When TRT released the 25t TIDD PC25 pick and carry crane in 2013, it incorporated a number of safety features such as a Robway LMI system that automatically de-rated the lift chart for articulation and side slope, a ROPS cab with FOPS option, ABS drum brakes and an electro-hydraulic steering system that reduced the steering response as speed increased to overcome the problem of speed wobbles at speed. Greg Keane reports.
However, the increased attention to safety with articulated pick and carry cranes, and their banning on some construction sites, meant that more was required to give the market confidence in the safety of these cranes.
This was something that TRT recognised, and it identified an issue where an operator could pick up a load safely over the front on firm level ground and then drive around a corner with a side slope, inadvertently moving the crane into overload for the chart applicable to the degree of articulation and side slope.
The combination of articulation and side slope has a significant impact on the Safe Working Load of the crane; and has been a factor in a number of crane rollovers – some involving fatalities.
TRT looked for a practical way to address this problem without affecting the functionality of the crane and Slew Safe (now patented) is the result. It has been tested extensively and is now ready for release to the market.
Slew Safe has a screen display that shows the operator where the crane is compared to its rated capacity. A circular display similar to a speedometer displays green when the crane is comfortably within its rated load, with the size of the green display reflecting the percentage of rated load.
There are separate load charts for up to 10° of articulation, between 11° and 20° of articulation and between 21° and 42° of articulation.
As the crane approaches its rated load, the colour of the display becomes amber to denote caution. If the load exceeds the rated load, the portion of the display above the rated load turns red and Slew Safe is activated.
The effect of Slew Safe is to:
- reduce the speed of the steering;
- make the steering harder, with feedback through the steering wheel to the driver;
- load up the engine, providing an audible change in engine tone to alert the operator; and
- activate a constant, audible alarm both inside and outside the cab to warn both the operator and dogman of the overload.
This steering restriction operates only when the operator is moving into overload: there is no restriction on the operator straightening the crane and thereby moving out of overload.
The Slew Safe system has been tested extensively in a range of scenarios; and has been found to operate as intended. Experienced crane hire operators have been involved in some of the testing and have provided positive feedback on how it operates.
Operator responsibility
While Slew Safe is a major advance in active pick and carry crane safety, TRT emphasises that it does not remove the need to embrace safe working practices for operating a pick and carry crane, such as:
- recognising that surface depressions and potholes have the same effect as a side slope;
- ensuring that tyres are inflated to the correct pressure;
- ensuring that the ground can support the axle loads of the crane;
- recognising that when lifting a load, crane sided slope will change due to tyre and boom deflection;
- recognising that as articulation is increased, this increases the induced crane side slope;
- using the minimum boom length and boom angle to keep the boom tip as close as possible to the ground, and use the minimum degree of articulation possible;
- where possible, keeping the load uphill of the crane (especially when articulated, as the working radius will increase if the load is positioned downhill);
- using a tag line where possible to prevent pendulum action of the load;
- making all crane movements as smooth as possible; and
- adequately planning a lift to minimise any factors that can give rise to a reduced load chart.