Ball Screw Servo Motors for Compact Linear Motion
A ball screw servo motor is an AC servo motor with a ball screw built onto the output shaft, so the motor turns its rotation straight into linear thrust. The servo runs closed-loop — an absolute encoder reports rotor position to the drive every cycle — so the screw drives to an exact position and holds it under load. Building the screw onto the shaft keeps the unit short and removes the coupling and alignment a separate motor-and-screw build needs. We make these on 40 mm, 60 mm and 80 mm servo motor frames, from 100 W to 1 kW, with the screw matched to your axial load, stroke and speed.
How a Ball Screw Servo Motor Works
The servo rotor turns the screw shaft, and a ball nut packed with recirculating ball bearings rides the thread and travels along it in a straight line. Rolling contact keeps friction low, so most of the motor torque reaches the load and the screw runs efficiently with little heat. Thrust and linear speed come from the screw lead: a short lead multiplies force and gives finer resolution, a long lead trades force for speed. Because the loop is closed on an absolute encoder, the axis corrects position continuously and keeps accuracy across the speed range.
Ball Screw or Lead Screw — Which to Specify
Both screw types mount on the same servo frames. The pick comes down to load, speed, duty cycle and whether the axis has to hold position with power off.
| Feature | Ball Screw | Lead Screw |
|---|
| Friction & efficiency | Recirculating balls, high efficiency | Sliding nut, lower efficiency |
| Axial load & speed | Heavier loads, higher speed | Light to medium load, lower speed |
| Repeatability & life | Tight repeatability, long life | Moderate, shorter life |
| Holding with power off | Back-drives, needs a brake on vertical axes | Self-locking, holds position |
| Noise | Higher | Quieter |
| Relative cost | Higher | Lower |
| Best for | CNC feed axes, high duty, fast moves | Light, vertical or low-duty axes |
Run hard, move fast or need micron-level repeatability — go ball screw. Light, vertical, intermittent or cost-driven — a lead screw is the simpler choice.
Sizing the Motor to Your Screw and Load
Matching the servo to the screw and load is what keeps the axis stable and the motor cool. Work through these before locking a frame:
- Continuous torque has to clear friction torque plus average load torque, or the motor overheats on long runs.
- Peak torque has to cover acceleration — total inertia times your acceleration rate — plus any load spike at startup.
- Keep reflected load inertia within about ten times the rotor inertia; a lower ratio gives faster, steadier response.
- Confirm the motor’s top speed clears the screw rpm your linear speed and lead demand.
- Check the screw’s critical speed — long, thin screws whip at speed, so root diameter, support length and end fixity matter.
Send us the numbers and we size the frame and recommend the lead, so the motor and screw work as a matched set instead of a guess.
Typical Applications
Ball screw servo motors fit axes that need controlled thrust and accurate positioning in a short body:
- CNC feed axes and machine-tool slides — repeatable positioning under cutting load.
- Electric cylinders and servo presses replacing pneumatics — controlled force and position.
- Pick-and-place and gantry Z-axes — fast, repeatable vertical moves.
- Precision dispensing, dosing and metering — exact thrust at low speed.
- Semiconductor, packaging and assembly stages — clean, quiet, repeatable motion.
- Test and measurement rigs — accurate, programmable travel.
Integrated Screw or a Servo Coupled to Your Screw
An integrated screw servo carries the screw on the motor shaft, which shortens the package, cuts part count and removes the coupling that can misalign and rob a coupled build of rigidity and accuracy. A servo coupled to a separate screw is easier to service and lets you swap the screw without touching the motor, at the cost of length and an alignment step. We build it either way: an integrated unit when space and rigidity drive the design, or a standard servo with a matched servo drive when you are driving a screw you already have.
What We Need to Quote
To match a motor and screw to your axis, send the axial thrust or moving mass, the stroke, the linear speed and the duty cycle. Add the mounting orientation, the positioning accuracy you are targeting and the working environment. From there we set the frame size, recommend ball or lead screw and the lead, and confirm whether a power-off brake is needed for a vertical axis. For lighter or cost-driven linear axes, a closed-loop stepper motor can also do the job, and we will say so when it is the better fit.