On a recent tour of a Middle East job site, one construction manager told visitors that, despite having eight towers working together, he’d chosen not to use any anti-collision system, as it caused unnecessary stoppages and would slow down his work schedule. In the UK, prominent tower crane users have expressed their own doubts about the systems, saying that they won’t actually stop cranes hitting each other.
Cranes Today put these complaints to SMIE general director Alain Voyatzis. He says: “Big French companies still use anti-collision systems, even in countries where they are not required to. These are very cost-conscious companies, but they still believe the total cost analysis of using anti-collision systems is positive. If the use of the system is well understood, there should be no constraints.
“The SMIE system will stop the crane, if it’s installed properly on the crane and if it is not overridden. The machine interface, if installed, will stop the crane when a collision risk is detected. The UK user may be referring to an instance where the system wasn’t set up or installed properly, or was overridden. If there is any error in the system programming, during installation, or if there is any change in the geometry of the site that is not reflected in the set-up, then the system won’t stop at the right positions. It’s only a matter of bad usage.”
Voyatzis continues, “There are sometimes technical questions on how the cranes brake, and how the machine interface can be fitted. This usually is due to the fact that some cranes are either too old or do not abide by the CE (Machinery Directive) requirement that all cranes (from 1994 on) must have provisions for adapting anti-collision systems on them. Also, there are some cranes where there is no place, or easy method, to fit a trolley sensor, however, we can normally find a way to make it work.”
The older the crane stock, the more difficult that process may be. More than 80%of the 1,200 tower cranes in Israel are more than 20 years old, with some up to 40 years old, according to Israeli crane consultant Felix Weinstein. “On many sites, there are more than two cranes working, and anti-collision systems are needed. However, fitting the systems is very complicated on these old cranes.”
Instead of using anti-collision systems, Israeli laws dictate a system of setting up cranes with minimum distances in between, and using slewing limiters. Weinstein explains, “Where two cranes are working in the same area, there must be a horizontal distance of 2m between the lifting jib of the lower crane and the mast of the neighbouring crane. There must also be a vertical distance of 2m between the hook of the higher crane to any part of the lower crane. These regulations are based on the French standards. The reason for setting these distances is that a crane will deflect during lifting. These distances are enough to ensure that the worst that can happen is that the lower crane may strike the cable of the higher crane.
“To prevent this happening, all cranes must be fitted with a limiter switch on the slewing ring. When either crane enters the common area, the switch will stop the crane. The crane operator will then have to look around to see if there are any obstacles around and then press a button, and the crane will slew at reduced speed through the common area. The operators will also have to be in communication with each other, and with a signaller working on the common area. Where both cranes want to work in the common area, the signaller will act like an air traffic controller, deciding which crane is allowed to work.”
The latest European tower crane safety harmonisation, EN14439:2006, requires that tower crane manufacturers wishing to sell their products in the EU make it possible for users to install anti-collision systems. In practical terms, this means that users should be able to fit sensors to slewing rings, hook carriages and luffing jibs, connect the whole system to a power cable, and have a machine interface access the crane’s braking system. The harmonisation echoes the requirements of the 1998 UKinterpretation of the Machinery Directive, which states, in clause 4.1.2.6 b, that:
where several fixed or rail-mounted machines can be manoeuvred simultaneously in the same place, with risks of collision, such machines must be so designed and constructed as to make it possible to fit systems enabling these risks to be avoided.
This requirement to ensure anti-collision systems can be fitted reflects a deeper commitment to their use in many neighbouring countries of the region. In one country, France, the devices have been mandatory on all tower crane installations, under a Ministry of Labour directive issued in 1987. This 20-year requirement to make use of the systems has meant that French companies such as AGS, SK Group, SMIE and Ascorel have come to dominate the market for the manufacture of third-party anti-collision systems.
Common characteristics
Guy Galand, formerly a technical manager for Potain, and now a consultant running his own company, Startec, explains, “In the past, before the devices were made mandatory in France in 1987, they were very simple, and weren’t a convenient solution. The newer devices on the market are in a good technological state, high quality and safe. They are easy to use, convenient for the driver, and convenient for people responsible for set up and maintenance, even with several machines.”
All of the systems built by these dominant manufacturers share a number of common components. The nerve centre of the system is a computer that monitors sensors on the crane, communicates with any other cranes working in the same area, and tracks potential hazards. All systems will stop the crane when a collision is imminent or when a crane is about to enter a protected area. Different systems also offer variations on operator feedback, data logging, and online monitoring.
The central processor monitors hazards in two ways. First, sensors around the crane provide data on the position of the crane’s mast and jib. A slewing sensor, a cog that fits into the teeth of the slewing ring, will monitor the crane’s rotation. On a trolley jib crane, a sensor on the hook trolley will keep track of the position of the hook. On a luffing jib, a sensor at the point where the jib meets the mast will track the luffing angle. Where the crane is mounted on rails, a third sensor will track its movements backwards and forwards. All of these sensors will be connected to the processor, using a cable network.
The processor will take the information on the crane’s position from the sensors, combine this with data on the load and the speed that the crane is moving at, so that it can not only track where the crane is at any given moment, but also predict, in real time, where it is headed and how fast it can be safely stopped. By taking additional data, such as wind speed from anemometers, the system can more accurately predict the potential movements of the crane and its load.
For a single crane, these sensors, used in combination with a map of the job site, will be enough to prevent over-flying a protected area. On job sites where more than one crane is in operation, the cranes will be connected on a wired or wireless network, making it possible to track potential collisions. As cranes move towards a protected area or a collision, a warning can be delivered to the operator. If the crane continues past this point, the crane will be stopped automatically, and movements limited to those that take the crane away from the hazard. Where necessary, the anti-collision system may be overridden. Typically, this will mean that a crane can pass through a protected area, but at a reduced speed. When the system is disabled in this way, a warning light on the mast will light up, to alert workers on the ground.
Setting up an anti-collision system involves three steps. First, the sensors and processors must be fitted to the crane. As Vincent Thevenet, technical manager for Ascorel, explains, “The same system can be used on all cranes, with no modification needed to the main system. It takes about one day to fit the components on to the crane. Depending on the type of crane, different sensors must be installed. For a luffing jib crane, an angle sensor is used, and for a trolley crane a carriage sensor. The same software is used for both type of cranes. The technician just needs to select which type when the system is being installed.
“The system can be fitted on cranes from all manufacturers. It is easy to remove the anti-collision device from, say, a Liebherr luffing jib crane, and then fit it on a Potain trolley jib crane. During installation, the technician needs to modify the parameters (such as dimensions or height) of the crane that it is installed on.”
Next, the position of the cranes at the site must be entered into the processor software. Thevenet continues, “The crane’s position can be programmed by marking X and Y coordinates on a map, using known measurements. If the crane’s position is not known in advance, you can slew the booms of neighbouring cranes so that they are in line, measure the distance between, and validate their position in the software. This process is repeated for each crane on the site, to determine the position of each crane.”
Finally, the position of any forbidden areas needs to be entered. There is growing debate over the best way to do this. One company, e-Build, claims that its TAC-3000 can use location information digitised in the office, and then uploaded to the crane. The firm claims that this means that setting up the system “requires about 1 to 1.5 days for installation and commissioning as compared to other systems requiring about 3 to 5 days.”
Alain Voyatzis, director general of SMIE, is sceptical of this claim: “Pre-programmed measurements are not accurate to the centimetre level. They rely on drawings and site plans.” Instead, SMIE, and most other anti-collision system manufacturers, recommend ‘teaching’ the system where forbidden zones are. Thevenet says, “The technician moves the hook to the edge of the limit area, and validates its position in the software. This process takes around a minute for each point.”
Conclusion
With European manufacturers launching updated products, and Asian competitors joining the fray, tower crane users find themselves presented with a range of anti-collision systems offering an array of different benefits and added features. However, this choice presents its own problems. As different contractors on adjacent inner city job sites choose their own anti-collision systems, they will find that the systems cannot communicate between each other, and they will still face a collision risk from the other site’s cranes. Perhaps anti-collision system manufacturers should be looking to develop an open communications standard, to allow their systems to work alongside each other? If they are reluctant to, maybe regulators should be choosing a communications
system for them?
An overview of the products
AGS
AGS’s AC3 system uses configurable software modules, to allow the user to set permanent and temporary exclusion zones. The first module, GACP, handles anti-collision management. A second module, ZISP, can manage 32 prohibited segments. Each segment is defined by a point at either end. This can be combined with the third DZISP module to activate and deactivate specific zones. Finally, the fourth DZIH module activates and deactivates specific zones by hook height. Up to 16 cranes can be covered by the system, and groups of cranes can be bridged, so that larger numbers could be covered if needed. The system is operated, and points acquired, using a touch-screen.
The anti-collision system can be used with a supervision unit in the site office. Thierry Valle, AGS engineer, says, “You can send this overview to another touch screen in the office, and record all of the values from each of the cranes. This can include additional data from other AGS products, such as anemometers. All of the data is available in CSV (comma separated value) format, on a USB stick, so it can be exported to PC software such as MS Excel. You can, for example, see the wind statistics for every day of the job. It records diagnostic and logging information for the anti-collision system, such as if the system was bypassed, or if there was a problem with power to the crane or radio transmissions.”
Ascorel
Ascorel’s system is sold by the tower crane manufacturer Potain, under the Top Tracing brand. Despite this association, it is suitable for use on all trolley- and luffing-jib tower cranes. The processing unit measures 330mm x 230mm x 110mm, and weighs 7kg. The system can control up to nine cranes, linked over either a wired RS 485 cable, or using wireless radio at 870MHz, 433MHz or 458MHz. Modules are connected using CAN-Bus. A monochrome graphical display shows the safety conditions of each movement, and information on radius, slewing angle and length of travel (for rail-mounted cranes).
Thevenet says, “Up to ten limit areas can be defined, with 16 points per area. Limit areas can be a single point, a line, or a complex pattern of lines. Of all our customers, I’ve never known anyone that needed to define more than five or six limit areas, and never more than eight points per area. All these parameters can be managed from the ground, with one technician selecting and activating them.”
Chengdu
Chengdu Hi-Tech Crane Safety, from Chengdu, China, manufactures a nine-crane anti-collision and zone protection system, the CXT/30A. A central computer at the site office can be used to update information on crane heights and to monitor the location and operational status of all cranes on the site in real time. Users also have the option to keep operational records for review.
e-Build
The TAC-3000, on show at Bauma, hall A7 stand 300.2, is designed to be set up using site drawings, rather than by teaching the crane the position of each point. While many users question the method, the company is confident of its accuracy and says it can save up to a day and a half of setting up. Uniquely, the system uses magnetic angle sensors to plot the crane’s movements. This is, again, aimed at cutting setup times, as the sensors do not need to be connected to the crane’s gears.
The TAC-3000 can monitor 10 cranes on a wireless system. Users can set a 25 point working area boundary, and six prohibited zones with eight points on each. Inter-module communication is by CAN-Bus, with cranes communicating wirelessly between themselves, to a distance of 500m. A full colour LCD TFT graphic display relays status and warning messages to the operator, and the system can be monitored from the ground using the same wireless network.
SK Group
SK Group’s Navigator combines information on position and speed, load and moment, wind speed and direction, in real time. As well as preventing collisions and overflying of protected areas, the system presents the level of collision risk as a percentage, allowing the operator to see when a collision may be approaching. Unlike some other systems (see ‘Editor’s View’ Cranes Today March p7) SK’s device includes a black box that maintains a log of collision risks and shunts. This information can be transferred to the site office, and can be archived.
Similar to the AGS system, the Navigator can be configured to allow over-flying of protected zones when no loads are carried. The system can monitor up to 32 prohibited areas, with 100 points in each. These can be programmed as x, y, and z coordinates, or entered by acquisition. The system uses high speed, encrypted, radio communications, and can be combined with a VoIP (voice over internet protocol) telephony system, to replace traditional two-way radio.
SMIE
SMIE has launched two new systems. The AC 243, launched last year, is marketed as the firm’s fourth generation. The AC 246, aimed at European users, will be launched at Bauma, and features a number of adjustments to comply with EN 14439.
Alain Voyatzis, SMIE director general, explained that the new AC 243 replaces a system that was about ten years old. It is claimed to be easier to install and uses improved materials. It can control nine cranes wirelessly, and 30 cranes on a cable network. It can be used with the company’s ENIA supervising and recording device, which can give a visual overview of all the cranes working on the site, either directly in the site office, or remotely over the internet.
The AC 246 has the same features as the AC 243. It also boasts mechanical protection of gears, a failsafe slewing sensor, auto testing software, and a test button in the operator’s cabin.
