KR20010038688A - Optical 3-D shape-measuring-apparatus using polarization - Google Patents

Abstract

PURPOSE: An optically shape-measuring device by using polarization is provided to control a local incident light amount of a camera according to a difference in the polarization maintenance degrees of reflected and scattered beams with polarization plates when the scattering degree of an object such as a PCB is ununiform, thereby obtaining images with proper contrast and removing noise images due to severe reflection. CONSTITUTION: An optically shape-measuring device by using polarization includes a first polarization plate(2) mounted in front of a lens of a laser beam radiating unit(1) which radiates a linear laser beam to an object(10) to measure, and a second polarization plate(3) mounted in front of a lens of a camera(5) which obtains images of the linear laser beam scattered on a surface of the object, so that polarization angles of the two polarization plates are appropriately controlled when a local reflection ratio of the object is too largely different to obtain images with uniform luminance.

Description

Optical shape measuring device using polarization {Optical 3-D shape-measuring-apparatus using polarization}

In general, the optical shape measurement technology used in the automation system and the like has not been influenced by remote, non-contact measurement, and many studies have been conducted because it is highly practical such that parallel / high precision measurement is possible and can be used for large objects. In particular, the shape measurement device using the laser triangulation method is used in a lot of industrial sites because the error due to the surrounding environment is small and the measurement speed is fast.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical shape measuring device that is widely used for on-line product inspection or shape measurement at a production site. Particularly, a polarizing plate is introduced into a shape measuring device using a linear laser beam to locally reflect and scatter a measurement object. The present invention relates to an apparatus capable of acquiring an improved linear laser beam image by controlling a difference in brightness depending on characteristics.

Conventional optical measuring apparatus using a linear laser beam and triangulation method is configured as shown in Figure 1, the laser beam irradiation apparatus 1 for producing a linear laser beam and to irradiate the measuring object 10, and the measuring object 10 A color filter 4 for transmitting only the linear laser beam reflected or scattered from the surface and blocking irrelevant light, a camera 5 for acquiring an image of the laser beam reflected from an object, and an image obtained from the camera. It consists of an image signal processing board 6 which stores in the memory and finds the center pixels in the obtained linear image and extracts three-dimensional shape information, and a computer 7 which operates the image signal processing program.

In the optical shape measuring apparatus configured as described above, the image of the laser beam acquired by the camera is deformed in the direction perpendicular to the reference line as shown in FIG. 2 when the object surface is not a plane, and this deformation amount has the height information at that point. do. The linear laser beam image modified according to the surface shape is acquired by the camera 5 to extract 3D shape information from the image signal processing board 6 and the computer 7.

Shape measuring apparatus using a linear laser beam that operates as described above, there are many prior arts proposed as existing patents, Korean Patent Publication No. 97-28614, 92-10548 and the like, US Patent 5,264,678 and 5,129,010.

However, such a conventional device has a nonuniform laser beam scattering and reflection state on the surface of the object to be measured. For example, in the case of a leaded PCB substrate, direct reflection is severe in the substrate portion and diffuse reflection (scattering) in the lead portion is observed. Severe-In the image of the laser beam acquired by the camera 5, the brightness difference is shown locally. In this case, if the sensitivity of the camera is increased to acquire the dark part of the image, the bright part of the image becomes saturated, and the laser beam of the highly reflective part causes secondary reflection in other areas, causing errors. .

In the "laser triangulation device using a point light source", this phenomenon can be solved by adaptive laser intensity control, etc., but in the "laser triangulation device using a linear beam" is a problem that is difficult to solve.

As a conventional technique using the concept of polarization in an optical shape measuring apparatus using a laser, a method of removing the noise generated by scattering of a laser beam from an object on a cross section of a laser beam having a normal distribution has been conventionally devised. Japanese patent 7-218231 A, Three-dimensional shape measuring apparatus). This design focuses on solving a polarizer in front of the camera lens that causes the second scattering caused by irregular scattering as the laser beam is scattered on the object, causing errors in extracting the centerline from the image of the linear laser beam.

An object of the present invention is to obtain an image of a linear laser beam obtained when the local scattering degree of the measurement object in the shape measuring apparatus using the linear laser beam is severely different (for example, a PCB substrate coated with lead, BGA, etc.). That the difference in brightness is so severe that measurement is difficult,

A polarizer is installed in the laser irradiation unit and the laser beam receiving unit, respectively, to make the laser beam irradiated to the object into a specific polarization state, and to adjust the angle of the polarizer in front of the camera lens that acquires the image of the laser beam. By adjusting the amount of light received by the laser beam (most of the polarization state of the laser beam is maintained) and the scattering beam (the polarization state of the laser beam is broken a lot), it is possible to obtain an improved image by reducing the difference in brightness depending on the position of the laser measurement object. It is to provide a device that can.

The present invention relates to an apparatus for acquiring an image of an improved laser beam having a small brightness difference by installing a polarizer and adjusting an angle thereof in an optical shape measuring apparatus using a linear laser beam. By adjusting the polarizer located in front of the laser irradiation device it is possible to adjust the polarization direction of the laser beam incident on the object (when the laser beam itself is polarized, the polarizer may be omitted and the polarization angle of the laser may be adjusted). If the object to be measured is locally different in reflection and scattering, adjusting the angle of the polarizer located in front of the light receiver (camera) can selectively reduce the intensity of the locally strong laser beam to make the entire image more uniform. The principle of this is that the local brightness of the laser beam image is determined by the degree of reflection / scattering of the object plane.In this case, if the reflection / scattering characteristics are different, the polarization characteristics are different. By selectively attenuating, the overall uniform laser beam image is obtained.

1 is an overall configuration diagram of a conventional optical shape measuring device

2 is a diagram illustrating a shape deformation of a laser beam linearly irradiated to a general measurement object.

3 is a principle diagram of a general triangulation method

4 is an overall configuration diagram of an optical shape measuring apparatus using polarization according to the present invention

5 is an exemplary view illustrating the angle installation of the polarizing plate in the shape measuring apparatus according to the present invention.

6A is a result of image acquisition of a device without a conventional polarizing plate

Figure 6b is a result of image acquisition of the device incorporating a polarizing plate according to the present invention

<Description of the code | symbol about the principal part of drawing>

(1): laser beam irradiation device (2): first polarizing plate

(3): second polarizing plate (4): color filter

(5): CCD camera (6): Video signal processing board

(7): Computer 8: Image Lens

(9): CCD sensor (10): measuring object

( ): Incident angle of the incident beam ( ): Observation angle of the sensor

(q): displacement of light spot image on sensor surface

(p): height of object

Features of the present invention for achieving the above object is a light receiving unit for installing a first polarizing plate (2) in front of the laser beam irradiation device (1) lens in the shape measuring apparatus using a linear laser beam as shown in Figure 4 to obtain a laser beam image The second polarizing plate 3 is installed in front of the lens of the camera 5 so that the local reflectance of the surface of the measuring object 10 is large and the brightness of the obtained image is uneven. Therefore, the angles of the two polarizing plates 2 and 3 are properly adjusted. By adjusting the intensity of the reflected beam and the scattered beam from the object can be obtained an improved laser beam image.

In particular, this method has a great effect in selectively obtaining polarized components of reflected or scattered beams and obtaining a uniform brightness when the reflectance of the measuring object is significantly different, such as inspection of a soldered PCB substrate. It also has the additional effect of blocking reflected or scattered beams from hitting other sites to create an image of the noise component.

First, referring to Figure 3 attached to the basic principle of a conventional triangulation method is as follows. In Fig. 3, the incident angle α of the incident beam, the observation angle (reception angle) β of the sensor, and the focal length f and magnification m (= s * / s) of the image lens are known parameters. In order to ensure that the image of the light spot irradiated on the object plane always fits on the sensor plane, the Scheimpflug condition must be satisfied. In this case, the displacement (q) of the light spot image on the sensor plane according to the height (p) of the object is Calculated as

[Relationship Formula 1]

----------- (One)

Such an optical shape measuring device usually has a configuration as shown in FIG. 1. However, in the optical system of the present invention, as shown in FIG. 4, the first polarizing plate 2 is installed in front of the lens of the laser beam irradiation apparatus 1, and the second polarizing plate 3 is provided in front of the light receiving camera 5 lens which acquires the laser beam image. If the brightness of the obtained image is not uniform because the local reflectance of the surface of the measurement object 10 is different, the angles of the two polarizing plates 2 and 3 are properly adjusted so that the intensity of the beam reflected from the object and the scattered beam can be adjusted. It is composed.

EXAMPLE

5 is a block diagram of a triangulation apparatus configured to have a laser incident angle and a light receiving angle almost similar to each other according to an embodiment of the present invention (α ≒ β). The problem arises when the surface state of the measurement object is not uniform, that is, when the rough and fine surfaces are distributed at the same time. An example of such a case is the inspection of a PCB substrate that is locally coated with lead. The PCB substrate has a fine surface, but the lead portion has a rough surface. Different brightness makes measurement difficult. Points and arrows in the circle indicate the polarization direction.

6 is an experimental result obtained in the device configuration as shown in FIG. FIG. 6A is an image obtained by a measuring apparatus without a conventional polarizing plate, in which a measuring object is a PCB substrate coated with lead, and an incident angle α and a light receiving angle β are 40 degrees. It can be seen that the intensity of the lower portion of the laser line (PCB substrate portion) is very strong compared to the upper portion (lead portion) of the line and is saturated, and there are many noise components due to diffuse reflection. On the contrary, FIG. 6B is a result of measuring the polarization angles of the two polarizing plates according to the present invention as shown in FIG. It can be seen that the intensity of the lower portion of the laser line (PCB substrate portion) is attenuated much compared to FIG. 6A and the noise is also much reduced.

(Variation of invention, application example)

The present invention relates to an optical shape measuring apparatus using a linear laser beam, and to an optical shape measuring apparatus that obtains a better image by installing a polarizing plate and adjusting the angle of each of the laser irradiation unit and the laser beam receiving unit. In the above embodiment, a case of using a pair of linear polarizers was mentioned, but similar effects may be obtained by using a circular polarizer or a general elliptical polarizer as well as linear polarized light.

In the linear optical shape measuring device using the polarized light operated as described above, when the light scattering degree of the measuring object is uneven, such as a PCB substrate coated with lead, a polarizing plate is introduced to determine the difference between the polarization maintaining degree of the reflection and the scattering beam. By adjusting the amount of local light incident on the camera, a contrast of brightness can be obtained as an appropriate image, and a noise image generated when the laser beam is severely reflected from the measurement object can be removed.

Claims (4)

A laser beam irradiation apparatus 1 for making a linear laser beam and irradiating the measurement object 10, a camera 5 for acquiring an image of a linear laser beam scattered from the surface of the measurement object 10, and storing the acquired image And an image signal processing board 6 for extracting three-dimensional shape information by finding center pixels in a linear image and a computer 7 for operating an image signal processing program. The first polarizing plate 2 provided in front of the laser beam irradiation apparatus 1 and the second polarizing plate 3 provided in front of the camera 5 lens for acquiring the laser beam image have a large local reflectance of the measurement object 10. If the brightness of the image obtained is different, the shape of the optical shape, characterized in that it is configured to adjust the intensity of the beam reflected and the scattered beam by reflecting the polarization angle of the two polarizing plates (2,3) appropriately Device. The method of claim 1, The first polarizing plate 2 installed in front of the lens of the laser beam irradiation apparatus may be omitted when the laser light source itself is already polarized. In this case, the second polarizing plate 3 may be provided only in front of the camera that acquires the image. Optical shape measuring device, characterized in that configured to adjust the contrast of the brightness of the laser beam image by adjusting the polarization angle of the laser beam and the angle of the second polarizing plate (3). The method of claim 1, Optical shape measuring apparatus, characterized in that the two polarizing plates (2, 3) is composed of a linear polarizing plate. The method of claim 1, Optical shape measuring device, characterized in that the two polarizing plates (2, 3) is composed of a circular polarizing plate.