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| AI-Generated Motor Resolver to determine the position of the rotor. |
The resolver is an electromechanical transducer or a rotary transformer that determines a motor's rotor position. The resolver is sometimes called as a Control Transmitter or Analog Trigonometric Function Generator.
The resolvers were initially developed for military applications to withstand harsh environments. Wherever we need to find the angular position of a rotary shaft we can use resolvers to measure it accurately and reliably.
Encoder:
Don't confuse a Resolver with an Encoder, Both are used to measure the speed and angular position of the rotating shaft, the main difference is the resolver is a mechanical device & the encoder is an electrically operated device and the output is analog in nature for resolver and digital in the encoder.
Let's dive deeper into how a resolver works.
Core Principle: Electromagnetic Induction
At its heart, a resolver functions based on the principle of electromagnetic induction, just like a transformer. This means that a changing magnetic field can induce an electrical current in a nearby conductor.
Think of it like a very precise dial:
- Imagine a dial that can tell you exactly how far it has turned. A resolver does something similar, but instead of a physical dial, it uses electrical signals.
- It has two main parts: a rotor (the part that turns) and a stator (the stationary part).
- These parts have wire coils that create magnetic fields. As the rotor turns, these magnetic fields change.
- These changes in the magnetic fields produce electrical signals that can be used to precisely determine the angle of the rotor.
Components:
- Rotor: The rotating part of the resolver, typically with a single winding (coil of wire) called the excitation winding or primary winding.
- Stator: The stationary part, usually with two windings placed at a 90-degree angle to each other. These are called the sine and cosine windings or secondary windings.
Working Mechanism:
R - Rotor (Excitation Winding)
S1 - Stator Winding
S2- Stator Winding
Note: The resolver's output is two sine and cosine waves that have a 90 electrical degree phase difference with respect to the reference voltage given in the Primary Excitation Winding.
Excitation: An AC (alternating current) voltage is applied to the rotor's excitation winding. This creates a magnetic field within the resolver.
From where the voltage is supplied from:
A simple electronic oscillator circuit can generate an AC signal. However, this is less precise and flexible than an RDC.
RDCs are designed to provide a very stable and accurate AC signal, which is crucial for precise angle measurement.
Magnetic Field Interaction: As the rotor turns, its magnetic field interacts with the stator windings. The strength of this interaction changes depending on the rotor's angular position.
Induced Voltages: This interaction induces AC voltages in the stator windings. The amplitudes (strengths) of these voltages vary sinusoidally with the rotor's angle.
- The voltage induced in one stator winding is proportional to the sine of the rotor angle.
- The voltage induced in the other stator winding is proportional to the cosine of the rotor angle.
Mathematical Representation:
If the excitation voltage applied to the rotor is:
V_excitation = V_peak * sin(ωt) (where ω is the frequency of the AC signal)
Then the voltages induced in the stator windings are:
V_sine = K * V_peak * sin(ωt) * sin(θ)V_cosine = K * V_peak * sin(ωt) * cos(θ)
Where:
K is a constant related to the resolver's construction.θ is the angle of the rotor.
Determining the Angle:
By measuring the amplitudes of the sine and cosine voltages from the stator, the angle θ can be precisely calculated using trigonometric relationships.
Still confused about resolver, here is an analogy:
Imagine a flashlight inside a tube.
- The tube: This is like the body of the resolver.
- The flashlight: This is like the "reference winding" in the resolver. It sends out light (or in the resolver's case, an electrical signal).
- Two light sensors on the tube's wall: These are like the "sine and cosine windings." They measure how much light hits them.
Now, imagine you can rotate the flashlight inside the tube.
- When the flashlight points directly at one sensor, that sensor gets the most light. The other sensor gets very little.
- As you rotate the flashlight, the amount of light hitting each sensor changes. Sometimes one gets more, sometimes the other.
This is similar to how a resolver works:
- The "flashlight" (reference winding) sends out an electrical signal.
- As the resolver's shaft rotates, it changes how much of that signal reaches the two "sensors" (sine and cosine windings).
- The amount of signal each sensor receives follows a sine wave and a cosine wave pattern as the shaft turns.
Hope you get an idea of how a resolver works inside an edrive or motor.
Why are resolvers used?
Resolvers are popular in applications where accuracy and reliability are crucial, such as:
- Robotics: To precisely control the movement of robotic arms.
- Aerospace: In aircraft control systems and navigation.
- Industrial automation: In machines that require precise positioning.
- Electric vehicles: To accurately control the motor and ensure smooth operation.
Advantages of resolvers:
- High accuracy: They can provide very precise measurements of rotation.
- Robustness: They can withstand harsh environments, including high temperatures, vibration, and shock.
- Reliability: They have a long lifespan and require minimal maintenance.
In essence, a resolver is a robust and accurate sensor that provides precise information about the rotational position, making it essential in various demanding applications.
