WO2017065617A1

WO2017065617A1 - Method and system for determining hight differences

Info

Publication number: WO2017065617A1
Application number: PCT/NO2016/050205
Authority: WO
Inventors: Svein HUSA
Original assignee: Tellu As
Current assignee: Tellu As
Priority date: 2015-10-12
Filing date: 2016-10-12
Publication date: 2017-04-20
Anticipated expiration: 2018-04-12
Also published as: NO20151375A1

Abstract

The invention discloses a method and system for determining a change in height of a first object being moved in a room where the background pressure fluctuates, comprising the steps of: - mounting at least a first pressure change sensor to the first object, and - mounting a second pressure change sensor to a second object, and - measuring the difference between signals from said first and second pressure change sensors.

Description

Method and system for determining height differences Field of the invention

[0001 ] The present invention relates to a method and system for determining a change in height of a first object being moved in a room where the background pressure fluctuates.

Background art

[0002] Over the last 15 years, a lot of effort has been put in developing a simple and well-functioning fall detector. Thus far, all such detectors rely on the use of a motion sensor as the primary fall detection sensor.

[0003] There also exist a multitude of «fall detectors» that rely on the use of

Smartphone applications.

Summary of the invention

[0004] The application of a differential pressure transmitter for detecting a fall as it will be disclosed in the following with a ventilated reference cell will require a sensitivity that is significantly higher than those indicated in the above- mentioned prior art. The measurement range will be only a few meters and typically have a resolution or accuracy of about 1 cm. Available on the market are MEMS (Micro-Electro-Mechanical Systems) differential pressure sensors having an operating range of +/- 250 Pa, corresponding to an altitude variation of +/- 19 m at normal atmospheric pressure.

Typically, the interference voltage from such sensors corresponds to an altitude variation of about 1 cm. Many applications only use a small part of the available measurement range, and such measurements would be more accurate if a differential pressure sensor could be used.

[0005] It is an object of the invention to provide a method for measuring a change in vertical position of objects or people. According to an aspect of the invention, there is provided a method of using a pressure change measurement for the accurate determination of a change in height of an object being moved in a room where the background pressure fluctuates, in that, instead of basing the measurement on the pressure change from a single sensor attached to the object, the measurement is based on a difference between the signals from two pressure change sensors, one being attached to the object and the other being fixedly installed in the room where the measurements are carried out.

[0006] According to an embodiment of the invention, there is provided a method of using a pressure change measurement for the accurate determination of a difference in height change between two objects which are both being moved in a room where the background pressure fluctuates, as indicated above, in that the fixedly installed sensor is also made movable and is attached to one of the objects.

[0007] According to an embodiment of the invention, there is provided a method of registering that a person staying in a room suffers a fall as indicated in the preceding paragraph in that a change in the vertical position of the person's body being characteristic of a fall is obtained from the difference between the pressure change measured by a sensor attached to the body of the person and the pressure change measured by a fixed-position sensor.

[0008] According to an embodiment of the invention, there is provided a method of registering that a person, who is staying indoors or outdoors, suffers a fall, in which a change in the vertical positions of two or more body parts of the person being characteristic of a fall is obtained from the difference between the pressure change measured by sensors attached to each of the body parts concerned.

[0009] According to an embodiment of the invention, there is provided a method for eliminating ambiguity in fall detection, in that the correlation between each of the sensor signals measured by sensors attached to each of the body parts concerned and the difference signal is calculated, to thereby determine to what extent each of the sensor signals contributes to the difference signal.

Brief description of the drawings

[0010] To facilitate the understanding of the invention, the following description is made with reference to the accompanying drawings, in which

[001 1] Fig. 1 shows how background noise is removed using a stationary and a moveable sensor, [0012] Fig. 2 shows how background noise is removed using two moveable sensors. The measurement signal indicates the difference in height between the sensors,

[0013] Fig. 3 shows a principle of a fall detector based on a sensor carried by a user and a stationary sensor, and

[0014] Fig. 4 shows a principle of a fall detector based on two sensors which are both carried by a user.

Embodiments of the invention

[0015] In the following, the present invention will be explained by describing

preferred embodiments, and by referring to the accompanying drawings. However, those skilled in the art will recognize other applications and modifications within the scope of the invention, as defined in the appended independent claims.

[0016] Use of barometric pressure sensors, that is, absolute pressure sensors having an operating range slightly above normal atmospheric pressure, is a well-established method for determining vertical position. The method has since long been used in different forms of navigation.

[0017] Today, modern micro-technology offers sensors measuring absolute, atmospheric pressure with a resolution of about 2 Pa. At normal pressures, this corresponds to an air column of 15 cm. In addition to resolution, long-term stability and temperature stability are important properties of a pressure sensor. In the present invention, however, resolution is the most important property.

[0018] Pressure sensors have evolved considerably in recent years. Improved micromachining technology and the development of analogue and digital microelectronics have resulted in increasingly better and less expensive sensors. The development will continue, but when it comes to resolution and sensitivity, however, much of the noise that limits the achievable improvements is caused by fundamental, physical processes. It does not seem realistic to expect major improvements in these properties.

[0019] The atmospheric pressure is determined by a number of meteorological factors besides vertical position, and an accurate pressure measurement alone is unable provide an accurate value of the vertical position of the sensor. Since the meteorological conditions vary relatively slowly with time, however, we can use an accurate measurement of the atmospheric pressure to determine rapid changes in vertical position. These are changes occurring on a considerably shorter time scale than the

meteorological.

[0020] When changes in pressure are measured, instead of an absolute pressure sensor, a sensitive differential pressure sensor of which one port is connected to a chamber that is vented to the surroundings through a large flow resistance element may be used. A capillary tube is suitable.

Together with the volume of the reference chamber a first order dynamic system having a time constant τ will form.

_T ^τ _— ¾— n ^Kfluid

^ref

[0021 ] In this equation, vol_ref is the reference volume, P_ref is the ambient

pressure, and Rfi_uid is the flow resistance

[0022] When pressure changes are measured with an accuracy corresponding to a change in altitude of about 1 cm at normal atmospheric pressures, it is quickly seen that the ambient pressure is fluctuating significantly. This is true both indoors and outdoors and may be due to a number of conditions. For example, doors and windows being opened and closed and pressure from fans and ventilating systems are obvious sources of this type of «pressure noise». Such pressure noise could exceed the pressure changes resulting from significant changes in altitude and often occurs on the same time scale as the altitude changes to be recorded.

[0023] According to an embodiment of invention, pressure noise from

measurement signals representative of changes in height can be completely or partially eliminated if two or more pressure sensors are used. Considering, for simplicity, two pressure sensors and looking at the difference between the pressures measured by these two pressure sensors, then the ambient pressure noise will be completely or partially cancelled and the measurement signal will indicate the variation in height between the two pressure sensors with the contribution from pressure noise being completely or partially eliminated. If one sensor is fixedly located in a room and the other sensor is attached to a body movable in a vertical direction, then it is possible to measure a change in height of the second sensor. Scenarios can also be envisioned where both sensors are movable. This is illustrated in Figs. 1 and 2. In both drawings the darker curve, 1 , represents the difference signal, that is, a measurement signal compensated for pressure noise, whereas the two more faint curves, 2 and 3, represent pressure signals from two sensors. In Fig. 1 , the sensor represented by curve 2 is kept stationary and the sensor represented by curve 3 is raised and lowered. It can be seen that significant background fluctuations are completely eliminated in curve 1 , i.e. the difference signal. In Fig. 2, both sensors are being moved. In this case, when starting from the same height, the difference signal will indicate the difference in height between the two pressure sensors.

In many cases, it is desired to detect rapid changes in altitude in the order of meters with an accuracy of 10 cm, or even with an accuracy of 1 cm. The measurement principle may find wide application. In an embodiment of the invention, a measurement principle with two or more sensors where background noise is completely or partially cancelled can be used as a fall detector or an apparatus for detecting if persons or animals have suffered a fall. Thus, according to an embodiment of the invention, there is provided an apparatus for detecting and notifying that a user has fallen and remained lying without being able to stand up. The user wears or carries a pressure sensor. The pressure sensor and associated necessary components may be wirelessly connected to a stationary part, e.g. the sensor installed in the room, which also includes a pressure sensor. The stationary part may perform any signal processing required to detect a fall based on the pressure changes measured, i.e. the stationary part can make comparisons between stored signal sequences and detected signal sequences, that is, it can discriminated between signal sequences known to indicate a fall and signal sequences that may be due to other events. It is conceivable to build a "library" of known signal sequences through simulations, for example, which known signal sequences are stored in a memory unit of the stationary part. In another embodiment, it is possible to include a remote database in which known signal sequences are stored. In this case, the stationary part may send signal sequences to the remote database, where comparisons are made between stored signal sequences and detected signal sequences (measurement signals) and the results are transferred back to the stationary part. Such a database could build a sizable library of real life events in a dynamic/adaptive manner and thus ensure an ever more reliable fall detection. Of course, it is possible for a distributed system in which the comparison and discrimination are accomplished in the stationary part to also include some form of library building, that is, an experience database. It is also conceivable that the signal sequences stored in a stationary part can be updated wirelessly, or by wire, through firmware upgrades or otherwise.

[0025] The stationary part may be connected to a notification system for providing a notification if a user has suffered a fall and remains lying without getting up again. Rapid pressure increases representing known changes in altitude that match falls from different positions will be detected as a fall unless the pressure subsequently decreases, indicating that the user gets up again.

[0026] In the following, specific implementations of fall detectors will be disclosed for several embodiments of the invention.

A first embodiment of a safety arrangement according to the invention

[0027] Reference is made to Figs. 1 and 3, with Fig. 1 showing signals measured by a first pressure sensor attached to a body, such as a human body, shown as curve 3 in the graph, and by a second pressure sensor with a fixed vertical position, shown as curve 2 in the graph. Curve 1 shows the difference between the pressure signals of the first and second sensors - that is, the difference signal. The difference signal will ensure a complete or partial cancellation of noise for the following reason: the pressure change measured by the first sensor includes a change in pressure due to vertical displacement AND changes in pressure in the form of background noise, whereas the second detector, which does not move vertically, only outputs a noise signal, that is, a signal indicating changes in pressure that are independent of vertical displacement, and when the signal from the second sensor is subtracted from the signal from the first sensor a resultant noise-compensated signal is obtained. Fig. 3 shows a first sensor located in the neck region of a person and a second sensor, denoted as SPC, mounted to a wall.

[0028] In a configuration in accordance with the first embodiment there are some sources of errors associated with the cancellation of noise sources. One such error source may be calibration/sensitivity of the sensors, and in addition there may be local pressure differences, background pressures within a small area, such as during aeration, for example, draught, fan usage and the like.

[0029] The first sensor is characterized in that it includes arrangements that allow it to be mounted to a person, and the sensor must also include means for communicating with the second sensor, denoted as SPC in Fig. 3. The communication means may be wireless Bluetooth transmitters, wireless WiFi-transmitters or other types of wireless transmitters, including proprietary transmitters. Advantageously, the protocol will include reception acknowledgments, that is, the first sensor may also be provided with radio receivers configured for receiving signals transmitted wirelessly by a transmitter. The first sensor may typically comprise an element for detecting pressure changes, a converter converting the signal from the detector element and generally also an analogue-to-digital converter as well as a transceiver. Also needed is a voltage source. The voltage source can be implemented using conventional batteries or a rechargeable source, such as rechargeable batteries, for example.

[0030] The second sensor, like the first sensor, comprises a detector unit in the form of a detector element. The detector element outputs a signal which is correlated with pressure changes. As the second sensor is located in a fixed vertical position, e.g. secured to a wall, the detector element of this second sensor should, in principle, not provide any output signal. In practice, however, as a result of local "pressure noise", it will provide output signals. Like the first sensor, the second sensor comprises a means for converting signals from the detector element as well as a means for wirelessly receiving and transmitting signals from/to the first sensor. It will be appreciated that the solution scales well, so that one may have several "first" sensors, that is, sensors configured for being attached to persons and communicating with a fixed second sensor. Typically, the protocols may include information about the senders' identities, which identities can be assigned to specific persons in a lookup table that may be stored in the second sensor or in a central database.

[0031] The second sensor may also comprise a local memory, preferably of a writeable type. Typically, a plurality of signal signatures will be stored in such a memory. It is conceivable that a person who suffers a fall will result in a specific set of output signals representative of pressure changes, and similarly it is conceivable that fans turning on and off, windows being opened and closed, doors being opened and closed, and other conditions may have output signals representative of such conditions. It is also conceivable that a person who falls or "almost falls" and then stands up again will have a specific "signal signature." When the second sensor, continuously or intermittently, reads signals from the or each first sensor, the second sensor will first compensate the signal in that the difference signal is obtained, and then this difference signal, which should

correspond to a "true" signal from the first sensor, is compared with known signal patterns, and in case of a match between the difference signal and a stored pattern indicating a fall, then the second sensor may trigger an alarm. That is, the second sensor does not only comprise means for communicating with one or more first sensors, but it also comprises means for communicating with an alarm unit. The alarm unit may be comprised in an apparatus that includes the second sensor with detector elements and associated signal processing electronics/logic. Alternatively, the alarm unit may be external, and be connected by wire or wirelessly to the second sensor.

[0032] In the case of an external alarm unit it is conceivable to have such a unit located in a guard room or at a security centre, from which a number of such second sensors can be monitored. If the alarm unit(s) is/are physically separated from the second sensor, then the alarm unit will include means for identifying the sender of received signals, either the sender in the form of the identity of the first sensor and the second sensor, or at least the identity of the first sensor. If the identity of the first sensor is known, then a lookup in a table may reveal the identity of the person who has suffered a fall, as a person's identity can be mapped to the identity of a first sensor.

[0033] In addition to the above functionality it is conceivable that a complete

monitoring system may include statistics, adaptive learning, through which both false and true alarms are learned and stored, alarm centres can be set for different levels, e.g. locally within an institution connected to a central alarm centre that covers several institutions, etc.

[0034] In the description above, the first sensor is attached to a person in order to illustrate the use. However, it is conceivable for the first sensor to be attached to animals or inanimate objects. For example, it could be of interest to follow products during transport or to follow products during production, etc.

[0035] Figure 3 shows a fall detector based on a movable and a fixedly installed sensor. The user carries a sensor s, and this sensor communicates with a fixed unit containing the sensor s, processing means p, and a

communication part c.

A second embodiment of a safety arrangement according to the invention

[0036] A fall detector can also be implemented in that a user carries or wears two first sensors. For this embodiment, particular reference is made to Figs. 2 and 4. In this case, the sensors must be located on different body parts for which a change in height resulting from a fall are significantly different. Exemplary locations could be the neck and calf, but other places may also be suitable. Moreover, the invention is not limited to using only two such first pressure change sensors. If more first sensors are used, we would expect increased sensitivity and fewer errors. The number of sensors used will be a trade-off between performance and complexity. [0037] When using two or more sensors attached to a user, ambiguity may arise in the difference signals since these signals indicate change in relative height between the two sensors. A person who falls down from a standing position and remains lying on the floor and a person who lies down to rest on a bed will produce the same change in the difference. In order to distinguish between different events producing the same change in the difference signal, it is necessary to analyze the match or correlation between the difference and each of the pressure change signals. Similarly to what was discussed for the first embodiment, it is conceivable to store signal signatures in order to identify fall or non-fall. As the noise

component is equal or substantially equal for all sensors attached to the same body, the difference in correlation between the difference signal and each of the measured signals will indicate how much of the change is attributable to each of the measured signals.

[0038] For the second embodiment of the invention it is understood that the same elements that are present in the first sensor according to the first embodiment are also present in the second embodiment. Further, one or more alarm centres according to the first embodiment are also needed. The second embodiment differs from the first embodiment in that the reference signal that indicates fall or non-fall are derived from sensors attached to the same body, while in the first embodiment, the second sensor was vertically fixed and thus could be considered a reference. Typically, according to the second embodiment, each first sensor will communicate with a fixed unit. This fixed unit, denoted by PC in Fig. 4, may typically correspond to the second sensor/apparatus of the first embodiment, exclusive of the detector element and the transducer. In this case, the fixed element receives pressure signals including background noise wirelessly from sensors attached to persons. Signals from a same person are processed and compared with "known signal patterns" and an alarm is triggered if a "fall" is detected in the comparison process.

[0039] The second embodiment has the advantage, especially when used with live individuals, of not being dependent on where the individual carrying the detectors is located as long as it is inside a coverage area of communication between the sensors and the fixed installation, PC.

Further, it is conceivable that many persons are provided with at least two sensors, each of these sensor pairs being assigned to a specific person in a table, so that when an alarm is triggered, it can be established who has triggered the alarm. However, the advantage of allowing persons provided with sensors of the second embodiment to move around relatively freely also means that it is not known where the alarm has occurred, so a "fall" may be more difficult to trace. In the first embodiment it will be necessary to have second sensors distributed over an area of coverage and each second sensor may have a given identity and a given position. When a triggered alarm is received by a central alarm unit, therefore, in the first embodiment, the identity of the second sensor and thereby its position and thus indirectly the position of the first sensor can be extracted directly. According to the second embodiment, determination of position can be accomplished in that at least one of the sensors attached to a person can be provided with a position indicating unit, such as a GPS device, for example.

[0040] Communication between sensors carried by a body may be provided

wirelessly or by wire.

[0041] Fig. 4 shows a fall detector based on several movable sensors. In this case, a user carries two sensors. In this drawing, these sensors are communicating with a fixed unit for processing p and communication c.

This device can be fixedly installed as shown in the drawing, but it may also be carried by the user. The system then becomes completely mobile and can be used both indoors and outdoors.

[0042] In a practical implementation of the invention communication must be provided for between the sensors and between the sensors and a central control module.

Applicability of the invention

[0043] Use of the invention for measuring changes in height by way of changes in pressure in an environment with fluctuating background pressures can be made in different measurement systems. The principle may be used for positioning in connection with storage and transport. It can also be used for recording height changes in connection with gaming, exercise, and other activity involving physical movement. The present invention will have significant advantages where accuracy in the order of centimetres is required. This would not be possible to achieve without the use of a reference in order to cancel fluctuations in the background pressure.

Claims

1. A method of determining a change in vertical position of a first body in a room where the background pressure fluctuates, comprising the steps of:

- mounting at least a first pressure change sensor to said first body, and

- mounting a second pressure change sensor to a second object, and

- measuring the difference between signals from said first and second pressure change sensors,

so that the difference between signals from said first pressure change sensor and second pressure change sensors is directly correlated with a change in the vertical position of said first body.

2. The method of claim 1 , wherein said first body and said second object are moved in a room where the background pressure fluctuates, and wherein said second pressure change sensor is made movable.

3. The method of claim 1 , wherein the method further comprises the steps of:

- registering that a person staying in a room suffers a fall,

- mounting said first sensor to a human body,

- mounting said second pressure change sensor to a fixed reference point,

- measuring a change in pressure of said first sensor attached to a person's body,

- measuring a change in pressure of the second pressure change sensor, and -providing the difference between the pressure change of said first and second pressure change sensors to thereby detect whether a fall has occurred.

4. A method of determining a change in vertical position of a first body or part of a first body around which the background pressure fluctuates, comprising the steps of:

- mounting least a first pressure change sensor in a first position on said first body, and

- mounting at least a second pressure change sensor in a second position at said first body, and

so that the difference between signals from said first and second pressure change sensors is directly correlated with a change in vertical position of said first body or part of said first body.

5. The method of claim 4, for eliminating ambiguity in fall detection, comprising the steps of:

-calculating a correlation between each of the signals from said pressure change sensors, and

- calculating the difference signal between the signals from said pressure change sensors, to thereby determine to what extent each of the sensor signals contributes to the difference signal.

6. A system for determining a change in height of a first body being moved in a room where a background pressure fluctuates, comprising:

- at least one first pressure change sensor mounted to said first body, and

- a second pressure change sensor located at a place different from said first pressure change sensor, and

- means for measuring the difference between signals from said first pressure change sensor and second pressure change sensors.

7. The system of claim 6, wherein said first pressure change sensor further

comprises a transducer and a transceiver, and wherein said second pressure change sensor comprises a transducer and a transceiver.

8. The system of claims 6 or 7, wherein the system further comprises an alarm centre.

9. The system of claim 8, wherein said alarm centre is provided with a transceiver for wireless communication.

10. The system of claims 6-9, wherein at least one of said pressure change

sensors comprises a position indicating means.