Abstract:
An optical window is disclosed through which light can be shone to generate a waveform. Windows are hourglass-shaped, to better conform the shape of the windows to the distribution of light intensity. The optical window can be incorporated into a variety of optical devices.

Description:
BACKGROUND OF THE INVENTION 
   The present disclosure is related to the field of optical devices, and more specifically to a wheel for use in generating a waveform. 
   Devices, such as computer mice, use opto-mechanical schemes to generate electrical waveforms which correspond to the movement of some element of the system. Other devices utilizing optics to generate a waveform are known in the automotive and manufacturing fields. Applications in these fields correlate wheel rotation to movement, e.g., rotation of an engine shaft. 
   In a mouse, for example, light emitted from a light source is detected by a detector. A stroboscopic wheel is interposed therebetween, such that the light passes through windows in the wheel. 
   The wheel is driven by mechanical contact with the mouse ball, and the pulses of light received by the receptor can be correlated with the speed of the ball, a reflection of the speed of the mouse itself. These pulses can then be integrated with respect to time to establish displacement of the mouse. 
   Ideally, a waveform corresponding to mouse displacement would be a perfect square wave. In such a perfect wave, voltage would rise instantaneously, dwell at maximum voltage for a finite period of time, then fall instantaneously to a minimum voltage where it would remain for a finite time before starting the process anew. In actual devices, waveforms are imperfect and are, at best, approximately sinusoidal. Considerable electronic circuitry is expended in filtering out noise and “squaring up” the signal so that it contains a sharp, readily discernable rising and falling edge. 
   The present invention addresses this and other problems associated with the prior art. The invention will become more readily apparent from the following Detailed Description, which proceeds with reference to the drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of a portion of the internal components of a prior art optical mouse pointing device. 
       FIG. 2  is an enlarged perspective view of a subset of the internal components of  FIG. 1 . 
       FIG. 3  is a is a polar plot of light intensity incident upon a detector in an optical device of the prior art. 
       FIG. 4  is a side view of an optical wheel having optical windows constructed according to the present disclosure. 
       FIG. 5  is an enlarged side view of a portion of the wheel of  FIG. 4 , showing in detail one of the plurality of optical windows. 
       FIG. 6  is a side view of an alternative optical device incorporating optical windows in accordance with the present disclosure. 
   

   DETAILED DESCRIPTION OF EMBODIMENTS 
     FIG. 1  shows a typical optical wheel in an optical mouse  10  of the prior art. Such devices typically include a light source  12  and a detector  14 . In conventional optical devices, e.g., an optical computer mouse ( FIG. 2 ), the light source and detector define a light path, the light passing through apertures  22  in an optical wheel  20 , the latter operating under a stroboscopic principle. 
   The intensity of light from an LED or other light source is not uniform when measured at a constant distance from the light source.  FIG. 3  is a qualitative polar plot of the intensity of light striking a detector in a conventional device. Peak intensity occurs along the optical axis of the device (90°) and falls off by the time one moves to plus or minus 90° from the optical axis, where the intensity is virtually zero. 
   In the computer mouse example, this non-uniform light then passes through straight-sided apertures  22  in the signal-generating wheel  20  ( FIG. 2 ). The resultant waveform does not present a square shape, thereby introducing inaccuracy into the device and necessitating additional processing to correct for the waveform imperfection. 
   A wheel comprising optical windows according to the present disclosure is shown in  FIGS. 4 and 5 . The optical windows  42  are hourglass-shaped, in that two opposing sides  44 , 46  are disposed so that the ends of the opposed sides are spaced farther apart than their centers. In one embodiment, the opposing sides can describe hyperbolic curves, whose function is dependent upon factors including the geometry and total area of the window, the pathlength of the light, and the orientation of the wheel along the light path. 
   Where the intensity of the emitted light is brightest, the “lens opening” (window  42 ) is smallest and vice versa. In other words, the optical axis of the LED would be at the same height as the narrowest part of the window, as would the photodetector&#39;s centerline. Thus, the shape of the window disclosed herein more closely matches the distribution of light intensity for the corresponding LED. As such, a truer signal is generated, i.e., the waveform has a more ideal shape. 
   Because the waveform shape is more accurate, less processing is required to translate the waveform into movement data. Bill of materials cost and power consumption are also reduced, as the cost of molding an hour-glass shaped hole is not significantly discernable from the cost of molding a straight-sided hole in, for example, a plastic wheel. 
   In the embodiment shown in  FIG. 5 , the optical windows  42  are shown as generally rectangular, with their long axes L congruent with radius R of the wheel  20 . 
   The shape of each window may be described as being defined by a base  52 , a top  54 , and first and second sides  56 , 58 . The top and base are opposed, and the first side and second side are also opposed. The first and second (i.e., long) sides  56 , 58  of the windows of  FIG. 5  are inwardly curved to present a more homogeneous light to the detector. 
   In an alternative embodiment, the optical windows can be linearly distributed. For example, windows according to the present disclosure can be disposed on a printer carriage ( FIG. 6 ). In one form of this embodiment, the light source  12  and detector  14  can be coupled to the printer body  60 , and the improved optical windows  62  can be linearly distributed along the printer carriage  61 . In this form, the light source and detector remain stationary while the windows are passed through the light path. 
   In a similar embodiment, the light source  12  and detector  14  can ride with a printer carriage  61 . Here, the windows  62  are intended to remain stationary with the printer body  60 , and the light source-detector pair  12 , 14  is adapted to be mobile contemporaneous with the printer carriage  61 . When the light source and detector move, the light path is then passed through the linearly distributed windows on the printer body. 
   “Windows” in the present disclosure is meant to encompass light-passing apertures, whether such apertures are voids in a solid object or windows of a transparent material. For example, a light-transparent disc or strip can be etched or otherwise frosted to render it opaque to light except for the windows. Such a disc or strip can be manufactured of material that is transparent to light of a defined wavelength but opaque to other wavelengths. The optical part thus produced would possess the benefits of the present windows and would not be transparent to light of wavelengths other than that employed in the device. 
   In the same vein, the present windows can be cut-outs in the edge of an optical wheel or strip ( FIG. 6 ). A representative optical part so constructed has a toothed or gear-like edge, wherein each window  62  is defined by the sides  64 , 66  of adjacent teeth  68 , that is, the gaps between teeth would correspond structurally to the optical windows. In this embodiment, the teeth would have a pair of crenate (i.e., outwardly-curved) sides, such that the window  62  was hourglass-shaped. 
   As discussed, a wheel according to the present disclosure can be employed in a computer mouse. There are other industries which can employ similar source/wheel/detector arrangements for signal generating. For example, devices operating under the same principle herein discussed can be used to detect both fine and course speeds in diesel engines and fuel pumps. Such fields possess general signal generating/detecting requirements to which the optical window shaped according to the present disclosure would be suitably and beneficially applied. 
   A person skilled in the art will be able to practice the present invention in view of the description present in this document, which is to be taken as a whole. The specific embodiments herein disclosed and illustrated are not to be considered in a limiting sense. Indeed, it should be readily apparent to those skilled in the art in view of the present description that the invention can be modified in numerous ways. The inventor regards the subject matter of the invention to include all combinations and sub-combinations of the various elements, features, functions and/or properties disclosed herein.