National Instruments NI-Motion - Manual (Page 52)

Chapter 4 What You Need to Know about Moves
© National Instruments Corporation 4-11 NI-Motion User Manual
You can calculate the maximum RPS/s using the following equation:
where Amax = 32 counts/sample 2
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:
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%.
Note The conversion from floating-point to fixed-point is performed on the host
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%.
maximum RPS/s Amax
1
Ts
-----
 
 
2
×
1
R
---
 
 
×
=
MAX
1
r
--- ×
32
1
250 µs
---------------
 
  2 1
2000
------------
Ч Ч 256,000 RPS/s =