A three-dimensional water tank positioning precision detection method based on laser tracker refraction compensation

Abstract

The application discloses a three-dimensional water tank positioning precision detection method based on laser tracker refraction compensation, which comprises the following steps: a laser tracker is used to measure the displacement of a target ball in a three-dimensional water tank filled with water according to a conventional method; then, an ADM refraction compensation model and an IFM refraction compensation model are respectively established; the position coordinates of the target ball are solved and the positioning precision of the three-dimensional water tank is calculated. The application has the beneficial effects that: by establishing the refraction compensation model, the measurement error caused by the refractive indexes of glass and water is compensated, the actual position coordinates of the target ball can be finally obtained, the positioning precision of the three-dimensional water tank is realized to be detected in a high-precision non-contact underwater mode, an effective method is provided for solving the metrology demand and value traceability problem of the positioning precision of the three-dimensional water tank, and the uncertainty in the whole radiotherapy process including simulation positioning, plan design, treatment implementation and the like is reduced, so that the accuracy and curative effect of the radiotherapy are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of three-dimensional water tank positioning accuracy detection method based on laser tracker refraction compensation, belong to medical equipment detection technical field.The method can also be applicable to all laser tracker under parallel multiple medium measurement occasion. BACKGROUND

[0002] In recent years, radiotherapy has become one of the three means of treating cancer, and medical linear accelerator is the main clinical equipment for implementing precise radiotherapy of tumor. Whether the radiotherapy dose is accurate or not is related to the treatment effect and life safety of patients. In the periodic verification and acceptance of medical linear accelerator and the data acquisition work of treatment planning system, three-dimensional water tank is an irreplaceable quality control tool. It realizes the automatic measurement of water absorption dose distribution of ray beam through the movement of probe by three-dimensional driving mechanism, and the measurement result is of great significance for the verification of radiotherapy dose, the formulation and implementation of treatment plan. In the measurement process, the accuracy of the position of the probe in the water will have a great influence on the measurement result. How to accurately and non-destructively detect the positioning accuracy of three-dimensional water tank becomes a necessary work. The existing detection method mainly detects the positioning accuracy by measuring the displacement of the motion trajectory extension device of the probe, which will cause a large weight on the motion guide rail, not only causing measurement error, but also easily damaging the motion guide rail. SUMMARY

[0003] The present application provides a kind of three-dimensional water tank positioning accuracy detection method based on laser tracker refraction compensation to solve the above problems existing in prior art.

[0004] The technical scheme adopted by the present application is: a kind of three-dimensional water tank positioning accuracy detection method based on laser tracker refraction compensation, characterized by comprising:

[0005] Step (1): using laser tracker to measure the displacement of target ball in the three-dimensional water tank filled with water according to the conventional method;

[0006] Step (2): error correction is carried out on the displacement measured by laser tracker;

[0007] Step (3): calculate the positioning accuracy of three-dimensional water tank.

[0008] The beneficial effects of the present application are: by establishing a refraction compensation model, the measurement error caused by the refractive index of glass and water is compensated, and finally the actual position coordinates of the target ball can be obtained, the positioning accuracy of three-dimensional water tank is realized. High-precision non-contact underwater detection provides an effective method for solving the metrology demand and value traceability problem of three-dimensional water tank positioning accuracy, which is beneficial to reduce the uncertainty in the whole radiotherapy process, including simulation positioning, plan design, treatment implementation, etc. so as to improve the accuracy and efficacy of radiotherapy. BRIEF DESCRIPTION OF DRAWINGS

[0009] Figure 1 is the framework diagram of the three-dimensional water tank positioning precision detection method of the present application;

[0010] Figure 2 is the detection principle schematic diagram of the present application;

[0011] Figure 3 is the target ball position dynamic measurement process and laser beam path change condition schematic diagram of the target ball position dynamic measurement process of the present application;

[0012] Figure 4 is the ADM phase method ranging refraction compensation principle schematic diagram of the present application;

[0013] Figure 5 is the IFM interference method ranging refraction compensation principle schematic diagram of the present application;

[0014] Figure 6 is the target ball position coordinate solving method flow chart of the present application.

[0015] BRIEF DESCRIPTION OF DRAWINGS: 1, laser tracker, 2, tripod, 3, three-dimensional water tank, 4, target ball, 5, motion guide rail, 6, trolley, 7, air laser beam, 8, ADM laser beam in water, 9, IFM laser beam in water, 10, water surface, 11, beam splitter, 12, reference beam, 13, air, 14, glass, 15, water. DETAILED DESCRIPTION

[0016] In order to make the purpose, technical scheme and advantages of the present application more clear and obvious, the present application is further described in detail below in combination with the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application, and are not used to limit the present application.

[0017] In combination with Figure 1 and Figure 2 shown, the three-dimensional water tank positioning precision detection method based on laser tracker refraction compensation of the present application first measures the displacement amount of the target ball 4 in the three-dimensional water tank 3 filled with water by using the laser tracker 1 according to the conventional method; then an ADM refraction compensation model is established and an IFM refraction compensation model is established; then the target ball position coordinates are solved, and the three-dimensional water tank positioning precision is calculated.

[0018] As Figure 2As shown, during the three-dimensional water tank positioning accuracy test, the laser tracker 1 is mounted on the tripod 2, the target ball 4 is fixed on the motion guide rail 5 of the three-dimensional water tank 3, and the three-dimensional water tank 3 is mounted on the trolley 6. During the measurement process, after the target ball 4 is initialized at the bird's nest position of the laser tracker 1, the light is first cut off on the outside of the glass wall of the three-dimensional water tank 3. In the waterless state, the target ball 4 is fixed on the motion guide rail 5 and the light is resumed. When the light is resumed, the absolute distance is measured by the ADM and used as the reference distance. Then, water is added into the three-dimensional water tank 3 (the water surface is above the target ball 4). Since the ADM and IFM use lasers of different wavelengths, the ADM will deviate from the center of the target ball 4 and will no longer participate in the measurement. Subsequently, the IFM measures the displacement of the target ball 4 relative to the coordinate origin O in the three-dimensional water tank 3.

[0019] like Figure 3 As shown, when target ball 4 is at position P0, this is its initial position. The laser beam (emitted from point O) travels through air, glass, and water to reach the target ball 4, corresponding to the optical path OB0—B0C0—C0P0. Q0 is a point on the extension line of OB0. If the length of OQ0 is equivalent to the measurement distance of laser tracker 1, then the actual measurement value of laser tracker 1 is the coordinate value of point Q0. According to the ADM phase method ranging principle, as... Figure 4 As shown, the laser beam travels from the emission point O to the reflection point P0 and then back to O'. The distance between the emission point O and the reflection point P0 is L. Then we have:

[0020]

[0021] The speed of light in a vacuum is c, and the air refractive index corresponding to ADM is n. a_ADM The glass refractive index is n g_ADM The refractive index of water is n w_AMD If the round-trip time of the laser is t, then:

[0022]

[0023] Decompose Δφ into the phase difference that travels back and forth between OB0. Phase difference between B0C0 and the round trip The phase difference between the round trip between C0P0 and C0P0 Then we have:

[0024]

[0025] In equation (3), f is the laser frequency, N is an integer multiple of 2π in the phase change, and Δφ1 is the co-phase of the incomplete periodic wave.

[0026] L can be solved from equation (3) as follows:

[0027]

[0028] The ADM of the laser tracker calculates L using the air refractive index, which will produce a measurement error, and the actual distance OQ0 measured by the ADM is:

[0029]

[0030] The measurement error of the ADM can be obtained from equations (4) and (5) as:

[0031]

[0032] When the target ball moves from point P0 to P1 with the three-dimensional water tank in water, the displacement of the target ball relative to the coordinate origin is measured by the IFM, and Q1 is the actual position coordinate measured by the laser tracker. According to the principle of interferometric ranging, as shown in Figure 5 , the optical path difference between the measurement light and the reference light at the P0 position is:

[0033]

[0034] In equation (7), d1 and d2 are the propagation distances of the IFM beams in glass and water, respectively.

[0035] The target ball moves Δd1 relative to the coordinate origin from P0 to P1, and the optical path difference at this time is:

[0036]

[0037] In this process, the change in the optical path difference is:

[0038]

[0039] The light interference fringes change alternately once, and the optical path difference changes by one wavelength. Assuming that the wavelength of the laser in vacuum is λ0, it can be seen that the number of times the interference fringes change alternately is:

[0040]

[0041] The laser tracker will calculate the distance of the target ball movement according to the wavelength of the laser in air, and the actual calculated distance of the target ball movement is:

[0042]

[0043] From equation (11), it can be seen that the IFM distance measurement error is:

[0044]

[0045] By analogy, when i > 2, the IFM distance measurement error at P i is: ​

[0046]

[0047] After obtaining the ranging errors of ADM and IFM, the target ball's position coordinates can be further calculated. The process for calculating the target ball's position coordinates is as follows: Figure 6 As shown, combined with Figure 3 The laser tracker measured Q i Coordinates OQ i The direction vector is

[0048] The plane equation of the outer surface of the glass, obtained by measurement, is as follows:

[0049] Ax + By + Cz + D = 0 (14)

[0050] Its normal vector is n = (A, B, C). The inner surface of the glass is parallel to the outer surface. The thickness of the glass is measured to be h. If n is a unit vector, then the plane equation of the inner surface of the glass is:

[0051] Ax + By + Cz + D + h = 0 (15)

[0052] Let B i The coordinates are From the plane equation of the outer surface of the glass and OQ i The direction vector can be used to obtain OQ. i Intersection B with the outer surface of the glass i and the angle with the normal.

[0053]

[0054]

[0055] E i For B i The projection points O and E on the inner surface of the glass. i B i It can form a refracting plane, let E i The coordinates are B i E i vector e is parallel to n, and E i On the inner surface of the glass, that is:

[0056]

[0057] E can be solved from equation (18) i The coordinates are used to determine the normal vector of the refraction plane, OB. i vector The normal vector t of the refractive plane is the outer product of e and b.

[0058] t = e x b (19)

[0059] That is the incident angle, according to the refractive index, the refractive angle can be obtained and When i = 0, n a = n a_ADM , n g = n g_ADM ; when i > 0, n a = n a_IFM , n g = n g_IFM .

[0060]

[0061]

[0062] The thickness of the glass is h, and then the propagation distance of light in the glass can be obtained:

[0063]

[0064] Let the coordinates of C i be OC i vector is perpendicular to t, C i satisfies the following equation group:

[0065]

[0066] From equation (23), the coordinates of C i can be solved.

[0067] From the measurement error of ADM and IFM, when i = 0, the length of C i P i is:

[0068]

[0069] When i > 0, the length of C i P i is:

[0070]

[0071] Let the target ball position coordinates be The direction vector of C i P i is P i satisfies the following equation group:

[0072]

[0073] From equation (26), the target ball position coordinate P can be solved i .

[0074] Finally, the positioning accuracy of the three-dimensional water tank is determined by comparing the compensated adjacent target ball position distance and the movement instruction of the three-dimensional water tank. If the movement instruction of the three-dimensional water tank is L i , then the positioning accuracy can be expressed as:

[0075]

[0076] The above describes the specific embodiments of the present application in combination with the drawings, but is not a limitation on the protection scope of the present application. Those skilled in the art should understand that various modifications or changes made by those skilled in the art on the basis of the technical solutions of the present application without creative labor are still within the protection scope of the present application.

Claims

1. A three-dimensional water tank positioning accuracy detection method based on laser tracker refraction compensation, characterized in that, The method comprises the following steps: Step (1): measuring the displacement of the target ball in the three-dimensional water tank filled with water by using a laser tracker according to a conventional method; Step (2): correcting the displacement measured by the laser tracker; Step (3): calculating the positioning accuracy of the three-dimensional water tank; The step (2) comprises establishing an ADM refraction compensation model and an IFM refraction compensation model, and solving the position coordinates of the target ball according to the ADM refraction compensation model and the IFM refraction compensation model. The method for establishing the ADM refraction compensation model is based on the phase ranging principle, and uses the refractive index of the medium to compensate the ranging error in glass and water. If the target ball is at the P0 position, the propagation distance of light in glass is The propagation distance in water is The air refractive index, glass refractive index and water refractive index corresponding to the ADM are na ADM, ng ADM and nw ADM respectively, and the measurement error of the ADM is represented as:

2. The three-dimensional water tank positioning precision detection method based on laser tracker refraction compensation according to claim 1, characterized in that, The method for establishing the IFM refraction compensation model is based on the interferometric ranging principle, and uses the refraction index of the medium to compensate the ranging error in the glass and water. If the target ball is at the Pi position, the propagation distance of the light in the glass is The propagation distance in the water is The air refraction index, the glass refraction index and the water refraction index corresponding to the IFM are na_IFM, ng_IFM and nw_IFM respectively, and the measurement error of the IFM is expressed as: In the formula, i-1 refers to the last position before the target ball moves to the ith position.

3. The three-dimensional water tank positioning precision detection method based on laser tracker refraction compensation according to claim 1, characterized in that, The specific method for solving the position coordinates of the target ball comprises: Step 1: inputting the value coordinates of the measurement points of the laser tracker; Step 2: determining the glass plane equation, and solving the incident point coordinates and the incident angle; Step 3: calculating the refraction angles of the laser beam in the glass and in the water respectively according to the refraction law; Step 4: measuring the glass thickness, and calculating the propagation distance of the light in the glass according to the refraction angle of the laser beam in the glass; Step 5: solving the projection point of the incident point on the glass plane, and determining the refraction plane equation; Step 6: solving the exit point coordinates from the three constraint conditions of the propagation distance of the laser beam in the glass, the exit point located in the glass plane and the refraction plane; Step 7: compensating the ranging error of the ADM and the IFM, and calculating the propagation distance of the laser beam in the water; and Step 8: solving the position coordinates of the target ball from the three constraint conditions of the propagation distance of the laser beam in the water, the refraction angle in the water and the target ball position located in the refraction plane.

4. The three-dimensional water tank positioning precision detection method based on laser tracker refraction compensation according to claim 1, characterized in that, The method for calculating the positioning accuracy of the three-dimensional water tank is: comparing the compensated adjacent target ball position interval and the moving instruction of the three-dimensional water tank to determine the positioning accuracy of the three-dimensional water tank, if the compensated adjacent target ball position interval The moving instruction of the three-dimensional water tank is Li, and the positioning accuracy can be represented as:

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