JPH03225207A - Pseudo transmission illuminator - Google Patents

Abstract

PURPOSE:To attain artificial transmitted illumination and to improve the reliability of inspections and measuring accuracy by using an 1/4 wavelength plate, a reflecting plate and a polarizing plate for polarized illumination. CONSTITUTION:Light projected from a light source 1 is converted into linearly polarized light by the polarizing plate 2 and then projected on an object. It is considered that light reflected on the surface of the object includes much polarized components having the same direction as the linearly polarized light, the reflected light is shielded by the polarizing plate 3 having crossed-Nicol relation with the polarizing plate 2 arranged in the front of an image pickup lens. On the other hand, light arriving at a background is converted into a circularly polarized light by the 1/4 wavelength plate 4, and after changing its phase by 90 deg. on the reflecting face 5, the phase-changed light passes the wavelength plate 4. The light directed to a camera is finally converted into linearly polarized light vertical to illuminating light and the linearly polarized light is made incident upon the lens through the polarizing plate 3. Thus, illumination of pseudo transmission can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the structure of an illuminator for an image input device using a photoelectric converter (hereinafter referred to as a camera).

"Prior Art" Transmitted illumination is widely used, especially in the industrial field, because it allows the outline of an object to be seen with high contrast without being affected by the shape or roughness of the object's surface.

However, when performing in-line product inspection, for example, it is often impossible to install a lighting device on the back of the object due to spatial constraints, etc. In such cases, reflective lighting is the only option.

``Problems to be Solved by the Invention'' However, in reflective lighting, the intensity of the illumination affects both the object and the background, so it has been difficult to increase the contrast by increasing the intensity of only one or the other.

[Means for solving the problem] Therefore, the reflected illumination is linearly polarized epi-illumination, and the front surface of the imaging lens is arranged so that the linearly polarized light and the linearly polarized light have an orthogonal nicol relationship.
A polarizing plate was placed. Further, on the back of the object, a quarter wavelength plate and a reflecting surface were arranged in order from the object.

"Effect" With this configuration, it is thought that the light that directly hits the object and reflects on the surface has many polarized components in the same direction as the illumination light, so it is cut by the polarizing plate on the front of the camera lens, and the background light is The more reflected light becomes a polarized component in the direction perpendicular to the illumination light due to the action of the 1/4 wavelength plate and the reflective surface, and thus enters the camera lens. As a result, the brightness of only the background can be increased, so that the contrast can be improved.

"Example" An embodiment of the present invention will be described with reference to FIG.

The target object is a circular container made of black plastic as shown in FIG.

Light emitted from a light source 1 becomes linearly polarized light by a polarizing plate 2 and is reflected onto an object.

At this time, the light reflected on the object surface is considered to have many polarized components in the same direction as the linearly polarized light, so it is blocked by the polarizing plate 3, which is provided in front of the imaging lens and has a crossed Nicol relationship with the polarizing plate 2. It will be done. Also, the light that reaches the background is
The light becomes circularly polarized by the quarter-wave plate 4, its phase changes by 90° at the reflecting surface 5, and the light passes through the quarter-wave plate again. in the end,
The light heading toward the camera becomes linearly polarized light in a direction perpendicular to the illumination light, passes through the polarizing plate 3, and enters the lens. In this way, pseudo transmitted illumination is created.

``Effects of the invention'' Not just reflective lighting, but polarized lighting and quarter-wave plate,
By using a reflecting plate and a polarizing plate, pseudo-transmitted illumination can be achieved. It is believed that the use of the present invention will have a significant effect on improving inspection reliability and measurement accuracy, particularly in the industrial field.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the configuration of an embodiment of the present invention, Fig. 2 is a diagram showing an object to be imaged in the embodiment, and Fig. 3 is a diagram explaining the polarization state of light on a quarter-wave plate and a reflecting surface. FIG. 4 is a diagram showing a captured image.

Claims (1)

[Claims] In an image input device that obtains an image by converting a formed image into an electric signal by an imaging lens using a photoelectric converter, epi-illumination lights 1 and 2 that emit linearly polarized light;
On the back side of the object to be imaged 6, a 1/
A pseudo-transmission illumination device characterized by a reflective surface attached via a four-wavelength plate 4 and a polarizing plate arranged in a direction that has a cross Nicol relationship with epi-illumination light in front of a photoelectric converter.