With topics that dominate everyday working life, such as Industry 4.0 or Smart Factory and IoT, developers and users are facing particular challenges. Internet capability is questioned in every application or the integration of higher artificial intelligence is required. This increased interest and the resulting greater demand for sensors is triggering an avalanche of innovation in many companies. This often affects the OEM companies themselves as well as suppliers in the field of sensors. Already established technologies are used to meet new measurement requirements, but new technologies are also being developed to sustainably reduce the existing weaknesses of existing technologies. These drivers are also ubiquitously visible in the hydraulic cylinder sector.
The actual function of a hydraulic cylinder, the concentration of large forces on small surfaces and the resulting mechanical movement that takes place in the background and the manufacturers focus on new customer requirements. The original benefit is thereby extended by several functions, thus the manufacturers of hydraulic cylinders hope for an extension of their value added chain. The first approaches to a smart cylinder were laid several years ago. The integration of path length sensors and force sensors was demanded and implemented due to legal guidelines, above all in the field of construction machinery and crane applications. The basis for these sensors was existing technologies such as e.g. the strain gauges as force sensors or optical systems for path length measurements. Various approaches to the integration of pressure sensors for force measurement have not prevailed due to the indirect measurement and the associated large measurement errors.
Hydraulic cylinders offer a particular challenge in that the possibilities for integrating sensors are either internal, which means it is limited to filled with hydraulic oil cylinder or the piston rod. The piston rod moves in the application always relatively to the cylinder, therefore, sensors mounted there are always associated with the challenge, so that the electrical contact must be designed by a cable for the cable to join the movement. The interior filled with hydraulic oil causes problems in so far as the materials used must be compatible with the oil and the existing high pressures in the interior do not damage the sensors. Also, the assembly in the interior and the related issue of sealing to the outside is not easy to get a grip on by conventional methods. For use on hydraulic cylinders, the use of magnetic inductive sensors has become increasingly important. For example, magnetostrictive path length sensors can be used to detect the piston position in the cylinder. The path length of the extended piston can be determined. The magnetostrictive path length sensors detect the positioning of a magnet mounted on the piston by means of sound wave reflection in ferromagnetic materials.
Another sensor technology that is suitable for use in hydraulic cylinders is the force measurement with magnetic inductive force sensors. This technology makes it possible to detect forces in ferromagnetic objects without sticking a strain gauge. By means of an inductance, an alternating field is coupled into a measuring point, the resulting field lines are detected in receiver inductances and the signals are processed. A force on the ferromagnetic object causes the permeability to change. This has a direct effect on the detected magnetic fields. Magnetic inductive force sensors can be integrated in different forms in a hydraulic cylinder, e.g. be screwed to the cylinder head of the sensor and addressed via a cable guide in the center of the piston. Another possibility is the mounting of the sensors at the cylinder end and the sliding measurement on the cylinder rod. Furthermore, there is the possibility to compensate for the resulting lateral forces by an intelligent arrangement of the sensors around the cylinder rod.
The integration of sensors in a variety of applications has just begun. By choosing the right technologies and a modular system, various questions can be answered. This results in a value added for the manufacturer of hydraulic cylinders. New business models will emerge that can generate a decisive advantage in every value added stage.