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Calculating Actuator Length and Slide Overtravel
Calculating Actuator Length and Slide Overtravel

Calculating Actuator Length and Slide Overtravel

When calculating the length of a linear actuator, there are a couple of approaches to take, depending on the information that is available to you. If you know the overall actuator length, you can subtract component lengths to reach the stroke limit for a given size. Or if you know the stroke, you can add the component lengths to find the resulting overall actuator length.

Just as important is the amount of space that is between the carriage and the end blocks when reaching the end of that stroke. This additional space is commonly known as “overtravel”. This should be considered a safety zone or the distance to safely stop the carriage on the actuator. Several factors affect the distance required to safely stop the carriage, including drive methods, screw, belt, etc., speed requirements, and the position of the end of travel sensors all need to be considered in determining the length of acceptable overtravel.

Diagram for calculating actuator length

PBC Linear recommends the following “minimum” guidelines for overtravel at each end of the stroke, dependent on how the system is being driven.

  • Knob or Hand Crank = 5mm each end
  • Stepper Motor = 10mm each end
  • Servo Motor = 25mm each end
Diagram for calculating actuator overtravel

Leaving this extra space or “safety zone” can alleviate potential problems. For example, the possibility of a crash situation where the carriage runs into the end plate resulting in damage to the drive nut or other drive mechanisms is minimized. Some drive types will experience increased friction at the ends of stroke that can be eliminated by building in the overtravel allowance. Finally, consistent performance over the life a system can be obtained by eliminating these stresses when maintaining the clearance that overtravel provides.

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