A macro-micro driving rotation system with large load and a performance analysis method thereof

Abstract

The application discloses a large-load macro-micro driving rotary system and a performance analysis method thereof, and belongs to the technical field of the large-load macro-micro driving rotary system, which comprises a workbench, a rotary table bearing, a micro rotary mechanism, a direct drive motor, a shell and a base, the inner ring top of the rotary table bearing is fixedly connected to the bottom of the workbench, the rotary table bearing adopts a single-row four-point contact rotary bearing, the output end of the micro rotary mechanism is fixedly connected to the bottom of the inner ring, the motor shaft of the direct drive motor is fixedly connected to the input end of the micro rotary mechanism, the shell has a containing cavity, the containing cavity contains the micro rotary mechanism and the direct drive motor, the upper end of the shell is fixedly connected to the bottom of the outer ring of the rotary table bearing, and the base is fixedly connected to the bottom of the shell and the direct drive motor. The single-row four-point contact rotary bearing is adopted as the axial supporting structure of the macro-micro driving system, so that the problem that the macro-micro driving rotary system cannot run under the large-load (greater than 1000N) working condition can be solved.

Description

Technical Field

[0001] This invention relates to the field of macro-micro drive rotary equipment technology, specifically to a large-load macro-micro drive rotary system for a CNC rotary table, and also to a method for analyzing the axial load performance of a large-load macro-micro drive rotary system. Background Technology

[0002] The CNC rotary table is a crucial component of a five-axis machining center, and its positioning accuracy directly impacts the ultra-precision machining accuracy of multi-axis (four-axis and above) CNC machine tools. Five-axis machining centers with sub-arcsecond positioning accuracy can be applied to the ultra-precision machining of high-end equipment components such as aero-engine blades, microlens arrays, semiconductor substrates, and thin-walled parts. Therefore, achieving sub-arcsecond positioning on the CNC rotary table is extremely important. Because the minimum pulse of the rotary table motor is affected by factors such as step angle, microstepping, and encoder resolution, even at the maximum microstepping, the minimum angular displacement corresponding to a single minimum pulse movement exceeds 3″, making it impossible to independently achieve sub-arcsecond positioning.

[0003] Macro-micro drive system is a dual drive system in which a macro-motion system provides a large stroke and a micro-motion system compensates for the motion error of the macro-motion system. It has attracted widespread attention because of its advantages that traditional single drive methods cannot match. Many scholars have used macro-micro drive technology to solve the problem of large stroke and high precision. The literature “Sun H, Qiao Y, Zhang Z, et al. Research on geometric error compensation of ultra-precision turning-milling machine tool based on macro–micro composite technology[J]. The International Journal of Advanced Manufacturing Technology, 2024, 132(1): 365-374(Research on geometric error compensation of ultra-precision turning-milling machine tool based on macro-micro composite technology[J]. International Journal of Advanced Manufacturing Technology” proposed geometric error compensation of ultra-precision turning-milling machining center based on macro-micro drive technology, and achieved micron-level machining accuracy. The literature “Yang M, Li L, Zhang C, et al. Research on continuous error compensation of a sub-arc-second macro / micro dual-drive rotary system[J]. Micromachines,2022, DOI:10.3390 / mi13101662(Sub-arc-second macro / micro dual-drive rotary system continuous error compensation[J]. Micromachines)” designed a sub-arc-second macro / micro dual-drive rotary system with a positioning accuracy of sub-arc-second (0.1″). The literature “Chen H, Li L, Li R, et al. Design and Analysis of a Long-Stroke and High-Precision Positioning System for Scanning Beam Interference Lithography[J]. Electronics, 2023”, DOI:10.3390 / electronics12244960 (Design and Analysis of Long-Stroke High-Precision Positioning System: Scanning Beam Interference Lithography [J]. Electronics) A macro-micro dual-drive positioning system based on a dual-frequency laser interferometer as the position reference was developed, achieving a long stroke of 1800 mm and nanometer-level positioning accuracy.

[0004] In macro-micro drive systems, the micro-motion system is driven by a higher-precision micro-actuator, such as a piezoelectric ceramic actuator. This can compensate for positioning errors at the arcsecond level, thus overcoming the positioning accuracy limitations inherent in CNC rotary tables and achieving sub-arcsecond positioning. However, CNC rotary tables require high longitudinal load-bearing capacity when used in multi-axis machining centers. The macro motors in macro-micro drive systems have limited driving force and cannot handle large loads (greater than 1000N), limiting their applications to small-load fields such as precision positioning and inspection. To apply macro-micro drive systems to CNC rotary tables, the issue of high load capacity needs to be addressed. Summary of the Invention

[0005] The technical problem to be solved by this invention is to provide a large-load macro-micro drive rotary system and its performance analysis method, so as to solve the problem of large loads restricting the motion of the macro-micro drive rotary system when the CNC rotary table is working.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: a large-load macro-micro drive rotary system, used to withstand loads of over 1000N. The macro-micro drive rotary system can achieve sub-arcsecond positioning and carry a 1000N load for machining. The overall structure includes a worktable, a rotary table bearing, a micro-motion rotary mechanism, a direct drive motor, a housing, and a base. The top of the inner ring of the rotary table bearing is fixedly connected to the bottom of the worktable. The rotary table bearing adopts a single-row four-point contact rotary bearing. The output end of the micro-motion rotary mechanism is fixedly connected to the bottom of the inner ring. The motor shaft of the direct drive motor is fixedly connected to the input end of the micro-motion rotary mechanism. The housing has an accommodating cavity, which accommodates the micro-motion rotary mechanism and the direct drive motor. The upper end of the housing is fixedly connected to the bottom of the outer ring of the rotary table bearing. The base is fixedly connected to the bottom of both the housing and the direct drive motor.

[0007] Furthermore, the aforementioned micro-motion rotary mechanism includes a pair of fixed bodies, a pair of rotating bodies, a movable body, and a piezoelectric ceramic actuator; the pair of fixed bodies are fixedly connected to the motor shaft of the direct drive motor via an input connector; the pair of rotating bodies are fixedly connected to the bottom of the inner ring via an output connector; the movable body is disposed within the intermediate space enclosed by the pair of rotating bodies and the pair of fixed bodies; wherein, a plurality of flexible hinges are provided between the fixed bodies and the movable body, and between the movable body and the rotating body; the piezoelectric ceramic actuator is installed in the inner cavity of the movable body and can drive the movable body to move, and after the movable body moves, it drives the rotating body to rotate via the hinges.

[0008] Furthermore, the aforementioned single-row four-point contact slewing bearing includes a ball bearing, an inner ring, and an outer ring.

[0009] Furthermore, a cylindrical intermediate rotating body is fixedly connected to the bottom of the aforementioned rotating body, and a circular grating is installed at the lower end of the intermediate rotating body.

[0010] Furthermore, the aforementioned large-load macro-micro drive rotary system also includes a pressure sensor, a force application device, and a zero-adjustment screw. A positioning groove is provided in the middle of the upper side of the output connector, and the pressure sensor is installed in the positioning groove. The inner ring of the turntable bearing is fixedly connected to the upper connector. The zero-adjustment screw is vertically screwed to the middle of the upper connector and its lower end abuts against the pressure sensor. Rotating the zero-adjustment screw can zero the pressure sensor. The force application device is installed above the worktable and is used to apply an axial load to the middle of the worktable. The pressure sensor is used to measure the axial load applied to the worktable.

[0011] Furthermore, the aforementioned force application device includes a gantry frame and a loading screw. The lower ends of the two columns of the gantry frame are fixedly connected to the base. The loading screw is vertically spirally connected to the middle of the crossbeam of the gantry frame. The lower end of the loading screw can contact the center of the worktable to apply axial load. Under the action of torque, the loading screw rotates and squeezes the worktable. The worktable contacts the measuring surface of the pressure sensor through the lower end of the zero-adjustment screw of the rotating shaft. The contact between the two is detected by the pressure display.

[0012] A performance analysis method for a large-load macro-micro drive rotary system includes an axial load performance experimental analysis method. The axial load performance experimental analysis method is as follows: a torque wrench is used to apply torque to the loading screw to simulate the axial input load on the macro-micro drive rotary platform. Different torques are applied to the loading screw by the torque wrench to simulate axial input loads of 250N-1500N. The pressure sensor measurement value is the force of the axial input load on the macro-micro drive system. The pressure sensor measurement value obtained in this experiment is then compared with the force calculated by Hertz contact stress theory and the force analyzed by finite element analysis for error.

[0013] Furthermore, if the specification of the loading screw is M10, then the relationship between the torque required for the loading screw and the force is shown in equation (12):

[0014] ,

[0015] In the formula, M is the applied torque; K is the torque coefficient; F is the axial input load; and d is the nominal diameter of the screw.

[0016] The beneficial effects of the present invention are as follows: Compared with the prior art, the present invention has the following advantages:

[0017] (1) This invention proposes a macro-micro drive rotary system based on a single-row four-point contact slewing bearing. Through load performance analysis of the macro-micro drive rotary system, the designed single-row four-point contact slewing bearing serves as the axial support structure of the macro-micro drive system. This can solve the problem of the macro-micro drive rotary system being unable to operate under heavy load (greater than 1000N) conditions, providing theoretical support for sub-arcsecond positioning of CNC turntables under heavy load. Moreover, the direct drive motor, micro-motion rotary mechanism, and the inner ring of the slewing bearing are fixed, and the inner ring will transfer the force to the outer ring. The direct drive motor and micro-motion rotary mechanism are not affected by any axial load, making the drive more stable and reliable.

[0018] (2) Based on Hertzian contact theory and finite element analysis, the Hertzian contact theory calculation values ​​on the inner and outer raceways are 4118.2 MPa and 3880.64 MPa, respectively, while the maximum contact stress values ​​in the finite element analysis are 4381.1 MPa and 4239.4 MPa. The difference between the two values ​​is 6% and 8.46%, respectively. The slewing bearing has good load-bearing performance under an axial load of 450 kN, which proves that the designed slewing bearing has excellent load-bearing performance under large loads and meets the design requirements.

[0019] (3) Through theoretical, finite element and experimental analysis of the load performance of the macro-micro drive rotary system under large load, the finite element results show that under axial input load of 250-1500N, the maximum force exerted by the large load on the macro-micro drive rotary system is only 2.0753×10. -5 N, and its force accounts for the largest proportion of 1.45 × 10 N. -6 Meanwhile, under axial input load performance tests of 250-1500N, the results show that the maximum force exerted on the macro-micro drive rotary system is only 9.88N, and its force accounts for a maximum of 0.69%. The research results verify the effectiveness and precision of the slewing bearing as a structural element for bearing large axial loads in the macro-micro drive system. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the macro-micro drive rotary system.

[0021] Figure 1 In the middle, 1. worktable, 4. micro-motion rotary mechanism, 5. input connector, 6. direct drive motor, 7. base, 10. piezoelectric ceramic actuator, 11. intermediate rotating body, 13. precision circular grating, 14. gasket;

[0022] Figure 2 This is a schematic diagram of the working principle of a macro-micro drive rotary system.

[0023] Figure 3 Diagram of the control structure of the macro-micro drive rotary system;

[0024] Figure 4 Diagram of the mechanical model of the system under combined loads;

[0025] Figure 5 This is a structural diagram of a single-row four-point contact slewing bearing;

[0026] Figure 6 This is a three-dimensional model diagram of a single-row four-point contact slewing bearing;

[0027] Figure 7 A schematic diagram illustrating the working principle of a large-load macro-micro drive rotary axial support;

[0028] Figure 7 In the middle, 1. worktable, 2. ball, 3. output connector, 4. micro-motion rotary mechanism, 5. connector, 6. direct drive motor, 7. base, 8. inner ring, 9. outer ring, 10. piezoelectric ceramic actuator, 11. intermediate rotating body, 12. outer shell, 13. precision circular grating;

[0029] Figure 8 This is a cross-sectional view showing the contact contour dimensions of the inner and outer raceways of the slewing bearing.

[0030] Figure 9 Mesh generation diagram for a 1 / 30 scale slewing bearing model;

[0031] Figure 10 This is a detailed mesh diagram of the outer raceway contact area.

[0032] Figure 11 This is a contour map of the contact stress in the inner raceway.

[0033] Figure 12 This is a contour map of the contact stress of the outer raceway.

[0034] Figure 13 This is an equivalent stress profile contour plot;

[0035] Figure 14 This is a force analysis diagram of a slewing bearing model;

[0036] Figure 15 The diagram shows the mesh generation of the 3D model; in the diagram, (a) shows the overall model mesh generation, and (b) shows the mesh refinement of the inner raceway model.

[0037] Figure 16 Set up a diagram for the force measurement surface;

[0038] Figure 17 Figure 1 shows the load performance test results of a large-load macro-micro drive rotary system.

[0039] Figure 18 The figures show the finite element and experimental analysis results of the axial support structure; in the figure, (a) the load value under finite element analysis, (b) the load value under experimental analysis, (c) the percentage of the load value under finite element analysis, and (d) the load value under experimental analysis. Detailed Implementation

[0040] The present invention will be further explained and described below with reference to the accompanying drawings to enable those skilled in the art to better understand it.

[0041] Example 1: As Figure 1-7 As shown, a large-load macro-micro drive rotary system includes a worktable 1, a turntable bearing, a micro-motion rotary mechanism 4, a direct drive motor 6, a housing 12, and a base 7. The top of the inner ring 8 of the turntable bearing is fixedly connected to the bottom of the worktable 1. The turntable bearing 8 adopts a single-row four-point contact rotary bearing. The output end of the micro-motion rotary mechanism 4 is fixedly connected to the bottom of the inner ring 8. The motor shaft of the direct drive motor 6 is fixedly connected to the input end of the micro-motion rotary mechanism 4. The housing 12 has an accommodating cavity that accommodates the micro-motion rotary mechanism 4 and the direct drive motor 6. The upper end of the housing 12 is fixedly connected to the bottom of the outer ring 9 of the turntable bearing. The base 7 is fixedly connected to the bottom of both the housing 12 and the direct drive motor 6.

[0042] The macro-micro drive rotary system is a dual-drive system consisting of a macro drive system and a micro drive system, such as... Figure 1 As shown, the macro-motion system provides large-stroke motion, while the micro-motion system compensates for the motion error of the macro-motion system. High-precision large-stroke rotary motion can be achieved through macro-micro linkage. The structure of the macro-micro drive rotary system is as follows: Figure 1 As shown, the macro motion system mainly consists of a direct drive motor 6, a motor driver, and a controller. The direct drive motor 6 outputs torque to drive the entire system to achieve a 360° large-stroke rotary motion. The micro motion system consists of a micro motion rotary mechanism 4, a piezoelectric ceramic actuator 10, and a controller. The micro motion rotary mechanism 4, designed based on the guiding principle and transmission conversion principle of a flexible hinge, can convert the linear displacement input by the piezoelectric ceramic actuator 10 into a rotary displacement output, thereby achieving error compensation for the macro motion system. The input connector 5 rigidly connects the direct drive motor 6 and the micro motion rotary mechanism 4. The worktable 1 is the positioning worktable of the system. The precision circular grating 13 performs progress detection and feedback for the system.

[0043] The working principle of the macro-micro drive rotary system is as follows: Figure 2As shown, the macro-motion system and the micro-motion system are independent of each other, each driven by its own motor, and the motion control of the macro and micro-motion systems is achieved by a PMAC (Programmable Multi-Axis Controller). When the PMAC controller inputs control signals to the macro and micro-motion systems respectively, the specific working principle of the system is as follows: the direct-drive motor and macro driver realize the internal closed-loop control of the macro-motion and drive the system to perform large-stroke rotary motion; the piezoelectric ceramic actuators (PZT) and micro driver realize the internal closed-loop control of the micro-motion and drive the micro-motion rotary mechanism to achieve the conversion of linear displacement to angular displacement, improving the positioning accuracy of the system; the output of the rotary motion of the precision circular grating is detected and fed back to the PMAC controller, where the control calculation of the macro-micro motion ratio is completed, and then distributed to the macro and micro drivers to achieve closed-loop control of the entire system.

[0044] The macro-micro drive rotary system adopts a threshold switching control strategy, and its control scheme is as follows: Figure 3 As shown, the direct-drive motor first moves with the target angle as a reference command. A precision circular grating detection system outputs and feeds back the rotation angle. When the actual angle of the system and the target position meet the threshold, the micro-motion system uses the tracking error as input to perform positioning compensation, thereby achieving precise positioning of the system.

[0045] The structure and driving principle of the micro-motion rotary mechanism 4 are the same as those of the micro-motion rotary mechanism in Chinese Patent Publication No. CN102501226B. It includes a pair of fixed bodies, a pair of rotating bodies, a moving body, and a piezoelectric ceramic actuator 10. The pair of fixed bodies are fixedly connected to the motor shaft of the direct drive motor 6 through the input connector 5. The pair of rotating bodies are fixedly connected to the bottom of the inner ring 8 through the output connector 3. The moving body is set in the middle space enclosed by the pair of rotating bodies and the pair of fixed bodies. Multiple flexible hinges are set between the fixed bodies and the moving body, and between the moving body and the rotating body. The piezoelectric ceramic actuator 10 is installed in the inner cavity of the moving body and can drive the moving body to move. After the moving body moves, it drives the rotating body to rotate through the hinge. The operating principle of this mechanism is prior art and will not be described in detail.

[0046] Load Performance Analysis of Macro-Micro Drive Rotary System: Based on the actual machining conditions of the CNC rotary table, a composite load mechanical model of the macro-micro drive rotary system considering both load and cutting load conditions is constructed, as follows: Figure 4 As shown, the loads in the vertical and other directions of the system under load and cutting force are analyzed. Where G is the workpiece weight, F is the cutting force, and Fo is the cutting force. x For the horizontal component of the cutting force, F yThe vertical component of the cutting force and M represent the motor driving torque. Loads in the non-vertical direction are borne by the direct-drive motor's driving torque, while large vertical loads are borne by the system's high-load structure. However, if the large vertical load exceeds the direct-drive motor's axial force bearing capacity, it will affect the normal operation of the macro-micro drive rotary system. Therefore, for large vertical loads (i.e., longitudinal loads greater than 1000N), an axial support structure needs to be designed to bear the load of the macro-micro drive rotary system through a slewing bearing. This avoids the macro-micro drive rotary system directly bearing the large load, effectively improving the overall system load condition and ensuring stable operation under high-load conditions.

[0047] Slewing bearings are widely used in the core components of large, heavy-duty rotating equipment. Single-row four-point contact slewing bearings, compared to other types, have a simpler structure and a larger axial load capacity. Therefore, to address the axial load problem of macro-micro drive slewing systems under high load (greater than 1000N) conditions, single-row four-point contact slewing bearings are adopted as the axial support structure for macro-micro drive slewing systems.

[0048] The design requirements for a single-row four-point contact slewing bearing in terms of dimensions and structure are that its inner ring is connected to the output end of the micro-motion slewing mechanism, and its outer ring is fitted to the outer casing. The main structural parameters of the slewing bearing are shown in Table 1, and the materials, Poisson's coefficient μ, and elastic modulus E of the inner and outer rings and rolling balls are shown in Tables 2 and 3. Figure 5-6 As shown. The three-dimensional model of a single-row four-point contact slewing bearing is as follows. Figure 6 As shown.

[0049]

[0050]

[0051] The working principle of large-load macro-micro drive rotation with the introduction of axial support structure is as follows: Figure 7 As shown. The direct-drive motor 6 provides large-stroke rotary motion, while the micro-motion rotary mechanism 4, under the action of a piezoelectric ceramic actuator, compensates for the motion error of the direct-drive motor. The input connector 5 connects the direct-drive motor 6 and the micro-motion rotary mechanism 4 in series, and the output connector 3 connects the micro-motion rotary mechanism 4 and the inner ring 8 of the slewing bearing in series. The outer casing 12 provides fixed support for the outer ring 9 of the slewing bearing, and the base 7 provides fixed support for the entire system. The output torque of the macro-micro drive rotary system drives the inner ring 8 of the slewing bearing to achieve rotary motion through the output connector 3; the output platform is the worktable 1, which is connected to the inner ring 8 of the slewing bearing.

[0052] The single-row four-point contact slewing bearing in the large-load macro-micro drive rotary system mainly consists of three parts: rolling balls 2, inner ring 8, and outer ring 9. The specific working principle of the axial support is as follows: The worktable bears the axial load F. a (F) aThe vertical component of the workpiece gravity G and the cutting force F y When the sum of the forces (Q, Q, and F) is applied, the upper raceway and 30 evenly distributed rolling balls in the inner ring 8 of the slewing bearing generate a normal force Q of the same magnitude at the contact point (along the contact angle θ). The rolling balls, in turn, exert a reaction force of the same magnitude but opposite direction on the inner raceway at the contact point. According to the principle of force balance, the rolling balls exert a force of the same magnitude on the lower raceway in the outer ring 9 of the slewing bearing at its contact point. Simultaneously, the reaction force F exerted by the lower raceway in the outer ring 9 on the rolling balls balances the axial load F. a The generated positive pressure Q. Since the outer shell 12 is the fixed support for the outer ring of the slewing bearing, the outer shell 12 and the outer ring 9 together bear the force exerted by the rolling balls on the lower raceway of the outer ring.

[0053] In order to achieve accurate measurement of rotation angle and error compensation, a cylindrical intermediate rotating body 11 is fixedly connected to the bottom of the rotating body. A circular grating 13 is installed at the lower end of the intermediate rotating body 11. The inverted setting improves the stability of the precision circular grating by lowering the center of gravity.

[0054] To enable loading tests, the aforementioned large-load macro-micro drive rotary system also includes a pressure sensor 14, a force application device 15, and a zero-adjustment screw 16. In this case, the connection between the output connector 3 and the inner ring 8 is replaced with a connection between the pressure sensor 14, the zero-adjustment screw 16, the upper connector 17, and the output connector 3. The outer casing 12 is replaced with a higher one, or a shim is added between the top surface of the outer casing and the outer ring to match the required height. A positioning groove 301 is provided in the middle of the upper side of the output connector 3, and the pressure sensor 14 is installed in the positioning groove 301. The inner ring 8 of the turntable bearing is fixedly connected to the upper connector 17, and the zero-adjustment screw 16 is vertically spirally connected to the middle of the upper connector 17 with its lower end abutting against... The zero-adjustment screw 16 on the pressure sensor 14 can be rotated to zero the pressure sensor 14. The force application device 15 is installed above the worktable 1 to apply an axial load to the middle of the worktable 1. The pressure sensor 14 is used to measure the axial load applied to the worktable 1. First, by rotating the zero-adjustment screw, its lower end is pressed against the pressure sensor. When the pressure sensor shows zero, it indicates that the inner ring is just in contact with the output connector. After zeroing, the upper connector and the output connector are pressed together. The axial load is applied to the worktable by the force application device, and the pressure sensor feeds back the axial load data to verify the influence of the bearing capacity change of the slewing bearing on the axial force of the micro-motion slewing mechanism 4. Specifically, the force application... Device 15 includes a gantry frame 1501 and a loading screw 1502. The lower ends of the two columns of the gantry frame 1501 are fixedly connected to the base 7. The loading screw 1502 is vertically spirally connected to the middle of the crossbeam of the gantry frame 1501. The lower end of the loading screw 1502 can contact the center of the worktable 1 to apply axial load. Under the action of torque, the loading screw 1502 rotates and presses the worktable. The worktable contacts the measuring surface of the pressure sensor through the lower end of the zero-adjustment screw on the rotating shaft. The contact between the two is detected by the pressure display. A precision torque wrench is used to connect the loading screw to apply torque to simulate the axial input load on the macro-micro drive rotary platform. Under the action of torque, the lower end of the zero-adjustment screw contacts the pressure sensor. The force sensor measures the surface contact, and the contact between the two is detected by the pressure display. The zero-adjustment screw can avoid interference fit between the pressure sensor and the upper connector. The upper connector is designed with a threaded hole structure. The pre-tightening of the zero-adjustment bolt ensures contact with the pressure sensor without interference fit. Alternatively, the output connector can be directly replaced with two thin plates, the thickness of which is less than that of the output connector 3, namely the upper thin plate and the lower thin plate. The lower thin plate has a groove in the middle and serves as the output connector. The upper thin plate is fixedly connected to the inner ring, and the zero-adjustment screw is spirally connected in the middle of the upper thin plate. In this case, it is not necessary to replace the outer shell or add shims to raise the outer shell to meet the requirements. The loading screw 1502 applies torque through the torque wrench 17.

[0055] Example 2: A performance analysis method for a large-load macro-micro drive rotary system includes an axial load performance experimental analysis method. The axial load performance experimental analysis method is as follows: a torque wrench is used to apply torque to the loading screw to simulate the axial input load on the macro-micro drive rotary platform. Different torques are applied to the loading screw by the torque wrench to simulate axial input loads of 250N-1500N. The pressure sensor measurement value is the force of the axial input load on the macro-micro drive system. The pressure sensor measurement value obtained in this experiment is then compared with the force calculated by Hertz contact stress theory and the force analyzed by finite element analysis for error.

[0056] Hertzian contact stress analysis of slewing bearings includes theoretical analysis of Hertzian contact stress and finite element analysis:

[0057] 1) Hertzian contact stress theory analysis

[0058] The contact problem of slewing bearings directly affects their load-bearing capacity. Hertzian contact theory is a necessary theory for analyzing slewing bearing contact, and Hertzian contact stress theory analysis is particularly necessary. This application focuses on the axial high-load support structure of a macro / micro-drive slewing system, using the designed NGSBM-310-170-50 single-row four-point contact slewing bearing as the research object. The contact stress, i.e., the load-bearing capacity, of this slewing bearing under axial force is studied. A relatively large axial load value Fa of 450,000 N is selected in the static load curve for load-bearing capacity analysis to ensure that the slewing bearing has good load-bearing performance under high load conditions.

[0059] Based on Hertzian contact theory, two spheres in an ideal, unloaded contact state contact at a single point. However, under normal pressure Q, the contact point area becomes a contact surface and is elliptical. Therefore, this paper analyzes a single-row four-point contact slewing bearing using the point contact problem in classical Hertzian contact theory, assuming that a and b are the major and minor semi-axles of the elliptical contact area, and the maximum contact pressure is... The major semi-axis a and minor semi-axis b of the contact area are shown in equations (1), (2) and (3):

[0060] ,

[0061] ,

[0062] ,

[0063] In the formula , E1 and E2 are the Poisson's ratios of the materials of the ball and the inner and outer raceways, respectively; E1 and E2 are the elastic moduli of the materials of the ball and the inner and outer raceways, respectively. α is the maximum contact stress; Q is the normal force; α and β are the Hertzian contact coefficients. The curvature is the sum of the curvatures of the two contacting objects. The Hertzian contact coefficients α and β of the elliptical contact region need to be obtained from Table 3 by combining the principal curvature function F(ρ), and then the contact stress is calculated.

[0064]

[0065] Under axial load, the 30 evenly distributed rolling balls on the slewing bearing bear the same load. The contact profile dimensions of the inner and outer raceways of the slewing bearing are as follows: Figure 8 As shown, point Point 1 is the center of the raceway. Point A is located on the central axis of the entire slewing bearing model. and The points are the center points of curvature of the raceway profiles in regions a and b of the outer ring. and Let point be the center point of the curvature of the raceway profile in the inner c and d regions, and point... and All of them pass through the center point of the raceway And on the contact line formed by the contact angle θ, similarly, point and The position is on another contact line. At the contact point between the rolling ball and the inner raceway region c, the normal force Q and the radius of curvature of the inner raceway are... Radius of curvature of the inner raceway in the normal direction of the contact surface The calculation formulas are as follows (4), (5) and (6), and the relevant dimensions at the contact point of the outer ring can be obtained in the same way.

[0066] ,

[0067] ,

[0068] ,

[0069] Among them, point All of them pass through the center point of the raceway The distance between the origin and the contact line formed by the contact angle θ As shown in equation (7), the other three curvature centers are similar.

[0070] ,

[0071] The formulas for calculating the curvature of the rolling ball in principal plane 1, the curvature of the rolling ball in principal plane 2, the curvature of the inner raceway circumferential section in principal plane 1, and the curvature of the inner raceway in principal plane 2 are shown in Equation (8). Among them, principal plane 1 is the plane formed by the contact point of the rolling ball and the inner raceway circumferential section passing through region c, and principal plane 2 is the plane formed by the rolling ball and the inner raceway along the contact angle θ direction passing through region c. The curvature of the convex surface is positive, and the curvature of the concave surface is negative.

[0072] ,

[0073] The sum of the principal curvatures of the ball and the inner raceway at the point of contact is

[0074] ,

[0075] The principal curvature function F(ρ) of the inner raceway is

[0076] ,

[0077] Combining equations (8), (9), and (10), the principal curvature function F(ρ) of the inner raceway can be obtained, and the Hertzian contact coefficient of the inner raceway can be obtained by linear interpolation from Table 2. and Hertzian contact coefficient of outer raceway and The calculation process for the outer raceway and the inner raceway is the same. Combining formulas (1), (2), and (3), we can solve for the major semi-axis a, the minor semi-axis b, and the elliptical area of ​​the contact region. and maximum contact stress σ max As shown in Table 4.

[0078]

[0079] According to the principle of force balance, the force exerted on the inner and outer raceways by the ball is the same. However, due to the difference in the contact area between the inner and outer rings, the contact stress on the inner ring is greater than that on the outer ring.

[0080] 2) Finite element analysis of Hertzian contact stress

[0081] Since the overall analysis and calculation of a single-row four-point contact slewing bearing is quite large, and the effects of fillets, screw holes, and spacers are ignored, a portion of the overall model, representing one-thirtieth of the contact model between the rolling ball and the inner and outer raceways, is used for mesh generation and contact stress simulation.

[0082] Before performing static contact finite element analysis on a single-row four-point contact slewing bearing, preprocessing of the model is required. Hypermesh software is used for hexahedral mesh generation with a mesh size of 5mm. The overall mesh generation is as follows: Figure 9 As shown. Because the slewing bearing has a portion of its inner and outer rings in contact with the rolling balls under axial force, to ensure the accuracy of the contact area calculation results, the mesh size is made smaller than the minor axis b calculated by Hertz theory (0.7043 mm). The mesh for the contact area of ​​the inner and outer rings is refined to 0.1 mm. The refined contact area is shown below. Figure 10 As shown, the total number of unit nodes is 1,340,879, and the total number of units is 1,302,246.

[0083] Before solving, import the generated mesh .inp file into Ansys Workbench and add contact settings and load constraints. Set the frictional contact between the upper half of the inner raceway and the lower half of the outer raceway and the ball, with a friction coefficient of 0.15, and keep the rest at default settings. Add a remote displacement constraint to the upper surface of the inner ring, retaining only the degree of freedom in the direction perpendicular to the upper surface of the inner ring, and setting the displacement to 0.02 mm, while setting the displacement in the other two directions to 0. Add an axial load of 21.27 MPa to the upper surface of the inner ring, and add a fixed support constraint to the outer ring. In post-processing, add equivalent (Von-Mises) stress and contact tools to analyze the contact surface of the inner and outer raceways.

[0084] Inner raceway contact stress cloud Figure 11 The maximum contact stress of the inner raceway is shown to be 4381.1 MPa, and the maximum contact stress of the outer raceway is shown to be... Figure 12 The maximum contact stress on the outer ring is shown to be 4239.4 MPa. Table 6 summarizes the Hertzian contact theory calculations and finite element analysis values. The Hertzian contact theory calculations and finite element analysis values ​​for the inner and outer raceways differ by 6% and 8.46% respectively, both within 10%. The main reason for this difference is that the Hertzian contact theory is based on ideal conditions, which differs from actual conditions. Furthermore, the finite element model is simplified, and the number of mesh elements also affects the results. Equivalent stress profile. Figure 13 The image shows the equivalent stress profile of the slewing bearing model. The maximum equivalent stress is 2627.3 MPa, which occurs 0.3 mm to 0.4 mm below the inner ring contact surface. However, during the manufacturing of slewing bearings, the hardened layer depth on the raceway surface is generally required to be greater than 3 to 5 mm. Therefore, the location of the maximum stress obtained by finite element analysis differs significantly from 3 to 5 mm.

[0085]

[0086] Based on Hertzian contact theory and finite element contact stress analysis, the results show that the designed slewing bearing can meet the strength requirements under an axial load of 450,000 N and has good load-bearing performance. Furthermore, since external load and contact stress are directly proportional, the smaller the external load, the smaller the contact stress. Since the actual operating conditions of the macro-micro drive slewing system are much smaller than 450,000 N, the contact stress of the slewing bearing under the actual system operating conditions is also much smaller than that under these conditions, thus increasing the service life of the slewing bearing.

[0087] Therefore, the slewing bearing designed in this application can meet the design requirements as an axial large load support structure for macro-micro drive slewing systems.

[0088] The axial load performance analysis methods include the following:

[0089] 1) Theoretical analysis of system axial load

[0090] When the large-load macro-micro drive rotary system is subjected to a vertical load F only, the axial force acting on the upper surface of the inner ring of the 1 / 30 slewing bearing model is F / 30, which causes a normal pressure to be generated in the contact area between the inner ring and the rolling ball. Because each ball is the same size and evenly distributed, the normal force exerted by each ball on the contact area with the upper surface of the inner race is the same. Under the interaction of forces, the forces exerted by the balls on the inner and outer raceways are equal in magnitude and opposite in direction, such as... Figure 14 As shown. Among them, and The action and reaction forces between the rolling ball and the inner raceway. and The forces and reactions between the rolling balls and the outer raceway are given. The force analysis expression for the entire slewing bearing is shown in equation (11):

[0091] ,

[0092] According to the principle of force balance, under the action of load F and the resultant force F1 of 30 rolling balls in the vertical direction, force balance is formed. The outer raceway bears the large load applied to the upper surface of the inner race, while the force exerted by the lower surface of the inner race on the macro-micro drive rotary system in the vertical direction is theoretically 0. This enables the macro-micro drive rotary system to effectively bear large loads and ensures stable operation of the system under large load conditions.

[0093] 2) Finite element analysis of system axial load: To evaluate the high load-bearing capacity of the slewing bearing for the macro / micro drive slewing system, it is necessary to test the force exerted on the system by the lower surface of its inner ring. Since the outer ring and the outer shell share the axial load transmitted by the ball bearings, and the inner ring is rigidly connected to the system by screws and transmits all the force, the load-bearing effectiveness of the slewing bearing can be determined by applying an axial load to the upper surface of the inner ring and analyzing the force on its lower surface.

[0094] 3) To reduce unnecessary structural analysis and computation, the action of the slewing bearing on the macro-micro rotary platform is simulated. The outer ring of the slewing bearing is fixed and constrained, a load is applied to the upper surface of the inner ring, and the force on the lower surface of the inner ring is measured to analyze its impact on the macro-micro drive rotary system. First, the slewing bearing is meshed with a 3mm tetrahedral mesh, and the inner and outer raceways and rolling balls are refined with a 1mm mesh, such as... Figure 15As shown. Next, friction settings were applied to the inner and outer raceways and the contact area of ​​the balls, with a friction coefficient set to 0.15; the rest was controlled by the program. Finally, a full displacement constraint was added to the outer ring, and a remote displacement and axial load were added to the upper surface of the inner ring, with the displacement set to 0.02 mm. Considering that the CNC rotary table typically needs to withstand a workpiece load of approximately 1000 N, the initial load was set to 250 N, and the load was gradually increased in 250 N increments to 1500 N, with multiple measurements taken of the force acting on the system.

[0095] During post-processing, a force response tool is added to measure the force exerted by the slewing bearing on the macro / micro drive slewing system. The force measurement surface is as follows: Figure 16 As shown in Table 7, the finite element results indicate that the force exerted on the macro-micro drive rotary system under axial input loads of 250N-1500N increases slowly, and the force measured under a 1500N load is only 2.0753 × 10⁻⁶. -5 N has a negligible effect on the macro-micro drive rotary system.

[0096] Therefore, slewing bearings can effectively bear large loads under operating conditions of 250N-1500N, avoiding damage to macro and micro drive slewing systems.

[0097] Experimental analysis of system axial load performance

[0098] The load-bearing performance test of the macro-micro slewing platform with the introduction of a slewing bearing is crucial to the platform's normal operation under heavy load conditions. Therefore, it is necessary to experimentally verify the load performance of the macro-micro driven slewing platform under actual working conditions. The experimental setup includes a pressure sensor (located inside the outer casing; see [link to specific details]). Figure 17 The equipment includes: force application device, torque wrench, 24V adjustable power supply, large-load macro-micro drive rotary system, pressure display, and the experimental site as follows: Figure 17 As shown.

[0099] Install the pressure sensor between the upper and lower connectors, such as Figure 17 As shown. To avoid an interference fit between the pressure sensor and the upper connector, a threaded hole structure is designed on the upper connector. The pre-tightening of the zero-adjustment screw ensures contact with the pressure sensor without an interference fit.

[0100] This invention uses a precision torque wrench to apply torque, simulating the axial input load on a macro-micro drive rotary platform. The loading screw is M10, and the relationship between the required torque and force for the loading screw is shown in equation (12):

[0101] ,

[0102] Where M is the applied torque; K is the torque coefficient; F is the axial input load; and d is the nominal diameter of the screw. The torque coefficient K is 0.2. Different torques are applied to the screw on the force application device using a precision torque wrench to simulate axial input loads ranging from 250N to 1500N, while the pressure sensor measures the force exerted by the axial input load on the macro-micro drive system.

[0103]

[0104] The load-bearing effectiveness of the axial support structure was analyzed using three research methods: theoretical analysis, finite element method, and experimental analysis. The results are shown in Table 7 and... Figure 18 As shown, under axial input loads of 250N-1500N, the maximum value obtained from the finite element analysis is 2.075×10⁻⁶. -5 N, with a maximum error of 1.45 × 10⁻⁶. -6 The experimental analysis results showed a maximum value of 9.88N and a maximum error of 0.69%.

[0105] Experimental results show that the axial support structure of the large-load macro-micro drive rotary system effectively bears the axial load, greatly reduces the axial load of the system, and ensures that the system can work normally under the large load conditions of the CNC rotary table.

[0106] In summary, this invention addresses the load-bearing capacity problem of macro-micro drive rotary systems under heavy load conditions by proposing an axial support structure design based on a single-row four-point contact slewing bearing. This design solves the application limitations of macro-micro drive rotary systems under heavy load machining conditions on CNC rotary tables. The conclusions are as follows:

[0107] (1) Through load performance analysis of macro-micro drive rotary system, a single-row four-point contact rotary bearing was designed as the axial support structure of macro-micro drive system. It can solve the problem that macro-micro drive rotary system cannot operate under large load (greater than 1000N) conditions, and provide theoretical support for sub-arcsecond positioning of large load CNC rotary table.

[0108] (2) Based on Hertzian contact theory and finite element analysis, the theoretically calculated Hertzian contact values ​​on the inner and outer raceways are 4118.2 MPa and 3880.64 MPa, respectively, while the maximum contact stress values ​​analyzed by the finite element analysis are 4381.1 MPa and 4239.4 MPa. The differences between the two values ​​are 6% and 8.46%, respectively. The slewing bearing exhibits good load-bearing performance under an axial load of 450 kN. This proves that the designed slewing bearing has excellent high-load load-bearing performance and meets the design requirements.

[0109] (3) Through theoretical, finite element and experimental analysis of the load performance of the macro-micro drive rotary system under large load, the finite element results show that under axial input load of 250-1500N, the maximum force exerted by the large load on the macro-micro drive rotary system is only 2.0753×10.-5 N, and its force accounts for the largest proportion, which is 1.45 × 10 N. -6 Meanwhile, under axial input load performance tests of 250-1500N, the results show that the maximum force exerted on the macro-micro drive rotary system is only 9.88N, and its force accounts for a maximum of 0.69%. The research results verify the effectiveness and precision of the slewing bearing as a structural element for bearing large axial loads in the macro-micro drive system.

Claims

1. A large-load macro-micro drive rotary system, characterized in that, For use in applications requiring loads exceeding 1000N, including: Workbench (1); Turntable bearing, the turntable bearing adopts a single-row four-point contact slewing bearing, the single-row four-point contact slewing bearing includes a ball (2), an inner ring (8) and an outer ring (9). As the slewing bearing is under the action of axial force, a part of the inner ring and the outer ring are in contact with the ball. The top of the inner ring (8) of the turntable bearing is fixedly connected to the bottom of the worktable (1). A micro-motion rotary mechanism (4) is provided, the output end of which is fixedly connected to the bottom of the inner ring (8); A direct drive motor (6) has its motor shaft fixedly connected to the input end of the micro-motion rotary mechanism (4); The outer casing (12) has a cavity for accommodating the micro-motion rotary mechanism (4) and the direct drive motor (6). The upper end of the outer casing (12) is fixedly connected to the bottom of the outer ring (9) of the turntable bearing. The base (7) is fixedly connected to the bottom of the outer shell (12) and the direct drive motor (6); The micro-motion rotary mechanism (4) includes: A pair of fixed bodies are fixedly connected to the motor shaft of the direct drive motor (6) via an input connector (5); A pair of rotating bodies are fixedly connected to the bottom of the inner ring (8) via an output connector (3); A movable body, which is disposed within the intermediate space enclosed by a pair of the rotating bodies and a pair of the fixed bodies; Among them, multiple flexible hinges are provided between the fixed body and the moving body, and between the moving body and the rotating body; A piezoelectric ceramic actuator (10) is installed in the inner cavity of the moving body and can drive the moving body to move. After the moving body moves, it drives the rotating body to rotate through the hinge. A cylindrical intermediate rotating body (11) is fixedly connected to the bottom of the rotating body, and a circular grating (13) is installed at the lower end of the intermediate rotating body (11).

2. The large-load macro-micro drive rotary system according to claim 1, characterized in that, It also includes a pressure sensor (14), a force application device (15), and a zero-adjustment screw (16). A positioning groove (301) is provided in the middle of the upper side of the output connector (3). The pressure sensor (14) is installed in the positioning groove (301). The inner ring (8) of the turntable bearing is fixedly connected to the upper connector (17). The zero-adjustment screw (16) is vertically spirally connected to the middle of the upper connector (17) and its lower end abuts against the pressure sensor (14). The zero-adjustment screw (16) can be rotated to zero the pressure sensor (14). The force application device (15) is installed above the worktable (1) and is used to apply an axial load to the middle of the worktable (1). The pressure sensor (14) is used to measure the axial load applied to the worktable (1).

3. The large-load macro-micro drive rotary system according to claim 2, characterized in that, The force application device (15) includes a gantry frame (1501) and a loading screw (1502). The lower ends of the two columns of the gantry frame (1501) are fixedly connected to the base (7). The loading screw (1502) is vertically spirally connected to the middle of the crossbeam of the gantry frame (1501). The lower end of the loading screw (1502) can contact the center of the workbench (1) to apply axial load.

4. The control method for a large-load macro-micro drive rotary system according to claim 3, characterized in that, The method is as follows: a torque wrench is used to apply torque to the loading screw to simulate the axial input load on the macro-micro drive rotary platform. Different torques are applied to the loading screw by the torque wrench to simulate axial input loads of 250N-1500N. The pressure sensor measurement value is the force of the axial input load on the macro-micro drive system. The measured pressure sensor value is then compared with the force calculated by Hertz contact stress theory and the force analyzed by finite element analysis for error.

5. The control method for a large-load macro-micro drive rotary system according to claim 4, characterized in that, If the loading screw is M10, the relationship between the required torque and force for the loading screw is as follows: （12）， In the formula, M is the applied torque; K is the torque coefficient; F is the axial input load; and d is the nominal diameter of the screw.

Images