JPH0587564A - Displacement measuring device - Google Patents

Abstract

PURPOSE:To provide an optical displacement measuring apparatus capable of accurately measuring the surface shape of an object to be measured having a transparent film. CONSTITUTION:The beam from a laser diode 1 is incident on the surface (boundary surface 8) of an object 5 to be measured at an angle theta from a projection lens 2 and the reflected beam is condensed to a position sensor 4 from a condensing lens 3. Since the beam 3 refracted from the boundary surface 8 into a transparent film 6 is incident on the boundary surface 8 at an angle equal to or more than a critical angle (i), said beam can not return to an air layer 7. Since only the beam refected from the boundary surface 8 is measured, the accurate surface shape of the object 5 to be measured is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a displacement measuring device capable of optically detecting the displacement of a measuring object having a transparent film in a non-contact manner.

[0002]

2. Description of the Related Art FIG. 2 illustrates the basic configuration of a non-contact type displacement measuring device. The light emitted from the laser diode 100 is narrowed down by the light projecting lens 101 and obliquely enters the measurement target 102. The reflected light from the measurement object 102 is condensed by the imaging lens 103 and forms an image of a light spot on the position sensor 104. This image shows the measurement target 1
When 02 moves up and down in the figure, it moves on the position sensor 104 accordingly. Since an electric signal corresponding to the movement of the light spot is extracted from the position sensor 104, the displacement of the measurement object 102 can be known from this signal.

[0003]

As shown in FIG. 2, when the object 102 to be measured has the transparent film 105, a part of the light is reflected by the surface of the transparent film 105 and enters the light receiving lens 103. , Part of which is refracted into the transparent film 105,
And the light receiving lens 1 after being reflected by the boundary line between the measuring object 102 and
Comes in 03. Therefore, since the light reflected from the two surfaces having different positions in the measurement direction enters the position sensor 104, the output signal thereof indicates an intermediate position between the two reflection surfaces, and the accurate surface of the transparent film 105. The shape could not be detected.

An object of the present invention is to provide an optical displacement measuring device capable of accurately measuring the surface shape of a measuring object having a transparent film.

[0005]

DISCLOSURE OF THE INVENTION The displacement measuring device of the present invention is a displacement measuring device for optically detecting the displacement of a measuring object having a transparent film, wherein the boundary of light refracted from the boundary surface into the transparent film. It is characterized in that the incident angle of the light incident on the boundary surface is set so that the incident angle with respect to the surface exceeds the critical angle.

[0006]

The light refracted from the boundary surface into the transparent film is reflected inside the transparent film and is incident on the boundary surface. However, since the angle exceeds the critical angle, it is totally reflected and almost never reaches the device side. Dont return. Since the light reflected on the surface of the transparent film returns to the device side,
The displacement of the surface of the transparent film, which is the surface of the measurement target, is accurately measured.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A displacement measuring device of one embodiment will be described with reference to FIG. In the figure, 1 is a laser diode as a light source, 2 is a projection lens, 3 is a condenser lens, and 4 is a position sensor. The angle of the light from the laser diode 1 is adjusted so that it is converged by the condenser lens 2 and is incident on the measurement target 5 at a predetermined incident angle θ. This incident angle θ is
The angle is set so that the light refracted in the transparent film 6 is not totally reflected by the boundary surface 8 between the transparent film 6 and the air layer 7 and returned to the device side.

If the incident angle i of the light incident on the air layer 7 side from within the transparent film 6 exceeds the critical angle, this light is totally reflected by the boundary surface 8 and does not return to the air layer 7 side. If the refractive indices of the air layer 7 and the transparent film 6 are n ₁ and n ₂ , respectively, sin i =
n ₁ / n ₂ holds. Therefore, the incident angle θ is expressed by the following equation. θ = sin ^-1 (n ₂ sin i)

For example, if n ₁ = 1.0 and n ₂ = 1.5, then i = 41.8 ° and θ = 62.9 °. If the incident angle from the device to the boundary surface 8 is set to 62.9 ° or more, only the light reflected by the boundary surface 8 is returned to the device for measurement and refracted in the transparent film 6. The light reflected on the lower surface of the transparent film 6 is hardly emitted from the transparent film 6. Therefore, the present apparatus can detect the displacement of the surface of the measurement target 5, that is, the surface of the transparent film 6, and thereby obtain the accurate surface shape.

[0010]

According to the displacement measuring apparatus of the present invention, the optical axis on the light emitting side is prevented so that the light refracted in the transparent film on the surface of the object to be measured is not totally reflected in the film and returned to the apparatus side. Since, is set, it is possible to measure an accurate surface shape of a measurement target having a transparent film on the surface.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of the present invention.

FIG. 2 is a diagram showing a conventional displacement measuring device and its problems.

[Explanation of symbols]

 5 Measurement target 6 Transparent film 8 Boundary surface

Claims (1)

[Claims] 1. A displacement measuring device for optically detecting a displacement of a measuring object having a transparent film, wherein an incident angle of light refracted from the boundary surface into the transparent film with respect to the boundary surface exceeds a critical angle, A displacement measuring device, wherein an incident angle of light incident on the boundary surface is set.