On 01/25/2020 01:38 AM, John Dammeyer wrote:
I agree there are all sorts of ways of doing this. Only Peter at MESA or
perhaps Jon could explain what they do but I don't know if it's proprietary to
their hardware.
Well, it is not real proprietary. I can only speak for the
Pico Systems products. Yes, as John says, the .ini file
tells the
trajectory planner all it needs to know about max velocity
and acceleration for each axis. So, (assuming correct
configuration) it will never ask for moves the drives cannot
do. Then, the TP feeds coordinated positions of all axes
to the PID component (or stepgen component for software
stepping) at the servo thread rate. Then, for all of my
boards, the encoder counter counts encoders (or with my
stepper controller in open-loop mode it can count the steps
issued)
and feeds this back to LinuxCNC at the servo rate. PID
calculates a velocity and sends that to the appropriate
device (step generator, PWM generator or DAC) and the drive
moves at the desired rate. Repeat every millisecond.
With encoder feedback, you can examine the real drive/axis
performance with Halscope and find the actual limits of speed
and acceleration. You can then decide how much to back off
of these limits and set the MAX_VELOCITY and
MAX_ACCELERATION ini file parameters accordingly. This is
harder to do in an open-loop system.
Jon
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