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.
Note. The position control of the revolution sensor can't detect the shaft rotation at the zero speed, i.e., if the motor is shut down and the shaft is rotated manually, it won't be detected.