4th Axis rotation angle limit problem

I have a 4 axis setup using a standard rotary table doing some work on continuous 4th axis milling.

During the finishing pass, I run a small ball nose end mill through the profile and it rotates many many many times around the A axis until the part is finished.

In step config I have the angle set to -9999 and 9999 but thats not even enough.

I find out recently in the middle of my run that the axis has hit the limit, which happened to be 6400 degrees even though I had set it to 9999 (which still isnt enough).

Is there a way to make EMC2 recognize that higher angle is an angle inside 0=<angle=<360 so that it never stops because it is 'out of limit'. Since my rotary table in reality has no angular limit.

How do I fix this? This is incredibly annoying. RIght now my temp fix is to split the gcode into small segments. So my finishing pass requires tens of files. I also have to re-zero the angle and run again.

Is there a solution to this?

I ran into the same problem yesterday.

My temporary solution was to comment out the MIN_LIMIT and MAX_LIMIT lines in the .ini file. This doesn't give an error message. Clearly, there is some default limit, but I don't know what that is. At least I was able to finish my run (which needed about 60 turns) without running into the 9999 limit.

I tried the WRAPPED_ROTARY option (which sounds like just the right thing). However, I had nothing but problems with that approach. The first thing I discovered was that G90.2 and G91.2 don't work like the wiki documentation says. Use of G90.2 or G91.2 gives an error message. The next thing I discovered was that you can't make a full turn or more. You can only turn something strictly less than 360 degrees. Then I discovered that going to a negative rotation gives you something other than what you would expect. For example C-90.0 goes 3/4 of a turn to the equivalent position of 270 degrees (but turns in the opposite direction). This is really counter-intuitive -- I'm thinking that C-90.0 should give only 1/4 of a turn. The real killer for me was that wrapped rotary options in EMC2 and MACH3 behave totally different. So developing software that generates g-code that will run the same on both EMC2 and MACH3 is impossible if you use wrapped rotary axes.

If there are any other solutions, I would be most happy to hear.

Even after 40 years of engineering experience, I guess I'm still naive enough to expect standards (RS274D or ISO6983) to serve some useful purpose. I haven't shelled out the money to buy a copy of ISO6983 to see if it actually addresses the issue of wrapped rotary axis.

On a more practical note, the documentation on WRAPPED_ROTARY axis at wiki.linuxcnc.org/cgi-bin/wiki.pl?WrappedRotaryAxes is just plain wrong and needs to be updated. The use of G90.2 or G91.2 give errors.

OK. Thanks for the additional information.

Hi

For example C-90.0 goes 3/4 of a turn to the equivalent position of 270 degrees (but turns in the opposite direction). This is really counter-intuitive -- I'm thinking that C-90.0 should give only 1/4 of a turn.

I hit something very similar to this when implementing a toolchanger routine using G Code some while back.

The ATC would try to take the shortest route to the commanded rotary position, which sometimes would mean it trying to rotate backwards against the pawl when the commanded movement angle was over 180 degrees.

Think I solved it by making all moves incremental from the current position.

May not be wholly useful for your situation as no move would be > 315 degrees ish for an eight station turret.

regards

I am also trying to get my 4th axis to spin continuously.

Here is what I have found so far:

www.linuxcnc.org/docs/2.5/html/hal/rtcomps.html
linuxcnc.org/docs/html/man/man9/stepgen.9.html

seem to say I should add the following

to .hal ->


At line 8 (in my case)


I have changed the bottom section from:
Code:

In to:


there is some more code below that that I have not touched about estop and toolchange.

After these changes the emc actually starts up, which is already something.

But when I turn the machine on I get a joint 3 following error.

The .ini file looks like this:

Now when I turn the emc on the a-axis immediately starts to move and stops at what seems to be just after the MIN_FERROR