How to Identify a Worn ABB Robot Gearbox Before It Fails?
We've seen it happen too many times in the field over the years. The ABB robot on the production line had been doing well, suddenly one day, the weld out of the weld began to deviate, the trajectory of the drift, the action of one after another, the seriousness of the direct alarm shutdown, the whole line is so dry there. Waiting for everyone in a mess to troubleshoot the program, check the encoder, check the tooling, and finally disassembled, only to find that the gear box has long been out of order, just before no one noticed those small signals.
Especially for welding, handling, loading and unloading and stamping of these robots, long-term high load continuous rotation, the gear box will rarely suddenly collapse without warning. In fact, it will be a long time in advance to give you a “hello”, but many workshops are used to think of it as “old machines are like this” and let it go.
The first time many people notice a problem is when the robot “isn't as accurate as it used to be.”
That's really the most common first sign. What's interesting is that field engineers hardly ever think of the gearbox as a first thought. Their troubleshooting sequence is often: first suspect the TCP is not biased, whether someone has hit the gun; and then go to check the program to see if the points are correct; and then look at the encoder to see if there is no loss of pulses; and even suspect that the servo parameters are not drifting, or fixtures are not loose. A round of checking down are very normal, and then finally take a meter to hit, found that the backlash of a certain axis is obviously larger. This is particularly easy to see in the welding robot, originally the seam goes very smooth, now began to appear the arc is not stable, the arc path is not uniform, the same program every time you run, the trajectory has a little slight deviation. Sometimes customers think that there is a problem with the vision system, but in fact, it is the gearbox internal clearance grinding, action transfer does not follow the hand.
ABB robot gearbox wear, “backlash” will become more and more obvious
Anyone who is involved in maintenance is familiar with the word “backlash”, which means that there is a gap in the joint. The motor side is obviously spinning, but the mechanical side has to wait for a little bit of empty travel before it moves. The joints of the new robot are very tight, but once the planetary gears and bearings inside the gearbox wear out for a long time, the gap between the teeth becomes larger, the bearings are also loose, and the precision of the mesh decreases, the robot starts to show repetitive positioning inaccuracies, trajectory drift, and a little bit of wobbling occurs when accelerating and decelerating. The most troublesome thing is that this state is not particularly serious at the beginning, many people can even make do for a few months, but once a certain axis wear over the threshold, the deterioration is very fast - may be the first two weeks is just a little bit off, and then suddenly reported a collision or overload.
Robot joints start to “rattle”, in fact, already very dangerous!
When running normally, the sound of the robot is very even, that kind of whirring motor sound with a very smooth mechanical sound. However, once the gear box began to have problems, the sound immediately changed, will be mixed with metal friction hissing, or click click click click, acceleration and deceleration can even be heard in a low voice, hand on the joints can be felt inside like something in the knocking. Many old operators on the line will say, “This robot doesn't sound right lately.” When you hear this kind of talk, don't delay, because at this time there is a high probability that the gears have been scratched, bearing cage damage, or grease has failed to cause the metal to touch the metal directly. Continue to do this, the slight wear soon develops into a hard bite between the gears, and once the teeth are bitten, the whole reducer is pretty much scrapped.
Speaking of which, we have seen too many gearbox problems in the workshop, in fact, the root is in the lubrication. Many factories run robots every day, lubrication and maintenance is done particularly casual, especially some of the old production line. Add grease cycle has long been regardless of the aging of the oil seals, no one pays attention to see the joints seepage of oil on the wipe continue to open, grease mixed into the water vapor, dust or metal powder is also used as usual. A long time, the lubrication conditions a deterioration in the friction inside immediately went up, the temperature followed by the rise in the tooth surface oil film can not hold, it began to abnormal wear and tear.ABB reducer itself is very high precision, gear meshing and bearing with the clearance are particularly small, it is actually very demanding lubrication, once the grease becomes dilute, dry or contaminated, the speed of wear is increased exponentially. Some gearboxes are hot to touch, which is often a signal that the lubrication has completely failed, the oil has long been unable to play a protective role.
The temperature thing is a pretty visual cue.
You can try to feel the joint temperatures of each axis after the robot has been running for a while. Under normal circumstances, the temperature rise is relatively stable, and one joint will not suddenly get much hotter than the others. Especially for large loaded joints like J2 and J3, if they are abnormally hot for a long period of time, it's most likely that there is too much internal friction, not enough lubrication, the bearings are already damaged, or they've been running overloaded. Many gearboxes have been silently running a “high fever” for a long time before they really seize. So we see more and more factories began to take a thermal imager regularly sweep the entire line of robot joints, this trick is really effective, many problems in the temperature can be seen in advance, do not have to wait until the robot failure.
ABB robots start to shake, many times the problem is not light anymore!
You may see the whole arm with a bit of shivering when accelerating, and then shake a few times as soon as it stops, and the trajectory is not round and smooth when running at high speeds, with a fine jagged feeling. Many people will think that the servo gain is not adjusted, but if you confirm that the encoder is not a problem, the motor is not a problem, the parameters have not been changed, then in all likelihood it is the internal rigidity of the reducer is not good. This is especially true of joints with RV gearboxes, where the vibration goes from nothing to nothing as soon as the cycloid and bearings start to wear out, and it becomes increasingly difficult to hide.
Then there's another one that's especially easy to overlook - oil leaks.
I've seen too many factories, as soon as they see a circle of oil seeping out of a joint of ABB robots, the first reaction is to take a cloth to wipe it off, saying “it's fine, it can still run”. But in fact, the oil leakage is basically telling you that the seals have deteriorated, the oil inside the outward run, the outside of the dirt may also go in. Gearboxes are most afraid of the lack of oil, especially those 24 hours a day continuous rotation occasions, lubrication a chain, wear and tear speed immediately up. A lot of gearboxes can be repaired, because of long-term oil leakage is not taken seriously, and finally all worn out inside, can only be replaced as a who
See here you may ask, why a lot of factory ABB robots with a few years, feel the gearbox began to pile up problems? In fact, think carefully quite normal. Industrial robots itself is a high-frequency operation of the machinery, welding robots all day long in that swing around, handling robots constantly start and stop acceleration and deceleration, heavy palletizing robots long-term high-speed full load, machine tool loading and unloading a day cycle of thousands of times, the gear box has been subjected to impact and alternating stress. No matter how good ABB's quality is, the wear and tear of mechanical components is a physical law that no one can escape. Especially those robots that run against the upper limit of the rated load all year round, the reducer life is shortened even more obviously.
Many people struggle with the question: should I repair or replace my gearbox?
Our experience is that if there is only a slight increase in backlash, an occasional rattle, or if the oil seals start to leak, in some cases it is possible to try to repair them by treating the bearings, oil seals, and readjusting the preload. But if the precision has been seriously lost, the internal gears have been strained, the vibration is so big that the whole arm shakes, the long-term high temperature operation, or dismantled and found that the inside is full of iron shavings, then most of the time it is more cost-effective to directly replace the new one. Because once the robot suddenly died because of the reducer stop line, the loss is calculated by the hour or even by the minute, compared to the cost of production line shutdown, the reducer itself that cost is really nothing.
Just because slowly understand this reasoning, now more and more factories have not wait until the bad and then repair, but take the initiative to do predictive maintenance. Regularly measure the vibration, use a thermal camera to see the temperature distribution, take the instrument to check the backlash changes, track the trend of trajectory accuracy, and listen to the operation of the new noise frequency. We gradually realized that the gearbox of ABB Robotics in the complete failure of the gearbox before, in fact, give sufficient warning, just before no one to systematically look at. Discovered earlier, low maintenance costs, without unplanned downtime, not suddenly disconnected in the middle of the night, but also to avoid the motor and encoder is dragged to cause secondary damage. That's why many up-scale automation lines now include robot reducer status in their regular inspection and monitoring plans.
