JPH0525043B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to three-dimensional measurement using striped patterns, sometimes typified by moiré topography.

(Prior art and its problems) Moiré topography projects a striped pattern onto a physical surface, superimposes the striped pattern deformed by the shape of the object and the standard striped pattern, and shows the contour lines generated as the difference frequency. By observing the stripes,
This is a method of measuring the shape of an object. For more information, see the magazine ``Applied Optics''.
(Applied Optics), 9 volumes, 1970, 1467-1472
It is described in the paper ``Moire Topography'' listed on the page. This method includes a grating irradiation type in which a point light source 21 illuminates a grating 22 placed just in front of an object 23 as shown in FIG. There is a grid projection type that forms an image. When comparing both methods, the latter is more flexible and has a wider range of applications in terms of operability. Regarding grid projection moiré topography, see, for example, the magazine "Applied Optics", Vol. 22,
1983, pp. 850-855, "Projection Moire' with moving grid method in automatic three-dimensional topography"
grantings for antomated 3-D
topography)”. In the projection moiré method, the grating is located near the light source and the camera 25, and the operability is better than in the irradiation moiré method. However, since both methods use a fixed grid, it is difficult to vary the stripe spacing. Moiré fringes are proportional to the fringe spacing. Therefore, as the number of moire fringes increases, the amount of information increases, making it possible to analyze complex objects, but on the other hand, it takes a lot of time to process images of moire fringes. Therefore,
It is effective to change the pitch of the stripes depending on the shape of the object. However, in order to achieve this using conventional methods, it is necessary to prepare a large number of gratings with different pitches, to exchange the gratings depending on the shape of the object, and to precisely fix them in the device. Therefore, it takes a lot of time to measure and cannot be used for automatic measurement.

(Object of the invention) The object of the invention is to generate a striped pattern of arbitrary pitch on the object surface in a short time without using a grid, with the optimum pitch according to the shape of the object, and to perform automatic measurement. The purpose of this invention is to provide a three-dimensional measurement method and device that make it possible.

(Structure of the Invention) The measurement method of the present invention scans an object to be measured with the intensity-modulated light while changing the modulation frequency of the intensity-modulated light according to the shape of the object to be measured, and creates stripes of optimal pitch in each part of the object. The method is characterized in that a pattern is formed on the object to be measured. The three-dimensional measuring device also includes a light source consisting of a semiconductor laser, a holographic laser scanner in which a plurality of hologram lenses are arranged on a disk, and a beam of monochromatic light emitted from the light source that is shaped to form the hologram lens. a signal generator for changing the current injected into the light source, a control device for controlling the signal generator, and a camera for observing the scanning beam scanned by the holographic laser scanner. , and an image processing device that extracts moiré fringes from the scanning fringe pattern and the deformed fringe pattern on the object plane obtained by the camera 12.

(Operation/Principle of the Invention) In a holographic laser beam scanning device such as a holographic laser scanner, several holograms are arranged and fixed on the circumference of a disk, and the laser beam is transmitted by rotating them at high speed. scan. If the front optical system of a holographic laser scanner is adjusted so that the scanning beam converges in the scanning direction on the object plane and diverges in the sub-scanning direction, the beam width in the sub-scanning direction
The length determined as the scan length is scanned over the entire surface. At this time, by intensity modulating the laser output,
A striped pattern similar to the prior art can be generated on the object plane. Furthermore, by variably controlling the frequency of the current injected into the laser, it is possible to project fringes with arbitrary phase and amplitude, and it is possible to freely generate fringes with the optimum pitch for the shape of the object. Usually, the intensity is modulated with a rectangular wave, but when modulated with a sine wave, it is possible to prevent the occurrence of high-order moiré fringes.

(Example) FIG. 1 shows an example of the present invention. The light emitted from the semiconductor laser 1 is collimated by a collimating lens 2, converted into an elliptical beam by a cylindrical lens 3, and then scanned onto an object 6 by a hologram lens 5 of a holographic laser scanner 4. . For example, a signal generator 11 such as a function generator having a GP-IB interface is controlled by an arithmetic control unit 12 such as a microcomputer having a GP-IB interface. The output voltage of the power source 10 having a face is changed, and the semiconductor laser 1 is modulated. At this time, a part of the scanning beam by the hologram lens 5 is taken out by the beam splitter 7, and two position detectors 8 are placed at the scanning end on a plane at the same distance as the scanning plane. Position detector 8
The signals are sent to the arithmetic control unit 12 through an arithmetic circuit (consisting of an operational amplifier) 13 that takes the differential of the output. The arithmetic and control unit 12 operates as shown in the flowchart shown in FIG. That is, when the beam scans the position detector 8 above the scanning end, a signal is generated to start modulating the semiconductor laser, and when the beam passes the position detector 8 below the scanning end, the modulation of the semiconductor laser is generated. The signal generator 11 is controlled by generating a signal to terminate the process. After finishing the modulation, a constant current is applied from the signal generator 11 in order to detect the modulation start position of the next scan.
Control the laser so that it oscillates continuously. FIG. 5 shows the signals that control each device at this time. Upon receiving the signal a from the position detector above the scanning end, the arithmetic and control unit 12 sends a modulation start control signal c to the signal generator 11. In response, the signal generator 11 sends a laser modulation signal e to the power source 10, which converts this signal into a current necessary to drive the laser and injects it into the laser. Figure 2 shows how the laser injection current changes over time. The modulation frequency is
It is controlled by the arithmetic and control unit 12 so that each part of the object has a striped pattern with an optimal pitch. The arithmetic and control unit 12, which has received the signal b from the position detector at the lower scanning end shown in FIG. 5, sends a modulation end control signal d to the signal generator. In response to this, the signal generator finishes transmitting the laser modulation signal to the current, and the power supply injects a constant current above the threshold into the laser. When a pulsed current Ia larger than the threshold current Ith of the laser is injected into the laser, a striped pattern is generated on the object surface. For example, when a holographic lens scanner 4 consisting of 20 hologram lenses is rotated at 6000 rpm,
Stripes can be generated over the entire scanning surface in 500 msec. Therefore, by using the TV camera 9 that can accumulate light for 500 msec or more, it is possible to image the deformed stripes on the object plane. The image processing device 14, which is equipped with a frame memory and an interface such as GP-IB and has image addition/subtraction and integration functions, has a striped pattern corresponding to the signal generated by the signal generator 11 from the arithmetic and control device 12 in advance. By inputting this information and superimposing it on an image captured by the TV camera 9, moiré fringes are generated and displayed on the data output device 15, such as a CRT. The four arithmetic operations for an image are to digitally represent the gradation of an image and perform gradation calculations for each dot. Since the semiconductor laser 1 can be modulated by the control device 12, a striped pattern having an arbitrary pitch can be generated. FIG. 3 is a diagram showing the effects of this invention when compared with the conventional example. The conventional method only generates stripes with a constant period, so even if an object has a large and small shape change as shown in Figure 3a, both parts will be the same as shown in b. It can only measure with a certain degree of accuracy. On the other hand, since the intensity of the laser beam is modulated in this invention, the stripe pitch can be changed arbitrarily. Since it is possible to generate a sparse striped pattern, it is possible to efficiently measure both accuracy and shape measurement time.

(Effects of the Invention) As described above, according to the three-dimensional measurement method and apparatus of the present invention, the pitch of the stripes can be arbitrarily controlled within the lattice plane simply by changing the modulation frequency of the light source, and the pitch of the stripes can be adjusted to the shape of the object. Stripes with optimal pitch can be generated in a short time. As a result, automatic measurement becomes possible because the troublesome work of replacing the grid is eliminated.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 2 is a diagram showing the time change of the current injected into a semiconductor laser, and FIG. 3 is a diagram comparing the effects of the present invention and a conventional example. 4 is a flowchart of the apparatus, FIG. 5 is a timing chart, FIG. 6 is a diagram showing a conventional example of grating irradiation type moire topography, and FIG. 7 is a diagram showing a conventional example of grating projection type moire topography. In the figure, 1... semiconductor laser, 2... collimating lens, 3... cylindrical lens, 4...
Holographic lens scanner, 5... Hologram lens, 6... Object, 7... Beam splitter, 8... Position detector, 9... TV camera, 10
. . . power supply, 11 . . . signal generator, 12 . . . arithmetic control device, 13 .

Claims (1)

[Scope of Claims] 1. The intensity-modulated light scans the object to be measured while changing the modulation frequency of the intensity-modulated light in accordance with the shape of the object to be measured, and creates a striped pattern with an optimal pitch in each part of the object. A three-dimensional measurement method characterized by forming on an object. 2. A light source consisting of a semiconductor laser, a holographic laser scanner including a plurality of hologram lenses arranged on a disk, an optical system that shapes a monochromatic light beam emitted from the light source and guides it to the hologram lens, and the light source. a signal generator for changing the current injected into the holographic laser scanner; a control device for controlling the signal generator; a camera for observing the scanning beam scanned by the holographic laser scanner; an image processing device that extracts moiré fringes from the obtained fringe pattern deformed on the object surface, and the control device generates a rectangular wave or a sine wave modulated by a constant frequency or a variable frequency. A three-dimensional measurement device characterized by output.