Rotary Axis Home Direction

[Fido57]

Hey guys. We are using a rotary table with a plate attached to it in the form of a trunion table. We are getting ready to put a fixture on there that will be tall enough to run into the actual table if it rotates all the way around. I have found the zero offset, and the way to limit the amount of travel. The only problem I see is when the table homes. It will go all the way around to home out. Do any of you know of a solution to this problem, other than an external limit switch tied into the E-stop button?

[Geof]

When someone gives you a solution I will be all eyes; I couldn't figure it out.

[HuFlungDung]

Yes, with Haas setting 108 "quick rotary G28 on", try this for your end lines:
G00 G91 G28 Z0 A0
G92 A0

You may wonder what the heck the G92 A0 does

Well, I was running a job where I was using G92 A commands regularly to prevent a whole lot of winding and unwinding in the middle of a 15 turns (of A) program. Worked like a treat.

But, at the end of the program, the G28 command as given in the above example, would return the A axis to zero positionally, but there was still a problem.

It seemed that any remainder value (mod 360, if I understand the use of that term) would be left in the G92 register, and would affect the next run of my program.

So by using the G92 A0 command, this cancelled out the nuisance value I was seeing in the G92 register.

So to my way of thinking, the Haas quick rotary G28 is a trick performed with G92, but perhaps in some older versions of the software, they forgot to deal with the fraction of a turn that remained when all the whole turns were removed from the current A position.

You can experiment with and without the G92 command, but check the G92 register after your machine reads the M30 and make sure that there is no value in there except zero.

[mactec54]

Hi fido57

Make a plate to go under the rotary table lift the rotary table by the amount you need to clear the work piece we do it all the time if you plain it right you can also gain some table space by off setting the rotary table over the end of the table you can get up to
6" more table space you just need to make sure the back of the rotary table is not going to hit your cabinet

[HuFlungDung]

My apologies, I misunderstood the exact question, so my G28 advice is not applicable and could even cause a problem if used.

My thoughts would be that the setup needs to be homed before the trunnion type fixture is mounted to determine a safe position.

Then, through a couple of trial shut downs, I would see which way the rotary wants to turn while homing. This should be consistent (I would imagine) every time the machine starts up.

Practice stopping the machine at shutdown at a certain position so that the rotation towards home will be a minimum distance travelled. I would not necessarily try to stop the machine at its home position before shutdown as this may result in a full turn of the indexer when homing.

Now, if the power goes out before you can park the rotary, then I guess you'll have to kill the setup before homing again. But perhaps if you mark the position of the platter where it should be parked at shutdown (with a paint stripe or something), you might be able to override and jog the rotary to that safe position after power up/restart before you home the machine.

Practice all these scenarios with no obstructions first.

[Geof]

A couple of ideas came into my mind.

Actually one is a question. Is the mounting surface of the plate on which you mount the fixture on the centerline of the rotary?

If the answer is yes can you drop this plate below center so the fixture does not protrude as far?

We have numerous fixtures that are used on plates, we call them bases, on our rotaries and these bases have the mounting face 2" below center. This means that the fixture can be 6 inches high above the base and still do a full rotation.

The other idea if you cannot bring it within the rotary swing is figure out some type of clutch mechanism between the platen of the rotary and your plate mounting with a trigger that makes contact with a stop and releases the clutch before the fixture hits and lets the rotary spin free.

[fuzzyracing1967]

If I am reading this right,you have a fixture on that you can do your work with out hitting the table with the fixture,witch means you are working within a certain amount of degrees( say 45 or so).If that is the case you can put the fixture on with the rotary close to it's home position set it's offset and when it's time to shut down have the operator manualy put the axis on home,then when you restart the next day it will only move a few degrees one way for homing.That said,if there was a shut down before the homing you would have to take the fixture off to home.

If that all makes sence,

[Donkey Hotey]

There should be an easy solution to this for one, simple reason: a bunch of their trunion (2 axis) rotaries are nothing more than a second rotary, bolted to the face of the first one.

Whataya' suppose would happen if that second rotary got wrapped around in the wrong direction? It would pull the control cable right out of it.

I don't know where the setting is but you can limit the travel somewhere in the settings for exactly this reason.

[Fido57]

Okay, I just got back to it. I'll try to cover everything I see, in order.


HuFlung, I see you answered your first response later. Good catch.

mactec54, We have already lifted our trunions. Our problem is the height of the part we need to put on there now. We're too tall sitting on our trunion, but before we take some of our riser out of our trunion, we want to make sure an operator can't wipe the fixture off the trunion by homing it out.

HuFlungDung, I was looking at something like that. Problem I encountered is when I use the travel limit (I forget which parameter #) it only allows travel in a positive direction. Zero is your limit one direction, and the encoder count you enter is the other. So I can't just put zero near home. Oh wait, I see where you were going. If home is in the middle of the range of motion I want to allow, I could manually jog the rotary, before homing, so that it only moves the safe direction. Couple that with a limit switch tied into E-stop, and it may be workable. No, wait. Home can't be in the middle of my range of motion. Home defines one end of my range limit.

Geof, Yes, our plate is near centerline. I hadn't thought about remaking our end plates (that bolt to our rotary) to lower our part height under centerline. Great thought! I'll look into that, as well.

Fuzzy, My fear with that is what you already said. If the rotary isn't homed out before shut down, we have to take fixture off and start over. Between you and HuFlung, though, my best answer may be there.

Donkey, I agree, there should be an easy way. That's why I was so surprised when I couldn't find one.

All, Thanks, you've given me a couple more things to play with. I hope lowering my centerline will work, as that seems to be the safest. If not, I'm sure I'll end up with an oh sh** switch, and making sure I rotate back to home before shut down.

[Donkey Hotey]

Originally Posted by Fido57 Donkey, I agree, there should be an easy way. That's why I was so surprised when I couldn't find one.

That's not a "should be"; it is there. I am now learning that there may not be any rotary experts at the factory anymore. It depends who you get in Applications as to how good your answer will be. I'm not saying that they don't know what they're doing but as your setup gets more specialized, the fewer Apps guys will know about it.

There is definitely a setting for maximum rotation. If you set that to something less than 360 degrees, it should solve your problem. I am just about to get around to putting my T5C (5C trunion rotary) into my machine so I've already asked these same questions. You can't believe how many different (contradictory) things I've been told about rotaries in a Haas mill. I've gotten to the point that the only way I'm going to get answers is to install the dumb thing and just do it.

Side note: 5-Axis wannabes <<----SPAM

At the Haas Demo day this week, I learned something very interesting. When I bought my VF-2, 4th axis was a popular option for whatever the cost was. I got it with a VOP, blah, blah.

5th axis was a huge jump in cost. I think it was $11,000 to get the second amplifier and wiring. My sales guy pointed out that if I only wanted semi-5th (5 axis positioning but not necesarily continuous 5-axis motion), I could just add their outboard servo control to run the 5th axis. That was only $1500. I didn't buy the servo from them but he found me a very good deal on a used one.

What I learned yesterday is the cost of 5th axis has come wayyyy down. It's now $5,600, and yes, that's the retrofit cost as well. The other rub is that the price of the servo control has gone up to $2,000 so they don't sell many semi-5th setups anymore: there's no point with a $3,600 price difference.

[HuFlungDung]

Fido,
When you say you can't have home in the middle of your allowable rotation, I don't think that really matters where it is (so long as it is reached safely), because you can easily assign the work home in the relevant A axis work offset.

The Estop limits are still probably a good idea against over-run in jog mode, etc.

[Fido57]

HuFlung and Donkey,

I found the way to limit the rotation amount. As a side note, it also limits your rotation in jog mode. Cool! The only problem remains as homing out. When I said you can't have your home position in the middle of your range, I meant the control won't let you put your home position in the middle of your range. When you set your travel limit for A axis, you can't go past home in one direction, you can't go past the encoder count you set in the other. Home is always your "minus" limit. So it looks like I have to be at home before powering down, so it won't try to swing all the way around when it homes. The travel limit doesn't apply to homing. Donkey, if you want me to give you a list of what had to be changed, I'd be glad to share. All it ended up being was turn a travel limit parameter on so it would look for a limit, and then another one is where you can tell it how many counts of the encoder you want it to go.