Patent Publication Number: US-2006017690-A1

Title: Apparatus and method for motion detection in three dimensions

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention relates to sensing motion in three dimensions. More particularly, it relates to processing a signal developed from the acceleration of piezoelectric crystals located in a computer pointing device such as a mouse or the like in order to determine a user desired position.  
      2. Description of the Prior Art  
      Prior art computer mouse pointing devices of varying designs are known. Many require contact with a relatively planar surface because they depend on detecting movement and motion by sensing distance and direction on the surface in contact with the mouse. Both wired and wireless versions of this type of prior art device are known.  
      Piezoelectric crystals and their properties are known, and their use is widespread. U.S. Patent Publication 2001/0012002 A1, Aug. 9, 2001 to Tosaya describes a piezoelectric transducer having utility in a transmitter pen data entry device for an electronic tablet or whiteboard. This reference also discloses a stationary, finger actuated pointing device which is capable of performing a three-dimensional (3D) input operation using an apparatus having light emitting and light receiving elements.  
      Problems arise in prior computer pointing devices due to the need to have the devices in contact with a planar surface. This need often gives rise to user difficulties. Hand and arm motion may cause physical problems for some people. There is a need for good human factors, especially for high volume users and those with arthritic or similar impairment which limit comfortable movement. As ever, speed and accuracy are sought after features for any pointing device.  
     BRIEF SUMMARY OF THE INVENTION  
      In a preferred embodiment, the present invention overcomes the aforementioned shortcomings in the prior art by providing apparatus and a method for sensing 3D motion utilizing the properties of piezoelectric crystals. Including such crystals as the basis of motion detection removes the necessity of maintaining a computer pointing device in contact with a planar surface. The invention proceeds from the recognition of a new use of the signal arising from deformation of a piezoelectric crystal experiencing acceleration. That signal may be converted into typical pointing device computer signals for positioning a cursor for clicking and the like. The inventive method of measuring motion enables new types of computer input devices. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
      The various aspects, features and advantages of the inventive apparatus and method will be evident from the detailed description appearing below taken in conjunction with the following drawing figures in which like reference numerals are used throughout to indicate the same elements and wherein:  
       FIG. 1  depicts a schematic view of a mouse pointing device equipped with piezoelectric crystals in accordance with the present invention;  
       FIG. 2  is a block diagram of a circuit for obtaining a voltage output from piezoelectric crystal acceleration;  
       FIG. 3  is a plan view of crystal  14 ;  
       FIG. 4  illustrates conversion of crystal disturbance into a voltage by showing an expansion of block  28  of  FIG. 1 ;  
       FIG. 5  compares operation of a prior art two-dimensional mouse with operation of the 3D mouse of the present invention;  
       FIG. 6  graphically shows the relation between acceleration, time and distance for any piezoelectric crystal included in the present invention;  
       FIGS. 7A and 7B  graphically depict use and performance of the present invention; and  
       FIG. 8  illustrates a 3D space in which a user may navigate. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Refer now to  FIG. 1 . Shown is a typical mouse housing  10  connected by cord  12  as is well understood to a computer (not shown). A piezoelectric crystal  14  is depicted for sensing motion in the X direction. In a similar manner piezoelectric crystal  16  is provided for Y direction sensing; and piezoelectric crystal  18  is provided for sensing motion in the Z direction. Each piezoelectric crystal  14 ,  16  and  18  is here represented as a rectangular crystal, but other crystal configurations may be successfully employed. In  FIG. 1  each crystal is preferably of the same dimensions. Crystals  14  and  16  stand on one of their smaller faces and the resting surfaces are disposed 90 degrees relative to each other while crystal  18  is disposed to rest on one of its large faces. The orientation of crystal  18  relative to crystals  14  and  16  is not material to the operation of the apparatus of the invention. Similarly, if the faces of crystals  14 ,  16 , and  18  are essentially square rather than rectangular, placement orientation with respect to each other is immaterial. Each crystal is disposed in a cavity in housing  10 . Cavities  15 ,  17 , and  19  are configured to hold crystals  14 ,  16 , and  18 , respectively, to constrain opposing faces of each crystal, which faces are orthogonal in orientation to the direction of motion for which the crystal is provided to sense.  
      The exact configuration of cavities  15 ,  17  and  19  is a matter of designer choice. What is necessary is that the force of acceleration be applied evenly across an entire face of a crystal. It should be clear that any means of placing a crystal in a movable housing, so as to constrain opposing faces of the crystal in a direction orthogonal to the direction of motion the crystal is to sense.  
       FIG. 2  depicts X direction piezoelectric crystal  14 , which may be a quartz crystal, provided for sensing acceleration in the direction of arrow  20 . Suitable piezoelectric crystals for use in the present invention are readily available. Suitable alternatives to piezoelectric crystals are piezoelectric ceramics such as Ceramic Gyros available from TOKIN.  
      Lines  24  and  26  connect crystal  14  to excitation and modulation detection means  28  which has an output voltage on line  30 , in cord  12 , representative of acceleration magnitude and direction, as will become more clear in the description of  FIG. 4 . Lines  24  and  26  are connected to opposing faces of crystal  14 , which faces are unconstrained by cavity  15 .  
      While  FIG. 2  shows crystal  14  only, those having skill in the art will understand that similar arrangements exist for crystals  16  and  18  and that the discussion in connection with crystal  14  is applicable to the other two crystals illustrated in  FIG. 1 .  
       FIG. 3  is a not to scale plan view of crystal  14  showing crystal deformation during acceleration in the direction of arrow  20  ( FIG. 2 ). The force of acceleration fa is applied evenly against faces  31  and  32  of crystal  14 , which faces are constrained by sides of cavity  15  in housing  10 . Dotted lines  33  and  34  indicate bulges at the end faces of crystal  14 , which faces are unconstrained by walls of cavity  15  in housing  10  ( FIG. 1 ). Crystal  14  is undergoing acceleration in the X dimension, represented by arrow  20 . The deformation, bulging, of crystal  14  is the crystal disturbance which is reflected in a voltage change as detected in means  28  as described below.  
       FIG. 4  shows a diagram useful in understanding how excitation and modulation detection means  28  operates to convert crystal disturbance, indicative of acceleration, into a voltage. For simplicity,  FIG. 4  is described in connection with crystal  14 , but as with  FIGS. 2 and 3 , the description below is equally applicable to crystals  16  and  18 .  
      AC oscillator  34  is provided to apply a voltage to crystal  14 . Excitation by oscillator  34  combined with movement of housing  10  lead to deformation in crystal  14 , which deformation causes a change in the reactance of crystal  14 , and thus a change in load to oscillator  36  as sensed by resistor  40 . Differential amplifier  42  senses this load change. Output from amplifier  42  is input to filter  44  for rectification and signal smoothing. Output from filter  44  is input to digitizer  46 , output from which represents acceleration experienced by crystal  14 .  
      Thus, it will be appreciated that signals from each of crystals  14 ,  16 , and  18  are processed in the same manner so that a composite signal representing digitized outputs from each are applied to conventional circuitry for transmission to a computer in wired or wireless mode. Have reference now to  FIG. 5  which is a graphic comparison of the protocol stream of prior art mouse operation as a function of distance traveled by a mouse element on a planar surface with the protocol stream of the operation of a mouse incorporating the present invention. A mouse using the present invention operates as a function of the acceleration experienced by the piezoelectric crystals, detected independent of mouse location. A desired position for a standard mouse is conventionally determined by combining its mechanical displacement along the X-axis, x d    50  with its displacement along the Y-axis, y d    52 . Added thereto is conventional button, scroll wheel, and/or other element, state information as indicated at  56  for use as a stream of data output over line  60  for computer implementation.  
      In the case of the present invention, it is the acceleration experienced by piezoelectric crystals  14 ,  16  and  18  that is determinative of future actions taken by a computer to which a mouse, or similar device, incorporating the features of the present invention is attached. As discussed above,  FIG. 2  depicts what happens for each of the three piezoelectric crystals  14 ,  16  and  18  of  FIG. 1 . Thus, there would be three output signals expressed as voltages on lines  30 ;  30   x ,  30   y  and  30   z . Detected accelerations x a  and y a    70  and  72 , respectively, are combined as described below, and thereafter combined with button and other element state information at  76 , akin to the manner in which conventional displacement based status information is used at  56  above. The protocol stream of the present invention is then further combined with z a  at  78  to generate output signal  80  for instructing a device driver associated with a computer (not shown). Computers with which the present invention is used require device drivers adapted to accept and interpret signal  80 .  
      The present invention has particular utility in detecting motion in three dimensions, but the advantages of the invention may be realized even when only two dimensions are needed. That is, a device in accordance with the present teachings may, as can be seen in  FIG. 5 , consider the Z dimension as an option and not a necessity. If two dimensional motion detection is desired, only two piezoelectric crystals  14  and  16  need be used to comprise a device which would be plug-in compatible with conventional pointing devices.  
      While the illustrative preferred embodiment depicts the present invention as used in a conventional mouse housing ( 10 ,  FIG. 1 ), the invention is not so limited. Piezoelectric crystals ( 14 ,  16 , and  18   FIG. 1 ) may be situated in other housing styles, such as a finger attachable housing. Movement of a user&#39;s hand or finger would be sufficient to cause crystal disturbance as described in connection with  FIG. 2 . Operation of such a wearable pointing device would be the same as that described above. Those skilled in the art will arrive at other implementations of the present invention. Other embodiments require only application tailored device drivers for accepting output signals from the present invention and computing desired placement of a cursor and indicated operations in a conventional manner.  
      Further, the teaching of the invention is not limited to computer pointing devices. Other applications of the principles include motion detection and measurement in aircraft control yokes, and virtual reality gloves or other garments. The motion of anything that moves may be monitored by incorporating piezoelectric crystals, the disturbance of which due to experienced acceleration may be converted into a representative signal.  
      Refer now to  FIG. 6 , a graphic description of the operation of the present invention.  FIG. 6  shows the relationship between detected crystal acceleration and traveled distance over time. In  FIG. 6  there are two vertical axes representing distance and acceleration. The horizontal axis represents time. Acceleration waveform  90  is representative of that output by filter  44 ,  FIG. 4 . It will be appreciated that the rate of acceleration affects the magnitude and shape of curve  98 . Curve  98  is a series of line segments A, B and C representing the integration of acceleration  90  events over three time periods, t 1 , t 2  and t 3 .  
      At time t 1 , a piezoelectric crystal such as crystal  14  experiences acceleration from a stop. The integrated distance is shown by line segment A. At time t 2 , crystal  14  has reached a steady state and the line segment B is indicative thereof. At time t 3 , crystal  14  has decelerated, reached steady state rate of movement, and the results of integration are shown as line segment C.  
      A user of a motion detection and measurement device in accordance with the invention enjoys better human factors and an enhanced experience because less energy is expended in accelerating as compared with prior art mechanical displacement.  
       FIG. 7A  depicts distance as a function of time.  FIG. 7B  shows time as a function of distance. In each case it can be seen that precise cursor placement results from properly interpreting crystal disturbance due to acceleration experienced thereby.  
       FIG. 8  is useful in understanding how the present invention enables position sensing in three dimensions. Thee classical right-hand orthogonal axis set, which has been used throughout in reference to three dimensions, comprises the standard planar horizontal X, vertical Y and Z axes, the last being perpendicular to the plane of X and Y. In  FIG. 8 , imaginary cube  100  defines a three dimensional space, representing for example a computer screen visible to a user of a game or other generated graphic display. Such a user may desire to move a cursor, or other position indicator, from a current location shown at  102  to a new location  104 . A user of a system which includes a pointing device embodying the present invention would then accelerate that device until the new location  104  is reached. The formula d=s i t+½at 2 , where d is distance; s i  is initial speed; a is acceleration; and t is time, describes the new cursor location  104  in the 3D space of imaginary cube  100 .  
      The formula for acceleration dependent distance is d=s i t+½a n t 2 , where n is an operational constant and the other values are as above defined. A value of 1 for n is normal. When n has a value &lt;1 there is relatively less cursor movement resulting from pointing device, mouse or other, movement. When n is &gt;1, there is greater relative cursor movement resulting from device movement.  
      Operational constant n may be  1  for general use, but for a better user experience, n may be varied by scaling acceleration a. If a device in accordance with the present invention is moved a lot, n becomes &gt;1 and the cursor moves quickly. If such a device moves a little, as when zeroing in on a spot to click, the value of n goes to &lt;1 and finer control results. When n=1 is the setting, less fine control results.  
      The feature here emphasized is cursor distance amplification as a function of acceleration experienced by piezoelectric crystals in a user accelerated pointing device. The above formulas apply to both 3D and 2D location determinations.  
      While the present invention has been described having reference to a particular illustrative preferred embodiment, it is not limited to the details shown. Rather, the above and other modifications in form and detail may be made without departing from the spirit of the invention as described in the appended claims.