Customer Solutions

LabVIEW-Controlled Robot Climbs and Inspects Highway Lighting Towers

Author(s):

Kurt Hudson, Virginia Technologies

Industry:

Energy/Power

Product:

LabVIEW, Motion Control, Vision

The Challenge:

Automating and improving the inspection of high-mast lighting towers to evaluate structural integrity.

The Solution:

Creating a PC-based robotic crawler and controller for remote inspection using motion and vision hardware controlled with LabVIEW.

Introduction
Periodic evaluation of the structural integrity of steel high-mast light poles and other highway utility structures is a necessary task for the timely detection and repair of cracks. Current inspection processes are completely manual. In one method, a Department of Transportation technician is lifted 70 to 120 ft up the pole via a bucket truck to inspect each joint. Another method is ground-level inspection using binoculars or telescope. These manual processes are labor intensive in both hours and in traffic lane closures. In addition, the manual process is hazardous and prone to inaccuracy because of difficulty in obtaining complete coverage of the pole surface.

Virginia Transportation Research Council contracted research at the University of Virginia and Virginia Technologies, Inc. to develop a mobile robot to perform the inspection of each pole joint. The objective is providing a more complete inspection of the pole joint for cracks and other signs of fatigue, without requiring visual inspection by an operator suspended near the pole. The system envisioned would include both remote visual and ultrasonic inspection capabilities. A portable computer with a graphical user interface would provide an operator with complete control of robot movement and the capability to view and store images of the pole surface. A specific requirement was for the robot to navigate the pole vertically and circumferentially to provide full coverage of joints in the pole.

System Design
Researchers at the University of Virginia developed the mechanical design of the robot. The robot motion is provided by six servomotors, each driving a wheel that is directed to climb vertically or traverse circumferentially. The wheels have magnets to provide friction and keep the robot attached to the pole. Each axis articulates individually relative to the robot frame, so that the robot can negotiate obstacles along the pole such as steps or tapers. To satisfy sensor focus requirements for visual and ultrasonic evaluation, the frame of the robot maintains a constant separation distance from the pole surface.

An RS-170 video camera attached to the front of the robot provides live visual inspection. We plan to install an ultrasonic sensor in a tube along the centerline of the robot frame. We tethered the robot to the ground to provide power, motion control, and video feedback.

Virginia Technologies, Inc. developed the robot controller. In the prototype, the user interface was provided by a joystick that controlled:

• Vertical and circumferential travel
• Forward and reverse direction
• Course corrections
• Power

We displayed video on a separate monitor, with no capability to store snapshots. In the prototype, we had no means of controlling speed or recording distance traveled.

System Description
In the current system, called Polecat Pro, a portable computer running Windows 98 and LabVIEW provides a graphical user interface. A PCI-FlexMotion-6C motion control board and NI-Motion driver software 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. This line drives a relay to select either vertical or circumferential motion. All power supplies and drive electronics are connected through a UMI-Flex6 motion interface. An IMAQ PCI-1407 color image acquisition board and NI-IMAQ software acquire video.

The LabVIEW application provides speed control from -5 to +5 ft/minute as well as course correction by adjusting the speed of the wheels on each side of the robot. We can adjust acceleration and turning rate. A live video window, resizable by the user, is part of the graphical user interface. It contains a pushbutton control for saving a particular snapshot to disk, and IMAQ Vision software provides all the image display tools needed.

System Performance
The LabVIEW-based robot shows marked improvement over the first prototype. The drive motors are now synchronized to start moving at the same time, with uniform velocity. This feature virtually eliminates the frequent course corrections that were required in the prototype because of the open-loop operation of the servo motors.

The LabVIEW-based system also provides continuous velocity control from zero to 5 ft/minute, which means the robot proceeds rapidly to the inspection site and then moves deliberately during the inspection. With the distance-traveled indicator, another useful improvement, you can record the distance traveled to the evaluation area and thus accurately document the location of a captured video image. In addition to providing the ability to store snapshots of evaluation areas, the live video image integrated into the front panel brings control and visual feedback together on one screen.

Results
The Polecat Pro is currently under evaluation by the Virginia Dept. of Transportation to supplement current inspection methods. We realized an estimated 60 percent saving in development time and cost by using a LabVIEW-based solution, in comparison to developing a custom hardware and software system. Our next revision will include remote camera control (zoom, aperture, and focus) to enhance the color image analysis of corrosion and fatigue features. Later, we plan to add the ultrasonic transducer for crack and pitting detection as well as an autonavigation system.

In January 2000, we demonstrated Polecat Pro to the Transportation Research Board meeting attended by DOT representatives from all 50 states as well as researchers from industries, universities, and suppliers. We will also show it at the American Association of State Highway and Transportation Officials meeting in June 2000.

For more information, contact:

 Kurt Hudson,
Virginia Technologies, Inc.

2015 Ivy Road, Suite 423

Charlottesville, VA 22903

Tel: (804) 970-2269

E-mail: kurth@cstone.net

361703A-01.pdf

View the entire user solution in Adobe Acrobat PDF format.