Posted Jul 15, 2020 9:53:27 AM

From industrial and materials handling systems to agricultural machinery and military/naval operations, many different industries and applications rely on the power of linear actuators. Since they offer unparalleled mechanical performance in moving loads in a straight line, linear actuators are literally driving these industries forward. As these applications evolve and get more advancement, so must the linear actuators that power them. That’s why design engineers are looking for superior actuators to power their systems.

Fueled by the advancement of microprocessor technology and the miniaturization of electronics, one type of linear actuator is becoming more and more prominent: the electromechanical actuator (EMA). Contrary to the cost prohibitive actuators of the past, electromechanical actuators are now a viable and cost-effective alternative to pneumatic and hydraulic driven linear motion systems. Compared to pneumatic and hydraulic systems, electromechanical actuators offer:

  • Smaller, lighter, and cleaner designs
  • Easier and quicker installations
  • Easy integration with modern PLCs and computers
  • Fewer maintenance requirements

EMAs are an especially attractive option for applications that require a high degree of accuracy, reliability, and programmability. They allow system designers to move heavy loads at high speeds with an unmatched degree of precision.

Like all integral pieces of technology, EMAs need to be properly specified for a system if you want to optimize their performance. In order to help design engineers specify the right EMA for their specific application, the experts at Hunt Valve Actuator Division have detailed out the considerations necessary to ensure proper actuator selection.

Define the Operational Parameters

Every solution starts with a problem. No matter whether you are working with a new build or replacing an old hydraulic or pneumatic actuator, you need to establish the specific needs of the application.

To define the operational parameters of a system, application engineers must analyze the key characteristics of the task at hand. Thankfully, with linear actuators, the work is relatively straightforward – moving a load from one location to another. However, to fully understand that journey, the following must be taken into account:

  • The weight of the load
  • The speed that the load must move at
  • The stroke, or how far the load must move
  • The force required to move the load across that distance
  • Dwell time, or how often the system will be inactive
  • Total cycle time
With all of this information, the goal is to calculate the number of cycles per day and be able to size a unit that can achieve that frequency for however long an application requires. Even with a seemingly simplest application, not having this data can cause a unit to be incorrectly sized, leading to premature failure.

These are the main items that engineers need to define, though more complex applications will require further considerations. This may involve designing a “move profile” that details the application’s speeds and loads in a table or graph. Additional factors may include:

  • Dimensional or envelope constraints
  • Available power supply
  • Mounting considerations
  • The environment the actuator will operate in 

Pick the Right Type of Electromechanical Actuator

Once your operational parameters are defined, you can use that information to help choose the right electromechanical actuator for the job. While every EMA will transform rotational movement of the device’s electric motor into linear motion, different EMA styles will offer different advantages and limitations based on the application that it’s used in.

Most EMAs can be classified as one of two main types: ram-style and rod-less.

Ram-Style EMAs

Ram-style EMAs are best suited for handling heavy loads in harsh environments, all while still offering a high degree of accuracy and reliability. In these units, a motor is used to turn a threaded screw, which causes a nut to translate along the length of the screw, causing the inner ram to move in and out of the actuator housing. Rod seals keep particulate from entering the actuator as the inner ram retracts. While mounting options vary, ram style actuators lend themselves to applications where loads are being pivoted or tipped. Generally, ram-style actuators are used when loads are in-line with the unit, allowing slightly higher tolerance to inertial loading and offering the flexibility to move loads quickly over shorter distances while maintaining performance.

Since the ram-style design doesn’t offer any support for the rod once it’s outside of the actuator housing, this limits the capabilities of the stroke length. Internal bushings help guide and support the ram, but applications with high side-loading (loads perpendicular to the motion of the actuator) will require additional support. Extremely long, unsupported, strokes may also negatively impact both the maximum travel speed and the column loading of the rod and screw, potentially resulting in whipping and buckling, respectively.

Rod-less EMAs

When applications require a longer stroke length, that’s where rod-less EMAs come in. There are two different variations of rod-less actuators: screw driven and belt driven.

For screw driven rod-less EMAs, a motor drives the screw, causing a mating nut/mounting carriage to travel down the length of the screw. These types of actuators are typically used in systems that require moving loads with a high degree of accuracy and reliability at higher speeds for longer strokes by using strategically placed supports keep the screw from whipping. This comes at a cost however, while there is generally good environmental protection, the unit itself is not completely sealed and this may allow unwanted particulate to enter the drive system.

Belt driven rod-less EMAs use a motor’s rotational energy to turn a pulley that drives a carriage attached to a timing belt. Compared to screw driven units, a belt system can travel at the highest speeds over longer stroke lengths.

Better EMAs at Hunt Valve

For decades, Hunt Valve has built a strong reputation as a reliable supplier of heavy-duty valves for harsh and rugged environments. The Actuator Division of Hunt Valve continues on this legacy of reliable and innovative products by offering the industry’s best electromechanical actuators.

Whether you need one of our standard, off-the-shelf electromechanical actuators or a customized system, the expert team at Hunt Valve Actuator Division can design and create the perfect solution for your specific needs.

If you want to learn more about how to select the right EMA for your application and see a more detailed breakdown of each type of EMA, read our white paper on How to Select the Appropriate Electromechanical Actuator.

 

Read the White Paper