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The conversion from floating-point to fixed-point is performed on the host
Note
computer, not on the motion controller. To load velocity override from an onboard variable,
you must use the integer representation of 0 to 384, where 384 corresponds to 150%.
© National Instruments Corporation
You can calculate the maximum RPS/s using the following equation:
maximum RPS/s
where
Amax = 32 counts/sample
Ts = sample period in seconds per sample
R = counts or steps per revolution
and is constrained according to the following equations:
acceleration ≤ 256 × deceleration
deceleration ≤ 65536 × acceleration
or
For a typical servo axis with 2,000 counts or steps per revolution operating
at the 250 µs update rate, calculate the maximum RPS/s increment using the
following equation:
×
32
RPS/s values stored in onboard variables are in double-precision
IEEE format (f64).
NI 73xx
Velocity Override in Percent
The Load Velocity Override function takes a single-precision
floating-point (f32) data value from 0 to 150%, but velocity override is
internally implemented as a velocity scale factor of 0 to 384 with an
implicit fixed denominator of 256. NI-Motion uses the velocity override to
increase the speed of the calculation for the sake of calculation speed—the
division is a shift right by eight bits. The resolution for velocity override is
therefore limited to 1/256, or about 0.39%.
Chapter 4
×
Amax
=
2
1
×
MAX
-- -
r
2
1
1
×
256,000 RPS/s
-------------- -
----------- -
=
250µs
2000
4-11
What You Need to Know about Moves
2
1
1
×
---- -
-- -
Ts
R
NI-Motion User Manual
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