Abstract:
A motion capture device for communicating with a host device in order to input captured motion. The device includes an amplifier module structured to weight displacement measurements by a gain, and an adjustment module structured to adjust the gain as a function of a speed of the capture device.

Description:
BACKGROUND  
       [0001]     1. Technical Field  
         [0002]     The present invention relates to motion capture devices cooperating with a host device in order to record captured motion, particularly, but not limited to, mice intended to communicate with a computer.  
         [0003]     2. Description of the Related Art  
         [0004]      FIG. 1  shows an example of a known motion capture and display system. A device  1 , for example an optical mouse, comprises measuring means  2 ,  3  comprising for example a lens and a sensor represented by  2 . The sensor captures images, which it sends to displacement determination means  3 . These means  3  compare the images received to determine a displacement between successive images.  
         [0005]     Such displacement is commonly measured in two dimensions. In the present description, the terms “displacement”, “points”, “counts”, “displacement measurement”, “number of pixels”, etc. are commonly understood to mean pairs of values, for example (X, Y). Of course, the concepts of “displacement”, “points”, etc. may also correspond to triplets of values for measurements in three dimensions, or single values for measurements in one dimension.  
         [0006]     Each displacement is counted in “counts”, with each count corresponding to a 32nd of a point.  
         [0007]     For example, if the sensor associates a point with a distance of 30 μm, and the lens has a gain of 2, then the determination means  3  associate a point with an actual displacement of 60 μm.  
         [0008]     A displacement of 25.4 mm (one inch) in a given direction therefore corresponds to the integer value of  
           25.4     2   *     3010     -   3           *   32     ,       
 
 which is 13546 counts. 
 
         [0009]     Weighting means 9 weight the number of counts by a gain motion_scaling. A shift in the corresponding register divides the result by 256. Thus for a motion_scaling of 8, a CPI (counts per inch) parameter equals the integer of  
         13546   *     8   256       ,       
 
 that is 423 counts per inch. 
 
         [0010]     The means  3 ,  9 , may be integrated into the same means for processing, for example a processor  10 .  
         [0011]     For each displacement, and for each direction x,y, the weighted counts are sent to an accumulator  4  which adds the number of counts sent to an accumulated number of counts.  
         [0012]     The values X, Y stored in the accumulator  4  are regularly read, truncated, then sent to a buffer of a processor  5  of a host device, for example a central processing unit  8 , using for example a USB bus. In the case of a wireless mouse, a wireless communication protocol may be provided for transmitting each number of accumulated counts to the processor of the central processing unit.  
         [0013]     After each read, the truncated, meaning rounded, value is deducted from the value stored in the accumulator  4 . In this manner the accumulator  4  continues to receive the values of the weighted number of counts between two reads.  
         [0014]     A driver program run by the processor  5  may be used to amplify by a given factor each value for the number of accumulated counts received. The driver also allows displacing a pointer  6  on a screen  7  by a number of pixels approximately proportional to each amplified value and in the corresponding direction. The motions of the pointer  6  on the screen are thus approximately proportional to the motion captured by the capturing means  2 .  
         [0015]     For a factor equal to 1, each count transmitted is represented by an apparent displacement of one pixel on the screen. The factor may be greater than or less than 1.  
         [0016]     With the improved resolution of monitors, the number of pixels per screen is tending to increase. In order to avoid a decrease in the apparent displacement of the pointer on the screen for a given mouse displacement, the number of pixels for a given actual displacement is also tending to increase.  
         [0017]     To increase the number of pixels corresponding to a given displacement, one may increase the factor applied by the driver in the host device and/or the CPI parameter applied in the mouse  1 .  
         [0018]     Currently there is no existing standard which imposes the value of the total gain (or CPI parameter) applied by the mouse. The motion_scaling gain may even be programmable, such that the value of the CPI parameter may be chosen relatively freely by the mouse manufacturer.  
         [0019]     In this manner, the usual value of the CPI parameter for mice has grown from around 400 CPI to around 800 CPI within only a few years. One may imagine mice with a CPI parameter of around 1600 or even 3200 CPI for high resolution monitors or certain video games.  
         [0020]     However, the value of the accumulated number of counts stored in the accumulator may then grow relatively quickly.  
         [0021]     The channel used to transmit the value stored in the accumulator to the host device has limited bandwidth. Reading the value stored in the accumulator is therefore done at a predetermined maximum report rate.  
         [0022]     For example, for a USB port, the HID (Human Interface Device) specification authorizes reading 8 bytes every 8 milliseconds. Of these 8 bytes, four are dedicated to the transmission of information about the mouse button clicks (not represented). The four remaining bytes are dedicated to the transmission of the values stored in the accumulator. Therefore for each direction x, y, two 8-bit bytes may be transmitted every 8 milliseconds.  
         [0023]     A PS2 port is limited to 4 bytes every 8 milliseconds.  
         [0024]     If transmitting using 27 MHz wireless technology, the bandwidth may be close to that of the HID specification, including the encoding which must occur for error protection. For example, for a wireless mouse capable of transmitting 8 signed bits of data every 10 milliseconds for each direction x, y, 127 counts (positive or negative) may be transmitted every 10 milliseconds, which is 12700 counts per second. If the value of the CPI parameter is 400 CPI, this limitation corresponds to a maximum mouse speed in direction x or y of  
         12700   400     *   25.4   *     10     -   3           
 
 meters per second, which is approximately 0.8 m/s. If the value of the CPI parameter is 1600 CPI, the maximum speed in direction x or y falls to approximately 0.2 m/s. If the user moves the mouse more quickly, transmission to the host device encounters overflow problems. This limitation may become an annoyance for certain applications, such as gaming applications. 
 
         [0025]     One solution consists of choosing a relatively low CPI parameter and a relatively high factor to be applied by the driver. This factor may be modified relatively easily via a user interface. In this manner, someone using the mouse is not constrained to move the mouse over relatively high distances in order to display a given pointer displacement on the screen. Also avoided are the problems related to overflow when transmitting the accumulated number of counts from the mouse to the host device.  
         [0026]     However, the displacements shown on the screen may be imprecise. The number of counts corresponding to a given displacement is relatively low, such that the displacement is translated into a number of counts in an approximate manner only. In addition, if the factor used by the driver is relatively high, the apparent minimum displacement, corresponding to one count, may be greater than a pixel.  
         [0027]     It is also known to provide a variable factor to be applied by the driver. If an acceleration is detected, the factor decreases. However, this solution does not eliminate the loss of precision related to the conversion into the number of counts. When no acceleration is detected, the factor may be relatively high, which increases the loss in precision. In addition, detection of acceleration by the software of the computer may lead to artifacts on the screen. One example would be relatively abrupt changes in the pointer direction.  
       BRIEF SUMMARY  
       [0028]     One embodiment remedies the disadvantages mentioned above. It proposes providing a CPI parameter that varies with the speed of the capture device.  
         [0029]     One embodiment is a motion capture device designed to communicate with a host device in order to input data on the captured motion, comprising weighting means for weighting the displacement measurements with a gain, and adjusting means to adjust the gain as a function of at least one speed of the capture device.  
         [0030]     In this manner one may decrease the gain when the capture device, for example a mouse, captures a relatively rapid motion. This avoids the problems related to overflow during transmission to the host device.  
         [0031]     When the capture device captures a relatively slow motion, the gain may be relatively high. The captured motion, represented for example by the apparent displacement of a pointer on a screen of the host device, is thus relatively high. For a screen comprising a relatively high number of pixels, this avoids a decrease in the apparent displacement of the pointer on the screen for a given displacement of the mouse. In addition, the precision remains relatively high. The loss of precision due to a quantification of the motion as a number of counts is relatively low. And the factor applied by the host device may be relatively low, avoiding minimum displacements on the screen that exceed one pixel. In other words, each pixel on the screen may be reached by the pointer.  
         [0032]     Advantageously, the adjusting means are arranged to modify the gain as a function of at least one previously acquired displacement measurement.  
         [0033]     If the measurements are acquired at regular intervals, the speed of the capture device and the measurement(s) are approximately proportional. Of course, other indicators of the speed may be used to adjust the gain of the capture device.  
         [0034]     Advantageously, the adjusting means are arranged to modify the gain as a function of the sum of multiple previously acquired displacement measurements. This corresponds to low-pass filtering (or smoothing), which avoids variations in the gain due to excessive sensitivity.  
         [0035]     Alternatively, the gain may be readjusted based on a single displacement measurement.  
         [0036]     Advantageously, the capture device comprises an accumulator connected to the weighting means, where the accumulator receives weighted displacement measurements and stores an accumulated displacement measurement. A communication means are provided, comprising a transmission buffer designed to receive an accumulated displacement measurement read from the accumulator. The communication means are designed to communicate to the host device the value received in the transmission buffer.  
         [0037]     Conventional mouse capture devices commonly integrate the accumulator and such a means of communication. For example, one may obtain mice according to the first embodiment of the invention relatively easily, for example by modifying a computer program executed by a mouse processor.  
         [0038]     Conventionally, the value read from the accumulator and received in the transmission buffer is truncated, and this truncated value is subtracted from the value stored in the accumulator. Because the weighting means are located upstream from the accumulator, a relatively high resolution may be maintained because the weighting is applied to the untruncated values.  
         [0039]     The present invention is, of course, not limited by any of these characteristics, meaning the accumulator, the transmission buffer, or the means of communication. For example, the weighted measurements may be communicated one by one to the host device, without prior accumulation in an accumulator.  
         [0040]     Advantageously, the adjusting means are connected to the transmission buffer, in order to modify the gain as a function of at least one measurement read from the accumulator. In this manner the gain is readjusted at each transmission to the host device, while multiple displacement measurements are acquired between two transmissions.  
         [0041]     Alternatively, the means of adjustment may be without a direct connection to the transmission buffer. One may, for example, have the means of adjustment itself read from the accumulator at regular intervals, independently of the read from the accumulator done for the transmission to the host device.  
         [0042]     The invention is not limited by the implementation of the communication with the host device: for example a PS2 port, a USB port, or wireless means of communication (radio link, Bluetooth, infrared, etc.) may be used. In the case of a mouse, it may of course be wired or wireless.  
         [0043]     The means of adjustment may take into account the nature of the communication means between the capture device and the host when calculating the value of the gain. Typically, the gain may be adjusted such that the data sent to the host are sufficiently small in size for the transmission to the host to occur without overflow.  
         [0044]     In one embodiment, the capture device is an optical mouse in which case the displacements measured are those of the mouse itself relative to a support such as a table or mouse pad, and the speed of the capture device is the speed of the mouse relative to this support. The mouse may also be a 3D mouse.  
         [0045]     In another embodiment, the capture device is a mouse that may comprise a trackball, in which case the displacements measured are those of the ball, and the speed of the capture device is the speed of the ball. The mouse may also be a conventional optical mouse, Alternatively, the capture device may be (or may be comprised within) a touchpad device or a trackpoint device, in which case the displacements measured are those of the user&#39;s finger across the touchpad or trackpoint. The speed of the capture device is then the speed of the touchpad (or trackpoint) relative to the finger, which is the same as speed of the finger relative to the touchpad (or trackpoint).  
         [0046]     Alternatively, the capture device may be (or may be comprised within) a graphics tablet, in which case the displacements measured are those of a tool, for example a stylus, across a surface of the tablet. Here again, the speed of the capture device is equal to the speed of the tool across the surface of the tablet.  
         [0047]     Therefore the invention is in no way limited by the nature of the capture device. The capture device may also be (or may be comprised within) a joystick.  
         [0048]     One embodiment is a motion capture system comprising the capture device according to the first aspect of the invention and a host device which is able to communicate with the capture device. The capture system may, for example, comprise an optical mouse and a computer&#39;s central processing unit.  
         [0049]     Another embodiment is a method to be implemented by a motion capture device which communicates with a host device in order to input the captured motion. Said method comprises modifying a gain as a function of at least one speed of the capture device, and using this gain to weight a displacement measurement of the capture device.  
         [0050]     Of course, the modifications to the gain and the weighting may be done at different frequencies. For example, the gain may be readjusted after one hundred weightings.  
         [0051]     Another embodiment is a computer readable medium having contents that cause a motion capture device to perform a method that includes: 
        receiving data from a sensor of the capture device,     determining a displacement measurement of the capture device from data received from the sensor,     weighting said displacement measurement by a gain, and     modifying the gain as a function of a speed of the capture device.       
 
     
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
       [0056]     Other features and advantages of the invention will become clear in the description of the embodiments which follows.  
         [0057]      FIG. 1 , already described, shows an example of a known capture system from the prior art.  
         [0058]      FIG. 2  shows an example of a capture system according to one embodiment of the invention.  
         [0059]      FIG. 3  is a flowchart showing an example of a process according to the embodiment in  FIG. 2 .  
         [0060]      FIG. 4  is a graph representing an example of a variation in the gain as a function of the capture device speed, according to the embodiment in  FIG. 2 .  
         [0061]      FIGS. 2, 3  and  4  correspond to the same embodiment and will be described at the same time. 
     
    
     DETAILED DESCRIPTION  
       [0062]     The capture system represented in  FIG. 2  comprises a capture device and a host device, which in this embodiment are respectively an optical mouse  21  and a central processing unit  28  of a computer.  
         [0063]     The mouse  21  comprises an optical sensor and a lens, labeled as number  22 . The sensor captures image data P 1 , P 2  and sends these image data to displacement determination means  23 . The image data P 1 , P 2  typically correspond to images captured at given instants. The determination means receive the image data (step  32  in  FIG. 3 ). By comparing the image data P 1 , P 2  captured between two instants, the determination means  23  determines a displacement measurement (Δx,Δy) in two dimensions x, y, corresponding to an interval of time between these two instants (step  33  in  FIG. 3 ).  
         [0064]     Each displacement measurement (Δx,Δy) is counted as counts, with each count corresponding to a 32nd of a point.  
         [0065]     For example, for a sensor associating a point with a distance of 30 μm, and for a lens with a gain of 2, an actual displacement of 25.4 mm (one inch) in direction x or y corresponds to the integer of  
           25.4     2   *   30   *     10     -   3           *   32     ,       
 
 which is 13546 counts. 
 
         [0066]     Weighting means  29  weight the displacement measurements by a gain G (step  34  in  FIG. 3 ). The gain G is equal to a gain motion_scaling divided by 256 via shifts in the register where the displacement measurement is temporarily stored (Δx,Δy).  
         [0067]     The gain motion_scaling may be modified by the means for adjusting the gain  31 , as a function of the mouse speed.  
         [0068]     The means  23 ,  29 ,  31  may be integrated into the same processing means, for example a processor  30 .  
         [0069]     The processor  30  is connected to an accumulator  24 . Each weighted displacement measurement (Δx′,αy′) is sent to the accumulator  24  and added (step  36  in  FIG. 3 ) to an accumulated displacement measurement (X, Y) in two dimensions x, y.  
         [0070]     The accumulator  24  is designed to allow storing relatively high values for each dimension x, y, of the accumulated displacement measurement (X, Y), in order to avoid problems related to a possible overflow.  
         [0071]     For each dimension x, y, the stored values are read and truncated (step  37  in  FIG. 3 ), then received in a transmission buffer  42  for transmission to a buffer of a processor  25  of the central processing unit  28 . Communication means including the buffer  42  are provided for this purpose.  
         [0072]     In the case of a wireless mouse, a wireless communication protocol may be provided for transmitting the number of counts accumulated in the processor  25 . In addition to the buffer  42 , the communication means may, among other components, comprise a wireless transmitter/receiver  40 .  
         [0073]     In the case of a USB bus operating according to the HID specification, not represented in  FIG. 2 , communication means may, among other components, comprise a wire between the mouse and the central unit.  
         [0074]     After each read, and for each direction, the truncated value is deducted from the value saved in the accumulator  24  (step  38  in  FIG. 3 ). Alternatively, the accumulator  24  may be reset to zero.  
         [0075]     The accumulator  24  continues to receive weighted values for the number of counts between two reads.  
         [0076]     In addition, for each direction x, y, the value received in the buffer  42  is sent to the gain adjusting means  31 . The gain adjusting means  31  in fact determine (step  35  in  FIG. 3 ) the value of the gain motion_scaling, and therefore the gain G, from the accumulated displacement measurement (X, Y) read from the accumulator  24  during the read step.  
         [0077]     In fact, the accumulated displacement measurement (X, Y) corresponds to the displacement captured between two reads from the accumulator. If the reads from the accumulator take place at regular intervals, the accumulated displacement measurement (X, Y) is representative of the mouse speed. From the values in the directions x, y of the accumulated measurement (X,Y), and from the current value of the gain motion_scaling, the processor  30  may easily determine a value approximately proportional to the mouse speed.  
         [0078]      FIG. 4  is a graph representing an example of variations in the motion_scaling as a function of the mouse speed.  
         [0079]     In this example, the motion_scaling is expressed as multiples of a value K equal to 8.  
         [0080]     While the speed of the mouse is less than 0.19 m/s, the motion_scaling is equal to 32, which is a gain G of 0.125 after considering the shifts in the shift register. An actual displacement of 25.4 millimeters (one inch) in one of the directions x, y thus corresponds to 1693 counts, which is a CPI parameter of 1693 counts per inch. For simplicity, this is called a CPI parameter of 1600 counts per inch.  
         [0081]     The gain motion_scaling decreases beyond the limit of 0.19 m/s.  
         [0082]     In fact, the wireless transmission protocol used in the illustrated embodiment allows, for each displacement direction x or y, the transmission of 8 signed bits of data every 10 milliseconds, which is 12700 counts (positive or negative) per second. For a CPI value of 1600 CPI, this limit corresponds to a maximum mouse speed in one of the directions x, y of  
         12700   1693     *   25.4   *     10     -   3           
 
 meters per second, which is approximately 0.19 m/s. 
 
         [0083]     The decrease in the gain motion_scaling for speeds exceeding 0.19 m/s allows avoiding overrun problems when transmitting the accumulated value to the central processing unit. The means for adjusting the gain  31  in  FIG. 2  thus take into account the bandwidth of the channel used to transmit the value stored in the accumulator to the host device.  
         [0084]     For a mouse speed of 0.76 m/s, the gain motion_scaling drops to 8, which is a CPI value of 423 CPI. In fact, in light of the report rate specified in the HID specifications, the maximum mouse speed for a CPI value of 423 CPI is  
         12700   423     *   25.4   *     10     -   3           
 
 meters per second, or approximately 0.76 m/s. 
 
         [0085]     In this example, the value of the motion_scaling varies with the speed by 1/x when the mouse speed is greater than 0.19 m/s. The means for adjusting the gain are therefore designed so that above 0.19 m/s, it uses approximately the maximum bandwidth of the channel for transmitting the value stored in the accumulator to the host device.  
         [0086]     Of course, the invention is not limited to such a curve. In particular, one may systematically underutilize the bandwidth of this channel. It is the previous accumulated measurement which serves as the basis for the gain calculation: providing a safety margin avoids an overrun in the channel if the mouse speed increases. The safety margin may for example be fixed, meaning the curve representing the variations in the motion_scaling as a function of the speed has the same appearance as the curve in  FIG. 4 , but with the values for the motion_scaling shifted by an identical value.  
         [0087]     There may also be linear variations with the speed, or stepwise variations. Depending on the desired application, there may also be a gain motion_scaling for low speeds which is higher or lower than 4*K, a speed limit beyond which the gain motion_scaling decreases differently, etc.  
         [0088]     If, for example, the values X, Y read from the accumulator are equal to +42 and −103 counts respectively, for a current motion_scaling of 16, the processor  30  in  FIG. 2  may calculate a mouse speed, or at least a value approximately proportional to the mouse speed. The corresponding displacement of the mouse is approximately equal to  
             (       42   2     +     103   2       )       *     256   16     *     1   32     *   2   *   30   *     10     -   6         ,       
 
 which is approximately 3.34 millimeters. If the values X, Y are read at a report rate of 10 milliseconds, this displacement corresponds to a speed of 0.334 m/s. The gain motion_scaling may then be readjusted using this new value for the speed. If one refers to the curve in  FIG. 4 , the gain motion_scaling assumes a value of about 18.2. 
 
         [0089]     Thus in 10 milliseconds, the gain motion_scaling increases from a value of 16 to a value of about 18. In order to avoid such variations in gain, one may use an average of the speeds over a longer period, on the order of a tenth of a second for example, or a sum of the displacement measurements accumulated over several read cycles.  
         [0090]     In an alternative embodiment not represented in the figures, one may instead readjust the gain at a much higher readjustment frequency, for example, at each acquisition of a displacement measurement (Δx,Δy).  
         [0091]     To return to  FIG. 2 , the measurement transmitted from the mouse to the central processing unit is received in the processor  25 , inputting the motion captured by the mouse. A driver run by the processor  25  may be used to amplify by a given factor each value for the number of accumulated counts received. The driver also allows moving a pointer  26  on a screen  27  by a number of pixels approximately proportional to the amplified value. The motions of the pointer  26  on the screen are thus approximately proportional to the motion captured by the sensor  22 .  
         [0092]     In this embodiment, beyond 0.19 m/s, the gain for the mouse is approximately as high as possible for the bandwidth of the channel between the mouse and the central processing unit. The loss in precision resulting from the quantification into the number of counts is therefore relatively low. In addition, the factor applied by the driver may be relatively low, such that the pointer  26  moves in a relatively precise manner.  
         [0093]     It will be appreciated that the various means discussed above could be implemented with hardware, code (software or firmware), or a combination of hardware and code.  
         [0094]     The various embodiments described above can be combined to provide further embodiments. Aspects of the embodiments can be modified, if necessary to employ concepts of the various patents, applications and publications to provide yet further embodiments.  
         [0095]     These and other changes can be made to the embodiments in light of the above-detailed description. In general, in the following claims, the terms used should not be construed to limit the claims to the specific embodiments disclosed in the specification and the claims, but should be construed to include all possible embodiments along with the full scope of equivalents to which such claims are entitled. Accordingly, the claims are not limited by the disclosure.