An accelerometer is a device that measures precise acceleration. The precise acceleration, being the acceleration (or rate of change of speed) of an object in its own frame of rest, is not the same as the acceleration coordinates, being the acceleration in the fixed coordinate system. For example, a silent accelerometer on the Earth's surface would measure the acceleration due to Earth's gravity, straight up (by definition) of g? 9.81 m/s 2 . Conversely, a free fall accelerometer (falling to the center of the Earth at a rate of about 9.81 m/s 2 ) will measure zero.
Accelerometers have many applications in industry and science. The highly sensitive accelerometers are components of inertial navigation systems for aircraft and missiles. Accelerometers are used to detect and monitor vibrations in a rotating engine. Accelerometers are used in tablet computers and digital cameras so images on the screen are always displayed upright. Accelerometers are used in drones for flight stabilization. Coordinated accelerometers can be used to measure differences in precise acceleration, especially gravity, above their separation in space; ie, the gradient of the gravitational field. This gravity gradiometry is useful because absolute gravity is a weak effect and depends on a fairly variable local density of the Earth.
Single and multi-axle accelerometer models are available to detect the exact magnitude and direction of acceleration, as vector quantities, and can be used to sense orientation (due to direction of weight change), coordinate acceleration, vibration, shock and fall in resistive media (cases where the exact acceleration changes, as it starts from zero, then increases). Micromachined microelectromechanical systems (MEMS) accelerometers are increasingly present in portable electronic devices and video game controllers, to detect the position of the device or provide game input.
Video Accelerometer
Physical Principles
An accelerometer measures precise acceleration, which is the acceleration experienced relative to freefall and is the acceleration felt by people and objects. In other words, at any point in time the principle of equality guarantees the existence of a local inertia framework, and the accelerometer measures the relative acceleration of the frame. Such acceleration is popularly symbolized by force; that is, compared to the standard gravity.
The accelerometer at rest relative to the Earth's surface will show about 1 g upward, as any point on the Earth's surface accelerates upward relative to the inertial local frame (the frame of the object falls freely near the surface). To obtain acceleration due to movement towards Earth, this "gravity weig" must be reduced and correction made for effects caused by the Earth's rotation relative to the inertial framework.
The reason for the offset of gravity is the principle of Einstein's equality, which states that the effects of gravity on an object can not be distinguished from acceleration. When held firmly in the gravitational field by, for example, applying a soil reaction force or an equivalent upward push, the frame of reference for the accelerometer (the casing itself) accelerates upward with respect to the free fall frame of reference. This acceleration effect can not be distinguished from other accelerations experienced by the instrument, so the accelerometer can not detect the difference between sitting on a rocket on the launch pad, and being on the same rocket in outer space while using the engine to accelerate at 1 g. For the same reason, the accelerometer will read zero as long as all types fall free. This includes use in spacecraft that glide deep in space far from any mass, a spacecraft orbiting Earth, an airplane with a "zero-g" parabolic bow, or free fall in a vacuum. Another example is the free fall at high altitude so that the atmospheric effect can be ignored.
This however does not include a fall (not free) where the air resistance produces a drag force that reduces acceleration, until a constant terminal velocity is reached. At terminal speed, accelerometer will show acceleration 1 g upwards. For the same reason a skydiver, having reached the terminal speed, does not feel as though he is in "freefall", but experiences the same feeling of being supported (at 1 g) on ​​the "bed" of rising air.
Acceleration is quantified in units of SI meters per second per second (m/s 2 ), in cgs gal (Gal) units, or popular in terms of standard gravity ( g ).
For the practical purposes of discovering the acceleration of objects with respect to the Earth, as for use in inertial navigation systems, knowledge of local gravity is required. This can be obtained by calibrating the device at rest, or from a known gravity model in the current position.
Maps Accelerometer
Structure
Conceptually, the accelerometer behaves as a damped mass in the spring. When accelerometers experience acceleration, the mass evacuates to the point that the spring is capable of accelerating mass at the same level as the casing. The displacement is then measured to provide acceleration.
In commercial devices, piezoelectric, piezoresistive, and capacitive components are typically used to convert mechanical movement into electrical signals. Piezoelectric accelerometers rely on piezoceramics (eg Lead zirconate titanate) or single crystals (eg quartz, tourmaline). They are unmatched in terms of their upper frequency range, low packet weight and high temperature range. Piezoresistive accelerometers are preferred in high shock applications. Capacitive accelerometers usually use micro-machining elements of silicon machines. Their performance is superior in low frequency range and they can be operated in servo mode to achieve high stability and linearity.
Modern accelerometers are often small micro electro-mechanical systems (MEMS), and indeed simple MEMS devices are possible, consisting of little more than cantilever beams with mass proof (also known as seismic masses ). Segregate results from residual gases that are sealed on the device. As long as the Q-factor is not too low, damping does not produce lower sensitivity.
Under the influence of external acceleration, the mass of evidence veers from its neutral position. This deflection is measured by analog or digital means. Most commonly, the capacitance between a fixed set of beams and a set of beams attached to the mass of evidence is measured. This method is simple, reliable, and inexpensive. Integrating piezoresistors in springs to detect spring deformation, and thus deflection, is a good alternative, although several more process steps are required during the fabrication sequence. For very high sensitivity, quantum tunnels are also used; this requires a special process that makes it very expensive. Optical measurements have been demonstrated on a laboratory scale.
Another relatively new type of MEMS accelerometer is a thermal (or convective) thermal accelerometer that contains a small heater at the bottom of a very small dome, which heats air/fluid inside the dome, producing a thermal bubble that acts as a mass proof. The accompanying temperature sensor (such as thermistor or thermopile) in the dome is used to determine the temperature profile inside the dome, therefore, telling us the location of the heated bubbles inside the dome. Now, because of the acceleration used, there is a physical shift of the thermal bubble and it is deflected from its center position inside the dome. Measuring this displacement, the acceleration applied to the sensor can be measured. Due to the absence of solid proof mass, the thermal accelerometer produces a high shock resistance rating.
Most micromechanical accelerometers operate in-plane , that is, they are designed to be only sensitive to directions in the dice field. By integrating two devices perpendicular to one die a two-axis accelerometer can be made. By adding other out-of-plane devices, three axes can be measured. Such combinations may have a much lower misalignment error than three separate models combined after packaging.
The micromechanical accelerometer is available in various measurement ranges, reaching up to thousands of g ' s. The designer must make a compromise between sensitivity and maximum measurable acceleration.
Apps
Engineering
Accelerometers can be used to measure vehicle acceleration. Accelerometers can be used to measure vibrations in cars, engines, buildings, process control systems and safety installations. They can also be used to measure seismic activity, slope, engine vibration, dynamic distance and speed with or without gravitational influence. Applications for accelerometers that measure gravity, where the accelerometer is specifically configured for use in gravimetry, are called gravimeters.
A notebook computer equipped with an accelerometer can contribute to Quake-Catcher Network (QCN), the BOINC project devoted to scientific research on earthquakes.
Biology
Accelerometers are also increasingly used in biological sciences. High-frequency recording of bi-axial or tri-axial acceleration allows discrimination of behavior patterns while animals are not visible. Furthermore, accelerated recording allows researchers to measure the rate at which an animal releases energy in the wild, either by determining the frequency or step of the limb-stroke as the overall dynamic body acceleration. Such an approach has largely been adopted by marine scientists because of the inability to study animals in the wild using visual observations, but more terrestrial biologists are adopting similar approaches. This device can be connected to the amplifier to amplify the signal.
Industry
Accelerometers are also used for machine health monitoring to report vibrations and their changes in axle time on spinning equipment bearings such as turbines, pumps, fans, rollers, compressors, or bearing faults which, if not handled immediately can lead to costly repairs. The accelerometer vibration data allows the user to monitor the machine and detect this error before the rotating equipment fails completely.
Monitoring of buildings and structures
Accelerometers are used to measure movement and vibration of structures that are exposed to dynamic loads. Dynamic loads come from a variety of sources including:
- Human activity - walking, running, dancing, or skipping
- Working machine - inside building or in surrounding area
- Construction work - pushing piles, unloading, drilling, and extracting
- Moves the load on the bridge
- Vehicle collision
- The impact load - falling debris
- The burden of concussion - internal and external explosions
- Collapse of structural elements
- Wind load and wind blow
- Air blast pressure
- Loss of support due to ground failure
- Earthquakes and aftershocks
Under structural applications, measuring and recording how structures dynamically respond to these inputs is critical to assessing the security and viability of a structure. This type of monitoring is called Health Monitoring, which usually involves other types of instruments, such as displacement sensors -Potentiometers, LVDT, etc.- Deformation Sensors - Tension Gauges, Extensometers-, Load Sensors - Load Cells, Piezo-Electrical Sensors-among others.
Medical applications
Zoll's AED Plus uses CPR-Dopadz containing an accelerometer to measure the depth of CPR chest compression.
In recent years, several companies have manufactured and marketed sports watches for runners that include footpods, which contain accelerometers to help determine the speed and distance for runners who are wearing the unit.
In Belgium, accelerometer-based step counter is promoted by the government to encourage people to walk several thousand steps each day.
Herman Digital Trainer uses an accelerometer to measure attack power in physical exercise.
It has been suggested to build a football helmet with an accelerometer to measure the impact of head collisions.
Accelerometers have been used to calculate gait parameters, such as phase stance and swing. Such sensors can be used to measure or monitor people.
The inertial navigation system is a navigation aid that uses computers and motion sensors (accelerometers) to continuously calculate through dead position calculation, orientation, and speed (direction and velocity of movement) of moving objects without requiring external references. Other terms used to refer to an inertial navigation system or a closely related device include an inertial guidance system, an inertial reference platform, and many other variations.
Accelerometers alone are not suitable for determining altitude changes at distances where significant vertical gravity decreases, such as for aircraft and rockets. In the presence of the gravity gradient, the calibration and data reduction processes are numerically unstable.
Transportation
Accelerometers are used to detect apogee in both amateur and professional rockets.
Accelerometers are also used in Intelligent Compaction rollers. Accelerometers are used with gyroscopes in inertial navigation systems.
One of the most common uses for MEMS accelerometers is in airbag deployment systems for modern cars. In this case, accelerometers are used to detect the rapid negative acceleration of the vehicle to determine when a collision has occurred and the severity of the collision. Another common automotive use is in electronic stability control systems, which use lateral accelerometers to measure cornering power. The wider use of accelerometers in the automotive industry has dramatically reduced costs. Other automotive applications are noise, vibration and hardness (NVH) monitoring, conditions that cause discomfort for drivers and passengers and may also be indicators of mechanical errors.
Tilt the train using an accelerometer and a gyroscope to calculate the required slope.
Volcanology
Modern electronic accelerometers are used in remote sensing devices intended to monitor active volcanoes to detect magma movements.
Consumer electronics
Accelerometers are increasingly incorporated into personal electronic devices to detect the orientation of the device, for example, the display screen.
The free fall sensor (FFS) is an accelerometer used to detect if a system falls and falls. Then it can implement security measures such as parking the hard disk head to prevent head crash and result in loss of data during a collision. These devices are included in many public computers and consumer electronic products manufactured by various manufacturers. It is also used in some data loggers to monitor handling operations for shipping containers. The length of free fall time is used to calculate the drop height and estimate the surprise on the packet.
Motion input
Some smartphones, digital audio players, and personal digital assistants contain accelerometers for user interface controls; often an accelerometer is used to present landscape landscapes or portrait device screens, based on the way devices are held. Apple has included an accelerometer in every generation of iPhone, iPad, and iPod touch, as well as on every iPod nano since the 4th generation. Along with the orientation orientation adjustment, accelerometers on mobile devices can also be used as pedometers, along with custom apps.
The Automatic Collision Notification (ACN) system also uses accelerometers in the system to request assistance in the event of a vehicle accident. The leading ACN system includes OnStar AACN service, 911 Ford Link Assist, Toyota Safety Connect, Lexus Link, or BMW Assist. Many smartphones with an accelerometer also have ACN software available for download. The ACN system is enabled by detecting accelerated force-crash.
Accelerometers used in vehicle Electronic stability control system to measure the actual movement of the vehicle. The computer compares the actual movement of the vehicle with steering wheel and throttle input. Computer stability control can selectively brake the individual wheels and/or reduce engine power to minimize the difference between the driver input and the vehicle's actual movement. This can help prevent the vehicle from spinning or rolling.
Some pedometers use the accelerometer to more accurately measure the number of steps taken and the mileage than the mechanical sensors can provide.
Nintendo Nintendo video game console uses a controller called Wii Remote that contains a three-axis accelerometer and is designed primarily for motion input. Users also have the option to purchase a motion-sensitive additional attachment, Nunchuk, so motion input can be recorded from both the hands of the user independently. Also used on Nintendo 3DS systems.
Sony PlayStation 3 uses DualShock 3 remote that uses a three-axis accelerometer that can be used to make the wheel more realistic in racing games, such as MotorStorm and Burnout Paradise .
The Nokia 5500 sports comes with a 3D accelerometer accessible from the software. This is used for step recognition (computation) in sports applications, and for tap movement recognition in the user interface. The tap movement can be used to control the music player and sports application, for example to move on to the next song by tapping the clothes while the device is in the pocket. Other uses for accelerometers in Nokia phones include Pedometer functionality in Nokia Sports Tracker. Some other devices provide tilt sensing features with cheaper components, which are not actual accelerometers.
The sleep phase alarm clock uses an accelerometer sensor to detect sleep movement, so it can wake people up when it is not in the REM phase, to wake people up easier.
Sensing orientation
A number of 21st century devices use an accelerometer to align the screen depending on the direction the device is on hold (for example, switching between portrait and landscape modes). These devices include many tablet PCs and some smartphones and digital cameras. Amida Simputer, a handheld Linux device launched in 2004, is the first commercial handheld device to have a built-in accelerometer. It combines many motion-based interactions using this accelerometer, including page changes, zoom-in and zoom-out images, portrait changes to landscape mode, and many simple motion-based games.
In January 2009, virtually all new phones and digital cameras contained at least a slant sensor and sometimes an accelerometer for the purpose of automatic image rotation, motion sensitive mini-games, and correcting wobble while taking photos.
Image stabilization
Camcorders use accelerometers for image stabilization, either by moving an optical element to adjust the light path to the sensor to undo the unwanted motion or shift the image digitally to smooth the motion detected. Some stills cameras use accelerometers to capture anti-blur. The camera keeps shooting while the camera is in motion. When the camera is still (if only for milliseconds, as is the case of vibration), the image is captured. Examples of applying this technology are Glogger VS2, a phone app that runs on Symbian-based phones with accelerometers like the Nokia N96. Some digital cameras contain an accelerometer to determine the orientation of the captured photo and also to rotate the current image while viewing.
Device integrity
Many laptops have accelerometers that are used to detect droplets. If a decrease is detected, the hard disk head is parked to avoid data loss and possible head or disk damage due to subsequent shocks.
Gravimetri
A gravimeter or gravitometer, is an instrument used in gravimetry to measure the local gravitational field. The gravimeter is a type of accelerometer, except the accelerometer is susceptible to all vibrations including noise, which causes oscillation acceleration. It is neutralized in the gravimeter by integrated vibration isolation and signal processing. Although the basic principle of design equals accelerometers, gravimeters are usually designed to be much more sensitive than accelerometers to measure very small changes in Earth's gravity, from 1 g . In contrast, other accelerometers are often designed to measure 1000 g or more, and many make multi-axial measurements. Constraints at the temporal resolution are usually less for gravimeters, so the resolution can be improved by processing the output with longer "time constants".
Accelerometer type
See also
- Accelerometer
- Degree of freedom
- g-force
- Geophone
- Gyroscope
- Inclinometer
- Inertial measurement unit
- Inertial navigation system
- Magnetometer
- Seismometer
- Vibration Calibrator
References
Source of the article : Wikipedia
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