CN101556141A - Fourier transformation method for measuring irregular slit width and device - Google Patents

Abstract

The invention discloses a Fourier transform method and device for measuring irregular slit widths. The method includes: adjusting the position of a light source, reflecting the received light source; adjusting the distance between the lens and the measured slit; obtaining The entire image of the measured gap; convert the collected image information into digital information and store it accordingly; read the data; perform corresponding calculations on the read data to obtain the gap width of the currently measured gap. The device includes: a light source, a lens and a CCD, an image acquisition and data storage module, a data reading unit, a Fourier transform and processing unit, and a personal computer (PC). The device of the present invention has a simple structure, and is suitable for measuring geometric dimensions such as the width and shape of seams and grooves with irregular shapes, uneven widths or gradually changing widths, and non-straight lines. In different measurements, there is no need to change the magnification of the lens, that is, the CCD Accurate and fast non-contact measurement can be realized.

Description

A Fourier transform method and device for measuring irregular seam width

technical field

The invention relates to a Fourier transform method and device for measuring irregular seam widths, in particular to a method and device for processing image data and measuring the width of various irregular seams and grooves by using Fourier transform.

Background technique

Various gaps, slits, and grooves will be encountered in industrial production, and it is necessary to measure and control the width, spacing, shape, etc. For example, when detecting the light leakage of the piston ring in the engine, the piston ring needs to be pressed into the ring gauge. If the piston ring has light leakage, an arc-shaped slit with uneven width will be formed between the outer edge of the piston ring and the inner edge of the ring gauge; In all kinds of welding, it is often necessary to measure the width of the weld seam in order to control the welding process and obtain the best welding effect; the plug-in card used to peel off the wire jacket has a V-shaped slot gap, in order to ensure that the plug-in card It can work normally, and there are strict regulations on the gap at a specific position on the card slot; the slit coater is a substrate processing device used to manufacture printed circuit boards, and the slit coater sprays the processing liquid from the nozzle during operation , in order to ensure the uniformity of the sprayed treatment liquid, the opening spacing of the nozzle is required to be uniform with high precision; in addition, as long as two close objects will form a gap. The measurement of the width and shape of these gaps has important application value and practical significance for evaluating product quality and controlling process flow.

There are two methods of measuring the gap width, contact and non-contact. The contact method uses various measuring tools for measurement, but manual operation is required, the automation level is low, and the measurement accuracy is difficult to improve due to the limitation of the accuracy of the measuring tools. There are many non-contact methods. Among them, the tool microscope has high measurement accuracy, but the cost is high, the volume is large, and it is not suitable for industrial field use; and the method of using CCD to capture the image of the gap and obtaining the width and shape of the gap through image processing has the advantages of small size. , flexible use, suitable for on-site use and other advantages.

At present, there are two methods of measuring gaps by taking images with CCD and applying image processing technology: the first method uses backlighting, and uses the diffraction effect to derive the gap width from the light intensity distribution of the diffraction pattern; the second method With forward lighting, the two edges that make up the gap are imaged on the CCD at the same time. Due to the low-pass effect of the imaging system, the edges are no longer clearly visible and become a blurred area. To measure the distance between the two edges that make up the gap, now There is a method to firstly improve the resolution of the CCD, so that the blurred areas of the two edges on the image are separated, and then perform image processing to complete the measurement of the gap width, such as the domestic patent "Measurement Method and Sensor for Roller Nozzle Distance" (Application No. 200310118466.3) It is to use a lens with a magnification of 60 to improve the resolution of the CCD and the image to complete the measurement. The first method has a principle error ([1] Uncertainty in measuring the diameter of a thin cylinder by optical diffraction method, Cui Jianwen, Zhang Jun, etc., Optoelectronic Engineering, 2005, 7: 55-58), and the gap after imaging cannot reflect The details of the actual gap, the measured result is the average width of the gap over a certain length. In the second method, the magnification of the lens, that is, the resolution of the CCD, must be adjusted according to the needs in each measurement, and this brings three disadvantages: ① After adjusting the magnification of the lens, in order to regain a clear image, it must At the same time, adjust the distance between the lens and the measured object, and these adjustment processes will prolong the measurement time; ② Adjusting the optical path needs to be equipped with a corresponding adjustment mechanism, which will inevitably increase the cost and volume of the measurement device; ③ With the increase of lens magnification, the CCD The measurement field of view will be reduced and the time to complete a full measurement will increase accordingly. To sum up, the existing methods and instruments have certain limitations, and they cannot solve the measurement problems of geometric dimensions such as width and shape of slits, especially irregular slits.

Contents of the invention

In order to solve the above-mentioned problems and defects, the present invention provides a method and device that utilizes CCD imaging and uses Fourier transform to process data to complete measurement, which not only realizes the rapid and accurate measurement of geometric dimensions such as the width and shape of irregular gaps Measurement, and on the basis of not adding measurement links and measurement components, keep the resolution of the CCD unchanged, achieve fast and accurate measurement, and avoid the influence of light diffraction effect.

The present invention is achieved through the following technical solutions:

A kind of Fourier transform method that the present invention relates to measuring irregular slit width comprises:

Adjust the position of the light source so that the objects forming the measured gap reflect the received light source;

Adjust the distance between the lens and the measured gap;

Obtain the entire image of the measured gap;

Convert the collected image information into digital information and store it accordingly;

read the data;

Perform corresponding calculations on the read data to obtain the gap width of the currently measured gap.

A Fourier transform device for measuring irregular slit widths involved in the present invention comprises:

The light source is used to irradiate the measured gap, and the objects constituting the measured gap reflect the light;

The lens and CCD receive the reflected light of the objects around the measured gap to obtain the image of the entire measured gap;

The image acquisition and data storage unit converts the image information in the CCD into digital information and stores the digital information;

The data reading unit reads data along the direction perpendicular to the direction of the slit, and sends the read data to the Fourier transform and processing unit;

The Fourier transform and processing unit performs corresponding processing and calculation on the read data to obtain the gap width of the measured gap.

The beneficial effects of the technical solution provided by the invention are:

1. Two strip light sources respectively irradiate the gap to be measured from obliquely above the two sides, which can provide uniform and bright illumination for various measurement objects;

2. In different measurements, there is no need to change the resolution of the CCD, which reduces the measurement process and shortens the measurement time;

3. The light source is consistent with the working band of the CCD, which reduces the image noise;

4. The Fourier transform and processing unit uses Fourier transform to process data, extracts the gap width information from the image data blurred by the imaging system, not only completes the measurement of the geometric size of the gap, but also restores its image under ideal conditions , and calculate the relevant evaluation indicators.

Description of drawings

Fig. 1 is the method flowchart provided by the present invention;

Fig. 2 is Fourier transform and processing flowchart;

Fig. 3 is the flowchart of calculating pixel equivalent;

Fig. 4 is the structural representation of this method;

Figures 5a and 5b are schematic diagrams of the evolution of the measured gap during the measurement process.

Detailed ways

In order to make the purpose, technical solutions and advantages of the present invention clearer, the implementation of the present invention will be further described in detail below in conjunction with the accompanying drawings:

Example 1

This embodiment provides a Fourier transform method for measuring the width of an irregular slit.

Referring to Figure 1, the method comprises the following steps:

Step 101: adjust the position of the light source, and reflect the received light source by the object constituting the measured gap;

The light source is adjusted relative to the position of the measured gap, and the two light sources are placed in a symmetrical state relative to the gap, and respectively illuminate the gap from both sides obliquely above to provide uniform illumination with sufficient brightness for the field of view area.

Step 102 adjusts the distance between the lens and the measured gap;

So that under the current focal length and image distance, a clear image of the gap can be obtained.

Step 103 obtains the entire image of the measured gap.

Step 104 converts the collected image information into digital information and stores it;

The speed and time of image acquisition are controlled by the image acquisition and data storage module set in the PC, and the path of image data storage is specified by the PC under the order of saving the image.

Step 105 visually displays the stored image data.

Step 106 reads a set of data within the measurement range;

Step 107 carries out corresponding operation on the read data to obtain the slit width at the current position of the measured slit;

It not only obtains the measurement of geometric dimensions such as the width of the gap, but also restores its image under ideal conditions, and calculates related evaluation indicators.

Step 108 judges whether the data in the measurement range has been read;

If the reading is complete, go to step 109, otherwise go to step 106.

Step 109 outputs the result.

The data includes multiple groups, one of which is read each time, and the read data is under the control of the PC, and the data is read by the data reading unit along the direction perpendicular to the direction of the seam, and the The read data is sent to the Fourier transform and processing unit.

Referring to Fig. 2, the algorithm flow of Fourier transform and processing provided by the present embodiment, the flow includes the following steps:

Step 201 performs noise filtering on the read image data;

The noise filtering is mainly to filter obvious noise.

Step 202 selects a suitable coordinate origin position for the read image data;

A suitable origin location facilitates subsequent data processing.

Step 203 performs discrete Fourier transform on the read image data according to the coordinate system formed by the coordinate origin.

Step 204 selects several special coordinate points, and the Fourier transform value at the special coordinate points contains the slit width at the current position.

Step 205 establishes an equation for the Fourier transform at each special coordinate point, and connects all the special coordinate points to form a system of equations.

Step 206 is to find geometric constraints for the coordinate system formed by the appropriate coordinate origin.

Step 207 solves the system of equations formed by the simultaneous connection of special coordinate points under the condition of geometric constraints.

Step 208 calculates the value of the seam width at the current position and related information on the image according to the solution of the equations and the conditions of geometric constraints, and then according to the calculated pixel equivalent (the ratio of the size of the known object to the number of recorded pixels, See Figure 3 for details), to obtain the actual value of the gap width and related information, and restore the gray distribution image of the measured gap under ideal conditions, that is, eliminate the blurring effect of the imaging system on the image and the ideal image after eliminating noise , and can also calculate related evaluation indicators, such as mean square error, signal-to-noise ratio, etc.

Step 209 outputs the required measurement results;

The results include the magnitude of the slit width, the ideal image after restoration, evaluation indexes and the like.

Referring to Figure 3, it provides the process of obtaining the pixel equivalent. When the focal length of the lens is fixed and the relative position to the CCD is fixed, when the size of the actual object is one pixel equivalent, the image on the CCD is just one pixel long. The specific process includes the following steps:

Step 301 fixes the focal length and image distance of the lens;

After the image distance and focal length are fixed, the focal length and image distance will not change in subsequent measurements.

Step 302 selected object imaging;

Select an object with a known size, which should be a relatively large size that is easy to measure, and use a lens with a fixed focal length and image distance and a CCD2 to take a picture of it to convert the size into image information.

Step 303 adjusts the working distance;

The working distance is the distance from the lens to the selected object. In order to reduce the error, the distance should make the image as clear as possible.

Step 304 records the number of pixels corresponding to the image;

The number of recorded pixels corresponds to the known size of the object.

Step 305 obtains the pixel equivalent;

The ratio of the known size to the number of recorded pixels is the pixel equivalent.

The measured gap provided in this embodiment may be a gap in the same object, or a gap between two different objects (a gap formed when two different objects are close to each other but not in contact).

Example 2

This embodiment also provides a Fourier transform device for measuring the width of the irregular slit.

Referring to Fig. 4, the Fourier transform device of measuring irregular slit width comprises: light source 10, lens and CCD30, image acquisition and data storage unit 40, data reading unit 50, Fourier transform and processing unit 60 and PC 70 . The light source includes two identical strip-shaped light sources, which are composed of light-emitting diodes, and output red light that is uniformly distributed in space, and illuminate the measured gap 20 from both sides obliquely above, so as to provide uniform illumination with sufficient brightness for the field of view area; the lens and The CCD receives the reflected light of the objects around the measured gap, and obtains a clear image of the entire gap from the front; the image acquisition and data storage module converts the image information into digital information by the CCD under the control of the PC, and stores it in the corresponding In the disk; under the control of the PC, the data reading unit reads the data along the direction perpendicular to the direction of the slit, and sends it to the Fourier transform and processing unit, and obtains the slit width at the current position of the slit through the corresponding algorithm. The fetching unit reads a set of data at another position on the gap, and then sends it to the Fourier transform and processing unit to complete the measurement of the gap width at this position. This process continues to circulate until the gap within the range specified by the user is completed. Measurement of wide geometric dimensions.

Referring to Fig. 5a and Fig. 5b, it is a structural schematic diagram of the evolution of the measured gap during the measurement process. The measured gap 20 undergoes diffuse reflection under the uniform illumination of the light source, and the reflected light becomes a plane image 502 after being received by the lens and CCD; Under the control of the image acquisition and data storage module, the image 502 is converted into a two-dimensional grayscale matrix 503, and stored in the corresponding disk of the PC; under the control of the PC, the data reading unit reads a set of Data, such as the data 504 of the ab section in the plane image 502, this is a group of discrete gray values, the interval of discrete points is determined by the magnification of the lens and the pixel size of the CCD, and is inevitably polluted by noise; Under the control, the data is sent to the Fourier transform and processing unit, and the corresponding algorithm measures the gap width at the current position, and recovers the gray distribution 505 of the gap at the current position under ideal conditions, and calculates the relevant evaluation indicators; Next, the data reading unit continuously reads new data, and the Fourier transform and processing unit do corresponding processing to complete all measurements. The present invention can measure the schematic diagram of the surface topography of various slits, including the measurement of slits and grooves with irregular shape, uneven width or gradual width change, and non-straight direction (as shown in Fig. 5b).

The measured gap provided in this embodiment may be a gap in the same object, or a gap between two different objects (a gap formed when two different objects are close to each other but not in contact).

Although the present invention has been described by way of example, the present invention is subject to many modifications and changes without departing from the spirit of the invention, and the claims of the present invention include such modifications and changes.

Claims (8)

1, a kind of Fourier transformation method of measuring irregular slit width is characterized in that, this method comprises:

Adjust the position of light source, the object that constitutes tested slit reflects the light source that receives;

Adjust the distance between camera lens and tested slit;

Obtain the entire image in tested slit;

The image information that collects is converted to numerical information, and stores accordingly;

Data are read;

The data that read are carried out corresponding computing, and the seam that obtains current tested slit is wide.

2, the Fourier transformation method of measurement irregular slit width according to claim 1 and 2 is characterized in that, described is to read along the perpendicular direction moved towards with seam by reading unit to reading of data.

3, the Fourier transformation method of measurement irregular slit width according to claim 2 is characterized in that, the data that described data-reading unit reads include many groups.

4, the Fourier transformation method of measurement irregular slit width according to claim 1 is characterized in that, described data are read also comprises before:

View data to storage is carried out visualization display;

Judging whether the data that read belong in the scope of measurement, is that data are read; Otherwise, read next group data.

5, a kind of Fourier transform device of measuring irregular slit width is characterized in that this device comprises:

Light source is used to shine tested slit, and the object that constitutes tested slit reflects light;

Camera lens and CCD receive the tested slit reflected light of object on every side, obtain the image in whole tested slit;

Image acquisition and data storage cell are converted to numerical information with the image information among the CCD, and its numerical information is stored;

Data-reading unit, along with seam move towards perpendicular direction reading of data, and the data that read are sent to Fourier transform and processing unit;

Fourier transform and processing unit are handled and computing accordingly to the data that read, and the seam that obtains tested slit is wide.

6, the Fourier transformation method of irregular slit width according to claim 5 is characterized in that, described light source comprises two strip light sources, and two strip light sources constitute by light emitting diode, and shines tested slit from the both sides in tested slit respectively.

7, the Fourier transformation method of irregular slit width according to claim 5 is characterized in that, described CCD is the image that obtains whole slit from the front.

8, the Fourier transformation method of irregular slit width according to claim 5 is characterized in that, the data that described data-reading unit reads include many groups, whenever after reading wherein one group of data, judge data in the measurement range whether read finish after, be that the result is read in output; Otherwise read next group data.

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