CNC pipe bending machine servo motor alarm? Follow this troubleshooting approach, and you'll likely be able to fix it.

Anyone who works with pipe bending machines knows that the biggest problem with CNC models is the servo motor alarm. A string of codes on the screen means the machine is completely grounded, delaying the entire project. This sounds scary, but it actually boils down to a few issues—mechanical load, electrical wiring, and parameter settings. Below, I've compiled my experience over the years, explaining each alarm type in turn.

Step 1: When an alarm occurs, write down the code.

Alarm codes are like the equipment's medical record; writing them down incorrectly is like prescribing the wrong medicine. Regardless of the system brand, immediately record the complete alarm code on the screen, the fault description, and the operating conditions at the time of the incident—for example, which pipe is being bent, what material it is, and the speed.

FANUC commonly reports "SRVO-414" for servo overload; Siemens often reports "25201" for contour monitoring; Mitsubishi has codes like "AL.E6" and "AL.16." After writing down the code, consult the manual or search online; many fault causes can be directly located.

Step 2: Overload Alarm (Most common, accounting for 60-70%)

If the motor surface is extremely hot and the driver displays codes like "OL" or "AL.50," it's almost certainly an overload.

The cause is mostly mechanical: insufficient lubrication of the guide rail, stuck lead screw, overly tight timing belt, or misaligned mold. Manually rotate the shaft to feel the resistance. Another possibility is that the acceleration/deceleration time is set too short, causing excessive instantaneous current in the motor, which is mistakenly interpreted as overload.

Solution: First, check the lubrication of the transmission components. Check if the guide rails are dry, if the lead screw is clean, and if the timing belt tension is appropriate. Then, try slightly increasing the acceleration/deceleration time in the driver parameters.

Step 3: Encoder Alarm (Angle accuracy depends entirely on it)

If the driver reports "AL.16" (Mitsubishi), "Encoder Error," or "25000" (Siemens), or if the angle is off-center or the motor vibrates excessively, it's basically a problem with the encoder link.

These are usually the following: loose encoder connectors or water/oil ingress, damaged shielding wires, or internal cable breaks at bends. Delta servo drives are particularly prone to problems, especially the rectifier bridge and encoder feedback loop. You can directly connect a resistor in parallel to test if the feedback is normal.

Solution: Re-plug and clean the connectors, and check for bends or damage to the cable. When troubleshooting, pay attention to distinguishing between software and hardware issues; the process of elimination is the most reliable way to locate the fault.

Step 4: Power Supply Voltage or Wiring Issues

If the equipment alarms immediately upon power-on, or the motor doesn't respond at all, first check the power supply. Use a multimeter to measure the input voltage (fluctuations should be within ±10%), check if the DC bus voltage of the driver is up to standard, and confirm that the circuit breaker has tripped.

When multiple servos alarm simultaneously, it's highly likely that the main power supply is experiencing a phase loss or undervoltage. If only a single axis alarms, focus on checking the power lines (U, V, W) and encoder lines of that axis, checking for water ingress into the connectors and bent pins.

Step 5: Communication Failure

If the screen displays "AL.E6" (Mitsubishi) or "AL.16" communication error, it's mostly due to poor wiring contact or lost parameters.

Troubleshooting: Unplug and re-tighten the communication cable, restore the backup PLC program, and verify the station number and baud rate settings in the driver. If interference is severe, shielded cables must be used for the signal lines, and the shielding layer must be grounded at one end at the driver. Cable fixing is also important; the cable should be securely fixed to a stationary location to minimize bending stress.

Step 6: Alarms Caused by Limit Switches or Interference

Alarms can be triggered by a shaft pressing against a hard limit switch, collisions between mechanical parts, or a safety door not closing properly. First, visually inspect the position of each shaft. If it's pressing against a limit switch, move it in the opposite direction to disengage. If it's not pressing against a limit switch, check if the limit switch signal is normal.

Practical Troubleshooting Sequence (Start with the Most Possible):

① Power off for 5 minutes and then restart—some false alarms will disappear automatically.

② Check the power supply and emergency stop circuit—phase loss or emergency stop errors are a large proportion of false alarms.

③ Confirm the encoder and power line—unplug and plug the connectors to measure continuity.

④ Eliminate mechanical load and lubrication issues—manually rotate the motor to check for any jamming.

⑤ Verify the drive parameter settings—focus on acceleration/deceleration times, electronic gear ratios, and torque limit values.

⑥ Exchange spare parts for verification—swap drives or motors of the same model to quickly locate hardware faults.

A core troubleshooting logic: If the alarm persists after removing a servo axis, the fault of that servo axis can generally be ruled out. This method can then be used to remove other servo axes until the alarm is cleared. This pinpoints the fault to a specific axis, allowing you to then use the previously described methods to troubleshoot the axis's driver, encoder, motor, cables, and external factors.

Routine Maintenance and Alarm Prevention Habits

Check the motor cooling fan monthly and clean surface dust. Every six months, when shutting down, wipe the inside of the electrical cabinet with a cloth and clean the encoder connectors. Open the driver housing and use a vacuum cleaner or soft brush to remove dust from the circuit board—industrial environments are complex, and many alarms are caused by short circuits due to accumulated dust.

During routine inspections, check the motor temperature and cooling fan for normal operation. Occasionally, use diagnostic software to check the load rate to get a general idea of the situation. Also, never use a hammer to directly strike the servo motor shaft to install or remove the coupling, as this will damage the precision encoder on the other end of the motor.

Servo alarms on CNC pipe bending machines are not a cause for alarm. As long as you follow a troubleshooting approach of "recording the code → examining the machine's feel → measuring the main circuit voltage → checking the encoder feedback cable → verifying system parameters," the root cause of most alarms can be identified within 30 minutes.