On-machine loading device for machine tool precision retentivity test and control method

Abstract

The invention discloses an on-machine loading device for a machine tool precision retentivity test and a control method. The on-machine loading device comprises a loading workbench, a mechanical loading device and a control device, the loading workbench is arranged on the numerical control machine tool; the mechanical loading device is installed on the loading workbench and comprises an installation base fixedly connected with the loading workbench, a plurality of identical motion branch chains fixedly connected with the upper surface of the installation base, a top hinge movably connected with the upper ends of the motion branch chains and a loading movable platform fixedly connected with the top end of the top hinge. A machine tool spindle is connected to the middle of the top of the loading movable platform, and a loading movable platform tool is connected between the top hinge and the loading movable platform. According to the invention, three-dimensional force loading can be carried out on different types of numerical control machine tools, specified variable loads are applied to the machine tools while the main shaft rotates, and the control precision of the loading device is improved.

Description

Technical Field

[0001] The invention relates to the technical field of machine tool precision retention testing, and in particular to an on-machine loading device and a control method for machine tool precision retention testing. Background Art

[0002] CNC machine tools are mainstream equipment in the machinery manufacturing industry. Their precision retention refers to the ability of CNC machine tools to maintain their original precision for a long time. The degradation process of CNC machine tool precision retention is a complex process caused by multiple factors, and the cutting load on CNC machine tools is one of the important factors. Therefore, it is necessary to establish a set of loading test devices that can simulate cutting loads, which can truly simulate the composite loads that CNC machine tools are subjected to in actual processing without the need for actual cutting processing, to conduct high-precision loading tests on CNC machine tools, and meet the needs of machine tool manufacturers for CNC machine tool performance testing.

[0003] Under current technical conditions, common multi-DOF loading devices all use the steward mechanism (a multi-purpose parallel robot structure) as the carrier mechanism of the loading device. As a closed-loop mechanism composed of multiple motion branches, the parallel mechanism has the advantages of simple structure, high rigidity, large load-bearing capacity, and high precision, and is widely used in the mechanical field. For example, some current machine tool performance testing institutions use parallel structure robots as driving components. At the same time, parallel robots are also used in precision motion platforms, robot error compensation, automobile driving simulation and other fields, indicating that the equipment and related theoretical technologies have matured.

[0004] However, on the one hand, the space required for this mechanism is large, which is not conducive to expansion to other types of machine tools; at the same time, since the cylinders or hydraulic cylinders and other components in the steward mechanism are floating components, it is more likely that the cylinders or hydraulic cylinders will be deformed by force due to dynamic loads during the loading process, thereby affecting the loading accuracy;

[0005] On the other hand, as a multi-degree-of-freedom motion mechanism, the input and output of the parallel mechanism are not simple linear input and output, but are affected by a variety of nonlinear factors. When the parallel mechanism is used as a loading device, the CNC machine tool and the loading device will be deformed due to the influence of different machine tool stiffness and the loading device itself. At the same time, during the experiment, the rotation of the machine tool spindle will cause a large amount of heat to be generated, resulting in thermal deformation of the loading device and the CNC machine tool. Various factors will make the input and output of the loading device difficult to obtain through theoretical calculations.

[0006] Therefore, in view of the problems that the common steward mechanism currently has poor stiffness, easy breakage and poor versatility, as well as the problem that the loading accuracy is easily reduced during the loading experiment and the loading device is seriously damaged, an on-machine loading device and control method for machine tool precision retention test are proposed to solve the above problems. Summary of the invention

[0007] The object of the present invention is to provide an on-machine loading device and a control method for testing the accuracy retention of a machine tool, so as to solve the problems raised in the above-mentioned background technology.

[0008] In order to solve the above technical problems, the present invention provides the following technical solutions: an on-machine loading device for machine tool precision retention test, comprising a loading workbench, a mechanical loading device and a control device;

[0009] The loading workbench is arranged on a CNC machine tool;

[0010] The mechanical loading device is installed on the loading workbench, and the mechanical loading device includes a mounting base fixedly connected to the loading workbench, a plurality of identical motion branches fixedly connected to the upper surface of the mounting base, a top hinge movably connected to the upper ends of the plurality of motion branches, and a loading movable platform fixedly connected to the top of the top hinge, a machine tool spindle is connected to the middle of the top of the loading movable platform, and a loading movable platform tooling is connected between the top hinge and the loading movable platform;

[0011] The control device is used to control the operating state of the mechanical loading device. The control device includes a three-dimensional force sensor for monitoring the three-dimensional force data of the mechanical loading device.

[0012] According to the above technical solution, a groove is provided at the central part of the loading platform, a tool handle tooling is connected inside the groove, and the three-dimensional force sensor is installed between the tool handle tooling and the groove;

[0013] A machine tool handle is connected inside the tool handle fixture, and the machine tool handle is connected to a machine tool spindle.

[0014] According to the above technical solution, the number of the moving branches and the top hinges is set to 3, and they are distributed at 120° on the horizontal plane.

[0015] According to the above technical solution, the motion branch chain includes an electric cylinder and an electric cylinder tooling. The tail end of the electric cylinder is fixed on the upper surface of the mounting base. The electric cylinder tooling is connected to the top of the electric cylinder. The electric cylinder includes a screw guide and a servo motor. The output ends of the screw guide and the servo motor are both equipped with pulleys, and a belt is connected between the two pulleys for transmission.

[0016] According to the above technical solution, the upper part of the electric cylinder fixture is configured as a through-hole cylindrical shape, and the lower part of the electric cylinder fixture is configured as a plate shape;

[0017] The output end of the lead screw guide rail is fixedly connected to the plate-shaped surface of the electric cylinder tooling by means of bolts.

[0018] According to the above technical solution, the top hinge includes two rows and two columns of Hooke's hinges arranged in a mirror image, and a Hooke's hinge connecting shaft is threadedly connected between the two Hooke's hinges in the same row. The Hooke's hinge connecting shaft is interference fit with the electric cylinder tooling to form a single-degree-of-freedom hinge.

[0019] According to the above technical solution, a single-degree-of-freedom hinge connecting axis is connected between the two Hooke's hinges in the same row, and the axial end of the single-degree-of-freedom hinge is connected to the axial end of another completely identical single-degree-of-freedom hinge through the single-degree-of-freedom hinge connecting axis to form a two-degree-of-freedom hinge.

[0020] According to the above technical solution, the control device also includes an electric control cabinet, a programmable logic controller, a motor servo driver and a data acquisition card, and the electric control cabinet is arranged outside the CNC machine tool.

[0021] A control method for an on-machine loading device for testing the accuracy retention of a machine tool is as follows:

[0022] S1: Install the mechanical loading device;

[0023] S2: Loading force is adjusted to zero;

[0024] S3: Offline training, training the back propagation neural network as the prediction model for model predictive control;

[0025] S4: Use genetic algorithm to solve and obtain the optimal control input;

[0026] S5: gradually increase the random range of random numbers, loop S, calculate the optimal solution by gradually increasing the range of random numbers and input it into the mechanical loading device, and determine whether the termination condition of the loop is reached;

[0027] The control method can compensate for nonlinear factors caused by force deformation and thermal deformation of a machine tool and a loading device during an experiment, improve the control accuracy of the loading device, and has wide applicability.

[0028] Compared with the prior art, the beneficial effects achieved by the present invention are:

[0029] By providing a mechanical loading device and a control device connected to its signal, three-dimensional force loading can be performed on different types of CNC machine tools, so that a specified variable load can be applied to the machine tool while the spindle rotates; at the same time, three-degree-of-freedom movement can be achieved, the structure is simple, and the installation is convenient, which increases the life of the loading device, enhances its loading accuracy, and improves the versatility of the loading device. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The accompanying drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the embodiments of the present invention, they are used to explain the present invention and do not constitute a limitation of the present invention. In the accompanying drawings:

[0031] Figure 1 It is a schematic diagram of the structure of the mechanical loading device of the present invention;

[0032] Figure 2 It is a schematic diagram of the electric cylinder structure connection of the present invention;

[0033] Figure 3 It is a schematic diagram of the mounting base and the kinematic branch chain structure of the present invention;

[0034] Figure 4 is a schematic diagram of the top hinge structure of the present invention;

[0035] Figure 5 It is a schematic diagram of the structure of the loading dynamic platform of the present invention;

[0036] Figure 6 It is a schematic diagram of the overall installation and loading of the loading device of the present invention;

[0037] Figure 7 is a flow chart of the control method of the present invention;

[0038] In the figure: 1. Loading workbench; 2. Mounting base; 3. Motion branch chain; 4. Top hinge; 5. Loading dynamic platform; 6. Machine tool spindle; 7. Pulley; 8. Belt; 9. Screw guide; 10. Servo motor; 11. Electric cylinder; 12. Electric cylinder tooling; 13. Hook's hinge; 14. Hook's hinge connecting shaft; 15. Single-degree-of-freedom hinge connecting shaft; 16. Loading dynamic platform tooling; 17. Three-dimensional force sensor; 18. Tool holder tooling; 19. Machine tool holder; 20. Electric control cabinet. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] For example, see Figure 1 The present invention provides a technical solution: an on-machine loading device for machine tool precision retention test, comprising a loading workbench 1 arranged on a numerically controlled machine tool, a mechanical loading device installed on the loading workbench 1, and a control device connected to the mechanical loading device by signal, the control device being used to control the operating state of the mechanical loading device to effectively perform the machine tool precision retention test;

[0041] The mechanical loading device comprises a mounting base 2, the lower surface of the mounting base 2 is fixed on the loading workbench 1, the upper surface of the mounting base 2 is fixedly connected with a plurality of identical motion branches 3, the upper ends of the plurality of motion branches 3 are movably connected with top hinges 4, the top ends of the top hinges 4 are fixedly connected with loading movable platforms 5 by bolts, and the mounting base 2 and the loading movable platforms 5 are both tooling made of aluminum alloy, such as Figure 1 As shown, preferably, the number of the moving branches 3 and the top hinges 4 are set to 3, and they are distributed at 120° on the horizontal plane. The loading platform 5 can realize movement in three directions of X, Y, and Z. The top middle of the loading platform 5 is connected with a machine tool spindle 6 for performing accelerated degradation loading experiments on accuracy retention.

[0042] refer to Figure 2 as well as Figure 3 The motion branch chain 3 includes an electric cylinder 11, the tail end of the electric cylinder 11 is fixed to the upper surface of the mounting base 2 by welding, and the top end of the electric cylinder 11 is connected to an electric cylinder tooling 12 to achieve connection with the loading platform 5;

[0043] Among them, the electric cylinder 11 includes a screw guide 9 and a servo motor 10, and the output ends of the screw guide 9 and the servo motor 10 are both installed with pulleys 7, and the two pulleys 7 are connected by a belt 8, that is, the servo motor 10 and the screw guide 9 are connected by the belt 8; the upper part of the electric cylinder tooling 12 is set to a through-hole cylindrical shape, and the lower part of the electric cylinder tooling 12 is set to a plate shape. The output end of the screw guide 9 is fixedly connected to the plate surface of the electric cylinder tooling 12 by bolts. By starting the servo motor 10, the output end of the servo motor 10 drives the pulley 7 and the belt 8 to rotate, and the pulley 7 connected to the input end of the screw guide 9 drives the output end of the screw guide 9 to move up and down linearly, thereby driving the electric cylinder tooling 12 to move up and down linearly synchronously.

[0044] refer to Figure 4The top hinge 4 includes two rows and two columns of Hooke's hinges 13 arranged in a mirror image, and a Hooke's hinge connecting shaft 14 is threadedly connected between the two Hooke's hinges 13 in the same row, and the Hooke's hinge connecting shaft 14 is interference-fitted in the cylindrical through-hole interior of the upper half of the electric cylinder tooling 12 to form a single-degree-of-freedom hinge; a single-degree-of-freedom hinge connecting shaft 15 is connected between the two Hooke's hinges 13 in the same row, whereby the shaft end of the single-degree-of-freedom hinge is connected to the shaft end of another identical single-degree-of-freedom hinge through the single-degree-of-freedom hinge connecting shaft 15 to form a two-degree-of-freedom hinge, thereby converting the linear motion of the electric cylinder 11 into translational motion in the three directions of X, Y, and Z;

[0045] The top of the top hinge 4 is fixedly connected with a loading platform fixture 16 by bolts, and the loading platform fixture 16 is fixed to the loading platform 5 by bolts. The top hinge 4 will drive the loading platform 5 to move synchronously through the loading platform fixture 16.

[0046] refer to Figure 5 A groove is provided at the center of the loading movable platform 5, and a tool holder tool 18 is connected to the inside of the groove through a thread and an interference fit. A three-dimensional force sensor 17 is also installed between the tool holder tool 18 and the groove to monitor the three-dimensional force data of the mechanical loading device; a machine tool holder 19 is connected to the inside of the tool holder tool 18 through a thread and an interference fit, and the machine tool holder 19 is connected to the machine tool spindle 6, thereby connecting the mechanical loading device to the CNC machine tool to load the CNC machine tool.

[0047] refer to Figure 6 The servo motor 10 and the three-dimensional force sensor 17 are both part of the control device, and the control device also includes an electric control cabinet 20, which is arranged outside the CNC machine tool;

[0048] The control device includes a programmable logic controller, a motor servo driver and a data acquisition card; the number of motor servo drivers is consistent with the number of motion branches 3; the data acquisition card is connected to a 24V power supply, and the 24V power supply is powered by 220V to 24V DC. The data acquisition card is connected to the signal of the three-dimensional force sensor 17, and is used to transmit the X, Y, and Z direction forces monitored by the three-dimensional force sensor 17 to the computer end;

[0049] The programmable logic controller is connected to the motor servo driver, and controls the motor servo driver to send instructions to the servo motor 10 through the programmable logic controller, thereby controlling the servo motor 10; the encoder is installed inside the servo motor 10 to monitor the motor displacement value in real time;

[0050] A 24V power supply, a programmable logic controller, a servo driver and a data acquisition card are assembled in an electric control cabinet 20. In this embodiment, a detection instruction is input into the programmable logic controller in advance, the motion branch chain 3 performs a corresponding linear motion, and the top hinge 4 converts the linear motion of the motion branch chain 3 into a translational motion in the three directions of X, Y, and Z, thereby loading the CNC machine tool. The three-dimensional force sensor 17 transmits the monitored forces in the three directions of X, Y, and Z to the computer via the data acquisition card, so as to realize the three-dimensional force loading of different types of CNC machine tools, so as to conduct an accelerated degradation loading experiment on the accuracy retention of CNC machine tools.

[0051] Embodiment 2, further based on the above-mentioned on-machine loading device, a control method of the on-machine loading device for machine tool accuracy retention test is as follows:

[0052] S1: Install the mechanical loading device;

[0053] The mechanical loading device is connected to the machine tool spindle 6 through the machine tool handle 19, and is fixed with a clamp by adjusting the position in the Z-axis direction of the CNC machine tool.

[0054] S2: Loading force is adjusted to zero;

[0055] The position of the electric cylinder 11 is adjusted so that the value monitored by the three-dimensional force sensor 17 is the same as before installation, and the three-dimensional force sensor 17 is reset to zero.

[0056] S3: offline training;

[0057] Using the displacement of the electric cylinder 11 as input and the output force of the mechanical loading device in three directions of X, Y and Z as output, the bp neural network is trained as the prediction model of model predictive control, where the full name of the bp neural network is back propagation neural network (Backpropagation Neural Network).

[0058] S4: Solve for the optimal control input;

[0059] Genetic Algorithm is used to solve and obtain the optimal control input; specifically,

[0060] S41, randomly generating a certain number of random numbers, which are random numbers within a specified range, and are used to represent the control input of the mechanical loading device;

[0061] S42, calculating the control output of the random control input using the BP neural network trained offline in S3;

[0062] S43, calculate the fitness value according to the control output. The higher the fitness value, the closer the control output is to the target value. The calculation formula is as follows: fitvalue = 1 / [(yp1 -y t1 ) 2 +(y p2 -y t2 ) 2 +(y p3 -y t3 ) 2 +y p1 2 +y p2 2 +y p3 2 ];

[0063] Among them, fitvalue represents the calculated fitness value, y t1 ,y t2、 y t3 Represents the target output force value in the three directions of X, Y, and Z. p1 ,y p2 ,y p3 Represents the output force values ​​in the X, Y, and Z directions calculated by the prediction model;

[0064] S44, fitvalue comprehensively predicts the difference between the output force value of the model and the target output force value and the value obtained by the output force value of the model itself to obtain the control input with the best fitness value.

[0065] S5: Circulatory regulation;

[0066] Gradually increase the random range of random number generation, indicating the gradual increase of control input;

[0067] The optimal control input calculated by S4 is input into the mechanical loading device as the actual input value, and S4 is looped to gradually increase the range of random numbers, calculate the optimal solution and input it into the mechanical loading device. The difference between the actual monitoring force value and the target output force value is obtained. ( y a1 -y t1) 2 + ( y a2 -y t2) 2 + ( y a3 -y t3) 2 , to determine whether the loop termination condition is reached, where y t1 ,y t2、 y t3 Represents the target output force value in the three directions of X, Y, and Z. a1 ,y a2 ,y a3Represents the actual monitoring force value in the X, Y, and Z directions. If the difference is less than the set value, the control is completed.

[0068] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device 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 device.

[0069] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. An on-machine loading device for testing the accuracy retention of machine tools, characterized in that: include: A loading workbench (1), wherein the loading workbench (1) is arranged on a numerically controlled machine tool; A mechanical loading device, the mechanical loading device being mounted on a loading workbench (1), the mechanical loading device comprising a mounting base (2) fixedly connected to the loading workbench (1), a plurality of identical motion branches (3) fixedly connected to the upper surface of the mounting base (2), a top hinge (4) movably connected to the upper ends of the plurality of motion branches (3), and a loading movable platform (5) fixedly connected to the top of the top hinge (4), a machine tool spindle (6) being connected to the middle of the top of the loading movable platform (5), and a loading movable platform tooling (16) being connected between the top hinge (4) and the loading movable platform (5); A control device, the control device is used to control the operating state of the mechanical loading device, the control device comprises a three-dimensional force sensor (17) for monitoring three-dimensional force data of the mechanical loading device.

2. The on-machine loading device for testing the accuracy retention of machine tools according to claim 1, characterized in that: A groove is formed at the center of the loading platform (5), a tool handle fixture (18) is connected to the interior of the groove, and the three-dimensional force sensor (17) is installed between the tool handle fixture (18) and the groove; A machine tool handle (19) is connected inside the tool handle fixture (18), and the machine tool handle (19) is connected to a machine tool spindle (6).

3. The on-machine loading device for testing the accuracy retention of machine tools according to claim 1, characterized in that: The motion branch chain (3) comprises: An electric cylinder (11), the tail end of the electric cylinder (11) being fixed to the upper surface of the mounting base (2); An electric cylinder tooling (12), the electric cylinder tooling (12) being connected to a top end of an electric cylinder (11), the electric cylinder (11) comprising a lead screw guide rail (9) and a servo motor (10); The output ends of the lead screw guide rail (9) and the servo motor (10) are both equipped with pulleys (7), and a belt (8) is connected between the two pulleys (7) for transmission.

4. The on-machine loading device for testing the accuracy retention of machine tools according to claim 3, characterized in that: The upper part of the electric cylinder fixture (12) is configured as a through-hole cylindrical shape, and the lower part of the electric cylinder fixture (12) is configured as a plate shape; The output end of the lead screw guide rail (9) is fixedly connected to the plate-shaped surface of the electric cylinder tooling (12) by means of bolts.

5. The on-machine loading device for testing the accuracy retention of machine tools according to claim 4, characterized in that: The top hinge (4) comprises two rows and two columns of Hooke's hinges (13) arranged in a mirror image, a Hooke's hinge connecting shaft (14) being threadedly connected between two of the Hooke's hinges (13) in the same row, and the Hooke's hinge connecting shaft (14) being interference-fitted with the electric cylinder tooling (12) to form a single-degree-of-freedom hinge.

6. The on-machine loading device for testing the accuracy retention of machine tools according to claim 5, characterized in that: A single-degree-of-freedom hinge connecting shaft (15) is connected between two Hooke's hinges (13) in the same row, and the shaft end of the single-degree-of-freedom hinge is connected to the shaft end of another completely identical single-degree-of-freedom hinge through the single-degree-of-freedom hinge connecting shaft (15) to form a two-degree-of-freedom hinge.

7. The on-machine loading device for testing the accuracy retention of machine tools according to claim 1, characterized in that: The number of the moving branches (3) and the top hinges (4) is set to 3, and they are distributed at 120 degrees on the horizontal plane.

8. The on-machine loading device for testing the accuracy retention of machine tools according to claim 1, characterized in that: The control device further comprises an electric control cabinet (20), a programmable logic controller, a motor servo driver and a data acquisition card, and the electric control cabinet (20) is arranged outside the numerical control machine tool.

9. The control method of an on-machine loading device for testing the accuracy retention of a machine tool according to claim 1, characterized in that: Here’s how: S1: Install the mechanical loading device; S2: Loading force is adjusted to zero; S3: Offline training, training the back propagation neural network as the prediction model for model predictive control; S4: Use genetic algorithm to solve and obtain the optimal control input; S5: gradually increase the random range of random numbers, loop S4, calculate the optimal solution by gradually increasing the range of random numbers and input it into the mechanical loading device, and determine whether the loop termination condition is reached.

10. The control method of an on-machine loading device for testing the accuracy retention of a machine tool according to claim 9, characterized in that: The specific content of S4 is: S41, randomly generating a certain number of random numbers, which are random numbers within a specified range, and are used to represent the control input of the mechanical loading device; S42, calculating the control output of the random control input using the back propagation neural network trained offline in S3; S43, calculating a fitness value according to the control output, wherein a higher fitness value indicates that the control output is closer to the target value; S44, the fitness value is integrated with the difference between the output force value of the prediction model and the target output force value and the value obtained by the prediction model output force value itself to obtain the control input with the best fitness value.

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