Abstract:
A footprint location system installed on footwear is disclosed. A user simply has to wear the shoes to track his/her locations without any setup or calibration efforts. The footprint location system measures and tracks the displacement vectors along a trail of footprints. The position of a user can be determined by summing up the current and all previous displacement vectors. In addition to being infrastructure-free, the footprint location method does not have problems found in existing indoor location systems, such as obstacles, multi-path effects, signal noises, signal interferences, and dead spots.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to a footprint location system, and more particularly to a footprint location system that can determine a user&#39;s position by summing up all displacement vectors 
   2. The Prior Arts 
   Conventional indoor location systems usually need expensive infrastructure and maintenance to determine a user&#39;s position precisely. That might be the reason that the conventional indoor location systems have been seldom used in commercial applications ranging from family to enterprise. 
   A conventional indoor location system usually sets up sensing devices in particular positions to detect a user&#39;s position. In order to enhance accuracy, the conventional indoor location system needs to increase numbers of sensing devices, such as infrared, WiFi and weight detectors, and therefore largely increases the expense of equipments, installing, operating and maintenance of the system. 
   SUMMARY OF THE INVENTION 
   A primary objective of the present invention is to provide a footprint location system and method on footwear, which a user simply has to wear the footwear to track his/her locations without any setup or calibration efforts. The footprint location system measures and tracks displacement vectors along a trail of footprints, and then determines the user&#39;s position by summing tip all displacement vectors without any advanced infrastructure. 
   A secondary objective of the present invention is to provide a footprint location system and method on footwear, which can determine the user&#39;s physical location solely by using sensors installed on footwear. With ultrasonic infrared transmitters and receivers respectively installed on a first shoe and a second shoe of the footprint location system, it provides highly accurate coordinates due to a short distance (less than 1.5 meters) between them, thereby overcoming many problems found in existing indoor location systems, such as obstacles, multi-path effects, signal noises, signal interferences, and dead spots. Moreover, video detection devices can replace the ultrasonic infrared transmitters and receivers and achieves a similar result. 
   A tertiary objective of the present invention is to provide a footprint location system and method that integrates with force sensors to confirm footwear in contact with ground. The force sensors are used to avoid obtaining incorrect displacement vectors under unstable conditions and to identify the user moves forward, backward, left or right. 
   A further objective of the present invention is to provide a footprint location system and method that integrates with orientation sensors to obtain rotation angle to simplify computational requirements of the system. 
   A further objective of the present invention is to provide a footprint location system and method that integrates with radio frequency identification (RFID) tags and readers to obtain a user&#39;s current location to correct the user&#39;s position in real-time. 
   To achieve the objectives mentioned above, a footprint location system in accordance with the present invention comprises a first shoe, a second shoe, a vector measuring unit and a location calculation unit. The footprint location system determines a user&#39;s position by tracking a trail of footprints. The trail of the footprints implying direction and translation information comprises first footprints of the first shoe and second footprints of the second shoe. 
   The first shoe has two ultrasonic infrared receivers and the second shoe has an ultrasonic infrared transmitter. While a user wearing the first and the second shoes walks, a vector measuring unit measures displacement vectors between the first and second footprints based on coordinates provided by the ultrasonic infrared transmitters and the ultrasonic infrared receivers (or by a camera device and a characteristic picture). The location calculation unit then calculates the user&#39;s position by summing up the current and all previous displacement vectors with reference to a starting point without additional advanced infrastructure. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be apparent to those skilled in the art by reading the following detailed description of a preferred embodiment thereof, with reference to the attached drawings, in which: 
       FIGS. 1A and 1B  are schematic views of shoes according to the present invention; 
       FIGS. 2A and 2B  are schematic views of a footprint location system according to the present invention; 
       FIGS. 3A-3C  are schematic views showing a user&#39;s walking status in the footprint location system according to the present invention; 
       FIGS. 4A and 4B  are schematic views showing a trail of the user&#39;s footprints in the footprint location system according to the present invention; 
       FIGS. 5A and 5B  are schematic views showing measured coordinates of the footprint location system according to the present invention; and 
       FIGS. 6A-6C  are schematic views showing accessory devices of the footprint location system according to the present invention. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   With reference to the drawings and in particular to  FIGS. 1A and 1B , a footprint location system in accordance with the present invention comprises a first shoe  5   a  and a second shoe  5   b . The first shoe  5   a  comprises measuring units, such as an ultrasonic infrared receiver  12  as shown in  FIG. 1A , or a first video detection device (such as a camera device)  16  as shown in  FIG. 1B , and generates first footprints  40   a - 40   c  as shown in  FIG. 4A  when both feet touch the ground. The second shoe  5   b  comprises measuring units, such as an ultrasonic infrared transmitter  14  as shown in  FIG. 1A , or a second video detection device (such as a characteristic picture)  18  as shown in  FIG. 1B , and generates second footprints  42   a  and  42   b  as shown in  FIG. 4A  when both feet touch the ground. Therefore, the footprint location system of the present invention can calculate a user&#39;s position by measuring every stride (the first footprints  40   a - 40   c  and the second footprints  42   a - 42   b ) generated by the user wearing the first shoe  5   a  and the second shoe  5   b . In the following description two different embodiments according to the present invention will be presented. The major difference between these two embodiments is the measuring units installed in the first shoe  5   a  and the second shoe  5   b . The method of determining the user&#39;s position is the same. The first video detection device (camera device)  16  and the easily recognizable second video detection device (characteristic picture)  18  can replace the ultrasonic infrared receiver  12  and the ultrasonic infrared transmitter  14  respectively. 
   With reference to the drawings and in particular to  FIGS. 2A-2B , the footprint location system of the present invention comprises an ultrasonic infrared receiver  12 , an ultrasonic infrared transmitter  14 , a vector measuring unit  20 , and a location calculation unit  22  as shown in  FIG. 2A , or a first video detection device (camera device)  16 , a second video detection device (characteristic picture)  18 , a vector measuring unit  20  and a location calculation unit  22  as shown in  FIG. 2B . 
   Briefly, the vector measuring unit  20  measures displacement vectors Vdi (as shown in  FIG. 4A ) between the first footprint  40   a - 40   c  and the second footprint  42   a  and  42   b  based on coordinates provided by the ultrasonic infrared receivers  12  and the ultrasonic infrared transmitters  14  (or by the first video detection device  16  and the second video detection device  18 ). The location calculation unit  22  then calculates the user&#39;s position by summing up the current and all previous displacement vectors 
           (       ∑     i   =   1     n     ⁢   vdi     )         
with reference to a starting point.
 
   The human walking motion can be modeled by stance-phase kinematics as shown in  FIGS. 3A-3C .  FIG. 3A  shows a heel strike stance;  FIG. 3B  shows a mid stance; and  FIG. 3C  shows a toe-off stance. Only in the heel strike stance and toe-off stance, both feet are in contact with the ground. In the mid stance, the body raises one foot and only one foot is in contact with the ground. The footprint location system of the present invention only measures displacement vectors Vdi under stable conditions (both feet touch the ground at the same time, as shown in  FIGS. 3A and 3C ) in consideration of accurateness. That means the footprint location system only measures the displacement vectors Vdi between the first footprints ( 40   a ,  40   b  and  40   c ) and the second footprints ( 42   a  and  42   b ) as shown in  FIG. 4A . 
   With reference to the drawings and in particular to  FIGS. 4A and 4B , the user walks 4 steps. When the first shoe  5   a  and the second shoe  5   b  are in contact with the ground at the same time (see  FIG. 4A ), the coordinates of ultrasonic infrared transmitters  14  on the second footprint are measured relative to a local coordinate system at the first footprint. The footprint location system of the present invention measures a displacement vector Vd 1  from the first footprint  40   a  to the second footprint  42   a , a displacement vector Vd 2  from the second footprint  42   a  to the first footprint  40   b , a displacement vector Vd 3  from the first footprint  40   b  to the second footprint  42   b , and a displacement vector Vd 4  from the second footprint  42   b  to the first footprint  40   c . With reference to the first footprints  40   a - 40   c , the footprint location system obtains the total displacement vector of user&#39;s four steps by summing up displacement vectors 
   
     
       
         
           
             Vd 
             1 
           
           - 
           
             
               
                 Vd 
                 4 
               
               ( 
               
                 
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                     = 
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                 Vdi 
               
               ) 
             
             . 
           
         
       
     
   
   The footprint location system of the present invention uses “time-of-flight” and “triangulation” technologies to obtain the coordinates of the footprints. First of all, the ultrasonic infrared transmitter  14  transmits infrared signal and ultrasonic signal simultaneously. The ultrasonic infrared receiver  12  then sequentially receives the infrared signal and ultrasonic signal. The time difference (ultrasonic signal&#39;s time-of-flight) between these two signals is measured to calculate the distance between the ultrasonic infrared transmitter  14  and the ultrasonic infrared receiver  12 . The footprint location system of the present invention then uses triangulation technology to obtain the coordinates of the ultrasonic infrared transmitter  14  relative to the local coordinate system at the first footprints  40   a - 40   c.    
   The user doesn&#39;t always walk in a straight line and changes the walking directions during his/her movement As shown in  FIG. 4B , the footprint location system uses rotation angles θi to describe the rotation of the local coordinate system at each first footsteps  40   a - 40   c  relative to the previous one. By employing the local coordinate system&#39;s rotation angles θ 0 -θ 2 , the footprint location system transforms Vdi from the local coordinate systems into a global coordinate system as shown in  FIG. 4B . 
   As the first shoe  5   a  moves, the local coordinate system at the first footprint  40   a - 40   c  rotates an angle θi and then translates. The rotation angle θi is a rotational angle between an i-th first footprint&#39;s local coordinate system and a (i−1)-th first footprint&#39;s local coordinate system The accumulative rotation angle θ can be obtained by summing up the current and all previous rotation angle θi. After transforming those local coordinate systems of the first footprints  40   a - 40   c  to the global coordinate system, the footprint location system obtains displacement vectors Vd 1 -Vd 4  in the global coordinate system, and then calculates the user&#39;s position at the 4th step as shown in  FIG. 4B . 
   In order to find the rotation angle θi and the translation (dx, dy), which are necessary for the coordinate system transformation, we need at least three equations. The first shoe  5   a  having at least two ultrasonic infrared receivers  12  and the second shoe  5   b  having at least two ultrasonic infrared transmitters  14  can give sufficient equations to solve the three unknowns. 
   Referring to  FIG. 5A , the (x t1 , y t1 ) and (x t2 , y t2 ) are measured coordinates of two ultrasonic infrared transmitters  14  on the second shoe  5   b  before moving the first shoe  5   a . The (x t1 ′, y t1 ′) and (x t2 ′, y t2 ′) are measured coordinates of two ultrasonic infrared transmitters  14  on the second shoe  5   b  after moving the first shoe  5   a  (first footprint moved from  40   a  to  42   a ). The coordinates (x t1 , y t1 ) and (x t2 , y t2 ) are relative to the local coordinate system at the first footprints  40   a  and the coordinates (x t1 ′, y t1 ′) and (x t2 ′, y t2 ′) are relative to the local coordinate system at the first footprints  40   b.    
   Using the coordinates measured above, we can have two matrix equations to solve three unknowns, rotation angle θi, and translation (dx, dy): 
   
     
       
         
           
             
               
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   Using the accumulative rotation angle θ obtained from summing up the current and all previous rotation angle θi, the translation (dx, dy) is transformed to the displacement vector Vd in the global coordinate system: 
   
     
       
         
           
             
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   As described above, when a user wears footwear with the footprint location system of the present invention, the user&#39;s position can be easily determined by measuring, tracking and calculating the displacement vectors along a trail of the footprints without additional advanced infrastructure. Moreover because the user&#39;s steps are not too large (less than 1.5 meters), the ultrasonic infrared receivers  12  and the ultrasonic infrared transmitters  14  respectively installed on the first shoe  5   a  and the second shoe  5   b  can provide with highly accurate coordinates, thereby overcoming many problems found in existing indoor location systems, such as obstacles, multi-path effects, signal noises, signal interferences, and dead spots. 
   The footprint location system of the present invention can also use a first video detection device (a camera device)  16  and a second video detection device (a characteristic picture)  18  to replace the ultrasonic infrared receivers  12  and the ultrasonic infrared transmitters  14 . They obtain the coordinates of the first footprints  40   a - 40   c  and the second footprints  42   a - 42   b  by camera&#39;s internal parameters and image processing. Moreover, the first video detection device  16  and the second video detection device  18  can determine whether the first shoe  5   a  and the second shoe  5   b  are in contact with ground. After the confirmation of the contact, the foot location system measures the coordinates of the first footprint  40   a - 40   c  and the second footprint  42   a - 42   b.    
   Referring to  FIG. 6A , the footprint location system of the present invention installs force sensors  60  on the first shoe  5   a  and the second shoe  5   b  to confirm the shoes are in contact with ground. The use of pressure sensors  60  can avoid obtaining incorrect displacement vectors under unstable conditions and identify the user moves forward, backward, left or right. 
   Referring to  FIG. 6B , the footprint location system of the present invention installs an orientation sensor  62  on the first shoe  5   a . Since the orientation sensor provides with rotation angles in the global coordinate system, it removes one unknown from the calculation Because the unknowns are reduced to the translations (dx, dy), the footprint location system only needs to install one ultrasonic infrared transmitter  14 . 
   The footprint location system is influenced by many factors and errors accumulate each time displacement vectors calculated. Referring to  FIG. 6C , the footprint location system of the present invention installs an RFID reader  64  at the bottom of the first shoe  5   a  or the second shoe  5   b , and a set of RFID tags placed in the grid fashion over the walking range. The RFID tags are with predetermined location coordinates. When the shoe step on top of an RFID tag, the current location of the user is set to the known location coordinate of this RFID tag rather than the calculated footprint location 
   Although the present invention has been described with reference to the preferred embodiments thereof, it is apparent to those skilled in the art that a variety of modifications and changes may be made without departing from the scope of the present invention which is intended to be defined by the appended claims