JPH03186801A - Condensing lens for infrared type detector - Google Patents

Abstract

PURPOSE:To obtain the condensing lens which is small in size and is good in efficiency by forming a 1st face of a plane and a 2nd face of a hyperboloid and diagonally intersecting the axis of rotation of the hyperboloid of the 2nd face with the plane of the 1st face. CONSTITUTION:The 1st face 10 is the plane and the 2nd face 20 is the hyperboloid. The axis C of rotation of the hyperboloid of the 2nd face 20 intersects diagonally with the plane of the 1st face 10. An angle can, therefore, be provided between the collimated beams of light condensed without aberrations at a focus and the normal H direction of the plane according to the angle formed by the axis C of rotation of the hyperboloid and the plane. The IR rays from a required direction are consequently efficiently condensed without directing the lens to this direction. The condensing lens for the IR type detector which is small in size and is excellent in efficiency is obtd. in this way.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to an infrared detection device, and particularly to a condenser lens in a passive detection device that detects the presence or absence of a human body by receiving and detecting infrared rays emitted from a predetermined detection area. [Conventional technology]

In an infrared detection device, the infrared detection element is generally not placed on the entire focal plane of the condenser lens, but rather at the focal position of the condenser lens, so the infrared rays detected by the infrared detection element are is only incident parallel to the optical axis of the condenser lens, and since obliquely incident light at an angle to the optical axis is not focused at the focal point, in order to widen the detection area, it is necessary to direct the light in a different direction. A plurality of condensing lenses each having a shaft are combined. At this time, if the focal positions of each condenser lens are made to coincide, the entire lens will be semispherical and the curvature will be small, making it difficult to manufacture. The curvature of the entire lens can be increased by making the rays incident obliquely from the lens focus on the position where the infrared sensing element is placed. - An example is shown in FIG. Each condenser lens l is formed as a Fresnel lens, and these lenses are combined.

[Problem to be solved by the invention]

However, when using obliquely incident light at an angle to the optical axis as described above, there is a problem of "blur" due to aberrations of the condenser lens. This is especially noticeable when a Fresnel lens is used, and if the detection beam spreads beyond a predetermined size due to "blurring", the amount of infrared rays incident on the infrared detection element decreases. Therefore, in addition to causing a decrease in sensitivity, if a twin element that uses differential output from two elements is used as an infrared detection element to improve environmental resistance and disturbance resistance, Since the outputs cancel each other out in the overlapping portion of the two detection beams generated by the element, the decrease in sensitivity becomes even more noticeable. In order to avoid this problem, some systems use a multi-segmented mirror combined with a parabolic mirror as a focusing optical system, but in this case, the effect of "blurring" is small, and the reflectance is usually 90.
% or more, it is possible to efficiently collect light, but there is a problem that the optical system becomes large. The present invention has been made in view of these points, and its object is to provide a condensing lens for an infrared detection device that is small and has excellent light condensing efficiency.

[Means to solve the problem]

Therefore, the present invention is characterized in that the first surface is a plane, the second surface is a hyperboloid, and the rotation axis of the hyperboloid of the second surface is oblique to the plane of the first surface. ing. [Function] According to the present invention, it is possible to create an angle between the parallel light that is focused on the focal point without aberration and the normal direction of the plane, depending on the angle formed between the rotation axis of the hyperboloid and the plane. Therefore, infrared rays can be efficiently collected from this direction without having to point the lens in the desired direction. That is, in FIG. 6, the first surface is formed as a plane 10 and the second surface is formed as a hyperboloid 20, and the rotation axis C of the hyperboloid 20 coincides with the normal IIH direction of the plane 10 of the first surface. It is a normal aberration-free single lens, and incident light parallel to the optical axis (in this case, coincident with the rotation axis of the hyperboloid and the normal to the plane) is focused on the focal point F without aberration. In the condensing lens 1 having such a hyperboloid surface 20, as shown in FIG. When the first plane 10 is tilted as shown in FIG. It will shine. Note that the angle δ here is an angle that satisfies Snell's law sin (θ+δ) = Ns i nθ, where N is the refractive index of the condenser lens 1. Figure 1 shows the case where the plane 10 of the first surface is considered as a reference, and the angle 〈θ+δ
) is focused on the focal point F without aberration. If the angle θ is increased, the angle (θ + δ) that the parallel light condensed at the focal point F without aberration and the normal H to the plane 10 of the first surface will also be increased, and a certain detection area is then set. In this case, the condenser lens 1 can condense the infrared rays emitted from the detection area onto the infrared detection element placed at the focal point F without aberration, even if the first plane 10 is not directed toward the detection area. . [Example] The present invention will be described in detail below based on the illustrated example.
The figure shows the normal H of the plane 10 on the first surface and the hyperboloid 20 on the second surface.
The angle θ formed by the axis of rotation C is 24842', the refractive index is 1.53, the focal length is 14°50, and the maximum thickness is 0.8 inch.
+ condenser lens 1 is shown. In this case, the angle between the parallel light condensed at the focal point F without aberration and the normal H to the plane 10 of the first surface is 400. By the way, polyethylene, which is generally used as a material for this type of lens, is inexpensive and has good processability, but as the thickness increases, the transmittance decreases due to absorption, so it is necessary to make the thickness of the condenser lens 1 as thin as possible. However, as shown in FIG. 3, by using a Fresnel lens, the lens can be made thinner without reducing the lens area. The hyperboloid 20 of the second surface includes a first ring 21 in the center, a second ring 22 surrounding it, and a third ring 22 that further surrounds the second ring 22.
In this condensing lens 1 consisting of a ring 23, each ring 21,
22. Each hyperboloid in 23 has the same axis of rotation and has a slightly different radius of curvature at the intersection with the axis of rotation,
They are superimposed in the normal H direction to the plane 10 of the first surface so that the maximum thickness is 0.8 mm and the minimum thickness is 0.3 x w, respectively. For this purpose, each wheel 21, 22, 23 is oval in shape. FIG. 4 shows four 7-lens type condensing lenses 1 in an annular shape in which the angle α between the normal H to the plane 10 on the first surface and the parallel rays condensed at the focal point F without aberration is α. and the above angle is α2 (α2〉α1) on their outer periphery.
) is shown in which eight Fresnel type condensing lenses 1 are arranged in an annular shape to form a flat type multi-segment lens. It goes without saying that the focal point F of each condenser lens (2) is at the same position, and that the infrared detecting element 3 is disposed at this position. [Effects of the Invention] As described above, in the present invention, there is an angle between the parallel light that is focused on the focal point without aberration and the normal direction of the plane, depending on the angle between the rotation axis of the hyperboloid and the plane. Because it can have a lens, it can efficiently collect infrared rays from this direction without pointing the lens in the required direction, and it is small and has excellent light collection efficiency. be able to.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a condenser lens according to the present invention, Fig. 2 is a sectional view of one embodiment, Figs. 3(a) and 3(b) are a front view and a sectional view of a Fresnel type lens, Figures (a) and (b) are front and side views of a multi-segmented lens, Figure 5 is a cross-sectional view explaining the present invention, Figure 6 is a cross-sectional view of a normal hyperboloid lens, and Figure 7 is a cross-sectional view of a normal hyperboloid lens. 1 is a perspective view of a conventional example, where 1 is a condenser lens, 10 is a plane, 20 is a hyperboloid, H is a normal to the plane, and C
indicates the rotation axis of the hyperboloid.

Claims (1)

[Claims] (1) An infrared detection device characterized in that the first surface is a plane, the second surface is a hyperboloid, and the rotation axis of the hyperboloid of the second surface is oblique to the plane of the first surface. condensing lens.