Tipping point

The tipping line on every complete crane load chart separates it into two halves. On one side of the line, an overload will tip over the crane. On the other side, an overload may damage the crane, but it will not tip over the crane. Current European standards require rated capacity indicators (RCIs) to prevent overloading on cranes over 1,000kg or 40kNm capacity (but not timber handling cranes). The planned revision of knuckleboom crane design standard EN 12999 will require that RCIs also monitor the crane’s stability, to also make sure it doesn’t tip. The standard has been revised by an industry working group, and is currently being translated, prior to being voted on by individual European countries. The states can vote yes or no, but cannot make further revisions. It is expected to be in force by 2010.

The convenor of the EN 12999 revision group was Lars Rydahl, manager of structural mechanics at Hiab. He explains, “The standard says that for cranes covered by the stabiliser supervision requirement, ‘the stability of the vehicle shall be included in the safety function of the rated capacity limiter.’ So, the safety system must ensure the vehicle is stable: how that is implemented is up to the manufacturer.

“Manufacturers are coming up with different solutions to meet the new standard. Some are sticking with simple proximity sensors which prevent the crane operating unless the stabilisers are deployed. Others are using more sophisticated devices such as encoders or other digital devices to monitor the position of the stabilisers and the slew angle of the boom.”

Reasonably foreseeable

The standard has been revised partly because of changes to the European Machinery Directive. The current version of the Machinery Directive, which was launched in 1998, requires manufacturers to make sure that their equipment is safe when used as intended. Manufacturers indicate compliance with this by posting a CE-mark on the machinery. To be sold in Europe, a crane or other piece of machinery must have a CE-mark. A new version of the Machinery Directive is coming into effect on 29 December 2009. It is based on a slightly different philosophy than before: not only must machines be safe when used as intended, but also when used in ways that could be reasonably foreseeable.

Rydahl says, “It’s reasonably foreseeable that an operator may use stabilisers on one side only, if he intends to work on that side, and then slew to the other side but forget the stabilisers aren’t extended.”

The standard was also revised because of pressure from the UK’s safety regulator, the Health and Safety Executive, according to Lars Rydahl. “The UK pushed quite hard to have stabiliser supervision included.”

Ian Simpson, HSE principal specialist investigator (mechanical engineering) says, “A few years ago, we pushed for interlocks on stabilisers, but that was rejected.” Stabiliser interlocks use proximity switches to tell if the stabilisers are fully extended, and stop the crane if they are not. “This time, we went for having the rated capacity limiter monitor the position of the stabilisers and limit the capacity according to their deployment. This time it got passed.”

Alan Johnson, technical director of the UK Association of Lorry Loader Manufacturers and Importers (ALLMI) and director of SJB Crane, says, “Ultimately, the standard has evolved to this stage as a result of the incorrect deployment and/or stowage of stabilisers being one of (if not the) highest causes of accidents and sometimes fatalities. To fail to address this issue is not an option.”

Danish loader manufacturer HMF already offers a stability supervision system as an option. René Dahlkilde, HMF product manager for cranes and a member of the CEN EN 12999 revision working group, says, “At HMF, we came up with our own solution, the EVS system, about 10 or 11 years ago. At the time we thought it would only be a short time before it was demanded by the standard. We were a bit surprised it took so long, not coming into effect until 2010. But, now we have a lot of units running, somewhere around 1,000–1,500. We look at the new norm with calm; all of our workshops are prepared and used to the system.”

The EVS system is a small box mounted on the crane. Once calibrated, it provides a precise measure of the inclination of the vehicle. This measure can be used to limit the crane’s capacity if risks becoming unstable.

Dahlkilde says, “It was an expensive option for customers, but some saw its possibilities. When the installer tests a crane’s stability, they have to do it with an empty truck. [In use,] the EVS system allows you to use the system with an [additional] stability load in the back of the truck, increasing its capacity. The EVS system senses the inclination angle of the vehicle. By putting weight on the body, you can keep the vehicle more stable. That allows you to use more of the crane’s capacity. We needed to put in that customer advantage, to make the system attractive when it wasn’t mandatory.”

“With no stabilisers down, the vehicle can still move very fast; but with the stabilisers extended only to 30cm [12in], using the EVS system, it is very hard to make the vehicle unstable.

“We think there are advantages to measuring the angle of the vehicle rather than, for example, the pressure on the stabiliser legs. We saw measuring the angle of inclination as a better and safer parameter. The installer can set the permitted inclination when the system is installed. For example, the system can be set up to allow a stabiliser leg to lift by no more than 5cm: that’s a very precise and defined measure of the vehicle’s stability.”

Terex Atlas has also developed its own stability systems for some cranes, but is working now on making them universal across its range, in line with the revision. Terex Atlas engineering and technical manager (and ALLMI representative at the CEN revision group) Bryan Flintham says, “Most Terex loader cranes offered for the commercial market have a stabiliser monitoring option available through the rated capacity limiter. However, at the moment this option cannot be used in combination with other options which monitor the slewing angle (such as protection for a raised platform or an area of reduced stability over the cab).

“Customers who required such combinations have been accommodated using special designs. These tended to be based on our 10.5t models, but due to the commonality of the base components, the same package could be implemented on most models between 8.5t and 12t. These designs were for specific contracts and have not been not updated, in line with developments of the standard products. Consequently they can only now be configured for use with remote control.

“In order to meet the revision of EN 12999, stability monitoring needs to become a core function of the control system rather than the add-on option offered currently. Given that the stability of any given truck and crane combination will be different from every other, our focus is to get the most flexibility from the fewest number of common components. This approach will give our customers the flexibility they require, minimise the cost increase, and maintain productivity. We are well on the way with development and are optimistic that the market will react positively to what we will be offering in 2010.”

Other manufacturers, including Hiab and Fassi, say they are working on new systems, but, like Terex Atlas, are not ready to announce the specifics.

Understanding stability

Developing systems that meet the requirements of the standard are just one step in the process. Dahlkilde points out that communication with users is key: “In our experience it is complicated for users to deal with stability. Even understanding how stability on a loader works can be difficult. Operators are good at assessing risk, in a way that the stability systems can’t. The operator can see the difference in risk between lifting a load two metres off the ground close to the crane, and lifting it 20m in the air. The stability system might stop the crane in both situations, depending on the load.

“The operator will need clear signals of what to do, and how to operate cranes using the system. The operator might be seeing warnings for different reasons: it may be overload or it may be stability; it may be he’s slewed into an unsafe area, or he’s tried to pick a load that’s too heavy for the crane. He has to know what the problem is, and what to do about it.

“There will be a number of manufacturers offering different stability systems. There will be a problem with operators needing to know each of the systems they use. We need to look at how we put signs on the loaders so the guy using it knows what he is doing, and that he can trust the stabiliser system.

“This may be somewhere where we, as manufacturers, don’t compete, but try to move towards the same sort of solution. I’ll be going to trade shows, and looking at what other people are offering. We want to make sure we don’t add to the confusion.”

Flintham says, “Cranes supplied today often have different rated capacities for different areas of the slewing range. The operators do not have any problems with this. The crane will stop when the rated capacity is reached and make a signal to the operator, who must make a movement which reduces the load moment in order to get it moving again. I can see no reason why this needs to any different whether the rated capacity is varied with either slewing angle or stabiliser position. The action required from the operator is the same in all cases.

“The planning, however, will be more complex. Due to the likely complexity of factoring in different slewing arcs, and different stabilising positions, rated capacity charts will become either much more numerous or much more complex. Appointed persons and other personnel may well require further training to better include these into the planning process, and I would expect the industry at large, though associations like ALLMI, to come up with updated training standards.”

Rydahl says that the philosophy behind the standard has changed too, in light of other standards. Specific machinery standards like EN 12999 refer to general standards for safe design. The standard that had been used as a reference, EN 954, required designers to carry out a risk assessment on each component, and classify them according to particular safety categories. The safety category defines the ability of the components to withstand faults, and how they will behave if a fault occurs. Industry standard like EN 12999 would then require that all components fell into a minimum safety category.

The new design safety standard, EN 13849, looks not just at individual hardware components, but at software and the overall safety function of a system. Instead of safety categories, it introduces a new concept, ‘performance level’. The two systems of classification do not match up neatly, and loader cranes will have to meet a performance level that is, Rydahl says, more demanding than the component safety categories that came before: “The old standard of safety used a classification of the hardware safety class of the components. The new standard puts in a requirement based on the function of the system: that includes how the system is put together, and the software it uses.

“In the old standard, components had to fulfil category 2 of EN 954. In the revised standard, the safety function of the crane must meet performance level C of EN 13849, which is quite a lot tougher. EN 12999 also requires that when the safety function is not fully working, the crane must stop.

“Manufacturers must provide safer and more reliable components, or users would see too many stoppages. The market will require we use better components so users are not troubled by malfunctions in the safety systems. The number of components used will increase, as the number of sensors on the crane and the requirements on the sensors increase.”

The demand that the crane will stop working if the safety function is not operational is a concern among users. Johnson says, “It is nearly always the case that most new safety devices meet with some market resistance both in terms of cost and ‘user-friendliness’. In terms of user friendliness, any operator using their crane correctly for its designed purpose and in accordance with the manufacturers’ instructions should experience little or no difference or difficulty.

“Operators who fail (deliberately or otherwise) to use the crane stabilisers properly are the ones who may experience some issues—and of course the standard has been evolved to this level to protect them.

“It is perhaps also not unfair to say that historically, the introduction of new systems and technologies into any market place can result initially in a higher level of breakdowns, partly as a result of ‘young’ technologies and partially from a lack of operator understanding or awareness.”

Maker’s mark

To sell any machinery in the EU, manufacturers must CE-mark their product, certifying that it has been manufactured in line with the Machinery Directive and relevant standards. The Machinery Directive defines a manufacturer as someone who assembles a device prior to offering it for sale. That could be a traditional manufacturer, but it could also be someone who modifies or installs another manufacturer’s device. The new revision, and changes to the Machinery Directive, will change the relationship between crane manufacturers and installers.

Rydahl says, “In the old Machinery Directive, the loader cranes as delivered by companies like Hiab aren’t included in the definition of a machine, as they don’t function until they are fitted on a vehicle and connected to a power source. The crane is fitted to the vehicle by the bodybuilder, not by us. So, it is the bodybuilders who have to CE-mark the installed crane, and do the paperwork.

“The definition of a machine in the new Machinery Directive has been changed, largely with loaders in mind, to say that a device is considered a machine, even if it has no power source, if it needs only to be connected to a power source. It is considered a machine, even if it needs to be fitted to a vehicle, if it only needs to be fitted to a vehicle.

“That means that now, when the crane leaves the factory, it is considered a machine, and we will CE-mark it.”

However, the manufacturer will only be able to certify that the crane meets the requirements of the standards if they know what chassis it will be installed on. Dahlkilde says, “A lot of information will have to go from the manufacturer to the installer. He has to know about testing, doing dynamic tests of the system. When we send a crane, we do not know what body it will be installed on, so we have to define the stabiliser spread, test loads, stabiliser position, for different axle configurations and vehicle weights.”

Terex Atlas’s Bryan Flintham says there is still work to be done on defining the calculations installers must make when fitting and testing stability systems on cranes with variable outriggers. “The effect on installers of cranes configured for variable rated load moments and variable stabiliser positions should not be underestimated. The revised standard talks about using stability calculations to predict the behaviour of the truck and crane when the stabilisers are in positions other than fully out and fully in, but does not appear to specify a calculation method, or the safety factors to be used in such a calculation. This is for the individual manufacturers to decide.

“The standard requires overload testing to confirm the stability at the fully out and fully in stabiliser positions, but then places a reliance on stability calculations to predict the stability of the truck at all other stabiliser positions.

“My own personal view (which is not necessarily that of Terex) is that the stability margin quoted in the standard to calculate the test load in the fully-out position may prove inappropriate for the fully-in position. The test load is calculated with respect to the load moment and with the legs fully out, the overturning moment is considerably less than the load moment. With the legs in, these values are much closer together and a greater margin may be advisable, especially with lighter trucks, which have a tendency to skip about with very little encouragement.

“The standard does not require overload testing for the intermediate stabiliser positions, only that the stability calculations may be confirmed using a load equal to the maximum load at maximum radius. It then goes on to say that the intermediate stabiliser positions can be tested at a reduced radius, provided that the overturning moment with respect to the tipping line is to be maintained.

“Using the ‘maxi load at maxi radius’; method of checking an intermediate position implies that a further calculation will be required to establish the overturning moment with respect to the tipping line. Furthermore, the standard does not say what action is appropriate should the stability of the truck not live up to the predictions of the calculations. Having discovered the maximum overturning moment, the installer would then use this to calculate what the rated capacity should be and have the crane’s control system updated accordingly.

“I expect that installers would welcome some industry guidance covering the application of this standard, not least in respect of the calculations required for verification of stability.”

While the work of revising and voting on the standard may soon be completed, manufacturers, installers and operators still have a lot to do to prepare themselves for 2010.