Accelerometer
An accelerometer is a device for measuring acceleration. An accelerometer inherently measures its own motion (locomotion), in contrast to a device based on remote sensing.
One application for accelerometers is to measure gravity, wherein an accelerometer is specifically configured for use in gravimetry. Such a device is called a gravimeter. Accelerometers are being incorporated into more and more personal electronic devices such as mobile phones, media players and handheld gaming devices. In particular, more and more smartphones are encorporating accelerometers for step counters, user interface control, and switching between portrait and landscape modes.
Accelerometers are used along with gyroscopes in inertial guidance systems, as well as in many other scientific and engineering systems. One of the most common uses for micro electro-mechanical system (MEMS) accelerometers is in airbag deployment systems for modern automobiles. In this case the 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.
An accelerometer is an instrument for measuring acceleration, detecting and measuring vibrations, or for measuring acceleration due to gravity (inclination). Accelerometers can be used to measure vibration on cars, machines, buildings, process control systems and safety installations. They can also be used to measure seismic activity, inclination, machine vibration, dynamic distance and speed with or without the influence of gravity.
Accelerometers are perhaps the simplest MEMS device possible, sometimes consisting of little more than a suspended cantilever beam or proof mass (also known as seismic mass) with some type of deflection sensing and circuitry. MEMS Accelerometers are available in a wide variety of ranges up to thousands of gn's. Single axis, dual axis, and three axis models are available.
The widespread use of accelerometers in the automotive industry has pushed their cost down dramatically.
Types of accelerometer
- Piezo-film or piezoelectric sensor
- Shear Mode Accelerometer — Connection Technology Center
- Surface Micromachined Capacitive (MEMS) — Analog Devices, Freescale, Honeywell, Systron Donner (BEI)
- Thermal (submicron CMOS process) — MEMSIC
- Bulk Micromachined Capacitive — VTI Technologies
- Bulk Micromachined Piezo Resistive
- Capacitive Spring Mass Based - Rieker Inc
- Electromechanical Servo (Servo Force Balance)
- Null-balance
- Strain gauge
- Resonance
- Magnetic induction
- Optical
- Surface acoustic wave (SAW)
- Laser accelerometer
Applications
The Wii Remote for the Nintendo Wii console contains accelerometers for measuring movement and tilt to complement its pointer functionality.
Within the last several years, Nike, Polar and other companies have produced and marketed sports watches for runners that include footpods, containing accelerometers to help determine the speed and distance for the runner wearing the unit.
More recently, Apple Computer and Nike have combined the footpod technology and Apple's iPod nano to provide real-time audio feedback to the runner on his/her pace and distance. [1]
A small number of modern notebook computers feature accelerometers to automatically align the screen depending on the direction the device is held. This feature is only relevant in Tablet PCs and smartphones, including the upcoming iPhone.
Some laptops' hard drives utilize an accelerometer to detect when falling occurs. When shock above a threshold is detected, the write current is turned off so that data on other tracks is not corrupted. When the shock ends, the data can be rewritten to the desired track, thus negating the effects of the shock.
Camcorders use accelerometers for image stabilization.
Still cameras use accelerometers for anti-blur capturing. The camera holds off snapping the CCD "shutter" when the camera is moving. When the camera is still (if only for a millisecond, as could be the case for vibration), the CCD is "snapped".
Some digital cameras contain accelerometers to determine the orientation of the photo being taken and some also for rotating the current picture when viewing.
The Segway and balancing robots uses accelerometers for balance.