Several common faults in the spindle drive system of CNC machine tools and how to repair it?

Trouble phenomenon:

When the vertical machining center supporting FANUC6 system is working, the machine tool vibrated severely, and the AC spindle drive displayed AL-04 alarm. During the vertical machining center supporting FANUC6 system is working, the machine tool vibrates severely, and the AC spindle drive displays AL-04 alarm. Analysis and process: FANUC AC spindle drive system AL-04 alarms which means “P1, F2, F3 fuses blown in AC input power".

The possible causes are:

1)The AC power output is too high. 2) Defective transistor inverter module . 3) Defective rectifier diode (or thyristor) module. 4) Defective surge absorber or capacitor. And then check the AC input power. If the measured R and S phase input voltage of the input power of the AC spindle drive is 220V, but the T phase is only 120V, it’s indicated that there is a problem with the drive’s three-phase input power supply. Further check the three-phase output of the spindle transformer, and found that the transformer input, output and machine tool power input are also unbalanced, indicating that the cause of the fault is not the machine tool itself. Check the three-phase fuse on the switch cabinet of the workshop, and found that one phase is hundreds of ohms. It was disassembled and inspected, and it was found that the fuse connection screw was loose, which caused the three-phase input power to be unbalanced; after reconnection, the machine tool returned to normal.

The drive has an alarm “A"

Fault: After starting a CNC machine tool supporting FANUC 0T, the system is in the “emergency stop" state, “NOTREADY" is displayed, and the spindle alarm light on the operation panel is on. Analysis and process: Check the AC spindle drive of the machine tool, and it is found that the drive is displayed as “A". According to the driver’s alarm display, the meaning of the driver’s alarm is “driver software error" according to the driver’s alarm display. Usually initialize the driver when the driver is accidentally disturbed by the outside. In this machine tool, the parameters are initialized according to the following steps: 1)Cut off the power supply of the driver and set the setting terminal S1 to TEST. 2) Turn on the driver power. 3) When the display changes from completely dark to “FFFFF", release all the keys and keep them for more than 1 second. 4) Press and hold the DATASET key for more than 1s, and the "GOOD" displays, when the standard parameter writing is completed. 5) Cut off the power of the drive and reset S1 (SH) to "DRIVE". Through the above operations, the drive returns to normal, the alarm disappears, and the machine tool resumes normal operation.

An OC fault

Fault: the spindle suddenly stops during processing a horizontal machining center equipped with FANUC11M system, and the driver displays an over-current alarm. Analysis and process: After checking the main circuit of the AC spindle drive, it was found that the fuses of the regenerative braking circuit and the main circuit were blown. After replacement the machine tool returned to normal. But after several days of normal operation of the machine tool, the same failure occurred again. Due to the repeated occurrence of the fault, it is proved that there is a problem with the spindle system of the machine tool. According to the alarm, the main reasons are as follows: 　　 1) The spindle drive control board is defective. 　　 2) The motor is continuously overloaded. 　　 3) The motor windings are locally short. According to the actual processing conditions on site, the motor is not overloaded. After replacing the components, the drive can work normally for several days. So there is a small possibility that the spindle drive control board is defective. Therefore, the most likely cause of failure is the partial shortness of the motor windings. We found that the U relative to ground insulation resistance is relatively small after carefully measuring the resistance of each phase of the motor winding during maintenance, which proves that the phase is locally short to the ground. The motor was disassembled and inspected, and it was found that the insulation sleeve at the connection between the inner winding of the motor and the lead wire had been aging; after reconnection, the resistance to ground returned to normal.After replacing the components again, the machine tool returns to normal.

AL-12 alarm of spindle drive

Fault: The spindle suddenly stopped and the driver displayed No. 12 alarm when the horizontal machining center equipped with FANUC11M system is working. Analysis and process: The meaning of No. 12 alarm on the AC spindle drive is "DC bus overcurrent". From the foregoing in this chapter, we can see that the possible causes of the failure are as follows: 　　1) The motor output terminal or the motor winding is partially short. 　　2) Defective inverter power transistor. 　 3) The drive control board is faulty. Then we found that the transistor component has been damaged. Check the drive power test terminal, the AC input power is normal; the DC output +24V, +15V, +5V are all normal, but the -15V voltage is "0". After further checking the power supply, it was found that the integrated voltage regulator (model: 7915) was damaged. After replacing the 7915, the -15V output voltage is normal, the spindle AL-19 alarm is eliminated, and the machine tool returns to normal.

AL-01 alarm of spindle drive

Fault: During the vertical machining center equipped with FANUC21 system’s machining process, the spindle suddenly stops running, the system displays ALM2001, ALM409 alarms, and the AC spindle drive displays AL-01 alarms. Analysis and process: The supporting system of this machine tool is FANUC21 system, and the meaning of the alarm displayed on the CRT is as follows: AL-01: The spindle motor overheats alarm. The above alarms can be cleared by the reset button. After clearing, the system can be started and the spindle has no alarm. However, after the manual reference point return of each axis is executed normally, when the Z axis moves downward, the above alarm occurs again. As the actual machine tool alarms, only the Z axis moves down, the spindle motor does not rotate, and at the same time it does not generate heat. Taking into account that the spindle motor moves up and down along with the Z axis, it can be roughly determined that the fault is due to the movement of the Z axis, which causes the spindle motor cable to bend and cause poor contact. Open the spindle motor junction box and check, it is found that the spindle motor thermistor wiring on the plug in the junction box is loose; after reconnection, the fault is eliminated and the machine tool returns to normal.

Abnormal vibration of spindle at high speed

Fault: In a CNC lathe supporting FANUC0TA2 system, when the spindle rotates at a high speed (above 3000r/min), the machine tool vibrates abnormally. Analysis and process: The vibration of the CNC machine tool is related to the design, installation, adjustment of the mechanical system, the natural frequency of the mechanical system, the natural frequency of the spindle drive system and other factors, and the reasons are usually more complicated. But on this machine tool, because the AC spindle drive system worked normally before the failure, it can rotate at high speed; and when the spindle exceeds 3000r/min, vibration exists at any speed, which can eliminate the cause of mechanical resonance. After disconnecting the connection between the spindle motor and the spindle of the machine tool, observe the spindle speed and torque display on the control panel, and found that the value has a large change. After carefully checking the connection of the spindle drive system of the machine tool, it was finally found that the ground wire of the spindle drive of the machine tool was not well connected. After the ground wire was reconnected, the machine tool returned to normal.

The spindle sound is dull and there is an OC alarm

Fault: It’s a CNC copy milling machine equipped with FIDIAl2 system and FANUCl5 DC spindle drive. After the spindle is started, the sound is dull during operation; when the spindle is braking, the CRT displays "FEEDHOLD", and the spindle drive device "overcurrent" .The warning light is on. Analysis and process: Since the mechanical transmission system, spindle motor, and connection reasons are excluded, it can be determined that the cause of the fault lies in the spindle drive. Compared with the principle diagram of the spindle servo drive system, the analysis and inspection were carried out focusing on the relevant lines of the current feedback link; the parts of the electric board that may be welded were re-welded, and all the connectors were surface treated, but the failure phenomenon still unchanged. Since there are no spare parts for the drive at the maintenance site, it is impossible to exchange the electrical boards of the drive. In order to determine the approximate location of the fault, the fault can automatically disappear after the machine is powered on for about 30 minutes. The method of local heating is used during maintenance. The hair dryer was used to locally heat up each part of the electric board at a distance of 8 to 10 cm from the electric board, and it was found that when the trigger line was heated up, the spindle operation could immediately return to normal. From this analysis, it is preliminarily determined that the fault location is on the trigger line of the driver. Observing the output waveform of the trigger part of the line through an oscilloscope, it is found that one of the integrated circuits has no trigger pulse generated at room temperature, causing the rectification back to the U-phase 4 thyristors (2 positive and negative groups) trigger pulse disappear: replace this Troubleshooting after the chip. After the repair is completed, further analyze the cause of the failure. When the spindle drive is working, the three-phase full-control bridge rectifier main circuit, one phase has no trigger pulse, which causes the DC bus rectification voltage waveform pulsation to become larger, the harmonic component increases, and the motor commutation is difficult. The running sound of the motor is dull. When the main shaft is braking, because the driver adopts feedback braking, the control line must first turn off the trigger pulse of the positive group, and trigger the thyristor of the inverse group to make it inverter. During the inverter, the energy cannot be fed back to the grid in time due to the lack of a phase trigger pulse. Therefore, the motor generates overcurrent, the driver generates an overcurrent alarm, and the electric action is taken.

The main shaft only has the fault repair of drifting speed

Fault: A CNC milling machine with FANUC7 system, the spindle speed can not reach the command speed in automatic or manual operation mode, only 1~2r/min, the forward and reverse conditions are the same, and the system has no alarm. Analysis and process: Because the machine tool has the function of spindle shifting, in order to verify the action of the mechanical transmission system, the high and low shifting action tests were carried out in the MDI mode during maintenance. It was found that the machine tool was operating normally, indicating that the transmission mechanism of the mechanical transmission system was working Normal, the cause of gear meshing is ruled out. Check the cable connection of the spindle drive and the status light on the spindle drive. They are all in a normal working state, and it can be preliminarily determined that the spindle drive is working normally. Further measure the command voltage input VCMD of the spindle drive, and found that under any S command, VCMD is always "0", that is, the drive has no speed command input. Check the CNC control cabinet and found that the plug XN of the spindle analog output on the control board is loose; after reinstallation, the machine tool returns to normal.

Failure:

An imported horizontal machining center supporting FANUCll system, the S command is invalid, the spindle speed is only 1~2r/min, and there is no alarm. Analysis and process: Measure the speed command PcMD signal of the spindle drive. It is found that under any S command of O-4500r/min, VCMD is always 0. Further measurement of the CNC S analog output, the value is also "0", indicating The CNC spindle speed control command is not output. Since the CNC has no alarm display, the possible reason for the spindle speed control command not being output is that the spindle does not meet the conditions for the speed output. Comparing the interface signals of the system, through the analysis of the PLC program ladder diagram, it is found that the spindle high/low gear shift flags in the PLC program and the high/low downshift detection switch input signals of the machine tool are all "0", which is inconsistent with the actual situation. Does not match. By manually controlling the solenoid valve, after the machine tool is shifted to the low-speed gear, the input signal of the low-speed gear detection switch of the machine tool is correct, and the flag of the low-speed gear shift of the spindle in the PLC becomes the correct state, which satisfies the spindle condition. Under this condition, start the spindle again and the machine tool returns to normal. In order to further determine the cause of the machine failure, through MDI mode, after executing M42 (high-speed shift command), it was found that the M42 command could not be completed. Check that the high-speed gear solenoid valve has been energized, but the high-speed gear in-position signal is "0", which determines that the cause of the fault lies in the mechanical or hydraulic part of the machine tool. Inspect the inside of the headstock, it is found that the shift fork of the machine tool's shifting mechanism is loose. At low gears, the shift fork moves downwards and can fall under its own weight, so the machine tool can work normally; when shifting high gears, the shift fork moves upwards and pulls out. The gear cannot be inserted after exiting. After reinstallation, the machine tool returned to normal.