Do You Know What IMU is?

Gyroscopes and accelerometers are the main components of IMU, and their accuracy directly affects the accuracy of inertial system. In practical work, due to various inevitable interference factors, gyroscopes and accelerometers produce errors. From the initial alignment, its navigation error increases with time, especially the position error, which is the main disadvantage of inertial navigation system. Therefore, it is necessary to use external information to realize integrated navigation, so as to effectively reduce the problem of error accumulation with time. In order to improve reliability, more sensors can be equipped for each shaft. Generally speaking, IMU should be installed on the center of gravity of the measured object.

Generally, an IMU includes three single axis accelerometers and three single axis gyroscopes. The accelerometers detect the acceleration signals of the independent three axes of the object in the carrier coordinate system, while the gyroscopes detect the angular velocity signals of the carrier relative to the navigation coordinate system, measure the angular velocity and acceleration of the object in three-dimensional space, and calculate the attitude of the object based on this. It has very important application value in navigation.

IMU is mostly used in devices that need motion control, such as cars and robots. It is also used in occasions that require precise displacement estimation with attitude, such as inertial navigation equipment of submarines, aircraft, missiles and spacecraft.

🎀Summary

Using the three-axis geomagnetic decoupling and three-axis accelerometer, it is greatly affected by the acceleration of external forces. In the environment of motion / vibration, the output direction angle error is large. This field magnetic sensor has shortcomings. Its absolute reference is the magnetic line of force of the geomagnetic field. Geomagnetism is characterized by a wide range of use, but the intensity is low, about a few tenths of a Gauss, which is very easy to be disturbed by other magnets. If the instantaneous angle of the z-axis gyroscope is combined, It can make the system data more stable. The acceleration is measured in the direction of gravity. In the absence of external force acceleration, it can accurately output the roll/pitch two axis attitude angle, and this angle will not have cumulative error, which is accurate in a longer time scale. However, the disadvantage of the acceleration sensor in measuring the angle is that the acceleration sensor actually uses MEMS technology to detect the small deformation caused by the inertial force, and the inertial force is the same as gravity in essence, so the accelerometer will not distinguish the acceleration of gravity and the acceleration of external force. When the system changes speed in three-dimensional space, its output is incorrect.

The output angular velocity of the gyroscope is an instantaneous quantity, which cannot be directly used in attitude balance. The angular velocity and time integration are required to calculate the angle. The angle change obtained is added to the initial angle to obtain the target angle. The smaller the integration time DT is, the more accurate the output angle is. However, the principle of gyroscope determines that its measurement benchmark is itself, and there is no absolute reference outside the system. In addition, DT cannot be infinitely small, so the cumulative error of integration will increase rapidly with the passage of time, resulting in the output angle inconsistent with the actual, so the gyroscope can only work in a relatively short time scale.

Therefore, on the basis of no other reference, in order to obtain a more real attitude angle, we should use the weighting algorithm to develop strengths and circumvent weaknesses, combine the advantages of the two, abandon their respective shortcomings, and design an algorithm to increase the weight of the gyroscope in a short time scale, and increase the speed weight in a longer time scale, so that the system output angle is close to the real value.

🎀Working principle of IMU

IMU is a strapdown inertial navigation system. The system consists of three acceleration sensors and three angular velocity sensors (gyroscopes). The accelerometer is used to sense the acceleration component of the aircraft relative to the vertical line of the ground, and the velocity sensor is used to sense the angle information of the aircraft. This sub component is mainly composed of two a/d converters ad7716bs and 64K e/eprom memory X25650. The a/d converter uses the analog variables of each sensor of IMU, After being converted into digital information and calculated by CPU, the aircraft pitch angle, tilt angle and sideslip angle are finally output. The e/eprom memory mainly stores the linear curve diagram of each IMU sensor and the part number and serial number of each IMU sensor. When the part is just started, the image processing unit reads the linear curve parameters in e/eprom to provide initial information for subsequent angle calculation. Ericco provides FOG IMU and MEMS IMU solution, if you are interested, please feel free to contact us.

If you want to know more about IMU, please contact me through the following ways:

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Tilt Sensor for 360° Dip Angle Measurement Under Coal Mine

Ericco 360D tilt sensor is designed by Ericco sensor for measuring tilt angle in coal mines. The tilt sensor can also be used in mining, steel, chemical industry and other fields that need to measure or control perpendicularity or tilt angle. Tilt sensors can be safely used in coal mines, oil fields and other environments with explosive gases.

360° Tilt Sensor (ER-TS-4250VO) Parameters:

Protection: intrinsically safe circuit design

Output interface: RS232,TTL, RS485,RS422, CAN, 0-5V, 0-10V, 4-20mA, 0-20mA optional, maximum output current＜45mA, accuracy class ≤0.1°, basic error＜+0.1%FS, protection level IP67

Measurement angle range: X.Y dual axis 0°~360° in any specified angle.

2. Material of tilt sensor:

The shell material of the tilt sensor is brass, fully sealed, and the leading wire is the mine explosion-proof flame-retardant wire, with high safety.

Ericco 360D Tilt sensor Features:

Easy installation, shock resistance, vibration resistance, high reliability, oil and corrosive gas resistance, explosion proof, cost-effective.

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

Please contact me in the following ways:

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What is Sensitivity and Measurement Range in Quartz Accelerometer?

 A quartz accelerometer is an instrument used to measure acceleration, commonly found in physics, engineering, and other related fields. When  design and select the quartz accelerometer,we need to consider the main specifications are: measurement range, sensitivity. The sensitivity of acceleration sensor is one of the most basic indicators of sensor. The sensitivity of the sensor directly affects the measurement of vibration signal. The measurement range of the acceleration value sensor refers to the maximum measurement value that the sensor can measure within a certain nonlinear error range. The nonlinear error of the universal piezoelectric acceleration sensor is mostly 1%. As a general principle,the higher the sensitivity, the smaller the measurement range,and the smaller the sensitivity, the larger the measurement range.

The sensitivity of the  quartz accelerometer

Sensitivity refers to the degree of response of a quartz accelerometer to changes in acceleration, usually expressed by changes in output voltage or current caused by changes in unit acceleration. The higher the sensitivity, the stronger the quartz accelerometer’s ability to detect small acceleration changes. Quartz accelerometer sensitivity – generally expressed in units such as WV/g or pC/g.

The capacitance of quartz flexible accelerometer is an important factor affecting its sensitivity. Generally,the larger the capacitor, the higher its vibration sensitivity, but the higher the sensitivity, the noise immunity will be reduced accordingly. Therefore, the capacitance size of the quartz flexible accelerometer needs to be selected reasonably.

The measuring range of the quartz  accelerometer

The measuring range of the quartz accelerometer is the maximum acceleration that can be measured under the specified performance index, which is measured and evaluated from both positive and negative directions. The level of acceleration supported by the acceleration sensor output signal specification is usually expressed as ±g, which is the maximum acceleration that the device can measure and accurately represent through its output. The ER-QA-03B designed for this purpose has measurement range of ±70g and bias repeatability of 10-30μg and scale factor repeatability of 15-50ppm. It is of great significance to improve the measuring range of quartz flexible accelerometer. First, with the rapid development of strapdown inertial navigation systems in recent years, the range of accelerometers that are required to be sensitive to has increased exponentially. If the magnitude of the linear acceleration exceeds the measurement range of the accelerometer, noise can be found in the output of the accelerometer, in which case the accelerometer does not properly reflect the input motion acceleration. Therefore, expanding the measuring range of quartz flexible accelerometer is an important strategic means to meet the needs of model development. In addition, the application field of quartz flexible accelerometer has gradually expanded, and many application fields have wider and wider measurement range requirements.

Application characteristics

The two basic indicators of sensitivity and measurement range have different requirements for different application scenarios. In the selection of quartz accelerometer, it is necessary to consider these indicators according to the actual needs to choose the most suitable quartz accelerometer. For example, in the field of aerospace, quartz accelerometers are required to have high sensitivity and a wide frequency response range in order to detect small changes in acceleration, and ER-QA-03A is designed for applications in this field with zero bias repeatability of 10-50μg and scale factor repeatability of 15-50 PPM. The second-order nonlinear repeatability is 10-30μg/g2.In the industrial production process, the linearity and temperature stability of the quartz accelerometer are required to ensure the accuracy of the measurement results.

Quartz  accelerometer has been widely used in various inertial navigation systems, and is one of the important measurement sensitive components in inertial navigation systems. With the development of inertial navigation systems, the requirements for inertial devices are becoming higher and higher. Sensitivity and measurement range as the most basic indicators of quartz accelerometer, but also the breakthrough point of the future development of quartz accelerometer technology.

If you want to know more about quartz accelerometers , please contact me through the following ways:

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What are the Advantages of Tilt Sensor

 

The tilt sensor is a very accurate measuring tool for small angles. It can measure the inclination of the measured plane relative to the horizontal position, the parallelism and perpendicularity of the two components. It has become an indispensable and important measuring tool in bridge construction, railway laying, civil engineering, oil drilling, aviation and navigation, industrial automation, intelligent platform, mechanical processing and other fields.

1. The principle of tilt sensor

The working principle of the inclination 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 tilt 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

The main benefits of tilt sensors include:

2.1 High Precision

The 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. ER-TS-12200-Modbus is a high-precision wireless inclination sensor, its accuracy can reach 0.001°, using industrial MCU, three-proof PCB board, imported cables, wide temperature metal shell and other measures, its industrial design has extremely high measurement accuracy and anti-interference ability. It is suitable for remote real-time monitoring and analysis of industrial sites, dilapidated buildings, ancient buildings, civil engineering, tilt deformation of various towers and other needs.

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. ER-TS-32600-Modbus its volume is 94*74*64mm, weight is only 460g, very easy to install and carry. Is an ultra-low power consumption, small volume, high-performance wireless inclination sensor, it uses lithium battery power, based on the Internet of Things technology Bluetooth and ZigBee(optional) wireless transmission technology, it meets the needs of users in industrial applications without power supply or real-time dynamic measurement of object attitude angle.

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. For example, the ER-TS-3160VO, which has a seismic resistance higher than 20000g, is adopted IP67 protection grade, it has the characteristics of strong shock and vibration resistance, especially suitable for a variety of harsh industrial environments.

Summary: With the continuous development of technology, inclination sensors will have wider prospects and advantages.

1. High precision and stability: With the continuous improvement of measurement accuracy and stability requirements in various fields, the future development direction of inclination sensors will be to improve the accuracy and stability of induction components.

2. Multi-functional: the inclination sensor will gradually develop in the direction of multi-functional, such as integrating the functions of gyroscopes, magnetometers and other sensors to achieve the measurement of a variety of parameters.

3. Intelligent: inclination sensor will be combined with artificial intelligence, internet of things and other technologies to achieve intelligent perception and data processing, improve application efficiency and user experience.

4. Miniaturization: In order to meet the application needs of some special scenarios, the volume of the inclination sensor will gradually shrink and develop in the direction of miniaturization.

5. Wide application: With the continuous progress of inclination sensor technology and the expansion of application scenarios, its application in various fields will be more extensive, bringing more convenience to people’s life and work.

Brief Introduction 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.

There are many types of accelerometers. Micro-mechanical accelerometers, also known as silicon accelerometers, are now widely used. The principle of sensing acceleration is the same as that of general accelerometers. According to the different reading elements, micro-mechanical accelerometers are classified into piezoresistive accelerometers, capacitive accelerometers, resonant beam accelerometers, and electrostatic force balanced accelerometers. The micro-mechanical accelerometer is small in size, easy to install, simple in measurement method, low in cost and strong in anti-overload capability, and satisfies the requirements for the structure and space limitation of the micro-mini aircraft.

Accelerometers consist of test masses (also called sensitive masses), supports, potentiometers, springs, dampers, and housings.  The detected mass is constrained by the support and can only move along the axis, which is often called the input axis or the sensitive axis. According to the number of input shafts, there are single-axis, dual-axis and triaxial accelerometers.

With the development of MEMS technology, inertial sensor is one of the most widely used MEMS devices, and micro-accelerometer is an outstanding representative of inertial sensor. The theoretical basis of the microaccelerometer is Newton’s second law, according to the basic principles of physics, within a system, the speed cannot be measured, but its acceleration can be measured. If the initial velocity is known, the linear velocity can be calculated by integrating, and the linear displacement can then be calculated. Combined with a gyroscope (used to measure angular velocity), the object can be precisely positioned. The high-precision MEMS accelerometer ER-MA-5 has a bias stability of 5 ug and a monthly bias repeatability of 100-300 ug.

Application

Car safety system

Accelerometers play an important role in automobile safety system. For example, when a car is in a collision, the accelerometer can detect changes in the vehicle’s acceleration and send signals to the airbag system to inflate it at the appropriate time, protecting the driver and passengers. In addition, accelerometers can also be used in vehicle stability control systems to help vehicles in emergency situations. Keep it steady.

Aerospace

Accelerometers are also widely used in the aerospace field. During a rocket launch, for example, an accelerometer can measure changes in the rocket’s acceleration to help control the trajectory of the rocket. In addition, the accelerometer can also be used in the aircraft’s autopilot system to help maintain stability.For example, the ER-QA-03A accelerometers commonly used in the aerospace field have a  bias stability of 10-50μg, and the Scale factor repeatability is 15-50ppm.

The existing problems and development trend 

The advancement of MEMS technology and the improvement of technological level also bring new opportunities to the development of micromechanical accelerometers. By understanding the research dynamics of micromechanical accelerometers at home and abroad, there are several development trends of micromechanical accelerometers in the future:

1. The  micromechanical  accelerometer with high resolution and large range has become the focus of research. Because the inertial mass block is relatively small, the inertial force used to measure acceleration and angular velocity is correspondingly small, and the sensitivity of the system is relatively low, so it is particularly important to develop a high-sensitivity accelerometer.

2. The development of multi-axis accelerometers has become a new direction. The inertial measurement combination has six output variables, three of which are mutually positive accelerations on the X, Y, and Z axes. There have been literature reports on the development of triaxial micro-silicon accelerometers, and the methods used are different, but its performance is still a long way from practical, and the structural design of multi-axis accelerometers is still a difficult point.

3. small temperature drift, small hysteresis effect has become a new performance target. The accuracy of micromachined accelerometers can be greatly improved by selecting suitable materials, adopting reasonable structure and applying new low-cost temperature compensation link.

If you want to get more details about quartz-accelerometer, pls visit https://www.ericcointernational.com/accelerometer/quartz-accelerometer/

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 What sensors are inside the IMU and how do they work?

Inertial measurement units typically consist of three different types of sensors. The first type of sensor is an accelerometer, which measures acceleration, or the rate at which an object accelerates or decelerates. While there are many different sensor technologies for accelerometers, by far the most common for wearable applications is MEMS (microelectromechanical systems). MEMS are sensor systems composed of electrical and mechanical components, typically etched from micron-sized silicon.

Whenever the MEMS accelerometer experiences acceleration, the proof mass also experiences that acceleration. An etched spring set resists this acceleration. Using Hooke’s law (spring force is proportional to the distance the spring is compressed) and Newton’s second law (force is proportional to acceleration), check that the distance a mass moves is proportional to the acceleration it experiences (see figure below). This movement is sensed using the electrical properties of capacitance, which is related to the distance between two conductors. A set of electronics is then able to measure the change in capacitance, calibrate the signal, and further process it to give acceleration.

The second type of sensor in an Inertial measurement unitis a gyroscope, which measures angular velocity, or the speed and direction of an object’s rotation or spin. Gyroscopes also typically use MEMS technology, although they are more complex than MEMS accelerometers. The main physical phenomenon used in gyroscopes is the Coriolis effect, which describes the forces involved when an object moves in a rotating reference frame.

MEMS gyroscopes have masses that reciprocate at a constant frequency. During the rotation of the gyroscope, due to the Coriolis effect, the mass will induce a force perpendicular to the direction of the reciprocating motion. This force is counteracted by an etched spring and sensed by a capacitive sensing arm such as an accelerometer. Signal processing electronics then process the change in capacitance relative to the reciprocating motion of the resonant mass (see figure below).

The final sensor commonly found in Inertial measurement units is a magnetometer, which measures the strength of a magnetic field and acts somewhat like a digital compass. Most magnetometers use the Hall effect to measure magnetic field strength. The basic premise of a magnetometer is that electrons moving in a conductor are deflected by the magnetic field to which the conductor is exposed. When charges pass through a conducting plate in a magnetic field, the magnetic field deflects the electrons to one side of the conducting plate. As more negative charge builds up on one side of the plate and more positive charge builds up on the other side of the plate, there is a measurable voltage between the two sides of the plate that is proportional to the strength of the magnetic field.

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Ericco’s Tilt Sensor Successfully Realizes Three Screen Display

 

Ericco’s sensor R & D department successfully achieved the tilt sensor data in the mobile phone screen, touch screen and computer screen display at the same time, it is reported that this is the first time to achieve the domestic attitude angle sensor data in the three terminals at the same time display, representing the domestic industry data display and control technology.

A major feature of the three screens is that the three terminals can be operated as the control terminal, can read the historical data detected by the tilt sensor, can be downloaded and stored through the U disk, can achieve the observation data curve, can set the relative zero (such as ER-TS-3160VO tilt sensor), etc., powerful, easy to control.

Ericco sensor R & D department in the high-precision sensor design, dynamic sensor research and development, digital display and control technology and other fields to pursue excellence, courage to explore, continuous innovation.

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