JPS628121A - Lighting device - Google Patents

Abstract

PURPOSE:To make the influence of reflected light extremely small and to maintain a sufficient contrast ratio by arranging a polarized light source on a circumference which has its center on an axis crossing the surface of a body to be detected and irradiating the intersection of the surface and axis with light which is emitted by the polarized light source and polarized in parallel to an incidence surface. CONSTITUTION:A lighting device is equipped with a ring-shaped light source 1 and the polarized light source 4 composed of a polarizers 41 arrayed along the ring-shaped light source 1 on the circumference having its center on the axis 51 crossing the surface 21 of the body 2 to be detected, and the intersection of the surface 21 and axis 51 with the light which is polarized in parallel to the incidence surface 52. The angle 53 of irradiation that the light incident on said intersection and the axis 51 is set twice or nearly twice the Brewster angle of the body 2 to be detected. A television camera 3 which has a lens 31 is provided on the prolongation of the axis 51 and an image of characters and symbols printed on the surface 21 is inputted to the television camera 3 through the lens 31.

Description

[Detailed Description of the Invention] [Summary] When photographing characters or symbols printed on the glossy surface of an object to be detected with a camera, etc., when light is irradiated from a normal ring-shaped light source, the characters or symbols can be identified by reflection. It may not be possible.

Therefore, light polarized in a direction parallel to the plane of incidence is irradiated to reduce the influence of reflection and make it easier to identify characters and symbols.

[Industrial application field]

The present invention relates to a device that uses a television camera or the like to photograph characters and symbols printed on the glossy surface of a detected object, and in particular, an illumination device that reduces the influence of reflection from the glossy surface and facilitates the identification of characters and symbols. Regarding.

Inspecting the arrangement of electronic components such as semiconductor integrated circuits mounted on printed wiring boards, or the arrangement of key tops mounted on keyboards, requires pattern recognition to determine pass/fail. was visually inspected by the inspector.

However, with the development of information processing equipment and information detection technology, tasks such as automatically reading characters and symbols printed on the detected object using a television camera, etc. and comparing them with pre-registered standard patterns have become easier. Various inspection devices have been developed to automatically perform these array inspections.

In order to accurately detect characters or symbols printed on a detected object in such an inspection device, it is more advantageous to have a higher contrast ratio between the printed characters or symbols and the background thereof. Further, even if the contrast ratio is high, the reflection from the surface on which characters or symbols are printed is large, and in the case of 1, the contrast ratio is relatively reduced.

Therefore, it is desired to develop a lighting device that can reduce the effects of reflection even if the surface on which characters or symbols are printed is, for example, a glossy surface.

[Conventional technology]

FIG. 5 is a cross-sectional perspective view showing an example of a conventional lighting device.

In the figure, a ring-shaped light source 1 is conventionally used as an illumination device, and the light emitted from the ring-shaped light source 1 is transmitted to a detected object 2.
The surface 21 on which characters and symbols are printed is irradiated. The image of the characters and symbols printed on the surface 21 is input to the television camera 3 through the lens 31.
Images of characters and symbols photographed by the camera are photoelectrically converted and output to an information processing device (not shown).

[Problem that the invention seeks to solve]

In such a device, if the surface 21 and the optical axis of the lens 31 are perpendicular to each other, the light emitted from the ring-shaped light source 1 will be reflected by the surface 21 and will not be directly input to the television camera 3 through the lens 31.

However, as shown in the figure (when the surface 21 is inclined and intersects the optical axis of the lens 31 at a specific angle, the light emitted from point A is reflected by the surface 21 and exits in a direction different from the optical axis of the lens 31, as shown by the broken line). However, if the direction of light reflected by the surface 21 matches the optical axis of the lens 31, such as the light emitted from point B, the reflected light from the surface 21 will be transmitted to the television along with the image of the printed characters or symbols. When the image is input to the camera 3, the contrast ratio decreases.Particularly when the surface 21 is a glossy surface, there is a problem that images of characters and symbols cannot be detected.

[Means for solving problems]

FIG. 1 is a cross-sectional perspective view showing the principle of the lighting device according to the present invention.

The above problem can be solved by disposing the polarized light source 4 on the circumference centered on the axis 51 intersecting the surface 21 of the detected object 2 shown in FIG.
This problem is solved by the illumination device according to the present invention, which irradiates the intersection of the surface 21 and the axis 51 with light polarized in a direction parallel to the incident surface 52 emitted from the polarized light source 4.

[Effect]

FIG. 2 is a diagram for explaining the operation of the lighting device according to the present invention.

In Fig. 2(a), the polarized light component parallel to the plane of incidence of the light incident on the surface 21 of the detected object 2 (the plane containing the optical axes of the incident light and reflected light) is P, and the polarized light component perpendicular to the plane of incidence is P. S, the reflected light reflected by the surface 21 has a property that it contains more polarized light components S perpendicular to the plane of incidence than polarized light components P parallel to the plane of incidence. In particular, when the angle of incidence of the light incident on the surface 21 and the Brewster angle of the object to be detected 2 match as shown in FIG. 2, the polarized light component P parallel to the surface of incidence becomes almost zero.

Therefore, in FIG. 1, by polarizing the light incident on the surface 21 in a direction parallel to the incident surface 52 and removing other polarization components in advance, for example, the exit direction of the light reflected on the surface 21 and the direction of the lens Even if the optical axis coincides with the reflected light and the reflected light is input into the television camera together with the image of printed characters or symbols, the influence of the reflected light is extremely small and a sufficient contrast ratio can be maintained.

〔Example〕

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 3 is a cross-sectional perspective view showing one embodiment of the lighting device according to the invention, and FIG. 4 is a schematic diagram showing a modification of the lighting device according to the invention. The same objects are represented by the same symbols throughout the figures.

In FIG. 3, the illumination device according to the present invention includes a ring-shaped light source 1 and polarizers 4 arranged along the ring-shaped light source 1 on a circumference centered on an axis 51 that intersects the surface 21 of the detected object 2.
1, which irradiates the intersection of the surface 21 and the axis 51 with light polarized in a direction parallel to the incident surface 52. Note that the illumination angle 53 formed by the axis 51 and the light incident on the intersection of the surface 21 and the axis 51 (not the angle of incidence on the surface 21) is set to be twice the Brewster angle of the known object 2 to be tested or an angle close to it. is set to . - A television camera 3 having a lens 31 is provided on the extension of the blade shaft 51, and images of characters and symbols printed on the surface 21 are input to the television camera 3 through the lens 31.

In such a device the surface 21 and the axis 51! If the optical axis of the lens 31 is perpendicular to the optical axis, the light emitted from the polarized light source 4 will be reflected by the surface 21 and will not be directly input to the television camera 3 through the lens 31.

Furthermore, even if the surface 21 is inclined and the exit direction of the light reflected by the surface 21 approaches the axis 51, that is, the optical axis of the lens 31, the polarized components other than those parallel to the incident surface are removed from the light irradiating the surface 21 in advance. Therefore, the reflected light input to the television camera 3 is only a very small polarized light component parallel to the plane of incidence. Further, at the point where the exit direction of the light reflected by the surface 21 and the optical axis of the lens 31 match, the light incident on the intersection of the surface 21 and the axis 51 and the axis 5
1 is set to twice the Brewster's angle of the detected object 2 or an angle close to it, and the angle of incidence on the surface 21 matches the Brewster's angle of the detected object 2. The polarized light component parallel to the plane of incidence that is input to 3 becomes almost zero.

Therefore, by using the illumination device shown in this example, even if the surface on which characters or symbols are printed is a glossy surface, there will be no reduction in contrast ratio due to defects in the illumination device, and the characters and symbols printed on the object to be detected by the television camera will not deteriorate. Characters and symbols can be detected accurately.

In addition, the illumination device shown in FIG. 4 inputs polarized light from one end of a polarized light source 4 disposed on a circumference centered on an axis 51 that intersects the surface 21 of the detected object 2. It is composed of a plurality of polarization preserving optical fibers 42 that guide the light to the other end without disturbing the light, a polarizer 41, and a light beam R43. 51
The intersection point with is illuminated. Also in this embodiment, the illumination angle 53 formed by the axis 51 and the light incident on the intersection of the surface 21 and the axis 51 is set to twice the Briester angle of the detected object 2 or an angle close to it. .

By using such an illumination device, even if the surface on which characters or symbols are printed is a glossy surface, there is no reduction in contrast ratio due to defects in the illumination device, and it is possible to prevent the contrast ratio from decreasing due to defects in the illumination device. Characters and symbols can be detected accurately.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide a lighting device that can reduce the influence of reflection even if the surface on which characters or symbols are printed is, for example, a glossy surface.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional perspective view showing the principle of the present invention, FIG. 2 is an explanatory diagram of the operation of the lighting device according to the present invention, FIG. A schematic diagram showing a modification of the invention, and FIG. 5 is a cross-sectional perspective view showing an example of a conventional illumination device. In FIG. A light source, 21 is a surface to be irradiated, 31 is a lens, 41 is a polarizer,
42 is a polarization maintaining optical fiber, 43 is a light source,
51 represents an axis, 52 represents an entrance plane, and 53 represents an illumination angle. 3 spears

Claims (1)

[Claims] 1) An axis (51) that intersects the surface (21) of the detected object (2).
) A polarized light source (4) is arranged on a circumference centered on the polarized light source (4), and the light emitted from the polarized light source (4) is polarized in a direction parallel to the plane of incidence (52). An illumination device characterized in that it irradiates a point of intersection with the axis (51). 2) The illumination angle (53) formed by the light incident on the intersection of the surface (21) and the axis (51) and the axis (51) is
2. The lighting device according to claim 1, wherein the lighting device is set at an angle that is twice the Brewster's angle or close to it.