Automated calibration of multiple long gauge blocks using the KRISS linear measurement system

For efficient calibration of multiple long gauge blocks (LGBs), an automatic alignment system, consisting of a multi-axis stage and an angle sensor, was developed and integrated with the Korea Research Institute of Standards and Science linear measurement system. The stage was designed to be installed in the limited space of the linear measurement system, with the ability to translate and align the linear and angular positions of LGBs. The auto-collimation angle sensor detected the tip-tilt angle of an LGB with an angular resolution of 0.11 '', by image processing the intensity profile of a beam reflected from one of the measured faces of an LGB. Using this automatic alignment system, up to five LGBs were calibrated sequentially without any manual operation or thermal instability. Therefore, multiple LGBs can be calibrated in a short time with small alignment errors and under optimal thermal conditions. When four LGBs with nominal lengths of between 250 mm and 1000 mm were measured, the measurement repeatability of each LGB length was less than 22 nm, and the calibration results agreed well with those obtained by an LGB interferometer within the expanded measurement uncertainty.