How do you call the Z-axis mechanism in a Cartesian 3D Printer?
Linear actuator would be the proper name for the mechanism driving the movement along a single axis. There are 2 linear actuators driving the X-axis platform (for a Prusa i3 Cartesian printer, or the build platform for a raising bed Cartesian printer like a CoreXY, H-bot, etc.), the collection of parts could be named the Z-axis assembly.