Chapter 4
What You Need to Know about Moves
©
National Instruments Corporation
4-7
and is constrained by acceleration/deceleration according to the following
equation:
velocity
≤
(65,536
×
deceleration) – acceleration
where velocity is in counts/sample and acceleration and deceleration are in
counts/sample
2
.
From the example, the maximum RPM is
RPM values stored in onboard variables are in double-precision IEEE
format (f64).
NI 73
xx
Velocity in Counts/s or Steps/s
Velocity values in counts/s or steps/s are also converted to the internal
16.16 fixed-point format in units of counts or steps per sample (update)
period before being used by the trajectory generator. Although the motion
controller can control velocity to 1/65,536 of a count or step per sample, it
is impossible to load a value that small with the Load Velocity function, as
shown in the following formula:
where
Vmin
= 1/65,536 counts/sample or steps/sample
Ts
= sample period in seconds per sample
Even at the fastest update rate,
Ts
= 62.5
×
10
–6
The Load Velocity function takes an integer input with a minimum value of
1 count/s or step/s. You cannot load fractional values. If you need to load a
velocity slower than one count or step per second, use the Load Velocity
in RPM function.
20 10
6
×
(
)
60
1
2,000
-------------
×
×
600,000 RPM
=
Velocity in counts or steps/s
Vmin
1
Ts
-----
×
=
1
65,536
----------------
1
62.5 10
6
–
×
---------------------------
×
0.244 counts or steps/s
=
