ECE5320 MechatronicsAssignment#01: Literature Survey on Sensors and Actuators Topic: Motion Sensor Prepared by: Prasad Subramanian Dept. of Electrical and Computer Engineering Utah State University 3/10/2006
Motion Sensor Outline • Reference list • To probe further • Technology Overview • Classification of Motion Sensor • Principle of Operation – PIR sensor • Limitation of PIR sensor • Example Configuration • Major specifications • Applications • Trends and Advances in Motion Sensor • Vendor List
Reference list Websites used for the purpose of this survey: • http://computer.howstuffworks.com/question238.htm • http://www.euclidres.com/motionSensors/motionSensors.html • http://www.sciencedaily.com/releases/2006/02/060210090229.htm • http://www.glolab.com/pirparts/infrared.html • http://www.nlectc.org/perimetr/full2.htm#preface • http://www.nlectc.org/perimetr/full2.htm#tr_26
To Probe Further - References • Intrusion detection for military and law enforcement agencies : - http://www.nlectc.org/perimetr/full2.htm#Section2 • Recent News and articles • http://www.sciencedaily.com/releases/2006/02/060210090229.htm • http://www.sensorsmag.com/articles/1299/34_1299/main.shtml • http://www.sensorsmag.com/resources/businessdigest/sbd0602.shtml • http://www.redherring.com/Article.aspx?a=14992&hed=Top+10+Trends%3A+Sensor+Motes • Comprehensive List of Commercial Motion Sensor http://www.motiondetectorsguide.com/Results.aspx?query=Motion%20Detectors
Technology Review… • Fence Vibration • Electric Field • Capacitance • Strain Sensitive Cable • Fiber Optic Fence • Taut Wire • In-ground Fiber Optic • Ported Coax Buried Line • Balance Buried Pressure • Buried Geophone • Video Motion Detection • Radar • Acoustic Detection (Air Turbulence)
Motion Sensor Classification Motion Sensors could be broadly classified into: • Area Sensor : Broader coverage area. Hence the name • Passive Infrared • Proximity (RF field) • Microwave/Radar • Ultrasonic • Vibration • Video • Local Sensor : Region of detection is localized. • Active Infrared (light beam) • Visible Light beam • Laser Beam • Contact • Tilt • Proximity • Strain/Stress A local event would be one like someone stepping on a floor mat which had a contact switch in it, walking through a light beam, or driving a car over a magnetic sensor. An area event would be someone moving within the 'field of view' of a particular sensor. This area is generally known or controllable, but it is large in comparison to the 'field' of a contact switch etc.
Types of motion sensor • Incremental Optical Encoders : Optical incremental encoders are linear/angular position sensors that use light and optics to sense motion. • Interrupters, Photo-Reflective Sensors, Proximity and Hall Effect Sensors : These sensors provide an indication of motion by sensing light, a magnetic field, or simply the presence of an object.
Motion Sensor Types… Generates a pulse whenever an opaque object interrupts a light beam passing across the gap of the sensor Interrupter Generates a pulse whenever the sensor receives reflected light. Photo Reflective Sensor Generates a pulse whenever the sensor comes in close proximity to an object. Depending on the sensor, the object may or may not be magnetic. Proximity and Hall Effect From: http://www.euclidres.com/motionSensors/motionSensors.html
Motion Sensor Types • Laser Interferometer • Laser interferometers are used to measure the linear displacement of an object. • Magnetostrictive Sensors : Magnetostrictive sensors are used to measure the linear displacement of an object. Magnetostrictive sensors operate by sending a radial magnetic field down a waveguide toward a permanent ring magnet. From: http://www.euclidres.com/motionSensors/motionSensors.html
Motion Sensor Types… Ultrasonic Sensors Measured distance by calculating time taken for echo/reflection to reach the sensor Cable Extension Transducer When the spool is connected to a potentiometer, the output is an analog signal representing the absolute position of the spool. From: http://www.euclidres.com/motionSensors/motionSensors.html
Motion sensor Types… LVDT - Linear Variable Differential Transformers LVTDs are used to measure the linear displacement and velocity of an object. LVTDs consist of a moving shaft/ferrite material and a set of coils: one primary and two secondary coils. Using the polarity and magnitude of the voltage, the position of the shaft can be determined. From: http://www.euclidres.com/motionSensors/motionSensors.html
Creating motion sensor Different ways to create a motion sensor: Active Motion Sensor: They inject energy into the environment in order to detect a change of some sort • Beam of light crossing the room, near the door with a photo sensor at the other end of the beam. When a person cuts the beam the photo sensor detects this intrusion. • RADAR detection : Direct microwave energy and detect the amount of energy that is reflected off the object. Microwave energy is bounced back from the object’s surface. • Similarly detect echo from ultrasonic waves.
Passive Infrared Sensor Passive Motion Sensor : (PIR) sensors are passive, that is the sensor does not transmit a signal; the sensor head simply registers an impulse when received. Known as PIR detectors ( Passive Infrared) • Use pyroelectric sensors in order to detected infrared energy/waves.
PIR Motion Detection Principle Infrared Radiation • Infrared radiation exists in the electromagnetic spectrum at a wavelength that is longer than visible light. It cannot be seen but it can be detected. • Objects that generate heat also generate infrared radiation and those objects include animals and the human body whose radiation is strongest at a wavelength of 9.4um.
Infrared radiation… • Infrared in this range will not pass through many types of material that pass visible light such as ordinary window glass and plastic. • However it will pass through, with some attenuation, material that is opaque to visible light such as germanium and silicon. • An unprocessed silicon wafer makes a good IR window in a weatherproof enclosure for outdoor use. It also provides additional filtering for light in the visible range.
Operating principle Detect Human beings: • Use PIR detectors • Human beings have average skin temperature of 93F • Radiate infrared energy of wavelength 9-10um. • Hence sensors should be tuned to be sensitive in that range of 8 to 12 um.
Operating principle • Light perceived by sensor is sensitive to motion • Electronics packaged within the sensor looks for change in infra-red energy being “seen” or sensed. • The sensor essentially requires a rapid change in amount of infra-red energy . • Hence when a person walks by, the amount of infrared energy in the field of view changes rapidly and is easily detected.
Operating principle… • Motion sensing light has a wide field of view because of the lens covering the sensor. • Infrared energy is a form of light, so you can focus and bend it with plastic lenses. • There is a single (or sometimes two) sensors inside looking for changes in infrared energy.
Pyroelectric Sensor • Made of a crystalline material • Generates a surface electric charge when exposed to heat in the form of infrared radiation. • Amount of charge generated varies as the intensity of infrared radiation falling on the sensor • Charge changes detected by measured with a sensitive FET device built into the sensor. • Sensor elements are sensitive to radiation over a wide range so a filter window is used to limit incoming radiation to the 8 to 14mm range which is most sensitive to human body radiation.
Sensor construction From : http://www.glolab.com/pirparts/infrared.html
Sensor construction • FET source terminal pin 2 connects through a pulldown resistor of about 100 K to ground and feeds into a two stage amplifier having signal conditioning circuits • The amplifier is typically bandwidth limited to below 10Hz to reject high frequency noise. • Window comparator responds to both the positive and negative transitions of the sensor output signal.
Fresnel Lens • A Fresnel lens (pronounced Frennel) is a Plano Convex lens that has been collapsed on itself to form a flat lens • retains its optical characteristics • smaller in thickness and therefore has less absorption losses.
Sensor in use From : http://www.glolab.com/pirparts/infrared.html
Sensor in use… • A body passing in front of the sensor will activate first one and then the other element • The radiation source must pass across the sensor in a horizontal direction when sensor pins 1 and 2 are on a horizontal plane so that the elements are sequentially exposed to the IR source. • A focusing device is usually used in front of the sensor
Typical Specification • Field of view and coverage area : typically 180o and 1400 – 2200 sq. feet • Maximum Sensing distance in front of the sensor: 30feet to 60 feet • Physical Specifications • Operating Temperature Range • Storage Temperature Range • Relative Humidity • Agency Approval : Should usually comply with UL Listed/California Certified; Compliance with California Energy Code & with FCC regulations
Limitations and pitfalls of PIR • Conditions for unreliable detection : • PIR looks for thermal radiation projected against a cooler background, detection is based on temperature. (PIR) sensors are passive, that is, the sensor does not transmit a signal; the sensor head simply registers an impulse when received. • As the environment approaches the same temperature as the intruder, the detectors become less sensitive. • Causes for nuisance alarm • Heat radiations from animals, rodents can trigger false alarms • Time activated space heaters, ovens and hot water pipes can also provide false alarms if they are in the field of view • Typical defeat Measures • Shadowing, cloaking or masking the intruding heat source • knowing the dead spots of the detection pattern can permit an intruder to bypass active regions. • Walking into the sensor rather than across the sensor's field of view can also reduce the detection capability by not allowing the boundaries of the detection beams to be broken.
Limitations of PIR sensor • Response Time : depending on the 'apparent background', they may take 'some time' to detect motion
Typical Specification - Electrical • Line Voltage : • Operational Frequencies • Wire Designation • Load Rating • Fluorescent: • 1200VA @ 120V • 2700VA @ 277V • Incandescent: • 800W @ 120V
Applications • Home Automation : Automatic control of switch, doors for use in Smart Homes. • Intrusion Detection • Automation industry : Airbag deployment-Used in vehicles to trigger the deployment of Airbags • Machinery and Robot safety • Monitoring Seismic Activity: data from several sensors provide valuable information that is used by earth scientists and other professionals to reduce earthquake-related hazards in the neighboring areas
Application Example from: http://www.nlectc.org/perimetr/full2.htm#MIL-APP
Interior Motion Sensor Application Model Courtesy : http://www.nlectc.org/perimetr/full2.htm#GIF-88
Application Example… Legend for previous slide
Doppler Motion Sensor - Specification • Operation Range 5 cm – 4 m • Operation Frequency 30-50 kHz, determined by piezoelectric sensor resonant frequency • Power Consumption 27 mA (alarm off) • Sensor Response Time 0.25 s • The Range of Detected Object’s Speed 10 cm/s – 1.5 m/s
Modern Applications • 3D motion tracking : 3D motion sensors have an extremely wide range of applications, because they can accurately indicate the oriental position of items they are attached to. • Can be used in virtual-reality • Remote controlled robot : Provides the same degree of control as the human hand
Modern applications Cell Phones and PDA : • In PDAs, they may allow users who are reading a book to “turn the page” by simply turning the PDA over in their palm and then turning it back again • In cell phones, the motion sensors may sense when the phone has been dropped and shelter the hard drive to prevent memory loss. • Protection from fall : The sensor detects when a notebook falls to the ground. In such cases, the hard drive heads are quickly parked to prevent loss of data.
Developments and trends • Sensor, which measures about 3 square millimeters or one-tenth of an inch have been designed in a chip • Miniaturization techniques developed as part of a relatively new field called Micro Electrical Mechanical Systems, or MEMS, have steadily reduced their size and cost.
End of Motion Sensor Next: Electrostatic Actuator -Prasad Subramanian