The German company, Uniflex Hydraulik GmbH manufactures a variety of tube production and processing machines, including a successful range of hose crimpers, which are used in factories and workshops around the world.
These machines rely on dependable position sensors because the press stroke must be adjustable to the respective tubular form and size according to the values set by the controller. Hubert Poth, who looks after development, software and electrical engineering at Uniflex, takes up the story:
"For a long time, linear conductive plastic potentiometers did a good job measuring the travel at the press lever. With regards to accuracy, reliability and durability, we were very satisfied with this type of sensor from Novotechnik. But in the long run, it was not always easy to deal with the functional principles of this type of potentiometer.
“Potentiometers work as voltage dividers, so different input voltages always have an effect on the measuring signal. This is particularly disadvantageous with regard to our export machines, since we often do not know where in the world they end up being used and the variability in the supply voltage that the sensor technology will be exposed to.”
The solution came in the form of Novotechnik’s new LS1 linear position sensor series with integrated electronics. LS1 series sensors are inductive as opposed to relying on potentiometers, but in terms of size are completely compatible with the T-series potentiometers previously used by the Uniflex hose crimpers. With dimensions of 18mm x 18mm and effective strokes from 25 to 200mm, they are an appropriate alternative to most standard potentiometers with a square cross-section.
The integrated signal processing feature of Novotechnik’s inductive linear position sensor ensures that the measured value is available as an absolute current or voltage signal at the output. Uniflex prefers to use the standard analogue 0-10V signal. The sensor can tolerate a wide input voltage range of between 16V and 30V, which is particularly beneficial for export market machines
Another useful feature is the integrated teach-in function with LED status indication. By pressing a push button built into the sensor, the user can choose the start and end points of the measurement, invert the measurement output slope, or set the desired signal amplitude.
Unlike potentiometers, a separate signal conditioner is not necessary, and so control is simplified and the user does not have to get involved in any control programming. Moreover, an auxiliary signal conditioner adds further complication as it needs to be housed, mounted and connected. As Mr Poth points out, the fewer components needed, the less there is the potential for error.
Novotechnik has also ensured that these sensors are easily installed. Mounting brackets are included in the delivery, and a ball coupling without play allows for a shear force-free application, even with parallel and angular displacement of linear sensor and measuring direction. With its compact design and actuating rods on both sides, the LS1 series is suitable for a variety of industrial applications.
Thanks to their contactless operation, LS1 linear position sensors are virtually wear-free. They also offer high repeatability and a linearity of better than +/- 0.15 percent of the measurement stroke. The update rate of the output signal is specified at approximately 1kHz, which is more than sufficient for most applications.
"The fact that the inductive linear position sensors work non-contacting and therefore without any mechanical wear is of course a nice bonus for us even though we were very happy with the reliability of the previous conductive plastic potentiometers," Mr Poth concludes.
Novotechnik sensors are available exclusively in the UK from Variohm EuroSensor.