Precision evaluation compensation method for door-shaped vertical machining center

Abstract

The invention discloses a door type vertical machining center precision evaluation compensation method, which specifically comprises the following steps of: establishing a vertical machining center control machine tool comprehensive error model by combining influence factors of machine tool precision; constructing a precision evaluation system; establishing a vertical machining center precision comprehensive evaluation model; performing error compensation on the door-shaped vertical machining center according to the evaluation result; according to the method, the precision of the high-speed and high-precision door-shaped vertical machining center is deeply analyzed, influence factors of the high-speed and high-precision door-shaped vertical machining center are discussed, an effective evaluation method is provided, a set of systematic precision evaluation process is provided in combination with establishment and analysis of a space error model, and corresponding error compensation is performed in combination with an evaluation result; and a theoretical basis and practical guidance are provided for improving the precision stability and the machining quality of the machining center.

Description

Technical Field

[0001] The invention relates to the technical field of machine tool processing, in particular to a precision evaluation and compensation method for a gate-type vertical machining center. Background Art

[0002] With the continuous advancement of advanced manufacturing technology, CNC machine tools, as its indispensable application equipment, are gradually developing towards high efficiency, high reliability, high precision and intelligence. The level of CNC machine tool processing performance is mainly reflected in the quality of the product. Therefore, to obtain high-precision and high-reliability products, it is necessary to improve the processing performance of the machine tool. And the evaluation of processing performance is the top priority. Before processing parts, a comprehensive evaluation of CNC machine tools can know the current status of CNC machine tools, so that the CNC machine tools can process parts under relatively good conditions, thereby avoiding the problem of poor product quality due to the fact that the processing performance of the CNC machine tools themselves cannot reach the expected processing state. CNC machine tools are complex and precise systems, and their processing performance is affected by many factors, from the machine tool's own errors (such as installation positioning errors, tool errors, part errors, etc.) to feed servo system errors and thermal errors. To improve the quality of parts, it is necessary to minimize the impact of these factors on the processing performance of CNC machine tools as much as possible. High-speed and high-precision portal vertical machining centers play a vital role in aerospace, automobile manufacturing, precision machinery and other fields. This type of machining center has become the backbone of modern manufacturing industry with its excellent machining performance and high efficiency. However, maintaining and improving the high precision of the equipment is one of the key factors to ensure product quality and machining efficiency. In practical applications, due to the influence of various factors, such as wear, thermal deformation, load changes, etc. of the machine tool itself, the precision of the machining center tends to decrease over time, thus affecting the dimensional accuracy and surface quality of the workpiece. Summary of the invention

[0003] The main purpose of the present invention is to provide a precision evaluation and compensation method for a portal type vertical machining center, aiming to solve the existing technical problems.

[0004] To achieve the above object, the present invention provides a method for evaluating and compensating the accuracy of a portal vertical machining center, which specifically includes the following steps:

[0005] Combined with the factors influencing the accuracy of machine tools, a comprehensive error model of vertical machining center controlled machine tools is established;

[0006] Constructing an accuracy evaluation system;

[0007] Establish a comprehensive evaluation model for the accuracy of vertical machining centers;

[0008] According to the evaluation results, error compensation is performed on the portal vertical machining center.

[0009] Furthermore, establishing the comprehensive error model specifically includes simplifying and merging the error elements of the three-axis precision CNC machine tool according to the linear superposition of the errors of the kinematic pair at the same degree of freedom, as follows:

[0010] When the worktable X-axis moves a distance x, there are three movement errors δ yX , δ xX , δ zX , three angle errors ε yX , ε xX , ε zX , 1 verticality error S yX , 3 thermal drift errors δ xX (t),δ yX (t),δ zX (t) and three force errors δ xX (f), δ yX (f), δ zX (f), so the error transformation matrix from the reference coordinate system to the X-axis is:

[0011]

[0012] There are 3 movement errors δ when the worktable Y axis moves a distance y yY , δ xY , δ zY , three angle errors ε yY , ε xY , ε zY , 3 thermal drift errors δ xY (t),δ yY (t),δ zY (t) and three force errors δ xY (f), δ yY (f), δ zY (f), according to the coordinate transformation and small error hypothesis theory, the transformation matrix from the Y axis to the reference coordinate system is:

[0013]

[0014] There are three movement errors δ when the worktable Z axis moves a distance z yZ , δ xZ , δ zZ , three angle errors ε yZ , ε xZ , ε zZ , 2 verticality errors S xZ , S yz , 3 thermal drift errors δ xZ (t),δ yZ (t),δ zZ (t) and three force errors δ xZ (f), δyZ (f), δ zZ (f), so the error transformation matrix from the reference coordinate system to the Z axis is:

[0015]

[0016] Furthermore, the accuracy evaluation system is constructed by measuring the machining accuracy of the machine tool and the static accuracy of the machine tool through machining the test piece, which includes three levels. The first level is the overall goal, that is, the machine tool factory accuracy factor set U = {U1, U2}; the second level is the second level target factor set U i (i=1,2), where U1 is the machining accuracy of the machine tool, U2 is the static accuracy of the machine tool, and U1={U 11 ,U 12 ,U 13},U2={u 21 ,U 22 ,U 23 ,U 24 ,U 25}, the third layer is the third level target factor set U 1i (i=1,2,3), U 2i (i=1,2,3,4,5), where,

[0017] U 11 ={J 11 ,J 12 ,J 13 ,J 14 ,J 15 ,J 16 ,J 17}

[0018] U 12 ={J 21 ,J 22 ,J 23}

[0019] U 13 ={J 31 ,J 32 ,J 33 ,J 34 ,J 35 ,J 36 ,J 37 ,J 38}

[0020] U 21 ={D 11 ,D 12 ,D 13 ,D 14}

[0021] U 22 ={D 21 ,D22 ,D 23}

[0022] U 23 ={D 31}

[0023] U 24 ={D 41 ,D 42 ,D 43}

[0024] U 25 ={D 51 ,D 52 ,D 53}.

[0025] Furthermore, establishing the evaluation model includes dividing the factors to be considered into several layers according to their attributes, performing a primary comprehensive evaluation on each layer, and then performing a higher-level comprehensive evaluation on the evaluation results of each layer, recursively layer by layer, to obtain the final evaluation result.

[0026] Furthermore, the primary comprehensive evaluation is recursively extended to the secondary fuzzy comprehensive evaluation, and the primary evaluation vector in the secondary fuzzy comprehensive evaluation is: B i =W i ·R i =(b1,b2,…,b i ),i=1,2,...,n, the generated Y i The evaluation matrix of the next level is formed, and the comprehensive evaluation vector of the second level is obtained through fuzzy operation: B = W·R, which is extended to the third-level fuzzy comprehensive evaluation and the fourth-level fuzzy comprehensive evaluation model; combined with the evaluation system, the corresponding weight vector W is obtained i , by empowering the overall system, the weight ratio of the three-level indicators is obtained.

[0027] Further, the corresponding single factor fuzzy comprehensive evaluation matrix is ​​obtained as follows:

[0028]

[0029] Substitute the obtained results into the evaluation matrix to obtain the three-level fuzzy evaluation matrix R corresponding to the sub-indicators of shape accuracy, dimensional accuracy, and position accuracy of the three-level evaluation 11 , R 12 , R 13 , combined with the weight vector of the three-level indicators, the fuzzy comprehensive evaluation result of the second-level indicators can be obtained, and then combined with the fuzzy comprehensive evaluation result of the second-level indicators of static accuracy to obtain the overall comprehensive evaluation result;

[0030] (1) By fuzzy comprehensive evaluation method, combined with the weight vector W of the three-level index of machining accuracy 11 , W 12 , W13 , the three-level indicators for machining accuracy are:

[0031] B 11 =W 11 ·R 11

[0032] Similarly

[0033] B 12 =W 12 ·R 12

[0034] B 13 =W 13 ·R 13

[0035] The obtained B 11 , B 12 , B 13 Further combined to obtain the secondary fuzzy comprehensive evaluation result B1, calculated as follows

[0036]

[0037] (2) The three-level indicators for static accuracy are:

[0038] B 21 =W 21 ·R 21

[0039] B 22 =W 22 ·R 22

[0040] B 23 =W 23 ·R 23

[0041] B 24 =W 24 ·R 24

[0042] B 25 =W 25 ·R 25

[0043] Combining the weight vector W2 of the three-level indicators, the second-level comprehensive performance evaluation result is obtained as follows:

[0044]

[0045] Finally, the overall comprehensive evaluation results can be further obtained from the secondary indicators of machine tool processing accuracy and static accuracy:

[0046] Furthermore, the error compensation specifically includes:

[0047] Accurate measurement and analysis of errors to determine the specific error terms that need to be compensated;

[0048] Develop compensation plans based on measurement results, including selecting appropriate compensation methods and setting compensation parameters;

[0049] Implement compensation strategies in control systems;

[0050] The machine tool performance is measured and evaluated again to verify the compensation effect, and the compensation strategy is further adjusted based on the feedback.

[0051] Furthermore, the compensation strategy includes:

[0052] Feedback interruption strategy: the computer calculates the spatial error based on the error synthesis model, converts it into a pulse signal, and performs addition and subtraction operations with the encoder feedback signal. The operation result is inserted into the servo system feedback loop in the form of a phase signal, and the machine tool control system uses it to drive the machine tool to implement the next movement;

[0053] The origin translation strategy first calculates the position error value of the machine tool, and converts its value into a compensation signal and sends it to the CNC system through the I / O port. The compensation signal is then sent to the control signal of the machine tool servo loop through the CNC system's external coordinate system origin offset function to achieve the compensation purpose.

[0054] Furthermore, the error measurement measures the natural error curve of the CNC machine tool through an independent measurement system, and the required compensation value is stored in the CNC system for compensation.

[0055] Furthermore, the independent measurement system compensation method includes:

[0056] Error modeling;

[0057] The detection strategy first compensates for the error terms in the XY plane, then compensates for the Z axis error, and finally compensates for the verticality error;

[0058] The compensation is implemented by analyzing the error characteristics of each measuring point and determining whether to use one-time linear compensation or multi-stage linear compensation methods.

[0059] The beneficial effects of the present invention are embodied in:

[0060] In the present invention, the accuracy of a high-speed and high-precision portal vertical machining center is deeply analyzed, its influencing factors are explored, and an effective evaluation method is proposed. Combined with the establishment and analysis of a spatial error model, a set of systematic accuracy evaluation processes is provided, and corresponding error compensation is performed in combination with the evaluation results, providing a theoretical basis and practical guidance for improving the accuracy stability and machining quality of the machining center. BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Figure 1 This is a flow chart of the evaluation compensation method of the present invention;

[0062] Figure 2 It is a schematic diagram of the process flow of the accuracy evaluation system of the present invention;

[0063] Figure 3 This is a schematic diagram of the error compensation process of the present invention;

[0064] Figure 4 A schematic diagram of the error compensation architecture of the present invention;

[0065] Figure 5 This is a schematic diagram of the compensation principle of the feedback interruption strategy of the present invention;

[0066] Figure 6 It is a schematic diagram of the compensation principle of the origin translation strategy of the present invention. DETAILED DESCRIPTION

[0067] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. In the absence of conflict, the embodiments in this application and the features in the embodiments can be combined with each other. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0068] See also Figure 1-6 The present invention provides a method for evaluating and compensating the accuracy of a portal vertical machining center, which specifically includes the following steps:

[0069] S1: Establish a comprehensive error model of vertical machining center CNC machine tools in combination with the factors affecting machine tool accuracy; specifically, establishing the comprehensive error model specifically includes simplifying and merging the error elements of three-axis precision CNC machine tools based on the linear superposition of the errors of the same degree of freedom of the kinematic pair, as follows: simplify and merge the error elements of three-axis precision CNC machine tools into 21 items. As shown in the following table:

[0070] Table 1 Geometric error elements

[0071]

[0072] Table 2 Thermal error elements

[0073]

[0074] Table 3 Force error elements

[0075]

[0076]

[0077] Based on the above table, in actual situations, there are three movement (geometric) errors δ when the worktable Y axis moves a distance y yY , δ xY , δ zY , three angle errors ε yY , ε xY , ε zY , 3 thermal drift errors δ xY (t),δ yY (t),δ zY (t) and three force errors δ xY (f), δ yY (f), δ zY (f) Based on the coordinate transformation and small error hypothesis theory, the following is obtained:

[0078] When the worktable X-axis moves a distance x, there are three movement errors δ yX , δ xX , δ zX , three angle errors ε yX , ε xX , ε zX , 1 verticality error S yx , 3 thermal drift errors δ xX (t),δ yX (t),δ zX (t) and three force errors δ xX (f), δ yX (f), δ zX (f), so the error transformation matrix from the reference coordinate system to the X-axis is:

[0079]

[0080] There are 3 movement errors δ when the worktable Y axis moves a distance y yY , δ xY , δ zY , three angle errors ε yY , ε xY , ε zY , 3 thermal drift errors δ xY (t),δ yY (t),δ zY (t) and three force errors δ xY (f), δ yY (f), δ zY (f), according to the coordinate transformation and small error hypothesis theory, the transformation matrix from the Y axis to the reference coordinate system is:

[0081]

[0082] There are three movement errors δ when the worktable Z axis moves a distance z yZ , δ xZ , δ zZ , three angle errors ε yZ , ε xZ , ε zZ , 2 verticality errors S xZ , S yZ , 3 thermal drift errors δ xZ (t),δ yZ (t),δ zz (t) and three force errors δ xZ (f), δ yZ (f), δ zZ (f), so the error transformation matrix from the reference coordinate system to the Z axis is:

[0083]

[0084] S2: Constructing the precision evaluation system: Through the processing and analysis of the test pieces, the machining precision index system of the machine tool can be obtained. Combined with the static precision index of the machine tool, the following system is established: Figure 2 The comprehensive evaluation index system shown.

[0085] The straightness of the bed guide rail is D 11 It refers to the degree of deviation between the geometric shape of the guide rail surface and the ideal straight line; the straightness D of the worktable surface 12 It refers to the degree of deviation between the working surface and the ideal straight line when the working surface of the machine tool moves along a certain axis direction; the rotation accuracy of the spindle D 13 It refers to the deviation range of the actual rotation center line relative to the ideal rotation center line during the rotation of the spindle; the parallelism of the spindle axis D 14 It refers to the condition that the actual axis of the spindle is equidistant from the reference axis, that is, the allowable deviation between the two within the specified range; spindle speed accuracy D 21 It refers to the radial and axial runout values ​​of the workpiece or tool installed at the front end of the spindle under no-load and low-speed conditions; the machine tool feed speed accuracy D 22 It refers to the degree of conformity and stability between the actual feed speed and the feed speed set by the program when the CNC machine tool executes the processing program; the machine tool feed stroke accuracy D 23 It refers to the degree of conformity between the actual moving distance of each feed axis and the program setting value and the accuracy of repeated positioning when the machine tool is processing; the transmission ratio accuracy of the machine tool D 31 It refers to the accuracy of the relative motion between the two ends of the transmission chain inside the machine tool, which is characterized by the actual transmission ratio / theoretical transmission ratio, while uniformity refers to the smoothness and continuity of this relative motion; the linear motion X-axis accuracy of the machine tool D 41It refers to the error between the actual moving distance of the X-axis and the ideal distance when the machine tool performs linear motion.

[0086] Specifically, the accuracy evaluation system is constructed by measuring the machining accuracy of the machine tool and the static accuracy of the machine tool through machining the test piece, which includes three levels. The first level is the overall goal, that is, the machine tool factory accuracy factor set U = {U1, U2}; the second level is the second level target factor set U i (i=1,2), where U1 is the machining accuracy of the machine tool, U2 is the static accuracy of the machine tool, and U1={U 11 ,U 12 ,U 13},U2={u 21 ,U 22 ,U 23 ,U 24 ,U 25}, the third layer is the third level target factor set U 1i (i=1,2,3), U 2i (i=1,2,3,4,5), where,

[0087] U 11 ={J 11 ,J 12 ,J 13 ,J 14 ,J 15 ,J 16 ,J 17}

[0088] U 12 ={J 21 ,J 22 ,J 23}

[0089] U 13 ={J 31 ,J 32 ,J 33 ,J 34 ,J 35 ,J 36 ,J 37 ,J 38}

[0090] U 21 ={D 11 ,D 12 ,D 13 ,D 14}

[0091] U 22 ={D 21 ,D 22 ,D 23}

[0092] U23 ={D 31}

[0093] U 24 ={D 41 ,D 42 ,D 43}

[0094] U 25 ={D 51 ,D 52 ,D 53}.

[0095] S3: Establish a comprehensive evaluation model for the accuracy of a vertical machining center: Specifically, establishing the evaluation model includes dividing the factors to be considered into several layers according to their attributes, performing a primary comprehensive evaluation on each layer, and then performing a higher-level comprehensive evaluation on the evaluation results of each layer, and recursively performing this evaluation layer by layer to obtain the final evaluation result.

[0096] In one embodiment, the primary comprehensive evaluation is recursively derived into the secondary fuzzy comprehensive evaluation, and the primary evaluation vector in the secondary fuzzy comprehensive evaluation is: i =W i ·R i =(b1,b2,…,b i ),i=1,2,...,n, the generated Y i The evaluation matrix of the next level is formed, and the comprehensive evaluation vector of the second level is obtained through fuzzy operation: B = W·R, which is extended to the third-level fuzzy comprehensive evaluation and the fourth-level fuzzy comprehensive evaluation model; combined with the evaluation system, the corresponding weight vector W is obtained i , by empowering the overall system, the weight ratio of the three-level indicators is obtained.

[0097] In one embodiment, an evaluation set is first given, which is a set of comments given to evaluation indicators at various levels in the industry. The evaluation set is imported into a computer, and different evaluation levels are quantified by membership to obtain a judgment statistics table, as shown in the following example.

[0098] Machining accuracy single factor evaluation statistics table

[0099]

[0100]

[0101]

[0102] Table Indicates the proportion of accuracy evaluation results for this indicator, and meets

[0103]

[0104] According to the corresponding single factor fuzzy comprehensive evaluation matrix:

[0105]

[0106] Substitute the obtained results into the evaluation matrix to obtain the three-level fuzzy evaluation matrix R corresponding to the sub-indicators of shape accuracy, dimensional accuracy, and position accuracy of the three-level evaluation 11 , R 12 , R 13 , combined with the weight vector of the three-level indicators, the fuzzy comprehensive evaluation result of the second-level indicators can be obtained, and then combined with the fuzzy comprehensive evaluation result of the second-level indicators of static accuracy to obtain the overall comprehensive evaluation result;

[0107] (1) By fuzzy comprehensive evaluation method, combined with the weight vector W of the three-level index of machining accuracy 11 , W 12 , W 13 , the three-level indicators for machining accuracy are:

[0108] B 11 =W 11 ·R 11

[0109] Similarly

[0110] B 12 =W 12 ·R 12

[0111] B 13 =W 13 ·R 13

[0112] The obtained B 11 , B 12 , B 13 Further combined to obtain the secondary fuzzy comprehensive evaluation result B1, calculated as follows

[0113]

[0114] (2) The three-level indicators for static accuracy are:

[0115] B 21 =W 21 ·R 21

[0116] B 22 =W 22 ·R 22

[0117] B 23 =W 23 ·R 23

[0118] B24 =W 24 ·R 24

[0119] B 25 =W 25 ·R 25

[0120] Combining the weight vector W2 of the three-level indicators, the second-level comprehensive performance evaluation result is obtained as follows:

[0121]

[0122] Finally, the overall comprehensive evaluation results can be further obtained from the secondary indicators of machine tool processing accuracy and static accuracy:

[0123] S4: Error compensation for portal vertical machining center based on evaluation results: see Figure 3 and Figure 4 Specifically, the error compensation includes:

[0124] Accurate measurement and analysis of errors to determine the specific error terms that need to be compensated;

[0125] Develop compensation plans based on measurement results, including selecting appropriate compensation methods and setting compensation parameters;

[0126] Implement compensation strategies in control systems;

[0127] The machine tool performance is measured and evaluated again to verify the compensation effect, and the compensation strategy is further adjusted based on the feedback.

[0128] In one embodiment, the compensation strategy includes,

[0129] Feedback interruption strategy: the computer calculates the spatial error based on the error synthesis model, converts it into a pulse signal, and performs addition and subtraction operations with the encoder feedback signal. The operation result is inserted into the servo system feedback loop in the form of a phase signal, and the machine tool control system uses it to drive the machine tool to implement the next movement;

[0130] For details, please refer to Figure 5 The working principle is that the computer calculates the spatial error based on the error synthesis model, converts it into a pulse signal, and performs addition and subtraction operations with the encoder feedback signal. The operation result is inserted into the servo system feedback loop in the form of a phase signal, and the machine tool control system uses this to drive the machine tool to implement the next step of movement.

[0131] The origin translation strategy first calculates the position error value of the machine tool, and converts its value into a compensation signal and sends it to the CNC system through the I / O port. The compensation signal is then sent to the control signal of the machine tool servo loop through the CNC system's external coordinate system origin offset function to achieve the compensation purpose.

[0132] For details, please refer to Figure 6 The working principle is to first calculate the position error value of the machine tool, and then convert it into a compensation signal and send it to the CNC system through the I / O port. The compensation signal is then sent to the control signal of the machine tool servo loop through the CNC system's external coordinate system origin offset function to achieve the compensation purpose. This strategy does not require changing the CNC system's hardware and software and instructions, but only requires adding data interaction program code to the PLC.

[0133] Among them, the compensation strategy system is a three-level evaluation index obtained from the above content, so that specific analysis can be carried out on specific evaluation indicators, and error measurement and error research on the evaluation indicators can be carried out to facilitate the subsequent error compensation; in terms of error measurement, independent measurement system compensation is a method of machine tool error compensation, which uses an independent measurement system (such as laser measurement) to measure the natural error curve of the CNC machine tool, and then saves the required compensation value in the CNC system for compensation. This method can effectively compensate for processing errors and make up for the static errors of the machine tool itself.

[0134] In one embodiment, the error measurement measures the natural error curve of the CNC machine tool through an independent measurement system, and the required compensation value is stored in the CNC system for compensation.

[0135] The independent measurement system compensation method includes error modeling;

[0136] The detection strategy first compensates for the error terms in the XY plane, then compensates for the Z axis error, and finally compensates for the verticality error;

[0137] The compensation is implemented by analyzing the error characteristics of each measuring point and determining whether to use one-time linear compensation or multi-stage linear compensation methods.

[0138] It should be understood that the above is only an example and does not constitute any limitation on the technical solution of the present invention. In specific applications, technicians in this field can make settings as needed, and the present invention does not limit this.

[0139] It should be noted that the workflow described above is merely illustrative and does not limit the scope of protection of the present invention. In practical applications, technicians in this field can select part or all of them according to actual needs to achieve the purpose of the present embodiment, and no limitation is made here.

[0140] In addition, for technical details not fully described in this embodiment, reference can be made to the evaluation method provided in any embodiment of the present invention, and will not be repeated here.

[0141] In addition, it should be noted that, in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or system including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or system. In the absence of further restrictions, an element defined by the sentence "comprises a ..." does not exclude the existence of other identical elements in the process, method, article or system including the element.

[0142] The serial numbers of the above embodiments of the present invention are only for description and do not represent the advantages or disadvantages of the embodiments.

[0143] Through the description of the above implementation methods, those skilled in the art can clearly understand that the above-mentioned embodiment methods can be implemented by means of software plus a necessary general hardware platform, and of course by hardware, but in many cases the former is a better implementation method. Based on such an understanding, the technical solution of the present invention, or the part that contributes to the prior art, can be embodied in the form of a software product, which is stored in a storage medium (such as a read-only memory (ROM) / RAM, a magnetic disk, or an optical disk), and includes a number of instructions for a terminal device (which can be a mobile phone, a computer, a server, or a network device, etc.) to execute the methods described in each embodiment of the present invention.

[0144] The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for evaluating and compensating the accuracy of a portal vertical machining center, characterized in that: The specific steps include: Combined with the factors influencing the accuracy of machine tools, a comprehensive error model of vertical machining center controlled machine tools is established; Constructing an accuracy evaluation system; Establish a comprehensive evaluation model for the accuracy of vertical machining centers; According to the evaluation results, error compensation is performed on the portal vertical machining center.

2. The method for evaluating and compensating the accuracy of a portal vertical machining center as claimed in claim 1, characterized in that: The establishment of the comprehensive error model specifically includes simplifying and merging the error elements of the three-axis precision CNC machine tool according to the linear superposition of the errors of the kinematic pair in the same degree of freedom, as follows: When the worktable X-axis moves a distance x, there are three movement errors δ yX , δ xX , δ zX , three angle errors ε yX , ε xX , ε zX , 1 verticality error S yX , 3 thermal drift errors δ xX (t),δ yX (t),δ zX (t) and three force errors δ xX (f), δ yX (f), δ zX (f), so the error transformation matrix from the reference coordinate system to the X-axis is: There are 3 movement errors δ when the worktable Y axis moves a distance y yY , δ xY , δ zY , three angle errors ε yY , ε xY , ε zY , 3 thermal drift errors δ xY (t),δ yY (t),δ zY (t) and three force errors δ xY (f), δ yY (f), δ zY (f), according to the coordinate transformation and small error hypothesis theory, the transformation matrix from the Y axis to the reference coordinate system is: There are three movement errors δ when the worktable Z axis moves a distance z yZ , δ xZ , δ zZ , three angle errors ε yZ , ε xZ , ε zZ , 2 verticality errors S xZ , S yZ , 3 thermal drift errors δ xZ (t),δ yZ (t),δ zZ (t) and three force errors δ xZ (f), δ yZ (f), δ zZ (f), so the error transformation matrix from the reference coordinate system to the Z axis is:

3. The accuracy evaluation and compensation method for a portal vertical machining center according to claim 1, characterized in that: The construction of the accuracy evaluation system includes the machining accuracy of the machine tool through the processing test piece and the static accuracy of the machine tool, which includes three levels. The first level is the overall goal, that is, the machine tool factory accuracy factor set U = {U1, U2}; the second level is the second level target factor set U i (i=1,2), where U1 is the machining accuracy of the machine tool, U2 is the static accuracy of the machine tool, and U1={U 11 , U 12 , U 13 },U2={U 21 , U 22 , U 23 , U 24 , U 25 }, the third layer is the third level target factor set U 1i (i=1,2,3), U 2i (i=1, 2, 3, 4, 5), where U 11 =U 11 ,J 12 ,J 13 ,J 14 ,J 15 ,J 16 ,J 17 } U 12 ={J 21 ,J 22 ,J 23 } U 13 ={J31,J 32 ,J 33 ,J 34 ,J 35 ,J 36 ,J 37 ,J 38 } U 21 ={D 11 ,D 12 ,D 13 ,D 14 } U 22 ={D 21 ,D 22 ,D 23 } U 23 ={D 31 } U 24 ={D 41 ,D 42 ,D 43 } U 25 ={D 51 ,D 52 ,D 53 }。 4. The method for evaluating and compensating the accuracy of a portal vertical machining center according to claim 1, characterized in that: Establishing the evaluation model includes dividing the factors to be considered into several layers according to their attributes, conducting a primary comprehensive evaluation on each layer, and then conducting a higher-level comprehensive evaluation on the evaluation results of each layer, recursively layer by layer to obtain the final evaluation result.

5. The method for evaluating and compensating the accuracy of a portal vertical machining center as claimed in claim 4, characterized in that: The primary comprehensive evaluation is recursively transferred to the secondary fuzzy comprehensive evaluation, and the primary evaluation vector in the secondary fuzzy comprehensive evaluation is: B i =W i ·R i =(b1, b2, ..., b i ), i = 1, 2, ..., n, the generated Y i The evaluation matrix of the next level is formed, and the comprehensive evaluation vector of the second level is obtained through fuzzy operation: B = W·R, which is extended to the third-level fuzzy comprehensive evaluation and the fourth-level fuzzy comprehensive evaluation model; combined with the evaluation system, the corresponding weight vector W is obtained i , by empowering the overall system, the weight ratio of the three-level indicators is obtained.

6. The accuracy evaluation and compensation method for a portal vertical machining center as claimed in claim 5, characterized in that: According to the corresponding single factor fuzzy comprehensive evaluation matrix: Substitute the obtained results into the evaluation matrix to obtain the three-level fuzzy evaluation matrix R corresponding to the sub-indicators of shape accuracy, dimensional accuracy, and position accuracy of the three-level evaluation 11 , R 12 , R 13 , combined with the weight vector of the three-level indicators, the fuzzy comprehensive evaluation result of the second-level indicators can be obtained, and then combined with the fuzzy comprehensive evaluation result of the second-level indicators of static accuracy to obtain the overall comprehensive evaluation result; (1) By fuzzy comprehensive evaluation method, combined with the weight vector W of the three-level index of machining accuracy 11 , W 12 , W 13 , the three-level indicators for machining accuracy are: B 11 =W 11 ·R 11 Similarly B 12 =W 12 ·R 12 B 13 =W 13 ·R 13 The obtained B 11 , B 12 , B 13 Further combined to obtain the secondary fuzzy comprehensive evaluation result B1, calculated as follows (2) The three-level indicators for static accuracy are: B 21 =W 21 ·R 21 B 22 =W 22 ·R 22 B 23 =W 23 ·R 23 B 24 =W 24 ·R 24 B 25 =W 25 ·R 25 Combining the weight vector W2 of the three-level indicators, the second-level comprehensive performance evaluation result is obtained as follows: Finally, the overall comprehensive evaluation results can be further obtained from the secondary indicators of machine tool processing accuracy and static accuracy:

7. The accuracy evaluation and compensation method for a portal type vertical machining center as claimed in claim 1, characterized in that: The error compensation specifically includes: Accurate measurement and analysis of errors to determine the specific error terms that need to be compensated; Develop compensation plans based on measurement results, including selecting appropriate compensation methods and setting compensation parameters; Implement compensation strategies in control systems; The machine tool performance is measured and evaluated again to verify the compensation effect, and the compensation strategy is further adjusted based on the feedback.

8. The method for evaluating and compensating the accuracy of a portal vertical machining center as claimed in claim 7, characterized in that: The compensation strategies include: Feedback interruption strategy: the computer calculates the spatial error based on the error synthesis model, converts it into a pulse signal, and performs addition and subtraction operations with the encoder feedback signal. The operation result is inserted into the servo system feedback loop in the form of a phase signal, and the machine tool control system uses it to drive the machine tool to implement the next movement; The origin translation strategy first calculates the position error value of the machine tool, and converts its value into a compensation signal and sends it to the CNC system through the I / O port. The compensation signal is then sent to the control signal of the machine tool servo loop through the CNC system's external coordinate system origin offset function to achieve the compensation purpose.

9. The accuracy evaluation and compensation method for a portal type vertical machining center as claimed in claim 7, characterized in that: The error measurement measures the natural error curve of the CNC machine tool through an independent measurement system, and saves the required compensation value in the CNC system for compensation.

10. The accuracy evaluation and compensation method for a portal type vertical machining center according to claim 9, characterized in that: The independent measurement system compensation method comprises: Error modeling; The detection strategy first compensates for the error terms in the XY plane, then compensates for the Z axis error, and finally compensates for the verticality error; The compensation is implemented by analyzing the error characteristics of each measuring point and determining whether to use one-time linear compensation or multi-stage linear compensation methods.

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