Inertial Measurement Unit (IMU) Technology and Applications in UAVs

1: Definition and composition of IMU An inertial measurement unit (IMU) is a device that integrates sensors such as accelerometers and gyroscopes and is used to measure the linear acceleration, angular velocity and direction of objects. An IMU typically consists of a three-axis accelerometer, a three-axis gyroscope, and possibly a magnetometer. These sensors can capture the movement of the drone and provide accurate attitude information.

2: IMU technical principle and working method The working principle of IMU is based on the basic principle of inertial measurement. Accelerometers derive information about an object's velocity and displacement by measuring the linear acceleration experienced by an object. The gyroscope measures the angular velocity of the object and derives the rotation attitude of the object. Magnetometers can help determine the direction of an object. The IMU uses data from these sensors and processes it with filtering and fusion algorithms to provide accurate flight status information.

3: Application scenarios of IMU in drones IMU has a wide range of application scenarios in drones. First of all, IMU is one of the key technologies to realize UAV navigation and positioning, and can provide precise position and attitude information. Secondly, in the stability control of the drone, the IMU can help the drone maintain balance and offset external interference. In addition, IMU is also commonly used to implement functions such as autonomous flight, path planning, and obstacle avoidance of UAVs. The ER-MIMU-03 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 rate required by the user is set through the communication protocol. Equipped with X, Y, Z three-axis precision gyroscope, X, Y, Z three-axis accelerometer, with high resolution, it can output the original hexadecimal complement of X, Y, Z three-axis gyroscope and accelerometer through RS422 code data (including gyroscope hexadecimal complement) numerical temperature, angle, accelerometer hexadecimal temperature, acceleration hexadecimal complement); it can also output gyroscope and accelerometer data that have been processed by underlying calculations Floating point dimensionless value. The application fields are also relatively wide, and can be used in heading, pitch, and roll measurement in UAV AHRS; guidance, navigation and control of satellite antennas in tactical MEMS weapon systems, stabilization and pointing in target tracking systems, and autonomous machines and unmanned aerial vehicles. Robot control and orientation in driving vehicles, etc.

Inertial measurement unit (IMU) technology in drones plays a vital role in the modern drone field. By in-depth understanding of the principles, composition and application scenarios of IMU, we can better understand the flight control system of drones and apply it to various practical scenarios.

In the future, with the continuous development and innovation of drone technology, IMU technology will also be further improved and improved. Through continued research and exploration, we can expect the emergence of more accurate and stable drone navigation and control systems. The widespread application of drones will bring more convenience to our lives, and at the same time promote the development and progress of the entire aviation field.

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Common Technical Problems before the Selection of Tilt Sensors

 

We often encounter some technical problems when choosing a tilt sensor, such as:

1. What is a sensor?

Sensors are devices used to measure various physical quantities, such as temperature measurement, pressure measurement, speed measurement, inclination measurement and so on.

2. What is inclination?

Inclination is the angle of inclination, is a special angle, generally speaking, is the angle between a measured plane and the horizontal plane.

3. What is an tilt sensor?

A tilt sensor is a sensor used to measure inclination.

4. What is a horizontal plane?

Roughly speaking, the plane formed after the water is completely relatively still, why add the word "relative"? Because no object is absolutely at rest, rest is relative. Relative to another object. There are infinite planes parallel to this plane. In fact, the definition of horizontal plane and plane are physical and mathematical concepts that help us understand the real world or find physical and mathematical laws as basic concepts.

5. What is the meaning of the output mode of the tilt sensor?

The output mode is divided into two aspects, one refers to the physical output mode, and the other is only the electrical output mode.

6. How many kinds of physical output modes are there for the tilt sensor?

Usually there is a cable output, connector output. Cable output depends on the length, color identification, connector output, pay attention to the number of cores, and pin definition.

7. What is the problem with cable output?

When purchasing products, if it is cable output, it is best to look at the manual, the manufacturer's standard output length is how much. Then according to their own application, installation requirements, determine their own cable length, if increased, will involve price changes, try to leave a little margin, in case the length is not enough. Sometimes the customer requirements are more special, the way of cable + connector, and the way of internal terminals are also uncommon.

8. What is the electrical output mode of the tilt sensor?

The electrical output mode is relative to the physical output mode, mainly refers to the electrical connection mode of the following bit machine, which is divided into many kinds, the largest is divided into two categories, that is, analog output and digital font output.

9. What is an analog output tilt sensor? 

Analog output means that the output signal is an analog signal, such as voltage output, current output.For example, Ericco’s ER-TS-3160VO is a voltage type output, its built-in (MEMS) solid pendulum measures the change of static gravity field, which is converted into the change of inclination, and the change is output through the voltage (0~10V, 0~5V optional).

10. What is digital output?

Digital output is relative to analog, there are many kinds of digital interfaces, such as RS232, TTL, RS485, CAN, PWM, and very rare RS422 interface, SII interface, and other master-slave communication methods.

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How to Choose an Appropriate North Finder？

 

North-seeking methods include inertial instrument north-seeking method, astronomical observation method, geodetic method, magnetic north-seeking method, satellite positioning method, reference object method and other methods. However, only the north-seeking instrument developed using the principle of inertia can independently complete the north-seeking task without being disturbed by natural conditions or environment, and has the characteristics of long continuous working time and high accuracy.

The north seeker mainly determines the true north value of the attached carrier by measuring the angular velocity of the earth’s rotation, without being interfered or affected by external magnetic fields or other environments. There are many types of inertial north seekers on the market, so it is particularly important to choose a north seeker. This article will introduce in detail how to choose a suitable north seeker through its core sensor, application environment, size, weight and accuracy.

Selection Factors for North Finder

Core Sensor

The core sensor plays a decisive role in the north seeker and greatly affects the north seeker accuracy. Therefore, the core sensor is crucial when choosing a north seeker. There are three main core sensors currently used in north seekers: ring laser gyroscopes (RLG). Gyroscope technology also includes fiber optic gyroscopes (FOG) and microelectromechanical systems (MEMS) gyroscopes, which can be selected according to the application field and requirements. Choose precision small, compact, lightweight and radiation resistant, the RLG is compact and self-contained and does not create friction, which can affect accuracy and increase “drift” over time. In fact, compared to mechanical gyroscopes that can drift 0.1-0.01 degrees per hour, the RLG drifts about 0.0035 degrees, making it suitable for low-cost vehicle positioning and north-finding applications. However, the ring laser gyroscope (RLG) has dominated the inertial navigation market since its first introduction in 1963. Its dominance is gradually being challenged by technological improvements in fiber optic gyroscopes (FOG), which are also slowly occupying RLG in the inertial navigation market.

Fiber Optic Gyroscopes (FOG) have higher inertial performance and lower bias than RLG gyroscopes, making them the solution of choice for high-precision applications such as GNSS rejection environments or antenna pointing. A fiber optic gyroscope is a solid-state device that does not use a dither mechanism, which means it does not produce any acoustic vibrations, making it more durable and reliable than an RLG. In addition, fiber optic gyroscope applications can be expanded by changing the length and diameter of the fiber coil.

MEMS technology has made great progress in recent years. MEMS rate gyroscopes measure the earth’s rotation angular velocity to calculate the azimuth angle, collect the output of the gyroscope at different azimuth angles, and perform signal processing to calculate the azimuth angle of the device. MEMS sensors achieve higher accuracy, improved error characteristics, and better sensitivity, significantly improving overall MEMS performance. While other companies produce millions of MEMS for commercial and consumer products, Ericco focuses on high-performance systems typically used in aerospace, defense and transportation applications. For example, ER-MNS-05 is fully temperature compensated and has high precision and sensitivity characteristics, which greatly improves work efficiency.

Therefore, when choosing a north seeker, special attention should be paid to its core sensor. Sensor accuracy can improve the overall performance of the north seeker. If the requirement for north seeking accuracy is slightly higher: around 0.1°, 0.2°~0.02°, you can choose an optical fiber sensor (FOG). If you require ultra-high accuracy and there are no strict requirements on volume, you can choose a laser sensor (RLG) as the seeker. The accuracy can reach about 0.01°~0.005°. You can choose a north-seeking instrument according to your own requirements for north-seeking accuracy, which can achieve twice the result with half the effort.

Size and Weight

Because the application fields of north seekers are different, the working spaces are also different, in some complex working areas such as drilling rigs, mines, tunnel boring machines, etc. There are two main types of north seekers: MEMS and FOG. The MEMS north seeker is small and lightweight. MEMS also consume less power than FOG, providing longer mission times for fuel-constrained vehicles. If you have strict requirements on size, MEMS is the most recommended. For example, ER-MNS-06 is the smallest north finder in the world, only 44.84×38.88×21.39mm, weight ≤60g, and accuracy of 0.25°-1. If the weight and size requirements are not strict, but accuracy is required, a laser sensor (RLG) can be selected as the north finder. If there are some requirements for size and accuracy, it is recommended to choose an optical fiber sensor (FOG) as the north finder. For example: ER-FNS-03, with dimensions of 200×100×90mm/210×125×105mm, and a weight of 2.0Kg. It has the same accuracy as the mems north finder and is small in size.

North Seeking Accuracy

Another north-finding capability unique to FOG, even in highly magnetic environments. In contrast to MEMS technology, which relies on magnetometers for accurate heading, FOG accurately measures the Earth’s angular rate of rotation even when it’s in motion and can accurately determine north direction within minutes. This is a particularly welcome feature for subsea applications that cannot rely on any GNSS signal for long periods of time. For example, the ER-FNS-03, a low-cost 3-axis FOG north seeker, is the leader among FOG north seekers.

If the requirements for north seeking accuracy are particularly high, one time Sigma, and an accuracy of 0.001 or above, a laser sensor will generally be selected as the north seeker. At around 0.01°~0.5°, an optical fiber sensor can be selected as the north seeker, while the mems north seeker generally The north accuracy is around 0.5°~1°, 2°. Once the important accuracy is determined, everyone will be able to purchase a high-quality north finder, which will also reduce errors for practical applications.

Application Areas

Gyroscopic orth-finding systems are widely used in various fields of the national economy and military. When using gyroscopic north-seeking systems to obtain azimuth information, there are many different observation methods and operating procedures based on different industry characteristics and constraints. The transmission and aiming of azimuth are the most commonly used and basic links. Many typical applications of gyro north-finding systems require the application of this technology.

Measurement of Centerline of Tunnel Project

During the construction and construction processes of mining, transportation and other industries, tunnel shield excavation is carried out underground, and the acquisition of northbound information is the basis for the smooth progress of the project. In excavation projects such as tunnels, the centerline measurement in the pit generally uses long-distance wires that are difficult to ensure accuracy. Especially when carrying out shield excavation, it is necessary to have high angle measurement accuracy and station shifting accuracy starting from the short reference center line of the pit. During the measurement, corresponding inspections on the ground and underground must be carried out frequently to ensure the accuracy of the measurement. However, in dense urban areas, it is difficult to ensure measurement accuracy because it is impossible to carry out too many inspection operations. If you use a gyro theodolite, you can get an absolutely high-precision azimuth reference, and it can reduce the cost-intensive inspection work (with the least number of inspection points), and it is a very efficient centerline measurement method.

Targeting of Weapon Systems in the Military

The gyroscopic north-seeking system can play a huge role in military geodesic operations, that is, to provide reference quasi-shooting directions for weapon systems such as artillery and missiles, and to conduct measurements to obtain northbound signals. Conventional operation methods make geodesic protection in mind. It is basic, but the effective use of the weapon’s power has been tested. For example, in the artillery unit’s geodesic operations, to a certain extent, whether it is controlled measurement or continuous measurement of artillery battle formations, the methods to obtain higher accuracy include the following: retrieving or calculating the orientation based on the result data, inducing the orientation, Astronomical orientation determination has great limitations in practical operations, which affects the speed and accuracy of geodetic operations to a certain extent. The introduction of the gyro north-finding system has solved the problem of all-weather accurate position acquisition, greatly improved the operating methods, facilitated the comprehensive implementation of the operating methods, and made fast and accurate geodetic support a reality.

Many Equipment in the Defense Industry

A large number of orientation requirements, for example: inertial navigation equipment needs to establish an indoor north direction reference, the zero direction or axis of the inertial navigation test turntable needs to point in a certain direction; the antennas of the radio frequency simulation laboratory (up to several hundred Even thousands) need to be distributed on the spherical array and required to point to the center of the sphere. Some require the true north direction. The zero direction of the spherical center turntable needs to be aligned with the zero position of the spherical array; inertial navigation test products need to determine the true north direction; inertial navigation test products need to determine the true north direction. The pilot test turntable needs to detect the accuracy of the rotation. With the development of my country’s national defense, aviation and manned space industry, these fields and disciplines are in urgent need of high-precision directional measurement technology support.

Azimuth Datum and Azimuth Datum Device

In situations where north direction information needs to be frequently used for reference, it is often necessary to save the azimuth information and establish various azimuth datums, such as the calibration azimuth of various instruments and equipment, the azimuth of landmarks, the north direction of the turntable installation, etc. The north direction of these datums Errors will directly affect the quality of work, such as inertial instrument testing accuracy, engineering construction azimuth accuracy, etc. The accuracy is often required to be as high as arcsecond level or above. In application scenarios such as dynamic initial calibration, static initial calibration, and direction control of radars, antennas, vehicles, etc., the fiber optic gyro north seeker ER-FNS-02 is a perfect match for these working scenarios and has the characteristics of strong stability and high reliability. , the accuracy reaches (0.02°-0.1°), used for high-precision initial alignment and direction control solutions, providing a lot of convenience for work. Accuracy can improve relatively over time. The north-finding time of a gyro-theodolite generally takes about 5 to 20 minutes, and the accuracy can reach 10”.

In the measurement application of the centerline of tunnel projects, the north-seeking accuracy is extremely high, generally around 0.005°. High-precision sensors must be selected as the north-finding instrument, such as RLG laser sensors as the north-seeking instrument. The aiming of weapon systems in the military generally uses sensors of about 0.5°~0.02°. The requirements for azimuth reference and azimuth reference devices are also relatively high. For calibration devices, sensors of 0.001° are generally used as north seekers.The application scope of the north seeker is quite wide. It plays an important role in modern national defense construction and national economic construction. If the north seeker does not meet your own requirements, you should choose it according to your own application needs and the parameters of the north seeker. Select or customize to achieve coordination between north-finding accuracy and north-seeking speed.

If you are interested in this north finder, you can leave me a message or send a quote and I will send you the price and technical description.
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How to choose an inertial measurement unit (IMU) for drone applications?

An Inertial Measurement Unit (IMU) is an electronic device that uses accelerometers and gyroscopes to measure acceleration and rotation, which can be used to provide position data.

IMUs are essential components in unmanned aerial systems (UAVs, UAS and drones) – common applications include control and stabilization, guidance and correction, measurement and testing, and mobile mapping.

The raw measurements output by an IMU (angular rates, linear accelerations and magnetic field strengths) or AHRS (roll, pitch and yaw) can be fed into devices such as Inertial Navigation Systems (INS), which calculate relative position, orientation and velocity to aid navigation and control of UAVs.

There are many types of IMU, some of which incorporate magnetometers to measure magnetic field strength, but the four main technological categories for UAV applications are: Silicon MEMS (Micro-Electro-Mechanical Systems), Quartz MEMS, FOG (Fiber Optic Gyro), and RLG (Ring Laser Gyro).

Silicon MEMS IMUs are based around miniaturized sensors that measure either the deflection of a mass due to movement, or the force required to hold a mass in place. They typically perform with higher noise, vibration sensitivity and instability parameters than FOG IMUs, but MEMS-based IMUs are becoming more precise as the technology continues to be developed.

MEMS IMUs are ideal for smaller UAV platforms and high-volume production units, as they can generally be manufactured with much smaller size and weight, and at lower cost.

FOG IMUs use a solid-state technology based on beams of light propagating through a coiled optical fiber. They are less sensitive to shock and vibration, and offer excellent thermal stability, but are susceptible to magnetic interference. They also provide high performance in important parameters such as angle random walk, bias offset error, and bias instability, making them ideal for mission-critical UAV applications such as extremely precise navigation.

Higher bandwidth also makes FOG IMUs suitable for high-speed platform stabilization. Typically larger and more costly than MEMS-based IMUs, they are often used in larger UAV platforms.

RLG IMUs utilise a similar technological principle to FOG IMUs but with a sealed ring cavity in place of an optical fiber. They are generally considered to be the most accurate option, but are also the most expensive of the IMU technologies and typically much larger than the alternative technologies.

Quartz MEMS IMUs use a one-piece inertial sensing element, micro-machined from quartz, that is driven by an oscillator to vibrate at a precise amplitude. The vibrating quartz can then be used to sense angular rate, producing a signal that can be amplified and converted into a DC signal proportional to the rate. These factors make it ideal for inertial systems designed for the space- and power-constrained environments of UAVs.

More information:

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How do MEMS Tilt Sensors Work?

 MEMS tilt sensors, as the name suggests, are tilt sensors manufactured by MEMS (microelectromechanical system) technology, which has the obvious advantage of very accurate measurement.

Here we explain the principle of MEMS tilt sensor through an example.

In simple terms, the MEMS tilt sensor is a non-contact measurement of the inclination of the target object through the Earth's gravity. In essence, the tilt sensor measures acceleration, especially gravitational acceleration, so it has an integrated accelerometer chip. The acceleration sensor chip consists of a MEMS sensing component and a peripheral signal processing circuit. The MEMS sensing components are shown as follows:

The blue part of the MEMS sensing component is mobile, while the red part is fixed. When accelerating or decelerating, the blue part will move left or right, and the capacitance between the blue and red parts will change accordingly. Acceleration can be determined by measuring the capacitors C1 and C2. As shown in the picture below:

That is, the acceleration or deceleration that occurs when the object is tilted causes the movable part of the MEMS sensing component to move to one side, as shown below:

It can be seen from this principle that the MEMS sensing component is very sensitive to vibration during the measurement process, and the vibration of the measured object will affect the measurement result. So filters must be added to eliminate interference beyond a certain frequency. Some MEMS tilt sensor manufacturers will also be equipped with filters according to user needs. There are two types of filters: Butterworth filters and Critically damped filters. Batvots is more suitable for measuring non-moving, high vibration objects, such as large drilling platforms; Critical damping filters are more suitable for measuring moving objects, such as engineering vehicles, agricultural vehicles, etc. The vast majority of tilt sensors on the market today are equipped with Butterwart filters only, or no filters at all.

Ericco’s ER-TS-3160VO built-in (MEMS) solid pendulum measures the change of static gravity field, which is converted into the change of inclination, and the change is output through the voltage (0~10V, 0~5V optional).

If you want to learn more about MEMS tilt sensors or buy

Please contact me in the following ways:

Email: info@ericcointernational.com

Whatsapp: 173 9198 8506

Difference Between An Accelerometer And A Gyroscope

 Accelerometer and gyroscope are two kinds of sensors commonly used in vibration monitoring of structures. They all measure changes in vibration or displacement by sensing changes in an object’s acceleration or angular velocity. But there are some differences in how they work and how they are applied. The following will be a detailed introduction to the role and differences between accelerometers and gyroscopes.

The function and principle of accelerometer

The accelerometer is used to measure acceleration. A triaxial accelerometer can be used to measure the motion of a fixed platform relative to the earth’s surface, but once the platform moves, the situation becomes more complex.  For example, the ER-3QA-02E is a high-performance three-axis accelerometer with digital output, high precision installation error, temperature compensation, and low power consumption.If the platform is free falling, the accelerometer measured the acceleration value is zero. If the platform is moving in a certain direction, the acceleration values of each axis will contain the acceleration value generated by gravity, so that the true acceleration value cannot be obtained. For example, the triaxial accelerometer mounted on the 60-degree roll Angle plane will measure the vertical acceleration value of 2G, whereas in fact the plane’s surface is about 60 degrees. Therefore, using the accelerometer alone cannot keep the aircraft in a fixed course.

The function and principle of gyroscope

Gyroscope measures the rate of rotation of the body around an axis. When the gyroscope is used to measure the rotation Angle of the aircraft’s body axis, if the plane is rotating, the measured value is non-zero, and the value of the measurement is zero when the plane is not rotating. Therefore, the angular velocity value of the gyroscope measured at the 60-degree roll Angle is zero, and the angular rate is zero when the plane is flying in a straight line. The current roll Angle can be estimated by the time integral of the angular velocity value, provided there is no error accumulation. Gyroscope to measure the value of the drift with time, after a few minutes or a few seconds will be the additional error accumulation, and eventually lead to the current relative horizontal roll Angle to the plane completely wrong cognition. Therefore, the use of gyroscopes alone cannot maintain a particular course of the aircraft.

The difference between accelerometers and gyroscopes

Accelerometers and gyroscopes are both sensors used to sense changes in vibration or displacement of structures, but there are some important differences between them.

1. Different measurement methods

The accelerometer mainly measures the linear acceleration of the object, while the gyroscope mainly measures the angular acceleration and angular velocity of the object. Their measurement methods are different, so they are suitable for different vibration test occasions. The high performance quartz flexible accelerometer represented by ER-QA-03A adopts high quality quartz crystal to achieve high precision acceleration measurement and has extremely high reliability and stability. Its special flexible construction enables it to adapt to high acceleration applications under various environmental conditions, such as high temperature, high pressure and high vibration environments.

2. Different measurement directions

The accelerometer mainly measures the vibration acceleration of the structure in the x, y and z directions, while the gyroscope mainly measures the angular velocity of the object in the x, y and z axes. Therefore, they are suitable for vibration tests that are not coaxial upwards.

3. Different application fields

Accelerometers are mainly used in the field of structural vibration testing, while gyroscopes can be used in a wide range of object motion testing fields, such as drones, aerospace and so on.
In summary, accelerometers and gyroscopes are commonly used sensors for vibration testing of structures and motion testing of objects. They have their own characteristics and application range. Accelerometers are generally more commonly used than gyroscopes in vibration measurement applications, but in the measurement of angular displacement and velocity of objects, gyroscopes are more suitable.

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IMU in Drones

The inertial measurement unit works by detecting the current acceleration using one or more accelerometers. IMUs use one or more gyroscopes to detect changes in rotation properties such as pitch, roll and yaw. Some IMUs on drones include magnetometers, which are primarily used to assist in calibration to prevent directional drift.

Onboard processors constantly calculate the drone’s current position. First, it integrates the perceived acceleration with an estimate of gravity to calculate the current velocity. The velocity is then integrated to calculate the current position.

To fly in any direction, the flight controller collects IMU data for the current position and then sends the new data to the motor Electronic Speed Controller (ESC). These electronic speed controllers send the thrust and speed signals needed for the quadrotor to fly or hover to the motor.

Now, you can have the best 6-axis gyroscope technology, but if your drone hardware (propellers, motors, bearings, shafts, etc.) is not straight, clean, or functioning properly, the drone will still fly irregularly or even crash.

It is always a good idea to inspect the parts of the drone before and after each flight. It’s a good idea to have spare parts in case they crack or bend. Keeping drones clean is another good practice. To check whether the propeller is straight, it is best to have a propeller balancer. If all the components look normal and the drone is flying erratically, put it back immediately.

If the drone flies erratically, recalibrate the IMU on a flat surface. Sometimes you need to calibrate the IMUs multiple times. You should also check the drone manufacturer’s website for firmware updates to address any issues within the flight controller. If there are other problems, then the drone could have a hardware failure in the IMU or flight controller.For example, the ER-MIMU-02 developed by Ericco has high performance and small size;

Gyroscope bias instability: 0.05 degrees/hour. It has a wide range of applications. It can be used not only on drones, but also in many fields such as mining and drilling. If you want to know more about IMU products, please click the link below and contact us.

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