Chapter 4
What You Need to Know about Moves
4-4
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grouping axes into coordinate spaces. Using a multi-start automatically
starts all axes virtually simultaneously. To simultaneously end the moves,
you must calculate the move constraints to end travel at the same time. In
coordinate spaces, this behavior is calculated automatically.
Trajectory Parameters
Use trajectory parameters to control the moves you program in NI-Motion.
All trajectory parameters for servo axes are expressed in terms of
quadrature encoder counts. Parameters for open-loop and closed-loop
stepper axes are expressed in steps. For servo axes, the encoder resolution,
which is expressed in counts per revolution, determines the ultimate
positional resolution of the axis.
For stepper axes, the number of steps per revolution depends upon the type
of stepper drive and motor you are using. For example, a stepper motor with
1.8°/step (200 steps/revolution) used in conjunction with a 10X microstep
drive has an effective resolution of 2,000 steps per revolution. Resolution
on closed-loop stepper axes is limited to the steps per revolution or encoder
counts per revolution, whichever value is more coarse.
Floating-point versus fixed-point parameter representation and time base
are two additional factors that affect the way trajectory parameters are
loaded to the NI motion controller as compared to how they are used by the
trajectory generators.
The NI SoftMotion Controller uses a 64-bit floating point trajectory
generator. The ranges for all move constraints are the full 64-bit range,
which includes maximum velocity, maximum acceleration, maximum
deceleration, maximum acceleration jerk, maximum deceleration jerk, and
velocity override percentage. All arc parameters that use floating point also
support the full 64-bit floating point range.
NI 73
xx
Floating-Point versus Fixed-Point
Note
The information in this section applies only to NI 73
xx
motion controllers. These
restrictions are not applicable to the NI SoftMotion Controller.
You can load some trajectory parameters as either floating-point or
fixed-point values, but the internal representation on the NI motion
controller is always fixed-point. You must consider this functionality when
working with onboard variables, inputs, and return vectors. This
functionality also has a small effect on parameter range and resolution.
