Hydraulic cylinders can range in size from less than
a foot in length to behemoths that are longer than a
semi-trailer truck. Photo courtesy of Bosch Rexroth
Hydraulic actuators, or cylinders, are versatile components known for superior power density. These components deliver significant linear or rotational force in a small space, which makes them suitable for demanding applications.
Over the past few years, there have been advances in cylinder technology of special interest to design engineers. Spurring a lot of these innovations is the oil and gas industry, with engineers in this market using hydraulic cylinders in new and different ways all the time, said Tony Casassa, application engineer, Aggressive Hydraulics.
“Hydraulic cylinders are replacing mechanical actuators, often initially for their compact size or reliability in harsh conditions,” he said. “Once the cylinders are in place, opportunities are identified for further innovation, often with more functionality integrated into the cylinder.”
A cutaway view of an L30
rotary hydraulic actuator,
which uses siding-spline
technology to convert
linear piston motion
into shaft rotation. Photo
courtesy of Helac Corp.
Similarly, Rene Coppens, global sales, large hydraulic cylinders, Bosch Rexroth B.V., said that large hydraulic cylinders often go into applications that deal with heavy loads and where there is a need for high power density.
“The offshore business is one of the best examples for large hydraulic cylinders,” said Coppens. “The need to explore and exploit resources located in deep waters is growing by the day. Next to that, with safety and environmental legislation becoming more stringent, [we are] focusing on developing our large hydraulic cylinders to meet and surpass the latest industry standards.”
Another example of safety-related innovation is in rotary-motion applications, where helical rotary actuators can deploy and retract access stairs for very large mobile equipment, said Chris Folk, global business manager for Helac Corp.
“Here, advancing safety regulations have driven the evolution of access to the operating cab from ‘free’ climbs, or simple pull-down ladders, to sloped stairs with handrails. Protecting the stairs during the equipment operation requires storing them into a position where they are out of danger while minimizing obstruction of the operator’s view,” said Folk. “This typically requires a range of motion that isn’t possible with a linear cylinder and linkage. Helical rotary actuators accommodate the greater range of rotation while minimizing the space claim, all of which results in a more overall elegant design.”
Large hydraulic cylinders are used in numerous
offshore applications, including riser tensioning,
heave compensation, skidding, deck mating and
jacking. Photo courtesy of Bosch Rexroth
Folk said that advances in hydraulic power units, combined with the low displacement characteristic of helical actuators, also makes for a very compact integrated component that qualifies for its own product category—that of electro-hydraulic rotary actuator. EHRAs operate with electrical power and can simplify system designs and increase reliability by eliminating separate hydraulic pumps, tubes or hoses, and control valves. They can easily deploy in applications that otherwise have no hydraulic components or systems.
All this said, over the past few years, most advances in hydraulic-actuator technology have been in surface technology, sealing, increased durability and the integration of position sensing.
“Better surface technologies…withstand the harshest environmental conditions,” said Coppens. “Plus cylinder-integrated measuring systems have improved significantly. They can monitor the hydraulic cylinder’s condition with more detail than ever before to provide useful information…so these improved condition monitoring solutions improve the total life time of a product.”
Using a rotary actuator can simplify
a design, provide a more compact
solution, and reduce the amount of
components required. Photo courtesy of
Helac Corp.
Folk said that his company is seeing a significant increase in the integration of position sensing in the application segments they serve.
According to Casassa, improvements in sealing technology have minimized hydraulic cylinder leaks even as operating pressures increase—but linear position sensors in cylinders have increased the functionality of cylinders.
“Over the last few years, position sensors have become more robust as well as more compact, so sensors can go where they would not fit or survive before,” he said. “There are more options, and the cost has decreased. In many applications, the best place for a sensor is inside the cylinder where it is protected from damage and the environment and does not take additional space on the machine.”
Folk agrees that sensing is a huge deal in hydraulic-actuator innovation.
“While electro-hydraulics and improved sealing will drive important new applications, the biggest gains will come from integration of sensors (position and load) with actuators,” he said.
Filed Under: Cylinders & Actuators, News
