How to calibrate the resolver of an ac servo motor?

As a seasoned supplier of AC servo motors, I've encountered numerous inquiries regarding the calibration of resolvers in these motors. Resolver calibration is a critical process that ensures the accurate operation of AC servo motors, which are widely used in various industrial applications, including robotics, CNC machines, and automation systems. In this blog post, I'll share some insights on how to calibrate the resolver of an AC servo motor effectively.

Understanding the Resolver in an AC Servo Motor

Before delving into the calibration process, it's essential to understand what a resolver is and its role in an AC servo motor. A resolver is a type of rotary electrical transformer used for measuring the angle of a rotating shaft. It consists of a stator and a rotor, with the stator having two windings: a reference winding and a signal winding. The rotor has a single winding that is coupled to the rotating shaft of the motor.

The resolver works by generating a sine and cosine signal based on the angle of the rotor. These signals are then processed by the motor controller to determine the position and speed of the motor. Accurate resolver calibration is crucial because any errors in the resolver's output can lead to inaccurate motor control, resulting in reduced performance and potential damage to the equipment.

Tools Required for Resolver Calibration

To calibrate the resolver of an AC servo motor, you'll need the following tools:

1. Oscilloscope: This is used to measure the sine and cosine signals generated by the resolver.
2. Function Generator: It is used to generate a reference signal for the resolver.
3. Multimeter: This tool is used to measure the voltage and resistance of the resolver windings.
4. Encoder Calibration Fixture: This fixture is used to hold the motor and resolver in a fixed position during calibration.

Step-by-Step Resolver Calibration Process

Step 1: Prepare the Motor and Tools

First, ensure that the AC servo motor is powered off and disconnected from the power source. Mount the motor on the encoder calibration fixture and connect the oscilloscope, function generator, and multimeter to the resolver windings according to the manufacturer's instructions.

Step 2: Generate a Reference Signal

Use the function generator to generate a reference signal with a frequency and amplitude specified by the motor manufacturer. Typically, the reference signal frequency is around 10 kHz, and the amplitude is between 5 and 10 volts. Connect the reference signal to the reference winding of the resolver.

Step 3: Measure the Resolver Output

Turn on the oscilloscope and set it to measure the sine and cosine signals generated by the resolver. Observe the waveforms on the oscilloscope screen. The sine and cosine signals should be 90 degrees out of phase with each other, and their amplitudes should be equal.

Step 4: Adjust the Resolver Alignment

If the sine and cosine signals are not 90 degrees out of phase or their amplitudes are not equal, you'll need to adjust the resolver alignment. This can be done by loosening the resolver mounting bolts and rotating the resolver slightly until the signals are in the correct phase and amplitude.

Step 5: Check the Resolver Resistance

Use the multimeter to measure the resistance of the resolver windings. The resistance values should be within the range specified by the motor manufacturer. If the resistance values are outside the range, it may indicate a problem with the resolver, such as a short circuit or an open circuit.

Step 6: Verify the Calibration

Once you've adjusted the resolver alignment and checked the resistance, verify the calibration by running the motor at a low speed and observing the motor's performance. The motor should run smoothly, and the position and speed control should be accurate. If there are still issues with the motor's performance, repeat the calibration process until the desired results are achieved.

Common Challenges in Resolver Calibration

Resolver calibration can be a challenging process, especially for those who are new to it. Here are some common challenges you may encounter and how to overcome them:

1. Signal Interference: Electrical noise and interference can affect the accuracy of the resolver signals. To overcome this, use shielded cables and ensure that the motor and calibration equipment are properly grounded.
2. Mechanical Misalignment: If the resolver is not properly aligned with the motor shaft, it can cause errors in the resolver output. Make sure to use a precision encoder calibration fixture and follow the manufacturer's instructions for mounting the resolver.
3. Temperature Variations: Temperature changes can affect the performance of the resolver. To minimize the impact of temperature variations, calibrate the resolver at a stable temperature and use temperature compensation techniques if necessary.

Benefits of Accurate Resolver Calibration

Accurate resolver calibration offers several benefits, including:

1. Improved Motor Performance: Calibrating the resolver ensures that the motor operates at its optimal performance, resulting in smoother operation, higher accuracy, and increased efficiency.
2. Reduced Maintenance Costs: By ensuring accurate motor control, resolver calibration can help reduce wear and tear on the motor and other components, leading to lower maintenance costs and longer equipment lifespan.
3. Enhanced Safety: Accurate resolver calibration helps prevent unexpected motor movements, which can pose a safety hazard to operators and equipment.

Conclusion

Calibrating the resolver of an AC servo motor is a critical process that requires careful attention to detail and the use of the right tools. By following the steps outlined in this blog post and overcoming common challenges, you can ensure accurate resolver calibration and optimal motor performance.

At our company, we offer a wide range of high-quality AC servo motors, including the 3000RPM Servo Motor, 7.5KW 380V AC Servo Motor, and Lathe Machine Servo Motor with Drive Control. If you have any questions about resolver calibration or need assistance with selecting the right AC servo motor for your application, please don't hesitate to contact us. We're here to help you make the most of your industrial automation projects.

References

• Servo Motor Handbook, published by a leading motor manufacturer.
• Technical papers on resolver calibration from industry experts.