In this paper, a new encoding method for single-track absolute shaft encoder is introduced based on the analysis of the characteristics of the code. This code using the new method has the characteristics of customizable code length and good code balance, which solves the problem that the traditional code length can only be some discrete value and the problem of poor code balance. The new code has abundant redundant information, based on which, it is easy to distinguish whether there is fault in the code recognition.
The nonlinear error of a homodyne interferometer is presented: the amplitudes, the phase and the offsets. An improved
compensation method is introduced since the conventional Heydeman modal' calculation is very time-consuming. First,
the "zero drift" problem is solved with the polarization phase-shifting technology; second, a fast algorithm based on the
Heydeman method is introduced to calculate the errors; and third, electronic circuit is used to remove the nonlinear
errors timely. The test result shows that the nonlinearity of the homodyne interferometer could be reduced to subnanometer
over the measuring range of 20cm, and the accuracy can be improved more than tenfold by the dynamic
compensation method.
Reflective optics is used widely in space optical systems for their achromatization, large aperture and lightweight
compared with refractive systems. Four-mirror system especially off-axis system is desired for its excellent imaging
performance and compact structure. Aberration theory of coaxial four-mirror system based on PW method is analyzed
and the design procedure is proposed to get the initial four-mirror system in this paper. A large field off-axis four-mirror
system is designed based on the theory and the design process. The system contains four conic aspheric mirrors. It has a
2°×0.32° rectangular field of view. The MTF of the system is diffraction-limited and the distortion is less than 0.1%. The
structure of the system is compact and the ratio of total axis length to focal length is about 1/3.9. The excellent imaging
performance and compact structure make it adaptable to space remote sensing systems.
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