The resolver is used in motion servo control systems as sensing and measuring for angular position. Early rotary transformers were used in computing solution devices as one of the main components of analog computers. The output is an electrical signal that varies with the rotor's angle as a function, usually sine, cosine, linear, and so on. These functions are the most common and easy to implement。

The electrical output of some special functions can also be produced when the windings are specifically designed. But such a function is only used for special occasions, not universal. Since the 1960s, rotary transformers have been used in servo systems as the generation and detection of angular signals. The three-wire three-phase self-aligning machine is applied to the system in a two-phase rotary transformer earlier than the four-wire. Therefore, as a resolver for angular signal transmission, it is sometimes called a four-wire self-aligning machine. With the development of electronic technology and digital computing technology, digital computers have long replaced analog computers。

So in fact, the resolver is currently mainly used in angular position servo control systems. Since two-phase rotary transformers are easier to improve accuracy than self-aligning machines, rotary transformers are more widely used.。

Rotary transformer application

The application of rotary transformers has recently developed rapidly. In addition to the traditional, highly reliable military and aerospace fields, it has also been widely used in industrial, transportation and civil applications. In particular, it should be mentioned that over the years, with the improvement of industrial automation level, with the increasing requirements for energy saving and emission reduction, the application of permanent magnet AC motors with high efficiency and remarkable energy saving has become more and more extensive. The position sensor of the permanent magnet AC motor was originally an optical encoder, but it has been rapidly replaced by a resolver over the years. There are several obvious examples. In home appliances, whether it is a refrigerator, an air conditioner, or a washing machine, it is currently developing to variable frequency shifting, using a sine wave controlled permanent magnet AC motor。

Among the electric vehicles that countries are highly valued, the position and speed sensors used in electric vehicles are all rotary transformers. For example, the position sensing of the driving motor and the generator, the position and speed sensing of the electric assist steering wheel motor, the gas valve angle measurement, the vacuum chamber conveyor angular position measurement, and the like are all using a resolver. In the application of plastic systems, textile systems, metallurgical systems and other fields, the servomotors of key components in the servo system applied are also used as position velocity sensors. The application of resolvers has become a trend。

Rotary transformer structure
According to the way of introduction and extraction of the rotor electrical signal, it is divided into a brushed rotary transformer and a brushless rotary transformer. In brushed rotary transformers, there are windings on the stator and rotor. The electrical signal of the rotor winding is introduced or extracted by a slip ring on the rotor and a brush on the stator through sliding contact. Due to the presence of the brush structure, the reliability of the resolver is difficult to guarantee. Therefore, there are few applications of this type of rotary transformer.。