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Exact Height Positioning

Zierer uses Turck's linear inductive position sensors with IO-Link interface

In its Flying Fish roundabout ride, Zierer Karussell- und Spezialmaschinenbau GmbH previously measured the horizontal position of the gondola arms using individual proximity switches. However, with five sensors for each of the twelve hydraulic cylinders, mounting, calibration and integration in the ride control system were really complicated, especially as the height measurement could only be approximated. For the first time, Zierer is now using inductive linear position sensors from TURCK, that supply an analog signal and can be parameterized from the PLC via IO-Link.

  • Inductive linear position sensors ensure reliable position sensing of the gondola arms

  • A 1,000 mm linear position sensor from TURCK now supplies the exact position of the arm

  • With short blind zones, IP67 and contact-free, the LI sensor is ideal for rugged use

Amusement rides must not only be enjoyable to their guests, but must also be safe. In this sector, the requirements are often higher than conventional industrial plants. “After all, this ultimately involves passenger transport,” managing director Wolfgang Brück points out. A classic in the Zierer offering is the Flying Fish roundabout ride. With this ride, passengers sit in twelve fish-shaped gondolas. Affixed to metal arms, the gondolas turn around the center of the ride. The twelve fish arranged in a star can be moved up and down hydraulically on their arm.

In order to determine the horizontal position of the arms, Zierer previously used five sensors on each hydraulic lift cylinder. Although this ensured safe operation, the installation of the sensors and their adjustment was relatively complex.

Alternative linear position sensor

A solution using linear position sensing was considered in October 2011. Zierer looked for a linear position sensor that measures the travel of the hydraulic cylinder up to its total length of 1,000 millimeters. Besides testing the sensors of other manufacturers, the Zierer project team also tested the LI-Q25 inductive linear position sensor from Turck.

The LI-Q25 has very short blind zones because the sensing electronics are integrated over the entire length of the sensor. The system is currently the only one of its kind on the market. Zierer was impressed by the test results of the Turck sensor. Even with rapid movements and the resulting centrifugal forces, the sensor reliably supplies the position of the positioning element via the 4…20 mA analog signal. The controller can determine from this the exact position of the arm. Project manager Klaus Gäck summed up as follows: “For us the quality and reliability in the operation is very important. The Turck linear position sensor seems to be the right choice here.”

Parameterization via IO-Link

Despite the positive test, two other requirements had to be clarified afterwards: for safety reasons, Zierer also wanted the possibility to indicate any failure of the positioning element. Although an LED on the sensor indicates if the positioning element is outside of the measuring range, Matthias Niedermeier, in charge of the electrical design, wanted to output this signal on the controller. Here the LI sensor was able to impress thanks to its ability to be parameterized via IO-Link. The IO-Link interface allows the user from the controller to define the measuring ranges, invert the output signal or simply output special signals like the failure signal.

Zierer had another requirement with regard to the MTBF (Meantime Between Failures) values. An analysis in accordance with directive SN 29500 (Ed. 99) has determined that the LI sensor can be operated for 138 years without failure. Managing director Brück was also impressed by the quality: “The sensor not only saves on investment costs but also increases the availability of the ride and contributes to greater operational safety.”

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