Bus-capable safety systems for mobile cranes

Edited by the Engineeringtalk editorial team May 30, 2000

For mobile crane manufacturer Liebherr, data bus technology offers significant advantages. As well as providing vital bus-capable components, Schmersal was involved in the design of a bus system too.

Close co-operation between manufacturers and suppliers is common in the automotive industry, with car manufacturers drawing on the knowledge and experience of specialist suppliers during the design and development of new models.

Acknowledging the trend, other industries have accepted the advantages of working partnerships with key component and system suppliers.

In the field of safety technology a recent example has been set with the co-operation between mobile crane manufacturer Liebherr and Schmersal, a specialist in man-machine safety systems.

Liebherr-Werke Ehingen Ltd are pioneers in the extensive use of data bus technology on mobile cranes.

Since 1998 all new mobile cranes with load capacities of 35 to 500 tons have been equipped with the 'Liebherr-system bus' (LSB) for data transfer, and as well as providing vital bus-capable components for these cranes, Schmersal was involved in the design of the bus system itself.

For Liebherr, data bus technology offers significant advantages.

For example, the 6km of cable and 1000 plug-in connections required by a middle range crane to connect electronic components, can be reduced to a single 250m standard cable.

This not only increases the machine's reliability but also improves the diagnostic capability because more data can be transmitted and evaluated.

Of course, the data bus requires bus-capable sensors and actuators.

All vital electrical and electronic components are provided with microprocessors.

A typical example is the lifting end switch, which prevents the crane hook from hitting the cantilever head while lifting a load and feeds the cable when the cantilever is moved out.

For these important operations Liebherr use a Schmersal electronic lifting end switch, which is provided with an LSB interface.

During operation the switch conducts a continuous self-test, which controls the function and sends out an immediate alarm signal if any irregularities are detected.

Sensors inside the cantilever monitor the position of the fixing of telescopic parts.

Schmersal non-contact proximity switches, designed in co-operation with Liebherr, are used for this application.

They provide up to 16 switching positions that are used for diagnostics in the safety circuit - a function normally controlled by complicated measuring devices.

Communication between the major central control unit and the numerous sensors and actuators is achieved using freely programmable I/O-modules, which operate as de-central control and master units for the LSB data bus.

These modules, which are responsible for the steering function (the operator can steer the crane in the "drive-by-wire" mode using a rocker); operation of the supports; and motor control, were also designed by Schmersal.

The components that Schmersal supply to Liebherr cannot be found in the company's catalogue.

They have been specially developed for the application in a design co-operation, which has resulted in an individual system solution - with obvious benefits for both parties and for the end-user, the crane operator.