be measured changes during measurement, for example, when the object is a workpiece in a machine tool, it has been impossible to measure displacement using eddy currents.

The present invention is not affected by such changes in the object to be measured.
The purpose is to measure displacement with high precision in a non-contact manner.The equations that lead to the present invention will be solved below.

Note that the constant used here means a numerical value that is not affected by the material, shape, or displacement of the object to be measured, or a value that can be ignored. Further, a variable means a numerical value that is affected by the material or shape of the object to be measured, or by displacement.

The relationship between the displacement and the impedance of each coil is approximated by a power function. The functions of this power are shown in equations ■, ■, and ■.

Zt = At X-” +c.

Z! = A x X-" + CyZ3"
As X-113+ Cs, Zs, Zs and Z3 are each three coils L1. L! and the impedance of A3.

X is the displacement between the coil and the object to be measured.

X-1 means X to the (-Bl) power. A, , A, and A3, which are the same below, are variables influenced by the material, shape, and displacement of the object to be measured.

B, , B, and R3 are variables influenced by the material and shape of the object to be measured.

Cs, Cs and C3 are constants.

From the above three equations, impedance 2. ．． 2° and z3
are replaced by impedance changes ff1y, , Y, and Ys as follows.

Yl = Z1 - C.

Y, =Z, -c.

Ys ” Zs Cs From these, formulas ■, ■, and ■ can be replaced with the following three formulas.

Y * = A t X-”” Yl = A, X-” Y s = A s It is expressed as a function.

A * = Rx. AI”” A,=R3゜A,”” still.

R1°, R□, R3° and R3□ are constants.

The variables B and R3 in formulas ■, ■, and ■ are as follows,
From a physical phenomenon, it is expressed by a linear equation of variable B1.

B z = D xoB 1 + D 2BB3
=D. B, +D3 degrees, D. , D□, R3° and R31 are constants.

The above formulas of AI, A, , B, and R3 are expressed as ■ and ■
By substituting into , the following formula is obtained.

Yl = A, X-"Y,: RzoA, 121 X-fD20R+
40211Ys =R3,A, ”'X'
-"""""'"If we take the logarithm of both sides of 1 in the three equations listed in 1, eliminate the variables A and B1, and find X, we find the above-mentioned equation (2). However, the coefficient E1 of formula ■,
Ex, B3 and E are constants determined by the following formula.

E I = (R3+Dxo Rz+D3o)/M
■Ez=(Da.-R3□)/M [Phase] B3=CR□-D2゜)/M ■E4'' (D mol, nR30R2+I-n
R3゜+ R3+LnRto D 3oLnRzo)
/M −@ Note that M in the above formula is expressed by the following formula.

M = D zoD 3I D 21D3 (+
+ R31D zx-RxID Constant E used in formula 31 ■ 1. Ex, B3 and B4 are the above constant D
to-D zs, D so, D sl, R! o,
It can be determined from R21, R3°, and R3□,
The constant D2゜, I)zt, B3゜, B31, R3゜,
R2I, R30, and R31 can be determined by experiment.

However, when implementing this method in an electronic circuit, the constant Dz
o, D! 1. B30. B31. RlO, Rx+
, R30, and R31, El, E
It is possible to determine x, B3 and B4 directly.

That is, since Er, Ex, E, and E are constants, the values of Y, , B2, and B3 are measured for four different known displacements, and the measured values are substituted into equation (1). By creating four simultaneous equations with E□, Ez, Es, and B4 as unknowns, and solving the equations, E
Find l, E, , El and B4.

If you enter the formula, you will find the formula ■.

However, the coefficient F of formula (■) is 1. Fx and B3 are constants determined by the following formula.

(2) The formula used in claim 2 is shown in formula (■). This formula (■) is derived from the formula by relaxing the physical conditions.

F r = (Dto B30)/NF! =
(D,.-1)/N LnX = F + Ln (Y + / Y x
) + p' z Ln (Yx / B3
) 10 Fyu ■ Here, F, , F, and B3 are constants.

Below, I will explain how to guide Ni〇.

Among the constants used in formulas (1), [phase], (2), (2), and 0, constants R31 and R31 physically take values close to 1. From this, Rx + = R3r = 1
Assuming this as
oD3. D! ID3G+D! Constant F1 of 1-D31 formula (■). F and Fyu are constants E1. E,,B3
And B4 can be calculated by finding the amount of change in impedance of the coil from the known displacement in the same way as finding B4.

Effects of the Invention When conventional methods are used, the impedance of the coil caused by eddy currents varies depending on the material or area of the object to be measured, in addition to displacement.

Therefore, when the material or shape of the object to be measured changes during measurement, for example when used in machining eliIIA, it is difficult to accurately measure displacement without contact.
It was impossible.

The present invention is capable of measuring displacement despite such changes in the material and shape of the object to be measured6.

[Brief explanation of drawings]

It is an object of the present invention to measure the Object to be measured oscillator magnetic field Coil L. Coil L2 Coil L3 displacement Spacing between coils Spacing between coils j11 figure

Claims (2)

[Claims] (1) An alternating current is passed through three coils placed at different distances from the object to be measured, and the amount of change in impedance of each of the three coils due to the eddy current generated in the object to be measured is calculated. A method of calculating and finding the distance between an object and a coil. (2) A method of determining the distance between the object to be measured and the coil using a simpler calculation formula that can be derived from the calculation method described in claim 1.