Tips to Get the Most from Your Electric Actuator

By Ryan Klemetson, Business Development Manager, Tolomatic, Inc.

With ever increasing demands to control costs while achieving high speed and high precision in industrial automation, it’s best to fully analyze a linear actuator application and precisely determine a project’s parameters. This is especially true with electric rod-style actuators because of their higher initial cost, more complex design and more predictable performance compared to fluid power cylinders.

Additional engineering and analysis at the front end of an electric actuator application will help reduce overall costs and help provide higher reliability, better performance, lower energy costs and less maintenance. Here are four tips to help you.

#1: Calculate loads precisely.

The ability of an electric rod-style actuator to perform its intended task with accuracy, speed and durability depends on matching the electric motor, the lead screw and the bearings to the anticipated loads. By knowing the precise static and dynamic loads of the application and matching them to the actuator’s peak and continuous load capabilities, the application will be both cost-effective and reliable.

#2: Calculate for electric, not fluid power (pneumatic or hydraulic).

Oversizing actuators is a habit carried over from fluid power applications in which oversizing was inexpensive insurance against not having enough power. With fluid power cylinders, the additional cost of a slightly larger bore size than required was minor compared to the extra engineering time that might be involved in sizing it correctly.

It’s common for engineers to build in a 2:1 safety factor on fluid power applications, for a variety of reasons. This includes erring on the conservative side to compensate for imprecise knowledge of the loads — fluctuations in available pressure. This margin would also be applied in anticipation of higher loads in the future because of production growth or application changes. Electric actuators can cost significantly more up front, so over-sizing is a costlier mistake and not necessary with an accurate sizing.

Avoid oversizing by properly matching the actuator to the application. Manufacturer actuator sizing software helps automate calculations with easy-to-use graphical interfaces to support proper actuator selection for the application.

#3: Know required force and velocity.

When considered together, force and velocity requirements dictate the capabilities of motors, screws and nuts in electric rod-style actuators. Relative to force and velocity, assessing these requirements properly will help avoid missteps in selecting a motor type and size.

A common error is specifying a low-cost motor, such as a stepper motor, to save money when a higher-performance solution, such as a servo motor, might be more appropriate for the velocity and force requirements. This will verify that as motor speed increases, the available torque at speed is properly aligned to the rated outputs.

Similarly, force velocity and duty-cycle requirements will dictate the type and pitch of the power screw — whether it’s an Acme screw with either composite or bronze nut, a ball screw or roller screw. By knowing the application’s precise speed duty cycle, and velocity requirements, you can specify an actuator with the proper components needed for high performance and long service life.

When the stroke of a rod-style actuator increases, so does the distance from the actuator’s support bearing. In some cases, if the distance becomes greater than the capacity the screw and bearing can handle, oscillation of the screw occurs, placing stress on the bearings. [CLICK TO ENLARGE]