What Are The Classifications of Commonly Used Resolvers

The resolver, also known as a synchronous resolver or an electrical transformer, is an electromagnetic sensor primarily used for measuring angular displacement and angular velocity of rotating objects. It consists of a stator and a rotor, with the stator windings acting as the primary side of the transformer, receiving excitation voltage, typically at frequencies such as 400Hz, 3000Hz, or 5000Hz. The rotor windings, functioning as the secondary side, induce voltages through electromagnetic coupling. Common types of resolvers are classified based on various criteria, including their output voltage-to-rotor angle relationship, structural characteristics, and operational principles. Here are some of the most frequently used resolver classifications:

1. Sine-Cosine Resolver

This type of resolver exhibits a sinusoidal or cosine functional relationship between its output voltage and the rotor angle. The primary and secondary windings are placed on the stator and rotor, respectively, with the degree of electromagnetic coupling between them closely related to the rotor's angle of rotation.

2. Linear Resolver (Proportional Resolver)

Linear resolvers display a linear functional relationship between their output voltage and rotor angle within a specific angular range. They can be further subdivided into implicit pole and salient pole types based on rotor structure. Proportional resolvers, on the other hand, offer an output voltage that is proportional to the rotor angle.

3. Special Function Resolver

These resolvers exhibit a specific functional relationship between their output voltage and rotor angle, other than sinusoidal, cosine, or linear. They are designed for particular applications requiring non-standard angular measurement characteristics.

4. Brushless Resolver

Brushless resolvers eliminate the need for brushes and slip rings, allowing for continuous rotation. They typically include an additional transformer to indirectly transmit electrical signals from the rotor windings, enhancing reliability and lifespan.

5. Multipolar Resolver

Multipolar resolvers have a pole pair number greater than one, providing higher precision compared to dipolar versions. They are particularly useful in high-accuracy absolute detection systems.

6. Dual-Speed Resolver (Two-Channel Resolver)

A dual-speed resolver combines a single-pole pair resolver with a multi-pole pair resolver. The former serves as the coarse machine for large angle measurements, while the latter functions as the fine machine for precise angle detection. They can be structured with a shared magnetic circuit or separate magnetic circuits.

7. Variable Reluctance Resolver

This type of resolver operates based on the principle of variable magnetic reluctance between the stator and rotor, often categorized under brushless resolvers due to their design.

8. Core-Type and Hollow Shaft Resolver

Core-type resolvers feature a structure composed of a soft magnetic core and windings, suitable for small to medium power transmission. Hollow shaft resolvers, with a hollow cylindrical design, offer high power transmission capabilities and are suitable for large and very large power applications.

In summary, resolvers are versatile devices categorized based on their functional relationships, structural designs, and operational principles. Each type serves specific applications, contributing to the precision and reliability of angular measurement in various industrial and technological fields.