Variable Reluctance Resolvers and Brushless Resolvers

Best Solution can provide bespoke designs for resolvers including variable reluctance resolvers, for specific customer requirements. We have produced designs for customers including 2 pole and 24 pole frameless (sometimes referred to as “slab” or “pancake” ) variable reluctance resolvers for rotor position sensing in motor control applications.

Resolvers have been around for many years, originally used for applications such as gun turret positioning systems, aircraft control surface position sensing, and more recently rotor position feedback for motor commutation. They are still the best choice for many rotary position sensing applications.

A resolver is essentially a variable transformer. Two secondary windings wound on orthogonal axes on the stator produce output voltages which have amplitudes as sine and cosine functions of rotor angular position. The rotor caries the primary winding, in a conventional device, and a shorted orthogonal cross winding would typically be present to inhibit any undesirable components of primary flux.

There are several distinct resolver types, including housed or frameless, (with or without integral shaft and bearings), brushless, which typically use a rotary transformer to provide AC excitation to the rotor, and variable reluctance types which have both primary and secondary windings on the stator, and use a salient laminated magnetic steel rotor to produce variable magnetic coupling with rotor angular position.

We can also provide demodulation electronics for all kinds of resolvers either as an off-the-shelf or bespoke PCB assembly, or a licence to manufacture to our design, depending on your requirements.

Advantages of Resolvers as Rotary Position Sensors

Resolvers have several advantages over other kinds of rotary position sensor:

They are mechanically robust and can withstand high vibration and high shock environments
They are passive sensors and can be made with materials that can withstand high temperatures for prolonged periods
They can be made from inert materials and so can withstand corrosive environments
They have excellent noise immunity and so can be used successfully in electrically noisy environments.

“Best Solution can support engineers engaged in their own development programmes. We can provide advice and guidance on simulation technique, or more specific coaching on design methods for electromagnetic devices, materials, test and measurement.”

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