# US 5,710,420 A · Method for embedding and recovering machine-readable information

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- Number: US 5,710,420 A
- Document ID: US5710420A
- Status: Granted
- Kind: A
- Application number: 08/567,786
- Filed: 1995-12-05
- Granted: 1998-01-20
- Earliest claimed: 1995-12-05
- Assignees: Xerox Corporation
- Inventors: Trevor I. Martin; John F. Oliver
- Web page: https://patentgrep.com/patent/US5710420A

## CPC

- G06K 7/143: {Glyph-codes}
- G06K 19/06018: {one-dimensional coding}
- G06K 19/06046: {Constructional details}
- G06K: GRAPHICAL DATA READING (image or video recognition or understanding G06V); PRESENTATION OF DATA; RECORD CARRIERS; HANDLING RECORD CARRIERS

## Abstract

Disclosed is a method of embedding and recovering machine readable information on a substrate which comprises (a) writing data in a predetermined machine readable code format on the substrate with a photochromic marking material having a first state corresponding to a first absorption spectrum and a second state corresponding to a second absorption spectrum; and (b) thereafter effecting a photochromic change in at least some of the photochromic marking material from the first state to the second state.

## Claims

### Claim 1

A method of embedding and recovering machine readable information on a substrate which comprises (a) writing data in a predetermined machine readable code format on the substrate with a photochromic marking material having a first state corresponding to a first absorption spectrum and a second state corresponding to a second absorption spectrum; and (b) thereafter effecting a photochromic change in at least some of the photochromic marking material from the first state to the second state, wherein a first portion of the photochromic marking material is caused to shift from the first state to the second state and a second portion of the photochromic marking material remains in the first state.

### Claim 2 (depends on 1)

A method according to claim 1 wherein the machine readable code format comprises a set of distinguishable symbols including a first symbol for encoding 0s and a second symbol for encoding 1s, wherein said symbols are written on a substantially constant center-to-center spacing.

### Claim 3 (depends on 1)

A method according to claim 1 wherein the machine readable code format comprises a set of glyphs wherein each glyph corresponds to a digital value of bit length n and wherein the set comprises 2.sup.n distinctive shapes.

### Claim 4 (depends on 3)

A method according to claim 3 wherein said glyphs are elongated along axes that are tilted at angles of plus and minus about 45.degree. with respect to a horizontal axis to discriminate at least some of said digital values from each other.

### Claim 5 (depends on 1)

A method according to claim 1 wherein the photochromic change in the photochromic marking material from the first state to the second state is effected by irradiation with radiation at a selected wavelength.

### Claim 6 (depends on 5)

A method according to claim 5 wherein said radiation is within the ultraviolet wavelength band.

### Claim 7 (depends on 1)

A method according to claim 1 wherein the photochromic marking material in the second state subsequently is caused to undergo another photochromic change, thereby returning it to the first state.

### Claim 8 (depends on 1)

A method according to claim 1 wherein the photochromic marking material in the second state subsequently is caused to undergo another photochromic change effected by irradiation with visible light, thereby returning it to the first state.

### Claim 9 (depends on 1)

A method according to claim 1 wherein the photochromic marking material in the second state subsequently is caused to undergo another photochromic change effected by heating, thereby returning it to the first state.

### Claim 10 (depends on 1)

A method according to claim 1 wherein the photochromic marking material comprises a material selected from the group consisting of spiropyrans, spirooxazines, spirothiopyrans, and mixtures thereof.

### Claim 11 (depends on 1)

A method according to claim 1 wherein the photochromic marking material is applied to the substrate by an electrostatic imaging process.

### Claim 12 (depends on 1)

A method according to claim 1 wherein the photochromic marking material is applied to the substrate by an ink jet printing process.