JP2009258020A - Display device and light guide used for the same - Google Patents

Abstract

By using an inexpensive light guide that enables efficient use of the amount of light from a light source as illumination, the occurrence of light emission brightness spots on the dial is suppressed, and visibility is improved with high brightness light emission. An excellent and inexpensive display device is provided.
Light from a light source is incident on a light guide plate having an arc shape in a plan view in a light guide disposed on the back side of the dial. The incident light is reflected toward the dial 3 by the reflecting surfaces 21A of the plurality of light reflecting grooves 21 formed radially from the center position of the light guide plate 5. At this time, since the light guide plate 5 is made of an inexpensive plastic material having a refractive index of 1.49 or more, high-luminance light emission having excellent illumination efficiency is generated while being an inexpensive material. The reflected light illuminates and transmits the scale portion 15 and the number portion 17 of the dial 3.
[Selection] Figure 1

Description

  The present invention relates to a display device and a light guide used in the display device, and more particularly to a display device for a vehicle such as a meter such as a speedometer and a tachometer, and a light guide applied to the display device as a lighting device.

  In general, scales, numbers, and the like of display devices used for instruments such as a speedometer for vehicles are arranged on an arc on the outer peripheral side of the dial along the rotational movement of the pointer. The scales, numbers, and the like are transmitted and illuminated by a plurality of light sources arranged in an arc shape immediately below the scales, numbers, and the like. However, in such a configuration, a large number of light sources are required to reduce unevenness in the light emission luminance of the dial, and power consumption and cost increase.

  Therefore, in order to transmit and illuminate with a small number of light sources with uniform brightness, a light guide plate made of a translucent material is disposed on the back side of the dial, and light from the light source is incident on the light guide plate, and the light guide plate makes the characters A technique for transmitting through a board is known. In this case, by adjusting the shape of the light guide plate, it is possible to reduce unevenness in the light emission luminance of the dial.

For example, in Patent Document 1, a plurality of light propagation reflecting surfaces are formed on the outer peripheral side surface of a light guide having an arc shape in plan view, and the plurality of light propagation reflecting surfaces are arranged at both ends of the light guide. By reflecting light from the light-emitting diodes that are the two light sources, the passage of the light trajectory in the light guide is expanded to emit light almost all over the surface of the light guide, and the light emission brightness spots on the dial are reduced. A reduced display device is disclosed. Further, a textured surface is provided on the back surface (surface opposite to the dial) of the light guide for diffusing light by directing light toward the dial.
JP 2007-139791 A

  By the way, in the conventional display device disclosed in Patent Document 1, the light guide is only described as a translucent material, for example, a transparent acrylic resin or polycarbonate resin, and the specification of the characteristic value is not described at all. That is, it is described that any translucent material can be used, but this is not the case.

  For example, a plastic material has a characteristic value called a refractive index, and at least a certain refractive index is required to function as a light guide with high luminance light emission. In addition, plastic materials are known to have a large change in the rate of precipitation depending on the type and degree of blending of antioxidants, stabilizers, colorants, etc. It is unclear whether it is a material with a chemical composition.

  Moreover, in patent document 1, the reflective surface for light propagation is provided in the outer peripheral side surface of a light guide, and the said light guide is irradiated by reflecting the light of a light emitting diode with the said light propagation reflective surface. It is. In other words, the reflecting surface is created by subjecting the light guide to external processing (machining). Therefore, although there is an explicit processing method, it does not limit a characteristic value such as a refractive index, nor does it explicitly indicate the type of material such as a thermoplastic resin or a thermosetting resin. That is, there is no particular material limitation.

  From the above, depending on the refractive index of the light guide and the type of plastic material, the illuminance decreases, and uneven brightness may occur in the light emitting region on the surface of the light guide. For this reason, the effect of reducing unevenness in the luminance of the dial is not sufficient.

  The present invention provides an inexpensive light guide that enables the light quantity of the light source to be used efficiently as illumination, suppresses the occurrence of light emission luminance spots on the dial by using this light guide, and An object of the present invention is to provide an inexpensive display device with high luminance emission and excellent visibility.

In order to solve the above-described problems, a display device according to the present invention includes a scale portion formed of a light-transmitting material, in which a plurality of scales are arranged in an arc shape, and a plurality of numbers are arc-shaped and concentric with the scale portion. A dial having numbers arranged thereon;
A translucent light guide plate that has a circular arc shape in plan view and is disposed on the back side of the dial so as to cover the scale portion and the numeric portion, and transmits light, and the arc shape of the light guide plate in the plan view Are formed radially from the center position of the arc in plan view on the light incident surface provided to enter light at one end in the circumferential direction of the light guide plate and the back surface opposite to the front surface of the light guide plate facing the dial. A light-reflecting groove having a substantially triangular cross-section having a reflecting surface that reflects the propagating light to the surface side of the light guide plate;
A light source arranged so that light can be incident on the light incident surface of the light guide plate,
The light guide plate is made of a plastic material having a refractive index of 1.49 or more.

  In the display device of the present invention, in the display device, the plastic material of the light guide plate is preferably a thermoplastic resin.

  Moreover, in the display device according to the present invention, in the display device, it is preferable that a reflection surface of each light reflecting groove is formed so as to cross the light guide plate in a width direction.

  In the display device of the present invention, in the display device, a light diffusing member that diffuses light emitted from the surface of the light guide plate is disposed on the surface of the light guide plate facing the dial. It is preferable.

The light guide of the present invention has a circular arc shape in plan view, and a light transmissive light guide plate that propagates light,
A light incident surface provided to allow light to be incident on one end of the light guide plate in a circular arc shape in plan view,
The light guide plate has a substantially triangular cross-section having a reflective surface that is provided on the back surface opposite to the front surface of the light guide plate in a radial manner from the center position of the arc shape in plan view and reflects the propagating light to the surface side of the light guide plate A light reflecting groove,
The light guide plate is made of a plastic material having a refractive index of 1.49 or more.

  Further, in the light guide according to the present invention, in the light guide, the plastic material of the light guide plate is preferably a thermoplastic resin.

  Further, in the light guide according to the present invention, in the light guide, it is preferable that a reflection surface of each light reflecting groove is formed so as to cross the light guide plate in a width direction.

  As will be understood from the means for solving the problems as described above, according to the display device of the present invention, it can be manufactured by simple processing, and the light emission luminance of the dial portion and the number portion of the dial face. And the visibility can be improved with high luminance light emission. In particular, by limiting the characteristic value of the refractive index as the material of the light guide plate, that is, by using an inexpensive plastic material having a refractive index of 1.49 or more, a display device that is much cheaper and excellent in illumination efficiency can be obtained. Can be provided.

  Further, according to the light guide of the present invention, it is possible to manufacture by simple processing, and when light from the light source is incident from the light incident surface at one end of the light guide plate, the refractive index is 1 as the material of the light guide plate. By using an inexpensive plastic material of .49 or more, the light quantity of the light source can be efficiently emitted with high luminance, and a light guide that is more inexpensive and excellent in illumination efficiency can be provided.

  Embodiments of the present invention will be described below with reference to the drawings.

  1 and 2, the display device 1 according to this embodiment includes a dial 3, a light guide 7 having a light guide plate 5, a light source 9, and, for example, a light diffusion member as a light diffusion member. A film 11 and a case 13 are provided. FIG. 1 shows an example in which the display device 1 of this embodiment is applied to an automobile speedometer.

  The dial 3 is composed of a thin plate made of a translucent material such as acrylic resin or polycarbonate resin. As shown in FIG. 1, the dial 3 is formed with a scale portion 15 in which a plurality of scales 15 </ b> A are arranged in an arc shape, and a plurality of numbers are arranged on the inner peripheral side of the scale portion 15. A numeral portion 17 is formed in which 17A is arcuate and arranged concentrically with the scale portion 15.

  The scale portion 15 and the number portion 17 are formed by printing or hot stamping the front surface or back surface of the dial 3. That is, while providing the colored layer which has translucency in parts other than the scale part 15 and the number part 17, measures, such as leaving the scale part 15 and the number part 17 transparent, or providing a translucent colored layer, etc. Is given.

  As the light guide 7, the light guide plate 5 that constitutes the main part is made of a light-transmitting plastic material that propagates light, and the thickness t is formed in a plate shape of, for example, about 1 mm to about 3 mm. As shown in FIGS. 1 and 2, the plan view shape is formed in an arc shape, and is arranged on the back side of the dial 3 so as to cover the scale portion 15 and the number portion 17.

  A light incident surface 19 for entering light emitted from the light source 9 is provided at one end of the light guide plate 5 in the circumferential direction of the circular arc shape in plan view.

  Generally, when a plastic material is irradiated with light, the light propagates using the plastic material as a medium. However, if there is a scratch or a defect on the surface of the plastic material, the propagated light is scattered (or reflected) at that location. It has been known. By utilizing this, the surface of the plastic material can be machined to scatter (or reflect) the propagated light.

  Therefore, as shown in FIGS. 3 and 4, the back surface 5 </ b> B, which is the surface opposite to the front surface 5 </ b> A facing the dial 3 of the light guide plate 5, has a plurality of portions over almost the entire area in the circumferential direction. The light reflecting grooves 21 are formed radially from the center position of the circular arc in plan view of the light guide plate 5 at predetermined angular intervals. The light reflecting groove 21 has a substantially triangular (or V-shaped) cross section and is formed so as to cross the light guide plate 5 in the width direction. The radial angle interval of the light reflecting groove 21 can be set to 2 °, for example. Alternatively, the angle interval can be set such that the pitch P of the light reflecting grooves 21 on the outer peripheral side of the arc of the light guide plate 5 in plan view is 4 mm.

  A reflective surface 21A that crosses the light guide plate 5 in the width direction is formed on one surface of the light reflecting groove 21. The reflection surface 21A is for reflecting the light traveling in the light guide plate 5 to the front surface 5A side, and is inclined at a predetermined inclination angle α with respect to the back surface 5B as shown in FIG. Is configured to do. By forming the reflecting surface 21A of the light reflecting groove 21 so as to cross the light guide plate 5 in the width direction, it is possible to reduce the occurrence of light emission luminance spots on the dial 3.

  Each of the reflection surfaces 21 </ b> A is formed so as to reflect light from the light source 9 toward the surface 5 </ b> A side of the light guide plate 5. For example, each light reflecting groove 21 is formed so as to face the light source 9 disposed on the left light incident surface 19 in FIG. 3 and to reflect the light from the light source 9 toward the surface 5A.

  If the inclination angle α of the reflecting surface 21A is too small, the inclination angle of the reflected light also increases, and the luminance of the dial 3 when the display device 1 is viewed from the front is lowered. If the inclination angle α is too large, the incident angle of light exceeds the critical angle and the proportion of light transmitted through the reflecting surface 21A increases, so that the light reflection efficiency decreases and the light use efficiency decreases. In order to suppress this decrease in the light utilization efficiency, a technique for increasing the light emission luminance by increasing the input power to the light source 9 is known. However, this method is not preferable because it causes an increase in power consumption and a decrease in the life of the light source 9.

  For this reason, the inclination angle α of the reflecting surface 21A is 45 ° or more and preferably 60 ° or less, more preferably 50 ° or more and 55 ° or less. By setting the inclination angle α in the above range, the light reflection efficiency can be increased and the light emission luminance of the dial 3 can be increased. In this embodiment, the inclination angle α of the reflecting surface 21A is, for example, 45 °.

  When the inclination angles α of the reflecting surfaces 21A are the same, if the heights γ (see FIG. 4) of all the light reflecting grooves 21 are the same, the reflected light in the light reflecting grooves 21 close to the light source 9 is reflected. In comparison, the brightness of the reflected light in the light reflecting groove 21 located far from the light source 9 tends to decrease.

  In this embodiment, as shown in FIG. 4, the light reflection groove 21 having a greater distance from the light source 9 is increased in height γ so that the amount of light reflected by each light reflection groove 21 is leveled. It is possible to make the luminance uniform. In short, by balancing the reduction in the amount of light as the distance from the light source 9 increases, and increasing the brightness of the reflected light by increasing the height γ stepwise as the distance from the light source 9 increases. The luminance in the range can be made uniform.

  The light source 9 is disposed so that light can be incident on the light incident surface 19 of the light guide plate 5, and can include one or a plurality of light emitting diodes, laser diodes, and the like. For example, the light source 9 is disposed so that light can be incident on the light incident surface 19 of the light guide plate 5, and can include one light emitting diode, a laser diode, or the like.

  The light diffusing film 11 is made of a resin that diffuses light or a film coated with the resin, and is formed in an annular shape or a circular arc shape when viewed from the top, is disposed on the surface 5A of the light guide plate 5, and extends from the surface 5A. Diffuses outgoing light.

  The case 13 stores and holds the above-described components.

  The speedometer is provided with a pointer pointing to the scale 15A of the dial 3, a movement for rotating the pointer, etc., but these portions are not directly related to the present invention, so illustration and description are omitted. Yes.

  Next, the plastic material of the light guide plate 5 will be described in detail.

  Irradiated light propagates using a plastic material as a medium, but it is known that a material having a high transparency and a material having a high refractive index transmit light efficiently because there is less light scattering in the medium.

  However, any translucent plastic material does not satisfy the function of high-intensity light emission, so it is cheap and has excellent illumination efficiency by providing restrictions based on the characteristic value using the refractive index and the material type. Efforts were made to satisfy the function of high brightness light emission.

  That is, in the light guide 7 described above, a plastic material having various refractive indexes is used as the light guide plate 5, and several investigation tests are performed, and the optimum plastic material for the light guide plate is inexpensive and excellent in illumination efficiency. Was selected.

  The above investigation test will be described in detail. Samples of the light guide 7 of Test Examples A to H were prepared, and an illuminance test was performed on each sample.

  The light guide 7 of Test Example D will be described as a representative example. As shown in FIG. 3, Test Example D is a light guide plate 5 made of commercially available polymethyl methacrylate (PMMA) having a thickness t of 3 mm. Was used. Polymethyl methacrylate has a sag rate of 1.49.

  A plurality of light reflecting grooves 21 were formed on the back surface 5B of the light guide plate 5 by a diamond cutting method. Each of the light reflecting groove portions 21 is a groove portion having a triangular cross section similar to that shown in FIG. 3 described above, and has a cutting angle with an inclination angle α of 45 ° and an angle θ of 90 °. Further, the cutting depth γ is 0.1 mm, and the cutting pitch P is 4 mm. For the cutting depth γ, the cutting tool push-in amount is gradually increased so as to gradually increase from the light incident surface 19 side of the light source 9 (the light receiving side of the light guide plate 5) toward the opposite side, The light guide plate 5 was cut radially from the center position of the arc in plan view.

  As the light guide body 7 of other test examples A to C and E to H, a sample having the same shape and size as the light guide body 7 of the test example D described above using some commercially available plastic materials. It was created.

  That is, the material of Sample A is polytetrafluoroethylene, and the segregation rate is 1.35. The material of Sample B is polytrifluoroethylene chloride, and the refractive index is 1.42. The material of Sample C is a vinyl acetate resin and has a refractive index of 1.46. The material of sample E is polyvinyl chloride, and the refractive index is 1.53. The material of Sample F is polystyrene = butadiene copolymer and has a refractive index of 1.56. The material of the sample G is polycarbonate and the refractive index is 1.59. The material of Sample H is an episulfide resin and has a refractive index of 1.70.

  With respect to the samples of the above test examples A to H, a bullet-type LED (manufactured by Toyoda Gosei Co., Ltd., model number; E1L33-AW0A-03, white, size; φ3) is used as the light source 9 to guide each sample. Light was incident from the light incident surface 19 (light receiving surface) of the body 7. An illuminance distribution (T-10M, manufactured by Konica Minolta Co., Ltd.) was used to investigate the illuminance distribution with 30 measurement points in the light guide 7 of each sample.

  The measurement results of the average illuminance in the samples of Test Examples A to H are as shown in the graph of FIG. In this graph, it is known that the so-called right-sided rise, and as is generally known, a material having a higher refractive index is better as a medium for propagating light. However, the samples D, E, F, G, and H of the test example have the average illuminance not significantly changed, whereas the samples A, B, and C have a relatively lower average illuminance. That is, in this test example, it is clearly shown that the illuminance with respect to the refractive index does not rise to the right with a simple constant gradient (that is, the gradient changes).

  From the above, it is preferable to use a plastic material having a refractive index of 1.49 or more as the light guide plate 5. This means that the lower limit of the refractive index has been clarified. The average illuminance of sample D is 2.7 lux, and the average illuminance of samples E, F, G, and H is slightly higher than 2.7 lux.

  The upper limit of the refractive index is not particularly limited. This is because, for example, H episulfide resin (refractive index: 1.70) is a material known as a plastic lens (optical lens), but is very expensive. Therefore, it can be determined that the episulfide resin is not preferable because it increases the cost for the use of the light guide plate 5. In short, it is possible to apply a material with a high refractive index in terms of satisfying the function of high-intensity light emission with excellent illumination efficiency, but there is a demerit that causes a high cost, so the manufacturer of the display device decides as appropriate It's just a design matter.

  Moreover, the manufacturing method of said light guide 7 is not specifically limited. For example, the light reflecting groove 21 can be formed on the light guide plate 5 by molding, diamond cutting, or cutting with a heating blade.

  All of the light reflecting grooves 21 of the samples A to H were formed by a cutting method. However, when mass production is assumed, it is expensive to cut and create the light reflecting grooves 21 one by one.

  Therefore, in general, a “die casting method” using a mold is known as a method for molding a plastic material at a low cost. This method is suitable for mass production and can be provided at low cost. However, this die casting method can be applied to “thermoplastic resins”, and it is theoretically difficult to apply “thermosetting resins”.

  Therefore, in this embodiment, it is preferable to use a thermoplastic resin plastic material for the light guide plate 5. In addition, it is preferable to create by die casting using a mold.

  In the display device 1 configured as described above, when power is supplied from the outside and the light source 9 emits light, the light incident on the light guide plate 5 from the light incident surface 19 is reflected on the front surface 5A, the back surface 5B, and The light guide plate 5 travels while being reflected from the side surface. As shown in FIG. 4, most of the light traveling through the light guide plate 5 and reaching the reflecting surface 21A of each of the plurality of light reflecting grooves 21 is reflected by the reflecting surface 21A. The light is emitted from the surface 5A side to the outside.

  At this time, since the light guide plate 5 is made of an inexpensive plastic material having a refractive index of 1.49 or more, high-luminance light emission having excellent illumination efficiency is generated despite being an inexpensive material.

  Further, the light reflected from the reflecting surface 21 </ b> A of each light reflecting groove 21 and emitted from the surface 5 </ b> A of the light guide plate 5 is diffused by the light diffusion film 11. The diffused light has a uniform luminance at the corresponding portion, and is transmitted and illuminated with uniform brightness to the scale portion 15 and the number portion 17 of the dial 3 and is displayed. Therefore, it is possible to suppress the occurrence of light emission luminance spots on the scale portion 15 and the number portion 17 of the dial 3 and to improve the visibility of the display device 1 with high luminance light emission.

  Note that the present invention is not limited to the above-described embodiment as it is, and can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. Various inventions can be formed by appropriately combining a plurality of constituent elements disclosed in the above embodiments. For example, some components may be deleted from all the components shown in the embodiment.

1 is a plan view of a display device according to an embodiment of the present invention. It is a disassembled perspective view of the display apparatus shown in FIG. It is a top view of the light guide of the display apparatus shown in FIG. FIG. 4 is a partially enlarged view showing a light reflection groove portion of the light guide plate as viewed in the direction of arrow IV in FIG. 3. It is a graph which shows the average illumination intensity in the sample of test example AH.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Display apparatus 3 Dial 5 Light guide plate 5A Front surface 5B Back surface 7 Light guide 9 Light source 11 Light diffusion film (light diffusion member)
13 Case 15 Scale 15A Scale 17 Number 17A Number 19 Light Incident Surface 21 Light Reflecting Groove 21A Reflective Surface

Claims (7)

A dial made of a translucent material, and having a scale portion in which a plurality of scales are arranged in an arc shape, and a number having a plurality of numbers arranged in an arc shape and concentrically with the scale portion,
A translucent light guide plate that has a circular arc shape in plan view and is disposed on the back side of the dial so as to cover the scale portion and the numeric portion, and transmits light, and the arc shape of the light guide plate in the plan view Are formed radially from the center position of the arc in plan view on the light incident surface provided to enter light at one end in the circumferential direction of the light guide plate and the back surface opposite to the front surface of the light guide plate facing the dial. A light-reflecting groove having a substantially triangular cross-section having a reflecting surface that reflects the propagating light to the surface side of the light guide plate;
A light source arranged so that light can be incident on the light incident surface of the light guide plate,
The display device, wherein the light guide plate is made of a plastic material having a refractive index of 1.49 or more.   The display device according to claim 1, wherein the plastic material of the light guide plate is a thermoplastic resin.   The display device according to claim 1, wherein a reflection surface of each of the light reflection grooves is formed so as to cross the light guide plate in a width direction.   The light diffusion member which diffuses the light radiate | emitted from the said surface of the said light-guide plate is arrange | positioned on the said surface facing the said dial of the said light-guide plate, The Claim 1, 2, or 3 characterized by the above-mentioned. Display device. A translucent light guide plate that propagates light in a circular arc shape in plan view;
A light incident surface provided to allow light to be incident on one end of the light guide plate in a circular arc shape in plan view,
The light guide plate has a substantially triangular cross-section having a reflective surface that is provided on the back surface opposite to the front surface of the light guide plate in a radial manner from the center position of the arc shape in plan view and reflects the propagating light to the surface side of the light guide plate A light reflecting groove,
The light guide plate is made of a plastic material having a refractive index of 1.49 or more.   6. The light guide according to claim 5, wherein the plastic material of the light guide plate is a thermoplastic resin.   The light guide according to claim 5 or 6, wherein a reflection surface of each of the light reflecting grooves is formed so as to cross the light guide plate in a width direction.

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