Prevent overloading of telescopic lifting arm on hook lift truck

Prevent overloading of telescopic lifting arm on hook lift truck


A hook lift truck utilizes a hydraulic system for loading and unloading a demountable container. The driver engages a lifting hook with the container before lifting it onto the vehicle’s load bed. Rugged sensor systems detect the position of the telescopic lifting arm prior to activating the lifting sequence, ensuring it is not extended. Sensors must be mechanically robust and withstand harsh outdoors conditions.


A specialist vehicle builder based in Switzerland manufactures hydraulic hook lift systems for commercial trucks. A hook lift truck employs a series of hydraulic rams to hook, lift and pull a demountable container onto the vehicle’s load bed. A full container may weigh up to 30 tons. Hook lift trucks operate all year round, often in harsh environments such as demolition and construction sites.

Hook lift systems are typically semi-automated. The driver positions the hook, which is mounted on a telescopic lifting arm, engages it with the container and initiates the lifting sequence. Before lifting, the extended section, which is immediately adjacent to the hook, must be fully retracted to avoid overloading the arm.

Before the lifting sequence can be enabled, a highly reliable sensor system must detect the position of the arm, ensuring that it is not extended. Sensors must be robust and must withstand water, mud, dirt and ice. They may also be subject to mechanical shock and vibration.


Before initiating the lifting sequence, the hydraulic hook lift system retracts the telescopic arm, which is extended when the arm is stowed. An M18-diameter sensor is mounted in the housing of the extending section. The sensor detects the position of the arm once it is retracted. A 10 mm sensing distance eliminates any risk of accidental collision between adjacent moving parts.

Once the arm is correctly positioned, the lifting mechanism is enabled. The sensor is configured with an industry-standard PNP normally-open interface; connection to the control system is via integral M12 connectors and PUR-sheathed cables, allowing easy removal and replacement during routine maintenance.

13th Dec 2018 S.Abedi

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