PLC and Operator Interface Advantages Stack Up for a Large Container Automatic Stacking Crane Project

PLC and Operator Interface Advantages Stack Up for a Large Container Automatic Stacking Crane Project
PLC and Operator Interface Advantages Stack Up for a Large Container Automatic Stacking Crane Project

The Port of Virginia operates two inland and four coastal marine ports. As shipping demand continued to grow, in 2017 the Port embarked upon a project to expand two of these sites, at the Norfolk International Terminal (NIT) and the Virginia International Gateway (VIG) facilities. A major part of this expansion included the supply and integration of 86 automated-stacking cranes (ASCs), which was the largest single ASC project ever initiated by a port (Figure 1).

Figure 1: The Port of Virginia added 86 automated-stacking cranes using PLC-based automation integrated by TMEIC under Konecranes’ turn-key ASC system delivery to VIG. Photo courtesy of Port of Virginia.

To carry out a project of this scale and complexity, the TMEIC Corporation (Toshiba Mitsubishi-Electric Industrial Systems Corporation) in Roanoke VA was retained to provide an industrial drive and automation solution for the Konecranes ASC system. TMEIC already had a long and successful history with the Port, having been involved with the original VIG ASC implementation with Konecranes a decade earlier.
The new expansion would rely in part on updated programmable logic controller (PLC) and human-machine interface (HMI) automation. Integration would provide advanced remote-control capabilities so operators could work from a centralized control room—instead of a crane cab—using video, advanced sensor technology, and HMI displays. The PLCs directly controlling this massive crane equipment with exquisite accuracy needed to provide robust operation, extensive connectivity, and scalable architectures.

Heavy lifting

Cranes designed to transfer standard shipping containers among ships, storage yard stacks, rail cars, and truck trailers have been a fundamental part of modern high-efficiency logistics and shipping for many years. Although to some the equipment may seem large, lumbering, and decidedly old-school, there is a great amount of detailed coordination and sophisticated technology operating behind the scenes (Figure 2).

Figure 2: Large cranes rely on modern PLCs, advanced sensors, and responsive integration with motor drives for positioning with an accuracy of better than 50mm. Photo courtesy of TMEIC.

These rail-mounted gantry (RMG) cranes move in 3 axes. The gantry is the entire assembly which rolls forward and backward on wheels along the entire length of container stacks, often on rails or tracks, while the trolley is the upper part of the gantry and it can move left and right along the width of the crane across the stacks. The hoist uses cables to support and position a gripping mechanism—also known as a spreader—to lift and lower containers in the vertical axis (Figure 3).

Figure 3: The gantry, trolley, and hoist provide three degrees of motion, and the automation system must act to dampen undesired cargo movement. Photo courtesy of TMEIC.

Payloads can be unevenly loaded, and this weight differential makes them more difficult to handle and place. Because the cargo containers hang down from cables and the whole assembly is movable, there are mechanical reeving features to dampen motion, and the drive systems must also incorporate active dampening. A standard cargo container is 40 feet long and can weigh up to 40 tons, yet it needs to be captured successfully, and then landed with an accuracy of 50mm.
Many years ago, cranes were fully controlled by operators who sat in cabs high on the gantry so they could have a clear view of the work. Once video and PLC technology improved sufficiently, it was possible to locate operators in a control room (Figure 4).

Figure 4: Integrated video and control consoles enable operators to monitor and control cranes. Photo courtesy of TMEIC.

This paradigm of remote ASC operation began internationally in the late 1980’s. In 2007, TMEIC automated the first North American ASC at VIG as part of Konecranes’ turn-key ASC system delivery. TMEIC has integrated and automated over 600 ASCs worldwide, establishing them as a leader in the field.
Remote operation makes cranes lighter and improves safety. It also lets a few expert operators control whichever crane is ready for operation, instead of having operators move from crane to crane, which in some cases requires traversing hundreds of yards.
The latest evolution is modern ASCs, which incorporate advanced computing, sensors, and networking to automate most aspects of operation. Operators closely monitor automatic operation and may become involved to perform the initial container capture, complete the final release (especially if the designation is a trailer chassis), or take action if there is an issue. Otherwise, the container will travel from pick-up to drop-off location automatically in the optimal manner (Figure 5).
Figure 5: Modern HMIs provide crane operators with detailed feedback regarding the status of crane and cargo handling operations. Photo courtesy of TMEIC.

Integration of advanced sensors with the automation platform makes this possible. The main instrument is a LIDAR-based laser distance sensor, and the gantry and trolly are instrumented with RFID pucks so their locations can be determined within a range of 15mm and 5mm respectively.
From a port logistics standpoint, a software-based overall management system called the terminal operator system (TOS) coordinates and schedules all movements. Loading and unloading vessels takes priority. When the ASCs are not occupied with loading and unloading operations, the TOS may direct a buried container to be made accessible, or perform background tasks like handling a queue of containers to be moved around the yard to groom the stacks and optimize upcoming operations. One last detail is that ASCs operate in pairs with overlapping paths, so special deadlock logic must be implemented to ensure neither ASC interferes with the other.

Technical and logistical challenges

To successfully achieve the necessary functionality and address all technical requirements, the right automation platform was required. Many capabilities had improved between 2007 and 2017, but after reviewing the TMEIC team determined PLC-based technology was still the right choice. New demands included networking and communication for integrating intelligent sensors, communicating with the supervisory TOS, and scaling up with so many ASCs.
For instance, the improved LIDAR systems use proprietary main control units in order to resolve distances with high accuracy. The PLCs would need to rapidly interrogate these intelligent distance sensors via the control units to obtain responsive positioning information. For all new PLC communications, the team wanted to take full advantage of modern OPC UA and Ethernet Global Data (EGD) communications. The latter would ensure compatibility of the 86 new ASCs with the 30 existing units to the greatest extent possible. In fact, at some point it would be likely that new automation devices and sensors might be retrofitted to existing equipment.
AC variable speed drives (VFDs) used in the motor drive panels had also gained intelligence over this time period, and the PLCs would need an even greater amount of communication capabilities to take advantage of these advances for remotely commanding parameters like speeds and ramp rates, and deeply interrogating the available performance and diagnostic data.
TMEIC scope included designing control panels, yard I/O panels, motor drive panels and all integration from their Virginia-based North American headquarters. On top of these technical tasks, there were the logistics of coordinating activities among many international team members from TMEIC’s Virginia-based location:

  • Konecranes is a Finland-based company
  • The cranes are physically fabricated and assembled in Poland
  • Pre-assembly would include a degree of electrical and functional testing in Poland
  • After pre-assembly and testing, the mechanical and electrical designs needed to support disassembly and transportation over the ocean via BigLift Shipping
  • Each remote operator station was built in Italy and would be shipped direct to VIG and NIT, except for a handful shipped to Poland for integrated testing, and yard I/O panels were assembled and shipped from various locations
  • TMEIC-supplied motor drive panels were fabricated in Japan and shipped to Poland for integration
  • Motors and other advanced sensors were procured from various sources worldwide

While the crane manufacturer designed and built the mechanical equipment, TMEIC provided all electrical and automation equipment by applying their specific knowledge of drives and automation developed in this sector over many years. With the requirements clearly defined, the TMEIC automation team proceeded with detailed design.

PLC integration advantages

The first generation of ASCs at VIG predominantly used PACSystems RX3i PLCs, which still serve reliably today. For best interoperability, the natural choice moving forward was to select the newest generation of Emerson’s robust PACSystems RX3i PLCs. Emerson’s strong focus on providing end users with a simple and easy upgrade path for both control hardware and software, along with its commitment to expanding open communications and advanced control capabilities within the PACSystems RX3i portfolio, also made this the best choice.
System architecture design proceeded (Figure 6), with each of the 86 ASCs to have its own local crane management system (LCMS) with a maintenance HMI and crane PLC on-board. A remote operator station (ROS) PLC would use remote I/O at each at each operator workstation to handle the signals needed for users to perform monitoring and control tasks. More PLCs would be used for tasks like coordinating truck traffic.

Figure 6: Each of the 86 local crane management systems employs Emerson’s PACSystems RX3i PLC, while a redundant pair of PLCs handles all remote operator station I/O and connects each operator with the crane they are managing. Figure courtesy of Emerson.

A key for the operation would be a crucial nexus formed with two of supervisory PLCs configured as a fully redundant pair, called the Yard Director PLC System. The Yard Director is logically interposed between all the crane PLCs and the ROS PLC, acting as a matrix switcher for cross connecting each ASC with the proper associated operator.
Each crane PLC installed locally on an ASC would be tasked with:

  • Interfacing to obtain payload source and destination assignments, and to identify when each transfer is complete. This is accomplished via a database exchange where commands are bidirectionally queued and processed by PC-based TMEIC CraneDirector software which communicates with the site’s TOS and the PACSystems RX3i PLCs.
  • Interfacing with other PLCs for command and control.
  • Performing all interlocks with field devices and other crane PLCs.
  • Interacting with the HMI system for operational and diagnostic indications.
  • Handling all I/O processing, local control and stability logic.
  • Monitoring and controlling the intelligent VFDs and handling active-dampening logic to stabilize the payload.
  • Monitoring the intelligent LIDAR subsystem, each of which has its own main control unit PLC acting as a black box to aggregate many different sensors. This is accomplished by PC-based TMEIC Maxview® software and interfacing with the crane’s PACSystems RX3i PLC.

Each ROS would pass the proper ASC information to the operator HMI, and it would send operator commands out to the assigned ASC.
The Yard Director PLC System interacts with all crane PLCs and the ROS PLC to:

  • Monitor a queue of cranes which are idle but have a job assignment from the TOS.
  • Assign the next available operator to the next crane in the queue.
  • Logically link the individual crane PLC and ROS controls for each job and ensure a responsive low latency connection is maintained.
  • The PLCs also select the proper camera views through IP address management.

Visualization is performed using PC-based HMI software, with each ASC running a standalone PC-based HMI to provide local visualization needs at the ASC. A site-wide view is provided with the same HMI software configured in a supervisory control and data acquisition (SCADA) role. The HMI/SCADA also historizes data, and it provides both centralized and remote alarming.

Keeping a clear path

With so much equipment, a variety of data, and dozens of PACSystems RX3i PLCs in play simultaneously, close and careful coordination is paramount. This came to light with regards to crane-to-crane and crane-to-operator interactions.
Crane-to-crane deadlocking
As noted earlier, ASCs generally operate in pairs with each crane focused on an end of the operation area. However, this means the paths overlap for each pair of cranes, introducing the possibility of potentially disastrous collisions.
To prevent this, each pair of crane PLCs is in rapid and constant communication with the other to identify the location and travel plans for the equipment. Each PLC runs meticulously crafted deadlock logic to ensure only one crane can enter the interference zone at a time. When a crane leaves the zone, the other crane is notified the space is available. Deadlock logic is critical not only to avoid a collision, but also to minimize delays and provide maximum efficiency and availability for operations.
Crane-to-operator signal mapping
The Yard Director PLCs must be redundant and always available because they are the linkage between ASC and ROS PLCs. Communication linkages established and maintained by the Yard Director must be very high-speed and flawless so operators can have real-time control of the cranes.
However, as they overall yard operations scale up with many more ASCs and ROSs, the cross-connection and bandwidth challenges become exponentially more complex. Not only are many more combinations possible, but there can be many more connections active in parallel at the same time. Fortunately, the latest PACSystems RX3i PLC hardware, software, communications protocols, and networking media were up to the task.

A better tomorrow

Looking to the future, data scientists from both the Port of Virginia and TMEIC are looking at how to most efficiently gather all the available “little data” and aggregate it into big data which can be analyzed to drive additional efficiencies. These initiatives are often called digital transformation, or industrial internet of things (IIoT) projects.
Predictive maintenance, key performance indicator (KPI) metrics, and enhanced diagnostics will help the port operate optimally, and provide valuable feedback so systems integrators and OEMs can improve performance. With Emerson’s PACSystems RX3i PLCs, the foundation is in place for this advanced data gathering and consolidation.
TMEIC has developed core knowledge from an extensive history of integrating and automating ASCs. For this world-class project at VIG, the size and scope demanded a lot from the automation platform. By choosing Emerson’s PACSystems PLCs, the team was able to deliver a technically superior solution for robust operation at a much larger scale than the previous installation.

About The Author

Jill Burdette is a strategic account leader for Emerson’s machine automation solutions business. She works to help customers with projects around the world to solve their toughest problems, by understanding their business needs, being a thought leader, and proactively bringing new ideas to the table. Jill holds a master’s degree and in Mechanical Engineering from West Virginia University, and is based in Richmond, Virginia.

Michael Cooper is marketing vice president at TMEIC Corporation Americas in Roanoke, VA. Michael oversees the company’s global marketing team and works with the various operating business units to expand into new markets worldwide. Mike has over forty years of experience doing business around the world and in particular in China and Asia. He was one of the first fifty US graduate students sent to China to study and do research following normalization of diplomatic relations between the two countries in 1979 and subsequently lived in Hong Kong having served as managing director of the Far East subsidiary of a German machine builder.
Michael has a B.A. in Modern Chinese History from Rutgers and an M.A. in Asian Studies and an M.B.A. in Marketing and International Commerce from Seton Hall. He currently serves on the Virginia-Washington D.C. District Export Council under the US Department of Commerce where he previously was vice chairman.

Matt Mandros is the system development manager in the technology department at TMEIC Corporation Americas in Roanoke, VA. Matt began his career as a field engineer in the late 1980’s at GE, holding roles including control engineer, software development engineer, and value engineer. Later, he spent 12 years running his own business. Matt joined TMEIC and has progressed through the project manager and operations manager roles there. Matt has a BSEE from University of Pittsburgh and an MBA from Virginia Tech.

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