Safety on board

15 April 2008

Examples of control joysticks used in modern cranes

Examples of control joysticks used in modern cranes

Modern electronic control systems offer much greater functionality and remove stress and strain from the operator. The result is an operator who can concentrate on the job in hand – moving materials efficiently from one place to another.

To take a simple example, an electronic system can routinely perform a full system check – verifying that the joystick is in the neutral position, the boom is not extended, and so on – before allowing the vehicle ignition to be started. Thus the risk of operator or mechanical error causing a problem is removed.

To support this task, information from linear and rotary position sensors can be used to provide detailed position data on the vehicle and its equipment. This can be used for load calculations to check that the crane is operating within its own safety limits, and those of its environment. For example, the system can be programmed to prevent the crane boom swinging beyond a certain point when a load is suspended from the hook, to protect neighbouring premises or other equipment on the site.

This type of sensing is the basis of the sophisticated anti-collision systems used where multiple cranes may be working in the same area. Data logging systems can also be used like flight recorders on aircraft to provide valuable historical data in the event of an accident or to calculate working hours for the equipment operators and rental companies.

Acceptance

So, with all this additional functionality, why are some still reluctant to embrace electronic control systems – can they go wrong? More and more electronic joysticks use Hall Effect sensors to provide contactless sensing. Hall Effect devices can be susceptible to interference from electromagnetic radiation. However, electromagnetic compatibility (EMC) issues are now well understood by the design community. The European EMC standards demand that such systems should be resistant to 20-30 V/m of electromagnetic radiation but, in reality, all the leading manufacturers do much better than this. Penny + Giles routinely designs to a 100 V/m capability. As a result, EMC is not a safety issue in crane and lifting equipment control systems.

Lack of expertise in electronics design is certainly a barrier for the smaller manufacturers and those providing specialist systems for niche markets. It is a brave decision to move away from a standards-compliant system – albeit a hydraulic one – to start again from the ground up with an electronic system. But there are plenty of specialist designers and system integrators that can help those that do not want to invest in an in-house design team and, as demonstrated by the big players in the crane market who have or are moving over to electronic systems, the benefits in safety and functionality cannot be ignored. As the rest of the market follows this irreversible trend, job sites where cranes are operating will become safer.

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