A home position is the reference position of a mechanical motion system. It is used to let numerically controlled machines know where the machine's parts (such as the toolhead) are in relation to the motion system's coordinate system.
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On machines using incremental encoders, a start-up procedure (so-called homing) is required to find the machine's home position at start-up [1] (the mechanical system's reference position, or origin) [2] or alternatively the machine's limitations in the x, y or z directions. A common method is to use some form of limit switch as a sensor. Examples of the use of limit switches are during start-up and operation of milling machines, [3] routers, [4] [5] robotics, [6] pick-and-place machines and 3D printers. Such a start-up procedure is not required with an absolute encoder. Regardless of whether an incremental encoder with a start-up procedure or an absolute encoder is used, knowledge of the absolute position is useful for maintaining consistent and accurate position, which provides repeatability.
Limit switches can also be used as endstops for crash detection by triggering an automatic stop when the machine has reached a physical limit. This can happen if something goes wrong with the machine that causes it to lose control of where the toolhead is and move outside of its normal working range. A limit switch then acts as a safeguard against the machine traveling too far and causing a catastrophic failure. [2]
