How to troubleshoot PLC faults with KUKA robots

PLC is an industrial small computer, it has a problem, the first thing to clean up is the PLC ontology problem is still a peripheral problem, if there is a problem with the PLC ontology, often the ERR light will be on, maybe the red light is flashing, the normal situation is generally RUN operation green light on, if this kind of problem occurs in the ontology, the probability of successful correction is not high.

Some PLC insists on data through the battery inside, when the battery voltage is lower than a certain threshold, there will be a battery alarm prompt light on, at this time the battery needs to be replaced, and the demand is charged to replace, if the battery is completely out of power, perhaps the replacement of the battery is not charged at the time, often the RAM data is lost, and the data of RAM is often lost, and the program and data need to be refreshed from scratch, so the PLC usually protects and maintains the time, and must have the habit of program and data backup, otherwise there is no time when it is critical. Just program and debug from scratch.

How to troubleshoot PLC faults with KUKA robots

How to troubleshoot PLC faults with KUKA robots

Power supply defects will also account for a certain proportion of ontology faults, PLC input is generally 220 AC, there are some things 24 volts or 12 volt input, but there is a chip inside, the need for 5VDC or 3.3VDC, so there is a switching power supply step-down circuit, this circuit due to the large current, high temperature, in some harsh high temperature or dust occasions are prone to problems, if the PLC indicator light is not lit, it is generally the switching power supply is broken. The switching power supply is broken, for people who generally have a little electronic repair level, it is not particularly difficult to repair, such as the control chip 384X, which may have a high probability of breaking the switch tube, and it is generally good to replace it.

If there is a red light flashing or the ERR light is on, it is often the motherboard is broken, or the program is lost, you can try it from the beginning, if it doesn't work, there is not much repair value, at most replace the watchdog IC and reset circuit of the chip, or replace the crystal oscillator of the chip, if it still can't solve the problem, it will be advocated to give up, this thing is too integrated, it is very difficult to repair, and the price of the motherboard is not particularly expensive, there is not much value.

The output output point is bad, it is also a more common PLC body problem, especially the relay output type of PLC, in some frequent switching actions, it will be easy to hang up the relay, the service life of the relay is about 100,000 times, often used for 3-5 years, it may be broken, this problem is also easy to find, after all, look at the output indicator light, but with a multimeter measurement no contact closure or disconnection can find the problem, disassemble, find some domestic similar small relay replacement, generally not a big problem. If the transistor is broken, it is common for the input to be connected to the high voltage, and the input and output may be damaged, and the optocoupler and some amplified transistor circuits often need to be replaced.

If it is a peripheral problem, you can analyze the logic of input and output according to the circuit diagram, analyze it from the macro level and the operation of the equipment, and you can also shield some input and output interlocking points to separate the test to find the problem. If there is a PLC program that is more brief, because the PLC has an online diagnosis function, it can be performed independently, and see if the performance is normal, and you can find the fault point.

The most difficult thing is still some system problems, especially the circuits that some people have repaired. One year, Chimelong's big pendulum had a problem, their equipment department had a PLC program, there was also a program of the industrial computer, the external circuit drawings were also complete, and various conditions could be diagnosed online, but the big pendulum ran to a certain logical point, it took the initiative to trip, and all of them were powered off, without any alarm and prompt. They tossed for a long time and couldn't find a problem, and they also looked for many people to see, but they couldn't find anything wrong. Later, I went to help them see, it seems that there is nothing special in the control room, because others have checked it, I personally climbed to a height of more than 10 meters, there is a small manipulator on the spot, there are some relays in it, because I repeatedly looked at their drawings and the operation logic of the site, the problem should be in this box. I asked them to turn on the machine several times, and each time they jumped the main switch when they ran to the direction of a relay, but this relay was an ordinary DC relay.

I tried to remove the relay coil wire, let them operate again, the result of the equipment to run to a certain moment, and stopped, but did not trip, I judged that there was a problem with this relay, removed it and checked carefully, and found that the relay was connected in the opposite direction of the freewheeling diode, so that the coil of the relay was electrified, which was equivalent to a 12-volt DC power supply, directly added to the freewheeling diode to form a positive guide, and the 12-volt power supply was short-circuited, so the power supply tripped and caused the system to trip. It would be good to turn this diode upside down, and estimate that it was caused by the wrong tap when someone checked the replacement site.

How to troubleshoot PLC faults with KUKA robots

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