A dual-turntable six-axis machine tool and method of use thereof

Abstract

The application discloses a double-rotary-table type six-axis machine tool and a use method thereof, wherein the double-rotary-table type six-axis machine tool comprises a machine bed, a double-rotary-table and a tool rest arranged on the machine bed; the double-rotary-table comprises a first rotary table rotatably arranged on the machine bed around a main rotary shaft and a second rotary table rotatably arranged on the first rotary table around a secondary rotary shaft; the intersection of the main rotary shaft and the secondary rotary shaft is defined as a pivot point, and the position of the pivot point is fixed; the second rotary table is provided with a three-dimensional linear motion platform; the three-dimensional linear motion platform is provided with a worktable for fixing a workpiece, and is used for driving the workpiece to linearly move along an X-axis, a Y-axis or a Z-axis with the second rotary table as a reference surface; the tool rest is slidably connected with the machine bed, the tool rest is provided with a tool, and the distance between a tool center point of the tool and the pivot point is changed by sliding the tool rest. The application compensates the chord height error of curve machining by using a nonlinear error principle, and can effectively improve the machining precision of a complex curve.

Description

Technical Field

[0001] This invention belongs to the field of machine tool processing technology, and in particular relates to a double rotary table type six-axis machine tool and its usage method. Background Technology

[0002] Five-axis CNC machine tools are essential equipment for machining complex curved surfaces. A five-axis CNC machine tool consists of three translational axes and two rotary axes. Based on the different configurations of the rotary axes, the structural types of five-axis CNC machine tools can be divided into three basic types according to the distribution of the rotary axes: dual-rotation table (double rotary table type), tool and table rotating separately (rotary table with tilting head type), and tool with double tilting (double tilting head type). The distance and relative position between the pivot point of the rotary axis and the tool position point are key factors affecting the machining of curved surfaces. Due to their different configurations, the three typical machine tool configurations described above also have different pivot point-related machining characteristics.

[0003] Double-swivel head machine tools can change the relative position of the pivot point and the workpiece within a certain range, while double-rotary table machine tools, once the workpiece's mounting position on the dual rotary tables is determined, will maintain a fixed relative position between the workpiece and the pivot point throughout the machining process. Without changing the tool, the distance from the tool center point to the pivot point is constant on a double-swivel head machine tool, but a variable on a double-rotary table machine tool, depending on the workpiece's mounting position and orientation relative to the pivot point. This results in the actual tool path's curvature direction and radius differing from the theoretical path.

[0004] For example, Chinese patent document CN107008954A discloses a small dual-rotary-table five-axis CNC milling machine, including a milling machine base, a column, an X-axis moving module, a Y-axis moving module, a Z-axis moving module, a spindle module, an A-axis rotation module, a C-axis rotation module, a retractable dust cover, and a spindle water cooling system; the column is fixedly installed on the milling machine base by a threaded connection; the X-axis moving module is slidably installed on the Y-axis moving module; the Y-axis moving module is fixedly installed on the milling machine base; the Z-axis moving module is fixedly installed on the front side of the column; the A-axis rotation module includes two rotary table bases, an A-axis servo motor, a reducer, a flange coupling, and a U-shaped rotary table; the A-axis rotation module is fixed on the X-axis moving module; the C-axis rotation module includes a C-axis servo motor, a C-axis motor base, and a rotary table.

[0005] Since the actual tool path is a composite motion of the translational and rotational axes, the curvature direction of the composite path always points towards the center of rotation (pivot). However, the curvature direction and radius of curvature of complex surfaces are constantly changing, resulting in a difference between the curvature direction of the actual tool path and the theoretical curvature direction of the workpiece surface. The actual curvature direction at the tool position point may be at an angle to the theoretical curvature direction or collinear but in opposite directions. Furthermore, the actual radius of curvature at the tool position point may differ from the theoretical radius of curvature. This leads to theoretical errors between the actual tool path and the theoretical curve of the surface, severely affecting the machining quality and accuracy of the surface. Summary of the Invention

[0006] To overcome the shortcomings of existing technologies, this invention provides a dual-rotor type six-axis machine tool and its usage method. By utilizing the principle of nonlinear error to compensate for the chord height error in curve machining, the machining accuracy of complex curved surfaces can be effectively improved.

[0007] A six-axis machine tool with a double rotary table includes a bed and a double rotary table and a tool post mounted on the bed;

[0008] The dual rotary tables include a first rotary table rotatably mounted on the bed about a main rotation axis and a second rotary table rotatably mounted on the first rotary table about a secondary rotation axis; the intersection of the main rotation axis and the secondary rotation axis is defined as the pivot point, and the position of the pivot point is fixed.

[0009] The second rotary table is equipped with a three-dimensional linear motion platform; the three-dimensional linear motion platform is equipped with a worktable for fixing the workpiece, which is used to drive the workpiece to move linearly along the X-axis, Y-axis or Z-axis with the second rotary table as the reference plane;

[0010] The tool holder is slidably connected to the bed, and the tool holder is equipped with a cutting tool. The distance between the cutting center point and the pivot point of the cutting tool can be changed by sliding the tool holder.

[0011] This invention changes the position of the three-dimensional linear motion platform in the motion chain, thereby changing the relative position of the workpiece and the pivot point and controlling the bending direction of the actual tool trajectory. This allows nonlinear errors to be used to compensate for the chord height error in surface machining.

[0012] Furthermore, the primary rotation axis and the secondary rotation axis are coplanar and perpendicular to each other.

[0013] Furthermore, the three-dimensional linear platform includes an X-axis assembly slidably mounted on a second rotary table, a Y-axis assembly slidably mounted on the X-axis assembly, and a Z-axis assembly slidably mounted on the Y-axis assembly, with the worktable fixed on the Z-axis assembly.

[0014] Alternatively, the aforementioned dual-rotor type six-axis machine tool may be a vertical, horizontal, or inclined machine tool structure.

[0015] Preferably, the first and second rotating platforms are hemispherical structures, with the first rotating platform fitted over the outer side of the second rotating platform. Other shapes or structures may also be used in specific applications.

[0016] In this invention, the relative positional relationship and relative distance between the workpiece tool position point and the pivot point are changed by a three-dimensional linear platform, so that the radius of curvature corresponding to the tool position point on the actual tool trajectory and the tool position point on the theoretical tool trajectory are equal in size and have the same curvature direction.

[0017] This invention adjusts nonlinear errors through a variable rotation radius. Specifically, the tool rotation radius affects the nonlinear error. Compensating for chord height errors using nonlinear errors requires not only that the directions be the same but also that the magnitude of the nonlinear error is appropriate. The nonlinear error must be matched with the chord height error; it is not necessarily better to be as small or as large as possible. When the radius of curvature of the tool path is small, reducing the tool rotation radius can effectively reduce the nonlinear error; when the radius of curvature of the tool path is large, increasing the tool rotation radius can effectively increase the nonlinear error. A method of using a dual-rotor-type six-axis machine tool includes the following steps:

[0018] S1, Fix the workpiece on the worktable;

[0019] S2, the first rotary table drives the second rotary table, the three-dimensional linear motion platform, and the workpiece to rotate around the main rotation axis; the second rotary table drives the three-dimensional linear motion platform and the workpiece to rotate around the secondary rotation axis; the X-axis component of the three-dimensional linear motion platform drives the Y-axis component, the Z-axis component, and the workpiece to translate along the X-axis direction; the Y-axis component drives the Z-axis component and the workpiece to translate along the Y-axis direction; the Z-axis component drives the workpiece to translate along the Z-axis direction; the tool holder drives the tool to translate linearly along the direction approaching or away from the pivot point.

[0020] S3, since the pivot point is fixed, the relative position of the workpiece and the pivot point is changed by the translational motion of the three-dimensional linear motion platform, so that the vector from the tool point to the pivot point and the curvature direction of the tool point are in the same direction.

[0021] The installation posture of the workpiece is changed by rotating the first rotary table and the second rotary table, so that the tool axis vector at the tool position point is collinear with the tool axis.

[0022] By changing the distance from the tool center point to the pivot point by the tool holder, the vector from the tool point to the pivot point is made to be in the same direction as the curvature direction of the tool point. The distance from the tool point to the pivot point is equal to the radius of curvature corresponding to the tool point.

[0023] S4. The curvature direction and radius of curvature of the tool position point are obtained from the tool position file of the workpiece, thereby determining the position of the pivot point corresponding to the tool position point relative to the workpiece and the distance from the tool center point to the pivot point.

[0024] S5 generates the actual machining trajectory through the combined motion of the translational motion of the three-dimensional linear motion platform, the rotational motion of the first and second rotary tables, and the translational motion of the cutting tool.

[0025] In step S3, when the machine tool size limitation prevents the distance from the tool position point to the pivot point from reaching the surface curvature radius, the maximum distance from the tool position point to the pivot point of the machine tool is used to adapt to the surface curvature radius.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] In traditional dual-rotor machine tools, the workpiece is directly connected to the two rotary tables. After the workpiece is clamped, the relative positional relationship between the workpiece and the pivot point remains fixed. Compared with the traditional dual-rotor configuration, the machine tool proposed in this invention adds a translational axis (i.e., a three-dimensional linear motion platform) between the workpiece and the two rotary tables. This allows the relative positional relationship and relative distance between the workpiece tool position point and the pivot point to be changed according to actual needs. As a result, the direction and distance from the tool position point to the pivot point on the actual tool trajectory are the same as the curvature direction and the curvature radius corresponding to the tool position point on the theoretical tool trajectory.

[0028] By adjusting the rotation radius, nonlinear errors can be mitigated. When the curvature directions are the same, the actual tool path and the theoretical curve path of the surface have the same bending direction, thus the nonlinear error can be used to compensate for the chord height error. Therefore, theoretically, the chord height error is reduced, and machining accuracy is improved. Attached Figure Description

[0029] Figure 1 This is a schematic diagram of the overall structure of the dual rotary table type six-axis machine tool in an embodiment of the present invention;

[0030] Figure 2 This is a schematic diagram of the bed of a dual rotary table type six-axis machine tool in an embodiment of the present invention;

[0031] Figure 3 This is a schematic diagram of the first rotary table of a dual-rotor type six-axis machine tool in an embodiment of the present invention;

[0032] Figure 4 This is a schematic diagram of the second rotary table of a dual-rotary-table six-axis machine tool in an embodiment of the present invention;

[0033] Figure 5 This is a schematic diagram of the three-dimensional linear motion platform of a dual-rotor-type six-axis machine tool in an embodiment of the present invention.

[0034] Figure 6 This is a schematic diagram of the cutting tool of a dual rotary table type six-axis machine tool in an embodiment of the present invention;

[0035] Figure 7 This is a schematic diagram of nonlinear error;

[0036] Figure 8 This is a schematic diagram of the machining principle of a dual rotary table type six-axis machine tool in an embodiment of the present invention.

[0037] In the diagram: 1-Z-axis assembly, 2-Y-axis assembly, 3-X-axis assembly, 4-second rotary table, 5-first rotary table, 6-bed, 61-bed base, 62-bed column, 7-tool post, P-pivot point, 8-tool, B-main rotary axis, C-secondary rotary axis. Detailed Implementation

[0038] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be noted that the embodiments described below are intended to facilitate the understanding of the present invention and do not constitute any limitation thereof.

[0039] like Figure 1 As shown, a six-axis machine tool with a double rotary table includes a bed 6 and a double rotary table and a tool post 7 mounted on the bed 6.

[0040] The dual rotary tables include a first rotary table 5 rotatably mounted on the bed 6 about the main rotary axis B and a second rotary table 4 rotatably mounted on the first rotary table 5 about the secondary rotary axis C; the main rotary axis B and the secondary rotary axis C are orthogonal (i.e., perpendicular to each other and intersecting), and their intersection point is defined as pivot point P, the position of pivot point P is fixed.

[0041] like Figure 2 As shown, the bed 6 mainly includes a bed base 61 for mounting the double rotary table and a bed column 62 for mounting the tool post 7.

[0042] like Figure 3 and Figure 4 As shown, in this embodiment, both the first rotating platform 5 and the second rotating platform 4 are hemispherical structures, and the first rotating platform 5 is fitted outside the second rotating platform 4. The first rotating platform 5 is rotatably installed in the hemispherical groove of the bed base 61. In specific applications, other shapes or structures can also be used, and it is not limited to a hemispherical structure.

[0043] The second rotary table 4 is equipped with a three-dimensional linear motion platform; the three-dimensional linear motion platform is equipped with a worktable for fixing the workpiece, which is used to drive the workpiece to move linearly along the X-axis, Y-axis or Z-axis with the second rotary table 4 as the reference plane.

[0044] As one implementation method, such as Figure 5 As shown, the three-dimensional linear platform includes an X-axis assembly 3 slidably mounted on a second rotary table, a Y-axis assembly 2 slidably mounted on the X-axis assembly 3, and a Z-axis assembly 1 slidably mounted on the Y-axis assembly 2. The worktable is fixed on the Z-axis assembly 1. In this embodiment, sliding is achieved through the cooperation of a sliding groove and a slider, and is driven by a motor and a lead screw.

[0045] In practical applications, there are no restrictions on the specific structure of the three-dimensional linear platform. Other structures and transmission methods besides those in this embodiment can also be used. Furthermore, the installation order of the X, Y, and Z axes is not limited to this embodiment.

[0046] The tool post 7 is slidably connected to the bed 6. The tool post 7 is equipped with a cutting tool 8. The distance between the center point of the cutting tool 8 and the pivot point P can be changed by sliding the tool post 7. The structure of the cutting tool 8 is as follows: Figure 6 As shown.

[0047] In this embodiment of the invention, the dual rotary table type six-axis machine tool has a vertical structure. In specific applications, other machine tool structures such as horizontal and inclined types can also be used.

[0048] In this embodiment, the method of using the dual rotary table type six-axis machine tool includes the following steps:

[0049] S1, Fix the workpiece on the worktable;

[0050] S2, the first rotary table 5 drives the second rotary table 4, the three-dimensional linear motion platform, and the workpiece to rotate around the main rotation axis B; the second rotary table 4 drives the three-dimensional linear motion platform and the workpiece to rotate around the secondary rotation axis C; the X-axis assembly 3 in the three-dimensional linear motion platform drives the Y-axis assembly 2, the Z-axis assembly 1, and the workpiece to translate along the X-axis; the Y-axis assembly 2 drives the Z-axis assembly 1 and the workpiece to translate along the Y-axis; the Z-axis assembly 1 drives the workpiece to translate along the Z-axis; the tool holder 7 drives the tool 8 to translate linearly along the direction close to or away from the pivot point P.

[0051] S3, since the position of pivot point P is fixed, the relative positional relationship between the workpiece and pivot point P is changed by the translational motion of the three-dimensional linear motion platform, so that the vector from the tool position point to pivot point P and the curvature direction of the tool position point are in the same direction.

[0052] The installation posture of the workpiece is changed by rotating the first rotary table 5 and the second rotary table 4, so that the tool axis vector at the tool position point is collinear with the tool axis.

[0053] By changing the distance from the tool center point to the pivot point P by the tool holder 7, the vector from the tool position point to the pivot point P is in the same direction as the curvature direction of the tool position point, and the distance from the tool position point to the pivot point P is equal to the radius of curvature corresponding to the tool position point.

[0054] S4. Calculate the curvature direction and radius of curvature of the tool position point using the tool position file of the workpiece, and then calculate the position of the pivot point P corresponding to the tool position point relative to the workpiece and the distance from the tool center point to the pivot point P.

[0055] S5 generates the actual machining trajectory through the combined motion of the translational motion of the three-dimensional linear motion platform, the rotational motion of the first rotary table 5 and the second rotary table 4, and the translational motion of the tool 8.

[0056] This invention can make the curvature direction of the actual tool path and the theoretical curve match, and the curvature direction of the actual tool path and the theoretical tool path between adjacent tool positions is approximately the same, and the bending direction of the actual tool path and the theoretical tool path is the same, so that the nonlinear error can be used to compensate for the chord height error.

[0057] This invention can also make the distance from the tool point to the pivot point match the curvature radius of the curved surface tool point. When the distance from the tool point to the pivot point cannot reach the curvature radius of the curved surface due to the limitation of the machine tool size, the maximum distance from the tool point to the pivot point of the machine tool is used to match the curvature radius of the curved surface.

[0058] like Figure 7 The diagram illustrates nonlinear error. Due to the addition of the rotary axis in a five-axis machine tool, the actual tool trajectory of the combined motion of the translational and rotary axes is a spatial curve. Existing tool trajectory planning algorithms use chord height error as a constraint to determine the tool position on the same tool trajectory. The distance from the theoretical machining trajectory to the theoretical straight line is the chord height error. When the curvature directions of the actual tool trajectory and the theoretical machining trajectory are the same (e.g., ...), ... Figure 7 Nonlinear error can be used to compensate for chord height error, but when the direction is opposite, it will increase the machining error.

[0059] like Figure 8 As shown, in this invention, during actual machining, the X-axis assembly 3 drives the combined motion of the Y-axis assembly 2, Z-axis assembly 1, tool holder 7, main rotary axis 5, and secondary rotary axis 4, so that the vector from the tool position point to the pivot point is the same as the curvature direction of the tool position point, the distance from the tool position point to the pivot point is approximately equal to the radius of curvature of the tool position point, and the tool axis vector of the tool position point is collinear with the tool axis.

[0060] The embodiments described above provide a detailed explanation of the technical solutions and beneficial effects of the present invention. It should be understood that the above descriptions are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, additions, and equivalent substitutions made within the scope of the principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A six-axis machine tool with a dual rotary table, characterized in that, Includes a bed (6) and a double rotary table and a tool holder (7) mounted on the bed (6); The dual rotary tables include a first rotary table (5) rotatably mounted on the bed (6) about a main rotary axis (B) and a second rotary table (4) rotatably mounted on the first rotary table (5) about a secondary rotary axis (C); the intersection of the main rotary axis (B) and the secondary rotary axis (C) is defined as the pivot point (P), and the position of the pivot point (P) is fixed; both the first rotary table (5) and the second rotary table (4) are hemispherical structures, and the first rotary table (5) is fitted outside the second rotary table (4); The second rotary table (4) is provided with a three-dimensional linear motion platform; the three-dimensional linear motion platform is provided with a worktable for fixing the workpiece, which is used to drive the workpiece to move linearly along the X-axis, Y-axis or Z-axis with the second rotary table (4) as the reference plane; The tool holder (7) is slidably connected to the bed (6). The tool holder (7) is equipped with a tool (8). By sliding the tool holder (7), the distance between the tool center point and the pivot point (P) of the tool (8) can be changed. The relative position relationship and relative distance between the tool position point and the pivot point (P) of the workpiece can be changed by the three-dimensional linear platform, so that the radius of curvature corresponding to the tool position point on the actual tool trajectory and the tool position point on the theoretical tool trajectory are equal in size and have the same curvature direction.

2. The six-axis machine tool with dual rotary tables according to claim 1, characterized in that, The primary rotation axis (B) and the secondary rotation axis (C) are coplanar and perpendicular to each other.

3. The six-axis machine tool with dual rotary tables according to claim 1, characterized in that, The three-dimensional linear platform includes an X-axis assembly (3) that can be slidably mounted on a second rotary table (4), a Y-axis assembly (2) that can be slidably mounted on the X-axis assembly (3), and a Z-axis assembly (1) that can be slidably mounted on the Y-axis assembly (2). The worktable is fixed on the Z-axis assembly (1).

4. The six-axis machine tool with dual rotary tables according to claim 1, characterized in that, The aforementioned dual-rotor type six-axis machine tool has a vertical, horizontal, or inclined machine tool structure.

5. The method of using the dual rotary table type six-axis machine tool according to any one of claims 1 to 4, characterized in that, Includes the following steps: S1, Fix the workpiece on the worktable; S2, using the first rotary table (5) to drive the second rotary table (4), the three-dimensional linear motion platform and the workpiece to rotate around the main rotation axis (B); using the second rotary table (4) to drive the three-dimensional linear motion platform and the workpiece to rotate around the secondary rotation axis (C); using the X-axis assembly (3) in the three-dimensional linear motion platform to drive the Y-axis assembly (2), the Z-axis assembly (1) and the workpiece to translate along the X-axis direction; using the Y-axis assembly (2) to drive the Z-axis assembly (1) and the workpiece to translate along the Y-axis direction; using the Z-axis assembly (1) to drive the workpiece to translate along the Z-axis direction; using the tool holder (7) to drive the tool (8) to translate linearly along the direction close to or far from the pivot point (P); S3, since the position of the pivot point (P) is fixed, the relative positional relationship between the workpiece and the pivot point (P) is changed by the translational motion of the three-dimensional linear motion platform, so that the vector from the tool position point to the pivot point (P) and the curvature direction of the tool position point are in the same direction. The installation posture of the workpiece is changed by rotating the first rotary table (5) and the second rotary table (4), so that the tool axis vector at the tool position point is collinear with the tool axis. By changing the distance from the center point of the tool (8) to the pivot point (P) by the tool holder (7), the vector from the tool point to the pivot point (P) and the curvature direction of the tool point are in the same direction, and the distance from the tool point to the pivot point (P) is equal to the radius of curvature corresponding to the tool point. S4. The curvature direction and radius of curvature of the tool position point are obtained from the tool position file of the workpiece, thereby determining the position of the pivot point (P) corresponding to the tool position point relative to the workpiece and the distance from the tool center point to the pivot point (P). S5 generates the actual machining trajectory through the combined motion of the translational motion of the three-dimensional linear motion platform, the rotational motion of the first rotary table (5) and the second rotary table (4), and the translational motion of the cutting tool (8).

6. The method of using the dual rotary table type six-axis machine tool according to claim 5, characterized in that, In step S3, when the machine tool size limitation causes the distance from the tool position point to the pivot point (P) to be unable to reach the size of the surface curvature radius, the maximum distance from the tool position point to the pivot point (P) of the machine tool is used to adapt to the size of the surface curvature radius.

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