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Rod axial position detector including plural scales wherein nonmagnetized portions have differing spacing and differing depths and means for calculating the absolute position are provided
Rod axial position detector including plural scales wherein nonmagnetized portions have differing spacing and differing depths and means for calculating the absolute position are provided
A magnetic scale is formed by a plurality of non-magnetic parts arranged at equidistant intervals in all axial direction on a magnetic rod which displaces in the axial direction. The non-magnetic parts consist of first non-magnetic parts having a constant depth, and second non-magnetic parts having a different depth. A magnetic sensor which outputs a signal according to the depth and positional change of the non- magnetic parts is installed at a fixed position opposite the magnetic scale. Further provided are a mechanism for identifying a second non- magnetic part which has passed the magnetic sensor based on the output of the sensor, a memory for individually storing the absolute positions of the second non-magnetic parts, and a mechanism for calculating the displacement of the rod from the identified second non- magnetic part to its current position based oil the sensor output. The absolute position of the rod is detected, in terms of a small displacement from its stationary position, by computing it from the absolute position of the identified second non-magnetic part stored in the memory and the displacement of the rod from this second non-magnetic part. This assembly comprises only a single magnetic scale having several types of non- magnetic parts, and is therefore more economical to manufacture than the conventional assembly having a plurality of magnetic scales.
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