How is IMU used?

The concept of IMU

The inertial measurement unit, referred to as IMU, is a device that measures the three-axis attitude angle (or angular velocity core) and acceleration of an object. Gyroscopes and speedometers are devices of an inertial navigation system.

The IMU has a built-in speed sensor and gyroscope, which can measure linear acceleration and rotational angular velocity in three directions.

Working principles for IMU

IMU is based on Newton’s laws of mechanics. By measuring the acceleration of the carrier in the inertial reference system, integrating it over time, and transforming it into the navigation coordinate system, the speed and yaw angle in the navigation coordinate system can be obtained. and location information.

The inertial measurement unit is a device that measures the three-axis attitude angle (or angular rate) and acceleration of an object. Generally, an IMU contains three single-axis accelerometers and three single-axis gyroscopes. The accelerometer detects the acceleration signals of the object in three independent axes of the carrier coordinate system, while the gyroscope detects the angular velocity signal of the carrier relative to the navigation coordinate system, and measures the object’s position in the carrier coordinate system. The angular velocity and acceleration in three-dimensional space are used to calculate the attitude of the object. It has very important application value in navigation.

The principle of an inertial measurement unit is very similar to taking small steps in the dark. In the dark, due to the error between your estimate of the step length and the actual distance walked, as you take more and more steps, the difference between your estimated position and the actual position will become farther and farther. When taking the first step, the estimated position is relatively close to the actual position; but as the number of steps increases, the difference between the estimated position and the actual position becomes larger and larger. This method is extended to three dimensions, which is the principle of the inertial measurement unit.

Therefore, in layman’s terms, the inertial measurement unit IMU is a strapdown inertial navigation system. The system consists of three acceleration sensors and three angular velocity sensors (gyros). The accelerometer is used to feel the acceleration component relative to the vertical line of the ground. The speed sensor is used to get a feel for the angle information.

It is worth noting that the inertial measurement unit provides relative positioning information. Its function is to measure the movement route of the object relative to the starting point, so it cannot provide information about your specific location. Therefore, it is often combined with GPS. Used together, when the GPS signal is weak in some places, the IMU can play its role, allowing the car to continue to obtain absolute position information and not get “lost.”

How three-axis accelerometer works

Most three-axis acceleration sensors use piezoresistive, piezoelectric and capacitive operating principles. The resulting acceleration is proportional to changes in resistance, voltage and capacitance and is collected by corresponding amplification and filtering circuits. This is the same principle as an ordinary acceleration sensor, so through certain technology, three single axes can be turned into a three-axis. For most sensor applications, a two-axis acceleration sensor is sufficient.

Working principle of three-axis gyroscope

The working principle of the three-axis gyroscope is based on the gyro effect. When the gyroscope’s axis of rotation is perpendicular to the direction of the force, it feels the force, which creates a torque that causes it to rotate in the coordinate system. The three gyroscopes in a three-axis gyroscope are mounted on three mutually perpendicular axes. They sense the angular velocity on the x, y, and z axes respectively, and output the signals to relevant circuits for processing.

Application areas and uses of IMU

Inertial navigation IMU has a wide range of application scenarios and is often used for pointing, steering and guidance monitoring, rock soil monitoring, etc. in advanced mining/drilling equipment, ships, automobiles, drones, robots, oil exploration, bridge exploration, high-rise buildings, iron towers, dams, etc. , navigation and positioning of transportation vehicles such as mining and missiles, and north-finding positioning in geodetic/land mobile mapping systems.

In the automotive field, inertial navigation IMU can help vehicles achieve autonomous driving and traffic jam identification, improving driving performance and safety. In land vehicles, IMUs can be integrated into GPS-based car navigation systems or vehicle tracking systems to provide dead reckoning capabilities to the system and the ability to collect as much accurate data as possible about the vehicle’s current speed, turn rate, heading and inclination and acceleration, combined with the vehicle’s wheel speed sensor output and reverse gear signal for purposes such as better traffic collision analysis. The ER-MG2-300/400 developed by ERICCO is a navigation-grade MEMS gyro sensor with a measurement range of up to 400 degrees/second and a bias instability of 0.05°/hour. It is designed for precision attitude in high-performance IMU/AHRS. Designed for azimuth measurement, positioning, navigation, guidance/GNSS-assisted INS, aviation/marine/land mapping/measurement systems/unmanned aerial vehicle/AUV and navigation-level MEMS weapon systems.

In the aviation field, inertial navigation IMU can realize motion control such as aircraft climbing, descending, turning, taxiing, etc., improving flight safety and accuracy. In a navigation system, data reported by the IMU is fed into a processor to calculate altitude, speed, and position. ER-MIMU-01 developed by ERICCO uses high-quality and reliable MEMS accelerometer and gyroscope. It communicates with the outside through RS422. The baud rate can be flexibly set between 9600~921600. The communication baud rate required by the user can be 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.

One of the earliest devices was designed and built by the Ford Instrument Company for the U.S. Air Force and was intended to help aircraft navigate in flight without requiring any input from outside the aircraft. The device, known as a ground position indicator, shows the pilot the aircraft’s longitude and latitude relative to the ground once the pilot inputs the aircraft’s longitude and latitude during takeoff.

A major disadvantage of using IMUs for navigation, then, is that they are often subject to cumulative errors. Because the guidance system continuously integrates acceleration versus time to calculate velocity and position (see dead reckoning), any measurement error, no matter how small, accumulates over time. This results in “drift”: an increasing discrepancy between where the system thinks it is and where it actually is. The ER-MG-067 developed by ERICCO is a high-precision tactical-grade MEMS gyroscope with an instability deviation of 0.3 degrees/hour and an angular random walk of 0.125°/√h. It is a single-axis MEMS angular rate sensor. (gyroscope), capable of measuring angular velocity up to ±400°/s, and the digital output complies with the SPI slave mode 3 protocol. Angular rate data is represented as 24-bit words.

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What is the Function of a Tilt Sensor in a Robot?

 

How tilt sensors work in robots, let's take a look.

A robot is a machine that performs work automatically. It can either be directed by humans, run pre-programmed programs, or act according to principles laid down by AI technology. Its mission is to help replace human jobs, such as manufacturing, construction, or dangerous jobs. The inspection robot is one of them. It carries a visible light camera, infrared thermal camera, pickup, ultrasonic wave, inclination sensor, etc. At the same time, it adopts trajectory navigation and can conduct autonomous or remote control inspection of outdoor high-pressure equipment according to the optimal path planning. Through machine vision, infrared temperature measurement, sound detection and other methods, the inspection robot can collect infrared heat map, image and audio information of the equipment. It also automatically identifies the thermal defects, abnormal appearance, switch or tool position, instrument reading, and oil level meter position of the equipment, generates unified and standardized alarm items and inspection reports, sends alarm information to the operator, and provides basic data for equipment status maintenance. In unattended, less attended substations or smart substations, especially in plateau, low oxygen, high cold and other geographical conditions or bad weather conditions, inspection robots can replace or assist manual inspection of substation equipment.

When the inspection robot is crossing obstacles, the partial moment caused by mass eccentricity damages the horizontal posture of the robot body. In order to ensure its smooth progress, a simple and reliable centroidness adjustment method is needed. The tilt sensor ER-TS-4258CU is used to measure the inclination angle between the robot body and the horizontal plane, so as to control the movement of the mobile motor of the counterweight block. When the center of mass of the robot is adjusted to the arm suspended on the overhead ground wire, the measurement angle should be controlled within the range of 90° with an accuracy of ±0.1°, so as to ensure that the robot body maintains a horizontal posture and ensure that the arm that needs to be off-line or online completes the corresponding action. Finally, the feasibility of the centroid control method is verified by simulation experiments.

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What Are The Components Of Accelerometers?

 Quartz accelerometer is a device that uses the piezoelectric effect of quartz crystal to measure acceleration. Quartz accelerometer has the characteristics of high precision, high stability and fast response, and has been widely used in space vehicle, navigation system, earthquake monitoring and other fields.

The structure of quartz accelerometer

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. Quartz crystals usually have a biaxial symmetrical structure and are composed of two piezoelectric crystal sheets. The piezoelectric axes of the two wafers are perpendicular to each other, allowing acceleration to be measured in any direction. The mass block is attached to the center of the quartz crystal, and when acceleration occurs, the mass block will move relative to the crystal, causing the crystal to produce pressure.

Electrodes are mounted on the surface of a quartz crystal and are used to measure the piezoelectric charge. When the crystal is subjected to pressure, the distribution of positive and negative charges inside the crystal changes, and positive and negative charges accumulate on the electrode, forming a potential difference. By measuring the potential difference on the electrode, the magnitude of the acceleration can be obtained indirectly.

Housing (fixed to the measured object), reference quality, sensitive components, signal output, etc. Accelerometers require a certain range and accuracy, sensitivity, etc. These requirements are often contradictory to some extent. Accelerometers based on different principles have different ranges (from a few g to hundreds of thousands of g), and their sensitivities to sudden acceleration frequencies are also different. The principles underlying common accelerometers are:

① The reference mass is connected to the housing by a spring (see figure). The relative displacement between it and the housing reflects the magnitude of the acceleration component. This signal is output as a voltage through a potentiometer;

② The reference mass is fixedly connected with the elastic thin rod and the shell. The dynamic load caused by the acceleration deforms the rod. The magnitude of the deformation is induced by the strain resistance wire. The output is an electrical signal proportional to the size of the acceleration disc;

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

④ The reference mass is connected to the case by a spring and placed inside the coil. The displacement reflecting the magnitude of the acceleration component changes the inductance of the coil, thereby outputting an electrical signal proportional to the acceleration. In addition, there are servo-type accelerometers, in which a feedback loop is introduced to improve the accuracy of the measurement. In order to measure the acceleration vector in a plane or space, two or three accelerometers are required, each measuring an acceleration component.

In the navigation system, the quartz accelerometer can be used to measure the acceleration of vehicles such as cars and aircraft, so as to achieve inertial navigation and positioning.

In earthquake monitoring, quartz accelerometers can be used to measure the acceleration of seismic waves, so as to study the occurrence mechanism of earthquakes and predict the risk of earthquakes.

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How to Correctly Select the Parameters of the Tilt Sensor

You need to choose your own tilt sensor according to your own needs.

Basic parameters of tilt sensor

1. Range

The range is the maximum range that can be measured by the sensor, which refers to the value of the difference between the upper and lower limits. Each sensor has its own measurement range, and when it is measured in this range, the output signal of the sensor has a certain accuracy. An acceleration sensor with a range of less than 1G is used as an inclination sensor, and a range of more than 1G is used as an acceleration sensor or vibration sensor. Because the larger the range, the less accurate. The biaxial tilt sensor ER-TS-4250VO can be selected in a range of +90°, while the uniaxial tilt sensor can be selected in a vertical direction of 360°.

2. Accuracy

In the process of testing and measurement, measurement errors are inevitable. There are two kinds of errors: systematic error and random error. The causes of system error, such as the inherent error of measurement principle and algorithm, inaccurate calibration, environmental temperature influence, material defects, etc., can be used to reflect the degree of influence of system error. The cause of random error is the gap of transmission components, aging of electronic components, etc. The precision can be used to reflect the influence of random error. Precision is a comprehensive index that reflects systematic error and random error, the higher the precision means the higher the accuracy and precision.

3. Zero offset

Zero drift means that when the input of the sensor is constant zero, the output value of the sensor will still change slightly to a certain extent. There are many reasons for zero drift, such as the change of the characteristics of the sensitive elements in the sensor with time, stress release, element aging, charge leakage, environmental temperature changes, etc. Among them, the zero drift caused by ambient temperature change is the most common phenomenon.

4. Input frequency

The frequency response characteristics determine the frequency range to be measured, and must allow the frequency range without losing the true measurement conditions, in fact, the sensor response will always have a certain delay. The higher the frequency response of the sensor, the wider the frequency range of the signal that can be measured, and the greater the interference. The lower the sensor frequency response, the narrower the frequency range of the signal that can be measured, and the lower the interference. In practical applications, a large number of measured signals are time changes, such as changes in current value, changes in object displacement, changes in acceleration, etc. This requires that the output of the sensor not only accurately reflect the size being measured, but also keep up with the speed of change being measured. In the frequency response range of the sensor, the amplitude of its output has a small change in the -constant range (maximum attenuation is 0.707). Therefore, when the input value is done sine

When changing, it is usually believed that the output value can correctly reflect the input value, but when the input value changes more frequently, the output value will produce significant attenuation, resulting in large measurement distortion.

5. Communication interface

RS232, TTL, RS485, RS232, CAN bus, voltage, current, SPI, IC, Profibus interface optional.If you want to learn more about tilt sensors or buy

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Application of Accelerometer in Vibration Detection

 Whether it is in consumer electronics, industrial automation or automotive applications, when monitoring the operating status and health status of the equipment, it is necessary to select the appropriate sensor according to the operation scenario of the equipment to ensure that the sensor can accurately obtain the information of the equipment, and detect, diagnose and even predict the fault.

Vibration detection is a practical measurement method. The detected vibration data is the key predictive variable for fault diagnosis. Accelerometer is a commonly used vibration detection sensor, widely used in consumer electronics, industrial automation, automotive sensing and other fields, it can collect the status information of a single device or the entire system, and then provide sensor data to facilitate the system to predict the state of the device or system.

With the rapid development of sensors, MEMS accelerometers have become the first choice for everyone. From the current products on the market, MEMS accelerometers are basically taking a capacitive route. This is because the piezoelectric MEMS accelerometer is supported internally by a rigid body. In general, it can only sense dynamic acceleration, but not static acceleration, so the application is limited. Capacitive MEMS accelerometers can detect both dynamic and static acceleration.       

Quartz flexible 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 the navigation, guidance, control and adjustment of various systems. It has been widely used in aerospace, aviation, ships, weapons, petroleum, geotechnical engineering and many other fields. Among them, the precision performance of quartz accelerometer products launched by ericco can reach the middle and high navigation level. Take ER-QA-03A as an example. its bias repeatability is 10-50μg,scale factor repeatability is 15-50 PPM and class II non-linearity repeatability is. Its bias repeatability is 10-50μg,scale factor repeatability is 15-50 PPM and class II non-linearity repeatability is 10 to 30 mu g/g2.

 Therefore, the accelerometer plays a very prominent role in vibration detection, with the improvement of the technology and accuracy of the accelerometer. In the future, accelerometers will be more widely used in the field of vibration detection.       

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How to choose MEMS IMU?

IMU (Inertial Measurement Unit) is an inertial measurement unit that can measure the three-axis acceleration and angular velocity of an object. It is generally used in the measurement part of the system to estimate the pose of the object. IMU generally includes a three-axis accelerometer and a three-axis gyroscope. The accelerometer detects the acceleration signal of the object on three independent axes of the carrier coordinate system, and the gyroscope detects the angular velocity signal of the carrier relative to the navigation coordinate system. The angular velocity and acceleration in space can solve the pose of the object. MEMS IMU is cheap and small, and is widely used in many fields such as navigation, drones, VR, robots, and smart bracelets. The detection accuracy of the IMU is very important to the overall performance of the system. If the noise detected by the IMU is very noisy, then the feedback the system gets is wrong, just like human eyes, ears and other sense organs get wrong information. How can we move freely? The bottom layer of the system is the foundation. If the bottom layer of the system is unstable, it will be difficult for the upper layer to function well. ERICCO has always strictly controlled the accuracy of IMU and has been pursuing the improvement of IMU system. Next, ERICCO will also launch new high-precision IMU products.

1. Zero bias temperature hysteresis characteristics

The zero-bias temperature hysteresis characteristic means that the corresponding zero-bias of the IMU is inconsistent during the heating phase and the cooling phase. Some IMU data manuals will give the zero-bias temperature hysteresis characteristic curve, and some will not. It is best to test it when applying the IMU. Since the IMU zero bias estimate is calibrated based on temperature (the IMU calibration algorithm is introduced in detail), if the temperature lag difference is not too large, the calibration accuracy will be relatively high; if the IMU zero bias hysteresis value is too large, the IMU zero calibration error will be relatively high. large, thus affecting the fusion effect.

2.Vibration characteristics

In the case of external vibration, the variation characteristics of IMU deviation with vibration frequency. Some MEMS IMU chips have abnormal frequency characteristics under high-frequency excitation. For applications such as rotor drones that are prone to high-frequency vibrations, vibration characteristics are generally tested. If the IMU frequency characteristics are abnormal, you can consider it. Add shock absorbers.

3. Effect of repeated power-on on IMU deviation

Ideally, it is thought that under the same external conditions, the bias of the IMU will remain the same each time it is powered up. In fact, under the same external conditions, the bias of the IMU will be different every time the IMU is powered up. If the difference is relatively large, it will be zero. The bias estimation error will be relatively large, affecting the fusion effect.

4. The impact of stress on prejudice

The influence of stress on IMU includes: the influence of stress moment on offset, and the influence of different stresses on offset. The stress mainly comes from: the stress exerted by the PCB board on the IMU chip and the stress exerted by the temperature control device on the IMU chip. If the IMU bias is too sensitive to the impact of stress, it will also affect the zero drift estimation error, thus affecting the fusion effect.

5. Impact of impact on zero deviation

When the IMU is subjected to an external impact (on the order of tens of G), it is possible that the IMU will get stuck or the deviation will change. In general, testing should be done.

6. Nonlinear factor (%Fs)

Ideally, we consider the sensor data to be linear over this range. In fact, the sensor changes are non-linear. As shown in Figure 2, the nonlinear characteristics of the IMU need to be tested before use. If the nonlinearity is too severe, nonlinear calibration should be performed. There are many such calibration methods, such as proportional calibration, quadratic fitting calibration, etc.

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Application of Tilt Sensor in Monitoring of Sand Dredging Ship

 

Tilt sensor can measure the pitch angle and roll angle of fishing vessel in real time.

Sand dredgers, fishing vessels, that is, fishing vessels, can carry out class fishing, processing, transportation vessels collectively referred to. Fishing vessels are vessels that catch and harvest aquatic plants and animals, and also include some of the auxiliary vessels of modern fishing production, such as vessels that carry out aquatic product processing and transportation, aquaculture, resource surveys, fisheries guidance and training, and fisheries administration tasks.

Most fishing vessels are small, in order to adapt to continuous navigation and operation in the wind and waves, they require better stability, seakeeping and seaworthiness, and the structure needs to be particularly strong. During the operation of the fishing vessel, the load varies greatly and is small and medium.

Type II fishing vessels are generally tens to hundreds of tons; Large fishing vessels up to 1,000 tons, even up to more than 40,000 gross tons. In addition to the general Marine equipment, the fishing boat also needs to be equipped with fishing and navigation communication instruments such as winch, tilt sensor and navigator. In particular, the tilt sensor, which plays a very important role for the driver, is an instrument for measuring the tilt angle of the object in real time. The ER-TS-3160VO tilt sensor can measure the real-time pitch angle and roll angle of the fishing vessel in real time, and can be displayed through the corresponding display instrument, so that the driver can control the current operating attitude of the ship in real time, and adjust the running direction in time. Thus, it is easier for the stable operation of the ship, and it has gradually become one of the indispensable instruments most commonly used by the driver.
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