CH704113B1 - LCD device i.e. segment display device, for use in wrist watch, for displaying figural patterns, has prisms distributed in zones of light guide such that red and blue rays issued from upper face of light guide are concentrated on electrodes - Google Patents

Abstract

The device (12) has a light guide (54) in form of a plate comprising a set of prisms (64, 66) for deflecting red rays (Rr) and blue rays (Rb) toward a display face (28). A series (S1) of prisms is oriented toward a colored LED (50) for deflecting the red rays emitted by the LED, and another series (S2) of prisms is oriented toward another colored LED (52) for deflecting the blue rays emitted by the LED. The prisms are distributed in zones of the light guide located facing electrodes (40) such that the rays issued from an upper face of the light guide are concentrated on the electrodes. An independent claim is also included for a timepiece, comprising an LCD device.

Description

The present invention relates to a liquid crystal display device of the segment display type and a timepiece comprising this display device, including a wristwatch.

Such a type of display device, in which it is considered that the display face is oriented upwards, comprises in particular: A liquid crystal cell comprising at least one upper substrate and one lower substrate, at least two electrodes and at least one counter-electrode which are structured on the faces facing the two substrates, each electrode representing a figurative pattern or a portion of a figurative motif, A control unit which controls the liquid crystal cell by applying a determined value control voltage between a selected electrode and the counter-electrode so as to modify the orientation of the liquid crystals and cause the corresponding figurative patterns to be displayed, and A backlight module, arranged under the liquid crystal cell, on the side opposite to the display face, comprising at least a first and a second light source of different colors which emit light rays inside the at least one light guide.

This type of display device has the advantage of being cheap because the liquid crystal cell, said segment display, is simple and proven technology. It uses electrodes shaped character segments which allows the use of a simplified control electronics, the supply of each electrode or segment being controlled directly in all or nothing, and the counter-electrode, generally in the form of plate, being grounded. The control of such a liquid crystal cell therefore does not require scanning rows and columns as in a display of the matrix type which, in addition to simplifying the control electronics, promotes the readability of the display patterns.

[0004] Generally, segment-display liquid crystal cells are monochromic. The display segments appear for example in black, when placing a reflective film under the cell and feeding said segments to prevent the reflection of light towards the display face. The display segments may also appear in the color of the light source of the backlight module.

To increase the display possibilities and improve the aesthetic appearance, it has been proposed to make the multicolor display device using a backlight module comprising several light sources of different emission colors.

Such a type of display device is described in JP 3 217 818 A. In this document, it is intended to synchronize the display command segments, the character display command, and the command lighting of the light sources via a central control circuit so as to display each segment successively in one of the colors.

This solution is not completely satisfactory because it requires complicated control electronics to achieve synchronization. In addition, at any given time, all displayed segments are illuminated with the same color, or the same color mixture obtained by lighting multiple sources simultaneously.

The present invention aims to overcome the aforementioned drawbacks by providing a display device simpler to manufacture and easier to control. The present invention also aims to provide a display device having a better light output thus a better visibility of the reasons to display.

For this purpose, the invention proposes a display device of the type described above, characterized in that at least one face of the light guide is provided with prisms which deflect the light rays towards the display face, a first set of prisms facing the first light source to deflect the light rays from the first source and a second set of prisms facing the second light source to deflect the light rays from the second source, and in that the prisms are selectively distributed in the areas of the light guide which are located under the electrodes, so that the light rays emitted by the light sources are distributed and concentrated on the electrodes.

With the display device according to the invention, it is possible to produce an economical multicolor display device. Indeed, this display device has a backlight system with high light output since most of the light emitted by the light sources is used for lighting portions of patterns. The light energy is not lost to illuminate areas of the cell not used for display.

According to an advantageous embodiment, the first series of prisms is arranged under a first series of electrodes, and the second series of prisms is arranged under a second series of electrodes separate from the first. Thus, the control circuit of the backlight device can be very simple. Indeed, the color of the figurative motifs is determined by construction. It is therefore sufficient to simultaneously turn on all the light sources and the figurative patterns are displayed in the predefined colors.

According to another advantageous embodiment, at least one electrode corresponding to a multicolored figurative pattern is arranged above prisms belonging to the first and second series, so as to allow the selective display of the multicolored pattern. in; A first color corresponding to the prisms of the first series, when the first light source is on and the other is off, A second color corresponding to the prisms of the second series, when the second light source is on and the other is off, - a combination of colors when both light sources are lit simultaneously.

According to a first version of this embodiment, the prisms of the first and second series are interlaced under the electrode corresponding to the multicolored pattern so that the simultaneous ignition of the two light sources produces a new color corresponding to the superposition of the two initial colors.

According to a second version of this embodiment, the prisms of the first series and the prisms of the second series are grouped in separate areas, under the electrode corresponding to the multicolored pattern, to allow the display of the multicolored pattern. in several colored areas when both light sources are lit simultaneously.

This embodiment therefore allows great freedom in the design of the patterns to be displayed, without it being necessary to provide a complex control circuit since it is sufficient to control the ignition or extinction of a source light.

Preferably, the figurative patterns are characters and each electrode has the shape of a character segment, which simplifies the realization of the display device and its control.

Advantageously, a transflective type absorbent polarizer is arranged on the underside of the liquid crystal cell and a reflective polarizer of the transmissive type is arranged between the light guide and the absorbing polarizer. In addition, a reflective polarizer of the transmissive type is arranged above the liquid crystal cell. Thanks to these reflective polarizers, we obtain a better contrast between the figurative motifs displayed and the background on which they appear. In addition, these reflective polarizers make the non-selected figurative patterns not visible to the observer.

Preferably, the light guide in the form of a plate, which facilitates in particular its arrangement under the LCD display cell minimizing its size. An optical diffusion film arranged on the upper face of the light guide provides a uniform illumination of the figurative patterns.

The present invention also proposes a timepiece characterized in that it comprises a display device according to one of the preceding characteristics. It is thus possible to economically produce a timepiece such as a watch with a multicolored display with low power consumption, and not requiring a complex control circuit.

Advantageously, the timepiece comprises a printed circuit board on which light-emitting diodes are mounted which constitute the light sources of the display device, and the light guide is arranged above the printed circuit board. . Thus, a timepiece of small axial thickness and easy to assemble, using a minimum of components and a minimum of assembly operations.

Other features and advantages of the present invention will appear more clearly on reading the detailed description which follows, made with reference to the accompanying drawings given by way of non-limiting example and in which: <tb> - fig. 1 <sep> is an axial sectional view which schematically shows a timepiece equipped with a display device according to the teachings of the invention according to a first embodiment; <tb> - fig. 2 <sep> is an enlarged view of a detail of FIG. 1; <tb> - fig. 3 <sep> is a top view diagrammatically showing the liquid crystal display cell of the display device of FIG. 1 and its electrodes; <tb> - fig. 4 <sep> is an enlarged top view which schematically shows a portion of the light guide fitted to the display device of FIG. 1 and which illustrates the positioning of the reflection prisms, <tb> - fig. <Sep> is a view similar to the previous one which schematically shows a second embodiment of the invention having a multicolor display segment; <tb> - fig. 6 <sep> is a view similar to the previous one which schematically shows an alternative embodiment of the second embodiment in which the multicolored segment comprises several colored areas.

In the remainder of the description, identical or similar elements will be designated by identical references.

In FIG. 1 schematically shows a timepiece 10 such as a wristwatch equipped with a liquid crystal display device 12 made in accordance with the teachings of the invention.

The timepiece 10 comprises a housing 14, generally cylindrical in shape of axis A1, which is closed in its upper part by a protective glass 16 allowing a user to consult the indications displayed by the device. display 12 arranged inside the housing 14.

In the remainder of the description, use will be made without limitation of a vertical orientation along the axis A1.

The housing 14 contains an electronic control circuit 20 which is arranged here on the underside of a printed circuit board 22 and which is powered by a battery 24. The electronic circuit 20 comprises in particular a control unit 26 allowing to control the display device 12 to display time or other information. External control means, such as a pushbutton 27, may be provided on the outer face of the housing 14 to enable a user to control the electronic circuit 20.

The display device 12, whose display face 28 is oriented upwards, on the side of an observer, comprises a liquid crystal cell 30 which comprises an upper substrate 32, or a front substrate, and a lower substrate 34, or back substrate. The two plate-like substrates 32, 34 are separated by a sealing frame 36 which defines a volume for the confinement of the liquid crystals 38. The cell 30 is preferably of the twisted nematic type.

The structure of the cell 30 is illustrated in particular in FIGS. 2 and 3.

The cell 30 comprises a series of electrodes 40 which are structured on the lower face of the upper substrate 32, and a plate-shaped counter electrode 42 which is structured on the upper face of the lower substrate 34.

Each electrode 40 represents a portion of figurative pattern. According to the embodiment shown, each electrode 40 has the shape of a rectilinear segment, and these segments are arranged so as to form two "8", which allows, by appropriately selecting the segments displayed at a given moment, to represent all the numbers from "0" to "9", as well as some letters.

Of course, according to alternative embodiments (not shown) of the invention, the electrodes 40 may have more complex shapes, for example an electrode 40 may itself represent a character, a symbol, or a decorative pattern such as a flower.

Each electrode 40 is connected to a power supply track 41 which comprises, at the end opposite the electrode 40, a contact zone 43 allowing, by connection means (not shown) such as Zébra connectors. the electrical connection of the electrode 40 to the electrical control circuit 20. The contact areas 43 of all the electrodes 40 are here aligned to facilitate this connection. The tracks 41 and the contact areas 43 are structured on the inner face of the upper substrate 32 as the electrodes 40.

Similarly, the counter-electrode 42 comprises connecting means (not shown) for its electrical connection with the electronic control circuit 20.

In a conventional manner, the cell 30 comprises an upper polarizing filter 44 and a lower polarizing filter 46 which are respectively arranged on the upper face of the upper substrate 32 and on the lower face of the lower substrate 34. The polarization planes of the light of these two filters 44, 46 form between them an angle of ninety degrees.

Advantageously, the upper polarizing filter 44 is constituted by a polarizing filter of the reflective type, also called reflective polarizer, and the lower polarizing filter 46 is constituted by a polarizing filter of the absorbent type, also called absorbing polarizer.

In the present application, the term "reflective polarizer" a polarizing filter that reflects the light received from the top, when it is arranged under another polarizing filter and that the two filters are crossed. With a cell operating in non-backlit mode, this type of filter can display segments of the ambient lighting color.

By contrast, the term "absorbing polarizer" a polarizing filter that absorbs the light received from the top, when it is arranged under another polarizing filter and that the two filters are crossed. With a cell operating in non-backlit mode, this type of filter is used to display dark gray segments.

In addition, the upper polarizing filter 44 is chosen from reflective polarizers of the transmissive type, that is to say that it is intended to let light in both directions.

The lower polarizing filter 46 is selected from absorbing polarizers transflective type with a reflective layer arranged on the side of its lower face to reflect the light upwards. Thus, in non-backlit mode, the ambient light that passes through the cell 30 is reflected on the lower polarizing filter 46 and, in backlit mode, the light emitted by a backlight module 48 located under the cell 30 passes through the lower polarizing filter 46 towards the display face 28.

The cell 30 is controlled by the control unit 26 which applies a determined value control voltage between a selected electrode 40 and the counter-electrode 42 so as to modify the orientation of the liquid crystals and cause the display of corresponding figurative motifs.

The backlight module 48 is arranged under the liquid crystal cell 30, on the opposite side to the display face 28. It comprises here first and second light sources 50, 52 of different colors that emit light. light rays Ri inside a light guide 54 in the form of a plate. The first light source 50 emits, for example, red rays Rr, and the second light source 52 emits, for example, blue rays Rb.

Of course, the backlight module 48 may comprise more than two light sources 50, 52. In this case, several light sources 50, 52 may be of the same color.

According to the embodiment shown here, the light sources 50, 52 are constituted by colored LEDs 50, 52 which are mounted on the upper face of the printed circuit board 22 and which are electrically connected to the electronic circuit 20. control. These diodes 50, 52 are provided to produce a light beam generally in an axial direction facing upwards. Each diode 50, 52 is received in a notch 56 formed in the lower extended face 58 of the light guide 54, near the peripheral edge 60 of the light guide 54, so that most of the light rays emitted by each diode 50, 52 enters the light guide 54 through an adapted inlet surface 62.

One face of the light guide 54, here its lower face 58, is provided with prisms 64, 66 which deflect the light rays Ri emitted by the diodes 50, 52 towards the display face 28. A first series S1 of Prisms 64 is oriented towards the first diode 50 to deflect the light rays Rr from the first diode 50 and a second series S2 of prisms 66 is oriented towards the second diode 52 to deflect the light rays Rb of the second diode 52.

The prisms 64, 66 are formed here by recesses formed in the lower face 58 of the light guide 54. Each prism 64, 66 has a reflection surface 68 whose normal corresponds to the bisector of the angle formed by a first straight line passing through the reflection surface 68 and the corresponding diode 50, 52, with a second straight line passing through the reflecting surface 68 and the observer's eye. Thus, a certain proportion of the light rays Ri emitted by each diode 50, 52 reaches the reflection surface 68 of the associated prisms 64, 66, either in direct incidence or after one or more prior reflections on at least one of the extended faces. lower 58 and upper 70 of the light guide 54.

The light rays Ri reaching the reflection surface 68 are reflected upward according to the principle of total reflection, given their angle of incidence, which produces a backlighting light beam emitted towards the face. display 28 through the cell 30.

The proportion of the light rays Ri which are reflected on the reflection surface 68 can be adjusted according to certain geometric parameters of a given prism 64, 66, in particular as a function of the distance separating the diode 50, 52 associated of the reflection surface 68 and as a function of the height of the prism 64, 66 relative to the thickness of the light guide 54. The skilled person will not encounter any particular difficulty to adapt these parameters according to his needs.

In FIG. 2, the angle between the reflection surface 68 and the lower extended face 58 is substantially forty-five degrees, so that the light rays Ri are deflected in a substantially axial direction.

The light guide 54 may be made of any material having the required qualities, including in particular the transparency vis-à-vis the propagation of light, especially in the visible range. In a preferred manner, the light guide 54 may be made of a plastic material of the PMMA (polymethyl acrylate) type, by injection, by replication, or by any other suitable method, the advantages of these solutions residing mainly in the ease of the processes. corresponding manufacturing and in the low cost of the product obtained for mass production.

By using current manufacturing techniques, it is conceivable to make prisms 64, 66 having dimensions of the order of 10 microns. In addition, the reflection surface 68 may have various shapes, planar or curved to modulate the shape of the reflected beam and make it slightly divergent, for example.

According to an alternative embodiment (not shown), the prisms 66, 66 may be made projecting on one of the extended faces 58, 70 of the light guide 54.

Advantageously, the peripheral portion 72 of the upper face 70 of the light guide 54 is curved towards the lower face 58, so that the light rays emitted by the diodes 50, 52 towards the peripheral edge 60 of the light guide 54 may be totally reflected on the peripheral portion 72 and thus be diverted to the prisms 64, 66 arranged in the central portion of the light guide 54,

Of course, according to an alternative embodiment (not shown), the diodes 50, 52 may be provided to emit light radially to the axis A1. The diodes 50, 52 must then be arranged facing radially an axial input surface 62.

According to another characteristic of the invention, the prisms 64, 66 are distributed in areas of the light guide 54 which are located under the electrodes 40, so that the light rays Ri coming from the upper face 70 of the light guides 54 are concentrated on the electrodes 40. Thus, the prisms 64, 66 generally reproduce the contour of the electrodes 40 on the lower face 58 of the light guide 54.

The prisms 64, 66 are situated only opposite electrodes 40. Outside the zones situated under the electrodes 40, the light guide 54 does not include prisms 64, 66. Therefore, the light guide 54 emits light rays Ri upwards only opposite the electrodes 40.

According to a first embodiment, shown in FIGS. 1 to 4, the first series S1 of prisms 64 is arranged under a first series E1 of electrodes 40, and the second series S2 of prisms 66 is arranged under a second series E2 of electrodes 40 distinct from the first. Thus, each electrode 40 can be illuminated only by a single diode 50, 52 and its backlight color corresponds to the color of the diode 50, 52 which illuminates it.

Preferably, an optical diffusion film 74 is arranged on the upper face 70 of the light guide 54. This optical film 74 is used to diffuse the light emitted by the light guide 54 over the prisms 64 transversely, 66 and allow uniform illumination of each electrode 40.

According to alternative embodiments, the optical film 74 could be a focusing or structuring film of the light emitted by the light guide 54, depending on the desired backlighting effect.

Advantageously, the cell 30 comprises a reflective polarizer 76 of the transmissive type, which is interposed between the lower polarizing filter 46 and the optical film 74. The function of this reflective polarizer 76 below will be explained later.

The operation of the display device 12 according to the first embodiment is as follows.

In non-backlit mode, also called reflective mode, the backlight module 30 is not powered and ambient lighting is used to obtain a contrast between the displayed segments, which correspond to electrodes 40 powered, and the non-displayed segments, which correspond to unpowered electrodes 40. The operation of the display device 12 is conventional and the displayed segments corresponding to the powered electrodes 40 appear in the color of the ambient illumination.

The light of the ambient light passes through the upper polarizing filter 44 and the cell 30 before being reflected on the reflective layer of the lower polarizing filter 46 and then redoing the path in the opposite direction to the display face 28.

In backlit mode, the backlight module 48 is powered and the segments corresponding to the electrodes 40 supplied each appear in a specific color.

In backlit mode, the two diodes 50, 52 are lit simultaneously. Consequently, the light guide 54 emits red light rays Rr under the electrodes 40 of the first series E1 and blue light rays Rb under the electrodes 40 of the second series E2.

When the electronic circuit 20 controls the supply of an electrode 40 determined to display the corresponding segment on the side of the display face 28, the liquid crystal located under this electrode 40 is oriented so as to let the light emitted by the backlight module 48 under this electrode 40.

For example, in FIG. 3, the character "6" is displayed by feeding the electrodes 40a, 40b corresponding to the display of this character. Since the electrodes 40a belong to the first series E1, then the two corresponding segments are displayed in red since the prisms 64 located under these segments are oriented towards the red diode 50. Since the electrodes 40b belong to the second series E2, then the four corresponding segments are displayed in blue since the prisms 66 located under these segments are oriented towards the blue diode 52.

According to this embodiment, each display segment is always illuminated by the same diode 50, 52.

According to a second embodiment, which is shown in FIG. 5, at least one electrode 40c corresponding to a so-called multi-color segment is arranged above prisms 64, 66 belonging to the first S1 and the second S2 series. In addition, the prisms 64, 66 of the first S1 and the second series S2 are interleaved. Thus, this embodiment makes it possible to selectively display the multicolored segment in several colors according to the diodes 50, 52 which are lit.

When the red diode 50 is on and the blue diode 52 off, and the electrode 40c corresponding to the multicolored segment is powered, the multicolored segment is illuminated in red.

When the blue diode 52 is lit and the red diode 50 off, and the electrode 40c corresponding to the multicolored segment is energized, the multicolored segment is illuminated in blue.

When the two diodes 50, 52 are lit simultaneously, and the electrode 40c corresponding to the multicolored segment is powered, the red light and the blue light of the two diodes 50, 52 are mixed to display the multicolored segment in magenta.

According to a variant of the second embodiment, illustrated in FIG. 6, the prisms 64 of the first series S1 and the prisms 66 of the second series S2 are grouped in distinct zones Z1, Z2, under the electrode 40c corresponding to the multicolored segment, to allow the multicolored segment to be displayed in several zones. colored Z1, Z2 when the two diodes 50, 52 are lit simultaneously. This embodiment allows a wide variety of appearance of multicolored segments that may appear with multicolored stripes or with multicolored circles.

Of course, the two embodiments described above can be combined so that some segments are multicolored and the others are displayed in one color.

The use of a reflective polarizer for the upper polarizing filter 44 has the advantage of improving the light output, so the brightness of the displayed segments, because it allows more light to pass than a filter of the absorbent type.

In addition, the outwardly reflecting effect of the upper polarizing filter 44 reduces the visibility of segments not displayed for the observer. Indeed, it is found that the visual effect obtained by means of the upper polarizing filter 44 prevents the observer from distinguishing the small amount of light that passes through the cell 30 at the electrodes 40 unpowered.

In backlit mode, the reflective polarizer 76 lower also reduces the visibility of segments not displayed. Indeed, when the light guide 54 emits light under all the electrodes 40, including the unpowered electrodes 40, a certain amount of the emitted light passes through the cell 30 at the electrodes 40 which are not powered, which can make the unselected segments visible to the observer. The lower reflective polarizer 76 minimizes this amount of undesired light. This is due in particular to the reflection of a portion of the light rays Rr, Rb on the reflective polarizer 76 below.

Claims (12)

A liquid crystal display device (12) comprising an upwardly facing display face (28) of the device (12) on an observer side, said device (12) comprising: A liquid crystal cell (30) (38) comprising at least one upper substrate (32) and one lower substrate (34), at least two electrodes (40) and at least one counter-electrode (42) which are structured on the faces facing the two substrates (30, 32), each electrode (40) representing a figurative pattern or a portion of a figurative pattern, A control unit (26) arranged to control the liquid crystal cell (30) by applying a determined value control voltage between a selected electrode (40) and the counter electrode (42) so as to modify the the orientation of the liquid crystals (38) and to cause the display of the corresponding figurative motifs, and A backlighting module (48) arranged under the liquid crystal cell (30), on the opposite side to the display face (28), comprising at least a first (50) and a second (52) source different-colored luminaires which emit light rays (Rr, Rb) within at least one light guide (54) comprising an upper surface (70) of light rays (Rr, Rb), characterized in that the light guide (54) comprises a plurality of prisms (64, 66) arranged to deflect the light rays (Rr, Rb) towards the display face (28), a first series (S1) of prisms (64) being oriented towards the first light source (50) for deflecting the light rays (Rr) emitted by the first source (50) and a second series (S2) of prisms (66) facing the second light source (52) ) to deflect the light rays (Rb) emitted by the second source (52), and in that the prisms (64, 66) are distributed in areas of the light guide (54) which are located solely opposite the electrodes ( 40) so that the light rays (Rr, Rb) from the upper face (70) of the light guide (54) are concentrated on the electrodes (40). 2. Display device (12) according to the preceding claim, characterized in that the first series (S1) of prisms (64) is arranged in a first series (E1) of electrodes (40a), and in that the second series (S2) of prisms (66) is arranged under a second series (E2) of electrodes (40b) distinct from the first (E1). 3. Display device according to claim 1, wherein at least one electrode corresponding to a multicolored figurative pattern is arranged above prisms belonging to at the first (S1) and at the second (S2) series of prisms, so as to allow the selective display of the multicolored pattern in: A first color corresponding to the prisms (64) of the first series (51), when the first light source (50) is on and the other is off, A second color corresponding to the prisms (66) of the second series (52), when the second light source (52) is on and the other is off, A combination of colors when the two light sources (50, 52) are lit simultaneously. 4. Display device (12) according to the preceding claim, characterized in that the prisms (64, 66) of the first (S1) and the second (S2) series are interlaced under the electrode (40c) corresponding to the multicolor pattern so that the simultaneous ignition of the two light sources (50, 52) produces a new color corresponding to the superposition of the two initial colors. 5. Display device (12) according to claim 3, characterized in that the prisms (64) of the first series (S1) and the prisms (66) of the second series (S2) are grouped together in distinct zones ( Z1, Z2), under the electrode (40c) corresponding to the multicolored pattern, to allow the multicolor pattern to be displayed in a plurality of colored zones (Z1, Z2) when the two light sources (50, 52) are lit simultaneously. 6. Display device (12) according to any one of the preceding claims, characterized in that the figurative patterns are characters and in that each electrode (40) has the shape of a character segment. Display device (12) according to one of the preceding claims, characterized in that an absorbing polariser (46) of the transflective type is arranged on the underside of the liquid crystal cell (30) and in that a reflective polarizer (76) of the transmissive type is arranged between the light guide (54) and the absorbing polarizer (46). Display device (12) according to one of the preceding claims, characterized in that a reflective polarizer (44) of the transmissive type is arranged above the liquid crystal cell (30). 9. Display device (12) according to any one of the preceding claims, characterized in that an optical diffusion film (74) is arranged on the upper face (70) of the light guide (54). 10. Display device (12) according to any one of the preceding claims, characterized in that the light guide (54) in the form of a plate. 11. Timepiece (10) characterized in that it comprises a display device (12) according to any one of the preceding claims. 12. Timepiece (10) according to the preceding claim, characterized in that it comprises a printed circuit board (22) on which are mounted diodes (50, 52) electroluminescent which constitute the light sources (50, 52). ) of the display device (12), and in that the light guide (54) is arranged above the printed circuit board (22).