Resizing COTS AMLCDs for Avionics Applications

Resizing COTS AMLCDs for Avionics Applications

LAWRENCE E. TANNAS, JR.
TANNAS ELECTRONICS
ORANGE, CALIFORNIA

Abstract

Avionics displays have been significantly advanced by the application of AMLCDs. AMLCD advantages lay in being sunlight-readable, easily dimmable, and versatile in the cockpit environment (Ref. 1). Nevertheless, the availability of custom-sized AMLCDs needed in avionics has been a major problem leading to a crisis in the aviation industry. A novel technique, used to resize Commercial-Off-The-Shelf (COTS) active-matrix liquid-crystal displays (AMLCDs) in order to achieve the custom sizes needed, has been developed. This technique takes advantage of the numerous high-performance COTS displays, with wide temperature range, available for resizing. The cost advantage of resizing COTS displays, rather than custom-manufacturing them, is significant and should have important implications for the avionics industry.

Avionics Issues

By the end of the 1980s, requirements for custom avionics-grade AMLCDs were formulated based upon 1980s technology. For example, 1) Wide viewing angle requiring normally-black mode, split electrode or unique optical compensation; 2) RGBG quad pixel arrangement for redundancy and high-resolution monochrome; and 3) Faster speed and higher temperature range requiring special LC compound mixes. The commercial world now has higher-performing AMLCDs with higher yields, longer life and lower cost than custom-made avionics AMLCDs. For example, 1) Wide viewing angle (plus or minus 60 degrees) is now achievable with in-plane twist or twisted nematic mode using optical compensators and normally-white mode; 2) RGB stripe or triad pixels are commercially used to improve quality, yield, aperture ratio and resolution at 120 lines/inch; 3) Temperature ranges of minus 10 to plus 85 degrees C are now available in many sizes and to plus 70 degrees C in many more; and 4) Speed of response of less than 48 m/sec is readily available yielding 20 frames/sec, all of which is sufficient for avionics head down displays. However, the direct-view AMLCD is not commonly made in a square format. Custom AMLCDs, manufactured in low volume to avionics specifications, are proving to not be economically viable (Ref. 2).

After ruggedization, many commercial AMLCDs meet aviation industry requirements. Filters and heaters can be laminated on the front and back of the display glass to meet sunlight readability, temperature and humidity requirements. The backlight can be replaced with a variable, high intensity backlight.

Unique Size

Aviation instrument sizes were standardized in an ARINC specification to accommodate the mechanical interface between instrument manufacturers and aircraft designers. For justifiable reasons at the time, almost all the sizes are square. For equally justifiable reasons, the television and computer industries standardized to an image aspect ratio of nominally 3:4.

A major paradox exists. We are in a world where high-quality, low-cost commercial electronic displays exist with an aspect ratio of 3:4 and the aviation industry desperately needs them but with a square aspect ratio. A worldwide inventory of over 200,000 airplanes exists today using six to 12 square primary flight instruments each. The Boeing 777 and other Boeing upgrades are using an ARINC D-size box and custom-made square AMLCD. Some cockpits are switching from square displays but a major portion of the industry is using square displays and desires to continue, if possible.

Resizing COTS AMLCDs

When considering the complexity of the display, to cut apart and reseal an AMLCD and expect it to continue to work sounds impossible. However, with today’s COTS AMLCD technology, it can be done. AMLCDs have been cut, resealed and operated. Square displays have been made and environmental testing has been completed demonstrating feasibility. Life testing to determine if any long-term detrimental effects exist needs to be completed.

Today’s AMLCD technology lends itself to resizing by cutting and resealing. For example, 1) The row drivers are now normally attached at only one edge, permitting the other edge to be removed without the need to replace row driver TABs; 2) Typically, the column drivers are in sets of four, allowing removal of one complete column TAB section, thereby making a square display; and 3) Multiple spacer spheres are used inside the cell ensuring the uniformity of spacing after cutting until resealing.

The reseal technique has been tested in several ways:

1) The reseal system has been subjected to boiling salt water for three hours and then temperature-cycled ten times between minus 20 degrees C and boiling water. No signs of fatigue, loss of strength, leakage or discoloration have been exhibited;

2) The reseal-system test samples and resealed display samples had been submitted to RTCA/D0-160, Section 6, Category B Severe Humidity Environment. This is a ten-day test cycling from 20 to 65 degrees C at 95% RH each day. When properly resealed, no sign of fatigue, loss of strength, LC misalignment, leakage or discoloration has been exhibited;

3) The reseal system and display samples have successfully survived thermal shock of from minus 70 to plus 100 degrees C. The COTS polarizer and its adhesive did show signs of failure except where protected.

Summary

Because of limited numbers of samples tested and lack of life testing, the status of this work should be characterized as still being in the R&D phase. Results are so encouraging it was decided to report on the progress. The task of cutting and resealing a COTS display has been reduced to a few steps requiring relatively low-cost machinery and general laboratory skills. Techniques for laminating antireflective/EMI filters and heaters and techniques for ruggedizing the COTS polarizer as an adjunct to the cutting and resealing for avionics application have been developed.

References:

1) Tannas, Jr., L. “Application of Backlit AMLCDs to Avionics” (Paper 7.1), SID Digest, pp 61-64, May 17-22, 1998.

2) Tannas, Jr., L. “Laws for the Design of the Universal Cockpit Display”, (Paper 3363-501), SPIE Cockpit Displays V, April 15-19, 1999s

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