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Proceedings Paper

Tape measuring system using linear encoder and digital camera
Author(s): Tae Bong Eom; Don Young Jeong; Myung Soon Kim; Jae Wan Kim; Jong Ahn Kim
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Paper Abstract

We have designed and constructed the calibration system of line standards such as tape and rule for the secondary calibration laboratories. The system consists of the main body with linear stage and linear encoder, the optical microscope with digital camera, and the computer. The base of the system is a aluminum profile with 2.9 m length, 0.09 m height and 0.18 m width. The linear stage and the linear encoder are fixed on the aluminum profile. The micro-stage driven by micrometer is fixed on the carriage of the long linear stage, and the optical microscope with digital camera and the tablet PC are on the this stage. The linear encoder counts the moving distance of the linear stage with resolution of 1 μm and its counting value is transferred to the tablet PC. The image of the scale mark of the tape is captured by the CCD camera of optical microscope and transferred to the PC through USB interface. The computer automatically determines the center of the scale mark by image processing technique and at the same time reads the moving distance of the linear stage. As a result, the computer can calculate the interval between the scale marks of the tape. In order to achieve the high accuracy, the linear encoder should be calibrated using the laser interferometer or the rigid steel rule. This calibration data of the linear encoder is stored at the computer and the computer corrects the reading value of the linear encoder. In order to determine the center of the scale mark, we use three different algorithms. First, the image profile over specified threshold level is fitted in even order polynomial and the axis of the polynomial is used as the center of the line. Second, the left side and right side areas at the center of the image profile are calculated so that two areas are same. Third, the left and right edges of the image profile are determined at every intensity level of the image and the center of the graduation is calculated as an average of the centers of the left and right edges at all intensity levels. The system can measure the line standards up to 2.5 m. The expanded uncertainty for the tape calibration is U = [(0.04)2+ (0.015•L)2]1/2 mm, where L is measured length of the tape or rule in meters. At this system, the long distance measuring instruments such as ultrasonic distance meter or laser displacement sensor can be also calibrated.

Paper Details

Date Published: 13 May 2013
PDF: 6 pages
Proc. SPIE 8788, Optical Measurement Systems for Industrial Inspection VIII, 87883P (13 May 2013); doi: 10.1117/12.2020470
Show Author Affiliations
Tae Bong Eom, Korea Research Institute of Standards and Science (Korea, Republic of)
Don Young Jeong, Korea Research Institute of Standards and Science (Korea, Republic of)
Myung Soon Kim, Korea Research Institute of Standards and Science (Korea, Republic of)
Jae Wan Kim, Korea Research Institute of Standards and Science (Korea, Republic of)
Jong Ahn Kim, Korea Research Institute of Standards and Science (Korea, Republic of)


Published in SPIE Proceedings Vol. 8788:
Optical Measurement Systems for Industrial Inspection VIII
Peter H. Lehmann; Wolfgang Osten; Armando Albertazzi, Editor(s)

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