Research on lock-in correction for mechanical dithered ring laser gyro

Fan, Zhenfang; Luo, Hui; Hu, Shaomin; Xiao, Guangzong

doi:10.1117/1.3554393

Cited by 10 publications

(7 citation statements)

References 2 publications

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“…The previous study to decline the dithering coupled noise mainly focuses on the optimization of the damping system [7], the rational design of the inertial principal axis [8], the damper characteristic analysis [9], the lock-in error correction method [10,11], and the increase of the moment of inertia of the platform [12][13][14]. The inertial measurement unit (IMU), which consists of accelerators, DRLG, and platform, of inertial navigation products is drawn in Figure 1.…”

Section: Introductionmentioning

confidence: 99%

The Application of the Vibration Absorber in Laser Inertial Navigation Products

Cheng

Zhang²,

Lei³

et al. 2021

Journal of Sensors

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The navigation accuracy of laser strap-down inertial navigation products declines with gyro dither, which is a bottleneck problem for the development of the important aviation instrument. The reason is that the dither of three gyros in the product couples and generates extra noise in the output signals of gyros. To decouple dither, this paper applies the vibration absorber in laser inertial navigation products. First of all, an angular vibration model of the three-rigid body system, which is constructed by the gyro, platform, and vibration absorber, is established. Then, the theoretical restriction of the absorber and the system response are derived. Finally, considering the power limitation for dither, the total power of the vibration system is analyzed. The analytical and experimental results show that the efficiency of the vibration absorber only relates to the frequency offset with gyros, and the absorber does lead to a sharp power increase.

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Section: Introductionmentioning

confidence: 99%

The Application of the Vibration Absorber in Laser Inertial Navigation Products

Cheng

Zhang²,

Lei³

et al. 2021

Journal of Sensors

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“…In terms of lock-in error compensation, Song [16] proposed a new algorithm to estimate the Sagnac phase errors due to lock-ins, and to compensate the random walk error of the RLG. Subsequently, Fan [17] proposed a novel lock-in error correction method to pick up the lost information and remove the random walk error effectively. The above studies have offered important technical support for the design of the dither bias system, and meanwhile laid the foundations for the structure design of the laser gyro IMU.…”

Section: Introductionmentioning

confidence: 99%

Coupled Dynamic Analysis and Decoupling Optimization Method of the Laser Gyro Inertial Measurement Unit

Fang

Zeng

2019

Sensors

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The mechanical dithered ring laser gyro (RLG) effectively overcomes the lock-in effect and ensures the sensitive accuracy of the low angular rate for the gyro. However, in the inertial measurement unit (IMU) system, the dither excitation of three RLGs causes the coupled vibration of the IMU structure, which could seriously limit the measuring accuracy of RLGs. In this paper, the vibration frequency response characteristic of laser gyro IMU is taken as the focus point, and the method of multi-rigid body dynamics is used to establish the dynamic model of IMU suitable for vibration frequency response analysis. On the basis of the model, the multi-degree-of-freedom coupling vibration of IMU with the gyro dither excitation is clearly described. A new IMU dynamic decoupling optimization method is proposed to minimize the coupled vibration frequency response, and compared with the previous optimal design method. The prototype experimental test results show that the coupled vibration of IMU is restrained more effectively by the proposed new method than by the previous optimal design method. Finally, on the basis of this new method, the measuring accuracy of the RLGs in the IMU system is improved, which is quite useful for practical engineering application.

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“…In Ref. [18] a curve-fitting method was proposed to obtain the values of a and b. In this method, when the lock-in error is compensated, the output of the RLG will have minimum variance.…”

mentioning

confidence: 99%

“…By using a parabolic approximation, when the direction changes from clockwise (CW) to counterclockwise (CCW), the phase error can be expressed as [18] …”

mentioning

confidence: 99%

Dynamic lock-in compensation for mechanically dithered ring laser gyros

Fan¹,

Luo²,

Lu³

et al. 2012

中国光学快报

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In ring laser gyros (RLGs), dynamic lock-in, which results from information loss in the lock-in region, occurs when a constant sine bias is introduced. However, sampling some signals in the lock-in region for a particular duration allows the retrieval of lost information. It is demonstrated how dynamic lock-in and the flat region in the input-output curve near the zero angle rate can be eliminated after compensation.OCIS codes: 140.3370, 140.3430, 230.5160. doi: 10.3788/COL201210.061403. Ring laser gyros (RLGs) have more advantages than traditional spinning-mass gyros. The operation principle of a RLG involves the Sagnac effect [1,2] . The laser cavity supports two independent waves traveling toward opposite directions. When an angle rate is introduced, the oscillation frequencies of the two beams differ. Thus, the angle rate can be measured by detecting the frequency difference. The RLG is, in fact, a ring laser whose gain media is He-Ne gas [3] . The lock-in phenomenon can significantly constrain the performance of the RLG [4−7] . Lock-in is caused by the mutual coupling between the opposite traveling waves [8−11] . With a low angle rate input, both waves lock to a common frequency, and the gyro becomes unresponsive to the input.The lock-in effect can be avoided by introducing a mechanical dither and placing the gyro far from the lock-in region most of the time [12] . The gyro that works in this manner is often called a "mechanically dithered ring laser gyro" [13] . However, if a pure sine wave dither is introduced, dynamic lock-in may occur. In other words, if the angle rate is below the dynamic lock-in threshold, the output also becomes zero [14] and a flat region near the zero input angle rate appears. Dynamic lock-in is the same as regular lock-in, except that the value is much smaller.Previous studies have indicated that dynamic lockin is mainly caused by information loss during lock-in traversal [15,16] . Information loss is related to the phase of the beat frequency signal and angle acceleration in the zero rate point [17] . This letter successfully compensates dynamic lock-in by sampling the signals in the zero rate point.The phase equation of a RLG can be written aswhere ψ is the phase of the beat frequency signal, Ω i is the input angle rate, and Ω L is the lock-in threshold, which must be positive.(1) has the following stationary solution:where the mean output is zero., the average frequency of ψ can be obtained. Changing the form of Eq. (1) yieldsTake integration of ψ over [0, 2π]; the mean period T can be obtained asThe average frequency of the beat frequency signal isIn Fig. 1, the response curve with the lock-in threshold is represented by the green line, whereas the ideal response curve without lock-in is denoted by the red line.When a sine dither is introduced, Eq. (1) can be written asψwhere Ω d is the peak dither angle rate and ω d is the dither frequency. Although the gyro works outside the lock-in region most of the time, it must traverse the lock-in region twice every dither cycle, ...

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Research on lock-in correction for mechanical dithered ring laser gyro

Cited by 10 publications

References 2 publications

The Application of the Vibration Absorber in Laser Inertial Navigation Products

The Application of the Vibration Absorber in Laser Inertial Navigation Products

Coupled Dynamic Analysis and Decoupling Optimization Method of the Laser Gyro Inertial Measurement Unit

Dynamic lock-in compensation for mechanically dithered ring laser gyros

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