External fault diagnosis and countermeasures of CNC machine tools

External faults of CNC equipment can be classified into soft faults and hard faults caused by external hardware damage. Soft faults are caused by improper operation and adjustment. These faults occur mostly during the pre-use period of the equipment or during the adjustment period of the equipment user. For the CNC system, another place that is prone to failure is the servo unit. Since the movement of each axis is realized by the servo unit controlling the servo motor to drive the ball screw. A rotary encoder is used for speed feedback, and a grating scale is used for position feedback. Generally, the faulty place is the drive module of the rotary encoder and the servo unit. There are also individual system confusion caused by power supply. Especially for those systems that have a computer hard drive to store data. For example, the German Siemens System 840C.

Example 1: When a CNC lathe is just put into use, it must be returned to the reference point when the system is restarted after the power is turned off. That is, when the axes are manually moved outside the non-interference zone, the axes are returned to the reference point. Otherwise, a crash may occur. Therefore, after machining every day, it is best to move the axis of the machine to a safe position. There will be no problems after this operation or power failure.

Faults caused by external hardware operations are common faults in CNC repairs. It is generally caused by problems with the detection switch, hydraulic system, pneumatic system, electrical actuators, and mechanical devices. Some of these faults can be used to find the cause of the fault through the alarm message. For general numerical control systems, there are fault diagnosis functions or information alarms. Maintenance personnel can use this information to narrow down the scope of diagnosis. Some faults have alarm information, but they do not reflect the true cause of the fault. At this time, it is necessary to analyze and solve according to the alarm information and the fault phenomenon.

Example 2: The SINUMERIK 840C system is used in one turning unit of our factory. The machine suddenly stopped while working. The spindle temperature alarm is displayed. After comparison check, the fault appears on the temperature meter, and the alarm disappears after adjusting the peripheral line. The new meter is replaced and the camera returns to normal.

Example 3: This is the same turning center. When working, CRT shows 9160 alarm.

"9160 NO PART WITH GRIPPER 1 CLOSED VERIFY V14-5". This means that the workpiece alarm has not been picked up. However, the robot that grasped the workpiece actually grabbed the workpiece, but showed that the robot did not grab the workpiece alarm. Check the PLC diagram, this fault is measured by the sensor switch. After checking the robot part, the working stroke of the manipulator is not in place, and the induction switch is not completely depressed. Then adjust the clamping force of the robot and this troubleshooting is eliminated.

Example 4: A vertical machining center uses the FANUC-OM control system. The 414# and 410# alarms appear when the machine is performing in the automatic mode until the X axis moves quickly. This alarm is a speed control OFF and an X-axis servo drive error. Since this fault can be eliminated by restarting, it will alarm every time the X-axis moves quickly. After checking that the servo motor power cord plug is caused by arc creep, the phase-to-phase short circuit is caused, and the fault is eliminated after trimming.

Example 5: Improper operator operation is also an important cause of failure. For example, another CNC lathe with 840C system in our factory is completely normal on the first day of work, but it can't be opened anyway when working the next day. When the work mode is changed to automatic mode, it will alarm “EMPTYINGED MOOEOR”. After the workpiece is machined, the spindle does not stop, the robot grabs the workpiece, and then carefully checks that there is no problem in each part, but a mode switch position under automatic working conditions is wrong. Therefore, when there are some alarms with unknown causes, it is necessary to check the switch position under each working mode.

There are still some faults that do not generate fault alarm information, but the action can not be completed. At this time, it is necessary to analyze and judge according to the maintenance experience, the working principle of the machine tool and the PLC operating condition.

For the repair of CNC machine tools, it is important to find the problem. Especially the external fault of CNC machine tools. Sometimes the diagnosis process is more complicated, but once the problem is found, it is easier to solve. The following two principles should be followed for external fault diagnosis. First of all, you must be proficient in the working principle and sequence of the machine. Second, you should use the PLC ladder diagram. The status display function of the NC system or the off-board programmer monitors the operating status of the PLC. Generally, as long as the above principles are followed, care should be taken, and general CNC faults will be eliminated in time.