Common faults and maintenance methods for CNC cutting machine tools - News - Global IC Trade Starts Here Free Join

Generally, in the design, use and maintenance of the numerical control system, it is necessary to give an alarm to the parts that often fail. After the alarm circuit works, on the one hand, the alarm information is given on the screen or the operation panel, and on the other hand, the protective interrupt instruction is issued. Stop the system to troubleshoot and repair.

According to the composition of the CNC system, working principle and characteristics, combined with our experience in maintenance, the common fault locations and fault phenomena are analyzed as follows.

Power section

The power supply is the energy support part that keeps the system working properly. The direct result of failure or failure is the system downtime or the destruction of the entire system. Generally, in Europe and the United States, there are few such problems, and there are not many factors in design. However, in China, due to large fluctuations in power supply and poor quality, there are hidden interferences such as high-frequency pulses, plus artificial Factors (such as sudden pull-off, etc.). These causes can cause power failure monitoring or damage. In addition, part of the numerical control system operating data, setting data and processing programs are generally stored in the RAM memory, and after the system is powered off, it is maintained by a backup battery or a lithium battery of the power source. Therefore, the downtime is relatively long, and the power supply or the memory may be lost, and the system may not operate.

Servo drive system

The servo drive system is associated with the power grid, mechanical system, etc., and is always in a state of frequent start-up and operation during operation, and thus this is also a part with more faults.

1. The main fault of the servo drive system

1 system is damaged. Generally due to network voltage fluctuations, or voltage shocks. In most parts of China, the quality of the power grid is not good, which will bring voltage overrun to the machine tool, especially the instantaneous overrun. If there is no special voltage monitor, it is difficult to measure. When looking for the cause of the fault, pay attention to it. Some are damage caused by special reasons. For example, a machine in North China caused damage to multiple machine tool servo systems due to lightning strikes at the plant substation and into the power grid.

2 There is no control command, and the motor runs at high speed. The cause of this failure is the speed loop open loop or positive feedback. For example, in a factory in Northeast China, the introduction of the West Germany WOTAN rotor milling machine in the commissioning, the machine X-axis in the absence of instructions, high-speed operation, after analysis we believe that is caused by positive feedback. Because the system zero drift, in the case of positive feedback, it will quickly accumulate the motor to run at high speed, and we check the line after the label is completely correct, the machine tool factory technicians think that it is impossible to connect wrongly, after full analysis and testing, we will The feedback line is reversed and the machine is operating normally. The technicians of the machine tool factory had to admit that the German side had made a mistake. There is another example. When we were training in a factory in Tianjin, we asked the factory to repair a precision grinding machine that had not been working properly after entering the factory. The fault was: the machine started to run when the motor started, and the more it came. The faster, up to the maximum speed. Our analysis believes that due to the speed loop open circuit, system drift cannot be suppressed. The reason for the inspection was that the speed feedback line was connected to the ground.

3 The surface of the workpiece does not meet the requirements during machining. When the circular interpolation axis is reversing, the boss appears, or the motor creeps or vibrates at a low speed. This type of fault is generally caused by improper adjustment of the servo system, and the gain systems of the axes are not equal or related to the motor. If the match is not appropriate, the solution is to optimize the adjustment.

4 The fuse is blown, or the motor is overheated and burnt. This type of fault is generally caused by excessive mechanical load or jam.

Position loop This is the key link for the CNC system to issue control commands and compare it with the feedback value of the position detection system to further complete the control task. It has a high frequency of operation and is connected to peripherals, so it is prone to failure.

2. Common faults in servo drive systems

1-position control loop alarm: It may be that the measurement loop is open; the measurement system is damaged, and the position control unit is damaged internally.
2 Movement without command, may be excessive drift, positive feedback, position control unit failure; measurement component damage.
3 measurement component failure, generally showed no feedback value; the machine tool can not return to the reference point; the high-speed leakage pulse can cause the alarm may be caused by the grating or the read head is dirty; the grating is broken.

Programmable controller logic interface

The logic control of the CNC system, such as tool magazine management, hydraulic start, etc., is mainly realized by plc. To complete these controls, it is necessary to collect state information of each control point, such as breaker, servo valve, indicator light and so on. Therefore, it is connected with various kinds of signal sources and actuators with a wide variety of externalities, and there are many changes, so there are many possibilities for failure, and the types of faults are ever-changing.

other

Due to environmental conditions, such as interference, temperature, humidity exceeding the allowable range, improper operation, improper parameter settings, may also cause downtime or failure. There is a CNC equipment in the factory. After the startup, the CNC is ready to lose the signal. The system can't work. After checking, the temperature of the body is very high. The reason is that the ventilation filter has been blocked, causing the temperature sensor to operate. After the filter is replaced, the system works normally. . Failure to remove the circuit board according to the operating procedures, or non-static protection measures, may cause downtime or even damage the system.