A system and method for in-machine measurement and error compensation of a five-axis profile grinding machine

Abstract

This invention discloses an in-machine measurement and error compensation system and method for a five-axis form grinding machine, belonging to the field of CNC machining and precision measurement technology. The system includes a five-axis form grinding machine, a rotary table, a contact probe, a data acquisition and processing module, and a CNC controller, integrated into a hardware system for closed-loop control. The corresponding method includes: first, calibrating the probe's pre-stroke error by comparing in-machine and offline measurement data; then, after machining, controlling the probe to perform in-machine measurement along the surface normal, accurately calculating the normal deviation through vector projection; next, correcting the data using calibration parameters, and generating complete surface deviation compensation data through coarse and fine registration and surface comparison analysis; finally, driving the machine tool to perform iterative compensation machining until the accuracy meets the standard. This invention achieves one-time high-precision forming and inspection of complex curved surface workpieces on a machining tool, significantly improving the machining efficiency and consistency of parts such as aero-engine blades.

Description

Technical Field

[0001] This invention relates to the field of manufacturing and measurement technology for high-temperature alloy blade parts for aerospace applications, and in particular to an in-machine measurement and error compensation system and method for a five-axis forming grinder. Background Technology

[0002] As aero-engine blades evolve towards lighter, higher-load, and more complex three-dimensional aerodynamic shapes, the requirements for profile grinding—specifically, surface accuracy, leading-edge radius consistency, trailing-edge thickness, and torsion distribution—have significantly increased. Traditional processes typically involve transferring the workpiece to a coordinate measuring machine (CMM) for offline inspection after machining. This process suffers from problems such as separation of machining and measurement, long feedback cycles, and the inability to correct in-machine errors in real time, resulting in limited efficiency and yield. In-machine measurement based on in-machine probes can move the measurement process inside the machine tool, enabling rapid feedback and online compensation. This technology is gradually being adopted in industry, especially scanning probes which support high-density data acquisition, making in-machine evaluation and adaptive machining of free-form surfaces possible.

[0003] However, five-axis in-machine measurement still faces multiple challenges. The nonlinear pre-stroke error of contact probes degrades measurement accuracy, while freeform surface point cloud registration and scanning of high-curvature regions of blades are susceptible to local deformation and distortion. Although existing technologies have explored error compensation and modeling, a system solution that can unify the probe, machine tool, and workpiece geometry into a closed-loop framework of "machining-measurement-correction" is still lacking. Therefore, in order to further meet the requirements of efficient inspection and high-quality machining of complex blade and disk parts in aerospace, a five-axis in-machine measurement and error compensation system and method for form grinding machines was designed. Summary of the Invention

[0004] This invention provides an in-machine measurement and error compensation system and method for a five-axis forming grinder, which realizes the requirements for efficient inspection and high-quality processing of complex blade and disk parts in aerospace, and improves the performance of blade and disk parts for aero-engines.

[0005] The objective of this invention can be achieved through the following technical solution: a five-axis profile grinding machine in-machine measurement and error compensation system, characterized in that it comprises:

[0006] A five-axis profile grinding machine has a linkage mechanism for performing X, Y, Z linear axis motion and A, C rotary axis motion, and the five-axis profile grinding machine also includes a grinding machine spindle;

[0007] A rotary table, mounted on the five-axis forming grinder, is used to clamp workpieces;

[0008] The contact probe is detachably mounted on the grinding machine spindle via a tool holder;

[0009] The data acquisition and processing module includes a wireless receiver and a data processing unit. The wireless receiver is used to receive the trigger signal of the contact probe, and the data processing unit is used to process the measurement data and calculate the deviation.

[0010] The CNC controller is communicatively connected to the data processing unit and the drive mechanisms of each axis of the five-axis forming grinding machine, and is used to control the five-axis forming grinding machine to perform compensation machining on the workpiece according to the deviation data output by the data processing unit;

[0011] The contact probe, data acquisition and processing module, CNC controller, and five-axis forming grinding machine together constitute a system for realizing closed-loop control of machining, measurement, and compensation.

[0012] A method for in-machine measurement and error compensation on a five-axis profile grinding machine, characterized by comprising the following steps:

[0013] Step S1: Probe pre-stroke error calibration. On the five-axis forming grinder, the contact probe is used to measure a reference workpiece to obtain probe measurement data; at the same time, a coordinate measuring machine is used to measure the same reference workpiece to obtain coordinate measuring machine measurement data; through data registration and regression modeling, the error mapping relationship between the probe measurement data and the coordinate measuring machine measurement data is established to obtain calibration parameters.

[0014] Step S2: In-machine measurement and normal deviation calculation. After machining the workpiece on the five-axis forming grinder, the contact probe is controlled to feed along the normal direction of the target point on the measured surface, and the machine tool coordinates are recorded when the trigger is triggered. The measured center coordinates of the sphere are calculated based on the probe radius compensation and compared with the theoretical center coordinates of the sphere at the target point. The normal deviation of the point is obtained by vector projection calculation.

[0015] Step S3: Deviation analysis and compensation amount generation. The calibration parameters are used to correct all the measurement point data obtained in step S2. The corrected measurement data and the reference three-dimensional model of the workpiece are coarse and fine registration and comparative analysis to calculate the complete deviation compensation data describing the overall surface error of the workpiece.

[0016] Step S4: Iterative compensation machining: Input the complete deviation compensation data into the CNC controller and drive the five-axis forming grinding machine to perform compensation grinding on the workpiece; repeat steps S2 to S4 until the workpiece machining accuracy meets the requirements.

[0017] In the above-mentioned method for in-machine measurement and error compensation of a five-axis profile grinding machine, in order to eliminate the anisotropic error of the contact probe and the cosine error caused by non-fixed-point contact, the following normal alignment and following strategy is adopted:

[0018] Step 1: Let P be a theoretical target point on the surface of the workpiece to be measured, and let n be the unit normal vector at this point, with the direction of n defined as pointing outwards from the surface. The motion commands generated by the CNC program must satisfy the following geometric constraints:

[0019] (1) Position constraint: control the tool axis vector a of the machine tool spindle to always keep parallel to the normal vector n of the target point of the surface (usually set a = n or a = −n, depending on the definition of the machine tool coordinate system), so as to ensure that the probe axis is perpendicular to the tangent plane of the surface being measured;

[0020] (2) Positioning constraint: Using the center of the probe ball as the control object, position the probe on the normal extension line of the theoretical contact position;

[0021] The probe parameters were calibrated using a standard sphere.

[0022] Step 2: Define the center point of the tool as the center of the probe ball;

[0023] Step 3: The machine tool executes the measurement command, and the probe feeds along the normal direction of the curved surface in the direction of -n;

[0024] Step 4: After the probe pole trigger signal is received, record the machine tool coordinates. If the probe does not trigger, continue to step 3.

[0025] Step 5: Construct the theoretical coordinates of the sphere's center;

[0026] Known workpiece surface point coordinates and the unit normal vector of that point Based on the probe radius R, calculate the coordinates of the sphere's center when the probe is triggered under theoretical conditions. The calculation formula is as follows:

[0027] ;

[0028] In the formula, This represents a vector that is offset outward along the normal direction by one radius of the sphere.

[0029] Step 6: Obtain the measured coordinates of the sphere's center;

[0030] The machine tool executes the measurement command, and the probe moves in the opposite direction of the normal vector (i.e., (Direction) Feed. When the pole of the probe ball (the vertex collinear with its axis) contacts the workpiece surface and triggers a signal, the CNC system records the current machine tool coordinates through a high-frequency interrupt and outputs the measured ball center coordinates. ;

[0031] Step 7: Calculate the position deviation vector;

[0032] Based on the motion strategy described in step 1, the calculation of the normal deviation in this embodiment no longer relies on complex trigonometric function compensation, but is transformed into a vector projection operation in three-dimensional space. Specifically, the three-dimensional spatial difference vector between the measured sphere center coordinates and the theoretical sphere center coordinates is calculated. :

[0033] ;

[0034] Step 8: Solve the algorithm's direction deviation;

[0035] Since the measurement motion is strictly along the normal direction, and the physical contact point is fixed at the pole of the measuring head, the machining error at this time is mainly reflected in the change of the normal distance. The position deviation vector... Projected onto unit normal vector Direction, thus obtaining the normal deviation in scalar form. :

[0036] ;

[0037] Step 9: Output normal deviation .

[0038] In the above-mentioned method for in-machine measurement and error compensation of a five-axis forming grinding machine, the regression modeling algorithm used in step S1 includes one or more combinations of second-order polynomial, radial basis function support vector regression (RBF-SVR), random forest regression, or gradient boosting regression.

[0039] In the above-mentioned method for in-machine measurement and error compensation of a five-axis profile grinding machine, the "coarse and fine two-level registration and comparison analysis" in step S3 includes:

[0040] First, coarse registration based on global transformation is performed between the corrected measurement point cloud and the reference model to calculate the initial positioning error;

[0041] Subsequently, fine registration based on iterative nearest point algorithm or feature matching is performed to calculate the density deviation between point clouds;

[0042] Finally, the measured point cloud is parameterized into a surface, the geometric deviation between the parameterized surface and the reference model surface is calculated, and the error of key feature points is identified.

[0043] In the above-mentioned five-axis forming grinding machine in-machine measurement and error compensation system, the contact probe (4) is a scanning contact probe or a point-triggered contact probe.

[0044] Compared to existing technologies, this five-axis forming grinding machine's on-machine measurement and error compensation system and method integrates online measurement and real-time error compensation, achieving closed-loop control of "machining-measurement-compensation." This enables dynamic correction of geometric and thermal errors during operation, thereby stably improving machining accuracy to the micron or even sub-micron level. This not only significantly improves production efficiency and reduces offline inspection and debugging time but also enhances the machine tool's adaptability to different working conditions and environments. Simultaneously, this solution reduces reliance on extreme hardware precision through intelligent compensation, helping to control costs and fundamentally reducing scrap and rework, ensuring high quality and consistency in mass production. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the overall structure of the on-machine measurement and compensation system of this five-axis forming grinding machine.

[0046] Figure 2 This is a schematic diagram of the in-machine measurement and compensation method for this five-axis forming grinding machine.

[0047] Figure 3 This is a method for calibrating the probe's pre-stroke error.

[0048] Figure 4 This is a method for calculating the five-axis normal deviation.

[0049] Figure 5 This is a two-stage deviation analysis method for point cloud-surface coarse and fine levels.

[0050] In the diagram, 1. Five-axis profile grinding machine; 2. Worktable; 3. Workpiece; 4. Contact probe; 5. Tool holder; 6. Grinding machine spindle; 7. Wireless receiver; 8. Data processing unit; 9. CNC controller. Detailed Implementation

[0051] The embodiments of the present invention will now be described in further detail with reference to the accompanying drawings.

[0052] like Figure 1As shown, this invention provides an in-machine measurement and error compensation system for a five-axis profile grinding machine. It mainly consists of a five-axis profile grinding machine 1, a worktable 2 housed inside the five-axis profile grinding machine 1, a contact probe 4 for measurement, a tool holder 5, a grinding machine spindle 6, and a control and processing unit composed of a wireless receiver 7, a data processing unit 8, and a CNC controller 9. In terms of physical connection, the workpiece 3 being tested is clamped on the worktable 2 of the five-axis profile grinding machine 1. The contact probe 4 is mounted on the front end of the tool holder 5, which is detachably mounted on the grinding machine spindle 6. The five-axis profile grinding machine 1 has multi-axis linkage functionality, specifically including movement along three linear axes (X, Y, and Z) and rotation along two rotary axes (A and C). Regarding signal transmission and control, the contact probe 4 is configured to emit measurement signals, which are received by the wireless receiver 7. The wireless receiver 7 is connected to the data processing unit 8 via a data transmission interface (preferably a serial port in this embodiment). The data processing unit 8 further establishes communication with the CNC controller 9 through a communication bus (preferably a fieldbus, such as PROFINET or EtherCAT in this embodiment), thereby forming a closed-loop measurement and compensation circuit.

[0053] like Figure 2 As shown, this invention provides an in-machine measurement and compensation method for a five-axis profile grinding machine. Before performing in-machine measurement and compensation operations on the five-axis profile grinding machine 1, it is necessary to start and inspect the five-axis profile grinding machine 1 and the coordinate measuring machine, and check the reference workpiece 3 and the reference model. First, the probe pre-stroke error calibration is performed, and then the in-machine measurement and compensation operation on the five-axis profile grinding machine 1 begins. The test workpiece 3 is placed on the worktable of the five-axis profile grinding machine 1, and the five-axis profile grinding machine 1 performs grinding on the test workpiece 3. After processing, an in-machine error measurement is performed using a contact probe 4 to obtain probe measurement data. The deviation between the probe measurement data and the reference model data is calculated according to the five-axis normal deviation calculation method, and the deviation compensation data is obtained for subsequent complete deviation solution of the grinding machine. The complete deviation data is calculated using the point cloud-surface rough and fine two-level deviation analysis method. If the deviation does not meet the requirements, deviation compensation is required, followed by profile grinding until the workpiece dimensional accuracy meets the requirements. After the accuracy meets the standard, the workpiece and the processing process are inspected and recorded, and the process parameter library is updated.

[0054] like Figure 3As shown, this invention provides a method for calibrating the pre-stroke error of a probe. Before performing on-machine measurement and error compensation on a five-axis profile grinding machine 1, the probe needs to be calibrated to facilitate subsequent accurate measurement and error compensation. First, the five-axis profile grinding machine 1 is powered on and inspected, and the reference workpiece 3 is placed on the grinding machine's worktable 2. The contact probe 4 of the five-axis profile grinding machine 1 performs on-machine measurement on the reference workpiece along a specified path, collecting the path point position and normal information of the reference workpiece on the specified path, which is defined here as probe measurement data. A coordinate measuring machine (CMM) collects the path point information of the same reference workpiece using the same trajectory, which is defined here as CMM measurement data. After data cleaning such as outlier removal, the probe measurement data and CMM measurement data are unified and best-fit registration is performed to ensure that the two data are in the best-fit state. Various regression algorithms (including but not limited to second-order polynomial, RBF-SVR, random forest regression, and gradient boosting regression) are used to establish the mapping relationship between the probe measurement data and the CMM data, followed by cross-validation and residual evaluation. After cross-validation and residual evaluation, the mapping parameters are obtained; otherwise, the model is modified and the features are enhanced, and the model selection steps are repeated until cross-validation and residual evaluation are successful.

[0055] like Figure 4 As shown, this invention provides a method for calculating five-axis normal deviation. To eliminate the anisotropic error of the contact probe and the cosine error caused by non-fixed-point contact, this embodiment adopts a "normal alignment and following" strategy;

[0056] Step 1: Let P be a theoretical target point on the surface of the workpiece to be measured, and let n be the unit normal vector at this point, with the direction of n defined as pointing outwards from the surface. The motion commands generated by the CNC program must satisfy the following geometric constraints:

[0057] (1) Position constraint: control the tool axis vector a of the machine tool spindle to always keep parallel to the normal vector n of the target point of the surface (usually set a = n or a = −n, depending on the definition of the machine tool coordinate system), so as to ensure that the probe axis is perpendicular to the tangent plane of the surface being measured;

[0058] (2) Positioning constraint: Using the center of the contact probe ball as the control object, the probe is positioned on the normal extension line of the theoretical contact position;

[0059] A standard ball was used to calibrate the parameters of the contact probe.

[0060] Step 2: Define the tool center point as the center of the contact probe ball;

[0061] Step 3: The machine tool executes the measurement command, and the probe feeds along the normal direction of the curved surface in the direction of -n;

[0062] Step 4: When the contact probe pole is triggered, record the machine tool coordinates. If the contact probe is not triggered, continue to step 3.

[0063] Step 5: Construct the theoretical coordinates of the sphere's center;

[0064] Known coordinates of points on the workpiece's three curved surfaces and the unit normal vector of that point Based on the probe radius R, calculate the coordinates of the sphere's center when the contact probe is triggered under theoretical conditions. The calculation formula is as follows:

[0065] ;

[0066] In the formula, This represents a vector that is offset outward along the normal direction by one radius of the sphere.

[0067] Step 6: Obtain the measured coordinates of the sphere's center;

[0068] The machine tool executes the measurement command, and the probe moves in the opposite direction of the normal vector (i.e., (Direction) Feed. When the pole of the probe ball (the vertex collinear with its axis) contacts the surface of the workpiece 3 and triggers a signal, the CNC system records the current machine tool coordinates through a high-frequency interrupt and outputs the measured coordinates of the ball center. ;

[0069] Step 7: Calculate the position deviation vector

[0070] Based on the motion strategy described in step 1, the calculation of the normal deviation in this embodiment no longer relies on complex trigonometric function compensation, but is transformed into a vector projection operation in three-dimensional space. Specifically, the three-dimensional spatial difference vector between the measured sphere center coordinates and the theoretical sphere center coordinates is calculated. :

[0071] ;

[0072] Step 8: Solve the algorithm's direction deviation;

[0073] Since the measurement motion is strictly along the normal direction, and the physical contact point is fixed at the pole of the contact-type measuring head ball, the machining error at this time is mainly reflected in the change of the normal distance. The position deviation vector... Projected onto unit normal vector Direction, thus obtaining the normal deviation in scalar form. :

[0074] ;

[0075] Step 9: Output normal deviation .

[0076] like Figure 5 As shown, this invention provides a two-stage coarse and fine deviation analysis method for point cloud-surface. In the formal on-machine measurement and error compensation process of a grinding machine, the most crucial part is to conduct comparative error analysis between the probe measurement data and the reference model data, so as to obtain deviation compensation data for subsequent error compensation execution on the five-axis forming grinding machine 1. After data cleaning such as anomaly removal for the contact probe measurement data, the contact probe data is mapped according to mapping parameters, and the processed data is defined as mapped contact probe measurement data. The mapped contact probe measurement data and the reference model data are coarsely registered, and the overall coarse deviation between the two is calculated, followed by fine registration. After fine registration, the point cloud-to-point cloud coarse deviation is calculated. Then, the mapped contact probe measurement data is parameterized to form a probe data parameterized surface (preferably a NURBS surface in this embodiment). The fine deviation and key feature point errors between the contact probe data parameterized surface and the reference model data are calculated, finally forming complete deviation compensation data.

[0077] The specific embodiments described herein are merely illustrative of the spirit of the invention. Those skilled in the art to which this invention pertains may make various modifications or additions to the described specific embodiments or use similar methods to substitute them, without departing from the spirit of the invention or exceeding the scope defined by the appended claims.

[0078] Although this document uses a considerable amount of technical terms, the possibility of using other terms is not excluded. These terms are used merely for the convenience of describing and explaining the essence of the invention; interpreting them as any additional limitation would be contrary to the spirit of the invention.

Claims

1. A method for in-machine measurement and error compensation on a five-axis profile grinding machine, characterized in that, This is achieved using a five-axis form grinding machine in-machine measurement and error compensation system, the system comprising: A five-axis forming grinding machine (1) has a linkage mechanism for performing X, Y, Z linear axis motion and A, C rotary axis motion, and the five-axis forming grinding machine (1) also includes a grinding machine spindle (6). A worktable (2) is set on the five-axis forming grinder (1) and is used to clamp the workpiece (3). The contact probe (4) is detachably mounted on the grinding machine spindle (6) via the tool holder (5); The data acquisition and processing module includes a wireless receiver (7) and a data processing unit (8). The wireless receiver (7) is used to receive the trigger signal of the contact probe (4), and the data processing unit (8) is used to process the measurement data and calculate the deviation. The numerical control controller (9) is communicatively connected to the data processing unit (8) and the drive mechanism of each axis of the five-axis forming grinding machine (1), and is used to control the five-axis forming grinding machine (1) to perform compensation processing on the workpiece (3) according to the deviation data output by the data processing unit (8); The contact probe (4), data acquisition and processing module, CNC controller (9), and five-axis forming grinding machine (1) together constitute a system for realizing closed-loop control of machining, measurement, and compensation. A method for in-machine measurement and error compensation of a five-axis profile grinding machine using the above system includes the following steps: Step S1: Probe pre-stroke error calibration. On the five-axis forming grinder, the contact probe (4) is used to measure a reference workpiece (3) to obtain probe measurement data; at the same time, the same reference workpiece is measured using a coordinate measuring machine to obtain coordinate measuring data; through data registration and regression modeling, the error mapping relationship between the probe measurement data and the coordinate measuring data is established to obtain calibration parameters. Step S2: On-machine measurement and normal deviation calculation. After machining the workpiece (3) on the five-axis forming grinder, control the contact probe (4) to feed and contact along the normal direction of the target point of the measured surface, and record the machine coordinates when triggered; calculate the actual sphere center coordinates based on probe radius compensation, and compare them with the theoretical sphere center coordinates at the target point, and obtain the normal deviation of the point through vector projection calculation. Step S3: Deviation analysis and compensation amount generation. The calibration parameters are used to correct all the measurement point data obtained in step S2. The corrected measurement data and the reference three-dimensional model of the workpiece (3) are coarse and fine registration and comparison analysis to calculate the complete deviation compensation data describing the overall surface error of the workpiece. Step S4: Iterative compensation machining: Input the complete deviation compensation data into the CNC controller (9) and drive the five-axis forming grinder (1) to perform compensation grinding on the workpiece (3); repeat steps S2 to S4 until the workpiece machining accuracy meets the requirements.

2. The method for in-machine measurement and error compensation of a five-axis forming grinding machine according to claim 1, characterized in that, To eliminate the anisotropic error and cosine error caused by non-fixed-point contact of the contact probe, the following normal alignment and following strategy is adopted: Step 1: Let P be a theoretical target point on the surface of the workpiece (3) to be measured, and let n be the unit normal vector at this point. The direction of n is defined as pointing outward from the surface. The motion command generated by the CNC program must satisfy the following geometric constraints: (1) Position constraint: control the tool axis vector a of the machine tool spindle to always keep parallel to the normal vector n of the target point of the surface, so as to ensure that the probe axis is perpendicular to the tangent plane of the surface being measured; (2) Positioning constraint: Using the center of the probe ball as the control object, position the probe on the normal extension line of the theoretical contact position; The probe parameters were calibrated using a standard sphere. Step 2: Define the center point of the tool as the center of the probe ball; Step 3: The machine tool executes the measurement command, and the probe feeds along the normal direction of the curved surface in the direction of -n; Step 4: After the probe pole trigger signal is received, record the machine tool coordinates. If the probe does not trigger, continue to step 3. Step 5: Construct the theoretical coordinates of the sphere's center; Known coordinates of the workpiece (3) surface points and the unit normal vector of that point Based on the probe radius R, calculate the coordinates of the sphere's center when the probe is triggered under theoretical conditions. The calculation formula is as follows: ； In the formula, This represents a vector that is offset outward along the normal direction by one radius of the sphere. Step 6: Obtain the measured coordinates of the sphere's center; The machine tool executes the measurement command, and the probe feeds in the opposite direction of the surface normal -n. When the pole of the probe ball contacts the workpiece (3) surface and triggers a signal, the CNC system records the current machine tool coordinates through a high-frequency interrupt and outputs the measured ball center coordinates. ; Step 7: Calculate the position deviation vector; The difference vector between the measured and theoretical coordinates of the sphere's center is calculated using vector projection operations in three-dimensional space. : ； Step 8: Solve the algorithm's direction deviation; Since the measurement motion is strictly along the normal direction, and the physical contact point is fixed at the pole of the measuring head, the machining error at this time is mainly reflected in the change of the normal distance. The position deviation vector is then converted into a vector. Projected onto the unit normal vector Direction, thus obtaining the normal deviation in scalar form. : ； Step 9: Output normal deviation .

3. The method for in-machine measurement and error compensation of a five-axis forming grinding machine according to claim 1, characterized in that, The regression modeling algorithm used in step S1 includes one or more combinations of second-order polynomial, radial basis function support vector regression (RBF-SVR), random forest regression, or gradient boosting regression.

4. The method for in-machine measurement and error compensation of a five-axis forming grinding machine according to claim 1, characterized in that, The coarse and fine two-level registration and comparison analysis mentioned in step S3 includes: First, coarse registration based on global transformation is performed between the corrected measurement point cloud and the reference model to calculate the initial positioning error; Subsequently, fine registration based on iterative nearest point algorithm or feature matching is performed to calculate the density deviation between point clouds; Finally, the measured point cloud is parameterized into a surface, the geometric deviation between the parameterized surface and the reference model surface is calculated, and the error of key feature points is identified.

5. The method for in-machine measurement and error compensation of a five-axis forming grinding machine according to claim 1, characterized in that, The contact probe (4) is a scanning contact probe or a point-triggered contact probe.

Images