Abstract
Optical encoders are mainly used in modern motion servo systems for high-resolution and reliable position and velocity feedback. Pseudorandom optical rotary encoders are single-track and use a serial pseudorandom binary code to measure absolute position. The realization and analysis of such a rotary encoder with advanced code scanning and error detection techniques, as well as an improved redundancy in operation, are presented. A presented serial code reading solution uses two phase-shifted code tracks and two optical encoder modules. So, the realized encoder, hybrid in nature, provides “output on demand” and more or less reliable position information using very efficient error checking. Compared to a standard absolute encoder, this encoder requires a smaller code disc, facilitates installation, has greater flexibility in operation, and is less sensitive to external influences.
Highlights
Optical rotary position encoders as widespread optoelectro-mechanical sensors enable the measurement of angular position in various industrial movable systems, such as robotic arms, elevators, telescopes, and others [1]–[5]
A window, n bits wide, that slides along the pseudorandom binary sequence (PRBS) code track of n-bit resolution extracts a unique code word providing position information [9]
Serial reading of pseudorandom code is possible since n - 1 bits of two adjacent code words are the same, which is an advantage over standard absolute encoders, where n code reading heads are required
Summary
Optical rotary position encoders as widespread optoelectro-mechanical sensors enable the measurement of angular position in various industrial movable systems, such as robotic arms, elevators, telescopes, and others [1]–[5]. Different methods [10] for detecting code reading errors can be applied to pseudorandom absolute encoders to increase their reliability. Since the pseudorandom encoder contains a synchronization track, all developed methods for estimating and correcting errors in incremental encoders [22] can be applied to this encoder to increase its accuracy and reliability. The additional head and code track in the proposed encoder have been used extensively to increase the reliability and flexibility of the encoder, which could not be feasible with the solutions presented in the references [6], [7], and [12]. Presented pseudorandom rotary encoder uses four signals from code reading heads to perform absolute position measurement within the implemented operation algorithm. The disadvantage of this solution is its complex practical realization since the code reading heads are at a very short distance, which is determined by the encoder resolution and disc diameter and is affected by vibration and temperature
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