JPH0222321B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention irradiates a light beam onto one point on a measurement surface.
The present invention relates to an optical displacement measuring device that measures displacement of a measurement surface using the scattered light.

BACKGROUND OF THE INVENTION Measuring minute displacements of optically rough surfaces is performed in a wide range of industrial fields, and many methods have been proposed.

One method is to irradiate a light beam onto one point on the measurement surface to create a bright spot, and then measure the displacement by observing the movement of this bright spot from a direction different from the incident beam due to the displacement of the measurement surface. There is known a device that combines a light-receiving element with a photoelectric conversion function for detecting the amount of movement of a bright spot, and a lens for forming a real image of the bright spot on the light-receiving element. (Special Publication No. 59-762) However, in this type of device, the measurement accuracy depends on the size of the bright spot, the optical properties of the measurement surface, the size of the observation angle between the incident beam and the observation section, and the light receiving element. is determined by the characteristics of the output and how its output is processed.

Common problems with this type of device include the following.

(1) In a device in which the beam irradiation part and the observation part are integrated, the angle between the two parts becomes smaller as the distance from the measurement object increases. decreases, and measurement accuracy decreases. Normally, as the distance between the measurement target and the observation unit increases, measurement accuracy decreases.
For example, even if it is possible to achieve a measurement accuracy of 10 μm from a distance of 50 mm, it is extremely difficult to obtain the same measurement accuracy from a distance of 1 m.

(2) Since no measures have been taken to correct for the irregularity of the brightness distribution within the bright spot due to the shape of the rough surface and the finite resolution of the optical system, the measurement is based on the size of the bright spot. Accuracy is limited.

OBJECTS OF THE INVENTION The present invention has been made to solve the above-mentioned problems in conventional devices, and its purpose is to provide an optical displacement measuring device with excellent measurement accuracy.

Composition of the Invention As a result of intensive research to achieve the above object, the present inventors have found that the above problems can be solved by providing a cylindrical lens or a concave mirror between the imaging lens and the light receiving element in addition to the imaging lens. The present invention was completed based on this knowledge.

The optical displacement measuring device of the present invention will be explained based on the drawings.

FIG. 1 is a configuration diagram when a cylindrical lens is used.

A condenser lens 2 placed substantially perpendicular to the measurement surface S and a laser 1 converge the laser beam to a point O on the measurement surface. The scattered light emitted by this bright spot O is
It passes through the imaging lens 3 arranged on the optical axis in the direction of the observation angle θ, and then is vertically reduced by the cylindrical lens 4 to form a real image P of the bright spot on the one-dimensional light receiving element 5. .

When the measuring surface S is displaced by d, the bright spot moves to O' and the corresponding image also moves to P'. At this time, if the distance between the imaging lens 3 and the bright spot is sufficiently larger than d, the relationship Δ=Msinθd (1) holds between the moving distance Δ from P to P' and d. However, M represents the magnification of the observation unit optical system.

Therefore, if M and θ are constant, d can be found from Δ.

Actually, the bright spot and its real image have a finite size, and the brightness distribution thereof is not necessarily constant, so if the moving distance Δ of the bright spot image is too small, it cannot be seen.

FIG. 2 shows how the brightness distribution of the bright spot image on the light receiving element 5 changes depending on the observation angle θ and the cylindrical lens 4.

First, if there is no cylindrical lens 4, θ
When is 0 or close to 0, the outline of the image of the bright spot is circular as shown in (a), and the brightness distribution on the transverse line detected by the one-dimensional light receiving element 5 is irregular in the shape of a mountain. The result is a superposition of peaks. This peak group is due to speckles specific to coherent light such as laser light, and is determined by the surface shape of the measurement surface and the resolution of the imaging lens.

FIG. 2b shows an example in which θ=70°, and the image becomes a vertically elongated ellipse, and the brightness decreases overall.

When the cylindrical lens 4 is inserted at an appropriate position between the imaging lens and the one-dimensional light receiving element 5, the second
As shown in Figure c, it is possible to reduce the elliptical image in the vertical direction, increase the brightness, and at the same time relatively reduce irregular brightness changes due to speckles.

The image thus obtained on the photodetector is the third
As shown in the figure, it moves with changes on the measurement surface. The electronic circuit 6 detects the center line of the image, converts the amount of movement into an electric potential, and indicates it on the indicator 7.

FIG. 4 shows an embodiment using a concave mirror.
In the figure, 4' indicates a concave mirror. This effect is the same as when using the cylindrical lens.

Example An example in which the present invention was applied to the measurement of film thickness during construction of a thermal spray coating will be described.

As the one-dimensional light receiving element 5 shown in Fig. 1, a MOS
Using a linear image sensor, the observation angle θ is 70°, and the beam irradiation part and observation part are approximately 1 m from the measurement surface.
Measurements were taken at a distance of

FIG. 5 shows the results of measuring the process in which the film thickness increases each time the film layering is repeated. The reason why the output d becomes 0 periodically is because the thermal spray gun that sprays the thermal spray powder blocks the optical path.

FIG. 6 shows a comparison of the film thickness measured with a micrometer after the completion of lamination and the value measured by the apparatus of the present invention, and shows good agreement.

Effects of the Invention According to the optical displacement measuring device of the present invention, even minute displacements can be measured with high accuracy in a non-contact manner.

[Brief explanation of drawings]

Fig. 1 is a diagram of one embodiment of the device of the present invention, Figs. 2 and 3 are explanatory diagrams of the principle of the invention, Fig. 4 is a diagram of another embodiment, and Figs. 5 and 6 are diagrams of the device of the present invention. It is a figure showing the effect in. 1: laser, 2: condensing lens, 3: imaging lens, 4: cylindrical lens, 4': concave mirror,
5: one-dimensional light receiving element, 6: electronic circuit, 7: indicator.

Claims (1)

[Claims] 1. In a device that measures displacement by irradiating a light beam onto one point on the measurement surface to generate a bright spot and observing the movement of the bright spot when the measurement surface is displaced,
A bright spot generator consisting of a laser placed almost perpendicular to the measurement surface, a condensing lens that focuses the laser beam onto a single point on the measurement surface, and an imaging lens placed on a different optical axis from the incident laser beam. , a bright spot moving observation device consisting of a cylindrical lens or concave mirror that vertically reduces the bright spot image, and a one-dimensional light receiving element that detects the position of the bright spot image, and an electronic circuit that processes the output of the light receiving element. What is claimed is: 1. An optical displacement measuring device comprising: a detection device;