Resolver (Electrical) | Rotary Electrical Transformer

Resolver (Electrical) | Rotary Electrical Transformer

Resolver (Electrical) | Rotary Electrical Transformer |
What is the purpose of a resolver?


A resolver is a type of rotary electrical transformer which is used for measuring degrees of rotation. t is regarded as an analogue device, while digital devices like the digital resolver and rotary (or pulse) encoder are its digital equivalents.

In a wide range of position and velocity feedback applications, whether light duty/servo, light industrial, or heavy-duty ones, a resolver is an electromagnetic transducer. Resolvers, often referred to as motor resolvers, are frequently utilised in servo motor feedback applications because of how well they work in hot environments.

The potential resolution of a single speed resolver is limitless because the resolver is an analogue device and the electrical outputs are constant during one full mechanical revolution. The resolver is a much more durable device than most other feedback devices due to its straightforward transformer design and lack of on-board electronics. It is the best option for applications where reliable performance is required in those high temperature, high shock and vibration, radiation, and contamination environments, making it the sensible design alternative for shaft angle encoding.

Resolver Design

A unique variety of rotary transformer called a resolver has a stator and rotor that are both cylindrical. Both the rotor and the stator are made using two sets of windings and multi-slot laminations. In the slotted lamination, the windings are typically arranged and distributed in either a constant pitch-varying turn or variable pitch-variable turn pattern. The distribution of the windings is sinusoidal in both situations.

Single speed resolver’s windings produce one full Sine and Cosine curve in one mechanical revolution, whereas multi-speed resolver’s windings produce several Sine and Cosine curves in a single mechanical revolution. While the multi-speed does not offer absolute feedback like the single speed does, it does offer higher precision. The size of the resolver places a cap on the speeds that can be used. In the laminations, the two sets of windings are arranged at a 90-degree angle to one another. The Sine and Cosine windings are what they are known as. To increase precision, one set of the rotor's windings is typically internally shorted.

How Does a Resolver Work?

In order to induce voltage into each of the output windings, a resolver must have its input phase activated with an AC voltage (VAC). The VAC input is modulated by the resolver's amplitude in proportion to the angle of mechanical rotation's sine and cosine. The resolver is often referred to as a control transmitter or an analogue trigonometric function generator. The resolver's job is to break down a vector into its component parts (Sine and Cosine). When the input winding is excited with the rated voltage, Electrical Zero (EZ) is the position of the rotor with respect to the stator at which the voltage amplitudes across the Sine and Cosine windings are minimum and largest, respectively.

The voltage output of the Sine winding divided by the output of the Cosine winding yields the simple formula for the rotor position or angle. This ratio metric format produces a significant amount of temperature adjustment as well as an intrinsic noise reduction feature for any injected noise that is about comparable in amplitude on both windings.

Polar coordinates to rectangular coordinates can be converted analogically using resolvers with incredible accuracy. The polar angle is the shaft angle, and the magnitude is the excitation voltage. The [x] and [y] components are the outputs. X and Y coordinates can be rotated using resolvers with four-lead rotors; the desired rotation angle is determined by the shaft position.

General-purpose sine/cosine computing devices are resolvers with four output leads. Their accuracy is improved when used with electronic driver amplifiers and feedback windings that are tightly coupled to the input windings. They can also be chained together (referred to as "resolver chains") to compute functions with multiple terms and possibly multiple angles, such as gun (position) orders that have been rolled and pitched into account.

Resolution-to-digital converters are frequently used for position evaluation. They transform the sine and cosine signal into a binary signal (10 to 16 bits wide), which the controller can use more readily.

Types of Resolver

The mechanical angle of the stator serves as the angular information in two-pole basic resolvers. These tools are capable of providing the exact angle position. Multipole resolvers are another variety of resolver. They can deliver p cycles in one rotation of the rotor since they have 2p poles (or p pole pairs) because the electrical angle equals p times the mechanical angle. The 2-pole windings are utilised for absolute position while the multipole windings are used for accurate position in some types of resolvers. A multipole resolver can provide superior precision, up to 10′′ for 16-pole resolvers and even 1′′ for 128-pole resolvers, whereas two-pole resolvers typically only achieve an angular accuracy of about 5.

Monitoring multipole electrical motors is another application for multipole resolvers. This tool can be utilised in any situation where precise rotation of one object in relation to another is required, such as in a robot or rotating antenna platform. The resolver is typically directly mounted to an electric motor in practise. The resolver feedback signals are typically observed by another instrument over a number of revolutions. As a result, rotating assemblies can be geared down and the resolver system's accuracy is increased.

The voltages utilised are typically low (24 VAC) for all resolvers because the power supplied to them does not result in any actual work being done. Utility frequency is typically used to drive resolvers made for use on land, while 400 Hz is typically used for maritime or aircraft applications (the frequency of the on-board generator driven by the engines). 2,930 Hz to 10 kHz at 4 VRMS to 10 VRMS voltages are used in aerospace applications. The position of an actuator or torque motor is often determined using aerospace applications. In control systems, higher frequencies are more common (5 kHz).

Other types of Resolvers include:

Receiver Resolvers

Unlike transmitter resolvers, these resolvers are utilized in the opposite manner (the type described above). The electrical angle is represented by the ratio between the sine and cosine, which is applied to the two diphased windings. To achieve zero voltage in the rotor winding, the system rotates the rotor. In this position, the electrical angle applied to the stator equals the mechanical angle of the rotor.

Differential Resolvers

Similar to a receiver, these types combine two diphased secondary windings in one stack of sheets and two diphased primary windings in the other. Secondary electrical angle, mechanical angle, and primary electrical angle are the relationships between the electrical angle produced by the two secondary windings and the other angles. For instance, these kinds were employed as analogue trigonometric function calculators.

The transolver, which combines a triphased winding like the synchro with a two-phase winding like the resolver, is another form that is similar.

The resolver operation is defined by seven functional operational parameters. These conditions are:

  1. Accuracy
  2. Input Excitation Voltage
  3. Input Excitation Frequency
  4. Input Current Maximum
  5. Phase shift of the Output Voltage from the Input Voltage
  6. Null Voltage
  7. Transformation Ratio of Output Voltage to the Input Voltage 

Resolver Applications

The resolver design's simplicity makes it dependable in a variety of challenging environments and demanding applications. Typical uses for resolvers include:

  • Servo motor feedback
  • Speed and position feedback
  • Oil and gas production
  • Jet engine fuel systems
  • Aircraft flight surface actuators
  • Communication position systems
  • Control systems in land-based vehicles (Militry)

Resolvers vs Encoders

Since resolvers lack onboard electronics, they are suited for applications where encoders would malfunction since they can withstand high temperatures as well as shock and vibration. Resolvers can be utilised as feedback devices in place of incremental encoders and absolute encoders. Whereas encoders produce digital signals, resolvers produce analogue signals and need a separate analog-to-digital conversion.

A resolver, which primarily consists of mechanical components, sends an analogue signal back to the encoder. Resolvers are perfect for applications where there are concerns about high temperatures, intense shock and vibration, and dust/dirt. Because resolvers are electrically operated and provide digital signals back to the encoder, they are different from encoders.

Resolves can be rad-hardened to be utilised in situations with radiation for applications where it is present. In radiated areas, their lack of onboard electronics is particularly advantageous.

Single-speed resolvers are an alternative to absolute encoders when the environment does not permit the use of absolute encoders since they offer absolute position and can be utilised as absolute devices.

AD2S1210 Digital Resolver

The AD2S1210 incorporates an on-board programmable sinusoidal oscillator that generates sine wave excitation for resolvers. It is a comprehensive 10-bit to 16-bit resolution tracking resolver-to-digital converter. The sine and cosine inputs of the converter accept signals with an input voltage of 3.15 V p-p 27% and a frequency range of 2 kHz to 20 kHz.

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