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Equipped with an accelerometer, the wireless LAN standard complies with IEEE 802.11 b / g / n.
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A small accelerometer (accelerometer)MEMSManufactured using technology.MEMSIn the case of the accelerometer, the mass is small, so the sensitivity is reduced, but dramatic miniaturization is possible, so the automobileAirbag,car navigationIt is used for inclinometers, game controllers, etc.Since the accuracy is specified based on the measurement axis, the accuracy proposed by the accelerometer becomes meaningless unless the direction of the axis is determined by the fixed surface of the housing (and its processing accuracy). It is difficult to apply it to measurement applications when it is just mounted.
Mechanical displacement measurement method
Therefore, accelerationa [m / s2] Is
And the spring constantkAnd weight massmIf is known, the displacement of the weightxAcceleration can be measured by detecting.Since the fundamental performance is determined by the spring constant and the mass of the weight, the main research and development targets are improvement of the detection method, stability and environmental resistance.
The mechanical accelerometer occupies a certain size and weight as a measuring device and tends to have a large inertial mass, so it is not suitable for measurement in a short time, and the spring itself causes vibration, so it is near the resonance range. There is a large error in the acceleration motion at.There is also a problem of deterioration over time due to the machine, such as lubrication of moving parts and rusting of metal parts.
Of the earth where high accuracy is requiredAcceleration of gravityIn the measurement of, there is also a measuring instrument called "absolute gravitational accelerometer" that accurately measures gravity by dropping a reflector called a corner cube in a high vacuum container and measuring the fall time.
Method using vibration
A spring with a weightresonanceVibrate at frequency.On the weightAccelerationJoins the spring whenstressChanges, so that the resonance frequency of the spring changes.this isGuitar OfstringIt is the same principle that the sound changes when you stretch or loosen.thisfrequencyAcceleration is detected by detecting the change in.
Q valueIf a spring structure with a high frequency (such as a tuning fork type is often used) is used, the accuracy of detecting frequency changes is improved, so that high measurement accuracy can be obtained.
This principle iselectronic balanceEtc. preciselyobjectIt is also used as a device for measuring the weight of.In this case, the stress applied to the spring changes depending on the weight of the object, so that the frequency changes.
There are several types of optical accelerometers, which are used for the purpose of optically transmitting, detecting, and amplifying changes in position caused by acceleration, and are finally converted into electrical signals by an optical sensor. In the FBG optical fiber type, the acceleration applied to the weight is FBG (Fiber Bragg Grating) Detects changes in wavelength by using tension on the optical fiber.Once the data measured by the semiconductor accelerometerOptical fiberThe thing to be transmitted on the device is sometimes called an optical type, and there are various types.
Mechanical and optical accelerometers are laborious to manufacture, adjust, and repair, increase costs, and are not suitable for miniaturization and intelligence. Therefore, semiconductor accelerometers are used in various devices in recent years. Is increasing.BothMEMS (Micro Electro Mechanical Systems) Using technology.
- Capacitive type
- Slight position changes in minute moving parts supported by beam structureCapacitanceDetected as a change in, amplified and measured by an electric circuit.The detection accuracy is improved by creating two types of comb tooth-shaped structures that detect capacitance, rough and fine.
- Piezoresistive type
- The surface is made thin in an annular shape by the silicon semiconductor manufacturing technology to form a diaphragm.Supporting the central weight with this thin metal makes it easier to detect displacement due to acceleration.Change the position of the diaphragmPiezoIt is detected by a resistance element and amplified and measured by an electric circuit.Acceleration detection in the three-axis direction is possible by devising how to attach the diaphragm and piezoresistive element.
- Gas temperature distribution type
- The movement of the lightened gas that has been warmed in the center of the cavity due to acceleration is detected by the resistance change of the ambient temperature measurement resistance bridge, and is amplified and measured by the electric circuit.That is, in other methods, a weight heavier than air is used as a mass, but in this method, a gas portion lighter than air is considered as a mass.Since there are no mechanical moving parts, the yield of the MEMS process is good, and as a result, it is said that it can be manufactured at low cost.
Number of detection axes
There are 1-axis, 2-axis, and 3-axis sensors depending on the number of detection axes.
The 3-axis acceleration sensor is a type of MEMS sensor that can measure acceleration in the three directions of the X, Y, and Z axes with a single device. The range of ± number [g] is measurable.
The following are typical 3-axis accelerometers.
- Piezoresistive 3-axis accelerometer
- Capacitive 3-axis accelerometer
- Heat detection type 3-axis accelerometer
As a manufacturer, the following companies manufacture.
- IM V(Japan)
- Hokuriku Electric Industry
- Hitachi Metals
- , Inc. (USA)
- ST Microelectronics(America)
- Analog Devices(America)
Scientific experiments that require strict accuracySeismographIn addition to being used as an acceleration measuring device such asPedometerThis sensor has a wide range of uses, such as being used to determine the vertical direction of a mobile phone screen.
- Mobile phone - Earth's gravityBy measuring the acceleration, the tilt of the mobile phone is detected so that the screen is always displayed in the correct orientation..
- Game controller - Wii remoteWait
- hard diskVibration detection
- Mech robotAttitude control, etc.
- DroneAttitude control,Inertial navigationWait
Seismograph-重力TotalTiltmeterCan be said to be a type of accelerometer, but depending on the application, performance such as accuracy, bandwidth used, dynamic range, and stability is characteristic.For example, seismographs suppress the detection of vibrations other than earthquakes (shorter than the period of earthquakes) by giving sensitivity near the period of seismic waves.