5i25 + 7i85s +....
Feels so good to see after being blind! I blame the X-mas trouble....
![;) ;)](/media/kunena/emoticons/wink.png)
For some Reason i figured out "axis" as the "real world axis" not as the user interface.
And all my following confusion based on it....
Well then... just two more Question:
Whats the difference between hm2_5i25.0.stepgen.XX.position-fb and hm2_5i25.0.encoder.XX.position?
hm2_5i25.0.stepgen.XX.position-fb = "Hello im hm2_5i25, I sent my steps, so the axis should be at..." ?
hm2_5i25.0.encoder.XX.position = "Hello im hm2_5i25, Im counting the encoder and this is my result" ?
Where exactly does the PID "operate" ? Axis or FPGA
I guess axis. Otherwise you wont need to send hm2_5i25.0.encoder.XX.position to axis.X.motor-pos-fb by X-pos-fb right?
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Whats the difference between hm2_5i25.0.stepgen.XX.position-fb and hm2_5i25.0.encoder.XX.position?
One is the local feedback from the stepgen the other is external position feedback from an encoder, they are used similarly
hm2_5i25.0.stepgen.XX.position-fb = Here's where the stepgen position is currently, use PID to check against the commanded position and adjust course as needed by adjusting the velocity
hm2_5i25.0.encoder.XX.position = Here's where the encoder position is currently, use PID to check against the commanded position and adjust course as needed by adjusting the velocity
Where exactly does the PID "operate" ? Axis or FPGA
I guess axis. Otherwise you wont need to send hm2_5i25.0.encoder.XX.position to axis.X.motor-pos-fb by X-pos-fb right?
Yes, the PID component performs the PID calculations every servo thread invocation in LinuxCNC
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Hm,... so the most important controlling circuit happens Software based. Good to know!
And sorry, but i found something more....
Where is the "go to" Signal from Axis to 5i25?
I see:
net X-pos-cmd <= axis.2.motor-pos-cmd
net X-vel-cmd <= axis.2.joint-vel-cmd
But there is nothing like:
net z-pos-cmd => hm2_5i25.0.stepgen.XX.positon
net z-vel-cmd => hm2_5i25.0.stepgen.XX.velocity
Also there are more open links leading to nowhere. (as far as i notice) Like:
net z-vel-fb <= hm2_5i25.0.encoder.XX.velocity
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stepgen, it just not quite as robust as the PID mode so pncconf uses the PID mode
In the PID stepgen control mode the equivalent of net z-vel-cmd => hm2_5i25.0.stepgen.XX.velocity
happens automatically due the the FF1 term
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So... the following should be my final signal setup for one axis. But two things:
For my understanding the arrows of x-output lead in the wrong direktion. Im right? (Made by PNCconf)
Otherwise i dont see, where PID talks to 5i25.
PNCconf missed to hookup x-vel-fb back to pid.x.feedback-deriv.
On the other Hand... is there really need for this or is it just waste of cycle time?
net x-pos-fb should do all the Work.
net x-enable <= axis.0.amp-enable-out
net x-enable => hm2_5i25.0.stepgen.00.enable
net x-enable => pid.x.enable
net x-enable => parport.0.pin-2-out
net x-pos-cmd <= axis.0.motor-pos-cmd
net x-pos-cmd => pid.x.command
net x-vel-cmd <= axis.0.joint-vel-cmd
net x-vel-cmd => pid.x.command-deriv
net x-output <= hm2_5i25.0.stepgen.00.velocity-cmd
net x-output => pid.x.output
net x-pos-fb <= hm2_5i25.0.encoder.00.position
net x-pos-fb => pid.x.feedback
net x-vel-fb <= hm2_5i25.0.encoder.00.velocity
net x-vel-fb => pid.x.feedback-deriv
net x-index-enable <=> pid.x.index-enable
net x-index-enable axis.0.index-enable <=> hm2_5i25.0.encoder.00.index-enable
Im still looking into manuals about the index stuff.
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net x-output => pid.x.output
The arrows here are both backwards (but it does not matter since the arrows are ignored)
net x-vel-fb <= hm2_5i25.0.encoder.00.velocity
net x-vel-fb => pid.x.feedback-deriv
is not necessary but will result in better control ( this is because the encoders velocity estimation is better than
the PID comps velocity estimation via D/DT of position )
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I start to like HAL!
Nice Information about hm2_5i25.0.encoder.00.velocity! didnt expect that!
Why are...
- addf hm2_5i25.0.read
- addf motion-command-handler
- addf motion-controller
- addf pid.x.do-pid-calcs
- addf pid.y.do-pid-calcs
- addf pid.z.do-pid-calcs
- addf hm2_5i25.0.write
...in the slower servo-threat instead of base-threat? Since i have no software-stepgen runnung.
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you dont need (or want) a high speed thread so only a servo thread is needed
(effectively the base thread = high speed functions are running in the FPGA)
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Or is the System more stable in servo-threat?
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1. The base thread cannot do floating point
2. You can run the servo thread as fast as your hardware and PC will function
_But_ there is no advantage to running it faster than about 10 times as fast as the
controlled systems bandwidth (and for CNC systems a few hundred HZ is about as
fast as the position bandwidth loop gets) Running the loop faster just wastes CPU time
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