PATENT DOCUMENT

Publication Number: US-9239422-B2
Application Number: US-201314049114-A
Country: US
Kind Code: B2

Title: Light guide plate with blunt edges

Abstract:
Electronic devices may include displays. A display may include display layers having an array of display pixels and a backlight unit that provides backlight illumination to the display pixels. The backlight unit may include a light guide plate that distributes light across the display layers and a stack of optical films that may be used to enhance backlight performance. The optical films may be interposed between the light guide plate and the display layers. The light guide plate may be provided with one or more rounded edges formed from curved surfaces and/or one or more beveled edges formed from chamfered surfaces. Providing the light guide plate with rounded or beveled edges may minimize abrasive contact between the light guide plate and the adjacent optical films. An injection molding tool may be used to mold a light guide plate with rounded or beveled edges.

Claims:
What is claimed is:  
     
       1. A backlight assembly configured to provide backlight illumination to display layers in a display, comprising:
 a light guide plate having a surface from which the backlight illumination is provided to the display layers, wherein the surface has a planar portion and a curved portion and wherein the curved portion forms a rounded edge, wherein the light guide plate has a straight edge on an opposing side of the light guide plate from the rounded edge, and wherein the light guide plate has a vertical sidewall that forms the straight edge; 
 at least one optical film adjacent to the surface of the light guide plate; and 
 a plurality of light-emitting diodes mounted on a substrate, wherein the light-emitting diodes are configured to emit light into the straight edge and wherein the light guide plate is attached to the substrate. 
 
     
     
       2. The backlight assembly defined in  claim 1  wherein the curved portion of the surface has a radius of curvature of greater than 50 microns. 
     
     
       3. The backlight assembly defined in  claim 1  wherein the light guide plate comprises alignment structures and wherein the alignment structures have rounded edges. 
     
     
       4. The backlight assembly defined in  claim 1  wherein the light guide plate comprises an injection molded light guide plate. 
     
     
       5. The backlight assembly defined in  claim 1  wherein the at least one optical film comprises a diffuser layer. 
     
     
       6. The backlight assembly defined in  claim 1  wherein the light guide plate comprises polymethyl methacrylate. 
     
     
       7. A method, comprising:
 with an injection molding tool, molding a rectangular light guide plate with four peripheral edges including first and second opposing edges, wherein the first edge is a rounded edge formed by a curved surface that runs along the rounded edge and wherein the second edge forms a vertical sidewall; and 
 attaching the light guide plate to a light-emitting diode substrate at the vertical sidewall such that light-emitting diodes on the light-emitting diode substrate emit light into the vertical sidewall opposite the rounded edge. 
 
     
     
       8. The method defined in  claim 7  further comprising:
 with a polishing tool, polishing the rounded edge of the light guide plate. 
 
     
     
       9. The method defined in  claim 8  wherein the polishing tool comprises a diamond edge polishing machine. 
     
     
       10. An electronic device, comprising:
 an electronic device housing; 
 display layers mounted in the electronic device housing; and 
 a light guide plate having opposing upper and lower surfaces and having four edges, wherein backlight illumination is provided to the display layers from the upper surface, wherein the upper surface comprises a curved surface that runs along at least one of the four edges, wherein the light guide plate comprises a plurality of alignment structures, and wherein the curved surface forms at least part of the alignment structures. 
 
     
     
       11. The electronic device defined in  claim 10  wherein the curved surface has a radius of curvature of greater than 50 microns. 
     
     
       12. The electronic device defined in  claim 10  further comprising:
 a plurality of optical films interposed between the display layers and the light guide plate. 
 
     
     
       13. The electronic device defined in  claim 12  wherein the plurality of optical films comprises a diffuser layer adjacent to the upper surface of the light guide plate, wherein the curved surface curves away from the diffuser layer. 
     
     
       14. The electronic device defined in  claim 10  wherein the curved surface of the light guide plate forms at least one rounded edge that extends from a first corner of the light guide plate to a second corner of the light guide plate. 
     
     
       15. The electronic device defined in  claim 10  wherein the display layers comprise:
 a color filter layer; 
 a thin-film transistor layer; and 
 a liquid crystal layer interposed between the color filter layer and the thin-film transistor layer. 
 
     
     
       16. The electronic device defined in  claim 10  wherein the lower surface of the light guide plate comprises light-scattering structures. 
     
     
       17. The electronic device defined in  claim 10  wherein the plurality of alignment structures comprises at least first and second protrusions that protrude from one of the four edges of the light guide plate. 
     
     
       18. The electronic device defined in  claim 17  wherein the first and second protrusions each comprise an opening.

Description:
This application claims priority to U.S. provisional patent application No. 61/739,931 filed Dec. 20, 2012, which is hereby incorporated by reference herein in its entirety. 
    
    
     BACKGROUND 
     This relates generally to electronic devices, and more particularly, to electronic devices with displays. 
     Electronic devices often include displays. For example, cellular telephones and portable computers often include displays for presenting information to a user. An electronic device may have a housing such as a housing formed from plastic or metal. Components for the electronic device such as display components may be mounted in the housing. 
     It can be challenging to incorporate a display into the housing of an electronic device. Size, weight, electrical grounding, robustness, ease of assembly, and light-tightness are often important considerations in designing electronic devices. If care is not taken, displays may be bulky, may exhibit undesired light reflections, or may be prone to damage during a drop event. The housing of an electronic device can be adjusted to accommodate a bulky display with large borders, but this can lead to undesirable enlargement of the size and weight of the housing and unappealing device aesthetics. 
     It would therefore be desirable to be able to provide improved ways to provide displays for electronic devices. 
     SUMMARY 
     An electronic device may be provided with a display. The display may include a display unit having an array of display pixels and a backlight unit for providing backlight illumination to the display pixels. 
     The backlight unit may include a light guide plate for distributing light from a light source across the display layers and an optical film stack for enhancing backlight performance. The optical film stack may be interposed between the light guide plate and the display layers. 
     The light guide plate may have a rectangular shape with four edges. One, two, three, or four of these edges may be blunt edges that minimize abrasive contact between the light guide plate and adjacent optical films such as an adjacent diffuser layer. In one suitable embodiment, a blunt edge may be a rounded edge formed from a curved surface having a radius of curvature of greater than 50 microns. In another suitable embodiment, a blunt edge may be a beveled edge formed from two or more planar surfaces that are angled with respect to one another by an angle of greater than 90 degrees. 
     The blunt edge may extend along an entire side of the light guide plate from one corner to another or may be formed along only a portion of a side of the light guide plate. In addition to rounded and/or beveled edges, the light guide plate may have vertical sidewall surfaces that extend vertically from an upper surface of the light guide plate to an opposing lower surface of the light guide plate, thereby forming a straight edge. The vertical sidewall surfaces may be on an opposing side of the light guide plate from the curved surfaces that form the rounded edge. 
     An injection molding tool may be used to mold the light guide plate with the curved surfaces and rounded edges. A polishing tool such as a diamond edge polishing machine may be used to grind and polish the edges of the light guide plate following the injection molding process. 
     Further features of the invention, its nature and various advantages will be more apparent from the accompanying drawings and the following detailed description of the preferred embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an illustrative electronic device such as a laptop computer with a display in accordance with an embodiment of the present invention. 
         FIG. 2  is a perspective view of an illustrative electronic device such as a handheld electronic device with a display in accordance with an embodiment of the present invention. 
         FIG. 3  is a perspective view of an illustrative electronic device such as a tablet computer with a display in accordance with an embodiment of the present invention. 
         FIG. 4  is a perspective view of an illustrative electronic device such as a computer display with a display in accordance with an embodiment of the present invention. 
         FIG. 5  is a schematic diagram of an illustrative electronic device with a display in accordance with an embodiment of the present invention. 
         FIG. 6  is a cross-sectional side view of illustrative display layers and backlight structures in accordance with an embodiment of the present invention. 
         FIG. 7  is a cross-sectional side view of illustrative display layers and backlight structures showing how a light guide plate may have rounded edges in accordance with an embodiment of the present invention. 
         FIG. 8  is a perspective view of an illustrative light guide plate having a rounded edge on one side and a straight edge on an opposing side in accordance with an embodiment of the present invention. 
         FIG. 9  is a perspective view of a portion of an illustrative light guide plate having blunt edges such as a chamfered edge in accordance with an embodiment of the present invention. 
         FIG. 10  is a perspective view of a portion of an illustrative light guide plate having blunt edges such as a demi bullnose edge in accordance with an embodiment of the present invention. 
         FIG. 11  is a perspective view of a portion of an illustrative light guide plate having blunt edges such as a tapered edge in accordance with an embodiment of the present invention. 
         FIG. 12  is a perspective view of a portion of an illustrative light guide plate having blunt edges such as a full bullnose edge in accordance with an embodiment of the present invention. 
         FIG. 13  is a perspective view of a portion of an illustrative light guide plate having blunt edges such as a beveled edge in accordance with an embodiment of the present invention. 
         FIG. 14  is a perspective view of an illustrative light guide plate having alignment features and blunt edges in accordance with an embodiment of the present invention. 
         FIG. 15  is a diagram of an illustrative injection molding system that may be used in forming light guide plates having blunt edges in accordance with an embodiment of the present invention. 
         FIG. 16  is a diagram of illustrative equipment that may be used to modify edges of a light guide plate in accordance with an embodiment of the present invention. 
         FIG. 17  is a diagram of illustrative equipment that may be used to modify edges of a light guide plate in accordance with an embodiment of the present invention. 
         FIG. 18  is a diagram showing how a molding tool and a grinding tool may be used in forming a light guide plate having blunt edges and showing how the light guide plate and additional device parts such as a housing are assembled to form a finished electronic device in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Electronic devices may include displays. The displays may be used to display images to a user. Illustrative electronic devices that may be provided with displays are shown in  FIGS. 1 ,  2 , and  3 . 
       FIG. 1  shows how electronic device  10  may have the shape of a laptop computer having upper housing  12 A and lower housing  12 B with components such as keyboard  16  and touchpad  18 . Device  10  may have hinge structures  20  that allow upper housing  12 A to rotate in directions  22  about rotational axis  24  relative to lower housing  12 B. Display  14  may be mounted in upper housing  12 A. Upper housing  12 A, which may sometimes referred to as a display housing or lid, may be placed in a closed position by rotating upper housing  12 A towards lower housing  12 B about rotational axis  24 . 
       FIG. 2  shows how electronic device  10  may be a handheld device such as a cellular telephone, music player, gaming device, navigation unit, or other compact device. In this type of configuration for device  10 , housing  12  may have opposing front and rear surfaces. Display  14  may be mounted on a front face of housing  12 . Display  14  may, if desired, have a display cover layer or other exterior layer that includes openings for components such as button  26 . Openings may also be formed in a display cover layer or other display layer to accommodate a speaker port (see, e.g., speaker port  28  of  FIG. 2 ). 
       FIG. 3  shows how electronic device  10  may be a tablet computer. In electronic device  10  of  FIG. 3 , housing  12  may have opposing planar front and rear surfaces. Display  14  may be mounted on the front surface of housing  12 . As shown in  FIG. 3 , display  14  may have a cover layer or other external layer with an opening to accommodate button  26  (as an example). 
       FIG. 4  shows an illustrative configuration for electronic device  10  in which device  10  is a computer display or a computer that has been integrated into a computer display. With this type of arrangement, housing  12  for device  10  is mounted on a support structure such as stand  27 . Display  14  is mounted on a front face of housing  12 . 
     The illustrative configurations for device  10  that are shown in  FIGS. 1 ,  2 ,  3 , and  4  are merely illustrative. In general, electronic device  10  may be a laptop computer, a computer monitor containing an embedded computer, a tablet computer, a cellular telephone, a media player, or other handheld or portable electronic device, a smaller device such as a wrist-watch device, a pendant device, a headphone or earpiece device, or other wearable or miniature device, a television, a computer display that does not contain an embedded computer, a gaming device, a navigation device, an embedded system such as a system in which electronic equipment with a display is mounted in a kiosk or automobile, equipment that implements the functionality of two or more of these devices, or other electronic equipment. 
     Housing  12  of device  10 , which is sometimes referred to as a case, may be formed of materials such as plastic, glass, ceramics, carbon-fiber composites and other fiber-based composites, metal (e.g., machined or cast aluminum, stainless steel, or other metals), other materials, or a combination of these materials. Device  10  may be formed using a unibody construction in which most or all of housing  12  is formed from a single structural element (e.g., a piece of machined metal or a piece of molded plastic) or may be formed from multiple housing structures (e.g., outer housing structures that have been mounted to internal frame elements or other internal housing structures). 
     Display  14  may be a touch sensitive display that includes a touch sensor or may be insensitive to touch. Touch sensors for display  14  may be formed from an array of capacitive touch sensor electrodes, a resistive touch array, touch sensor structures based on acoustic touch, optical touch, or force-based touch technologies, or other suitable touch sensor components. 
     Displays for device  10  may, in general, include image pixels formed from light-emitting diodes (LEDs), organic LEDs (OLEDs), plasma cells, electrowetting pixels, electrophoretic pixels, liquid crystal display (LCD) components, or other suitable image pixel structures. In some situations, it may be desirable to use LCD components to form display  14 , so configurations for display  14  in which display  14  is a liquid crystal display are sometimes described herein as an example. It may also be desirable to provide displays such as display  14  with backlight structures, so configurations for display  14  that include a backlight unit may sometimes be described herein as an example. Other types of display technology may be used in device  10  if desired. The use of liquid crystal display structures and backlight structures in device  10  is merely illustrative. 
     A display cover layer may cover the surface of display  14  or a display layer such as a color filter layer or other portion of a display may be used as the outermost (or nearly outermost) layer in display  14 . A display cover layer or other outer display layer may be formed from a transparent glass sheet, a clear plastic layer, or other transparent member. 
     Touch sensor components such as an array of capacitive touch sensor electrodes formed from transparent materials such as indium tin oxide may be formed on the underside of a display cover layer, may be formed on a separate display layer such as a glass or polymer touch sensor substrate, or may be integrated into other display layers (e.g., substrate layers such as a thin-film transistor layer). 
     A schematic diagram of an illustrative configuration that may be used for electronic device  10  is shown in  FIG. 5 . As shown in  FIG. 5 , electronic device  10  may include control circuitry  29 . Control circuitry  29  may include storage and processing circuitry for controlling the operation of device  10 . Control circuitry  29  may, for example, include storage such as hard disk drive storage, nonvolatile memory (e.g., flash memory or other electrically-programmable-read-only memory configured to form a solid state drive), volatile memory (e.g., static or dynamic random-access-memory), etc. Control circuitry  29  may include processing circuitry based on one or more microprocessors, microcontrollers, digital signal processors, baseband processors, power management units, audio codec chips, application specific integrated circuits, etc. 
     Control circuitry  29  may be used to run software on device  10 , such as operating system software and application software. Using this software, control circuitry  29  may present information to a user of electronic device  10  on display  14 . When presenting information to a user on display  14 , sensor signals and other information may be used by control circuitry  29  in making adjustments to the strength of backlight illumination that is used for display  14 . 
     Input-output circuitry  30  may be used to allow data to be supplied to device  10  and to allow data to be provided from device  10  to external devices. Input-output circuitry  30  may include communications circuitry  32 . Communications circuitry  32  may include wired communications circuitry for supporting communications using data ports in device  10 . Communications circuitry  32  may also include wireless communications circuits (e.g., circuitry for transmitting and receiving wireless radio-frequency signals using antennas). 
     Input-output circuitry  30  may also include input-output devices  34 . A user can control the operation of device  10  by supplying commands through input-output devices  34  and may receive status information and other output from device  10  using the output resources of input-output devices  34 . 
     Input-output devices  34  may include sensors and status indicators  36  such as an ambient light sensor, a proximity sensor, a temperature sensor, a pressure sensor, a magnetic sensor, an accelerometer, and light-emitting diodes and other components for gathering information about the environment in which device  10  is operating and providing information to a user of device  10  about the status of device  10 . 
     Audio components  38  may include speakers and tone generators for presenting sound to a user of device  10  and microphones for gathering user audio input. 
     Display  14  may be used to present images for a user such as text, video, and still images. Sensors  36  may include a touch sensor array that is formed as one of the layers in display  14 . 
     User input may be gathered using buttons and other input-output components  40  such as touch pad sensors, buttons, joysticks, click wheels, scrolling wheels, touch sensors such as sensors  36  in display  14 , key pads, keyboards, vibrators, cameras, and other input-output components. 
     A cross-sectional side view of an illustrative configuration that may be used for display  14  of device  10  (e.g., for display  14  of the devices of  FIG. 1 ,  FIG. 2 ,  FIG. 3 , or  FIG. 4  or other suitable electronic devices) is shown in  FIG. 6 . As shown in  FIG. 6 , display  14  may include backlight structures such as backlight unit  42  for producing backlight  44 . During operation, backlight  44  travels outwards (vertically upwards in dimension Z in the orientation of  FIG. 6 ) and passes through display pixel structures in display layers  46 . This illuminates any images that are being produced by the display pixels for viewing by a user. For example, backlight  44  may illuminate images on display layers  46  that are being viewed by viewer  48  in direction  50 . 
     Display layers  46  may be mounted to chassis structures such as a plastic chassis structure and/or a metal chassis structure to form a display module for mounting in housing  12  or display layers  46  may be mounted directly in housing  12  (e.g., by stacking display layers  46  into a recessed portion in housing  12 ). Display layers  46  may form a liquid crystal display or may be used in forming displays of other types. 
     In a configuration in which display layers  46  are used in forming a liquid crystal display, display layers  46  may include a liquid crystal layer such a liquid crystal layer  52 . Liquid crystal layer  52  may be sandwiched between display layers such as display layers  58  and  56 . Layers  56  and  58  may be interposed between lower polarizer layer  60  and upper polarizer layer  54 . If desired, upper polarizer layer  54  may be attached to an outer cover layer such as cover layer  49  ( FIG. 6 ). 
     Layers  58  and  56  may be formed from transparent substrate layers such as clear layers of glass or plastic. Layers  56  and  58  may be layers such as a thin-film transistor layer and/or a color filter layer. Conductive traces, color filter elements, transistors, and other circuits and structures may be formed on the substrates of layers  58  and  56  (e.g., to form a thin-film transistor layer and/or a color filter layer). Touch sensor electrodes may also be incorporated into layers such as layers  58  and  56  and/or touch sensor electrodes may be formed on other substrates. Display layers  46  may sometimes collectively be referred to herein as a “display cell” or a “display unit.” 
     With one illustrative configuration, layer  58  may be a thin-film transistor layer that includes an array of thin-film transistors and associated electrodes (display pixel electrodes) for applying electric fields to liquid crystal layer  52  and thereby displaying images on display  14 . Layer  56  may be a color filter layer that includes an array of color filter elements for providing display  14  with the ability to display color images. If desired, layer  58  may be a color filter layer and layer  56  may be a thin-film transistor layer. 
     During operation of display  14  in device  10 , control circuitry  29  (e.g., one or more integrated circuits such as components  68  on printed circuit  66  of  FIG. 6 ) may be used to generate information to be displayed on display  14  (e.g., display data). The information to be displayed may be conveyed from circuitry  68  to display driver integrated circuit  62  using a signal path such as a signal path formed from conductive metal traces in flexible printed circuit  64  (as an example). 
     Display driver integrated circuit  62  may be mounted on thin-film transistor layer driver ledge  82  or elsewhere in device  10 . A flexible printed circuit cable such as flexible printed circuit  64  may be used in routing signals between printed circuit  66  and thin-film transistor layer  58 . If desired, display driver integrated circuit  62  may be mounted on printed circuit  66  or flexible printed circuit  64 . 
     Printed circuit  66  may be formed from a rigid printed circuit board (e.g., a layer of fiberglass-filled epoxy) or a flexible printed circuit (e.g., a flexible sheet of polyimide or other flexible polymer layer). However, these examples are merely illustrative. If desired printed circuits  64  and  66  may be formed from a combination of rigid and flexible printed circuit layers (e.g., printed circuit  66  may be formed from a rigid printed circuit board with a layer of flexible printed circuitry that extends from an edge of printed circuit  66  to form flexible printed circuitry  64  that attaches to thin-film transistor layer  58 ). 
     Backlight structures  42  may include a backlight light guide plate such as light guide plate  78 . Light guide plate  78  may be formed from a transparent material such as clear glass or plastic. During operation of backlight structures  42 , a light source such as light source  72  may generate light  74 . Light source  72  may be, for example, an array of light-emitting diodes. 
     Light  74  from light source  72  may be coupled into edge surface  76  of light guide plate  78  and may be distributed laterally in dimensions X and Y throughout light guide plate  78  due to the principal of total internal reflection. Light guide plate  78  may include light-scattering features such as pits or bumps or other light-scattering structures. The light-scattering features may be located on an upper surface and/or on an opposing lower surface of light guide plate  78 . 
     Light  74  that scatters upwards in direction Z from light guide plate  78  may serve as backlight  44  for display  14 . Light  74  that scatters downwards may be reflected back in the upwards direction by reflector  80 . Reflector  80  may be formed from a reflective material such as a layer of white plastic or other shiny materials. 
     To enhance backlight performance for backlight structures  42 , backlight structures  42  may include optical films  70 . Optical films  70  may include diffuser layers for helping to homogenize backlight  44  and thereby reduce hotspots, compensation films for enhancing off-axis viewing, and brightness enhancement films (also sometimes referred to as turning films) for collimating backlight  44 . Optical films  70  may overlap the other structures in backlight unit  42  such as light guide plate  78  and reflector  80 . For example, if light guide plate  78  has a rectangular footprint in the X-Y plane of  FIG. 6 , optical films  70  and reflector  80  may have a matching rectangular footprint. 
     If care is not taken, the layers in a display such as optical film layers may be susceptible to damage. For example, conventional light guide plates have sharp edges around the periphery of the light guide plate that can scratch optical film layers such as an adjacent diffuser layer. This type of abrasive contact between sharp edges of the light guide plate and the adjacent optical films can produce dust particles which in turn can damage other optical films in the display. 
     To minimize abrasive contact between light guide plate  78  and optical films  70 , light guide plate  78  may have one or more blunt edges. A cross-sectional side view of backlight structures  46  in which light guide plate  78  is provided with blunt edges is shown in  FIG. 7 . 
     As shown in  FIG. 7 , light guide plate  78  may be interposed between reflector  80  and optical films  70 . A light source such as light source  72  may emit light into edge surface  76  of light guide plate  78 . Light-scattering features  92  (e.g., pits, bumps, or other light-scattering structures) may help scatter light upwards through display layers in display  14 . Light-scattering features  92  may be formed on lower surface  78 L (as shown in  FIG. 7 ) or may be formed on opposing upper surface  78 U. 
     Light source  72  may, for example, be a strip of light-emitting diodes that runs along edge surface  76  of light guide plate  78 . Light-emitting diodes  72  may be mounted on a substrate such as substrate  84 . Substrate  84  may be formed from a flexible printed circuit substrate material such as polyimide or a sheet of other flexible polymer or may be formed from a rigid printed circuit board material (e.g., fiberglass-filled epoxy material such as FR4). Light guide plate  78  may be attached to substrate  84  using adhesive such as adhesive  86 . Adhesive  86  may be pressure-sensitive adhesive, light-cured adhesive, liquid adhesive, or other suitable adhesive. 
     Light guide plate  78  may have an upper surface such as upper surface  78 U and a lower surface such as lower surface  78 L. Upper surface  78 U may be adjacent to optical films  70  (e.g., adjacent to a diffuser layer such as diffuser layer  70 D in optical films  70 ), whereas lower surface  78 L may be adjacent to reflector  80 . Upper surface  78 U may have a curved portion such as curved portion  78 S that joins the planar portion of upper surface  78 U with planar lower surface  78 L. Curved surface  78 S may, for example, have a radius of curvature R of greater than 10 microns, greater than 50 microns, greater than 100 microns, greater than 500 microns, or less than 500 microns. Curved surface  78 S of light guide plate  78  may form a blunt edge that minimizes abrasive contact between light guide plate  78  and optical films  70 . 
     If desired, light guide plate  78  may have a combination of blunt edges such as blunt edge  78 S and straight edges such as straight edge  76 . As shown in  FIG. 8 , for example, light guide plate  78  has a rectangular shape with four edges. One, two, three, or all four of these edges may be blunt edges formed from curved or beveled surfaces. In the example of  FIG. 8 , edge  78 S is a blunt edge formed from a curved surface. Opposing edge  76 , on the other hand, is a straight edge. If desired, blunt edge  78 S may extend along an entire side of light guide plate  78  from corner C 1  to corner C 2  or may extend only partially along a side of light guide plate  78 . 
     Edge  76  may be formed from a flat vertical sidewall surface that extends along an entire side of light guide plate  78  or edge  76  may be formed from portions with curved surfaces and portions with vertical sidewall surfaces. In configurations where edge  76  is used as a light coupling edge for receiving light from light source  72  ( FIG. 7 ), edge  76  may have light coupling regions with surface variations that facilitate light coupling. For example, edge  76  may have light coupling regions that include vertically extending corrugations or other surface textures (e.g., curved surfaces, scalloped surfaces, sawtooth surfaces, angled surfaces, a combination of these surfaces, etc.). If desired, edge  76  may have vertical sidewall surfaces (e.g., sidewall surfaces that are oriented perpendicularly to upper surface  78 U and lower surface  78 L of light guide plate  78 ) interspersed among other surface regions (e.g., curved edge segments, beveled edge segments, other blunt edge segments, etc.). 
     A “blunt” edge may refer to an edge formed from a curved surface (e.g., a surface having a radius of curvature R of greater than 50 microns) or may refer to an edge with an interior angle of greater than 90 degrees, for example. A “straight” edge may refer to an edge with an interior angle of approximately 90 degrees, for example. Edge  76  in the example of  FIG. 7  is defined by an interior angle of approximately 90 degrees and is sometimes referred to as a flat or square edge. If desired, light guide plate  78  may have one blunt edge and three straight edges, two blunt edges and two straight edges, three blunt edges and one straight edge, the entire periphery of light guide plate  78  may have blunt edges, etc. The example of  FIG. 8  is merely illustrative. 
     Different surface geometries may be used in forming blunt edges such as edge  78 S of light guide plate  78 . Illustrative examples of different surface geometries that may be used to form blunt edges such as edge  78 S are shown in  FIGS. 9-13 . 
     In the example of  FIG. 9 , blunt edge  78 S of light guide plate  78  is formed from a chamfered surface (sometimes referred to as a beveled surface). With this type of configuration, a series of planar surfaces  88  that are angled with respect to one another (e.g., by an interior angle of greater than 90 degrees) may join upper surface  78 U with lower surface  78 L of light guide plate  78 . In the example of  FIG. 9 , three planar surfaces  88  are used to join upper surface  78 U with lower surface  78 L of light guide plate  78 . This is, however, merely illustrative. If desired, there may be more than three surfaces  88  or less than three surfaces  88  joining upper surface  78 U with lower surface  78 L. For example, a single planar surface  88  (e.g., angled with respect to planar surface  78 U by an interior angle of greater than 90 degrees) may be used to form a beveled edge that joins upper surface  78 U with lower surface  78 L. 
     In the example of  FIG. 10 , blunt edge  78 S of light guide plate  78  is formed from a rounded surface. This type of edge is sometimes referred to as a half bullnose, a demi bullnose, or eased edge. With this type of configuration, a smooth curved surface may join planar upper surface  78 U of light guide plate  78  with planar lower surface  78 L of light guide plate  78 . Curved surface  78 S may, for example, take the place of a planar sidewall at an edge of light guide plate  78 . 
     In the example of  FIG. 11 , blunt edge  78 S of light guide plate  78  is formed from a curved surface that forms a tapered edge. The central portion of light guide plate  78  may have a first thickness T 1  in between upper surface  78 U and lower surface  78 L. The edge portion at edge  78 S may have a second thickness T 2  less than thickness T 1 . The curved surface of tapered edge  78 S of  FIG. 11  may transition gradually from the central portion to the edge portion such that abrasive contact between light guide plate  78  and adjacent optical films  70  ( FIG. 7 ) is minimized. 
     In the example of  FIG. 12 , blunt edge  78 S of light guide plate  78  is formed from a curved surface that forms a full bullnose edge. With this type of configuration, edge  78 S has a c-shaped cross section in which upper surface  78 U and lower surface  78 L are joined by a smooth c-shaped curved surface  78 S. 
     In the example of  FIG. 13 , blunt edge  78 S of light guide plate  78  is formed from a beveled edge (e.g., a half-beveled edge, a quarter-beveled edge, etc.). The example of  FIG. 13  is similar to that of  FIG. 9  except that the example of  FIG. 13  includes a vertical side wall portion  99 . 
     In some configurations, light guide plate  78  may have alignment features that help align and secure light guide plate  78  within housing  12  of device  10 . For example, as shown in  FIG. 14 , light guide plate  78  may have alignment structures  78 E that protrude out laterally from light guide plate  78 . Alignment structures  78 E (sometimes referred to as protrusions or tabs) may be received by corresponding alignment structures in housing  12  of device  10  or in other structures surrounding display  14 . If desired, light guide plate alignment structures  78 E may have engagement features such as openings  79  for receiving corresponding engagement features such as posts or protrusions to hold light guide plate  78  in place within device  10 . 
     The example of  FIG. 14  in which light guide plate  78  has two alignment structures  78 E formed on a single edge of light guide plate  78  is merely illustrative. If desired, there may be one or more alignment structures  78 E on one, two, three, or all four sides of light guide plate  78 . 
     If desired, light guide plate alignment structures  78 E may have blunt edges  78 S to minimize abrasive contact between alignment structures  78 E and adjacent optical films  70  ( FIG. 7 ). Blunt edges of alignment structures  78 E may take the form of any of the illustrative blunt edges shown in  FIGS. 9-13 . 
     An illustrative injection molding system that may be used to mold light guide plate  78  with one or more blunt edges  78 S is shown in  FIG. 15 . As shown in  FIG. 15 , injection molding system  200  may include a mold such as mold  202 . Mold  202  may include a mold cavity  202 C. Mold cavity  202 C may have the negative shape of light guide plate  78  with blunt edge  78 S such that, when filled with plastic, the resulting part has the shape of light guide plate  78  with blunt edge  78 S. As shown in  FIG. 15 , upper mold  202 C has curved surface  202 S that helps form blunt edges  78 S of light guide plate  78 . 
     As shown in  FIG. 15 , a shot of pelletized thermoplastic material (e.g., thermoplastic granules or “resin”) may be added to a hopper such as hopper  282 . The material may be gravity fed into a screw-type plunger such as plunger  284 . The heat generated by heating unit  286  and the rotation of the screw in plunger  284  may result in elevated temperatures and a shearing action on the thermoplastic pellets that causes the pellets to melt into molten plastic. Screw rotation in plunger  284  may push the molten plastic towards nozzle  288  and into mold cavity  202 C. 
     When mold  202  has been completely filled, the molten plastic may be cooled. When the plastic has solidified, mold  202  may be removed (e.g., mold  202  may be opened by separating upper portion  202 U from lower portion  202 L along line  244 ). 
     The plastic that solidifies within cavity  202 C may form light guide plate  78  with blunt edge  78 S. If desired, additional processing operations may be performed to light guide plate  78 . For example, following the injection molding process that forms light guide plate  78 , the edges of light guide plate  78  such as edge  78 S (and other edges of light guide plate  78 , if desired) may be grinded and/or polished. Illustrative equipment that may be used to modify edge surfaces such as edge surface  78 S of light guide plate  78  is shown in  FIGS. 16 and 17 . 
     As shown in  FIG. 16 , equipment  234  (e.g., a diamond edge polishing machine, an edge grinding tool, an edge polishing tool, a laser cutting tool, a milling tool, a machining tool such as a drill bit, milling machine cutter, or other cutting tool, etc.) may include computer-controlled positioner  236  and machining tool head  238 A. Head  238 A has a surface profile that is configured to grind and/or polish edge surface  78 S to form a rounded surface with a c-shaped cross section (e.g., a full bullnose edge). During operation, positioner  236  rotates machining tool head  238 A (e.g., using a motor) about axis  240  while moving tool  238 A along edge  78 S of light guide plate  78 , thereby machining edge surface  78 S of light guide plate  78  into a desired shape. If desired, different arrangements of positioners may be used. As an example, computer-controlled positioner  235  may be used to move light guide plate  78  during edge polishing operations while equipment  234  remains in a fixed position. 
     In the illustrative example of  FIG. 17 , equipment  234  includes machining tool head  238 B. Head  238 B has a surface profile that is configured to grind and/or polish edge surface  78 S to form a partially rounded surface (e.g., a demi bullnose edge or a half bullnose edge having a curved surface portion and a planar surface portion). 
     If desired, equipment  234  may be used to modify (e.g., grind and/or polish) all four edges of light guide plate  78  or equipment  234  may be used to modify one or more of the edges of light guide plate  78 . The machining tool head that is used to modify a given edge of light guide plate  78  may have a surface profile corresponding to the desired surface profile of that edge. For example, in arrangements where light guide plate  78  has a combination of rounded and straight edges, a combination of machining tool heads having different surface profiles may be used to treat the four edges of light guide plate  78  (e.g., machining tool heads with flat surface profiles, machining tool heads with curved surface profiles, etc.). 
     A flow chart of illustrative steps involved in forming light guide plate  78  using the injection molding tool of  FIG. 15  and equipment  234  of  FIGS. 16 and 17  is shown in  FIG. 18 . 
     As shown in  FIG. 18 , equipment such as molding tool  200  may receive polymer material  300  (e.g., a clear resin such as polymethyl methacrylate resin or other acrylic resin, a polycarbonate resin, etc.). Molding tool  200  may be used in molding polymer  300  into light guide plate  78  having blunt edge  78 S. In some configurations, the resulting part formed by molding tool  200  may have a tail portion such as tail portion  78 T at edge  78 S. Light guide plate  78  may taper from a first thickness T 1 ′ at the central portion of light guide plate  78  to a second thickness T 2 ′ at tail portion  78 T of light guide plate  78 . The blunt edge formed by curved surface  78 S may minimize abrasive contact with and scratches on adjacent optical films  70  in display  14  of device  10 . 
     Following formation of light guide plate  78  having blunt edge  78 S, light guide plate  78  may be grinded and polished using a grinding tool such as grinding tool  234 . Grinding tool  234  may be used to grind down and thereby remove all or a portion of tail portion  78 T at edge  78 S. Grinding tool  234  may also be used in shaping and polishing one or more edges of light guide plate  78  to form smooth edges. For example, any plastic that seeps between upper mold  202 U and lower mold  202 L (e.g., at interface  244 ) during the injection molding process (sometimes referred to as flash or burrs) may be removed during the grinding/polishing step of  FIG. 18 . If desired, all four edges of light guide plate  78  may be polished using grinding tool  234 . 
     Following grinding and polishing operations, light guide plate  78 , other layers of display  14 , housing  12 , and other parts in electronic device  10  (shown as parts  306  in  FIG. 18 ) may be assembled using assembly equipment  304 , thereby forming finished electronic device  10 . This may include, for example, attaching light guide plate  78  to light-emitting diode substrate  84  of  FIG. 7 . 
     The foregoing is merely illustrative of the principles of this invention and various modifications can be made by those skilled in the art without departing from the scope and spirit of the invention. The foregoing embodiments may be implemented individually or in any combination.

Metadata:
Filing Date: 20131008
Publication Date: 20160119
Grant Date: 20160119
Priority Date: 20121220
Inventors: ZHU XINYU
CHIU PO-WEN
QI JUN
Assignee: APPLE INC
CPC Classifications: [{"code": "G02F1/133615", "inventive": true, "first": false, "tree": "[]"}, {"code": "B29D11/00663", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0093", "inventive": true, "first": true, "tree": "[]"}, {"code": "G02F1/133615", "inventive": true, "first": false, "tree": "[]"}, {"code": "G02B6/0093", "inventive": true, "first": true, "tree": "[]"}, {"code": "B29D11/00663", "inventive": true, "first": false, "tree": "[]"}, {"code": "B29D11/00663", "inventive": true, "first": true, "tree": "[]"}]
Family ID: 50974257