JP7716748B2 - External illumination light passing through the lens barrel - Google Patents

Description

The present invention relates to a lens barrel, and in particular to a compact lens barrel with external illumination light passing through the barrel, which is attached to the outside of the lens barrel and introduces annular illumination light into the barrel, allowing it to illuminate an object from inside the lens.

When inspecting semiconductor devices or high-density printed circuit boards, the light reflected from the object being inspected is captured by an image sensor to obtain inspection information such as the position of each component, the presence or absence of scratches, and the condition of the soldering. The inspection information obtained varies greatly depending on the type and placement of the light source used, so it is important to configure the optical system using a light source that is appropriate for the object being inspected.

Conventionally, an illumination device such as an annular light is placed at the tip of an imaging lens barrel to illuminate an inspection object. For example, Patent Document 1 proposes an optical device in which an annular light with light sources arranged at approximately equal intervals in the circumferential direction is placed outside the lens to illuminate the inspection object from outside the lens. However, this technology requires an even larger illumination device to be attached outside the diameter of the imaging lens barrel, which results in a larger imaging lens section and makes it unsuitable for environments requiring a small, compact design.

Also available is coaxial epi-illumination, in which external illumination light is incident from the side of the lens barrel perpendicular to the optical axis, a half-mirror prism is placed on the internal optical axis, and the illumination light is reflected parallel to the optical axis by the half-mirror surface to illuminate the object being observed (see, for example, Patent Document 2). However, because the illumination light with this technology is perpendicular to the object being inspected, it has the problem of not being optimal for applications where it is desired to illuminate the object being inspected with illumination light at an angle.

Patent Document 3 proposes a lens barrel with a built-in annular light source in which LED elements are arranged in a circumferential direction. However, because the lens barrel is assembled with the built-in annular light source, it is not possible to change the light source for each inspection object or replace faulty LED elements; changing the LED element requires replacing the entire lens, which poses issues in terms of availability and cost.

JP 2010-257585 A JP 2016-085480 A Japanese Patent Application Laid-Open No. 2021-021864

The objective of this invention is to provide a compact lens barrel that irradiates illumination light from a detachable annular light source attached to the outside of the imaging lens barrel onto an object to be observed through a tip lens inside the barrel.

The most important feature of this invention is a lens barrel in which a first lens group, a transparent plastic light guide ring, and a second lens group are arranged in this order from the objective side of the lens barrel, with the first lens group, transparent plastic light guide ring, and second lens group sharing a common optical axis, and the transparent plastic light guide ring having an inner edge that extends into the barrel and has a reflective surface that reflects external light toward the object being viewed.

It is preferable that this lens barrel further comprises a detachable annular LED light source body that emits illumination light from the outside of the transparent plastic light guide ring toward the reflective surface.

It is also preferable that a circular first linear polarizer (polarizer) with a hole in the center is provided between the first lens group and the transparent plastic light guide ring, and a circular second linear polarizer (analyzer) is provided between the second lens group and the first linear polarizer, with the linear polarization directions of the first linear polarizer and the second linear polarizer being orthogonal to each other.

The lens barrel of the present invention uses a transparent plastic light guide ring with a reflective surface on its inner edge to reflect external illumination light toward the object being observed within the lens barrel, providing a compact lens barrel that irradiates the object with optimal illumination light.

In addition, by providing a thin, annular LED light source body with multiple LEDs arranged inside that can be attached and detached to the outside of the transparent plastic light guide ring, it is possible to provide a lens barrel in which only the light source can be replaced as needed.

Furthermore, a circular first linear polarizer (polarizer) with a hole in the center is provided between the first lens group and the transparent plastic light guide ring, and a circular second linear polarizer (analyzer) is provided between the second lens group and the first linear polarizer. By orthogonally orthogonalizing the polarization directions of these, illumination light is prevented from being internally reflected within the lens barrel and entering the imaging element, preventing degradation of the captured image.

FIG. 1 is a cross-sectional view showing the configuration of an embodiment of a lens barrel according to the present invention. 2A and 2B are a cross-sectional view and a conceptual diagram showing the transparent acrylic light guide ring 14 shown in FIG. 1 alone. FIG. 3 is a schematic diagram showing the annular LED light source body 24 shown in FIG. 1 in isolation. FIG. 4 is a schematic diagram showing the linear polarizers 26 and 28 shown in FIG. 1 individually. FIG. 5 is a reference diagram showing the lens barrel 1 with the annular LED light source body 24 removed.

Embodiments of the present invention are described in detail below with reference to the accompanying drawings. Figure 1 is a cross-sectional view showing the configuration of an embodiment of a lens barrel according to the present invention. The lens barrel of the present invention is used, for example, to inspect semiconductor devices and high-density printed circuit boards. It irradiates light onto an object under observation and captures the reflected light with an imaging element to obtain inspection information such as the arrangement of each component on the object, the presence or absence of scratches, and the condition of soldering. For example, to inspect the presence or absence of scratches on a planar structure, irradiating light obliquely rather than parallel to the lens optical axis creates a shadow that makes detection easier. However, the lens barrel of the present invention is not limited to the inspection of precision parts and can be used for a variety of other purposes. Therefore, Figures 1 to 5 are merely examples, and the present invention is not limited thereto.

The lens barrel 1 of the present invention comprises, from the objective side, a first lens group 12, a transparent acrylic (plastic) light guide ring 14, and a second lens group 16, arranged in this order and sharing a common optical axis 18. The first lens group 12 is held in a first lens barrel section 20, and the second lens group 16 is held in a second lens barrel section 22. The first lens barrel section 20, the transparent acrylic light guide ring 14, and the second lens barrel section 22 are each integrated by screwing together. An annular LED light source body 24 is attached to the outer periphery of the transparent acrylic light guide ring 14. The end of the second lens barrel section 22 on the imaging element (camera) side has a male thread structure that can be attached to, for example, a C-mount standard camera. The first lens group 12 and the second lens group 16 are each designed appropriately depending on the object to be inspected using the lens barrel 1, the required magnification, etc., and are typically composed of a combination of multiple lenses.

Figure 2 shows a cross-sectional view (a) and a conceptual diagram (b) of the transparent acrylic light guide ring 14 shown in Figure 1 . The transparent acrylic light guide ring 14 is molded from a transparent acrylic material. Its central portion, located between the first and second lens barrels 20 and 22, protrudes inward. A reflective surface 14a is formed on its inner edge, reflecting light incident from the lateral exterior toward the object of observation. This state is shown in Figure 2(b). This reflective surface 14a may satisfy the conditions for total reflection, thereby reflecting all light incident from outside the lens barrel toward the object of observation. Alternatively, the inner surface of the transparent acrylic light guide ring 14 (only the upper side, including the reflective surface 14a) may be mirror-coated to reflect light. The angle, position, and size of the reflective surface 14a can be appropriately designed depending on the object of observation to be illuminated and the required image information. Furthermore, the transparent acrylic light guide ring 14 can be removed from the first and second lens barrels 20 and 22 and replaced with another light guide ring having a different reflective surface, as needed.

Figure 3 is a schematic diagram showing the annular LED light source body 24 shown in Figure 1 alone. As shown in Figure 3, the annular LED light source body 24 of this embodiment is constructed by creating a cavity on the inner surface of an annular body having an inner periphery 24a with a diameter approximately equal to (strictly speaking, slightly larger than) the outer periphery of the transparent acrylic light guide ring 14. Multiple illumination chip LED light sources 24c mounted on a flexible wiring board 24b are positioned inward and covered with a transparent acrylic ring 24d. As shown in Figure 1, the outer surfaces of the first lens barrel section 20 and the transparent acrylic light guide ring 14 are flush with each other, allowing the annular LED light source body 24 to be slid into place from the lens tip side (object plane side). In this embodiment, as shown in Figure 1, the annular LED light source body 24 is configured so that sliding it to its stop position introduces LED light into the lens barrel. A wiring cable 24e extends from the flexible wiring board 24b to the outside of the unit and is connected to a power source (not shown). Additionally, the annular LED light source body 24 can be fixed in place by threading and tightening a detachable fixing screw 24f into a threaded hole that passes through the annular LED light source body 24. In this way, the annular LED light source body 24 is configured to be detachable (i.e., replaceable). Furthermore, since a thin annular LED body can be attached to the outer periphery of the lens barrel for illumination, it is ideal for environments where miniaturization and compactness are required. Figure 5 is a reference diagram showing the lens barrel 1 with the annular LED light source body 24 removed.

The LEDs built into the annular LED light source body 24 may be arranged in high density around the entire inner circumference of the body 24, or may be arranged in only a few locations (e.g., 3-4 locations). The LEDs can emit light in a variety of colors, such as R (red), B (blue), G (green), and W (white). The color and intensity of the light irradiated inside the lens barrel may also be changed by providing an IC chip on the wiring board 24b or connecting a control unit to the end of the wiring cable 24e. Such control technology is well known, so a detailed description will not be provided here.

Optionally, the lens barrel 1 of this embodiment incorporates two linear polarizers (a polarizer 26 and an analyzer 28) to prevent internal reflection of light irradiated by the first lens group 12 from entering the imaging element and causing image degradation. As shown in FIG. 1, the lens barrel 1 includes a first linear polarizer 26 (polarizer) between the first lens group 12 and the transparent acrylic light guide ring 14, and a second linear polarizer 28 between the second lens group 16 and the first linear polarizer 26. FIG. 4 is a schematic diagram showing these linear polarizers 26 and 28. As shown in FIG. 4, the first linear polarizer 26 is a circular polarizer with a hole in its center, which polarizes light emitted from the transparent acrylic light guide ring 14 in a first direction (horizontal in FIG. 4). In contrast, the second linear polarizer 28 is a circular analyzer that polarizes light passing through the second lens group 16 in a second direction (vertical in FIG. 4). By orthogonally arranging the linear polarization directions of the first linear polarizer 26 and the second linear polarizer 28, internally reflected light that passes through the polarizer, is reflected by the first lens group, etc., and heads toward the image sensor is blocked by the analyzer, preventing the internally reflected light from reaching the image sensor and preventing image degradation.

While one embodiment of the present invention has been described in detail above, the present invention is not limited to the above-described embodiment or examples and can be realized in various modified forms. For example, while the above embodiment includes first and second polarizing plates, these may not be included in other embodiments. In the distribution format of the present invention, the tube lens 1 does not necessarily have to be sold as a set with the annular LED light source body; instead, a user can selectively purchase and use one with a light source that best suits their needs from among several different types of annular LED light source bodies. Furthermore, the material of the transparent plastic light guide ring is not limited to acrylic; other transparent plastics such as polyethylene terephthalate (PET), polycarbonate (PC), and cycloolefin polymer (COP, e.g., ZEONEX or ZEONOR (all registered trademarks)) can also be used. Furthermore, the angle and size of the reflective surface 14a of the light guide ring can be appropriately determined depending on the actual environment, such as the object to be inspected and the desired information to be acquired. Furthermore, the tube lens of the present invention is not limited to optical inspection of precision parts; it can also be designed for other applications, such as close-up lenses.

The lens barrel lens of the present invention provides a compact imaging illumination lens barrel by detachably attaching a thin, annular LED light source body to the outside of the imaging lens barrel as an external illumination light source, and is suitable for use in inspecting semiconductor elements, high-density printed circuit boards, etc.

REFERENCE SIGNS LIST 1 Lens barrel 12 First lens group 14 Transparent acrylic (plastic) light guide ring 14a Reflecting surface 16 Second lens group 18 Optical axis 24 Annular LED light source body 26 First linear polarizing plate (polarizer)
28 Second linear polarizer (analyzer)

Claims (4)

A lens barrel in which a first lens group, a transparent plastic light guide ring, and a second lens group are arranged in this order from the objective side of the lens barrel,
the first lens group, the transparent plastic light guide ring, and the second lens group have a common optical axis, and the transparent plastic light guide ring has an inner edge portion extending into the lens barrel and a reflective surface that reflects light from outside toward an object to be observed;
a first lens group held in a first barrel portion, a second lens group held in a second barrel portion, and the first and second barrel portions removably connected to the transparent plastic light guide ring. 2. The lens barrel according to claim 1, wherein the first barrel portion and the transparent plastic light guide ring are configured so that their outer surfaces are flush with each other. The lens barrel described in claim 1 or 2 further comprises a detachable annular LED light source body that emits illumination light from the outside of the transparent plastic light guide ring toward the reflective surface, and the annular LED light source body is detachably mounted on the outer surfaces of the first barrel section and the transparent plastic light guide ring. The lens barrel described in any one of claims 1 to 3, further comprising: a circular first linear polarizer with a central hole between the first lens group and the transparent plastic light guide ring; and a circular second linear polarizer between the second lens group and the first linear polarizer, the linear polarization directions of the first linear polarizer and the second linear polarizer being orthogonal to each other.