Abstract: To address challenges commonly encountered with optical projection-type length measuring machines during use,such as difficulty in reading, inaccurate readings, and accuracy degradation caused by optical system aging, a technical solution for upgrading the traditional human eye-based engraved line optical system to a grating-based digital display system was proposed. Based on grating length measurement technology,the solution included the design and installation of a marble guide and a grating measurement system to achieve high-precision digital length measurement. High-precision grating micrometer sensors were employed to ensure accurate probe zeroing and consistency in the contact force applied to the measured components during the measurement process. A specialized grating digital display unit,developed using Complex Programmable Logic Device (CPLD) technology,enabled high-speed real-time processing of signals from the grating scale and micrometer sensors.Additionally,software for the upper computer of the length measuring machine was developed,incorporating modules for error correction and compensation algorithms,data processing and display,database management,and auxiliary function control. Experimental results demonstrate that the upgraded length measuring machine achieves a resolution of 0.1 μm. Within a 2 m measurement range,the display error is ±(0.5+L/300) μm. Compared to the original optical projection-type length measuring machine,the upgraded system offers significantly improved accuracy,simplified readings,and enhanced stability of the display values. The system meets the requirements for metrological verification of measuring instruments.In conclusion,this method has high application value and strong potential for widespread adoption.

Key words: measuring instruments, length measuring machine, raster digital display, upgrade and renovation