Appendix F: General Comments on the Scanner Types

Appendix F
General Comments on the Scanner Types

A. Ideal- Scanner

Each of the eight basic scanner designs that are available commercially has advantages and disadvantages that differentiate them from the ideal scanner. The ideal scanner would be one that normal experienced airline maintenance NDI personnel can use with ease and confidence to obtain meaningful, repeatable, reliable, easy-to-interpret, and quantitative C-scan images of the inspection data. The ideal scanner would provide accurate XY position data for multimode NDI testing methods without undue physical effort by the examiner for a variety of scanner positions, orientations, structural geometry and surface conditions. The scanner would be affordable and the set-up time, scan time, and relocation time must be quick and compatible with cost effective implementation.

B. Scanner Type Comparisons

From observations made while witnessing the hands-on operation of each scanner type, a table of strong points, weak points, and future improvements was constructed to compare the available scanners with the ideal scanner characteristics. Potential operators of scanners may use the table to compare the benefits of one scanner versus another. Suggestions for improvements are given to aid vendors in developing a favorable scanner system that would increase their general acceptance by the airline inspection industry.

SCANNER TYPE COMPARISONS
Scanner Type	Strong Points	Weak Points	Future Improvements
1. Dual Axis Tilting Arm and Bridge Manual Scanner	Light weight; works well with modular systems; can be used around raised rivets; price is moderate. Integrates easily with eddy current, ultrasonic, and resonance instruments.	Encoder slides when arm gets wet; mechanism holding sensors not well designed; labor intensive to operate; adequate for small area scans only.	Independent hand vacuum pumps for three suction cup feet that provides adaptability to many surface geometries and overhead operation.
2. Dual Axis Tilting Arm and Bridge Automated Scanner	Efficient, easy operation over long inspection times; compact and light weight automated system; good for small and large area scans.	Spring forces on tilting arm are not adequate or constant for general vertical and overhead operation; sensor holder scratches aluminum surface	Develop a pneumatic tension system for the tilting arm to provide adequate and constant pressure at the sensor to surface interface.
3. Radial Axis Tilting Arm with Rotation Axis Bridge Manual Scanner	Versatile for many surface geometries and large curvatures; can articulate over a large area without repositioning. Integrates easily with eddy current, ultrasonic, and resonance instruments.	Labor intensive for scan times longer than one hour and overhead operation; sensor holder leaves scratches on aluminum surfaces even with Teflon tape over sensor.	Design of a frictionless sensor holder; a set of larger suction cup feet needs to be available for greater adherence to the surface in the overhead operation.
4. Dual Axis Cantilever Arm Bridge Manual or Automated Scanner	Very adaptable for large area scans; automated system is not labor intensive; Areal coverage for C-scan images is easier to obtain than with manual tilting arm systems.	System design is heavy and not as easy to implement as tilting arm scanners; manual system is labor intensive in vertical and overhead operation.	Design of a frictionless sensor holder that maintains sensor perpendicularity over nominal panel curvatures; check valves on multiple suction cup feet need to be installed for positive adherence at all times.
5. Mobile Automated Ultrasonic Scanner	Fast, efficient linear areal scans of widths from 2, 4, 6, or 8 inches, fast and easy mode change for eddy current, ultrasonic, or resonance testing.	Encoder wheels slide when they get wet from the ultrasonic couplant; scanner head is heavy and nor easy to operate for vertical and overhead operation	Design of a light weight head; frictionless sensor holders; and positive traction encoder wheels are needed.
6. Dual Axis Rectangular Bridge Automated Scanner	Adaptable for large area scans of moderate curvatures; most useful for squirter technology over raised rivets and protrusions etc.	System design is heavy and rigid; not flexible for different surface geometries.	Design of a surface tracking device for implementation with squirter or captured water column technology.
7. Hands Free X-Y Digitizer	Free movement of sensor over complex surface geometries.	False position data occurs frequently from environmental noise and multiple paths within the aluminium structure.	Noise immunity algorithm needs to be developed and a method of decoupling the source waves from the structure surface.
8. 2-D Square Transducer Array	Adaptable for fast characterization of inspected area; straight forward to apply and obtain inspection data; Excellent resolution of thin skin thickness and defect location for boron/epoxy repair patches.	Transducer array can not be used over protrusions like raised rivets etc. Gray scale display used during demonstration lacked contrast needed for easy interpretation of the inspection results.	Large color monitor would improve viewing and interpreting the inspection results, a number of parallel vacuum seals with check valves to improve initial application of the array to the surface.

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