What Is a Rotary Transformer?
A resolver / transformer is an electromagnetic sensor, also known as a synchronous resolver. It is a small AC motor for measuring angle. It is used to measure the angular displacement and angular velocity of the rotating shaft of a rotating object. It consists of a stator and a rotor. The stator winding is used as the primary side of the transformer and receives the excitation voltage. The excitation frequency is usually 400, 3000 and 5000HZ. The rotor winding serves as the secondary side of the transformer, and the induced voltage is obtained through electromagnetic coupling.
- Chinese name
- Resolver
- Foreign name
- resolver / transformer
- Meaning
- Electromagnetic sensor
- Alias
- Synchronous resolver
- A resolver / transformer is an electromagnetic sensor, also known as a synchronous resolver. It is a small AC motor for measuring angle. It is used to measure the angular displacement and angular velocity of the rotating shaft of a rotating object. It consists of a stator and a rotor. The stator winding is used as the primary side of the transformer and receives the excitation voltage. The excitation frequency is usually 400, 3000 and 5000HZ. The rotor winding serves as the secondary side of the transformer, and the induced voltage is obtained through electromagnetic coupling.
Introduction to Resolver
- The working principle of a resolver is basically similar to that of an ordinary transformer. The difference is that the primary and secondary windings of an ordinary transformer are relatively fixed, so the ratio of the output voltage to the input voltage is constant. The relative position of the rotor's angular displacement changes, so its output voltage changes with the rotor's angular displacement. The voltage amplitude of the output winding and the rotor's rotation angle are in a sine or cosine function relationship, or maintain a certain proportional relationship, The range of the rotation angle is linear with the rotation angle. Resolver can be used to transmit the rotation angle or electric signal in synchronous servo system and digital servo system; it can also be used as a function in the solving device, so it is also called a solver.
- Rotary transformers generally have two structural forms of two-pole winding and four-pole winding. The stator and rotor of the two-pole winding resolver each have a pair of magnetic poles, and the four-pole winding has two pairs of magnetic poles each, which are mainly used for high-precision detection systems. In addition, there are multi-pole resolvers for high-precision absolute detection systems.
Resolver classification
- According to the functional relationship between output voltage and rotor rotation angle, there are three main types of rotation
- Resolver
- 1. Sine-cosine resolver ---- The relationship between the output voltage and the rotor angle is a sine or cosine function.
- 2. Linear resolver ---- its output voltage and the rotor angle are a linear function. Linear rotary transformers are divided into two types of salient poles and salient poles according to the rotor structure.
- 3. Proportional rotary transformer ---- its output voltage is proportional to the rotation angle.
- Multi-pole resolvers are similar to multi-pole auto-anglers, the main difference is only the number of phases in the windings. Multi-pole products are more than an order of magnitude more accurate than bipolar ones.
A two-channel resolver is a combination of two resolvers with unequal pole pairs. Generally, those with a small number of pairs are called rough machines, and those with a large number of pairs are called fine machines. Its structure has two forms of common magnetic circuit and divided magnetic circuit. The latter is a combination of roughing and precision machinery, each winding has a separate iron core, and the magnetic circuit is separated. The former is that the windings of the rough and fine machines are embedded in the core at the same time, the windings are independent of each other and the magnetic circuit is shared. The above two resolvers are composed of a two-channel resolver system with electrical speed. It is different from two identical and independent resolvers and reducers to form a mechanically variable two-channel resolver system. Because the dual-channel system using mechanical variable speed in the synchronous follow-up system cannot meet the requirements, an electric variable-speed dual channel system must be adopted. This system not only improves the accuracy to the second pole, but also has a simple and reliable structure.
Magnetoresistive resolver is a special form of multi-pole resolver. It uses the principle of magnetoresistance to achieve electrical signal conversion. The stator core is provided with large and small teeth, and the small teeth are evenly distributed on the tooth end portions of the large teeth. The single-phase excitation winding and two-phase output winding are simultaneously embedded in the large slots on the stator. The rotor core is formed by punching pieces of uniformly distributed small teeth, and the number of teeth is the number of pole pairs. After the excitation winding is energized, the air-gap permeance changes with the rotor rotation angle, so that the output voltage change period of the output winding is the number of teeth of the rotor, which functions as a multi-pole. Its simple structure, small size, high accuracy, and non-contact greatly improve the reliability of the system, and its accuracy is in the order of seconds.
Resolver works
- The stator windings D1-D2 are connected to AC power for excitation, and the rotor windings Z1-Z2 are connected to the load Z L. When the main command shaft drives the rotor to rotate through the angle , the induced voltages in the rotor windings are
- Conversion formula
- Conversion formula
- A single-channel angle measuring system can be formed by using two identical sine and cosine resolvers. One resolver is the transmitter and the other is the control transformer. The transmitter is excited by an AC power source. The accuracy of the resolver is 6 , and the accuracy of the single-channel system is not less than 6 . In order to improve the control accuracy of the system, a dual-channel angle measuring system can be used (Figure 2). Using four resolvers with the same structure, two XZ 1 and XZ 2 constitute a coarse channel angle measuring system, and the other two XZ3 and XZ4 constitute a fine channel angle measuring system. XZ 1 and XZ3
- Resolver schematic
Resolver structure
- The structure of a resolver is similar to that of a two-phase wound asynchronous motor, and it can be divided into two parts: a stator and a rotor. The iron cores of the stator and the rotor are stacked by slot-shaped core pieces punched out of iron-nickel soft magnetic alloy or silicon steel sheet. Their windings are embedded in their respective slot-shaped cores. The stator winding is led out directly through the terminal fixed on the housing. There are two different ways of drawing out the rotor windings. According to two different lead-out methods of the rotor winding, the resolver is divided into two types of structure: brushed and brushless.
- Figure 1 is a brushed resolver. Its rotor winding is directly led out by the slip ring and the brush. Its characteristics are simple structure and small size. However, because the brush and the slip ring are in mechanical sliding contact, the reliability of the resolver is poor and the life is short.
- Figure 1 Brushed resolver
- Figure 2 Brushless resolver
- Figure 2 is a brushless resolver. It is divided into two parts, namely the resolver body and the additional transformer. The primary and secondary iron cores of the additional transformer and their coils are ring-shaped, and are respectively fixed on the rotor shaft and the casing, with a certain gap left in the radial direction. The rotor winding of the resolver body is connected with the primary winding of the additional transformer. The electrical signal in the primary winding of the additional transformer, that is, the electrical signal in the rotor winding, is sent indirectly through the secondary winding of the additional transformer through electromagnetic coupling. This structure avoids the influence caused by the bad contact between the brush and the slip ring, and improves the reliability and service life of the rotary transformer, but its volume, quality and cost are increased.
- Common rotary transformers generally have two structural forms of two-pole winding and four-pole winding. The stator and rotor of the two-pole winding resolver each have a pair of magnetic poles, and the four-pole winding has two pairs of magnetic poles, which are mainly used for high-precision detection systems. In addition, there are multi-pole resolvers for high-precision absolute detection systems. [1]
Resolver application
- Resolver is a kind of precision angle, position and speed detection device, suitable for all
- Resolver