JPH05282491A - Reading method for stamp - Google Patents

Abstract

PURPOSE:To automatically read a stamp which is inferior in contrast by finding the spectrum of the spatial frequency of a stamp character and recognizing the stamp character. CONSTITUTION:An image processing circuit 3 codes data from a CCD camera 2 into binary data, line by line, with an indication from a scanner controller 5, stacks them and performs a two-dimensional binary-coding process to generate two-dimensional binary-coded pattern data, and sends them to a computer 4. The computer 4 sends an indication to the scanner controller 5 at the same time and performs Fourier transformation in the polar coordinate form of the two-dimensional binary data to obtain the spectrum of the spatial frequency. The correlation between this spectrum and the previously generated spectrum of the spatial frequency as a reference of the stamp and makes a sequential comparison to recognize the character with the maximum correlation. Consequently, a pattern which is formed of variation in geometrical shape can easily be read without contacting.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for reading characters, and more particularly to a method for reading inscriptions stamped on the surface of a material such as metal.

[0002]

2. Description of the Related Art Conventionally, as a method of reading characters, there is a method disclosed in Japanese Patent Publication No. 54-37549. In this reading method, the pattern recorded on the film is irradiated with coherent light, the transmitted light is Fourier transformed by a Fourier transform lens, and the Fourier transformed image is received and quantized by a two-dimensional photoelectric element array, Characters are recognized by comparing the quantized information with known reference information in a decision matrix circuit.

[0003]

The object to be read in the above-described method for reading characters is a pattern of good contrast formed of white and black (or vice versa) or transparent and opaque (or vice versa). It was not possible to recognize the pattern formed by the change in the geometrical shape such as.

The present invention has been made in view of the above circumstances, and provides a method for reading a marking in which a pattern formed by a change in geometrical shape can be easily read in a non-contact manner. The purpose is to

[0005]

In the present invention, as a means for obtaining basic data of a pattern with poor contrast formed by a change in geometrical shape such as unevenness, for example, a light cutting method using a laser is used. To do. The light cutting method is a means for grasping the cross-sectional shape, and a line drawing corresponding to the cross-sectional shape is obtained by performing light cutting once. This is imaged by, for example, a CCD camera and binarized by an image processing device. By combining with scanning means, this operation is repeated at a constant pitch to obtain a two-dimensional binarized image. Then, this is loaded into a computer, and Fourier transform in polar coordinates is applied to this two-dimensional binarized image using a computer (software) to obtain a spectrum of spatial frequency. Using a computer (software), the correlation between the spectrum of this spatial frequency and the spectrum of the spatial frequency that is a known reference that has been calculated in advance for each pattern is obtained, and the specific pattern is recognized by its maximum value. In this way, a method of recognizing and identifying a pattern with poor contrast formed by a change in geometrical shape can be achieved.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a diagram showing the construction of an apparatus for carrying out a marking reading method according to an embodiment of the present invention. Fan-shaped light source 1
Is composed of a laser source and an optical system consisting of at least two convex lenses and a cylindrical lens, and emits a fan-shaped laser beam 10 onto the surface of a material such as metal at an angle not orthogonal to the surface. Then, the reflected light 11 from the markings 12 stamped on the material surface at regular intervals is imaged by the CCD camera 2, and the imaged data is sent to the image processing circuit 3.
The fan-shaped light source 1 and the CCD camera 2 are supported by an arm 14, and a scanner 6 is attached to the upper part of the arm 14, and a drive system 7 and an encoder 8 are mounted on the scanner 6. Then, the scanner 6 moves on the scanner rail 13, and the fan-shaped light source 1 and the CCD camera 2 are moved.
To scan. The scanner controller 5 controls the drive system 7 of the scanner 6, receives data from the encoder 8, and instructs the image processing circuit 3 to perform image processing at a fixed pitch, and also ends one character processing determined by the pitch and the number of processings. The signal is sent to the image processing circuit 3.

The image processing circuit 3 performs binarization for each line according to data from the CCD camera 2 and an instruction from the scanner controller 5, and stacks them to perform two-dimensional binarization to perform two-dimensional binarization. Create pattern data and send it to the computer 4. Upon receipt of this, the computer 4 gives an instruction to the scanner controller 5 to repeat the above-mentioned operation and perform Fourier transform in the polar form of the two-dimensional binarized data to obtain the spectrum of the spatial frequency.
The correlation between the spectrum of this spatial frequency and the spectrum of the spatial frequency that is the reference of the marking that has been created in advance is calculated, and the characters are recognized by the maximum value of the correlation and displayed on the display 9.

The Fourier transform and the calculation of the correlation do not have to be performed in real time, and the two-dimensional binarized data may be temporarily stored in the buffer memory of the computer 4 depending on the scan speed. Further, in FIG. 1, γ and ψ of the marking 12 mean the starting and terminating symbols of the marking, but of course other characters or symbols may be used.

[0009]

As described above, according to the present invention, the established technique called the optical cutting method is utilized to obtain the spectrum of the spatial frequency of the imprinted character to recognize the imprinted character. It is possible to read the stamp automatically. In addition, since the software can be used to the maximum for calculation and the like, the device configuration is simple.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of an apparatus for carrying out a marking reading method according to an embodiment of the present invention.

[Explanation of symbols]

 1 Fan-shaped light source 2 CCD camera 3 Image processor 4 Computer 5 Scanner controller 6 Scanner 7 Drive system 8 Encoder 9 Display 10 Fan-shaped laser light 11 Reflected light 12 Engraved characters / symbols 13 Scanner rails 14 Arms

Claims (2)

[Claims] 1. A step of scanning while irradiating a material surface having a marking on the surface with linear slit light, a step of imaging the slit light irradiated on the material surface, and binarizing an imaging signal. A step of obtaining a binarized two-dimensional image, a step of applying a Fourier transform to the binarized two-dimensional image to obtain a spectrum of spatial frequencies, and a space serving as a reference of the spectrum of the spatial frequencies and preset markings. A method of reading a marking, which comprises a step of recognizing a corresponding marking with a maximum value by sequentially correlating with a frequency spectrum and sequentially comparing. 2. The method for reading a marking according to claim 1, wherein the slit light is a laser.