Assembly structure and process for a backlight device of a display system

A backlight device comprises a mounting case and a stack of optical sheets attached to one another. The attached optical sheets includes at least a first optical sheet adhered with one or more tabs protruding from a side edge of a second optical sheet. The prearranged stack of attached optical sheets is assembled with the mounting case with one single placement operation conducted by one operator.

FIELD OF THE INVENTION

The present invention generally relates to the manufacture of backlight devices, and more particularly to the assembly of optical components in a backlight device for a liquid crystal display.

DESCRIPTION OF THE RELATED ART

Transmissive and transflective liquid crystal displays conventionally use a backlight device to illuminate a liquid crystal panel from behind, i.e. opposite to the viewer side. Light produced by the backlight travels through the liquid crystal panel where it is modulated to generate an image display on the viewer side.

A conventional backlight device incorporates many components mounted within a mounting case, including a light-emitting source (often light-emitting diodes or fluorescent lamps) and optical sheets such as prism sheets, a light guide plate, and a rim sheet. The assembly of these optical components in the backlight device usually requires a number of restrictions. First, the optical components have to be assembled in a restrictive working environment free of dust or other contaminants that may affect the optical properties of the backlight components. In addition, the assembled optical sheets must be able to freely expand and contract under varying conditions of temperature and humidity in order to release an induced thermal stress that may affect the optical properties of the optical sheets. Thus, in a conventional assembly process, the optical sheets are placed in the mounting case detached from one another in successive order. In this assembly process, each optical sheet is mounted by a separate operator in the backlight device, which then moves on to a next operator for assembling a next optical sheet.

The foregoing sequential assembly of the optical sheets has a number of disadvantages. First, as many operators work in series to successively mount each optical sheet in a backlight unit, the handling time for each operator being relatively short, buffers thus are conventionally needed to ensure a correct progress from an upstream operator to a downstream operator. As a result, the assembly process is less efficient. Second, multiple handling operations by many operators increase the risk of contamination by dust or finger prints as well as scratch damages and misalignment of the optical sheets, which adversely lowers the yield. Furthermore, the assembly of separate optical sheets requires that each optical sheet be separately packaged to prevent contamination or damages before it is assembled in the backlight unit, which incurs extra waste of packaging materials.

Therefore, what is needed is an improved assembly structure and process that can overcome the problems of the prior art and increase the manufacture efficiency with a reduced cost.

SUMMARY OF THE INVENTION

The application describes an assembly structure and process for assembling a backlight device.

In an embodiment, the backlight device comprises a mounting case and a stack of optical sheets attached to one another. The attached optical sheets includes at least a first optical sheet adhered with one or more tab protruding from a side edge of a second optical sheet. The prearranged stack of attached optical sheets is assembled with the mounting case with one single placement operation conducted by one operator.

The assembly structure and process according to the present invention advantageously simplify the assembly of optical sheets in the backlight device and reduce the manufacturing cost.

The foregoing is a summary and shall not be construed to limit the scope of the claims. The operations and structures disclosed herein may be implemented in a number of ways, and such changes and modifications may be made without departing from this invention and its broader aspects. Other aspects, inventive features, and advantages of the invention, as defined solely by the claims, are described in the non-limiting detailed description set forth below.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The application describes an assembly structure and process of a backlight device that can reduce its manufacture cost and increase the assembly efficiency. In particular, the present invention provides an assembly structure and process in which optical sheets are prearranged in stack units of attached sheets. Each stack of attached optical sheets then can be assembled in one backlight unit with one single operation.

FIGS. 1A through 1Dare schematic views illustrating the assembly of optical sheets for a backlight device according to an embodiment of the invention. The optical sheets to be included in the backlight device may include, for example, a rim sheet102, a light-diffuser sheet104, a vertical prism sheet106and a horizontal prism sheet108, which are respectively aligned and placed over one another to form a stack of optical sheets, generally designated with reference number110. The stack110may also include a protection foil112placed below the rim sheet102. The rim sheet102has an opaque peripheral area that extends beyond the borders of the light-diffuser sheet104and vertical and horizontal prism sheets106and108for preventing light leakage at the borders of the stack of optical sheets110. The light-diffuser sheet104may include a light guide element used to guide and diffuse light. The vertical and horizontal prism sheets106and108are configured to control the direction of light propagation. The illustrated stack of optical sheets110has a generally rectangular shape to accommodate conventionally rectangular display panels; however, any shapes may be suitable. In addition, the present invention may be suitable for assembling any optical sheets other than the above instances of optical sheets.

According to the present invention, before it is assembled in a backlight unit, the stack110is prearranged with all the optical sheet components attached to one another.FIGS. 1C and 1Dare cross-sectional views showing how the optical sheets are joined to form a stack of attached optical sheets according to one embodiment of the invention. Referring toFIG. 1C, the light-diffuser sheet104is securely glued to the rim sheet102all around the boundary area of the sheet104. The vertical prism sheet106is stacked on the light-diffuser sheet104opposite the side of the rim sheet102. The vertical prism sheet106is configured to join with the rim sheet102and remain free of attachment relative to the light-diffuser sheet104. For this purpose, two tabs116extend from one side edge114of the vertical prism sheet106beyond a corresponding border of the light-diffuser sheet104to glue to the underlying rim sheet102. The tabs116may be cut out from the material of the prism sheet106. The adhesion of the vertical prism sheet106through localized tabs116allows free sheet expansion or contraction of the vertical prism sheet106under varying thermal conditions to release the thermal stress and avoid optical artifacts. A person skilled in the art will appreciate that any numbers or modified shapes of the tabs116may be possible.

As shown inFIG. 1D, the horizontal prism sheet108is stacked on the vertical prism sheet106opposite the side of the light-diffuser sheet104. The horizontal prism sheet108is configured to join with the rim sheet102and remain free of attachment relative to the other optical sheets of the stack110. For this purpose, two tabs118extend from one side edge119of the horizontal prism sheet108beyond corresponding borders of the underlying vertical prism sheet106and light-diffuser sheet104. The tabs118adhere to the rim sheet102through respective glue layers120. The thickness “t” of the glue layers120may be configured to cushion the accumulated thickness of the vertical prism sheet106and light-diffuser sheet104, so that the tabs118do not bend downward from an excessive height to adhere with the rim sheet102. To allow more convenient gluing operations, the side119where the horizontal prism sheet108attaches with the rim sheet102is preferably different from the side114where the adjacent vertical prism sheet106attaches with the rim sheet102. In the illustrated embodiment, the side114where the vertical prism sheet106attaches with the rim sheet102is exemplary opposite the side119where the horizontal prism sheet108attaches with the rim sheet102. The adhesion of the horizontal prism sheet108through localized tabs118to the rim sheet102allows its free expansion or contraction of horizontal prism sheet108relative to the other sheets under varying thermal conditions to release the thermal stress and avoid optical artifacts.

Though the foregoing illustration describes a particular number of optical sheets in one stack, more optical sheets may be added and attached if required. As the optical sheets are prearranged in stacks of aligned and joined optical sheets, the assembly of the optical sheets in the backlight unit can be conducted with one simple placement by a single operator of the glued stack in a mounting case of the backlight unit. Because no optical sheets are separately handled during the backlight assembly, the problems encountered in the prior art, such as operators-induced contaminations, scratch damages or misalignment of the optical sheets, are alleviated. Therefore, the manufacture cost can be reduced and the yield increased.

Reference now is made toFIG. 2in conjunction withFIGS. 1A through 1Dto describe a process for assembling a backlight device according to one embodiment of the invention. For the purpose of illustration, in the present example, various steps are described in a particular order; however, when supported by accompanying equipment, these steps can be performed in any order, serially or in parallel.

Initially, in step202, a stack of optical sheets is built up by successively aligning and attaching optical sheets. For example, one provided optical sheet may be configured as the vertical prism sheet106shown inFIGS. 1A through 1D, with one or more tabs116that extend from one side edge of the optical sheet and adhere with an underlying sheet102to form stack110. Step202is repeatedly conducted for each additional optical sheet (such as the horizontal prism sheet108) to incorporate in the stack, as indicated by loop204. Preferably, the optical sheets added in the stack are attached at alternated sides. Once the last optical sheet is attached, the resulting stack of optical sheets is completed in step206. Subsequently, in step208, the completed stack of attached optical sheets can be assembled in a mounting case of a backlight unit.

In an exemplary application of the method described above, steps202through206may be conducted on one stack assembly line that supplies stacks of attached optical sheets. In turn, step208may be conducted on another backlight assembly line where the stacks of optical sheets are received and mounted in backlight units. The stack assembly line and backlight assembly line may be processed in parallel or series. As stacks of grouped optical sheets, rather than separate optical sheets, are shipped from the stack assembly line to the backlight assembly line, the packaging material and requisite carrying equipment for the optical sheet stacks can be advantageously reduced.

FIG. 3is a schematic view of a display panel assembly incorporating a backlight unit constructed according to an embodiment of the invention. Reference number300generally designates the display system, which includes a backlight unit310and a liquid crystal panel320assembled to each other. The backlight unit310includes a mounting case312in which are secured a light source314and a stack of attached optical sheets316. The stack316is mounted with the rim sheet facing up to attach with the liquid crystal panel320. Light emitted from the light source314thus travels through the stack of optical sheets316before reaching the liquid crystal panel320.

FIG. 4is a conceptual diagram of a display system according to one or more aspects of the invention. The display system may be implemented in any electric appliances, including, but not limited to, portable handheld devices such as portable multimedia players (such as DVD players), mobile phones, digital cameras, personal digital assistants (PDA), desktop computer monitors, television sets, in-car displays, laptop computers, or the like. Display system400includes a display panel402, lighting unit404, display controller406and power source408. The display controller406transmits input data and various control signals to the display panel402for generating an image display on the display panel402. The lighting unit404may be similar in structure as any of the backlight unit embodiments described above, and is suitably configured to illuminate the display panel402operating in a lighting mode. Power required for the operation of the display system400is provided by a power source408coupled with the display panel402and lighting unit404.

Realizations in accordance with the present invention have been described in the context of particular embodiments. These embodiments are meant to be illustrative and not limiting. Many variations, modifications, additions, and improvements are possible. Accordingly, plural instances may be provided for components described herein as a single instance. Structures and functionality presented as discrete components in the exemplary configurations may be implemented as a combined structure or component. These and other variations, modifications, additions, and improvements may fall within the scope of the invention as defined in the claims that follow.