Mark Lemire
Product manager

Lido Boni
R&D engineering manager

Ben Furnish
Linear product manager Parker Hannifin Corp.

Linear actuation is employed everywhere, for packaging, life sciences, transportation, and factory automation jobs. Pneumatic and hydraulic linear actuators operate on pressure differentials; electromechanical actuators are either linear motors or rotary motors driving a screw or belt. The selection and use of these technologies is greatly influenced by the user's technical knowledge, the project's budget, energy sources, and performance tradeoffs.

For example, pneumatic actuators don't deliver high force output, but are well suited when a cost-effective, easy start-up solution is required. Hydraulic linear actuators generate a lot of noise and can leak nasty fluid, but are ideal for high force applications that require precise control. Electromechanical actuators have high energy requirements and are more difficult to install and maintain, but are preferred for complex, multi-axis, motion control applications. Let's look at all of this in more detail.

Pneumatics: Nice and easy

Pneumatic actuation is the conversion of compressed air into linear force. Forms of this technology have been employed for centuries; bellows in basic metal forming is one example. However, pneumatics were largely manual until the advent of electricity and the mechanical compressor in the early 19^th century.

The interaction of pressure, volume, and temperature of a gas are governed by the perfect gas laws, courtesy of Boyle, Charles, and GayLussac. Combining these is the general gas law:

P₁ x V₁ / T₁ = P₂ x V₂ / T₂

This relationship, plus the resultant force derived from pressure acting on an area, governs the use of pneumatics: Force = Pressure x Area.

Typical applications (die casting, extrusion, injection molding, and precision machining) involve extreme temperature, safety and inspection, and magnetic systems — because pneumatic actuators don't have the magnetic field issues of motors. Too, there have been several recent improvements in pneumatic design.

Position feedback with proximity sensors and LPSOs is used for part location, inspection, or control-loop feedback, taking pneumatics beyond simple bang-bang applications, moving parts from point A to point B.

Better sealing from contamination, with wiper and metallic scraper options that remove external debris and adherents, has increased the use of pneumatic linear actuators in applications requiring wash down — such as food processing and packaging — as well as applications involving weld flash, paint, or concrete. And, enhanced surface coatings, such as powder coat, lectrofluor, and anodizing of the two typical pneumatic cylinder materials (aluminum and steel) are expanding pneumatics use in caustic wash down environments.