Difference Between Stroke, Working Stroke, and Safety Stroke

When working with stroke actuators in electric linear systems, it’s essential to understand the three distinct ways of expressing stroke length. Understanding this is important when selecting the right actuator for your application and ensuring optimal performance.

Maximum Stroke:

Unless otherwise indicated, any expressions of stroke in Rollon literature should be assumed to be the maximum stroke or full range of motion possible with a given linear-motion component. Sometimes called the effective stroke, this is the total distance the carriage on an electric linear actuator can move — from one end to the other.

When discussing stroke for linear actuators with a fixed carriage and moving profile, it’s important to understand the maximum stroke. In fact, this is a design featured in a lot of Rollon’s solutions.

It’s defined as the total distance traveled by the actuator end that bears the axis end effector, spanning from its fully retracted position to its fully extended state. This measurement is crucial for determining the actuator’s range of motion and its suitability for specific applications.

Working Stroke:

The Working stroke is an important aspect of understanding stroke actuators. It’s the distance a piece of machinery needs to travel for a specific application to fulfill its intended goal.

Typically, working stroke is the stroke value that a machine builder will use in their design work and initial communications with their component suppliers.

Safety Stroke:

Always longer than the other expressions of stroke, safety stroke imparts buffer zones at each linear-axis end to protect the actuator, machine, and workpieces should the actuator overtravel and go slightly beyond the specified working stroke. Ideally, this safety stroke prevents the carriage from slamming into the physical actuator ends.

By default, Rollon engineers will define a safety stroke value by adding:

• The application’s working stroke and
• Four times the linear travel prompted by one revolution of the electric motor driving the linear axis.

For example, a linear actuator sporting a gearmotor assembly with a 25:1 ratio will have a safety-stroke value that’s only modestly different from the initial working-stroke value. While, a 3:1 ratio will have a safety-stroke value that’s a lot longer than the initial working-stroke value. This is a practical approach to setting safety stroke, as an axis fitted with a 3:1 gearmotor assembly is likely designed to move quite fast — a condition for which more safety stroke is probably warranted.

117-01 linear actuator to show working stroke.ai with CAPTION >>>> Overtravel should be prevented by setting a sufficiently conservative safety stroke.

Safety Measures and Controls:

If safety stroke is exceeded, the carriage may run into bumpers at the end of the actuator and cause damage. Bigger linear-motion systems such as Rollon robot transfer units (RTUs) feature shock absorbers at their ends to minimize the damage incurred should the axis overtravel for some reason.

Other system components such as proximity sensors and electronic controls specified by the machine builder or system integrator can guarantee the axis stays within the safety-stroke envelope.

The simplest controls, upon receipt of sensor feedback indicating overtravel, cut power when the carriage gets too close to the end of travel. More sophisticated systems include absolute encoders and electronics to prompt a preset correction routine.

Industry Best Practices:

It’s a rule of thumb to establish safety-stroke values this way. However, Rollon can adjust the safety stroke to meet specific requirements. For more information, download the Rollon white paper: Reliable linear motion.

For more information on linear systems capable of delivering a wide range of strokes, visit rollon.com. Or to enter your own application’s working stroke requirements and explore potential solutions, visit the myRollon configurator.

At Rollon, we offer numerous actuators and linear motion solutions to meet your needs. Whether you’re looking for belt-driven actuators, ball screw driven, or rack and pinion – we have solutions to meet your needs. Contact us to learn more today!