Hydraulics needs a better moustrap

When I first became a staff member of Hydraulics & Pneumatics, I was quickly indoctrinated on what the hot topics were at the time. One of the hottest topics then, 20 years ago, was the integration of electronics into hydraulics — which I came to know as electrohydraulics.

Since then, we have published hundreds of articles about electrohydraulics in this magazine. Of course, back then, electrohydraulics meant analog electronics. More recently, we’ve written about digital electrohydraulics. And even more recently, it’s been digital electrohydraulics in fieldbus systems — both in stationary and mobile equipment.

One thing hasn’t changed, though: the need for a universal linear displacement transducer (LDT) that can easily and inexpensively be integrated into most hydraulic cylinders.

Don’t get me wrong, several different designs of acceptable LDTs already exist, each with characteristics that suit them to specific types of applications. At the low end are resistive sensors, at the high end are magnetostrictive transducers, and in between are various other designs that have gained limited acceptance. The problem is, resistive sensors have physical limitations that will likely prevent them from ever gaining widespread use in hydraulic cylinders. Magnetostrictive transducers have become the favored technology for high-performance applications. Magnetostrictive transducers have been a real success story for electrohydraulics. They have allowed incorporating electrohydraulic cylinders into countless applications that would not have been possible otherwise. However, their relatively high cost prevents them from being used in most applications. Furthermore, the extensive machining required to accommodate in-cylinder installation only adds to their initial cost.

Therefore, a key to more widespread use of electrohydraulic cylinders is development of an LDT with the performance on par with magnetostrictive transducers but with a lower cost and that does not require extensive machining of the cylinder.

Eventually, though, someone will develop a low cost, high-performance LDT for use in hydraulic cylinders that can be installed in a drilled and tapped port on the cap end of the cylinder — making an LDT as easy to install as a pressure transducer. When they do, you can bet that the hydraulics world will beat a path to their door.