Y axis positioning error

[Brian L]

This happened once and I thought I had inadvertently hit a button or something, but now it's happened several times. Running a part on a fixture, made the fixture, centered the machine on it and G54 set my 0,0 position.

Come back the next day to run some parts and home the machine, hit MDI and G00 x0y0 and she goes to center on the X, but .100" in the Y minus direction. Moved back the .100" and redid my G54 for Y.

Different job, drilled a hole on 0,0 one day, came back the next to machine a taper on the outside and find I'm off again in the Y, again, exactly .100".

Any suspected things to check? Belt from servo to ballscrew is tight, pulleys appear to be tight on the ballscrew, and I doubt I'd get exactly .100" jump if the pulley slipped, so could it have to do with the resolver/encoder? Does one turn of that equal .100" and I'm either missing the home index or ????

[FanFan]

Brian, I have seen this type of problem when a switch is used to detect home postion.. If you are having this problem after homing or referencing the y axis out I would check/change/adjust the y axis home switch and/ or the dog used to triggger the home switch. FanFan

[Brian L]

I will check the Y axis home switch and dog.... I wondered if that could be the issue, as it only seems to happen after being homed... no problems once it's on and running for the day. Thanks for the suggestion!

[sportybob]

Hi Brian, The home sequense is 3 steps
1. move the table twards the home switch.
2. make contact with the switch and back away from the switch until the switches closes.
3.after the switch closes, go find the marker pulse on the encoder.

If the switch is real sticky or shorted, the table just moves away untill it hits a limit switch, if it is slightly sticky then it might just be a little slow.
NOTE. one should not leave the axis sitting on the switches, leaving the switches depressed for long periods is hard on them.

Sportybob

[Brian L]

Hi Sportybob,

Thanks for that, I do routinely leave the machine off the limit switches, well at least X and Y, Z pretty much is usually at the top. I tend to center the table when I shut it down, as since I replaced all the metering units, it's a drooler.... If I center the table, it all falls in the drip pan instead of on the floor... so I tend to home it first thing, then go back to my vise area, which is middle of the table roughly.

[sportybob]

Hi Brian, 2 things, 1. check the switch using the display diag screen F2 for Y axis look at the "home" input. toggel the home switch and see if you can see any "lag" in the input response. sometimes a little WD or similar product will clean any sticky stuff off the switch.
2. on your autolube being a "drooler" the oilers are usually set to run more way lube then needed from the factory. ( better to have too much then too little when the machine is new) you can adjust the oiler amount and time either by the display panel on the lube unit or by adjusting the knob settings under the cover. adjust to use about a tank in 40 hours of operation.

Sportybob

[Brian L]

Will check into the switch. As for the oiler, I have it close to the minimum pump amount now, could probably drop it back a 1/2 cc or so, it pumps 3cc-6cc per stroke and I can't change the time interval as it's a clock style motor that runs a cam that lifts the plunger. I timed it once and it's pretty often, like every six minutes (10 cycles per hour) if I remember correctly.

I would rather clean the oil up than be dry.... when I'm putzing around it's way too much oil, but when I'm doing some 3D profiling and it's wiggling all around at 40-60 ipm then it's probably a good thing.

[sportybob]

Brian L: did you get the problem resolved?

[Brian L]

Hi Bob,

I did not get it "fixed", but I'm pretty sure what the issue is. I seem to have a sticky limit switch, or plunger in the housing... something that is causing the switch to be inaccurate. I have had several occasions where the machine goes to home itself, stops moving Y+, reverses to the Y- direction, then creeps back to home, and have it just continue creeping until it hits the over travel.

I have to take the belt cover off the front, manually spin the machine back into range, reach up with a finger and jiggle the limit switch buttons, rehome and everything is good for a couple of days. By the way, is there a way to come off the hard limits without taking the belt off and moving it manually? Fanuc controls we used to have had a switch you could over ride and get servo movement again... not sure if the Milltronics does that.

I did find a label on the limit switch, says Honeywell/Yamatake, and actually just came in for lunch and to do a search on where I might be able to get replacements, or a manual or something showing if I can rebuild them... new switch, o-rings around the plungers, not sure what it takes.

Thanks for asking, I had kind of forgotten about this post....

[sportybob]

Hi Brian, To jog off the limits, from an E stop condition, Press and HOLD the reset button, with one hand and then select jod with the other, then press the jog key for the axis(s) you want to move.

I carry several types of switches, at resonable prices. PM me for more info

Sportybob