Design of a Rotating Brush Underwater Grooming Device with a Focus on Brush Optimization, Motor Control and Design for Reliability
The design and control of Remotely Operated Vehicles (ROV) to groom or clean the underwater surface of ship hulls is becoming an important aspect of the maintenance of vessels to the United States Navy. The biological growth below the waterline of the vessels can be the cause for drag penalties near 21% causing up to 32% increase in shaft power at 15 knots (Schultz, 2007). Research conducted by the Center for Corrosion and Biofouling Control at Florida Institute of Technology (FIT) indicated that weekly grooming can prevent high profile biological growth (Hearin, et al., 2015). The design of a rotating brush grooming device for use underwater was based on both laboratory and field tests. The results from laboratory testing generated a new suction brush design that determined the brush torque is related to the suction force. A system identification test was also conducted in the lab using a Brushless Direct Current (BLDC) Motor and a direct link was determined between the error in the mathematical model and the changes in torque requirements. Comparing the power data from the laboratory and field tests determined that the motor power is related to the amount of fouling. A full-scale prototype grooming system was built and tested at Port Canaveral and was driven by a SeaBotics Remotely Operated Vehicle on test panels deployed in the saltwater environment. This demonstrated that the suction brushes were capable of attachment and effective removal of biological fouling. This data determined the necessary design requirements of 1.5 Newton-meter (N-m) torque and the ability to set a fixed RPM using a closed loop BLDC motor speed controller. The addition of Pareto analysis and design for reliability during the design phase allowed for the addition of three components to increase the time between mission failure from 814 hours to 9,030 hours.