A Capstone Project on Robust Dynamic Positioning and Data Acquisition Systems

The United States Coast Guard is responsible for enforcing Dynamic Positioning System (DPS) standards in the maritime industry. It is important for the members of the U. S. Coast Guard to understand how these systems work. Students have gained a much greater understanding of how DPS platforms work and what might be required to maintain them by building one from scratch. Aside from this, the project has served as a great opportunity to work on a one year term project that may resemble engineering or acquisitions projects that might be encountered in the students’ future careers. The overall goal of the Robust Dynamic Positioning and Data Acquisition System project was to prototype a dynamic positioning system similar to the ones on buoy tenders in the fleet. The primary goal was to maintain a desired heading and position within a certain range. The secondary goals included robust capabilities (the ability to continue functioning despite motor failures) and data acquisition (to analyze system performance post-testing). Students built a vessel from scratch out of a salvage drum and an inner tube for buoyancy. The internal construction consists of three tiers containing batteries at the lowest level, an onboard computer at the second level, and control hardware at the top level (micro controllers, H-bridges, and fuse boxes). Students successfully used a light detection and ranging (LIDAR) device to determine the relative position to two stationary poles. They were able to communicate with the onboard computer via either a wired connection or a remote desktop connection through an ad-hoc wireless network. All programming for this project was done in MATLAB®. Students have completed all project milestones through the application of past courses they have taken in computer control systems, network communication, and digital signal processing at the U.S. Coast Guard Academy. The first challenge of this project was to focus on constructing the vessel and installing the control hardware. One of the obstacles for the students was establishing communication between the various pieces of software, hardware, and the power distribution system. The LIDAR sensor determined the vessel’s relative position and heading to two stationary poles. Using the position and heading resolution algorithms, students conducted a set of system identification tests in an indoor tank to determine how the system reacts to various thrusts from the motors. This allowed students to collect “Open-Loop” system data. Using the data acquisition system, students were able to identify the system and calculate coefficients for the controller and implement a “Closed- Loop” control system. Students successfully implemented a proportional integral derivative (PID) controller that satisfies all design requirements including robust functionality. Currently, all milestones for the project have been accomplished and plans for continuation of the project are underway

Closed bore XMR (CBXMR) systems for aortic valve replacement: Investigation of rotating-anode x-ray tube heat loadability

In order to improve the safety and efficacy of percutaneous aortic valve replacement procedures, a closed bore hybrid x-ray∕MRI (CBXMR) system is proposed in which an x-ray C-arm will be positioned with its isocenter ≈1 m from the entrance of a clinical MRI scanner. This system will harness the complementary strengths of both modalities to improve clinical outcome. A key component of the CBXMR system will be a rotating anode x-ray tube to produce high-quality x-ray images. There are challenges in positioning an x-ray tube in the magnetic fringe field of the MRI magnet. Here, the effects of an external magnetic field on x-ray tube induction motors of radiography x-ray tubes and the corresponding reduction of x-ray tube heat loadability are investigated. Anode rotation frequency fanode was unaffected when the external magnetic field Bb was parallel to the axis of rotation of the anode but decreased when Bb was perpendicular to the axis of rotation. The experimental fanode values agreed with predicted values to within ±3% over a Bb range of 0–30 mT. The MRI fringe field at the proposed location of the x-ray tube mounted on the C-arm (≈4 mT) reduced fanode by only 1%, so x-ray tube heat loadability will not be compromised when using CBXMR systems for percutaneous aortic valve replacement procedures. Eddy current heating power in the rotor due to an MRI fringe field was found to be two orders of magnitude weaker than the heating power produced on the anode due to a fluoroscopic exposure, so eddy current heating had no effect on x-ray tube heat loadability