An FPGA-based controller design for a five degrees of freedom robot for repairing hydraulic turbine blades

This paper presents the design of a FPGA-based embedded system for controlling and monitoring a 5-D.O.F. spherical topology robot specialized in welding for repairing hydraulic turbine blade surfaces. The embedded controller has been developed using a hardware/software co-design approach in which a Nios II soft-processor is configured on a Terasic DE2-115 development kit, along with several support modules (timer, JTAG, I/O, memory and RS-232). Additionally, other dedicated hardware modules were designed to control the motors, encoders, the welding system and a joystick while daughter boards were designed to provide an opto-coupled connection from the FPGA kit to their respective external peripherals. Furthermore, the control system also provides a RS-232 interface to the pan-tilt, which provides the last two degrees-of-freedom to the manipulator. While the control algorithm runs on the FPGA it receives spatial coordinate points via a USB connection maintained with a PC where higher level software uses image processing techniques to map the turbine surface using a 3D LASER scanner and compute the welding trajectories. Finally, the validity of the system is verified with repeatability and welding tests.