EP3314312A1

EP3314312A1 - Optical mirror assembly for a head-up display and production method thereof

Info

Publication number: EP3314312A1
Application number: EP15751076.9A
Authority: EP
Inventors: Álvaro Miguel DO CÉU GRAMAXO OLIVEIRA SAMPAIO; António José VILELA PONTES; Nuno Antonino FERREIRA PINTO; José António AZEVEDO GONÇALVES; Vítor Manuel QUEIRÓS PAIS
Original assignee: Universidade do Minho; Bosch Car Multimedia Portugal SA
Current assignee: Universidade do Minho; Bosch Car Multimedia Portugal SA
Priority date: 2015-06-29
Filing date: 2015-06-29
Publication date: 2018-05-02
Also published as: WO2017001889A1

Abstract

Optical mirror assembly for a head-up display comprising a moulded mirror (2) having a front- and a back-surface, wherein the front-surface is metalized (with e.g. aluminium) and a plurality of moulded members (5-7) laser-welded to the back-surface for supporting and rotating said optical mirror assembly. The moulded members can be two rotational bearings (5, 6) or couplings (e.g. poka-yoke), a motor- and a spring-support (7). The moulded mirror (2) can be made of a thermoplastic material that is transparent to the laser-wavelength used for welding and the moulded members (5-7) made of a thermoplastic material that is not transparent to this laser-wavelength.

Description

D E S C R I P T I O N

OPTICAL MIRROR ASSEMBLY FOR A HEAD-UP DISPLAY AND

PRODUCTION METHOD THEREOF

Technical field

[0001] The present disclosure relates to a head-up display (HUD) system and respective reflective mirror and support part, and production method thereof.

Background Art

[0002] In recent years, the automobile industries have been implementing lean production concepts. In this sense, companies have been optimizing production processes, by reducing the cycle time, number of tasks, transport times and design optimizations. This last case (i.e., design optimizations) emerges as a strategy to overcome assembly processes, since components can be developed in order to avoid assembly tasks or to minimize those tasks (e.g., in terms of time, efficiency, non-error- prone).

[0003] To achieve assembly process optimization, reducing errors and the so-called dead-times, various technologies have been implemented over the last few years. One paradigmatic case is the use of laser welding for polymers that only recently, has been applied to industrial processes. It is well know that bonding of polymers mostly requires surface pre-treatment and the need to use organic solvents. Hot plate or hot air welding is cost-efficient, but slow and subject to wear. A large surface of the component is heated up what is disadvantageous for sensitive components. Friction, ultrasonic or vibration welding expose components to high mechanical load and therefore require a complex design and regular maintenance of the machines. Laser polymer welding, however, means low thermal and mechanical load to the component, being a clean procedure (no particles nor solvents are used) and highly flexible.

[0004] To perform the task mentioned exist on the market different types of laser, the most common are diode lasers and Nd:YAG. What differs between this two types is the wavelength emitted by the respective laser beams, 980nm for the diode's case and 1060 nm in the case of Nd:YAG, nevertheless, for both cases the laser beam emitted is transparent to most polymers. In terms of welding this behaviour can become an advantage, since it allows for the welding to become invisible in the welded components. To achieve the perfect welding result it is necessary to overlap a material, transparent to the laser bean and, a material with the ability to absorb the laser beam. In order for a polymeric material to absorb the laser beam, additives are typically used (e.g., carbon black).

[0005] Therefore the use of laser welding as a production process can lead to optimization of the assembly process, nevertheless, it is needed to make some design considerations at the development phase, in order to be able to use such a technology. So, design optimizations in terms of assembling components with laser welding technology is mandatory, but this optimization is obviously more demanding in complex systems such has head-up display (HUD).

[0006] HUD systems have come into use in the automotive sector, as information requested by a driver for driving increases and is more diversified. HUD systems display critical information as a reflected image in the immediate viewing area of the driver, so that drivers do not need to take their eyes from the road to read the information since the information is deliver in a superimposed manner.

[0007] In such an HUD system, a display unit is provided inside an instrument panel of the vehicle, and at least one reflector, such as magnifying mirror, reflects the light of image-forming containing information, from the display unit onto a projection surface, such as a windshield or a combiner. In HUD systems (i.e., Combiner HUD, augmented reality HUD, windshield HUD), reflection mirrors play a central role, since they are responsible for image projection. Projection image can be done by several types of mirrors (e.g., flat, concave, aspherical) depending on the scope for the inclusion of the mirror in the HUD.

[0008] The inclusion of reflective elements on HUD systems assumes: (i) several elements, such as, the mirror (US539403A, US7532175B2, US6809872B2, US8885260B2) and, a panel (US539403A), and/or a mirror holder (US539403A, US7532175B2, US8885260B2), and/or pins (US6809872B2), and (ii) distinct configurations, such as, assembling a panel to a mirror by a ball and socket arrangement and a cam (US539403A), or assembling a mirror holder with a rotational shaft and a mounting part for the motor gear (US7532175B2), or a mirror is connected to a pair of pins and is mounted in a rotational axis (US6809872B2), or a mirror a mirror holder, a base plate and a step motor are assembled (US8885260B2).

[0009] Therefore, independently of the configuration, a mirror assembly is adopted before being mounted in the HUD housing. Being applied in the mirror some features that differ in terms of mechanical design, customer specifications and type of mirror. This assembly imposes a complex production process with different assembly methods and many tasks that raise the possibility for errors and production costs.

[0010] These facts are disclosed in order to illustrate the technical problem addressed by the present disclosure.

General Description

[0011] One of the main goals of this disclosure is to present a new design concept of an aspherical optical element for HUD systems and the assembly process of the features on the reflective mirror, using laser welding technology.

[0012] The present disclosure describes a different approach to the assembly phase of several features into the reflective mirror, the fixation of these features is performed using a laser welding and the manufacturing of the different parts is by injection moulding. With this concept and the integration of all the technologies presented, the assembly process becomes simpler and controllable, reducing the risk of having optical elements with defects.

[0013] On HUD devices, a reflective mirror is often bounded to mirror features using glue or double faced adhesive, processes that contain some problems.

[0014] The double face adhesive could not compensate the dimensional tolerances between the mirror and the mirror support. Fixing a mirror on a support that has not absolutely the same shape of the mirror results in deformations of the mirror when it is fixed with tape. Using adhesive foam it is possible to compensate slight tolerances but the foam has a higher thickness tolerance, which has an influence on the mirror position. The adhesive strength reduces at high temperatures, the tape never cure/hardens, so there is always a risk that the mirror could present variations in is nominal position at high temperatures due to the flowing of the adhesive tape.

[0015] The glue unlike the double faced adhesive, cures and do not flow with the temperatures, nevertheless, is complicated to control on production and it is normally used in parts with added value, so the cost of rejection is very high.

[0016] On automobile industries there is a need to decrease components and also the size of those components, on HUD systems, this trend represents a high impact on future models, in these devices the optical element is the one which have the higher value and also the higher dimensions, this is due to the optical properties, therefore it is important that features could be develop in order to achieve the optimum size and make all system smaller.

[0017] Therefore, one of the main challenges of the proposed disclosure is to present an aspherical mirror solution, that integrates, two bearings for the rotational axis (that enables adjustments in the mirror so that the reflected light could be adjust towards the eye points of the drivers), a motor support (used to accomplish the adjustments needed) and a spring support (used in order to prevent tilting forces) taking into account that these features are assembled, in a precise position, in the back of the mirror reflector by laser welding. [0018] With this disclosure it is possible to ensure that the optical element is designed and manufactured in the most desirable and compact way, since features instead of being assembled on the borders of the mirror are on the back of the mirror, decreasing the overall size and enabling the reflective mirror to assume the maximum size permitted by the housing, leaving at the same time the entire front face to be metallized in aluminium. The production of the reflective mirror and the features are based on an injection moulding tool with a thermoplastic material. For the features case a thermoplastic material with an additive is preferably used.

[0019] The correct assembly of the features on the back of the reflective mirror is through different "poka-yoke" designs, which enables the precise alignment and position of the features and the use of laser welding technology.

[0020] The method of bonding the features is made through the process of laser welding, this enables the possibility of having more accurate control and more precision, decreasing the risk of defecting the optical element.

[0021] It is described an optical mirror assembly for a head-up display, comprising a moulded mirror part having a front surface and a back surface, wherein the front surface has been metalized for being a mirror surface,

and said assembly further comprising, laser-welded to the back surface of the mirror part, a plurality of moulded members for supporting and rotating the assembly.

[0022] In an embodiment, said members are two rotational axis bearings, a motor support and a spring support.

[0023] In an embodiment, said members comprise couplings for coupling to the back surface and said back surface comprises couplings for receiving the couplings of said members,

wherein all said couplings are shaped such that each member can be coupled to one, and only one, coupling of the back surface.

[0024] In an embodiment, said couplings are poka-yoke couplings. [0025] In an embodiment, each said back surface coupling is shaped as an embossment and each said member coupling is shaped as a recess for receiving the embossment of a back surface coupling.

[0026] In an alternative embodiment, each said member coupling is shaped as an embossment and each said back surface coupling is shaped as a recess for receiving the embossment of a member coupling.

[0027] In an embodiment, the front surface is metalized with aluminium.

[0028] In an embodiment, the mirror part is of a thermoplastic material transparent to a laser wavelength, and said members are of a thermoplastic material not transparent to said laser wavelength.

[0029] In an embodiment, said members are of the same thermoplastic material of the mirror part further comprising an additive for absorbing a laser wavelength.

[0030] In an embodiment, the mirror part is of Polyetherimide, PEL

[0031] In an embodiment, said members are of PEI with an additive for absorbing a laser wavelength that is not absorbed by PEI.

[0032] It is also described a head-up display comprising the optical mirror assembly according to any one of the described embodiments.

[0033] In an embodiment, the head-up display is an automotive head-up display.

[0034] It is also described an automotive mirror part set comprising the optical mirror assembly according to any one of described embodiments.

[0035] It is also described a method for manufacturing an optical mirror assembly for a head-up display, said method comprising the steps of:

injection-moulding a mirror part having a front surface and a back surface;

laser-welding to the back surface of the mirror part, a plurality of injection-moulded members for supporting and rotating the assembly;

metalizing the front surface such as to be a mirror surface. [0036] In an embodiment, the mirror part is of a thermoplastic material transparent to a laser wavelength, and

said members are of a thermoplastic material not transparent to said laser wavelength,

wherein the laser is applied through the mirror part for laser-welding said members to the back surface of the mirror part.

Brief Description of the Drawings

[0037] The following figures provide preferred embodiments for illustrating the description and should not be seen as limiting the scope of invention.

[0038] Figure 1: Schematic representation of an optical element:

(1) represents an optical element,

(2) represents a reflective mirror,

(3) represents a rotational axis,

(4) represents a motor and spring support.

[0039] Figure 2: Schematic representation of a different "poka-yoke" configurations:

(5) represents the right bearing,

(6) represents the left bearing,

(7) represents the rotational axis the motor and spring support.

[0040] Figure 3: Schematic representation of different configurations in the reflective mirror.

[0041] Figure 4: Schematic representation of the Assembly section view of feature 3.

[0042] Figure 5: Schematic representation of the mould core of the reflective mirror:

(8) represents a mould core,

(9) represents a reflective mirror, with film/flash gate,

(10) represents a ejector pin marks,

[0043] Figure 6: Schematic representation of the mould core of the features:

(11) represents a mould core of the features, with three mould core movements, (12) represents the movement for the bearings,

(13) represents the two movements for the motor and spring support.

[0044] Figure 7: Schematic representation of the robot with a laser:

(14) represents a robot,

(15) represents a laser head,

(16) represents a support for the laser.

[0045] Figure 8: Schematic representation of the assembly process of feature 3 by laser welding, wherein (17) represents a laser bean, and (18) represents the border (18) of the feature.

[0046] Figure 9: Schematic representation of the production and assembly process flow.

Detailed Description

[0047] In an embodiment, Figure 1 represents the optical element (1) that includes the reflective mirror (2), two bearings for the rotational axis (3), and the motor and spring support (4). In order to establish the correct positioning of the several features on the reflective mirror it was designed three different poka-yoke. From figure 2 it is possible to see the different configurations that were used according to an embodiment for the correct and fast positioning of the features on 2. The different configurations were design in a bas-relief in the features, "square" for the right bearing (5), "triangular" for the left bearing (6) and, "rectangular" for the motor and spring support (7), according to this embodiment. In 2 the same configurations are embossed (figure 3). A detailed view of the assembly can be seen in figure 4 for the case of feature 3.

[0048] In an embodiment, the optical element is produced using two injection- moulding (IM) tools. One injection moulding produces the reflective mirror and uses a thermoplastic material, for example Polyetherimide (PEI). Figure 5 shows the mould core (8) of the reflective mirror, with film/flash gate (9), ejector pin marks (10) and the several configurations for the features positioning (5,6,7). [0049] To produce the features (3,4) another IM tool is needed and it is used a thermoplastic material with additives, for example Polyetherimide (PEI). Figure 6 shows the mould core (11) of the features, with three mould core movements. One movement for the bearings (12), and two movements (13) for the motor and spring support. This was needed, since the parts have some undercuts.

[0050] After producing the several parts of the optical element the process of assembling the features on the reflective mirror is through the process of laser welding.

[0051] Due to the high number of possibilities of robots which can be used on laser welding, and therefore on this disclosure, the figures have the objective to illustrate the tools, which can be used to allow the construction of functional laser system. Figure 7, shows a robot (14) with a laser head (15), and the support for the laser (16).

[0052] In order to assemble the different features, by laser welding, it is necessary to use a material transparent to the laser and a material with capacity to absorb the laser. As stated, this last material should have an additive component, in this way it allows the energy of the laser bean (17) to be a bsorbed and melted, due to the conduction process of heat the welding on this process is made locally between the border (18) of the feature (3) that contains configuration 5 and the non reflective area of the optical part (2)(Figure 8). This process is repeated for all the features.

[0053] The production and assembly of the different components are made in an embodiment according to the diagram of figure 9.

[0054] The process of manufacturing the optical element is made in two different tasks, the first one is responsible for injection moulding the different components (mould 1, for the reflective mirror; mould 2, for all the features), and after a stage time, to enable the components to stabilize, these are bonded using laser welding technology, after this process the part is ready to be metallized in aluminium and then mounted on a HUD device.

[0055] The systems of head up displays and augmented reality are starting to become largely used on the automotive field, normally this system uses two or more mirrors for projecting the information to the driver, this optical elements are very sensitive and any imperfection on the manufacturing phase or assembly phase will cause bad functionality and consequently distortion on the image. Therefore, the present disclosure allows the possibility to obtain the optical element, which fulfils all the requirements simplifying the assembly process and consequently the cost of the whole systems.

[0056] As described before, this type of assembly can be used in any system which uses reflective mirrors as a mean to project the information related to the process of driven an automobile, this optical element is capable to be used on other optical systems, not restricted to the use on the automotive field only.

[0057] The term "comprising" whenever used in this document is intended to indicate the presence of stated features, integers, steps, components, but not to preclude the presence or addition of one or more other features, integers, steps, components or groups thereof.

[0058] Flow diagrams of particular embodiments of the presently disclosed methods are depicted in figures. The flow diagrams do not depict any particular means, rather the flow diagrams illustrate the functional information one of ordinary skill in the art requires to perform said methods required in accordance with the present disclosure.

[0059] It will be appreciated by those of ordinary skill in the art that unless otherwise indicated herein, the particular sequence of steps described is illustrative only and can be varied without departing from the disclosure. Thus, unless otherwise stated the steps described are so unordered meaning that, when possible, the steps can be performed in any convenient or desirable order.

[0060] The disclosure should not be seen in any way restricted to the embodiments described and a person with ordinary skill in the art will foresee many possibilities to modifications thereof.

[0061] The above described embodiments are combinable.

[0062] The following claims further set out particular embodiments of the disclosure.

Claims

C L A I M S

1. Optical mirror assembly for a head-up display, comprising a moulded mirror part having a front surface and a back surface, wherein the front surface has been metalized for being a mirror surface,

2. Optical mirror assembly according to the previous claim wherein said members are two rotational axis bearings, a motor support and a spring support.

3. Optical mirror assembly according to any of the previous claims wherein said members comprise couplings for coupling to the back surface and said back surface comprises couplings for receiving the couplings of said members, wherein all said couplings are shaped such that each member can be coupled to one, and only one, coupling of the back surface.

4. Optical mirror assembly according to the previous claim wherein said couplings are poka-yoke couplings.

5. Optical mirror assembly according to claim 3 wherein each said back surface coupling is shaped as an embossment and each said member coupling is shaped as a recess for receiving the embossment of a back surface coupling.

6. Optical mirror assembly according to claim 3 wherein each said member coupling is shaped as an embossment and each said back surface coupling is shaped as a recess for receiving the embossment of a member coupling.

7. Optical mirror assembly according to any of the previous claims wherein the front surface has been metalized with aluminium.

8. Optical mirror assembly according to any of the previous claims,

wherein the mirror part is of a thermoplastic material transparent to a laser wavelength, and

said members are of a thermoplastic material not transparent to said laser wavelength.

9. Optical mirror assembly according to the previous claim wherein said members are of the same thermoplastic material of the mirror part further comprising an additive for absorbing a laser wavelength.

10. Optical mirror assembly according to any of the previous claims wherein the mirror part is of Polyetherimide, PEL

11. Optical mirror assembly according to the previous claim wherein said members are of PEI with an additive for absorbing a laser wavelength that is not absorbed by PEL

12. Head-up display comprising the optical mirror assembly according to any one of the previous claims.

13. Head-up display according to the previous claim wherein the head-up display is an automotive head-up display.

14. Automotive mirror part set comprising the optical mirror assembly according to any one of the claims 1 - 11.

15. Method for manufacturing an optical mirror assembly for a head-up display, said method comprising the steps of:

injection-moulding a mirror part having a front surface and a back surface;

laser-welding to the back surface of the mirror part, a plurality of injection- moulded members for supporting and rotating the assembly;

metalizing the front surface such as to be a mirror surface.

16. Method according to the previous claim wherein said members are two rotational axis bearings, a motor support and a spring support.

17. Method according to any of the claims 15 - 16 which comprises, before laser- welding said members, coupling said members to the back surface of the mirror part, wherein said members comprise couplings for coupling to the back surface and said back surface comprises couplings for receiving the couplings of said members,

18. Method according to the previous claim wherein said couplings are poka-yoke couplings.

19. Method according to claim 17 wherein each said back surface coupling is shaped as an embossment and each said member coupling is shaped as a recess for receiving the embossment of a back surface coupling.

20. Method according to claim 17 wherein each said member coupling is shaped as an embossment and each said back surface coupling is shaped as a recess for receiving the embossment of a member coupling.

21. Method according to any of the claims 15 - 20 wherein the metalizing the front surface is with aluminium.

22. Method according to any of the claims 15 - 21, wherein the mirror part is of a thermoplastic material transparent to a laser wavelength, and

23. Method according to the previous claim wherein said members are of the same thermoplastic material of the mirror part further comprising an additive for absorbing a laser wavelength.

24. Method according to claim 22 wherein the mirror part is of Polyetherimide, PEI.

25. Method according to the previous claim wherein said members are of PEI with an additive for absorbing a laser wavelength that is not absorbed by PEI.

26. Head-up display comprising the optical mirror assembly obtainable by the method according to any one of the claims 15 - 25.

27. Head-up display according to the previous claim wherein the head-up display is an automotive head-up display.

28. Automotive mirror part set comprising the optical mirror assembly obtainable by the method according to any one of the claims 15 - 25.