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Analysis of machine tool drive failure

Common faults and maintenance of servo motor system

1. Mechanical oscillation (during acceleration/deceleration)
The common causes of such failures are:
The pulse encoder is malfunctioning. At this time, check whether the voltage on the feedback line terminal of the speed detection unit has dropped at a certain point. If there is a drop, it indicates that the pulse encoder is defective, and the encoder should be replaced;
The pulse encoder cross coupling may be damaged, causing the shaft speed to be out of sync with the detected speed. Replace the coupling;
The tachogenerator is malfunctioning. Repair and replace the tachometer. In the maintenance practice, the tachometer motor brush is worn and jammed. At this time, the brush of the tachometer should be removed and polished with sandpaper a few times. At the same time, clean the dirt of the commutator, and then reinstall the servo motor.

2. Mechanical movement is abnormally fast (speeding)
For such failures, while checking the position control unit and speed control unit, you should also check:
Whether the pulse encoder wiring is wrong;
Whether the pulse encoder coupling is damaged;
Check whether the servo motor of the tachogenerator terminal is connected reversely and whether the excitation signal wire is connected incorrectly.

3. The spindle cannot move in a directional direction or the directional movement is not in place
For such failures, while checking the setting adjustment of the orientation control circuit, checking the adjustment of the orientation board and the spindle control printed circuit board, you should also check whether the output waveform of the position detector (encoder) is normal to judge whether the encoder is good or bad ( It should be noted that the normal output waveform of the encoder should be measured when the equipment is normal, so that it can be checked in case of failure).

4. Vibration during axis feed
The connection between the motor coil, mechanical feed screw and the motor, servo system, pulse encoder, coupling, and tachometer should be checked.

5. NC error alarm occurs
The alarm caused by program error and operation error in NC alarm. For example, the Nc of FANUC6ME system has an alarm of 090.091. reasons may be:
The common causes of such failures are:
Caused by main circuit failure and too low feed speed;
Bad pulse encoder;
The pulse encoder power supply voltage is too low (at this time, adjust the power supply 15V voltage so that the voltage value on the +5V terminal of the main circuit board is within 4.95-5.10V);
There is no one-turn signal input from the pulse encoder and the reference point return cannot be performed normally.

6. Servo system alarm
The following alarm numbers often appear when the servo system fails, such as FANUC6ME system 416, 426, 436, 446, 456 servo alarm; STEMENS880 system 1364 servo alarm; STEEMENS8 system 114, 104 and other servo alarms, you should check at this time:
The feedback signal of the shaft pulse encoder is broken, short-circuited and lost. Use the indicator to measure the A and B phase one-revolution signals to see if they are normal;
The internal fault of the encoder causes the signal to be unable to be received correctly. Check that it is contaminated, dirty, deformed, etc.

7. For example, common faults of Siemens servo motor
(1) OH alarm for Siemens servo motor repair.
OH is the overheating alarm of the speed control unit. The possible reasons for this alarm are:
The S1 setting on the printed circuit board is incorrect.
The servo unit is overheated. The thermal switch on the heat sink operates. When the drive is not damaged or defective, the cutting conditions or load can be changed to eliminate the alarm.
The regenerative discharge unit is overheated. It may be Q1 failure. When the drive has no hardware failure, the acceleration and deceleration frequency can be changed to reduce the load and eliminate the alarm.
The power transformer is overheated. When the transformer and the temperature detection switch are normal, the cutting conditions can be changed to reduce the load, eliminate the alarm, or replace the transformer.
The overheating switch of the radiator of the electric cabinet is activated because the electric cabinet is overheated. If the switch still works at room temperature, the temperature detection switch needs to be replaced.

(2) OFAL alarm for Siemens servo motor repair.
The digital servo parameter setting is wrong, and the relevant parameter setting of the digital servo needs to be changed at this time. For the FANUC0 system, the relevant parameters are 8100, 8101, 8121, 8122, 8123 and 8153~8157, etc.; for the 10/11/12/15 system, the relevant parameters are 1804, 1806, 1875, 1876, 1879, 1891 and 1865~1869 Wait.

(3) FBAL alarm for Siemens servo motor repair. FBAL is a pulse encoder connection error alarm. The reasons for the alarm are usually as follows:
The encoder cable connection is bad or the pulse encoder itself is bad.
The external position detector signal is faulty. To
The detection circuit of the speed control unit is defective.
The gap between the motor and the machine is too large.

(4) The 7-segment digital tube alarm on the servo drive FANUCC series and α/αi series digital AC servo drives usually have no status indicator display, and the driver’s alarm is displayed through the 7-segment digital tube on the drive. According to the different status display of the 7-segment digital tube, it can indicate the cause of the driver’s alarm.

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