CN111596612A - Numerical control machine tool thermal error compensation method and system based on workpiece dimension data - Google Patents

Abstract

A method and system for thermal error compensation of CNC machine tools based on workpiece size data. Through process capability index (Cpk) analysis based on processing procedures, key temperature points are parsed from measured temperature data of cutting work; according to the key temperature points and machine tool load conditions According to the workpiece size data processed under the control, a multi-layer perceptron neural network (MLP) is used to construct the thermal error model of the CNC machine tool based on the workpiece size detection data, and then the motion compensation amount of the motion axis corresponding to the workpiece size characteristics under the actual processing conditions is obtained, and The thermal error compensation is realized by the external coordinate zero offset function of the CNC machine tool. The invention takes into account the thermal deformation of the machine tool and the workpiece caused by the processing process, and effectively compensates the thermal error of the machine tool under actual processing conditions.

Description

Method and system for thermal error compensation of CNC machine tool based on workpiece size data

technical field

The invention relates to a technology in the field of machining, in particular to a method and system for compensating thermal error of a numerically controlled machine tool based on workpiece size data.

Background technique

Error is the main index to evaluate the accuracy of machine tools. Machine tool errors can generally be divided into geometric errors, thermal errors and errors caused by cutting forces. Among them, the thermal error accounts for 40% to 70% of the total error. Therefore, effective control of thermal error is crucial to improve workpiece accuracy. However, the establishment of the thermal error model of the existing CNC machine tools is usually based on the test data under the no-load condition of the machine tool, and does not take into account the thermal deformation caused by the machining process and the thermal deformation of the workpiece, resulting in the accuracy of the model built in practical industrial applications. Due to the poor effect of lowering and compensation, the current modeling and compensation method for thermal error of machine tool under the condition of machine tool load is not yet mature.

SUMMARY OF THE INVENTION

Aiming at the above-mentioned deficiencies in the prior art, the present invention proposes a method and system for compensating the thermal error of a numerically controlled machine tool based on workpiece size data. The external coordinate zero offset function compensates the motion of each motion axis of the machine tool, and realizes the direct use of the workpiece measurement data on the production line, thus taking into account the thermal deformation of the machine tool and the workpiece caused by the processing process, and the thermal error of the machine tool under actual processing conditions. effective compensation.

The present invention is achieved through the following technical solutions:

The invention relates to a method for compensating the thermal error of a numerically controlled machine tool based on workpiece size data. Through the process capability index (Cpk) analysis based on the machining process, the key temperature points are parsed from the actual measured temperature data of cutting work; The workpiece size data processed under the conditions, the multi-layer perceptron neural network (MLP) is used to construct the thermal error model of the CNC machine tool based on the workpiece size detection data, and then the motion compensation amount of the motion axis corresponding to the workpiece size characteristics under the actual processing conditions is obtained. And realize thermal error compensation through the external coordinate zero offset function of CNC machine tool.

The cutting work is preferably cutting work of various shaft and hole parts such as drilling, turning and boring.

For the actual measured temperature data of the cutting work, by setting the workpiece to be cut horizontally on the worktable of the CNC machine tool, and arranging temperature sensors at the corresponding temperature sensitive points, the actual cutting work of a large number of workpieces is carried out after the tool setting work is completed. The standard center value and tolerance value of the dimensional feature of the cut workpiece are collected in real time through the temperature sensor at the corresponding position, and the data of each temperature sensor at this time is recorded through the temperature acquisition module.

The dimension data of the workpiece processed under the load condition of the machine tool, through each completion of the cutting of a workpiece, the workpiece is removed, and the workpiece is set horizontally on the workbench of the CMM, and the workpiece is measured according to the measurement standard of the CMM. Dimensional features are measured and recorded in order of workpieces.

The process capability index analysis refers to: using the data of all temperature measuring points and workpiece size data to model by multiple linear regression to obtain a full-temperature workpiece size prediction model; and then substituting the data of a single temperature measuring point T _i into The full-temperature workpiece size prediction model can obtain the workpiece size prediction value D(T _i ) and the corresponding Cpk value under the influence of a single temperature, which is recorded as Cpk(△T _i ), when the Cpk(△T _i ) of any temperature measuring point If it is less than the minimum Cpk requirement, this point is the critical temperature point.

The Cpk minimum requirement is preferably 1.33.

The numerical control machine tool thermal error model based on workpiece size detection data refers to: the key temperature point temperature data obtained by the process capability index analysis and the size detection data obtained from the online/offline detection of the workpiece actually processed under the load condition of the machine tool. According to the principle of time correspondence, the mathematical mapping relationship between the temperature data and the workpiece size data is constructed through the multilayer perceptron neural network (MLP) as the thermal error model of the CNC machine tool.

The multi-layer perceptron neural network adopts but is not limited to the records in "Intelligent Classification Algorithm Based on Multi-layer Perceptron Neural Network" (Li Xinyu; Li Xiaohang; Li Zhiwei; Li Dongxue, "Communication Power Technology" 2020-03-10 Journal) technical realization.

The thermal error model of the CNC machine tool is different from the thermal error model of the CNC machine tool constructed based on the temperature data, the position change error between the cutting point of the machine tool and the workpiece in the traditional method, and directly uses the size detection of the workpiece actually processed on the production line. data, thus including the thermal deformation of the machine tool as well as the thermal deformation of the workpiece caused by the machining process.

The invention relates to a compensation system for realizing the above method, comprising: a temperature sensor, a temperature acquisition module, a three-coordinate measuring machine and an error compensation module, wherein the temperature sensors are respectively arranged in the air, on the surface shell of the lubricating oil tank, and the surface shell of the hydraulic oil tank On the spindle housing where the front bearing of the spindle is located, the bottom of the coolant, the Z-axis screw nut, the spindle housing where the rear bearing of the spindle is located, and the machine housing, and output temperature data information to the temperature acquisition module. It is connected to the error compensation module and transmits temperature information. The CMM measures the workpiece size data and outputs it to the error compensation module. The error compensation module establishes a thermal error model according to the temperature information and workpiece size data, and then calculates the motion axis corresponding to the workpiece size feature. The compensation amount is transmitted to the CNC system.

The temperature acquisition module and the error compensation module are preferably both arranged in the electric control cabinet of the numerically controlled machine tool.

technical effect

The invention solves the problem of thermal deformation of the machine tool caused by the machining process as a whole; the invention establishes a numerical control machine tool thermal error model considering the thermal deformation of the workpiece by using the dimensional data of the workpiece actually processed on the production line, and provides a model for the thermal error of the machine tool under actual processing conditions. The thermal error of the machine tool is effectively compensated.

Description of drawings

1 is a schematic diagram of the system structure of the present invention;

Figure 2 is a schematic diagram of the temperature difference between the temperature measured by each sensor relative to the room temperature;

Figure 3 is a schematic diagram of workpiece size measurement data;

Fig. 4 is a schematic diagram of a key temperature point identification process;

Figure 5 is a schematic diagram of a thermal error model fitting result;

Figure 6 is a schematic diagram of the working principle of the compensation system;

Fig. 7 is a schematic diagram of the predicted data of the inner diameter of the workpiece before compensation and the measured data of the inner diameter of the workpiece after compensation;

In the figure: temperature sensor 1, temperature sensor 2, temperature sensor 3, temperature sensor 4, temperature sensor 5, temperature sensor 6, temperature sensor 7, temperature sensor 8, temperature acquisition module 9, CNC machine tool 10, workpiece to be cut 11 , a coordinate measuring machine 12 , and an error compensation module 13 .

Detailed ways

As shown in FIG. 1 , this embodiment relates to a measuring device for measuring the thermal error of a numerically controlled machine tool and its specific application scenario, including: a temperature sensor 1 for measuring room temperature, a temperature sensor 2 for lubricating oil temperature, a hydraulic pressure Oil temperature temperature sensor 3, spindle front bearing temperature temperature sensor 4, coolant temperature temperature sensor 5, Z-axis screw temperature temperature sensor 6, spindle rear bearing temperature temperature sensor 7 and machine bed temperature temperature sensor 8. A temperature acquisition module with the functions of real-time temperature acquisition and data storage 9, a CNC machine tool 10 for cutting tasks, a workpiece 11 for cutting, a three-coordinate measuring machine 12 for measuring the dimensional characteristics of the workpiece, and a CNC machine tool The system interacts and can write the motion axis compensation amount output by the thermal error model into the error compensation module 13 in the numerical control system.

In the present embodiment, for the drilling and cutting work, it is preferable to collect temperature data through eight temperature sensors and perform a method for compensating the thermal error of a CNC machine tool based on the workpiece size data. The specific steps are as follows:

1) Set the workpiece to be cut horizontally on the worktable of the CNC machine tool, and the temperature sensors are respectively set in the air and numbered T1, on the surface shell _of the lubricating oil tank and numbered T2, _on the surface _of the hydraulic oil tank and numbered T3 , on the main shaft housing where the front bearing of the main shaft is located and numbered T ₄ , at the bottom of the coolant and numbered T ₅ , at the Z axis screw nut and numbered T ₆ , on the main shaft housing where the main shaft rear bearing is located and numbered T 5 _7. The machine tool shell is numbered _T8 , and then the workpiece clamping and tool setting work are carried out, and the CNC machine tool processing code is written.

2) Carry out large-scale actual drilling and cutting work of 152 workpieces. The center value of the hole diameter specification of the workpiece to be cut is 45.600mm, and the tolerance is ±10μm, that is, the upper limit of the hole inner diameter specification is 45.610mm, and the lower specification limit is 45.590mm.

In the middle, according to the actual production situation, 3 normal shutdowns are carried out. The temperature sensor collects temperature data in real time, and records the data of each temperature sensor when each workpiece is processed through the temperature acquisition module. For each workpiece, the temperature difference of each point relative to the room temperature is recorded in the table below, and the corresponding relationship curve between the temperature difference and the workpiece serial number is shown in Figure 2.

3) Each time a piece of workpiece is cut, the workpiece is removed, and the workpiece is set horizontally on the workbench of the CMM. According to the measurement standard of the CMM, the inner diameter of the hole feature is measured, and the data is recorded according to the workpiece serial number as follows Table, the corresponding relationship between workpiece size and workpiece serial number is shown in Figure 3.

serial number Inner diameter/mm serial number Inner diameter/mm serial number Inner diameter/mm serial number Inner diameter/mm serial number Inner diameter/mm serial number Inner diameter/mm serial number Inner diameter/mm serial number Inner diameter/mm 1 45.607 20 45.594 39 45.604 58 45.595 77 45.591 96 45.590 115 45.592 134 45.596 2 45.606 twenty one 45.595 40 45.602 59 45.594 78 45.591 97 45.590 116 45.591 135 45.595 3 45.604 twenty two 45.594 41 45.604 60 45.593 79 45.590 98 45.589 117 45.591 136 45.595 4 45.602 twenty three 45.593 42 45.603 61 45.595 80 45.590 99 45.599 118 45.589 137 45.595 5 45.600 twenty four 45.594 43 45.603 62 45.594 81 45.589 100 45.598 119 45.590 138 45.595 6 45.601 25 45.595 44 45.601 63 45.593 82 45.591 101 45.597 120 45.590 139 45.594 7 45.601 26 45.594 45 45.600 64 45.595 83 45.590 102 45.595 121 45.589 140 45.594 8 45.600 27 45.593 46 45.600 65 45.594 84 45.590 103 45.597 122 45.589 141 45.593 9 45.599 28 45.593 47 45.599 66 45.593 85 45.591 104 45.595 123 45.590 142 45.595 10 45.599 29 45.592 48 45.599 67 45.593 86 45.589 105 45.595 124 45.590 143 45.594 11 45.598 30 45.593 49 45.598 68 45.592 87 45.590 106 45.593 125 45.588 144 45.594 12 45.598 31 45.593 50 45.598 69 45.593 88 45.589 107 45.594 126 45.590 145 45.593 13 45.597 32 45.592 51 45.599 70 45.592 89 45.588 108 45.594 127 45.600 146 45.592 14 45.596 33 45.594 52 45.597 71 45.592 90 45.591 109 45.593 128 45.601 147 45.591 15 45.596 34 45.594 53 45.596 72 45.591 91 45.589 110 45.592 129 45.599 148 45.592 16 45.595 35 45.593 54 45.597 73 45.592 92 45.590 111 45.594 130 45.599 149 45.591 17 45.596 36 45.592 55 45.595 74 45.591 93 45.589 112 45.593 131 45.599 150 45.592 18 45.596 37 45.595 56 45.595 75 45.591 94 45.590 113 45.592 132 45.598 151 45.591 19 45.594 38 45.593 57 45.595 76 45.590 95 45.590 114 45.591 133 45.599 152 45.590

4) After the whole large-scale cutting task is completed, Cpk-based analysis is performed on the continuously collected temperature data and the inner diameter of the workpiece, and the key temperature points are identified. The process is shown in Figure 4:

4.1) Using the data of all temperature measuring points and the inner diameter of the workpiece, the multiple linear regression method is used to model, and the full-temperature workpiece size prediction model D(T)=-0.005ΔT ₂ +0.003ΔT ₃ +0.001ΔT ₄ -0.006ΔT is constructed. ₅ +0.021ΔT ₆ -0.008ΔT ₇ -0.014ΔT ₈ +45.587;

4.2) Substitute the data of a single temperature measurement point Ti into the full temperature prediction model expression one by one, and obtain the predicted value D(T _{i )} of the workpiece size under the influence of a single temperature and the corresponding Cpk value, denoted as Cpk(△T _i ). The Cpk calculation here takes the sample mean as the center value, and the upper and lower tolerances remain unchanged.

Taking T ₂ as an example, the calculation formula of D(T ₂ ) is: D(T ₂ )=-0.005ΔT ₂ +45.587. The Cpk value calculated based on the D(T ₂ ) data is Cpk(ΔT ₂ ).

4.3) Compare the size between Cpk(△T _i ) and the minimum Cpk requirement of 1.33. When the Cpk(△T _i ) of any temperature measurement point is less than 1.33, this point is a critical temperature point. Based on the above Cpk influence analysis, T ₂ , T ₆ and T ₇ were selected as key temperature points, and the Cpk (ΔT _i ) values corresponding to each temperature were recorded in the table below.

△T_i △T₂ △T₃ △T₄ △T₅ △T₆ △T₇ △T₈ Cpk(△T_i) 1.29 1.74 6.13 2.35 0.32 0.26 2.79

5) Based on the key temperature points identified above, under the condition that the thermal error of the translation axis has been compensated, the inner diameter of the workpiece is mainly related to the radial thermal error of the spindle. Therefore, it can be considered that the change of the inner diameter of the workpiece directly reflects the change of the radial thermal error of the spindle. The radial thermal error R(T) of the spindle can be represented by the difference between the inner diameter of the workpiece and the standard center value. The spindle radial thermal error model is constructed by the multilayer perceptron neural network (MLP) method, and the corresponding value of each workpiece is calculated through the model. The corresponding thermal error results are recorded in the following table, and the result curve of the corresponding relationship between thermal error and workpiece serial number is shown in Figure 5.

serial number R(T)/μm serial number R(T)/μm serial number R(T)/μm serial number R(T)/μm serial number R(T)/μm serial number R(T)/μm serial number R(T)/μm serial number R(T)/μm 1 4.688 20 -6.007 39 1.033 58 -5.952 77 -7.692 96 -9.602 115 -8.916 134 -4.397 2 4.238 twenty one -5.232 40 -0.527 59 -4.172 78 -7.608 97 -9.869 116 -8.251 135 -4.114 3 2.377 twenty two -6.027 41 -0.437 60 -5.531 79 -7.966 98 -10.519 117 -9.900 136 -3.678 4 2.079 twenty three -6.185 42 -0.887 61 -5.798 80 -8.198 99 -6.084 118 -9.970 137 -5.164 5 1.699 twenty four -6.641 43 -1.281 62 -6.835 81 -7.926 100 -5.324 119 -9.939 138 -5.455 6 1.900 25 -6.494 44 -1.273 63 -7.791 82 -7.975 101 -5.393 120 -9.712 139 -6.177 7 0.553 26 -5.041 45 -0.848 64 -8.289 83 -8.151 102 -5.989 121 -10.509 140 -6.013 8 -0.016 27 -6.470 46 -1.987 65 -8.334 84 -8.189 103 -6.703 122 -10.325 141 -5.681 9 -1.598 28 -5.631 47 -1.914 66 -7.382 85 -8.877 104 -7.290 123 -10.104 142 -4.346 10 -2.073 29 -5.268 48 -1.809 67 -8.319 86 -8.716 105 -7.716 124 -11.042 143 -5.470 11 0044 30 -5424 49 -1931 68 -8804 87 -8064 106 -8451 125 -10695 144 -5806 12 -1.457 31 -5.493 50 -1.765 69 -9.066 88 -8.078 107 -7.372 126 -11.212 145 -5.882 13 -3641 32 -5264 51 -3691 70 -9300 89 -8504 108 -8169 127 1963 146 -6170 14 -4.753 33 -6.929 52 -2.618 71 -9.746 90 -8.301 109 -7.346 128 1.275 147 -6.164 15 -4.095 34 -6.218 53 -3.162 72 -8.918 91 -8.558 110 -7.754 129 -0.667 148 -5.815 16 -5.613 35 -6.101 54 -3.108 73 -8.797 92 -8.768 111 -8.458 130 -2.364 149 -5.892 17 -5.758 36 -6.205 55 -5.417 74 -6.955 93 -9.851 112 -7.996 131 -4.072 150 -7.089 18 -5.454 37 -5.868 56 -4.687 75 -7.568 94 -9.022 113 -7.669 132 -3.886 151 -6.148 19 -5.727 38 -0.550 57 -3.582 76 -7.543 95 -8.797 114 -8.899 133 -4.279 152 -6.483

6) According to the working principle of the compensation system in Figure 6, based on the FOCAS function library of the Ethernet and FANUC CNC system, the interaction between the error compensation module and the CNC system is realized. Based on the external coordinate zero offset function of the CNC machine tool, the thermal error model will be passed. The calculated motion compensation value of the motion axis corresponding to the dimension feature of the workpiece is output to the numerical control system to complete the error compensation.

In this embodiment, the error compensation module is connected to the numerical control system through the Ethernet interface, and the FOCAS function library of the FANUC numerical control system is used for data interaction with the numerical control system. Modeling of thermal errors and calculation output of compensation values for machine tool motion axes.

7) After compensation, 135 workpieces are continuously processed on the CNC machine tool, and the inner diameter data of each workpiece before compensation is predicted and the results are recorded in the following table.

Use a coordinate measuring machine to measure the inner diameter data of each workpiece after compensation, and record the results in the following table. The corresponding relationship curve between the predicted data of the inner diameter of the workpiece before compensation and the measured data of the inner diameter of the workpiece after compensation and the workpiece serial number is shown in Figure 7. Show.

Comparing and analyzing the inner diameter error data before and after compensation for the 135 workpieces, the maximum error of the inner diameter before compensation is 12.8 μm, which exceeds the tolerance range, and the Cpk is 0.76. After compensation, the variation range of the inner diameter of the workpiece is between 45.596mm and 45.606mm, the maximum error of the inner diameter is 6μm, all within the tolerance range, and the Cpk is 1.48, which meets the production requirements. It can be seen that the compensation effect of the established thermal error model is remarkable.

Compared with the method of establishing the thermal error model of the numerical control machine tool based on the temperature data, the position change error between the cutting point of the machine tool and the workpiece in the prior art, the present invention directly utilizes the size detection data of the workpiece actually processed on the production line to analyze and construct. The whole method is analyzed based on the measured workpiece size data on the production line, so it includes the thermal deformation of the machine tool and the thermal deformation of the workpiece caused by the processing process. By analyzing the heat source that affects the thermal error of the machine tool, the pre-set temperature distribution points are implemented, and the key temperature points are identified based on the Cpk analysis. In the task of cutting a large number of workpieces, the three-coordinate measuring machine is used to measure the dimensional features of each workpiece that has been cut and record the measurement data. The error compensation module builds the thermal error model of the CNC machine tool based on the temperature data of the key temperature points and the size data of the large batch of workpieces processed under the machine tool load condition, and interacts with the machine tool CNC system through the error compensation module, based on the external coordinate zero offset Function, output the compensation amount of the motion axis corresponding to the size feature of the workpiece to complete the compensation, and realize the direct use of the size data of the workpiece actually processed on the production line, so as to consider the thermal deformation of the machine tool and the thermal deformation of the workpiece caused by the processing process. The thermal error of the machine tool under the actual processing conditions can be effectively compensated.

The above-mentioned specific implementation can be partially adjusted by those skilled in the art in different ways without departing from the principle and purpose of the present invention. The protection scope of the present invention is subject to the claims and is not limited by the above-mentioned specific implementation. Each implementation within the scope is bound by the present invention.

Claims (4)

1. A numerical control machine tool thermal error compensation method based on workpiece size data is characterized in that key temperature points are obtained by analyzing actually measured temperature data of cutting work through process capability index analysis based on machining procedures; according to the key temperature point and the size data of the workpiece processed under the machine tool load condition, a numerical control machine tool thermal error model based on workpiece size detection data is established through a multilayer perceptron neural network, so that the motion compensation quantity of a motion axis corresponding to the workpiece size characteristic under the actual processing condition is obtained, and thermal error compensation is realized through the external coordinate zero offset function of the numerical control machine tool;

the process capability index analysis refers to: modeling by using data of all temperature measuring points and workpiece size data in a multiple linear regression mode to obtain a full-temperature workpiece size prediction model; then measuring the single temperature point T one by one_iSubstituting the data into a full-temperature workpiece size prediction model to obtain a workpiece size prediction value D (T) under the influence of single temperature_i) And the corresponding Cpk value, denoted Cpk (△ T)_i) Cpk at any temperature measurement (△ T)_i) If the minimum Cpk requirement is less than the minimum Cpk requirement, the point is a key temperature point;

the numerical control machine tool thermal error model based on the workpiece size detection data is as follows: according to key temperature point temperature data obtained by process capability index analysis and size detection data obtained by online/offline detection of a workpiece actually machined under the condition of machine tool load, a mathematical mapping relation between the temperature data and the workpiece size data is established through a multilayer perceptron neural network according to a time corresponding principle and is used as a numerical control machine tool thermal error model.

2. The numerical control machine tool thermal error compensation method based on the workpiece dimension data according to claim 1, characterized in that the actually measured cutting temperature data of the cutting work is obtained by horizontally arranging the workpiece to be cut on a workbench of the numerical control machine tool, arranging temperature sensors at corresponding temperature sensitive points, performing actual cutting work on a large number of workpieces after the tool setting work is completed, determining a standard central value and a tolerance value of the dimension characteristics of the cut workpiece, acquiring the temperature data of corresponding positions in real time through the temperature sensors, and recording the data of each temperature sensor at the moment through a temperature acquisition module.

3. The method for compensating thermal error of numerical control machine tool based on workpiece dimension data according to claim 1, wherein the workpiece dimension data processed under the machine tool load condition is directly derived from the on-line/off-line detection of the actual processing process, the off-line detection is obtained by cutting each workpiece, removing the workpiece, horizontally arranging the workpiece on the worktable of the coordinate measuring machine, measuring the workpiece dimension characteristics according to the measurement standard of the coordinate measuring machine, and recording the workpiece sequence, and the on-line detection adopts a proper sensing detection method to obtain the workpiece dimension data, including but not limited to a laser displacement sensor, a contact micro displacement sensor, an eddy current sensor detection method and the like.

4. A compensation system for implementing the method of any of claims 1 to 3, comprising: temperature sensor, temperature acquisition module, three coordinate measuring machine and error compensation module, wherein: the temperature sensors are respectively arranged in the air, on a surface shell of a lubricating oil tank, on a surface shell of a hydraulic oil tank, on a main shaft shell where a front bearing of a main shaft is located, at the bottom of cooling liquid, at a screw nut of a Z shaft, on a main shaft shell where a rear bearing of the main shaft is located and on a machine tool shell, and output temperature data information to the temperature acquisition module, the temperature acquisition module is connected with the error compensation module and transmits the temperature information, the three-coordinate measuring machine measures workpiece dimension data and outputs the workpiece dimension data to the error compensation module, the error compensation module establishes a thermal error model according to the temperature information and the workpiece dimension data, and then the compensation quantity of a motion shaft corresponding to the workpiece dimension characteristic is obtained through calculation and transmitted to the numerical control.

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