JPH0559403B2 - - Google Patents

Description

[Detailed description of the invention]

[Field of Application of the Invention] The present invention relates to a lens installed to cover the front surface of a lamp body, and in particular, when the shape of the outer peripheral surface is already determined and is a curved surface inclined with respect to the optical axis, the inner surface of the lens is fixed. The present invention relates to a method of forming a peripheral surface. [Background of the Invention] FIG. 1 is a horizontal cross-sectional view of a conventional automobile lamp as an example of this type of lens, in which the front surface of a lamp body 1 is covered with a lens 2.
The lamp body 1 is provided with a light source bulb 1b near the focal point of a reflector 1a shaped like a paraboloid of revolution, and an inner lens 1c is attached to the front opening of the reflector 1a. The lens 3 is inclined with respect to the optical axis X-X' of the lamp body 1 in order to reduce air resistance, and has a substantially constant thickness t. The light emitted from the light source bulb 1b is reflected by the reflector 1a.
The light is reflected into a substantially parallel light beam by the inner lens 1c, and is then modulated by the inner lens 1c, passes through the lens 3, and is projected. In areas where the lens 2 has a substantially planar lens shape, such as near parts A and C shown in FIG. 1, light incident parallel to the optical axis X-X' Although the light is emitted almost parallel to the curved surface, there is a problem that the emitted light is tilted with respect to the incident light at a curved surface such as the part B. FIG. 2 is an explanatory diagram of the above problem, and numeral 3 indicates a lens having an outer circumferential surface 3a and an inner circumferential surface 3b having concentric cross sections. R indicates the radius of the outer peripheral surface 3a. When light parallel to the optical axis x-x' as shown by arrow A enters a point _S1 looking at the center O of the lens at an angle α, it travels as shown by arrow B at an incident angle α and a refraction angle β, and then as shown by arrow C. When the light is emitted from the outer circumferential surface 3a, the emitting direction is inclined by an angle Δγ with respect to the optical axis x-x'. For this reason,
If the lens 3 is provided with a curved surface as shown in part B in FIG. 1, the light distribution of the lamp body 1 will be disturbed even if the lens thickness is constant. Furthermore, if a portion E having a curved surface that is concave in the light projection direction is provided on the lens 2 as shown in FIG. 3 in consideration of the design of the entire automobile, this portion also has a difference between the incident light and the output light. There is a problem that there is a slope between the two. FIG. 4 is an explanatory diagram thereof. As clearly understood from FIG. 3, in section E, light enters from the convex side of the curved surface and exits from the concave side. FIG. 4 shows the optical path of light that is incident on the outer circumferential surface 3a of the lens 3, as indicated by arrow D, parallel to the optical axis x-x' at an incident angle α'. The incident light in the direction of the arrow 2 is refracted as shown by the arrow E, exits as shown by the arrow, and is tilted by an angle Δγ with respect to the optical axis x-x'. [Object of the invention] The present invention has been made in view of the above circumstances, and
When a lens made of a transparent body having a curved surface inclined with respect to the optical axis of the lamp body is provided to cover the front surface of a lamp body including a light source bulb and a reflector, as explained in FIGS. 1 and 2, If the shape of the outer circumferential surface of the lens has already been determined due to the overall design of the vehicle, etc., the inside of the lens should be designed such that the light incident on the lens parallel to the optical axis can be emitted parallel to the optical axis. The present invention provides a method for forming a peripheral surface to prevent the light distribution from being distorted by the lens. [Summary of the Invention] In order to achieve the above object, a method for forming a lens according to the present invention is provided in which the lens is attached to the front surface of a vehicle lamp having a light source bulb and a reflector, and is tilted with respect to the optical axis of the vehicle lamp. When forming the inner circumferential surface of a lens having a curved surface such that the shape of the outer circumferential surface is given as a predetermined condition, _a .
The incident angle of the light incident parallel to X' is α, the refraction angle of the light incident at the incident angle α is β, the radius of curvature of the outer circumferential surface at the above incident point S ₂ is R, and the transparent material forming the lens is Let n be the refractive index of b, find the values of X and Y that satisfy the following formula, find the point _S3 whose coordinates are (X, Y), and calculate y=tan(α-β){x- Rcosα}+Rsinα ……(1) sinβ=sinα/n ……(2) dy/dx=−1/tanα ……(3) c Take many points on the outer peripheral surface of the lens, and calculate each of these many points. Find a large number of points with coordinate values that satisfy equations (1), (2), and (3) above for
The feature is that a curved surface on the inner circumferential side is obtained by connecting these many points. [Embodiment of the Invention] FIG. 5 is an explanatory diagram showing an embodiment of the method for forming a lens according to the present invention. In the lens 3' formed in this example, the inner circumferential surface 3b' is determined based on the given outer circumferential surface 3a' by the following procedure. This FIG. 5 is for convenience of explanation, and the outer circumferential surface 3a' is shown as a circular arc of radius R (center point
O′), but if we detail the actual conditions,
This indicates that the center of curvature at the point of incidence _S2 of the incident light indicated by arrow T is O', and the radius of curvature is R. Point S ₂ looking at the center point O′ of the arc on the outer peripheral surface at an angle α
As shown by arrow T, light incident parallel to the optical axis x-x' at an incident angle α is directed to the exit point _S3 at a refraction angle β, and the line _O'S2
is the normal line drawn to the incident point _S2 , and line _l1 is the tangent line drawn to the incident point _S2 . The coordinates (x, y) of _the point _S3 for emitting light parallel to the optical axis x-x' as shown by arrow R are as follows, where n is the refractive index of the transparent body constituting the lens 3'. It is expressed by the formula. l ₂ is the tangent drawn to the exit point S ₃ . y=tan(α-β) {x-Rcosα}+Rsinα...(1) sinβ=sinα/n...(2) dy/dx=-1/tanα...(3) In this example, the above outer peripheral surface The radius R of is 30 mm, the refractive index n of the transparent body is 1.5, and calculations are made as follows.
That is, by eliminating α and β from equations (1), (2), and (3) above, f(x,
Find the differential equation for y, dy/dx = 0, find the solution using a computer, and draw a special solution F (x, y, x ₀ , y ₀ ) = 0 that gives the initial values x ₀ and y ₀ . and inner peripheral surface 3
Find the shape of b′. The computer solution in this example is as shown in the following table.

【table】

〔Effect of the invention〕

As detailed above, according to the lens forming method of the present invention, when a lens outer circumferential surface consisting of a curved surface inclined with respect to the optical axis of the lamp body is given as a predetermined condition, the optical axis of the lens is The light incident parallel to the optical axis can be emitted parallel to the optical axis, and it is possible to prevent disturbance of light distribution due to the lens, which is an excellent practical effect.

[Brief explanation of the drawing]

FIG. 1 is a horizontal cross-sectional view of an example of a conventional automotive lamp equipped with a lens, and FIG. 2 is a diagram of the optical path in the lens. FIG. 3 is a sectional view of a conventional example different from the above, and FIG. 4 is an optical path diagram thereof. FIG. 5 is an explanatory diagram of one embodiment of the method for forming a lens according to the present invention, and FIG. 6 is an explanatory diagram of an embodiment different from the above. 1...Lamp body, 1a...Reflector, 1b
...Light source bulb, 1c...Inner lens, 2,
2'... Conventional lens, 3... Lens having a concentric cross section, 3,3''... Lens to which the present invention is applied, 4... Prism.

Claims (1)

[Scope of Claims] 1. A lens that is attached to the front surface of a vehicle lamp that includes a light source bulb and a reflector, and that has a curved surface that is inclined with respect to the optical axis of the vehicle lamp, wherein the shape of the outer peripheral surface meets a predetermined condition. When forming the inner circumferential surface of a lens given as a, the optical axis X- with respect to any point _S2 on the outer circumferential surface.
The incident angle of the light incident parallel to X' is α, the refraction angle of the light incident at the incident angle α is β, the radius of curvature of the outer circumferential surface at the above incident point S ₂ is R, and the transparent material forming the lens is Let n be the refractive index of b, find the values of X and Y that satisfy the following formula, find the point _S3 whose coordinates are (X, Y), and calculate y=tan(α-β){x- Rcosα}+Rsinα ……(1) sinβ=sinα/n ……(2) dy/dx=−1/tanα ……(3) c Take many points on the outer peripheral surface of the lens, and calculate each of these many points. Find a large number of points with coordinate values that satisfy equations (1), (2), and (3) above for
A method for forming a lens characterized by connecting a large number of these points to obtain a curved surface on the inner peripheral side.