A method for confirming the virtual center position of an ultra-precision machine tool based on straight groove cutting.

Abstract

This invention relates to a method for confirming the virtual center position of an ultra-precision machine tool based on straight groove cutting. The workpiece and a diamond turning tool are fixed on the C-axis and B-axis of the ultra-precision machine tool, respectively. The workpiece is turned to eliminate Z-axis tool setting errors. After tool setting is completed using a tool setter, the initial virtual center position is recorded, and the diamond turning tool is controlled to plan the first straight groove. The virtual center function is activated, and the B-axis is rotated by an angle α, controlling the diamond turning tool to plan the second straight groove. Then, the B-axis rotation angle is adjusted to -2α, controlling the diamond turning tool to plan the third straight groove. The depth of the three straight grooves is measured along the Z-axis and recorded. The angle θ between the initial virtual center, the actual virtual center, and the B-axis rotation center, as well as the distance L' from the actual virtual center to the B-axis rotation center, are calculated to confirm the position of the actual virtual center. When machining complex feature structures, this invention can greatly improve the efficiency of toolpath programming, effectively reduce machining path deviations, and improve the surface quality of ultra-precision machining.

Description

Technical Field

[0001] This invention relates to the field of ultra-precision machining technology, and in particular to a method for confirming the virtual center position of an ultra-precision machine tool based on a straight groove. Background Technology

[0002] Ultra-precision machining technology is an advanced, high-precision processing and manufacturing technology, primarily used to produce parts and components with nanoscale surfaces, high precision, and ultra-fine structures. This technology is widely applied in aerospace, military, medical, electronics, and optics fields. Currently, for high-precision, difficult-to-machine optical structural components, the application of virtual centers on multi-axis ultra-precision machine tools has become an indispensable part of ultra-precision machining. It can expand the machining capabilities of machine tools, improve their accuracy and stability, simplify machine tool operation and programming, and realize multi-axis linkage and collaborative machining. Specifically, the virtual center can precisely control its relative position to the workpiece, allowing it to rotate while its relative coordinates with the workpiece remain unchanged. Furthermore, ultra-precision machining based on virtual centers enables the machine tool to automatically compensate for the offset distances of the Y and Z axes when the tool rotates freely around its tip center point, ensuring the tool's cutting position on the workpiece remains unchanged, and preventing additional interference between the tool and workpiece. This allows for the completion of complex surface machining and helical machining in a single operation, eliminating the need for multiple tool settings and workpiece disassembly, thus guaranteeing machining accuracy.

[0003] The virtual center position of a machine tool is a crucial factor affecting ultra-precision machining; improper setting can lead to severe dimensional deviations in curved surface or helical machining. Confirming the virtual center position typically involves the following steps: First, confirm the initial position of the virtual center, which may have some deviation. Then, calculate the positional deviation after rotation of the virtual center. Finally, set the actual coordinates of the virtual center to the virtual center position parameter system, ultimately confirming the virtual center position of the ultra-precision machine tool. Currently, traditional methods mainly include the tool setting method and the trial cut observation method. The tool setting method uses CDD camera imaging technology to detect the virtual center position parameters. Real-time imaging is displayed by the camera, capturing images of the target position. The tool setting device is then moved along the machine tool guideway to further confirm the virtual center position. The trial cut observation method first sets an arbitrary virtual center position and then performs a trial cut. The operator then controls the rotary table to rotate the B-axis at multiple angles and performs a trial cut on the workpiece surface. The deviation between the trial cut position and the initial position is then observed to calculate the virtual center offset. This process continues until it is subjectively judged that there is no deviation between the trial cut position and the initial position, i.e., the Y-axis displacement caused by rotating the B-axis is equal to the compensation value of the virtual center. The current tool tip center position is then regarded as the location of the virtual center.

[0004] While the effectiveness of traditional methods for confirming the virtual center position of ultra-precision machine tools has been verified, the following drawbacks remain: 1) The tool setter method relies entirely on the accuracy of the equipment and the experience of the operator, making it dependent on the equipment; 2) The tool setter method is limited by the initial B-axis position accuracy of the machine tool, and the tool setter camera cannot accurately capture the tool edge point, thus making it difficult to achieve sub-micron level virtual center position confirmation; 3) The trial cutting and observation method is limited by the stability of online measurement equipment, making it difficult to measure the cutting depth at the nanometer level, requiring many trial cuts for virtual center position confirmation with low repeatability; 4) The trial cutting and observation method is too cumbersome, and the operation is affected by the operator's experience, easily leading to different results from multiple trial cuts, greatly reducing the accuracy of the virtual center position, which is fatal for ultra-precision multi-axis linkage machining.

[0005] Therefore, it is essential to propose a highly accurate, efficient, and effective method for confirming the virtual center position of a machine tool. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention aims to disclose a method for confirming the virtual center position of an ultra-precision machine tool based on straight groove cutting. When machining complex feature structures, this technology can realize multi-axis linkage and collaborative machining of the machine tool, greatly improve the efficiency of tool path programming, effectively reduce machining path deviation, and ultimately improve the surface quality of ultra-precision machining.

[0007] To achieve the above objectives, the present invention employs the following technical solution:

[0008] S1: The workpiece is fixed on the C-axis of the ultra-precision machine tool by a vacuum chuck, and the diamond turning tool is fixed on the B-axis of the ultra-precision machine tool by a tool post. After the spindle dynamic balance is adjusted by a dynamic balancing machine, the workpiece is turned to eliminate the Z-axis tool setting error. The workpiece material is oxygen-free copper, and both the C-axis and B-axis are high-rigidity air spindles.

[0009] S2: Perform virtual center tool setting using a CCD optical tool setter and record the initial virtual center position.

[0010] S3: Move the diamond cutting tool 10mm away from the workpiece along the negative X-axis, then move the diamond cutting tool a distance -d along the Z-axis, where d is 5μm. Finally, control the diamond cutting tool to move along the X-axis to plan the first straight groove at a feed rate of 500 mm / min.

[0011] S4: Enable the virtual center function of the ultra-precision machine tool. First, move the diamond cutting tool a distance d along the Z-axis, then rotate the B-axis by an angle α in the positive direction, where α is 30°. Then calculate the distance L of the workpiece's compensated movement along the Z-axis. α Calculated L α Represented as ; Recalculate the distance L that the actual virtual center moves along the Z-axis. 34 Calculated L 34 Represented as Then, move the diamond cutting tool along the Z-axis by a distance -d, and then control the diamond cutting tool to move along the X-axis to plan the second straight groove.

[0012] S5: Keep the ultra-precision machine tool virtual center function enabled. First, move the diamond cutting tool a distance d along the Z-axis, then rotate the B-axis by an angle -2α in the negative direction. Then calculate the distance L of the workpiece's compensated movement along the Z-axis. -α Calculated L -α Represented as ; Recalculate the distance L that the actual virtual center moves along the Z-axis. 35 Calculated L 35 Represented as Then, move the diamond cutting tool along the Z-axis by a distance -d, and then control the diamond cutting tool to move along the X-axis to plan the third straight groove.

[0013] S7: Remove the workpiece for cleaning. Along the Z-axis, use a white light interferometer to measure the depths of the first, second, and third straight grooves on a surface measuring device and record them as d3, d4, and d5.

[0014] S8: When rotating at B-axis angles α and -2α, establish a set of equations for the actual virtual center moving along the Z-axis at distances L34 and L35, the workpiece (1) at compensation distances Lα and L-α along the Z-axis, and the depths d3, d4, and d5 of the first straight groove (3), the second straight groove (4), and the third straight groove (5). The specific equation set is as follows:

[0015]

[0016] Substituting the expressions for L34, L35, and Lα, we get:

[0017]

[0018] Solving this system of equations yields the angle θ between the initial virtual center, the actual virtual center, and the rotation center along the B-axis, as well as the distance L' from the actual virtual center to the rotation center along the B-axis. Based on the position coordinates of the initial virtual center, the coordinates Y of the actual virtual center are then set. O’ and Z O’ , represented as:

[0019]

[0020] The beneficial effects of this invention are as follows:

[0021] This invention discloses a method for confirming the virtual center position of an ultra-precision machine tool based on straight groove cutting. First, an optical tool setter is used to initially confirm the virtual center position of the ultra-precision machine tool. Second, a straight groove structure is machined on the workpiece surface using a diamond turning tool. After activating the virtual center function, two straight groove structures are machined on the workpiece surface by rotating it at two different angles, and the groove depth is measured under a white light interferometer. Then, a relationship is established between the groove depth, the actual virtual center compensation distance, and the workpiece compensation distance, thereby obtaining the relationship between the initial virtual center position and the actual virtual center position, ultimately confirming the virtual center position of the ultra-precision machine tool. The proposed method for determining the virtual center by rotating the B-axis and trial-cutting straight grooves is independent of the tool setter's accuracy, resulting in more objective calculations. Secondly, the high-precision white light interferometer measurement accurately obtains the depth of the trial-cut straight grooves, greatly ensuring the reliability of the calculation results, and the measurement process is highly efficient and fast. Furthermore, the proposed method only requires a single trial cut of three straight grooves, making the tool setting process simple and easy to operate, and eliminating the need for multiple workpiece installations, thus avoiding the impact of workpiece installation errors and ensuring high repeatability. Importantly, this method solves the problem of excessively large errors in confirming the virtual center position in traditional methods, leading to extremely low utilization rates. It enables accurate confirmation of the virtual center position on ultra-precision machine tools, greatly improving toolpath programming efficiency and facilitating the machining of complex and special structures. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of steps 1 and 2 in the virtual center position confirmation method for ultra-precision machine tools based on straight grooves provided in an embodiment of the present invention;

[0023] Figure 2 This is a schematic diagram of step 3 in the virtual center position confirmation method for ultra-precision machine tools based on straight grooves provided in an embodiment of the present invention;

[0024] Figure 3 This is a schematic diagram of step 4 in the virtual center position confirmation method for ultra-precision machine tools based on straight grooves provided in an embodiment of the present invention.

[0025] Figure 4 This is a schematic diagram of step 5 in the virtual center position confirmation method for ultra-precision machine tools based on straight grooves provided in an embodiment of the present invention.

[0026] Figure 5 This is a schematic diagram of step 6 in the virtual center position confirmation method for ultra-precision machine tools based on straight grooves provided in an embodiment of the present invention.

[0027] Figure 6 This is a schematic diagram of steps 7 and 8 in the virtual center position confirmation method for ultra-precision machine tools based on straight grooves provided in an embodiment of the present invention;

[0028] Figure 7 This is a schematic diagram of step 9 in the virtual center position confirmation method for ultra-precision machine tools based on straight grooves provided in an embodiment of the present invention.

[0029] In the diagram: 1-Workpiece; 2-Diamond cutting tool; 3-First straight groove; 4-Second straight groove; 5-Third straight groove. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the embodiments and accompanying drawings. The illustrative embodiments and descriptions of this invention are only for explaining this invention and are not intended to limit this invention.

[0031] Example:

[0032] like Figure 1 As shown, S1: Fix workpiece 1 to the spindle of the ultra-precision machine tool using a vacuum chuck, adjust the dynamic balance of the spindle using a dynamic balancing device, and fix the diamond turning tool 2 on the B axis; move the diamond turning tool 2 away from the workpiece along the X axis and rotate the C axis to turn the end face of workpiece 1; after machining, set the corresponding machine tool Z axis coordinate value to zero to eliminate Z axis tool setting error, and lock the C axis after completion, so that workpiece 1 does not rotate.

[0033] like Figure 1 As shown, S2: The virtual center tool setting is completed by the tool setting device, and the initial virtual center position V is determined. Its coordinates are denoted as Y. V and Z V At this point, there is a deviation between the initial virtual center position and the actual virtual center position; the actual virtual center position is denoted as O', and its coordinates are denoted as Y. O’ and Z O’ Let O be the rotation center of the B-axis, L' be the length of OO', L be the length of OV, and θ be the angle ∠O'OV between the initial virtual center, the actual virtual center, and the rotation center of the B-axis.

[0034] like Figure 2 As shown, S3: Move the diamond cutting tool 2 10mm away from the workpiece 1 along the negative X-axis, and then move the diamond cutting tool 2 a distance -d along the Z-axis; move the diamond cutting tool 2 along the X-axis to plan the first straight groove 3, with a planing depth of d3. Note that d3 is equal to d.

[0035] like Figure 3As shown, S4: After the first straight groove 3 is machined, the diamond cutting tool 2 is moved along the Z-axis by d to move it away from the workpiece 1, and then moved a certain distance away from the workpiece 1 along the negative X-axis; the virtual center function is activated, and the B-axis is rotated by an angle α in the positive direction. At this time, the initial virtual center and the actual virtual center will also rotate along the B-axis; the distance the actual virtual center moves along the Z-axis after rotation is expressed as... Then, the diamond cutting tool 2 is moved along the Z-axis to make the machine tool's Z-axis coordinate value change to -d, and then the diamond cutting tool 2 is moved along the X-axis to plan the second straight groove 4.

[0036] like Figure 4 As shown, S5: After the second straight groove 4 is machined, the diamond cutting tool 2 is moved a distance d along the Z-axis to move it away from the workpiece 1, and then moved 10mm away from the workpiece 1 along the negative X-axis; the B-axis is rotated by an angle 2α in the negative direction, and the distance the actual virtual center moves along the Z-axis after the rotation is expressed as... Then, the diamond cutting tool 2 is moved along the Z-axis to make the machine tool's Z-axis coordinate value change to -d, and then the diamond cutting tool 2 is moved along the X-axis to plan the third straight groove 5.

[0037] like Figure 5 As shown, S6: For S4 and S5, during the activation of the virtual center function, the two rotations of the B-axis will cause compensating movements of workpiece 1 along the Y-axis and Z-axis. The two compensating distances of workpiece 1 along the Z-axis are equal, represented as... .

[0038] like Figure 6 As shown, S7: After the third straight groove 5 is machined, retract the machine tool to a safe position, remove the workpiece 1 for cleaning, and perform morphological measurement on the surface measuring equipment. Along the Z-axis, the depths of the first straight groove 3, the second straight groove 4, and the third straight groove 5 are denoted as d3, d4, and d5, respectively.

[0039] like Figure 6 As shown, S8: Along the Z-axis, establish the actual virtual center displacement L in S4 and S5. 34 and L 35 The compensation distance L along the Z-axis of workpiece 1 α The relationship between the depths d3, d4, and d5 of the first straight groove 3, the second straight groove 4, and the third straight groove 5 is expressed as:

[0040] ;

[0041] Substituting the expressions for L34, L35, and Lα, we get:

[0042] ;

[0043] Solving this system of equations yields the angle θ between the initial virtual center, the actual virtual center, and the rotation center along the B-axis, as well as the distance L' from the actual virtual center to the rotation center along the B-axis.

[0044] like Figure 7 As shown, S9: After completing steps S1-S8, based on the initial virtual center's position coordinates Y... V and Z V Set the coordinates Y of the actual virtual center. O’ and Z O’ , represented as:

[0045] ;

[0046] The obtained coordinates can be input into the machine tool virtual center control system to confirm the virtual center position of the ultra-precision machine tool.

[0047] The vacuum chuck used in this invention can fix the workpiece to be processed through air pressure difference. This method has the advantages of simple and convenient operation, high workpiece adsorption stability, and minimal workpiece surface damage. The spindle selected in this invention is a high-rigidity air spindle, which requires high-rigidity air hydrostatic bearings supported by air as a lubricant. Air bearings have characteristics such as low friction, high temperature resistance, and no pollution, and can be used in high-speed spindles, high-precision instruments, and other equipment. The ultra-precision air spindle has extremely high axial, radial, and angular stiffness, and its corresponding natural frequency is relatively large, ensuring processing stability and precision. The dynamic balancing detection device used in this invention is a dynamic balancing instrument, which can detect the magnitude of rotational eccentricity in all 360° directions of the spindle. By adding or removing weight in the corresponding directions, the dynamic balance of the spindle can be precisely adjusted to achieve optimal rotational symmetry. Furthermore, stable dynamic balancing can effectively reduce the inherent vibration and harmonic vibration of the spindle during processing, making the spindle rotation smoother, thereby improving the accuracy and efficiency of ultra-precision machining.

[0048] The material used for workpiece 1 is oxygen-free copper, which is readily available and possesses advantages such as high strength, good toughness and plasticity, suitability for both cold and hot working without deformation, and strong corrosion and oxidation resistance. It is a common material in the field of ultra-precision machining. The diamond turning tool 2 has extremely high hardness and wear resistance, good stability, and ensures machining accuracy and surface finish. The diamond turning tool exhibits stable cutting during machining, and the dimensional changes caused by cutting heat are almost negligible, guaranteeing the quality of the planed straight grooves. In this invention, an optical tool setter is used to confirm the position of the initial virtual center. The optical tool setter uses a high-resolution camera for imaging, offering advantages such as high efficiency and clear image of the tool edge. The cutting depths d of the first straight groove 3, the second straight groove 4, and the third straight groove 5 are the same, aiming to make the theoretical minimum point standard of these three straight grooves the same. The depth difference obtained by the measuring device is the error caused by the actual virtual center position offset. This not only facilitates the acquisition of measurement results but also makes data calculation easier. The measuring device in this invention is a white light interferometer, a non-contact optical ultra-precision measuring instrument. The white light interferometer is based on optical interference technology. It disperses and recombines the light source through a beam splitter prism, which produces alternating bright and dark interference fringes on the photosensitive surface of the CCD camera. By measuring the brightness and position of the interference fringes, the relative height of the workpiece surface can be accurately calculated, thus achieving nanometer-level precision measurement of surface height.

[0049] The above method enables precise confirmation of the virtual center position in ultra-precision machining: First, the proposed method of determining the virtual center by rotating the B-axis and trial-cutting straight grooves does not depend on the accuracy of the tool setter, resulting in more objective calculations. Second, high-precision white light interferometer measurement can accurately obtain the depth of the trial-cut straight grooves, greatly ensuring the reliability of the calculation results, and the measurement process is efficient and fast. Furthermore, the proposed method only requires a single trial cut of three straight grooves, making the tool setting process simple and easy to operate, and eliminating the need for multiple workpiece installations, thus avoiding the influence of workpiece installation errors and achieving high repeatability. Importantly, this method solves the problem of excessive errors in confirming the virtual center position in traditional methods, leading to extremely low utilization rates. It enables accurate confirmation of the virtual center position of ultra-precision machine tools, greatly improving the efficiency of toolpath programming and facilitating the machining of complex and special structures.

[0050] The above are embodiments of the present invention. The above embodiments and specific parameters are only for clearly illustrating the invention verification process and are not intended to limit the patent protection scope of the present invention. The patent protection scope of the present invention shall still be determined by its claims. Similarly, any equivalent structural changes made based on the description and drawings of the present invention shall also be included within the protection scope of the present invention.

Claims

1. A method for confirming the virtual center position of an ultra-precision machine tool based on straight groove cutting, applied to the control center of an ultra-precision machine tool, characterized in that, include: The workpiece (1) is fixed on the C-axis of the ultra-precision machine tool by a vacuum chuck, and the diamond turning tool (2) is fixed on the B-axis of the ultra-precision machine tool by a tool holder. The spindle dynamic balance is adjusted by a dynamic balancing instrument, and the workpiece (1) is turned to eliminate the Z-axis tool setting error. The virtual center tool setting is completed by a tool setting instrument, and the initial virtual center position is recorded. The diamond turning tool (2) is controlled to move along the X-axis to plan the first straight groove (3). The virtual center function of the ultra-precision machine tool is turned on, the B-axis is rotated by an angle α, and the diamond turning tool (2) is controlled to move along the X-axis to plan the second straight groove (4). The virtual center function of the ultra-precision machine tool is turned on, the B-axis is rotated by an angle -2α, and the diamond turning tool (2) is controlled to move along the X-axis to plan the third straight groove (5). The depths d3, d4 and d5 of the first straight groove (3), the second straight groove (4) and the third straight groove (5) are measured and recorded by a white light interferometer. The virtual center tool setting is completed by a tool setting device and the initial virtual center position V is determined. The coordinates of the initial virtual center are recorded as Y. V and Z V At this point, there is a deviation between the initial virtual center position and the actual virtual center position; the actual virtual center position is denoted as O', and its coordinates are denoted as Y. O’ and Z O’ Let the rotation center of the B-axis be O, the length of OO' be L', the length of OV be L, and the angle ∠O'OV between the initial virtual center, the actual virtual center, and the rotation center of the B-axis be θ. Construct a system of equations for the positional deviation between the initial virtual center and the actual virtual center. When the rotation angles of the B-axis are α and -2α, establish the distance L that the actual virtual center moves along the Z-axis. 34 and L 35 The compensation distance L along the Z-axis of the workpiece (1) α and L -α And the system of equations between the depths d3, d4 and d5 of the first straight groove (3), the second straight groove (4) and the third straight groove (5), the system of equations being: ， Solving the system of equations yields the included angle θ and the distance L' from the actual virtual center to the rotation center of the B-axis. Based on the recorded initial virtual center position, the actual virtual center position can then be confirmed. The coordinates of the confirmed actual virtual center are specifically: 。 2. The method as described in claim 1, characterized in that, The C-axis of the ultra-precision machine tool is specifically a high-rigidity air spindle; the B-axis of the ultra-precision machine tool is specifically a high-rigidity air spindle; the tool setter is a CCD optical tool setter; the workpiece (1) is specifically made of oxygen-free copper; the specific feed rate for planing is 500 mm / min.

3. The method as described in claim 1, characterized in that, The control of the diamond cutting tool (2) to move along the X-axis to plan the first straight groove (3) is specifically to move the diamond cutting tool (2) 10mm away from the workpiece (1) along the negative X-axis, then move the diamond cutting tool (2) along the Z-axis by a distance -d, where d is 5μm, and finally move the diamond cutting tool (2) along the X-axis to plan the first straight groove (3).

4. The method as described in claim 1, characterized in that, The B-axis is rotated by an angle α, and the diamond cutting tool (2) is controlled to move along the X-axis to plan the second straight groove (4). Specifically, the diamond cutting tool (2) is first moved a distance d along the Z-axis, and then the B-axis is rotated by an angle α in the positive direction, where α is 30°. Then, the distance L of the compensated movement of the workpiece (1) along the Z-axis is calculated. α Calculated L α Specifically represented as ; Recalculate the distance L that the actual virtual center moves along the Z-axis. 34 Calculated L 34 Specifically represented as Then move the diamond cutting tool (2) a distance -d along the Z-axis, and then control the diamond cutting tool (2) to move along the X-axis to plan the second straight groove (4).

5. The method as described in claim 1, characterized in that, The adjustment of the B-axis rotation angle by -2α and the control of the diamond cutting tool (2) to move along the X-axis to plan the third straight groove (5) are specifically as follows: first, the diamond cutting tool (2) is moved a distance d along the Z-axis, then the B-axis is rotated by an angle of -2α in the negative direction, and then the distance L of the compensated movement of the workpiece (1) along the Z-axis is calculated. -α Calculated L -α Specifically represented as ; Recalculate the distance L that the actual virtual center moves along the Z-axis. 35 Calculated L 35 Specifically represented as Then move the diamond cutting tool (2) a distance -d along the Z-axis, and then control the diamond cutting tool (2) to move along the X-axis to plan the third straight groove (5).

6. The method as described in claim 1, characterized in that, The method of using a white light interferometer to measure and record the depths d3, d4 and d5 of the first straight groove (3), the second straight groove (4) and the third straight groove (5) is as follows: the workpiece (1) is removed and cleaned, and the depths of the first straight groove (3), the second straight groove (4) and the third straight groove (5) are measured on a surface measuring device along the Z-axis and recorded as d3, d4 and d5.

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