Patent Description:
The document <CIT> discloses a method for positioning and bonding components of a high precision optical system or the like. Two components can be positioned relative to each other and adhesively bonded together without any displacement resulting from contraction of the adhesive by forming on the first component an annular protrusion having its center at a point to be aligned. On the second component is formed an annular groove having its center at a corresponding point to be aligned. The width of the groove is significantly larger than the width of the protrusion. The protrusion is aligned within the groove and then adhesive is poured into the gaps between the protrusion and the sides of the groove.

The document <CIT> discloses an image forming apparatus with a lens mounting device for an optical housing comprising a base, a lens bonding member provided on the base, an adhesive layer of a defined thickness applied to the lens bonding member, and a scanning lens mounted on the lens bonding member through the adhesive layer. The lens mounting device prevents the lens from being affected by fluctuations in an ambient temperature around the optical housing.

Precise adjustment of light sources and optical components, e.g. lenses, reflectors or optical waveguides, relative to each other is a key challenge in assembling lighting devices of motor vehicles. During mounting of the light source group and/or related optical components on a carrier of the lighting device, e.g. a platform or a holding frame, their relative positions are varied by a manipulator while the light source is operated and the resulting lighting effect is monitored. The target position of the components is then finally defined by the constitution of a desired target lighting effect. The fixation of the components in this target position is usually established by adhesive joints, especially between pin members of the first component and associated cavities of the carrier.

A major issue concerning such adhesive joints is the effect of volumetric shrinkage of the adhesive during curing, caused e.g. by the evaporation of a solvent or by a crosslinking reaction. This shrinkage effect yields a subsequent alteration of the adjusted position of the light source or optical component and therefore a potentially critical deterioration of the lighting effect generated by the lighting device.

In an exemplary process, a cavity of the carrier is filled with a flowable adhesive and the optical component is held and positioned by a manipulator so that a pin member of the optical component at least partially extends into the cavity and the adhesive. During the following fine adjustment of the optical component relative to an operating light source, the displacements of the pin remain confined to the cavity, e.g. the cavity exhibits a depth of <NUM>, the pin exhibits a length of > <NUM> and the displacement range of the pin in a vertical direction, i.e. along its longitudinal axis, during the fine adjustment amounts to about <NUM>. The shrinkage of a conventional ultraviolet(UV)-light curable adhesive then typically yields an undesired subsidence of the pin during curing on the order of <NUM> in the vertical direction.

In the context of a lighting device for a motor vehicle, such shifts along the vertical axis are most disadvantageous, because they strongly affect the position of the light cut-off line projected onto the road, which represents a key performance criterion of the lighting device subject to strict regulations and customer specifications.

The document <CIT> teaches a method for glueing two workpieces with an adhesive, wherein after adjustment of the workpieces connecting parts wetted with a fixing glue are placed against appropriate surfaces, so that the connecting parts are in contact with both workpieces and support the workpieces during curing of the adhesive.

It is an object of the present invention to provide a method of joining a pin member of a first component to a second component with a cavity by means of an adhesive in order to fasten the pin in a target position extending at least partially into the cavity with a distance between the bottom surface of the cavity and the facing end of the pin, wherein the method especially comprises measures to prevent the pin from repositioning towards the bottom surface of the cavity during curing of the adhesive.

This object is achieved by a method as taught by claim <NUM> of the present invention. Advantageous embodiments of the invention are defined in the subclaims.

The invention discloses the technical teaching that the method of joining comprises at least the following steps:.

The core of the invention lies in the use of a spacer filling the space between the bottom surface of the cavity and the facing end of the pin, thus eliminating basically any adhesive from the volume below the pin. The joint between the pin and the second component is constituted by the adhesive surrounding the circumferential surface of the pin. The shrinkage of the adhesive during curing therefore can only affect the horizontal position of the pin, which is much less critical regarding the aforementioned use in a lighting device, but the spacer prevents the pin from any repositioning towards the bottom surface of the cavity.

It is an essential feature of the invention to use a spacer of dedicated flexibility, i.e. the spacer can be deformed by the pin without significant resistance during the positioning of the pin to the target position. Such deformation is preferably of elastic nature, so that the deformed spacer remains in proper contact to the pin during any pin displacement in the fine adjustment process.

In opposite to the prior art of the <CIT> the present invention thus allows to execute the fine adjustment of the components to join with the spacer already in place, so that after completed adjustment to the target position the adhesive can immediately be cured.

As a preferred embodiment of the invention the first component is chosen from a light source group or from an optical component associated with a light source and the second component is chosen from a carrier, wherein during positioning the pin inside the cavity the light source is operated and a resulting lighting effect is monitored in order to locate the target position by the constitution of a target lighting effect. The invention was motivated by this application and yields a major benefit over prior art joining methods in this context.

Advantageously, the flexible spacer is formed by a slice of a polymeric foam or by a mechanical spring element or by a slice of cured adhesive. Polymeric foams can be formed from a large number of different polymers, e.g. (poly)ethylene-vinyl acetate ((P)EVA), low-density polyethylene (LDPE), nitrile rubber (NBR), polychloroprene, polyimide, polypropylene (PP), polystyrene (PS), polyurethane (PU), polyvinyl chloride (PVC), silicone, or microcellular foam. Polymeric foams thus offer a large variety of mechanical properties and a dedicated type can be chosen based on the appropriate flexibility for the application as the spacer. Alternatively, an adhesive with suitable flexibility in the cured state, e.g. a type used for sealings, can be used to form the spacer, which is convenient in practise since the equipment to dose adhesive into the cavity is in place anyway.

Advantageously, the thickness of the flexible spacer exceeds the distance between the bottom surface of the cavity and the facing end of the pin in the target position by <NUM>% - <NUM>%, so that during positioning the pin to the target position the pin is pushed into the flexible spacer and the flexible spacer deforms accordingly. A significant deformation of the flexible spacer by the pin yields a robust contact between spacer and pin and an effective embracing of the end of the pin, so that the pin is less prone to horizontal displacements by shrinkage of the curing adhesive. The use of a flexible spacer of the aforementioned dimensions thus stabilizes the pin in the target position against both vertical and horizontal shifts.

Advantageously, the adhesive used for the joint between the pin and the cavity and/or the adhesive used to form the flexible spacer are chosen from an UV-light curing type. These adhesives allow for a fast and technically simple curing process compared to the use of heat-curable adhesives.

According to another preferred embodiment of the invention the first component is chosen from a light source group or from an optical component of a lighting device of a motor vehicle and the second component is chosen from a carrier of the lighting device. The optical component is for instance represented by a reflector, which is mounted on a mounting platform and adjusted to a target position relative to a fixed light source of a vehicle head light.

Furthermore, the invention concerns a joint assembly at least comprising a first component with a pin member and a second component with a cavity, wherein the pin extends at least partially into the cavity and a joint between the pin and the second component is formed by an adhesive inside the cavity, characterised in that a flexible spacer is positioned between the bottom surface of the cavity and the facing end of the pin.

Such joint assembly is advantageously established by the inventive joining method and in a preferred embodiment the pin is pushed into the flexible spacer and the flexible spacer is deformed accordingly.

Additional details, characteristics and advantages of the object of the invention are disclosed in the following description of the respective figures - which in an exemplary fashion - shows preferred embodiments of the joining method and the joint assembly according to the invention.

The Figures show schematic illustrations of the four steps <NUM>, <NUM>, <NUM>, <NUM> of the inventive method to yield an embodiment of the inventive joint assembly <NUM>, depicted in cross-sectional representation. The pin <NUM> is a member of a first component 1a, for instance an optical component to be positioned most accurately relative to a light source of a lighting device of a motor vehicle, and the second component 2a exhibits a cavity <NUM> to receive the pin <NUM>. In the depicted example, the pin <NUM> is formed by a cone with a flat end <NUM> and the cavity <NUM> exhibits a cylindrical volume, whereat matching pin-cavity combinations of differing shapes can be equally appropriate for the invention on hand.

<FIG> shows the pin <NUM> in the target position extending partially into the cavity <NUM> with the distance D between the bottom surface <NUM> of the cavity <NUM> and the facing end <NUM> of the pin <NUM>. It is the central task of the present invention to fasten the pin <NUM> in this target position inside the cavity <NUM> by means of a bonding process based on an adhesive, wherein during the curing of the adhesive the distance between the bottom surface <NUM> and the end <NUM> remains right at its target value D.

<FIG> illustrates the first step of the inventive method, namely positioning <NUM> the flexible spacer <NUM> on the bottom surface <NUM> of the cavity <NUM>, wherein the thickness <NUM> of the spacer <NUM> exceeds the distance D below the pin <NUM> in the target position. The pin <NUM> is actually removed from the cavity <NUM> at this stage of the process and it is only indicated here by the dotted contour to illustrate the difference between spacer thickness <NUM> and target distance D. The thickness <NUM> of the spacer <NUM> surpasses the target distance D by about <NUM>% in the depicted example. The spacer <NUM> is preferably formed by a slice of a polymeric foam <NUM> with tailored mechanical properties, i.e. a dedicated flexibility.

<FIG> illustrates the second step of the inventive method, namely filling <NUM> the adhesive <NUM> into the cavity <NUM> onto the flexible spacer <NUM>. The pourable adhesive <NUM> preferably consists of an UV-light curable resin if the cavity <NUM> is sufficiently accessible for illumination, or alternatively a heat-curable type of adhesive is deployed. The microstructure of the polymeric foam <NUM> of the flexible spacer <NUM> preferably cannot be penetrated by the adhesive <NUM>.

<FIG> illustrates the third step of the inventive method, namely positioning <NUM> the pin <NUM> to the target position. To this end, the bottom section of the pin <NUM> is dipped into the flowable adhesive <NUM> and pushed into the flexible spacer <NUM>, which deforms accordingly. In the context of an application of the inventive method in the assembly process of a vehicle lighting device, wherein the pin <NUM> for instance is a member of a reflector to be arranged relative to a light source and the second component 2a is represented by a mounting platform, the light source is operated during positioning <NUM> the pin <NUM> and the resulting lighting effect is monitored in order to locate the target position by the constitution of a target lighting effect. The flexibility of the polymeric foam <NUM> of the spacer <NUM> must be appropriate to allow for an unhampered fine adjustment of the pin <NUM> to the target position. The related deformation of the flexible spacer <NUM> lies preferably in the elastic regime, so that a significant contact area between the pin <NUM> and the spacer <NUM> is preserved during the fine adjustment in positioning <NUM> the pin <NUM> to the target position.

<FIG> illustrates the inventive joint assembly <NUM> and the fourth step of the inventive method, namely curing <NUM> the adhesive <NUM> and obtaining a joint between the pin <NUM> and the second component 2a. To this end, the adhesive <NUM> is irradiated by UV-light <NUM>, which typically yields a crosslinking reaction within the adhesive <NUM> and a related hardening effect. The adhesive joint is established between the circumferential sections of the pin <NUM> and the cavity <NUM> inside the component 2a. The volume of the cavity <NUM> below the pin <NUM> is filled by the deformed flexible spacer <NUM> and thus basically free of any adhesive <NUM>. This represents the key innovation of the present invention, because in such an assembly, the shrinkage of the adhesive <NUM> during curing <NUM> does not affect the vertical position of the pin <NUM>, so that the end of the pin <NUM> remains unaltered at the target distance D above the bottom surface of the cavity <NUM>. Furthermore, the significant penetration depth of the pin <NUM> into the flexible spacer <NUM> due to the difference between the thickness <NUM> of the undeformed spacer <NUM> and the target distance D results in a rather robust fixation of the pin1 during curing <NUM> also in the horizontal plane.

Therefore, the inventive method of joining enables to build a highly precise joint assembly <NUM> of an optical component 1a in a carrier 2a relative to the light source as parts of a vehicle lighting device.

Claim 1:
Method of joining a pin (<NUM>) member of a first component (1a) to a second component (2a) with a cavity (<NUM>) by means of an adhesive (<NUM>) in order to fasten the pin (<NUM>) in a target position extending at least partially into the cavity (<NUM>) with a distance (D) between the bottom surface (<NUM>) of the cavity (<NUM>) and the facing end (<NUM>) of the pin (<NUM>), characterised in that the method comprises at least the following steps:
- positioning (<NUM>) a flexible spacer (<NUM>) on the bottom surface (<NUM>) of the cavity (<NUM>), wherein the thickness (<NUM>) of the spacer (<NUM>) equals or exceeds the distance (D) between the bottom surface (<NUM>) of the cavity (<NUM>) and the facing end (<NUM>) of the pin (<NUM>) in the target position,
- filling (<NUM>) the adhesive (<NUM>) into the cavity (<NUM>) onto the flexible spacer (<NUM>),
- positioning (<NUM>) the pin (<NUM>) to the target position,
- curing (<NUM>) the adhesive (<NUM>) and obtaining a joint between the pin (<NUM>) and the second component (2a).