Machine tool space precision evaluation method and system based on ball bar instrument, terminal and medium

Abstract

The invention belongs to the field of machine tool space positioning precision evaluation, and particularly discloses a machine tool space precision evaluation method and system based on a ball rod instrument, a terminal and a medium. A ball rod instrument assembly is installed, a workpiece coordinate system with a set ball center as a benchmark is established on a machine tool workbench, and measuring points are evenly distributed on the upper semi-spherical surface through an adjustable lengthening rod; and collecting the instruction position of the corresponding measuring point and the actual measurement length of the ball bar. And based on a length calculation model, calculating an allowable length range of each measuring point, comparing the actually measured length with an allowable interval point by point, and dynamically judging whether the space positioning precision of the machine tool meets a preset requirement or not. And if not, analyzing the contribution ratio of each axis error to the space error through an error traceability module according to the projection sensitivity coefficient of the three-axis error to the length of the ball bar, and positioning a key error axis or an inter-axis coupling error. The system does not depend 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 evaluating the spatial positioning accuracy of machine tools, and particularly relates to a method, system, terminal and medium for evaluating the spatial accuracy of machine tools based on a ball bar. Background Art

[0002] The detection of the spatial positioning accuracy of CNC machine tools is mainly to ensure that when the machine tool performs machining tasks in a three-dimensional space, each moving axis can accurately reach the target position according to the instructions, so as to ensure the geometric accuracy and consistency of the machined parts. At present, the detection of the spatial positioning accuracy of CNC machine tools mainly adopts the body diagonal measurement method with a laser interferometer and the face diagonal positioning error measurement method.

[0003] The body diagonal measurement method measures the positioning error in the direction of the body diagonal of the machine tool space through a laser interferometer to reflect the geometric error under the combined movement of the three axes. The face diagonal measurement method selects several typical diagonal directions in the working space and measures their positioning deviations. Although these two methods have high accuracy, they have the problems of strong equipment dependence, cumbersome measurement preparation work and long test time. Especially in the actual on-site working conditions, the deployment efficiency is low, and it is difficult to meet the application requirements of multi-machine and multi-point rapid detection.

[0004] In addition, during the actual measurement process, the existing methods usually use a laser interferometer or a fixed reference sphere as a reference, and calculate the spatial error 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 at the workpiece end or the installation error of the laser mirror, resulting in systematic deviations in the measurement data and affecting the accuracy and stability of the evaluation. Summary of the Invention

[0005] Aiming at 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 ball bar, and solves the problems of strong equipment dependence, cumbersome measurement preparation work and long test time in the detection of the spatial positioning accuracy of CNC machine tools by using the body diagonal measurement method with a laser interferometer and the face diagonal positioning error measurement method in the prior art.

[0006] The technical solution adopted by the present invention is as follows: In the first aspect, the present application provides a method for evaluating the spatial accuracy of a machine tool based on a ball bar, including the following steps: Step S1: Install the center seat and the tool cup, set a measurement reference point on the workbench of the CNC machine tool, and establish a workpiece coordinate system with this reference point as the origin; Step S2: Obtain the length of the extension rod and the length of the ball bar body, specify the allowable range of spatial error and the simplified length calculation formula of the ball bar, calculate the allowable length range of the ball bar based on the error allowable range and the simplified length formula of the ball bar, select a number of measurement points on the upper hemisphere, and collect the commanded position corresponding to each measurement point and the actual measured length of the ball bar; Step S3: Compare the actual measured length of the ball bar with the allowable length range at the corresponding measurement points 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, change the length of the extension rod, i.e., the allowable length range of the ball bar, and jump 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: According to the sensitivity projection coefficient of the ball bar length to the three-axis errors, analyze the contribution ratio of each axis error to the change in the ball bar length, conduct spatial error traceability, and identify the key axis or inter-axis coupling error that causes the reduction of local positioning accuracy.

[0007] Furthermore, in Step S2, during the calculation of the ball bar body length, introduce the three-axis axial error terms to the commanded position of the measurement points in the workpiece coordinate system. The length calculation formula of the ball bar is:

[0008] where are respectively the commanded positions of the three axes in the workpiece coordinate system, are respectively the axial errors of the three axes; The commanded position can be directly expressed in the spherical coordinate system as:

[0009] where is the nominal length of the ball bar, are respectively the polar angle and the azimuth angle in the spherical coordinate system, Ignoring the second-order terms, the simplified length calculation formula of the ball bar is: .

[0010] Furthermore, in Step S2, based on the polar angle and azimuth angle of the measurement points in the spherical coordinate system, adopt an angular distribution function to construct a set of measurement points with uniform distribution of polar angle and azimuth angle to cover the working space area.

[0011] Furthermore, when the polar angle is , and the nominal length of the ball bar is , the polar angle change amount and the azimuth angle change are respectively:

[0012] Then the number of polar angle points and the corresponding polar angle the number of azimuth angle points at are:

[0013] After the ballbar measurement is completed, the set of measured ballbar lengths in the measurement area is:

[0014] Among them, is the measured ballbar length when the polar angle and azimuth angle are respectively , is the th azimuth angle degree at the polar angle , the polar angle set is , and the azimuth angle set is .

[0015] Further, in step S3, each measured length element in the set D of measured ballbar lengths is compared with the allowable length range at the corresponding measurement point, and the allowable length range is , where is the error threshold, and it is determined whether there is a measured length element that exceeds the allowable length range.

[0016] Further, when comparing the measured lengths of the measurement points in the set D of measured lengths, a regional error weighted average method is adopted. When the average error value of several adjacent measurement points in the region exceeds the set tolerance, it is determined that there is a positioning error abnormality in this region.

[0017] Further, in step S4, from the simplified length calculation formula of the ballbar, it can be seen that the projection coefficient of the actual axial error value on the ballbar length is:

[0018] Among them, is the projection coefficient on the axis; At any measurement point the contribution ratio of the axial spatial error to the ballbar length is:

[0019] Among them, ; Trace the error through the contribution ratio of the axial error. The single axis with a large contribution ratio or the multi-axis with a large contribution ratio is the reason for the reduction of the spatial positioning accuracy.

[0020] In a second aspect, the present application provides a machine tool spatial accuracy evaluation system based on a ballbar, and the system includes: A ballbar assembly, including a center seat, a tool cup and an adjustable extension rod, is used to form a ballbar measurement path in the working space of the numerical control machine tool and obtain the measured length data of the ballbar; A coordinate system construction module is used to establish a workpiece coordinate system on the working table of the numerical control machine tool with the center of the ball at the center seat end as the reference, so as to facilitate the unified description of the measurement point position and error modeling; A measurement point planning module is used to construct a uniformly covered measurement point set according to the set polar angle and azimuth angle distribution functions in the spherical coordinate system and output the corresponding three-axis command positions of each measurement point; A length calculation module is used to introduce three-axis axial error parameters for each measurement point position and calculate the length of the ballbar; An error comparison and judgment module is used to compare the measured length of the ballbar with the allowable length range point by point, judge 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 according to the result; An error tracing module is used to calculate the contribution ratio of the spatial error of each axis to the change in the measured length of the ballbar based on the projection sensitivity coefficient of the three-axis error to the ballbar length, and output the positioning information of the key axis or the inter-axis coupling error.

[0021] In a third aspect, the present application provides a terminal, including: A memory for storing a machine tool spatial accuracy evaluation program of the ballbar; A processor for implementing the steps of the machine tool spatial accuracy evaluation method based on the ballbar as described in the first aspect when executing the machine tool spatial accuracy evaluation system based on the ballbar.

[0022] In a fourth aspect, the present application provides a computer-readable storage medium, and 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 described in the first aspect.

[0023] It can be seen from the above technical solutions that the advantages of the present invention are: (1) The present invention constructs a workpiece coordinate system based on a set sphere, combines an adjustable extension rod and a ball bar assembly, uniformly arranges measurement points in the upper hemisphere space with polar angle and azimuth angle, collects the measured lengths of multiple points in space, and performs point-by-point comparison in combination with the body length model, so as to quickly evaluate the positioning accuracy of the CNC machine tool within the full working space range; this method can significantly improve the spatial coverage rate of the measurement points, realize spatial error detection in multiple angles, multiple directions and multiple positions, and solve the problems of sparse measurement points and insufficient coverage in the existing methods. The measurement path design and length calculation method using the workpiece coordinate system as a reference avoids the systematic influence of the installation error of the workpiece end ball seat on the measurement result, and improves the accuracy and repeatability of the evaluation result. The measurement process does not require high-precision standard devices and complex laser systems, has the advantages of convenient deployment, high efficiency and strong on-site adaptability, and is suitable for carrying out rapid accuracy detection and trend judgment at the production site.

[0024] (2) By introducing the three-axis axial error term into the ball bar length calculation formula, the measurement point length calculation has the ability of error modeling, 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 distinguish error sources and the credibility of the measurement result.

[0025] (3) By using the polar angle and azimuth angle distribution function to generate measurement points in the spherical coordinate system, uniform coverage of the measurement points in the spherical space can be realized, ensuring the representativeness and reasonable distribution of the measurement points in all directions and regions, and providing basic data support for the comprehensive evaluation of spatial errors. By deriving the formula for the number and distribution of measurement points based on the relationship between the polar angle, azimuth angle and the length of the ball bar, 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 problems of non-uniformity and non-repeatability caused by manual point selection, and improving the measurement space coverage efficiency.

[0026] (4) Using the projection coefficient of the three-axis error on the ball bar length to establish an error sensitivity model and combining the contribution ratio for error tracing, the dominant sources of spatial errors can be effectively identified, including single-axis errors or multi-axis coupling errors, providing a technical basis for machine tool maintenance, error compensation and inter-axis coordination adjustment. Description of the Drawings

[0027] In order to more clearly illustrate the technical solutions of the present invention, the drawings required for description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0028] Figure 1 Schematic flow chart of a machine tool spatial accuracy evaluation method provided by an embodiment of the present invention; Figure 2 Spherical coordinate system of an embodiment of the present invention and distribution diagram of measurement points at this polar angle. Specific implementation manners

[0029] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0030] Please refer to Figure 1 and Figure 2 As shown, the present invention provides a machine tool spatial accuracy evaluation method based on a ballbar, including the following steps: Step S1: Install the center seat and the tool cup, set a measurement reference point on the workbench of the numerical control machine tool, and establish a workpiece coordinate system with this reference point as the origin; Before the machine tool performs spatial accuracy detection, it is necessary to first construct a unified spatial reference coordinate system so that the subsequent measurement point positions and length data can be calculated and compared under a unified benchmark. By installing one end of the ballbar on the center seat on the workbench and the other end in the tool cup of the tool holder, a measurement chain is formed, and a workpiece coordinate system is established based on this assembly position to achieve three-dimensional coordinate consistency description; Before the measurement starts, place the center seat at a position close to the center of the machine tool workbench. At the same time, clamp the tool cup on the spindle tool holder, place the setting ball on the center seat, control the machine tool to move to the tool cup to adsorb the setting ball on the center seat and fix the position of the center seat, record the machine tool command coordinate at this time as the origin (0, 0, 0) of the workpiece coordinate system, and establish a workpiece coordinate system with this point as the origin. Control the tool holder to move to the starting point of the measurement position, remove the setting ball, and adsorb the two ends of the ballbar on the tool holder and the center seat respectively.

[0031] Step S2: Obtain the length of the extension rod and the length of the ballbar body, give the allowable range of spatial error and the simplified length calculation formula of the ballbar, calculate the allowable length range of the ballbar based on the error allowable range and the simplified length formula of the ballbar, select several measurement points on the upper hemisphere, and collect the command position corresponding to each measurement point and the actual measured length of the ballbar; This step is used to collect ballbar spatial measurement data and calculate the allowable range. After determining the test radius of the ballbar, select multiple representative measurement points in the spherical space, move the spindle to each point in turn, 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; The test radius of the ballbar is determined based on the combination of extension rods used. The system then automatically generates a set of measurement point positions in the upper hemisphere, which are evenly distributed by angle. The CNC system controls the spindle to move to each measurement point position in turn and records the actual length measured by the ballbar. The system determines the allowable length range of the point based on the theoretical length calculation of the position and the set error tolerance range, and saves the number, position, measured value and allowable range data of each measurement point.

[0032] 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 to modify the test length 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; After completing the data collection at each measuring point, the actual measured length value needs to be compared with the allowable length range of the corresponding position one by one to determine whether the measuring point meets the accuracy requirements. If all measuring points meet the requirements, it is considered that the positioning accuracy within the measurement range is qualified. Otherwise, it means that there is a problem with the spatial positioning accuracy, and the error source needs to be further analyzed.

[0033] The system compares each measuring point one by one to see if the actual measured length falls within the corresponding allowable range. If the measurement results of all points are within the allowable range, the system records the test result under the current extension rod length as qualified, and prompts you to replace the longer extension rod to continue testing other areas. If it is found that the measured length of any measuring point exceeds the allowable range, the area is judged to have abnormal positioning accuracy, and the system enters the error tracing process.

[0034] Step S4, analyzing the contribution of each axis error to the change in ballbar length according to the projection coefficient of the sensitivity of the ballbar length to the three-axis error, tracing the spatial error source, and identifying the key axis or inter-axis coupling error that causes the reduction of local positioning accuracy; When certain measurement points are detected to exceed the allowable range, this step will conduct a traceability analysis of 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 result, thereby identifying the main axis or the coupling relationship between axes where errors may exist, providing a basis for subsequent repair, compensation, or adjustment; After the system detects that the measured length of a certain measurement point exceeds the error range, it will further analyze the position direction of this point in the three-dimensional space. Based on the sensitivity of this point to errors in different directions, the system calculates the influence ratio of each direction error on the measurement result. By comparing the magnitudes of the influence ratios, it can be determined which motion axis the error of this measurement point mainly comes from, or the result of the combined action of multiple axes, and then the key error source causing the decline in the positioning accuracy of this area can be located.

[0035] In this embodiment, in step S2, during the calculation of the body length of the ball bar, the three-axis axial error terms are introduced into the commanded position of the measurement point in the workpiece coordinate system. The length calculation formula of the ball bar is:

[0036] Where are respectively the commanded positions of the three axes in the workpiece coordinate system, are respectively the axial errors of the three axes; The commanded position can be directly expressed in the spherical coordinate system as:

[0037] Where is the nominal length of the ball bar, are respectively the polar angle and the azimuth angle in the spherical coordinate system, And ignoring the second-order terms, the simplified length calculation formula of the ball bar is: .

[0038] In this embodiment, in step S2, based on the polar angle and azimuth angle of the measurement point in the spherical coordinate system, an angular distribution function is used to construct a set of measurement points with uniform distribution of polar angle and azimuth angle to cover the working space area; To comprehensively cover the spatial working area of the machine tool and ensure the representativeness and balanced distribution of the evaluation results, an angular distribution model of the spherical coordinate system is introduced in the measuring point planning process of the present invention. Specifically, by setting the variation step sizes of the polar angle and the azimuth angle, a set of reasonably distributed measurement points is generated using the angular uniform distribution function. These measuring points are evenly distributed in the accessible upper hemisphere area of the ball bar in space, so as to obtain measurement data in different spatial directions and positions, and achieve a comprehensive evaluation of the positioning accuracy within the working space of the machine tool; After the workpiece coordinate system is established, the system determines the test radius of the ball bar according to the current extension bar combination. To make the measurement points more evenly distributed in space, the system constructs a set of measuring points based on the spherical space with the center of the ball at the center seat end as the origin.

[0039] The specific implementation method is as follows: The system first sets the variation interval of the polar angle, and the measuring points gradually expand from the vertical direction of the spindle to the horizontal direction. At each polar angle level, the system determines the required number of azimuth angles according to the spatial coverage range of this level to avoid over-dense or over-sparse measuring points. The finally generated measuring points form an approximately evenly distributed spatial network on the entire upper hemisphere. These measuring point positions will be converted into three-axis coordinate points, serving as the command target points for the numerical control system to control the movement of the tool subsequently; This strategy ensures that the ball bar measurement covers as many spatial directions and regions as possible, making the collected spatial accuracy data comprehensive and representative, and effectively supporting subsequent error evaluation and traceability analysis.

[0040] In this embodiment, when the polar angle is and the nominal length of the ball bar is , the variation amount of the polar angle and the variation amount of the azimuth angle are respectively:

[0041] Then the number of polar angles and the number of azimuth angles at the corresponding polar angle are:

[0042] After the ball bar measurement is completed, the set of actually measured lengths of the ball bar within the measurement area is:

[0043] Among them, is the actually measured length of the ball bar when the polar angle and the azimuth angle are respectively , is the th azimuth angle number at the polar angle , and the set of polar angles is , the azimuth angle set is .

[0044] In this embodiment, the calculation of the length of the ballbar body: Assume The allowable error ranges of the axial positioning errors are respectively plus or minus . Since when the polar angle and the azimuth angle change, the influence of the same error on the change amount of the ballbar length is different, it is necessary to calculate the corresponding allowable length range of the ballbar according to the polar angle, azimuth angle of the measurement point and the allowable error range of each axis.

[0045] For example, when , always holds. When 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 takes the minimum value, the ballbar length is the shortest. Similarly, for other octants of the spatial coordinate system, let When the error coefficient in the actual length calculation formula of the ballbar is selected to have the same sign, the ballbar length is the largest, and when the signs are opposite, the ballbar length is the smallest. And ignoring the second-order term, the allowable length range of the ballbar under the allowable error range is calculated according to the simplified length formula of the ballbar: ; In step S3, each measured length element in the measured length set D of the ballbar is compared with the allowable length range at the corresponding measurement point. The allowable length range is , where is the error threshold, and it is determined whether there is a measured length element that exceeds the allowable length range.

[0046] In this embodiment, 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 value of several adjacent measurement points in the region exceeds the set tolerance, it is determined that there is an abnormal positioning error in the region; To improve the stability and robustness of the spatial accuracy evaluation, the present invention introduces a regional error analysis mechanism when judging the measurement results. Different from the simple judgment method of whether the single-point error exceeds the limit, this method divides multiple spatially adjacent measurement points into several measurement regions, and calculates the weighted average of the error values of multiple measurement points in each region to obtain the average error level of the region. If the average error in a certain region exceeds the preset accuracy tolerance threshold, it is determined that there is an abnormal spatial positioning error in the region.

[0047] This strategy can effectively avoid misjudgments caused by individual isolated points, improve the accuracy of error judgment, and is especially suitable for identifying systematic errors or local rigidity decline with certain spatial range characteristics, which better meets the requirements for stable accuracy judgment in engineering practical applications.

[0048] After collecting the measured lengths of all measurement points and making a preliminary comparison with the allowable range, the system divides the spherical measurement points into several continuous measurement regions according to their spatial distribution. Each region consists of several adjacent measurement points, such as five to ten points that are close in spatial angular distribution.

[0049] For each region, the system calculates the measurement error values of all measurement points within the region and performs a weighted average on these error values. The weights can be set according to factors such as the importance of the spatial position where the measurement points are located and the azimuthal distribution density. When the average error value within a certain region exceeds the upper limit of the error tolerance set by the system, the system determines that there is an abnormal positioning error in this region and marks this result in the diagram or output report, prompting the user that there is a risk of decline in the positioning accuracy of this spatial region.

[0050] This method avoids excessive sensitivity to outliers of individual measurement points, making the spatial error assessment more robust and meeting the overall verification requirements of the machine tool. It is applicable to usage scenarios such as batch measurement points, high-frequency measurement, and trend analysis.

[0051] In this embodiment, in step S4, it can be seen from the simplified length calculation formula of the ballbar that The projection coefficient of the actual axial error value on the length of the ballbar is:

[0052] Among them, is the projection coefficient on the axis; At any measurement point The contribution ratio of the axial spatial error to the length of the ballbar is:

[0053] Among them, ; By tracing the error through the contribution ratio of the axial error, the single axis or multiple axes with a relatively large contribution ratio are the reasons for the reduction of spatial positioning accuracy.

[0054] In some embodiments, the present application provides a machine tool spatial accuracy evaluation system based on a ballbar. The system includes: A ballbar assembly, including a center seat, a tool cup, and an adjustable extension rod, for forming a ballbar measurement path within the working space of a numerically controlled machine tool and obtaining the measured length data of the ballbar; The ballbar assembly is the core hardware part of this measurement system, including a center seat, a tool cup and an adjustable extension rod. The center seat is fixed inside the CNC machine tool and serves as the reference point of the ballbar; the tool cup is used to install the ballbar probe to ensure a stable connection of the measuring device; the adjustable extension rod can flexibly adjust the measurement range to meet various dimensional requirements of the machine tool working space. This assembly can form a movable ballbar measurement path within the working space of the CNC machine tool, thereby realizing the length measurement of each measuring point of the workpiece or the machine tool and obtaining the measured length data of the ballbar; The coordinate system construction module is used to establish a workpiece coordinate system on the CNC machine tool table with the center of the ball at the center seat end as the reference, so as to facilitate the unified description of the measuring point positions and error modeling; This module takes this center of the ball position as the reference point and establishes a unified workpiece coordinate system on the CNC machine tool table. Through this coordinate system, the measuring point positions can be uniformly described, realizing the accurate positioning of the measuring points and subsequent error modeling. The establishment of the coordinate system makes the ballbar measurement data match the machine tool space data, facilitating accurate spatial error analysis; The measuring point planning module is used to construct a uniformly covered set of measuring points in the spherical coordinate system according to the set polar angle and azimuth angle distribution functions and output the corresponding three-axis command positions of each measuring point; According to the set polar angle and azimuth angle distribution functions, the measuring point planning module generates a uniformly distributed set of measuring points in the spherical coordinate system to ensure uniform coverage of the working space by the measurement path. Each measuring point position corresponds to a unique three-axis command position, providing accurate position commands for the CNC machine tool to execute the measurement path; The length calculation module is used to introduce three-axis axial error parameters for each measuring point position and calculate the ballbar length; This module corrects the theoretical position of each measuring point by introducing the three-axis axial error parameters of the machine tool and calculates the actual length of the ballbar. This calculation can reflect the influence of the three-axis errors on the actual length of the ballbar, and is used to calculate the ballbar body length of each measuring point under the corresponding three-axis error tolerances to determine whether the measured length is within the acceptable error range, ensuring the compliance of the spatial positioning accuracy; The error comparison and judgment module is used to compare the measured length of the ballbar with the allowable length range point by point, judge whether the corresponding measuring point meets the spatial positioning accuracy requirements, and control whether to replace the extension rod or enter the error traceability process according to the result; This module compares the measured ballbar length with the body length interval of the corresponding measuring point point by point to judge whether the measuring point meets the spatial positioning accuracy requirements. According to the judgment result, it automatically controls whether to replace the extension rod or start the error traceability program to ensure the dynamic adjustment and accuracy guarantee of the measurement process; An error traceability module, which is used to calculate the contribution ratio of the spatial error of each axis to the change in the measured length of the ball bar based on the projection sensitivity coefficient of the three-axis error to the length of the ball bar, and output the contribution of the key error axis or the inter-axis coupling error; The error traceability module quickly evaluates the key error axis or the inter-axis coupling error by calculating the contribution ratio of the three-axis error to the measurement of the ball bar length. This function provides technical support for quickly evaluating the key error axis of the machine tool and improving the measurement accuracy.

[0055] In some embodiments, the present application provides a terminal, including: A memory, which is used to store the machine tool spatial accuracy evaluation program of the ball bar; A processor, which is used to execute the steps of the machine tool spatial accuracy evaluation method based on the ball bar when implementing the machine tool spatial accuracy evaluation system based on the ball bar.

[0056] In some embodiments, the present application provides a computer-readable storage medium, and 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 ball bar.

[0057] The above content is only an example and illustration of the concept of the present invention. Those skilled in the art of this technology can make various modifications or supplements to the described specific embodiments or use similar methods to replace them, 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 protection scope of the present invention.

Claims

1. A method for evaluating the spatial accuracy of a machine tool based on a ballbar, characterized in that, It includes the following steps: 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 this reference point as the origin; Step S2: Obtain the length of the extension rod and the length of the ballbar body, specify the allowable range of spatial error, calculate the allowable length range of the ballbar based on the body length, select several measurement points on the upper hemisphere, and collect the commanded position corresponding to each measurement point and the actual measured length of the ballbar; Step S3: Compare the actual measured length of the ballbar with the allowable length range at the corresponding measurement points 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, change the length of the extension rod, i.e., the allowable length range of the ballbar, and jump 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: According to the sensitivity projection coefficient of the three-axis error to the ballbar length, analyze the contribution ratio of each axis error to the change in the ballbar length, conduct spatial error tracing, and identify the key axis or inter-axis coupling error that causes the reduction of local positioning accuracy.

2. The method for evaluating the spatial accuracy of a machine tool based on a ballbar according to claim 1, wherein In Step S2, during the calculation of the body length of the ballbar, introduce three-axis axial error terms to the commanded position of the measurement points in the workpiece coordinate system. The length calculation formula of the ballbar is: Among them They are respectively the command positions of the three axes They are respectively the axial errors of the three axes; Instruction position It can be directly expressed in the spherical coordinate system as: where is the nominal length of the ballbar, are the polar angle and azimuth angle in the spherical coordinate system respectively, Ignoring the second-order terms, the simplified length calculation formula of the ballbar is: 。 3. The method for evaluating the spatial accuracy of a machine tool based on a ballbar according to claim 2, characterized in that, In Step S2, based on the polar angle and azimuth angle of the measurement points in the spherical coordinate system, adopt an angular distribution function to construct a set of measurement points with uniform distribution of polar angle and azimuth angle to cover the working space area.

4. The method for evaluating the spatial accuracy of a machine tool based on a ballbar according to claim 3, characterized in that, When the polar angle is , and the nominal length of the ballbar is , the change in the polar angle and the change in the azimuth angle are respectively: Then the number of polar angle points and the corresponding polar angle the number of azimuth points are as follows: After the ballbar measurement is completed, the set of actual measured lengths of the ballbar in the measurement area is: Wherein, is the measured length of the ball bar when the polar angle and the azimuth angle are respectively . is the th azimuth angle degree at the polar angle . The polar angle set is , and the azimuth angle set is .

5. The method for evaluating the spatial accuracy of a machine tool based on a ballbar according to claim 4, wherein, In step S3, each measured length element in the measured length set D of the ballbar is compared with the allowable length range at the corresponding measurement point, and the allowable length range is , where is the error threshold, and it is determined whether there is a measured length element that exceeds the allowable length range.

6. The method for evaluating the spatial accuracy of a machine tool based on a ballbar according to claim 5, wherein When comparing the actual measured lengths of the measurement points in the actual measured length set D, adopt a regional error weighted average method. When the average error value of several adjacent measurement points within a region exceeds the set tolerance, it is determined that there is a positioning error anomaly in this region.

7. The method for evaluating the spatial accuracy of a machine tool based on a ballbar according to claim 2, wherein, In step S4, it can be seen from the simplified length calculation formula of the ballbar that The projection coefficient of the actual axial error value on the length of the ballbar is: Among them, is the projection coefficient of the axis; At any measurement point The contribution ratio of the axial spatial error to the length of the ball bar is: Among them, ; Trace the error through the contribution ratio of the axial error. The single axis with a larger contribution ratio or the multi-axis with a larger contribution ratio is the reason for the reduction of spatial positioning accuracy.

8. A machine tool spatial accuracy evaluation system based on a ballbar, characterized in that, The system includes: A ballbar assembly, including a center seat, a tool cup, and an adjustable extension rod, used to form a ballbar measurement path within the working space of the CNC machine tool and obtain the actual measured length data of the ballbar; A coordinate system construction module, used to establish a workpiece coordinate system on the CNC machine tool workbench with the center position of the center seat end as the reference to facilitate the unified description of the measurement point positions and error modeling; A measurement point planning module, used to construct a uniformly covered set of measurement points according to the set polar angle and azimuth angle distribution function in the spherical coordinate system and output the three-axis commanded positions corresponding to each measurement point; A length calculation module, used to introduce three-axis axial error parameters to each measurement point position and calculate the length of the ballbar; An error comparison and judgment module, used to compare the actual measured length of the ballbar with the allowable length range point by point, judge 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 according to the result; An error tracing module, used to calculate the contribution ratio of each axis spatial error to the change in the measured length of the ballbar based on the projection sensitivity coefficient of the three-axis error to the ballbar length, and output the positioning information of the key axis or inter-axis coupling error.

9. A terminal, characterized in that, Including: A memory for storing a machine tool spatial accuracy evaluation program of a ballbar; A processor for implementing 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.

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

Images