Trajectory Parameters
All trajectory parameters for servo and closed-loop stepper axes are expressed in terms of quadrature encoder counts. Parameters for open-loop stepper axes are expressed in steps. For servo axes, the encoder resolution 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 driver and motor being used. For example, a stepper motor with 1.8°/step (200 steps/revolution) used in conjunction with a 10x microstep driver would have 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 is coarser.
There are two other factors that affect the way trajectory parameters are loaded to the NI motion controller versus how they are used by the trajectory generators: floating-point versus fixed-point parameter representation, and time base.
You can load some trajectory parameters as either floating-point or fixed-point values. The internal representation on the NI motion controller is always fixed-point, however. This fact is important when working with onboard variables, input, and return vectors. It also has a small effect on parameter range and resolution, as shown in the example in the Velocity in RPM topic.
The second factor is the time base. Velocity and acceleration values are loaded in counts/s, RPM, RPS/sec, steps/s, and so on—all functions of seconds or minutes. But the trajectory generators update target position at the Trajectory Update Rate, which is programmable with the Enable Axes function. This means that the range for these parameters depends on the update rate selected, as shown in the example in the Velocity in RPM topic.
RPM values stored in onboard variables are in double-precision IEEE format (f64). Refer to Onboard Variables and Input and Return Vectors, for information about the number of variables required to hold an RPM value.
NI 73xx Velocity in Counts/s or Steps/s
NI 73xx Acceleration in Counts/s2