Could someone help a newbie with emc2

[locodave]

Could anyone help with a problem I am having with EMC2.

Firstly my computer is 2.5ghz athlon with 512 MB memory and a 40 gig hard drive. I did a clean install from the ubuntu live CD that I downloaded approx 2 weeks ago. My machine is a dovetail column mill which I converted to ball screws that are in turn driven by size 34 double stack stepper motors. I am using home made stepper drivers that just take step/ direction signals from the parrallel port on my computer,

I have tweaken the standard_pinout.hal file to match how the pins are connected to my port and I have tweaked the stepper_inch.ini to get feed rates that I am comfortable with.

As a test run I loaded the cds.ngc file and ran it. It seems to run alright with no lost steps but I have noticed somthing odd when it executes the G codes

If for example I am running th following lines of G code:-

g0 z2.1
g1 x1
g1 y1
g1 z1

I start the program running

Z axis ramps up to normal speed and then starts to ramp down to a stop but as it start to ramp down the x axis starts to ramp up to move to the required position before the z axis as even finished moving. Then it will happen again, as the x axis starts to ramp down the y axis will start to ramp up for its move to the required position.

It seams as though it is interpolating the ramp down at the finish of one move with the ramp up of the start of the next move. It even happens if I change the G1 commands for G0 commands.

I hope someone can shed some ligh on this problem.

[samco]

I would guess you are seeing the 'blending' that emc does by default. If your acceleration is set lowish - you will really see it. As one axis aproches its position the other axis will start up.. This is g64 (emc defaults to it)

If you want it to exactly stop at each end point - then you want to use g61 'exact stop mode'

or you can do a tolerence mode g64 pX.XXX where x.xxx is the maximim distance from actual path allowed.

http://wiki.linuxcnc.org/cgi-bin/emc...jectoryControl

sam

[samco]

Also - I showed the emc experts your ini file.. (I am more of a emc2 user/evangelist)

These where some of thier comments.

locodave's real problem is that he has [TRAJ] MAX_ACCELERATION=1.0 (inch/s^2) - if he wants axis accels of 5 in all cases, TRAJ accel should be 8.66 (5 * sqrt 3)

sam

[andy55]

hi locodave,

there was a bug in the trajectory planner, but that was fixed some time ago, and the latest version EMC2.0.5 should not have any problems, even with ACCEL values set really slow.

if after upgrading to 2.0.5 you still see strange behaviour, do post your ini and a screenshot of the blended motion!

btw, the different traj modes are:
G61.1 exact stop mode
G61 exact path mode
G64 blend mode

AW