Sensor Sense: Data Matrix Positioning Systems

Sept. 9, 2010
A camera tracking a 2D data-matrix code strip creates a linear-positioning system that reports an absolute position within ±0.2 mm over a distance of 6 miles.

Data-matrix codes in industrial environments are quite common. Their small size, large data capacity, and readability when large segments of the symbol have been lost or destroyed provide secure and reliable performance in the areas of production, identification, inventory, sorting and other areas.
Most data-matrix codes to date fall under the read-and-react category. The code is read and some action taken based upon the value of the code. For example, the code provides traceability and verification that a pallet passed a specific production point, or that a code-stamped package shipped.

However, recent advancements in camera technology have expanded applications for data-code technology from the single-shot read and process to continuous monitoring for positioning and tracking. One such use creates an X-Y position-feedback tool for automated storage and retrieval machinery. Another use permits monitoring and control of overhead monorails because the technology can follow curved paths.

One such system is the Data Matrix Positioning System by Pepperl+Fuchs, Twinsburg, Ohio. In that system, strips of adhesive-backed 2D data-matrix codes sit along the travel path of a carrier. Each code is unique for that position along the strip, creating an absolute encoding environment that does not need homing. By reading the code pattern and position using an optical camera, the system continuously updates the position of the read head with ±0.2-mm resolution.

The camera reads several code patterns on the strip at once. Final position is determined by the numeric value of the data-matrix code and its position within the camera frame. Should some of the code patterns be damaged, there is enough redundant information to rebuild the missing information from the other patterns. If a section of the code strip becomes too badly damaged, Web-based software tools let users generate and print replacement code sections.

Camera read speeds can reach 41 ft/sec, while the high data density of the 2D code square permits continuous readings over a distance up to 6 miles. Scanner-to-code-tape separation up to 3 in. is typical, and a ±15-mm axial-movement tolerance means random alignment variances between the scanner and code strip do not degrade system stability.

Pepperl+Fuchs ( supplied information for this column.

Edited by Robert Repas

© 2010 Penton Media, Inc.

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