Velocity problems

The mess with speeds, or need to be?

As I configure my 5 axis machine I got little confused about speeds, and limits. Can someone explain why so much settings for same thing?
For now I'm knowing these:

ini file:

[DISPLAY] Section
DEFAULT_LINEAR_VELOCITY = 1
MAX_LINEAR_VELOCITY = 200
MIN_LINEAR_VELOCITY = 0.1
DEFAULT_ANGULAR_VELOCITY = 1
MIN_ANGULAR_VELOCITY = 0.1
MAX_ANGULAR_VELOCITY = 80

[TRAJ] Section
DEFAULT_VELOCITY = 80
DEFAULT_ACCELERATION = 80
MAX_VELOCITY = 80
MAX_ACCELERATION = 80

[AXIS_<num>] Section
#Linear
MAX_VELOCITY = 200
MAX_ACCELERATION = 200
STEPGEN_MAXVEL = 300
STEPGEN_MAXACCEL = 300

#angular
MAX_VELOCITY = 80
MAX_ACCELERATION = 80
STEPGEN_MAXVEL = 120
STEPGEN_MAXACCEL = 120

I think that limits in [AXIS] should never be exceded. But it is! And as result I got joint folowing error.

if I jog machine in joint mode everithing is ok. But when I switch to world mode then I got problems. XYZ are ok. But if I jog B axis the X axis got folowing error. But velocity in OSD are way to high. Then I try to lower jog speed slider and I be able to jog B axis (and X make move too as is needed). Then I increase jog speed in slider and make jog in B. In some point the commanded speed is over that reqired in axis section ] and I got folowing error.

So what relation betwen all that speeds is needed?
I was thinking the [AXIS] section is ultimate limit, and don't know why other even exists?


And where (and who) need to calculate the actual speed?
For example:
Assume B is tilted 90 deggre, and pivot is 250mm.
If I then jog C with max available speed (for C axis) the XY isn't fast enought to folow! So who need to make limit? I was thinking the slowest axis is limiting one, but is not true.
If I limit the B/C speed (taking pivot as pivot length+max tool length) then I should be never exceds speed limit for XYZ. But in that case I had limited even jogs in joint mode.

So what is correct configuration?!?

Thanks


p.s.
Hopefuly I do not overpost forum these day. (I have a lot of question to solve...)

Hi

See www.linuxcnc.org/docs/devel/html/config/ini_config.html

The entries in [DISPLAY] relate to overrides and jogging only, ie those items you can set in the Axis display.

The items in [TRAJ] are general trajectory figures for any axis or co-ordinated axis moves
DEFAULT_xxx relates to jogs
MAX_xxx is the highest figure of the individual axes to set the overall machine speed (axes not stepgens)

The items in [AXIS_?] are per axis and this is where the STEPGEN_MAX_xxx value should be up to 20% higher than the MAX_xxx value (not 100%, unless you have significant backlash issues)
This is to enable the stepgens to maintain co-ordinated motion with 1 or more other axis.

Rotary axes are normally set much slower and there can be issues with co-ordinated moves involving a rotary axis, these have been covered many times before

Hopefully that answers some of it

regards

So if I understand correctly then [DISPLAY] are just for slides setings but not the motors. But if I remember correctly the wrong setting fut motor to go faster than [AXIS] is set! I will check.
in [AXIS_x] I think all is clear
but [TRAJ] still confuse me. If I understand the value in [TRAJ] is combined speed of all axes (ie speed of tool).

The slowing BC motors down seems bad idea.
Let's think about normal 3 axis machine making bal, and it's just in the half of the bal. The X and Y just make path (circle) wich radii is radii of bal+radii of cutter.
Now imagine 5 axis machine doing same thing. The X and Y must go a lot quicker to keep same tool speed around ball as X and Y path is now the ball radii+pivot_length+tool_lenght. So for that case keeping BC slow seems practical. But in the start of ball cutting (at the top) the C axis is fastest one and for that reason is not practical to slow it down if it has mechanical capabilites to be fast.

I still don't understand why I got joint folowing error. I can jog in joint mode all axes with top speed, but in world mode jogging B/C cause to overspeed XYZ.

andypugh wrote:

I think that the problem might be the other way round. You get a following error _because_ the linear axis can't move fast enough to track the rotary axis.
LinuxCNC only properly does trajectory calculations for moves in XYZ, rotary axes are not considered. I think that the solution is to set the rotary axis limits low enough that the linear axes can keep up for the longest tool you have.

I do think this is the problem too. The keeping rotary to be so slow seems like bad dream.
I use precompiled 2.5.3 LinuxCNC.
Where is Joints_axes3? Where is manual?

To waiting for 2.6 release I think it will take just to much time.

Maybe just changing 7i43 to paralel port stepgen. If I didn't mess thing on my head then just few lines need to be changed. (step pos/cmd signals) and simplified estop.
But this is just thinking of greenhorn.....

Maybe is something wrotten in source code... How trajectory is calculated..