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MACHINE VISION INSPECTION ALGORITHM OF SEVEN SEGMENT LCD'S

IP.com Disclosure Number: IPCOM000006341D
Original Publication Date: 1991-Dec-01
Included in the Prior Art Database: 2001-Dec-26
Document File: 4 page(s) / 224K

Publishing Venue

Motorola

Related People

David Karpinia: AUTHOR [+2]

Abstract

As the complexity of pager LCD's increases, the accuracy, reliability and repeatability of human inspec- tion becomes questionable. In order to meet the corpo- rate goal of six sigma, machine inspection is providing part of the solution. LCD inspection is being accom- plished with a machine vision system utilizing a Macintosh IIfx computer with Data Translation frame grabber Board and a Pulnix TM 745 CCD camera. The system delivers a resolution of 640 x 480 pixels with 256 gray levels. The programming was done in Rail, a language developed by Automatix Inc. Biller&, Mass. Rail is a high level interpretive language similar to PASCAL with its own vision processing fonctions.

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MOIOROLA INC. Technical Developments Volume 14 December 1991

MACHINE VISION INSPECTION ALGORITHM OF SEVEN SEGMENT LCD'S

as possible. In order to effec- tively test for the segments

by David Karpinia and John Christopher Lewis

  As the complexity of pager LCD's increases, the accuracy, reliability and repeatability of human inspec- tion becomes questionable. In order to meet the corpo- rate goal of six sigma, machine inspection is providing part of the solution. LCD inspection is being accom- plished with a machine vision system utilizing a Macintosh IIfx computer with Data Translation frame grabber Board and a Pulnix TM 745 CCD camera. The system delivers a resolution of 640 x 480 pixels with 256 gray levels. The programming was done in Rail, a language developed by Automatix Inc. Biller&, Mass. Rail is a high level interpretive language similar to PASCAL with its own vision processing fonctions.

  Working from prior concepts of LCD inspection programs, the testing algorithm was developed. Several factors critical to design and implementation, i.e. light- ing (wavelength, frequency, intensity), camera angle, dii ferent vision routines strengths/weaknesses were considered and values weighed to produce the most robust over the conveyor and short cycle time process

in the display two variables must be determinable; the location of the segment and when the segment is on or off. Once the location is determined a region of inter- est (ROI) must be placed over the segment within the Figure 1 confines of the segment, see Figure 1, then vision processing may commence.

  It is important to note that an alignment routine must be run on each LCD prior to the test algorithm in order to compensate for radio and fuaure tolerances. The rou- tine for dynamic location utilized in previous machine inspection stations was not precise enough to effectively place the windows on some pager LCD displays, such as the Wrist Watch Pager LCD, due to the small size of the segments, so care must be exercised in order to opti-

R.O.1.

126 0 Matorola. 1°C. ,991

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MOTOROLA INC. Technical Developments Volume 14 December 1991

mize the precision in other applications when using the previously mentioned routine,

  In pager applications with small displays, it was nec- essary to develop a new dynamic 'location algorithm to guarantee correct placement of the windows. This rou- tine takes a picture of a blank LCD and subtracts from it a picture of the LCD with the top bars of the seven

segment displays energized on a pixel by pixel basis. The ROI's are size limited to the features of interest in order to decrease the amount of time required for the subtraction. Noting that the gray scale is; 0 = black and 255 = white, the resulting image of the absolute value of the diEerence of the two initial images yields a completely dark ROI where the images were the same and gray where they are different (the top bars...