How to calculate the "SPU (Steps Per Unit)" axis parameter?

Last modified by writer on 2024/02/28 16:48

STEPs are usually considered formulas:

To calculate the STEP of the rack:To calculate the STEP ball screw:
STEP = (full revolutions count of motor * microstep) / π * rail module * count of teeth in a gear)STEP = (number of complete steps per revolution * microstep) / screw pitch
Where to find parameters
  • full revolutions count of motor: specified in the motor passport;
  • microstep: set by driver settings;
  • π: Pi (~ 3.14);
  • rail module: the parameter can be found in the technical documentation of the rail;
  • count of teeth in a gear: the parameter is indicated in the product passport;
  • count of full steps per turn: the parameter can be found in the motor passport;
  • screw pitch: the parameter is indicated in the technical documentation of the passport.

PUMOTIX version 3.2.4 introduces the axis "Calibration Wizard" window, which helps to calculate STEP using custom measurements.

To calculate, go to "Configuration" → "Calibration Wizard" (with the controller selected and the machine turned on):

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  1. Select the axis to be calibrated (i.e. the axis you want to calibrate).
  2. Enter the speed of movement along the selected axis.
  3. Enter the specified travel distance (this is the distance the selected axis will move; it is preferable to specify round, whole numbers to simplify measurements).
    The window also contains a display of the current number of STEP signals (the parameter is given for information).1709117286806-215.png
  4. Click on the "Run" button to move the selected axis to the previously specified distance and previously specified speed.
    As soon as the movement is completed, the right side of the "Calibration Wizard" window is activated (Stage 2).
    1709117273846-740.png
  5. Now it is necessary to measure the crossing distance as accurately as possible and enter the result into the "Measured distance" parameter (to make changes, then press the "Enter" button on the keyboard).
    The new recalculated STEP value is displayed in the "Steps Per Unit calculated" parameter.

To complete the calibration, press the "Apply New Settings" button.

For a more accurate calibration of the axes, it is desirable:

  1. Specify movement distance along the entire available axis length.
  2. Make several calibrations with different movement distances.