DMG Mori 5 axis DDRT

[Ewood42]

We just had a shiny new NVX5080 with a 5th axis DDRT installed this last summer as part of a robotic cell, and we've had several issues with the DDRT. We've had issues with internal leaks, causing problems ranging from the brakes failing during machining (yep, it moved with a tool buried in it...) to the machine just halting code execution when it reaches a lock/unlock code. Initially we were told it was a design flaw with the size of the oil reservoir, but they came out and went through a retrofit to supposedly address the issue... fast forward a few months and it just failed on us again and will not respond to lock/unlock commands again. Has anyone else had major issues with one of these, or did we just get a bad unit? Any pointers? The cell Mori installed, as a whole, works pretty damn well now that we've ironed out all the kinks... but no DDRT means no chips.

[Colin Gilchrist]

I know that the DDRT units are new. It is a "Direct Drive Rotary Table", for anyone else that isn't familiar. (I wasn't until a few weeks ago.)

 

I've never used one myself. I know they are "Direct Drive", which should mean that they are using magnetic coupling to rotate, and 'lock' the rotary into position. It sounds to me like some "new technology" issues, but I have no direct experience with them, so it could just be that you got a lemon?

 

The "promise" behind the technology (if it works) is "no brake to wear out", but obviously that isn't true with your unit. Also, they are supposed to deliver faster positioning and rotation speeds over conventional geared units.

[Mr. M]

DMG Mori rep was just telling me the other day,"They have NEVER seen one fail". I guess never was a bit strong

[Orvie]

I was looking at these too.

They are only available for Fanuc & Mitsubishi controls.

I wanted to package them with 2 brand new Okuma MB-66 verticals we are having quoted. (among other machines)

Okuma will only use their own motors & encoders for DDRTs, so the Tsudakoma & Nikken units will not work.

I have an RFEQ with OCJ, to see what can be done.

[Rstewart]

The place I just left had a 4th axis DDRT on a Mori for 4ish years with zero problems.  I programmed it the whole time.

They are sweet!  Maybe you got a lemon?

[GoetzInd]

My experience if with the fanuc version. We've had a couple and they've functioned flawlessly. 

 

Mike

[?Mark]

Never heard a bad think about them, quite the opposite. Super accurate, rigid and fast. The same technology that they use for b axis on hmc.

[Ewood42]

Don't get me wrong, it is fast as hell and accurate when it's working, but this one has been down for repairs 3 times since June. They don't want to replace the entire unit since it would require some reprogramming on the robot side of the cell, or be a huge pain in the xxxx to line it back up where the old one was (and still have to tweak the robot program a bit). And I can't just tear into myself since that will void the warranty, so here I sit with my thumb up my xxxx waiting for Mori service department...

 

Thanks, just wanted to know if anyone else had issues, or if we just got a defective unit. I think it probably is the latter.

[generaldisarray]

I know that the DDRT units are new. It is a "Direct Drive Rotary Table", for anyone else that isn't familiar. (I wasn't until a few weeks ago.)

 

I've never used one myself. I know they are "Direct Drive", which should mean that they are using magnetic coupling to rotate, and 'lock' the rotary into position. It sounds to me like some "new technology" issues, but I have no direct experience with them, so it could just be that you got a lemon?

 

The "promise" behind the technology (if it works) is "no brake to wear out", but obviously that isn't true with your unit. Also, they are supposed to deliver faster positioning and rotation speeds over conventional geared units.

 

No worm to wear out, and no backlash. Still has a brake.

[Ewood42]

Yeah, still has brakes, and those brakes can still fail. The really crappy part is that when the brake is engaged, the feedback system is disabled so if the brake does not have enough clamping force, the axis will deflect away from and not re-position until it receives another motion command. Not an issue if you're doing 5 axis simultaneous milling since it will constantly be adjusting to stay in position, but we're just using it in an NVX5080 as a 5 axis drilling machine for rock drill bits... had to make some adjustments to the vision system and the PLC program after the first time the brake failed. It just happened to start failing when we were running it lights out for the first time, so it made about 80 bad parts and the cell was not programmed to handle that contingency so it ran all of the inventory that was loaded that night. Hopefully, it's just a bad DDRT and they'll replace it this time around.

[Guest]

That is an INHERENT limitation in DDR Technology. They ALL have it. Unless you are clamping hydraulically you just cannot get the same holding power with DDR. Not a knock on Mori, THe FANUC DDR's have the same issue. You just have to be careful when you're out close to the edges, machining hard and fast, using large diameter tools, etc... If you can work within it's limitations, you'll be happy. If you want to machine on it like it's a regular rotary table, well, you'll be sorely disappointed.

 

JM2CFWIW

[Ewood42]

Refilled and bled the hydraulic system for the brakes with the mori tech on friday, pressure switch lit up like it was supposed to when we were done, so assumed it had just worked some more air bubbles up and we left it at that. Come in this morning after the weekend, and no pressure. I guess it must have an internal leak somewhere still. Those mori DDRTs have an inner and outer housing, so if the hydraulic system for the brakes is leaking, you will almost never see it outside the unit. Uses an air over oil system with the brakes, so a few bubbles can cause major problems.

 

Are we the only ones having this issue, or has anyone else had issues with the brakes on these things? I asked them this morning (still under warranty, thankfully) if they will just swap it out for another unit and we'll deal with reteaching the robot and adjusting our drilling macro. Unfortunately, I can't just crack the damn thing open myself, as that will void the warranty. 

[huskermcdoogle]

.....and adjusting our drilling macro.

 

Are you not using G68.2?  Or at the very least calculating the transformations in the macro itself based on some simple adjustable offsets?

[Ewood42]

Using G54.2,so we might need to adjust distance to center of rotation if the replacement is not exactly the same. More concerned with getting the robot touched up than the mill program. We don't have much tolerance for depth on the features machined there, but we also probe in several locations to get more accurate numbers so there's usually not much more than a thousandth variation from one part to the next, even if the previous ops are a little off. Not too bad for parts that are loaded by a robot... but getting the robot to drop the part in just the right spot was not easy.