With the integration of electronics and advanced CAN-Bus controls, mobile hydraulic systems and components have gotten a lot more intelligent. But one of the areas that has lagged a bit has been hydraulic cylinders. One of the "muscle groups" of hydraulics, cylinders are used for a variety of functions on a machine, including steering, lifting and lowering, etc.

A key factor in the successful adaptation of advanced controls is understanding where a specific component is at a given time. To precisely control a cylinder, step one is understanding where that cylinder is in its stroke at a given time. There are ways to do that--LVDTs or magnostrictive probes, for example--but these can have some significant drawbacks in mobile machinery. In an effort to overcome some of those drawbacks and add some intelligence to cylinders, Parker Hannifin is working on a photo-optical position feedback system that can be incorporated into hydraulic and pneumatic cylinders, as well as other linear actuators. A prototype of the Intellinder technology has been adapted to a telehandler that will be on display at the company's booth at the ICUEE show in Louisville, Ky.

The Intellinder system is designed to be part of a fully functional electrohydraulic circuit controlled by Parker's IQAN CAN-Bus control systems. Unlike conventional position sensing systems, no movement is required to acquire the precise position of the actuator. Instead, the system is able to sense the position optically, through a combination of an innovative marking system and the use of an external fiberoptic sensor.
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"The more commonly used technology for position sensing is to have a probe-mounted device," said Ulrich Neumann, chief engineer, product development at Parker's Mobile Cylinder Division. "Using a probe-mounted device means that the cylinder rod or the piston rod has to be gun drilled. That's not really practical in the mobile hydraulics industry.

"There are other devices that have been used, flexible probes and things like that, but the difficulty is you always end up with an additional leak path. If your probe is mounted internally, you need to get cables in or out, either to get the information or to power the probe.

"The idea we had was to come up with something different. Rather than add something to the cylinder, what we wanted to do is try to make part of the cylinder the scale itself. The rod lends itself wonderfully to that."

The key to the technology is a proprietary marking system that discolors the chrome rod surface. "Our process does not disturb the surface of the rod," said Neumann. It's basically imprinting markings on the road and if you feel it, there are no surface undulations."

In the rod used in the telehandler's steering system, the surface marking appears as a series of dark rings, which are read by a fiberoptic sensor mounted on the side of the cylinder.

The technology is scalable and can be used in cylinders with strokes as long as 23 ft., and multiple sensors can be mounted around the rod to provide double or triple redundancy. The resolution of the optical system is well within mobile equipment industry standards and there is no deadband on either end of the sensing range, the company said, along with no measurable hysterisis. It is also fully ruggedized for application in mobile equipment, according to Parker.

The Intellinder system is in the initial phases of commercialization of the technology, having completed lab testing under a variety of conditions such as temperature, vibration, shock, contamination, EMF and EMP. The system is currently in selected prototype machine applications.

The prototype telehandler provides a good glimpse of what the future might hold, however, as the Intellinder system is used to provide a steer-by-wire system, as well as provide programmable lifting functions.

"In a forklift or telehandler, a vertical lift is a combination of raising the boom and moving the boom out in order to keep the load on a vertical path," noted Neumann. "You have to superimpose the two motions and the rate constantly changes. It takes a lot of skill to do it.

"With this system, you can write a simple lifting program that will tell the machine to lift a load vertically from the ground to however high the machine goes and the controller would literally meter out and perform a perfect vertical lift.