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Getting Started with NI 9501 Modules and NI SoftMotion
Synchronization Loop
The Synchronization Loop synchronizes the FPGA clock (slave) to the RT clock (master) to
correct for drift and jitter. This is the preferred synchronization method to use with the
NI SoftMotion Module. Figure 11 shows the Synchronization Loop from the Stepper Drive
(Getting Started) example.
Figure 11.
Stepper Drive (Getting Started) Synchronization Loop
The Synchronization Loop is required to be implemented as-is for proper operation. Refer to the
Synchronization VIs
section of the
NI SoftMotion Module Help
for more information.
Position Loop and Step Generation Loop
The Axis 1.Position Setpoint UDV is used in the Position Loop. Figure 12 shows the Position
Loop from the Stepper Drive (Getting Started) example.
Figure 12.
Stepper Drive (Getting Started) Position Loop
The Position Loop receives position setpoints from the NI SoftMotion trajectory generator and
uses the Spline Interpolation VI to generate intermediate setpoints, resulting in smoother motion.
The Position Loop receives input from the Synchronization Loop as well as timing information
calculated by the NI SoftMotion Engine. This timing information is provided to divide down the
Scan Clock evenly to run the position loop at the user-specified stepper
Position Loop Period
.
1
NI SoftMotion Scan - Generate Sync Scan Synchronization VI
1
Synchronization Inputs
2
NI SoftMotion Scan - Loop Timer VI
3
Spline Configuration Information from NI SoftMotion
4
Axis 1.Position Setpoint UDV
5
Spline Interpolation Motor Control VI
1
1
2
3
4
5
