Siemens 840C 611D Module Replacement Guide

Gearbox functional verification:

If the machine tool uses the "Electronic Gearbox" (ELG) function for synchronization or interpolation, the synchronization accuracy must be retested after replacing the relevant drive.

Under a simple G401/G402 programming, observe the position of the driving shaft and the driven shaft. Evaluate the synchronization quality through the "synchronization error" or "roundness test" function in the service display area.

If the synchronization error is large, it is necessary to re optimize the compensation controller parameters of the driven shaft (such as MD 1420 * P component, MD 1424 * I component), or adjust the "time constant of the parallel model" (MD 1432 *). This time constant T should be set as the equivalent time constant of the driven shaft position loop (T=1/Kf_factor).

Quadrant Error Compensation (QEC) relearning:

After replacing the feed axis drive, the original quadrant error compensation value may become invalid due to possible changes in friction characteristics.

If "neural quadrant error compensation" is used, the "learning phase" should be initiated in the "drive servo start" application. Let the axis run automatically according to the test signal, and the neural network will automatically learn the optimal compensation characteristics within a few cycles.

After completing the learning, it is necessary to save the learned data to the user file through the "file function" and update it to the boot file to prevent data loss after power failure.

Troubleshooting: Common Problems and Countermeasures

During the debugging process, you may encounter some typical alarms and issues.

*Alarm 156 "Speed Setpoint Alarm Limit Triggered" * *: This alarm typically indicates that the speed command calculated by the NC exceeds the upper limit that the drive can handle. Common reasons: The speed limit of the new motor after replacement (drive MD 1147) is set too low, or the maximum shaft speed in NC (NC MD 280 *) is set too high.

*Alarm 116 "contour monitoring" * *: This is one of the most challenging issues. It indicates that the actual position deviates from the position calculated by NC theory by more than the tolerance (MD 332 *). The reasons are complex and may include: high servo gain (Kv) causing system instability, improper speed loop optimization, mechanical lag, or interference with encoder feedback signals. The solution is to first observe whether the "following error" is stable at a constant speed through the service display. If it shakes, it is mostly due to electrical interference or speed loop problems; If the acceleration/stop exceeds the tolerance, it is mostly due to Kv or acceleration overshoot.

High noise or vibration during shaft operation: This is usually related to the filter settings of the speed loop or current loop. The new driver may need to readjust the current setpoint filter (driver MD 1200-1221) or speed setpoint filter (driver MD 1500-1521). You can enable the "Spectrum Analysis" function in the "Drive Servo Start" to analyze the spectrum of the actual speed value, identify the resonance frequency, and then set a suitable band stop filter in the drive to suppress this frequency.

Communication interruption between PLC and NC: During the replacement process of the drive module, if misoperation or module failure affects the bus, it may cause the PLC to stop. Check the LED status on the PLC CPU. If the PLC is in STOP state, the "USTACK" detailed error code can be read through the "PLC Diagnosis" function in the diagnostic area. If the error code points to bus access timeout, check the driver bus cable and terminal resistance, and ensure that there is no damage in the bus connector.