Movement adjustment based on feedback from encoder
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but this does raise the cost and is it worth it for the type of machine use etc ..
you would probably need to use a Mesa or pico Interface due to the fact that you will need quite a few more pins than a parrell port can give you
as well as being able to interrogate the pulse stream efficiently .
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Why can't i use second lpt port to increase amount of input pins?
And the question is still open - is it possible to setup closed loop system drived by linuxcnc and where can i read about it?
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Certainly, closed loop system raises cost of instrument in whole, but also it increases precision, which is bottle neck of a ball-screw gear w/ stepper motor.
Why can't i use second lpt port to increase amount of input pins?
And the question is still open - is it possible to setup closed loop system drived by linuxcnc and where can i read about it?
yes this can be done in linuxcnc
no amount of electronics can increase precision , that is inherent in the machine build mostly in the mechanics
encoders are used to keep the path requested within a margin of error or to indicate if you are outside of tolerance ( ferror )
as this is all dependant of time and speed in realtime , a good read ahead and other factors , the faster you can read the pulse from encoders and process the required result
their is a great dependence on hardware and speed , the faster your moving the axis the faster you need to read and process the encoders , Parrell port can do it , but not to close enough tolerances
the faster you go .. this becomes quite a process hog , and is better served using using off board electronics such as FPGA etc
and depends on the type and quality of the encoder used of course . will all have an effect on the result obtained
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For example with a 1 u resolution linear scale. somewhere around 25 mm/s is about as fast as you will be able to move without losing count with a parallel port system (25 KHz reliable count rate assuming 50 % headroom and 20 usec basethread)
Also for a feedback system you need more scale resolution than control accuracy (a reasonably well tuned system may only keep within 5 counts or so)
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yes this can be done in linuxcnc
can you help me find manual?
no amount of electronics can increase precision , that is inherent in the machine build mostly in the mechanics
definitely so
encoders are used to keep the path requested within a margin of error
this is what i need - to keep requested path within a margin of 50 µm
sorry for my poor english
![:-) :-)](/media/kunena/emoticons/smile.png)
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Just to add my 2 cents, you _can_ create a feedback control system with parallel ports reading encoders and step motors running in velocity mode, but you have to consider the maximum rate that you can read the scale and the scale resolution. I know of LinuxCNC users who have done this, one application is a rotary table, but this has quite a slow encoder count rate.
For example with a 1 u resolution linear scale. somewhere around 25 mm/s is about as fast as you will be able to move without losing count with a parallel port system (25 KHz reliable count rate assuming 50 % headroom and 20 usec basethread)
Also for a feedback system you need more scale resolution than control accuracy (a reasonably well tuned system may only keep within 5 counts or so)
Yes, i've realized mesa card inevitability, thx.
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yes this can be done in linuxcnc
can you help me find manual?
no amount of electronics can increase precision , that is inherent in the machine build mostly in the mechanics
definitely so
encoders are used to keep the path requested within a margin of error
this is what i need - to keep requested path within a margin of 50 µm
sorry for my poor english
to add encoders is simply a few lines additional to the hal file
and then tuning the pid for the encoders , there is some comments on the forum and the wiki.
linuxcnc.org/docs/html/man/man9/encoder.9.html
note: following and correcting the path is open to interpretation as to the accuracy and the form of action taken
i.e ferror for example will just stop the machine if outside the tolerance value .
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will it do this automatically w/o addition setup?
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This customization is done in HAL (xxx.hal) and initialization (xxxx.ini)
files.
Most closed loop configurations use encoder feedback, the PID component and PWM or analog output schemes to drive the motor.
Probably the best way to get a feel for this is to look at some existing closed loop configurations: (etch-servo, hm2-servo, ppmc, motenc are good places to look)
git.linuxcnc.org/gitweb?p=linuxcnc.git;a...9fa424b55dc4;hb=HEAD
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