RV Reducer vs. Harmonic Drive in ABB Robots
When some people first come into contact with ABB industrial robots, their eyes are focused on control cabinets, servo motors, and teach pendant. But really, a robot moves in the end “stable or not, accurate or not, durable or not”, the root of the things actually hidden in the joints - is that a few reducers.
Most of the brothers in ABB robot maintenance have experienced this gear: robot with a few years later, slowly began to appear track bias, weld is not stable, shaking, noise, positioning the old deflection of these problems, along with a circle of checking out the joints in the joints of the speed reducer is often pulled out. ABB robot joints in the head of the most commonly dealt with two kinds of reducer, a called RV reducer, a called harmonic reducer.
Customers often ask: “What is the difference between these two reducers?”, "Why does ABB have to do this? Why does ABB use RV for some shafts and harmonic for others?" “Which one is more durable?” “Which one is more accurate?” Today, we will talk to you, purely from the experience in the workshop.
RReduction gearbox in the robot in the end is what to make
Industrial robot servo motors, turn up that is a fast, but there is a fatal problem - turn fast does not equal to the strength of the big. When the real work, the robot wants low speed, high torque, high precision, but also stable output. Think about it, when welding, follow the weld, the movement must be particularly smooth; when handling hundreds of pounds of workpiece, the joints must be able to eat the strength, can not shake. What the gearbox does is to bring down the motor's stupid speed, amplify the strength, and also make the output shaft stop in the right position. Therefore, you can think of the reducer as a “force amplifier” and “precision gatekeeper” in the joints. Many ABB robots, as long as the reducer is worn, you can feel: trajectory more and more floating, repeat the positioning error day by day, the arm began to shake, acceleration and deceleration of the time one after another, the welding quality to follow the good and bad, strong point directly to the alarm are dry out.
RV reducer: solid and anti-manufacturing bearer
What is the role of the RV reducer? Many people also call it a cycloid reducer. The best thing about this thing is just one thing: it's stiff, and it's especially resistant to fabrication. It is to run to the heavy-duty industrial robots to carry the beam to go, so those who do welding, handling, palletizing of large ABB robots, especially the base, arm, arm of the most ruthless joints, the stomach is basically loaded with RV reducer. You think ah, a big ABB robot to the whole arm when swung up, the base of the several bearings to carry the inertia of the force has to be how big. If the reducer is not rigid enough in that place, the whole robot will be working like a drunk and swaying. the strongest part of the RV reducer is this hard bone.
Why is the RV reducer so strong? It has something to do with its inner structure. Ordinary gear reducer, at the same time may be one or two teeth in the effort, but RV is not the same, it is a lot of teeth in contact at the same time, the force is spread out. It's like a group of people lifting something heavy together, rather than relying on one person to carry it. In this way, the force is uniform, impact resistance is strong, the risk of tooth breakage is also small, long time to carry heavy work is also stable. This is why many ABB heavy-duty robot RV reducer can be carried for many years. Especially in the automotive welding workshop to see especially obvious, those ABB welding robot a day to do more than ten hours, continuous rotation for several years, the first can not hold out is often not the controller, but the joints in the mechanical part of the slowly grinding out the gap. But in general, the overall life of the RV reducer is really long.
Harmonic reducer: born for “extreme accuracy”.
The harmonic reducer is a completely different approach from the RV, which is designed to be “built”, while the harmonic reducer is designed to be “extremely accurate”. Harmonic reducer has a particularly obvious characteristics: small size, light weight, backlash is extremely low, low to almost negligible, high precision scary. So you look at the wrist of the ABB robot those axes, especially near the tool end of the sections, such as what painting, precision assembly, grasp small parts, the electronics industry with the robot, the wrist is almost all harmonic reducer. The space in that area is already tight, and the requirement of movement precision is perversely high, so harmonic is just right.
Why can the harmonic reducer be so accurate? The key lies in the fact that it has almost no transmission gap, which is what we often call “backlash”. A lot of ordinary reducers have this problem, the motor end moves a little bit, the output does not follow the immediate movement, there is always a gap. The larger the gap is, the more uncertain the robot's localization will be. Harmonic gearheads rely on a set of flexible transmission principles, the backlash to a very low level. That's why you can feel the ABB robot wrist turn up especially smooth, without that kind of loose gap feeling. Especially in the paint robot is the most obvious, the trajectory of the spray gun slightly shaking, the paint surface immediately out of the stripes, uneven thickness, orange peel or leakage of spray, so the paint robot on the wrist harmonic reducer precision relies on a particularly strong.
Why doesn't ABB just use one gearhead?
So why doesn't ABB just use all of them, and have to install RV on the big axle and harmonic on the small axle? To put it bluntly, industrial robots inherently need both strength and accuracy, and each of these two things is taken up by the RV and harmonics, and ABB's design approach is usually to use the RV for the big joints at the front and the harmonics for the small joints at the back. So a ride, the overall rigidity of the heavy load to stabilize, the end of the action is fine enough, the trajectory control is also smooth. In fact, most of the industrial robots on the market now are the mainstream program.
RV and harmonics, which is more likely to go bad?
Which is easier to break is also the customer always ask. Realistically speaking, we can not simply say who is more delicate than who, because they work in different environments. However, according to the actual workshop repair down the feeling, harmonic reducer is relatively more “delicate” so a little. Because it is inside the flexible wheel has been in the state of elastic deformation, long time high frequency tossing back and forth, slowly will be fatigued. Especially those high-frequency small-amplitude action, day and night non-stop work, frequent start-stop work, will make the harmonic wear faster. RV reducer is more afraid of the heavy load impact, such as robots crashed, overload, emergency stops, or the old in high inertia under the hard to support, these cases are easy to give the inside of the gears and bearings to do out of the dark injury.
What are the precursors to a gearbox that's dying?
In the field, the precursor of the reducer out of trouble is especially obvious, but a lot of people at first thought it was a servo or motor, but the result is a reducer. If you want me to say, when you come across the following symptoms, you have to think about the reducer. Robot positioning is getting more and more inaccurate, this is the most typical. Especially the welding robot, at first the welding point is correct, and then more and more deviation, recalibrate the zero point good for a day or two and then run, this kind of nine out of ten is the reducer gap grinding. Robot action began to shiver, low-speed time is especially obvious, some ABB robots you take the handwheel slow pointing time, feel one after another, there is a fluttering, fluttering feeling, not smooth enough, most likely the inside is worn out. Joints out of the noise, click, metal friction sound, low thud, do not take it seriously. Especially when the bearings in the RV reducer are bad, the noise is especially obvious, and many people still insist on it, and finally the whole joint is ruined. There is also the joints are very hot, reducer once the wear, friction is a lot, you feel the temperature of the shaft is obviously higher than the other a cut, great when you can smell the grease deterioration of the paste flavor.
How to maintain it in order to make it carry more years?
Maintenance of this piece, many factories are prone to ignore the mechanical part, think can turn on the line. But the robot reducer is the most afraid of a long time no one care. Especially the kind of three-shift rotating ABB robots, we generally nagged customers a few words: feel the temperature changes, listen to the noise, feel the vibration, pay attention to the difference is not bigger than one day, lubrication should also look at the situation regularly. A lot of reducer is not suddenly scrapped all of a sudden, in fact, it has been grinding for a long time, just no one found. Early discovery may change a bearing, change the oil on the solution, delayed the whole reducer into scrap metal.
Precision decline, the root is mostly on the reducer
Many ABB robots precision down, the root is really not necessarily in the encoder or motor. Because you think ah, your control system and then cattle, calculated again accurate, if the mechanical part of itself has a gap, the final action must still be biased. This is why some ABB robots encoder is normal, motor is normal, no one has moved the parameters, but the trajectory is not stable. When the joints are disassembled, the reducer has been worn out. This is especially common on welding robots that have been in use for several years.
Whether to repair or replace the reducer
Whether to repair or replace the gearbox depends on the actual situation. In some cases, such as bearing wear, lubrication failure, and just a little bit of clearance, it can be repaired. But if the gears inside are already broken, the flex wheel is fatigued and broken, or the internal wear is very serious, then very often it is more cost-effective to directly replace the new one. This is because the damage from robot downtime is often much more expensive than the gearbox itself. Especially in automotive lines, where a day's downtime is enough to buy several gearheads.
