Actuator sizing starts with one question: how much force does the actuator need to produce to move your guide or shifting stand reliably? The answer depends on more than just the weight on the bearings.
Roll-2-Roll Technologies uses a 6-term force model that accounts for every significant resistance the actuator must overcome:
- Bearing friction — the dominant term for heavy loads on linear bearings
- Inertia — force to accelerate the mass at your target correction rate
- Web tension lateral component — the sideways pull from web wrap angle on guide rollers
- Umbilical drag — hoses, cables, and air lines that resist carriage motion
- Floor grade — gravity component if the travel axis is not perfectly level
- Misalignment friction — additional drag from rail or bearing misalignment
Our actuator sizing calculator offers two approaches:
- Simple mode — enter load weight and bearing type for a quick estimate. Uses a factor of safety of 2.0 or higher to compensate for forces not explicitly modeled.
- Detailed mode — model all six force terms individually for a precise result, typically with a factor of safety of 1.5 to 1.75.
If you want a reality check before running the calculator, try a spring-scale pull test: attach a calibrated spring scale to the carriage and pull horizontally at a steady, slow rate. The peak reading gives you the actual installed friction force — often 2 to 5 times the catalog bearing friction value.
For a deeper walkthrough of the force model and worked examples, see the full actuator sizing technical article.