[inthezone]

I am trying to get my FeatureCAM code working with our Fanuc 0M controller attached to the Bridgeport Series II VMC.

FeatureCAM has the post processor that fits the Fanuc 0M perfectly, but I am running into some troubles...

Fcam issues up a G28 right away in our code,

G28 Z1.0

That should move the bit to 1" above the reference position right?

Problem is our reference position on the machine seems to be set below our limit switches and this code kills the machine.

How do I edit the reference position? I am not sure which parameter controls it.. I tried looking in the Fanuc Manual, but it vaguely mentions reference position. Is it one of the work coordinate systems? All of my work coordinate systems are set to zero...

When I power off the machine it resets the abs. coordinate system. How is this reference position still stored? I put the machines abs coordinate system as high as I can, but it is still killed by the reference position... it must be really far down there..

There is definitely something obvious I am not seeing here..

[inthezone]

Update:

So I tried setting my G28 up a little differently.

I changed the code to


G28 Z-2.0

That way the table wont dip below the limit switch.. WRONG.

The table moves up the two inches, but then plunges right back down to the limit switch immediately afterwards..!!!

[bob1371]

Here is a little info to read.

http://www.cncci.com/resources/tips/...28%20works.htm


Link fixed
http://www.maintenanceresources.com/...ry/cnc/g28.htm

Bob

[inthezone]

Yeah those links are the first two search items on a google search. One gives some useful information about G28, the other is a dead link.

My question really lies here:

How do I adjust the reference position on my machine? Our machine reference point is set so that we get a Z excess error when doing a G28.

I need to change this!!! Anyone familiar with the fanuc OM?

[Al_The_Man]

It all depends on what home system you have and how it is set up.
Is this an absolute system with battery back up for home position, or do you have to home to the home limit switch dog?
If home by LS dog, it can be set so the machine travels over the dog or comes off the dog in reverse and seeks the marker pulse, this point can be extended or reduced by adjusting the grid point.
When a G28 0 is issued the axis should travel back to the marker or grid point, previously set.
Al.

[inthezone]

I am not sure how the home position is set up on the controller.

I will try to give you some details:

We have a battery backup, but it doesn't seem to store the last position during a power off. Every time I turn the machine on we get zero again for our absolute and relative coordinates.

On each axis there are two limit switches. I assume that one is for a reference position, and the other is to kill the power to the motor before the table goes too far.

In MDI mode, when I enter a G28, the machine table lowers into what I assume is the "stored reference position".

Before I played around with the machine, the x and y axis returned to reference just fine. The only problem was that the z axis would give an excess error because it moved too far, and our program would stop.

I was playing around trying to figure out how the two limit switches were working, when I pressed one limit switch on my x axis (by my finger, not by the table). It just killed the power to the servo motors. When I pressed the second limit switch, I got an x axis excess error.

Now my x axis can't move its full travel range, and is limited to half the area it was before! I triggered a new reference position!

I tried pulling the batteries out, and turning the machine on and off, but the x axis still cannot move more than halfway through its full travel.

Thus, I assume that the reference position is in fact "stored". It just boggles my mind how the reference position is stored without the battery backup, but the absolute coordinates are not.


I have the the Fanuc Parameter Manual, and it references to parameter 0076,

My parameter 0076 reads "00000000" at the moment.

According to the manual:

Parameter No. | Symbol | Description
0076#1 JZRN The function for setting the reference position without dogs is disabled/enabled.

How does this translate into entering the 8 bit string? "00000001"?"10000000"? The manual doesn't provide me with instructions on how to make the change!

[Al_The_Man]

Be carefull whay batteries you pull as you can lose the parameters, hopefully you have these backed up.
If you have encoder position backed up by battery then you do not need to home the machine to the dog limit.
Otherwise the dog limit home routine has to be performed every time.
It is possible also that you have a stroke limit stored and this can be eliminated by pressing Cancel & P key and power up and hold the buttons untill boot up.
Then try homing to the home limit dog it you have them.
Al.

[inthezone]

Your the man!

Turns out it was the stroke limit after all. The key combination at boot up followed by a G28 z0, x0, y0 in MDI mode reset my reference position.

Thank you!