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Ultra High Precision Magnetic Absolute Linear Encoder

IP.com Disclosure Number: IPCOM000029458D
Original Publication Date: 2004-Jun-29
Included in the Prior Art Database: 2004-Jun-29
Document File: 1 page(s) / 8K

Publishing Venue



Disclosed is a method to build a high resolution absolute magnetic linear encoder, with ultra low temperature dependency combining Schott's Zerodur ceramics with IBM's tapehead-technology.

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Ultra High Precision Magnetic Absolute Linear Encoder

Today, linear encoders typically consist of a glass scale and an optical readout unit . The long time accuracy of this technology is limited by the thermal behavior of the glass and the resolution is limited by the optical diffraction limit .

    Instead of using a glass scale in the linear encoder, it is proposed to use a material like Zerodur (reg. trademark of Schott Glas: http://www.schott.com/optik/english/products/zerodur/index.html). This glass ceramic material has a vanishing coefficient of linear thermal expansion (less than
0.02*10^6/K). In addition, marks on the scale should not be made optically but magnetically on a thin magnetic film sputtered on top of the scale .

    These magnetic markers can be read by magnetic heads (using MR oder GMR effect). Compared to optical sensors, the density of markers can be increased up to ten times, since there is no diffraction which limits optical resolution of glass scales. It is easy to (magnetically) print 5000 markers per Millimeter with a magnetic write head, whereas the optical limit is about 500 lines per Millimeter. Thus, we have the accuracy and the reproducabilty of an interferometric encoder with only a fraction of expenditure.

    Additionally it is very easy to write a magnetic cray code onto the scale, that can be read out by an array of maybe 8 magnetic heads in a scanning head-assembly (like a Tape Head used in LTO applications ). Evaluating this cray code...