Stepper Settings

Use the Stepper Settings tab to configure settings for stepper motors.

Tip  Refer to Resource Allocation for information about using multiple resources on NI motion controllers.

Stepper steps per revolution

Steps can be full steps, half steps, or microsteps depending upon how you have the external stepper driver and motor configured.

Closed-loop stepper functionality relies on the ratio of counts to steps and not on the absolute values of counts or steps per revolution. For closed-loop operation, any unit of measure (UOM) that allows you to enter both counts per UOM and steps per UOM that are within their valid ranges work.

Caution  For closed-loop stepper controllers, steps per revolution/counts per revolution must be in the range of 1/32,767 < steps/counts < 32,767.

Stepper Loop Mode

You can operate stepper axes in both open-loop and closed-loop modes. In open-loop mode, the stepper axis controls the trajectory profile and generates steps but has no feedback from the motor or actuator to determine if the profile is followed correctly.

In closed-loop mode, the feedback position is constantly compared to the number of steps generated to see if the stepper motor is moving correctly. When the trajectory profile is complete, missing steps (if any) are made up with a pull-in move. If, at any time during the move, the difference between the instantaneous commanded position and the feedback position exceeds the programmed following error threshold, the axis is killed and motion stops.

You use p-command mode for systems in which a servo drive receives step/dir (CW/CCW) from the motion controller. The drive closes the PID loop, and the motion controller provides the trajectory generation. Any time you use the axis in p-command mode and the axis goes from a kill state to a halt state, it is recommended to reset the axis position to synchronize the encoder and the step generation with the drive. Like in closed-loop mode, in p-command mode the axis trips on following error.

Note  P-command mode does not use pull-in moves.

Caution  For proper closed-loop and p-command operation, steps per revolution/counts per revolution must be in the range of 1/32,767 < steps/counts < 32,767. An incorrect counts to steps ratio can result in failure to reach the target position and erroneous closed-loop stepper operation.

To operate in closed-loop or p-command mode a stepper axis must have a primary feedback resource mapped to it prior to enabling the axis. Set these values on the Axis Configuration tab. You can operate an axis with a primary feedback resource in open-loop, closed-loop, or p-command mode and you can switch the mode at any time. You can still read the position of the mapped feedback resource even when the axis is in open-loop mode.

Stepper Polarity

Set stepper active polarity for active low or active high. For example, if the axis is configured for Step & Direction output mode, the stepper polarity determines whether a high direction output is forward or reverse. The polarity also determines the resting states of outputs when they are not pulsing. When configured as active low, the output is active when there is a low signal on the output pin. Conversely, active high means that the output is active when there is a high signal on the output pin.

You may need to change this setting so that the controller output matches the expected drive physical input.

Set Stepper Output Mode

NI-Motion supports the two industry standards for stepper control outputs. The most popular mode is Step & Direction, where one output produces the step pulses and the other output produces a direction signal.

In Clockwise/Counterclockwise (CW/CCW) mode, the first output produces pulses when moving forward, or CW, while the second output produces pulses when moving reverse, or CCW.

For the 7350 controller, you can set the stepper output Drive Mode to Open Collector or Totem Pole. On the 7330/40, stepper output is Open Collector and cannot be changed. On the 7390, stepper output is isolated so Drive Mode does not apply and the option is not selected and cannot be changed. For more information about Open Collector and Totem Pole drive modes, refer to the documentation for your 7350 device.