WO2013108229A2

WO2013108229A2 - Robust presence detection through audible components analysis

Info

Publication number: WO2013108229A2
Application number: PCT/IB2013/050484
Authority: WO
Inventors: Jurgen Mario Vangeel; Wijnand Johannes Rietman; Roger Peter Anna Delnoij; Willem Franke Pasveer; Jelena MATOVINA; David Ricardo CAICEDO FERNANDEZ; Michel Albertus Theodorus Klein Swormink
Original assignee: Koninklijke Philips N.V.
Priority date: 2012-01-20
Filing date: 2013-01-18
Publication date: 2013-07-25
Also published as: WO2013108229A3

Abstract

The invention relates to an occupancy sensor (1) for detecting occupancy comprising an ultrasound transmitting device (2), at least one microphone (M1-M4), a processor unit (3) adapted to receive data from said microphone and send and receive information to/from said ultrasound transmitting device (2), a memory (4) storing instructions to be performed by the processor unit (3), wherein said processor unit (3) is adapted to detect movements and presence of objects from data of reflected ultrasound measured by said at least one microphone (M1-M4), wherein the at least on microphone (M1-M4) is a broad band microphone used for receiving both ultrasound and audible sound, wherein said processor unit (3) is further adapted to use audible sound to enhance detection of living presence. The invention further relates to a method of determining occupancy using an occupancy sensor (1) for detecting occupancy comprising an ultrasound transmitting device (2), at least one broad band microphone (M1-M4), able to record both audible sound and ultrasound, a processor unit (3), a memory (4) storing instructions to be performed by the processor, said method comprising the steps of: sending an ultrasound pulse from said ultrasound transmitting device, receiving data from said microphone of the echo of said ultrasound pulse, making a first calculation using said processor unit of a probability of movements and/or presence of objects from data of the measured reflected ultrasound measured by said microphone, making a second calculation using said processor unit of a probability of movements and/or presence of objects from measured audible sound.

Description

Robust presence detection through audible components analysis

FIELD OF THE INVENTION

The present invention relates generally to a sensor for measuring occupancy using ultrasound and audible sound. More particularly, the present invention relates to an occupancy sensor as defined in the introductory parts of claim 1 and a method for detecting occupancy as described in claim 7.

BACKGROUND OF THE INVENTION

An occupancy sensor is an energy conservation device designed to detect the presence of human occupants in a given area. Many commercial, industrial and government facilities require a significant number of lighting fixtures for adequate illumination, and therefore use a significant amount of power to operate the lighting fixtures. A number of facilities use lighting control systems to control when the lighting fixtures are energized and thereby reduce the amount of power that is consumed to light these facilities.

An occupancy sensor can be provided with an ambient light sensor and control input therefore. The ambient light sensor and control input can be used to select a minimum level of light above which a lighting fixture is prevented from being switched and powered on following detected motion. Occupancy sensors typically sense the presence of one or more persons within a designated area and generate occupancy signals indicative of that presence. These signals activate or deactivate one or more electrical appliances, such as, for example, a lighting unit or a heating, ventilating, and air conditioning system. When occupancy is sensed, the various electrically-powered loads in that area controlled by the sensor are energized. When that same area has been unoccupied for a predetermined period of time, the sensor de-energizes the electrical loads that it controls. The two most prevalent types of occupancy sensors are passive infrared and active ultrasonic devices.

A passive infrared (PIR) sensor will turn on the load whenever it detects a moving or appearing heat source with a difference (contrast) to the background. Passive infrared occupancy detection technology allows continuous detection of moving objects that emit infrared energy. This method of occupancy detection is quite sensitive even though it is based on passive sensing of moving sources of infrared energy. This method of occupancy detection also has several limitations: it is insensitive to sources generally not in the line of sight of the receiver; it is subject to being blinded by intense, stationary sources of infrared energy; it is subject to false tripping due to rapid fluctuations in the intensity of stationary infrared sources; and it is subject to a detection coverage tradeoff involving the number of lens facets versus detection range. Warm environments are thus not particularly good for the PIR- technique.

An ultrasonic occupancy sensor will typically transmit ultrasonic sound waves via one or more transmitters which then reflect off of objects in the room and are detected by one or more receivers.

The ultrasonic sensor emits vibrations at frequencies of 25 kHz or higher and listens to the return echoes. The analysis of the echo will be typically done by one or multiple microphones.

An ultrasonic sensor can base its detection on Doppler shift. If it detects a significant Doppler shift, indicating the presence of a moving body, then it turns the load on. Another type of ultrasonic measurement is time-of-flight measurement. If a change in time- of-flight is detected then a moving body is detected, and the load will be switched on.

The performance of any occupancy sensor will be judged by a couple of criteria, of which sensitivity to movement and absence of so-called false-triggers are probably the most important ones. A delicate balance between these two criteria needs to be found. When systems are more sensitive they are generally also more likely to be triggered by false triggers.

An example of a false trigger is airflow generated by a blowing fan (or ventilation) could cause a plant in the room to move slightly. However this should not lead to presence detected as the object in question is not a human, so this could be seen as a false trigger. Other drawbacks of ultrasonic occupancy sensors are that they are basically insensitive to motion generally not in the line of sight of the receiver; and it may be subject to false tripping due to other sources of ultrasonic energy.

A further technique that has been used for occupancy sensing is passive audio acoustic occupancy detection. This technology allows continuous detection of objects that emit audio acoustic energy. This method of occupancy detection is quite sensitive but is subject to false tripping due to non-occupant sources of audio acoustic energy such as facsimile machine, telephone and security system tones, automobile and emergency vehicle horns, etc. All of the occupancy techniques have their drawbacks and weaknesses leading to false triggers. There is thus a need to develop the technique to be more reliable. Since the sensors are commonly used and since there is a need for occupancy sensors in many places, there is a need to keep the solution cheap.

SUMMARY OF THE INVENTION

It is an object of the present invention to improve the current state of the art, to solve the above problems, and to provide an improved occupancy sensor without making it too expensive. These and other objects are achieved by an occupancy sensor for detecting occupancy comprising an ultrasound transmitting device, at least one microphone, a processor unit adapted to receive data from said microphone and send and receive information to/from said ultrasound transmitting device, a memory storing instructions to be performed by the processor, wherein said processor unit is adapted to detect movements and presence of objects from data of reflected ultrasound measured by said microphone, wherein the microphone is a broad band microphone used for receiving both ultrasound and audible sound, wherein said processor unit is further adapted to use audible sound to enhance detection of living presence.

Since an ultrasound occupancy sensor needs to have at least one microphone for the detection of echoes (i.e. reflected ultrasound) the only extra requirement for also measuring audible sound is to use a broad band microphone for sound/ultrasound detection. The broad band microphone should thus be sensitive in all or at least part of the audible sound range from 0 - 20 000 Hz, and in all or part of the ultrasound range of 20 kHz - 200 MHz. It is, however, preferred to use frequencies up to 100 kHz, thus making it sufficient to use a microphone with an upper sensitivity limit of 100 kHz. If audible sound is recorded above a certain threshold a probability of presence of an object is higher, which may be compared with the occupancy information received by the ultrasound occupancy measurement. If both the ultrasound measurement and the measurement of audible sound indicate presence, the probability of occupancy is increased, otherwise it is decreased. In that way the risk of false indications of occupancy can be reduced.

The determination of what should be considered as an audible sound signal is determined by a predetermined sound threshold. The threshold could be relative to the constant background noise or a fixed predetermined threshold. It should be noted that the microphone in the sensor above could be separate, i.e. detached, from the ultrasound emitter, merely being in wired or wireless communication with each other.

The occupancy sensor according to the invention may be adapted to find Doppler shifts in echoes from the transmitted ultrasound to detect movements of objects. A Doppler shift in the echo indicates that the ultra sound was reflected by a moving object. By measuring time of flight of the Doppler shifted ultrasound echo the distance to the moving object may be calculated. Directed ultrasound pulses may also be used in combination with measurement of time of flight of ultra sound pulses to detect distance to an object in accordance with pulsed Doppler or FMCW techniques

The occupancy sensor may also have two or more microphones and the processor unit may be adapted to calculate direction from audible and/or ultrasound received by said two or more microphones. By using multiple microphones the direction to a moving object giving a Doppler shift in the ultrasound may be calculated. An audible sound detected in the same direction will strengthen the probability of occupancy, reducing the risk of a false detection. Since the microphones of prior art sensors are often placed close together to optimize estimation of direction of ultrasound at, e.g., 40 kHz, the microphones typically being placed half a wavelength apart, e.g., in a square pattern. Since audible sound has much longer wavelengths calculations of direction will be less precise, but still give an estimated position of the origin of the sound. Audible sound at high frequencies, e.g., above 10 kHz are preferably used to find direction, since the sound wavelength then will be shorter.

The occupancy sensor according to the invention may also according to a further embodiment consist of multiple sensors placed at different positions in a room while being linked in a wired or wireless network, sharing data of transmission of ultrasound and reception of ultrasound and audible sound. By, e.g., comparing directional data of detected objects, the position of the object may be estimated by triangulation. Even if only two sensors have detected an object a known layout of the room where the sensors are placed may be used to still estimate the position to some extent. The calculations of direction of the sound and also determination of a position could thus be improved by comparing measurements among the sensors in a room or area.

The wireless network connection may be achieved via a traditional wireless network protocol, e.g. WLAN, Bluetooth, Zigbee, or the like, but may also be achieved by sending ultrasound pulses according to a predetermined protocol. The information will in that case need to be communicated when measurements are not performed. The occupancy sensor according to the invention may also be adapted to switch between ultrasound measurement and audible measurements to reduce computational requirements of the processor. If calculations for the different measurements are not done simultaneously the requirements of the processor will be lower. If a network of

communicating occupancy sensors is used, a transmission scheme may be set up to avoid sending ultrasound at the same time to reduce interference between the sensors.

The invention further relates to a method of determining occupancy using an occupancy sensor for detecting occupancy comprising an ultrasound transmitting device, at least one broad band microphone, able to record both audible sound and ultrasound, a processor unit, a memory storing instructions to be performed by the processor, said method comprising the steps of: sending an ultrasound pulse from said ultrasound transmitting device, receiving data from said microphone of the echo of said ultrasound pulse, making a first calculation using said processor unit of a probability of movements and/or presence of objects from data of the measured reflected ultrasound measured by said microphone, making a second calculation using said processor unit of a probability of movements and/or presence of objects from measured audible sound.

The method may further, in the step of making the first calculation of said probability of movements, comprise finding Doppler shifts in echoes from the transmitted ultrasound to detect movements of objects.

The method may further in the step of making the first calculation of said probability of movements and/or presence comprise measuring time of flight of echoes of ultra sound pulses to detect distance of objects.

The occupancy sensor may, as earlier described, have two or more microphones and the method may further comprise the step of calculating direction from audible sound received by said two or more microphones. The direction may be compared with the last known direction of presence, increasing said probability of presence if they are substantially the same.

When calculating direction from audible sound the microphones furthest away from each other may be used to estimate direction, e.g. the diagonal pair if four microphones are placed in a square pattern.

Multiple sensors may be linked in a wired or wireless network, sharing data of transmission of ultrasound and/or reception of ultrasound and/or audible sound. The method may then further comprise the steps of sharing information that a ultrasound pulse transmission has occurred, calculating Doppler shifts from microphone measured echo in each occupancy sensor in said network, sharing information about Doppler shifts, calculating movement direction from differences in Doppler shifts calculated at different positions.

The method of determining occupancy when said multiple sensors are linked in a wired or wireless network, sharing data of transmission of ultrasound and/or reception of ultrasound and/or audible sound, may further comprise the step of comparing direction of last presence to calculate a position of the presence.

A possible detected object may, e.g., be a speaker in a presentation situation. A speaker in a room may then be detected by Doppler shift detection when the speaker is moving and by sound when the speaker is talking. The method may in one embodiment further comprise the step of adjusting technical equipment according to a calculated position of the speaker. The technical equipment could, e.g., be lights, shades.

The skilled person in the art realises that the advantages discussed in relation to the inventive occupancy sensor are the same for the corresponding part of the method. BRIEF DESCRIPTION OF THE DRAWINGS

The above objects, as well as additional objects, features and advantages of the present invention, will be more fully appreciated by reference to the following illustrative and non-limiting detailed description of preferred embodiments of the present invention, when taken in conjunction with the accompanying drawings, wherein:

Fig. 1 is a schematic drawing of the parts of the occupancy sensor.

Fig. 2 shows a flow chart of the inventive method of increasing the probability of detection of a movement using directional measurements.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Fig. 1 shows the parts of the occupancy sensor for one embodiment of the present invention. The occupancy sensor according to Fig. 1 has one circuit/mounting board 1 having a ultrasound emitter 2, a processing unit 3, memory 4 for storing instructions for performing measurement and storing temporary measurement results of direction and position of present object. The sensor further has four microphones M1-M4 to measure ultrasound and audible sound and the direction of the measured sound signals.

When measuring Doppler shifts the processor will ignore measured sound of the emitted frequency and only look at the frequencies above and below the emitted frequency, i.e. Δί. If a higher frequency is measured, the detected moving object is moving towards the sensor and if a lower frequency is measured, the object is moving away from the sensor. The difference in time when the Doppler shifted signal reaches the different microphones will give the direction of the signal.

Fig. 2 shows a flow chart of the inventive method of increasing the probability of detection of a movement using directional measurements of both ultrasound and audible sound. An ultrasound pulse is transmitted and is reflected against a moving object. The direction is calculated by comparing measurements from the microphones. Audible sound is also measured by all the microphones. If the direction of a sound detected by the audible sound matches the direction of the detected movement by ultrasound measurement, the probability of occupancy (movement) is increased. If they do not match, the probability is decreased.

To reduce the amount of false triggers, the invention provides a method to extract more information out of the environment to assist in the detection process. As mentioned not only ultrasound components of received echoes but also audible components will be analysed by the occupancy sensor. The microphones used typically have a wide bandwidth, so they can detect both ultrasound components and audible components.

Furthermore, when used in a system which has multiple microphones, direction-of-arrival algorithms can be used on the audible components to determine whether the audible sounds are coming from the same location as detected by the ultrasound presence detection.

This way the ultrasound presence detection results can be matched with for example location of voice (phone) conversations, keyboard typing noises, etc.

Presence detection algorithms are performed using an ultrasound pulse and measuring back ultrasound echoes on the available microphones. A score can be devised based on previous results, amount of movement detected from previous measurements which gives an indication on how reliable the information is.

Sometimes this may not be enough to be able to confidently decide whether human presence is in the sensing area. In that case audible noise may be measured taking additional steps to gain confidence:

When the occupancy sensor has only a single microphone and audible noise is observed with a significant volume above reference, and a person is likely to be present based on ultrasound measurements and maybe talking, typing, etc., then confidence level can be increased. If not then algorithm cannot increase confidence.

When the occupancy sensor has multiple microphones and audible noise is observed with a significant volume above a certain reference, and audible noise is coming from the same direction as where presence has been detected (although weakly), the algorithm has extra confirmation that a person is present and confidence can be increased.

To sum up the advantages of the invention, an ultrasound part is used to detect size of movement, position of movement and provide some presence information. An audible part is used to recheck the presence information from the ultrasound. Additionally, the audible part may provide information on level of noise, frequency (human voice), interval (low frequent modulation), and direction.

Direction-of-arrival algorithms are used in order to determine from what direction the audible sounds are observed and check whether that direction matches the last known location of a human person that was previously measured with ultrasound. This will help robustness such as a person sitting still, but making noises will still be detected (e.g. typing), whereas some external, random directional noise coming in will be disregarded.

This all leads to more reliable information and provides a system that provides much more context information on activities in the room. For example, in a meeting room, the speaker could be detected as the person who is moving (detected by ultrasound) and speaking (detected by acoustic sound). This information could be used to provide context- based lighting settings.

Furthermore, the use of time slots is proposed. With this, the ultrasound measurements and acoustical measurements can be done in different time slots decreasing the required computational power and creating a cost effective solution.

It is understood that other variations in the present invention are contemplated and in some instances, some features of the invention can be employed without a corresponding use of other features. Accordingly, it is appropriate that the appended claims be construed broadly in a manner consistent with the scope of the invention.

Claims

CLAIMS:

1. Occupancy sensor (1) for detecting occupancy comprising

an ultrasound transmitting device (2),

at least one microphone (M1-M4),

a processor unit (3) adapted to receive data from said microphone and send and receive information to/from said ultrasound transmitting device (2),

a memory (4) storing instructions to be performed by the processor unit (3), wherein said processor unit (3) is adapted to detect movements and presence of objects from data of reflected ultrasound measured by said at least one microphone (Ml-

M4),

wherein the at least one microphone (M1-M4) is a broad band microphone used for receiving both ultrasound and audible sound,

wherein said processor unit (3) is further adapted to use audible sound to enhance detection of living presence.

2. Occupancy sensor according to claim 1, wherein said processor unit (3) is adapted to find Doppler shifts in echoes from the transmitted ultrasound to detect movements of objects.

3. Occupancy sensor according to any one of the preceding claims, wherein said processor unit (3) is adapted to measure time of flight of echoes of ultra sound pulses to detect distance from the sensor to an object.

4. Occupancy sensor according to any one of the preceding claims, wherein said occupancy sensor (1) has two or more microphones (M1-M4) and said processor unit (3) is adapted to calculate direction from audible and/or ultrasound received by said two or more microphones (M1-M4).

5. Occupancy sensor according to any one of the preceding claims, wherein multiple sensors are linked in a wired or wireless network, sharing data of transmission of ultrasound and reception of ultrasound and audible sound.

6. Occupancy sensor according to any one of the preceding claims, wherein said sensor (1) is adapted to switch between ultrasound measurement and audible measurements.

7. Method of determining occupancy using an occupancy sensor (1) for detecting occupancy comprising

an ultrasound transmitting device (2),

at least one broad band microphone (M1-M4), able to record both audible sound and ultrasound,

a processor unit (3),

a memory (4) storing instructions to be performed by the processor, said method comprising the steps of:

sending an ultrasound pulse from said ultrasound transmitting device, receiving data from said microphone of the echo of said ultrasound pulse, making a first calculation using said processor unit of a probability of movements and/or presence of objects from data of the measured reflected ultrasound measured by said microphone,

making a second calculation using said processor unit of a probability of movements and/or presence of objects from measured audible sound.

8. Method of determining occupancy according to claim 7, wherein the step of making the first calculation calculating of said probability of movements comprises finding

Doppler shifts in echoes from the transmitted ultrasound to detect movements of objects.

9. Method of determining occupancy according to any one of claims 7-8, wherein the step of making the first calculation of said probability of movements and/or presence comprises measuring time of flight of echoes of ultra sound pulses to detect distance of objects.

10. Method of determining occupancy according to any one of claims 7-9, wherein said occupancy sensor (1) has two or more microphones (M1-M4) and said method further comprises the step of calculating direction from audible sound received by said two or more microphones.

11. Method of determining occupancy according to claim 10, wherein said calculated direction is compared with the last known direction of presence, increasing said probability of presence if they are substantially the same.

12. Method of determining occupancy according to any one of claims 7-11, wherein multiple sensors are linked in a wired or wireless network, sharing data of transmission of ultrasound and/or reception of ultrasound and/or audible sound, said method further comprising the steps of

sharing information of that a ultrasound pulse transmission has occurred, calculating Doppler shifts from microphone measured echo in each occupancy sensor in said network,

- sharing information about Doppler shifts,

calculating movement direction from differences in Doppler shifts calculated at different positions.

13. Method of determining occupancy according to any one of claims 7-12, wherein said sensor is adapted to switch between ultrasound measurement and audible measurements.

14. Method of determining occupancy according to any one of claims 7-13, wherein said multiple sensors are linked in a wired or wireless network, sharing data of transmission of ultrasound and/or reception of ultrasound and/or audible sound, said method further comprising the step of

comparing direction of last presence to calculate a position of the presence.

15. Method of determining occupancy according to any one of claims 7-12, wherein a speaker in a room is detected by Doppler shift detection when the speaker is moving and by sound when the speaker is talking, wherein the method further comprises the step of adjusting technical equipment according to a calculated position of the speaker.