Motion applications: Electric actuators in new designs

Electric actuators come in versions as small as syringes for medical applications to those big enough to drive industrial presses. These muscles of precision motion usually incorporate an electric motor and rotary-to-linear device for conversion of torque to linear force.

No matter the application, electric actuators deliver repeatability that’s indispensable for moving loads to a given positions. Often they’re also more controllable than fluid-power actuators, giving engineers a way to shape speed, force and acceleration of machine-axis moves.

Another benefit for applications that need multiple outputs over time is that most electric actuators are programmable so adapt to changing conditions.

Applications with similar dynamics often make use of the same actuator types — those that pair motors with ballscrews or leadscrews; incorporate brushless dc motors and belt-and-pulley setups; take a rod-style morphology; use motors with planetary roller screws; or integrate built-in guides.

Electric actuators running closed-loop or with a micro-stepping motor can match force and speed output commands best with feedback to overcome most of the mechanical limitations of rotary-to-linear devices.

Some application tips: Establish the design’s power draw and determine whether the machine will draw power continuously or intermittently or both, as that ultimately determines actuator size and type. Remember that overly large electric actuators are often less responsive than well-sized units.

That said, appropriate safety factors ensure that electric actuators run coolly. Plus, lighter loads on the mechanical components can extend life. Halving load on a leadscrew can extend its life eightfold, for example. Also account for where the actuator will operate. Will it need to withstand exposure to dirt, chemicals and liquids? If so, its O-rings and seals must be made of materials to withstand application contaminants. Another tip: Analyze the final installation point to ensure that the electric actuator can handle side, radial and axial loads.

Getting under hood just got easier thanks to linear actuators

Engineers at DEUTZFAHR no longer use simple tilt mechanisms and gas springs on their 150-kg vehicle hoods, because these designs are impractical.

Now they use kinematics driven with actuators from LINAK. These don’t tilt the hood, but raise and lower it parallel to the vehicle. More specifically, the kinematics run off a LINAK LA36 actuator that can move up to one ton over stroke lengths from 100 to 999 mm. The actuator also withstands the high heat associated with sitting right above the engine. That’s another reason why the OEM picked the LA36.

Farmers who have tried the technology on new tractors praise it. The actuator gives them electric hood adjustment so they can easily access all areas in the engine compartment.

One caveat: The solution is more complex than basic mechanical offerings, so is harder to service during maintenance. To prevent this from being a problem, the LA36 is solid and rugged to operate under tough and harsh conditions, with a die-cast aluminum housing and quality components. So the LA36 withstands cold, heat, and high temperature fluctuations of being so close to an engine in a vehicle that operates outside. It also withstands splashes and moisture from precipitation and chemicals. In the static state the LA36 is rated to IP69K and in operation to IP66.

Electrification in agricultural machinery makes this a growth industry for LINAK, according to Johannes Gruber, product manager at DEUTZFAHR. The sheer size of off-highway machines and demand for ergonomics and user-friendliness will only increase demand for electric adjustments in the future.

“Electrification with attachments and tractors will increase in coming years,” Gruber added.

Matching actuators to design demands

Electric actuators for automation must deliver set levels of speed and force requirements. Here, better feedback and controls can increase responsiveness to overcome any mechanical limitations while boosting output-motion accuracy. OEMs and end users can pick from myriad actuators to get needed accuracy for everything from lumber-processing machines to those medical applications that need accuracy to a few micrometers. Electric-motor actuators that use belts and acme screws for rotary-to-linear conversion of motion abound. That said, the majority of general motion applications (including positioning tables, workpiece-pivoting stations, robotic end effectors and machining axes) make use of actuators that integrate ballscrews. With precision of down to micrometers, these satisfy designs that need thrust to thousands of pounds-force or linear positioning speeds to several feet per second.

Elsewhere, on injection-molding applications, packaging machines, presses and other setups that need high thrust, actuators that pair electric motor with roller screw (sporting a nut loaded with roller bearings that work like planetary gears around the screw) are a newer and increasingly common option. Stroke is about 2 m with acceleration to a few gs.