A machine tool multi-degree-of-freedom thermal error detection method and system

Abstract

The application provides a machine tool multi-degree-of-freedom thermal error detection method and system. It belongs to the field of machine tool thermal error detection. The method comprises the following steps: installing a standard mandrel on a machine tool spindle; under the cold state of the machine tool, controlling the machine tool to move the standard mandrel to a plurality of measurement points arranged in a matrix form on a workbench in advance; synchronously collecting multi-dimensional geometric data of the standard mandrel through a plurality of sensor units integrated at the measurement points; obtaining complete multi-dimensional geometric data of all measurement points under the cold state; after the machine tool runs to a target thermal state, repeating the above steps to obtain complete multi-dimensional geometric data of all measurement points under the thermal state; and comparing the multi-dimensional geometric data of the same measurement point under the cold state and the thermal state to calculate the multi-degree-of-freedom thermal error value at the point. The method can improve the detection precision of machine tool thermal error.

Description

Technical Field

[0001] This application relates to the field of machine tool thermal error detection, and more specifically, to a method and system for detecting multi-degree-of-freedom thermal errors in machine tools. Background Technology

[0002] In precision machining on CNC machine tools, thermal deformation caused by frictional heat generated by moving parts is a major factor affecting machining accuracy. Existing thermal error detection methods suffer from a core deficiency: their measurement methods are mostly "single-point, single-dimensional," meaning they can only measure displacement in one direction (e.g., axial) at a single location each time. However, the actual thermal deformation of a machine tool involves complex multi-degree-of-freedom coupled motion, including linear and angular displacements in multiple directions. Existing methods cannot simultaneously and efficiently acquire multi-degree-of-freedom error data at the same measurement point during a single positioning operation, resulting in a severely distorted and incomplete description of the thermal deformation state, making it difficult to support subsequent high-precision error compensation. Summary of the Invention

[0003] The purpose of this application is to provide a method and system for detecting multi-degree-of-freedom thermal errors in machine tools, which can improve the accuracy of thermal error detection in machine tools.

[0004] This application is implemented as follows: In a first aspect, this application provides a method for detecting multi-degree-of-freedom thermal errors in machine tools, comprising the following steps: S1. Install the standard mandrel on the machine tool spindle. In the cold state of the machine tool, control the machine tool to move the standard mandrel to multiple measurement points that are pre-arranged in a matrix on the worktable. The multi-dimensional geometric data of the standard mandrel are collected synchronously by the multi-sensor unit integrated at the measurement points. The complete multi-dimensional geometric data of all measurement points in the cold state are obtained. S2. After the machine tool reaches the target hot state, control the machine tool to move the standard mandrel to multiple measurement points that are pre-arranged in a matrix on the worktable; synchronously collect the multi-dimensional geometric data of the standard mandrel through the multi-sensor unit integrated at the measurement point to obtain the complete multi-dimensional geometric data of all measurement points in the hot state; S3. For the same measurement point, compare its multidimensional geometric data under cold and hot conditions, and calculate the multi-degree-of-freedom thermal error value at that point.

[0005] Based on the first aspect, in step S1, the multiple pre-arranged measurement points are arranged in a regular matrix of M rows × N columns, where M and N are both integers greater than or equal to 2.

[0006] Based on the first aspect, in step S1, the integrated multi-sensor unit includes at least a bottom sensor for measuring axial displacement, and an upper sensor group and a lower sensor group for measuring the radial position of the standard mandrel at two different height sections; the synchronously acquired multidimensional geometric data includes: the axial displacement obtained by the bottom sensor, and the local axis vector of the standard mandrel calculated from the readings of the upper sensor group and the lower sensor group.

[0007] Based on the first aspect, in step S3, the calculation of the multi-degree-of-freedom thermal error value at that point specifically includes: Calculate the three-dimensional linear displacement error (ΔX, ΔY, ΔZ) based on the changes in the center coordinates of the standard mandrel under cold and hot conditions. Calculate the angular displacement error around at least two orthogonal axes based on the change in the included angle of the local axis vector under cold and hot conditions.

[0008] Based on the first aspect, in step S2, the target thermal state is determined by any of the following methods: the machine tool has been running for a preset time; or the temperature sensor of a key part of the machine tool has reached a preset temperature threshold.

[0009] Based on the first aspect, in step S2, during the process of the machine tool running to the target thermal state, the spindle is controlled to rotate at a preset speed so that the thermal error calculated in step S3 is the combined error of the feed axis thermal error and the spindle thermal error.

[0010] Secondly, this application provides a machine tool multi-degree-of-freedom thermal error detection system, applied to the aforementioned machine tool multi-degree-of-freedom thermal error detection method, the system comprising: A standard mandrel is used to be mounted on the machine tool spindle as a measurement reference. The sensor matrix is ​​fixedly installed on the machine tool worktable and consists of multiple integrated sensor units arranged in a matrix. Each unit integrates multiple sensor probes. The control and data processing unit is used to control the machine tool to move the standard mandrel to multiple measurement points arranged in a matrix on the worktable, control the sensor matrix to collect data to obtain cold and hot data, and perform comparison of cold and hot data and thermal error calculation.

[0011] Thirdly, this application provides an electronic device, comprising: Memory, used to store one or more programs; processor; The above method is implemented when one or more programs are executed by the processor.

[0012] Fourthly, this application provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor, implements the above-described method.

[0013] Compared with the prior art, this application has at least the following advantages or beneficial effects: This invention provides a method and system for detecting multi-degree-of-freedom thermal errors in machine tools. Its hot-state measurement completely replicates the path, position, and static conditions of cold-state measurement, with the only variable being the thermal state of the machine tool. This comparative measurement using the same point, same posture, and same method minimizes errors introduced by the measurement system itself, ensuring direct comparability between cold and hot-state data and laying the foundation for accurate calculation of thermal deformation. Since the measurement process involves point-to-point movement and static acquisition, the entire hot-state data acquisition can be completed within minutes, far faster than methods requiring complex linkage scanning, and can "capture" a relatively stable thermal state. Static measurement further avoids additional errors caused by potential changes in the dynamic performance of the machine tool under hot conditions, ensuring the fidelity of the hot-state data. Each measurement point outputs a thermal error vector containing at least five degrees of freedom (δx, δy, δz, εx, εy). The set of error vectors from all 25 points intuitively represents the multi-degree-of-freedom thermal deformation field of the machine tool within the measurement area. This setup allows for clear and quantitative separation of angular displacement errors that are difficult to obtain using traditional methods, overcoming the limitation of traditional methods that only focus on linear displacement. The calculated five-degree-of-freedom thermal error data provides the most direct and ideal data foundation for establishing high-precision thermal error compensation models (such as spatial interpolation models and neural network models). Complete multi-degree-of-freedom information enables the compensation model to more realistically reproduce the complex deformation behavior of the machine tool, thereby raising the compensation accuracy to a new level. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a flowchart of a multi-degree-of-freedom thermal error detection method for machine tools according to this application; Figure 2 This is a schematic diagram of the structure of a multi-degree-of-freedom thermal error detection system for machine tools according to this application; Figure 3 This is a schematic diagram of the structure of an electronic device according to this application.

[0016] icon: 1. Standard mandrel; 2. Sensor matrix; 3. Control and data processing unit; 4. Processor; 5. Memory; 6. Communication interface. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. The components of the embodiments of this application described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0018] The following detailed description of some embodiments of this application is provided in conjunction with the accompanying drawings. Unless otherwise specified, the various embodiments and features described below can be combined with each other. Example

[0019] This application provides a method and system for detecting multi-degree-of-freedom thermal errors in machine tools, which can improve the accuracy of thermal error detection in machine tools.

[0020] Please refer to Figure 1 The method for detecting multi-degree-of-freedom thermal errors in machine tools includes the following steps: S1. Install the standard mandrel on the machine tool spindle. In the cold state of the machine tool, control the machine tool to move the standard mandrel to multiple measurement points that are pre-arranged in a matrix on the worktable. The multi-dimensional geometric data of the standard mandrel are collected synchronously by the multi-sensor unit integrated at the measurement points. The complete multi-dimensional geometric data of all measurement points in the cold state are obtained. Furthermore, the pre-arranged measurement points are arranged in a regular matrix of M rows × N columns, where M and N are both integers greater than or equal to 2.

[0021] Furthermore, the integrated multi-sensor unit includes at least a bottom sensor for measuring axial displacement, and an upper sensor group and a lower sensor group for measuring the radial position of the standard mandrel at two different height sections; the synchronously acquired multidimensional geometric data includes: the axial displacement obtained by the bottom sensor, and the local axis vector of the standard mandrel calculated from the readings of the upper sensor group and the lower sensor group.

[0022] Specifically, the standard mandrel is a uniform, precision cylindrical rod with a diameter of 30cm, made of a material with a low coefficient of thermal expansion (such as Invar alloy or ceramic-coated steel). The standard mandrel can be automatically clamped by the CNC machine tool spindle, and its axis is strictly aligned with the spindle's rotation center after clamping. The outer surface of the cylinder undergoes ultra-precision grinding and polishing, with a surface roughness Ra ≤ 0.05 μm and a roundness error ≤ 0.5 μm, serving as a high-precision geometric reference. The spindle drives the standard mandrel to be precisely positioned above the sensor matrix, and its side is used to perform contour scanning of multiple sensors to achieve position and attitude calculation. In this embodiment, a precision standard mandrel made of a material with a low coefficient of thermal expansion (such as Invar alloy) (e.g., 30mm in diameter, 180mm in length, roundness error <0.5μm) is first installed on the machine tool spindle. Simultaneously, a sensor matrix consisting of 25 integrated sensor units (5 rows × 5 columns) arranged in a regular pattern is fixed to the center area of ​​the machine tool worktable using a rigid base. Each sensor unit integrates five high-precision eddy current sensor probes. The upper two and lower two form two radial measurement groups, while the bottom center probe is used for axial measurement. The CNC program is started, controlling the machine tool to move the spindle, which in turn moves the standard mandrel to one of the 25 measurement points. At each position, the machine tool stops all feed axes, and the standard mandrel remains completely stationary. At this point, the corresponding sensor unit is triggered, simultaneously reading the instantaneous readings of all five sensors. Based on the readings of the upper two sensors and their installation radii, the planar coordinates (X_upper, Y_upper) of the center of the upper section of the standard mandrel are calculated; similarly, the coordinates (X_lower, Y_lower) of the center of the lower section are obtained from the lower sensor group. Combined with the bottom sensor reading Z, a single positioning operation yields the multidimensional geometric data of that point: a three-dimensional spatial point (X, Y, Z) and a local axis vector (reflecting pitch and yaw attitude) determined by the line connecting the centers of the upper and lower sections. After traversing all 25 points, a high-density, multidimensional cold-state reference dataset covering a portion of the worktable area is obtained.

[0023] This setup allows for the simultaneous deployment of a dense measurement network (e.g., 25 points) in space, comprehensively covering the critical travel range of the machine tool and overcoming the shortcomings of traditional single-point or limited-point measurements in terms of representativeness. At each measurement point, an integrated sensor unit can simultaneously capture axial displacement and radial attitude information with a single trigger, even when the machine tool and mandrel are completely stationary. This solves the problems of single-point, single-dimensional measurement and incomplete measurement information inherent in traditional methods. Furthermore, static measurement completely avoids tracking errors and vibration interference introduced by dynamic scanning, ensuring high accuracy and reliability of the reference data. All sensor units have a consistent structure and are arranged in a strict grid, allowing the establishment of a unified coordinate system for the entire measurement field using the machine tool's high positioning accuracy or through a single global calibration. This greatly simplifies the system calibration process and ensures the consistency of the measurement data.

[0024] S2. After the machine tool runs to the target thermal state, control the machine tool to move the standard mandrel to multiple measurement points arranged in a matrix form on the workbench in advance; synchronously collect multi-dimensional geometric data of the standard mandrel through the multi-sensor unit integrated at the measurement points to obtain the complete multi-dimensional geometric data of all measurement points in the thermal state. Preferably, the target thermal state is determined by any of the following methods: the machine tool runs to reach the preset time; or the temperature sensors at the key parts of the machine tool reach the preset temperature threshold.

[0025] Preferably, during the process of the machine tool running to the target thermal state, control the main shaft to rotate at a preset speed so that the thermal error calculated in step S3 is the comprehensive error of the feed axis thermal error and the main shaft thermal error.

[0026] Specifically, start the warm-up program of the machine tool. For example, make each feed axis run idle for a long time (such as 30 minutes) at the maximum rapid traverse speed to simulate the heat generation under typical machining conditions. Monitor the temperature rise of key parts (such as the feed screw and the spindle headstock) through the built-in temperature sensors or infrared thermometers of the machine tool. When the machine tool runs to reach the preset time or the temperature at the key point reaches the stable threshold (i.e., the "target thermal state"), pause all automatic programs of the machine tool and immediately repeat the measurement process of step S1. Control the machine tool to position the standard mandrel to the same 25 measurement points in sequence with the same path and accuracy, and after standing still at each point, trigger the same sensor unit to synchronously collect the multi-dimensional geometric data in the thermal state. Separate the influence of different heat sources. This step can be carried out in a series of tests. For example, in one test, only let the feed axis move (the main shaft stops rotating), and the measured error is mainly the feed axis thermal error; in another test, the main shaft rotates at a preset speed, and the measured is the comprehensive thermal error of the feed axis and the main shaft.

[0027] With such a setting, the thermal state measurement completely reproduces the path, position, and stationary conditions of the cold state measurement. The only variable is the thermal state of the machine tool. This "same point, same posture, same method" comparative measurement maximally eliminates the errors introduced by the measurement system itself, ensures the direct comparability of the cold and thermal state data, and lays a foundation for accurately calculating the thermal deformation. Since the measurement process is point motion and static acquisition, the entire thermal state data acquisition can be completed within a few minutes, much faster than the method that requires complex linkage scanning, and can "capture" a relatively stable thermal state. The static measurement avoids the additional errors caused by the possible changes in the dynamic performance of the machine tool under the thermal state again, and ensures the fidelity of the thermal state data. By designing different warm-up working conditions (such as whether to start the main shaft), the contributions of different heat sources (feed axis, main shaft) to the overall error can be systematically separated and identified, providing in-depth data insights for subsequent targeted compensation.

[0028] S3. For the same measurement point, compare its multidimensional geometric data under cold and hot conditions, and calculate the multi-degree-of-freedom thermal error value at that point.

[0029] Furthermore, the calculated multi-degree-of-freedom thermal error value at this point specifically includes: Calculate the three-dimensional linear displacement error (ΔX, ΔY, ΔZ) based on the changes in the center coordinates of the standard mandrel under cold and hot conditions; calculate the angular displacement error around at least two orthogonal axes based on the changes in the included angle of the local axis vectors under cold and hot conditions.

[0030] Specifically, this step performs differential calculations on the collected data to directly extract the thermal error value. The hot-state dataset obtained in step S2 is then mapped one-to-one with the cold-state reference dataset from step S1 based on the measurement point number. For each measurement point, the following calculations are performed: Linear displacement error calculation: Subtract the three-dimensional center coordinates (X,Y,Z) of the point in its hot and cold states directly to obtain the three-dimensional linear displacement thermal error (ΔX,ΔY,ΔZ) of that point.

[0031] Angular displacement error calculation: Perform vector operations on the local axis vectors of the point in both hot and cold states. Calculate the angle between the projections of the two vectors onto the XY plane to obtain the yaw angle error εz around the Z-axis; calculate the change in the angle between the two vectors and the Z-axis to decompose and obtain the pitch and roll angle errors εx and εy around the X and Y axes.

[0032] Output Results: Finally, a thermal error vector containing at least 5 degrees of freedom (δx, δy, δz, εx, εy) is output for each measurement point. The set of error vectors for all 25 points intuitively represents the multi-degree-of-freedom thermal deformation field of the machine tool within the measurement area.

[0033] This setup allows for the clear and quantitative separation of angular displacement errors, which are difficult to obtain using traditional methods. It overcomes the limitation of traditional methods that only focus on linear displacement. The calculated five-degree-of-freedom thermal error data provides the most direct and ideal data foundation for establishing high-precision thermal error compensation models (such as spatial interpolation models and neural network models). Complete multi-degree-of-freedom information enables the compensation model to more realistically reproduce the complex deformation behavior of the machine tool, thereby raising the compensation accuracy to a new level. The thermal error results, presented in vector field form, are highly intuitive, clearly showing the magnitude, direction, and distribution of deformation. This data is not only used for compensation but also provides a powerful data tool for evaluating the thermal characteristics of machine tools, structural optimization design, and maintenance diagnosis.

[0034] Please refer to Figure 2 This embodiment also provides a machine tool multi-degree-of-freedom thermal error detection system, applied to the above-mentioned machine tool multi-degree-of-freedom thermal error detection method. The system includes: Standard mandrel 1 is used to be mounted on the machine tool spindle as a measurement reference; Sensor matrix 2 is fixedly installed on the machine tool worktable and consists of multiple integrated sensor units arranged in a matrix. Each unit integrates multiple sensor probes. The control and data processing unit 3 is used to control the machine tool to move the standard mandrel to multiple measurement points that are pre-arranged in a matrix on the worktable, control the sensor matrix to collect data to obtain cold and hot data, and perform comparison of cold and hot data and thermal error calculation.

[0035] For a detailed implementation of the multi-degree-of-freedom thermal error detection system for machine tools, please refer to the detailed implementation of the multi-degree-of-freedom thermal error detection method for machine tools mentioned above. Further details will not be elaborated here.

[0036] Please refer to Figure 3 This embodiment also provides an electronic device, including: Memory 5 is used to store one or more programs; Processor 4; Processor 4 and memory 5 are connected via communication interface 6; When one or more programs are executed by processor 4, all or some of the above methods are implemented.

[0037] Fourthly, this application provides a computer-readable storage medium having a computer program stored thereon, which, when executed by a processor 4, implements all or part of the methods described above.

[0038] It will be apparent to those skilled in the art that this application is not limited to the details of the exemplary embodiments described above, and that this application can be implemented in other specific forms without departing from the spirit or essential characteristics of this application. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of this application is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within this application. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A machine tool multi-degree-of-freedom thermal error detection method, characterized by, Includes the following steps: S1. Install the standard mandrel onto the machine tool spindle. In the cold state of the machine tool, control the machine tool to move the standard mandrel to multiple measurement points that are pre-arranged in a matrix on the worktable. Simultaneously collect the multi-dimensional geometric data of the standard mandrel through the multi-sensor unit integrated at the measurement points. Obtain complete multidimensional geometric data of all measurement points in the cold state; S2. After the machine tool reaches the target hot state, control the machine tool to move the standard mandrel to multiple measurement points that are pre-arranged in a matrix on the worktable; synchronously collect the multi-dimensional geometric data of the standard mandrel through the multi-sensor unit integrated at the measurement points to obtain the complete multi-dimensional geometric data of all measurement points in the hot state; S3. For the same measurement point, compare the multidimensional geometric data under cold and hot conditions to calculate the multi-degree-of-freedom thermal error value at that point.

2. The method of claim 1, wherein, In step S1, the pre-arranged multiple measurement points are arranged in a regular matrix of M rows × N columns, where M and N are both integers greater than or equal to 2.

3. The method of claim 1, wherein, In step S1, the integrated multi-sensor unit includes at least a bottom sensor for measuring axial displacement, and an upper sensor group and a lower sensor group for measuring the radial position of the standard mandrel at two different height sections; the synchronously acquired multidimensional geometric data includes: the axial displacement obtained by the bottom sensor, and the local axis vector of the standard mandrel calculated from the readings of the upper sensor group and the lower sensor group.

4. The method of claim 3, wherein, In step S3, the calculation of the multi-degree-of-freedom thermal error value at that point specifically includes: The three-dimensional linear displacement error (ΔX, ΔY, ΔZ) is calculated based on the changes in the center coordinates of the standard mandrel under cold and hot conditions. Based on the angle change of the local axis vector under cold and hot conditions, calculate the angular displacement error around at least two orthogonal axes.

5. The method for detecting multi-degree-of-freedom thermal errors in machine tools according to claim 1, characterized in that, In step S2, the target thermal state is determined by any of the following methods: the machine tool has been running for a preset time; or the temperature sensor of a key part of the machine tool has reached a preset temperature threshold.

6. The method for detecting multi-degree-of-freedom thermal errors in machine tools according to claim 1, characterized in that, In step S2, during the process of the machine tool running to the target thermal state, the spindle is controlled to rotate at a preset speed so that the thermal error calculated in step S3 is the combined error of the feed axis thermal error and the spindle thermal error.

7. A multi-degree-of-freedom thermal error detection system for machine tools, applied to the method according to any one of claims 1 to 6, characterized in that, The system includes: A standard mandrel is used to be mounted on the machine tool spindle as a measurement reference. The sensor matrix is ​​fixedly installed on the machine tool worktable and consists of multiple integrated sensor units arranged in a matrix, with each unit integrating multiple sensor probes. The control and data processing unit is used to control the machine tool to move the standard mandrel to multiple measurement points pre-arranged in a matrix on the worktable, control the sensor matrix to collect data to obtain cold and hot data, and perform comparison of cold and hot data and thermal error calculation.

8. An electronic device, characterized in that, include: Memory, used to store one or more programs; processor; When the one or more programs are executed by the processor, the method as described in any one of claims 1-6 is implemented.

9. A computer-readable storage medium having a computer program stored thereon, characterized in that, When the computer program is executed by a processor, it implements the method as described in any one of claims 1-6.

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