Patent Publication Number: US-2007103550-A1

Title: Method and system for detecting relative motion using one or more motion sensors

Description:
BACKGROUND  
      Motion detection systems are used in a variety of applications, such as security and energy conservation. One type of motion sensor detects motion when an object, such as a person or animal, breaks a beam of light by walking past the motion sensor. This type of motion sensor detects motion passively by requiring the object move in front of the sensor. Thus, the sensor can be accidentally or intentionally bypassed simply by not walking or moving in front of the sensor. Moreover, the motion sensor produces limited information because the sensor can only report the object is in a specific location.  
      Another type of motion sensor is a heat sensitive sensor. This type of sensor detects the presence of a person by detecting the heat generated by the human body. But electrical devices, such as computers, also generate heat. The motion sensor can therefore falsely detect the presence of a person when it detects the heat generated by electrical devices.  
     SUMMARY  
      In accordance with the invention, a method and system for detecting relative motion using one or more motion sensors are provided. One or more optical motion sensors are connected to a central processing device. At least one of the motion sensors captures representations of a region, such as images or patterns that represent the region. Each optical motion sensor processes its representations to generate resulting data that are used to detect whether an object moved in relation to a respective motion sensor. Any relative motion may be detected by each optical motion sensor or by the central processing device using resulting data received from the optical motion sensor or sensors.  
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a block diagram of a motion sensor network in an embodiment in accordance with the invention;  
       FIG. 2  is a flowchart of a method for detecting relative motion in an embodiment in accordance with the invention;  
       FIG. 3  is a block diagram of a first motion sensor in an embodiment in accordance with the invention;  
       FIG. 4  is a block diagram of a second motion sensor in an embodiment in accordance with the invention;  
       FIG. 5  is a block diagram of a third motion sensor in an embodiment in accordance with the invention;  
       FIG. 6  is a graphic illustration of a motion sensor network employed in a hallway in an embodiment in accordance with the invention; and  
       FIG. 7  is a graphic illustration of a motion sensor network employed in a conference room in an embodiment in accordance with the invention.  
    
    
     DETAILED DESCRIPTION  
      The following description is presented to enable embodiments of the invention to be made and used, and is provided in the context of a patent application and its requirements. Various modifications to the disclosed embodiments will be readily apparent, and the generic principles herein may be applied to other embodiments. Thus, the invention is not intended to be limited to the embodiments shown but is to be accorded the widest scope consistent with the appended claims. Like reference numerals designate corresponding parts throughout the figures.  
      Embodiments in accordance with the invention use one or more optical motion sensors to capture images or patterns and process the images or patterns to generate resulting data. Relative motion is detected by each motion sensor using its resulting data and a particular motion detection technique in an embodiment in accordance with the invention. In another embodiment in accordance with the invention, the one or more optical motion sensors transmit the resulting data to a central processing device that detects relative motion using the resulting data and a particular motion detection technique. Motion detection techniques include, but are not limited to, speckle translation, image correlation, and pattern analysis using light and shadow imaging or laser interferometry.  
       FIG. 1  is a block diagram of a motion sensor network in an embodiment in accordance with the invention. Motion sensor network  100  includes optical motion sensors  102 ,  104 ,  106 ,  108  connected to central processing device  110  through connections  112 ,  114 ,  116 ,  118 , respectively. Connections  112 ,  114 ,  116 ,  118  are implemented as wireless connections in an embodiment in accordance with the invention.  
      Motion sensors  102 ,  104 ,  106 ,  108  are positioned in different locations and form a distributed network of optical motion sensors. Motion sensors  102 ,  104 ,  106 ,  108  are positioned in a self-contained region in an embodiment in accordance with the invention. Examples of a self-contained region include a room or hallway. In another embodiment in accordance with the invention, motion sensors are positioned in separate regions, such as, for example, throughout a building or a floor in the building.  
      Motion sensors  102 ,  104 ,  106 ,  108  are fixed in their locations and capture representations of one or more regions in an embodiment in accordance with the invention. For example, optical motion sensors  102 , 104 ,  106 , 108  may be placed in a conference room and each sensor captures representations of one or more regions or sections of the room. Each motion sensor processes its representations to generate resulting data. The resulting data are used to determine whether one or more objects moved with respect to the fixed location of each motion sensor. Relative motion may be determined by each optical motion sensor itself or by central processing device  110  using the resulting data received from motion sensors  102 ,  104 ,  106 ,  108  over the wireless connection.  
      Central processing device  110  is implemented as a computer in an embodiment in accordance with the invention. Central processing device  110  is positioned in the same location as one or more of the motion sensors  102 ,  104 ,  106 ,  108  in an embodiment in accordance with the invention. In another embodiment in accordance with the invention, central processing device  110  is positioned in a different location from motion sensors  102 ,  104 ,  106 ,  108 .  
      Referring to  FIG. 2 , there is shown a flowchart of a method for detecting motion in an embodiment in accordance with the invention. Initially the central processing device is programmed with one or more motion detection programs or parameters, as shown in block  200 . The motion detection programs are used to detect relative motion using one or more motion detection techniques.  
      Motion detection parameters allow a motion detection program to be optimized or customized for a particular environment or application. For example, motion detection parameters can be used to define a region or zone that is to be excluded from the motion detection analysis. The zone may be excluded because any motion in that zone is not of interest. By way of another example, a motion detection program may include the ability to count the number of moving objects in the region or to determine the locations in the region where the motion occurred.  
      Next, at block  202 , one or more motion sensors capture representations of one or more regions. The representations are images or patterns in an embodiment in accordance with the invention. Each sensor processes its representations to generate resulting data at block  204 . The representations may be processed using a variety of techniques. For example, an image from one motion sensor may be correlated with another image in an embodiment in accordance with the invention. By way of another example, speckle or diffraction patterns may be analyzed to determine the presence or absence of motion.  
      A determination is then made at block  206  as to whether each sensor is to detect relative motion. If so, the method passes to block  208  where each optical motion sensor detects relative motion using the resulting data it generated. In other embodiments in accordance with the invention, one motion sensor may communicate with another motion sensor prior to detecting relative motion.  
      The optical motion sensors then transmit information to the central processing device regarding the presence or absence of relative motion (block  210 ). For example, only the motion sensors that detect relative motion may transmit a detect message to the central processing device in an embodiment in accordance with the invention. The central processing device initiates an action at block  212  based on the presence or absence of any relative motion. When motion is not detected, for example, the central processing device reduces or turns off the air conditioning in a room to save energy in an embodiment in accordance with the invention. As another example, if motion is detected, the lights in a room are turned on or maintained on in an embodiment in accordance with the invention.  
      Another action that may be initiated by the central processing device is additional processing of the resulting data in another embodiment in accordance with the invention. For example, the central processing device may determine the number of people in a room based on the locations where motion is detected and compare the number with a previously determined number in an embodiment in accordance with the invention. If the number of people in the room has increased, the level of air conditioning is increased in order to compensate for the increase in the number of people. When the comparison determines the number of people in the room has decreased, the level of air conditioning is decreased.  
      Returning to block  206 , when the optical motion sensors are not to detect relative motion, the method passes to block  214  where each optical motion sensor transmits the resulting data to the central processing device. The central processing device then determines the presence or absence of any relative motion (block  216 ) and initiates an action based on the presence or absence of any relative motion (block  212 ).  
       FIG. 3  is a block diagram of a first motion sensor in an embodiment in accordance with the invention. Motion sensor  300  includes light source  302 , motion detection system  304 , and transmitter  306 . Light source  302  is implemented as one or more light-emitting diodes in an embodiment in accordance with the invention. In another embodiment in accordance with the invention, light source  302  is implemented with one or more lasers, such as, for example, vertical cavity surface emitting lasers (VCSEL). And finally, in yet another embodiment in accordance with the invention, light source  302  is not used and motion sensor  300  uses ambient light to capture images or patterns.  
      Transmitter  306  is implemented with any type of wireless transmitter. Transmitter  306  is implemented as a low power wireless transmitter using a bulk acoustic wave (BAW) resonator in an embodiment in accordance with the invention. The film bulk acoustic resonator (FBAR) designed by Agilent Technologies, Inc. is one example of a BAW resonator.  
      Motion detection system  304  includes imager  308  and analyzing system  310 . Imager  308  and analyzing system  310  are constructed in accordance with a given motion detection technique in an embodiment in accordance with the invention. Motion detection techniques include, but are not limited to, speckle translation, image correlation, and the use of diffraction patterns using coherent imaging or laser interferometry. Motion detection system  304  captures representations such as images or patterns, processes the representations, and transmits the resulting data to a central processing device for further processing in an embodiment in accordance with the invention. The motion may be detected by the motion sensor or by the central processing device using the resulting data.  
      For example, when motion sensor  300  uses speckle translation to detect relative motion, motion detection system  304  captures speckle patterns and detects changes in the speckle patterns. Imager  308  includes one or more spatial filters and analyzing system  310  includes phase quadrature decoder (PQD)  312 , memory  314 , controller  316 , and measurement circuit  318 . The implementation of analyzing system  310  is disclosed in commonly assigned U.S. patent application Ser. No. 11/016,651 filed on Dec. 17, 2004, which is incorporated herein by reference.  
      The Q and I channels output from the spatial filter or filters are input into PQD  312 . PQD  312  generates a pulse every time a transition is made in either the forward (+) or backward (−) direction. It is assumed in one embodiment in accordance with the invention that the transitions move in a clockwise or counter-clockwise direction. Any transitions contrary to this assumption are then ignored. This assumption may be used to reduce spurious noise when determining velocity.  
      The pulses output from PQD  312  are transmitted to buffer  314 . Controller  316  analyzes the pulses in buffer  314  to determination if there is a trend in the pulses. A trend occurs when a desired number of similarly signed pulses (“+” or “−”) are output from PQD  312 . In an embodiment in accordance with the invention, the desired number of similarly signed pulses ranges from three to ten.  
      If controller  316  detects a trend in the pulses, one or more pulses are transmitted from buffer  314  to a central processing device (not shown) by transmitter  306 . The central processing device can determine the velocity of the moving object by calculating the speed as inversely proportional to the average time between the successive or consistent output pulses of PQD  312 . The direction of the motion is given by the sign of the pulses in an embodiment in accordance with the invention.  
       FIG. 4  is a block diagram of a second motion sensor in an embodiment in accordance with the invention. Motion sensor  400  includes light source  302 , imager  402 , analyzing system  404 , and transmitter  306 . Analyzing system  404  includes memory  406 , difference image generator  408 , correlator  410 , and processing device  412 . Motion sensor  400  detects relative motion using image correlation in an embodiment in accordance with the invention. Analyzing system  404  is disclosed in commonly assigned U.S. patent application Ser. No. 11/014,482 filed on Dec. 16, 2004, which is incorporated herein by reference.  
      Imager  402  captures an image I(n) and transmits the image to memory  406 . Imager  402  then captures another image, image I(n+1). Image I(n+1) is also stored in memory  406 . The images are then input into difference image generator  408  in order to generate a difference image. The difference image and one of the images used to create the difference image are correlated by correlator  410 . Processing circuit  412  then performs a thresholding operation and generates a navigation vector when motion has occurred between the time image I(n) and image I(n+1) are captured.  
      A clock (not shown) is connected to imager  402  in an embodiment in accordance with the invention. The clock permits imager  402  to capture and transmit the images to memory  406  synchronously. This allows motion sensor  400  to determine an absolute magnitude reference in an embodiment in accordance with the invention. In other embodiments in accordance with the invention, the clock may not be included in motion sensor  400 .  
      Embodiments in accordance with the invention are not limited to the implementation of analyzing system  404  shown in  FIG. 4 . Other motion detection techniques may use different components or only a portion of the components shown in  FIG. 4 . For example, motion sensor  400  may detect relative motion using patterns of light and shadows in an embodiment in accordance with the invention. Analyzing system  404  would therefore include memory  406  and correlator  410 . Light source  302  emits light towards a region while imager  402  captures representations of the region using reflected light. The reflected light produces patterns of light and shadow that are stored in memory  406 . Correlator  410  correlates the patterns to determine whether there are any changes in the patterns. The motion of an object is determined by the changes in the patterns.  
      Referring to  FIG. 5 , there is shown a block diagram of a third motion sensor in an embodiment in accordance with the invention. Motion sensor  500  includes laser  502 , imager  504 , and analyzing system  506 . Analyzing system  506  includes correlator  412 . Laser interferometry is the motion detection technique used in conjunction with motion sensor  500  in an embodiment in accordance with the invention.  
      Laser  502  emits light towards a region. A portion of the emitted light is also input to imager  504 . Imager  504  captures representations of the regions using light reflected from the region. The representations are interference patterns created by the differences between the emitted light and the reflected light. Correlator  412  correlates the interference patterns to determine whether there are any changes in the patterns. The motion of an object is determined by the changes in the patterns.  
       FIG. 6  is a graphic illustration of a motion sensor network employed in a hallway in an embodiment in accordance with the invention. Hallway  600  includes optical motion sensors  102 ,  104 ,  106 ,  108 . The dashed lines illustrate a field of view  602 ,  604 ,  606 ,  608  for the imager in each motion sensor  102 ,  104 ,  106 ,  108 , respectively. Motion sensors  102 ,  104 ,  106 ,  108  are used to detect any relative motion in hallway  600 .  
      One or more of the motion sensors  102 ,  104 ,  106 ,  108  capture representations of its field of view  602 ,  604 ,  606 ,  608  and process the representations to determine whether a person or object moves with respect to at least one of the motion sensors. Processing of the representations generates resulting data that are transmitted to a central processing device (not shown). If motion is detected in hallway  600 , one or more actions are taken, such as, for example, turning on lights, activating an alarm, or turning on a security video camera in order to view the object that caused the motion.  
       FIG. 7  is a graphic illustration a motion sensor network employed in a conference room in an embodiment in accordance with the invention. Conference room  700  includes motion sensors  102 ,  104 ,  106 ,  108 . The dashed lines depict a field of view  702 ,  704 ,  706 ,  708  for the imager in each motion sensor  102 ,  104 ,  106 ,  108 , respectively. Motion sensors  102 ,  104 ,  106 ,  108  are fixed in their locations in order to detect any relative motion in conference room  700 .  
      One or more of the motion sensors  102 ,  104 ,  106 ,  108  capture representations of its field of view  702 ,  704 ,  706 ,  708  and process the representations to determine whether a person moves with respect to at least one of the motion sensors. Processing of the representations generates resulting data that are transmitted to a central processing device (not shown). If motion is detected in conference room  700  or entryway  710 , one or more actions are taken, such as, for example, turning on lights and air conditioning for conference room  700 .