Abstract:
A handheld optical navigation device may include a first radiation source configured to produce a first beam of radiation onto a surface below the device, a first sensor configured to receive a first image based upon reflected radiation from the surface below the device, and to identify movement of the device based upon the first image for providing a first control action, and a second sensor configured to receive a second image based upon reflected radiation from an object different from the surface below the device, and to identify movement of the object based upon the second image for providing a second control action.

Description:
FIELD OF THE INVENTION 
       [0001]    This present disclosure relates to the field of handheld optical navigation devices, and in particular to those handheld optical devices used for computer navigation and control. 
       BACKGROUND OF THE INVENTION 
       [0002]    A computer mouse is a common user input device for a graphical environment. These devices may be handheld with the user moving the mouse with their hand, and more specifically, by twisting their wrist or moving their elbow. While this may produce large amounts of movement, the human body does not have very accurate control over the relevant muscles. Furthermore, the navigation/correlation technique used in the optical mouse may be inefficient at low speeds as there is little movement between successive images. 
         [0003]    There have been a number of approaches to provide additional controls to the typical mouse. One such approach is the scroll wheel. The scroll wheel may provide extra control over the PC, but with usually a very coarse input, for example, to scroll a whole window. The movement, and hence control, is in one direction, usually the “Y” axis. One approach is a rotating wheel. There may be alternative input approaches, such as the Logitech (RTM) travel mice, which implement this using a capacitive touch pad. 
         [0004]    The functionality of the scroll wheel may be improved, for example, by adding a “tilt” function to the scroll wheel. This has control in the orthogonal axis to the scroll, but by only a limited amount (−X, 0 or +X). As an alternative, another approach may replace the scroll wheel with a trackball on the top of the mouse. This is used to provide functionality similar to the tilt wheel, i.e. horizontal scrolling. Probably due to its small size, it may not be suitable as a main cursor control device. For some applications, for example, gaming, high speed may be desirable. For other applications, for example, Computer Aided Design (CAD), image drawing etc., very precise operation at low speed may be desirable. 
       SUMMARY OF THE INVENTION 
       [0005]    In a first aspect of the present disclosure, there is provided a handheld optical navigation device that may comprise a first radiation source capable of producing a beam of radiation onto a surface below the device, and a first sensor for receiving a first image based upon reflected radiation from the surface, and to identify movement of the device based upon the image to thereby enable a first control action to be carried out. The device may further comprise a second sensor for receiving a second image based upon reflected radiation from an object other than the surface and to identify movement of the object based upon the image to thereby enable a second control action to be carried out. The second sensor may provide at least one combined navigational output based upon the first and second control actions, i.e. the first and second control actions co-operate so as to provide for a single navigational output. 
         [0006]    The device may comprise a second radiation source for producing a beam of radiation onto the object so as to obtain the second image. The device may comprise a mouse surface, the second sensor imaging movement of the object on the mouse surface. The device may be designed such that the mouse surface is easily manipulated by a finger or thumb. 
         [0007]    The device may further comprise an optical element including at least one frustrated total internal reflection (F-TIR) surface capable of causing frustrated total internal reflection of the beam of radiation when the object contacts the mouse surface of the optical element, to thereby generate the second image. The optical element may comprise at least one further surface for directing radiation from the radiation source to at least one F-TIR surface. The optical element may comprise at least one additional surface for directing radiation from the F-TIR surface to the second sensor. The optical element may be formed from a single piece construction. 
         [0008]    The first sensor and the second sensor may both share a single substrate. The device may comprise a controller for controlling the first and second sensors and the radiation source. The device may comprise separate control lines, motion lines and shutdown lines connecting the controller independently to each of the first and second sensor, the motion line for signaling if a sensor has detected movement and the shutdown line for enabling the controller to power down a sensor. Alternatively, the controller and the first and second sensors may be connected in series, such that the controller has direct control, i.e. motion and shutdown lines to only one of the sensors. In another embodiment, the device may comprise an additional control line such that the control pins of the first and second sensors are connected in parallel to a single controller pin. 
         [0009]    The device may be operable such that for high speed operation, data from the first sensor is used, and for high precision operation, data from the second sensor is used. The device may be operable such that should a parameter related to the speed of movement of the device across the surface indicate a speed above a threshold, data from the first sensor is used for the control action and should the parameter related to the speed of movement of the device across the surface indicate a speed below the threshold data, data from the second sensor is used for the control action. The device may be operable such that the second sensor is deactivated when not being used for deriving the control action. 
         [0010]    The device may be operable such that the second sensor is less sensitive to movement than the first sensor. The output resolution of the first sensor may be larger than the output resolution of the second sensor. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Embodiments of the present invention may now be described, by way of example only, by reference to the accompanying drawings, in which: 
           [0012]      FIG. 1  shows a prior art mouse device; 
           [0013]      FIG. 2  shows a mouse device according to an embodiment of the present invention; 
           [0014]      FIG. 3  shows a mouse device according to a further embodiment of the present invention; 
           [0015]      FIG. 4  shows a first system architecture for a mouse device according to an embodiment of the present invention; 
           [0016]      FIG. 5  shows a second system architecture for a mouse device according to an embodiment of the present invention; 
           [0017]      FIG. 6  shows a third system architecture for a mouse device according to an embodiment of the present invention; 
           [0018]      FIG. 7  shows a plot of the speed of the mouse, according to the present invention, as detected by the down-facing sensor against its actual speed; and 
           [0019]      FIG. 8  shows a plot of the speed of the mouse, according to the present invention, as detected by the up-facing sensor against its actual speed. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0020]      FIG. 1  shows the cross section of a typical optical mouse. Shown is a light source (LED or VCSEL)  100 , from which light is directed/focused onto an object (table, desk, paper, mouse mat)  110 , and the resulting image observed on an optical sensor  120  which tracks movement. Typically there are low-friction pads  130  mounted on the optical mouse to reduce friction and allow the mouse to move smoothly over the surface. Typically there are one or more buttons on the top of the mouse (not shown), and usually a scroll wheel or tilt wheel  140 . 
         [0021]      FIG. 2  shows a cross section of a mouse device according to one embodiment of the invention. This mouse includes a second optical sensor unit  250  and associated light source  260 . Preferably the “Mouse surface”  270  provided by this second sensor arrangement  250 ,  260  is positioned directly underneath the position of the index finger when it is in a relaxed or comfortable state. Consequently the sensor unit  250  may receive an image based on light reflected off an object, such as a finger, on the mouse surface  270 . The first optical sensor  220  and light source  200  are located on a first, main substrate (printed circuit board, PCB)  280 . The second optical sensor (and associated light source) is mounted on a second substrate (PCB)  290 . As an alternative to the arrangement depicted, the mouse surface could be on a side of the device (with a plane approximately perpendicular to that depicted) for manipulation by a thumb. 
         [0022]      FIG. 3  shows an improved mouse from that of  FIG. 2 . By careful design of the mouse housing, the second optical sensor  250  and associated light source  260  has been mounted on the same substrate  280  as the first optical sensor  220 . This reduced the thickness and provides greater comfort to the user and also decreases the manufacturing cost. 
         [0023]      FIG. 4  illustrates one of a number of exemplary implementing architectures according to an embodiment of the invention. It shows the first motion sensor (looking down)  220 , the second motion sensor (looking up)  250  and the controller  400 , which may be an I2C or SPI or similar control interface. In particular, the connections of the “control,” “Motion,” (used to signal if the sensor has detected movement) and (optionally) “Shutdown,” (used by a host to power down a sensor to save energy) pins are shown for the sensors  220 ,  250  and controller  400 . In this example “Motion” and “shutdown” are independently connected to the controller device  400 . The output from the controller  400  is preferably a USB (universal serial bus) output or may even be a signal suitable for RF (radio frequency) modulation, in the case of a wireless mouse. The disadvantage of this system is the extra wires and input pins used add to the complexity and cost of the mouse. 
         [0024]      FIG. 5  shows an optimized system where the controller device  400  is connected to only one sensor  250 . Due to size constraints, the down-facing sensor {desk}  250  has more space available than the up-facing {finger} sensor  220 . Therefore, the down-facing sensor  250  would typically receive the inputs from the up-facing sensor  220  and modify/relay these to the controller  400 . In the arrangement of  FIG. 4 , the decision to use either the down-facing sensor or up-facing sensor is made by the controller device  400 . In the arrangements of  FIGS. 5 &amp; 6 , the up facing sensor  220  would be programmed (typically via the control interface) with the speed threshold and the switching between the sensors being made by up facing sensor  220 . 
         [0025]      FIG. 6  shows a more efficient system architecture which may be possible, depending on the control bus uses. For example, if an I2C bus is used, there is no need to have a control input on the down-facing sensor  220 , thus dispensing with the need of two extra pads/connections on the device. Furthermore, the I2C bus supports multiple (slave) devices, which means that the two sensors  220 ,  250  can be connected in parallel. 
         [0026]    In a main embodiment, an aspect to the invention is the operation of the device, in that the device operates by using the two control signals from the two optical sensors in a co-operative manner so as to output a single navigation output. For large movements and high speed operation, the mouse itself is moved across the surface below it, and motion data from the down-facing sensor  220  is used. For high precision movements, the mouse is kept largely stationary and the finger (typically index) is moved over the mouse surface  270  of the device. As the human body possesses fine motor control on the fingers, this operation results in a device which provides increased accuracy control. In order to best achieve this operation, data from the down facing sensor  220  should be ignored for the purposes of control when the mouse is largely stationary, or its speed is below a threshold level. 
         [0027]    As noted above, the output from the two sensors provides for a single navigational output. This is as opposed to an output that comprises two separate positional signals as is the case with a mouse and scroll wheel, where the mouse controls a cursor and the scroll wheel controls the scrolling in a window. 
         [0028]    In the present embodiment, the two control signals would, for example, control the same cursor, providing a coarse control and fine control of the cursor. Clearly, control is not limited to that via a cursor, and the control method could be any other suitable method, including scroll, zoom etc. 
         [0029]      FIG. 7  shows a plot of the speed of the mouse as detected by the down-facing sensor  220  against its actual speed for a mouse configured in this way. When the detected speed of the mouse is above a certain threshold T, for example, 2-5 mm/sec, the navigation data from the down-facing sensor  220  is used, and the reported speed increases linearly with increase in actual speed (Of course, this relationship does not need to continue in a linear fashion but instead may “accelerate” as is known in the art). During this second period, data from the up facing sensor  250  is being ignored, and the sensor  250  and corresponding light source  260  may in fact be switched off. 
         [0030]    When the speed drops below the threshold T, the data from the down-facing sensor  220  is disregarded and the reported speed drops to zero (first period on graph). During this period data from the up-facing sensor  250  is used instead. This technique avoids small nudges in the mouse when a user is sliding a finger on the top surface from being used as valid cursor movement data. 
         [0031]    Optionally, the output resolution (counts per inch) from the two sensors can be made different, such that the down-facing sensor outputs 800 cpi, i.e. one inch of travel outputs 800 counts, while the up facing sensor outputs  200  cpi. Therefore, in the latter case, the finger has to move further to output the same number of counts. This decrease of sensitivity increases the positional accuracy of the system. The different output counts may be achieved either by changing the motion gain on the sensor or by varying the magnification in the optics (×0.5 Vs ×0.25) or by using sensors with different array sizes (20*20 pixels Vs 40*40 pixels). 
         [0032]      FIG. 8  shows a graph similar (axes are scaled the same) to that of  FIG. 7  for the up facing sensor  250  during the first period of graph  7 . It can be seen that the reported speed increases linearly with actual speed of the finger on the sensor, but with a different slope than that of  FIG. 7 , representing the difference in output resolution. Of course, the reported speed on this graph drops to zero should the mouse speed recorded by the down facing sensor  220  pass the threshold value T. 
         [0033]    It should be noted that the output from a mouse is rarely the actual “speed,” but is usually measured in counts. The speed is deduced by the controller, PC or mobile phone handset by monitoring the speed and time, i.e. speed =distance/time. Speed is used on  FIGS. 7 and 8  as it clearly explains the operation of the device. The above embodiments are for illustration only and other embodiments and variations are possible and envisaged without departing from the spirit and scope of the invention.