A ballbar-based machine tool spatial accuracy evaluation method, system, terminal and medium

Abstract

The present invention belongs to the field of machine tool spatial positioning accuracy assessment. Specifically, it discloses a method, system, terminal and medium for machine tool spatial accuracy assessment based on a ballbar. By installing a ballbar assembly, a workpiece coordinate system based on a set sphere center is established on the machine tool workbench. Adjustable extension rods are used to evenly distribute measurement points on the upper hemisphere, and the command position of the corresponding measurement point and the actual length measured by the ballbar are collected. Based on a length calculation model, the allowable length range of each measurement point is calculated, and the actual measured length is compared with the allowable range point by point to dynamically determine whether the machine tool spatial positioning accuracy meets the preset requirements. If not, the error tracing module is used to analyze the contribution of each axis error to the spatial error based on the projection sensitivity coefficient of the three-axis error on the ballbar length, and locate the key error axis or inter-axis coupling error. The system does not rely on high-precision laser equipment and has the advantages of convenient deployment, comprehensive measurement point coverage, high measurement efficiency and accurate error diagnosis.

Description

Technical Field

[0001] The present invention belongs to the field of machine tool spatial positioning accuracy assessment, and in particular relates to a machine tool spatial accuracy assessment method, system, terminal and medium based on a ballbar. Background Art

[0002] Testing the spatial positioning accuracy of CNC machine tools is primarily intended to ensure that when the machine tool performs machining tasks in three-dimensional space, each motion axis can accurately reach the target position according to instructions, thereby ensuring the geometric accuracy and consistency of the machined parts. Currently, the spatial positioning accuracy of CNC machine tools is mainly tested using the laser interferometer body diagonal measurement method and the surface diagonal positioning error measurement method.

[0003] The body diagonal measurement method uses a laser interferometer to measure the positioning error of the machine tool's spatial body diagonal direction, reflecting the geometric error under three-axis combined motion. The face diagonal measurement method selects several typical diagonal directions in the workspace and measures their positioning deviation. Although both methods have high accuracy, they are highly equipment-dependent, require cumbersome measurement preparation, and have long testing times. In particular, their deployment efficiency is low under actual field conditions, making them difficult to meet the application requirements of rapid multi-machine and multi-point inspection.

[0004] In addition, in the actual measurement process, existing methods usually use laser interferometers or fixed standard spheres as references, and perform spatial error calculations without fully eliminating the influence of installation errors or axial system errors. As a result, the measurement results are easily affected by the fixed deviation of the workpiece end or the installation error of the laser reflector, resulting in systematic deviations in the measurement data, affecting the accuracy and stability of the evaluation. Summary of the Invention

[0005] In response to the problems in the prior art, the present invention provides a method, system, terminal and medium for evaluating the spatial accuracy of machine tools based on a ballbar, which solves the problems in the prior art of using a laser interferometer body diagonal measurement method and a surface diagonal positioning error measurement method to detect the spatial positioning accuracy of CNC machine tools, such as strong equipment dependence, cumbersome measurement preparation work and long testing time.

[0006] The technical solution adopted in the present invention is as follows:

[0007] In a first aspect, the present application provides a method for evaluating the spatial accuracy of a machine tool based on a ballbar, comprising the following steps:

[0008] Step S1: Install the center seat and the tool cup, set a measurement reference point on the CNC machine tool workbench, and establish a workpiece coordinate system with the reference point as the origin;

[0009] Step S2: obtaining the length of the extension rod and the length of the ballbar body, and calculating the allowable length range of the ballbar based on the allowable error range and the simplified length calculation formula of the ballbar, selecting several measurement points on the upper hemisphere, and collecting the command position and the actual measured length of the ballbar corresponding to each measurement point;

[0010] Step S3: comparing the actual length measured by the ballbar with the allowable length range at the corresponding measuring point to determine whether the spatial positioning accuracy of the CNC machine tool meets the preset requirements;

[0011] When the spatial positioning accuracy of the CNC machine tool meets the preset requirements, the length of the extension rod is changed, i.e., the allowable length range of the ballbar, and the process jumps to step S2;

[0012] When the spatial positioning accuracy of the CNC machine tool does not meet the preset requirements, jump to step S4;

[0013] Step S4: Analyze the contribution of each axis error to the change in ballbar length based on the projection coefficient of the ballbar length sensitivity to the three-axis error, trace the spatial error source, and identify the key axis or inter-axis coupling error that causes the local positioning accuracy to decrease.

[0014] Furthermore, in step S2, during the calculation of the ballbar body length, a three-axis axial error term is introduced into the command position of the measurement point in the workpiece coordinate system. The ballbar length calculation formula is:

[0015]

[0016] in They are respectively in the workpiece coordinate system The command position of the three axes, They are Axial errors of the three axes;

[0017] Instruction location It can be directly expressed in the spherical coordinate system as:

[0018]

[0019] in is the nominal length of the ballbar, are the polar angle and azimuth angle in the spherical coordinate system, Ignoring the second-order terms, the simplified length calculation formula of the ballbar is:

[0020] .

[0021] Furthermore, in step S2, based on the polar angles and azimuth angles of the measurement points in the spherical coordinate system, an angle distribution function is used to construct a set of measurement points with uniform polar angles and azimuth angles to cover the workspace area.

[0022] Furthermore, when the polar angle is , the nominal length of the ballbar is When the polar angle changes and azimuth angle change They are:

[0023]

[0024] The number of extreme points and the corresponding polar angle The number of azimuth points under for:

[0025]

[0026] After the ballbar measurement is completed, the ballbar measured length set within the measurement area is obtained as:

[0027]

[0028] in, The polar angle and azimuth angle are The actual length measured by the ballbar at For the polar angle The next The number of azimuth angles, the polar angle set is , the azimuth set is .

[0029] Furthermore, in step S3, each measured length element in the ballbar measured length set D is compared with the allowed length range at the corresponding measurement point. The allowed length range is ,in is the error threshold, which determines whether there are any elements with measured lengths exceeding the allowable length range.

[0030] Furthermore, when comparing the measured lengths of the measurement points in the measured length set D, a regional error weighted average method is adopted. When the average error values ​​of several adjacent measurement points in a region exceed the set tolerance, it is determined that there is a positioning error anomaly in the region.

[0031] Furthermore, in step S4, it can be seen from the simplified length calculation formula of the ballbar that: The projection factor of the actual value of the axial error on the ballbar length is:

[0032]

[0033] in, For Axis projection coefficient;

[0034] At any measuring point The contribution of axial spatial error to the ballbar length is:

[0035]

[0036] in, ;

[0037] The error is traced to its source through the contribution ratio of the axial error. The single axis with a larger contribution ratio or the multiple axes with a larger contribution ratio are the reasons for the reduction in spatial positioning accuracy.

[0038] In a second aspect, the present application provides a machine tool spatial accuracy assessment system based on a ballbar, the system comprising:

[0039] The ballbar assembly, comprising a centre mount, tool cup and adjustable extension rod, is used to establish a ballbar measurement path within the CNC machine tool workspace and to obtain actual ballbar length data;

[0040] The coordinate system construction module is used to establish the workpiece coordinate system on the CNC machine tool workbench with the center of the center seat end ball position as the reference, so as to facilitate the unified description of the measurement point position and error modeling;

[0041] The measurement point planning module is used to construct a uniformly covered measurement point set in the spherical coordinate system according to the set polar angle and azimuth angle distribution function and output the three-axis command position corresponding to each measurement point;

[0042] Length calculation module, used to introduce three-axis axial error parameters to each measuring point position and calculate the ballbar length;

[0043] The error comparison and judgment module is used to compare the actual length measured by the ballbar with the allowable length range point by point, determine whether the corresponding measurement point meets the spatial positioning accuracy requirements, and control whether to replace the extension rod or enter the error tracing process based on the results;

[0044] The error tracing module is used to calculate the contribution of each axis's spatial error to the change in the ballbar's measured length based on the projected sensitivity coefficients of the three-axis errors on the ballbar length, and output the positioning information of the key axis or inter-axis coupling errors.

[0045] In a third aspect, the present application provides a terminal, including:

[0046] a memory for storing a machine tool spatial accuracy evaluation program of the ballbar;

[0047] A processor is configured to implement the steps of the ballbar-based machine tool spatial accuracy assessment method as described in the first aspect when executing the ballbar-based machine tool spatial accuracy assessment system.

[0048] In a fourth aspect, the present application provides a computer-readable storage medium, which stores computer instructions. When a computer reads the computer instructions in the storage medium, the computer executes the machine tool spatial accuracy evaluation method based on the ballbar as described in the first aspect.

[0049] It can be seen from the above technical solutions that the advantages of the present invention are:

[0050] (1) The present invention constructs a workpiece coordinate system based on a set ball, combines an adjustable extension rod with a ballbar assembly, evenly distributes measurement points in the upper hemisphere space at polar angles and azimuth angles, collects the actual measured lengths of multiple points in space, and compares them point by point in combination with the body length model. This method can quickly evaluate the positioning accuracy of the CNC machine tool within the entire working space. This method can significantly improve the spatial coverage of the measurement points, realize multi-angle, multi-direction, and multi-position spatial error detection, and solve the problem of sparse measurement points and insufficient coverage of the existing methods.

[0051] The measurement path design and length calculation method based on the workpiece coordinate system is adopted to avoid the systematic influence of the ball seat installation error on the measurement results, thus improving the accuracy and repeatability of the evaluation results.

[0052] The measurement process does not require high-precision standard devices and complex laser systems. It has the advantages of easy deployment, high efficiency, and strong on-site adaptability. It is suitable for rapid precision detection and trend judgment at production sites.

[0053] (2) By introducing the three-axis axial error term into the ballbar length calculation formula, the measurement point length calculation has the error modeling capability, which can actively shield the influence of the ball seat or installation reference deviation on the measurement value, realize the accurate mapping between the measurement data and the actual spatial error, and improve the system's ability to resolve the error source and the credibility of the measurement results.

[0054] (3) By using the polar angle and azimuth angle distribution functions to generate measurement points in the spherical coordinate system, uniform coverage of measurement points in the spherical space can be achieved, ensuring the representativeness and reasonable distribution of measurement points in all directions and regions, and providing basic data support for the comprehensive evaluation of spatial errors;

[0055] The number and distribution formula of measuring points are derived based on the relationship between polar angle, azimuth angle and ballbar length. The number of polar angle points and azimuth angle points can be automatically planned according to the expected distribution density, improving the efficiency of measuring point layout, avoiding the unevenness and non-repetition caused by manual point selection, and improving the efficiency of measurement space coverage.

[0056] (4) The error sensitivity model is established by using the projection coefficient of the three-axis error to the length of the ballbar, and the error source is traced in combination with the contribution ratio. This can effectively identify the dominant source of spatial error, including single-axis error or multi-axis coupling error, and provide a technical basis for machine tool maintenance, error compensation and inter-axis coordination adjustment. BRIEF DESCRIPTION OF THE DRAWINGS

[0057] In order to more clearly illustrate the technical solution of the present invention, the following is a brief introduction to the drawings required for the description. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0058] Figure 1 A schematic flow chart of a method for evaluating machine tool spatial accuracy based on a ballbar provided in an embodiment of the present invention;

[0059] Figure 2 1 is a spherical coordinate system of an embodiment of the present invention and a distribution diagram of measurement points at the polar angle. DETAILED DESCRIPTION

[0060] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0061] See also Figure 1 and Figure 2 As shown, the present invention provides a method for evaluating the spatial accuracy of a machine tool based on a ballbar, comprising the following steps:

[0062] Step S1: Install the center seat and the tool cup, set a measurement reference point on the CNC machine tool workbench, and establish a workpiece coordinate system with the reference point as the origin;

[0063] Before performing spatial accuracy testing on a machine tool, a unified spatial reference coordinate system must be established so that subsequent measurement point positions and length data can be calculated and compared using a unified benchmark. By mounting one end of the ballbar on the center seat of the workbench and the other end in the tool holder cup, a measurement chain is constructed. A workpiece coordinate system is established using this assembly position as a reference, achieving consistent three-dimensional coordinate description.

[0064] Before measurement begins, place the centering block near the center of the machine table. Clamp the tool cup to the spindle toolholder, place the setting ball on the centering block, and control the machine until the tool cup attracts the setting ball on the centering block. The centering block is then fixed in place. The machine command coordinates at this point are recorded as the origin of the workpiece coordinate system (0,0,0). A workpiece coordinate system with this point as the origin is established. Control the toolholder to move to the starting point of the measurement position, remove the setting ball, and attach the ballbar to the toolholder and centering block, respectively.

[0065] Step S2: obtaining the length of the extension rod and the length of the ballbar body, and calculating the allowable length range of the ballbar based on the allowable error range and the simplified length calculation formula of the ballbar, selecting several measurement points on the upper hemisphere, and collecting the command position and the actual measured length of the ballbar corresponding to each measurement point;

[0066] This step is used to collect ballbar spatial measurement data and calculate the allowable range. After determining the ballbar's test radius, select a number of representative measurement points in the spherical space, move the spindle to each point in sequence, collect the actual length measured by the ballbar at each measurement point, and combine the simplified ballbar length formula and the allowable error range to calculate the allowable length range corresponding to each measurement point, providing a basis for subsequent comparison and judgment.

[0067] The ballbar's test radius is determined based on the extension rod combination used. The system then automatically generates a set of measurement points on the upper hemisphere, evenly distributed by angle. The CNC system sequentially controls the spindle to each measurement point, recording the ballbar's measured length. The system combines the theoretical length calculation for that point with the set tolerances to determine the permissible length range for that point. The system then stores each measurement point's number, location, measured value, and permissible range.

[0068] Step S3: comparing the actual length measured by the ballbar with the allowable length range at the corresponding measuring point to determine whether the spatial positioning accuracy of the CNC machine tool meets the preset requirements;

[0069] When the spatial positioning accuracy of the CNC machine tool meets the preset requirements, the length of the extension rod is changed to modify the ballbar test length, and the process jumps to step S2;

[0070] When the spatial positioning accuracy of the CNC machine tool does not meet the preset requirements, jump to step S4;

[0071] After completing data collection at each measurement point, the actual measured length value must be compared with the allowable length range at the corresponding location to determine whether the measurement point meets the accuracy requirements. If all measurement points meet the requirements, the positioning accuracy within the measurement range is considered acceptable. Otherwise, there is a problem with spatial positioning accuracy, and further analysis of the error source is required.

[0072] The system compares each measured point to see if its actual length falls within the permitted range. If all measurement results are within the permitted range, the system records the test result as acceptable for the current extension rod length and prompts you to replace it with a longer extension rod to continue testing other areas. If the measured length of any point is found to be outside the permitted range, that area is deemed to have positioning accuracy anomalies, and the system initiates the error tracing process.

[0073] Step S4: Analyze the contribution of each axis error to the ballbar length change based on the projection coefficient of the ballbar length sensitivity to the three-axis error, trace the spatial error source, and identify the key axis or inter-axis coupling error that causes the local positioning accuracy to be reduced;

[0074] When it is detected that some measurement points are outside the allowable range, this step will trace the spatial errors of these points. Specifically, by analyzing the directional characteristics of each measurement point, it is determined which direction of error has the greatest impact on the measurement results. This will identify the main axis or coupling relationship between axes where errors may exist, providing a basis for subsequent maintenance, compensation, or adjustment.

[0075] When the system detects that the measured length of a point exceeds the error range, it further analyzes the position and orientation of that point in three-dimensional space. Based on the point's sensitivity to errors in different directions, the system calculates the proportional impact of each directional error on the measurement result. By comparing the magnitudes of these impact ratios, the system can determine which axis of motion is primarily responsible for the error at that point, or whether it is the result of the combined effects of multiple axes. This allows the system to pinpoint the key source of the error that is causing the drop in positioning accuracy in that area.

[0076] In this embodiment, in step S2, during the calculation of the ballbar body length, a three-axis axial error term is introduced into the command position of the measurement point in the workpiece coordinate system. The ballbar length calculation formula is:

[0077]

[0078] in They are respectively in the workpiece coordinate system The command position of the three axes, They are Axial errors of the three axes;

[0079] Instruction location It can be directly expressed in the spherical coordinate system as:

[0080]

[0081] in is the nominal length of the ballbar, are the polar angle and azimuth angle in the spherical coordinate system, Ignoring the second-order terms, the simplified length calculation formula of the ballbar is:

[0082] .

[0083] In this embodiment, in step S2, based on the polar angles and azimuth angles of the measurement points in the spherical coordinate system, an angle distribution function is used to construct a set of measurement points with uniform polar angles and azimuth angles to cover the workspace area;

[0084] To fully cover the machine tool's spatial working area and ensure representative and balanced evaluation results, this invention incorporates an angular distribution model of a spherical coordinate system into the measurement point planning process. Specifically, by setting the step size for polar and azimuth angle changes, a uniform angular distribution function is used to generate a set of rationally distributed measurement points. These measurement points are evenly distributed across the upper hemisphere accessible to the ballbar, allowing measurement data to be acquired at different spatial directions and positions, enabling a comprehensive assessment of positioning accuracy within the machine tool's working space.

[0085] After establishing the workpiece coordinate system, the system determines the ballbar's test radius based on the current extension rod combination. To ensure a more even distribution of measurement points in space, the system constructs a set of measurement points based on a spherical surface with the center of the ball at the center seat as the origin.

[0086] The specific implementation is as follows: the system first sets the polar angle variation interval, so that the measurement points gradually expand from the vertical direction of the main axis to the horizontal direction. At each polar angle level, the system determines the required number of azimuth points based on the spatial coverage of that level, avoiding too dense or too sparse measurement points. The resulting measurement points form a spatial network with a nearly uniform distribution across the entire upper hemisphere. These measurement point positions are converted into three-axis coordinate points, which serve as the target points for the CNC system to subsequently control tool movement.

[0087] This strategy ensures that the ballbar measurement covers as many spatial directions and areas as possible, making the collected spatial accuracy data comprehensive and representative, and effectively supporting subsequent error assessment and traceability analysis.

[0088] In this embodiment, when the polar angle is , the nominal length of the ballbar is When the polar angle changes and azimuth angle change They are:

[0089]

[0090] The number of extreme points and the corresponding polar angle The number of azimuth points under for:

[0091]

[0092] After the ballbar measurement is completed, the ballbar measured length set within the measurement area is obtained as:

[0093]

[0094] in, The polar angle and azimuth angle are The actual length measured by the ballbar at For the polar angle The next The number of azimuth angles, the polar angle set is , the azimuth set is .

[0095] In this example, the ballbar body length is calculated as follows: The allowable error range of axial positioning error is positive and negative respectively. Since the same error has different effects on the change in ballbar length when the polar angle and azimuth angle change, it is necessary to calculate the corresponding allowable length range of the ballbar based on the polar angle, azimuth angle and allowable error range of each axis of the measurement point.

[0096] For example, when hour, Heng established, when When the value is determined, only the spatial error in the axial direction is a variable. When the error takes the maximum value, the ballbar length is the longest. When the minimum value is taken, the length of the ballbar is the shortest. Similarly, for other quadrants of the spatial coordinate system, let Select the error factor in the calculation formula for the actual ballbar length When the signs are the same, the ballbar length is maximum, and when the signs are opposite, the ballbar length is minimum. Ignoring the second-order terms, the allowable length range of the ballbar within the allowable error range is calculated using the simplified length formula of the ballbar:

[0097] ;

[0098] In step S3, each measured length element in the ballbar measured length set D is compared with the allowed length range at the corresponding measurement point. The allowed length range is ,in is the error threshold, which determines whether there are any elements with measured lengths exceeding the allowable length range.

[0099] In this embodiment, when comparing the measured lengths of the measurement points in the measured length set D, a regional error weighted average method is adopted. When the average error value of several adjacent measurement points in a region exceeds the set tolerance, it is determined that there is a positioning error anomaly in the region;

[0100] To improve the stability and robustness of spatial accuracy assessment, this paper introduces a regional error analysis mechanism when evaluating measurement results. Unlike the simple method of determining whether a single point's error exceeds the limit, this method divides multiple spatially adjacent measurement points into several measurement regions. The average error level for each region is calculated by taking a weighted average of the error values ​​of multiple measurement points within each region. If the average error within a region exceeds a preset accuracy tolerance threshold, a spatial positioning error anomaly is determined in that region.

[0101] This strategy can effectively avoid misjudgments caused by individual isolated points and improve the accuracy of error judgment. It is particularly suitable for identifying problems such as systematic errors with certain spatial range characteristics or local rigidity reduction, and is more in line with the needs of stable accuracy judgment in actual engineering applications.

[0102] After collecting the measured lengths of all measurement points and performing a preliminary comparison with the allowable range, the system divides the spherical measurement points into several continuous measurement areas based on their spatial distribution. Each area consists of several adjacent measurement points, such as five to ten points with similar spatial angular distribution.

[0103] For each region, the system calculates the measurement error values ​​for all measuring points within that region and takes a weighted average of these error values. The weights can be set based on factors such as the spatial importance of the measuring points and the azimuth distribution density. When the average error value within a region exceeds the system-set error tolerance limit, the system determines that there is a positioning error anomaly in that region and annotates the result in a diagram or output report, alerting the user to the risk of a decrease in positioning accuracy in that spatial region.

[0104] This method avoids excessive sensitivity to outliers at a single measuring point, making spatial error assessment more robust and in line with the overall verification requirements of machine tools. It is suitable for use in scenarios such as batch measurement points, high-frequency measurement, and trend analysis.

[0105] In this embodiment, in step S4, it can be seen from the simplified length calculation formula of the ballbar that: The projection factor of the actual value of the axial error on the ballbar length is:

[0106]

[0107] in, For Axis projection coefficient;

[0108] At any measuring point The contribution of axial spatial error to the ballbar length is:

[0109]

[0110] in, ;

[0111] The error is traced to its source through the contribution ratio of the axial error. The single axis with a larger contribution ratio or the multiple axes with a larger contribution ratio are the reasons for the reduction in spatial positioning accuracy.

[0112] In some embodiments, the present application provides a machine tool spatial accuracy assessment system based on a ballbar, the system comprising:

[0113] The ballbar assembly, comprising a centre mount, tool cup and adjustable extension rod, is used to establish a ballbar measurement path within the CNC machine tool workspace and to obtain actual ballbar length data;

[0114] The ballbar assembly is the core hardware component of this measurement system, consisting of a center base, a tool cup, and an adjustable extension rod. The center base is fixed inside the CNC machine tool and serves as the ballbar's reference point. The tool cup is used to mount the ballbar probe, ensuring a stable connection to the measuring device. The adjustable extension rod allows for flexible measurement range adjustment to meet the various dimensions of the machine tool workspace. This assembly creates a movable ballbar measurement path within the CNC machine tool workspace, enabling length measurements at various points on the workpiece or machine tool, and obtaining actual ballbar length data.

[0115] The coordinate system construction module is used to establish the workpiece coordinate system on the CNC machine tool workbench with the center of the center seat end ball position as the reference, so as to facilitate the unified description of the measurement point position and error modeling;

[0116] This module uses the center of the ball as a reference point to establish a unified workpiece coordinate system on the CNC machine table. This coordinate system allows measurement point positions to be uniformly described, enabling accurate positioning of measurement points and subsequent error modeling. The establishment of this coordinate system allows the ballbar measurement data to match the machine tool's spatial data, facilitating accurate spatial error analysis.

[0117] The measurement point planning module is used to construct a uniformly covered measurement point set in the spherical coordinate system according to the set polar angle and azimuth angle distribution function and output the three-axis command position corresponding to each measurement point;

[0118] Based on the set polar angle and azimuth distribution functions, the measurement point planning module generates a uniformly distributed set of measurement points in the spherical coordinate system to ensure that the measurement path evenly covers the workspace. Each measurement point position corresponds to a unique three-axis command position, providing precise position instructions for the CNC machine tool to execute the measurement path;

[0119] Length calculation module, used to introduce three-axis axial error parameters to each measuring point position and calculate the ballbar length;

[0120] This module uses the machine tool's three-axis axial error parameters to correct the theoretical position of each measuring point and calculate the actual length of the ballbar. This calculation reflects the impact of three-axis error on the actual length of the ballbar. It calculates the ballbar length of each measuring point within the corresponding three-axis error tolerance, and is used to determine whether the measured length is within the acceptable error range, ensuring compliance with spatial positioning accuracy.

[0121] The error comparison and judgment module is used to compare the actual length measured by the ballbar with the allowable length range point by point, determine whether the corresponding measurement point meets the spatial positioning accuracy requirements, and control whether to replace the extension rod or enter the error tracing process based on the results;

[0122] This module compares the measured ballbar length with the length interval of the corresponding measuring point point by point to determine whether the measuring point meets the spatial positioning accuracy requirements. Based on the judgment result, it automatically controls whether to replace the extension rod or start the error tracing program to ensure dynamic adjustment and accuracy of the measurement process.

[0123] The error tracing module is used to calculate the contribution of each axis's spatial error to the change in the ballbar's measured length based on the projected sensitivity coefficients of the three-axis errors on the ballbar length, and output the contribution of the key error axis or inter-axis coupling error;

[0124] The Error Source Tracking module calculates the contribution of three-axis errors to ballbar length measurements, allowing rapid assessment of critical positioning error axes or inter-axis coupling errors. This functionality provides technical support for rapidly assessing critical error axes on machine tools and improving measurement accuracy.

[0125] In some embodiments, the present application provides a terminal, including:

[0126] a memory for storing a machine tool spatial accuracy evaluation program of the ballbar;

[0127] A processor is configured to implement the steps of the ballbar-based machine tool spatial accuracy assessment method when executing the ballbar-based machine tool spatial accuracy assessment system.

[0128] In some embodiments, the present application provides a computer-readable storage medium, which stores computer instructions. When a computer reads the computer instructions in the storage medium, the computer executes the ballbar-based machine tool spatial accuracy assessment method.

[0129] The above contents are merely examples and explanations of the concept of the present invention. Those skilled in the art may make various modifications or additions to the described specific embodiments or replace them in a similar manner. As long as they do not deviate from the concept of the invention or exceed the scope defined by the present invention, they should all fall within the scope of protection of the present invention.

Claims

1. A method for evaluating the spatial accuracy of machine tools based on a ballbar, characterized in that: The following steps are involved: Step S1: Install the center seat and the tool cup, set a measurement reference point on the CNC machine tool workbench, and establish a workpiece coordinate system with the reference point as the origin; Step S2: Obtain the length of the extension rod and the length of the ballbar body, calculate the allowable length range of the ballbar based on the length of the body, and select several measurement points on the upper hemisphere. Then, collect the command position and the actual measured length of the ballbar corresponding to each measurement point. When calculating the ballbar's body length, a three-axis axial error term is introduced into the command position of the measuring point in the workpiece coordinate system. The ballbar length calculation formula is: in They are respectively in the workpiece coordinate system The command position of the three axes, They are Axial errors of the three axes; Instruction location It can be directly expressed in the spherical coordinate system as: in is the nominal length of the ballbar, are the polar angle and azimuth angle in the spherical coordinate system, Ignoring the second-order terms, the simplified length calculation formula of the ballbar is: ； Based on the polar angle and azimuth angle of the measurement points in the spherical coordinate system, an angle distribution function is used to construct a set of measurement points with uniform polar angle and azimuth angle distribution to cover the workspace area. When the polar angle is , the nominal length of the ballbar is When the polar angle changes and azimuth angle change They are: The number of extreme points and the corresponding polar angle The number of azimuth points under for: After the ballbar measurement is completed, the ballbar measured length set within the measurement area is obtained as: in, The polar angle and azimuth angle are The actual length measured by the ballbar at For the polar angle The next The number of azimuth angles, the polar angle set is , the azimuth set is ; Step S3: comparing the actual length measured by the ballbar with the allowable length range at the corresponding measuring point to determine whether the spatial positioning accuracy of the CNC machine tool meets the preset requirements; When the spatial positioning accuracy of the CNC machine tool meets the preset requirements, the length of the extension rod is changed, i.e., the allowable length range of the ballbar, and the process jumps to step S2; When the spatial positioning accuracy of the CNC machine tool does not meet the preset requirements, jump to step S4; Step S4: Analyze the contribution of each axis error to the change in ballbar length based on the projection coefficient of the ballbar length sensitivity to the three-axis error, trace the spatial error source, and identify the key axis or inter-axis coupling error that causes the local positioning accuracy to decrease.

2. The ballbar-based machine tool spatial accuracy evaluation method according to claim 1, characterized in that: In step S3, each measured length element in the ballbar measured length set D is compared with the allowed length range at the corresponding measurement point. The allowed length range is ,in is the error threshold, which determines whether there are any elements with measured lengths exceeding the allowable length range.

3. The ballbar-based machine tool spatial accuracy assessment method according to claim 2, characterized in that: When comparing the measured lengths of the measurement points in the measured length set D, the regional error weighted average method is adopted. When the average error values ​​of several adjacent measurement points in a region exceed the set tolerance, it is determined that there is a positioning error anomaly in the region.

4. The ballbar-based machine tool spatial accuracy assessment method according to claim 1, characterized in that: In step S4, it can be seen from the simplified length calculation formula of the ballbar that: The projection factor of the actual value of the axial error on the ballbar length is: in, For Axis projection coefficient; At any measuring point The contribution of axial spatial error to the ballbar length is: in, ; The error is traced to its source through the contribution ratio of the axial error. The single axis with a larger contribution ratio or the multiple axes with a larger contribution ratio are the reasons for the reduction in spatial positioning accuracy.

5. A machine tool spatial accuracy assessment system based on a ballbar, characterized in that: The system is used to implement the ballbar-based machine tool spatial accuracy assessment method according to claim 1, and the system comprises: The ballbar assembly, comprising a centre mount, tool cup and adjustable extension rod, is used to establish a ballbar measurement path within the CNC machine tool workspace and to obtain actual ballbar length data; The coordinate system construction module is used to establish the workpiece coordinate system on the CNC machine tool workbench with the center of the center seat end ball position as the reference, so as to facilitate the unified description of the measurement point position and error modeling; The measurement point planning module is used to construct a uniformly covered measurement point set in the spherical coordinate system according to the set polar angle and azimuth angle distribution function and output the three-axis command position corresponding to each measurement point; Length calculation module, used to introduce three-axis axial error parameters to each measuring point position and calculate the ballbar length; The error comparison and judgment module is used to compare the actual length measured by the ballbar with the allowable length range point by point, determine whether the corresponding measurement point meets the spatial positioning accuracy requirements, and control whether to replace the extension rod or enter the error tracing process based on the results; The error tracing module is used to calculate the contribution of each axis's spatial error to the change in the ballbar's measured length based on the projected sensitivity coefficients of the three-axis errors on the ballbar length, and output the positioning information of the key axis or inter-axis coupling errors.

6. A terminal, characterized in that: include: a memory for storing a machine tool spatial accuracy evaluation program of the ballbar; A processor is configured to implement the steps of the ballbar-based machine tool spatial accuracy evaluation method as claimed in claim 1 when executing the ballbar-based machine tool spatial accuracy evaluation system.

7. A computer-readable storage medium, characterized in that The storage medium stores computer instructions. When the computer reads the computer instructions in the storage medium, the computer executes the machine tool spatial accuracy evaluation method based on the ballbar as claimed in claim 1.

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