Precision Angle Measurement Systems on the Basis of Ring Laser Gyro

The main application of a ring laser gyroscope is navigation. It is currently the most widely used device for strapdown inertial navigation systems. However, it is also applicable for high-precision angle metrology systems. This paper discusses the properties of a laser dynamic goniometer (LDG) based on the ring laser gyroscope and designed for the calibration of optical polygons and digital angle converters, and for the measurement of angles between external mirrors (theodolite operating mode). We consider the main sources of uncertainty, such as the ring laser gyro bias due to an external magnetic field and the instability caused by the velocity of rotation along with applicable methods of their compensation. The reversal method providing separation of uncertainties of the LDG and the calibrated angle converter is analyzed in detail. The simplified cross-calibration method is also considered. The results of calibration of optical encoders of various designs—with and without their own rotors (on-axis and off-axis in Euramet terminology)—are presented. Some results of the dynamic goniometer for the measurement of angles between external mirrors are presented. It is shown that the LDG in this mode of operation demonstrates better accuracy than modern theodolites and total stations.

Method for investigating the error of a laser dynamic goniometer

A method for investigating the error of a laser dynamic goniometer by cross-calibration using a new calculation algorithm is proposed. The algorithm is based on the method of serial angle shifts of a polygon relative to ring laser of the goniometer. The results of using this algorithm for estimating the error of a laser dynamic goniometer are presented. The dominant source of error of this goniometer is determined ‒ the irregularity of the angular scale of the ring laser, which is caused by the slope of the scale to the axis of rotation of the goniometer spindle. Corrective corrections were calculated and introduced into the calculation algorithm, which allowed reducing the systematic error of the goniometer to 0.03″.