JPH03186803A - Condenser lens for infrared-ray type detector - Google Patents

Abstract

PURPOSE:To obtain a compact, efficient condenser lens having a wide detecting area by crossing slantingly the rotation axis of respective hyperboloids of the 2nd face consisting of respective lenses of a multi-divided lens obtained by combining a 1st face shaped in plane and the 2nd face shaped in hyperboloid. CONSTITUTION:The condenser lens is a multi-divided lens obtained by combining the 1st face 10 shaped in plane and the 2nd face 20 shaped in hyperboloidal lenses, and the rotation axis C of the hyperboloids of the 2nd face 20 is crossing slantingly the plane constituting the 1st face 10 in respective lenses. Since an angle can be formed between parallel beams converged upon a focus without generating aberration and the normal H of the plane 10 in accordance with the angle formed between the rotation axis C shared by respective hyperboloidals of the Fresnel's face constituting the 2nd face and the plane 10, infrared rays can be efficiently converged from a required direction without directing the lens to the necessary direction. Thus, the compact infrared-ray type condenser lens for a detector having high converging efficiency and a wide detecting area can be obtained.

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 1 is formed as a Fresnel lens, and these lenses are combined to form a multi-segment lens.

[Problem to be solved by the invention]

However, as mentioned above, when using obliquely incident light at an angle to the optical axis, there is the problem of "blurring" due to the aberration of the condensing lens.6 This is the case when using a Fresnel lens. This is especially noticeable, and if the detection beam spreads beyond a predetermined size due to "blurring", the amount of infrared rays that enters the infrared detection element will decrease, resulting in a decrease in sensitivity. In order to improve environmental resistance and disturbance resistance, when a twin element that uses differential output from two elements is used as an infrared sensing element, the 2
Since the outputs cancel each other out in the portion overlapping the detection beam, the decrease in sensitivity becomes even more pronounced. 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 purpose is to provide a condensing lens for an infrared detection device that is small in size, has excellent light condensing efficiency, and is capable of widening the detection area. be.

[Means to solve the problem]

Therefore, the present invention is a multi-segment lens in which a first surface is a flat surface and a second surface is a hyperboloid. It is distinctive in that it is oblique to the [Function] According to the present invention, depending on the angle formed between the rotation axis shared by each hyperboloid of the Fresnel surface and the plane, there is a difference between the parallel light that is focused on the focal point without aberration and the normal direction of the plane. Since the lens can be angled, infrared rays can be efficiently focused from this direction without having to point the lens in the desired direction. That is, in FIG. 8, the first surface is a flat surface 10. It is a normal aberration-free single lens in which the second surface is formed as a hyperboloid 20, and the rotation axis C of the hyperboloid 20 coincides with the normal H direction of the plane 10 of the first surface, and the optical axis ( In this case, incident light parallel to the axis of rotation of the hyperboloid (which coincides with the normal to the plane) is focused on the focal point F without aberration. In the condensing lens 1 having such a hyperboloid 20, as shown in FIG. 7, the normal H to the plane 10 on the first surface and the rotation @C of the hyperboloid 20 on the second surface form an angle θ. 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: 5 in (θ+δ) = Ns i n θ, where N is the refractive index of the condenser lens 1. Figure 1 shows the case where the plane lO 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. By combining such a condensing lens 1 into a multi-segment lens, infrared rays from multiple directions can be condensed. [Example 2] The present invention will be described in detail based on the illustrated example below.
The figure shows an embodiment of the condensing lens l which is the basis of the present invention, and shows the normal H to the plane 10 of the first surface and the hyperboloid 2 of the second surface.
The condenser lens 1 has an angle θ of 24.842° with the rotation axis C of 0, a refractive index of 1.53, a focal length of 14.5IllIll, and a maximum thickness of 0.8jv. 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 40°. FIG. 3 shows such a condensing lens 1 in which the hyperboloid 20 side is a Fresnel surface. Here, the second surface hyperboloid 20
A first wheel body 21 in the center and a second wheel body 22 surrounding it.
, consists of a third wheel body 23 that further surrounds the second wheel body 22, and the rotation axis of each wheel body 21, 22, 23 is the same, and the radius of curvature at the intersection with the rotation axis is slightly different. Each hyperboloid has a maximum wall thickness of 0.8
I1M, the minimum thickness is 0.3xz, and they are superimposed in the direction of the normal H to the plane IO of the first surface. For this reason, each wheel 21, 22, 23 has an elliptical shape. Although polyethylene, which is generally used as a material for this type of lens, is inexpensive and has good processability, 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. By using a Fresnel lens, it is possible to make the lens thinner without reducing the lens area. The present invention is characterized in that it is a multi-segment lens that is a combination of the above-mentioned condensing lens 1, and an example thereof is shown in FIG. Here, four Fresnel tube condensing lenses 1 are arranged in a ring shape, and the angle α1 between the normal H to the plane 10 of the first surface and the parallel ray condensed without aberration at the focal point F is arranged in an annular manner. This figure shows a case where eight Fresnel type condensing lenses 1 having the angle α2 (α2>α1) are arranged in a ring shape around the outer periphery of the lens to form a flat type multi-segment lens. It goes without saying that the focal point F of each condenser lens 1 is at the same position, and that the infrared detecting element 3 is disposed at this position. As the infrared detection element 3, as shown in FIG.
When using a device equipped with four detection elements 30, the detection beam B formed by the above-mentioned multi-segment lens and each detection element 30, at a certain distance,
The arrangement is shown in FIG. Although a multi-segment lens combined to form a flat type is shown here, it is of course possible to use a combination of cylindrical or other shapes.

【Effect of the invention】

As described above, in the present invention, each lens to be combined is configured to create a gap between the parallel light that is condensed at 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. Because it can be angled, it is possible to efficiently collect infrared rays from this direction without having to point the lens in the desired direction, and such lenses are combined. Therefore, it is small, has excellent light collection efficiency, and can have a wide detection area.

[Brief explanation of drawings]

Figures 1 and 2 are cross-sectional views of the basic shape of the condensing lens according to the present invention, Figures 3 (a) and (b) are front views and cross-sectional views of a Fresnel type, and Figures 4 (, ) ( b) is a front view and a side view of an embodiment of the present invention, FIG. 5 is a front view of the infrared detection element as described above, FIG. 6 is an explanatory diagram showing the arrangement of the detection beam as described above, and FIG. 8 is a sectional view of a normal hyperboloid lens, and FIG. 9 is a perspective view of a conventional example, where 1 is a condenser lens, 10 is a plane, 20 is a hyperboloid, and H is a plane. The normal C indicates the rotation axis of the hyperboloid.

Claims (1)

[Claims] (1) It is a multi-segment lens in which the first surface is a flat surface and the second surface is a hyperboloid, and each lens has a rotation axis of the hyperboloid of the second surface relative to the plane of the first surface. A condensing lens for infrared detection devices that is characterized by oblique lines.