1. Debugging Context and Product Information:
Debugging Location: Final assembly workshop of an automotive production line.
Test Machines: AGV units No. 1, 2, and 8.
AGV Drive Wheel Motor Parameters:
Model: MRT20.0142
Rated Power: 1000W
Rated Voltage: 48VDC
Rated Current: 26A
Peak Current: 70A
Rated Speed: 1700RPM
Maximum Operating Temperature: 110°C
Drive Controller Parameters:
Maximum Voltage: 60VDC
Rated Current: 60A
Peak Current: 120A
Maximum Operating Temperature: 85°C
Issue Identified: Smoking observed from the traction motor of AGV No. 1.
2. Monitoring Data Summary for AGV Units No. 1, 2, and 8:
3. Preliminary Analysis of Normal Operation Monitoring Data:
Straight-line Movement:
During normal operation in a straight line, motor current fluctuates between a few amps to around ten amps. This indicates that the motor load rate is less than 50%, confirming that the motor and drive controller selection meet the straight-line operation requirements.
Lateral Movement:
During lateral movement, peak current can reach up to 70A (as set by the drive controller) but lasts for less than 2 seconds under normal conditions. This confirms that the motor and drive controller selection can handle lateral movement requirements.
Battery Voltage's Impact on Motor Current:
During lateral movement, when the battery voltage drops below 48V, the motor compensates by increasing current to generate sufficient torque to move the load. Despite these unfavorable conditions, motor overload was minimal, further validating that the motor and drive controller are adequate for maximum power output during lateral operation.
Motor Overheating:
Monitoring data from three motors during normal operation confirms that overheating is unlikely. This can be validated in future testing and production by using an infrared thermometer. After 20 minutes of continuous AGV operation (approximately the time required to reach thermal equilibrium), measure the motor housing's maximum temperature. Add 5–10°C (to account for thermal transfer from the windings to the housing) to approximate the winding's actual temperature. If this value is below 110°C, the motor can operate stably over long periods. Despite two instances of smoking, AGV No. 1 did not exhibit further abnormalities during subsequent tests, indicating reliable motor performance.
4. Analysis of Potential Causes for Motor Overheating (Smoking) in AGV No. 1:
Potential Causes:
Motor Stalling:
Possible causes include incomplete brake release, leading to motor overload.
Unsynchronized Motor Speeds:
Discrepancies between the speeds of two motors may cause a "push-pull" or "tug-of-war" scenario, resulting in overload.
Obstructions:
Wheel blockage due to floor debris could cause motor stalling. This issue was ruled out as the AGV moved away under its own power after an emergency stop.
Misaligned Drive Wheels:
Misalignment during operation (e.g., not on a straight line, parallel track, or concentric arc) could reduce the combined force output, causing overload. This was ruled out since the smoking occurred after the AGV traveled over one meter in a straight line.
Battery Power Deficiency:
Insufficient battery output power could increase motor current, causing overheating. Subsequent tests confirmed significant battery capacity depletion in AGV No. 1.
Controller Parameter Misconfiguration or Fault:
Improper settings or malfunctions in the controller could lead to uncontrolled current surges, overwhelming the motor.
Lack of Motor Temperature Protection:
The motor's built-in temperature protection was either not functional or not utilized.
5. Actions and Recommendations:
Set Drive Controller Undervoltage Protection:
Configure the undervoltage threshold to 44–45V. When battery power is insufficient, reduce motor speed to lower current output (this protection mechanism is embedded in the controller and cannot be reset). AGVs will slow down and eventually stop to protect the controller, motor, and battery.
Note: Prior to the smoking incident, some AGVs lacked this protection. It is recommended to implement this setting during future debugging and operation.
Adjust Current Limiting Protection Settings:
Current settings: peak current limit at 70A, delayed current limit protection at 44A with a 5000ms duration. If the output current exceeds 44A for 5000ms, the controller will shut down until a new operation command is received.
Note 1: Some AGVs lacked this protection before the smoking incident. Future debugging should ensure proper settings.
Note 2: Peak current, current limit, and delay time parameters can be fine-tuned based on actual operating conditions.
Enable Motor Temperature Protection:
Activate the motor's overheat signal to ensure effective protection.
Check for Mechanical or Connection Issues:
For causes like incomplete brake release or speed discrepancies between motors, recheck and confirm connections to eliminate loose or faulty components.
Integrate Data Upload to Upper Control Systems:
Upload motor data to the upper control system before shutdown or post-fault to compare with new data during restart. Additionally, incorporate encoder zeroing operations into the HMI for easier troubleshooting.
By addressing these points, AGV motor reliability and operational safety can be significantly enhanced.
