Month: February 2025

Closed-Loops vs Open-Loop Control System

Ken Cheng Leave a comment

In industrial automation, servo amplifiers play a crucial role in motion control systems. They ensure precise motor operation by controlling voltage and current. One of the key distinctions in servo amplifier operation is whether they use open-loop or closed-loop control. These two control strategies significantly impact system performance, accuracy, and efficiency. Understanding their differences is essential for selecting the right control method for specific applications.

Read more: Closed-Loops vs Open-Loop Control System

Loop Control System

Before getting into the nitty gritty of knowing the differences between open and closed-loop systems, it’s probably important to establish what a loop control system is in regards to servo amplifiers. A loop control system for a servo amplifier regulates the operation of a motor by adjusting voltage and current based on a control algorithm. This system ensures the motor performs as intended by operating in either an open-loop or closed-loop configuration.

Open-Loop Control System

An open-loop control system operates without feedback, meaning the servo amplifier sends commands to the motor without verifying whether the desired motion has been achieved. This approach is simpler and cost-effective, often used in applications where high precision is not a priority. Open-loop systems are commonly found in stepper motor applications, where a predefined sequence of electrical pulses determines movement. However, these systems are susceptible to inaccuracies due to external disturbances, such as load variations or mechanical wear, since they lack a mechanism to correct errors.

Closed-Loop Control System

A closed-loop control system continuously monitors and adjusts motor performance. They perform this using real-time feedback from sensors like encoders or resolvers. Unlike open-loop systems, closed-loop control measures actual motor position, speed, or torque and compares it to the desired set-point. This allows the servo amplifier to make instant corrections if deviations occur. The results are higher accuracy, improved stability, and better responsiveness. This makes closed-loop systems ideal for precision applications such as robotics, CNC machines, and industrial automation. By compensating for disturbances, mechanical variations, and load changes, closed-loop servo amplifiers enhance reliability and efficiency, though they require more complex hardware and tuning compared to open-loop systems.

Control Loop Chart

Conclusion

The choice between open-loop and closed-loop control ultimately depends on the application’s requirements. Open-loop systems are suitable for cost-sensitive applications where precision is not critical. In contrast, closed-loop systems excel in environments demanding accuracy, adaptability, and reliability. As automation technology advances, closed-loop control is becoming increasingly prevalent, offering enhanced efficiency and performance across various industries.

Having Issues With Your Servo Amplifier?

Do you have a servo amplifier not breaking down or not working? Let our team of experts help you get back up and running as soon as possible. Call us: 800) 691-8511 or email: sales@mroelectric.com

Updated on February 24, 2025 by Ken Cheng

Understanding Alarm Code 8: Fanuc Servo Motors

Ken Cheng Leave a comment

Fanuc servo amplifiers are widely used in CNC machines, offering precise control and high efficiency. However, like any complex system, they can encounter faults, with specific alarm codes indicating different issues. One such alarm is Code 8, which signals an abnormal current detection in the servo system.

Read more: Understanding Alarm Code 8: Fanuc Servo Motors

What is an Alarm Code 8?

Alarm Code 8 on a Fanuc servo amplifier typically indicates an overcurrent condition in the motor or drive system. This means that excessive current is flowing through the servo amplifier, which can lead to potential damage if not addressed promptly. The amplifier detects this anomaly and shuts down the system to prevent further harm.

Common Causes of Alarm Code 8

Several factors can contribute to an overcurrent condition in a Fanuc servo system, including:

Fanuc Alarm Code 8
  1. Motor Short Circuit – A short circuit in the motor windings can cause excessive current draw, leading to the alarm.
  2. Damaged Power Cables – If the cables between the servo amplifier and the motor are frayed, pinched, or shorted, they can create an overcurrent situation.
  3. Faulty Servo Amplifier – Internal component failure, such as a defective IGBT (Insulated Gate Bipolar Transistor) or power module, may trigger this alarm.
  4. Mechanical Overload – Excessive load on the motor, such as a jammed or misaligned mechanical system, can cause it to draw more current than normal.
  5. Incorrect Parameter Settings – Improperly set servo parameters, such as excessive gain values or current limits, can lead to overcurrent faults.
  6. Contaminants or Moisture – Dust, oil, or moisture inside the servo amplifier can cause short circuits and lead to overcurrent conditions.

Troubleshooting Steps

1. Power Cycle the System

  • Turn off the machine and disconnect power.
  • Wait a few minutes, then power it back on to see if the alarm clears.
  • If the issue persists, continue with further diagnostics.

2. Inspect Cables and Connections

  • Check the motor power cables for damage, loose connections, or wear.
  • Ensure the grounding is secure and properly connected.

3. Check for Motor Short Circuits

  • Use a multimeter to measure resistance between motor phases and between each phase and ground.
  • A very low resistance reading indicates a potential short circuit.

4. Examine the Servo Amplifier

  • Look for burnt or damaged components on the amplifier board.
  • Check for signs of contamination, such as dust, oil, or moisture.

5. Reduce Load and Verify Mechanics

  • Ensure the motor isn’t overloaded or jammed.
  • Manually move the axis to check for mechanical resistance.

6. Verify Parameter Settings

  • Check the CNC control parameters related to the servo system.
  • Restore default settings if any recent changes were made.

7. Swap Components for Testing

  • If you have a spare amplifier or motor, swap them one at a time to isolate the faulty component.

Conclusion

Fanuc servo amplifier Alarm Code 8 is a critical warning that requires immediate attention to prevent damage to the motor or drive system. By systematically troubleshooting the issue—checking cables, inspecting components, and verifying parameters—you can identify and resolve the root cause.

By understanding this alarm and taking the right corrective actions, you can minimize downtime and maintain the reliability of your CNC machine.

If your Fanuc is experiencing a different alarm code, then this previous article written covers various alarm codes that you may be able to diagnose.

Having Problems with Your Fanuc?

Do you have a Fanuc that is throwing more than just an Alarm 8? Let our team of experts help get you back up and operational quickly. Contact us via email: sales@mroelectric.com or phone: (800) 691-8511

Updated on February 12, 2025 by Ken Cheng