IMPROVING ON THE ESTABLISHED
06 November 2012
Integrated electro-hydraulic actuators address the tough challenges set down by machine builders and users says Andy Lindgren, product manager at Cylinder Division Europe, Parker Hannifin
In a global market, the level of competition between manufacturers to produce cost effectively and reliably is continually increasing. From production vehicles to offshore equipment, the machines that automate assembly must be as fast, efficient, accurate and reliable as possible. Actuators that control moving parts are a key element of the machine that can directly impact throughput and the quality and consistency of finished parts.
The emergence of electrohydraulic actuators has given machine builders a unique set of characteristics that combine the versatility of electronic control and the power of hydraulics.
IMPROVING ON THE ESTABLISHED
Considered on its own, hydraulics could be viewed as a very mature technology. However, recent developments that have seen fluid power innovatively combined with electronic control, have come at an appropriate time for machine builders seeking greater speed, precise control, reliability and easeof- use from the actuation methods they employ in their designs. Prior to this evolution, much larger electro-mechanical systems were often the default choice. While capable of delivering a good degree of control, such systems have limitations in terms of the force they can generate and, in some applications, can be beset by issues including electrical interference, heat, wear and backlash.
From a supply, installation and set-up perspective, the develop - ment of highly integrated and pre-assembled electro-hydraulic actuators brings multiple benefits to both machine builders and users. For those tasked with specifying and purchasing at the OEM, being able to source a complete unit from one supplier not only simplifies the supply chain and stocking, but can also help minimise the volume and complexity of warranty issues. For those actually building the machines, fitting an integrated electro-hydraulic unit that includes the cylinder, manifold and pipework plus a ready to use interface between the hydraulic actuation and electronic control elements of the system, is far quicker and simpler than assembling separate sub-assemblies.
THE DEVELOPMENT OF HIGHLY INTEGRATED AND PRE-ASSEMBLED ELECTRO-HYDRAULIC ACTUATORS BRINGS MULTIPLE BENEFITS
ADDING NON-CONTACT MEASUREMENT
Advanced integrated position measurement has been a key benefit of electro-hydraulic approaches to linear actuation. Adding a transducer and conditioning electronics to a hydraulic actuator can create a closed loop system which is able to respond rapidly and accurately to control signals for position and velocity over the full stroke of the cylinder without mechanical re-setting. Alternatively, an open loop configuration can be achieved to give continuous, infinite resolution position monitoring.
To achieve this, Parker Hannifin’s HMIX electro-hydraulic cylinders use an internally mounted magnetostrictive transducer that measures the interaction between two magnetic fields. This provides either analogue or digital information that determines the exact position of the actuator. Being internally mounted affords protection to the sensitive transducer components ensuring reliability and accuracy, even in the most challenging operating environments. The noncontact nature of this measurement technology means that wear is not an issue and so a long working life can be guaranteed.
THE MANIFOLD TOO
Where the manifold block can also be included in the integrated electrohydraulic solution – as is the case with HMIX cylinders – the OEM and user benefits can be further improved. With pipework and connections already in place, the speed and ease of fitting is of course further enhanced. In addition, the short fluid paths and optimised design made possible by directly mounted blocks deliver the best possible fluid dynamics, supporting faster response times and greater positional accuracy of the actuator.
In summary, by combining the sophistication of the latest electronics and sensing technology with the enormous power densities offered by hydraulic motion, electro-hydraulic actuators can offer greater machine flexibility, simplify the set-up process and reduce set-up times.
The adoption of advanced noncontact measurement techniques and optimised manifold blocks in pre-assembled units adds to the potential of this technology to deliver the speed, accuracy and degree of control demanded by machine builders in a diverse range of industry sectors where pressure to deliver high quality at high speed is a stringent requirement.
• Recent developments have seen fluid power innovatively combined with electronic control
• Electro-hydraulic actuators can offer greater machine flexibility
• Advanced integrated position measurement is a key benefit of electro-hydraulic approaches to linear actuation