ADVERTORIAL FEATURE | ABB STACKER CRANES
DRIVE AWAY THE SWAY FOR
JOON-SUNG LEE, OEM MANAGER, MATERIAL HANDLING, ABB DRIVES, EXPLAINS HOW VARIABLE SPEED DRIVES (VSDS) WITH BUILT-IN ANTI-PENDULUM FUNCTIONALITY CAN OVERCOME OSCILLATION PROBLEMS FOR TALL STACKER CRANES.
work faster and more efficiently. To reduce material handling times and operational costs, automated storage and retrieval systems (AS/RS) have come to dominate the intralogistics industry. A common feature of these systems is the automated stacker crane. Stacker cranes that operate on rails
W
in narrow aisles have become popular because they are effective, safe, and relatively inexpensive. Now, warehouse operators are installing taller, faster, and lighter-weight stacker cranes – but this has created a new problem: “sway”.
arehouses play a crucial role in the modern economy, and operators face constant pressure to
THE SWAYING PROBLEM As these large, fast-moving machines operate, the inherent flexibility in their frames mean they can move, swaying from their normal position. In this way, they act as an inverted pendulum. If this is not kept under control, a stacker crane can suffer instability and loss of positional accuracy. In severe cases, this oscillation can also compromise safety and cause damage to the crane itself or surrounding infrastructure. The movement involved can be significant. For example, a 35m tall stacker crane running at full speed can sway by around 1m in the axis of travel. The sway can last for more than ten seconds. It is not safe for the crane to store or retrieve a
pallet while it is swaying, so this reduces the system’s throughput. One way to address this issue would be to operate the cranes more slowly, but this isn’t an attractive option as it would also reduce productivity. Another solution is to apply more precise and smarter control to the motors that move the crane.
ANTI-PENDULUM DRIVE CONTROL Variable Speed Drives (VSDs) control the torque and speed of the motors powering the stacker cranes. Reduced swing can be achieved by utilizing drives with an integrated anti-pendulum function. This works by creating a mathematical model of the crane’s movement and the load’s height
Stackers have become popular because they
are effective, safe, and relatively inexpensive
22 | October 2022 |
www.hoistmagazine.com
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