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.
Floating-Point versus Fixed-Point Parameters
On NI 73xx motion controllers, 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.
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 73xx Move Constraint Values
The following sections define the minimum and maximum values for move constraints as well as additional information about the resolution of the velocity override value and arc angle. Velocity and acceleration values are loaded in counts/s, RPM, RPS/s, steps/s, and so on, which are all functions of seconds or minutes. However, the trajectory generator updates target position at the Trajectory Update Rate, which is programmable with the Enable Axes VI or function. This means that the range for these parameters depends on the update rate selected.
NI 73xx Velocity in Counts/s or Steps/s
NI 73xx Acceleration in Counts/s2