Abstract:
The present invention discloses an optical displacement detection apparatus and an optical displacement detection method. The optical displacement detection apparatus comprises: at least two light sources for projecting light of different spectrums to a surface under detection, respectively; an image capturing unit for receiving light reflected from the surface under detection and converting it into electronic signals; and a processor and control circuit for calculating displacement according to the electronic signals from the image capturing unit, wherein the processor and control circuit is capable of switching between the light sources.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to an optical displacement detection apparatus and an optical displacement detection method, which adaptively adjust the light spectrum according to reflected light from a detected object, so as to calculate the displacement more accurately. 
       BACKGROUND OF THE INVENTION 
       [0002]    Optical displacement detection apparatus has been widely used in many applications, one of which is the optical mouse. In an optical mouse, light emitted from a light source is projected on the surface of a desk or an object, reflected thereby, and received by a sensor chip inside the optical mouse. The sensor chip converts the optical signals into electronic signals, which are processed by a processor to determine the displacement of the mouse. 
         [0003]    Currently there are two types of mice, one of which employs a general light emission diode (LED), most often red LED, to emit light, and the other of which employs a laser LED to emit light. In the context of this specification, a mouse which employs a general LED is referred to as a “general optical mouse”, while a mouse which employs a laser LED is referred to as a “laser mouse”, and collectively, “optical mice”. 
         [0004]    The general optical mouse and the laser mouse operate under the same principle; their differences are in the light spectrums they use and the capability to recognize the surface under detection. A general optical mouse detects the pattern on the surface, and a laser mouse detects the roughness of the surface. Hence, each type of mouse has its strength and weakness. 
         [0005]    More specifically, for a general optical mouse, when the surface under detection has a color similar to that emitted by the LED, the strong light scattering effect will reduce the sensitivity of the sensor chip to recognize the pattern on the surface. The features of the pattern become less recognizable, causing inaccurate displacement calculation. 
         [0006]    For a laser mouse, when the roughness of the surface under detection is too low, even if there is a clear pattern on the surface, misjudgment may occur. 
         [0007]    U.S. Pat. No. 6,963,059 proposes a method to regulate the power of a light source. However, this does not solve the above problem. 
         [0008]    The present invention proposes a solution to the above problem in prior art. 
       SUMMARY OF THE INVENTION 
       [0009]    A first objective of the present invention to provide an optical displacement detection apparatus, which adaptively adjusts the light spectrum according to reflected light from a detected object, so as to calculate the displacement more accurately. 
         [0010]    A second objective of the present invention is to provide an optical displacement detection method. 
         [0011]    To achieve the foregoing objectives, and from one aspect of the present invention, an optical displacement detection apparatus comprises: at least two light sources for projecting light of different spectrums to a surface under detection, respectively; an image capturing unit for receiving light reflected from the surface under detection and converting it into electronic signals; and a processor and control circuit for calculating displacement according to the electronic signals from the image capturing unit. 
         [0012]    In the above-mentioned apparatus, the light sources may be general LEDs of different colors, or a general LED and a laser LED. 
         [0013]    In another aspect of the present invention, an optical displacement detection apparatus comprises: a light sources for projecting mixed light to a surface under detection, the mixed light includes at least two primary wavelengths; an image capturing unit for receiving light reflected from the surface under detection and converting light of different wavelengths into different electronic signals; and a processor and control circuit for calculating displacement according to the electronic signals from the image capturing unit. 
         [0014]    In the above-mentioned apparatus, preferably, the image capturing unit includes two sensor circuits having color filter layers of different colors, respectively, or the apparatus further includes two color lenses to filter light to be sensed by the two sensor circuits, respectively. 
         [0015]    From yet another aspect of the present invention, an optical displacement detection method, comprising: providing at least two light sources for projecting light of different spectrums, respectively; projecting light from one of the light sources; receiving an image formed by the light; determining the quality of the image; when the quality is good, calculating displacement according to the image; and when the quality is not good, switching to another light source. 
         [0016]    In the above-mentioned method, when an image does not present a meaningful feature, its quality is not good (poor). 
         [0017]    From a further aspect of the present invention, an optical displacement detection method, comprising: projecting mixed light including at least two primary wavelengths; sensing light of the at least two primary wavelengths, to capture at least two images respectively corresponding to the light of the at least two primary wavelengths; determining the quality of at least one of the images; when the quality is good, calculating displacement according to this image whose quality is determined to be good; and when the quality is not good, calculating displacement according to another image. 
         [0018]    In the above-mentioned method, the step of determining the quality of at least one of the images determines the quality of at least two of the images, and the displacement is calculated according to the image with a better quality. Or, the step of determining the quality of at least one of the images determines the quality of only one image at a given time point, and when the quality is not good, the method further comprises the step of switching to another image. 
         [0019]    For better understanding the objects, characteristics, and effects of the present invention, the present invention will be described below in detail by illustrative embodiments with reference to the attached drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0020]      FIG. 1  shows a first embodiment of the present invention. 
           [0021]      FIGS. 2 and 3  show the spectrums of different LEDs. 
           [0022]      FIG. 4  shows a flow chart corresponding to the embodiment of  FIG. 1 . 
           [0023]      FIGS. 5A and 5B  show two embodiments of the processor and control circuit  18 . 
           [0024]      FIG. 6  shows another embodiment of the present invention. 
           [0025]      FIG. 7  shows a flow chart corresponding to the embodiment of  FIG. 6 . 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0026]      FIG. 1  shows a first embodiment of the present invention. The mouse  10  of this embodiment includes, in its housing  11 , two light sources  12  and  13  so that the mouse  10  can switch its light source. The two light sources may be two general LEDs of different colors, such as red and green, or a general LED and a laser LED. The spectrums of red and green LEDs are shown in  FIG. 2 , and the spectrums of a general LED and a laser LED are shown in  FIG. 3 . As shown in the figures, different LEDs have different bandwidths and light sensitivities. 
         [0027]    Referring to  FIG. 1  in conjunction with the flow chart of  FIG. 4 , when the mouse  10  starts to operate, it can arbitrarily select one of its light sources, such as the light source  12  (step S 41 ). The light emitted from the light source  12 , after condensed by a first lens  14 , passes through an opening  15  on the mouse housing and projects on the surface of a desk or an object (not shown). The light reflected from the surface passes though a second lens  16  and is received by an image capturing device (step S 42 ). In one embodiment, the image capturing device is a sensor chip  17 ; however, it can be any other device capable of capturing an image. The sensor chip  17  converts the received optical signals into electronic signals, and outputs the electronic signals to a processor and control circuit  18  for analysis (step S 43 ). 
         [0028]    When the image received by the sensor chip  17  presents recognizable features, the processor and control circuit  18  calculates displacement according to any proper method well known by those skilled in this art (step S 45 ). For example, if the light source  12  is a general LED, the displacement can be calculated by comparing the patterns of two successive images. If the light source  12  is a laser LED, the displacement can be calculated by comparing the locations of a roughness feature in two successive images. The details of such calculation are omitted here because they are not the critical part of the present invention. 
         [0029]    When the surface under detection has a color similar to the color of the light source  12  so that the image received by the sensor chip  17  does not present a good quality feature, the processor and control circuit  18  sends a control signal to switch to the other light source  13  (step S 46 ). The light spectrum changes and thus it avoids the trouble caused by scattering. Or, if the light source  12  is a laser LED, when the surface under detection has low roughness so that the image received by the sensor chip  17  does not present a good quality feature, the processor and control circuit  18  sends a control signal to switch to the other light source  13  (step S 46 ). When the image received by the sensor chip  17  presents recognizable features, the processor and control circuit  18  calculates displacement of the mouse based on the features (step S 45 ). 
         [0030]    By way of example, the “feature” mentioned above can be extracted, or recognized, according to a method below: generating a brightness distribution map for the received image, and defining pixels which have an absolute or relative brightness value larger than a threshold to be features. The displacement can be calculated by comparing the features of two successive images. On the other hand, if there is no meaningful feature in an image, for example when the feature ratio (the feature area over total area) of an image is too high or too low, it means that the image has poor quality. 
         [0031]      FIGS. 5A and 5B  show internal circuit structure of the processor and control circuit  18 . If both the light sources  12  and  13  are general LEDs, only one sensor circuit and a corresponding processor unit  181  are required. If the light sources  12  and  13  are a general LED and a laser LED, it requires two sensor circuits  171  and  172  to sense normal light and laser light, and two processor units  181  and  182  to calculate displacement according to different types of features. Note that the hardware structures in the figures are only examples among many possible arrangements. The two sensor circuits  171  and  172  can be integrated into one circuit, and the calculation of displacement according to different types of features can be done by the same processor unit according to different algorithms, e.g., different programs or different subroutines in the same program. 
         [0032]      FIG. 6  shows another embodiment of the present invention. The mouse  20  in this embodiment includes only one light source  22 . The light source  22  emits mixed light which includes at least two primary wavelengths. For example, the light source  22  can be a white LED, or any other light source capable of emitting mixed light. 
         [0033]    The light emitted from the light source  22 , after condensed by a first lens  14 , passes through an opening  15  on the mouse housing and projects on the surface of an object (not shown). It is reflected by the surface and returns to the inside of the mouse. This embodiment is different from the previous embodiment in that the image capturing unit  27  includes two sensor circuits  271  and  272  to sense different wavelengths of light. In one embodiment, different wavelengths of light may be sensed by providing two filter lenses  161  and  162  of different colors, as shown in the figure. In another embodiment (not shown), only one lens is provided, but the two sensor circuits  271  and  272  are each provided with a color filter layer of a different color. The two sensor circuits  271  and  272  sense different wavelengths of light and convert the optical signals into electronic signals. The electronic signals are transmitted to the processor and control circuit  18 . The processor and control circuit  18  calculates displacement according to the signals from one of the sensor circuits. More specifically, in one embodiment, the processor and control circuit  18  receives the signals from both sensor circuits  271  and  272 , and calculates displacement according to the signals with better image quality. In another embodiment, the processor and control circuit  18  switches between signals from two sensor circuits  271  and  272 , that is, it only receives signals from one of the sensor circuits at a given time point, and it judges the image quality according to the received signals. If the image quality is poor, the processor and control circuit  18  switches to signals from the other sensor circuit, as shown by steps S 71 -S 76  of  FIG. 7 . 
         [0034]    By switching between signals resulting from different wavelengths of light, this embodiment also avoids the problem caused by light scattering due to similar colors of the surface under detection and the light source. 
         [0035]    The optical displacement detection apparatus and method disclosed by the present invention not only can be applied to optical mice, but also can be applied to any other apparatus which is designed to trace the movement of an object. 
         [0036]    The features, characteristics and effects of the present invention have been described with reference to its preferred embodiments, for illustrating the spirit of the invention rather than limiting the scope of the invention. Various other substitutions and modifications will occur to those skilled in the art, without departing from the spirit of the present invention. For example, the lenses shown in the embodiments are not necessarily required. Each of the circuits  17 ,  18 ,  171 ,  172 ,  181 ,  182 ,  183 ,  271  and  272  does not have to be a stand-alone circuit as shown, but instead can be integrated with other circuits in various manners. Thus, all such substitutions and modifications are intended to be embraced within the scope of the invention as defined in the appended claims.