3. A special fault of CT4-OS3 type frequency detector CT4-os3 type frequency converter is often used for the tool magazine drive of 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. Since a single tube oscillation is used, and the oscillating circuit is connected to the current limiting resistor and the two triodes, and the output load of the transformer is added, the oscillating circuit has large loss and low gain, which is liable to cause accidental oscillation of the circuit and insufficient pulse amplitude. A motor phase failure occurs 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 syndromes
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
Since the various units of the CNC machine tool (except the drive) and the CNC system realize the signal transmission and control through the PC interface (1/O), many faults will be reflected by the PC interface signal. We can refer to the PC machine tool. The side 1/O signal diagnoses various complex machine faults or discriminates 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 (or form a table) of all PC (machine side) interface signals, and the current state and normal state of all PC (machine side) interface signals during diagnosis. Check the comparison one by one to find out the faulty interface signal, and then find out the cause of the fault based on the external logic 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.
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