When you lift something, it is a good idea to know what you are lifting. In the old days a guess about its weight was probably the best you could do, plus a rough idea of whereabouts its centre of gravity might be. But we are in the information age now; and we can know much more about the load, what it is doing, the way that we are lifting it, the stresses and wear we are putting on our ropes and machinery, and how many more weeks or months or years will go by before we should think about replacing one of the worn-out parts. This is what load monitoring is about; and given the pace of the advancement of digital technology, and its ever-increasing affordability, it is a rapidly-progressing field.
Ohio-based R&M Materials Handling sells to independent crane builders. “R&M has offered load- and condition-monitoring via our Hoist Monitor for quite a while,” says director of sales, Damian Mulcahy. “However, only recently has the technology been developed to transform the information into an easy-to-read application for improvements in safety and enhanced predictive maintenance.
“So now R&M’s Hoist Monitor collects real-time performance data from the hoist and transmits it wirelessly to our OLI (Overhead Lifting Information) app installed on your Apple or Android device.
“The OLI app then organizes and displays the data into a user-friendly format that can be exported and shared with R&M’s technical support team for remote troubleshooting.”
Three main elements make up the app. “First, the ‘Usage’ screen displays current hoisting conditions, such as the current load, operating temperatures, cycles, and runtime, along with important safety information including the number of emergency stops that have been made. Next, the ‘Events’ screen displays the faults recorded by the Hoist Monitor. This helps to warn the crane operator of potential problems and assists service technicians in troubleshooting issues that may affect hoist performance. Lastly, the ‘Condition’ screen predicts needed maintenance, plans downtime, and ultimately reduces overall maintenance costs. The designed working period is also displayed, for the hoist as a whole and for typical wear items such as contactors and brakes.”
As Mulcahy has implied, load monitoring requires two things: sensors – such as load cells – to acquire data, and software to analyse it.
Manuel Cornil, technical sales director at Sensy, takes us through the main types of load cell that are available. He is well placed to do this because Sensy has been a pioneer of load cells on lifting gear; and one reason Sensy has been a pioneer is because it is Belgian. As he explains:
“Sensy started 35 years ago, making weighing load cells for the agricultural industry – compression cells, tension cells and so on. Then in 1991 Belgium was the first country in the world to make it mandatory for any hoist over one ton capacity to have overload protection. So that started a huge retro-fitting campaign on overhead cranes, especially in the steel industry which at that time was still strong in Belgium. We have been involved in load cell overload protection devices ever since, and now we export worldwide.”
Simplest and cheapest of the devices that measure the strain in a rope is the clamp-on. It does what it says: it is clamped on the wire lifting-rope, between the hook and the drum; in the process the rope is bent slightly out straight. The load on the rope tends to straighten it out again.
“The technology is very simple,” says Cornil. “The more the wire straightens out the more it presses against and deflects the clamp; a sensor measures that deflection and sends a current accordingly to the overload protection device.
“When the current reaches a set value it triggers a relay which sets off an audiovisual alarm signal.
“The clamp-on load cell is cheap, quick to install, and a very cost-effective solution,” he says “but it has some disadvantages. You need to clamp on at some distance from the anchor point and at some distance from the hook block. That means that you lose at least 0.5 metre of lifting height from your hoist.
“The other disadvantage that customers should be aware of is that the signal depends on the bending characteristics of the wire rope, so recalibration of the system will be necessary each time they replace the wire rope.
“Clamp-ons generally send their signal by cable, but it is usually simple to arrange a cable-reel to avoid it fouling the drum. Overload protection is almost always hardwired. Wireless overload protection does exist but is an expensive solution. That is because safety requires that you must be sure that it will work every time. With a wireless system, that requires a double channel, which makes it costly.
“More accurate than the clamp-on, but also significantly more expensive, is the load link. Here too, you lose lifting height, because it attaches by shackles between the rope and the hook; but since the link itself takes the strain of the load and is part of the load-path there is no need to recalibrate when you renew the rope.
“The third option is the load pin, which I think of as the Rolls Royce option. It is the sturdiest solution. Being directly integrated into the anchor point or upper sheave you lose no lifting height; and again you do not have to recalibrate with a new rope. There is a fourth solution, the last man standing, which is the running line tension meter; it works like a clamp-on but is fixed to the upper sheave rather than the rope, so instead of going up and down with the rope, the rope runs through it, pushing against rollers.
“Which option you chose does not depend entirely on capacity: as important is the work-cycle of the hoist and how vital it is for your operations.” The overload alerts are sounded by Sensys Crane Boy or Bridge Boy modules: they have three relay set points, of which one can be set for overload protection, one for slack rope alert, and the third for a pre-alarm or some interim value that is of interest.
“The legal requirements of any load limiter,” says Cornil, “are, first, positive safety; that means that the relay must trip if the signal between the sensor and the end limiter is lost. The relay must also trip if the overload protection device is not powered, because you can’t use a crane if you have no overload warning; the relay must give full overload protection at 110% or 125% of the crane capacity depending on country; and it must also have a test button that lets you check the functionality of the overload relay without having to lift a real, live, overloading weight. All of those features are available on our whole range of overload monitors.”
For the analysis part of load monitoring, David Mullard, business development manager of Crosby Straightpoint, talks us through the process. US hoist-makers Crosby acquired UK load-cell makers Straightpoint in 2019; the reason says much about the growing importance, indeed centrality, of load monitoring, as he explains: “Straightpoint is a load cell and load monitoring business, and what comes with that is you can get loads of data about your hoist and load. Crosby make lifting and rigging hardware. One reason they acquired us was because of the growing importance of monitoring loads and data and the advent of Industry 4.0.
“Crosby have a massive focus on traceability and vertical integration. They like to be in control of their supply chain, to know exactly where the steel is coming from and to do in-house all the processing of everything that they sell. So they also wanted to be in control of the monitoring and data acquisition aspects.
“Straightpoint is the same: we mill and turn our own parts, so we have that full traceability of where the material came from, and do our own pre-testing and installing the strain gauges and calibrating, all in-house; and that was one of the things that Crosby found really attractive when they started talking to us in 2018.”
Straightpoint’s data analysis product is called Insight. “It is something that we’d been working on prior to Crosby acquiring us; we think is the easiest and most intuitive piece of software out there. It is a little bit special in that it fuses three resource-critical things all in one software package. The first thing it can do is monitoring and logging; and it can handle very complex lifts.
“Suppose you have a lift that has, say, 50 load cells: it could be that you are lifting from 50 points and you want to know the load at every single point around that lift. You could monitor it with this piece of software, and you could see immediately if something wasn’t stable, or if something was snagging so there was a risk of overloading one side, or you could simply be reassured that your lift is nicely set up, that all the ropes are taking equal strain, and that you’re not overloading or stressing about the thing that you’re lifting as well.
“You can monitor that entire lift from start to finish, and you can see in real time if there is anything that is getting overloaded; and by sending the data readout to your customer you can also prove to him at the end of the lift that everything has been done right and his precious cargo also didn’t get overloaded. It protects the contractor, it protects the customer, and it hugely increases safety. Insight can handle up to 126 load cells at a time.
“So that’s for the lift itself. Before that you need to plan the lift; and for that you want to know where the centre of gravity is. ‘Insight’ will tell you.
“The customer or the engineering drawings can tell you roughly or theoretically, but you need better than that: the load may have had 10 tons of paint applied to it, it may have sumps filled with oil that has weight, and the lifting rig itself has weight that must be considered. The solution here is to use compression load cells. Support the load on them – again as many as you want, up to 126.
“Each one transmits wirelessly to the ‘Insight’ monitor; and from the position of each and the load upon it the software calculates the overall centre of gravity of the item to be lifted, to the millimetre if you want. So you can position your hook directly over that and achieve a smooth lift without sway,” adds Mullard.
“The third thing that Insight can do is that it can monitor proof tests. It could be a crane or a hoist or a shackle, or an offshore crane that is being tested by lifting waterbags that are filled with a known volume and so a known weight. Either way you need evidence to prove that your machine can lift an exactly calibrated, certified weight. Our load cells are calibrated when they leave the factory against independent standards that are themselves calibrated against the National Standard; so there is traceability back to that, and a digital record from our load cells is evidence of compliance.”
Crosby Straightpoint’s prime load cell is its Radiolink Plus: “That is our Number One global best-seller. It is a massive product and very popular. We can supply them up to 300t capacity, and for high and low temperatures – minus 10C up to plus 50C: and we have ATEX explosion-proof and subsea versions as well.”
Load monitoring is becoming standard in the industry but is not quite there yet.
“As with any new technology, heightened awareness is essential,” says R&M’s Mulcahy. “Early adopters are experiencing the benefits in field service, reducing downtime, and creating a safer working environment. The only additional costs for them are for the hardware, which is minimal in comparison to the overall cost of the hoist, and the benefits vastly outweigh the investment.”
And this, he says, is just the beginning. “Moving forward, we will see advancements in condition monitoring of all of the traveling motion components, and not just on one single crane but facility-wide, with systems that are all sharing data and working together. It’s an exciting time.” Big Data Monitoring, here we come….
