4.3.7. Steps loss detection
This mode is generally used while operating the stepper motor at full speed or limit loads when the shaft jam resulting to the steps loss
is possible. In this case an additional position sensor (revolution sensor) or encoder allows tracking this moment, informing the user
about it. This feature should be applied with stepper motors only and it allows detection of the steps loss. Steps and microsteps are
the measurement units for all coordinates and shaft positions.
When the encoder is used, the controller stores both number of steps and number of encoder's counts per revolution (see the Settings
of kinematics folder of XiLab program). When the feature is activated, the controller saves the current position in steps of the motor
and the current position according to the encoder data. Then, during the motion, the position data according to the encoder converts
to steps and if the difference exceeds the predefined value then the slippage is indicated and the Alarm mode turns on (if the related
option is active). For more information regarding use of encoder as the steps loss detector please refer to Operation with encoders
chapter.
If the revolution sensor is used, the position is controlled according to it. The controller stores the current position in steps according to
active and inactive edges at the sensor's input. Then, at every revolution (number of steps per one full revolution is set by Steps per
turn parameter, see the Settings of kinematics (Stepper motor) chapter) the controller checks if the shaft has been displaced and how
many steps for. If the mismatch exceeds the predefined Threshold value (which is defined in position control settings, see the Position
control chapter), the slippage is indicated by the state structure flag. If the appropriate flag is set and if the error is detected, the
controller turns the Alarm mode on and the motor shuts down, otherwise the motion is continued. If the slippage indication flag is
active, the controller turns the Alarm mode on when the appropriate parameter in the settings is active.
Also you can enable the position correction option in the position control settings. If this option is enabled and the steps loss is
detected the controller stops the movement, adjust the step position on the basis of the encoder data and try to start the movement
again. The flag of the control position error The position control error flag is set when the desynchronization of the steps and the
encoder position is detected and it will be unset automatically when the position becomes corrected. If the controller is not able to
eliminate the desynchronization the controller is set the position control error flag and goes to the Alarm mode. If the steps loss
happens during the movement the movement command status will not be changed while the position is correcting. If the steps loss
happens during holding a position the move to position command will be executed for return the motor axis to the holding position.
Note. For using the position correction function you should have the encoder with the resolution at least two counts
per the motor step.
Note. For correct operation of the position correction option you should let the controller to hold the position during 1
second for calibration before moving. It necessary to repeat the calibration after the transition to the Alarm mode or
after changing the settings.
Note. If the automatically position correction is used it is not recommend to set the Threshold value above than 3
steps because in this case not any slippage will be corrected.
Note. The soft stop and the hard stop commands could be ignored by the controller if it was sent during position
correction process. In this case you can send the soft stop command twice for power off the motor windings.
Note. If you use the software limit switches it is not recommend to use the automatic position correction because the
limit switches positions will be changed during position correction process.
Note. A hard STOP launches the the re-calibration process of the revolution sensor position, and the calibration starts
after the revolution sensor activates during the motion controlled by the motor. It means that the slippage won't be
detected if the shaft has been rotated manually right after the hard stop since the calibration hasn't been performed
yet.
Note. If the motor revolution sensor is bouncing (mechanically), the misoperations of the revolution sensor are
possible at the very low speeds.
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