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      BEST SOLUTION Finite Element Analysis Consultancy 

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. 
Picture of a solid model of a variable reluctance resolver rotor and stator core Screen shot of spreadsheet based calculations for variable reluctance resolver winding distribution Finite element plot of a variable reluctance resolver showing flux density in the core
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