It is not too unusual to use the torsion in a rotating shaft as a load
indicator. Sensors at both ends aligned at zero force. The app I saw was
using this on the turbine shaft for a 125 Mw generator. Just a comment. ;-)
On 9/18/19 5:30 PM, Chris Albertson wrote:
One way to measure force is with a spring. Force is measured by looking at
spring displacement. It is kind of like the load cell idea but you use
a spring scale.
Another way that is not quite to accurate is to measure the current in the
motor. Current is proportional to torque.
On Wed, Sep 18, 2019 at 4:39 PM Curtis Dutton <curtd...@gmail.com> wrote:
my experiment is to use a force measuring device to proportionally control
torque output on a servo attached to a ball screw.
as a thought experiment imagine a platform hoisted by said ball screw. as
you added weight to the platform the motor torque would increase to offset
the weight and keep it steady. or you could set the required force equal to
X kgs and with less than X kgs on the platform it would travel up
proportionally. the motor would increase torque to maintain the force
value. if more force than X the platform would travel down proportionally.
the motor would decrease torque to maintain the set force value.
in effect not a position commanded but a force commanded linear actuator.
is there some othere device that would be better for this type of force
measurement? in the 0 to about 500kg range.
On Wed, Sep 18, 2019, 11:51 AM Chris Albertson <albertson.ch...@gmail.com>
wrote:
in any case, even with lower 16-bit precision, the most important part of
the design is the analog portion that sits between the load cell and the
A/D converter.
On Wed, Sep 18, 2019 at 6:38 AM Curtis Dutton <curtd...@gmail.com>
wrote:
Chris thanks for the info.
I'm not exactly certain at this point what precision I need. I'll be
determining that experimentally later. I will keep in mind what you
have
said, I'll deal with it after I get my hardware running.
On Tue, Sep 17, 2019 at 6:17 PM Chris Albertson <
albertson.ch...@gmail.com
wrote:
If you want better than 16-bits and 1KHz then you also are going to
need
a
very good quality analog signal conditioning and instrumentation
amplifier.
The analog circuit between the A/D converts and the load cell
really
does
matter. You have to reject common-mode or the low bits will
just
be
filled with 60Hz noise. And you can not simply use a "brick wall"
filter
or you will not get the desired bandwidth through. (If you are
needing
to
sample at 1K then you must care about 500Hz bandwidth.
This matters a LOT more than which A/D chip you use.
22 bits is better than one part per million. Do you really need that?
It
will be hard to isolate all of the electrical and mechanical noise
especially
On Tue, Sep 17, 2019 at 2:26 PM Curtis Dutton <curtd...@gmail.com>
wrote:
I have a pet project I'm starting that will involve reading a load
cell
in
as near as real time as possible and using that input for servo
control.
I plan on using mesa hardware to interface to the equipment. Does
anyone
know of a nice way to interface hotsmot2 to a load cell?
I would like a fairly high resolution. 16 bit minimum, the higher
the
better up to 22 bit I suppose. As well as the ability to sample at
the
servo thread rate of 1 Khz.
Thanks,
Curtis
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