Fiber optic gyroscope with spherical helix
technical manual
technical name
with global helix
Fiber Optic Gyroscope
Technology category
Electrical Equipment
Fundamental contents:
The method can successfully manufacture a high-precision fiber optic gyroscope, and the fiber optic gyroscope has extremely high spatial positioning accuracy.
Product Description
The fiber optic gyroscope is a sensitive element based on a fiber optic coil, and the light emitted by a laser diode propagates along the fiber optic fiber in two directions. The change of the light propagation path determines the angular displacement of the sensitive element. The realization of the fiber optic gyroscope is mainly based on Segnik’s theory: when the light beam advances in a circular channel, if the circular channel itself has a rotational speed, then the time required for the light to advance along the direction of channel rotation is shorter than that along this It takes more time for the channel to turn in the opposite direction to go forward. That is to say, when the optical loop rotates, the optical path of the optical loop will change relative to the optical path of the loop when it is stationary in different forward directions. By using the change of the optical path, detecting the phase difference of the two optical paths or the change of the interference fringe, the rotational angular velocity of the optical path can be measured. This is the working principle of the fiber optic gyroscope. The parameters involved are mainly light vector, which is calculated by the following formula.
The light vectors of two monochromatic lights with the same frequency at a certain point in space: the fiber optic gyroscope adopting the global helix = the fiber optic gyroscope adopting the global helix, the fiber optic gyroscope adopting the global helix = the fiber optic gyroscope adopting the global helix Fiber optic gyroscope.
The light vector synthesized after superposition adopts the fiber optic gyroscope with spherical helix, and the fiber optic gyroscope with spherical helix
1
in:
Fiber Optic Gyroscope Using Spherical Helix
Fiber Optic Gyroscope Using Spherical Helix
Incoherent superposition: For two common light sources, the fiber optic gyroscope using the spherical helix = 0, the fiber optic gyroscope using the spherical helix, that is, the fiber optic gyroscope using the spherical helix.
Interference: the same light source, the phase difference is constant, then
Fiber Optic Gyroscope Using Spherical Helix
A fiber optic gyroscope using a spherical helix is described below for the Sagnac effect
picture
picture
As shown in (a), under the condition of no rotation, the transmission time of the two beams of light is equal, which is
Fiber Optic Gyroscope Using Spherical Helix
The fiber optic gyroscope using a spherical helix is shown in (b), under the condition of rotation,
Fiber Optic Gyroscope Using Spherical Helix
Fiber optic gyroscope with spherical helix, transmission time difference
transmission path difference
Fiber Optic Gyroscope Using Spherical Helix
Transmission phase difference of fiber optic gyroscope using spherical helix
For the optical fiber ring, multi-turn optical fiber is used to enhance the Sagnac effect, and the optical fiber gyroscope using a spherical helix is the length of N-turn optical fiber ring for light waves to propagate in a closed loop.
Detect phase difference by detecting interference light intensity changes:
A fiber optic gyroscope using a spherical helix such as
Fiber Optic Gyroscope Using Spherical Helix
The direction of rotation is ambiguous, the sensitivity is low when the phase shift is small, and the response curve is periodic, which will produce multiple values when measuring the output of the gyroscope.
The fiber optic gyroscope signal processing technology is introduced below
A square wave bias modulation
Fiber Optic Gyroscope Using Spherical Helix
B closed loop control:
Reduce the working range of the photodetector and improve the detection accuracy
Fiber Optic Gyroscope Using Spherical Helix
The basic principle of the digital closed-loop fiber optic gyroscope: add a feedback element to the coil of the fiber optic gyroscope, introduce a non-reciprocal phase difference to compensate the Sagnac phase shift caused by the rotation, so that the phase difference is controlled at zero, so that Measuring this compensation signal is equal in size and opposite in direction to the Sagnac phase shift, so the phase difference of the compensation is linearly related to the phase shift caused by Sagnac, and closed-loop processing technology is the key to solving nonlinear problems.
Performance index of fiber optic gyroscope
A. Scale factor
The ratio of gyroscope output to input angular rate. It is represented by the slope of a specific straight line, which is obtained by fitting the least squares method based on the input and output data measured within the entire input angular rate range. The scale factor belongs to the dynamic performance index of the fiber optic gyroscope. The scale factor requires that the test is the output value under a series of angular rate inputs, so it is a quasi-dynamic experiment. For this reason, a turntable with a certain accuracy and speed range is required to drive the fiber optic gyroscope so that it has a standard angular velocity input, so as to obtain an output-input relationship. This indicator, namely the scale factor, is an important basis for system application. The size of the scale factor value can often be adjusted according to needs in order to meet the requirements of use. Therefore, what people care about is the stability or accuracy of this index. In addition, there are its linearity (or nonlinearity), symmetry (or asymmetry), and repeatability issues that vary with the environment and time. Scale factor nonlinearity: refers to the ratio of the maximum deviation of the output of the fiber optic gyroscope relative to the straight line fitted by the least squares method to the maximum output within the range of the input angular rate.
B. Zero bias
The output of the gyroscope when the input angular rate is zero. Expressed as the equivalent input angular rate corresponding to the average value of the output measured within a specified time. Zero bias belongs to the static performance index of the gyroscope, which is used to describe the static output characteristics of the fiber optic gyroscope.
The calculation of the zero bias is the average value of multiple tests of the steady-state output value for a long time under static conditions, and it is a constant value in practice. Therefore, this indicator implies that the random process tested is a stationary random process, whose probability characteristics are normally distributed. In this sense, the magnitude of the drift value also marks the degree of dispersion of the observations around the zero-biased mean. The performance indicators related to zero bias include zero bias stability and zero bias repeatability. Bias Stability: When the input angular rate is zero, it measures the degree of dispersion of the gyroscope output around its mean value. Expressed by the angular rate corresponding to the standard deviation of the output within a specified time, it can also be called zero drift.
C. Random walk coefficient
Time-accumulated gyroscope output error coefficient generated by white noise. The main error source of the random walk of the fiber optic gyroscope using the spherical helix is the relative brightness noise caused by the output power oscillation of the light source, the noise of the detector and the signal processing circuit, the shot noise, the noise of the detector, the amplifier and the circuit, D/A noise, etc., can be fitted by the Allan method to obtain the random walk coefficient.
D. Bandwidth
The frequency bandwidth refers to the bandwidth, which refers to the corresponding frequency range when the amplitude of the amplitude-frequency characteristic decreases by 3dB in the frequency characteristic test of the fiber optic gyroscope. This indicator reflects the frequency range in which the FOG can accurately measure the input angular rate.
E. Threshold
The minimum input angular rate to which the gyroscope is sensitive. The output quantity produced by this input angular rate should be at least equal to 50% of the expected output value by the scale factor. The threshold belongs to the dynamic performance index of the fiber optic gyroscope.
The following introduces the principle of fiber optic gyroscope
Fiber Optic Gyroscope Using Spherical Helix
Fiber Optic Gyroscope Using Spherical Helix
As shown in the figure above, the broadband light source emits a laser beam into the coupler, passes through the fiber optic tube, enters the fiber ring, and then enters the fiber tube (the intensity of the incident light and outgoing light in the fiber tube is controlled by the modulation voltage signal), and then enters the coupling The coupler (in which the incident light and the outgoing light interfere) enters the photodetector. After the photoelectric detector detects the interference light signal, it sends the signal to the logic circuit through the AD sampling circuit, and the logic circuit generates a speed signal and outputs it to the outside. At the same time, the logic circuit controls the intensity of the optical fiber in the optical fiber guide through the DA circuit. However, since the rotation of the optical fiber ring does not occur in a plane, but in a three-dimensional plane, it is difficult to determine the intensity of the interference light detected by the photodetector, and how many degrees the optical fiber has rotated in space. Three-axis optical fibers are usually used to realize motion positioning in three-dimensional space. The optical fiber it uses is three circular optical fibers, which are X-axis circular optical fiber, Y-circumferential circular optical fiber, and Z-axis circular optical fiber. The three optical fibers are perpendicular to each other, and the angles between the planes where they are located are all 90 degrees. The laser light enters or exits at the intersection point of the three optical fibers respectively, and finally enters the coupler through the optical fiber conduit to generate interference. Since the three-axis fiber optic gyroscope uses three mutually perpendicular circular optical fibers, when the gyroscope rotates, the three mutually perpendicular circular optical fibers all rotate, which makes the movement of the optical fiber reflect the position change of the three-dimensional space, and also It is the movement of the laser in the optical fiber that reflects the changes in the three-dimensional space, so the three-axis laser gyroscope has higher spatial positioning accuracy. Its optical fiber structure is shown in the figure below.
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Fiber Optic Gyroscope Using Spherical Helix
Fiber Optic Gyroscope Using Spherical Helix
The following introduces a fiber optic gyroscope using a spherical helical fiber optic. Its structure is similar to that of the above fiber optic gyroscope. The only difference is that the optical fiber used in this spherical helical fiber optic gyroscope is a spherical helical Line fiber, this fiber is a fiber coiled along a spherical helix, the structure of this fiber is shown in the figure below.
Fiber Optic Gyroscope Using Spherical Helix
Fiber Optic Gyroscope Using Spherical Helix
As shown in the figure above, the incident light enters from one end of the spherical helix and exits from the other end of the spherical helix. The laser travels along the trajectory of the spherical helix inside the spherical helix, and finally the outgoing light is emitted from the spherical helix and passes through the optical fiber. The catheter enters the coupler and interferes with the incident light, and is collected by the logic circuit to obtain the azimuth signal of the gyroscope. The spherical helix fiber above is a bundle of optical fibers spirally coiled into a sphere, and this helix is called a spherical helix. Spherical helix[1] (spherical helix) is a common curve. The moving point moves along the meridian of the sphere in a constant-velocity circular arc, and at the same time the meridian makes a constant-angular-speed revolving motion around its axis. The trajectory of the moving point is called a spherical helix. Line, as shown in the figure. The lead T of the spherical helix is measured along the meridian. There are two kinds of left-handed and right-handed.
Fiber Optic Gyroscope Using Spherical Helix
Fiber Optic Gyroscope Using Spherical Helix
Its shape is like a tower-shaped sandalwood in a temple, spirally wound into a round ball. This special shape determines the movement of the fiber in three-dimensional space. The laser inside the fiber does not just rotate in a circular ring on a plane, but rotates in a spiral spherical ring in three-dimensional space, so the laser is affected by The spatial movement is three-dimensional rather than planar, which ensures that the movement reflected by the fiber is movement in three-dimensional space rather than a planar movement. At the same time, the distance generated by the movement of the optical fiber at any point in the three-dimensional space is different, which also determines that when the spherical helix moves, the laser light inside the optical fiber moves different distances, and the interference it produces is also different, which is It will improve the accuracy of fiber optic gyroscope measurement.
2. Creative background and motivation:
The optical fiber gyroscope of the spherical helical fiber uses the optical fiber interference generated by the movement of the spherical helical fiber in the three-dimensional space to measure the spatial coordinates.
3. Referenced materials:
In 1913, the French physicist Sagnac discovered the Sagnac effect, that is, the influence of the rotational angular rate on the interference light intensity.
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Original link: https://blog.csdn.net/zhangluan2019/article/details/102583615