Browse Prior Art Database

Variable Optical Read Head

IP.com Disclosure Number: IPCOM000085235D
Original Publication Date: 1976-Mar-01
Included in the Prior Art Database: 2005-Mar-02
Document File: 5 page(s) / 92K

Publishing Venue

IBM

Related People

Metzler, JC: AUTHOR [+2]

Abstract

The Delta A Code also known as retrospective pulse modulation, encodes binary data by the intervals between bars. A binary 0 is manifested by a change between adjacent intervals and a binary 1 is recognized by an equal spacing between bars. An example of this code is illustrated in Fig. 1A.

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Variable Optical Read Head

The Delta A Code also known as retrospective pulse modulation, encodes binary data by the intervals between bars. A binary 0 is manifested by a change between adjacent intervals and a binary 1 is recognized by an equal spacing between bars. An example of this code is illustrated in Fig. 1A.

The Delta A Code may be etched, for example, on a stainless steel tag having the following physical specifications: Data Code

Bar width 0.005 + 0.002"

- 0.001"

Bar single space 0.016 + 0.001"

Bar double space 0.032 + 0.001".

The Delta A Code reader of the prior art is composed of two assemblies, (1) the optical head and (2) an electronic logic gate. The purpose of the latter is to receive two input lines of binary data (pulse train) and decode them into one binary coded decimal (BCD) word, and store the BCD word in a hold register. The structure described herein is concerned with an improved optical head so the electronic logic gate assembly is not discussed.

The present optical head 10 is illustrated in Fig. 1. The light from the lamps 11 is reflected off the surface of the tag 12 only when a bar is directly under the lens 13 opening. Two light rays 14 and 15 are directed by a prism 16 to two photodetectors labeled LED and LAG which generate an electrical signal. The LED generates a signal first and then the LAG as the tag 12 moves from left to right.

The detector receives light separated by 24 x 10/-13/ inch so the LAG generates a signal delayed in time depending on the velocity of the tag 12. But because the electrical signals are referenced to each other, a fixed delay is experienced regardless of the tag velocity. The fixed delay may be varied by changing the distance between the photodetectors and another fixed delay.

The function of the fiber block 17 is to maintain a separation between the LED and LAG of 24 x 10/-13/ inch. Since a photodetector's dimension is larger than the distance between the detectors, the present optical head must utilize the fiber block 17 for diverging the beams 14 and 15 while maintaining the predetermined distance at the input to the fiber block. The analog signals generated by the photodetectors are converted into binary signals by an analog convert card, sometimes called the level setting card, and the time delay with respect to each signal is preserved.

The obvious problem is when tag dimensions change because of physical requirements. When the bar single spacing is changed from 0.016'' to 0.008'',
0.010'', 0.014'' or 0.018''; the fiber block design and dimensions must also change to 0.012'', 0.015'', 0.021'' and 0.035'', respectively. Thus the same optical head can not be utilized with different bar spacing (other than 0.016'').

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As is explained more completely below, if a variable optical read head 10 is employed, no modified fiber block 17 or head design is necessary. In addition, a benefit derived from the variable optical read head is greater light intensity recei...