Two-probe optical encoder for absolute positioning of precision stages by using an improved scale grating.

Area of Science:

• Metrology
• Optical Engineering
• Instrumentation

Background:

• Precision stages require accurate measurement of both displacement and absolute position.
• Conventional encoders often necessitate multiple tracks or complex configurations for simultaneous measurement.
• Existing methods face challenges in integrating reference codes with incremental tracks efficiently.

Purpose of the Study:

• To present a novel optical encoder capable of simultaneously measuring displacement and position.
• To develop an encoder with a simplified single-track scale grating.
• To achieve high-precision measurements for advanced positioning systems.

Main Methods:

• Development of an improved single-track scale grating with superimposed reference codes.
• Design of a compact two-probe reading head for code identification and incremental measurement.
• Utilizing grating interferometry for linear displacement reading and a stationary mask for reference code identification.

Main Results:

• Experimental validation of a prototype optical encoder.
• Achieved distance code precision of 0.5 μm.
• Demonstrated linearity error of less than 0.06% for linear displacement measurement.

Conclusions:

• The novel optical encoder successfully enables simultaneous displacement and position measurement.
• The single-track design with superimposed codes offers a more compact and efficient solution.
• The achieved precision and linearity meet the stringent requirements for precision stage applications.