Method for physically marking objects using continuous functions

#This invention relates generally to marking objects, and more particular to marking the objects with marks generated by continuous functions.

#A number of techniques are known for marking objects, e.g., linear barcodes and matrix codes such as a QR code. Most conventional marking schemes use unique and discrete number of observable symbols to encode information. For example, an information bit “0” is represented by a black patch, and an information “1” is represented by a white patch. Sometimes, a symbol can represent multiple bits of information, such as done for an optical orthogonal code, see U.S. application Ser. No. 12/640,949. Marks can also be used on road surfaces, see U.S. application Ser. No. 12/495,419.

#Some marks have the property that enables sensors with different resolutions to decode different amount of information, e.g., DataGlyphs in U.S. Pat. No. 5,245,165, and MiniCode in U.S. Pat. Nos. 5,153,418, 5,189,292, and 5,223,701. However, the sensors for those codes need multiple observations of the same discrete symbol, where each symbol contains at most 4.39 bits of information as in the MiniCode.

#FIG. 1A is a flow diagram of a method for physically marking an object to encode symbols according to embodiments of the invention;

#FIG. 1B is a schematic for OFDM optical markings when underlying information that is encoded in the mark in one case is known and in an other case is unknown;

#FIG. 2 is a schematic for encoding information onto OFDM marks using QPSK according to embodiments of the invention;

#As shown in FIG. 1A, a method for visibly marking a physical object 115 encodes 101 each symbol of a set of symbols 102 using a continuous mapping function 103 to produce corresponding encoded functions 104, wherein values of the encoded functions are real and vary continuously.

#One way to obtain the continuous mapping function is by Frequency Division Multiplexing (OFDM) coding. Other ways include Code Division Multiplexing (CDM), and Constant Amplitude Zero Autocorrelation (CAZAC).

#Then, the encoded functions are summed 108 to produce a summed function 109. A positive bias function B 105 is added 106 to the summed function to produce a biased function 107. Then, a physical property of the object 115 is altered 116 according the biased function to mark the object with a mark 100. The mark can be printed or embossed, for example. The mark can be sensed, e.g., optically by a camera or a range scanner 119 and appropriately decode.