Home Sensor Detection has been an issue at times The Die direction is chosen based on the initial state of the home sensor and up until now, the search for the home sensor was based on its current state rather than the expected transition.

The problem this change solves is to better deal with home sensors that have a small position sensing window. If the Referencing Velocity is too high or the acceleration is too low, the die can coast beyond the sensor and turn back off. This violated an assumption that was critical to the Homing Algorithm operation.

For example, if the die was returning to the home sensor and the sensor turned ON, the die would stop. If the die coasted beyond the sensor, the next move to move forward off the sensor would terminate before any move took place, because the sensor was already OFF. The next move, looking for an ON would then reverse the die into the overtravel’s looking for an ON state that was never going to come.

Now that we have changed the routine to look for a specific transition, ON to OFF or OFF to ON, the prior example will no longer be a problem. The die will return home looking for an OFF to ON transition, which it will find. Even though the die has coasted beyond the sensor, when it moves forward it will be looking for an ON to OFF transition. It will move forward until it see the OFF to ON transition and continue moving until the ON to OFF transition occurs.

Higher Referencing speeds and lower accelerations may now be used, and the homing routine can still function correctly, provided the die does not coast into an overtravel.

There is a limit to this new method. The home sensor inputs are debounced at 20msec. In order for the new routine to work properly, when searching for the home sensor, the sensor must be ON or OFF for a minimum of 20msec or the transitions may not be sensed.