An improved three-dimensional measurement method based on three-frequency heterodyne

Abstract

The application provides an improved three-dimensional measurement method based on three-frequency heterodyne, comprising the following steps: selecting a suitable period combination of the fringe according to a fringe selection method, projecting three groups of fringe images with different periods, collecting the deformed fringe by a CCD, calculating the wrapped phase by using a multi-step phase shift method, obtaining a continuous phase image by using an improved phase difference operation, obtaining a phase image with a frequency higher than the projected fringe frequency by using an improved phase sum operation, calculating the order information of the phase sum image by using the continuous phase difference image, and finally obtaining the continuous phase distribution of the object. The application provides an improved three-dimensional measurement method based on three-frequency heterodyne, the method uses a fringe period optimization method, a better period combination is obtained before measurement, the improved phase operation can obtain a phase distribution with a higher equivalent frequency and a better noise resistance, and the measurement precision is effectively improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of three-dimensional measurement, in particular to an improved three-dimensional measurement method based on three-frequency heterodyne. BACKGROUND

[0002] The fringe projection profilometry is an optical three-dimensional profilometry technology based on grating projection and phase measurement. With the development of digital projectors and sensor devices, the method can obtain high-precision three-dimensional information at a very low cost, and is widely used in many fields such as mechanical assembly, device modification, biological medicine and cultural relic protection.

[0003] In structured light three-dimensional measurement, the core content is to obtain the continuous phase distribution of the measured object. Since the phase extraction is calculated by using the inverse trigonometric function, the calculated phase value is truncated, and therefore the truncated discontinuous phase needs to be recovered.

[0004] There are two main methods for phase recovery, namely spatial phase recovery and temporal phase recovery. The spatial phase recovery method is susceptible to noise, and the error caused by noise will spread to other positions. The temporal phase recovery method is to recover the phase by using the pixels at the same position at adjacent times, and the error caused by noise will not spread to other positions. In the temporal phase recovery method, the three-frequency heterodyne phase recovery method is widely used in many fields due to its high precision, simple implementation and moderate data requirement. However, due to the reduction of equivalent frequency and the increase of noise in the phase calculation process of the method, the measurement accuracy is reduced.

[0005] Therefore, it is necessary to provide an improved three-dimensional measurement method based on three-frequency heterodyne to solve the above technical problems. SUMMARY

[0006] The present application provides an improved three-dimensional measurement method based on three-frequency heterodyne, which solves the problem of reduction of equivalent frequency and increase of noise in the phase calculation process of the method, resulting in reduction of measurement accuracy.

[0007] To solve the above technical problems, the present application provides an improved three-dimensional measurement method based on three-frequency heterodyne, comprising the following steps:

[0008] S1: selecting a suitable fringe period combination according to the fringe selection method;

[0009] S2: projecting three groups of fringe images with different periods, and collecting the deformed fringe by CCD;

[0010] S3: calculating the wrapped phase using the multi-step phase shift method;

[0011] S4: obtaining the continuous phase image using the improved phase difference operation;

[0012] S5: Obtain phase image with frequency higher than the projected fringe frequency using the improved phase and operation;

[0013] S6: Calculate the order information of the phase and image using the continuous phase difference image, and finally obtain the continuous phase distribution of the object.

[0014] Preferably, the S1 comprises the following steps:

[0015] S101: Fringe selection method, according to the linear function fitted by the small error period combination point, the optimal period combination is calculated by the linear function.

[0016] S102: Fit the obtained linear function as:

[0017] T2=round{k1T3+k2}

[0018] T1=round{k3T2+k4}

[0019] Where round{·} is the nearest rounding, T1, T2, T3 are fringe periods, and T1

[0020] k1=0.9691

[0021] k2=-0.2224

[0022] k3=0.934

[0023] k4=1.498

[0024] Preferably, the S3 comprises the following steps:

[0025] S301: According to the deformed fringe obtained in S2 step, its expression is:

[0026]

[0027] Where I n (x,y) is the obtained deformed fringe, A(x,y) is the background light intensity, B(x,y) is the modulation light intensity, n is the phase shift step index, N is the phase shift step, is the phase of the object.

[0028] S302: Calculate the wrapped phase using the obtained deformed fringe image, and the calculation formula is:

[0029]

[0030] Preferably, the S4 comprises the following steps:

[0031] S401: using the wrapped phase to perform twice improved phase difference operation, the first phase difference operation formula is:

[0032]

[0033] wherein is the wrapped phase obtained by calculating three kinds of periodical fringes, and is the phase obtained by the first phase difference operation, after the first phase difference operation is completed, the synthetic phase period is enlarged.

[0034] S402: before the next phase difference operation is performed, according to the statistical rule of the difference value divided into two parts, the Otsu threshold segmentation algorithm is used to calculate the intermediate threshold of the phase difference value, the calculation formula is:

[0035] T h = Ostu{φ 12d - φ 23d}

[0036] wherein Ostu{·} is the Otsu threshold segmentation operation, T h is the threshold obtained by calculation.

[0037] S403: after the threshold is obtained, the second phase difference operation is performed:

[0038]

[0039]

[0040] f 12d = f1-f2,f 23d = f2-f3,f 123d = f 12d -f 23d

[0041] f 123d <f 23d <f 12d <f3<f2<f1

[0042] Preferably, the S5 comprises the following steps:

[0043] S501: using the wrapped phase to perform twice improved phase and operation, the first phase and operation formula is as follows:

[0044]

[0045] and is the phase obtained by the first phase and operation, after the first phase and operation is completed, the obtained phase distribution frequency is improved.

[0046] S502: In order to ensure that the correct frequency phase distribution can be obtained after the second phase and operation, the first result is numerically moved, and the calculation formula is:

[0047]

[0048] wherein is the phase distribution after numerical movement.

[0049] S503: Using the result obtained by the first operation, the second phase and operation is carried out, and the operation formula is as follows:

[0050]

[0051] f 12s = f1+f2, f 23s = f2+f3, f 123s = f 12s + f 23s

[0052] f3 < f2 < f1 < f 23s < f 12s < f 123s

[0053] Preferably, the S6 comprises the following steps:

[0054] S601: Using continuous phase difference to solve the order information of higher frequency phase sum, the phase sum is restored to continuous phase, and the calculation formula is as follows:

[0055]

[0056]

[0057] Preferably, the CCD collects the deformed stripes in S2, and a collecting device is required, the collecting device comprises a fixing seat, a rotating disc is rotatably connected to the surface of the fixing seat through a rotating shaft, and a fixing ring is arranged on the surface of the fixing nail seat.

[0058] Preferably, the surface of the fixing ring is provided with a supporting assembly, the supporting assembly comprises an annular groove, an arc-shaped sliding block is slidably connected to the inside of the annular groove, a supporting seat is connected to the surface of the arc-shaped sliding block, a rotating seat is connected to the surface of the supporting seat, a fixing piece is arranged on one side of the rotating seat, a positioning piece is connected to the bottom of the arc-shaped sliding block, and an annular communication groove is formed in the bottom of the inner wall of the annular groove.

[0059] Preferably, an adjustment component is provided on one side of the rotating seat, the adjustment seat includes a fixed rod, a scale rod is provided on the surface of the rotating seat on the side opposite to the fixed rod, and an adjustment seat is provided between the fixed rod and the scale rod.

[0060] Preferably, a fixing component is provided on one side of the adjusting seat. The fixing component includes a fixing frame, and connecting rods are connected to both sides of the surface of the fixing frame. A movable part is provided between the two connecting rods, and snap-fit ​​parts are provided on both sides of the movable part. A connecting part is provided inside the fixing frame.

[0061] Compared with related technologies, the improved three-dimensional measurement method based on three-frequency heterodyne provided by this invention has the following beneficial effects:

[0062] This invention provides an improved three-dimensional measurement method based on three-frequency heterodyne. This method uses a fringe period optimization method to obtain a better period combination before measurement. The improved phase operation can obtain a phase distribution with a higher equivalent frequency and better noise resistance, effectively improving the measurement accuracy. Attached Figure Description

[0063] Figure 1 A schematic diagram of the structure of a first embodiment of an improved three-dimensional measurement method based on three-frequency heterodyne provided by the present invention;

[0064] Figure 2 This is a schematic diagram of the measurement system.

[0065] Figure 3 The results obtained from each operation are shown in the graph;

[0066] Figure 4 This is a statistical chart of the results of the first phase difference calculation.

[0067] Figure 5 The measurement results are shown in the figure.

[0068] Figure 6 A graph showing the error comparison between different methods and the true value;

[0069] Figure 7 This is a schematic diagram of the structure of a second embodiment of an improved three-dimensional measurement method based on three-frequency heterodyne provided by the present invention;

[0070] Figure 8 for Figure 7 The enlarged schematic diagram of part A shown below;

[0071] Figure 9 for Figure 7 A schematic diagram of the overall three-dimensional structure of the device shown;

[0072] Figure 10 forFigure 9 B part enlarged schematic view.

[0073] Figure label: 1, fixed seat, 2, rotating disc,

[0074] 3, support assembly, 31, annular groove, 32, arc-shaped sliding block, 33, support seat, 34, rotating seat, 35, fixing piece, 36, positioning piece, 37, annular communication groove,

[0075] 4, adjusting assembly, 41, fixed rod, 42, scale rod, 43, adjusting seat,

[0076] 5, fixed ring,

[0077] 6, fixing assembly, 61, fixing frame, 62, connecting rod, 63, movable piece, 64, clamping piece, 65, connecting piece. DETAILED DESCRIPTION

[0078] The application will be further described below in conjunction with the drawings and embodiments.

[0079] First embodiment

[0080] Please refer to Figure 1 , Figure 2 , Figure 3 , Figure 4 , Figure 5 and Figure 6 , among them, Figure 1 is a structure schematic view of the first embodiment of an improved three-dimensional measurement method based on three-frequency heterodyne provided by the application; Figure 2 Figure 3 is a result graph obtained by each operation; Figure 4 is a first phase difference operation result statistical graph; Figure 5 is a measurement result graph; Figure 6 is an error comparison graph of different methods and true value. An improved three-dimensional measurement method based on three-frequency heterodyne, comprising the following steps:

[0081] S1: selecting appropriate stripe period combination according to stripe selection method;

[0082] S2: projecting three groups of stripe images with different periods, and CCD collecting deformed stripes;

[0083] S3: calculating wrapped phase using multi-step phase shift method;

[0084] S4: obtaining continuous phase image using improved phase difference operation;

[0085] S5: obtaining phase image with frequency higher than that of projected stripe using improved phase sum operation;

[0086] ​S6: using the continuous phase difference image to calculate the phase and the order information of the image, and finally obtaining the continuous phase distribution of the object.

[0087] The S1 comprises the following steps:

[0088] S101: a stripe selection method, according to the linear function fitted by the small error period combination points, the optimal period combination is calculated by the linear function.

[0089] S102: the obtained linear function is fitted as:

[0090] T2 = round{k1T3+k2}

[0091] T1 = round{k3T2+k4}

[0092] Where round{·} is the nearest rounding, T1, T2, T3 are the stripe periods, and T1 < T2 < T3, through multiple repeated experiments, the values of k1, k2, k3, k4 are obtained as follows:

[0093] k1 = 0.9691

[0094] k2 = -0.2224

[0095] k3 = 0.934

[0096] k4 = 1.498

[0097] Before measurement, first determine the maximum period of the selected stripe, and then calculate the size of the other two groups of stripes by the function.

[0098] The S3 comprises the following steps:

[0099] S301: according to the deformed stripe obtained in the S2 step, the expression is:

[0100]

[0101] Where I n (x, y) is the obtained deformed stripe, A(x, y) is the background light intensity, B(x, y) is the modulation light intensity, n is the phase shift step index, N is the phase shift step, is the phase of the object.

[0102] S302: using the obtained deformed stripe image to calculate the wrapped phase, the calculation formula is:

[0103]

[0104] The phase obtained by using the above formula is the wrapped phase, and the three-frequency heterodyne method is used to restore the wrapped phase to the continuous phase.

[0105] The S4 includes the following steps:

[0106] S401: using the wrapped phase to perform twice improved phase difference operation, the first phase difference operation formula is:

[0107]

[0108] Wherein is the wrapped phase obtained by calculating three kinds of periodical fringes, and is the phase obtained by the first phase difference operation, after the first phase difference operation is completed, the synthetic phase period is expanded.

[0109] S402: before the next phase difference operation is performed, according to the statistical rule of the difference value divided into two parts, the Otsu threshold segmentation algorithm is used to calculate the intermediate threshold value of the phase difference value, the calculation formula is:

[0110] T h =OSTU{φ 12d -φ 23d}

[0111] Wherein OSTU{·} is the Otsu threshold segmentation operation, T h is the threshold value obtained by calculation.

[0112] S403: after the threshold value is obtained, the second phase difference operation is performed:

[0113]

[0114]

[0115] f 12d =f1-f2,f 23d =f2-f3,f 123d =f 12d -f 23d

[0116] f 123d <f 23d <f 12d <f3<f2<f1

[0117] Wherein is the phase obtained by the second phase difference operation, f id is the frequency of the synthetic phase (i=12, 23, 123), after twice phase difference operation, the final phase obtained is the continuous phase.

[0118] The S5 includes the following steps:

[0119] S501: using the wrapped phase to perform twice improved phase and operation, the first phase and operation formula is as follows:

[0120]

[0121] And The phase obtained by the first phase and operation, after the first phase and operation, the obtained phase distribution frequency is improved.

[0122] S502: in order to ensure that the correct frequency phase distribution can be obtained after the second phase and operation, the numerical value of the first result is moved, and the calculation formula is as follows:

[0123]

[0124] Among them The phase distribution after numerical value movement.

[0125] S503: using the result obtained by the first operation to perform the second phase and operation, the operation formula is as follows:

[0126]

[0127] f 12s =f1+f2,f 23s =f2+f3,f 123s =f 12s +f 23s

[0128] f3 23s 12s 123s

[0129] Among them The phase obtained by the second phase and operation, f is The frequency of the synthesized phase (i=12,23,123), after the second phase and operation, the frequency of the obtained phase sum is higher than the frequency of all the projection stripes.

[0130] The S6 includes the following steps:

[0131] S601: using continuous phase difference to solve the order information of higher frequency phase sum, restoring the phase sum to continuous phase, the calculation formula is as follows:

[0132]

[0133]

[0134] Where k is the order of phase, Φ​​i Φ is the continuous phase of lower frequency h Φ is the continuous phase of higher frequency, the phase is unfolded step by step, and finally the continuous phase of the highest frequency is obtained.

[0135] Embodiment one

[0136] The improved three-dimensional measurement method based on three-frequency heterodyne of the embodiment is shown in the flow chart as Figure 1 The method comprises the following steps:

[0137] Step a, select appropriate period combination of the fringe according to the fringe selection method.

[0138] Step b, project three groups of fringe images with different periods, and CCD collects the deformed fringe.

[0139] Step c, calculate the wrapped phase using the multi-step phase shift method.

[0140] Step d, perform the first phase difference and phase sum operation.

[0141] Step e, perform the second phase difference and phase sum operation.

[0142] Step f, use the phase difference to assist the recovery of the phase sum, and finally obtain the continuous phase of the object.

[0143] Embodiment two

[0144] The measurement system diagram of the embodiment is shown in the specific embodiment one.

[0145] Embodiment three

[0146] The period selection of the embodiment is further limited on the basis of the specific embodiment one, and the specific steps of step a are as follows:

[0147] Step a1: the fitting function is:

[0148] T2=round{k1T3+k2}

[0149] T1=round{k3T2+k4}

[0150] Wherein:

[0151] k1=0.9691

[0152] k2=-0.2224

[0153] k3=0.934

[0154] k4=1.498

[0155] First, determine the maximum fringe period required for measurement, and then use the function to calculate the values of the other two groups of periods.

[0156] Embodiment four

[0157] This embodiment is based on specific embodiment one, and the step d scheme is described. After the first phase difference operation, the threshold value between the middle two groups of data is calculated according to the distribution rule of the difference value using the Otsu threshold segmentation algorithm, as shown in Figure 3 .

[0158] Embodiment five

[0159] The phase difference and phase sum technology of this embodiment is based on specific embodiment one, and the specific steps of step e are as follows:

[0160] Step e1: the second phase difference is operated using the threshold value obtained by the Otsu method, and the calculation formula is:

[0161]

[0162] Step e2: the second phase sum is operated using the phase after numerical movement, and the calculation formula is:

[0163]

[0164] Embodiment six

[0165] The phase unwrapping method of this embodiment is based on specific embodiment one, and the specific steps of step f are as follows:

[0166] The order of using continuous low-frequency phase to solve high-frequency phase is used for phase recovery step by step, and the calculation formula is:

[0167]

[0168]

[0169] Through step-by-step recovery, the continuous phase distribution with the highest frequency is finally obtained.

[0170] Embodiment seven

[0171] The improved three-dimensional measurement method based on three-frequency heterodyne of this embodiment can obtain three-dimensional information with higher precision than specific embodiments one to six. Figure 4 is the phase operation result, Figure 5 is the phase distribution image of the object obtained by measurement, Figure 6 is compared with other methods.

[0172] Compared with the related art, the improved three-dimensional measurement method based on three-frequency heterodyne provided by the present application has the following beneficial effects:

[0173] The application provides an improved three-dimensional measurement method based on three-frequency heterodyne, which uses a stripe period optimization method, obtains better period combination before measurement, and has improved phase operation, higher equivalent frequency phase distribution and better noise resistance, thereby effectively improving the measurement precision.

[0174] Second embodiment

[0175] Please refer to Figure 7 , Figure 8 , Figure 9 and Figure 10 , based on the first embodiment of the application, an improved three-dimensional measurement method based on three-frequency heterodyne is provided, and the second embodiment of the application proposes another improved three-dimensional measurement method based on three-frequency heterodyne. The second embodiment is only a preferred mode of the first embodiment, and the implementation of the second embodiment does not affect the separate implementation of the first embodiment.

[0176] Specifically, the difference between the improved three-dimensional measurement method based on three-frequency heterodyne provided by the second embodiment of the application is that an improved three-dimensional measurement method based on three-frequency heterodyne, the CCD acquisition deformed stripe in S2 needs to use an acquisition device, the acquisition device includes a fixed seat 1, the surface of the fixed seat 1 is rotationally connected with a rotating disc 2 through a rotating shaft, and the surface of the fixed nail seat 1 is provided with a fixed ring 5.

[0177] The use of the rotating disc 2 can adjust the position of the object, and the rotating disc 2 is fixedly connected with the fixed seat 1 by arranging a fixed bolt on the surface of the rotating disc 2.

[0178] The surface of the fixed ring 5 is provided with a supporting assembly 3, the supporting assembly 3 includes an annular groove 31, the annular groove 31 is slidably connected with an arc-shaped sliding block 32, the surface of the arc-shaped sliding block 32 is connected with a supporting seat 33, the surface of the supporting seat 33 is connected with a rotating seat 34, one side of the rotating seat 34 is provided with a fixing piece 35, the bottom of the arc-shaped sliding block 32 is connected with a positioning piece 36, and a ring-shaped communication groove 37 is formed in the bottom of the inner wall of the annular groove 31.

[0179] One side of the arc-shaped sliding block 32 is connected with an arc-shaped limiting block, an arc-shaped limiting groove matched with the arc-shaped limiting block is formed in one side of the inner wall of the annular groove 31, and the positioning piece 36 is used to fixedly connect the arc-shaped sliding block 32 with the fixed ring 5, and the ring-shaped communication groove 37 facilitates the movement of the positioning piece 36.

[0180] One side of the rotating seat 34 is provided with an adjusting assembly 4, the adjusting seat 4 includes a fixed rod 41, the surface of the rotating seat 34 and located on the side opposite to the fixed rod 41 is provided with a scale rod 42, and the adjusting seat 43 is arranged between the fixed rod 41 and the scale rod 42.

[0181] The fixed rod 41, the scale rod 42 and the top end of the two connecting rods 62 are connected with the stopper, the height value of the adjusting seat 43 is adjusted and watched conveniently.

[0182] The adjusting seat 43 is provided with the fixing assembly 6 on one side, the fixing assembly 6 comprises the fixing frame 61, the both sides of the surface of the fixing frame 61 are connected with the connecting rod 62, the movable piece 63 is arranged between the two connecting rods 62, the both sides of the movable piece 63 are provided with the clamping piece 64, and the inside of the fixing frame 61 is provided with the connecting piece 65.

[0183] The movable piece 63 is provided with the movable communication hole matched with the two clamping pieces 64 on the both ends, the surface of the movable piece 63 is provided with the bolt, and the surface of the clamping piece 64 is provided with the plurality of screw holes matched with the bolt.

[0184] The working principle of the improved three-dimensional measurement method based on the three-frequency heterodyne is as follows:

[0185] When in use, when the camera is installed, first, the camera is placed on the surface of the fixing frame 61, when the camera is placed, the connecting piece 65 is used to pass through the bottom of the fixing frame 61 and extend to the surface of the fixing frame 61 and be connected with the camera, when the camera is fixed, the angle of the fixing frame 61 with the camera is adjusted, when the angle of the fixing frame 61 is adjusted, the fixing frame 61 is screw-connected with the adjusting seat 43 through the bolt, when the fixing frame 61 and the adjusting seat 43 are fixed, according to the specified height value, the adjusting seat 43 is moved between the fixed rod 41 and the scale rod 42, when the adjusting seat 43 is moved to the specified value, the bolt is used to pass through the surface of the adjusting seat 43 and be screw-connected with the fixed rod 41.

[0186] When the adjusting seat 43 is fixed, the rotating seat 34 on the surface of the supporting seat 33 is used to adjust the angle of the whole device, when the device is adjusted, the fixing piece 36 is used to fix the rotating seat 34.

[0187] When the angle of the whole device is adjusted, the arc-shaped sliding block 32 is moved in the inside of the annular groove 31 through the pushing of the supporting seat 33, when the supporting seat 33 is moved, the position of the whole device is adjusted, when the position of the device is adjusted, the arc-shaped sliding block 32 is connected with the fixing ring 5 through the bolt, and the device can be used.

[0188] When the projector is fixed, the connecting piece 65 is separated from the fixing frame 61, after the connecting piece 65 is separated from the fixing frame 61, the projector is placed on the fixing frame 61, after the projector is placed, the movable piece 63 with the two clamping pieces 64 between the two connecting rods 62 is moved to the surface of the projector by pushing, after the movable piece 63 and the clamping piece 64 contact with the projector, the movable piece 63 and the clamping piece 64 are screw-connected by using bolts.

[0189] Compared with the related art, the improved three-dimensional measurement method based on three-frequency heterodyne has the following beneficial effects:

[0190] The improved three-dimensional measurement method based on three-frequency heterodyne is provided, the rotating disc 2 is arranged on the surface of the fixing seat 1, the object is conveniently placed, and the position of the object is conveniently adjusted, the fixing ring 5 with the annular groove 31 is arranged on the surface of the fixing seat 1, the position adjustment of the used instrument is facilitated by cooperating with the supporting assembly 3, the measurement of the angle can be performed, the fixing assembly 6 is arranged on one side of the adjusting seat 43, and the camera and the projector are fixed.

[0191] The above is only the embodiment of the present application, and does not limit the patent range of the present application, and any equivalent structure or equivalent flow transformation obtained by using the content of the specification and the drawings, or direct or indirect application in other related technical fields, is also included in the patent protection range of the present application.

Claims

1. An improved three-dimensional measurement method based on three-frequency heterodyne, characterized in that, It comprises the following steps: S1: selecting a suitable fringe period combination according to a fringe selection method; S2: projecting three groups of fringe images with different periods, and collecting the deformed fringe by a CCD; S3: calculating the wrapped phase by using a multi-step phase shift method; S4: obtaining a continuous phase image by using an improved phase difference operation; S5: obtaining a phase image with a frequency higher than that of the projected fringe by using an improved phase sum operation; S6: calculating the order information of the phase sum image by using the continuous phase difference image, and finally obtaining the continuous phase distribution of the object; The collecting device is arranged when the CCD collects the deformed fringe in S2, and the collecting device comprises a fixing seat, a rotating disc is rotationally connected to the surface of the fixing seat through a rotating shaft, and a fixing ring is arranged on the surface of the fixing seat; A support assembly is arranged on the surface of the fixing ring, the support assembly comprises an annular groove, an arc-shaped sliding block is slidably connected to the inside of the annular groove, a support seat is connected to the surface of the arc-shaped sliding block, a rotating seat is connected to the surface of the support seat, a fixing piece is arranged on one side of the rotating seat, a positioning piece is connected to the bottom of the arc-shaped sliding block, and an annular communication groove is formed in the bottom of the inner wall of the annular groove; An adjusting assembly is arranged on one side of the rotating seat, the adjusting seat comprises a fixing rod, a scale rod is arranged on the surface of the rotating seat and located on the side opposite to the fixing rod, and an adjusting seat is arranged between the fixing rod and the scale rod; A fixing assembly is arranged on one side of the adjusting seat, the fixing assembly comprises a fixing frame, connecting rods are connected to the surfaces of the fixing frame on both sides, an active piece is arranged between the two connecting rods, clamping pieces are arranged on both sides of the active piece, and a connecting piece is arranged in the inside of the fixing frame.

2. The improved three-dimensional measurement method based on three-frequency heterodyne according to claim 1, characterized in that, The S1 comprises the following steps: S101: according to the linear function fitted by the small error period combination points, the optimal period combination is calculated by the linear function; The linear function obtained in S102 is: ， wherein is rounded to the nearest integer, , , is the period of the stripes, and , by repeating the experiment several times, the value of is: 。 3. The improved three-dimensional measurement method based on three-frequency heterodyne according to claim 1, characterized in that, The S3 comprises the following steps: S301: according to the deformed fringe obtained in S2, the expression is: ， wherein is the obtained deformed fringe, is the background light intensity, is the modulated light intensity, is the phase shift step number index, is the phase shift step number, is the phase of the object; S302: the wrapped phase is calculated by using the obtained deformed fringe image, and the calculation formula is: 。 4. The improved three-dimensional measurement method based on three-frequency heterodyne according to claim 2, characterized in that, The S4 comprises the following steps: S401: the wrapped phase is used to perform twice improved phase difference operations, and the first phase difference operation formula is: ， wherein the wrapped phase calculated for the three periodic fringes, and the phase obtained from the first phase difference operation, the phase period being enlarged after the first phase difference operation is completed; S402: before the next phase difference operation, according to the statistical law of the two parts of the difference value, the Otsu threshold segmentation algorithm is used to calculate the intermediate threshold of the phase difference value, and the calculation formula is: wherein is the Otsu thresholding operation, is the computed obtained threshold; S403: after the threshold value is obtained, the second phase difference operation is performed: ， 。 5. The improved three-dimensional measurement method based on three-frequency heterodyne according to claim 4, characterized in that, The S5 comprises the following steps: S501: the wrapped phase is used to perform twice improved phase sum operations, and the first phase sum operation formula is as follows: ， and the phase obtained by the first phase and operation, after the first phase and operation, the obtained phase distribution frequency is improved; S502: in order to ensure that the correct frequency phase distribution can be obtained after the second phase sum operation, the numerical value of the first result is moved, and the calculation formula is: ， wherein is the numerically shifted phase distribution; S503: the result obtained by using the first operation is used to perform the second phase sum operation, and the operation formula is as follows: ， 。 6. The improved three-dimensional measurement method based on three-frequency heterodyne according to claim 5, characterized in that, The S6 comprises the following steps: S601: Use the continuous phase difference to solve the higher frequency phase and order information, restore the phase sum to the continuous phase, and the calculation formula is as follows: 。

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