Homing  

Homing

For many of the makers the word Homing is well known. But there are probably still some newcomers, they could use this information.

Usually at the starting phase of the print job you can recognise the hotend and the bed intensively bumping to their ends. There is nothing wrong or weird, just the hotend  and bed are homing. Why?

Let us explain the reason. There are no real-time location sensors in any of the printer's movable components. Their moves are managed by Stepper motors. With 1,8° of precision for every step and even more accuracy when employing micro steps, the stepper motor rotation may be controlled by firmware. Through a belt or a threaded gear, the motor shaft's rotation is transferred to the rectilinear motion.

Even though the movable part would remember its exact coordinates before the printer being turned off, homing is still necessary, because there is a chance that the user may reposition the hotend or the bed before the printer was turned back on. 

Let us compare the human with the printer. You (the printhead) must relocate to some position  of the a dark room working area(the printhead to the print) area.

What you have: You do not know, where you are. You remember the room's dimensions (X-max and Y-max coordinates in the printer's memory). You can perform accurate little steps (same as the stepper motor) in both directions.

First you move to the corner of the room which you can uniquely identify. For the printer it is usually the left end of the X axis and and back end of the bed on the Y axis.This will represent for us  the X=0, Y=0 coordinates. There are different ways how to identify the axis end (see below)

Since then the printhead reached the X=0 and Y=0, the printer starts to store the actual coordinates in the memory. During the move the old coordinates are re-wrote by the new ones.

Now you are to move to the real home position. Be aware that the print area (your working area) is always smaller than the maximum axis length at any direction.  The reason is that the printer must prevent to bump to the axis end while printing. The home position, which also represents the beginning of the print area is defined by the distance from X=0,Y=0 coordinates. This is usually measured in millimeters. The printer FW recalculates this distance to the number of the steps forward (Y axis) and to the right (x-axis) and moves the hotend and the bed those steps.

From this point you recalculate your (hotend) distance and travel the required number of X  steps and moving the bed backwards you travel the Y direction. So here you are!  

I hope, that for some people this article can be useful. 

Happy printing.