How to specify linear actuator travel?

One of the most important criteria for choosing a linear actuator is how far it needs to travel.Stroke or stroke length can determine the type of practical drive mechanism(ball screw,lead screw,rack and pinion or linear motor).Specifying the wrong stroke or travel may make your linear actuator too short to perform the required task or process.Unnecessarily long linear actuators will take up valuable space and may interfere with other components in the system.

Manufacturers use a variety of methods to specify the length of linear actuators,and knowing which method to use for a given product is crucial.The following are several ways that manufacturers specify the length of linear actuators.

●Stroke length

This is the most basic length specification.Stroke length,also known as nominal stroke or working stroke,usually refers to the working travel,that is,the distance required to perform a process or application.The travel length is usually the length between limit switches.

 

Rod-type actuators are usually provided in standard stroke lengths,such as 100,150,200 mm.While some linear actuators also offer standard stroke length,most manufacturers allow customers to specify their exact stroke length in millimeters.

●Safety travel

Also known as overrange or safety travel,this is an allowance that provides room for the linear actuator to coast to a stop in the event of an emergency stop(e-stop).The safety stroke is designed to prevent the bearing table(and load)from hitting the end of the linear actuator.

 

 

Some linear actuators contain mechanical stops or bumpers at both ends.However,unlike pneumatic linear actuators,electromechanical designs(those driven by ball screws,lead screws,racks and pinion gears,or linear motors)are not designed to repeatedly encounter hard stops.Hard stops should only be used as a fail-safe mechanism in out-of-control situations,if needed.

●Total stroke

Some manufacturers only want to know the total travel required from one end of the linear actuator to the other,and leave the allocation between the work and safety travel to the customer.This specification is less commonly used,but if the manufacturer does not provide guidelines or specifications for safe travel,they may indicate the travel of the linear actuator in terms of total stroke.

●Housing length

Because many linear actuators are made of aluminum sections cut to a certain length,the length of the housing(sometimes called the body length)is a relatively common specification.The length of the housing length is usually equal to the total stroke(working travel plus safety travel)plus the length of the bearing table.

●Overall length

Although it does not directly affect the working stroke of the linear actuator,the overall length is useful for designing the linear actuator into the system.It is usually calculated by adding the housing length(stroke length + safety stroke + bearing table length)and the end cap length.

 

●Other factors that affect linear actuator travel

External components such as bellows,cover strips,transmissions,motor mounts and motors reduce linear actuator stroke and total travel.Be sure to check these components for interference when calculating the required stroke and total stroke.

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