Periodic evaluation of the structural integrity of steel high-mast highway poles is necessary for the detection and repair of cracks. Current inspection processes are manual and labor-intensive and cause traffic-lane closures. In addition, the procedures are hazardous and prone to inaccuracy. To automate this inspection task, Virginia Transportation Research Council (Charlottesville, VA) contracted the University of Virginia and Virginia Technologies (both Charlottesville, VA) to develop a mobile robot that inspects pole joint for signs of fatigue without requiring operator intervention.
"In the current system, called Polecat Pro, six servomotors each drive a magnetic wheel that can be directed to climb vertically or traverse around the pole," says Kurt Hudson, a laboratory engineer with Virginia Technologies. A FlexMotion control board and NI-Motion driver software from National Instruments (Austin, TX) provide closed-loop control of the servo axes, each of which is equipped with an optical encoder. "The FlexMotion board also senses the status of two limit switches and controls a digital output line that drives a relay to select either vertical or circumferential motion," says Hudson.
A robot controller tethered to the ground provides power and motion control. With it, operators can apply course corrections. National Instrument's LabView provides speed control from -5 to +5 ft/min and course correction by adjusting the speed of the wheels on each side of the robot. On-board the robot, an RS-170 video camera attached to the front of the robot provides live visual inspection.
"To acquire video from the camera, National Instrument's Imaq PCI-1407 color image-acquisition board and NI-IMAQ software were used," Hudson says. "A live video window is part of the LabView GUI and contains pushbutton control for saving snapshots to disk, and Imaq Vision software provides the image display tools needed," he adds. With LabView, drive motors are synchronized to start moving at the same time with uniform velocity.
Because LabView also provides continuous velocity control from 0 to 5 ft/min, the robot can proceed rapidly to the inspection site and move deliberately during inspection. With the distance-traveled indicator, the distance traveled to the evaluation area can be recorded and the location of a captured video image documented.
Currently, the Virginia Department of Transportation is evaluating the Polecat Pro to supplement current inspection methods. In the next version of the robot, Hudson plans to perform color image analysis of corrosion and fatigue features and add an ultrasonic transducer for crack and pitting detection.
