Problem- VF-2 Y axis work coordinates off after power down and reboot?

[peter.blais]

Hello again guys-

My machine has started doing something odd in the last few weeks. After I power it up in the morning, and let everything home, do the warmup program, etc- I now double check my G54 X0 Y0 just to make sure (learned the hard way). This morning my Y axis was off by .146"- seems odd to me. X and Z never do this.

It's done this a few times now, but it's not every time. I'd like to figure it out so I can stop worrying about it.

Possibly a problem with the limit switch, or perhaps some chips have gotten in there? The machine is just over a year old.

Thanks!

Pete

[Delw]

Peter
I was told the machines DONT have limit switchs anymore its all software stuff now. I was also told( dont know if its true or not that its impossible for the machine to get a wrong number after it goes home due to software .

is your G54 work offset on a fixed work pcs everytime?
try using a G55 or different work offset and see if you get the same problem
what does your program look like that calls up your work fixture offset?
does it always change after the machine goes home or is it once in a while, just at power up?
does it only happen in the y axis?
is the motor loose? thats the only thing I can think of that would cause a change.
Delw

[peter.blais]

The origin is currently on the corner of a fixture plate that doesn't move. It will run fine all day long, it's just wrong sometimes the next morning. It seems to only be on the Y axis, the X & Z always seem to be right where they should.

I'll try homing the Y axis with the machine powered up a few times today, and see if it moves around any. I don't normally do that after I power up and warm up, so I have no idea what that'll do.

It definitely seems to be a "once in a while" problem- more of a hassle then anything really. It'd be nice to walk in, load more stock and push go without worrying about it, especially when you have a helper running the machine that isn't setup savvy.

[Geof]

I don't understand how a machine can find home without some form of limit switch or proximity sensor. All my machines have these and the machine moves the axis slightly past where the home position is until the switch or sensor is triggered then goes the other way until it gets the Z channel signal from the encoder; this signal defines the home position. Once the home position is set the machine knows it position and will not touch the limit switch again.

It is possible to get a false home position if the limit switch hangs up or if a chip is on the proximity sensor. My experience is that it will be one turn of the ballscrews out.

[hercules]

I have had my machines home to strange positions on start up a couple of times and subsequently found a chip stuck to the limit switch. Same as Geof mentioned.

[Delw]

Geoff
Neither could I, its just what I was told. reason being I had a part 2inches longer than my table movement , Figured I could move the limit switchs and was told it doesnt have any.
If I remember correctly I thought he said it was built into the motor.or some little chip or something, they are not moveable from what I was told.
hopefully haas man can set us straight.

Originally Posted by Geof I don't understand how a machine can find home without some form of limit switch or proximity sensor. All my machines have these and the machine moves the axis slightly past where the home position is until the switch or sensor is triggered then goes the other way until it gets the Z channel signal from the encoder; this signal defines the home position. Once the home position is set the machine knows it position and will not touch the limit switch again. It is possible to get a false home position if the limit switch hangs up or if a chip is on the proximity sensor. My experience is that it will be one turn of the ballscrews out.

[NWSERVICEGUY]

The problem you are haveing if I understand correctly is that sometimes y-axis position is off from where it should be after a zero return at power up. The problem you have is 99.9% for sure your y-axis limit switch. No haas machine either old nor new uses software to go to the home position at power-up. Haas does not use absolute encoders on their axis's. Therefore the machine will move till it hits the limit switch and then back off of the switch. The machine needs to see that the motor rotated between 1/8 and 7/8 rotation of the ballscrew when it comes off of the limitswitch. If it does not see that it came off the switch in this amount of rotation you get either a "z margin to small or z margin to large" alarm. This is fixed by applying a grid offset in the parameter for the axis giving the problem. Now to address you problem. If you have roller switches for limit switches then you need to replace the switch since it is more than likely sticky. I say replace the switch since in order to get to the switch you need to pull the front way cover back anyway to clean it. This switch is usually on the left side of the ball screw and easily accessed with the way cover pulled back and the table jogged toward the back of the machine.

Now if your machine is equiped with proximity switches (magnetic) then I would bet a kidney that it is dirty and probably has a chip on it. So clean it and all should be good. The proximity switch will be in the same place a roller switch would be.

[NWSERVICEGUY]

I forgot to address your issue of having a part that is a bit to big and you would like to move the switch in order to cut your part. Well you can do this but you will have to make a change in your parameter. Let me explain. Your machine after doing a zero return will only be able to move a certain distance. This parameter i think is called "max travel or max encoder steps" I would have to look at the controller to see exactly the name. From the position the axis is after a zero return the machine will only move so far. To increase the allowable travel you need to increase the parameter value. Here is where you can get into trouble. You need to make sure that you actually have enough travel in the axis physically. To find out what your maximum physical travel is you can turn setting 53 on and jog the machine till you hit the dead stops. (NOT WISE but effective). Then you can adjust where you need the limit switch to be.

[Geof]

Originally Posted by Delw Geoff Neither could I, its just what I was told. reason being I had a part 2inches longer than my table movement ....

Very unlikely you can squeeze two inches, maybe half an inch.

I have increased travels on some machines as follows but you do this at your own risk :-).

As mentioned you can carefully jog with Setting 53 on. Have the Current Commands screen open and watch the servo load, as soon as you see it start to climb stop and go back about 0.08 to 0.10 and record the travel. Multiply the travel by the (STEPS/UNIT) for the axis and enter this number in the MAX TRAVEL (STEPS).

Backing up the 0.08 to 0.10 is to give a little space for the machine to overrun should you happen to run it to the end of the travel very fast using Handle Jog.