Flexible endoscope binocular calibration method and device

Abstract

The invention belongs to the technical field of endoscope calibration, and particularly relates to a flexible endoscope double-target calibration method and device. Comprising the steps that a calibration plate is horizontally placed in a calibration working area of a calibration table top; the two to-be-calibrated flexible endoscopes are clamped on the linear sliding table modules respectively, lenses of the to-be-calibrated flexible endoscopes face the calibration plate, and the distance between the two to-be-calibrated flexible endoscopes is adjustable; the two to-be-calibrated flexible endoscopes are driven by the linear sliding table module to move up and down in the Z-axis direction and sequentially stay at a plurality of specified heights, and at each specified height, the to-be-calibrated flexible endoscopes collect image information of the calibration plate at the height; according to information of multiple images collected by the to-be-calibrated flexible endoscope, the calibration computer performs dual-target calibration on the to-be-calibrated flexible endoscope. The method is beneficial for improving the efficiency of dual-target calibration of the flexible endoscope and improving the precision of three-dimensional reconstruction.

Description

Technical Field

[0001] The present invention belongs to the technical field of endoscope calibration, and in particular relates to a flexible endoscope binocular calibration method and device. Background Art

[0002] Minimally invasive surgery has been widely used in clinical practice over the past decade or so, thanks to its advantages of minimal trauma, low infection rate, few complications, less pain for patients, and faster recovery. This has driven significant medical advancements. However, compared with traditional open surgery, it suffers from issues such as limited field of view, imprecise endoscopic positioning, and a lack of information about the surrounding environment. Traditional monocular laparoscopes commonly used in minimally invasive surgery can only capture two-dimensional images, leading to insufficient estimation of the advancement distance of surgical instruments and the depth of the body cavity. This makes it impossible to intuitively and three-dimensionally display the relationship between lesions, blood vessels, and surrounding organs and tissues in the abdominal environment. This greatly increases the difficulty and complexity of the surgery, making it more dependent on the surgeon's experience.

[0003] With the maturity of binocular vision theory and the development of computer technology, binocular endoscopes are used to calculate the depth information of the body cavity environment, stereoscopically locate the lesion area, and perform real-time and dense three-dimensional reconstruction of the collected body cavity information by computer. Simultaneous Localization and Mapping (SLAM) technology is used to establish an abdominal organ tissue model and track the laparoscope trajectory, which more accurately and realistically reflects the abdominal tissue structure and the spatial relationship of the lesion, provides doctors with visual depth information, and realizes endoscopic positioning and navigation, greatly improving the scientificity and success rate of laparoscopic minimally invasive surgery. In addition, the endoscope cannot observe the information under the surface of the organ. After using SLAM to quickly and densely reconstruct the abdominal environment, it can be fused and registered with the preoperative diagnostic CT or MRI images to display the patient's anatomical structure during the operation. At the same time, it can be combined with AR technology to superimpose additional information in the three-dimensional scene, such as annotations of the target lesion, the outline distance of the organ, the measurement of the tumor, etc., which can also achieve the expansion of the current endoscopic field of view.

[0004] The calibration accuracy of binocular endoscopes determines the accuracy of three-dimensional reconstruction. After calibration, the distance between the two endoscopes is often fixed in the existing binocular calibration method, which cannot meet the requirements of complex intra-abdominal conditions. Therefore, a flexible endoscope binocular calibration method and device are proposed to solve the above problem. Summary of the Invention

[0005] The purpose of the present invention is to provide a flexible endoscope binocular calibration method and device, which is conducive to improving the calibration efficiency of the flexible endoscope and improving the accuracy of the three-dimensional reconstruction model.

[0006] To solve the above technical problems, the present invention provides a flexible endoscope binocular positioning method, comprising the following steps:

[0007] Step 1: Place the calibration plate horizontally on the calibration work area of ​​the calibration table;

[0008] Step 2: Mount the two flexible endoscopes to be calibrated on the linear slide module respectively, so that the lenses of the flexible endoscopes to be calibrated face the calibration plate, and the distance between the two flexible endoscopes to be calibrated is adjustable;

[0009] Step 3: The linear slide module drives the two flexible endoscopes to be calibrated to move up and down along the Z axis and stop at multiple specified heights in sequence. At each specified height, the flexible endoscope to be calibrated collects image information of the calibration plate at that height;

[0010] Step 4: Based on the multiple image information collected by the flexible endoscope to be calibrated, the calibration computer performs binocular calibration on the flexible endoscope to be calibrated.

[0011] Preferably, the step two specifically includes: when the steel wire rope of the flexible endoscope to be calibrated is in an unbent state, adjusting the position of the flexible endoscope to be calibrated so that the distance between the flexible endoscope to be calibrated and the flexible endoscope to be calibrated is minimized, and at this time, it is set as the initial position L0, and adjusting the height of the linear slide module in the Z-axis direction so that the checkerboard image of the calibration plate occupies the maximum camera field of view of the flexible endoscope to be calibrated and the flexible endoscope to be calibrated, and recording the height of the linear slide module in the Z-axis direction at this time as H1.

[0012] Preferably, the step three specifically includes: starting from height H1, controlling the linear slide module to move upward ΔH along the Z-axis direction each time, for a total of N1 times, until it moves to height H2, at which time H2 = H1 + N1 * ΔH; each time the linear slide module performs a ΔH away movement, the calibration computer obtains a calibration image, and a total of N1+1 groups of checkerboard images at different Hi heights are obtained.

[0013] Preferably, the step 4 specifically includes:

[0014] Step a: The calibration computer determines the internal parameters and external parameters of the flexible endoscope to be calibrated 1 and the flexible endoscope to be calibrated 2 at the initial position L0 according to the N1+1 group of checkerboard images;

[0015] Step b: First, the position of the flexible endoscope to be calibrated in the radial direction of the circle is controlled to remain unchanged, and the steel wire rope of the flexible endoscope to be calibrated is driven, and the change of the steel wire rope at this time is recorded as ΔS; then the angle of the flexible endoscope to be calibrated on the circle is rotated N2 times in total, so that the rotation angle is 180° with the initial position L0. At this time, the change of the steel wire rope is S, where 180° = N2*ΔS, S = N2*ΔS; repeat steps 3 and a for each change;

[0016] Step c: Control the flexible endoscope to be calibrated to return to the initial position L0, drive the wire rope of the flexible endoscope to be calibrated to move the flexible endoscope in the radial direction by a distance of ΔL, record the change of the wire rope at this time as ΔX, repeat step b, move N3 times in total, move the position of the flexible endoscope to be calibrated to L, and the change of the wire rope at this time is S1, where L = N3*ΔL, S1 = N3*ΔX; repeat step b for each change;

[0017] Step d: Obtain the relationship between the calibration data of the flexible endoscope to be calibrated 1 and the flexible endoscope to be calibrated 2 and the change amount of the steel wire rope of the flexible endoscope to be calibrated 1.

[0018] Preferably, the step a specifically includes:

[0019] First, after calibrating the computer to obtain N1+1 sets of checkerboard images, the sub-pixel positions of the checkerboard corners are extracted using the checkerboard corner detection function;

[0020] Then, the Zhang Zhengyou calibration method is used to calibrate the internal parameter matrix parameters K∈R of the lens of the flexible endoscope to be calibrated 1 and the flexible endoscope to be calibrated 2 3*3 , external parameter matrix parameters R∈R 3*3 And the lens distortion parameter vector D = (k1, k2, p1, p2), where k1 and k2 are the radial distortion coefficients of the lens, and p1 and p2 are the tangential distortion coefficients.

[0021] Preferably, in the step b, the flexible endoscope to be calibrated is rotated clockwise and counterclockwise respectively, so that the flexible endoscope to be calibrated is 180° away from the initial position L0 after the rotation angle.

[0022] Preferably, the step d further includes: obtaining calibration results of the two calibrated flexible endoscopes to be calibrated based on the actual positions of the two flexible endoscopes to be calibrated and the change in the wire rope of endoscope 1 to be calibrated.

[0023] The present invention also provides a flexible endoscope binocular positioning device, which adopts the flexible endoscope binocular positioning method as described above, comprising:

[0024] a calibration table, on which a calibration plate is horizontally placed;

[0025] The linear slide module is installed on the calibration table;

[0026] The rotating disc is rotatably mounted on one end of the bracket via a rotating shaft and is parallel to the calibration plate. The other end of the bracket is connected to the driving end of the linear slide module. The rotating disc further comprises: a waist-shaped groove and a clamping slider. The rotating disc is circumferentially provided with a plurality of waist-shaped grooves, and the clamping slider is slidably clamped in the waist-shaped grooves. The clamping slider is used to fix the first flexible endoscope to be calibrated, and the rotating shaft is used to fix the second flexible endoscope to be calibrated, and the lens of the flexible endoscope to be calibrated faces the calibration plate.

[0027] The calibration computer is used to perform binocular calibration on the flexible endoscope to be calibrated according to image information collected by the flexible endoscope to be calibrated.

[0028] Preferably, the clamping slider further includes a circular through hole, through which the lens of the first flexible endoscope to be calibrated is inserted and fixed by a locking screw.

[0029] Preferably, one end of the rotating shaft is fixed to the bracket, and the other end is rotatably connected to the rotating disc through a bearing, and the rotating shaft is a hollow shaft structure, through which the lens of the second calibrated flexible endoscope is inserted and fixed by a locking screw.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] The present invention uses a linear slide module to move the flexible endoscope to be calibrated to different heights for image acquisition, and drives the clamping slider to move along the waist-shaped groove through the steel wire rope of the flexible endoscope to be calibrated, driving the rotating disk to rotate, and establishes a relationship between the steel wire rope change amount of the flexible endoscope to be calibrated in the working area and the binocular calibration result, thereby improving the flexibility of the flexible binocular endoscope in the abdominal cavity, and improving the efficiency and accuracy of the flexible endoscope binocular calibration, thereby improving the accuracy of three-dimensional reconstruction and better adapting to the complex working environment in the abdominal cavity. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a schematic structural diagram of the flexible endoscope binocular positioning device provided by the present invention.

[0033] Figure 2 This is a schematic structural diagram of the flexible endoscope provided by the present invention with a snake tube having a driving rope and a fixing rope.

[0034] Figure 3 This is a flow chart of the flexible endoscope binocular positioning method provided by the present invention.

[0035] In the figure: 1-calibration table, 2-linear slide module, 3-rotating disc, 31-waist groove, 32-clamping slider, 33-round through hole, 4-rotating shaft, 5-bracket, 6-fixing rope 1, 7-driving rope 1, 8-fixing guide hole, 9-traction guide hole, 10-driving rope 2, 11-fixing rope 2, 12-snake bone. DETAILED DESCRIPTION

[0036] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of the present invention will become more apparent from the following description. It should be noted that the drawings are greatly simplified and not to exact scale, and are only used to facilitate and clearly illustrate the embodiments of the present invention.

[0037] like Figure 1 As shown, the embodiment of the present invention specifically discloses a flexible endoscope binocular calibration device, including: a rotating disk 3, a clamping slider 32, a bracket 5, a linear slide module 2, a calibration table 1, a calibration plate ( Figure 1 Not shown) and calibration computer ( Figure 1 (not shown); the calibration plate is placed horizontally on the calibration table 1; the rotating disk 3 is parallel to the calibration table 1; one end of the bracket 5 is fixed to the linear slide module 2, and the other end is connected to the rotating disk 3 via a rotating shaft 4 and a bearing. The linear slide module 2 comprises a motor, a lead screw, a nut, a guide rod, and a guide rail. This structure is well known in the art and will not be described in detail.

[0038] like Figure 2 As shown, the embodiment of the present invention provides a structure of a flexible endoscope end snake bone, including a fixing rope 1 6, a fixing rope 2 11, a driving rope 1 7 (wire rope), a driving rope 2 10 (wire rope), a fixing guide hole 8, a driving guide hole 9 and a snake bone 12; wherein, as shown in FIG. Figure 1 As shown, the rotating disc 3 has eight identical waist-shaped grooves 31 , and the clamping slider 32 is installed on any waist-shaped groove 31 of the rotating disc 3 .

[0039] The clamping slider 32 is installed on the waist-shaped groove 31 of the rotating disk 3, and the flexible endoscope to be calibrated is fixed on the clamping slider, and the lens of the flexible endoscope to be calibrated is facing the calibration plate; the flexible endoscope to be calibrated is installed on the rotating shaft 4, and the lens of the flexible endoscope to be calibrated is facing the calibration plate.

[0040] The linear slide module 2 drives the rotating disc 3 to move up and down along the Z-axis direction and stop at multiple specified heights in turn. At each specified height, the flexible endoscope to be calibrated collects image information of the calibration plate at that height and sends it to the computer.

[0041] The rear ends of the first and second flexible endoscopes to be calibrated are connected to an endoscope acquisition control card, which is connected to a calibration computer via USB. Images captured by the first and second flexible endoscopes to be calibrated are transmitted to the calibration computer via the endoscope acquisition control card. The calibration computer performs dual-target calibration on the endoscopes based on the multiple images captured by the endoscopes to be calibrated.

[0042] like Figure 1 As shown, a circular through hole 33 is provided at the axial end of the clamping slider 32, and the end of the flexible endoscope to be calibrated is fixed to the circular through hole 33 of the clamping slider 32 by a locking screw and a locking threaded hole, and the lens of the flexible endoscope to be calibrated is facing the calibration plate; the flexible endoscope to be calibrated is installed on the rotating shaft 4 with a hollow shaft structure, and the lens of the flexible endoscope to be calibrated is kept parallel to the lens of the flexible endoscope to be calibrated, and the lens of the flexible endoscope to be calibrated is facing the calibration plate; the circular through hole 33 and the hollow shaft can clamp a flexible endoscope with a pipeline diameter less than 8 mm. The endoscope pipelines in the embodiment of the present invention are two specifications of pipelines with diameters of 6 mm and 4 mm.

[0043] like Figure 1 As shown, the rotating disc 3 is connected to the bracket 5 via the rotating shaft 4 and the bearing. Moreover, the lenses of the flexible endoscope to be calibrated in the embodiment of the present invention are all direct-view lenses.

[0044] The calibration plate is a checkerboard calibration plate. When the linear slide module 2 drives the rotating disk 3 to move along the Z-axis direction, the checkerboard calibration plate is placed on the calibration table to provide a checkerboard image for the flexible endoscope 1 and the flexible endoscope 2 to be calibrated.

[0045] like Figure 3 As shown, the present invention also provides a flexible endoscope calibration method, which specifically includes the following steps:

[0046] S1. Calibration preparation: Place the calibration plate horizontally in the calibration work area of ​​the calibration table and adjust the linear slide module to a certain distance H0. For example, the square size of the checkerboard can be 1.5mm, with a total of 9 rows and 7 columns of checkerboard.

[0047] S2. Install the flexible endoscope to be calibrated: Install the first flexible endoscope to be calibrated into the mounting slider, secure the end of the first flexible endoscope to be calibrated with the locking screw, and place the mounting slider in the extreme position of the waist groove near the center end when the two drive ropes and two fixed ropes of the first flexible endoscope to be calibrated are in an unbent state, setting it as the initial position L0. Install the second flexible endoscope to be calibrated into the rotating shaft on the bracket, and make the lenses of the first and second flexible endoscopes to be calibrated parallel and the main light direction perpendicular to the calibration table. Adjust the height of the linear slide module in the Z-axis direction so that the checkerboard image of the calibration plate occupies the maximum camera field of view of the first and second endoscopes to be calibrated, and record the height of the linear slide module as H1.

[0048] During the specific installation, the lenses of the first and second flexible endoscopes to be calibrated must be kept parallel, and the through holes must not block the lens images.

[0049] S3. Control the linear slide module to start from the height H1, and make pure translational motion upward along the Z axis at intervals of ΔH, away from the calibration plate. During the movement, the X and Y coordinates of the linear slide module remain unchanged. Move N times in total to a height of H2, where H2 = H1 + N * ΔH, ΔH can be 2 mm, and N can be 30 to 50 times.

[0050] Every time the linear slide module performs a ΔH away movement, the calibration computer obtains a calibration image, and a total of N+1 sets of checkerboard images at different Hi heights are obtained;

[0051] S4. The calibration computer determines the internal and external parameters of the flexible endoscopes to be calibrated, i.e., the first and second flexible endoscopes in the initial state L0, based on the N+1 sets of checkerboard images. Specifically, the parameters are:

[0052] Use the checkerboard corner detection function to extract the sub-pixel position of the checkerboard corners;

[0053] The internal parameter matrix parameters K∈R of the endoscope lens are calibrated using Zhang Zhengyou calibration method 3*3 , external parameter matrix parameters R∈R 3*3 And the lens distortion parameter vector D = (k1, k2, p1, p2), where k1, k2 are the radial distortion coefficients of the lens, and p1, p2 are the tangential distortion coefficients.

[0054] S5. Keep the position of the flexible endoscope to be calibrated on the waist-shaped groove unchanged, drive the driving rope of the flexible endoscope to be calibrated, record the change of the driving rope as ΔS, and the rotation angle Δθ of the rotating disk. The rotation angle Δθ is 3°~5°. Move it N times in total, and N can be 36~60 times. Move it to the rotation angle Δθ of the rotating disk so that the angle between it and the initial position L0 is 180°. The change of the driving rope at this time is S, where 180°=N*Δθ, S=N*ΔS; the snake bone end of the flexible endoscope to be calibrated can be regarded as a continuous robot. The continuous robot has the characteristics of multi-redundancy, but the bending angle and the driving amount of each segment are a single mapping relationship, and the driving amount can be calculated from the bending angle.

[0055] Repeat S3 and S4 at each change, and rotate 180° clockwise and counterclockwise at the L0 position to obtain the corresponding relationship between different changes in the drive rope and the calibration results.

[0056] S6. Return the flexible endoscope to be calibrated to its initial position L0, drive the driving rope of the flexible endoscope to be calibrated, move the clamping slider on the waist-shaped groove by ΔL, record the change ΔX of the driving rope at this time, and obtain the relationship between the change of the driving rope when the waist-shaped groove moves by ΔL and the calibration result. Repeat S5 for a total of N moves. The position of the clamping slider is L, and the change of the driving rope at this time is S1, where L = N*ΔL, S1 = N*ΔX; repeat S5 for each change.

[0057] S7. Obtain the relationship between the calibration data of the flexible endoscopes 1 and 2 to be calibrated and the change in the wire rope of the endoscope 1 to be calibrated. According to the actual positions of the two endoscopes and the change in the wire rope of the endoscope 1 to be calibrated, obtain the calibration results of the two calibrated endoscopes.

[0058] The above description is only a description of the preferred embodiments of the present invention and does not limit the scope of the present invention. Any changes and modifications made by ordinary technicians in the field of the present invention based on the above disclosure shall fall within the scope of protection of the claims.

Claims

1. A flexible endoscope binocular positioning method, characterized in that: The steps include: Step 1: Place the calibration plate horizontally on the calibration work area of ​​the calibration table; Step 2: Mount the two flexible endoscopes to be calibrated on the linear slide module respectively, so that the lenses of the flexible endoscopes to be calibrated face the calibration plate, and the distance between the two flexible endoscopes to be calibrated is adjustable; Step 3: The linear slide module drives the two flexible endoscopes to be calibrated to move up and down along the Z axis and stop at multiple specified heights in sequence. At each specified height, the flexible endoscope to be calibrated collects image information of the calibration plate at that height; Step 4: Based on the multiple image information collected by the flexible endoscope to be calibrated, the calibration computer performs binocular calibration on the flexible endoscope to be calibrated.

2. A flexible endoscope binocular positioning method according to claim 1, characterized in that: The step two specifically includes: when the steel wire rope of the flexible endoscope to be calibrated is in an unbent state, adjusting the position of the flexible endoscope to be calibrated so that the distance between the flexible endoscope to be calibrated and the flexible endoscope to be calibrated is minimized, and at this time, it is set to the initial position L0, and adjusting the height of the linear slide module in the Z-axis direction so that the checkerboard image of the calibration plate occupies the maximum camera field of view of the flexible endoscope to be calibrated and the flexible endoscope to be calibrated, and recording the height of the linear slide module in the Z-axis direction at this time as H1.

3. A flexible endoscope binocular positioning method according to claim 2, characterized in that: The step three specifically includes: starting from height H1, controlling the linear slide module to move upward along the Z-axis direction by ΔH each time, for a total of N1 times, until it moves to height H2, at which time H2 = H1 + N1 * ΔH; each time the linear slide module performs a ΔH away movement, the calibration computer obtains a calibration image, and a total of N1 + 1 sets of checkerboard images at different Hi heights are obtained.

4. A flexible endoscope binocular positioning method according to claim 3, characterized in that: The step 4 specifically includes: Step a: The calibration computer determines the internal parameters and external parameters of the flexible endoscope to be calibrated 1 and the flexible endoscope to be calibrated 2 at the initial position L0 according to the N1+1 group of checkerboard images; Step b: First, the position of the flexible endoscope to be calibrated in the radial direction of the circle is controlled to remain unchanged, and the steel wire rope of the flexible endoscope to be calibrated is driven, and the change of the steel wire rope at this time is recorded as ΔS; then the angle of the flexible endoscope to be calibrated on the circle is rotated N2 times in total, so that the rotation angle is 180° with the initial position L0. At this time, the change of the steel wire rope is S, where 180° = N2*ΔS, S = N2*ΔS; repeat steps 3 and a for each change; Step c: Control the flexible endoscope to be calibrated to return to the initial position L0, drive the wire rope of the flexible endoscope to be calibrated to move the flexible endoscope in the radial direction by a distance of ΔL, record the change of the wire rope at this time as ΔX, repeat step b, move N3 times in total, move the position of the flexible endoscope to be calibrated to L, and the change of the wire rope at this time is S1, where L = N3*ΔL, S1 = N3*ΔX; repeat step b for each change; Step d: Obtain the relationship between the calibration data of the flexible endoscope to be calibrated 1 and the flexible endoscope to be calibrated 2 and the change amount of the steel wire rope of the flexible endoscope to be calibrated 1.

5. A flexible endoscope binocular positioning method according to claim 4, characterized in that: The step a specifically includes: First, after calibrating the computer to obtain N1+1 sets of checkerboard images, the sub-pixel positions of the checkerboard corners are extracted using the checkerboard corner detection function; Then, the Zhang Zhengyou calibration method is used to calibrate the internal parameter matrix parameters K∈R of the lens of the flexible endoscope to be calibrated 1 and the flexible endoscope to be calibrated 2 3*3 , external parameter matrix parameters R∈R 3*3 And the lens distortion parameter vector D = (k1, k2, p1, p2), where k1 and k2 are the radial distortion coefficients of the lens, and p1 and p2 are the tangential distortion coefficients.

6. A flexible endoscope binocular positioning method according to claim 4, characterized in that: In the step b, the flexible endoscope to be calibrated is rotated clockwise and counterclockwise respectively, so that the flexible endoscope to be calibrated is 180° away from the initial position L0 after the rotation angle.

7. A flexible endoscope binocular positioning method according to claim 4, characterized in that: The step d also includes: obtaining calibration results of the two calibrated flexible endoscopes to be calibrated based on the actual positions of the two flexible endoscopes to be calibrated and the change in the wire rope of the endoscope 1 to be calibrated.

8. A flexible endoscope binocular positioning device, using a flexible endoscope binocular positioning method according to any one of claims 1 to 7, characterized in that: include: a calibration table, on which a calibration plate is horizontally placed; The linear slide module is installed on the calibration table; The rotating disc is rotatably mounted on one end of the bracket via a rotating shaft and is parallel to the calibration plate. The other end of the bracket is connected to the driving end of the linear slide module. The rotating disc further comprises: a waist-shaped groove and a clamping slider. The rotating disc is circumferentially provided with a plurality of waist-shaped grooves, and the clamping slider is slidably clamped in the waist-shaped grooves. The clamping slider is used to fix the first flexible endoscope to be calibrated, and the rotating shaft is used to fix the second flexible endoscope to be calibrated, and the lens of the flexible endoscope to be calibrated faces the calibration plate. The calibration computer is used to perform binocular calibration on the flexible endoscope to be calibrated according to image information collected by the flexible endoscope to be calibrated.

9. The flexible endoscope binocular positioning device according to claim 8, characterized in that: The clamping slider further comprises a circular through hole, through which the lens of the first flexible endoscope to be calibrated is inserted and fixed by a locking screw.

10. The flexible endoscope binocular positioning device according to claim 8, characterized in that: One end of the rotating shaft is fixed to the bracket, and the other end is rotatably connected to the rotating disc through a bearing. The rotating shaft is a hollow shaft structure, and the lens of the second calibrated flexible endoscope is inserted through the hollow shaft structure and is locked and fixed by a locking screw.

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