High on safety

Powerful development tools helped crane controls manufacturer NTK to boost intelligent safety by using the built-in maths functions of ABB’s new safety PLC
 Construction sites are tending to become very congested – in efforts to better exploit the available building space and speed project times. The workhorse tower crane is critical to the efficiency of such sites, and crane operators today often have to work in very complex 3D space envelopes with many potential collision zones.
The crane controls designer NTK is making light of these issues by providing an advanced new safety system for tower cranes – which can be recognised easily by the company’s distinctive crane cabs with their circular or oval cab windows. NTK is now installing a control system based around a new generation of safety PLC from ABB. This system continuously monitors load torque as well as working and collision areas in real time – to SIL3 (IEC 61508 and 62061) PLe (ISO 13849-1) functional safety level. It provides instant and comprehensive visibility for the operator of all key crane status indicators. The crane’s maximum movement speed is also now controlled by a fully dynamic calculation of load moment. This enhances crane productivity by providing an infinitely adjustable hoisting performance envelope – rather than using more restrictive gradated maximum speed bands.
The safety PLC used – ABB’s AC500-S – simplified this control upgrade project because of its built-in maths capabilities. Unlike other safety controller options the PLC supports trigonometric mathematical functions, greatly speeding static and dynamic crane load safety calculations. The position of the trolley, radius of the crane, plus load and wind conditions are all displayed by NTK’s graphical touch-screen user interface.
The safety PLC ensures that maximum permissible load moments are never exceeded, to prevent an overload tipping the crane. At a glance, the operator can see where the trolley or hoist is, for instance, and what the load is. When you are working on congested sites or at high altitudes, this is a huge advantage.
NTK has consistently been at the forefront of crane control safety. For this iteration of its control system, which upgraded the control system to dual-PLC architecture with the new maths-capable AC500-S safety PLC, NTK agreed to be one of ABB’s beta users. This gave NTK access to the new safety PLC very early in the development cycle. In return, NTK developers gave ABB feedback on the PLC and its development tools.
NTK’s PLC crane control system is housed in a protected cabinet that sits in the operator cab. However, the PLC can equally be provided in an ‘extreme conditions’ variant that allows users to configure functional safety PLC solutions that are also ruggedised and suitable for operating in harsh conditions and extreme climates – as can be commonly found on some crane and winch applications for instance.

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