JPH05167129A - Method of calculating center of laser spot by image processing - Google Patents

Abstract

PURPOSE:To accurately find the center of a laser spot by only using the rising and falling parts of the intensity characteristic waveform of the laser spot for calculating the center of the laser spot. CONSTITUTION:A laser generator 3 generates a laser spot 2 and the intensity distribution in the laser spot 2 in, for example, X-axis direction appears on the surface of an object 4 with a Gauss distribution or intensity characteristic closely resembling the distribution. The image of the laser spot 2 is sensed with an industrial camera 5 and sent to an processing system 1 after the picture is converted into image output data of a signal level proportional to the energy intensity of the spot 2. The system 1 finds the center of energy distribution in the spot 2 on A-axis by executing a center calculating program for the spot 2 and can improve the measurement accuracy by using absolute values of differences or differential of signal level between data of neighboring positions.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of calculating the center of a laser spot from an energy distribution curve by image processing technology.

[0002]

2. Description of the Related Art The center of a laser spot must be determined for positioning the laser spot during various measurements and processing using the laser spot light. Usually, the energy distribution of the laser spot shows a Gaussian distribution or an intensity characteristic close to this when the object is irradiated. Therefore, the centroid method is often used as a method for calculating the center point of the laser spot. The center-of-gravity method is a method of dividing the area of the energy distribution graph into two equal parts at a certain coordinate, and it is possible to calculate the center point of the laser spot with high accuracy in spite of its simplicity.

The conventional center-of-gravity method is used in a region of the entire signal level proportional to the energy intensity at each position of the laser spot, or in a region in which a portion below a certain threshold level is truncated, that is, in a range close to the peak level of the signal level. The center of gravity of output data is calculated. According to such a calculation method, in the portion near the center of the laser spot, the contribution to the calculation of the center of gravity is low, and moreover, the error is likely to occur due to the influence of optical factors such as saturation and interference of the light receiving element. , The improvement was desired.

[0004]

SUMMARY OF THE INVENTION Therefore, the object of the present invention is to eliminate the drawbacks of the prior art without utilizing the portion of low contribution to the calculation of the center point, and to obtain the center point of the laser spot accurately by a simple calculation. Is to be done.

[0005]

In view of the above object, the present invention focuses on the rising and falling portions of the intensity characteristic waveform of the laser spot, and uses only that portion for calculating the center of the laser spot. The influence of the error due to the peak portion is reduced, and the measurement accuracy is improved by using the difference in signal level or the absolute value of the differential between the data at the positions near the rising and falling portions of the energy distribution.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 shows an outline of an image processing system 1. The laser generator 3 generates a laser spot 2,
The surface of the object 4 to be measured or processed is irradiated. FIG. 2 illustrates the intensity distribution of energy of the laser spot 2 in the X-axis direction in a rectangular coordinate system as a graph. Here, the laser spot 2 appears on the surface of the object 4 with a Gaussian distribution or an intensity characteristic close to this. The laser spot 2 is imaged by the industrial camera 5, converted into image output data having a signal level proportional to the energy intensity of the laser spot 2, and sent to the image processing system 1. The image processing system 1
The center of the energy distribution of the laser spot 2 is obtained on the X axis by executing the program of the method for calculating the center of the laser spot of the present invention.

FIG. 3 shows the order. First, A
The / D converter 6 converts the image output of the industrial camera 5 from analog amount data to digital amount data of 256 gradations, for example. The CPU 7 stores the digital amount of data in the memory 8 together with the corresponding position (bit),
From these data, the absolute value of the difference between the signal levels between adjacent positions, for example, the data of adjacent bits, or the absolute value of the differential of the data (energy intensity) with respect to the change of the position,
A larger position and its signal level are taken out as a pair from a pair of data having an absolute value equal to or more than a predetermined value. After that, the CPU 7 calculates the center of gravity of the extracted data group by a conventional method, and uses this center of gravity as the laser spot 2
The center point of. Note that these absolute values are represented by the graph shown in the lower part of FIG.

Here, the data at the neighboring position may be not only the data of the adjacent bits but also the data of the bit position where a predetermined bit is skipped. Smoothing is performed as necessary in the A / D conversion process or in the process of obtaining the absolute value of the signal level difference or the differential between the data of the neighboring positions. When this smoothing is performed, the error signal having low reliability is erased, so that the reliability of measurement is improved.

In this way, the signal level difference between the two data is obtained, and the absolute value of this signal level difference is used as it is, or the difference between the two output data is differentiated by the position, and a predetermined value among the absolute values is determined. The peak level of the waveform of the energy distribution,
And the gentle rising and falling parts are removed and only the steep rising parts are extracted. Therefore, the obtained center of gravity, that is, the center point of the laser spot 2 is extracted only from the characteristics of the steep rising waveform of the signal level waveform.

[0010]

Other Embodiments In the above embodiment, the image processing is performed after the signal is converted into the digital signal, but it is also possible to deal with the analog processing alone. Further, although the above description has been made only in the X-axis direction of the Cartesian coordinates, it is similarly made in the Y-axis direction orthogonal thereto. With the center of gravity in the X-axis direction and the center of gravity in the Y-axis direction, a more accurate center on a plane can be determined by the two coordinates.

[0011]

The present invention has the following effects. Of the signal level waveform of the laser spot, the data of the peak portion and the gentle skirts, that is, the waveform with a low contribution to the calculation of the center of gravity is not used, and the portion that causes saturation of the light receiving element or light interference is also used. Therefore, errors based on these are eliminated, and the accuracy and reliability of spot center calculation are improved. Since a lot of data is involved in the center calculation at the steep rising or falling part of the signal level waveform,
An averaging effect can be obtained, and even if a camera with a small total number of bits is used, higher speed measurement can be performed. In the case of the same device configuration, the number of data to be calculated is smaller than that in the conventional method, the processing speed is increased accordingly, and the speed of calculating the center of the laser spot is accelerated.

[Brief description of drawings]

FIG. 1 is a block diagram of an image processing system.

FIG. 2 is a graph of a Gaussian distribution intensity characteristic of a laser spot, an absolute value of a difference and a differential.

FIG. 3 is a flowchart of a laser spot center calculation method.

[Explanation of symbols]

 1 Image Processing System 2 Laser Spot 3 Laser Generator 4 Object 5 Industrial Camera 6 A / D Converter 7 CPU 8 Memory

Claims (2)

[Claims] 1. A laser spot having a Gaussian distribution or an intensity characteristic similar to the Gaussian distribution is converted into signal level data proportional to the intensity at each position, and the absolute value of the signal level difference between data at neighboring positions is converted from these data. A method for calculating the center of a laser spot by image processing, characterized in that the center of gravity of a data group at a position corresponding to an absolute value equal to or greater than a predetermined value is calculated, and the position of this center of gravity is used as the center of the laser spot. 2. A laser spot having a Gaussian distribution or an intensity characteristic similar to the Gaussian distribution is converted into signal level data proportional to the intensity at each position, and the absolute value of the differential according to the position is obtained from these data to obtain a value not less than a predetermined value. A method for calculating the center of a laser spot by image processing, characterized in that the center of gravity of a data group at a position corresponding to an absolute value is calculated, and the position of this center of gravity is used as the center of the laser spot.