Encoders

Optical encoder performance degrades when contaminants enter the sensing gap. The failure modes differ by contamination type: particulates obscure the scale progressively, while liquid mist can cause sudden signal loss. Contamination-tolerant optical architectures use wide-area averaging and signal processing to extend reliable operation in non-cleanroom environments.

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.

Encoder interface cables carry differential position signals that are highly susceptible to noise, crosstalk, and impedance discontinuities. Correct cable selection — including characteristic impedance, conductor gauge, shielding type, and jacket material — determines whether the encoder achieves its specified noise immunity and signal quality at the required cable length.

Cable shield termination and ground loop prevention are the most common sources of encoder signal noise in servo motor installations. This article defines the correct shielding method for motor and encoder cables, identifies the conditions that create ground loops, and describes practical mitigation techniques.

Glass scales outperform metal tape scales in optical encoders across three critical parameters: coefficient of thermal expansion, grating uniformity, and sustainable accuracy at elevated temperatures. This article establishes when glass is technically required and when tape scales are an acceptable alternative.