Don't Overlook the Hydraulics in Motion Control Applications

For engineers who are laying plans for the Fourth Industrial Revolution, aka Industry 4.0, aka the Industrial Internet of Things, executives at Bosch Rexroth have a bit of advice: Don't forget the hydraulics.

That message came out loud and clear recently when the drives and control company distributed a brief treatise titled, "That's how it is: six surprising capabilities of modern hydraulics." The statement, authored by a Bosch Rexroth executive board member, outlined the advantages of hydraulics in the kinds of smart machinery applications typically associated with the modern factory's next great advancement: Industry 4.0.

The position statement was intriguing, not just for what it said, but for what it didn't say. Its subtext is that today's engineers may be underestimating the capabilities of modern hydraulics. "To some degree, there's a lack of awareness and understanding of the advancements that have occurred in modern hydraulics," Michael Boehm, vice president of sales for machinery applications and engineering, told Design News. "There's an assumption in motion control that high tech is only an AC servo drive solution."

Bosch Rexroth's statement makes the case for a broader view. In factory automation, industrial presses, processing machinery, metallurgy, and oil and gas applications, among others, Bosch Rexroth believes that hydraulics offer capabilities often overlooked by design engineers. Following is a brief look at those "surprising" capabilities:

Micrometer precision: "Electrohydraulic axis controllers close the loop decentrally, similar to electro servo drives, and harmonize the target/actual position in real time within milliseconds," wrote Dr. Steffan Haack of Bosch's executive board. Haack says that hydraulic actuators can reliably position axes down to a few micrometers (microns), making them candidates for plastics machinery and tooling.

Compactness: "It is often difficult to place electromechanical drives with sufficient performance in tight construction spaces," Haack wrote. "Unlike hydraulic drives, they also add significant heat." Haack suggests that the decentralized nature of hydraulics and its low level of heat is often optimal for applications with minimal construction space.

Energy efficiency: Haack points out that hydraulic power units can reduce energy consumption by up to 80%. "Even older facilities and machines can be retrofitted without major efforts to significantly reduce the energy consumption in production," he wrote.

Balanced drive physics: Engineers know well that fluid power mediums may display non-linear performance characteristics, but Haack says it shouldn't be an issue. "Drive software for hydraulic actuators takes these particularities into consideration and harmonizes them automatically," he wrote.

Open and outgoing: Today, many engineers want to incorporate real-time industrial Ethernet protocols. That, however, should never preclude the use of hydraulics, Haack says. "Modern motion controls for hydraulic drives support all common protocols, e.g, Sercos, EtherCAT, Ethernet IP, Profinet RT, Powerlink, and Varan," he wrote.

Simply exchangeable: "Ready-to-install servo-hydraulic axes have an integrated fluid loop and are driven by the same servo drives as the electromechanical versions," Haack wrote." Since axes are encapsulated systems, engineers must only connect power and communication cables for assembly and start-up, and start-up can begin."

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Senior technical editor Chuck Murray has been writing about technology for 31 years. He joined Design News in 1987, and has covered electronics, automation, fluid power, and autos.