EP2057500A2

EP2057500A2 - Autostereoscopic display device and method of manufacturing the same

Info

Publication number: EP2057500A2
Application number: EP07805430A
Authority: EP
Inventors: Hans Zuidema; Sipke Wadman; Raymond G. A. Van Agthoven; Esther A. W. G. Janssen
Original assignee: Koninklijke Philips Electronics NV
Current assignee: Koninklijke Philips NV
Priority date: 2006-08-18
Filing date: 2007-08-17
Publication date: 2009-05-13
Also published as: CN101506716A; WO2008020417A3; WO2008020417A2; CN101506716B; JP2010501880A; JP5366806B2

Abstract

An autostereoscopic display device comprises a display panel having an array of display pixels for producing a display, the display pixels being arranged in rows and columns; and an imaging arrangement for directing the output from different pixels to different spatial positions to enable a stereoscopic image to be viewed. The display panel and imaging arrangement are coupled together around a seal line, and a volume defined between the display panel, the imaging arrangement and the seal line has a reduced pressure. At least one of the display panel and the imaging arrangement is provided with a channel within the volume. This channel enables the volume defined to be increased in size but whilst maintaining a small spacing between the display panel and imaging arrangement. This increased volume means that the pressure will change less quickly in response to gas leakage across the seal line.

Description

Autostereoscopic display device and method of manufacturing the same

FIELD OF THE INVENTION

This invention relates to an autostereoscopic display device of the type that comprises a display panel having an array of display pixels for producing a display and an imaging arrangement for directing different views to different spatial positions. A first example of imaging arrangement for use in this type of display is a barrier, for example with slits that are sized and positioned in relation to the underlying pixels of the display. The viewer is able to perceive a 3D image if his/her head is at a fixed position. The barrier is positioned in front of the display panel and is designed so that light from the odd and even pixel columns is directed towards the left and right eye of the viewer. A drawback of this type of two-view display design is that the viewer has to be at a fixed position, and can only move approximately 3 cm to the left or right. In a more preferred embodiment there are not two sub-pixel columns beneath each slit, but several. In this way, the viewer is allowed to move to the left and right and perceive a stereo image in his eyes all the time. The barrier arrangement is simple to produce but is not light efficient. A preferred alternative is therefore to use a lens arrangement as the imaging arrangement. For example, an array of elongate lenticular elements can be provided extending parallel to one another and overlying the display pixel array, and the display pixels are observed through these lenticular elements. The lenticular elements are provided as a sheet of elements, each of which comprises an elongate semi-cylindrical lens element. The lenticular elements extend in the column direction of the display panel, with each lenticular element overlying a respective group of two or more adjacent columns of display pixels.

In an arrangement in which, for example, each lenticule is associated with two columns of display pixels, the display pixels in each column provide a vertical slice of a respective two dimensional sub-image. The lenticular sheet directs these two slices and corresponding slices from the display pixel columns associated with the other lenticules, to the left and right eyes of a user positioned in front of the sheet, so that the user observes a single stereoscopic image. The sheet of lenticular elements thus provides a light output directing function.

In other arrangements, each lenticule is associated with a group of four or more adjacent display pixels in the row direction. Corresponding columns of display pixels in each group are arranged appropriately to provide a vertical slice from a respective two dimensional sub-image. As a user's head is moved from left to right, a series of successive, different, stereoscopic views are perceived creating, for example, a look-around impression. The above described device provides an effective three dimensional display. However, it will be appreciated that, in order to provide stereoscopic views, there is a necessary sacrifice in the horizontal resolution of the device. This sacrifice in resolution is unacceptable for certain applications, such as the display of small text characters for viewing from short distances. For this reason, it has been proposed to provide a display device that is switchable between a two-dimensional mode and a three-dimensional (stereoscopic) mode. One way to implement this is to provide an electrically switchable lenticular array. In the two-dimensional mode, the lenticular elements of the switchable device operate in a "pass through" mode, i.e. they act in the same way as would a planar sheet of optically transparent material. The resulting display has a high resolution, equal to the native resolution of the display panel, which is suitable for the display of small text characters from short viewing distances. The two-dimensional display mode cannot, of course, provide a stereoscopic image.

In the three-dimensional mode, the lenticular elements of the switchable device provide a light output directing function, as described above. The resulting display is capable of providing stereoscopic images, but has the inevitable resolution loss mentioned above. In order to provide switchable display modes, the lenticular elements of the switchable device are formed of an electro-optic material, such as a liquid crystal material, having a refractive index that is switchable between two values. The device is then switched between the modes by applying an appropriate electrical potential to planar electrodes provided above and below the lenticular elements. The electrical potential alters the refractive index of the lenticular elements in relation to that of an adjacent optically transparent layer. A more detailed description of the structure and operation of the switchable device can be found in US patent number 6,069,650. SUMMARY OF THE INVENTION

This invention relates generally to the mounting of such lens arrangements (whether static or switchable) to the display panel. These lens arrangements have to be mounted in close proximity with the underlying 2D-displays used. This is a requirement of the device operation, which requires the focal point of the lenses on the lenticular plate to be at a (controlled) distance from the colour filter of the 2D-panel. Moreover, this distance has to be kept constant across the display active area in order to ensure the same performance across the display output.

The invention is defined by the independent claims. The dependent claims define advantageous embodiments.

According to the invention, there is provided an autostereoscopic display device according to claim 1.

The channel enables the volume defined to be increased in size but whilst maintaining a small spacing between the display panel and imaging arrangement. This increased volume means that the pressure will change less quickly in response to gas leakage across the seal line.

A spacing between facing surfaces of the display panel and the imaging arrangement is preferably less than 200μm, and more preferably less than lOOμm. The maximum spacing between the display panel and the imaging arrangement is preferably at the seal line and the reduced pressure gives rise to a smaller spacing across the remainder of the display.

The channel preferably extends at least partially around a periphery of the display within the seal line. This means the seal line does not need to be increased substantially in length, nor does the display panel area. The channel preferably has a width and a depth greater than the maximum spacing between the facing surfaces of the display panel and the imaging arrangement, so that the additional volume of the channel is dominant. The volume of the channel may be more than double, or even more than five times the remaining defined volume.

For example, the channel width can be in the range 0.5 to 10mm and the channel depth can be within the range 0.2 to 2mm.

The display panel can comprise an array of individually addressable emissive, transmissive, refractive or diffractive display pixels, for example a liquid crystal display panel. The invention also provides a method of manufacturing an autostereoscopic display device.

This method uses a vacuum to reduce the gap size before seal curing. The spacing between facing surfaces of the display panel and the imaging arrangement can be reduced to less than 200μm, or more preferably less than lOOμm. The seal may be cured before or after closing the fill port.

The method may further comprise defining a channel in the lenticular array which extends at least partially around a periphery of the display within the seal line. This provides the advantages outlined above.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described, purely by way of example, with reference to the accompanying drawings, in which:

Fig. 1 is a schematic perspective view of a known autostereoscopic display device;

Figs. 2 and 3 are used to explain the operating principle of the lens array of the display device shown in Fig. 1;

Fig. 4 shows schematically how the lens arrangement provides different views (i.e. the output from different sets of pixels) to different spatial locations; Fig. 5 shows the known 2D display which is the starting point for the manufacture of a 3D display;

Fig. 6 shows a mounting method of the invention;

Fig. 7 shows the way of mounting a lenticular array to a display panel in accordance with the invention; and Fig. 8 is used to explain a modification to the device shown in Fig. 7.

DETAILED DESCRIPTION OF EMBODIMENTS

In one aspect, the invention provides an autostereoscopic display in which a lenticular array is vacuum mounted to a display panel, and a channel arrangement is used to increase the volume of the vacuum chamber, to make the mounting less susceptible to gas leakage over time, whilst maintaining a small gap between the lenticular array and the display panel. In another aspect, the invention provides a vacuum mounting method. Fig. 1 is a schematic perspective view of a known direct view autostereoscopic display device 1. The known device 1 comprises a liquid crystal display panel 3 of the active matrix type that acts as a spatial light modulator to produce the display.

The display panel 3 has an orthogonal array of display pixels 5 arranged in rows and columns. For the sake of clarity, only a small number of display pixels 5 are shown in the Fig.. In practice, the display panel 3 might comprise about one thousand rows and several thousand columns of display pixels 5.

The structure of the liquid crystal display panel 3 is entirely conventional. In particular, the panel 3 comprises a pair of spaced transparent glass substrates, between which an aligned twisted nematic or other liquid crystal material is provided. The substrates carry patterns of transparent indium tin oxide (ITO) electrodes on their facing surfaces. Polarising layers are also provided on the outer surfaces of the substrates.

Each display pixel 5 comprises opposing electrodes on the substrates, with the intervening liquid crystal material therebetween. The shape and layout of the display pixels 5 are determined by the shape and layout of the electrodes. The display pixels 5 are regularly spaced from one another by gaps.

Each display pixel 5 is associated with a switching element, such as a thin film transistor (TFT) or thin film diode (TFD). The display pixels are operated to produce the display by providing addressing signals to the switching elements, and suitable addressing schemes will be known to those skilled in the art.

The display panel 3 is illuminated by a light source 7 comprising, in this case, a planar backlight extending over the area of the display pixel array. Light from the light source 7 is directed through the display panel 3, with the individual display pixels 5 being driven to modulate the light and produce the display. The display device 1 also comprises a lenticular sheet 9, arranged over the display side of the display panel 3, which performs a view forming function. The lenticular sheet 9 comprises a row of lenticular elements 11 extending parallel to one another, of which only one is shown with exaggerated dimensions for the sake of clarity.

The lenticular elements 11 are in the form of convex cylindrical lenses, and they act as a light output directing means to provide different images, or views, from the display panel 3 to the eyes of a user positioned in front of the display device 1.

The autostereoscopic display device 1 shown in Fig. 1 is capable of providing several different perspective views in different directions. In particular, each lenticular element 11 overlies a small group of display pixels 5 in each row. The lenticular element 11 projects each display pixel 5 of a group in a different direction, so as to form the several different views. As the user's head moves from left to right, his/her eyes will receive different ones of the several views, in turn.

It has been proposed to provide electrically switchable lens elements, as mentioned above. This enables the display to be switched between 2D and 3D modes.

Figs. 2 and 3 schematically show an array of electrically switchable lenticular elements 35 which can be employed in the device shown in Fig. 1. The array comprises a pair of transparent glass substrates 39, 41, with transparent electrodes 43, 45 formed of indium tin oxide (ITO) provided on their facing surfaces. An inverse lens structure 47, formed using a replication technique, is provided between the substrates 39, 41, adjacent to an upper one of the substrates 39. Liquid crystal material 49 is also provided between the substrates 39, 41, adjacent to the lower one of the substrates 41.

The inverse lens structure 47 causes the liquid crystal material 49 to assume parallel, elongate lenticular shapes, between the inverse lens structure 47 and the lower substrate 41, as shown in cross-section in Figs. 2 and 3. Surfaces of the inverse lens structure 47 and the lower substrate 41 that are in contact with the liquid crystal material are also provided with an orientation layer (not shown) for orientating the liquid crystal material.

Fig. 2 shows the array when no electric potential is applied to the electrodes 43, 45. In this state, the refractive index of the liquid crystal material 49 is substantially higher than that of the inverse lens array 47, and the lenticular shapes therefore provide a light output directing function, as illustrated.

Fig. 3 shows the array when an alternating electric potential of approximately 50 to 100 volts is applied to the electrodes 43, 45. In this state, the refractive index of the liquid crystal material 49 is substantially the same as that of the inverse lens array 47, so that the light output directing function of the lenticular shapes is cancelled, as illustrated. Thus, in this state, the array effectively acts in a "pass through" mode.

Further details of the structure and operation of arrays of switchable lenticular elements suitable for use in the display device shown in Fig. 1 can be found in US patent number 6,069,650. Fig. 4 shows the principle of operation of a lenticular type imaging arrangement as described above and shows the backlight 50, display device 54 such as an LCD and the lenticular array 58.

The invention concerns the mounting of the lenticular (or other) lens array device onto the display panel. Fig. 5 shows the basic known design of a 2D-module. The arrangement comprises the LC module 60 and a stack 62 of a polariser and brightness enhancement foil on a substrate 76.

The LC module includes two glass substrates 64 which sandwich the LC material layer 66, and two polarisers 68 are provided. The seal is shown as 70. The LC module typically has a thickness of around 2mm.

The display module has a base plate 72, and a bezel 71 is used to create mechanical stability in the 2D-module, with a spacing block/damping element 74 determining the mounting position of the LC cell with respect to the stack 62. The spacer 74 may be approximately 2mm thick, and the resulting space between the facing surfaces of the LC panel and the stack 62 may be approximately 3.8mm.

The stack is typically approximately 0.9mm thick. The backlight is not shown in Fig. 5.

One conventional way to manufacture a 3D display is to start with a complete 2D display module, and update this to a 3D display.

In order to assemble the structure shown in Fig. 5, using this approach, the following steps are carried out: disassemble the 2D-panel from the 2D-module, by removing the bezel 71, and dismounting the electronics; - put the 2D-panel on a flat table; apply the lenticular array using an edge seal resulting in a 3D-panel; introduce an additional glass plate behind the 3D-panel to be able to squeeze the panel between the lenticular and the additional plate; assemble the 3D-panel in the original 2D-module resulting in a 3D-module. There are a number of problems encountered in this manufacturing process: the electronics can be damaged during the assembly and disassembly of the display. the manufacturing process is very time consuming and laborious; the lenticular is only mounted to the panel at the edges, so that it is very difficult to guarantee performance since the panel plates and lenticular lenses may be curved; the display panel itself may not be perfectly flat and have peaks and valleys which make it very difficult to guarantee performance; the requirement for an additional plate behind the 3D-panel increases the weight of the system, and changes the thermal behaviour of the system, leading possibly to a change in performance.

This method of disassembly and reassembly thus has many drawbacks. The invention provides a vacuum mounting method which still enables a standard 2D panel to be modified, thereby enabling off the shelf display modules to be used, but addresses some of the problems identified above.

Fig. 6 is a flowchart illustrating the assembly method of the invention.

The lenticular sheet is processed by cleaning 78 and applying a seal to the surface of the sheet at step 79. This seal line includes a fill port and is around the edge of the lenticular sheet so that it surrounds the display area in the finished product. The seal may instead be applied to the display panel side. The lenticular array is typically 2 to 5mm thick.

The 2D display module is processed by removing the bezel 71 from the 2D- module in step 80. However, there is no need to remove the two-panel display and thereby disconnect the display electronics.

After cleaning in step 82, in step 84, the lenticular array is aligned on the seal line and the two panels are coupled together in step 85.

In step 86 a vacuum is applied to the space defined by the lenticular array, the seal line and the 2D-panel. In step 88 the fill port is closed and the seal is cured in step 90.

This process allows the LCD panel & lenticular plate to be mounted together as close as possible, having a gap that is as small as possible, comparable with the tolerances levels for the LCD panel and lenticular plate. The use of a seal line means that the plates cannot move after the process is completed. The seal line is preferably a curable fluid, to form a gasket, and the seal is used to couple the LCD panel and lenticular plate together.

The vacuum is used to reduce the cavity dimension between the LCD and lenticular plate. By evacuating the air in the cavity, the volume of the cavity is reduced.

Preferably, the seal line is be pressed to a thickness of 50 to 100 μm thickness. The application of vacuum is ceased when the spacing between the LCD panel and the lenticular plate has reached the desired spacing. This spacing will be lower in the centre of the display area, and will be greatest at the seal line where the spacing increases to the 50-100 μm dimension.

The seal line can be cured by water permeation, or else a two component seal material can be used with temperature and/or UV driven curing being applied. As a result, both plates are mounted very closely together. The presence of vacuum inside the cavity is not required maintain the plate fixing, but is used as part of the alignment process rather than the fixing process.

This method prevents damage to the electronics during assembly and disassembly as the display no longer requires full dismounting. The lenticular array and the panel are mounted in close proximity all over the active area of the display by the pressure difference inside and outside the lenticular-panel-combination, thus providing gap uniformity. The method avoids the need for a further glass plate.

After checking the seal in step 92, the bezel 71 is reapplied in step 94, having been modified in step 96 to fit the additional lenticular array.

Finally, a protective plate is applied in step 98 and the finished product can be supplied to the set maker.

Fig. 7 shows the assembled device of the invention, using the same reference numerals as Fig. 5. The lenticular array is shown as 100 and the seal line is shown as 102, and the modified bezel is shown as 71 ' .

As mentioned above, the volume to which the vacuum is applied has a very low volume. For example, the gap size across most of the area of the display may be in the range of between 0 and 10 μm. For an area inside the seal line of 940 x 530 mm², an average thickness of 1 μm, gives a vacuum containing volume of 498 mm³. The vacuum gives rise to a pressure difference across the seal line. For an imperfect seal, this acts as a driving force for nitrogen, oxygen and other gases to penetrate the vacuum area. Consequently, the level of vacuum will reduce very slowly, dependent on the permeability of the seal material.

Although the mounting is mechanically fixed by the seal line, this pressure variation can give rise to slight variations in spacing over time, in particular an increase in the gap between the lenticular array and the panel plate.

A modification explained with reference to Fig. 8 enables the rate at which the level of vacuum is reduced by permeability to be significantly reduced. As a result, the rate of increase of the gap between lenticular array and display panel plate can be significantly reduced. This contributes to an increase in the lifetime of the product.

As shown in Fig. 8, the volume of the vacuum space 110 is increased by a channel arrangement 112, and without increasing the seal line length. These channels can be considered to comprise a vacuum buffer. Adjacent to the seal line defined by the seal 102, an additional buffer space is created that enlarges the vacuum containing area. For example, compared to the vacuum volume of 498 mm explained above, the volume can increase by 2940 mm assuming a channel width and depth of 1 mm. This is an increase by a factor of approximately 7. As a result, the influence of the permeating gases is reduced significantly.

The examples described above employs a liquid crystal display panel having, for example, a display pixel pitch in the range 50μm to 1000 μm. However, it will be apparent to those skilled in the art that alternative types of display panel may be employed, such as organic light emitting diode (OLED) or cathode ray tube (CRT) display devices. The manufacture and materials used to fabricate the display device and lenticular array have not been described in detail, as these will be conventional and well known to those skilled in the art.

Various other modifications will be apparent to those skilled in the art.

Claims

CLAIMS:

1. An autostereoscopic display device comprising: a display panel having an array of display pixels for producing a display, the display pixels being arranged in rows and columns; and an imaging arrangement for directing the output from different pixels to different spatial positions to enable a stereoscopic image to be viewed, wherein the display panel and imaging arrangement are coupled together around a seal line, and wherein a volume defined between the display panel, the imaging arrangement and the seal line has a reduced pressure, and at least one of the display panel and the imaging arrangement is provided with a channel within the volume.

2. A device as claimed in claim 1, wherein a spacing between facing surfaces of the display panel and the imaging arrangement is less than 200μm.

3. A device as claimed in claim 2, wherein the spacing between the facing surfaces of the display panel and the imaging arrangement is less than lOOμm.

4. A device as claimed in claim 2 or 3, wherein the maximum spacing between the display panel and the imaging arrangement is at the seal line.

5. A device as claimed in any preceding claim, wherein the channel extends at least partially around a periphery of the display within the seal line.

6. A device as claimed in claim 5, wherein the channel has a width and a depth greater than the maximum spacing between the facing surfaces of the display panel and the imaging arrangement.

7. A device as claimed in claim 6 wherein the channel width is in the range 0.5 to 10mm and the channel depth is within the range 0.2 to 2mm.

8. A device as claimed in any preceding claim, wherein the display panel comprises an array of individually addressable emissive, transmissive, refractive or diffractive display pixels.

9. A device as claimed in any preceding claim, wherein the display panel is a liquid crystal display panel.

10. A method of manufacturing an autostereoscopic display device, comprising removing a bezel from a display module to expose a display panel; providing an imaging arrangement for directing the output from different pixels to different spatial positions to enable a stereoscopic image to be viewed; applying a closed seal line at the outer edges of the 2D-panel or the outer edges of the imaging arrangement, the seal line including a fill port; aligning the imaging arrangement and the display panel with the seal line therebetween; applying a vacuum to the space defined between the imaging arrangement, the seal line and the display panel, thereby to reduce a gap between facing surfaces of the display panel and the imaging arrangement; closing the fill port and curing the seal.

11. A method as claimed in claim 10, wherein a spacing between facing surfaces of the display panel and the imaging arrangement is reduced to less than 200μm.

12. A method as claimed in claim 11, wherein the spacing between the facing surfaces of the display panel and the imaging arrangement is reduced to less than lOOμm.

13. A method as claimed in claim 10 or 11, wherein the maximum spacing between the display panel and the imaging arrangement is at the seal line.

14. A method as claimed in any one of claims 10 to 13, further comprising defining a channel in the lenticular array which extends at least partially around a periphery of the display within the seal line.

15. A method as claimed in claim 14, wherein the channel is defined to have a width and a depth greater than the maximum spacing between the facing surfaces of the display panel and the imaging arrangement.

16. A method as claimed in claim 15 wherein the channel width is defined to be in the region 0.5 to 10mm and the channel depth is defined to be within the range 0.2 to 2mm.