On Mon, 30 Jan 2012, Viesturs L?cis wrote:
> Date: Mon, 30 Jan 2012 12:18:51 +0200
> From: "[UTF-8] Viesturs L?cis" <[email protected]>
> Reply-To: "Enhanced Machine Controller (EMC)"
> <[email protected]>
> To: "Enhanced Machine Controller (EMC)" <[email protected]>
> Subject: [Emc-users] US Digital encoders?
>
> Hello!
>
> The conclusion of my struggle with tuning servo motors is that I shall
> change encoders. I based it on Jon's findings, when testing AMT 102
> encoders and I also got a feedback from a local guy, who also had used
> them on a cnc machine.
> Sorry, Peter, I could not figure out, how to precisely stop machine at
> the same spot to check for lost/gained encoder counts. With 3277
> pulses per 1 mm I do not see a way to detect any deviance of less than
> thousand pulses.
>
> I would like to ask, if anyone could provide some recommendations for
> US Digital encoders - I chose them, because they seem to be next in
> the line in terms of affordability.
>
> I was particularly looking at E7P.
>
> I have Keling KL23BLS_115 Nema 23 servo motors:
> http://kelinginc.net/KL23BLS_115.pdf
>
> Viesturs
Before you change encoders, and noting that others have used the CUI/AMT
encoders with success, can you try a little experiment to make sure this is
not a noise --> losing count/commutation issue?
The CUI/AMT encoders may have some problems that would affect final tuning but
these would not cause oscillation with low gains nor would they cause a change
in behaviour at high speeds.
A little background first:
HostMots2s encoder counters on the 5I23 have a input sample rate of 48 MHz.
you have the input filter enabled which means that the A/B/I inputs need to be
steady for 15 clocks before being recognized as a high or low. This is ~300 ns
and allows count rate up to about 6 MHz. This is much faster than you need.
Input noise immunity can be improved by lowering the input sample frequency so
that the (typically short) noise pulses are rejected. For example if we set
the input sample frequency to ~3 Mhz, we can still count up to 400 KHz or so
but now an input pulse less than 5 uSec in width will be rejected.
The encoder sample frequency is a settable parameter in the HostMot2 firmware
but there is no direct HAL access to this parameter.
To set it you must enable the raw mode. This is done by adding the enable_raw
keyword to the firmware load line in your .INI file. See the raw mode section
of the hostmot2 manual page.
Once this has been done you need to
setp write_address 13312 # = 0x3400 = encoder Sample Rate Register
setp write_data 14 # sample rate is clocklow (48 MHz)/SRR+2
# so divide by 16 = 3 Mhz
setp write_strobe true # do write
This can be done by hand in the "show hal configuration" window
>
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Peter Wallace
Mesa Electronics
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