Cylinders use pneumatics and hydraulics
There are many linear actuation applications where the choice between hydraulics and pneumatics is a trade-off. The designer wants the speed of pneumatic operation, but the accuracy or controllability of hydraulics.
Now there is no need to compromise, because a new breed of hybrid cylinder from Hoerbiger-Origa offers the best of both worlds by operating off both fluid power technologies.
Over the years, the boundaries between pneumatic and hydraulic cylinder technologies have blurred, and the choice between the two is not clear cut. At the same time, there are competing electric drive technologies as well. But even with so many options, there are still applications where the ‘perfect solution’ does not seem to present itself.
Consider, for example, applications where the benefits of speed afforded by pneumatic cylinders are necessary, but where the compressibility of air becomes a problem for the system designer. These are applications where, for instance, smooth motion control is needed but with a varying load, or where the starting and stopping needs to be much smoother than can be provided by conventional pneumatic operation.
Consider a machine tool, such as a saw of some kind, where the positioning of the saw is controlled by the linear actuator – a cylinder. The upstroke of the cylinder will be without load, and the machine designer will, in order to maximise productivity, ideally want to be able to position the saw as quickly as possible. Such an operation is usually best achieved using pneumatics. The return motion, in contrast, where the saw is performing its cutting operation, will be a slower motion under load – and that will most likely be a changing load. Hydraulics are better suited to this aspect of the design.
An innovative solution to this problem is the hybrid cylinder, which combines the strengths of hydraulic and pneumatic operation in a single product. Such products are typified by Hoerbiger-Origa’s AZ series cylinders, which operate off both a compressed air supply and low-pressure hydraulics.
The AZ piston rod cylinder is described as the epitome of a good OEM product, with exceptional configuration flexibility. Highly versatile, the AZ cylinder is available in profile tube or tie-rod versions, in both single- and double-acting versions, and with the option of through-piston-rod operation. Users can specify single- or double-end air connections, and can select the position of these air connections. Further options include non-rotating or guided versions, high-temperature versions (up to 150°C), ATEX versions, and corrosion-resistant versions. For use in the most aggressive environments, users can also specify metal scraper seals to help keep contaminants out.
Most interesting, though, for machine designers working in applications whose requirements are typified by the conditions discussed, is the ability of the AZ to work in hydraulics mode. This achieved by means of a pneumatic valve that is used to operate the cylinder by putting air on the appropriate reservoir, forcing the oil in to the cylinder to generate the cylinder movement. The oil on the other side of the cylinder is returned to the other reservoir. Control is achieved via the adjustable restrictors in the oil lines and, when the control valve is in the neutral position, the oil is ‘locked’ in the cylinder by the two valves holding the cylinder in position.
For more information, visit www.hoerbiger-origa.co.uk
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