A method for eliminating swing error of a three-dimensional laser imager

Abstract

A method for eliminating oscillation error in a three-dimensional laser imager is provided, which can effectively eliminate the influence of oscillation error on measurement accuracy. It includes: (1) using two transmission signals with a phase difference of π / 4 to measure the same distance position, obtaining the phase values ​​of the two measurements, and generating a measurement vector; (2) combining the correlation Kalman filter and the maximum likelihood criterion method to evaluate the noise covariance matrix, using the measurement vector as the input value and the state vector as the output value, to eliminate random errors in the operation of the three-dimensional laser imager; (3) using the two measurement vector sequences obtained in step (1) as the input values ​​of step (2), outputting the state vector and returning it to step (1) for processing, generating a state vector sequence, and calculating the measurement phase value, processing the two measurement results in step (1) respectively to obtain the corrected phase value.

Description

Technical Field

[0001] This invention belongs to the technical field of three-dimensional laser imagers, and particularly relates to a method for eliminating the swing error of a three-dimensional laser imager. Background Technology

[0002] The 3D laser imager uses indirect time-of-flight (I-TOF) technology to perform correlation calculations on the optical modulation signal at the transmitting end and the electromodulation signal at the receiving end. Specifically, it first selects four sampling points on the waveform, then calculates the phase difference based on the charge of each sampling point (I0, I1, I2, I3), and finally derives the time delay between the transmitted and received signals and calculates the depth information.

[0003] The method of calculating phase by performing correlation operations on the transmitted and received signals usually assumes that both the reference signal and the echo signal are standard sine waves. However, due to the irregularity in the modulation process of the transmitting light source, the actual form of the transmitted information and the received signal is not a standard sine wave. In addition to the fundamental component, there are also noise interferences such as DC components, higher harmonics, and non-harmonic signals. Therefore, swing error will be introduced in the distance measurement process, which will significantly affect the distance accuracy. Summary of the Invention

[0004] To overcome the shortcomings of the prior art, the technical problem to be solved by the present invention is to provide a method for eliminating the swing error of a three-dimensional laser imager, which can effectively eliminate the impact of the swing error on the measurement accuracy.

[0005] The technical solution of this invention is: a method for eliminating the wobbling error of a three-dimensional laser imager, which includes the following steps:

[0006] (1) Two transmitted signals with a phase difference of π / 4 are used to measure the same distance position d, the phase values ​​of the two measurements are obtained, and the measurement vector z is generated. k ;

[0007] (2) The noise covariance matrix is ​​evaluated by combining the relevant Kalman filter and the maximum likelihood criterion method, and the measurement vector z k As input, the state vector x k As an output value, it eliminates random errors during the operation of the 3D laser imager;

[0008] (3) The two measurement vector sequences z obtained in step (1) 1st and z 2nd The values ​​are used as inputs to step (2), and the output state vector x is generated. k Return to step (1) for further processing to generate the state vector sequence x. k[], and calculate the measured phase value, and process the two measurement results in step (1) respectively to obtain the corrected phase value.

[0009] This invention can obtain the swing error characteristics through two measurements, eliminating the need for multiple experiments, thus saving manpower and resources and providing a relatively simple method for eliminating the error. At the same time, this method eliminates random errors through correlation filtering, resulting in high stability and effectively avoiding the influence of other random factors on measurement accuracy. Attached Figure Description

[0010] Figure 1 This is a schematic diagram of the method for eliminating the wobbling error of a three-dimensional laser imager according to the present invention.

[0011] Figure 2 This is a flowchart of the two-measurement method according to the present invention. Detailed Implementation

[0012] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0013] To make the description of this disclosure more detailed and complete, illustrative descriptions of embodiments and specific examples of the present invention are provided below; however, these are not the only forms of implementing or utilizing the specific examples of the present invention. The embodiments cover features of multiple specific examples and methods and steps for constructing and operating these specific examples, and their order. However, other specific examples may also be used to achieve the same or equivalent functions and order of steps.

[0014] The formula for calculating the phase value of a 3D laser imager is shown below:

[0015]

[0016] The correlation function intensity I' with third and fifth harmonics n Measurement can be expressed as:

[0017]

[0018] In the formula, A1, A3, and A5 are the amplitudes of the fundamental harmonic, the third harmonic, and the fifth harmonic, respectively.

[0019] When the correlation function contains harmonics, the phase calculated using equation (1) is as follows:

[0020]

[0021] The oscillation error can be expressed as:

[0022]

[0023] Using the properties of the tangent function, equation (4) can be simplified to:

[0024]

[0025] In the formula, q = A3 / A1 and r = A5 / A1. Using Taylor's formula, the above formula can be simplified to:

[0026]

[0027] Under normal circumstances, A1>A3, and A3>A5. Therefore, r<<q<<1, and the phase calculation error can be expressed as...

[0028] for:

[0029]

[0030] like Figure 1 As shown, this method for eliminating the wobbling error of a three-dimensional laser imager includes the following steps:

[0031] (1) Two transmitted signals with a phase difference of π / 4 are used to measure the same distance position d, the phase values ​​of the two measurements are obtained, and the measurement vector z is generated. k ;

[0032] (2) The noise covariance matrix is ​​evaluated by combining the relevant Kalman filter and the maximum likelihood criterion method, and the measurement vector z k As input, the state vector x k As an output value, it eliminates random errors during the operation of the 3D laser imager;

[0033] (3) The two measurement vector sequences z obtained in step (1) 1st and z 2nd Each as a step

[0034] (2) Input value, output state vector x k Return to step (1) for further processing to generate the state vector sequence x. k [], and calculate the measured phase value, and process the two measurement results in step (1) respectively to obtain the corrected phase value.

[0035] This invention can obtain the swing error characteristics through two measurements, eliminating the need for multiple experiments, thus saving manpower and resources and providing a relatively simple method for eliminating the error. At the same time, this method eliminates random errors through correlation filtering, resulting in high stability and effectively avoiding the influence of other random factors on measurement accuracy.

[0036] Preferably, step (1) includes the following sub-steps:

[0037] (1.1) In the first measurement, the phase value of the reflected signal is directly measured. Its measured phase value Swing error value and theoretical phase value They are respectively:

[0038]

[0039]

[0040]

[0041] Where q is a constant, representing the ratio of the third harmonic coefficient to the fundamental coefficient;

[0042] (1.2) In the second measurement, the phase difference between the transmitted signal and the first measurement is π / 4. The phase shift of the measured echo signal will also increase by π / 4. The phase value of the second measurement...

[0043] Swing error value and theoretical phase value They are respectively:

[0044]

[0045]

[0046]

[0047] (1.3) The swing error values ​​of the two phase measurements are opposite. The two measurement values ​​are processed and the swing error value is eliminated to obtain the final measured phase value.

[0048]

[0049]

[0050] Preferably, step (2) includes the following sub-steps:

[0051] (2.1) Initialize state estimates Error covariance matrix P0, process noise covariance matrix Q, and measurement noise covariance matrix R;

[0052] (2.2) Predicted State Estimates And error covariance matrix

[0053]

[0054]

[0055] Where F is the state transition matrix;

[0056] (2.3) Calculate the gain value K k Updated error covariance P k ,new information sequence r k and the updated state estimate

[0057]

[0058]

[0059]

[0060]

[0061] (2.4) Calculate the maximum likelihood estimate covariance of the new sequence And correct the process noise covariance matrix Q:

[0062]

[0063]

[0064] (2.5) The measurement vector z k As input, the state vector x of the 3D laser imager k As output, using x k Calculate the measured phase value after eliminating random errors.

[0065]

[0066] Preferably, step (3) includes the following sub-steps:

[0067] (3.1) State estimation: The intensity data from the two measurements are respectively used as the measurement vector sequence z 1st and z 2nd Input into step (2) to obtain the system state vector sequence x 1st and x 2nd ;

[0068] (3.2) Phase calculation: Using the system state vector sequence, the phase sequence of the two measurements is calculated. and

[0069] (3.3) Phase correction: Calculate the phase sequence after eliminating wobbling error and random error.

[0070] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the protection scope of the present invention.

Claims

1. A method for eliminating the wobbling error of a three-dimensional laser imager, characterized in that: It includes the following steps: (1) Two phase differences are used The transmitted signal is at the same distance position Perform measurements, obtain the phase values ​​of two measurements, and generate a measurement vector. ; (2) The noise covariance matrix is ​​evaluated by combining the relevant Kalman filter and the maximum likelihood criterion method, and the measurement vector is... As input, the state vector As an output value, it eliminates random errors during the operation of the 3D laser imager; (3) The two measurement vector sequences obtained in step (1) and The state vector is output as the input value of step (2). Return to step (1) for further processing to generate a state vector sequence. And calculate the measured phase value, process the two measurement results in step (1) respectively, and obtain the corrected phase value; Step (1) includes the following sub-steps: (1.1) In the first measurement, the phase value of the reflected signal is measured directly. Its measured phase value Oscillation error value and theoretical phase value They are respectively: （1） （2） （3） in This is a constant, representing the ratio of the third harmonic coefficient to the fundamental frequency coefficient; (1.2) In the second measurement, the phase difference between its transmitted signal and the first measurement is... The phase shift of the measured echo signal will also increase. The second measurement of the phase value Oscillation error value and theoretical phase value They are respectively: （4） （5） （6）； (1.3) The swing error values ​​of the two phase measurements are opposite. The two measurement values ​​are processed and the swing error value is eliminated to obtain the final measured phase value. : （7） （8）。 2. The method for eliminating the wobbling error of a three-dimensional laser imager according to claim 1, characterized in that: Step (2) includes the following sub-steps: (2.1) Initialize the state estimate Error covariance matrix Process noise covariance matrix and measurement noise covariance matrix ; (2.2) Predicted state estimate And error covariance matrix : （9） （10） in It is the state transition matrix; (2.3) Calculate the gain value Updated error covariance New interest sequence and the updated state estimate : （11） （12） （13） （14） (2.4) Calculate the maximum likelihood estimate covariance of the new sequence And correct the process noise covariance matrix. : （15） （16） (2.5) Measurement vector As input, the state vector of the 3D laser imager As output, utilize Calculate the measured phase value after eliminating random errors. : （17）。 3. The method for eliminating the wobbling error of a three-dimensional laser imager according to claim 2, characterized in that: Step (3) includes the following sub-steps: (3.1) State estimation: The intensity data from the two measurements are used as measurement vector sequences respectively. and Input into step (2) to obtain the system state vector sequence. and ; (3.2) Phase calculation: The phase sequence of the two measurements is calculated using the system state vector sequence. and ; (3.3) Phase correction: Calculate the phase sequence after eliminating wobbling error and random error. .

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