In 2010, the Hong Kong International Airport replaced Memphis International Airport as the biggest, top-ranking cargo airport in the world. According to figures provided by Airports Council International (ACI), the airport handled more than 4.1 million tons of freight in 2010, almost twice the amount that was handled at Frankfurt/Main airport that same year.
Hong Kong Air Cargo Terminals Limited (Hactl) is the world’s leading air cargo terminal operator. About 70 percent of Hong Kong's air cargo is handled in Hactl's facilities, more specifically in SuperTerminal 1, which has been in operation since 1998. The six-storey air cargo terminal that was designed by Sir Norman Foster provides approximately 46,6436.3 square yards (390,000 m²) of storage space. At both the main and express terminal standard air freight containers with frozen goods or livestock, among other goods, are handled.
The stacker cranes in many of the terminal’s high-bay storage warehouses are still being controlled by Trimble ICS5000 systems, which were discontinued in 2005.
Quality made in Germany
When looking for a positioning solution that would be both extremely reliable and easy to integrate Hactl came across PSI Technics, a German manufacturer headquartered near Koblenz. “Two things were important to us, said Hactl Engineering Service team lead Toby Wong: A proven track-record with similar retrofitting projects and a system that could be integrated into the existing hardware with minimum downtime”. Having installed its Positioning Solution System at Volkswagen, Daimler and Bosch facilities, among others, PSI Technics possessed the relevant experience an important operation like Hactl needed.
The comprehensive preparation guaranteed fast installation and commissioning. The retrofitting of a stacker crane in the terminal's Bulk Storage System (BSS) in 2010 marked the beginning of a successful partnership between the companies. A high-bay warehouse with more than 10,000 storage slots houses all types of general cargo, such as electronic goods and clothing. Typically, the BSS handles between 10,000 and 15,000 storage and retrieval tasks per day. Hactl's request for minimum downtimes was met by an in-depth analysis of the facilities provided by PSI Technics engineers during an on-site audit in the Autum of 2010. The insights gained during the audit regarding the old positioning system and the PLC ensured that the new positioning system would be installed and fine tuning within a short period-2 working days at the end of 2010.
Optimized control loop
The installed Positioning Solution System is a stand-alone digital control system. The system permits the continued use of existing components such as PLCs, converters and motor drives. On site, the system is controlled by a PLC using the MODBUS TCP protocol. Another unique feature that supported a fast commissioning is the system's largely automated configuration. The Positioning Solution System automatically performs a characterization, eliminating the need for a time-consuming manual control parameter configuration and adjustment. The characterization provides an optimized control loop modeling based on the existing conditions.
The control loop is the part of a system that needs to be specifically optimized. The system provided by PSI Technics is a dynamic system that transfers motion equation`s to the controlled stacker crane. In this case, the primarily optimized control variable is the traveling distance.
The stacker crane is supposed to follow a motion profile from point A to point B. A controller monitors the control variable by means of control parameters. In a closed control loop, the controller uses sensor feedback to achieve a desired, predefined system behavior over the entire travel distance.
The travel profile calculated for Hactl also factors in the maximum acceleration and maximum velocity. At the Hong Kong terminal, the velocity of the stacker crane's horizontal axis could thus be increased by nearly 7% while the start delay decreased by nearly 40%, meaning Hactl could improve throughput that can result in enhanced profitability.
During system operation, the Positioning Solution System uses feedback from optical distance meters (in this case a SICK DME5000) to continuously monitor the stacker crane's movements. It optimizes the motion path in real time and completes storage and retrieval tasks within the shortest possible time. Acceleration and velocity profiles are based solely on linear ramps, irrespective of load, which significantly eliminates creeping speed. The shorter storage and retrieval times ensure the high throughput required by Hactl. PSI Technics' web-based software interface provides access to all of the system's characterization, control and diagnostic functionalities. The user-friendly software only requires a brief introduction—no programming skills are needed.
PSI Technic's Energy Optimizing Software (EOS) was installed as part of the Positioning Solution System. This unique software solution synchronizes the x- and y-axis while the stacker crane is moving and adjusts the velocity of the shorter axis. The EOS software has proven to reduce mechanical stress, increases the life span of components, and has optimized energy consumption by up to 15% in select applications.
Hactl operates a total of 24 stacker cranes in their BSS. PSI Technics retrofitted the first stacker crane on site. A total of thirteen stacker cranes were retrofitted to date. After the modernization the stacker cranes moved with the same acceleration and velocity with visibly lower oscillations, which significantly reduces facility wear.
Hactl was satisfied with the results of the PSI Technics approach and solution and initiated a follow-up project in 2012. PSI Technics retrofitted another Trimble ICS5000L system within a short period of stoppage – two working days. This time an Elevating Transport Vehicle (ETV) was modernized.
“The references of PSI Technics' positioning solution and the high service quality were crucial for our investment decision”, concludes Wong. The decision to partner with PSI Technics (psi-technics.com) has paid off, and is planning the modernization of the other stacker cranes in SuperTerminal 1. By now, PSI Technics' technicians have become quite familiar with the terminal. With their help, the airport will continue to strengthen its position as the world's biggest air cargo hub in the future.