New crane control systems and operator interfaces improve safety, reliability, and flexibility of old ships, making them ready for new missions.
New control systems and operator interfaces for cranes used on old U.S. Coast Guard ships improve safety, reliability, and flexibility, making them ready for new missions.
The Coast Guard has two older polar class icebreakers, the Polar Star and its twin, the Polar Sea, originally launched in 1976 and 1978, respectively. Key pieces of equipment on the Seattle-based research vessels are at the end of their service lives and are scheduled for replacement in the coming months. (The Polar Star is the first of the pair to be overhauled, and the Polar Sea will be next.) Among the items that are being replaced are the hydraulically operated cranes on the bow and stern of each ship. Along with new crane hardware and new hydraulic power units, the Coast Guard wanted to install new crane control systems and operator interfaces that will improve the safety, reliability, and flexibility of the ships’ operations. Allied Systems of Sherwood, Ore., and Concept Systems Inc. of Albany, Ore., experts in material handling and control systems development, did the work.
Each ship has three cranes, one on the bow and two aft. The bow crane handles loads of up to 6,000 lb and is used to lower provisions intended for the ship’s stores into the forward hold. In addition to running the bow crane, the associated hydraulic power units (HPUs) also run the anchor windlasses. The aft cranes are heavy-duty units with operator cabs and a jackknife structure to enable a long reach. They are used for onloading and offloading scientific gear in portable shipping containers (ISO standard conex boxes) and for lifting work boats.
Crane retrofit requirements
Several factors were important in the Coast Guard’s list of requirements for the new cranes. In addition to wanting touchscreen operator interfaces at the crane stations, the Coast Guard wanted a master control panel in the engineering room. Centralized control makes it easier to monitor what the various control stations are doing, as well as monitor hydraulic power unit (HPU) status and generate alarms for conditions, such as high or low hydraulic oil levels and high temperatures. The centralized monitoring requirement dictated the need for a shipboard network.
Another key requirement was flexibility in providing backup systems to keep the cranes operational in the case of control system, network, or HPU malfunction.
HMIs are designed with intuitive interfaces that can be reconfigured easily for different control tasks, or can be used for displaying diagnostics as shown. Courtesy: Concept SystemsA flexible hydraulic design includes a hydraulic circuit that allows fluid flow diversion with the flow path selectable via the network to enable operation of all crane systems in the case of individual HPU failures. If a bow HPU should fail, fluid from the other bow HPU is rerouted to power the bow crane or windlasses.
The Coast Guard selected Allied Systems to provide the cranes and hydraulic systems. Allied specializes in developing low-volume, highly engineered cranes, and has done several material handling crane projects for the U.S. government in the past, so it was natural for the Coast Guard to select the company to help with refurbishment of the two icebreakers. The new crane control system designs were tested at Allied’s facility in Sherwood, Ore. (see Figure 1), prior to installation on the ships at the Todd Shipyard in Seattle.
Control system design
To do the control system and operator interface development, Allied Systems selected Concept Systems. Allied had worked with Concept Systems on other projects, including an automated 3D vision-guided crane system for the U.S. Navy, and Concept’s experience with developing reliable control systems using the latest technologies made it a natural choice for this project.
Allied Systems and Concept Systems worked closely together in the control system design, resulting in a Rockwell ControlLogix PLC-based system with a PanelView Plus Operator Interface. To ensure the system performs well in harsh environments, care was taken to specify proper components, such as conformally coated modules and electrical devices.
A programmable logic controller (PLC) at the center controls everything, with Rockwell Flex I/O located at each HPU. The hydraulic pumps selected are variable-displacement piston units, actively controlled by software developed for the PLC by Concept Systems. The design provides a pressure feedback loop that senses the load at each crane and tells the HPU pumps when to stroke, adjusting each pump’s pressure output to ensure there’s adequate pressure available to control the system, while allowing energy savings if full power is not needed.
Concept Systems’ controls allow the two forward hydraulic power units to be teamed up if necessary to produce maximum power. In the aft, each hydraulic power unit is dedicated to a particular crane, but the units have sufficient reach to enable them to take over the other’s job.
Concept Systems also developed control systems for heating or cooling the hydraulic fluid tanks to keep them ready for service in all environments. This is done by controlling valves that direct the flow of seawater when cooling is to be done, and by operating heaters in the tanks when the oil must be kept warm. (There’s a common oil tank for the HPUs at the bow, and there are two tanks at the stern.) Other sensors were also incorporated into the system to monitor such things as when hydraulic fluid filters need servicing.
Concept Systems engineers programmed the operator interface in the control room to monitor status of all four HPUs, and they programmed the operator interface at the windlass to see the two forward HPUs. Alarming specific to the units being controlled is available at the operator interface for those units, as well as communicated to the central control panel. Emergency stop control inputs were established to de-energize the HPUs in separate zones, one for the bow systems and one for those in the aft. Hitting the windlass E-stop de-energizes the hydraulics at the bow of the ship, whereas the E-stop in the main control room will de-energize the ship’s hydraulics.
To save effort and promote maximum flexibility, Concept Systems designed all of the operator interfaces around a common program and display architecture that can be configured for the specific HPU that is being controlled. For example, if the operator interface that controls HPU number 1 was to experience a failure of the touch panel, then HPU 2’s operator interface could be reconfigured quickly to control the first HPU.
“This wasn’t a requirement of the design,” said Concept Systems engineer Scott VanDelinder, “but it made sense from a development perspective.”
The Polar Star icebreaker sits outside the McMurdo station in Antarctica. The Polar Star can break ice up to 21 ft thick and steam continuously through 6-ft-thick ice at 3 knots. Courtesy: Concept SystemsConcept Systems programmed the operator interface modules, developing a common look and feel for a particular HPU that would be intuitive from an operator perspective. Common on-screen objects were used that look and feel familiar to operators who have experience using other crane and winch systems. Beyond the control functions, Concept Systems added diagnostic capabilities to the operator interfaces that would allow for IO wiring troubleshooting in the case of problems with the system. Maintenance screens show the status of the I/O signals, such as tank sensor values, to make it easier for the Coast Guard’s staff to diagnose and deal with problems in the field, a feature that makes a significant impact on downtime related to troubleshooting.
Completing a project as complex and unforgiving of errors as this research vessel upgrade requires thorough testing in addition to advanced design. The Coast Guard’s acceptance testing checklist for the new crane systems was 52 pages long, involving checking all system inputs and outputs, calibrating all analog I/O connections, and verifying that everything operates as required in normal and problem response modes.
This project is an example of how companies with specific areas of technical expertise can work together to develop unique solutions for special needs.
“We’re good at designing cranes, but we’re not networking and controls experts,” said Dan Gott, Allied Systems engineer. “The innovations that Concept developed, such as the electronic load sensing and active pump controls, and their experience with advanced, intuitive human interface design, helped us enable the Coast Guard to return these two old icebreakers to service functioning better than when they were new.”
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