In-situ measurement method for form and position tolerances of large-sized ring-shaped parts

Abstract

The application discloses a kind of in-situ measurement methods of large-size annular part shape and position tolerance, belong to detection technical field, for large-size annular optical, in-situ measurement of mechanical parts, its steps are: (1) using scale, laser interferometer, standard ball calibration numerical control machining center precision;(2) using indicating meter measurement and debugging workpiece and turntable parallel, concentric;(3) using laser tracker measurement workpiece parameter establishes workpiece coordinate system;(4) using laser tracker combines machine tool to measure part profile parameters;(5) analysis part geometric quantity shape and position error.The application method solves the in-situ measurement problem of large-size annular workpiece machining process, reduces the risk and cost that workpiece needs to be repeatedly transported and inspected, with the characteristics of convenient operation, safe and efficient, high measurement precision.

Description

Technical Field

[0001] This invention belongs to the field of testing technology, specifically relating to an in-situ measurement method for the form and position tolerances of large-sized ring-shaped parts. Background Technology

[0002] Large-size optical and mechanical components are core components of large optoelectronic equipment, characterized by their large size, heavy weight, and high precision. Due to the large number of form and position parameters of the core components and their high precision, each parameter requires repeated processing and testing during the development process to meet the technical requirements. At the same time, the testing of the parameters requires the use of large-scale metrology coordinate measuring machines to complete the relevant precision testing work, which makes the testing cost too high. In addition, the risk of repeatedly lifting and transporting parts for testing is high, and the testing and debugging time is uncontrollable. Summary of the Invention

[0003] To address the issue of in-situ measurement of shape tolerances in the development of large-sized annular optical-mechanical components (2m and above), this invention provides an in-situ measurement method for the shape and position tolerances of large-sized annular parts. This invention utilizes a gantry machining center and a precision rotary table, combined with spatial measurement technology using a laser tracker, to achieve in-situ detection of geometric parameters for large-sized optical-mechanical components. It offers good detection accuracy and precision, effectively reducing product development cycle and risk, and saving time and costs.

[0004] The technical solution adopted in this invention is: an in-situ measurement method for the form and position tolerances of large-sized annular parts, the method comprising the following steps:

[0005] Step 1: Accuracy calibration and correction of the X, Y, Z, and C axes of the CNC machining center;

[0006] Step 2: Adjust the workpiece to be parallel and concentric with the rotary table;

[0007] Step 3: Measure workpiece parameters and establish the workpiece coordinate system;

[0008] Step 4: Measure the spatial points of the outer contour of the workpiece's annular plane, outer cylindrical surface, and inner cylindrical surface;

[0009] Step 5: Data processing, analysis of geometric tolerances, and determination of the deviation direction of workpiece geometric error based on the coordinate system for rework and inspection until the requirements are met.

[0010] The advantages of this invention compared to the prior art are:

[0011] (1) Traditional coordinate measuring machines (CMMs) are not suitable for in-situ inspection of optical and mechanical components due to limitations in measurement principles, measurement range, and high requirements for the measurement environment. Furthermore, the equipment purchase cost is high, and the procurement, installation, commissioning, and application cycle are long. Additionally, the risk of transporting parts back and forth for inspection is significant, and the development cycle is uncontrollable. Using a laser tracker for measurement via a transfer station method results in some loss of accuracy and can only measure external parameters of the workpiece. By combining a laser tracker with a gantry CNC machining center, the problem of in-situ inspection of high-precision geometric tolerances of precision optical and mechanical components is solved, and in-situ guidance for machining is achieved. Simultaneously, calibrating the distance between the target center and the indicator probe allows for synchronous measurement of the workpiece's external dimensional tolerances. Therefore, this invention reduces the significant risks associated with the lifting and transport of precision optical and mechanical components, shortens the development cycle at this stage, and provides good inspection accuracy.

[0012] (2) The detection method of the present invention is convenient to operate, safe and efficient, and relatively low in cost;

[0013] (3) The detection method of the present invention is not limited to the in-situ detection of large-diameter optical components and precision mechanical form and position tolerances, but can also be applied to the in-situ detection of the dimensions and form and position tolerances of large precision special material product parts in various industries. Attached Figure Description

[0014] Figure 1 This is a flowchart illustrating an in-situ measurement method for the geometrical and positional tolerances of a large-sized ring-shaped part.

[0015] Figure 2 This is a structural diagram of a CNC machining center;

[0016] Figure 3 A schematic diagram of the workbench accuracy calibration for an in-situ measurement method of form and position tolerances for large-sized ring-shaped parts;

[0017] Figure 4 This is a schematic diagram illustrating the implementation of an in-situ measurement method for the geometrical and positional tolerances of a large-sized ring-shaped part.

[0018] Figure 5 This is a schematic diagram showing the distribution of measurement points for an in-situ measurement method of geometric tolerances for a large-sized ring-shaped part. Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other. To achieve the above objectives, this invention adopts the following technical solution.

[0020] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Implementation process: The process of detecting the form and position tolerances of a 2200mm × 500mm ring-shaped part in place using the method of the present invention will be described in detail.

[0021] This invention proposes an in-situ measurement method for the form and position tolerances of large-sized annular parts, such as... Figure 1 As shown, follow these steps:

[0022] Step 1: Accuracy calibration and correction of the X, Y, Z, and C axes of the CNC machining center;

[0023] Among them, before the workpiece is processed, such as Figure 2 , Figure 3 As shown, firstly, the straightness of the X, Y, and Z linear motion axes of the CNC machining center, as well as its perpendicularity to the machine tool table, are detected and corrected using a standard ruler and square. Secondly, a laser interferometer is used to detect and correct the positioning and repeatability accuracy of the X, Y, and Z linear motion axes. Then, an autocollimator is used to calibrate and correct the positioning and repeatability accuracy of the C-axis of the CNC machining center's rotary table. Finally, as shown... Figure 3 As shown, a standard ball is fixed to the center of the rotary table, and the axial and radial runout errors of the rotary table are measured using radial and axial measuring indicators.

[0024] The three-dimensional adjustment mechanism is installed at the center of the rotary table. It is then checked and aligned to be parallel to the rotary table using an axial measurement indicator. A standard ball is then fixed to the upper end face of a cylindrical fixture with a fulcrum height > 200mm and a diameter of 50mm. The lower end face is fixed to the upper surface of the three-dimensional adjustment mechanism. Finally, a radial measurement indicator is used to measure and adjust the standard ball to be concentric with the rotary table.

[0025] Step 2: Adjust the workpiece to be parallel and concentric with the rotary table;

[0026] like Figure 4 As shown, the indicator is fixed on the spindle of the CNC machining center. The indicator probe first contacts the workpiece's annular plane. The rotary table is then rotated to 0°, 120°, and 240° respectively, and the indicator's runout difference is recorded. The workpiece is then adjusted to be parallel to the rotary table with a distance ≤0.01mm using the workpiece's bottom three-dimensional adjustment mechanism. Next, the indicator probe contacts the workpiece's outer cylindrical surface. The rotary table is then rotated to 0°, 180°, 90°, and 270° respectively. The indicator's runout difference is recorded, and the workpiece is then adjusted to be concentric with the rotary table with a distance ≤0.01mm using the workpiece's bottom three-dimensional adjustment mechanism.

[0027] Step 3: Measure workpiece parameters and establish the workpiece coordinate system;

[0028] The workpiece's annular plane and outer cylindrical surface are evenly distributed with 16 measurement points along the circumference. The flatness and center of the circle are directly measured and fitted using a laser tracker combined with a target. Then, the straight line between the +X target point and the center point is measured to establish the workpiece's Cartesian coordinate system.

[0029] Step 4: Measure the spatial points of the outer contour of the workpiece's annular plane, outer cylindrical surface, and inner cylindrical surface;

[0030] Among them, such as Figure 4 As shown, the rotary table is controlled to move the workpiece to its initial position. A target and indicator of a laser tracker are fixed on the spindle of the CNC machining center, ensuring the indicator probe contacts the annular plane. The rotary table is synchronously controlled to rotate at 16 equally spaced positions. The laser tracker, combined with the target, measures and records the coordinates of these 16 points distributed circumferentially on the annular plane. Figure 5 As shown, the measurement points for the contours of the annular plane, outer cylindrical surface, and inner cylindrical surface were collected.

[0031] The rotary table C-axis rotates at 22.5° intervals, with a 6-second delay after each rotation. The CNC machine tool spindle is synchronously controlled to ensure the indicator probe contacts the measured point, maintaining a contact force variation of less than 2 micrometers. The laser tracker uses IFM interferometric stable point measurement mode to synchronously acquire position information. The measurement sequence, starting from the +X target point, first measures 16 coordinate points evenly divided circumferentially on the annular plane; secondly, measures 16 coordinate points evenly distributed circumferentially on the outer cylindrical surface, and 80 coordinate points evenly distributed axially across five truncated circles; finally, measures 80 coordinate points across five truncated circles on the inner cylindrical surface.

[0032] The rotary table needs to rotate twice before measurement to eliminate backlash error. The index table uses a high-precision digital display inductive sensor to keep the measuring force consistent. The number of measurement points can be increased or decreased according to the size of the part and the level of accuracy. The inner and outer cylindrical surfaces are measured according to the distribution of cylindrical generatrices or spirals.

[0033] Step 5: Data processing, analysis of geometric tolerances, and determination of the direction of deviation of part geometric error based on coordinate system for rework and inspection until the requirements are met.

[0034] In the coordinate system described in step three, the coordinate values ​​of the 16 measurement points (X, Y, Z) at the annular plane are first exported. The cylindrical coordinate values ​​(ρ, Ф, z) are generated by taking the radius of the outer cylinder center of the annular plane as the polar diameter ρ, the rotation angle of the rotary table at 22.5-degree intervals as the polar angle Ф, and the axial error as the height value Z.

[0035] Next, as described in step four, the following will be performed: Figure 5The coordinate values ​​(X, Y, Z) of 80 measurement points on the inner and outer cylindrical surfaces are derived. The radius of the inner and outer cylindrical surface contour measurement points relative to the workpiece center is taken as the polar diameter ρ, the rotation angle of the rotary table at 22.5 degrees interval is taken as the polar angle Ф, and the height difference between the upper and lower corresponding cross-sections from the first to the fifth cross-section measurement points is taken as the height value Z. The coordinate values ​​(ρ, Ф, z) of the inner and outer cylinders are generated respectively.

[0036] Finally, as Figure 5 As shown, under a unified reference coordinate system, the cylindrical coordinate values ​​(ρ, Ф, z) generated by the annular plane, inner cylindrical surface, and outer cylindrical surface are imported into the SA measurement and analysis software to fit and evaluate various geometric tolerances of the workpiece, such as cylindricity, perpendicularity, coaxiality, and flatness. If there are any deviations, the direction of deviation is determined in the coordinate system, and rework and inspection are carried out until the requirements are met.

[0037] The techniques known in the art involved in this invention are not described in detail.

Claims

1. A method for in-situ measurement of the form and position tolerances of a large-sized ring-shaped part, characterized in that, The method includes the following steps: Step 1: Accuracy calibration and correction of the X, Y, Z, and C axes of the CNC machining center; Step 2: Adjust the workpiece to be parallel and concentric with the rotary table; Step 3: Measure workpiece parameters and establish the workpiece coordinate system; Step 4: Measure the spatial points of the outer contour of the workpiece's annular plane, outer cylindrical surface, and inner cylindrical surface; Step 5: Data processing, analysis of geometric tolerances, and determination of the workpiece's geometric error deviation direction based on the coordinate system for rework and inspection until the requirements are met; In step one, before machining the workpiece, the straightness of the X, Y, and Z linear motion axes of the CNC machining center and its perpendicularity to the machine tool table are first checked and corrected using a standard ruler and square. Then, a laser interferometer is used to check and correct the positioning and repeatability accuracy of the X, Y, and Z linear motion axes. An autocollimator is used to calibrate and correct the positioning and repeatability accuracy of the C-axis of the CNC machining center's rotary table. Finally, a standard ball is used to calibrate the rotary table's axis wobble error. The standard ball is fixed to the center of the rotary table, with its fulcrum located on the upper surface of a cylindrical fixture with a height > 200mm and a diameter of 50mm. The lower surface of the cylindrical fixture is fixed to the three-dimensional adjustment mechanism and simultaneously installed to the center of the rotary table. An indicator is used to measure and adjust the concentricity of the standard ball and the rotary table. In step two, the spindle of the CNC machining center is fixed using an indicator, and the probe of the indicator is brought into contact with the annular plane of the workpiece. The rotary table is controlled to rotate to 0°, 120°, and 240° respectively, and the runout difference of the indicator is recorded. The workpiece is then adjusted to be parallel with the rotary table. Next, the probe of the indicator is brought into contact with the outer cylindrical surface of the workpiece, and the rotary table is controlled to rotate to 0°, 180°, 90°, and 270° respectively, and the runout difference of the indicator is recorded sequentially. The workpiece is then adjusted to be concentric with the rotary table. The bottom of the workpiece is supported by a three-dimensional adjustment mechanism, and the workpiece is accurately aligned through translation and tilting functions. In step three, the annular plane and the outer circle are divided into 16 points in the circumferential direction. The flatness and the center of the circle are measured and fitted using a laser tracker. Then, the straight line between the +X target point and the center point is measured to establish the Cartesian coordinate system of the workpiece. In step four, the rotary table is controlled to move the workpiece to its initial position. A laser tracker target and indicator are fixed on the spindle of the CNC machining center. The rotary table is controlled to rotate at equal intervals of 22.5 degrees. Simultaneously, the spindle of the CNC machining center is controlled to drive the indicator to contact the annular plane. The laser tracker is used to measure and record the displacement information. The measurement points of the annular plane, outer cylindrical surface, and inner cylindrical surface are collected in sequence. The laser tracker adopts the IFM interferometric stable point measurement mode. Before measurement, the rotary table rotates 2 revolutions to eliminate backlash error. The measurement sequence starts from the +X target point. First, the annular plane is measured by dividing it into 16 coordinate points in the circumferential direction. Then, the outer cylindrical surface is measured by evenly distributing 5 cross-circles. Each cross-circle is divided into 16 coordinate points in the circumferential direction, for a total of 80 measurement points. The Z-axis measurement sequence is from the first cross-circle measurement point to the fifth cross-circle measurement point. Finally, the inner cylindrical surface is measured by five cross-circle measurement points, for a total of 80 measurement points. The indicator gauge maintains consistent contact force, and the number of measurement points is increased or decreased according to the workpiece size and accuracy. The inner and outer cylindrical surfaces are measured according to the distribution of cylindrical generatrices or spirals.

2. The in-situ measurement method for the form and position tolerances of a large-size ring-shaped part according to claim 1, characterized in that: In step five, 16 coordinate points (x, y, z) of the annular plane are exported and converted into cylindrical coordinate values ​​through data processing. 16 lines and 80 contour coordinate points (x, y, z) are exported from the inner and outer cylindrical surfaces respectively, and converted into inner and outer cylindrical coordinate values ​​respectively through data processing. These values ​​are then input into the SA laser tracker software, and the cylindricity, perpendicularity, coaxiality, and flatness errors are analyzed under a unified reference coordinate system. If any deviation is found, the direction of deviation is determined in the coordinate system, and rework and inspection are carried out until the requirements are met.

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