possibly ignorant question about acceleration... also reversing direction

[jvanick]

... I've built a JGro-type cnc router that's being controlled with a hobby cnc card and their 305oz steppers.

I'm trying to use the emc ubuntu distribution to control it.

i've got motion, but I'm having intermittent problems with movement.

sometimes the steppers will just hum or make a grinding sound instead of moving. if I slow my feed rate down the problem seems to go away.

so what I'm thinking is that I have an acceleration problem when jogging the axises...

is there a easy way I can configure an acceleration ramp so that it doesn't go from 0 to 100ipm immediately, but starts slower and then speeds up? Or is this something I don't want to do?

secondly.. it appears that my direction is reversed from what EMC is showing on the screen in Axis... how do I change the control signals? I tried adding the -invert options in the hal file, but i'm not really sure what hal file emc is reading... so I'm kinda lost on that front too.

Thanks!
-J

[Ray Henry]

Congrats on running.

The definitive answers to your questions are in the integration manual that should be under the menu Applications->CNC. There is quite a bit of stuff there on how to set up the ini file, which one is being used, and such. Short of that I'll add a few notes to a snipped version of your post here.

Originally Posted by jvanick ... sometimes the steppers will just hum or make a grinding sound instead of moving. if I slow my feed rate down the problem seems to go away. so what I'm thinking is that I have an acceleration problem when jogging the axises... is there a easy way I can configure an acceleration ramp so that it doesn't go from 0 to 100ipm immediately, but starts slower and then speeds up? Or is this something I don't want to do?

Sounds like the problem. The solution is to find the configuration you are starting with. If you used stepconf to build that so the distances and all match to the machine it is probably in a directory named my-mill and lives in your home directory in emc2/configs/my-mill. In any case, you can find it in the tree widget when you fire up emc2's config selector.

In the ini file you are using there are sections for each axis. For each you'll see several accel variables. Again if you are using stepconf you can change these in the motor config page. You can also edit them directly but I'd advise reading the integration manual first.

Originally Posted by jvanick ... secondly.. it appears that my direction is reversed from what EMC is showing on the screen in Axis... how do I change the control signals?

Stepconf has checkbuttons alongside the signals on that page that invert the direction. You'd put a minus in front of, or erase the minus in front of the scale variable if you directly edit the relevant ini file.

Originally Posted by jvanick ... I tried adding the -invert options in the hal file, but i'm not really sure what hal file emc is reading... so I'm kinda lost on that front too.

It will take a bit for you to get comfortable with config editing. I'd create a couple of them and switch between with the emc startup chooser. One might be named something like last-best-version (don't uses spaces in file names) for running your machine. Others might be for experimenting with ini or hal stuff. When you succeed in an experimental version, move that change to the last best one. You can do this with either stepconf or hand edited configurations.

There is a specific manual on the HAL available in the documents section of www.linuxcnc.org but most of the necessary info is in the integration book.

Hope this helps

[Big John T]

If you used the stepconf wizard to generate the config then just go back to the wizard and open the file up and lower your acceleration until they test good. Also reverse the direction pin in the wizard as needed. Info on stepconf wizard is in the User Manual and the html is here.

http://www.linuxcnc.org/docview/html..._stepconf.html

John

[samco]

you really should run the latency-test from terminal (without emc running). Load the system - surf, run glxgears, edit something in open office.... See what the the max jitter is. It could be a hardware issue also - if the computer can't put out a decent pulse stream.

http://www.linuxcnc.org/docs/2.2/htm...c:Latency-Test

sam

[Big John T]

sam wouldn't he get a rtapi error if his speed was set too fast?

John

[samco]

some people ignore that error

sam

Originally Posted by Big John T sam wouldn't he get a rtapi error if his speed was set too fast? John

[jvanick]

well after playing around with stepconf for a while last night, I got things running pretty good.

I'm still having some binding issues here and there, but i think that's more due to machine setup and alignment than the controller/software.

one more question tho...

what's the 'standard' way that you reference Home...

do you do something like:

X: 0-30
Y: 0-13
Z: 0-4

--or--

X: -15 - +30
Y: -6.5 - +6.5
Z: -2 - +2

or... do you make multiple profiles???

or ???

-J

[Big John T]

Glad to hear you got it up and running. One question if you don't mind... Did you use the Getting Started Guide to get up and running. If so were there any parts that just were not clear or strait forward to understand? You can probably guess that I work on the manuals .

I'm not sure what you mean "reference home". If you have homing switches they are used to locate the home position. If you don't have homing switches then when you move to a position you want to be home and press the homing button that becomes your home. A tip if you move to your favorite home position before powering down then you are there (if nothing moved) when you power up.

I normally work with Y0 = the fixed jaw of my vise and X0 = to the left side of the part and Z0 = to the top of the material. I don't have home switches on my mill so I use an edge finder to set up when powering up. I have home switches on my plasma cutter so that one is easy.

John

[Ray Henry]

Many commercial machine tools use the plus end of each axis as home. This means that an ordinary CAD drawing in the top left quadrant is outside the normal range of the machine. I would find several different home configs really confusing but offsetting from home using g55-59.3 is really valuable.

For the Mazak at fest the home switches are all in the positive direction but then we used a home offset to place 0,0 in the center of table travel. I don't really have an opinion about that setup.

[jvanick]

Actually the manuals were really good... much better than most of the stuff I read for my day job.

*after* I read them that is.

when I was asking about the reference, i was more looking at how people typically reference... if they did 0x0x0 as home or if they went negative. I'm going to set up for 0x0x0 as home. should I set up so that the cutting bed is 0 and the upper limit of travel is +4 ?

one thing tho that I find confusing (maybe?) is that there's no max speed override... that is, I can put a feed rate of say F300 on a gcode command and the machine will happily try to do that. Vs. using the slider on the interface or max of my settings.

I didn't know about the offsetting G code commands...
I'll definitely be looking into that more.

-J

[Ray Henry]

Ah. I leave g54 at the home position so when I command home I issue

g0 g54 x0y0z0

I would not set z0 at the bed because if I did this and selected a tool but failed to set a tool length zero would be under the bed by the actual tool length. I set z0 as far away from the bed as possible. Then if I want to set z0 at the top of a part I do that with the coordinate system offsets. Just seems a bit easier for me to understand.

But then EMC2 is configurable and others configure much different than I do.

[Big John T]

If you used the stepconf wizard it is MAX_VELOCITY on the axis page.

http://www.linuxcnc.org/docview/html...-Configuration

If you did your config by hand it is the MAX_VELOCITY in each axis section of your ini file.

http://www.linuxcnc.org/docview/html...nfig.html#sub:[AXIS]-Section

In any case the planner will not exceed the max velocity for an axis no matter what you program in your g code. Keep in mind that a diagonal RAPID move will be faster than your max vel due to the fact that even though both axis are moving at your max speed your traveling a greater distance when moving only one axis.

John