Subdivision Error Analysis and Compensation for Photoelectric Angle Encoder in a Telescope Control System

Abstract

As the position sensor, photoelectric angle encoder affects the accuracy and stability of telescope control system (TCS). A TCS-based subdivision error compensation method for encoder is proposed. Six types of subdivision error sources are extracted through mathematical expressions of subdivision signals first. Then the period length relationships between subdivision signals and subdivision errors are deduced. And the error compensation algorithm only utilizing the shaft position of TCS is put forward, along with two control models; Model I is that the algorithm applies only to the speed loop of TCS and Model II is applied to both speed loop and position loop. Combined with actual project, elevation jittering phenomenon of the telescope is discussed to decide the necessity of DC-type subdivision error compensation. Low-speed elevation performance before and after error compensation is compared to help decide that Model II is preferred. In contrast to original performance, the maximum position error of the elevation with DC subdivision error compensation is reduced by approximately 47.9% from 1.42″to 0.74″. The elevation gets a huge decrease in jitters. This method can compensate the encoder subdivision errors effectively and improve the stability of TCS.

Analysis of the Subdivision Errors of Photoelectric Angle Encoders and Improvement of the Tracking Precision of a Telescope Control System

“…The coarse code represents the completed period numbers of subdivision signals A and B the shaft has rotated. The subdivision of A and B is described by the fine code, which includes the subdivision errors [14]. …”

“…In the following Equations, $Q$ is the resolution of the angle encoder, $Q_C$ is the resolution represented by the coarse code, $Q_F$ is the resolution represented by the fine code. The total bits of the angle encoder are the combination of the coarse code bits and the fine code bits [14]. These parameters are expressed as follows:$Q={\left(360/2^{TotalBits}\right)}^{°},$ $Q_C={\left(360/2^{CoarseBits}\right)}^{°},$ $Q_F={\left(360/2^{FineBits}\right)}^{°},$ $TotalBits=CoarseBits+FineBits,$ $CodeAll=CoarseCode\ast 2^{FineBits}+FineCode,$ $FineCodeCorrected=FineCode+\Delta \theta \ast Q_F,$ $CodeAllCorrected=CoarseCode\ast 2^{FineBits}+F...$…”

Study on high precision magnetic encoder based on PMSM sensorless control

“…Rotary encoders are widely used in many applications, and magnetic and photoelectric encoders are very popular ones which have been widely used in control systems (Ellin and Dolsak, 2008;Hao, 2015, 2016). The photoelectric encoder's maximum position error with direct current (DC) subdivision error compensation is reduced by approximately 47.9 per cent from 1.42Љ to 0.74Љ (Su et al, 2015), but with higher precision, its volume also increases (Faudzi et al, 2013). Compared to optical encoder, magnetic encoder is not affected in dusty environment, and it has a simple structure.…”

Adaptive Time Delay Compensation Realization for Remote Ship Main Engine Rotation Measurement

“…Ship main engine rotation speed mesurement is very important and there are already many different kinds of measurement method and instrument for engine rotation speed measuring or cylinder pressure measuring. In those methods opto-elemetronic method is used to measure the rotation speed, which is non-contact speed measuring method [1,2]. Photoelectric speed sensor does not connect with the object to be measured and has no additional load, so photoelectric speed sensor with less measurement error and higher precision and the measurement capability is good.…”