Illumination apparatus for a digitizer tablet with improved light panel

• US 5,736,686 A
• Filed: 03/01/1995
• Issued: 04/07/1998
• Est. Priority Date: 03/01/1995
• Status: Expired due to Fees

• Current Assignee: GTCO Corporation (GTCO Calcomp, Incoporated)
• Original Assignee: GTCO Corporation (GTCO Calcomp, Incoporated)
• Inventors: Ice, Donald A., Kautter, William J., Perret, Joseph F. Jr.
• Primary Examiner(s): Kuntz, Curtis
• Assistant Examiner(s): Shankar, Vijay
• Application Number:
  US08/396,617
• Time in Patent Office: 1,133 Days
• Field of Search: 178/18, 178/19, 178/20, 178/87, 345/173, 345/175, 345/176, 362/31
• US Class Current: 178/18.11
• CPC Class Codes: G02B 6/0031 Reflecting element, sheet or layer
• CPC Class Codes: G02B 6/0061 to provide homogeneous light output intensity
• CPC Class Codes: G02B 6/0068 Arrangements of plural sources, e.g. multi-colour light sources
• CPC Class Codes: G02B 6/0071 with elongated shape, e.g. tube
• CPC Class Codes: G02B 6/0085 Means for removing heat created by the light source from the package heat extraction or cooling elements for semiconductor light sources in general H01L33/64
• CPC Class Codes: G02B 6/0086 Positioning aspects

Abstract

An illumination apparatus for a digitizer tablet includes a support structure and a solid sheet optical light guide supported by the support structure and having first and second opposing surfaces and a plurality of edges. Light sources are carried by the support structure and positioned to direct light into light-receiving edges of the light guide. Reflecting structure is disposed adjacent the first surface of the light guide. A predetermined pattern is disposed on the first surface of the light guide structured and arranged in accordance with distance from the light sources.

Claims

1. An illumination apparatus for a digitizer tablet, the apparatus comprising:

a support structure;

a solid sheet optical light guide positioned above said support structure and having first and second opposing surfaces and a plurality of edges;

at least one light source carried by said support structure and positioned to direct light into at least one light-receiving edge of said light guide; and

reflecting structure disposed adjacent said first surface of said light guide,

a predetermined non-uniform pattern of surface disturbances associated with said first surface of said light guide, said pattern being structured and arranged in accordance with distance from said at least one light source.

2. The apparatus according to claim 1 wherein said at least one light source comprises a at least one fluorescent light bulb positioned adjacent said at least one light-receiving edge.

3. The apparatus according to claim 2, wherein exposed edges of said light guide, which are not adjacent said light bulb, are covered with a reflective coating such that light will not leak from said exposed edges.

4. The apparatus according to claim 1, wherein said edges including at least one light-receiving edge and at least one non-light-receiving edge, said non-light-receiving edge including a light reflecting coating thereon so as to define a virtual light source, and wherein said pattern is structured and arranged in accordance with distance from said at least one light source and said virtual light source.

5. The apparatus according to claim 1, wherein said at least one light source comprises a fluorescent light bulb with a reflective coating on the inside surface thereof and an aperture therein, said aperture being disposed adjacent a respective light-receiving edge so that light from said light bulb may be directed through the aperture and into said light guide.

6. The apparatus according to claim 1, wherein exposed edges of said light guide, which are not adjacent a respective one of said at least one light source, are covered with a reflective coating such that light will not leak from said exposed edges.

7. The apparatus according to claim 1, wherein said support structure comprises:

four frames, one frame being associated with one edge of said light guide, three of said frames having a portion which substantially surrounds an associated one of said at least one light source, each said portion having a curvature which corresponds to a curvature of an associated light bulb, an inner surface of each said portion including a reflective coating so as to reflect light which escapes from the associated light source back through the light source so as to be directed into the light guide; and

a digitizer core supported by the frames, said light guide being disposed on a surface of said digitizer core.

8. The apparatus according to claim 7, wherein a heat conductive spacer is provided between a surface of a light source and a surface of an associated frame so as to remove heat from the associated light source.

9. The apparatus according to claim 1, wherein said light guide comprises a light guide of optically clear material.

10. The apparatus according to claim 9, wherein said light guide comprises a clear plastic light guide.

11. The apparatus according to claim 9, wherein said light guide comprises an acrylic light guide.

12. The apparatus according to claim 1, wherein said predetermined pattern comprises individual elements having respective locations and sizes determined in accordance with distances from said at least one light source.

13. The apparatus according to claim 12, wherein said individual element sizes vary inversely with the distance from said at least one light source.

14. The apparatus according to claim 4, wherein said predetermined pattern comprises individual elements having respective locations and sizes determined in accordance with distances from said at least one light source and a distance from said virtual light source.

15. A method for generating a predetermined pattern on a surface of a solid sheet optical light guide illuminated by at least one light source, said light guide having a predetermined illumination area, the method comprising:

dividing said predetermined area into a plurality of square cells;

calculating initial half tone density values of elements of the pattern for each said cell;

performing a linear interpolation of the density values from edge to edge of the cells so as to generate cell half tone density values;

forming a predetermined surface disturbance on a light guide based on the generated cell half tone density values; and

measuring light output from the light guide of each cell.

16. The method according to claim 15, further comprising:

calculating a new half tone value for each cell so as to reduce the amount of light emission differential across a surface of the light guide; and

forming another predetermined surface disturbance on a light guide based on the new half tone value for each cell.

17. The method according to claim 15, wherein a plurality of light sources are provided and at least one virtual light source is created by reflected light, and the method further includes:

calculating the half tone values in accordance with distance from the light sources and the virtual light source.

18. The method according to claim 17, wherein the calculating of the initial half tone density value of the elements includes calculating in accordance with the following formula:

##EQU3## where;

D_cht the cell half tone density.

D_mht is the max half tone density. constant.

d_L1 is the distance to light source 1.

d_L2 is the distance to light source 2.

d_L3 is the distance to light source 3.

d_L3.sbsb.--_LV is the distance from light source 3 to the reflective edge virtual bulb.

d_LV is the distance to the reflective edge virtual bulb

and wherein the calculating of the new half tone value for each cell includes calculating in accordance with the following formula;

##EQU4## where;

D_cht is the cell half tone density

I_avg is the average non-border photometer reading

I_Lc is the left cell photometer reading

I_rc is the right cell photometer reading

D_cht.sbsb.p is the previous cell half tone density

k_mht is the max density normalization constant.

19. A method for constructing a solid sheet optical light guide for a digitizer tablet illuminated by at least one light source and a predetermined pattern associated therewith, the method comprising:

dividing a predetermined illumination area of the light guide into a plurality of cells;

calculating initial half tone density values of elements of the pattern for each of said cells;

performing a linear interpolation of the density values from edge to edge of the cells so as to generate cell half tone density values; and

forming a predetermined surface disturbance on the light guide based on the generated cell half tone density values.

20. The method according to claim 19, further comprising:

measuring light output from the light guide of each cell;

calculating a new half tone value for each cell so as to reduce the amount of light emission differential across a surface of the light guide; and

forming another predetermined surface disturbance on a light guide based on the new half tone value for each cell.

21. The method according to claim 20, wherein a plurality of light sources are provided and at least one virtual light source is created by reflected light, and the calculating of the initial half tone density values of elements of the pattern includes calculating the values in accordance with distance from the light sources and the virtual light source.

22. The method according to claim 21, wherein the calculating of the initial half tone density value of elements includes calculating in accordance with the following formula:

##EQU5## where;

D_cht the cell half tone density

K_mht is the max half tone density constant

d_L1 is the distance to light source 1

d_L2 is the distance to light source 2

d_L3 is the distance to light source 3

d_L3.sbsb.--_LV is the distance from light source 3 to the reflective edge virtual bulb

d_LV is the distance to the reflective edge virtual bulb

and wherein the calculating of the new half tone value for each cell includes calculating in accordance with the following formula;

##EQU6## where;

D_cht is the cell half tone density

I_avg is the average non-border photometer reading

I_lc is the left cell photometer reading

I_rc is the right cell photometer reading

D_cht.sbsb.p is the previous cell half tone density

k_mht is the max density normalization constant.

23. A method for generating a predetermined pattern of surface disturbances applied to a surface of a surface lighting panel illuminated by at least one light source, said lighting panel having a predetermined illumination area, the method comprising the steps of:

applying a homogenous half-tone pattern to said surface of said lighting panel;

measuring light output from the lighting panel; and

calculating a new half tone value for the surface lighting panel so as to reduce the amount of light emission differential across the light guide surface.