Segment detection method and system based on two-dimensional slide rail and binocular structured light

Abstract

The invention provides a segment detection method and system based on a two-dimensional slide rail and binocular structured light, and the method comprises five steps: the five steps automatically complete full-coverage scanning through the two-dimensional slide rail, improve the measurement efficiency, effectively solve the problem of weak texture surface matching in combination with a binocular light sensing unit and coding structured light, and improve the detection precision. Through automatic splicing of system calibration, accumulated errors are eliminated, a complete three-dimensional model is obtained, and objective and accurate three-dimensional data support is provided.

Description

Technical Field

[0001] This invention relates to the field of three-dimensional optical measurement and industrial automation inspection technology, and in particular to a method and system for inspecting pipe segments based on two-dimensional sliding rails and binocular structured light. Background Technology

[0002] The dimensional accuracy of prefabricated tunnel segments directly affects the overall verticality, structural safety, and service life of the tower. Currently, onshore wind power is trending towards larger rotor diameters and higher installed capacities, which places higher demands on tower height. Hybrid tower segments are mostly large, curved components. Each shipment requires inspection of the segment's external dimensions and the quantity and location of embedded parts. Current mainstream inspection methods rely on manual inspection, requiring significant manpower. Furthermore, the quality of inspection often depends on the inspector's skill level. Moreover, the segments are generally curved, gradually tapering upwards, and their irregular geometry makes comprehensive measurement difficult using traditional methods.

[0003] In recent years, three-dimensional optical measurement technologies such as laser scanning and structured light scanning have been increasingly applied to industrial inspection. However, applying them to large-size wind turbine hybrid tower segments still faces challenges: First, the segments are huge, and the field of view in a single measurement is limited, requiring multiple measurements and stitching. However, handheld scanners have low stitching efficiency and are prone to introducing cumulative calculation errors. Second, concrete surfaces are weakly textured surfaces, making it difficult for traditional binocular stereo vision algorithms to perform accurate feature matching. Furthermore, the ambient lighting on site is complex, placing high demands on the robustness of the optical measurement system. Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a tube sheet inspection method based on two-dimensional sliding rails and binocular structured light. This method can solve the problems of low efficiency, poor accuracy, and incompleteness of manual inspection, as well as the low splicing efficiency of handheld scanners and the easy introduction of cumulative calculation errors, and the difficulty of matching weak texture surfaces in traditional optical inspection.

[0005] Therefore, the present invention adopts the following technical solution: A method for inspecting tunnel segments based on two-dimensional sliding rails and binocular structured light includes the following steps: Step 1: Establish the coordinate system transformation relationship between the binocular structured light sensing unit and the two-dimensional motion platform through system calibration; Step 2: Based on the size of the tube segment to be tested, plan the full-coverage scanning path of the two-dimensional motion platform; Step 3: Control the two-dimensional motion platform to drive the binocular structured light sensing unit to move along the scanning path. At each scanning station, the projector of the binocular structured light sensing unit projects the coded structured light pattern onto the surface of the tube segment. The camera of the binocular structured light sensing unit collects the image of the tube segment surface illuminated by the coded structured light and transmits it to the control and processing unit. The control and processing unit decodes and stereo matches the collected image and reconstructs the local three-dimensional point cloud of the current scanning station. Step 4: Based on the coordinate system transformation relationship and the displacement data of the two-dimensional motion platform, stitch together the local three-dimensional point clouds of all scanning stations into a complete three-dimensional model of the tunnel segment. Step 5: Based on the complete 3D model, calculate the dimensional parameters of the tunnel segment and compare them with the design values ​​to obtain the deviation values.

[0006] Based on the above technical solutions, the present invention may also employ the following further technical solutions, or combine these further technical solutions: The system calibration in step one includes calibrating the camera intrinsic parameters, extrinsic parameters, and projector of the binocular structured light sensing unit, and performing hand-eye calibration between the binocular structured light sensing unit and the two-dimensional motion platform.

[0007] The coded structured light pattern includes a forward Gray code pattern and a complementary reverse Gray code pattern.

[0008] The acquired images, including forward and reverse Gray code patterns, are subtracted to eliminate ambient light interference and complete the decoding.

[0009] The scanning path in step two involves controlling the two-dimensional motion platform to move stepwise along the X-axis, and performing continuous or intermittent scanning along the Y-axis at each X-axis station.

[0010] In step five, the dimensional parameters of the tube segments include flatness, inner diameter, chord length, and arc length.

[0011] The calculation of the dimensional parameters of the tunnel segment includes the calculation of the flatness of the tunnel segment. Specifically, a specified region is extracted from the complete 3D model, a plane or curved surface is fitted, and the distance deviation from the point cloud to the fitted surface is calculated.

[0012] Another objective of this invention is to overcome the shortcomings of the prior art and provide a tube sheet inspection system based on two-dimensional sliding rails and binocular structured light, which can solve the problems of low efficiency, poor accuracy, and incompleteness of manual inspection, as well as the low splicing efficiency of handheld scanners and the easy introduction of cumulative calculation errors, and the difficulty of matching on weak textured surfaces by traditional optical inspection.

[0013] Therefore, the present invention adopts the following technical solution: The tube segment inspection system based on two-dimensional sliding rails and binocular structured light includes a binocular vision sensing unit, a two-dimensional motion platform, and a control and processing unit. The binocular vision sensing unit includes two industrial cameras and a projector. The two-dimensional motion platform includes X-axis and Y-axis sliding rails arranged perpendicularly to each other. The binocular vision sensing unit can move along the length directions of the X-axis and Y-axis sliding rails respectively. The control and processing unit is used to control the two-dimensional motion platform and the binocular vision sensing unit to work together according to instructions, and to perform image processing, three-dimensional reconstruction, point cloud stitching, and size calculation.

[0014] Based on the above technical solutions, the present invention may also employ the following further technical solutions, or combine these further technical solutions: The bottom of the Y-axis slide rail is fixed with a support base, the X-axis slide rail is slidably connected to the front of the Y-axis slide rail, and the binocular sensing unit is slidably connected to the front of the X-axis slide rail.

[0015] Both the X-axis slide rail and the Y-axis slide rail are independently equipped with a grating ruler or encoder for closed-loop position feedback.

[0016] Compared with the prior art, the present invention has the following advantages and beneficial effects: it can automatically complete full-coverage scanning through a two-dimensional sliding rail, thereby improving measurement efficiency; it can effectively solve the problem of weak texture surface matching by combining a dual-eye optical sensing unit and coded structured light; and it can eliminate accumulated errors through automatic stitching by system calibration, thereby obtaining a complete three-dimensional model and providing objective and accurate three-dimensional data support. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the overall structure of the segment inspection system of the present invention. Figure 2 This is a side view of one embodiment of the segment inspection system of the present invention.

[0018] Figure 3 This is a top view of one embodiment of the segment inspection system of the present invention.

[0019] Figure 4 This is a flowchart of the overall detection method of the present invention.

[0020] Figure 5 This is a flowchart of the measurement process for the two-dimensional motion platform of the present invention.

[0021] Figure 6 This is a schematic diagram of the forward Gray code pattern and the reverse Gray code pattern of the present invention. Detailed Implementation

[0022] To enable those skilled in the art to better understand the technical solutions of the present invention, preferred embodiments of the present invention are described below in conjunction with specific examples. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote elements with the same or similar functions throughout. However, it should be understood that the drawings are for illustrative purposes only and should not be construed as limiting the present invention. To better illustrate this embodiment, some parts in the drawings may be omitted, enlarged, or reduced, and do not represent the actual product size. It is understandable for those skilled in the art that some well-known structures and their descriptions may be omitted in the drawings. The positional relationships described in the drawings are for illustrative purposes only and should not be construed as limiting the present invention.

[0023] The present invention will be further described below with reference to the accompanying drawings and embodiments, but this should not be construed as limiting the present invention.

[0024] The tube segment inspection method based on two-dimensional sliding rails and binocular structured light provided by this invention includes the following steps: Step 1: Establish the coordinate system transformation relationship between the binocular structured light sensing unit and the two-dimensional motion platform through system calibration; Step 2: Based on the size of the tube segment to be tested, plan the full-coverage scanning path of the two-dimensional motion platform; Step 3: Control the two-dimensional motion platform to drive the binocular structured light sensing unit to move along the scanning path. At each scanning station, the projector of the binocular structured light sensing unit projects the coded structured light pattern onto the surface of the tube segment. The camera of the binocular structured light sensing unit acquires the image of the tube segment surface illuminated by the coded structured light and transmits it to the control and processing unit. The control and processing unit decodes and stereo matches the acquired image and reconstructs the local three-dimensional point cloud of the current scanning station. Step 4: Based on the coordinate system transformation relationship and the displacement data of the two-dimensional motion platform, stitch together the local three-dimensional point clouds of all scanning stations into a complete three-dimensional model of the tunnel segment. Step 5: Based on the complete 3D model, calculate the dimensional parameters of the tunnel segment and compare them with the design values ​​to obtain the deviation values. This can also help managers identify and quantify surface defects of the tunnel segment.

[0025] The system calibration in step one includes calibrating the camera intrinsic parameters, extrinsic parameters, and projector of the binocular structured light sensing unit, and performing hand-eye calibration between the binocular structured light sensing unit and the two-dimensional motion platform.

[0026] Encoded structured light patterns include forward Gray code patterns and their complementary reverse Gray code patterns.

[0027] The projector projects positive and negative Gray code patterns onto the surface of the tube segment. The edge positions with sub-pixel precision are located by finding the intersection points of the grayscale profiles in the same row of pixels in both images. In other words, the precise edges of the striped image are first detected using the intersection method. Then, the image sequence is decoded. Because the positions of the camera and projector within the binocular structured light measurement unit are relatively fixed during the measurement process, the edge points displayed in the positive and negative images deviate from their correct positions in opposite directions and are of equal size. Therefore, the diffusion of bright stripes at the edges in the positive and negative images cancels each other out, ensuring measurement accuracy. The acquired images, including forward and reverse Gray code patterns, are subtracted to eliminate ambient light interference, thus completing the decoding process and achieving a reliable forward and reverse Gray code-binary-decimal decoding.

[0028] The decoding process is the reverse of the encoding process. It converts the Gray code value into a natural binary value. After calculating the corresponding binary code value of the Gray code, the binary code value is then converted into a decimal code value, which is the decoded value of the row or column corresponding to that pixel.

[0029] The scanning path in step two involves controlling the two-dimensional motion platform to move stepwise along the X-axis, and performing continuous or intermittent scanning along the Y-axis at each X-axis station.

[0030] In step four, due to the limited field of view of the projector and camera in traditional binocular measurement methods, and the cumbersome process of moving and leveling the fixed tripod, in order to quickly obtain complete three-dimensional point cloud data of large-sized workpieces such as concrete pipe segments, it is necessary to perform multi-angle omnidirectional scanning measurement of the object to obtain a global point cloud data. On this basis, point cloud denoising and point cloud sparsification processing are performed, and then global point cloud stitching is performed to establish a complete three-dimensional model of the pipe segment.

[0031] In step five, the dimensional parameters of the tube segments include flatness, inner diameter, chord length, and arc length.

[0032] The calculation of the dimensional parameters of the tunnel segment includes the calculation of the flatness of the tunnel segment. Specifically, this involves extracting a specified area from the complete 3D model, performing planar or curved surface fitting, and calculating the distance deviation from the point cloud to the fitted surface.

[0033] The present invention provides a pipe segment inspection system based on two-dimensional slide rails and binocular structured light, comprising a binocular vision sensing unit, a two-dimensional motion platform, and a control and processing unit. The binocular vision sensing unit includes two industrial cameras and a projector. The two-dimensional motion platform includes X-axis and Y-axis slide rails arranged perpendicularly to each other. The binocular vision sensing unit can move along the length directions of the X-axis and Y-axis slide rails respectively. The control and processing unit is used to control the two-dimensional motion platform and the binocular vision sensing unit to work collaboratively according to instructions, and to perform image processing, three-dimensional reconstruction, point cloud stitching, and size calculation. A support base is fixed to the bottom of the Y-axis slide rail, and the X-axis slide rail is slidably connected to the front of the Y-axis slide rail. The binocular vision sensing unit is slidably connected to the front of the X-axis slide rail.

[0034] Both the X-axis and Y-axis slide rails are independently equipped with grating rulers or encoders for closed-loop position feedback.

[0035] Both the X-axis and Y-axis slide rails are driven by servo motors.

[0036] like Figure 1 As shown, the detection system of the present invention mainly includes three core parts: a binocular structured light sensing unit 1, a two-dimensional precision motion platform 2, and a system control and data processing unit 4.

[0037] The binocular structured light sensing unit 1 integrates two high-resolution industrial cameras (1.1, 1.2) and a DLP structured light projector 1.3 via a rigid mounting plate. During installation, the two cameras and the projector are fixed to the mounting plate with a certain baseline distance (i.e., the straight-line distance between them). The projector is positioned in the center, with the two cameras symmetrically distributed on either side. All fastening screws are secured with anti-loosening screws to ensure they do not loosen under vibration. Simultaneously, the optical axes of the cameras and projector are adjusted to ensure their optical fields of view collectively cover the target measurement area of ​​the tube segment. The two-dimensional precision motion platform 2 adopts a high-rigidity cross-slide structure, including mutually perpendicular X-axis slide rails 2.1 and Y-axis slide rails 2.2. The sensing unit 1 is fixed to the slider of the X-axis slide rail 2.1. The system control and data processing unit 4 is an industrial computer, connected to the drivers of the sensing unit 1 and the motion platform 2 via data cables.

[0038] Before testing, place the system in front of the wind turbine hybrid tower segment 3 to be tested, and adjust the overall position so that the Y-axis slide rail 2.2 is roughly parallel to the generatrix (height direction) of the segment.

[0039] The process of the method of the present invention is as follows: Figure 2 As shown, the specific implementation steps are as follows: The first step is system calibration. Using a high-precision checkerboard calibration board, the intrinsic and extrinsic parameters of the binocular cameras 1.1 and 1.2, and the projector 1.3, are calibrated. The specific system calibration steps are divided into two parts. First, the binocular structured light unit is calibrated. Specifically, the calibration board (using a checkerboard) is placed in front of the sensing unit at different positions and orientations. For each position, the projector projects a series of Gray code patterns, and the binocular cameras simultaneously acquire images. By processing these images, the camera intrinsic parameters (focal length, principal point, distortion coefficients), stereo extrinsic parameters (the relative position and orientation between the two cameras (rotation and translation matrices)), and projector parameters (the projector is virtually treated as a "reverse camera," and its relationship with the camera coordinate system is calibrated) are calculated. This determines the precise geometric relationship between the two cameras and the projector. Subsequently, hand-eye calibration is performed to accurately obtain the transformation matrix T between the coordinate system of sensing unit 1 and the coordinate system of the two-dimensional precision motion platform 2.

[0040]

[0041] Where R is a 3x3 rotation matrix, describing the attitude of the binocular structured light sensor unit coordinate system relative to the two-dimensional precision motion platform base coordinate system, and t is a translation vector, describing the coordinates of the origin of the binocular structured light sensor unit coordinate system in the two-dimensional precision motion platform base coordinate system.

[0042] The specific steps are as follows: The calibration plate is fixed at the location of the tube segment or a fixed position. The slide rail is controlled to move the binocular structured light unit to at least three different stations. At each station, the sensor measures and photographs the same fixed calibration plate. An algorithm is used to calculate the fixed transformation relationship between the sensor coordinate system and the motion platform coordinate system. This determines the transformation relationship between the "binocular structured light unit" and the "two-dimensional motion platform" coordinate system, serving as the basic data for automatic point cloud stitching.

[0043] The second step is scanning path planning. Input the approximate dimensions of the tunnel segment into the software interface, and the system automatically generates a path. Figure 3 The rasterized scanning path is shown. The path planning principle is to ensure that the fields of view of adjacent scanning stations partially overlap to facilitate subsequent data stitching. The rasterized scanning motion path of the sensor unit in this step is described in detail below: Starting from the initial point, the sensing unit first moves along the Y-axis (height direction) to complete the scanning of the first column of data.

[0044] Subsequently, the sensing unit moves one step along the X-axis (circumferential direction) to reach the starting point of the next column.

[0045] Next, the sensing unit moves in the opposite direction along the Y-axis to complete the scanning of the second column of data.

[0046] Repeat steps 2 and 3 until the entire area to be measured is covered. It is important to note that throughout the scanning process, the binocular structured light sensor unit is a rigid, integral component that remains fixed to the mounting plate of the X-axis slider. When scanning along the Y-axis (height direction), the Y-axis slide rail operates, causing its slider to move. When scanning along the X-axis (circular stepping), the slider moves along the X-axis guide rail. During this process, the Y-axis slider remains stationary.

[0047] The third step is multi-station 3D data acquisition and reconstruction. System control platform 2 moves sensor unit 1 to the starting point of the path. At each station: Projector 1.3 projects a series of coded patterns sequentially. Preferably, a combination of positive and negative Gray codes is used (e.g., ...). Figure 4 (As shown), for example, first project a forward black and white Gray code image, then project its perfectly complementary reversed pattern.

[0048] When projecting each pattern, both cameras 1.1 and 1.2 are triggered synchronously to capture the deformed stripe image.

[0049] The central processing unit decodes the acquired image sequences. For positive and negative Gray codes, subtracting the corresponding positive and negative images effectively eliminates the ambient light component, resulting in a pure coded signal, thus assigning a unique and reliable binary sequence to each pixel. For each pair of complementary coded images, the decoded value S at any point in the coordinate system is determined by the following decision function.

[0050] Tnoise is the positive threshold set for the on-site noise level.

[0051] By decoding the sequence, the pixel matching problem of the left and right camera images is solved. Then, by combining the principle of triangulation, the local three-dimensional point cloud of the tube surface in the current field of view is calculated.

[0052] The fourth step is global point cloud stitching. After acquiring the local point clouds of all stations, the hand-eye calibration matrix obtained in the first step and the precise X and Y displacements fed back by the motion platform are used to transform each local point cloud into the same global coordinate system and fuse them into a complete and seamless 3D digital model of the tunnel segment.

[0053] Step 5: Dimensional calculation and quality assessment. On this complete model: Flatness: Select the splicing surface or key plane area of ​​the segment, use the least squares method to fit an ideal plane, and then calculate the distance of all point clouds in the area to this plane. The maximum deviation value is the flatness error.

[0054] Inner diameter and profile: The point cloud of the circumferential section of the tube segment is extracted, and an ideal circular arc is fitted using the least squares method to obtain the actual radius value (inner diameter). The deviation of the section point cloud from the ideal circular arc is calculated as the profile error.

[0055] Chord length and arc length: The chord length is obtained by directly extracting the edge points on both sides of the tube segment from the complete point cloud model and calculating the straight-line distance; the accurate arc length can be obtained by connecting the edge points and integrating.

[0056] Defect detection: Using algorithms such as curvature filtering and region growing, it automatically identifies defects such as cracks, holes, and protrusions, and can accurately measure their three-dimensional dimensions (length, width, depth, and area).

[0057] Based on the description and accompanying drawings of this invention, those skilled in the art can easily manufacture or use the tube segment inspection method and system based on two-dimensional sliding rails and binocular structured light of this invention, and can achieve the positive effects described in this invention.

[0058] It should be noted that the terms "comprising" and "having," and any variations thereof, in the specification, claims, and accompanying drawings of this invention are intended to cover non-exclusive inclusion. The terms "installed," "set," "equipped with," "connected," "linked," and "sleeve" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral construction; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium, or an internal connection between two mechanisms, elements, or components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0059] In the description of this invention, it should be understood that the terms "one end," "the other end," "outer side," "inner side," "horizontal," "end," "length," "outer end," "left," and "right," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this invention and for simplifying the description, and do not indicate or imply that the mechanism or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention. The terms "first" and "second" are also used only for the sake of brevity in description and do not indicate or imply relative importance.

[0060] Furthermore, in practicing the claims of this invention, those skilled in the art can understand and influence variations to the disclosed embodiments through a study of the drawings, the disclosure, and the appended claims. Additionally, in the claims and description, words such as "comprising" and "containing" do not exclude other elements or steps, and non-plural nouns do not exclude their plural forms.

[0061] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of the present invention. All equivalent changes and modifications made in accordance with the present invention are covered by the scope of the claims of the present invention, and will not be listed here.

Claims

1. A segment detection method based on two-dimensional slide rail and binocular structured light, characterized in that, The method comprises the following steps: Step one, establishing the coordinate system conversion relationship between the binocular structured light sensing unit and the two-dimensional motion platform through system calibration; Step two, planning the full-coverage scanning path of the two-dimensional motion platform according to the size of the pipe sheet to be measured; Step three, controlling the two-dimensional motion platform to drive the binocular structured light sensing unit to move along the scanning path, at each scanning station, the projector of the binocular structured light sensing unit projects a coded structured light pattern onto the pipe sheet surface, the camera of the binocular structured light sensing unit collects the pipe sheet surface image illuminated by the coded structured light and transmits it to the control and processing unit, the control and processing unit decodes and stereo matches the collected image and reconstructs the local three-dimensional point cloud of the current scanning station; Step four, based on the coordinate system conversion relationship and the displacement data of the two-dimensional motion platform, the local three-dimensional point clouds of all scanning stations are spliced into a complete three-dimensional model of the pipe sheet; Step five, based on the complete three-dimensional model, the size parameters of the pipe sheet are calculated and compared with the design value to obtain the deviation value.

2. The segment detection method based on two-dimensional slide rail and binocular structured light according to claim 1, wherein, The system calibration in step one includes camera intrinsic parameter calibration, camera extrinsic parameter calibration and projector calibration of the binocular structured light sensing unit, and hand-eye calibration of the binocular structured light sensing unit and the two-dimensional motion platform. 3.The segment detection method based on two-dimensional slide rail and binocular structured light according to claim 1, wherein, The coded structured light pattern comprises a forward Gray code pattern and a reverse Gray code pattern complementary thereto. 4.The segment detection method based on two-dimensional slide rail and binocular structured light according to claim 3, wherein, The collected image comprising the forward Gray code pattern and the reverse Gray code pattern is subjected to subtraction operation to eliminate environmental light interference and complete decoding. 5.The segment detection method based on two-dimensional slide rail and binocular structured light according to claim 1, wherein, The scanning path in step two is that the two-dimensional motion platform is controlled to move step by step in the X-axis direction, and at each X-axis station, continuous or intermittent scanning is performed along the Y-axis direction. 6.The segment detection method based on two-dimensional slide rail and binocular structured light according to claim 1, wherein, The size parameters of the pipe sheet in step five include flatness, inner diameter, chord length and arc length. 7.The segment detection method based on two-dimensional slide rail and binocular structured light according to claim 1, wherein, The calculation of the size parameters of the pipe sheet comprises calculating the flatness of the pipe sheet, specifically, extracting a specified area on the complete three-dimensional model, fitting a plane or a curved surface, and calculating the distance deviation of the point cloud to the fitted surface.

8. A two-dimensional slide rail and binocular structured light based segment detection system for implementing the method of any one of claims 1-7, characterized in that, The system comprises a binocular light sensing unit, a two-dimensional motion platform and a control and processing unit, the binocular light sensing unit comprises two industrial cameras and a projector, the two-dimensional motion platform comprises an X-axis slide rail and a Y-axis slide rail arranged perpendicular to each other, the binocular light sensing unit can move along the length direction of the X-axis slide rail and the Y-axis slide rail respectively, and the control and processing unit is used for controlling the two-dimensional motion platform and the binocular sensing unit to work cooperatively according to instructions and performing image processing, three-dimensional reconstruction, point cloud splicing and size calculation.

9. The two-dimensional slide rail and binocular structured light based segment detection system of claim 8, wherein, The bottom of the Y-axis slide rail is fixed with a support base, the X-axis slide rail is slidingly connected to the front of the Y-axis slide rail, and the binocular sensing unit is slidingly connected to the front of the X-axis slide rail.

10. The two-dimensional slide rail and binocular structured light based segment detection system of claim 8, wherein, The X-axis slide rail and the Y-axis slide rail are respectively independently configured with a grating ruler or an encoder for closed-loop position feedback.

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