Abstract:
A system for identifying a change in walking speed of a person includes plurality of sensors ( 8,9,10,11,18 ) disposed among a plurality of locations in a living space ( 20 ). Each of the plurality of sensors ( 8,9,10,11,18 ) is operable to detect one of motion of the person or location of the person. Travel times (tt) for a path ( 19 ) traveled by the person through the living space ( 20 ) are measured based on the signals of the plurality of sensors ( 8,9,10,11,18 ). A reliability indication (R 1 ) of the likelihood that another person is visiting the living space ( 20 ) is established. A change in the person&#39;s walking speed is identified by identifying changes in the travel times (tt), disregarding travel times (tt) which are indicated as unreliable by the reliability indication (R 1 ).

Description:
FIELD OF THE INVENTION 
       [0001]    The invention relates to a system for identifying a change in walking speed of a person on the basis of a changing in travel times measured when the person walks along a known path in his living space. 
       BACKGROUND OF THE INVENTION 
       [0002]    Many elderly people live alone. The elderly also are at risk from disease and illness. Among other symptoms, a person may begin walking slower as their health declines or when they become ill. Similarly, a person recovering from an illness may begin walking faster as their health improves. Thus, a person&#39;s walking speed may be used as an indicator of health. 
         [0003]    A system for identifying the walking speed of person in his living space is disclosed in U.S. Pat. No. 7,535,368. 
         [0004]    The disclosed system comprises a plurality of sensors disposed in various rooms of a home. The sensors provide signals representative of motion and/or the location of the person within the home. The system also includes a unit receiving the sensor signals. The unit derives the location of the person on the basis of the sensor signals. The unit establishes a travel time for a path traveled by the person through the structure based on the established locations and stores the travel time. The unit measures the time traveled by the person through his home along a path defined by a number of sensor locations. The unit identifies a change in the person&#39;s walking speed by identifying changes in the travel time for the path traveled by the person. 
         [0005]    The system may alert a caregiver to inform them of the change in walking speed identified by the system. 
         [0006]    It is important that the reliability of the determined changing in walking speed is high, so that the caregiver can trust the information about the walking speed changings and false alerts are prevented. 
       SUMMARY OF INVENTION 
       [0007]    It is an object of the invention to provide a system, which determines the changing of the walking speed with an improved reliability. 
         [0008]    This object is achieved by a system for identifying a change in walking speed of a person, the system comprising: a plurality of sensors to be disposed among a plurality of locations in a living space, wherein each of the plurality of sensors is operable to detect one of motion of the person or location of the person, means to establish a travel time for a path traveled by the person through the living space based on the signals of the plurality of sensors and to store the travel time, means to establish a reliability indication of the likelihood that another person is visiting the living space, and means to identify a change in the person&#39;s walking speed by identifying changes in the travel time for the path traveled by the person through the living space, disregarding travel times which are indicated as unreliable by the reliability indication. 
         [0009]    The invention is at least partly based on the insight that visitors can substantially disturb the measurements of the travel times. By determining the presence of a visitor and disregarding the measurements of the walking times in the period that the presence of the visitor is detected a substantial improvement of the reliability of the measurements of the travel times and consequently also a substantial improvement of the reliability of the identification of changings in walking speed is achieved. 
         [0010]    In an embodiment of the invention the system is operable to establish event signals from the signals received from said sensors and/or additional signals received from additional sensors detecting a status and/or activities of persons in the living space, which event signals are indicative for events caused by persons in the living space, wherein the reliability indication is dependent on a number of established events in an observation period in which the related travel time (tt) is established. 
         [0011]    In case a further person is visiting the living space, this will result in an increase of a number of detected events. So the presence of the further person can be easily and in cost-effective manner determined. 
         [0012]    In an embodiment of the system according to the invention system only two detectors are used for establishing the travel speed, a first one of two sensors is a sensor for detecting the presence of the person in the bathroom or toilet and as second one of two detector sensors is a sensor for detecting the presence of the person in another room. 
         [0013]    It appears that the persons visiting the toilet usually uses the same path. They seldom make a detour. So the travel time between leaving the toilet and entering a room is a reliable indication of the travel time. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    These and other aspects of the invention will be apparent from and elucidated further with reference to the embodiments described by way of example in the following description and with reference to the accompanying drawings, in which 
           [0015]      FIG. 1  shows an embodiment of an unattended autonomous surveillance, 
           [0016]      FIG. 2  shows a map of a living space, 
           [0017]      FIG. 3  shows a flow diagram of an exemplary program for determining the walking speed for use in an embodiment of the system according to the invention, 
           [0018]      FIG. 4  shows an exemplary format for a list comprising the determined travel times for use in an embodiment of the system according to the invention, 
           [0019]      FIG. 5  shows a flow diagram of an exemplary program routine for determining the likelihood that a further person is in the living space for use in an embodiment of the system according to the invention, and 
           [0020]      FIG. 6  shows a diagram of an embodiment of a program for determining the change in the walking in travel time over time for use in an embodiment of the system according to the invention, and 
           [0021]      FIG. 7 . shows an embodiment of the central unit  15  for use in an embodiment of the system according to the invention. 
       
    
    
     DETAILED DESCRIPTION OF EMBODIMENTS 
       [0022]    In the subsequent paragraphs, various aspects of a technique for unobtrusively measuring the walking speed of a person in their own home and for identifying a change in the person&#39;s walking speed will be explained. 
         [0023]      FIG. 1  shows an embodiment of a lifestyle monitoring system  1  for monitoring for example, elderly residents in their own house or in a nursery house. The system  1  comprises three major groups of components, indicated by reference signs  100 ,  101  and  102  respectively 
         [0024]    Group  100  is a group of components placed in a living space of a person to be monitored. It forms a sensor network comprising a plurality of sensors  8 ,  9 ,  10 ,  11 , and  18 . Sensors  9 ,  10  and  11  comprise detectors, actuated by opening or closing a door or drawer These detectors can for example be switches, accelerometer based sensors or any other detector which can detect the opening and closing of a door or drawer. Sensors  8  and  18  comprise motion sensors. The network is connected to Internet  25  via a gateway  15  of a usual type, e.g. a Zigbee gateway. The gateway  15  receives sensor signals generated by the sensors  8 , 9 , 10 , 11  and  18  and outputs a data signal representing the sensor signals to the internet  25 . 
         [0025]    Group  101  forms a processor controlled system, for example an internet server. Group  101  comprises a communication module  103  also connected to the internet  25  for receiving the data signal and extracting the sensor signals from the data signal. The monitoring functionality and functionality for detection of behavior deviation and notification of detected deviation is implemented in a software module  104 . The software module  104  is combined with another software module  105  software for user management and scalability. All software runs on the processor controlled system. 
         [0026]    Group  102  comprises a message receiving device, for example a smartphone provided with a so-called smartphone app  106 . The smartphone app  106  is coupled with group  101  via a mobile phone/data network. The smartphone app  106  can be used by a caregiver or family member to install and configure the system, to inspect trends in the behavior of the elderly persons and to receive notifications/alerts about detected (mild or severe) deviations in their usual behavior. 
         [0027]    In operation the software module  104  analyses the signals of the sensors  8 ,  9 ,  10 ,  11  and  18  and automatically detects deviations from the usual behavior or other deviations, which could be indicative of an emergency. The family of the elderly person or caregiver is notified/alerted via the smartphone app  106  if a deviation occurs which exceeds a predetermined threshold. This gives the caregiver or family member an opportunity to verify the situation (i.e. by phone). 
         [0028]    After that, depending on the nature of the deviation (mild or severe), they can take care that a suitable medical intervention is implemented or can involve appropriate emergency services. 
         [0029]      FIG. 2  shows a map of a living space  20 , in the form of a typical apartment for elderly persons. The apartment comprises a hall  2 , a living room  3 , a kitchen  4 , a bedroom  5 , a bathroom  7  and a toilet  6 . 
         [0030]    The sensors  8 ,  9 ,  10   11  and  18  are installed for detecting the presence and/or activity of a person in the living space  20 . The motion sensor  8  is located in the living room  3  for detecting the presence of a person in the living room  3 . The motion detector  18  is located in the bathroom  7  for detecting the presence of a person in the bathroom  7 . The sensor  9  is a detector fixed to a drawer  16  for the utensils in a kitchen counter  12  in the kitchen  4  for detecting the opening and closing of the drawer  16 . The sensor  10  is a door detector for detecting the opening and closing of a door  13  of the toilet  6 . Sensor  11  is a door detector for detecting the opening and closing of an outside door  14 . The gateway  15  is located in the hall  2 . The sensors  8 ,  9 ,  10 ,  11  and  18  are coupled to the gateway  15  to submit sensor signals to the gateway  15 . This coupling is preferably a wireless connection, but alternatively a wired connection can be used. 
         [0031]    The program module  104  comprises a sub program of an usual type to derive events E 1 , . . . E 10  from the sensor signals. These events indicate activities caused by the person in the living space  20 . Event E 1 , indicating that a person is leaving the living room  3  and event E 2 , indicating that a person is entering the living room  3 , are derived from the sensor signal provided by motion sensor  8  in the living room  3 . Event E 3 , indicating the opening of the drawer  16 , and event E 4  indicating that the drawer  16  is closed are derived from the signal provided by sensor  9 . Event E 5  indicating that a person opens the door  13  of the toilet  6  and event E 6  indicating that the person closes the toilet door  13  are derived from the sensor signals provided by sensor  10 . Event E 7 , indicating that a person is leaving the bath room  7 , and event E 8 , indicating that a person is entering the bath room  7 , are derived from the sensor signal provided by motion sensor  18  in the bath room  7 . Event E 9  indicates that outside door  14  is opened and event E 10  indicates that the outside door  14  is closed. Events E 9  and E 10  are derived from the detector  11 . 
         [0032]    In the embodiment described above two motion sensors and three door/drawer detectors are used as basis for the detection of the events. It will be clear that the number of detectors can vary. More or less detectors can be used in the sensor network. 
         [0033]    Also other type of sensors may be used, for example a sensor, which detects that an apparatus or lamp is switched on and/or off or a sensor, which detects whether a telephone call is made. Also camera in combination with an image analyzer can be used to detect the presence or activity of a person. 
         [0034]    The software module  104  comprises a program which derives from the events a walking speed and changing in the walking speed of the person living in the living space  20 . A decrease in walking speed is often a symptom that the health condition declines or that the person is becoming ill. Similarly, a person recovering from an illness may begin walking faster as their health improves. Thus, a person&#39;s walking speed may be used as an indicator of the health of the person. 
         [0035]    The walking speed can be determined by measuring the time that it takes for the person to walk over a distance between two known locations. The events E 1  to E 8  all indicates a position of the person at the moment that the event is detected. So measuring the time difference between two different events provides information about the walking speed, assumed that the person is walking along a known path between these two locations. In principle many combinations of two events can be used for determining the walking speed. The best suitable combinations are those for which almost always the same path is followed and whereby the person bridges the distance between the locations without stops to perform other activities. 
         [0036]    A very suitable path for determining information about the walking speed is a path  19  ( FIG. 2 ) between a door of the toilet  6  and the door  17  of the living room  3 . This path  19  is often used when visiting the toilet  6 . Usually the person is walking directly to the living room and will seldom make a detour. In principle also the path in the other direction, from living room  3  to the toilet  6 , can be used. However the path in the direction from toilet to living room is preferred. This is because typical motion sensors (located in the living room  3 ) are faster (more accurate) in signaling motion than in signaling absence of motion. 
         [0037]    The program has a routine for detecting a sequence of event E 6 , indicating that the person is leaving the toilet  6 , followed by event E 2  indicating that the person has entered the living room through the door  17  and determining a travel time (tt), which is equal to the time difference between the detection of the two subsequent events E 6  and E 2 . 
         [0038]      FIG. 3  shows a flow diagram of an exemplary program for determining the walking speed. In a loop comprising step S 1  it is continuously checked whether event E 6  occurs. If so, then a waiting step S 2  is executed. In step S 2  a timer is started and a wait loop is performed until a next event is detected. In Step S 3  it is checked whether the next detected event is event E 2 . If not, then the program jumps to step S 1 . If the detected next event was event E 2  then in step S 4  the timer value is determined. This value is the travel time (tt), indicating the time difference between event E 2  and event E 6 . The travel times (tt) are stored in a list in the data memory  26 . Subsequently the program jumps to step S 1  again. 
         [0039]    Several formats are possible for the list with travel times (tt). In a simple format the travel times (tt) are stored in the list in the order in which the travel times (tt) are determined. 
         [0040]    With this format a change in travel speed can be derived by comparing travel times (tt) which are recently placed in the list with travel times (tt) which are earlier placed in the list. 
         [0041]      FIG. 4  shows another possible format for the list, indicated by reference sign  45 . The list  45  in  FIG. 4  comprises  4  columns. The dates and times at which the travel times (tt) are determined are stored in column  40  and  41  respectively. The corresponding travel times (tt) are stored in column  42 . 
         [0042]    Column  43  comprises a reliability indicator RI which indicates whether the determined travel time (tt) is reliable. 
         [0043]    For several reason the determined travel time (tt) may be unreliable. This will for example be the case in case the person does not walk directly from the toilet  6  to the living room, but entering the bedroom before he is going to the living room  3 . This will result in a travel time (tt) which is substantial longer than usual. Row  44  in the list shows a typical value of a travel time (tt) for the situation that the person did not directly walk from the toilet  6  to the living room. The determined travel time (tt) has a value of  27  seconds which is substantial higher that the other values of the travel times (tt) determined in the last period. So by checking whether the determined travel time (tt) is substantial different from the other walking times determined in the same period it can be determined whether the travel time (tt) is reliable or not. This can for example be done by determining the average travel time (tt) of a day and declare all travel times (tt) which are a certain threshold (th 1 ) higher than the average as unreliable. The threshold (th 1 ) is chosen such that only or almost only travel times (tt) pass the reliability test which correspond with an uninterrupted walk along the path  18 . 
         [0044]    The determined travel times (tt) areas also unreliable in case another person is visiting the home. This may cause measurements of travel times (tt) for other persons than the monitored person. Moreover it is not sure whether the subsequent events E 6  and E 2  used for the measurement of the travel times (tt) are caused by the same person. This might lead to very short travel times (tt) measurements. Such very short times (much lower than average) must be marked unreliable. In the system according to the invention an indication of the likelihood that another person was visiting the living space  1  is determined for an observation period in which travel times (tt) are determined. In case in such observation period it determined that likely another person was visiting the living space  1 , all determined travel times (tt) in that observation period are declared unreliable. There exist several possibilities to determine the likelihood of the presence of visitor, for example by using several presence sensors and detect whether at the same time more than one persons are present in the living space  1 . 
         [0045]    Cameras can be used in combination with image analyzing technology to detect more than one person in the images captured by the cameras. 
         [0046]    Another possibility is to detect events, which occur with such a short time distance from each other that it is impossible that the they are caused by the same person. 
         [0047]    A very simple, cost effective, method is the detection of the number of events that occurs in the certain observation period and compare this number with the number of events with a reference indicating the usual number of events that is detected in corresponding observation periods. If in the observation period the detected number is substantial higher than the reference this is an indication of the presence of a visitor. In that case all determined travel times (tt) for that observation period are declared unreliable. As observation period a period of 24 hours is very suitable, because the activities of a person are in general the same per day. 
         [0048]    A flow diagram of an exemplary program routine for determining the likelihood in this manner is shown in  FIG. 5 . In step S 50  it is continuously checked whether an event occurs. If so than an event counter is incremented in step S 51 . Step S 51  is followed by step S 52  in which it is detected whether the observation period has expired. If not, then step S 52  is followed by step S 50 . In case in step S 52  an expiration of the observation period is determined, then in step S 53  it is checked whether the number of events is substantial higher than the reference by comparing this number with a threshold value (th 2 ). This threshold value (th 2 ) can be a fixed value, but preferably this threshold is related to the average number of events in the observation period, for example 130% of the average value. If the threshold value (th 2 ) is not exceeded step S 55  is executed in which the event counter is reset and a jump to step S 50  is made. If the threshold value is exceeded then in step S 54  all travel times (tt) determined in the corresponding period are declared unreliable and the reliable indicator RI is set. In de list of  FIG. 4  this is done for de travel times (tt) determined on Mar. 7, 2014. After the executing of step S 54  the program continues with step S 55 . 
         [0049]    In case the travel times (tt) are stored together with the moment that the travel time (tt) is determined, change in travel time (tt) can be determined by comparing travel times (tt) determined at earlier moments. This can for example be done by comparing the average travel time (tt) of last week with the average travel time (tt) a number of weeks earlier, for example 8 weeks earlier. It will be clear that several other methods can be used to determine a change in travel speed. For example by comparing the average of the last week with the average for the last 3 months. In case the walking speed is decreased substantial such that it indicates a declining health or illness this can be reported to a caregiver or a family member of the monitored person. 
         [0050]    Hereinbefore the change is determined by comparing an average of recent travel times (tt) with the average of travel times (tt) determined earlier. It will be clear for the skilled man that instead of the average of recently determined travel times also one recently determined travel time (tt) can be used in the comparison. This can be for example the median of value of sequence recently determined travel times (tt) or another recently determined travel time (tt). 
         [0051]      FIG. 6  shows a flow diagram of an embodiment of a program for determining the change in the walking in travel time (tt) over time. This program is periodically executed, for example with a frequency of one execution per day. The program starts with an initiating step S 60 . After step S 61  is executed. In this step the average travel time (tt) for a recent period in the near past is determined. This recent period can for example be the 7 days directly preceding the start of the program. The calculation of the average is done on the bases of the data in the list with travel times (tt) stored in the data memory  26 . 
         [0052]    After step S 61  step S 62  is executed in which the average travel time (tt) for period  2  located before the recent period  1  is calculated on the basis of the list of travel times. Period  2  can for example be a 7 days period located a number of days before the recent period  1 . Subsequently the average travel times (tt) for recent period  1  and the average travel time (tt) for period  2  are compared in step S 63 . A difference (dt) between these average indicates a changing in walking speed. In step S 64  it is detected whether the difference dt exceeds a threshold value (th 3 ), indicating a serious decrease of the walking speed. If so then an alert message is send to a caregiver or family member via the smartphone app  106 . It is also possible to report the actual change periodically, so that the caregiver or family member has a good view on the development of the walking speed and indirectly a good view on the development of the health of the monitored person. 
         [0053]    It will be clear that alert messages can be sent via other communication channels, for example to a so-called tablet computer connected to the internet  25 . 
         [0054]    In the embodiments described above the software module is incorporated in an internet server. However it will be clear for the skilled man that this software can also be incorporated in a central unit located in the living space  20 . 
         [0055]      FIG. 7 . shows an embodiment of a suitable central unit  15 . The central unit  15  comprises a program controlled processor  22 . Processor  22  is of usual type which can execute program instructions of a computer program loaded in a program memory  23 . The processor  22  is coupled with a wireless transmission unit  20  for the wireless communication with the sensors  8 ,  9   10  and  11  via an antenna  21 . The processor  22  is further coupled with an internet communication unit  24  enabling communication to the outside world via the internet  25 . The central unit  15  is further provided with a data memory  26  for storing information derived during the execution of the computer program in the program memory  23 . 
         [0056]    It will be appreciated by those skilled in the art that the methods and algorithms described hereinabove may be utilized to see if the monitored person&#39;s walking speed has increased. For example, it may be expected that a medication taken by the person would improve the health of the resident. This improvement may be manifested by an increase in the monitored person&#39;s walking speed over a period of time, which would result in shorter travel times. For example, if the monitored person is recovering from a bypass surgery, the recovery may be manifested by an improved walking speed of the monitored person. The methods and algorithms described hereinabove may be utilized to monitor the improvement in walking speed and therefore the progress in recovery over a number of days, weeks or months. Thus, such statistical walking speed data may be used as a prognostic tool. 
         [0057]    It will be appreciated by those skilled in the art that the methods and algorithms described hereinabove may be embedded in a dedicated processor such as an ASIC (application specific integrated circuit) or, a digital signal processor configured for processing the signals. 
         [0058]    While the invention has been described in detail in connection with only a limited number of embodiments, it should be readily understood that the invention is not limited to such disclosed embodiments. Rather, the invention can be modified to incorporate any number of variations, alterations, substitutions or equivalent arrangements not heretofore described, but which are commensurate with the spirit and scope of the invention. Additionally, while various embodiments of the invention have been described, it is to be understood that aspects of the invention may include only some of the described embodiments. Accordingly, the invention is not to be seen as limited by the foregoing description, but is only limited by the scope of the appended claims.