Understanding Fanuc 21-T axis limit numbers in parameters

[BobM3]

I had to replace my Axis Drive Unit for my Hardinge Cobra 42. I found a thread that gave a detailed explanation of the homing procedure. Now I'm trying to set the limits for X and Z axis. The original numbers are:

Parameter
1320 x 333553
z 400609
1321 x -60350
z 45009

I had to make z 400609 a bigger number to complete the homing process. I tried resetting it back to 400609 but then I hit a limit about 5 inches too soon when stroking positive z. By trial and error I found a number that works (hits limit before Excess Current Alarm).

I'm wondering what the numbers mean. I'm guessing they are pulse counts from a certain reference pulse? The machine uses absolute encoders. Is there one reference pulse per entire stroke of the axis (14.00" stroke for the z axis on the Cobra)? Is there another parameter that multiplies the pulse count by a factor to get a display of inches?

 

[Ox]

Stroke and such values that I have witnessed have been a metric value without any decimal point.

It sounds like you must not have used exactly the right HOMING procedure for your machine if you are 5" off.

You were working in param 1815?

Well, either way, if you found some values that work - OK I guess.
But make note of what all you did....


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Think Snow Eh!
Ox

 

[13engines]

I believe all the numbers relating to stroke limits and home position are as Ox said, in metric and entered in the Least Input Increment. So your 333553 = 333.553mm.

There really is no homing on an absolute machine. I have a Zero Return button on an absolute lathe, but it does nothing more then send the turret fully home without over-traveling. Not something you can easily do manually. When you turn your machine on, it should already know where it is. At least that's my understanding. Can't say 100% that the above covers all instances of a Funuc Control on every brand machine.

Go to www.machinetoolhelp.com for a bunch of good information about setting home position on machine tools. (As well as other good stuff)

 

[Ox]

Well, "Homing" an ABS machine is not a button sequence. It is essentially that you place the slide in a certain position and tell the control that you ARE HERE, and it resets. Not nearly that simple, but that is the quick/dirty.

It sounds like he was 5" away from "HERE" when he did what it is that he did.


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Think Snow Eh!
Ox

 

[BobM3]

Thanks on the metric info. The position I put it in was turret 3" from spindle nose. I suspect that number is not the correct one but it was in the procedure I found.

 

[newcomer]

I may be wrong but par 1320 is the distance settings for X and Z in the positive direction from home. It is called soft limit and this value should be very small. I have it set to 5000 (=5mm). I believe it is a safety function to prevent excessive over travel in the event of failure of the hard stop limit switch.
The reason you had to increase par1320 to be able to home is because you probably changed some other parameters(those that require power on/off) that automatically flips 1815#4. This set your turret current position as the new home position and therefore new soft limits. Instead of changing the soft limits which you shouldn't btw, you should set 1815#4 to 0, do not turn off machine yet, set it back to 1 and restart machine. You should be able to home now.
If you have your sram backed up before open CNCPARAM.DAT and look up the original 1320 values.
Side note; soft limit over travel and hard stop throws a different alarm. In normal operations the machine should never hit the hard stop as that's your last line of defence against over travel.