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Tie-rod cylinder features novel position feedback technology

28 January 2011

The new HMIX cylinder from Parker Hannifin is a fully integrated sub-system, combining Parker's tie-rod cylinder technology with a high precision feedback transducer, manifold and pipework, in a single, easy-to-fit unit. This enables machine developers and builders to enhance the functionality and performance of machine systems, quickly and simply, while reducing installation, configuration and maintenance times.

At the heart of the new HMIX electro-hydraulic cylinder is a magnetostrictive transducer, which provides continuous analogue or digital feedback of actuator position, derived from the interaction of two magnetic fields. These are generated by a permanent magnet attached to the actuator piston, and by a magnetic pulse produced by a current pulse launched along a copper core inside a waveguide tube, which runs the length of the piston rod.

The interaction between the two fields produces a torsional strain pulse, which travels down the waveguide tube and is sensed by a coil at the end of the device. The position of the piston-mounted permanent magnet is established by measuring the elapsed time between the start of the current pulse and the arrival of the strain pulse, with interface electronics then being used to convert this information to a digital or analogue output.

This robust and reliable technology can be used under closed or open loop control.  For the former, the transducer can provide accurate information of position, velocity or motion control over the full stroke of the cylinder, while in the latter mode the transducer acts as a continuous, infinite resolution position monitoring device.

The compact design of the transducer means that the new HMIX electro-hydraulic cylinder is only slightly longer than a standard device, helping to simplify machine layout. Similarly, the non-contacting design of the transducer, the tough steel protection tube for the transducer electronics and connector, plus the use of high tensile, carbon alloy steel piston rods and one-piece steel piston, mechanically locked to the rod, ensures a long and trouble-free operating life. 

HMIX electro-hydraulic cylinders accept an operating pressure of up to 210bar, and are available in a range of eight mounting styles, with bore sizes from 40mm to 200mm and stroke lengths up to 3,000mm.


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