Encoders

Verapath optical encoder technology uses a large-area illumination and detection system with a low-coherence LED source to achieve contamination tolerance without sacrificing accuracy. This article describes the sensing architecture, signal quality characteristics, and the reliability advantages of the wide-area approach for industrial environments.

Resolvers and modern digital rotary encoders both provide angular position feedback for servo motors. Resolvers dominate applications above 150°C operating temperature where encoder electronics would fail. Below 150°C, digital encoders provide better resolution, direct digital output, and lower system integration cost. This article defines the boundary conditions for each technology.

Incremental and absolute rotary encoders solve fundamentally different feedback problems. Understanding how each encodes position determines which technology is appropriate for a given motion control architecture.

SATCOM antenna pointing systems require absolute position feedback with high accuracy, wide temperature range, and immunity to EMI from the antenna itself. This article defines the pointing accuracy budget, environmental constraints, and encoder technology selection for SATCOM-on-the-Move (SOTM) and fixed SATCOM systems.

CNC machine tool axis position feedback requirements differ from general motion control applications in their combination of high resolution, tight accuracy specification, wide speed range, and tolerance for machining coolant. This article defines the encoder parameters required for CNC servo axis, spindle speed, and linear position feedback applications.

Torque motors are frameless, high-pole-count brushless motors designed for direct drive without gear reduction. Position feedback for torque motors requires absolute encoders with sufficient resolution to provide commutation data across the large number of pole pairs, while achieving the axis accuracy required by the application.

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.