On 09/25/2016 11:21 AM, Jon Elson wrote:
On 09/25/2016 11:52 AM, Kirk Wallace wrote:
Hmm... I found this which means I need to look a little
closer at my pin list: "... (All float output)
'ppmc.<port>.encoder.<channel>.velocity - Velocity scaled
in user units per second. On PPMC and USC this is derived
from raw encoder counts per servo period, and hence is
affected by encoder granularity. On UPC boards with the
8/21/09 and later firmware, velocity estimation by
timestamping encoder counts can be used to improve the
smoothness of this velocity output. This can be fed to the
PID HAL component to produce a more stable servo response.
This function has to be enabled in the HAL command line
that starts the PPMC driver, with the timestamp=0x00
option. ..."
On older PWM boards without the timestamp feature, and all
USC boards, velocity is just delta scaled by the the encoder
scale factor. On the newer PWM and PPMC boards with the
timestamp feature, then the velocity is smoothed by
estimation based on time since the last encoder count. This
is considerably smoother than velocity derived from delta,
which is just current position - last position, and this
quite noisy.
(My last message went to moderation due to the attachments, I made them
smaller on this one)
For fun I attached a screen shot of my HNC lathe running the G33 code
Rob posted. I don't have a Z acceleration pin so I have Z velocity on
the bottom trace and the spindle encoder velocity on top, at two
resolutions. I don't know if this indicates anything with Rob's issue.
--
Kirk Wallace
http://www.wallacecompany.com/machine_shop/
http://www.wallacecompany.com/E45/
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