Fig. 1. Schematic of using plane mirror-autocollimation theodolite to measure angle error

Fig. 2. (a) Relative position relationship between encoder and plane mirror coordinate system; (b) relative position relationship between plane mirror coordinate system and theodolite coordinate system

Fig. 3. Angle system error with different ω when δ, α are 0

Fig. 4. Elevation angle of theodolite with different ω when δ, α are 0

Fig. 5. Angle system error with different δ when ω is 2° and α is 1°

Fig. 6. Elevation angle of theodolite with different δ when ω is 2° and α is 1°

Fig. 7. Angle system error with different α when ω is 2° and δ is 10°

Fig. 8. Elevation angle of theodolite with different α when ω is 2° and δ is 10°

Fig. 9. Experimental device for testing the angle error of the encoder

Fig. 10. Angle error of encoder with zero system error

Fig. 11. Angle error of encoder with system error

Fig. 12. Angle error after correcting system error