ANTI-SWAY
Radio Receiver
Bridge Inverter
WiFi Inclinometer ECU Gateway IoT
Trolley Inverter
Operator Commands and operational data flowing in both direction on the fieldbus.
Schematic of the Fieldbus Crane control systems.
crane intelligence device now is getting real- time information and live feedback. It ‘knows’ the position of the load, not just theoretically, but for real; even if someone has given the load a shove, or if it has bumped into something or if the wind has blown it sideways,” he continues. “Now it is actually using the real-time
measured position of the rope and it modifies the speed of the trolley and bridge machinery to keep that rope in a non-swaying state.” Active sway control is now powered by an inclinometer attached to the rope that provides a real time measurement of the rope angle and direction of movement. The rope position and movement is actively measured rather than passively calculated. The inclinometer feeds the position measurement to the HoistMonitor Enclave crane intelligence device that communicates with and coordinates the bridge and trolley inverters to eliminate any sway detected, whether is it created by the crane movement or by an external force placed on the load.
So passive anti-sway is dead? According
to Roland Najbar, it still has its place. Najbar is business development manager for cranes at Siemens. Siemens have both open-loop and closed-loop sway systems in their portfolio. “Open-loop or sensorless systems are less
expensive,” he says, “because they are based solely on a control algorithm in the drive. They are not suitable for outdoors application, where wind and the like can be a large factor: mathematical algorithms alone cannot predict ever-varying wind forces, so sensor-led
systems are required for those applications. For applications where there are external forces, such as wind, closed-loop systems are required. “Another scenario that an open-loop system cannot detect is where a person – usually someone rigging the load – introduces movement on the load, or if it swings due to the initial lift not being quite vertical. A truly open- loop, sensor less system will have no way of determining if the load is swaying or moving: it always assumes that the load is starting from a standstill. So, if a load is already moving, the open-loop sway control system will have a difficult time stabilising it.” Closed-loop systems, however, have input
from sensors and closed the control loop. They use this feedback to automatically adjust their behaviour for a desired outcome.
Safety and experience Anti-sway in one direction is easy to understand. In many cases – in an overhead bridge and trolley system, for example – loads may sway in both X and Y axes. In the case of a jib crane, slewing will make for more complex motions still.
“In a typical crane with hoist, bridge and
trolley, the sway control occurs in the bridge and trolley directions,” Najbar says. “Usually, this is all controlled by the same motion control system, and if sensors are involved, it would usually only involve sensors – say, a camera – on the hoist where the cable pays out and a sensor, a reflector, on the load block.” The camera sends a pulse to the reflector, and from the time of the
journey can work out the distance the pulse has travelled. “That way the system can actively calculate the angle of the load and eliminate the sway in the system based on the desired speed or positioning of the load. A slewing system is harder to control because more calculations go into it, but it can be done with the correct closed- loop sway control system.” Najbar goes through some of the advantages – obvious and less obvious – of anti-sway. Primary, of course, is safety. “Absolutely, and especially in tight spaces that use manually controlled cranes, such as some automotive or battery assembly applications where people are involved. Reducing the sway or preventing off-centre picks can reduce injuries and fatalities because the load is no longer swaying around. In some systems, off-centre picks are automatically not allowed. This system will require the trolley to auto-centre over the load before lifting to prevent the case where a load is lifted off the ground and swung into a person.” There is also ease of operation. “The beauty of sway control systems now is that you can have an on-the-fly active damping factor that determines how much sway control is offered. So, for example, if you have a new operator, you can increase the damping factor which will increase the gain on the sway control system, most likely making the new operator’s job easier. But if during the next shift you have an operator that has been doing this for 40 years, they are the sway control, and may want to reduce the system’s contribution to the bare
www.hoistmagazine.com | October 2025 | 23
Trolley Panel Hoist
Inverter
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