By Randy Bowman, Market Manager – TECHLINE™ Div., LINAK
Crystal McGrew, Marketing Communications
If you’ve not looked at electric linear actuators lately, you may be missing out. Today’s electric linear actuators exemplify mechatronic principles as well as offer more power than earlier versions, with advances in other features including force and load capabilities, and control.
Rapid technological advances and changes in environmental, safety and ergonomic requirements have increased the options and capabilities available in motion control systems. Despite these advances, though, the temptation to stay with previous choices can be strong. In some industries, there are biases toward certain motion systems, either because of limited knowledge about alternatives or because of precedent. For example, hydraulic powered motion is traditionally the standard in the agriculture industry, pneumatics in certain process industries, and highprecision stepper motors and linear guides in automation. However, motion industry advances have made it necessary for companies and engineers to re-evaluate current choices and biases, and make an educated decision as to what may be the best overall option for the application.
Whether you are re-evaluating or staying with what has worked, knowing your system requirements is the first step needed to make your selection. The basic motion requirements for an application remain the same across most industries. While this list is not exhaustive, the following can help begin the research and decision process:
Load/force requirements, travel distance (stroke length), electrical power requirements
Speed requirements, environmental conditions, ruggedness, noise level, accuracy/repeatability, product lifetime, duty cycle
Failure mode evaluation, ergonomic factors/requirements, operator and maintenance safety, certifications, environmental impact
Feedback requirements, positioning, system complexity
Total system costs, lifetime maintenance costs, lost revenue from downtime, installation costs, space requirements, and energy consumption.
After you have determined needed requirements, then it’s on to the analysis phase.
One motion approach that is on the increase is the use of electric actuators for new and replacement applications that used hydraulics, pneumatics, stepper motors and manual operation. The main reason for the growth of electric linear actuators is their substantial development over the last decade. There have been advances in force and load capabilities, ruggedness, speed, duty cycle, control, and other key factors. These developments are helping to overcome misconceptions about the limitations of electric actuators.
Examples of how electric linear actuators compare to alternative motion solutions can best be shown through comparison of some aspects of the basic motion requirements areas.
1. Technical specifications:
Today’s electric linear actuators are strong, fast, and rugged. Many can be configured to lift loads in excess of 2200 lb, with some actuators able to lift significantly more. New designs, stronger components, and advances in manufacturing techniques allow developers to gradually increase the maximum load capabilities of each product. Thus, in applications that require high load capacities, electric actuators can be chosen as an alternative to hydraulics.
More electric actuators offer longer travel distances (stroke length) in the range of 48 to 60 in. Examples include RV slide-outs or electrically powered bollards.
In earlier versions of electric actuators, power input options were limited to 12 V and 24 Vdc. Newer configurations use 36 V and even 48 Vdc power. These versions suit applications needing higher voltage and lower amperage combinations, such as electric/hybrid mowers, fork trucks and utility vehicles.
2. Performance specifications:
Speed is a key requirement in many applications. While electric linear actuators may not approach the top speeds of some pneumatics or hydraulics, constant improvements now allow for speeds of six inches per second or more.
Newer electric linear actuators are designed for rugged environments. They are made from corrosion resistant materials. Improvements in seal design prevent moisture and dust from entering the housing. You will find these actuators in agriculture applications such as combine harvesters and fertilizer spreaders, as well as indoor applications exposed to cleaning solvents found in food processing. Robust designs readily withstand vibration, shock and extreme hot and cold temperatures and can sustain long lifetimes in such environments.
Even for applications that demand precise motion, electric linear actuators can offer precision with many types of feedback including analog potentiometers as well as digital Reed and Hall
Effect signals. They can provide a sufficient degree of precision to meet the requirements of many applications at a lower system cost.
Noise level is sometimes overlooked as a criterion for a motion control system. Not every linear actuator is designed for quiet operation. However, some designs are very quiet while moving large loads. Medical applications and powered furniture, such as recliners and beds, need quiet motion, but industrial applications, such as laboratory ventilation, may also require low noise levels and can use electric actuators.
3. Safety needs:
Safety is a high priority in any application. Once power is removed, the electric actuator does not move and integral braking systems lock the load in position so it does not drift.
Personnel safety cannot be addressed properly without a look at long-term injuries occurring from poor ergonomics. Recent trends show a need to address diversity in industrial applications; for example, workstations that adjust from the 5 ft-3 in. first shift employee to the 6 ft-3 in. second shift employee. Attention to the motion required in this application can pay dividends and provide a return on investment in improved worker performance, attendance, and moral. In addition, worker compensation costs from repetitive strain injuries can be reduced simply because electric actuators allow employees to adjust the position of the work surface to meet their needs.
Many companies are looking into the effects motion systems have on environmental safety. The option of not having to deal with potential leaks from hydraulic systems is increasingly a factor in the choice of motion system.
4. Control Specifications:
In the motion control market, there is a misconception that control systems for linear actuators are particularly complex. In fact, many times they are less complex than alternative systems requiring the same level of control and communication.
The level of complexity of electric actuator control systems is diverse and can range from a simple toggle switch to raise and lower a snowplow, to a sophisticated control system involving multiple actuators in a factory automation setting.
Many of today’s electric actuators follow a mechatronic design with integrated electronics. They offer a level of control and information feedback never before seen; and while positioning feedback has long been a feature of linear actuators, even more information can be provided from the actuator to the control system. In many cases, this information can be custom configured to the needs of the application and the desires of the manufacturer and end-user.
5. Economic Factors:
In the design phase of a system, adding a cylinder is not necessarily less expensive than adding an actuator. The total cost of a motion system should include the cost of hardware, control devices, mounting, fluids, protection for hoses, as well as labor costs incurred in the assembly and installation, plus the final system leak checks and repairs that occur with a hydraulic or pneumatic system. Close examination can show that these additional costs are low, or non-existent, with an electric linear actuator system.
Another economic factor to consider is the after-the-sale costs to the end user. These costs include maintenance, downtime, total power consumption and consumable replacement parts. The product with lower lifetime costs can have an advantage.
Most electric actuators are maintenance free and installed by inserting mounting pins and plugging in a connector. And electric linear actuators only consume power when in operation.
Finally, don’t overlook the space required for a motion control system when evaluating electric systems. Generally speaking, electric systems require less overall space.
The diversity of electric linear actuators available in the motion control industry reflect the diverse needs of each application in motion control. Few applications are identical and there is no one motion control system for every application. However, it is clear that alternatives to traditional solutions do exist.
LINAK U.S. Inc.
1. Consortium for Energy Efficiency, Inc., Motor Decisions Matter Energy Efficiency/Usage Fact Sheet,
2. Average US energy rate, 2007, according to Energy Information Administration, www.eia.doe.gov