JP2714152B2 - Object shape measurement method - Google Patents

Description

The present invention relates to an object shape measuring method for measuring an object shape in a non-contact manner using laser light.

(B) Prior Art Conventionally, there are mainly the following three methods for recognizing a three-dimensional shape of an object.

(1) Moiré method This method applies contouring moiré fringes according to the shape of an object by applying the principle of moire fringe generation using two gratings, and performs three-dimensional measurement. It is roughly divided. In any case, when a normal grid (reference grid) casts a shadow on a three-dimensional object, the shape of the shadow of the reference grid changes according to the shape of the object, resulting in a deformed grid. By superimposing the deformed grating and the reference grating, Moire fringes corresponding to contour lines are obtained.

(2) Method using a displacement meter The distance between the displacement meter and the object is measured by a triangulation method using a laser displacement meter consisting of a laser beam irradiation unit and a position sensor that detects the position of the bright spot of the laser beam irradiated on the object. The three-dimensional shape of the object is measured by sequentially moving the object or the displacement meter.

(3) Light cutting method The object surface is irradiated with laser light or other light as slit light (sheet beam), a band-like pattern formed on the object surface is imaged by a camera, and the optical system and the object are relatively moved. Then, three-dimensional information of the object is obtained.

(C) Problems to be Solved by the Invention However, the above-mentioned various methods have advantages and disadvantages, and are insufficient depending on the purpose of use or measurement.

In other words, the moire method is suitable for checking the qualitative properties of the object shape, but the use of interference fringes limits the quantitative measurement accuracy. With the displacement meter method, high measurement accuracy can be obtained, but it is necessary to measure each point of the object, and to measure the three-dimensional shape of the object, the displacement meter or the object must be moved sequentially No. Even in the light cutting method, the optical system or the object must be moved in order to measure the three-dimensional shape of the object.

An object of the present invention is to move a measurement system or an object without moving the object.
Another object of the present invention is to provide an object shape measuring method capable of measuring a three-dimensional shape of an object with high accuracy.

(D) Means for Solving the Problems The object shape measuring method of the present invention is to transmit a laser beam through a transmission plate of a rough surface or an inhomogeneous medium, or to reflect the laser beam on a reflection plate of a rough surface, and to apply the laser beam Projecting a speckle pattern, moving the transmission plate or the reflection plate, imaging the speckle pattern on the surface of the object, capturing image data at different timings, and taking a two-dimensional correlation between the two image data. It is characterized in that a velocity vector of the speckle pattern is obtained.

(E) Function FIGS. 1 to 3 are explanatory diagrams of the object shape measuring method of the present invention.
Shown in the figure.

In FIG. 1, reference numeral 1 denotes a laser light source for generating laser light,
2 is ground glass, 3 is a lens, 4 is an object to be measured, and 5 is a camera. The laser light emitted from the laser light source 1 is diffused by passing through the frosted glass 2. The diffused light is spread by the lens 3 and illuminates the object 4. When the laser light passes through the frosted glass 2, random phase modulation is applied to the laser light, and the intensity distribution of the light becomes random on the surface of the object 4 due to the interference between the diffused lights, and a speckle pattern appears. In this state, if the ground glass 2 is moved in the direction of the arrow in the drawing, the speckle pattern on the surface of the object also moves. Data processing unit 6
Captures the image data of the speckle pattern on the object surface at different timings captured by the camera 5 and obtains the two-dimensional correlation between the two image data to obtain the velocity vector of the speckle pattern.

FIGS. 2A and 2B show image data captured at two different timings. Image data for one screen is represented by, for example, 256 × 256 pixels, which are divided into 16 × 16 sections as shown in the figure, and a two-dimensional correlation is obtained for each section. That is, a two-dimensional correlation between each section shown in FIG. 2A and each section shown in FIG. 2B is obtained, and sections having a strong correlation are associated with each other. The numbers shown in some of the sections in FIG. 2 (B) indicate the correspondence with the image data of the sections shown in FIG. 2 (A). In this way, the speed vector (moving direction and speed) of the speckle pattern between the sections in the image data is obtained. Then, for example, by extracting sections having the same velocity vector, it is possible to find a plane at a certain angle with respect to the light source. For example, as shown in FIGS. 2A and 2B, a section where the speckle pattern moves downward in the figure is a, and a section where the speckle pattern moves obliquely downward in the figure. Is represented by b, as shown in FIG. In this manner, the shape of the surface of the object can be measured without moving the measurement system or the object and with high measurement accuracy.

(F) Embodiment FIG. 4 shows a configuration of an optical system of an object shape measuring apparatus according to an embodiment of the present invention. In FIG. 4, 1a is a red laser light source, 1b is a green laser light source, and 2 is a disc-shaped ground glass. The disc-shaped ground glass 2 is rotated by a motor (not shown). Ground glass 2 of the two laser light sources 1a and 1b
Is set to be perpendicular to the rotation center of the frosted glass 2. Reference numerals 3a and 3b denote lenses for increasing the directional angle of light diffused by the frosted glass 2. Reference numeral 4 denotes an object to be measured, and reference numeral 5 denotes a camera for imaging a speckle pattern projected on the surface of the object 4.

In the optical system shown in FIG. 4, if the frosted glass 2 rotates in the direction of the arrow, the irradiation point of the frosted glass 2 by the red laser light source 1a always moves rightward in the horizontal direction, and the green laser light source
The irradiation point of the ground glass 2 by 1b always moves vertically downward. Therefore, the speckle pattern by the red laser light projected on the surface of the object 4 moves in the direction of the broken line in the figure, and the speckle pattern by the green laser light moves in the direction of the solid line in the figure.

FIG. 5 is a block diagram of a control unit of the object shape measuring device. In FIG. 5, a CPU 14 controls the entire control unit. ROM
A program to be executed by the CPU 14 is written in 15 in advance. The RAM 16 is used as a working area when calculating two-dimensional correlation between two image data and calculating a velocity vector. 1a is a red laser light generator used as a red laser light source, for example, He-Ne laser,
A semiconductor laser, a dye laser, or the like is used. Reference numeral 1b denotes a green laser light generator used as a green laser light source, for example, an Ar laser, a semiconductor pump YAG laser, a Dye laser, or the like. Reference numeral 12 denotes a control circuit for performing on / off control of both laser light generators. Reference numeral 10 denotes a motor for rotating the disc-shaped ground glass shown in FIG. 4, and reference numeral 11 denotes a control circuit for the motor.
The laser control circuit 12 and the motor control circuit 11 are controlled by the CPU 14 via the I / O port 13. Reference numeral 5 denotes a color CCD camera which images a speckle pattern projected on the surface of an object. The A / D converters 17a and 17b convert the red component video signal and the green component video signal into digital data. The image data processing circuit 18 supplies a synchronizing signal to the camera 5 and performs A / D converters 17a and 17b.
Is output and sequentially written into the image memories 19 to 22. The image memories 19 and 20 are memories for storing red component image data. The image memory 19 stores the odd-numbered image data, and the memory 20 stores the even-numbered image data. Further, the image memories 21 and 22 are memories for storing green component image data, respectively. The image memory 21 stores the image data captured at odd-numbered times, and the image memory 22 stores the image data captured at even-numbered times.

The processing procedure of the control unit described above will be described with reference to the flowchart of FIG. First, at a predetermined sampling timing, the image data processing circuit 18 shown in FIG. 5 creates red component image data and green component image data from the video signal obtained by the imaging of the camera 5 respectively. To write to the image memory. That is, if the sampling is an odd number of times, the image data of the red component is written to the image memory 19, and the image data of the green component is written to the image memory 21, respectively. If the sampling is an even number of times, the image data of the red component is written to the image memory 20 and the image data of the green component is written to the image memory 22. After the new image data is written to the image memory in this manner, the CPU 14
Calculates a two-dimensional correlation between a predetermined section of newly written image data and a predetermined section of previous image data for the red component image data and the green component image data, respectively. Subsequently, a velocity vector of each part in the screen is obtained for each color component based on the sampling timing interval and the moving direction of the speckle pattern. As described above, the angular relationship between each part of the object surface and the laser light source and the camera becomes clear from the velocity vector. Then, for example, the third
As shown in the figure, a region where the same velocity vector is distributed is regarded as a plane constituting a part of the outline of the object, and a boundary line of each plane is extracted to create outline data of the object by a so-called wire frame. .

According to the above-described embodiment, while speckle patterns of different colors are projected on the object surface, and both speckle patterns are moved at an angle of 90 degrees to each other, even for an object having an uneven surface. , The uneven shape can be obtained.

In the above embodiment, the red laser light generator and the green laser light generator are separately used. However, a blue laser light generator may be provided to use the blue component signal of the camera. Further, as shown in FIG. 7, for example, a predetermined color light source can be obtained by using a white laser light generator and a color filter half mirror or a prism for color-separating the white laser light.

In the embodiment, the object is irradiated with laser light from one direction. However, a plurality of sets of measurement systems may be arranged around the object to simultaneously measure the shape of the object from all directions. Can also. An example is shown in FIG. In FIG. 8, 30, 31 are half mirrors, 32, 33, 34 are mirrors, 2a, 2b, 2
c is ground glass, 5a, 5b and 5c are cameras, and 4 is an object to be measured. With this configuration, the laser light emitted from the laser light source position is guided to the three ground glasses 2a, 2b, and 2c by the half mirror and the mirror, and the speckle pattern is projected onto the object 4 from three directions. Therefore, it is possible to measure the outer shape of the entire circumference of the object.

Further, in the embodiment, as a method of projecting a speckle pattern on the surface of an object, a laser beam is obtained by transmitting frosted glass, but a transmission plate having a non-uniform medium may be used. Further, the light may be reflected by a reflecting plate having a rough reflecting surface, and the scattered light may be irradiated.

(G) Advantageous Effects of the Invention According to the present invention, it is possible to measure the outer shape of an object without moving the object to be measured and the measurement system, and furthermore, the amount of movement of the speckle pattern is made relatively small, and the two-dimensional correlation is reduced. By increasing the resolution at the time of taking, the object shape can be measured with the same or higher accuracy as the conventional light sectioning method.

[Brief description of the drawings]

1 to 3 are diagrams for explaining the operation of the present invention. FIG. 1 is a configuration diagram of an object shape measuring device, and FIGS. 2 (A) and (B) take two-dimensional correlation. Diagram illustrating the method,
FIG. 3 is a diagram showing an example of the obtained velocity vector. 4th
FIG. 5 is a configuration diagram of an optical system of an object shape measuring apparatus according to an embodiment of the present invention. FIG. 5 is a block diagram of a control unit of the apparatus, and FIG.
The figure is a flowchart showing the processing procedure. 7 and 8 are configuration diagrams of an optical system of an object shape measuring apparatus according to another embodiment. 1 ... laser light source (laser light generator), 2 ... ground glass, 3 ... lens, 4 ... measured object, 5 ... camera.

Claims (1)

(57) [Claims] 1. A speckle pattern is projected on the surface of an object by transmitting a laser beam through a transmission plate of a rough surface or a heterogeneous medium or reflecting the laser beam on a reflection plate of a rough surface. Moving, capturing a speckle pattern on the surface of the object, capturing image data at different timings, and obtaining a two-dimensional correlation between the two image data to obtain a velocity vector of the speckle pattern. Object shape measurement method.