Abstract
Photoelectric angle encoders, working as position sensors, have a great influence on the accuracy and stability of telescope control systems (TCS). In order to improve the tracking precision of TCS, a method based on subdivision error compensation for photoelectric angle encoders is proposed. First, a mathematical analysis of six types of subdivision errors (DC error, phase error, amplitude error, harmonic error, noise error, and quantization error) is presented, which is different from the previously used analysis based on the Lissajous figure method. In fact, we believe that a mathematical method is more efficient than the figure method for the expression of subdivision errors. Then, the distribution law and period length of each subdivision error are analyzed. Finally, an error compensation algorithm is presented. In a real TCS, the elevation jittering phenomenon occurs, which indicates that compensating for the amplitude error is necessary. A feed-forward loop is then introduced into the TCS, which is position loop- and velocity loop-closed, leading to a decrease of the tracking error by nearly 54.6%, from 2.31” to 1.05”, with a leading speed of 0.25°/s, and by 40.5%, from 3.01” to 1.79”, with a leading speed of 1°/s. This method can realize real-time compensation and improve the ability of TCS without any change of the hardware. In addition, independently of the environment and the kind of control strategy used, this method can also improve the tracking precision presumably because it compensates the measuring error inside the photoelectric angle encoder.
Highlights
With the development of free space optical communication, a higher tracking precision of telescope control systems (TCS), which usually display arc second-scale accuracy [1,2], is a necessity.The photoelectric angle encoder is a kind of angular sensor, which achieves high resolution by the subdivision of two-way orthogonal moire pattern signals from a fine code disk [3].Obviously, high-precision angle encoders contribute to the high accuracy of TCS
The real photoelectric parameters are not well matched with the processing circuit, and the normal subdivision methods are based on standard sine and cosine signals, which causes subdivision errors [4]
To compensate the subdivision error of the photoelectric angle encoders, whose code disks are small, Wang et al proposed an error compensation method based on an improved Back Propagation (BP) neural network, which brought a 15% improvement in accuracy [8]
Summary
With the development of free space optical communication, a higher tracking precision of telescope control systems (TCS), which usually display arc second-scale accuracy [1,2], is a necessity. Wan et al from Changchun Institute of Optics, Fine Mechanical, and Physics, Chinese Academy of Sciences, designed a high-precision photoelectric angle encoder with a dual-reading system, which satisfies the technique requirements of spaceborne equipment [6] All these high-resolution angle measurements depend on large code disks. To compensate the subdivision error of the photoelectric angle encoders, whose code disks are small, Wang et al proposed an error compensation method based on an improved Back Propagation (BP) neural network, which brought a 15% improvement in accuracy [8]. When working in real systems, neural network-based methods need a considerable time to match the data input with the training sets This is not practical for spaceborne equipment. This method works in real time and can satisfy the requirements of spaceborne equipment
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
