Inductive sensors prevent overloading of hook-lift truck arm

When a specialist manufacturer of hydraulic hook-lift systems for commercial trucks needed a solution to detect the position of the telescopic lifting arm, ensuring that it is retracted, before the lifting sequence, it turned to Contrinex.

A hook-loader truck employs a system of hydraulic rams to hook, lift and pull a container onto the vehicle’s load bed. These demountable containers can weigh up to 30 tons when full and the system must work all year round, often in harsh environments such as demolition and construction sites.

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

Therefore, before the lifting sequence can be enabled, a sensor must reliably detect the position of the arm to ensure that it is not extended. The sensors must be robust and withstand water, mud, dirt and ice, as well as being exposed to mechanical shocks and vibration.

Contrinex’s extremely robust ‘700 Series’ sensors are renowned for their reliability in demanding environments. Their robustness and ability to survive impact and shocks is typically demonstrated to customers, by using them to hammer 2-inch nails into wood. These rugged stainless-steel inductive sensors are therefore ideal for the hook-lift application.

Highly reliable and rated to IP68/IP69K, these embeddable units feature one-piece AISI 303 (V2A) stainless-steel construction with vacuum-encapsulated electronics, making them well suited to hostile operating conditions.

The container lifting sequence begins with the hydraulic system retracting the hook-lift’s telescopic arm, from its extended position 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 and its long 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 truck’s lift control system is via the sensors M12 connector and using PUR coated cables, which allows for easy removal and replacement of cables or sensors during routine maintenance.

Rugged sensor construction ensures excellent resistance to shock and vibration. The sensors are corrosion-resistant and impervious to water ingress, mud, ice and salt. The system's reliability has been excellent, with Contrinex inductive sensors delivering a cost-effective solution that satisfies the customer’s requirements for a simple, fit-and-forget system.