FR2688599A1 - Lamp lens with Fresnel steps or prism steps - Google Patents

Abstract

The invention relates to a lens in which a large number of Fresnel lens steps are formed on an incident surface of the lens, including a plate-shaped part and a curved part, characterised in that the Fresnel lens steps are arranged substantially at regular intervals along a first radial line located in the plate-shaped part of the lens, and at irregular intervals along a second radial line located in the curved part of the lens. This lens is intended for vehicle lamps.

Description

LENS FOR FRESNEL STEP LAMPS OR STEP LAMPS
PRISM
BACKGROUND OF THE INVENTION 1. Field of the Invention
The present invention is designed to provide a lens for use in a lamp which can provide uniform brightness distribution and good visibility.

2. Description of the Prior Art
Among vehicle lamps there is a type having a structure in which an inner lens for controlling direct light from a light source and reflection light from a reflector is arranged in a lamp space defined by a body of lamp and an external lens. The inner lens is a product formed from a transparent synthetic resin, and has Fresnel lens rungs and prism rungs on one of its surfaces.

 As shown in Figure 16, a lamp 1 is designed to have a curved outlet surface of an outer lens 2 which conforms to a body shape of a vehicle.

 In the lamp 1, the optical axis xx of a reflector 3 extends in the front-rear direction of the vehicle passing through the center of a filament of a bulb 4. An interior lens 5 is disposed between the bulb 4 and the outer lens 2. That is, the inner lens 5 is placed immediately next to the outer lens 2, and is influenced, like the outer lens 2, by the shape of the vehicle body to have a surface output 6 assuming a curved shape.

 The inner lens 5 is made up of a plate-shaped part 5a and a curved part 5b which is in continuous relation with the plate-shaped part 5a and curved increasingly when the direction reaches an end in the longitudinal position . Fresnel lens steps 7, 7 -, ... are formed on the inner surface in the vicinity of the optical axis x-x, and 8.8 prism steps ...

are formed around the echelons of Fresnel lens 7.7 ...

 Figure 17 is a sectional view showing the main part of an inner plate-shaped lens 5.

 The Fresnel lens steps b, b, ...

are shaped on an incidence surface of the inner lens a in the vicinity of the optical axis xx of the reflector 3, and the prism rungs c, c ... are shaped around the Fresnel rungs b, b ... By refraction through the Fresnel lens rungs b, b, ... the paraxial rays of the light emitted from a bulb d are controlled to become parallel to the optical axis of the lamp. The external rays of the light coming from the bulb d which move away from the optical axis of the lamp to go towards the peripheral surface of the interior lens are controlled by the total reflection through the rungs of prism c, c, ... to become parallel to the optical axis.

 This structure is used because the paraxial rays have small angles of incidence relative to the inner lens a and can be controlled by the phenomenon of refraction, but the external rays starting from the optical axis have large angles of incidence relative to the inner lens a. As a result, it is difficult to control the outer rays by refraction.

 In order to adapt to the recent design trend which makes the vehicle bodies rounded or of aerodynamic line to improve the aerodynamic characteristics of the vehicles and to meet the requirements of the drawing, it is necessary to draw a lamp shape having a curve which conforms to the external shape of a vehicle body or has an inclination with respect to the vertical direction. Therefore, it is not possible for the inner lens to be limited to a plate-like shape, i.e., in general the inner lens should include a curved shape.

 Figure 18 conceptually shows an example of a method of shaping lens rungs on a curved surface of an inner lens.

 To simplify the description, it is assumed that the lens rungs must be formed on a spherical surface, as shown in Figure 18. A method can be devised in which an inner plate-shaped lens f on which lens rungs are to be formed on the basis of concentric reference circles e, e ... is used as a reference model of the drawing, and in which the concentric reference circles e, e ... are projected onto a spherical surface g. In this case, the steps of a Fresnel lens and the prism steps are shaped on the spherical surface g on the basis of the reference circles h, h ... which are concentric with the optical axis.

 While the above process allows for relatively easy drawing, it will encounter difficulty in the precise control of light paths. As a result, parallel rays cannot be obtained over the entire surface of the inner lens, and the brightness distribution will be irregular.

 This is a natural result of the fact that a fine optical construction is not carried out on the lens rungs according to the surface shape of the inner lens. The part of the inner lens which is not very curved, that is to say, in general the flat part 5a, will not cause any problem. But the part 5b in which the curvature varies greatly will cause a considerable deviation from the desired brightness distribution due to an unexpected contribution of rays.

 To avoid the above problem, it is necessary to modify the process of shaping the lens rungs. However, according to the above process, correct construction progress cannot be obtained easily. Therefore, a lot of time and work is required to draw the inner lens, and its final design and performance will depend on the experiences of the designer.

SUMMARY OF THE INVENTION
To solve the problems described above, the subject of the present invention is a lens for a lamp in which a large number of Fresnel lens steps and / or prism steps are formed on an incidence surface of the lens comprising a plate-shaped part and a curved part, characterized in that the Fresnel lens rungs or the prism rungs are arranged substantially at regular intervals along a first radial line located in the plate-shaped part of the lens, and at irregular intervals along a second radial line located in the curved part of the lens.

In addition, there is a method of fabricating a die for shaping a lamp lens in which a large number of lens steps
Fresnel and / or prism steps are formed on a lens incidence surface having a plate-shaped part and a curved part. According to this method, a direction of an incident ray with respect to an exit surface is first determined according to the law of refraction and on the basis of a normal direction at a point of refraction of the exit surface. and of a direction of parallel rays so that the exit rays from the lens become the parallel rays.Then a refractive limit surface is determined according to the law of refraction in the case of Fresnel lens steps or a surface of total reflection is determined according to the law of reflection in the case of prism steps, on the basis of a direction of an incident ray with respect to the surface of incidence of the lens and the direction of the incident ray with respect to the exit surface which is obtained above. Then, a vector calculated as a vector product of a normal vector of the refraction limit surface of the Fresnel lens rungs or of the total reflection surface of the prism rungs and of the normal vector at the refraction point of the exit surface is used as direction vector to determine a shaping direction of the limit refraction surface or the total reflection surface. A closed curve is then generated by connecting these direction vectors as tangential vectors using a spline approximation. Finally, a V-shaped groove having an inclined surface corresponding to the refractive boundary surfaces and / or to the total reflection surfaces is formed on a matrix material along the closed curve.

BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a diagram of the light path illustrating a Fresnel lens step according to the present invention
Figure 2 is a drawing showing refraction by an exit surface of a lens in connection with the Fresnel lens rung.

 Figure 3 is a drawing showing the refraction by a refractive boundary surface of the Fresnel lens rung.

 Figure 4 is a drawing showing a direction in which the refractive area of the Fresnel lens rung is shaped.

 Figure 5 is a drawing showing a closed curve which is necessary in a method of manufacturing the refractive limit surface of the rung of the Fresnel lens.

 Figure 6 is a drawing showing a light path relative to part of the Fresnel lens echelons.

 Figure 7 is a drawing showing a V-shaped groove formed on a matrix which corresponds to the refractive limit surface of the Fresnel lens rung.

 Figure 8 is a light path diagram illustrating a prism step according to the invention.

 Figure 9 is a drawing showing refraction by the exit surface of the lens in relation to the prism rung.

 Figure 10 is a drawing showing a reflection by a total reflecting surface of the prism rung.

 Fig. 11 is a drawing showing a direction in which the total reflecting surface of the prism rung is shaped.

 Figure 12 is a drawing showing a closed curve which is necessary in a method of manufacturing the total reflecting surface of the prism rung.

 Figure 13 is a drawing showing a light path relative to part of the prism rung.

 Figure 14 is a drawing showing a V-shaped groove formed on the matrix which corresponds to the total reflection area of the prism rung.

 Figure 15 is a drawing showing the closed curves used for the formation of V-shaped grooves in the manufacture of the matrix for an inner lens.

 Figure 16 is a sectional view schematically showing an example of a conventional configuration of a vehicle lamp.

 Figure 17 is a sectional view schematically showing Fresnel lens rungs and prism rungs shaped on an inner plate-shaped lens.

 Figure 18 is a schematic drawing showing how concentric reference circles, which are required in the drawing step of a method of shaping Fresnel lens rungs and prism rungs on the inner lens in the form of plate, are projected onto a spherical surface.

DESCRIPTION OF THE PREFERRED EMBODIMENTS
Figure 16, which has been described previously, shows a configuration of an interior lens of a rear lamp of a vehicle to which the invention can be applied.

According to the invention, the inclination of the refractive limit surface of the lens rung of
Fresnel or the total reflection surface of the prism rung which corresponds to the point of refraction on the exit surface of the lens is determined so as to conform to the curved shape of the exit surface, i.e. so that the rays refracted by the refractive limit surface of the lens rung of
Fresnel or totally reflected by the total reflection surface of the prism rung are refracted by the exit surface to become parallel rays.

As a result, an irregularity in the brightness distribution which would otherwise be caused by light not precisely controlled can be avoided. In addition, the Fresnel lens rungs and the prism rungs can be drawn according to the procedure which is obvious in terms of optical properties.

 A lens for a lamp and a method of manufacturing a matrix therefor according to the present invention are described below by way of embodiment accompanied by the drawings.

 Figure 1 illustrates a refraction action of the Fresnel lens rungs 7.7 ..., where a light ray is refracted twice as it passes through a lens rung. The reference number 9 denotes a curve which represents the exit surface 6 of the inner lens 5, and is a line in cross section obtained when the exit surface 6 is cut by a horizontal plane containing the optical axis. This line is first given as a shape conforming to the shape of the vehicle body. A dotted line Lf in Figure 1 indicates a light path. A vector V ~ IN is a direction vector of an incident ray, and a vector V is a direction vector of a refracted ray.

 The reference character A denotes a straight line representing a limit surface S of refraction.

A vector N ~ IN is a normal vector of the limit surface S at an incident point PI.

 A vector V ~ OUT is a direction vector of a ray refracted on the exit surface 6, and a vector N ~ OUT is a normal vector of the exit surface 6 at the level of a point PO on the line of intersection 9.

If it is required that the direction vector
V ~ OUT of the finally determined radius is parallel to the optical axis xx, the trajectory Lf is determined only according to Snell's law when the thickness of the lens is specified.

That is, the direction of the vector V can be determined from the parallelism of the vector
V ~ OUT and the optical axis xx, an angle of refraction formed by the normal vector N ~ OUT and the vector V ~ OUT, and a refractive index of the inner lens 5. In addition, the vector normal N ~ IN and the limit surface S can be determined from the vectors V and
V ~ IN.

 Figures 2-7 show, step by step, a method of fabricating a matrix for the Fresnel lens rungs 7.7 ... As is apparent from the fact that a cross section obtained by cutting 1 ' Fresnel lens rung 7 by a plane including the optical axis has a triangular shape, a matrix for manufacturing the lens can be produced by shaping, by NC machining (with numerical control), V-shaped grooves corresponding to the respective rungs on a matrix material.

First, as shown in Figure 2, on a drawing output surface K, the vector V is determined according to Snell's law from the normal vector N ~ OUT at the exit point PO and the direction vector
V ~ OUT of a refracted ray which passes through the point PO and which is parallel to the optical axis xx. In general, the exit surface K is a free surface which cannot be expressed by an analytical function.

 Then, as shown in Figure 3, the refractive limit surface S and the normal vector N ~ IN thereof are determined according to Snell's law from the vector V and the direction vector V ~ IN of the incident ray.

 Then, as shown in Figure 4, a vector product (vector product) of the vectors N OUT and N IN is calculated as vector W, which is contained in the limit surface S and has a direction indicating a shaping direction of the limit surface S.

 Figure 5 shows a closed curve 10, which is a spline curve having vectors W obtained sequentially at the respective variable points PO as tangential vectors. The closed curve 10 presents the optical axis x-x as its central line and is placed on the side of the light source of the output surface K, and serves as a reference line for machining the matrix.

 In general, the closed line 10 is not circular when viewed along the optical axis, which is understood by considering that it is a very special case that the boundary surfaces S at the respective points are included in a single sphere.

 As shown in Figure 6, the incident ray is refracted by the very small surface S formed under the exit surface K, and moreover refracted by the exit surface K to exit as a ray parallel to the optical axis. By connecting the very small surfaces S along the closed curve 10, a continuous limit surface relating to a Fresnel rung 7 is formed.

Figure 7 shows how a V-shaped groove 11 is formed on a matrix material M by controlling the movement of a cutting tool along the closed curve 10. An outer tilt surface ila of the shaped groove of V 11 concerns the formation of the surface of incidence of the lens rung of
Fresnel 7. An angle of an inner inclination surface of the V-shaped groove 11 with respect to the optical axis is set to a constant value for convenience of extracting the matrix.

 Then, the formation of the prism steps 8,8, ... is described.

 Figure 8 illustrates actions of total reflection and refraction of the prism rungs 8,8 .... While passing through lens rung 8, the light ray is first refracted,. then fully reflected, and refracted again.

The reference number 12 indicates a curve which represents the exit surface 6 of the inner lens 5, and which is a line in transverse section obtained by cutting the exit surface 6 by a horizontal plane including the optical axis. This curve is first given as a shape conforming to the shape of the vehicle body
A dotted line Lp in Figure 8 indicates a light path. A vector v IN is a direction vector of an incident ray, and a vector v is a direction vector of a refracted ray.

 The reference character B indicates a straight line which represents a total reflection surface R, and a vector n-IN is a normal vector of the total reflection surface R at the level of an incident point QI.

 A vector v ~ OUT is a direction vector of a refracted ray on the exit surface 6, and a vector n OUT is a normal vector of the exit surface 6 at a point QO on the line of intersection 12.

 If it is required that the direction vector v ~ OUT of a finally determined radius be parallel to the optical axis xx, the path Lp is only determined according to Snell's law and the total reflection law when the thickness of the lens is specified.

 That is to say that the direction of the vector v can be determined from the parallelism of the vector v OUT and the optical axis xx, of a refraction angle formed by the normal vector n-OUT and the vector v ~ OUT , and of a refractive index of the inner lens 5. In addition, the normal vector n-IN and the total reflection surface R can be determined from the vectors v and v ~ IN.

 It is noted that in the above calculation an approximation is used, namely that the direction of the incident ray is not changed through the first refraction, or that a change in direction is negligibly small.

 Figures 9-14 show, step by step, a method of constructing a matrix for the 8.8 prism steps. The matrix is produced by shaping, by NC machining, V-shaped grooves corresponding to the respective steps on the matrix material.

 As shown in Figure 9, on the exit surface K, the vector v is determined according to Snell's law from the normal vector nOUT at the exit point QO and the direction vector v ~ OUT of the refracted ray which passes through the point Q0 and which is parallel to the optical axis xx.

 Then, as shown in Figure 10, the total reflection surface R and the normal vector n ~ IN thereof are determined according to the law of reflection of the vector v and the direction vector v ~ In of the incident ray.

 Then, as shown in Figure 11, a vector product (vector product) of the vectors n ~ OUT and n ~ IN is calculated as vector w, which is contained in the total reflection surface R and indicates a shaping direction of the surface total reflection R.

 Figure 12 shows a closed curve 13 which is obtained as a spline curve which is a spline curve having vectors w obtained sequentially at the respective variable points Q0 as tangential vectors. The closed curve 13 is a machining line having the optical axis x-x as its center line and located on the side of the light source of the output surface K.

 It is noted that in general the closed curve 13 is not circular when viewed along the optical axis.

 As shown in Figure 13, the incident light is first refracted by a very small surface of incidence I formed under the exit surface K, then reflected by the very small total reflection surface R, and refracted again by the surface outlet K, to finally exit parallel to the optical axis. A continuous total reflection surface relating to a prism rung 8 is formed by connecting the very small total reflection surfaces R along the closed curve 13.

Figure 14 shows a V-shaped groove shaped by a cutting tool along the closed curve 13. An inner inclination surface 14a of the V-shaped groove 14 relates to the formation of the incident surface I of the prism rung 8, and an external inclination surface 14b of the groove 14 relates to the formation of the total reflection surface
R of the prism step 8. An angle of the inclination surface 14a with respect to the optical axis is established at a constant value for convenience of the extraction of the matrix.

 In Figure 15, the part, located near the optical axis, of the matrix (including the closed curves 10, 13) for the inner lens 5 is enlarged.

 As described above, it is rare for a lens for a vehicle lamp to have a complicated surface. That is to say that in general, it consists of a main part in the form of a plate and a part with increasing curvature which is in continuous relation with the main part.

 The reference numbers 15,15, ... in Figure 15 denote closed curves serving as a reference for the formation of V-shaped grooves on the matrix. The part of the closed curves 15,15, ... located on the right side of the line VV relates to the echelons to be formed on the plate-shaped part 5a of the inner lens 5, and has the same intervals on the line HH .

 Points on the line H-H are chosen as the origins of the closed curves 15,15, ...

 The remaining part of the closed curves 15,15 ... located on the left side of the line VV relates to the steps to be formed on the curved part 5b of the inner lens 5. We can find a tendency for the interval of the closed curves 15.15 ...

gradually increases as the position advances along the closed curve of its intersection with the line
VV towards its intersection with line HH.

 Namely that the closed curves 15,15 .. are obtained by first arranging, at regular intervals, the origins for the shaping of these curves on a line of intersection obtained by cutting the flat part of the reference surface of the matrix by a horizontal plane including the optical axis, and then performing the spline approximation as described above in connection with Figures 5 and 12. A closed curve generally assumes an arc around the flat part of the matrix , and assumes an outwardly expanded shape from an arc around the curved part of the matrix.

 Consequently, the inner lens 5 has configuration features such that the boundary lines between the adjacent rungs formed on the plate-shaped portion Sa are arcs of concentric circles, and that the boundary lines between the adjacent rungs formed on the curved part 5b are curves deviating progressively from concentric arcs of a circle.

So, as is apparent from the process of shaping the lens rungs of
Fresnel 7.7, ... and prism steps 8.8, ..., the refractive limit surfaces and the total reflection surfaces are defined with the exit surface 6 of the inner lens 5 as a reference so that 'at each position the refracted ray is directed parallel to the optical axis xx. Consequently, the precise control of the light path can be carried out according to the surface shape of the inner lens 5.

 In particular, the prism or Fresnel lens rungs are arranged substantially at regular intervals along a first radial line located in the plate-like part of the lens, and at irregular intervals along a second radial line located in the curved part of the lens.

 As is apparent from the above description, depending on the lens to be used in a lamp and the method of manufacturing the matrix for this lens of the invention, the steps can be drawn by defining the slopes of the boundary surfaces of refraction of the rungs of a Fresnel lens or those of the surfaces of total reflection of the rungs of the prism according to the curved shape of the exit surface of the lens so that the refracted rays always leave the exit surface as parallel rays. As a result, a precise light distribution control can be obtained according to the laws of optical properties.

 Although the above embodiment is directed to the case in which the invention is applied to the interior lens of the lamp of a vehicle, it is apparent that the invention is not limited to such a case but can generally be applied to a wide variety of lens lenses.

Claims (2)

 1. Lens for a lamp in which a large number of Fresnel lens steps (7) are formed on a lens incidence surface comprising a plate-shaped part (5a) and a curved part (5b), characterized in that the Fresnel lens rungs (7) are arranged substantially at regular intervals along a first radial line located in the plate-like part (5a) of the lens, and at irregular intervals along a second radial line located in the curved part (5b) of the lens.  2. Lens for a lamp in which a large number of prism steps (8) are formed on an incidence surface of the lens comprising a plate-shaped part (5a) and a curved part (5b), characterized in that the prism steps (8) are arranged substantially at regular intervals along a first radial line located in the plate-like part (5a) of the lens, and at irregular intervals along a second radial line located in the curved part (5b) of the lens.