Hello
I'm a lurker on the list and I noticed you haven't had a reply. I am
also a control systems engineer and I may be able to help out.
Before you tackle this problem, are you sure you have one. If the
sample rate is sufficiently higher than the time constants, then
corrections/adjustments probably aren't going to make much difference.
Any benefits may be lost in noise.
Are the adjustments already in the code, or is this something that has
been identified as a worthwhile enhancement?
Regards
Darren Conway
Joel C. Salomon wrote:
I’m trying to work through the math for trapezoidal motion-profile
generation, and I could use some pointers on this subject.
Reading through the EMC documentation, at
<http://wiki.linuxcnc.org/cgi-bin/emcinfo.pl?Simple_Tp_Notes#simple_tp_math>,
I saw written, “This is the math for the continuous time case. In the
actual code there are correction terms which are required due to the
discrete time sampling... these should be described here.” Looking at
the code (src/emc/kinematics/tc.c, …/tc.h, …/tp.c, & …/tp.h) did not at
all enlighten me as the the algorithm used. (Am I even looking in the
right place?)
I tried the Google search [motion profile discrete time velocity
acceleration limit], and found
<http://www.kuka.com/usa/en/products/software/educational_framework/arm_tutorials/PS_Content_Arm1.htm>,
where they write, “However, in practice [the various time constants]
usually won’t match exactly an integer multiple of [the time step] h. To
avoid inaccuracies some corrections have to be made[…]. The
implementation of these adjustments is left for the user as an exercise.”
For my job, I need to understand how adjustments are made to (what I’m
calling) velocity–ramp-up/-down–time, and constant-velocity–coast–time
in order to ensure that these are integer multiples of the time step.
If you can explain the code to me (cradek, perhaps), or the algorithm,
or even know a good reference for this, please let me know (on- or
off-list, as seems appropriate).
Thanks,
—Joel
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