The Structure of Accelerometer

 

An accelerometer is an instrument that measures acceleration. Acceleration measurement is an important subject in engineering technology. When the object has a large acceleration, the object and the instruments and equipment carried by it and other objects without relative acceleration are subjected to forces that can produce the same large acceleration, that is, dynamic loads. To know the dynamic load, you need to measure the acceleration. Secondly, to know the spatial position of the instantaneous aircraft, rockets and ships, its acceleration can be measured continuously through inertial navigation , and then the velocity component is obtained through integral calculation, and the position coordinate signal is obtained by integrating again.

The components of common accelerometers are as follows: housing (fixed to the measured object), reference quality, sensitive components, signal output devices, etc. Accelerometers require a certain amount of range and accuracy, sensitivity, etc. These requirements are often somewhat contradictory.

Accelerometers based on different principles have different ranges (from several g to hundreds of thousands of g), and their sensitivities to catastrophic acceleration frequencies are also different. Common accelerometers are based on the following principles:

1.The reference mass is connected to the housing by a spring . The relative displacement between the housing and the housing reflects the magnitude of the acceleration component. This signal is output via the potentiometer as a voltage.

2.The reference mass is fixed by the elastic thin rod and the shell, the dynamic load caused by acceleration deforms the rod, the strain resistance wire senses the size of the deformation, and its output is an electrical signal proportional to the size of the acceleration sub-disk.

3.The reference mass is fixedly connected to the housing through the piezoelectric element. The dynamic load of the mass exerts pressure on the piezoelectric element. The piezoelectric element outputs an electrical signal proportional to the pressure, that is, the acceleration component.

The accelerometer for measuring aircraft overload was one of the first aircraft instruments to be used. They are also commonly used in aircraft to monitor engine failure and fatigue damage to aircraft structures. Accelerometer is an important tool to study the flutter and fatigue life of various aircraft in flight test. In inertial navigation system, high precision accelerometer is one of the most basic sensitive elements. The performance of accelerometers in different applications is very different. The high precision inertial navigation system requires the resolution of accelerometers up to 0.001g, but the range is not large. The accelerometer for measuring aircraft overload may require a range of 10g, but the accuracy is not high. Therefore, Ericco designed ER-QA-03A high performance quartz accelerometer and ER-QA-01A aerospace quartz for the application characteristics in this field The characteristics of accelerometer are: ER-QA-03A’s bias repeatability is 10-50μg,scale factor repeatability is 15-50 PPM and class II non-linearity repeatability is 10-30μg/g2. ER-QA-01A’s bias repeatability is 10μg,scale factor repeatability is 10 PPM and class II non-linearity repeatability is 10μg/g².

From this, we can simply understand the definition, structure and application of the accelerometer in aircraft overload, if you want to know more about the accelerometer related knowledge. Please click here,get more https://www.ericcointernational.com/accelerometer

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Selecting an Inertial Measurement Unit (IMU) for UAV Applications

An inertial measurement unit (IMU) is an electronic device that uses accelerometers and gyroscopes to measure acceleration and rotation and can be used to provide position data.

IMUs are an important component of unmanned aerial systems (UAVs, UAS, and drones) and common applications include control and stabilization, guidance and correction, measurement and testing, and mobile mapping.

Raw measurements output from an IMU (angular rate, linear acceleration, and magnetic field strength) or AHRS (roll, pitch, and yaw) can be fed into devices such as an inertial navigation system (INS) to calculate relative position, direction, and speed to help UAV navigation and control.

IMUs are manufactured with a wide range of features, parameters and specifications, so the most suitable choice will depend on the requirements of the specific drone application. This article outlines some of the key options and considerations when selecting an IMU for drone applications, such as underlying technology, performance, and durability.

There are many types of IMUs, some of which incorporate magnetometers to measure magnetic field strength, but the four main technology categories for drone applications are: silicon MEMS (microelectromechanical systems), quartz MEMS, FOG (fiber optic gyroscopes), and RLG (Ring Laser Gyroscope).

Silicon MEMS IMUs are based on tiny sensors that measure the deflection of a mass due to motion, or the force required to hold the mass in place. They typically have higher noise, vibration sensitivity, and instability parameters than FOG IMUs, but as technology continues to advance, MEMS-based IMUs are becoming more accurate.

MEMS IMUs are well suited for small UAV platforms and high-volume production units because they can often be manufactured at smaller size and weight and at lower cost. The tactical-grade ER-MIMU03 and ER-MIMU07 developed by Ericco can be widely used on UAVs. If you want to know more about IMU products, please click the link below to contact us.

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The Difference and Selection of Gyroscope and Tilt Sensor

 

Tilt sensors and gyroscopes are commonly used in inertial navigation technology, but they have some differences in measurement, working principle and accuracy.

1. Tilt sensor

The tilt sensor (inclinometer) is induced tilt deviation angle, and only data feedback without command feedback. Tilt sensor measures static dip angle.

Tilt sensors measure the angle between the object and the horizontal plane to obtain the tilt angle. Common tilt sensors include uniaxial and biaxial tilt sensors, which detect the tilt of an object in a plane.

The working principle of the inclination sensor is mainly divided into two types: capacitive type and vibration gyroscope type. Capacitive inclination sensor uses the object’s inclination to change the capacitance in the capacitor to detect the inclination angle. The vibration gyro inclination sensor uses the motion state of the gyroscope to determine the tilt of the object.

In applications, inclination sensors are often used in aviation, ships, construction and other fields, such as attitude control of aircraft and automatic navigation of ships.

2. Gyroscopes

Compared with tilt sensor, gyroscope measures the movement of the dip angle, dip in static measurement result is not accurate. The gyroscope is the induction action variable, and then controls the steering gear to repair the movement command.Gyroscope is not measuring equipment, it is auxiliary equipment, like a tank gun barrel in order to make the tank in the procession precision fire, which installed the gyroscope, full automatic control the angle of the gun barrel.

A gyroscope is a device that measures the angle of rotation of an object in space. According to their different structures and characteristics, gyroscopes can be divided into mechanical gyroscopes and fiber optic gyroscopes.

The working principle of the gyroscope is based on the gyro effect, that is, the rotating axis has the characteristics of stable direction in the rotating state. When the object rotates around a fixed axis, the gyroscope generates a “moment” and outputs the corresponding rotation rate signal, thus measuring the angle of rotation of the object. Gyroscopes are widely used in modern aerospace, navigation, geological exploration and military fields.

So we measure the angle in daily life, is to choose the angle sensor or gyroscope choice, we can choose according to the nature. Measuring the static angle, the choice of the tilt sensor, for example ER-TS-12200-Modbus can be used in the following fields: bridge construction, ship navigation attitude measurement, high railway foundation, tunnel monitoring, satellite solar antenna positioning, medical equipment, angle control of various construction machinery; measurement is the movement of the dip angle, then choose a gyroscope. Gyroscopes are classified including: ball bearing free gyroscope, liquid floatation gyroscope, electrostatic gyroscope, flexible gyroscope, fiber optic gyroscope, laser gyroscope and so on.

What Does IMU Mean for A Drone?

Definition of drone:

The full name of “unmanned aircraft” is unmanned aircraft, which is operated by radio remote control equipment and self-provided program control devices, or by the on-board computer fully or intermittently autonomous operation. In order to make the UAV fly perfectly, IMU(Inertial Measurement Unit), gyroscope stabilization and flight controller technology are essential.

Working principle

The flight control of UAV is composed of main control MCU and inertial measurement module IMU. IMU provides the original sensor data of the aircraft’s attitude in space, and the data of the aircraft is generally provided by the gyroscope sensor/acceleration sensor/electronic compass. Gyroscopic stabilization technology is one of the most important components, allowing the drone to fly super-smoothly even in strong winds and gusts. This smooth flight allows us to take fantastic aerial views of the beautiful planet. With excellent flight stability and waypoint navigation, the UAV can generate high-quality 3D photogrammetry and liDAR images. The latest drones use an integrated head, which also includes built-in gyroscopic stabilization technology, so that the on-board camera or sensor has little to no vibration. This allows us to capture perfect aerial film and photographs. In order to meet the requirements of UAV equipment, the ER-MG2-300/400 gyroscopes not only use advanced differential sensor design, can eliminate the effects of linear acceleration and operate in the presence of shock and vibration in the extremely harsh environment, but also have a measurement range of 400 degrees/second and 0.01°/ hour bias instability. Capable of measuring angular velocities up to ±400°/s and has a digital output protocol compliant with SPI from mode 3. Angular rate data is expressed as 24-bit words.

Technical influence

The application of IMU in UAVs is not limited to attitude control and flight stability. It can also be used with other sensors such as GPS (Global Positioning System) and magnetometers to provide more accurate navigation and positioning information. At the same time, IMU can also be used for UAV attitude estimation, motion detection, obstacle avoidance and other functions, improve the autonomy and safety of the UAV, provide key data for the control and navigation of the UAV, so that the UAV can efficiently perform various tasks. The application of IMU will vary depending on the design and use of different types of UAVs, but whether it is fixed wing, multi-rotor or vertical take-off and landing and conversion UAVs, IMU is the core to achieve its flight control and navigation.

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What are the advantages of MEMS IMU?

 The performance index of a gyro north-seeking device depends on two aspects: north-seeking precision and north-seeking time. The traditional north-seeking device has a good performance in north seeking performance, but its equipment is expensive and heavy. With the continuous optimization of the performance and accuracy of MEMS gyroscope, the future gyro north-seeking device will develop towards the trend of high north-seeking accuracy, low north-seeking time, low cost, small size and high operational flexibility. MEMS IMU has been widely used in general civil navigation, tactical weapons and unmanned systems because of its advantages of small size, low cost, high reliability and easy installation.

IMU in inertial navigation system

The inertial navigation system is an auxiliary navigation system that uses accelerometers and gyroscopes to measure the acceleration and angular velocity of objects and uses computers to continuously estimate the attitude, speed and position of objects through navigation solutions. Inertial navigation system is an inseparable system in the modern navigation field.

According to the physical platform, the inertial navigation system can be divided into platform inertial navigation system and strapdown inertial navigation system.

The advantages of the platform inertial navigation system are that the computing burden of the computer is light, and the dynamic range of the gyro in the platform inertial navigation system can be small because the rotation of the navigation coordinate system is very slow. Its disadvantages are also obvious: complex structure, large size, heavy weight, and poor reliability.

With the development of gyro technology and the improvement of computer ability, strapdown inertial navigation system (Strapdown inertial navigation system) has gradually replaced the platform inertial navigation system (INS) in some fields and become a research hotspot in modern times. The characteristic of the strapdown inertial navigation system is that the navigation coordinate system is established by algorithm, that is, the mathematical platform replaces the physical platform, which makes the system simple in structure, small in size, easy to maintain and high in reliability. The attitude update solution is the key algorithm of the strapdown inertial navigation system, and the strapdown inertial navigation system uses IMU to obtain the carrier information for the attitude solution.

Inertial Measurement Unit (IMU) is a device used to measure the three-axis angular velocity and acceleration of a carrier. Generally, a gyroscope and accelerometer are installed on the orthogonal three axes of an IMU, with a total of 6 degrees of freedom, to measure the angular velocity and acceleration of the carrier in three-dimensional space, and then the strapdown inertial navigation system can calculate the attitude of the carrier.

Integration of MEMS technology and inertial devices

As the core sensor of the inertial navigation system, the development of inertial devices (gyroscope and accelerometer) plays an important role in the development of the inertial navigation system. According to the working principle, the early gyroscopes are mainly rotor gyro, according to the different support types of liquid float gyro, dynamic tuning gyro, electrostatic gyro and maglev gyro, etc. After the 1970s, laser gyro and fiber optic gyro based on the optical Sagnac effect appeared.

From the aspect of gyroscope accuracy (bias stability) statistics, electrostatic gyro precision is the highest, can reach 10–6 °/h, the precision level of dynamic tuning gyro is about 0.01°/h, laser gyro precision level is about 0.01~0.001°/h level, compared with laser gyro, fiber optic gyro smaller volume, low power consumption, and low price. Although the precision is not as good as laser gyro, but with the continuous improvement of optical fiber manufacturing technology, its potential advantage is more obvious.

MEMS is an industrial technology that merges microelectronics and mechanical engineering with a range of operations on the micron scale. Along with the improvement of the silicon semiconductor process for making integrated circuits, the micromechanical manufacturing technology of micro-machinery, micro-sensor and micro-actuator emerged in the 1980s, making MEMS technology become a real product. The achievements of MEMS technology in the field of inertial navigation are reflected in the MEMS IMU, which is composed of three silicon micro gyroscopes, three silicon micro accelerometers and the corresponding control circuit. MEMS IMU has the advantages of small size, light weight, easy mass production and low cost, and has been widely used in the general civil and some unmanned system navigation fields. But its disadvantages are obvious: relatively low accuracy, bias stability is about 10~20°/h.

But Ericco’s ER-MIMU-01&ER-MIMU-05 use High Performance North Seeking MEMS Gyroscope(ER-MG2–100) that can reach 0.1°/h. The accuracy is more accurate than the lowest-precision IMUs of many large companies, and It can reflect its high performance in complex environments.

Even ER-MIMU-03&ER-MIMU-07, its bias stability is only 3°/h, which can be used in the stable control system.

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Quartz Accelerometer VS MEMS Accelerometer

 Principle and structure

Quartz accelerometer is a kind of precision inertial sensor which can detect the acceleration by sensitive quartz pendulum relative position change. The speed and position of the system can be accurately obtained by calculation, and the accurate acceleration measurement signal can be provided for navigation, guidance, control and adjustment of various systems. The pendulum plate of the quartz accelerometer is formed by the quartz material after laser cutting, acid etching and other special processing, the thermal expansion coefficient is very small of ordinary glass 1/10~1/20, and the thickness of the flexible beam is 0.03mm. Quartz accelerometers are generally composed of quartz crystals, mass blocks and electrodes. The quartz crystal is used as the core component of the sensor, the mass block is used to sense the acceleration, and the electrode is used to measure the piezoelectric charge. Among them, the precision performance of quartz accelerometer products launched by ericco can reach the middle and high navigation level. ER-QA-03A is taken as an example, with bias repeatability of 10-50μg, scale factor repeatability of 15-50ppm, and Class II nonlinear repeatability of 10-30μg/g2.

MEMS accelerometers are also known as microelectromechanical systems (MEMS). An acceleration sensor is an embedded acceleration sensor that can measure the acceleration of an object in space. It can also be used to measure the linear acceleration and angular velocity of an object. The working principle of MEMS accelerometers is to detect the dynamic behavior of objects in space through one or more components in MEMS systems, which can be micro-capacitors, micro-oscillators, micro-mechanical switches, etc. When the object accelerates, the parameters of these elements change, so that the acceleration is detected and the acceleration is measured.

The structure of the MEMS accelerometer is basically composed of four parts: mass block, spring, induction circuit and package. Among them, the mass block is the core component used to sense the acceleration, the spring is used to support and constrain the movement of the mass block, the induction circuit is used to convert the mechanical displacement into an electrical signal, and the package is used to protect the structure and electronics of the MEMS accelerometer.

Application

Quartz accelerometer is widely used in aviation, inertial navigation platform and other fields ,because its long-term stability is superior to MEMS accelerometers, and it also has the characteristics of high precision, high stability and fast response. In the process of aircraft manufacturing, quartz accelerometers can be used to test the structural strength and flight characteristics of aircraft. In the flight mission, the quartz accelerometer can be used to measure the acceleration of the aircraft in different directions and transmitted to the flight control system for analysis and processing in real time. In addition, the quartz accelerometer can also be used for real-time measurement of aircraft attitude, gyroscope drift and vibration during flight. In addition to its small size, the ER-QA-03C quartz accelerometer designed for aviation inertial navigation systems can be used not only for aerospace inertial testing, but also for static and dynamic acceleration measurements.

MEMS accelerometer is widely used in various fields. In the field of mobile devices, MEMS accelerometers are used in navigation, attitude detection, image stabilization and so on. In the automotive field, MEMS accelerometers can be used for vehicle stability control, collision detection, etc. In the field of industrial control, MEMS accelerometers can be applied to vibration monitoring, robot navigation, etc. MEMS accelerometers are also often used with MEMS gyroscopes, and their design and processing technology has become increasingly mature. For example, ER-MA-5 has a bias stability (Allen variance) of 5 ug and a bias monthly repeatability of 200ug.

Advantages and disadvantages

The quartz accelerometer can stand out among many accelerometers, in addition to playing its own unique attributes, the important reason is that its long-term stability is better and its sensitivity is better. Its disadvantage is that the measurement range is limited by the stiffness and size of the vibration beam and other factors, the general measurement range is not more than tens of g, and it is vulnerable to stress damage in high acceleration environment.

MEMS accelerometers have many advantages, such as small size, light weight, low power consumption, and low price. In addition, MEMS accelerometers also have high sensitivity and large measurement range. However, MEMS accelerometers also have some shortcomings, such as large temperature drift, large noise, and unstable sensitivity.

Development trend

At present, quartz accelerometers and MEMS accelerometers still have a lot of room for development in terms of performance and application. With the continuous progress of technology, researchers are trying to solve the problems of accelerometer noise, temperature drift and so on, and constantly improve its sensitivity and stability.

What’s the Advantages of Tilt Sensor?

 

A tilt sensor is a sensor used to measure the tilt angle of an object and is commonly used in fields such as engineering measurement, mechanical control, and aerospace. It can monitor the tilt state of the object in real time, and convert it into an electrical signal output, which is provided to the computer or other equipment for processing and analysis, so as to achieve accurate control and adjustment of the object.

1. Principle of tilt sensor

The working principle of the tilt sensor is based on microelectromechanical system (MEMS) technology and accelerometer principle. It is equipped with tiny accelerometers, and by using gravity, inertia and other mechanical principles, to detect the object's tilt angle relative to the Earth's horizontal plane.

When the object is at rest, the inclination sensor is subjected to gravity, which causes the accelerometer to align with the vertical direction of the Earth. When the object tilts, the direction of the accelerometer changes accordingly, resulting in an electrical output indicating the angle and direction of the object's tilt.

2. Advantages of tilt sensor

Tilt sensors offer a variety of benefits, some of which are important:

2.1 High Precision

The ER-TS-12200-Modbus tilt sensor adopts MEMS technology, which has the characteristics of high precision, high stability and low noise, and can realize the high precision measurement and control of the tilt angle of the object.

2.2 Compact and Lightweight

The tilt sensor is small in size, light in weight, easy to install and carry, and is suitable for various occasions and environments.

2.3 High Reliability

The tilt sensor has high vibration resistance, impact resistance, water and dust resistance, and can run stably in complex environment for a long time.

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