ANTI-SWAY
SWAY AWAY
Traditional cranes are prone to swaying, which can lead to accidents and damage. The digital age has brought anti-sway and collision avoidance systems to increase efficiency and safety. Julian Champkin investigates.
T
echnology moves quickly. The sci-fi fantasies of a very few years ago are the unremarked realities of today. Anti-
sway is one of them.
Josh Childers is training and technology manager at Ohio-based R&M Materials Handling, and was working in the crane industry when anti-sway was introduced to the market. “In 2005, I was working for R&M’s parent company and they were the ones who, around that time, brought sway control to the marketplace. It was what was called passive sway control. Calculated sway control is another term for it.” Sway control comes in two types. One type is passive; it is also called sensor-less sway control, open-loop or calculated. The other type is sensor-based, also called active or closed-loop. Passive sway control is the simpler of the two.
“It works off the pendulum principle. A load
on a rope or chain is essentially a pendulum, and how much it moves when you move the bridge or trolley does not depend on the weight of the load. It only depends on how long the
rope is. You have to add in the length of the sling as well, but once you have that it is just a mathematical calculation to work out how the load is going to swing,” explains Childers. “The technology at that time just used a small encoder that counted how much rope had been paid out (for example, do I have 1m or 2m?) and they added a compensation for the sling length. That gave the total pendulum length, and once that was known, the PLC did a small calculation and said, ‘Hey, the pendulum is this long. So, if we give it a horizontal movement, we need to compensate for that up top where the trolley is.’ And it told the bridge and trolley inverters how to move, how much to accelerate or decelerate to keep the pendulum from swaying,” says Childers. It is known as passive because it was based on calculations, rather than knowing how much the load is swaying. The only input is the rope length, speed and directions of the trolley’s horizontal movements. “ “If a passer-by walks up and gives the load a push, or if a forklift bumps into it, or if the wind blows the load around – the system has no
clue. That was a limitation. It is working in a perfect world of its own,” says Childers.
Reality strikes
Real life or course is not perfect. Forklifts and passers-by do exist. “For that reason, you really wanted an operator keeping an eye on it, to stop it when real life intervenes,” explains Childers.
What, then, was the advantage? “You
have to remember that this was 20 years ago, back in digital prehistory before things like the smartphone were invented. Back then, it was revolutionary. Sure, you still needed an operator. But even newer operators who maybe didn’t have the experience to manually control the weights could now be entrusted with it. And if you had sensitive or delicate loads, it could really reduce the damage to them. So for the time it was phenomenal.” But time moves on, and we now have active sway control – sensor-based or closed loop systems. “Rather than relying solely on calculations we clamp an inclinometer to the rope. It sends back the angle of the rope, so the
R&M overhead crane with fieldbus sway control 22 | October 2025 |
www.hoistmagazine.com
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