RESEARCH & DEVELOPMENT
Ken Korane • Contributing Editor
Smart hydraulic cylinder measures force Supporting cylinder with integrated force measurement from Weber-Hydraulik is used to help stabilize mobile cranes.
The trend toward “intelligent” components, those with highly integrated sensors and control capabilities, is becoming increasingly important in hydraulic applications. Drive-systems with electronic control systems help maximize performance, energy efficiency and ease of use. However, control systems need to acquire information from various processes, which is often challenging, as sensors must be protected against harsh environments typical on construction, mining and agricultural sites.
The integrated measuring sensor detects cylinder position by optical recognition of a binary barcode applied on the piston rod, which has a unique code structure in every position. A redundant version meets more strict safety requirements. The compact sensor includes an exposure unit, a sensor unit to capture the image and an electronic module for image processing and communication. The exposure unit momentarily illuminates a section of the code which the sensor then detects. This takes place at specific intervals adapted to suit the maximum traversing speed of the rod. Images are analyzed individually to determine the respective position. The sensor mounts on the cylinder outside the pressure chamber and directly behind the wiper. It is thus an external sensor, albeit highly integrated into the cylinder design. In many cases the sensor doesn’t increase the retracted length of the cylinder. Due to the design, component reliability and safety measures implemented, the sensor meets requirements corresponding to PLe (EN ISO 13849). The maximum measuring
Weber-Hydraulik, based in Güglingen, Germany, has been at the forefront of developments involving highly integrated, reliable and reasonably priced sensors for hydraulic cylinders. In a presentation at this year’s IFK Fluid Power Conference held in Aachen, Germany, authors Roman Weidemann, Mehdi Javdanitehran, Torsten Winkler and Torsten Boldt discussed the company’s work on an optical position measurement system for hydraulic cylinders — now in mass production — and ongoing research into in-cylinder integrated force measurement. 26
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length for the current system is about 6 m. Weber-Hydraulik engineers are also actively involved in application-specific solutions for integrated cylinder force measurement. To monitor the stability of supported mobile vehicles such as cranes, aerial ladders and concrete mixer pumps, it would be advantageous to have information about conditions in outriggers and supporting arms. In practice, the load capacity of the supporting base is often unknown because surrounding conditions don’t allow for a complete outrigging of supporting plates, or the load carrying capacity of the ground is limited. An electronic monitoring system that measures both outrigger positions as well as the supporting load of each supporting cylinder would increase safety. The force of a supporting cylinder is commonly measured indirectly via internal pressure, but this method is not particularly precise and measurements can deviate by more than 20% under transversal loading conditions. To ensure safe operation, sizeable safety factors are required which consequently reduces the available load capacity of the system. The new design involves a supporting cylinder with an integrated force measurement
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12/14/18 2:50 PM
