Abstract
The magnetic scale is an incremental pattern device which is utilized as position encoder to measure linear displacement digitally.
It has two tracks of the sinusoidal remanence pattern of the same period, the phase of which is shifted 90°each other, hence both the magnitude and the direction at a displacement can be determined.
The remanence pattern is written by the magnetic recording head onto the thin magnetic layer which is coated on a square glass rod.
The sinusoidal pattern is obtained by making flow a signal current of frequency f superposed with the ac bias current into the recording head which moves at a constant speed v relative to the magnetic coating. The period of the pattern 2 is determined by λ=ν/f.
The pattern is detected by a flux-sensitive head, hence the detection is possible even at rest.
The output signals from the detector are shaped squarely. One of the squared signals branches out to two buses which emit pulses each time when the signal rises up or falls down, respectively. These pulses are gated by the signal from the other track, hence the pulses in the two buses pass the gates according to the direction of the displacement each time when the detecting head comes to the points of zero remanence.
These pulses are counted by a reversible counter.
The period of the pattern can be made as small as 30 /μ.
An improved read-out circuit which can be easily constructed utilizing the above mentioned circuitry can interpolate digitally the period into one-fourth.
The precision of the read-out of the pattern is about 0.6 μ.
