CN116829985A - Passive infrared sensor occupancy detector, microcontroller, and method of operation - Google Patents

Abstract

An apparatus for occupancy detection of a space comprising: a Passive Infrared (PIR) sensor (100) having a fixed field of view; an infrared reflector (410) positioned near the PIR sensor for redirecting infrared radiation received from the space toward the PIR sensor; an electromechanical device (420) coupled to the infrared reflector and operable to change a pointing angle of the infrared reflector in response to a control signal (431); and detection and control circuitry (or microcontroller) (430) coupled to the PIR sensor (100) and the electromechanical device (420), operable to receive signals from the PIR sensor indicative of movement of the person (302) within the space, and further operable to selectively change the pointing angle of the infrared reflector (410) using the electromechanical device (420), thereby shifting the relative position of the person (302) within a fixed field of view of the PIR sensor (100) so as to simulate movement of the person even when the person is in a stationary state.

Description

Passive infrared sensor occupancy detector, microcontroller, and method of operation

The present disclosure relates generally to occupancy detectors, and more particularly to an apparatus for occupancy detection with a Passive Infrared (PIR) sensor, and related microcontrollers and methods.

Background

An occupancy sensor is a device that detects that space is occupied, for example, automatically turns on a light (or triggers some other action); conversely, if it is determined that space is not occupied, the device may turn off the lights, thereby saving energy. The Lawrence Botryi national laboratory indicates that occupancy-based strategies can save on average 24% of the illumination energy. Because of the relative simplicity and potential energy savings of these strategies, coupled with the requirements of energy regulations, occupancy sensors are a major part of new construction and retrofit projects.

Modern buildings are being installed with wireless sensor nodes for improved energy and system efficiency. These sensor nodes must maintain a long battery life (preferably up to 10 years) while continuously monitoring key parameters such as temperature, humidity, occupancy, etc. In building automation, occupancy sensors are incorporated into the overall system, including comfort control to airflow control and lighting, security and assurance in heating, ventilation and air conditioning (HVAC) systems. Motion detectors comprising a PIR sensor, fresnel lenses with cone beams and binary outputs are very efficient for detecting any type of motion, including human or pet. PIR sensors are therefore commonly used in motion detector applications, but are not commonly used in occupancy detection devices. Typical occupancy detection methods involve more complex and expensive modalities such as optical time-of-flight or millimeter wave sensing.

Referring to fig. 1, a general structure of a conventional PIR sensor 100 is illustrated. PIR sensor 100 includes a hermetically sealed metal can 110 to protect first pyroelectric sensor element 121 and second pyroelectric sensor element 122 from humidity. There is a window and/or lens 130 made of IR transmissive material (typically coated with silicon) that also protects the sensor elements. PIR sensor 100 has a limited field of view 140 defined by the geometry of the package and whether it includes a lens. When the sensor is in an idle state, the amount of IR detected by the two sensor elements 121 and 122 is the same, i.e. the amount of environment radiated from the room or wall or from the outside. When a human or animal isothermal body passes, the IR emissions from the isothermal body first strike half of PIR sensor 100, which results in a positive differential change between the two sensor elements 121 and 122. The opposite is true when the warm body leaves the sensing region, whereby the sensor produces a negative differential change. These varying pulses are the detected content.

PIR sensor 100 further includes circuitry 150 coupled to pyroelectric sensor elements 121 and 122 for generating an electrical output signal VIR in response to infrared radiation striking the sensor elements; a typical peak-to-peak voltage of the output signal VIR may be about 3.6 millivolts (mVpp). The sensor elements 121, 122 may be calibrated to be sensitive to human thermal wavelengths (i.e., 8-14 μm), for example; however, these sensor elements will only detect a person when the person is moving.

Referring now to fig. 2, the operational characteristics of PIR sensor 100 as a person moves relative to the sensor are illustrated. The output signal characteristics of PIR sensor 100 may vary depending on the direction of movement of the person, the distance of the person from the sensor, and the speed of movement of the person (as shown in graphs 200-a, 200-B, and 200-C, respectively). For example, a person moving from left to right (i.e., "direction 1") relative to the sensor elements 121, 122 will generate a first signal 201; and when moving from right to left (i.e., "direction 2"), will generate a second signal 202. The waveforms of signals 201 and 202 are identical but differ in time depending on which of the sensor elements 121, 122 detected the person first. Similarly, the amplitude of the signal from sensor 100 will vary with the distance of the person from the sensor, as shown by signals 211 and 212 in graph 200-B; an example peak-to-peak voltage value of the signal, which varies according to the distance of the person from the sensor, is shown in table 213. Finally, the output signal may vary with the speed of movement of the person, as shown by signals 221 ("speed 1") and 222 ("speed 2") in graph 200-C.

PIR sensors are designed such that an alarm is only raised when the temperature of an object changes relatively rapidly compared to the background temperature. Thus, while these PIR sensors are acceptable for use as motion sensors, they are not practical for use as occupancy sensors, as the occupancy sensor should be able to detect the presence of a person even when the person is in a stationary state. However, because PIR sensors are lower in cost and power requirements, it would be advantageous to design occupancy sensors using PIR sensors rather than more expensive and complex technologies.

Disclosure of Invention

To address the deficiencies of the prior art, an apparatus for occupancy detection of a space using a Passive Infrared (PIR) sensor having a fixed field of view is disclosed; the PIR sensor comprises at least two pyroelectric infrared elements. The apparatus includes: an infrared reflector positioned adjacent to the PIR sensor for redirecting infrared radiation received from the monitored space toward the PIR sensor; an electromechanical device coupled to the infrared reflector and operable to change the pointing angle of the infrared reflector in response to a control signal; and detection and control circuitry (or a microcontroller) coupled to the PIR sensor and the electromechanical device, operable to receive signals from the PIR sensor indicative of movement of the person within the monitored space, and further operable to selectively change the pointing angle of the infrared reflector using the electromechanical device, thereby shifting the relative position of the person within a fixed field of view of the PIR sensor so as to simulate movement of the person even when the person is in a stationary state. A method of operation for the device is also disclosed, which may be embodied in a microcontroller.

In an example, the nominal pointing angle of the infrared reflector is 45 degrees from the normal of the PIR sensor. In a related example, selectively changing the pointing angle includes: if no human movement has been detected within the predefined waiting time, the infrared reflector is caused to periodically translate in a first direction away from the nominal pointing angle. If translating the infrared reflector in a first direction does not cause the PIR sensor to generate a signal indicative of movement of the person, translating the infrared reflector in a second direction away from the nominal pointing angle; for example, the first direction may be left and the second direction may be right. If translation of the infrared reflector in the first direction or the second direction causes the PIR sensor to generate a signal indicative of movement of the person, the controller circuitry is operable to generate a signal indicative of space being occupied. The controller circuitry is operable to place the device in a standby state if translation of the infrared reflector in the first direction or the second direction does not cause the PIR sensor to generate a signal indicative of movement of the person.

In an example, the standby state includes positioning the infrared reflector to a nominal pointing angle. In a related example, the standby state has a predefined duration. In this example, the controller circuitry resumes selectively changing the pointing angle of the infrared reflector upon expiration of the predefined duration. The PIR sensor is preferably operable to detect motion during a standby state.

The foregoing has outlined rather broadly the general features of the disclosed examples so that those skilled in the art may better understand the detailed description of the examples that follow. Those skilled in the art should appreciate that they can readily use the disclosed conception and examples as a basis for designing or modifying other structures and methods for carrying out the same purposes of the present disclosure. Those skilled in the art should also realize that such equivalent constructions do not depart from the spirit and scope of the disclosure in its broadest form.

Drawings

For a more complete understanding of the present disclosure, reference is made to the following detailed description, taken in conjunction with the accompanying drawings, in which:

FIG. 1 illustrates a general structure of a Passive Infrared (PIR) sensor;

FIG. 2 illustrates the operational characteristics of a PIR sensor;

FIG. 3 illustrates the challenges faced by using PIR sensors for occupancy detectors;

FIG. 4 illustrates a device architecture of an occupancy detector utilizing a PIR sensor with a fixed field of view and an angle-controllable infrared reflector;

Detailed Description

Fig. 3 illustrates the challenges faced by using PIR sensors for occupancy detectors. As described above, PIR sensors output a voltage according to the extent of infrared radiation they receive. They are commonly used for motion detection because when a person 301 whose body is warm passes through the field of view of the sensor, the output voltage can be disturbed beyond its baseline level (which otherwise drifts based on background radiation and other factors). However, when the person is not moving 302, the received IR signal is unchanged and it is difficult to distinguish the person's IR signal from the baseline IR level of the monitored space.

For PIR motion sensing devices, detector circuit 310 is coupled to PIR sensor 100 and receives a voltage signal from the PIR sensor. The detector circuit 310 may be, for example, a discrete analog implementation or an integrated digital implementation. In a typical discrete analog implementation, the output of PIR sensor 100 is scaled and filtered by multiple op-amp stages within detector circuit 310; this helps to ensure a sufficiently large signal amplitude and concentrate the detection only in the frequency range that may correspond to human motion. The processed waveforms then go to a comparator stage that switches to a digital logic output to alert the system that the voltage deviation has exceeded a configured sensitivity threshold and to monitor that motion has occurred in the space. After selecting the correct components, the standby current may be below 2uA. For integrated digital implementations, the waveform of the PIR sensor may be acquired through the ADC input of the microcontroller, and then a digital signal processing algorithm is applied to the human motion filter and determines whether motion has occurred. Since a very low sampling rate (e.g., 20 samples/second) can be achieved with a low motion signal frequency, the total current consumption can still be kept low (e.g., less than 10 uA) with this approach. This allows the system to be in a low power sleep state most of the time (greater than 99%). However, some analog signal conditioning may be required to interface with PIR sensor 100. One example of a microcontroller suitable for an integrated digital implementation is the texas instruments MSP430FR2355 MCU.

Turning now to fig. 4, an occupancy detection device architecture 400 for an occupancy detector utilizing a PIR sensor 100 with a fixed field of view and an angle-controllable infrared reflector 410 is illustrated. Rather than rely on movement of an object, such as the stationary person 302, to create an alternating infrared profile through the sensor's fixed field of view, the monitored space may be periodically swept by an infrared reflector 410 positioned near the PIR sensor 100 for redirecting infrared radiation received from the monitored space toward the PIR sensor. An electromechanical device 420 (such as a micro motor) is coupled to the infrared reflector and is operable to change the pointing angle of the infrared reflector in response to a control signal 431 from the detector and controller circuitry 430; the detector and controller circuitry may be integrated together, for example, in a microcontroller, such as a microcontroller from the MSP430 microcontroller family of texas instruments; the highly integrated intelligent analog combining function of the MSP430 microcontroller can be used to condition and process the signal 101 received from the PIR sensor 100 and to control the electromechanical device 420 via signal 431 to change the pointing angle of the infrared reflector 420; an example of a control scheme is described below with reference to fig. 6. Changing the pointing angle of the infrared reflector 410 redirects infrared waves from the monitored space to the PIR sensor 100, shifting the viewing angle perceived by the sensor to the left or right, which causes the received IR signal to be comparable to the moving target signal received by a stationary sensor. Thus, the occupancy detection device architecture 400 relies on a single standard analog PIR sensor 100 rather than the more complex electronics known in the art.

Referring now to fig. 5, an example infrared reflection from an angle-controllable infrared reflector 410 (as perceived by PIR sensor 100 having a fixed field of view) is illustrated as the pointing angle of the reflector translates from left to right such that a stationary person 501 is perceived by the sensor to move from right to left in the order of images 510, 520, 530, and 540, respectively. From the perspective of PIR sensor 100 and associated detection circuitry, the relative position of person 501 shifts within the fixed field of view of the PIR sensor, simulating movement of the person even when it is at rest. The artificial movement of the person 501 as perceived by the PIR sensor (and associated detection circuitry) triggers a sensor response similar to the response of a person walking perpendicular to a stationary sensor, as shown by signals 201 and 202 in fig. 2.

Finally, referring to fig. 6, an example control scheme 600 (or "state diagram") for an occupancy detector that utilizes the PIR sensor 100 with a fixed field of view and the angle-controllable infrared reflector 410 shown in fig. 4 is illustrated; the control scheme may be implemented, for example, in the detector and controller circuitry 430. Based on the output signal from PIR sensor 100 and the pointing angle of infrared reflector 410, control scheme 600 is characterized by various states, as well as the response/action that causes a transition between states.

Beginning at state 610 ("standby state"), PIR sensor 100 is in an active state and any associated detector circuitry of detector and controller circuitry 430 is operational; this is a low power state in which preferably only a minimal amount of circuitry is enabled. In state 610, infrared reflector 410 is also preferably positioned to a nominal pointing angle; for example, the nominal pointing angle of the infrared reflector 410 is set at 45 degrees to the normal of the PIR sensor 100.

While in the standby state 610, if movement of an object (i.e., a person) is detected 620, indicating that space is occupied, the controller enters state 620, which may be used to trigger an action 630, such as turning on lighting or adjusting an HVAC thermostat, via a signal 621. Once the triggered action is completed, the control scheme returns to the standby state 610. If further movement of the person is detected, the control scheme again steps into state 620 and performs any programmed actions. However, if no motion is detected within a predefined time (i.e., no signal is received from PIR sensor 100 indicating motion of a person within the monitored space), the previously perceived person may move to a location within the space outside of the field of view of PIR sensor 100. Or the person may remain within the field of view of PIR sensor 100 but be at rest and thus not trigger a signal from the PIR sensor indicating that the person is still present. In either case, the control scheme 600 generates a signal to cause the electromechanical device 420 to change the pointing angle of the infrared reflector 410 in the absence of a signal indicating continued occupancy within a predefined wait time (tWAIT).

In the example control scheme 600, the infrared reflector is rotated 640 to the right in the absence of a signal from the PIR sensor 100 indicating continued occupancy for a predefined time (tWAIT), thereby shifting the field of view of the PIR sensor to the left by an angle(as described above with respect to fig. 5). If motion 642 is not yet detected, infrared reflector 410 is rotated to the left, shifting the field of view of the PIR sensor to the right by an angle +.>In this example, a->Can be equal to->This means that the field of view of the PIR sensor translates to the left and right by equal amounts, thereby expanding the nominal field of view of the PIR sensor 100. In addition to expanding the nominal field of view, translating the field of view without detecting motion will change the relative position of the person within the fixed field of view of the PIR sensor (if still taking up space) so that the person's motion can be simulated even when it is at rest.

The example control scheme 600 may be modified as needed to balance the time spent acknowledging the monitored space with the power added by the device. For example, a predefined wait time (tWAIT) may be extended, which will delay the acknowledgement of continued occupancy, but will reduce the power consumption of the device. Similarly, selectively changing the pointing angle of the infrared reflector may be performed iteratively and/or progressively left and then right, or alternately left and right at progressively larger angles, to sweep completely through the monitored space. However, increasing the frequency of changing the pointing angle of infrared reflector 410 will increase the power requirements of the controller circuitry of detector and controller circuitry 430 and of electromechanical device 420. However, only battery-powered occupancy detectors are typically involved in this concern for power demand.

The technical principles disclosed herein provide a basis for designing occupancy detection devices that utilize a single PIR sensor. The examples presented herein illustrate application of technical principles and are not intended to be exhaustive or limited to the specifically disclosed circuit topologies or methods of operation; it is intended that the scope of the technical principles be defined only by the claims appended hereto and their equivalents.

Claims (33)

1. An apparatus for occupancy detection of a space, the apparatus comprising:

a Passive Infrared (PIR) sensor, the PIR sensor having a fixed field of view;

an infrared reflector positioned proximate to the PIR sensor for redirecting infrared radiation received from the space toward the PIR sensor;

an electromechanical device coupled to the infrared reflector and operable to change a pointing angle of the infrared reflector in response to a control signal; and

detector and controller circuitry coupled to the PIR sensor and the electromechanical device, operable to receive signals from the PIR sensor indicative of movement of a person within the space, and further operable to selectively vary the pointing angle of the infrared reflector using the electromechanical device, thereby shifting the relative position of the person within the fixed field of view of the PIR sensor so as to simulate movement of the person even when the person is in a stationary state.

2. The apparatus of claim 1, wherein the nominal pointing angle of the infrared reflector is 45 degrees from a normal of the PIR sensor.

3. The apparatus of claim 1, wherein selectively changing the pointing angle of the infrared reflector comprises: if the person movement has not been detected within a predefined waiting time, the infrared reflector is periodically translated in a first direction away from the nominal pointing angle.

4. The apparatus of claim 3, wherein if translating the infrared reflector in the first direction does not cause the PIR sensor to generate a signal indicative of the movement of the person, translating the infrared reflector in a second direction away from the nominal pointing angle.

5. The apparatus of claim 4, wherein the first direction is left and the second direction is right.

6. The apparatus of claim 4, wherein the controller circuitry is operable to generate a signal indicating that the space is occupied if translation of the infrared reflector in the first direction or the second direction causes the PIR sensor to generate a signal indicating movement of the person.

7. The apparatus of claim 4, wherein the controller circuitry is operable to put the apparatus in a standby state if translating the infrared reflector in the first direction or the second direction does not cause the PIR sensor to generate a signal indicative of the movement of the person.

8. The apparatus of claim 7, wherein the standby state comprises positioning the infrared reflector to the nominal pointing angle.

9. The device of claim 7, wherein the standby state has a predefined duration.

10. The apparatus of claim 9, wherein the controller circuitry resumes selectively changing the pointing angle of the infrared reflector upon expiration of the predefined duration.

11. The apparatus of claim 8, wherein the PIR sensor is operable to detect motion during the standby state.

12. The apparatus of claim 1, wherein the PIR sensor comprises at least two pyroelectric infrared elements.

13. A method for detecting space occupancy using a Passive Infrared (PIR) sensor having a fixed field of view, the method comprising the steps of:

receiving, by the detector circuit, a signal from the PIR sensor indicative of movement of a person in the space;

generating, by control circuitry, a signal to control an electromechanical device coupled to an infrared reflector positioned in proximity to the PIR sensor for redirecting infrared radiation received from the space toward the PIR sensor; and

the electromechanical device is used to selectively change the pointing angle of the infrared reflector, thereby shifting the relative position of the person within the fixed field of view of the PIR sensor, thereby simulating the movement of the person even when it is stationary.

14. The method of claim 13, wherein the nominal pointing angle of the infrared reflector is 45 degrees from the normal of the PIR sensor.

15. The method of claim 13, wherein selectively changing the pointing angle of the infrared reflector comprises: if the person movement has not been detected within a predefined waiting time, the infrared reflector is periodically translated in a first direction away from the nominal pointing angle.

16. The method of claim 15, wherein if translating the infrared reflector in the first direction does not cause the PIR to generate a signal indicative of the movement of the person, translating the infrared reflector in a second direction away from the nominal pointing angle.

17. The method of claim 16, wherein the first direction is left and the second direction is right.

18. The method of claim 16, wherein the controller circuitry is further operable to generate a signal indicating that the space is occupied if translating the infrared reflector in the first direction or the second direction causes the PIR to generate a signal indicating the movement of the person.

19. The method of claim 16, wherein the controller circuitry is operable to enter a standby state if translating the infrared reflector in the first direction or the second direction does not cause the PIR to generate a signal indicative of the movement of the person.

20. The method of claim 19, wherein the standby state comprises positioning the infrared reflector to the nominal pointing angle.

21. The method of claim 19, wherein the standby state has a predefined duration.

22. The method of claim 21, wherein the controller circuitry resumes selectively changing the pointing angle of the infrared reflector upon expiration of the predefined duration.

23. The method of claim 20, wherein the PIR sensor is operable to detect motion during the standby state.

24. A microcontroller for use with a Passive Infrared (PIR) sensor having a fixed field of view to detect space occupancy, the microcontroller comprising:

detector circuitry operable to receive signals from the PIR sensor indicative of movement of personnel within the space; and

controller circuitry operable to generate signals to control an electromechanical device coupled to an infrared reflector positioned in proximity to the PIR sensor for redirecting infrared radiation received from the space toward the PIR sensor, the controller circuitry operable to use the electromechanical device to selectively change the pointing angle of the infrared reflector, thereby shifting the relative position of the person within the fixed field of view of the PIR sensor to simulate movement of the person even when it is at rest.

25. The microcontroller according to claim 24, wherein the controller circuitry is operable to nominally adjust the pointing angle to 45 degrees from a normal of the PIR sensor.

26. The microcontroller according to claim 24, wherein the controller circuitry is operable to: if the person movement has not been detected within a predefined waiting time, a signal is periodically generated to translate the infrared reflector in a first direction away from a nominal pointing angle.

27. The microcontroller according to claim 26, wherein if translating the infrared reflector in the first direction does not cause the PIR to generate a signal indicative of the movement of the person, a signal is generated to translate the infrared reflector in a second direction away from the nominal pointing angle.

28. The microcontroller according to claim 27, wherein the control circuitry is operable to generate a signal indicating that the space is occupied if translation of the infrared reflector in the first direction or the second direction causes the PIR to generate a signal indicating movement of the person.

29. The microcontroller of claim 27 wherein the controller circuitry is operable to enter a standby state if translating the infrared reflector in the first direction or the second direction does not cause the PIR to generate a signal indicative of the movement of the person.

30. The microcontroller according to claim 29, wherein the standby state comprises generating a signal to position the infrared reflector to the nominal pointing angle.

31. The microcontroller of claim 29 wherein the standby state has a predefined duration.

32. The microcontroller according to claim 31, wherein the control circuitry restarts selectively changing the pointing angle upon expiration of the predefined duration.

33. The microcontroller according to claim 31, wherein the detector circuitry is operable to receive and process signals from PIR sensors during the standby state.