Under Control

24 May 2019

Digital control systems have advanced hugely; the more that digital control can do the less the strain on the operator, the greater the efficiency and safety. Julian Champkin looks at control systems that aid the operator, and at how manufacturers have used them in their cranes.

What stands the crane operator in best stead? Is it skill, training, experience, intuition? Anything that can aid the beginner, or supplement those years of knowledge that the expert has acquired, is to be welcomed. The easier a crane is to operate, the more efficient it will be, and the greater the safety it will offer.

Control systems for cranes are increasingly digital and virtual. Games-control-style joysticks have replaced levers and cables in cabins; screens convey to the operator images from cameras at the end of the boom, giving them a birds-eye or closer view of the hook and the load. Feedback from sensors into software warn them when load chart limits are being approached, and indeed will calculate those load charts, not just for ideal setups, but for real-life situations where ground may be sloping, track widths asymmetrical, clearances limited and ground conditions far from ideal.

The common purpose of all these changes is to reduce complexity, make the crane easier to use, more intuitive, less reliant on operator's skill and judgement, so that it becomes in effect an extension of their arm and mind. ‘Immersive’ is the vogue tech-jargon word for software that transforms user, machine and the world around them into one single seamless system, but it does describe the objective very well.

Software relies for its data on hardware. Sensors from makers such as MTS and Siko can now digitise almost anything, from positions and angles to accelerations and force loadings, and are so small that they can be fitted inside a hydraulic cylinder with no loss of stroke. You need a data-rich environment to control a crane, but supplying the data is now not a problem.

As a starting point for this digitally-enabled transformation, the obvious place for a crane operator to be is high up on the crane. Or is it? The cabin of a tower crane gives an overview from height, but is distant from both the load, and from the lift and dropping points.

Give the operator alternative views and magnified views, from cameras mounted on the boom or the hook or elsewhere and relayed to the cab, and the job becomes easier and safer.

Take that to its logical conclusion and there is no need for the operator to be in the crane cabin at all. Many companies offer remote control systems, even for large and complex cranes. Smaller cranes can be operated by hand control pads, not unlike a TV remote; for larger cranes, with more functions, a controlling transmitter slung at waist level from the operator’s neck is more usual; these are commonly known by the unglamorous name of bellyboxes.

Control At Hand

The Italian company Imet has been in the field of remote control for decades; it offers systems for, among others, tower cranes, gantry cranes and knucklebooms. “Radio remote controls exist to help operatives do the job better, more safely, in a more comfortable and a more efficient way,” says Edgar Antonio Jiménez Dorigo, export area manager at Imet. “If the operator is not high up on top of the crane he is away from danger. Control at a distance offers that option.” Imet’s systems can be installed by manufacturers or retrofitted into existing cranes.

“Programmability of the software means that you can add as many functions as you like. It is very flexible. We have customisability,” he says. Data feeds from the machine back to the operator’s 3.5in small screen, up to 300m away.

For continuous operation over long periods the Twin B model has two battery compartments. When the first accumulator enters ‘low battery’ status the second takes over with no interruption of power supply and hence no transmitter shut-down.

Åkerströms’ Remotus Jupiter is a robust standardized remote-control product line developed for industrial and overhead cranes. The system has pre-programmed selections and works on general frequency bands, so users, they say, can easily install and start up the system. The transmitters of their most recent model in the range, the Jupiter Era, have dual CPUs for safety and an active stop function, which means that the receiver will activate the stop function in less than 100 milliseconds.

Abitron has introduced a new transmitter series, the T-series. Their design feeds back data from the machine to a colour display, which can also show video from webcams on the machine. “It can control anything anywhere,” is their boast.

Critical functions on the transmitter have a dead man’s switch: unless the joystick is pressed while it is being moved it will not send a signal, which makes it hard accidentally to set the crane in motion.

Safety and reliability are obviously crucial in this area. Autec is another manufacturer in this field, and their bellybox transmitters are resistant to temperature extremes, to shock and vibrations, even to electromagnetic disturbance. Casings are resistant to oils, paints and thinners. Electronic as well as physical robustness is emphasised by all manufacturers.

A failure of wireless communication between transmitter and machine— or even, these days, a hacking attack—must not imperil safety.

Thus: “RF communication is made through a certified and proprietary system which is suitable for safety critical applications,” says Manfred Pauli, technical manager sales and service at Autec Deutschland. “Each remote system uses its own unique code which cannot be reproduced.”

Even so, as with other manufacturers, the system is designed so that each receiver can be paired with any transmitter in the series. Autec’s multiple ‘Take and release’ transmitter systems allows several operators, up to 15 of them, sequentially to control a single machine. Each operator has their own transmitter; in order for a transmitter to assume (‘Take’) control of the machine a previous operator must ‘release’ the machine.

Autec have taken the idea to its logical conclusion with its ‘pooled resource’ system, where multiple users can control multiple machines across multiple shifts, and even across multiple jobsites. The same remote can control several different machines, and each machine can be controlled by one of several transmitters; but each machine can only be controlled by a single transmitter at a time. The pool can involve between two and four receivers and transmitters.

Similarly, with Imet’s system, two or three operators in turn can control one machine. “That is useful if lines of sight are obscured,” says Jimenez Dorigo. Imet’s KAPTA option allows pairing of any transmitter to any receiver on the same project. Imet also offers wired remote controls via cable, without the need for radio interfaces, for environments where RF is unsafe or disallowed. Åkerström users can also manoeuvre several machines from the same transmitter; alternatively several users can manipulate the same machine—for example during a lift in which the start points and drop points cannot both be seen from the same place.

A concern with controlling mobile machinery—or indeed static machinery—remotely by an operator standing some distance away is that should they trip, fall, or otherwise become suddenly incapacitated the driverless machine would run on out of control. Åkerströms’ Era’waist transmitter has a built-in tilt function, which means that if you fall while you are wearing it, the machine will stop. Autec’s Zero-G sensor activates when the transmitting unit falls from a height greater than one metre, or when it is tilted at more than a defined angle, or when it experiences impact or is thrown or rolled.

The Man Machine

A second step in simplifying control is to make crane and operator a single unit. This is machine as extension of man. The more intuitive the control system, and the more that intellectual and mechanical demands are replaced by software, the easier and simpler, and safer, is the operator’s task. Moving a boom and hook to lift a load should be as easy and as intuitive as stretching out your arm and hand to grasp a teacup. Progress towards immersive control systems have come a considerable way.

Liebherr’s LICCON intelligent crane control system was first devleoped in 1989. In its current incarnation it incorporates load moment limiters, is tailored individually to each crane, and can be programmed and adjusted flexibly to suit the needs of the individual operator.

The company is particularly excited about its ‘Boom up and down aid’ addition. It is available for lattice crawlers in the 100t to 300t range.

When lowering the boom to near or below horizontal, for example for dismantling, there is a risk that the crane might tip. This is so even when the hook is unloaded: the moment of the boom itself at such angles is huge. “Normally LMI (Load Moment Indicators) and LML (Load Moment Limiters) have to be turned off or do not work in such situations, because the boom angle is negative,” Wolfgang Pfister, head of strategic marketing and communications for the Nenzing smaller crawler factory. “You need to do an inverse calculation in such situations, which is something that has not been possible up to now.” Liebherr claim to be the first manufacturers to solve that problem. “The ‘Up and Down Aid’ safety system automatically stops the operation before it enters an unsafe zone. This is really a huge safety advance,” says Pfister.

The software’s calculations also take wind speeds into consideration. Data from wind sensors on the main boom and jib is fed into the system, which automatically derates the load charts accordingly. “The operator no longer has to make estimates of how great a safety margin he should leave,” he says. Such estimates naturally, and properly, err on the side of safety. “Now he will know exactly how much he should deduct from the zero-wind-speed charts for the wind conditions he is experiencing.”

Liebherr have yet another addition to their crane control aids, in the form of ground pressure visualisation. It is a system that has crossed over to the crane sector from Liebherr’s range of piling and drilling rigs. Sensors and software calculate the distribution of pressures that the crane is exerting on the ground, and displays it on a screen. Typically ground pressure will be greatest at the front of the crane, which is taking the weight of the jib and load, and least at the rear—an overloaded crane would tend to tip forward, the rear of the crawlers leaving the ground first.

The screen displays this variation on a silhouette of the crane; a band of colour tapers from broad at the front, where pressure is greatest, to narrow—or in the limiting case nothing—at the rear. “Once you know the maximum allowed ground pressure you can put it into the system and again the operator can see directly both the actual and the allowed pressures. It shows both; and he can always see the difference between what he has at that moment and the maximum that he is allowed to have,” says Pfister.

“As soon as he slews the crane the ground pressure diagram adjusts itself to the new conditions. And when it approaches a safety limit, it will warn him.”

It uses Liebherr’s Crane Planner software. Now in its version 2.0, parameters of a projected lift can be fed into it, and its visualised displays of crane, loads and surroundings will give snapshots of a lifting project at every stage of its progress, with lift radii, load charts, ground pressures, and other data. It will even suggest the best crane to use for the job.

Tadano’s Lift Compass allows the operator to move loads with a single joystick, controlling both lifting and slewing; this, according to Matthias Schneider, marketing editor for Tadano, significantly reduces the operator's workload. In the interests of still further removing any unnecessary physical barrier between crane and operator the joystick has an adjustable sensitivity control, working at the touch of a button, so that it can be set to the pressure that best suits the operator.

Tadano also have their Lift Visualiser: cameras mounted on the end of the boom, halfway along it, and at the height of the crane hook give the operator a bird’s-eye view of the lifting, lowering and moving of the load. The image can be sent to a screen in the cabin; or, as with Liebherr’s Crane Planner, the whole lift can be modelled and simulated, away from the site and before the lift happens, in virtual reality.

In this set-up the user can be an apprentice learning the trade or an experienced operator establishing the best possible options for a complex move. They wear a set of virtual reality goggles, and with joysticks on a bellybox control the virtual movements of the virtual crane; the crane and its movements are modelled, with the surrounding buildings and load, as 3D images seemingly surrounding the user, who is effectively part of this virtual world.

They can choose their own position in it, operating the crane from the cab, or standing on the ground or on a rooftop up to 50 (virtual) metres horizontally or 100m vertically from the cab.

“It is a lot safer that way,” says Schneider, happily conflating real and virtual worlds. “He can see people in danger and tell them to move.” This virtual world can be populated with virtual people to add realism.

A yellow circle on the screen or in the goggles’ viewing field shows the position of the hook. When you slew the hook the load on its end sways as a real load would.

Readouts give the height of the load above the ground, the speed of the crane, and so on. Yellow and red lines show boundaries of safety and change position as loads and boom positions change. If you are using a bellybox it will vibrate when these are approached too closely. “It aims to give the equivalent of the intuition of experienced operators who can ‘feel’ when a crane is nearing its limits of stability,” says Schneider. “It really is an immersive experience.” Curiously, perhaps, raw beginners take to the whole experience much more readily than do experienced operators.

Tadano hopes to have the system available in Europe in two years' time, when regulatory processes about wireless frequencies and the like have been passed.

But it will not be the final step.“Tadano’s aim for the future of this technology is ‘Building Information Modelling’, BIM,” says Schneider. It will be a planning aid for major long-term projects such as high-rise housing complexes.

Clearances and heights of lift change as such projects progress. The early stages may need low lifts and offer wide spaces to do them; as the project nears completion, higher lifts are needed and structures already built may impede access and restrict clearances. The planning can be complex; BIM will allow such projects to be tried out in virtual reality in advance. From the architect’s plans, a three dimensional digital data model is built up inside the computer of the project at various stages of completion. The weight, size and shape of each part to be lifted is also fed into the model.

“We can simulate the whole project in advance, in virtual space, and show it to the customer,” says Mizuki Yoneda of Tadano’s Advanced Technology Research Centre. That way potential problems can be identified in advance, and solutions found, instead of incurring real-life delays and costs. Estimated time-scales are two to three years for the technology to be available for simple structures, and ten years at the latest for complex projects.

The rate of change of digital technology has been accelerating in all fields, and crane control is one of them. Whether this will remove the need for skilled operators is something that only time can tell. It is to be hoped that human expertise in crane operation, hard-won over many years, will remain valuable and valued, and that new crane control systems will aid crane operators, not replace them.

A tower crane under Autec remote control
Imet’s THOR2 radio remote control
An Åkerströms controller, suspended from its crane
A Siko position sensor inside a hydraulic cylinder
Abitron’s T5 controller, with joysticks and digital screen