LDPS – Long Distance Measurement for Cranes

Usually, optical laser measurement systems or radar sensors are used for displacement and distance measurements over long distances of up to several hundred meters. However, these optical distance sensors do not work reliable in the long term under all environmental conditions. In the case of crane tracks operating outdoors and in the manufacture of steel products in steel mills, the ambient conditions are characterized by heat, dust and dirt. Outdoors, frost, snow and rain, but also heat and direct sunlight are disturbance factors for optical measuring systems. The Long Distance Positioning System LDPS can be a good alternative also for gantry cranes and overhead cranes.

Portalkran Positionierung mit Magnettrack
Portal crane positioning with LDPS

Long Distance Positioning System LDPS

Magnetostrictive distance measurement systems can be used together with the LDPS to easily measure long distances. Normally, such linear transducers have a measuring range of a few centimeters up to a maximum of around 8 meters.

Previously, when positioning over longer distances was required, it was possible to cascade several transducers to achieve longer measuring distances. However, this approach is relatively expensive and the evaluation of the position data is sometimes quite complex.

Therefore, we have reversed the procedure for this long-distance positioning system. The actual measuring system moves with the part of the plant to be positioned. This can be, for example, a crane or a rail-bound vehicle. The marking of the positions is done by magnetic markers, which are distributed over the distance to be measured.

The function of the LDPS system, combined with a magnetostrictive transducer, is based on a PLC function-block, which is integrated into the PLC of the crane control system.
There, the absolute positions of several magnetic position sensors are recorded and compared with each other. This results in a unique assignment for each position along the travel path of a crane. The position markers here are simple magnets that have to be mounted at a specified distance from each other.

There are various methods for optimally adapting the LDPS to specific applications.

Linear Transducer with PROFINET interface and magnetic shield

Magnetostrictive Transducers

Non-contact linear transducers working on the principle of Magnetostriction are state of the art and standard in factory automation since decades. The position detection is non-contact and therefor wear-free via magnets, which are moving along the transducer. Also in Hydraulic cylinders this kind of measurement system has proven reliable.

Principle of Magnetostriction – Graphic: Balluff


Magnetostrictive transducer inside a hydraulic cylinder

Discrete LDPS System

With this discrete system, the position markers consist of individual but specially dimensioned magnets. These are mounted at precisely defined distances along the travel path. On each section of the distance to be measured, at least 2 or 3 of the position markers are located within the measuring range of the transducer. The absolute position of the crane can be derived from the distances between the position sensors. The disadvantage of the system is that the position magnets have to be mounted quite accurately. If, for example, the position of a magnet is changed by external influences, the system will detect this as an error.

LDPS Long Distance Positioning System Magnettrack
Transport trolley for pipeline-tubes with LDPS Positioning system

Adaptive LDPS System

In the adaptive system, the position markers consist of a combination of several magnets. This means that each magnet can be assigned to a specific position. In contrast to the standard system, the mounting of the markers is much more flexible. Problems with mounting due to obstacles along the travel path, such as control cabinets or steel beams, can be avoided by the distances not being fixed.

Adaptive positioning is a standard solution that can be integrated easily and convenient.
Here, the position markers can be mounted very flexibly along the travel path without specific specifications. Even identical position markers can be present several times along the crane’s travel path. This makes it easier to replace them if necessary, e.g. after damage. There ie no need to keep many different position markers in stock as spare parts.
The fault-tolerant system can even be expanded during operation. New or modified position markers will be recognized during regular operation.

By clicking on the following application picture you will be forwarded to a govie to simulate the function of the LDPS

Upgrade of existing equipment with LDPS

Due to its flexibility, the LDPS is also suitable for retrofitting and thus automating existing plants.

LDPS an einem Transportwagen in einer Rohrproduktion
Transport cart for tubes retrofitted with LDPS
LDPS am Kran montiert
LDPS mounted on overhead crane
LDPS Positionsgeber entlang der Kranbahn eines Portalkrans
LDPS position markers along the travel path of an overhead crane

Advantages of LDPS Positioning

  • Insensitive againts vibration and shock
  • Resistant to environmental conditions in steel production such as steam, dust, slag, etc. 
  • Long measurement distance, almost infinite measurement range
  • Absolute positioning without reference travel
  • Maximum travel speed up to 10 m/s
  • High accuracy even at large distance
  • Maintenance free
  • Long lifetime
  • Wide temperate range -40…+85°С
  • Protection class IP67

LDPS application – positioning of coke machines in a steel mill

Long Distance Positioning systems are already successfully in use in several coking plants as well as in the production of pipes for pipelines and work reliably despite adverse environmental conditions. Depending on the system and position markers selected, different distances are possible. Tolerances along the travel path, such as those caused by wear on the wheels, can be compensated.

Kokerei mit LDPS
LDPS position marker at the charging car
LDPS am Pusher Car einer Kokerei
LDPS position marker at the pusher car
LDPS Long Distance Positioning System Magnettrack montiert an einem Koksofen
Snow capped LDPS with markers on both sides (yellow) at the pusher car of a coke plant

More information on the LDPS in this onepager:

If you have any question on the LDPS you can get in touch with me

Other automation solutions for Metallurgy you can find here

Steel and Metallurgical Industry

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June 22, 2021 4:47 pm

Really a very helpful article thanks for sharing and keep on sharing!
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August 12, 2021 3:47 pm

Thanks for sharing! I’ve much to learn about cranes especially we are having our own mobile crane hire company launching soon.

July 13, 2022 5:28 pm

Aiming at the anti-collision monitoring of tower crane, the models of state equation and observation equation for obstacle are established, and distance measurement method based on ultrasonic sensor for tower crane obstacle is proposed. According to the multi-sensor information fusion theory and obstacle kinematic model, Kalman filter principle is used to respectively deal with single ultrasonic sensor information and multi-ultrasonic sensor information fusion, then those simulation and experiments results are analyzed and contrasted. The results show that multi-sensor distance measurement is more accurate and stable than single sensor distance measurement, and verify the feasibility and superiority of multi-sensor information fusion… Read more »

March 15, 2023 8:49 am

Thank you for showing the process of the long-distance positioning system with a proper diagram.

September 21, 2023 2:48 pm

Your ability to break down complex concepts into easily understandable terms is truly commendable. As someone involved in the crane industry, I found your explanations and examples particularly helpful. Your emphasis on the various technologies available for long-distance measurement, such as laser-based systems and ultrasonic sensors, was enlightening. It’s evident that staying up-to-date with these technologies can significantly improve crane operations, making them more precise and reliable.

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