Problem with error or missed steps or something?

[rustyolddo]

Update:

Spent the afternoon playing with the setup. The problem was indeed missed steps. I lowered the rates and it did the job albiet realllllly slow. Guess I'll need larger motors to run higher rates.

Still have three other problems:

Using a DI, when I jog using the Alt-G command, from 0-2" I don't get 2" of travel, I'm about .004" shy. All I can figure at this point is since the ball screws were fitted for minimal backlash, that the thread pitch has changed ever so slightly. I suspect I could correct this in software? Suggestions?

Secondly, how is the best way to measure & adjust backlash? Been trying to jog +\- .0005" and adjust the backlash so that I get .0005" of movement. Don't seem to be having much success.

In the jog mode, I can jog the axis by using the discrete mode but the continous mode doesn't work, it just kinda grunts.


Lastly, the G28 home function won't work. I've got my N/O home switches wired to 10,12,13 & Gnd. Set the ports to active low, "Home is Limit" enabled. When I enter the G28 command, it sounds like the controller trys to move the motors, they kinda grunt but nothing happens. Also, when I'm running a program, it randomly stops due to a "limit error" yet no limit switch is activated. Using the port monitor, I can see the switches change states when manually activated. I may post this as a seperate subject in a new post. Thanks.

[ger21]

Originally Posted by rustyolddo Using a DI, when I jog using the Alt-G command, from 0-2" I don't get 2" of travel, I'm about .004" shy. All I can figure at this point is since the ball screws were fitted for minimal backlash, that the thread pitch has changed ever so slightly. I suspect I could correct this in software? Suggestions? Secondly, how is the best way to measure & adjust backlash? Been trying to jog +\- .0005" and adjust the backlash so that I get .0005" of movement. Don't seem to be having much success.

If you're not using ground ballscrews, they can vary slightly as you move along them. Try the same 0-2" test at different parts of the screw, and see if the results are different in different places. This might tell you if it's screw error.

Do you mean you're adjusting backlash on the nut itself, when you're trying to get .0005? Or using software backlash comp?

[rustyolddo]

Originally Posted by ger21 If you're not using ground ballscrews, they can vary slightly as you move along them. Try the same 0-2" test at different parts of the screw, and see if the results are different in different places. This might tell you if it's screw error. Do you mean you're adjusting backlash on the nut itself, when you're trying to get .0005? Or using software backlash comp?

Software backlash comp. No room for a second 5/8 ballnut to adj. mechanical backlash.

[ger21]

I don't think backlash comp works during jogging. And even if you MDI a single axis move, it probably doesn't work there either. I don't know the specifics, but I believe it only comes into play when an axis changes direction.

I forgot to mention, regarding uneven screw lead. Mach3 now has screw mapping, which let's you compensate for uneven screw lead. Not sure how complicated it is to set up, but it will (should, anyway) help to make machines more accurate. Provided you can run Mach3.

[rustyolddo]

Originally Posted by ger21 I don't think backlash comp works during jogging. And even if you MDI a single axis move, it probably doesn't work there either. I don't know the specifics, but I believe it only comes into play when an axis changes direction. I forgot to mention, regarding uneven screw lead. Mach3 now has screw mapping, which let's you compensate for uneven screw lead. Not sure how complicated it is to set up, but it will (should, anyway) help to make machines more accurate. Provided you can run Mach3.

Backlash comp does work during jogging.

Going to back figure and see if I can correct for the screw but I need to get the backlash comp correct first so It's not introducing error. Mach3 would be nice but I'm using an old laptop and that's all I have room for right now, Windoze is very slow on the old laptop. Many new laptops don't have parallel ports, you have to use a USB port replicator which is a pita in itself.

[ger21]

So if you make one jog move, then the backlash comp doesn't do anything, but if you then jog in the other direction, it then compensates? Just trying to understand how it works.

If you're screw is off by the same amount in different locations, you should be able to adjust out the error by playing with the step size.

[rustyolddo]

Originally Posted by ger21 So if you make one jog move, then the backlash comp doesn't do anything, but if you then jog in the other direction, it then compensates? Just trying to understand how it works. If you're screw is off by the same amount in different locations, you should be able to adjust out the error by playing with the step size.

Correct. If I keep jogging to -X, it simply moves, if I jog +X, I'll get a backlash comp movement+jog then it will continue to jog until the next direction change.