When engineers use rotary-stepper-driven axes instead of linear stepper motors wholesale, they face a different set of design considerations. For starters, the engineer must pick the leadscrew’s lead and pitch. Lead defines the distance a screw thread advances in one revolution. Pitch is the distance between adjacent threads. A small lead with more threads per inch outputs higher force and resolution; large leads (or fewer threads) output lower force but higher speed.

Screws also have their own inertia. In setups where the motor body houses the screw-engaging nut, this inertia increases as the screw extends … which in turn reduces maximum design speed. In fact, it’s fairly common for stepper-driven leadscrews to have embedded drive nuts. Even where the setup takes a more traditional arrangement—with the nut outside the motor, and fixed to rails that bear the loads the axis advances—nut material selection is another design consideration. Engineers must ask: will this axis experience heat and the effects of friction? Plastic exhibits low friction but cannot withstand high heat; bronze nuts resist heat but have a high coefficient of friction.

One final note on rotary-stepper-driven axes: Because these Linear Actuator incorporate mechanical components, they exhibit wear and life limitations. That said, when engineers properly size for the load and create a forgiving operating environment (with low humidity, protection from harsh chemicals and dirt, and controlled temperature) rotary-stepper-driven exhibit long life—to millions of cycles.

Different ways of stepper motors going into linear actuators