Linear Actuator and Slide Overtravel Recommendations
When specifying a linear slide or linear actuator, the length of stroke is important. 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.
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
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.
View this PDF for a full explanation of length, stroke, and overtravel calculations for actuators and linear slides. Be sure to take into account all application details when specifying the stroke, including possible future expansion of the equipment’s capabilities that could require longer strokes thus eliminating the useable overtravel safety zone.