Understanding the Functionality of Rotary Encoders
Rotary encoders serve as vital components in achieving precise position feedback for both rotary and linear servo motor control, playing a crucial role in high-performance automation. This article delves into the intricate workings of rotary encoders, shedding light on their principles of operation.
Types of Rotary Encoders: Rotary encoders utilize various technologies, including optical, magnetic, capacitive, and inductive. Optical encoders stand out for applications demanding the highest resolution and accuracy. While magnetic and inductive encoders excel in harsh environments, our focus here centers on the optical rotary encoder.
Working Principles of Rotary Encoders:
Selecting a Rotary Encoder: Different rotary encoder technologies suit varying applications. Optical rotary encoders, known for exceptional resolution, accuracy, and repeatability, are our primary focus. While magnetic and inductive encoders thrive in challenging environments, magnetic encoders may be sensitive to external magnetic fields, impacting accuracy over temperature variations.
Optical Rotary Encoder Theory of Operation: Rotary encoders can be either incremental or absolute. Incremental encoders generate position change information, requiring a homing routine to define the zero position. In contrast, absolute encoders provide the actual physical position, eliminating the need for time-consuming homing.
Incremental Rotary Encoders: These encoders use optical scanning of a rotary scale, composed of reflective and non-reflective lines. Incident light creates a projection of the scale, and as it moves, the lines are counted to provide incremental position information. The number of reflective lines determines the resolution, but careful sensor design allows for interpolation to achieve higher resolution. Incremental Rotary Scale
Absolute Rotary Encoders: Incorporating an incremental scale, absolute rotary encoders use a pseudo-random pattern of reflective lines to determine absolute position. This pattern, resembling a barcode, is used during startup to identify a specific line on the incremental track, indicating the absolute position.
Interface and Installation: The interface for an incremental rotary encoder is labeled ABZ, with A and B as square waves, indicating the direction of motion. Z is the index signal or zero reference. Absolute rotary encoders typically use high-speed synchronous serial interfaces, such as BiSS-C.
Installing a modular rotary encoder involves mounting the scale disc to a hub, with concentric alignment critical to minimizing angular error. Eccentricity can be compensated using two readheads, while wide alignment tolerances simplify installation and reduce production costs.
Understanding the intricacies of rotary encoders, especially optical ones, provides a foundation for leveraging their capabilities in diverse industrial applications.