First, Sanguang brand CNC wire cutting machine
Fault phenomenon: Stepper motor is out of step.
The working principle of the stepper motor is shown in Figure 1. S1 is a feed switch that uses a normally closed contact. The PA of NAND input 2 is the stepper motor control signal from the computer. When the feed switch is turned off, or the control signal PA is at a low level (0.8 V or less), the output of the NAND gate is at a high level, and the input terminal of the photocoupler V1 does not have a current sufficient to cause the light emitting diode to emit light, so the output The phototransistor at the end is turned off, and the +12V power supply saturates the triode V2 through the resistors R3 and R4. The potential value of V2 to 2M is as follows: the base is about 0.7V, the collector is about 0.3V, and the transistors V5 and V6 in the driving circuit are turned off. The potential values at each point are as follows: the emitter is about 0V, and the collector is about 8V or more. The stepping motor winding L has no current passing due to the cutoff of V6. When the feed switch is turned on and the control signal PA is high level, the output is low level (0.5V or less), so that V1 is saturated and turned on, so that the base potential of V2 is turned off below 0.5V, and the +12V power supply passes through R4 and V3. R5 provides the base current of V5 and V6 to make it turn on, and the working current flows through the winding of the stepping motor. R9 and V4 are overcurrent protection circuits. When V6 current is too large, the voltage across R9 rises, and the current flowing through V4 increases, which reduces the base current of V5, thus reducing the output current of V6. At this time, the voltage across R9 decreases again, and the current in V4 also decreases. The base current of V5 increases, and the output current of V6 also increases, so that the current of the stepping motor winding tends to be stable when it is turned on.
The stepping motor stepless fault is generally V6 damage. The common fault is the breakdown short circuit between the collector and the emitter. It is caused by the failure of the freewheeling circuit composed of V7 and R8. The V7 and R8 circuits should be checked at the same time during maintenance. In the case of an open circuit between the collector and the emitter of the V6, the reason is that the protection circuit consisting of R9 and V4 is faulty, and the circuit should be repaired at the same time.
Second, DK7732 CNC key wire cutting machine
Fault phenomenon: The high-frequency pulse power supply is not working properly. When cutting the wire, the cutting spark is large and small. When the motor is short-circuited, it neither retreats nor stops, resulting in broken wire, as shown in Figure 2.
When the cutting spark is large and small, it is suspected that the pulse power supply is not working properly. The visual inspection shows that the voltage indication is normal and the cutting current indication is abnormal. When short circuit occurs, sparks are generated at the short circuit, and the gap voltage is not zero; the waveform and potential of each part of the pulse power supply are normal, and the pulse power supply output is also normal. When the short circuit is not retracted, no downtime, generally the computer control loop is not normal, the suspect is to adjust the internal frequency of the inverter potentiometer, the fault phenomenon remains after replacement; then find that the conductive block on the wire frame has been seriously worn, and the aluminum wire is in poor contact with it. After the conductive block is ground, the machine is re-adjusted and the machine is running normally.
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