Classifications

• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
  • G01J5/0022—Radiation pyrometry, e.g. infrared or optical thermometry for sensing the radiation of moving bodies
  • G01J5/0025—Living bodies
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
  • G01J5/02—Constructional details
  • G01J5/0265—Handheld, portable
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
  • G01J5/02—Constructional details
  • G01J5/06—Arrangements for eliminating effects of disturbing radiation; Arrangements for compensating changes in sensitivity
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
  • G01J5/10—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors
• • G—PHYSICS
  • G01—MEASURING; TESTING
  • G01J—MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY
  • G01J5/00—Radiation pyrometry, e.g. infrared or optical thermometry
  • G01J5/10—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors
  • G01J5/12—Radiation pyrometry, e.g. infrared or optical thermometry using electric radiation detectors using thermoelectric elements, e.g. thermocouples
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F1/00—Details not covered by groups G06F3/00 - G06F13/00 and G06F21/00
  • G06F1/26—Power supply means, e.g. regulation thereof
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F1/00—Details not covered by groups G06F3/00 - G06F13/00 and G06F21/00
  • G06F1/26—Power supply means, e.g. regulation thereof
  • G06F1/32—Means for saving power
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F1/00—Details not covered by groups G06F3/00 - G06F13/00 and G06F21/00
  • G06F1/26—Power supply means, e.g. regulation thereof
  • G06F1/32—Means for saving power
  • G06F1/3203—Power management, i.e. event-based initiation of a power-saving mode
  • G06F1/3234—Power saving characterised by the action undertaken
  • G06F1/3287—Power saving characterised by the action undertaken by switching off individual functional units in the computer system
• • G—PHYSICS
  • G08—SIGNALLING
  • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
  • G08B13/00—Burglar, theft or intruder alarms
  • G08B13/18—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength
  • G08B13/189—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using passive radiation detection systems
  • G08B13/19—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using passive radiation detection systems using infrared-radiation detection systems
• • G—PHYSICS
  • G08—SIGNALLING
  • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
  • G08B29/00—Checking or monitoring of signalling or alarm systems; Prevention or correction of operating errors, e.g. preventing unauthorised operation
  • G08B29/18—Prevention or correction of operating errors
  • G08B29/185—Signal analysis techniques for reducing or preventing false alarms or for enhancing the reliability of the system
• • H—ELECTRICITY
  • H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
  • H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
  • H02J50/00—Circuit arrangements or systems for wireless supply or distribution of electric power
  • H02J50/60—Circuit arrangements or systems for wireless supply or distribution of electric power responsive to the presence of foreign objects, e.g. detection of living beings
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B47/00—Circuit arrangements for operating light sources in general, i.e. where the type of light source is not relevant
  • H05B47/10—Controlling the light source
  • H05B47/105—Controlling the light source in response to determined parameters
  • H05B47/115—Controlling the light source in response to determined parameters by determining the presence or movement of objects or living beings
  • H05B47/13—Controlling the light source in response to determined parameters by determining the presence or movement of objects or living beings by using passive infrared detectors
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F1/00—Details not covered by groups G06F3/00 - G06F13/00 and G06F21/00
  • G06F1/26—Power supply means, e.g. regulation thereof
  • G06F1/32—Means for saving power
  • G06F1/3203—Power management, i.e. event-based initiation of a power-saving mode
  • G06F1/3206—Monitoring of events, devices or parameters that trigger a change in power modality
  • G06F1/3231—Monitoring the presence, absence or movement of users
• • G—PHYSICS
  • G08—SIGNALLING
  • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
  • G08B13/00—Burglar, theft or intruder alarms
  • G08B13/18—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength
• • H—ELECTRICITY
  • H05—ELECTRIC TECHNIQUES NOT OTHERWISE PROVIDED FOR
  • H05B—ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
  • H05B47/00—Circuit arrangements for operating light sources in general, i.e. where the type of light source is not relevant
  • H05B47/10—Controlling the light source
  • H05B47/105—Controlling the light source in response to determined parameters
  • H05B47/115—Controlling the light source in response to determined parameters by determining the presence or movement of objects or living beings
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
  • Y02B20/00—Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
  • Y02B20/40—Control techniques providing energy savings, e.g. smart controller or presence detection
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02D—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN INFORMATION AND COMMUNICATION TECHNOLOGIES [ICT], I.E. INFORMATION AND COMMUNICATION TECHNOLOGIES AIMING AT THE REDUCTION OF THEIR OWN ENERGY USE
  • Y02D10/00—Energy efficient computing, e.g. low power processors, power management or thermal management

Definitions

• This invention relates to systems and methods for detecting the presence of a person using infrared radiation, and in particular to wake up a device.
• Presence detection is the ability of devices or systems to detect if a person is present. It is known to use IR sensors for contactless presence detection by detecting body heat. Pres ence detection may be used, for example, to adjust the operation of a device, for example switching a device on or off. Examples of devices that use contactless presence detection include heating /air-conditioning systems that go to power save mode and illumination de vices such as lamps, that are automatically switched on when a person is present.
• thermopile is an IR sensor that can deliver output as absolute temperature and not only a temperature change.
• thermopiles are difficult to calibrate with respect to the background IR ra diation in the room, in particular in "noisy" environments where the room temperature fluctuates.
• a method for determining the presence of a person where the method involves a system that can be in a present or a non-present state, the method comprising receiving an IR sensor signal and using the IR sensor signal to determine a smoothed IR sig nal, in a first mode, determine a threshold as an offset from the smoothed IR signal, where presence determination is carried out in the first mode by comparing the IR sensor signal to the threshold, and where presence determination is carried out in a second mode by comparing the IR sensor signal to the smoothed IR signal, where switching from the first mode to the second mode occurs when the IR sensor signal passes the threshold value and switching from the second mode to the first mode occurs when the variability of the IR sensor signal is below a variability threshold.
• the two different modes of detection avoid triggering change of state due to fluctuating background temperature while providing high sensitivity when someone is approaching or moving away from the IR sensor.
• the smoothed IR signal is adjusted to the IR sensor signal over time with a first rate in the first mode and adjusted to the IR sensor signal over time with a sec- ond rate in a second mode, where the first rate is lower than the second rate.
• Presence determination may be carried out in the first mode by comparing the IR sensor signal to the threshold, such that a transition from the non-present state to the present state occurs when the IR sensor signal passes the threshold and where presence detection in the second mode occurs by comparing the IR sensor signal to the smoothed IR signal such that a transition from the present state to the non-present state occurs when the IR sensor signal passes the smoothed signal.
• an upper threshold may be determined as the smoothed IR signal plus an offset value and a lower threshold is determined as the smoothed IR signal minus an off set value and where, in the first mode, the upper threshold is used to determine transition from the non-present state to the present state, and the lower threshold is used to deter mine transition from the present state to the non-present state.
• transition from the non-present state to the present state and transi tion from the non-present state to the present state may occur when the IR sensor signal passes the smoothed IR signal.
• the system may be predetermined to be is either in the present state or the non-present state. This results in a self-learning system.
• the IR sensor is preferably a thermopile.
• thermopile has the advantage that it responds quickly to temperature changes and re ports absolute temperature values.
• the state (present or non-present) is preferably updated repeatedly, preferably with a predetermined time interval which preferably is at least every second.
• presence determination is carried out in the first mode by comparing the IR sensor signal to the threshold, and not comparing the IR sensor signal to the smoothed signal and where presence determination is carried out in a second mode by comparing the IR sensor signal to the smoothed IR signal, and not comparing the IR sensor signal to the threshold of the first mode.
• a system being configured to carry out the method according to the first aspect of the invention.
• the system may be config ured to determine if a person is present in a field of view of an IR sensor, the system com prising a signal processing module, a threshold determination logic and presence determi nation logic, the signal processing module being configured to receive voltage from the IR sensor and to determine an IR signal and a smoothed IR signal, and further configured to determine the variability of the IR sensor signal, where the threshold determination logic is configured to determine a threshold as an offset from the smoothed IR signal, and where the presence determination logic is configured to determine presence in a first mode by comparing the IR sensor signal to the threshold, and configured to determine the presence in a second mode by comparing the IR sensor signal to the smoothed IR signal, and where switching from the first mode to the second mode occurs when the IR sensor signal passes the threshold value and switching from the second mode to the first mode occurs when the variability of the IR sensor signal is below a variability threshold.
• a powered device comprising a system according to the second aspect of the invention.
• the device may for example be an access control device.
• the device may be configured to, when receiving information from the sys tem that no person is present to put the device in power save mode, or, to, when receiv ing information from the system that a person is present, to wake up the device from power save mode.
• Fig. 1 is a schematic drawing of a system.
• Fig. 2 is schematic drawing of a memory.
• Fig. 3 is a schematic drawing of a system and a person.
• Fig. 4a is a schematic drawing of a system comprising a display, and a person.
• Fig. 4b is a schematic drawing of a laptop computer.
• Fig. 4c is a schematic drawing where the system is used to detect approach.
• Fig. 5 is a flow chart that shows a method.
• Fig. 6a are two graphs.
• Fig. 6b is a schematic graph.
• Fig. 7 is a diagram.
• Fig. 1 shows one embodiment of a presence determination system 1 comprising an IR sen sor 2 which preferably is an IR sensor that can measure an absolute temperature value, preferably a thermopile 2.
• IR sen sor 2 which preferably is an IR sensor that can measure an absolute temperature value, preferably a thermopile 2.
• a useful thermopile is described in W020040968256 but other types of thermopiles can be used also. However, any suitable type of IR sensor can be used, for example a bolometer.
• the thermopile 2 is able to detect IR radiation and to provide voltage, to subsystem 3.
• Subsystem 3 may be implemented in hardware or software or com binations thereof and Fig. 1 shows an embodiment implemented in hardware and software.
• Subsystem 3 comprises input interface 4 that receives voltage from the IR sensor 2.
• Subsys tem 3 further comprises processor 5, memory 6 and output interface 7.
• the system 1 may also include one or more of a signal filter, an amplifier, an A/D converter and similar devices known in the art of signal processing, and in particular for processing the voltage from the IR sensor 2.
• System 1 is powered by a power source.
• Subsystem 3 may be mounted into the same device as IR sensor 2 or may be separate from IR sensor 2. In one embodiment, all steps in the methods described herein are carried out by the same proces sor 5.
• memory 6 is able to store data such as IR sensor data 8 and thresh old data 9, present state data 12, mode data 20 and smoothed IR signal data 21.
• Memory 6 has threshold determination logic 10 and presence determination logic 13.
• Memory 6 also has signal processing module 11. In general, and as described elsewhere herein, such com ponents may be implemented using any suitable combination of hardware and software.
• the system 1 is typically able to output information about at least two states: "person pre sent” and “person not present”, or alternatively information about transit from the "pre sent” to the "non-present state", and back again.
• the current state (present/non-present) of system 1 is stored as present state data 12 in memory 6.
• the system 1 is furthermore able two switch between a first mode and a second mode, and back again as described in more detail below. This is also carried out by presence determi nation logic 13 as is described in more detail below.
• presence determination logic 13 is able to compare the IR sensor signal 50 to thresholds 52, 53, and compare the IR sensor signal 50 to the smoothed IR signal 51.
• Presence determination logic 13 is also use the var iability 54 of the IR sensor signal 50 and compare the variability 54 to a variability threshold 55.
• Presence determination logic 13 is able to output the state to output interface 7 and to output the mode to signal processing module 11 (signal processing module 11 uses the state to know how to determine smoothed IR signal 51).
• System 1 is able to store information about which mode the system is as mode data 20.
• the IR sensor 2 has a field of view 15 where IR sensor 2 detects IR radiation and where the system 1 determines if a person 16 is present.
• Person 16 typically radiates IR radiation that is stronger than the background IR radiation (which is caused by the ambient room temperature, for example).
• the IR radiation detected in the field of view 15 can be used to determine if a person 16 is present in the field of view 15 or not.
• the system comprises one thermopile 2.
• system 1 may have a plurality of thermopiles 2 each with a different field of view 15.
• a plurality of IR sensors 2 may use the same subsystem 3, and subsystem 3 then may provide data storage, signal processing and threshold determination for each of the IR sensors 2.
• System 1 is able to provide information to a second device 17 about if a person is present or not, with the use of output interface 7.
• Second device 17 is preferably a powered device, hence it is powered by electric power.
• Output interface 7 may be any suitable interface with which system 1 is able to provide data to second device 17, and output interface 7 may be implemented in hardware and/or software.
• the second device 17 may be a computer sys tem. Information provided from system 1 to second device 17 can be information about state (present/non-present) or information about state transition from one state to the other.
• the second device 17 may be able to use the output from system 1 in various manners.
• the present and the non-present state may be used to switch on or switch off a second device 17 as the case may be.
• Second device 17 may be any type of device that may benefit from contactless presence detection, such as for example a personal computer such as a laptop computer, a heating system, air condition system or ventilation system, such as to make sure that such systems are shut down or put in power save mode when a person is not present during a set time period, or similar.
• the present or non-present state may trigger a timer.
• the second device 17 may also be an appliance providing light such as an indoor or outdoor lamp.
• the second device 17 may also be switched on by the present state, such that a computer, an information or advertising display, a lamp, an access control de vice, or a ventilation system is switched on when a person is present. Second device 17 may also be an alarm device, such as an intruder alarm. In general, all of these devices may ben efit from being switched on become activated, or switched off, being put in power save mode or being woken up from power save mode by the methods and system herein.
• the output from system 1 may be used to put a second device 17 in power save mode and/or shut down a display 18.
• the second device 17 may be put in power save mode, possibly after a non-present state has been detected for a certain minimum time.
• the present state provided by system 1 may be used to wake up the second device 17.
• parts of subsystem 3, such as for example the processor 5 and/or memory 6, may be a part of the second device 17, in particular when second device 17 comprises or consists of a computer. Then the software described herein may installed on the hard drive of the computer and used by the CPU of the computer. In general, parts of system 1 may be integrated with parts of second device 17, such that processor 5 or memory 6 can be a part of second device 17. The whole system 1 may also be fully inte- grated in second device 17, as a subpart thereof implemented in a suitable combination of hardware and software.
• system 1 may be mounted into a second device 17 or may be separate from second device 17.
• the IR sensor 2 is mounted next to a display 18 for a computer, which may be the display 18 of a laptop computer, a tablet computer, a smartphone (such as an iPhone or an Android phone) or a free-standing display 18 for a stationary computer.
• the field of view 15 is preferably directed towards the intended posi tion of the person 16 in front of the display 18.
• Fig. 4b shows a second device 17 which is a laptop computer where system 1 is integrated into the laptop.
• the method and systems herein may be used to wake up a laptop from power save mode, or put a laptop into power save mode.
• the system 1 is used to detect a person 16 that is approaching the IR sensor 2 and used to activate or deactivate a second device 17.
• the system 1 may be a part of, or provide output to, an access control device.
• the system 1 may be used to open or unlock a door upon detecting a person 16, or to wake up an access control device from sleep.
• Examples of access control devices that may be woken up include an electronic lock, a tag reader, a fingerprint reader or a face recognition device.
• the system 1 may activate the access control device which enables the person 16 to unlock a door, for exam ple.
• the system 1 may be used to activate an electronic display 18, when a person 16 ap- proaches.
• the display 18 may be a display 18 that is fixedly mounted indoors or outdoors.
• the display 18 may be sign that shows directions, an advertisement display or a different type of information display.
• the system 1 may be used to activate a display 18 on the door of a refrigerator. Hence the system 1 may be used to switch on the display so that it displays information.
• IR sensor voltage is provided from the IR sensor 2 to the subsystem 3.
• Subsystem 3 analyses the sensor voltage and provides present/non-present output to a second device 17.
• System 1 may sample heat data in the field of view 15 and using any suitable sampling interval. Preferably the sampling frequency is from once every 5 seconds to 100 times/second.
• Sam- pling of IR sensor voltage to obtain IR sensor signal 50 is carried out by signal processing module 11 and is stored as IR sensor data 8.
• the thermopile 2 delivers its output as an output voltage.
• all IR sensor data herein are - or can be converted to - absolute temperature values, hence not relative temperature values. Hence, preferably a thermopile is used as the IR sensor 2.
• Signal processing module 11 is able to produce (provide) a smoothed IR signal 51.
• the smoothed IR signal 51 may be a moving average of the IR sensor signal 50.
• Smoothed IR signal 51 is IR sensor data 8 that has been treated with a (preferably digital) smoothing method to remove extreme values in order to show trends, and may be a moving average of the IR sensor signal 50. Examples of useful smoothing methods include moving average or median values. In some embodiments, outliers in the IR sensor data 8 are removed.
• Sig nal processing module is also able to determine the variability of the IR sensor signal 50 and to provide it to presence determination logic 13. A method for determining that a person is present or absent will now be described with reference to Figs. 5-7.
• system 1 is arranged to perform such a method. Below it is mostly described how the system 1 is initially in the non-present state and in the first mode, but switching from present state to the non-present state is done according to the same principles. Also switching from the first mode to the second mode and from the second mode to the first mode is done using the same principles as set forth below.
• IR sensor 2 provides voltage to the subsystem 3 to produce IR sensor signal 50, and an example of how the IR sensor signal varies over time is shown in Fig. 6a.
• the signal processing module 11 uses the IR sensor signal 50 to determine a smoothed IR signal 51.
• the smoothed IR signal 51 represents historic IR sensor data 8 that has been treated with a (preferably digital) smoothing method to remove extreme values in order to show trends.
• a smoothing method to remove extreme values in order to show trends. Examples of useful smoothing methods include moving average or median values. In some embodiments, outliers in the data are removed.
• Signal processing module 11 may for example use a moving average of the IR sensors signal 50 to produce the smoothed IR signal 51.
• the smoothed IR signal 51 may closely follow the IR sensor signal 50 for example by using a moving average across a short time period (sec ond mode) or may be follow the IR sensor signal 50 more slowly, by using a moving average across a longer time (first mode).
• first mode a moving average across a longer time
• a moving average for a longer time period is determined in the first mode than in the second mode.
• the time period may be longer with a factor of from 3- 100, more preferably from 3 to 20 in the first mode compared to the second mode.
• a moving average may be determined for a period of from 1 to 20 seconds in the first mode, but from 0.5 to 0.1 sec onds, for example 0.25 seconds in the second mode.
• the smoothed IR signal is adjusted with a first rate in the first mode and with a second rate in the second mode, where the first rate is lower than the second rate.
• a moving average is a useful way to determine the smoothed IR signal, however there are other useful statistical methods that can be used.
• first and second thresholds 52, 53 are determined by threshold determination logic 10.
• Threshold determination logic 10 uses the smoothed signal 51 to determine the first and second thresholds 52, 53.
• the threshold values 52, 53 are determined as the smoothed IR signal 51 +/- an offset.
• Second threshold Smoothed IR signal - offset.
• the offset may be predetermined. The offset may be determined for the particular applica tion and the IR sensor 2 that is used. The offset may or may not be the same for upper threshold 52 and lower threshold 53, but in a preferred embodiment the same offset (ab solute value of offset) is used for upper threshold 52 and lower threshold 53.
• the offset is chosen dependant on configuration of the IR sensor and choice of amplifier and A/D con- verter, and may be determined using the particular configuration of system 1. As a rule of thumb, the offset may be around 10%-70% of the difference between a typical difference of the measured signal strength in the present state and in the non-present state.
• IR sensor signal 50 and the smoothed IR signal 51 may fluctuate with ventilation, sunshine, opening a window, etc in the non-present state.
• the offset should be selected to avoid er roneous triggering from the first mode to the second mode and false triggering of pres- ence/non-presence.
• the determined thresholds 52, 53 are continuously updated (see be low) and stored as threshold data 9 in memory 6. Steps 100 and 101 may be carried out repeatedly, thereby dynamically changing the smoothed IR signal 51 and the thresholds 52, 53. In the first mode, it is repeatedly checked, in step 102, if the IR sensor signal 50 passes above or below the first or second thresholds 52, 53.
• IR sensor value that is determined after the determination of the threshold, preferably immediately after determining the threshold (in the following cycle). If the IR sensor signal 50 is higher than the upper threshold 52 it is determined that a person is present. It may be enough with one single measurement in IR sensor signal 50 that is higher than the threshold 52 (thus passing the threshold), but it may also be required that the threshold 52 is passed for a minimum duration, such as continuously or repeatedly. Determination of presence is preferably done with the same frequency as updating of the thresholds 52, 53.
• the mode changes from the first mode to the second mode and 2) the state changes from non-present to present. If the lower threshold 53 is passed nothing happens to the state because the system 1 is already in the non-present state. However, the mode may change to the second mode.
• the change in state is stored as present state data 12.
• the change in state may be output using output interface 7.
• the change in mode is stored as mode data 20 in memory 6. The change in mode does not need to be output from system 1.
• Fig. 6a shows how an I R sensor signal 50 changes over time where initially there is no person 16 in the field of view 15, and the system 1 is initially in the non-present state, first mode, and a person 16 then enters the field of view 15, stays in the field of view 15 and then leaves the field of view 15.
• the system 1 is initially in the non-present state, first mode. In this particular example there is no person 16 in the field of view 15 and the system 1 is detecting background temperature only. However, a person 16 enters the field of view 15 at 29 seconds which makes the IR radiation in the field of view 15 to increase sharply. At 29 seconds, the IR sensor signal 50 therefore passes the upper threshold 52.
• change from the non-present state to the present state is not done using thresholds 52, 53 but instead by comparing the IR sensor signal 50 to the smoothed IR signal 51.
• the presence determination logic 13 detects a sensor signal value 50 that is lower than the smoothed IR signal 51
• the system changes state from present to non-present (if not already in the non-present state) (a schematic example of this is shown in Fig 6b, where the non-present state is triggered at time T)
• the pres ence determination logic 13 detects a value from IR sensor signal 50 that is higher than the smoothed IR signal, the system changes from the non-present state to the present state (if not already in the present state).
• the variability of the IR sensor signal 50 is determined.
• the lower graph in Fig. 6a shows how the variability 54 of the IR sensor signal 50 varies over time for the IR sensor signal 50 in the upper graph.
• the lower graph of Fig. 6a also shows the variability threshold 55.
• the variability threshold 55 is selected based on the configura- tion of the system 1.
• the variability threshold 55 is preferably predetermined.
• the variabil ity threshold 55 may be, for example, from 5% to 40% of the typical difference of the meas ured signal strength in the present state and in the non-present state.
• the variability thresh old 55 may also be determined using experiments or by the system l.
• the variability thresh old 55 may be stored in the presence determination logic 13.
• step 103 the variability of the IR sensor signal 50 is determined. This determina tion is performed by the signal processing module 11. Any useful dispersion parameter or variability measure can be used and applied to IR signal 50. For example, the standard de viation, the absolute variation, the mean absolute deviation or the variance of the IR sensor signal 50 may be used.
• the variability 54 may be determined as the difference between the highest value and the lowest value for the first time period. In one embodiment, the variability 54 of the smoothed signal 51 is determined instead of variability 54 of the IR sensor signal 50.
• the variability 54 is determined for the IR sensor signal 50 over a predetermined time period which may be from 3 to 15 cycles. Thus, in one embodiment the standard deviation of IR sensor signal 50 is used to determine variability 54 of the IR sensor signal 50.
• the variability 54 When the variability 54 is high, the system 1 stays in the second mode. But when the varia bility falls below the variability threshold 55, the mode of system 1 changes from the second mode to the first mode in step 104. This happens at 38 seconds in Fig. 6a, where it can be seen how the IR sensor signal 50 stabilizes from about 31 seconds, triggering the first mode at time 38. Hence, there may be a delay, such that the variability 54 needs to be below the variability threshold 55 for a certain time, for example from 3 to 15 cycles in order to trigger transition to the first mode.
• Fig. 6a from time point 29 to time point 38 the system is in the present state, second mode, and the state could revert back to the non-present state if (step 105) the IR sensor signal 50 would become lower than the smoothed IR signal 51 (i.e. be below smoothed IR signal 51 at some time point). However, that does not occur in the example of Fig. 6a. In stead, in Fig. 6a, from time point 38 the system 1 which is in the present state, enters the first mode because the IR sensor signal 50 has stabilized sufficiently for the variability 54 to fall below the threshold 55 (step 104).
• the IR sensor signal 50 passes below the lower threshold 53 because the person 16 is leaving the field of view 15. This triggers the non-present state and the second mode (step 106). Hence, the smoothed IR signal 51 now begins to adjust to the IR sensor signal 50 fast.
• the variability 54 of the IR sensor signal 50 is being determined and when the variability 54 falls below the variability threshold 55, the system reverts to the first mode at time point 61.
• the system may have four different combinations of states and modes as seen in Table 1.
• Table 1 Fig. 7 shows the four possible combination of modes and states and the possible transitions between them.
• the present state and mode are stored as present state data 12 and mode data 20 in the memory 6 of system 1.
• Presence determination logic 13 determines the state (present, non-present) and the mode (first, second).
• the system 1 repeatedly samples the IR sensor signal 50 and determines the state and the mode. Voltage is provided from IR sensor 2 to subsystem 3, IR sensor signal 50 and smoothed IR signal 51 are determined by signal processing module 11, which provides these to presence determination logic 13.
• Signal processing module 11 also provides the smoothed IR signal 51 to threshold determination logic 10.
• the IR sensor signal 50 is used by presence determination logic 13, which has access to thresholds 52,53 in the form of threshold data 9 in memory 6, and access to the smoothed IR signal 52, to determine presence.
• the state (present or non-present) is updated repeatedly, with a predetermined frequency.
• the smoothed IR signal 51, the thresholds 52, 53 and the variability 54, and the state and mode are preferably updated repeatedly, with a predetermined frequency.
• the smoothed IR signal 51, the thresholds 53, 53 and the variability and the mode and state may be determined.
• variability 54 is not determined in the first mode (because it is not used).
• thresholds 52, 53 are not determined in the second mode (because they are not used).
• the frequency may be at least once every 5 seconds, more preferably at least every 1 seconds more preferably at least 2 times per second, and most preferably at least ten times per second. Update may occur faster in the second mode than in the first mode.
• the thresholds 52, 53 may be used by presence determination logic 13 in the cycle imme diately following the cycle where they are determined by threshold determination logic 10. In a similarfashion, the value of the smoothed IR signal 51 may be compared to the IR sensor signal 50 determined in the immediately following cycle.
• Smoothed IR signal 51, thresholds 52, 53 and variability 54 may be determined using data from several previous cycles, for example from a sliding window of cycles.
• Parameters not needed in a certain mode or state may be left non-updated in that mode or state.
• the variability 54 of the IR sensor signal 50 does not need to be determined.
• Thresholds 52, 53 does not need to be determined in the second state.
• the first state it does not need to be checked weather the IR signal 50 crosses the smoothed IR signal 51.
• the second mode it does not need to be checked whether the IR signal 50 crosses the thresholds 52, 53 (which are not needed to begin with).
• system 1 When the system 1 is starting up, system 1 may in one embodiment, be predetermined to be in one state selected from the present and the non-present state. The system 1 may then change state depending on if the upper threshold 52 or the lower threshold 53 is crossed.
• system 1 may in one embodiment, be predetermined to be in one mode selected from the first mode and the second mode, where the first mode is preferred.
• the system will self-calibrate as follows. If a person 16 subsequently comes int o the field of view 15, the upper threshold 52 will be passed, in a situation similar to the one at 29 seconds in Fig. 6a. The system will then remain in the present state. The IR signal 50 will eventually stabilize at a new higher level (similar to the situation at 38 seconds in Fig. 6a) and new thresholds 52, 53 will be determined at this higher level. The system is now correctly calibrated, because it will go to the non-present state when the lower threshold 53 is passed (as at 54 seconds in Fig. 6a). Hence the system is self-calibrating.
• signal processing module 11 has been described as a software unit above it may also comprise hardware such as an A/D converter. Any suitable program ming language may be used for the software units and methods described.

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• 2020
  • 2020-04-14 SE SE2050418A patent/SE544639C2/en unknown
• 2021
  • 2021-04-13 CN CN202180038089.9A patent/CN115698657A/zh active Pending
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