KUKA robot maintenance overcurrent alarm phenomenon

1, the flow

Overcurrent is the most frequent phenomenon of frequency converter alarm.

1.1 the phenomenon

(1) when restarting, trip at a liter speed. This is a very serious phenomenon of overcurrent. The main reasons are: load short circuit, mechanical parts are stuck; Inverter module is damaged; The torque of motor is too small.

(2) when the power is on, it will jump, which cannot be reset generally. The main reasons are: bad module, bad drive circuit, and bad current detection circuit.

(3) the main reasons are: the acceleration time is set too short, the upper limit of current is set too small, and the torque compensation (V/F) is set too high.

1.2 instance

(1) a lg-is3-43.7kw frequency converter will jump "OC" as soon as it is started.

Analysis and maintenance: no sign of burning was found when the cover was opened. The IGBT(7MBR25NF-120) was measured online, and the basic judgment was ok. To further determine the problem, the high-power transistors of 7 units were well turned on and off after the IGBT was removed. When measuring the driving circuit of the upper half bridge, it is found that there is a significant difference between one circuit and the other two circuits. After careful inspection, it is found that an optocoupler A3120 output pin has a short circuit with the negative electrode of the power supply. The three circuits after replacement are basically the same. The module is installed and running well.

(2) a beltro-vert2.2kw frequency conversion power will jump "OC" and cannot be reset.

Analysis and maintenance: first check the inverter module and find no problem. Then check the drive circuit is not abnormal phenomenon, estimated that the problem is not in this part, may be in the over-current signal processing this part, the circuit sensor removed after the power, it shows that everything is normal, it is considered that the sensor is broken, find a new product with load after the experiment all normal.

2, over voltage,

Overvoltage alarm usually occurs when the machine is stopped, and the main reason is that the deceleration time is too short or the brake resistance and brake unit have problems.

(1) instance

One station an N2 series 3.7kw frequency converter jumps "OU" when stopping.

Analysis and maintenance: before repairing the machine, the first thing to understand "OU" alarm why, this is because the frequency converter is slowing, motor rotor winding cutting speed rotating magnetic field, rotor electromotive force and the current increases, the motor is in a state power, the energy feedback through the inverter link with power switch tube parallel diode to dc link, make dc bus voltage rise caused by, so we should focus on check brake circuit, measuring discharge resistance there is no problem, when measuring brake pipe (ET191) found a breakdown, running on electricity after replacement, and stop quickly.

3, undervoltage

Undervoltage is also a problem we often encounter in use. Mainly because of main loop is too low voltage (220 v series is lower than 200 v, 380 v series is lower than 400 v), the main reason: a rectifier bridge damage or silicon controlled all the way with work of three way in normal are likely to cause under-voltage fault, the second main circuit contactor is damaged, leading to loss of dc bus voltage on charge resistance may cause under-voltage, and voltage detection circuit malfunction and undervoltage problems.

For example, 3.1

(1) a ct18.5kw frequency converter power "Uu".

Analysis and maintenance: through inspection of the frequency converter rectifier bridge charge resistance are good, but didn't hear after electricity contactor action, because the charging circuit of frequency converter instead of using thyristor by contactor close to complete the process of absorption, so that failure may in the contactor or control circuit and the power part, disconnect the contactor with 24 v dc contactor work alone. Then check the 24V dc power supply. After careful inspection, the voltage is output after the voltage is stabilized by the voltage regulator of LM7824. It is measured that the voltage regulator is damaged

(2) a DANFOSSVLT5004 frequency converter shows normal power supply, but after loading, "DCLINKUNDERVOLT" (dc circuit voltage is low) is switched on.

Analysis and maintenance: the frequency converter from phenomenon is special, but if you carefully look at the problem is not so complicated, the frequency converter is also through the charging circuit, contactor to complete the charging process, when the electricity didn't find any abnormal phenomenon, estimation is added when the load voltage drop caused by the dc circuit, the voltage of the dc circuit is through full-wave rectifier bridge rectifier, and then provided by capacitance after flat wave, so should check the rectifier bridge emphatically, has found that the measured open circuit, a bridge rectifier bridge arm after replacement of new problems to solve.

4, overheating

Overheating is also a relatively common fault, the main reasons: excessive ambient temperature, fan blocking rotation, poor performance of temperature sensors, motor overheating.

For example, 4.1

A customer of ABBACS50022kW inverter reported jumping "OH" in about half an hour of operation.

Analysis and repair: for it is defective only after running for a period of time, so the temperature sensors are unlikely to bad possibility that the temperature of the inverter is too high, after electrify found fan turn slowly, shield wall inside is full of a lot of cotton (because of the frequency converter is used in the textile industry), after cleaning the fan operation is good, the boot operation hours after didn't jump this failure.

5. Unbalanced output

The output imbalance is generally manifested as motor jitter and unstable speed, the main reasons are: bad module, bad drive circuit, bad reactor, etc.

For example, 5.1

A Fuji G9S11KW inverter, the output voltage difference is about 100V.

Preliminary online analysis and maintenance: open the machine check inverter module (6 mbi50n - 120) didn't found the problem, measuring 6 road driving circuit also didn't find fault, the module will be removed measuring found along the way bridge power transistor conduction and close properly, the module has been damaged, after confirm the driver circuit trouble-free replacement product after everything is normal.

6, overload

Overload is one of the frequency converter to beat more frequent failure, usually see that overload phenomenon, we should first analyze the motor overload or overload, inverter itself in general motor due to overload ability is strong, as long as the motor parameter is set properly, the inverter parameter table generally appear unlikely to motor overload. The inverter itself is easy to be poor due to the overload capacity overload alarm. We can detect the inverter output voltage, electric current detection circuit, such as failure prone to troubleshoot.

For example, 6.1

An LGIH55KW inverter often jumps "OL" when running.

Analysis and maintenance: according to the customer's report, this machine was originally used for 37kw motor, but now it is used for 55kw motor. The parameters have not been reset, so the problem may be caused by the parameters. After checking the frequency conversion current limit, the rated current of the 37kw motor is set. After parameter reset, everything is normal with the load.

Source: guangke intelligent reprint source