Analysis of Technical Issues in Extending the Service life of Gyro Theodolite

https://www.ericcointernational.com/application/analysis-of-technical-issues-in-extending-the-service-life-of-gyro-theodolite.html

The gyro theodolite is a high-precision precision directional instrument that integrates light, machinery and electricity and is widely used in mining, construction, surveying and mapping, military, aviation, aerospace and other fields. Because it is not limited by time and environment, observation is simple, convenient and efficient, and it can ensure high accuracy, so it is an advanced directional instrument. Compared with traditional geometric orientation, gyroscopic orientation has huge advantages; compared with GPS global positioning system, it is not subject to electromagnetic wave propagation conditions and still has many advantages. Especially in production mine measurement, it is currently the most advanced directional instrument. However, due to some limitations in the design of domestic gyro-theodolite, most of the gyro-theodolite in most production units and colleges and universities in my country have been damaged to varying degrees, which not only increases the repair cost sharply, but also seriously affects production, teaching and research. In view of this, the author conducted research on how to improve the service life of the gyro-theodolite based on the principle and use experience of the gyro-theodolite, and improved some circuits to provide specific methods to extend the service life of the gyro-theodolite.

1.The composition and working principle of the gyro-theodolite

1∙1 Composition of gyroscopic theodolite

 

The gyro-theodolite consists of a gyroscope, theodolite, and an inverter power supply. The functions of each part are as follows:

Theodolite: Determination of direction value during orientation;

Gyroscope: Determination of true north direction when orienting;

Inverter power supply: Convert 24V DC power into 36V, 400Hz, three-phase medium-frequency AC power through the inverter circuit to drive the gyro motor to rotate at high speed to achieve orientation.

 

1.2 Working principle

Suppose a gyro theodolite is set up on the earth's surface at a geographical latitude of , and point O is the intersection point between the gyro room and the suspension. With O as the origin, establish a coordinate system OXYZ fixed to the ground. The OX axis points horizontally to the north, and the OY axis points horizontally to the west. OXYZ rotates at the Earth's rotation angular speed of relative to the geocentric reference frame.At the same time, a moving coordinate system Oxyz fixedly connected to the gyro room is established at point O. The Ox axis is parallel to the main axis of the gyro. Looking in the forward direction counter to the Ox axis, the top rotates counterclockwise, and the angles are all counterclockwise. The meaning of angle is the deflection angle of the main axis relative to the meridian plane, the angle is the pitch angle of the axis relative to the horizontal plane, and the angle is the nutation angle of the gyro. The principle is shown in Figure 1.

Figure 1 Principle of gyro-theodolite gyro motion

 

2.Factors that restrict the service life of gyro theodolite and methods to extend its service life

From the working principle of the gyro theodolite, it can be seen that in order to measure the true azimuth angle of a certain side of the mine, it is necessary to observe the gyro movement for a long time. The gyro motor works in a high-speed rotation state. Therefore, the factors that restrict the service life of the gyro should be studied from the following aspects. consider.

 

2∙1 Instrument factors

The instrument factors that affect the service life of gyroscopes are mainly analyzed from the two aspects of gyro motor and inverter power supply. At present, most of the hanging gyros are used, which are relatively representative gyros in the world. They have their own characteristics in specific structures. . But the overall structure is basically similar. The core component of the gyroscope is the gyro motor, which is installed in a sealed, hydrogen-filled gyro room and hung up through a suspension strap. Two guide wires, a suspension strap and a bypass structure are used to power the motor. Therefore its structure is very compact. What is particularly important is that the suspension belt must not only withstand the torque of the gyromotor when it rotates at high speed, but also the weight of the gyromotor, as well as the passage of strong current. The complexity of the process can be imagined, so if you are not careful during use, will cause it to be damaged.

 

2∙2 Observer quality

Gyroscope operators should be trained in advance. On the one hand, they should ideologically strengthen their subjective awareness of caring for the instrument; on the other hand, their professional quality should be improved, especially so that they have an accurate understanding of the principles of the gyroscope. In this way, the operator will consciously operate according to the operating procedures during the instrument observation process, thereby reducing man-made damage to the instrument.

 

2∙3 Observation environmental conditions

As mentioned before, when the gyroscope is working, the gyro motor rotates at high speed, generating a large precession torque. At the same time, the motor's guide wire and suspension carry strong current through it, and the power amplifier part of the inverter power supply works with high current. state, so high heat will be generated in the gyro room and inverter power supply, causing the gyro motor and inverter power supply to heat up. In addition, the operation process takes a long time, so in high temperature weather and direct sunlight, the instrument is easy to burn and shorten the instrument. life.

 

It can be seen from the above analysis that the service life of the gyrotheodolite is restricted by many factors. If a certain link is not paid attention to properly, the instrument will be damaged. Therefore, operating the instrument reasonably and carefully and improving the efficiency of the inverter power supply are the keys to extending the service life of the gyro-theodolite. Based on many years of use experience, the author conducted corresponding theoretical analysis and research, and came up with the following specific methods to extend the service life of the gyro-theodolite:

(1) Operate the gyro-theodolite strictly in accordance with the operating procedures, which is the basis for ensuring that the gyro-theodolite is protected from accidental damage. The following points should be noted:

1. The instrument must be used by personnel with certain operating experience who are familiar with the performance of the gyro-theodolite.
2. Before starting the gyro motor to reach the rated speed and during the process of braking the gyro motor. The sensitive part of the gyro must be in a locked state to prevent damage to the suspension guide wire.
3. When the sensitive part of the gyro is in a locked state and the motor is rotating at high speed, it is strictly forbidden to move or rotate the instrument horizontally, otherwise a large torsional force will be generated, compressing the bearings and damaging the instrument.
4. Before turning on the gyro inverter power supply, check the connections repeatedly. When using an external power supply, pay attention to whether the voltage polarity is correct. Do not turn on the inverter when there is no load.
5. When storing the gyroscope, put it in the instrument box and add desiccant. The instrument should be stored correctly and not placed upside down or lying down.
6. When carrying out long-distance transportation, special shock-proof packaging boxes should be used.
7. During summer or sunny weather observations, try to avoid direct sunlight on the instrument.

 

（2）Improve the high current and high voltage circuit part of the inverter power supply (the power supply circuit is shown in Figure 2).

 

Figure 2 Gyro inverter power supply circuit

The cadmium-nickel battery of the inverter power supply is also an important factor that restricts the service life of the power supply. Nickel-cadmium batteries have a strict memory effect. In order to eliminate the memory effect, the author recommends using nickel-metal hydride batteries to replace nickel-cadmium batteries or installing a protection device on the gyro-theodolite discharger. To this end, the author designed a protection circuit for reference by each unit. The circuit is shown in Figure 3.

Figure 3 Principle of gyro discharger

 

Summarize

The above gives specific methods to extend the service life of the gyro-theodolite. Judging from the actual application results of this unit, it not only extends the

The service life of ERICCO can ensure the yield rate of experiments and save a lot of instrument repair costs. ERICCO's gyro theodolite includes ER-GT-03 Quick Gyro Theodolite, ER-GT-05 Low Temperature Gyro Theodolite, and ER- GT-20 Portable Gyro Theodolite. They can be used in tunnel penetration measurement, subway engineering measurement, mine penetration measurement, and navigation equipment calibration. Our company has strict requirements for the preservation and use of gyro theodolite.

 

If you want to purchase a gyro-theodolite, please contact our relevant technical staff.

Research on external measurement method of aircraft rudder surface deflection angle based on inertial measurement unit

https://www.ericcointernational.com/application/research-on-external-measurement-method-of-aircraft-rudder-surface-deflection-angle-based-on-inertial-measurement-unit.html

Why is Tilt Sensor Used?

 

Tilt sensors are also known as inclinometers. They are a type of position sensor used to measure the Angle or slope of an object.

Inclinometers are one of the most common types of position sensors and are widely used in many industries.

1.Tilt sensor application

Tilt sensor Angle and slope. So anything that works on Angle will use a inclinometer sensor or a rotary position sensor.
Some sample applications include:
Robotics: Tilt sensors are used to sense the Angle of the robot arm to ensure that the arm movement is in a precise position.
Marine applications: inclinometer sensors are used in a variety of Marine applications, especially boom Angle sensing.
Industrial vehicles: In industrial vehicles, tilt sensors are used to monitor tip protection and for a variety of applications in cranes and construction vehicles.
Aerospace: tilt sensors are used for aircraft orientation and applications on the red arrow.
Industrial applications: Platform leveling is a popular application in the industrial sector that uses inclinometer sensors.
Safety: Tilt sensor Monitors security camera Angle sensing and mobile safety systems.
Mobile phones: Mobile phones are integrated with a very small tilt sensor that changes the orientation of the screen depending on how the phone is held.
Measure ski slope: for safety reasons.

2.How the tilt sensor works

There are different types of inclinometer sensors, and they work slightly differently.
A simple tilt sensor works by using a metal ball that connects two pins and moves within the sensor. When the sensor is tilted, the ball moves position, which connects the circuit that turns the sensor on or off.
More sophisticated inclinometer sensors use an internal gyroscope to measure the direction of the gravitational pull to determine the orientation of the device.

Ericco's tilt sensor is actually the use of MEMS plus meter in the static state can measure the principle of angular velocity. At present, there are conventional (single-axis), dynamic (two-axis), wireless inclinometer sensors, wired and wireless have their own advantages and disadvantages. We can choose the model according to the application scenario and accuracy requirements.

The single-axis ER-TS-3160VO, with an accuracy of 0.01°, is a very popular one with a wide range of applications. Is a very good choice, wireless ER-TS-12200-Modbus, accuracy up to 0.001°, is an ultra-low power, small volume, high-performance wireless inclinometer sensors, for industrial applications users do not need power supply or real-time dynamic measurement of object attitude Angle needs. Using lithium battery power supply, based on the Internet of Things technology Bluetooth and ZigBee(optional) wireless transmission technology, all internal circuits are optimized design, using industrial MCU, three-proof PCB board, imported cables, wide temperature metal shell and other measures to improve the industrial level of the product. Good long-term stability, zero drift small, can automatically enter low-power sleep mode, get rid of the dependence on the use environment. The product has compact structure, precise design, temperature and linearity compensation function, and integrates short-circuit, instantaneous high voltage, polarity, surge and other comprehensive protection functions, easy to use. Wireless digital signal transmission mode eliminates the tedious wiring and noise interference caused by long cable transmission; Industrial design has extremely high measurement accuracy and anti-interference ability. Wireless sensor nodes can form a huge wireless network, supporting thousands of measurement points to monitor the tilt at the same time, and support professional computer software. Without on-site investigation, it can measure and record the status of the tested object in real time. The safety monitoring system is suitable for remote real-time monitoring and analysis of industrial sites, dilapidated buildings, ancient buildings, civil engineering, various tower incline deformation and other needs.

3.Tilt sensor characteristics and specifications

The tilt sensor has the following characteristics;
High reliability
High accuracy
Easy to operate
Not using much electricity
Low cost
Small size, light weight, low power consumption
Anti-vibration, anti-impact, waterproof and dustproof
High stability, low noise, strong anti-interference ability

Different types of inclinometer sensors have different specifications to suit different applications. When choosing a tilt sensor, it is important to consider the following factors;
Sensitivity Some tilt sensors are more sensitive than others, depending on how the increment you need to measure affects the sensitivity of the desired sensor.
Axis number: The number of axes affects the Angle and direction that the sensor can measure.
Resolution: The resolution affects the minimum tilt that the sensor needs to detect.
Measuring range: What is the measuring Angle in the application? This will affect the type of sensor selected.
Accuracy: Different applications may require different degrees of accuracy, so it is important to choose a inclinometer sensors that reflects the requirements.
Noise tolerance: Our inclinometer sensors provide standard noise tolerance.
Certification: requires that we provide inclinometer sensors for intrinsically safe environments as well as underwater applications.

Optimization method of attitude information of shipborne inertial measurement unit

The advancement of my country's geostationary satellite technology has made satellite communication resources more and more abundant and diverse. The development of the Internet has also made big data and the Internet of Things widely used. The ocean communication network that cannot be realized by the ground wired base station communication mode must be realized through satellite communication. Therefore, the demand for shipboard communication equipment to be instantly accessible has also been greatly released. The inertial measurement unit based on the microelectronic system is the core component of the shipborne communication-in-motion antenna system and is the key to ensuring stable tracking of communication-in-motion equipment. Generally, the inertial measurement unit uses the Kalman filter method to fuse the three-axis measured angular velocity and the three-axis measured acceleration information to obtain relatively accurate dynamic attitude information of the market. However, in the actual dynamic use process, only the market information obtained through this method is The effect of applying to ship roll isolation is not ideal. It is proved by mechanism analysis and large amounts of data collection. This is due to the measurement information deviation caused by the three-axis measurement acceleration being contaminated by other accelerations when the measurement unit moves in space. In order to facilitate the distinction, This type of acceleration that affects attitude measurement is collectively called harmful acceleration. This article will analyze the causes of harmful acceleration and its impact on measuring carrier attitude Euler angle information, and propose a filtering method for harmful acceleration, which further improves the accuracy of microelectronic sensors in measuring carrier attitude information. This filtering method can be expanded to be applied to a variety of devices with interference information, especially providing convenience for the promotion and application of mobile communication series products and similar devices.

 

1. Kalman filter method

In order to understand how harmful acceleration affects the attitude measurement information of the inertial measurement unit, we must first understand the basic algorithm of the attitude measurement of the inertial measurement unit, namely the Kalman filter method. The principle of the Kalman filter method is to obtain the original measurement data in a probabilistic sense through multi-channel sensor measurement when the noise status of each measurement plan is known in advance. In order to cooperate with the application of Kalman filtering method, it is necessary to construct other carrier attitude measurement channels different from the direct measurement channel. Angular velocity meters and accelerometers are respectively installed on the three sign vectors of the inertial measurement unit: The actual measured attitude obtains low-noise, high-precision attitude information in a probabilistic sense, thereby obtaining accurate filtering results. The Kalman filtering process can be divided into 5 steps:

(1)The attitude estimation is set at time T, that is, when there is no carrier attitude measurement information, the attitude information estimation is obtained by the state equation operation of the attitude rotation quaternion:

(2)One-step prediction error variance matrix:

(3)Filter gain matrix:

(4)State matrix estimation:

(5)Estimated error variance matrix:

After the above five steps, the carrier attitude information expressed in the form of quaternions processed by the Kalman filter method can be accurately obtained, and then the rotation matrix and attitude Euler angle information can be obtained.

 

2.Harmful acceleration analysis

The inertial measurement unit (conventional strapdown inertial navigation) based on the measurement principle of three-axis angular velocity and three-axis acceleration uses the Kalman filter method to fuse the rotating eccentric attitude integral matrix with the measured gravity acceleration vector scalar data to obtain high maneuverability dynamic posture information. Since the attitude information is based on the gravity acceleration vector scalar information of the three-axis acceleration measurement, the accuracy and stability of the gravity acceleration of the three-axis acceleration measurement are an important basis for the accuracy and stability of the attitude information of the inertial measurement unit. But in actual use. The spatial motion of the inertial measurement unit is not a rational rotation of the center of mass. In the earth's inertial system, changes in the magnitude and direction of its spatial motion speed will also produce acceleration. Therefore, in addition to the acceleration due to gravity, triaxial acceleration will also measure other accelerations due to changes in space motion. The participation of these accelerations will interfere with attitude convergence and affect the accuracy of attitude information. During the attitude convergence calculation process, they are collectively called harmful accelerations.

 

During the use of shipboard mobile communication, the inertial measurement unit must participate in space motion. As long as the form of motion changes, there will be harmful acceleration mixed in the measured gravity acceleration data to interfere with the attitude convergence calculation. For the convenience of analysis, harmful acceleration is now divided into two categories according to its mode of action. One type of harmful acceleration is relatively stationary relative to the geodetic system, such as the linear motion acceleration of the carrier in space. This type of acceleration is relatively stationary in space with the acceleration of gravity, and its effect does not affect the attitude change of the inertial measurement unit. Therefore, the measurement information of the three-axis angular velocity and the three-axis acceleration cannot be separated, that is, it is objectively uncontrollable. Fortunately, this kind of harmful acceleration occurs instantaneously during the actual use of the shipboard communication system and its value is not large. Its interference can be reduced through appropriate Kalman filter coefficients. Another type of harmful acceleration is relatively stationary relative to the measurement coefficient of the inertial measurement unit, such as normal acceleration and tangential acceleration during ship rolling. This kind of acceleration continues to periodically interfere with the measurement data during the ship rolling process, affects the Kalman filter convergence process, and is an important factor affecting the dynamic data of the inertial measurement unit. In order to improve system performance and reduce costs, such harmful acceleration needs to be measured from three-axis acceleration

 

It can be seen that when the rotation radius of the instantaneous measurement system is known, the harmful acceleration can be separated from the measurement information of the three-axis acceleration through the three-dimensional angular velocity information, so as to achieve the purpose of filtering out such harmful acceleration.

 

However, in practical applications, the rotation radius of the roll and pitch measurement systems is related to the installation height of the ship's moving centerline and the hull draft, and the rotation radius of the yaw angle is related to the motion radius. Therefore, the rotation radius of the measurement system is not applicable. Obtained intuitively, in order to filter out such harmful acceleration, mathematical statistics must be calculated.

 

Summarize

The attitude information optimization method of the shipborne inertial measurement unit filters out the interference acceleration from the three-axis acceleration measurement information of the inertial measurement unit through numerical analysis, making the measured three-axis acceleration closer to the real local gravity acceleration, improving the inertial measurement unit The authenticity of the feedback information reduces the deviation between the measured attitude Euler angle and the real attitude information, thereby improving the spatial pointing accuracy of the shipborne satellite communication antenna in motion, increasing the environmental adaptability of the shipborne satellite communication system, and achieving the expected control Effect. Due to the complexity of the working environment of shipborne communication systems in the ocean and the uncertainty of interference, more testing research on inertial measurement units is needed to expand the applicable scope of inertial measurement units. ERICCO's independently developed inertial measurement units such as ER-MIMU-01 are suitable for more complex environments. The built-in gyroscope has high accuracy and can provide good positioning and orientation during work. If you want to know more, please contact our relevant technical personnel.

What is an Inertial Measurement Unit?

 

An inertial Measurement Unit (IMU) is a device that typically consists of a gyroscope for measuring angular rate and an accelerometer for measuring linear speed. In this article, we'll delve into the inner workings of an inertial measurement unit to explore all the relevant specifications and information you need to choose the right IMU for your application.

1. What is IMU?

An Inertial Measurement Unit (IMU) is a device that can measure and report the specific gravity and angular rate of an object to which it is attached. Imus typically include:
Gyro: provides angular rate measurement
Accelerometer: Provides specific force/acceleration measurement
Magnetometer (optional) : Measures the magnetic field around the system
Adding magnetometers and filtering algorithms to determine directional information results in a device called the Attitude and Heading Reference System (AHRS).
Imus are available in a variety of performance levels. According to the specifications of accelerometers and gyroscopes, they are divided into one of four categories:
Consumer/Automotive grade
Industrial grade
Tactical level
Marine class
These performance categories are often defined in terms of the sensor's operational bias stability, which plays such an important role in determining inertial navigation performance. The following table summarizes the various levels of performance for these specifications.

Class	Cost	gyroscope operation bias stability	GNSS reject navigation time	applications
Consumer	< $10	--	--	Smartphone
Industrial grade	100$- 1000$	<10°/h	<1 minute	UAV
Tactical level	$5,000- $50,000	<1°/h	<10 minutes	smart ammunition
Navigation class	< $100,000	<0.1°/h	a few hours	military

Let's dive into the specific sensors used in IMUs, namely accelerometers and gyroscopes.

2. Accelerometers

Accelerometers are the primary sensors responsible for measuring changes in inertial acceleration or velocity over time, and there are many different types, including mechanical accelerometers, quartz accelerometers, and MEMS accelerometers. MEMS accelerometers are essentially mass blocks suspended by springs, as shown in Figure 2. This mass block is called the test mass, and the direction in which the mass block is allowed to move is called the sensitivity axis. When the accelerometer is subjected to linear acceleration along the sensitivity axis, the acceleration causes the mass block to move sideways, and the amount of deflection is proportional to the acceleration.

3. Gyroscope

A gyroscope is an inertial sensor that measures the angular rate of an object with respect to an inertial reference frame. There are many different types of gyroscopes on the market with varying levels of performance, including mechanical gyroscopes, fiber optic gyroscopes (FOG), ring laser gyroscopes (RLG), and quartz /MEMS gyroscopes. Quartz and MEMS gyroscopes are typically used in the consumer, industrial, and tactical markets, while fiber optic gyroscopes cover all four performance categories. Ring laser gyroscopes typically have in-operation bias stability and range from 1°/ hour to less than 0.001°/ hour, covering tactical and navigation levels. Mechanical gyroscopes are the highest performing gyroscopes on the market with bias stability of less than 0.0001°/ hour in operation.

4. Magnetometer

A magnetometer is a sensor that measures the strength and direction of a magnetic field. While there are many different types of magnetometers, most MEMS magnetometers rely on magnetoresistance to measure the surrounding magnetic field. Magnetoresistive magnetometers are composed of permalloy, and their resistance changes in response to changes in the magnetic field. Typically, MEMS magnetometers are used to measure a local magnetic field that is a combination of the Earth's magnetic field and any magnetic fields generated by nearby objects.

5. How does the Inertial Measurement Unit (IMU) work?

A single inertial sensor can only sense measurements along or around a single axis. To provide a three-dimensional solution, three separate inertial sensors must be mounted together to form an orthogonal cluster called a triplet. This set of inertial sensors installed in a triplet is often referred to as a triaxial inertial sensor because the sensor can provide a measurement along each of the three axes. Similarly, an inertial system consisting of a 3-axis accelerometer and a 3-axis gyroscope is called a 6-axis system because it provides two different measurements along each of the three axes for a total of six measurements.
The Inertial Measurement Unit (IMU) measures and reports the raw or filtered angular rate and specific force/acceleration experience of the object to which it is attached.
The data output of the IMU is typically body frame acceleration, angular rate, and (optionally) magnetic field measurements.
The user is then responsible for determining the pose by implementing an independent fusion algorithm, such as a Kalman filter.

6 Summary

Ericco's FOG Inertial Measurement Unit ER-FIMU-50, gyro bias stability is 0.5°-1°/h, ER-FIMU-60, gyro bias stability is 0.1°-0.5°/h, these two belong to the tactical class of fiber optic IMU. ER-FIMU-70 gyro bias stability is 0.05°-0.1°/h, it belongs to the navigation level of fiber optic inertial measurement unit, mainly used in the inertial navigation of surface-to-air missiles, air-to-air missiles and navigation missiles, space stability system, mapping system, attitude reference system and other fields.

Research on inertial measurement unit output delay and time synchronization measurement method

 

As an important feedback link in the control system, the inertial measurement unit's delay characteristics of its gyroscope channel and accelerometer channel are an important technical indicator. In actual attitude control and navigation solution systems, the output delay of the inertial measurement unit is required to be as small as possible. The better the real-time performance, the easier it is for the control system to make timely and accurate attitude corrections. Then studying the measurement method of output delay is the key to accurately evaluate the dynamic performance of inertial measurement equipment. At present, conventional delay measurement only examines the output delay of the gyro channel, and does not involve the time asynchronous problem between the acceleration channel and the angular velocity channel. In order to make up for this shortcoming, this paper proposes an angular vibration test based on the sinusoidal swing motion of the angular vibration table. On the basis of the process, the synchronous acquisition of three accelerometer channel signals is added, the raw data of the gyroscope and accelerometer are converted into the frequency domain, and then the characteristic frequency points are extracted. Finally, the time delay is calculated from the phase angle of the characteristic frequency point and the time synchronization of the inertial device is achieved of calibration.

 

1.Delay analysis

The output delay of the inertial measurement unit is mainly affected by the superposition of its own structural transmission , the response of the gyroscope and meter-added inertial device, digital filtering, data transmission and other links.

 

Structural transmission: In order to ensure a good working environment for the inertial instrument, rubber shock absorbers are usually elastically installed between the inertial instrument and the measured carrier. The response delay for the angular velocity and linear velocity transmission in the low frequency band is negligible, but for high-frequency excitation There is a certain delay in response.

 

The response of the inertial device itself: Due to the influence of the structure and the sensitivity of the electronic devices, the gyroscope and the meter-added inertial device themselves have a certain delay when they are sensitive to external excitation.

 

Digital filtering: The digital signal processing of the gyroscope itself will cause delays to the entire system during the step height filtering and output signal filtering stages, reducing the ability of the inertial instrument to track external inputs, and there is some inherent delay. After the inertial measurement unit collects instrument data, it needs to undergo low-pass filtering to remove signal noise. If the filter order is high, the phase group delay generated will affect the system response time. Taking the 50th-order FIR low-pass filter as an example, from the amplitude-frequency phase-frequency curve of the digital filter in Figure 1, we can find that: 2kHz sampling data, the phase delay generated by the excitation below 200Hz in the phase-frequency curve is linear, then the group The delay is a fixed constant value of about 12.5ms.

2.Time synchronization analysis

Research on traditional strap down inertial navigation system algorithms is based on ideal measurements from gyroscopes and accelerometers. However, in an actual IMU, the signal output of each inertial device may be asynchronous in time. The output time of the gyroscope may be later than the output time of the accelerometer, or it may be faster than the output time of the accelerometer. This is because the physical limitations of the sensor inside the inertial measurement unit will affect the conversion of the bandwidth signal, ultimately resulting in the time of the output parameter. Delay. The frequency band width of fiber optic gyroscopes is generally several thousand Hz, which is much higher than the frequency bandwidth of accelerometers, and will eventually be processed to a unified output frequency. This processing process may also cause desynchronization of the actual output signal. In addition, the filter before the AD converter may also cause additional delays in the gyroscope and accelerometer signals, which are determined by factors such as the time it takes the sampled information to be transmitted to the computer. In addition, the inertial device also needs to be processed by some auxiliary hardware to make the inertial device output a more accurate signal. Therefore, it is necessary to compensate for the sum of all physical delays of the accelerometer and gyroscope and additional software and hardware delays, that is, to test the time delay parameters through SINS. The calibration results in the process are partially compensated to synchronize the accelerometer and gyroscope outputs.

 

3.Measurement method

In order to fully measure the time asynchronous parameters between the three accelerometers, the time asynchronous parameters between the three gyroscopes, and the asynchronous time error between the inertial device and the standard output, the analog signal output by the closed-loop angular vibration table is used as the standard output time reference. The product under test is fixed at a certain distance from the center of the off-angle vibration table table through the vibration tooling (as shown in Figure 2). The digital signal output by the inertial measurement unit and the analog signal output by the closed-loop angular vibration table are collected by the signal receiving system and stored in the computer.

 

The angular vibration test is performed at a given maximum rotation angular rate of 10º/s to ensure that the input value at each frequency point remains consistent.

 

In the test, if the angular vibration table has an angular rate setting input, the maximum angular rate is set to 10º/s. If the angular shaking table is an amplitude setting input, the swing amplitude for each frequency needs to be calculated. The following numerical relationships exist between the two input methods. In the angular vibration test, the instantaneous rotation angle of the turntable is:

Then the instantaneous angular velocity of the turntable is:

When the maximum angular rate of the turntable rotation is known, it can be obtained from the turntable formula:

The angular vibration frequency and amplitude requirements obtained by the above formula are as shown in Table 1

Figure 2 Installation diagram

The gyro is sensitive to the sinusoidal rocking motion of the shaking table; due to the offset of the installation position, the meter has a lever arm effect, which produces centripetal acceleration during the swing process. The meter data in three directions will also reflect the characteristic frequency of the shaking table. The Fourier transform is used to respectively extract the analog signal (reference voltage) output from the closed loop of the angular shaking table and the swing frequency component in the actual output of the inertial measurement unit. Finally, the time delay is calculated and the calibration of the time synchronization of the inertial device is achieved.

Table 1 Angular vibration test frequency and amplitude relationship

4 Angular vibration test

4.1 Test process

The angular vibration test uses a pure strapdown optical fiber inertial group to conduct the test according to the installation method in Figure 2. During the test process, when the data frame sent by the inertial measurement unit is sent to the receiving acquisition system, the analog signal of the AD sampling angular vibration table of the receiving acquisition system is simultaneously triggered ( Reference voltage), and then send the inertial measurement data and reference voltage data package to the host computer test software. After the test is completed, the spectrum of the saved test data is analyzed to calculate the response delay of the inertial measurement unit and the asynchronous time between the inertial devices.

 

4.2 Test results

During the test, the angular vibration table was set up to swing at a frequency of 2Hz. The data output frequency of the inertial measurement unit was 2000Hz. The data were normalized to facilitate waveform comparison with the reference voltage. Perform FFT processing on the saved data of the meter channel and gyro channel to extract the characteristic frequencies, and compare the phase differences at the characteristic frequencies.

Figure 3 Characteristic frequency

Figure 4 Data Curve

Summarize

The above article describes the output delay and time synchronization measurement method of the inertial measurement unit, and conducts an angular vibration test on it. The test results show that the waveforms between the three gyroscopes of the inertial measurement unit (and between the three plus meters) are basically consistent. The asynchronous time between similar devices is not greater than 0.1ms, which is much smaller than the data sampling time and does not require compensation. The MEMS IMU independently developed by ERICCO is divided into navigation grade and tactical grade. For example, navigation grade ER-MIMU-01 and tactical and ER-MIMU-03 have relatively high accuracy. If you want to know more, please contact us.

What can Fiber Optic Gyroscopes be Used for?

 

1.What is a fiber optic gyroscope?

A fiber optic gyroscope (FOG) is a device used to measure angular velocity and direction. It provides extremely accurate rotational speed information with low maintenance costs and long service life.
Fiber optic gyroscopes are becoming more affordable, and the technology has proven beneficial for an ever-expanding array of different high-performance inertial navigation systems (INS). As a result, FOG has become the default choice for strategic and tactical level applications that require long-term navigation in environments where GNSS (Global Navigation Satellite System) is not available.

2.How does a fiber optic gyroscope work?

Fiber optic gyroscopes use the properties of light in closed circuits to estimate changes in direction. Two beams of light are sent in opposite directions in the fiber coil.
As the vehicle rotates, the beam traveling against the rotation experiences a slightly shorter path delay than the other beams, a phenomenon known as the Sagnac effect. The phase shift difference between the two beams is then used to estimate the rotation rate.

3.What is the difference between a ring laser gyroscope and a fiber optic gyroscope?

Similar to the FOG, the ring Laser gyroscope (RLG) is an optical gyroscope that utilizes the Sagnac effect. The main difference between the two is the way they are constructed, because a ring laser gyroscope uses a laser passing through a system of mirrors to determine the rotation of the vehicle, rather than a simple fiber optic coil.
In addition to requiring extremely high manufacturing precision and special mirrors, the RLG is also filled with gas, and the laser needs to be "dithered," or mechanically vibrated, to prevent laser locking to eliminate small rotations.
While both types of gyroscopes work similarly and are very accurate, the older toroidal laser gyroscope technology is more sophisticated due to its construction, requires more maintenance, and is generally more expensive. In contrast, the fiber optic gyroscope is a solid-state device that does not use a jitter mechanism, which means it does not produce any acoustic vibrations, making it more durable and reliable than the RLG. In addition, the application of fiber optic gyroscopes can be extended by changing the length and diameter of the fiber optic coils.

4.What is the difference between a fiber optic gyroscope and a MEMS gyroscope?

A MEMS (Micro-electro-mechanical System) gyroscope is a smaller, lighter gyroscope made from tiny devices. MEMS gyroscopes have significantly reduced SWaP-C, which means they are preferred for applications requiring small payloads.
FOG has higher inertial performance and lower deviation, making it the preferred solution for high-precision applications such as GNSS rejection environments or antenna pointing.

5.What can fiber optic gyroscopes be used for?

Fiber optic gyroscope technology facilitates a growing number of applications where accurate heading and navigation are critical. This includes both manned and driverless vehicles.
Surface Ocean Vehicles: Ocean survey vessels use fiber optic gyroscopes to determine pitch, roll, and heading in real time and build accurate position data for unmanned underwater vehicles (UUV). They are particularly useful for side-scan sonar and similar applications.
Undersea vessels: Manned vehicles (such as submarines) and UUVs (unmanned underwater vehicles), including autonomous underwater vehicles (AUVs) and remotely operated vehicles (ROVs), rely on fiber-optic gyroscopes for precise navigation in extremely challenging and dangerous environments at minimal cost. Or an unreliable source of absolute location. Rovs and AUVs for hydrology in particular benefit from FOG's precision.
Aviation: Helicopters can be subject to electromagnetic interference and can benefit greatly from FOG-based INS. Unmanned aerial vehicles (UAVs) and commercial aircraft typically require FOG-level performance to reduce the risk of losing GNSS locations while in flight. The accuracy of roll, pitch and yaw data is critical to the safe operation of the aircraft.
Defense: Ground-based defense vehicles must not rely on GPS/GNSS because of the risk of local interference or spoofing of these signals, or simply the risk of terrain blocking or altering satellite positioning data. Fibre-based INS allows these vehicles to operate seamlessly, preventing adversaries from gaining an advantage from these tactics.
Space exploration: Fiber optic gyroscopes are ideal for space applications due to their long service life, virtually maintenance-free, extremely low power consumption, and accurate navigation data.
Robotics: Directional data from the fiber optic gyroscope is used to navigate the robot, ensuring safe operation when adjusting for any changes in speed, position or acceleration.
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