Lisandro Piacentini

Multi-turn absolute encoders extend single-turn absolute position measurement across multiple revolutions, providing absolute angular position data for axes that may rotate more than 360°. Two principal implementation methods — gear reduction with additional encoder tracks, and revolution counting with non-volatile memory — offer different tradeoffs in complexity, power consumption, and resolution.

Velocity control in servo systems is computed from position encoder data — differentiated over time, filtered, and fed back to the velocity regulator. The differentiation method, filter design, and feedback rate determine the achievable velocity bandwidth and low-speed smoothness. This article covers the four principal velocity estimation methods and their performance tradeoffs.

Absolute encoder position data is transmitted via synchronous serial protocols. BiSS-C, SSI, and SPI each handle clock generation, data framing, and error detection differently. The choice of protocol affects maximum achievable update rate, cable length, error detection capability, and compatibility with existing servo drive hardware.

Accuracy, resolution, and repeatability are three independent performance parameters of a rotary encoder. All three appear in datasheets, but they measure different things. Confusing them leads to incorrect encoder selection and missed specifications. This article defines each parameter with measurement context and explains how they interact in a complete position feedback system.

Electric encoder technology uses capacitive field modulation — rather than optical or magnetic principles — to measure absolute angular position. The holistic sensing approach measures the entire encoder area simultaneously, providing inherent immunity to localized contamination and relaxed installation tolerances without sacrificing accuracy.

Optical encoder alignment tolerances for small-diameter rotary scales (≤ 20 mm) are significantly tighter than for linear scales or large-diameter rotary discs. This article defines the radial (Y-axis) tolerance reduction for small scales, explains the optical geometry responsible for the tighter requirement, and provides mounting design recommendations.