Special diagnostic methods for troublesome faults in CNC machine tools - News - Global IC Trade Starts Here.

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1. Example of using a resistor comparison method to diagnose a short-circuit fault of a power supply load: FANUC-BESK servo drive board with a 15V load soft breakdown fuse.
When we repaired, it was determined through preliminary inspection that the cause of the fault was a partial short circuit of the load, and the “15” ground resistance was measured with a digital meter. The normal board was 1.3KΩ and the fault board was 300Ω. Because the fuse is energized and burned, it is impossible to check the power at all, so only the resistance measurement or the component inspection can be done.
However, since the servo circuit's ten 15V power supply and its load (24 integrated components) are printed in a radial configuration, it is impossible to perform circuit cutting separation during resistance measurement, and it is impossible to directly solder because of many components. Disassemble the inspection one by one. The actual operation of the maintenance is very difficult, and even if the fault is solved, the board is often scarred. Handling this kind of failure that can not be done by circuit cutting separation or component disassembly and power failure inspection, we use the resistance comparison method to check is very convenient. During the diagnostic inspection, the circuit is not cut and the component is not soldered, but the resistance value of the relevant pin of the 1015V terminal and each integrated component is directly measured, and the corresponding value of the faulty board and the normal board are compared, and the fault can be detected. . When dealing with the above faults, considering the number of component pins, first analyze the internal circuit of the thick film block (marked in the figure) and the integrated block pin function diagram, and then select some main test points from it to do the resistance measurement. When measuring Q7, it is found that its 3 pin (+ 15V) to 14 pin (output) resistance is 150Ω (normally 6KΩ, suspected Q7 (LM339) has a problem, after replacing Q7, the servo board returns to normal, indicating Q7 pin Abnormal resistance is an internal soft breakdown, causing a short circuit in the power supply.
2. Step-by-step simulation of fast process Some control processes, such as the automatic lifting speed of the stepper motor, the parking brake process of the DC governor, only a fraction of a second. Looking for circuit faults in such a fast process, it is obviously impossible to use general instrumentation for fault tracking detection, so fault diagnosis is difficult. In the following, through the failure example, the 5V DC thyristor main drive has a long stop time, and introduces the special method we use a step-by-step simulation method.
After a preliminary check of the faulty board, it is judged that the cause of the fault is in the V5 main drive brake circuit. The brake control logic is complicated, involves many circuits, and the diagnosis fault is by no means an effort. Moreover, because the braking process is short and cannot be measured, we use a step-by-step simulation method for diagnostic inspection. The braking process is known by the circuit principle as follows: (1) the bridge is inverted, releasing energy; (2) automatic bridge switching, regenerative braking; (3) switching bridge again, circuit recovery.
For the needs of step-by-step measurement, the speed process, speed feedback and current feedback are set as the set amount, the above process is subdivided into eight steps (listed into a table), and then the corresponding set amount is gradually changed to detect the relevant circuit signals. Check the circuit logic to find out the fault. When we do the step-by-step test to the second step (that is, the speed command changes from 1 to 0), we find that "a back shift" and "integral stop" are both high, according to the circuit logic, it should be low, according to this Check the circuit and quickly find out that there is a problem with the NAND gate Dl06 (model: FZHI01) in the A2 board. After replacement, the fault is eliminated.
3. A special fault of CT4-OS3 type frequency detector
The CT4-os3 type inverter is often used for the tool magazine drive of the YBM90 and MK5oo machining centers. During the maintenance, we encountered the phase loss fault of the inverter many times, and the phase loss voltage was only 60 to 2 ooV (normally 400v). Since this is a kind of soft fault that is good or bad, the diagnosis is difficult.
However, we found that most of the failure of this inverter is due to the pulse isolation stage problem - the oscillation is unstable. This kind of fault phenomenon, with an oscilloscope check, it is difficult to find "waveform loss", but generally there are three groups of pulse amplitudes are not equal, or even the difference is soft. In fact, a careful analysis of the characteristics of the isolation circuit can be seen, this is a special intermittent oscillator, only two three-stage tube, respectively, the oscillation tube and oscillator power switch. Due to the single-tube oscillation, the oscillating circuit is connected to the current limiting resistor and the two triodes, and the output load of the transformer is added, so the oscillating circuit has large loss and low gain. It is easy to cause the accidental oscillation of the circuit and the insufficient amplitude of the pulse, that is, the phase loss of the motor when it is good or bad. It can be seen from the above analysis that this circuit has strict requirements on the Q value of the pulse transformer and the beta value of the triode. When the user is repairing, the following measures can be used to compensate: (1) select a high β (120 to 180) oscillation tube; (2) Appropriately reduce the resistance of the current-limiting resistor, that is, connect 100-270Ω on the 51Ω resistor.
4. Diagnosing Multiple Fault Syndrome The following is a typical example of a CVT035 transistor DC driver to illustrate the diagnosis of multiple fault syndromes. The faulty servo board, after preliminary inspection, shows that the appearance of the circuit board is dirty and the output stage burns seriously. It can be seen that the user's maintenance is relatively lacking. To deal with such a fault, the dirt should be removed first, the output level should be repaired, and the power should be rushed. Failure to do so may cause a short circuit and enlarge the fault surface. For example, the conductive short circuit of the iron powder dust, the output stage switch tube breakdown, the short circuit of the front stage and the power supply, and the like. After the above treatment, the power-on check found the following faults: (1) "undervoltage" red light sometimes flashes ("READY" green light flashes); (2) motor does not turn; (3) switching power supply (±15V) transformer Tl and power switch tube V69 are abnormally hot.
This is a typical syndrome, and there may be some causal relationship between the faults, so the faults need to be processed in order, otherwise it may be half the effort, or even cause the fault surface to expand. Through analysis, we make the following maintenance order: switching power supply 1> "undervoltage" light -> motor running. First check the power board, after measuring the main circuit 150V DC voltage and disconnecting the ±15V load, it is known that the fault is inside the switching power supply board. In the inspection power board, the voltage of the 10V voltage regulator V32 is only 9.5V. This check goes on and finds the cause of the fault: the resistance of the current limiting resistor Rl85 of V32 becomes larger. After replacing the Rl85, the ±15V power supply board and the "undervoltage" lamp returned to normal, but the motor still does not turn. It can be seen that the above lamp flash and component hot are caused by the Rl85 variable value, and the motor does not rotate for another reason. According to the usual inspection method, it can be detected step by step, but due to the experience, we only do a simple transformation steering test, and found that the reverse operation is normal, so the cause of the failure is quickly identified: the integrated circuit of the commutation circuit N5 (TL084 ) failure, after replacing N5, everything is normal.
5. PC interface method Because the CNC machine tool unit (except the driver) and the CNC system realize the signal transmission and control through the PC interface (1/O), therefore, many faults will be reflected by the PC interface signal, we can pass Check the 1/O signal on the PC machine side to diagnose various complex machine faults or to identify faults in the CNC system or in the machine tool electronics. The method is very simple, that is, it is required to be familiar with the current state and normal state of all PC (machine side) interface signals (or make a form), (by article: http://) The current state and normal state of all PC (machine side) interface signals are compared one by one to find out the faulty interface signal, and then the cause of the fault is found according to the external logic relationship of the signal. When you are familiar with the PC interface signal, the application of this PC interface comparison method is very simple and fast, and avoids the complicated ladder program of the board.
6. Siemens 3GG system data recovery abnormally Switzerland STUDER s45-6 grinding machine equipped with Siemens 3GG system, double NC double plc structure, the system has a strong self-diagnosis function, when the fault occurs, you can use the screen prompts to quickly diagnose and repair the fault. However, if the system fails to start, and the PLC is in a stopped state, the screen does not light, then the system's self-diagnosis function will not work, resulting in difficult diagnosis. There are many reasons for this failure. If the battery voltage is lower than 2.7V, the battery must be replaced. If the NC or PLC hardware is damaged, the circuit board needs to be replaced. If the 24V power supply of the machine is lower than 21V, check the power supply circuit and load.
But the more faults we encounter are not hardware failures, but soft faults such as machine data anomalies. The reasons are complicated. For example, grid interference, electromagnetic interference, battery failure, and operational errors may cause loss or confusion of machine data, so that the system cannot be started.
Like this kind of soft fault, we can use the full recovery method to make the system resume running. The steps for clearing the 3GG system are as follows:
(1) Clearance of machine data, user program, setting data and background memory;
(2) initialization of the 3GG system;
(3) PLC clearing;
(4) Restore all data and programs that have been cleared. Generally, you need to set the baud rate, call up 128KB of memory, and then input data and programs through media such as disk.
(5) Test and check the full KV coefficient of the servo system.
(6) After completing these steps, the system returns to normal.