A resolver helps you find where the shaft is in a motor. It checks how the shaft turns by looking at magnetic field changes. This device tells you exactly where the shaft is and how fast it moves. Engineers use it because it works well in tough systems.
Key Takeaways
Resolvers help find the position and speed of a motor shaft. They are important for controlling motors very well. They can work in places with dust, dirt, or heat. This makes them good for hard jobs. Resolvers use inductive coupling to turn spinning into electrical signals. They give steady feedback and do not have moving parts. Resolvers are more accurate and last longer than other sensors. But they can be harder to set up and take care of. Using a resolver can make motor systems work better and last longer. This is helpful in tough jobs like aerospace and military.
Resolver Basics
What Is a Resolver
A resolver is a kind of rotary electrical transformer. People use it to measure how much something turns. It works by sending electrical signals through coils inside. These coils are on two main parts called the stator and the rotor. The stator has three windings. One is an exciter winding. Two are two-phase windings set at right angles. The rotor has its own coil and spins inside the stator. When you send a signal into the primary winding, it makes a changing magnetic field. This field goes through the rotor. It creates feedback signals. These signals help you find the exact angle of the shaft.
Here is a table showing the main parts of a resolver:
Component | Description |
Stator | Has three windings: an exciter winding and two two-phase windings called 'x' and 'y'. |
Exciter Winding | Sits on top and spins around the horizontal axis to make a rotary transformer. |
Two-Phase Windings | Placed at 90 degrees from each other and wound on a lamination. |
Rotor | Has a coil (secondary winding) and a primary winding. It excites the two-phase windings. |
Primary Winding | Fixed to the stator. It gets a sinusoidal electric current and makes current in the rotor. |
Feedback Signals | Two-phase windings make sine and cosine feedback currents to show rotor angle. |
Role in Motor Control
Resolvers are used in motor control systems. They help you know the position and speed of a motor shaft. This is important for servo motors that need precise control. Many industries use resolvers because they work well in tough places. You can find them in steel plants, paper mills, oil and gas production, jet engines, and aircraft. They also help control systems in military vehicles. If you need reliable feedback in harsh places, a resolver is a good choice.
Comparison to Other Sensors
Resolvers are different from other sensors like encoders or Hall effect sensors. Resolvers give high accuracy and work well even with dust, dirt, or moisture. They can handle very high temperatures, sometimes over 200°C. Encoders can give even finer accuracy and higher resolution. But encoders are more sensitive to dirt and need cleaner places. Hall effect sensors cost less and are easier to take care of. But they do not give the same accuracy or last as long as a resolver. Here is a table to help you compare:
Sensor Type | Accuracy | Reliability | Durability in Harsh Environments | Temperature Tolerance | Cost | Maintenance |
Resolvers | ±30 arc-seconds | High and consistent | Excellent | Over 200°C | Higher | Low |
Encoders | Very fine | High but sensitive | Moderate | Limited | Varies | Moderate |
Hall Effect Sensors | Good, less precise | Usually reliable | N/A | N/A | Lower | Moderate |
How a Resolver Works
Inductive Coupling Principle
A resolver works by using inductive coupling. This means it uses electromagnetic induction to measure rotation. When you send an AC signal to the primary winding, it makes a magnetic field. The rotor spins inside the stator. This spinning changes how much energy goes to the secondary windings. The amount of energy depends on where the rotor is. The resolver uses this change to find the shaft angle.
The resolver does not use brushes. This makes it last longer and need less fixing. You can use it in hot or dusty places. It does not have weak electronic parts.
Here is a table that shows how inductive coupling helps find shaft position:
Aspect | Description |
Principle | Electromagnetic induction measures how much something turns. |
Components | Uses primary and secondary windings. |
Functionality | Coupling changes when the rotor moves. |
Signal Usage | Signals in secondary windings show shaft position. |
The primary wire gets the AC signal.
Secondary windings pick up the signal.
The rotor's spot changes how much energy goes to the secondaries.
Sine and Cosine Modulation
The resolver gives two signals: sine and cosine waveforms. These signals change as the shaft turns. The resolver makes these waveforms by changing the output with the rotor's angle. When you check these signals, you can find the direction and position of the shaft. The sine signal shows one part of the angle. The cosine signal shows another part. By using both, you can find the shaft's position very well.
The resolver uses math to link the signals to the rotor angle. When you send a sinusoidal signal to the primary winding, the secondary windings make signals that shift by 90 degrees. These signals are changed by the sine and cosine of the rotor angle. A resolver-to-digital converter reads these signals. It figures out the shaft's position and speed.
Main Components
A resolver has several important parts. Each part does a special job:
Component | Function |
Excitation | Gives the AC signal that powers the resolver. |
Cosine | Sends out the cosine signal based on the rotor's spot. |
Sine | Sends out the sine signal based on the rotor's spot. |
Stator | Holds the windings and helps with inductive coupling. |
Rotor | Spins to change the coupling and affect the signals. |
Windings | Copper wires in stator and rotor make signals that show the shaft's position. |
Resolvers work well for tough jobs. Their strong design and no moving parts make them good for harsh places. You will see them work in places with heat, dust, and moisture. The resolver can run fast and still give accurate feedback. This makes it great for aerospace, military, and other hard jobs.
Resolver Signal Processing
AC Excitation
You start by sending an AC signal into the resolver. This signal powers the resolver. It helps measure where the shaft is. Most systems use programmable excitation up to 28Vrms. The frequency can go up to 10kHz. You can see common voltage and frequency ranges in the table below:
Voltage Range (VL-L) | Frequency Range (VRMS) | Frequency Range (kHz) |
2 - 28 | 2 - 115 | 10 - 20 |
The AC signal makes a changing magnetic field inside. This field lets the resolver sense how the shaft moves.
Output Signals
When the shaft turns, the resolver gives two output signals. These signals are sine and cosine waveforms. Each signal changes as the shaft moves. You can use a multimeter set to AC voltage mode to check them. Put the probes on the sine and cosine wires. You will see the voltage change when the shaft rotates.
Signal Type | Description |
Sine | Proportional to the sine of the angle |
Cosine | Proportional to the cosine of the angle |
The sine signal shows one part of the shaft’s angle.
The cosine signal shows another part.
Both signals help you find the exact position.
Resolvers use these signals because they resist noise. The angle comes from the ratio of sine and cosine voltages. This method helps block outside interference. You may get interference from electrical paths or RF noise. The resolver’s design keeps the output steady.
Position Calculation
You need to process the analog signals to get digital position data. Signal processing uses several steps and parts:
Component | Description |
Input Isolation Transformer | Keeps the input signal separate for better processing. |
Digital-to-Analog Converter | Multiplies the analog SIN and COS inputs by digital functions. |
Summing Amplifier | Combines signals but may have harmonics and quadrature. |
Phase-Sensitive Synchronous Demod. | Cleans error voltage from the output. |
Integrator | Removes lag error from constant shaft speed. |
Voltage-Controlled Oscillator | Makes a steady frequency to follow the input signal. |
Up-Down Counter | Checks polarity to count which way the shaft turns. |
Phase Shifter and Reference Squarer | Helps the demodulator process signals correctly. |
You use these parts to turn the analog sine and cosine signals into digital data. This process lets you know the shaft’s position and speed very well.
Advantages and Challenges
Benefits in Motor Applications
Resolvers give many good things for motor control. They work well in places with heat, dust, or vibration. You can trust them to keep working in tough spots. Here is a table that lists the main benefits:
Advantage | Description |
High-temperature tolerance | Handles temperatures from -55°C up to 175°C. |
Robustness in extreme conditions | No direct electrical or mechanical connection, so it works in harsh places. |
Resistance to contaminants | Dirt, oil, and heat do not affect its performance. |
Direct mounting on motor shaft | Gives strong and accurate speed and position signals. |
High-speed capability | Can measure speeds up to 90,000 rpm. |
You also get other benefits. The rugged design blocks EMI noise. It can handle vibration and shock. Some models work at very high temperatures, up to 230°C. Brushless types last longer and need less fixing. You spend less time on repairs, so your system works better.
Resolvers are very stable and strong. They keep working even when things change fast. You do not need to worry about noise or sudden breakdowns.
Limitations
Resolvers can have some problems too. The analog signals make things more complicated. You need special tools to work with these signals. This can make the system cost more and take longer to finish. Here is a table that shows some common problems:
Challenge | Impact on System Complexity and Cost |
Parasitic Effects | You must manage signal problems, which makes design harder. |
Designer Productivity | You spend more time on analysis and debugging, which can delay your project. |
Growing Size of Analog Designs | Large analog systems need better tools, which increases cost. |
Increased Parasitic Values | Longer simulation times and more complex interactions make design harder and more expensive. |
You might also have trouble with wires and cables. Different brands use different pinouts and connectors. This can make it hard to hook things up. You need to watch out for supply chain problems and follow safety rules, especially in places like the EU.
Wiring can be hard to match.
Non-standard cables may cause trouble.
Pinout differences can slow things down.
You should plan for these problems before you start. Careful design and testing help you avoid delays and extra costs.
You can see how a resolver turns movement into signals. This device helps you know where the motor shaft is. It also tells you how fast it moves.
You get good feedback in hard places.
Resolver-to-digital converters make results more exact.
Resolvers are used in robots, servos, and big motors.
Advantages | Challenges |
Works well in tough places | Needs careful setup |
Handles very hard conditions | Costs more money |
Blocks electrical noise | Needs good alignment |
Simple design, breaks less | Needs correct coupling |
If you want strong and exact feedback, use a resolver for hard motor jobs.
FAQ
What is the main job of a resolver in a motor?
A resolver tells you the exact position and speed of the motor shaft. You use this information to control the motor with high accuracy. This helps machines work smoothly and safely.
Can you use a resolver in dirty or hot places?
Yes! You can use a resolver in places with dust, oil, or high heat. The strong design keeps it working when other sensors might fail.
How do you get digital data from a resolver?
You use a resolver-to-digital converter (RDC). This device takes the analog sine and cosine signals and turns them into digital numbers. You can then use these numbers in your control system.
Do resolvers need a lot of maintenance?
No, you do not need much maintenance. Resolvers have no brushes or fragile parts. You can trust them to last a long time, even in tough jobs.
