Browse Prior Art Database

Automatic Keytop Inspection D Device

IP.com Disclosure Number: IPCOM000048882D
Original Publication Date: 1982-Apr-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 3 page(s) / 32K

Publishing Venue

IBM

Related People

Griffith, JE: AUTHOR [+3]

Abstract

The herein-described device automatically inspects symbolic legends on the tops of typewriter keys and reports four types of defects: missing keys, incorrect keys. misoriented keys and defective legends (smudges, breaks, etc).

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Automatic Keytop Inspection D Device

The herein-described device automatically inspects symbolic legends on the tops of typewriter keys and reports four types of defects: missing keys, incorrect keys. misoriented keys and defective legends (smudges, breaks, etc).

This device inspects symbolic legends on the tops of e.g., typewriter, keys (Fig. 1) after they have been assembled onto a keyboard. Fig. 2 illustrates the structure of the device, whose essential elements are now described.

The positioning table 1 is a device capable of translating the keyboard in two directions to bring keys to be inspected into the field of view of the image acquisition device 2. The XY Table 1 is moved under control of computer 3.

The image acquisition device is a vidicon, solid-state imaging array (e.g., GE2200 Automation Camera), or other device for acquiring and digitizing a 2- dimensional image. Such a device must be capable of converting this image to binary (1 bit per picture element (pixel)) form by comparing intensity values against thresholds specified by the computer 3.

The computer is a general-purpose computer capable of controlling the XY table 1, imaging device 2, and error reporting mechanism 6, and carrying out the inspection algorithm.

The Inspection Algorithm set forth in Fig. 3 illustrates the structure of the inspection algorithm, which uses a modified form of template matching to compare the binary image of the key under inspection (Fig. 4) with the image of a master key (Fig. 5) previously acquired during the training operation described subsequently. First, the test image is registered with the master image by determining the center of the symbolic legend in each image; this is done by finding the average X and Y coordinates of of all 1-valued pixels in each image (shown in black in the figure).

If the centers in the two images differ by an amount exceeding a threshold, a "key translated" error is reported. Otherwise, the test image is shifted in the X and Y directions so that the centers of the legends in the two images coincide (Fig. 6). Next, a difference image (Fig. 7) is formed by performing the exclusive- OR (XOR) operation between corresponding pixels in the master and test images: in the difference image, 1-valued pixels correspond to points where the two images differ. Next, the difference image is thinned, removing 1-valued pixels from the p...