Proper procedure to drain and refill counterbalancing system on a KR200

    Hi,


    I'm looking for any information on how to properly, safely depressurize and recharge the counterbalancing system's gas cylinder for servicing. Manuals, videos, written step-by-step procedure by someone who's done it, anything. Regular maintenance manuals (the ones labeled "Maintenance, Manipulator without Wrist") that I was able to find don't go beyond "check the gauge, look for leaks".


    The counterbalance on my KR200 blew the gland seal and ejected most of the oil. I can handle seal and wiper replacement on hydraulics just fine, I should be able to figure out and fabricate the tooling needed to remove the mounting pins, but before I start working on the thing, I'd like to know what the official procedure is just to keep on the safe side. I've done some quite sketchy repairs in the past, but over 100bar of stored pressure is probably where I want to draw the line and have more than just experience and intuition to go by when draining it.


    Some additional info that I would be glad to have is:

    - what type and brand of hydraulic oil is recommended, if there's a specific recommendation at all

    - what's the correct amount of oil in the system

    - what type of quick-connect couplings are used on the recharge ports


    The robot is a VKR200/1A, floor mounted, mechanically appears to be as standard and normal as it gets for a KR200.

    its way to long ago for me to remember but what i do remember is we used a special fitting and a pump for the nitrogen tanks to fill them. Theres a cap on the top of the counter balance that you take off to fill the tanks with nitrogen and pressurize the oil can.


    Think we also used a similar fitting for the oil.I will speak to someone to find out if you have not figured it out already.

    Please do, if you still can reach someone who remembers the process or has access to any relevant manuals. There's literally nothing about this service procedure available online.


    Just to be sure we're talking about the same parts, I snapped a couple photos of all the ports on my counterbalance: https://imgur.com/a/PSR5AGU


    So there's two quick-connect-ish ports on the manifold block, the upper has a knurled protective cap that I removed for the photos. I've seen a very short video clip of a bunch of guys scrapping an old KUKA arm, where they used that upper port to drain oil, but I have no idea what they did to depressurize the gas tank.


    On the very end of the tank itself, opposite the manifold block connection, is another port protected by a red plastic cap. This one looks from the outside like a regular grub screw, so it's either a protective plug on top of an actual gas valve, or it's just a plug by itself that's got nothing to do with the draining procedure and the last thing I want to do is touch it under pressure. Obviously, I can't tell which it is without the risk of finding out that it was the latter.


    I understand that some people with this knowledge might be reluctant to share it because it could be used by an inexperienced tinkerer thinking they can handle it, only to get themselves killed in the process - but an important part of the safe and cautious approach to servicing high pressure systems is to stay away from the damn thing until you know the procedure, which causes a bit of a chicken-and-egg problem for qualified technicians who just never worked on that particular type of assembly.


    Besides, there's a multitude of different ways an inexperienced tinkerer might get themselves killed with an industrial robot, one more or less makes little difference...

    So, after getting some hints from a repair tech who sometimes works on KUKA robots I was able to identify the connectors first, and then, using that information, find an extensive manual for KR QUANTEC K prime - whose hydropneumatic counterbalance, while not identical, shares the basic design and many parts with the one on KR200. As far as I can tell, the same maintenance procedures should be safe to apply to both.


    What I was able to figure out by now:


    1. The allen grub screw on the back of the tank is indeed the gas bladder service port valve. The port accepts a standard M28x1.5 collar-fastened accumulator recharging adapter (also referred to as "filling and testing device") that features a hex extension shaft used to turn the grub screw (and thus, operate the valve) through the adapter's body. See e.g. page 45 of this catalog/guide PDF. Needless to say, trying to remove this screw with an allen wrench is an extremely bad idea that could get you killed. The KUKA manual does actually recommend loosening it slightly with a wrench before attaching the adapter, but no more than a quarter turn, and only to avoid applying excessive torque to the adapter's valve mechanism.


    2. The upper connector on the manifold block is the vent valve, used to drain hydraulic oil from the system under pressure, as well as to vent air when refilling. It's an ISO 15171-2 M16x2.0 fitting with a one-way valve. The manual refers to a Parker Ermeto 530017 part (ungooglable), for comparison see e.g. Hydrotechnik 1620 series valves or Hydroll HGV M16x2 valves. An adapter with a manually operated valve is needed to safely drain oil out of a pressurized system.


    3. The lower connector on the manifold is used to refill the system with oil. The manual mentions a Parker Ermeto RHV series part (ungooglable). I haven't removed the protective cap on that one yet - and I don't intend to before draining the system just in case, so I'll update this post with dimensions and a part number when I actually get around to fixing that counterbalance.


    4. Unless the gas bladder tank develops a recharge port leak (which can happen, there's an o-ring in there that can go bad), there's no need whatsoever to actually touch the recharge port, depressurize the gas bladder and repressurize it. The hydraulic part of the system can be serviced while the bladder is under pressure. In fact, oil must not be refilled otherwise. Which means I don't need to touch the gas side to do my repair. Knowing that, I can proceed safely.


    5. The oil used should be ARAL Vitam GF 46 or equivalent.


    What I still need to figure out:

    - how much oil exactly needs to be refilled into the counterbalance on a KR200/1A - anyone?

    - what sizes and types of piston and gland seals and wipers are needed on the cylinder - I'll update this as soon as I get there and have chance to measure the original parts and locate replacements



    I don't know when I'll actually perform the repair, I'm looking forward to a busy couple of weeks and the robot did not leak all of the oil yet, so it's still usable (it's a KR200 and we're loading it with no more than 2-4kg of payload), but as soon as I do, I'll be sure to post some photos and more information for anyone trying to do that in the future.

    Edited 2 times, last by Elia_ ().

    The only thing I can add to this is that, when refilling the counterbalance, you must use "ultra-pure nitrogen." Which apparently is available from most suppliers of pressurized gasses. We had to get a Titan counterbalance refilled on-site by a KUKA tech, but while the tech brought KUKA's own oil, we had to supply the nitrogen, and find a local supplier for same.

    For the seals, you will most likely have to end up sending it to kuka as i doubt they will sell you those parts. Thats money for them to be made by coming out or receiving the counter balance to service it. oil quantities that is robot specific so you will either need to find the service manual documents for that robot or just contact Kuka and ask them as refilling is not a specialized job so im sure they will give those details atleast.


    I think if you subscribe to Kuka Expert you might find all that info for the specific robot on there

    Quote from rhino

    DM me your email address, i can only set one attachment to a post. i will email you screenshots of what needs to be done exactly.

    This diagram definitely shows a part the same procedure as the one I found for Quantec. Thanks for the offer, but it seems I already have what I need as far as documentation is concerned. If anyone has the equivalent docs for KR200/1A specifically, I'd be interested, otherwise that Quantec is probably a closer match than the robot on this diagram.


    Quote from rhino

    For the seals, you will most likely have to end up sending it to kuka as i doubt they will sell you those parts. Thats money for them to be made by coming out or receiving the counter balance to service it.

    Actually, I don't think I'll need anything from KUKA.


    They don't actually make those cylinders themselves - for KR200 and Quantec at least, they subcontracted Olhydraulik Altenerding Dechamps & Kretz GmbH & Co KG. I highly doubt there's any non-standard sealing parts in it. Have you seen a hydraulic seal and wiper catalog? They easily go over a thousand pages of tightly packed product selection tables - and that's for just a single application range per catalog. Why incur the enormous initial expense and ongoing supply chain problems of manufacturing completely custom versions of a bunch of stupid orings and lip seals?


    Sure, I'll have to figure out what parts to buy, but a major part of hydraulics overhaul is being able to identify the seals or wipers based on the shape and measured size of existing parts.


    Quote from rhino

    oil quantities that is robot specific so you will either need to find the service manual documents for that robot or just contact Kuka and ask them as refilling is not a specialized job so im sure they will give those details atleast.

    Upon re-reading the procedure I realized that this information is not directly relevant - the right amount of oil is however much gives the right pressure reading after being pumped in. I just need to be sure I have enough to fill the whole thing completely, which isn't that much anyway. Another problem solved.


    BTW, if you'd like to download that Quantec manual, google for "OLHYDRAULiK 1144.01.000". That's the cylinder part number for Quantec and as it happens, that manual is the only instance of this text on the internet (until now, that is).

    Quote from rmzn81

    reserve. I follow you . I am working for same problem :smiling_face:

    What exact model of robot are you trying to fix?



    Status update from my side:


    1. The robot lost all oil in the system last Wednesday, so I was pretty much forced to go ahead with the repair as it's no longer safe to use. At the same time, it is being used for learning and experimentation and there's one guy running tests for his engineering thesis on it, he'd be utterly screwed by a long outage.


    2. I ordered all the equipment needed and got it on Friday. That's less than $250 worth of specialized tools and materials required. I'll post a list when I'm done and know for sure that it's complete.


    3. Lacking a gantry crane or another attachment point on the ceiling to support the link arm so it doesn't fall, I invented a way to restrict its movement using chains attached to lifting eyebolts on the rotating base of the robot. A good lifting-grade chain and safety grab hooks are needed. When done properly, the link arm is not going anywhere beyond a +/-5deg range out of vertical.


    4. Releasing whatever oil was left in the system was uneventful, with 50bar of pressure left and most of it being air pulled in through the same crack in the seal that leaked oil.


    5. Removal of the whole counterbalance assembly requires either a specialized puller, or just some fiddling with a regular hex bolt and some spacers. After pulling the link arm pin and unbolting the base pin, the whole assembly slides out of the robot easily and can be comfortably handled by two people to do it.


    6. At this point, you could just take the whole counterbalance to any construction equipment repair shop and let them take care of replacing seals and checking accumulator pressure. I am going to take care of the seals myself and only have a repair shop check pressure on the accumulator, as I don't have a proper adapter.


    7. Disassembly of the cylinder is easy but requires proper tools. Nothing specialized, just big and sturdy. In the case of KR200/1A, a *big* 27mm spanner and a 36mm socket with a *long* and solid handle. A pipe vise with soft jaws makes things much easier, too.


    8. The seals, wipers and locating rings couldn't be any more standard and off the shelf. Everything follows ISO 5597 preferred dimensions. I'll be ordering a new set on Monday.


    I was in too much of a hurry to record a video, but I took some photos of the procedure. I'll publish them when the robot is put back together and operational again.

    Just a quick update here: the repair was successful, it cost less than $250 in total (parts, equipment, external services), took one workday (spread over two days, could be done in one day), involved three people (me and two assistants) and did not require any prior experience or training specific to KUKA counterbalances, just some general technical aptitude, minimal experience with hydraulics and awareness of the dangers that have to be mitigated.


    I'd go as far as saying that generally, it's within reach of any small business that's capable of using an old industrial robot to repair those counterbalances without any involvement of KUKA service department whatsoever. It can be done safely, it's not difficult, it's not expensive. There's no reason to treat them as mythical black boxes that they seem to be made out to be in the online robot community.


    Now I need to set aside some time to write a repair guide based on the experience I had here, but if anyone needs help fixing a counterbalance *now*, just reply in this thread or PM me.

    Quote from rmzn81

    Hello dear enleth I'm glad you solved the problem. My problem is continue. You help me ? Do you have any video ? How can ı do that ?

    No video, but I took a lot of photos.


    I can try to help you now before I write some sort of repair guide, but I need a few things from you:


    1. Exact model of the robot

    2. Description of what happened (where the leak is, how it was noticed, did it happen suddenly)

    3. Photo of the whole counterbalance with manometer visible

    4. Photo of the spot that leaks

    5. Photo of the whole robot taken from the side with the counterbalance


    I need those to figure out if the steps I took to fix it can be applied exactly to your situation.

    Edited once, last by Elia_ ().

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