JP2010217142A - Optical sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical sensor of a simple configuration in which light condensed by a condenser lens is guided without waste toward a light-receiving element through a prism serving as a reflecting body. <P>SOLUTION: In a side-view optical sensor including a condenser lens that condenses light coming from an outside source, a light-receiving element provided so that its light-receiving surface faces in such a direction as to intersect with the optical axis of the condenser lens, and a prism body for reflecting light condensed by the condenser lens and guiding the light toward the light-receiving surface, the condenser lens is optically rotated asymmetrically to the central axis of the beam of light, condensed by the condenser lens, so that the beam of light is incident at an angle equal to or greater than its critical angle with respect to a reflecting surface of the prism body. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an optical sensor, and more particularly to an optical sensor that includes a condensing lens and a reflector, and detects light arriving at the sensor from a direction that intersects the direction of the light receiving surface of the light receiving element.

  For example, a condensing lens 1 having a lens surface facing a detection region as shown in a schematic configuration in FIG. And a reflector such as a prism body 3 that reflects the light (light beam) collected through the condenser lens 1 toward the light receiving element 2 having the light receiving surface 2a directed in a direction crossing the optical axis of the light. There is something configured. Incidentally, the prism body 3 has, for example, one of two surfaces orthogonal to each other as an incident surface facing the condenser lens 1 and the other surface as an exit surface facing the light receiving surface of the light receiving element 2. It is composed of a right-angle prism having an inclined surface that forms an angle of 45 degrees with respect to the surface as a reflecting surface 3a.

  Note that an optical (photoelectric) sensor that realizes a side view using such a prism body 3 is known as, for example, a side viewer attachment disclosed in FIG. Moreover, if such a prism body 3 is used as a reflector, it is possible to eliminate problems such as high manufacturing costs as in the case of using a metal vapor deposition mirror.

Japanese Patent Laid-Open No. 7-14478

  By the way, in order to increase the amount of light received by the light receiving element 2 and increase its detection sensitivity, the aperture area of the condensing lens 1 is exclusively made as wide as possible within the limits of the sensor structure, and the collection is made wide. The lens is designed so that light incident on the periphery of the aperture of the optical lens 1 is guided to the light receiving surface 2a of the light receiving element 2 without waste. However, when the lens design of the condensing lens 1 is performed in this way, as shown in FIG. 4, the light incident from the periphery of the opening of the condensing lens 1 is not reflected by the prism body 3 and is not reflected by the prism body. The problem of exiting 3 occurs.

  That is, the light passing through the condenser lens 1 is bent (refracted) at a larger angle as it is away from the central axis M of the lens 1 and is narrowed down toward the focal position f of the condenser lens 1. On the other hand, the reflecting surface 3 a of the prism body 3 is provided to be inclined with respect to the central axis M of the condenser lens 1. For this reason, the light guided to the position away from the main surface L of the condensing lens 1 of the reflecting surface 3a of the prism body 3 through the periphery of the condensing lens 1 has a small incident angle with respect to the reflecting surface 3a. Therefore, the light is transmitted without being totally reflected by the reflecting surface 3a. As a result, there is a problem that the amount of light that can be guided to the light receiving element 2 cannot be increased in spite of increasing the aperture area of the condenser lens 1.

  The present invention has been made in consideration of such circumstances, and its purpose is to guide light collected through a condenser lens to a light receiving element without waste through a prism body as a reflector. An object of the present invention is to provide an optical sensor having a simple configuration.

In order to achieve the above-described object, an optical sensor according to the present invention includes a condensing lens for condensing light from the outside, and a light receiving element provided with a light receiving surface facing in a direction intersecting with the optical axis of the condensing lens. And a prism body that includes a prism body that reflects the light collected by the condenser lens and guides it to the light receiving surface of the light receiving element,
In particular, the condensing lens is optically arranged with respect to the central axis of the light beam so that the light beam collected by the condensing lens is incident on the reflecting surface of the prism body at an angle greater than the critical angle. It is characterized in that it is rotationally asymmetric or the focal length of the lens periphery is set longer than the center of the lens.

  Incidentally, the rotational asymmetry of the condensing lens with respect to the central axis of the light beam, or the setting of the focal length is performed by setting the central axis (optical central axis) of the condensing lens from the central axis of the light beam incident on the condensing lens. By shifting the position, or by partially increasing the curvature of the lens surface of the condenser lens, or partially reducing the refractive index of the condenser lens, and increasing the focal length of the lens portion. Reached by. Of course, these methods can be used in combination.

  The prism body has, for example, one of two surfaces orthogonal to each other as an incident surface facing the condenser lens and the other surface as an exit surface facing the light receiving surface of the light receiving element. This is a right angle prism having a reflecting surface with an inclined surface forming an angle of 45 degrees, for example. In addition, the said condensing lens and the said prism body include what shape | molded these integrally. The light receiving element includes a light receiving lens or an optical fiber for guiding light to the light receiving surface.

  According to the optical sensor having the above configuration, the light passing through the condensing lens can be reflected by the prism body without waste by merely making rotational asymmetry of the condensing lens with respect to the central axis of the light beam or setting the focal length to the light receiving element. Therefore, the amount of light received by the light receiving element can be increased, and its detection sensitivity can be increased. In addition, the structure is simple, and there is an advantage that it can be manufactured at a low cost as compared with the case of using a metal vapor deposition mirror.

The principal part schematic block diagram of the optical sensor which concerns on the 1st Embodiment of this invention. The principal part schematic block diagram of the optical sensor which concerns on the 2nd Embodiment of this invention. The figure which shows the other example of the condensing lens which implement | achieves the rotational asymmetry with respect to the optical axis of a light beam. The figure which shows the modification of this invention. The figure for demonstrating the structure of the conventional optical sensor, and its problem.

Hereinafter, a photoelectric sensor as an embodiment of an optical sensor according to the present invention will be described with reference to the drawings.
As shown in FIGS. 1 and 2, the photoelectric sensor according to this embodiment basically includes a condenser lens 1 that collects light (for example, a parallel beam) coming from a detection region, and the condenser lens. A light receiving element 2 provided in a direction crossing the optical axis 1, for example, at a right angle with its light receiving surface 2 a facing, and a light receiving surface of the light receiving element 2 that reflects the light collected by the condenser lens 1. It consists of a so-called side view type comprising a prism body 3 leading to 2a. The condensing lens 1 is arranged such that its lens main surface L is perpendicular to the parallel beam bundle. The prism body 3 serving as the reflector has one of two surfaces orthogonal to each other as an incident surface facing the condenser lens 1 and the other surface as an exit surface facing the light receiving surface 2a of the light receiving element 2. This is a right-angle prism in which an inclined surface that forms a predetermined angle with respect to the two surfaces, for example, 45 degrees, is used as the reflection surface 3a.

  Incidentally, the condenser lens 1 and the prism body 3 are each made of a light transmissive material having a predetermined refractive index, for example, a glass material or a transparent synthetic resin material, and the light receiving element 2 is, for example, a photodiode (PD). ). Further, the condenser lens 1, the light receiving element 2, and the prism body 3 are integrally assembled in a housing (not shown) under a preset optical arrangement to construct a photoelectric sensor or a photoelectric sensor head. Here, the photoelectric sensor including the photoelectric sensor head is collectively referred to as a photoelectric sensor.

  The photoelectric sensor receives, for example, a parallel light beam projected from a light projecting unit (not shown) toward the detection region through the detection region, and detects the presence or absence of an object in the detection region from the received light amount. Composed. Note that the photoelectric sensor having the above-described light receiving system may be provided so as to be aligned with the light projecting / receiving direction integrally with the light projecting unit that emits light toward the detection region.

  Now, the photoelectric sensor according to the first embodiment of the present invention will be described with reference to FIG. 1. This photoelectric sensor uses the central axis M of the condenser lens 1 as the central axis N of the light beam incident on the condenser lens 1. By shifting the lens from the center, the condenser lens 1 is rotationally asymmetrical with respect to the central axis N of the light beam, so that more of the light beam collected by the condenser lens 1 is It is characterized in that it is incident on the reflecting surface 3a at an angle greater than the critical angle. That is, the light passing through the condenser lens 1 is incident on the reflecting surface 3a of the prism body 3 at an angle greater than the critical angle, and is totally reflected by the reflecting surface 3a to receive the light receiving surface of the light receiving element 2. It is characterized by being guided to 2a.

  More specifically, the condensing lens 1 itself is rotationally symmetric with respect to the central axis M of the condensing lens 1 and basically becomes a peripheral portion away from the central axis M. The bending angle with respect to light incident in parallel with the central axis M increases, and the light passing through the condenser lens 1 has an optical characteristic of forming an image at a predetermined focal position f on the central axis M. In the first embodiment, the condensing lens 1 having such optical characteristics is separated from the central axis N of the light (parallel light bundle) guided to the condensing lens 1 with the central axis M of the condensing lens 1. In particular, by shifting to the light receiving element 2 side where the light reflected by the prism body 3 is guided, the bending angle of the light at the light receiving element 2 side end (lower end side in FIG. 1) of the condenser lens 1 is changed. In this way, light passing through the condenser lens 1 is incident on the reflecting surface 3a of the prism body 3 at an angle greater than the critical angle.

  Incidentally, the critical angle means that light incident at a predetermined angle with respect to the normal line of the reflecting surface 3a of the prism 3 is not refracted and transmitted at the interface (reflecting surface 3a) between the prism body 3 and air. The angle at which all of the light is reflected (totally reflected) at the interface. For example, when the prism 3 is made of a synthetic resin material such as acrylic or polycarbonate or a glass material called BK7, the refractive index n2 is about 1.514, so the aforementioned critical angle is about 41 degrees. It becomes. On the other hand, since the reflecting surface 3a of the prism body 3 is provided at an angle of 45 degrees with respect to the central axis M of the condenser lens 1, the bending angle of light passing through the lower end of the condenser lens 1 is approximately 3. If the angle is less than 7 degrees, most of the light passing through the condenser lens 7 is incident on the reflecting surface 3a at an angle greater than the critical angle described above, and the light is totally reflected. As a result, more light that has passed through the condenser lens 1 can be totally reflected and guided to the light receiving element 2 as compared with the prior art. Ideally, the condenser lens 3 is moved by shifting the central axis M of the condenser lens 1 with respect to the central axis N of the luminous flux so that the luminous flux transmitted through the lower end of the condenser lens 1 satisfies the above condition. All of the light that has passed through can be totally reflected and guided to the light receiving element 2, which is more effective.

  When the refractive index n2 of the prism 3 is approximately 1.414, the critical angle at the reflecting surface 3a is approximately 45 degrees. Therefore, when the central axis M of the condenser lens 3 is provided coaxially with the central axis N of the light beam and the inclination angle of the reflecting surface 3a is 45 degrees, the central axis M of the condenser lens 3 In addition, the light passing through the upper side is totally reflected, and the light passing below the central axis M is transmitted without being totally reflected. Accordingly, in such a case, for example, if the central axis M of the condenser lens 1 is shifted with respect to the central axis N of the light beam so that only the upper half region of the condenser lens 3 is an aperture region, the light is condensed. The light that has passed through the lens 3 can be totally reflected and guided to the light receiving element 2.

  When the central axis M of the condensing lens 3 is shifted from the central axis N of the light beam in this way, the amount of deviation is determined by the focal length f of the condensing lens 1 or the condensing lens 1 and the prism body 3. It is sufficient to set the optical conditions so as to satisfy the above-described total reflection condition in accordance with the arrangement interval and the inclination angle of the reflecting surface 3a of the prism body 3 with respect to the central axis N of the light beam. Of course, the optical arrangement of the light reflected by the prism 3 in this way is determined so as to be guided into the light receiving surface of the light receiving element 2.

  Thus, according to the photoelectric sensor in which the optical system is set as described above, more light that comes from the detection region and is collected by the condenser lens 1 than the photoelectric sensor in which the conventional optical system is set. It can be totally reflected. As a result, since the light passing through the condenser lens 1 can be guided to the light receiving element 2 without waste, the amount of light received by the light receiving element 2 can be effectively increased and the detection sensitivity can be increased. In addition, the amount of light received by the light receiving element 2 can be simply and effectively increased without using an expensive metal deposition mirror or by depositing a metal film on the reflecting surface 3a of the prism body 3. Therefore, it is possible to produce a highly sensitive photoelectric sensor at a low cost.

  Incidentally, in order to satisfy the total reflection condition at the reflecting surface 3a of the prism body 3, for example, as shown in FIG. 2, the curvature of the lens surface of the condenser lens 1 is partially increased, and the focal length at the lens portion is increased. By increasing the length, the condenser lens 1 can be rotationally asymmetric with respect to the central axis N of the luminous flux. That is, as shown in FIG. 2 according to the second embodiment of the present invention, the light bending angle at the light receiving element 2 side end (the lower end side in FIG. 2) of the condenser lens 1 is reduced. The curvature of the lens surface is partially increased. And the incident angle with respect to the reflective surface 3a of the prism body 3 is set to be equal to or larger than the above-mentioned critical angle by increasing the focal length of the light passing through the portion.

  In this way, even when the rotational asymmetry of the condenser lens 1 is realized by partially changing the curved surface (curvature) of the condenser lens 1 itself, it passes through the condenser lens 1 as in the previous embodiment. More light can be totally reflected by the reflecting surface 3 a of the prism body 3 and guided to the light receiving surface 2 a of the light receiving element 2. In this case, as described above, with respect to the focal length at the part where the curvature of the lens surface is partially increased, the reflected light is reflected from the focal length (lower limit) where the light passing through the part satisfies the total reflection condition described above. It is sufficient to set within the range of the focal length (upper limit) guided to the light receiving surface 2a of the light receiving element 2. However, the focal length (upper limit) at which the reflected light from the reflecting surface 3 a is guided to the light receiving surface 2 a of the light receiving element 2 is the size of the light receiving surface 2 a of the light receiving element 2 and the arrangement relationship between the light receiving element 2 and the prism body 3. It is prescribed by. Therefore, even if the condensing lens 3 is rotationally asymmetric with respect to the central axis N of the light beam in this way, the same effect as that of the first embodiment described above can be obtained.

  For example, as shown in FIG. 3A, the condensing lens 1 in which the curved surface (curvature) of the lens surface is partially changed has the lens center side region 1a as a lens having a short focal length, and its peripheral region 1b. May be realized as a compound lens having a long focal length. In this case, without considering the direction (rotation) of the lens itself, it can be easily incorporated into the photoelectric sensor simply by shifting the central axis of the condenser lens 1 from the central axis N of the light beam.

  Further, when the light passing through the peripheral region 1b in which the focal length of the condenser lens 3 is set long is incident on the reflecting surface of the prism body 3 at an angle satisfying the total reflection condition described above, the condenser lens 1 is used. Even if the central axis M of the light beam and the central axis N of the light beam coincide with each other, more light passing through the condenser lens 1 is totally reflected by the reflecting surface 3a of the prism body 3, and the light receiving surface 2a of the light receiving element 2 Can lead to. Accordingly, in this case, it is only necessary to mount the condensing lens 1 so that the central axis of the condenser lens 1 coincides with the central axis N of the light beam, so that the configuration can be greatly simplified and the manufacturing procedure can be simplified. It becomes possible to plan.

  Further, a part of the condenser lens 1, specifically, a region on the lower half side of the lens, for example, a refractive index n2 (which is smaller than the refractive index n1 of the main portion 1c as shown in FIG. 3B). It is also possible to manufacture so as to have <n1). In this case, even if there is no change in the curvature of the lens surface, the focal length of the lens portion 1d having the refractive index n2 is longer than that of the main portion 1c. It becomes possible.

  The present invention is not limited to the embodiment described above. Here, the case where a 45-degree right-angle prism is used as the prism body 3 has been described as an example, but the angle formed between the reflecting surface 3a and the central axis N of the light beam is not particularly limited. It is of course possible to set the total reflection condition on the reflecting surface 3a of the prism body 3 by using the method shown in the first embodiment and the method shown in the second embodiment in combination, and its optical design. In doing so, it goes without saying that the refractive index of the condensing lens 1 and the prism body 3 and the arrangement thereof are taken into consideration.

  Further, as shown in FIG. 4 (a), the condensing lens 1 and the prism body 3 forming the reflector may be integrally formed to form the optical system. The prism body as shown in FIG. 4 (b). It is also possible to guide the light reflected by 3 to the light receiving surface of the light receiving element 2 through the optical fiber 4. Furthermore, it is of course possible to provide a light receiving lens 5 between the prism body 4 and the light receiving element 2 as shown in FIG. In addition, the present invention can be variously modified and implemented without departing from the scope of the invention.

DESCRIPTION OF SYMBOLS 1 Condensing lens 2 Light receiving element 3 Prism body 3a Reflecting surface

Claims (7)

A condensing lens that condenses light from the outside, a light receiving element provided with a light receiving surface facing the optical axis of the condensing lens, and reflecting the light collected by the condensing lens And a prism body that leads to the light receiving surface of the light receiving element,
The condensing lens is optically rotated with respect to the central axis of the light beam so that the light beam collected by the condensing lens is incident on the reflecting surface of the prism body at an angle greater than the critical angle. An optical sensor characterized in that it is asymmetrical or the focal length of the lens periphery is set longer than the center of the lens.   2. The optical according to claim 1, wherein the rotational asymmetry of the condensing lens with respect to the central axis of the light beam or the setting of the focal length is arranged by shifting the central axis of the condensing lens from the central axis of the light beam. Sensor.   The rotational asymmetry of the condenser lens with respect to the central axis of the light beam or the setting of the focal length is realized by partially increasing the curvature of the lens surface of the condenser lens and extending the focal length at the lens portion. The optical sensor according to claim 1.   The rotational asymmetry of the condenser lens with respect to the central axis of the light beam or the setting of the focal length is realized by partially reducing the refractive index of the condenser lens and extending the focal length at the lens portion. The optical sensor according to claim 1.   The prism body has one of two surfaces orthogonal to each other as an incident surface facing the condenser lens, and the other surface as an exit surface facing the light receiving surface of the light receiving element. 2. The optical sensor according to claim 1, wherein the optical sensor is a right-angle prism having an inclined surface forming an angle as a reflecting surface.   The optical sensor according to any one of claims 1 to 3, wherein the condensing lens and the prism body include those integrally molded.   The optical sensor according to claim 1, wherein the light receiving element includes a light receiving lens or an optical fiber that guides light to the light receiving surface.

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