Electromagnetic induction type position detector

摘要

A control unit of a linear scale includes: excitation current supplying device for causing excitation currents each having two different angular frequencies to flow through slider coils; sampling device for sampling induced voltage V induced in a scale coil, at a timing of t=(2j+1)π/(2ω) (j: an integer); position detecting device for calculating Va(j) which is a sum of samples of the induced voltage at multiple sampling points, calculating an excitation position α at which the Va(j) is equal to 0, and setting the α as a detected position X; and abnormality detecting device for calculating Vb(j) which is a sum of absolute values of the induced voltage at multiple sampling points, comparing the Vb(j) with a threshold value, and determining that the electromagnetic induction type position detector is in an abnormal state when the Vb(j) is equal to or lower than the threshold value.

主权项

1. A position detector using electromagnetic induction, comprising:
a detection unit including a primary-side member and a secondary-side member, the primary-side member including a first primary-side coil and a second primary-side coil, the secondary-side member including a secondary-side coil and arranged in parallel to the primary-side member to face the primary-side member; and a control unit, wherein the control unit includes:
excitation current supplying means for causing a first excitation current Ia to flow through the first primary-side coil and causing a second excitation current Ib to flow through the second primary-side coil,where
Ia=−I cos(kα)sin(ωt)+I′ sin(ω′t)Ib=I sin(kα)sin(ωt)+I′ cos(ω′t) provided that
I, I′: magnitudes of the excitation currentsk: 2π/pp: a value of one pitch of the coilsω, ω′: different angular frequencies of the excitation currents and ω′=(n+1/2)ω (n: an integer) is satisfiedt: a time pointα: an excitation position; sampling means for sampling an induced voltage V induced in the secondary-side coil, at a timing of t=(2j+1)π/(2ω) (j: an integer); and abnormal state detecting means for selecting samples of the induced voltage V at a plurality of sampling points from the samples of the induced voltage V obtained by the sampling means, calculating Vb(j) which is a sum of absolute values of the samples of the induced voltage V at the sampling points, comparing the thus-calculated Vb(j) with a threshold value L, and determining that the position detector is in an abnormal state when the Vb(j) is equal to or lower than the threshold value L.