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Bonus: Heavy-duty electric actuation in off-highway applications

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In a recent three-part series, we outlined how screw-based and other types of electric actuation increasingly finds use in today’s presses and other machine tools.

Part 1 of 3: Heavy-duty electric actuation — in presses
Part 2 of 3: Heavy-duty electric actuation — to replace hydraulics
Part 3 of 3: Heavy-duty electric actuation — on large-scale gantries

Off-highway equipment is also making copious use of screw-based electric actuation. In fact, electric actuators have sometimes replaced fluid power-based actuators on off-highway or other equipment where the axes are linear. This is because electromechanical systems consume energy only when moving an axis, resulting in an average efficiency of 82% in converting input power into output work. In contrast, hydraulics typically have an end-to-end efficiency of only 45% or so. Plus, utility electricity is generally cheaper than fossil fuels.

Related: Linear actuators power mobile machinery

This is a Schaeffler Ewellix EMA 100 actuator to replace hydraulic cylinders. Maximum forces reach 60 kN with the ballscrew version and 82 kN with the roller-screw version. Efficient electric motors with holding brakes are standard, and adapters allow motors from other manufacturers. The gear unit is flanged between actuator and motor for either a spur gear or belt drive; motors can also directly mount to the mechanical screw drive.

As evidenced by exhibits at this year’s ConExpo, there’s an increasingly wide array of stock ballscrew and roller-screw electromechanical actuators for heavy lifting applications. Certain actuators capable of multiple tons of force are targeted to heavy lifting applications. Developed for construction, agricultural machinery, and automation applications, those with a modular design let design engineers select base components — screw drive, gearbox, motor, and mounting — to accommodate preferred motor types or connect to existing controls for reduced design and programming costs.

Shown at this year’s ConExpo, the Schaeffler Ewellix EMA-80 3-ton electromechanical actuator has a compact, modular, and fully electric (oil-free) design. In fact, this actuator delivers high power density and energy efficiency for heavy lifting applications. Based on a modular platform, the EMA-80 easily integrates into machinery while offering high force output and extended service life. The EMA-80 also supports peak loads to 31 kN, strokes to 1,500 mm, and speeds to 160 mm/sec. The actuators are often fitted with efficient asynchronous or synchronous motors with peak outputs to 5 kW. A B-side brake in the motor for static holding works even during power outages.

Some ballscrew-based electric actuators enable energy recovery during braking or lowering. Complementing this capability are ballscrews (along with spur gears and seals) that are friction-optimized. Such components can yield top efficiency — especially when they’re paired with a synchronous servomotor of efficiency class IE4 or higher.

Related: Update on electrification

With some actuator series, design engineers can specify a speed limit with a centrifugal brake so there’s safe load lowering without power.

Multiple mounting options simplify integration into different applications. For example, some push tubes are available with a T-Bar, threaded male-connection pin, internal threads, or a screwed-on rod end. Motor-side mounting options can include trunnion mounts on the bearing housing or two rear attachments on the gearbox.

Shown at this year’s ConExpo, Schaeffler’s Ewellix CAHB-2xS is part of the Ewellix CAHB line of linear actuators, suitable for replacing pneumatics and light hydraulics in low- to medium-load, low duty cycle applications. Able to handle to 10 kN of force and speeds to 55 mm/sec, this smart linear actuator offers absolute position feedback and status monitoring with synchronization and integration into higher-level machine control systems via CAN bus.

Very large ballscrew actuators capable of many tons of output force often feature vents to maintain IP66 while in motion.

Actuator product series that come in ballscrew and roller-screw versions are often offered to replace hydraulic cylinders on mini excavators and mini wheel loaders. These actuators feature a compact design and various mounting options. High positioning accuracy and controllability via bus system lets several drives operate synchronously for more combined power. Typical speeds reach 750 mm/sec and strokes 2 m.

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