Abstract:
A surface having specular regions shaped to reflect incident light toward an optical sensor provides an ideal surface to be scanned by an optical mouse. When light is shined upon the surface, the reflections off of the specular regions appear as white points in the image acquired by the optical sensor, which gives the optical sensor the distinguishing characteristics it needs to differentiate between images. Since the specular regions reflect light so well, less light is needed to obtain an image, and power is conserved. The surface appears as a dark background in the image, providing contrast to the light reflecting off the specular regions. To protect the specular regions, an optically transparent coating can be layered on top of the surface. An alternative surface that may be easier to manufacture is a light colored surface dotted with darker colored regions.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates generally to the field of mousepads and, more particularly, to the field of mousepads for optical mice.  
           [0002]    Most computers now have an input device that controls the movement of a cursor on a computer screen. Examples of such devices include trackballs, joysticks, and mice. A common form of the mouse is a mechanical mouse; it has a small ball on its underside in contact with the surface upon which the mouse rests. When the mouse is moved, the ball rolls and activates sensors in the mouse that translate the rolling of the ball into movement of the cursor on the computer screen. Another kind of mouse is an optical mouse. The optical mouse has an optical sensor that scans a surface and acquires a series of images of the surface. The optical mouse determines its own position relative to the surface by comparing the differences between consecutive images.  
           [0003]    A typical optical mouse illuminates the surface it is scanning, generating shadows and reflections used by the optical sensor to acquire a good image. Depending on the surface type, the amount of light needed can vary. For instance, a dark surface absorbs light, requiring more light to adequately illuminate the surface in order for the optical sensor to acquire a usable image. The more light used by the optical mouse, however, the more power it consumes. This is a problem for low-power applications such as battery operated cordless mice, or for laptop computer users.  
           [0004]    The performance of the optical mouse also depends on the surface that it scans. If a surface is too homogeneous, the images acquired by the optical sensor while the optical mouse is moving will all be very similar, perhaps even identical. Since the optical mouse depends on differences between images to determine its position relative to the surface, similar images trick it into thinking that it has not changed position, when in fact it has. It is therefore important that the surface has enough distinguishing characteristics to eliminate such confusion.  
         SUMMARY OF THE INVENTION  
         [0005]    A surface having specular regions shaped to reflect incident light towards the optical sensor provides an ideal surface to be scanned by the optical mouse. When light is shined upon the surface, the reflections off of the specular regions appear as bright white points in the image acquired by the optical sensor, which gives the optical sensor the distinguishing characteristics it needs to differentiate between images. Since the specular regions reflect light so well, less light is needed to obtain an image, so power is conserved. The surface itself should either reflect light away from the optical sensor, or at least scatter light, so that it appears in the image to the optical sensor as a dark background, providing contrast to the light reflecting off of the specular regions.  
           [0006]    In accordance with an illustrated preferred embodiment of the present invention, the specular regions are depressions that are either made of, or are coated with, a specular material, and are shaped to reflect incident light toward the optical sensor. The surface is made of or coated with a specular material as well, or a material that scatters light. The reflections off of the depressions give the surface its distinguishing characteristics so the mouse is able to differentiate between images as it moves. Additionally, the brightness of the reflections helps the mouse conserve power.  
           [0007]    In another embodiment of the present invention, a surface is dotted with protrusions that reflect incident light toward the optical sensor. The protrusions are also either made of, or are coated with, a specular material, and perform the same function as the depressions.  
           [0008]    In a third embodiment of the present invention, the surface, whether dotted with depressions or protrusions, is coated with an optically transparent material that protects the surface from contamination or damage. The optically transparent material still allows light to pass through, but prevents the optical mouse from eroding away the specular regions as it traverses over the surface.  
           [0009]    In a fourth embodiment of the present invention, the surface has contrasting regions of two colors: one light, one dark. The lighter color is used in the background of the surface to minimize power consumption. The darker colored regions provide distinguishing characteristics on the surface for the optical sensor. Unlike the depressions and protrusions, however, the dark-colored regions do not reflect light well. As a result, when the optical sensor scans the surface, the dark colored regions appear to it as dark spots against a lighter background. This embodiment does not conserve as much power as the embodiments with the specular regions, but a colored surface may be easier to manufacture than a surface with depressions or protrusions.  
           [0010]    Further features and advantages of the present invention, as well as the structure and operation of preferred embodiments of the present invention, are described in detail below with reference to the accompanying exemplary drawings. In the drawings, like reference numbers indicate identical or functionally similar elements.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a three-dimensional view of a portion of the surface along with a lens and an optical sensor.  
         [0012]    [0012]FIG. 2 is a cross-sectional side view of the objects in FIG. 1, taken along a vertical plane passing through line C-C′ shown in FIG. 1. A light source and relative position determinator have been added, and the light beams from the light source reflect off of multiple depressions.  
         [0013]    [0013]FIG. 3 is a detailed view of the pixels in the optical sensor shown in FIGS. 1 and 2.  
         [0014]    [0014]FIG. 4 is a cross-sectional side view of the objects shown in FIG. 2. The light beams from the light source reflect off of a single depression.  
         [0015]    [0015]FIG. 5 is a cross-sectional side view of a portion of a surface with protrusions, a lens, an optical sensor, light source, and relative position determinator.  
         [0016]    [0016]FIG. 6A is a cross-sectional side view of the surface with depressions and an optically transparent coating.  
         [0017]    [0017]FIG. 6B is a cross-sectional side view of the surface with protrusions and an optically transparent coating.  
         [0018]    [0018]FIG. 7 is a top-down, blown-up and partial view of the surface with dark colored areas against a lighter colored background.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0019]    The present invention is a surface that is scanned by an optical sensor of a relative position determinator such as an optical mouse or a trackball device. The surface has characteristics to reduce the amount of power needed by the optical mouse in order to light the surface, and so it can easily differentiate between the images the optical sensor acquires of the surface.  
         [0020]    [0020]FIG. 1 illustrates a preferred embodiment of a portion of a surface made in accordance with the teachings of the present invention, hereinafter referred to as a surface portion  11 . Depressions  13  are located on the surface portion  11  in either an ordered or random fashion. The areas between the depressions  13  are non-distorted regions  17 . The surface portion  11  is scanned by an optical sensor  16 , which exists in prior art. A lens  10 , also from prior art, is fixed in front of the optical sensor  16 , between the optical sensor  16  and the surface portion  11 . The lens  10  projects an image of the surface portion  11  onto the optical sensor  16 .  
         [0021]    [0021]FIG. 2 shows a cross-sectional side view of the surface portion  11 , lens  10 , and optical sensor  16 , taken along a vertical plane passing through the line indicated by C-C′ in FIG. 1. A light source  14  is added, as well as a relative position determinator  18  that is electrically coupled to the optical sensor  16 . The relative position determinator  18  is a device well known in the art, and is found in common computer input devices such as trackballs and mice. The optical sensor  16  lies a distance D away from the surface portion  11 . The lens  10  has a focal length F, and lies a distance X away from the surface portion  11 . The distance X is chosen by determining the image size to be projected by the lens  10  onto the optical sensor  16 . The preferred embodiment uses a 1:1 image ratio, with X=2F and D=4F. To obtain a 2:1 image ratio, use X=3F and D=4.5F. Other image ratios are possible by varying distance X, distance D, and focal length F.  
         [0022]    The light source  14  shines light beams onto the surface portion  11 . The light source  14  is preferably a light-emitting diode, although any light-emitting device can be used. The depressions  13  are shaped such that light beams  15 , with angles of incidence A 1  through A 2 , hit the depressions  13  and are reflected towards the lens  10 . The lens projects the light beams  15  onto the optical sensor  16 . The angles at which the light beams  15  hit the surface portion  11  will vary depending on the positioning of the light source  14 . The light beams used to develop the present invention had an angle of incidence upon the surface portion  11  of approximately 20 to 30 degrees. In the embodiment shown, the optical sensor  16  and lens  10  are located directly above the lighted region; therefore, the depressions  13  of this embodiment should be shaped to reflect the light beams  15  normal to the surface portion  11 .  
         [0023]    The surface portion  11  is made of machined metal, molded plastic, aluminized mylar, or any other material that has the ability to hold small features. The depressions  13  should be made of or coated with a specular material that reflects light. A material is specular if a light beam hitting the material has an angle of incidence equal to its angle of reflectance. The non-distorted regions  17  are made of or coated with the same specular material as the depressions  13 . This is the preferred embodiment and the simplest to manufacture. The non-distorted regions  17  are also made of or coated with a diffuse light-scattering material, or any other material as long as the non-distorted regions  17  do not reflect incident light towards the lens  10 . Although the surface portion  11  in FIGS. 1 and 2 is drawn as flat and planar, the surface portion  11  can be curved, bent, or any other shape that can hold the depressions  13 .  
         [0024]    Since the light beams  15  can have varying angles of incidence due to the variance in the positioning of the light source  14 , the shape of the depressions  13  can also vary. One possibility for the shape of the depressions  13  is a smoothly curved surface, like the inside of a bowl. The curvature of the depressions  13  are shaped to allow light beams  15  with a range of angles of incidence A 1  through A 2  to be reflected toward the lens  10  and optical sensor  16 . Other shapes can also be used. For instance, a curved surface can be approximated by a faceted depression  13  with from three to an infinite number of sides. For optimal performance, the depressions  13  should be rotationally symmetric, because the orientation of the optical sensor  16  to the surface portion  11  can be random.  
         [0025]    The relative position determinator  18  acquires the images of surface portion  11  projected onto optical sensor  16  by lens  10 , as the optical sensor  16  moves relative to the surface portion  11 . This relative movement can be achieved by moving the optical sensor  16  over the surface portion  11 , which is the situation when the relative position determinator  18  is an optical mouse. The relative movement can also be obtained by keeping the optical sensor  16  stationary while the surface portion  11  is moved, which is the case when the relative position determinator  18  is a trackball device. A combination of both methods can also be used, as long as there is relative movement between the optical sensor  16  and the surface portion  11 .  
         [0026]    [0026]FIG. 3 depicts an exemplary optical sensor  16  that exists in prior art, showing the side of the optical sensor  16  that faces the lens  10  in FIG. 1. The optical sensor  16  typically has a pixel array  23 , a structure well known in the art. The pixel array  23  comprises individual pixels  25  arranged in a close-packed grid. A pixel  25  is the smallest unit in the optical sensor  16  that is capable of detecting an image. A depression  13  is detectable by a pixel  25  if the image of the depression  13  is larger than the pixel  25 . Only half of the depression  13  can show up in an image sensed by the optical sensor  16 , since light can only bounce off of half of the depression  13  at any given time. If a 1:1 image of the surface portion  11  is projected by the lens  10  (shown in FIG. 2) onto the optical sensor  16 , the size of each depression  13  should be at least twice as large as a pixel  25 .  
         [0027]    The depressions  13  are spaced such that at least one depression  13  is detectable by the pixel array  23  of the optical sensor  16  at all times. To account for the possibility of noise, and for improved performance, two or more depressions  13  should be detectable by the pixel array  23  at any given time. The depressions  13  should not be on the same spacing as the pixels  25  in the pixel array  23  in order to avoid aliasing.  
         [0028]    The optical sensor  16  is able to detect light beams  15  reflecting off of multiple depressions  13 . FIG. 2 only shows light beams  15  reflecting off of two depressions, since it is a cross-sectional view, but the optical sensor  16  is able to detect light beams  15  reflecting off of all depressions  13  immediately underneath the optical sensor  16  and lens  10 . For example, all the depressions  13  shown in FIG. 1 will be detected by the optical sensor  16 , since they are all immediately underneath the optical sensor  16  and lens  10 . Although it is preferable to have multiple depressions  13  underneath the optical sensor  16  at all times, the relative position determinator  18  will still work if light beams  15  only reflect off of a single depression  13  toward the lens  10  and optical sensor  16 , as is shown in FIG. 4.  
         [0029]    [0029]FIG. 5 shows another embodiment of the present invention. The depressions  13  of FIG. 2 are replaced with protrusions  31 . The curvatures of the protrusions  31  are shaped such that light beams  15  with angles of incidence A 3  through A 4  are reflected toward the lens  10 . The protrusions  31  should be rounded and rotationally symmetric for optimal performance. If a 1:1 image of the surface portion  11  is projected by the lens  10  onto the optical sensor  16 , the size of each protrusion  31  should be at least twice as large as a pixel  25  (shown in FIG. 3). The protrusions  31  are spaced such that at least one protrusion  31  is detectable by the pixel array  23  of the optical sensor  16  shown in FIG. 3 at all times. To minimize the possibility of aliasing, the protrusions  31  should be on a different spacing than the pixels  25  in the pixel array  23 . The protrusions  31  can also be approximated by faceted protrusions  31  with from three to infinite sides. The surface portion  11  and non-distorted regions  17  remain as described in FIG. 2.  
         [0030]    In FIGS. 6A and 6B, the present invention is covered with an optically transparent coating  41  that protects the surface portion  11  from contamination and damage. In FIG. 6A, the surface portion  11  and the depressions  13  are covered with the optically transparent coating  41 . This prevents foreign particles from falling into the depressions  13  and blocking the incoming light. In FIG. 6B, the optically transparent coating  41  fills the valleys between the protrusions  31  and covers the surface portion  11 . This prevents the protrusions  31  from wearing down as the lens  10  and optical sensor  16  pass over it.  
         [0031]    A final embodiment of the present invention is shown in FIG. 7. FIG. 7 is a top-down, blown-up partial view of the surface portion  11 . This illustrated embodiment has contrasting regions of two colors, although more colors can be used. A first color is used in colored regions  51  against a background  53  of a second color. The colored regions  51  can be any shape, but for convenience of illustration the colored regions  51  in this embodiment are circular. For optimal performance, the colored regions  51  should be darker than the background  53 . The lighter the background  53 , the less light is needed to illuminate the surface portion  11 , which results in less power being consumed. For example, the colored regions  51  can be black while the color of the background  53  can be white, as shown in FIG. 7. The optimal colors for the colored regions  51  and the background  53  depend on the wavelength of light being shined on the surface portion  11  from the light source  14  shown in FIG. 2. If a  1 : 1  image of the surface portion  11  is projected by the lens  10  onto the optical sensor  16 , the size of each colored region  51  should be at least the size of a pixel  25  shown in FIG. 3, and spaced such that at least one colored region  51 , is detectable by the pixel array  23  of the optical sensor  16  shown in FIG. 3. The colored regions  51  should not duplicate the spacing of the pixels  25  in the pixel array  23  to avoid aliasing.  
         [0032]    Although the present invention has been described in detail with reference to particular preferred embodiments, persons possessing ordinary skill in the art to which this invention pertains will appreciate that various modifications and enhancements may be made without departing from the spirit and scope of the claims that follow.