interaxis

Interaxis refers to the angular relationship between the stator and rotor winding sets in a resolver, specifically whether they maintain the correct 90-degree mechanical separation. A resolver converts rotational position into electrical signals by using two fixed stator windings spaced 90 degrees apart; when one winding is excited, the rotor couples energy to both stator windings in proportions that encode the shaft angle. Interaxis error occurs when this 90-degree relationship degrades, causing the output windings to deviate from true perpendicularity.

In precision resolvers used for aircraft flight control systems, radar antenna drives, or industrial servo feedback, interaxis accuracy is specified in minutes of arc or fractions of a degree. A well-built resolver might hold interaxis error under 10 arcminutes, while military-grade units can reach 5 arcminutes or better. The error manifests as crosstalk between output channels: instead of producing clean sine and cosine outputs, the resolver generates small quadrature errors that corrupt position readback, especially problematic in closed-loop systems where small errors accumulate into control lag or instability.

Sources and consequences

Interaxis error arises during resolver manufacture from mechanical misalignment of the stator laminations, winding fixture tolerances, or rotor imbalance. Thermal cycling, mechanical vibration, and bearing wear degrade interaxis performance over time. The electrical consequence is that excitation of the primary winding produces not purely orthogonal outputs in the secondary pair but instead outputs contaminated with fundamental-frequency feedthrough, reducing effective resolver accuracy by effectively coupling unwanted signal directly into the feedback path.

Designers account for interaxis error through calibration tables loaded into resolver-to-digital converters or through the analog resolver signal conditioning stage. Some systems use dual-speed resolvers or multiple resolver pairs to cancel out known interaxis artifacts. The term sits within broader resolver nomenclature alongside "transformer ratio error" (amplitude balance between channels) and "phase shift" (time delay in coupling), all of which degrade the fidelity of angle-to-voltage conversion that makes resolvers valuable in environments where digital encoders would fail.