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National Instruments Corporation
6-1
6
Arc Moves
An arc move causes a coordinate space of axes to move on a circular,
spherical, or helical path. You can move two-dimensional vector spaces in
a circle only on a 2D plane. You can move a 3D vector space on a spherical
or helical path.
Each arc generated by the motion controller passes through a cubic spline
algorithm that ensures the smoothest arc. This also ensures negligible
chordal error, which is error caused when two points on the surface of the
arc join with each other using a straight line. A cubic spline algorithm
generates multiple points between every two points of the arc, ensuring
smooth motion, minimum jerk, and maximum accuracy at all times. The
data path is shown in Figure 6-1.
Figure 6-1.
Arc Move Data Path
Circular Arcs
A circular arc defines an arc in the XY plane of a 2D or 3D coordinate
space. The arc is specified by a radius, starting angle, and travel angle.
Also, like all coordinate space moves, the arc uses the values of move
constraints—maximum velocity, maximum acceleration, and maximum
deceleration.
Tip
For the NI SoftMotion Controller, the arc generation also uses acceleration jerk and
deceleration jerk while calculating the arc move.
Note
When you use an NI 73
xx
motion controller to move a motor in an arc, you can use
only trapezoidal profiles. You do not use jerk to calculate the profile for arc moves.
Cubic Spine
Arc Generation
Output to DACs or
Stepper Output
