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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Quartz Accelerometer Specification Properties

 An accelerometer is an instrument used to measure the acceleration of an object. It has a wide range of applications in many fields, including aerospace, automotive engineering, and sports medicine.

1. Sensitivity: for an instrument, the higher the sensitivity, the better, because the higher the sensitivity, the easier the acceleration changes in the surrounding environment, the greater the acceleration changes, the natural output voltage changes correspondingly larger, so that the measurement is easier, more convenient, and the measured data is more accurate. Ericco's quartz accelerometer ER-QA-03A has a scaling factor of 15-50ppm, bias repeatability is 10-50μg and Class II non-linearity repeatability is 10-30μg/g2.

2. Bandwidth: Bandwidth refers to the effective frequency band that the sensor can measure. For example, sensors with hundreds of Hertz bandwidths can measure vibrations; A sensor with a bandwidth of 50 Hz can effectively measure inclination.

3. Range: The range required to measure the movement of different objects is not the same. It should be measured according to the actual situation. The measuring range of the accelerometer is usually in the unit of gravitational acceleration (g), and the common range is +2g, +4g, +8g, etc. This means that an accelerometer can measure the acceleration of an object in any direction, whether it is negative (deceleration) or positive (acceleration).As a wide range accelerometer ER-QA-03B's capable of measuring up to ±70g

4. Measurement accuracy: It is also an important technical specification. Measurement accuracy is usually expressed in terms of displacement error or percentage error. For example, an accelerometer with an accuracy of +0.1g means that its measurement is within +0.1g of the true value. The higher the accuracy, the more accurate the measurement results.

5. Response time: Also a key metric. Response time refers to the time it takes for the accelerometer to receive a change in acceleration to produce a stable result. In general, the shorter the response time, the better, because it means the accelerometer can detect the acceleration change more quickly.

The technical specifications of the accelerometer include measurement range, measurement accuracy, response time, resolution, sampling rate, operating temperature range and interface type. These technical specifications determine the performance and reliability of the accelerometer in different application scenarios. When selecting and using accelerometers, we need to weigh these technical specifications according to the specific needs to obtain the best measurement results and performance.

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Differences in application scope of IMU and AHRS

System reference differences

The measurement reference system chosen by AHRS is the earth itself, and the location of its measurement object is also a specific geographical location. The inertial measurement unit is different in that it measures position and motion relative to a specific inertial reference frame, which can be a fixed point such as a house, building, or a uniform motion system. Conceptually, inertial units of measurement are more widely applicable because the reference point of the AHRS, the Earth, is also an inertial reference frame (not absolute, just the Earth). using the Sun as the inertial reference frame in the solar system).

System composition difference

Although the measuring elements of AHRS and IMU are basically the same, due to the different reference systems of AHRS, AHRS has more electronic compass than inertial measurement unit. When AHRS monitors motion trajectories and status, due to the time drift problem of the gyroscope, when integrating the rotation angle during motion, the error will become larger and larger as time goes by. Therefore, an electronic compass is needed to calibrate the geographical azimuth of movement in time.

The main difference between an inertial measurement unit  and an AHRS is the addition of an onboard processing system to an AHRS, which provides attitude and heading information, whereas an inertial measurement unit only transmits sensor data to additional equipment that calculates attitude and heading. In addition to attitude determination, AHRS can also form part of an inertial navigation system.

Nonlinear estimation forms such as the extended Kalman filter are often used to compute solutions from these multiple sources.

AHRS has proven to be highly reliable and is commonly used on commercial and business aircraft. AHRS is typically integrated with the electronic flight instrument system (EFIS), which is a core part of the so-called glass cockpit and forms the primary flight display. AHRS can be combined with an air data computer to form the Air Data, Attitude and Heading Reference System (ADAHRS), which provides additional information such as airspeed, altitude and outside air temperature.

Scope of application

AHRS is not as widely used as inertial measurement unit due to its choice of reference system. For example, the ER-MIMU-01 developed by Ericco uses high-quality and reliable MEMS accelerometers and gyroscopes. It communicates with the outside via RS422. The baud rate can be flexibly set between 9600 and 921600. The communication baud required by the user is set through the communication protocol. Rate. Its application fields are relatively wide, and can be widely used in pointing, steering and guidance in advanced mining/drilling equipment, initial alignment of weapons/drone launch systems, direction pointing and tracking in satellite antennas and target tracking systems, Precision attitude and position measurement in navigation-grade MEMS IMU/INS, north-seeking positioning in geodesy/land mobile mapping systems, oil exploration, bridges, high-rise buildings, towers, dam monitoring, geotechnical monitoring, mining and many other fields. AHRS usually uses sensors such as electronic compasses to be used in aviation flight measurement, ground motor vehicle remote control, drone tracking and other fields. Since inertial measurement unit has a flexible reference system, inertial measurement is often used in oil exploration, drilling and production systems, mobile surveying and mapping systems, and attitude reference systems for vehicle and ship attitude measurement.

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Tilt Sensors for Solar Photovoltaic Power Generation Tracking Systems

 

Tilt sensors are real-time measurements of the eye in solar photovoltaic tracking systems.

Solar power generation, divided into solar photovoltaic power generation and solar thermal power generation two, the current development of solar photovoltaic power generation faster, more rapid, is a rapid development of the field, currently China, the United States, Europe, Japan, India, Australia and other countries, the rapid development, Ericco has developed more than a dozen different types of tilt sensors for photovoltaic tracking systems to meet customers in different countries.

Solar photovoltaic tracking system composition:

1. Solar photovoltaic tracking system is generally composed of tilt sensor, motor, worm gear and controller. According to the specific application, solar photovoltaic tracking system is divided into horizontal single-axis photovoltaic tracking system, oblique single-axis photovoltaic tracking system, two-axis photovoltaic tracking system, which can not only comprehensively improve the power generation of the power station, but also adapt to local conditions, and better adapt to various complex terrain and application scenarios.

2. The solar photovoltaic tracking system needs to adjust the tilt angle of the solar photovoltaic panel, so that the solar photovoltaic panel can be adjusted in time according to the changes in the movement of the sun, so that the sun rays are always vertically illuminated on the solar photovoltaic panel to obtain the maximum solar radiation.

3. Although the angle of the sun varies widely during the day, the angle of the sun is almost constant at a certain time. The system can calculate the local sun's orientation and angle information every day of the year according to the local latitude and longitude, and the information is stored in the controller's software, so that the angle information of the photovoltaic panel measured by the inclination sensor can be compared with the angle information of the sun stored by the controller, and then the control motor can adjust the photovoltaic panel at that time for the best position.

4. The ER-TS-3160VO tilt sensor, as the eye of real-time measurement in the solar photovoltaic tracking system, is one of the key equipment to optimize the solar reception rate. The accuracy of the inclination sensor has certain requirements, Ericco self-developed inclination sensor is currently on the market has been mature application in a number of solar photovoltaic projects, the use of industrial devices stable performance, high reliability, and with anti-touch, anti-misconnection protection function, anti-wind sand, anti-salt spray anti-ultraviolet, Fully consider the complex application scenarios of solar photovoltaic.

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