Hybrid actuation makes its mark in industrial applications
Electric and hydraulic actuation are often seen as rival technologies, but there are an increasing number of technologies that combine them for a range of industrial applications.
The first of these to emerge was Parker Hannifin's Compact EHA electro-hydraulic actuator, which has won a strong following for its combination of power, speed and durability, making it an ideal choice for space-critical, portable and remote applications. With the launch of Compact EHA generation II, Parker has added universal orientation and the option of a manual release function, providing greater versatility for the designer and enhanced safety for the operator.
Compact EHA is a fully self-contained, double-acting actuator which offers exceptionally high power density at operating speeds of up to 84mm/sec. This makes it a robust and maintenance-free alternative to conventional hydraulic, electro-mechanical and pneumatic systems, in applications ranging from military and aerospace, to marine, leisure, construction and general industrial use.
The new generation of Compact EHA offers benefits for both the designer and end user, making for easier specification, enhanced versatility and greater operator safety. Universal orientation also reduces the need to stock different variants as all new Compact EHA models will work in any position. The new manual release option allows the operator to manually move the load in emergency conditions such as loss of power. Where a complete, single source solution is needed, Parker now offers a bespoke design service including wiring harness, switchgear and power supply.
The design of Parker's Compact EHA sees all components integrated into an anodised aluminium one-piece housing, resulting in a rugged and compact construction. The unit comprises a high performance, double-acting hydraulic actuator, driven via a reversible gear pump, which is powered by an integrated 12v or 24V DC motor. The pump is enclosed within the hydraulic fluid reservoir, with pressure relief and check valves also being incorporated within the system assembly.
Actuator piston rods are manufactured from stainless steel, with a micro-finished cylinder bore featuring buna-nitrile and polyurethane sealing elements, to prevent both leakage and the ingress of contaminants. Trunnion pin mounting holes are set within the base of the housing and at the end of the piston rod for ease of installation. Compact EHA is corrosion resistant and sealed to IP67 standard, and is supplied by Parker fully tested, flushed and filled with fluid, ready for operation. Commissioning requires only mounting pins and motor connections.
According to Andy Lindgren, cylinder applications engineer at Parker Hannifln, this ease of application is a major advantage. He says: "One of the virtues is that it's very easy to implement. Mounting it is essentially just a pivot at either end and driving it is essentially just a 12 or 24V power supply. So it's very easy to integrate without a great deal of design work into all sorts of applications."
In terms of applications, the new Compact EHA's chief benefit is that it is free-standing. Says Lindgren: "When you need a high force that cannot be provided by an electro-mechanical unit. Normally, the only way to do it is to put a power take-off unit onto an engine and drive a pump and a valve. There are many applications where you don't have that facility available, but you need that force, positioning and holding ability."
The design and construction of the Compact EHA actuator enables it to produce exceptionally high levels of force, delivering up to 21.3kN on extension and up to 16kN on retraction. By comparison with conventional ballscrew or linear motion systems, Compact EHA is free from problems of backlash and does not require any form of gearing, so is unaffected by wear and loss of positional accuracy.
The new actuator can be used at operating temperatures of between -34ºC and +65ºC, and generates less than 70dB of noise. Compact EHA is offered with a range of options for motor, pump, bore and stroke length, making the new system an ideal choice for machine builders looking for a simple and efficient method of providing fast, high power linear motion.
Another example of hybrid technology was revealed by Moog Industrial Group at the IPC Drives Show 2011, held in Nuremburg in November last year. It consisted of a prototype for a new Electro Hydrostatic Actuator (EHA). Combining hydraulic and electric technology in a self-contained system, Moog's EHA concept deploys the company's expertise in both electric and hydraulic technologies to develop this optimised energy-efficient and reliable system. Moog has been providing industry-leading EHA systems for flight controls for over 18 years and now has begun working with machine builders to apply this expertise to industrial applications that require high force, energy savings, environmental cleanliness and elimination of hydraulic piping.
"At Moog, we refer to ourselves as 'technology-neutral' because we design both hydraulic and electric solutions," says Dr. Sherif El Henaoui, Moog Industrial. "Therefore we have developed a deep understanding of the advantages and disadvantages of each technology for particular applications. This solution leverages this know-how to create innovative hybrid designs that combine both technologies, in compact, reliable and highly efficient systems."
Unlike an electric actuator, Electro Hydrostatic technology requires no screws or gearing. It differs from hydraulic actuators in that it requires no hydraulic piping, thereby reducing cost and improving reliability. The system is fully self-contained as all hydraulic and electric components are highly integrated in the actuator assembly.
Electro Hydrostatic Actuators receive power from an electric source by wire and transform a typically electronic input command signal into motion. EHA uses fluidic transmission between the electric motor and actuator. Motors rotate only when movement is demanded, saving energy and wear. Low duty cycle or actuation on demand applications, that require the high force density of a hydraulic system, can benefit greatly from the energy savings of an EHA system. EHA includes hydraulic components and fluid, both are self-contained within the actuator assembly, eliminating the potential of leaks and environmental contamination.
This hybrid solution of hydraulic and electric drive technology allows the selection of the benefits of both technologies: The low energy consumption of the electric system by power only on demand, the easy energy storage for the fail safe movement and the high reliability of the hydraulic system.
EHAs also offer a number of overall system benefits and cost savings. Moog's EHA design offers machine builders high energy efficiency and reliability, reduced envelope size, less wear on components and up to 40% less weight. The self-contained EHA package removes the need for long hydraulic line lengths and rotary couplings, offering significant cost savings in applications such as oil and gas, and power generation equipment. The integrated systems approach means greater reliability for the customer as less individual components are required, lowering costs and downtime. Redundancy and fail-safe features are also fully integrated offering minimal impact on cost, weight, envelope and reliability.
EHA is an ideal option for applications that have high force requirements and require redundant or advanced fail-safe systems, while also delivering energy, cost and environmental benefits. Typical applications include power generation, industrial machinery and oil and gas equipment.
The motion control industry is seeking new technologies that address the need for better energy efficiency and reliability at lower weight and size," concludes Dr. El Henaoui. "Smart systems like EHA hybrid technology offer a new and innovative solution suited to a range of industrial applications."
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