An on-site measurement method for the concentricity and thickness uniformity of the inner and outer spherical surfaces of a hemispherical resonator

Abstract

The present invention discloses an on-site measurement method for the concentricity and thickness uniformity of the inner and outer spherical surfaces of a hemispherical resonator. An inductive lever probe and a grinding wheel are provided on the B-axis of a machine tool, and the hemispherical resonator to be measured and / or a standard sphere are provided on the C-axis of the machine tool. The method comprises: using the inductive lever probe in a first and second posture to respectively measure the coordinates of the center of the standard sphere to obtain a coordinate difference ΔC; after the hemispherical resonator to be measured is machined, using the inductive lever probe in the first and second postures to respectively measure the coordinates of the target points on the inner and outer spherical surfaces, and then converting them to the first posture coordinate system based on the coordinate difference ΔC, and then calculating the concentricity of the hemispherical resonator to be measured; using the inductive lever probe in the first and second postures to respectively measure the inner and outer spherical contours, and then converting them to the first posture coordinate system based on the coordinate difference ΔC, and then calculating the thickness distribution of the hemispherical resonator to be measured. The present invention adapts to the inner and outer spherical surface characteristics of the hemispherical resonator, improves the spherical surface measurement accuracy, and realizes the measurement of non-transparent spherical shells.

Description

Technical Field

[0001] The invention relates to the technical field of precision and ultra-precision machining, and in particular to an on-site measurement method for the concentricity and thickness uniformity of the inner and outer spherical surfaces of a hemispherical resonator. Background Art

[0002] The hemispherical resonator gyroscope is one of the most accurate, stable, reliable and longest-lasting inertial sensors in the world. It has broad application prospects in aerospace, aviation, vehicles, ships and other navigation fields. The hemispherical resonator (HRG) anchored by the central rod is the core component of the hemispherical resonator gyroscope. Its structure is as follows: Figure 1 As shown, it is a hemispherical thin-walled shell with a central support rod, with a diameter of usually 15-40 mm, a wall thickness of 1-2 mm, and a fillet radius of about 1 mm.

[0003] The key components of a hemispherical resonator are the inner and outer spheres, requiring high-precision control of sphericity and concentricity. Ultra-precision grinding can improve forming accuracy and reduce machine defects, thus saving time in subsequent polishing. When using a cup grinding wheel to produce spherical surfaces, two different cup grinding wheels are required for the inner and outer spheres, respectively, which can lead to tool setting errors. If a ball-end grinding wheel is used, wheel dressing or replacement can also cause tool setting errors. Tool setting errors can lead to concentricity errors between the inner and outer spheres. Furthermore, regardless of the grinding method used, grinding wheel wear develops during the grinding process, affecting the profile and concentricity of the inner and outer spheres.

[0004] To represent and compensate for tool setup and wear errors in grinding, profile and concentricity must be tested after each grinding cycle. Off-machine measurement introduces secondary clamping errors. In-situ measurement, where the workpiece is measured on the machine after machining, avoids this issue and significantly improves machining efficiency.

[0005] Patent CN112344865A discloses an in-situ measurement system and method for the wall thickness and wall thickness uniformity of a hemispherical resonator. The wall thickness of the hemispherical resonator is measured using a color confocal sensor. The color confocal sensor probe has poor angular adaptability, and the optical axis can only be measured near the normal direction of the spherical surface, resulting in a very limited measurement range.

[0006] Patent CN112729159A discloses a method for detecting the spherical surface shape of a hemispherical resonator, which uses a laser interferometer and a parabolic standard mirror for offline measurement. The construction cost is high, and only a transparent resonator can measure the inner and outer spherical surfaces simultaneously, which places high demands on surface quality. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to realize in-situ measurement of the concentricity and thickness uniformity of the inner and outer spherical surfaces of hemispherical resonators with various surface qualities and to improve the measurement accuracy.

[0008] In response to the technical problems existing in the prior art, the present invention provides an on-site measurement method for the concentricity and thickness uniformity of the inner and outer spherical surfaces of a hemispherical resonator. The method adopts an inductive probe to contact and measure the inner and outer spherical surfaces, which is adaptable to the large curvature and deep concave characteristics of the inner spherical surface. The spherical surface measurement accuracy is at the 0.1μm level, and a unified measurement coordinate system for the inner and outer spherical surfaces of the hemispherical resonator is used to calculate their concentricity and thickness uniformity.

[0009] In order to solve the above technical problems, the technical solution proposed by the present invention is:

[0010] A method for in-situ measurement of the concentricity and thickness uniformity of the inner and outer spherical surfaces of a hemispherical resonator is applied to an in-situ measurement system. The in-situ measurement system includes a machine tool. A first spindle of the machine tool moves linearly along the X-axis of the machine tool coordinate system and rotates along the C-axis of the machine tool coordinate system. A second spindle of the machine tool moves along the Z-axis of the machine tool coordinate system and rotates along the B-axis of the machine tool coordinate system. The hemispherical resonator to be measured and / or a standard ball are mounted on the C-axis of the first spindle, and an inductive lever probe and a grinding wheel are mounted on the B-axis of the second spindle. The method includes the following steps:

[0011] S1) controlling the second spindle to adjust the inductive lever probe to a first posture and a second posture, respectively, and using the inductive lever probe in the first posture and the second posture to measure the coordinates of the center of the standard sphere, respectively, and calculating the coordinate difference ΔC between the first posture coordinate system and the second posture coordinate system based on the measurement results;

[0012] S2) after the hemispherical resonator to be measured is processed, the coordinates of the outer spherical target point of the hemispherical resonator to be measured are measured with the inductive lever probe in a first posture, the coordinates of the inner spherical target point of the hemispherical resonator to be measured are measured with the inductive lever probe in a second posture, and then the coordinates are converted to the first posture coordinate system according to the coordinate difference ΔC, and the concentricity of the hemispherical resonator to be measured is calculated according to the coordinates of the outer spherical target point and the coordinates of the inner spherical target point in the first coordinate system;

[0013] S3) measuring the outer spherical profile of the hemispherical resonator to be measured using the inductive lever probe in a first posture, measuring the inner spherical profile of the hemispherical resonator to be measured using the inductive lever probe in a second posture, and then converting the outer spherical profile and the inner spherical profile in the first posture coordinate system according to the coordinate difference ΔC to obtain the thickness distribution of the hemispherical resonator to be measured by taking the difference between the outer spherical profile and the inner spherical profile in the first coordinate system.

[0014] Furthermore, step S1) includes the following steps:

[0015] S11) Control the B axis of the second spindle to rotate so that the inductive lever probe reaches the first posture, control the C axis of the first spindle to rotate so that the target meridian of the standard ball reaches a preset position, control the first spindle to move along the X axis of the machine tool coordinate system, and control the second spindle to move along the Z axis of the machine tool coordinate system. When the inductive lever probe in the first posture contacts the target point on the target meridian, obtain the corresponding XZC axis displacement as the first coordinate of the target point, and calculate the center coordinate (x cs1 , z cs1 );

[0016] S12) Control the B axis of the second spindle to rotate so that the inductive lever probe reaches the second posture, control the C axis of the first spindle to rotate so that the target meridian of the standard ball reaches the preset position, control the first spindle to move along the X axis of the machine tool coordinate system, and control the second spindle to move along the Z axis of the machine tool coordinate system. When the inductive lever probe in the second posture contacts the target point on the target meridian, the corresponding XZC axis displacement is obtained as the second coordinate of the target point, and the center coordinate (x cs2 , z cs2 );

[0017] S13) Calculate the center coordinates (x cs1 , z cs1 ) and the coordinates of the center of the standard ball in the second posture coordinate system (x cs2 , z cs2 ) is taken as the coordinate difference ΔC between the first posture coordinate system and the second posture coordinate system.

[0018] Furthermore, step S11) and step S12) include the steps of calculating the center coordinates of the standard sphere based on the set of coordinates, specifically including: calculating the eccentricity error of the standard sphere relative to the center line of rotation of the C-axis, adjusting each coordinate in the set of coordinates according to the eccentricity error, and fitting the center coordinates of the standard sphere in the corresponding coordinate system using the least squares method for all adjusted coordinates.

[0019] Furthermore, step S2) includes the step of converting the coordinate system according to the coordinate difference ΔC, specifically including: converting the coordinate Q in the second posture coordinate system j,2 (x j,2 , z j,2 ) minus the coordinate difference ΔC to obtain the corresponding coordinate Q in the first posture coordinate system j,1 (x j,1 , z j,1 ).

[0020] Furthermore, in step S2), the concentricity of the hemispherical resonator to be measured is calculated based on the coordinates of the outer spherical target point and the inner spherical target point in the first coordinate system, specifically comprising: using the least squares method to calculate the outer spherical target point coordinate set P in the first coordinate system i,1 and the inner sphere target point coordinate set Q j,1 Spherical fitting is performed to obtain the best fitting radius and sphere center position of the outer sphere and inner sphere of the hemispherical resonator to be measured, and the concentricity of the outer sphere and inner sphere of the hemispherical resonator to be measured is calculated based on the best fitting radius and sphere center position of the outer sphere and inner sphere.

[0021] Furthermore, step S3) includes the step of measuring the spherical profile with an inductive lever probe, specifically comprising:

[0022] S31) selecting at least two sampling points on a target meridian of the spherical surface, and for each sampling point, moving the inductive lever probe along the Z axis at a first speed from the current sampling point to the vicinity of the next sampling point, and then moving the inductive lever probe along the X axis at a second speed until the inductive lever probe reads zero, and collecting displacement signals along the X axis and the Z axis at this time;

[0023] S32) taking the displacement signals of the X-axis and Z-axis corresponding to each sampling point as the sampling point coordinate measurement value, and returning to step S31) until all sampling points are measured;

[0024] S33) rotating the spherical surface along the C-axis at a constant linear velocity, moving the inductive lever probe to the vicinity of the target latitude to measure the roundness runout;

[0025] S34) Calculating the spherical profile based on the coordinate measurement values ​​of the sampling points on the spherical target meridian and the roundness runout value of the target latitude.

[0026] Furthermore, step S31) specifically includes the following steps:

[0027] S311) calculating the Z-axis coordinate of each sampling point;

[0028] S312) starting from position point 1' corresponding to the current sampling point, moving the second spindle (12) along the Z-axis direction at a first speed so that the inductive lever probe reaches position point 2' corresponding to the Z-axis coordinate of the next sampling point;

[0029] S313) fixing the second spindle (12) and moving the first spindle (11) along the X-axis at a first speed so that the inductive lever probe approaches the next sampling point until the inductive lever probe moves a preset distance relative to the next sampling point to position point 3';

[0030] S314) moving the first spindle (11) along the X-axis direction at a second speed so that the inductive lever probe continues to approach the next sampling point until the reading returned by the inductive lever probe is zero, and collecting the Z-axis displacement of the second spindle (12) corresponding to the position point 4' of the inductive lever probe at the next sampling point, and the X-axis displacement of the first spindle (11);

[0031] S315) moving the first spindle (11) along the X-axis at a first speed so that the inductive lever probe moves away from the next sampling point and reaches position point 5';

[0032] S316) Return to step S312 until the Z-axis displacement of the second main axis (12) and the X-axis displacement of the first main axis (11) corresponding to the position point 4' of each sampling point are collected.

[0033] Furthermore, the position 1' of the current sampling point coincides with the position 3' and the position 5' of the previous sampling point.

[0034] Furthermore, in step S24), the trigger delay corresponding to the second speed is less than a preset threshold.

[0035] Furthermore, the threshold is 0.03 μm.

[0036] Compared with the prior art, the advantages of the present invention are:

[0037] 1. The method of the present invention uses an inductive lever probe to measure the inner and outer surfaces of a hemispherical resonator. The inductive lever probe employs contact measurement, is less susceptible to environmental fluctuations, and can adapt to the harsh machining environments of machine tools. The inductive lever probe has excellent angular adaptability and can measure most of the inner and outer spherical surfaces of a hemispherical resonator without interference from the resonator's support rods.

[0038] 2. The present invention utilizes a standard ball installed on the first spindle of the machine tool to unify the coordinate systems of the inductive lever probes with different postures, thereby increasing the detection range of the probe and realizing the measurement of the concentricity and thickness uniformity of non-transparent spherical shells.

[0039] 3. When generating the contours of the inner and outer spheres, the present invention sets sampling points for the warp and measures the coordinates of the sampling points using an inductive lever probe. For the weft, the C-axis is rotated at a constant speed, and the inductive lever probe is brought into contact with the weft to measure the roundness runout of the weft. Separate sampling of the warp and weft improves sampling speed. From the perspective of the hemispherical resonator's operating performance, the uniformity of the weft is more important. Therefore, scanning measurement is used for the weft to increase sampling density, while trigger measurement is used for the warp to save sampling time. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 Schematic diagram of the structure of a hemispherical resonator.

[0041] Figure 2 FIG. 4 is an XZ plane diagram of a system according to an embodiment of the present invention.

[0042] Figure 3 Flowchart of a method according to an embodiment of the present invention.

[0043] Figure 4 Schematic diagram of the operation of step S1 of the method according to an embodiment of the present invention.

[0044] Figure 5 Schematic diagram of the operation of step S2 of the method according to an embodiment of the present invention.

[0045] Figure 6 Schematic diagram of the sampling trajectory of step S3 of the method according to an embodiment of the present invention.

[0046] Figure 7 Schematic diagram of the warp sampling operation in step S3 of the method according to an embodiment of the present invention.

[0047] Figure 8 Schematic diagram of the weft sampling operation in step S3 of the method according to an embodiment of the present invention.

[0048] Legend: 1-machine tool, 2-signal amplification unit, 3-data acquisition unit, 4-control unit, 11-first spindle, 12-second spindle, 13-height adjustment table. DETAILED DESCRIPTION

[0049] The present invention will be further described below in conjunction with the accompanying drawings and specific preferred embodiments, but the scope of protection of the present invention is not limited thereby.

[0050] The challenges of in-situ measurement of hemispherical resonators include: 1) requiring a contact probe with a slender tip to accommodate the large curvature and deep concavity of the inner sphere; 2) ensuring spherical surface measurement accuracy of 0.1 μm; and 3) establishing a unified coordinate system for measuring the inner and outer spheres of the hemispherical resonator for calculating concentricity and thickness uniformity.

[0051] In order to solve the above problems, we consider integrating the inductive probe (LVDT) into the ultra-precision machine tool and designing an in-situ measurement system, such as Figure 2As shown, the in-situ measurement system in this embodiment includes a machine tool 1. In this embodiment, the machine tool 1 adopts an XZCB four-axis ultra-precision machine tool, including a first spindle 11 on which a hemispherical resonator to be measured and / or a standard ball are installed, and a second spindle 12 on which an inductive probe and a grinding wheel are installed. The first spindle 11 includes a first motor and a first turntable. The first motor drives the first turntable to move linearly along the X-axis of the machine tool coordinate system, and the first turntable rotates along the C-axis of the machine tool coordinate system. The second spindle 12 includes a second motor and a second turntable. The second motor drives the second turntable to move along the Z-axis of the machine tool coordinate system, and the second turntable rotates along the B-axis of the machine tool coordinate system. In this embodiment, the hemispherical resonator to be measured is installed on the center part of the first turntable through a three-jaw chuck, and the standard ball can be installed on one side of the first turntable through a vacuum suction cup. The inductive probe and two grinding wheels for machining the inner sphere and outer sphere of the hemispherical resonator are respectively installed on the B axis of the second spindle 12, that is, installed on the edge part of the second turntable. In the above structure, the radius of the standard ball is 9.4999 mm, the radial and axial rotation accuracy of the first spindle 11 is less than 50 nm, the straightness of the two feed axes in the Z and X directions is less than 50 nm / 25 mm, and the positioning resolution is less than 1 nm.

[0052] In this embodiment, the inductive probe adopts an inductive lever probe with a repeatability accuracy of 0.03μm. It is installed on the edge of the second turntable through a height adjustment platform 13. The height adjustment platform 13 can drive the lever-type inductive probe to move linearly along the Y-axis of the machine tool coordinate system.

[0053] like Figure 2 As shown, the in-situ measurement system in this embodiment further includes a signal amplification unit 2, a data acquisition unit 3, and a control unit 4. The inductive lever probe is connected to the data acquisition unit 3 via the signal amplification unit 2, and the data acquisition unit 3 is connected to the machine tool 1. The control unit 4 is connected to the data acquisition unit 3 and the machine tool 1, wherein:

[0054] The signal amplification unit 2 uses a signal amplifier with a display resolution of 0.01μm. The display signal of the inductive lever probe is amplified by the signal amplifier and output in real time analogy;

[0055] The data acquisition unit 3 uses a Dewesoft data acquisition card to synchronize the displacement signals of the X-axis and Z-axis of the machine tool 1 with the reading signals of the inductive lever probe;

[0056] The control unit 4 uses a PC to control the movement and rotation of the first spindle 11 and the second spindle 12 of the machine tool 1 through an NC (numerical control) program, and sets the trigger collection conditions to collect the corresponding XZC axis displacement signal when the inductive lever probe reading is zero.

[0057] We call the set trigger acquisition condition "zero-position trigger mode", that is, when measuring a certain point, the coordinates of XZC in the machine tool coordinate system are collected when the probe is deflected to a fixed zero position (the display is zero). When moving only along the X-axis and Z-axis, the position of the probe coordinate system relative to the machine tool coordinate system will not change, and the linearity error of the probe will not be introduced. Because the repeatability positioning accuracy of the moving axis of the ultra-precision machine tool is much higher than the repeatability accuracy of the inductive lever probe, then under the premise of ignoring the error of the probe ball, theoretically, the accuracy of the collected value of the probe at a certain measuring point depends on the zero point repeatability of the probe - 0.03μm in this embodiment. The detection method is to fix the feed amount of the Z axis, approach the workpiece surface along the X axis and contact the fixed zero position of the probe, at this time triggering the collection of the displacement signals of the X axis and Z axis.

[0058] This embodiment proposes an on-site measurement method for the concentricity and thickness uniformity of the inner and outer spherical surfaces of a hemispherical resonator, which is applied to the on-site measurement system described in this embodiment. Figure 3 As shown, the following steps are included:

[0059] S1) controlling the second spindle 12 to adjust the inductive lever probe to a first posture and a second posture, respectively, and using the inductive lever probe in the first posture and the second posture to measure the coordinates of the center of the standard sphere, respectively, and calculating the coordinate difference ΔC between the first posture coordinate system and the second posture coordinate system based on the measurement results;

[0060] S2) after the hemispherical resonator to be measured is processed, the coordinates of the outer spherical target point of the hemispherical resonator to be measured are measured with the inductive lever probe in a first posture, the coordinates of the inner spherical target point of the hemispherical resonator to be measured are measured with the inductive lever probe in a second posture, and then the coordinates are converted to the first posture coordinate system according to the coordinate difference ΔC, and the concentricity of the hemispherical resonator to be measured is calculated according to the coordinates of the outer spherical target point and the coordinates of the inner spherical target point in the first coordinate system;

[0061] S3) measuring the outer spherical profile of the hemispherical resonator to be measured using the inductive lever probe in a first posture, measuring the inner spherical profile of the hemispherical resonator to be measured using the inductive lever probe in a second posture, and then converting the outer spherical profile and the inner spherical profile in the first posture coordinate system according to the coordinate difference ΔC to obtain the thickness distribution of the hemispherical resonator to be measured by taking the difference between the outer spherical profile and the inner spherical profile in the first coordinate system.

[0062] In this embodiment, step S1) is performed before the hemispherical resonator to be tested is processed. At this time, the hemispherical resonator is not installed on the first spindle 11. Through manual operation, the standard ball is installed near the C-axis rotation center line of the first spindle 11 through a vacuum suction cup, and the position of the ball is manually adjusted to be aligned with the C-axis, so that the eccentricity can be adjusted to less than 1 μm. Figure 3 and Figure 4As shown, to avoid probe interference, measuring the inner and outer spherical surfaces requires two different probe postures, each controlled by the B-axis of the machine tool 1. To measure the concentricity of the inner and outer spherical surfaces, the coordinate systems of the two probe postures must be aligned. Therefore, before installing the hemispherical resonator workpiece blank, the probe coordinate system is aligned to the center of the calibration sphere using a calibration sphere at the center of the C-axis in step S1).

[0063] The repeatability of the measurement system's positioning accuracy is determined by the repeatability of the probe. Equally important is the positioning accuracy of the measurement system, that is, the accuracy of the probe's measurements. Since the coordinates of the measured point are in the machine tool's coordinate system, the alignment of the probe center with the machine tool's C-axis is crucial for positioning accuracy. Aligning the probe center with the machine tool's C-axis is performed sequentially along the Y and X axes of the machine tool's coordinate system. Therefore, step S1 includes the following steps:

[0064] S11) controls the B axis of the second spindle 12 to rotate so that the inductive lever probe reaches the first posture (i.e. Figure 4 In posture 1), the C-axis of the first spindle 11 is controlled to rotate so that the target meridian of the standard ball reaches a preset position. In this embodiment, the target meridians include four meridians of 0°, 90°, 180° and 270°, and there are 20 target points on each meridian. The preset position selects the XZ plane where the rotation center line of the C-axis is located. After the inductive lever probe is driven to reach the preset position by adjusting the height adjustment table 13, the operation control unit 4 controls the first spindle 11 to move along the X-axis of the machine tool coordinate system, and controls the second spindle 12 to move along the Z-axis of the machine tool coordinate system. When the inductive lever probe in the first posture contacts the target point on the target meridian (close to the target point and the reading is zero), the corresponding XZC-axis displacement is obtained as the first coordinate of the target point. This step is repeated 4 times to obtain the set of first coordinates of all target points on the 4 target meridians, and the coordinates of the center of the standard ball (x cs1 , z cs1 );

[0065] S12) Similarly, the B axis of the second spindle 12 is controlled to rotate so that the inductive lever probe reaches the second posture (i.e. Figure 4 In posture 2), the C-axis of the first spindle 11 is controlled to rotate so that the target meridian of the standard ball reaches the preset position, the first spindle 11 is controlled to move along the X-axis of the machine tool coordinate system, and the second spindle 12 is controlled to move along the Z-axis of the machine tool coordinate system. When the inductive lever probe in the second posture contacts the target point on the target meridian (close to the target point and the reading is zero), the corresponding XZC-axis displacement is obtained as the second coordinate of the target point. This step is repeated 4 times to obtain the set of second coordinates of all target points on the 4 target meridians, and the coordinates of the center of the standard ball (x cs2 , z cs2);

[0066] S13) Calculate the center coordinates (x cs1 , z cs1 ) and the coordinates of the center of the standard ball in the second posture coordinate system (x cs2 , z cs2 ) is taken as the coordinate difference ΔC between the first posture coordinate system and the second posture coordinate system, and the expression is as follows:

[0067] ΔC=(x cs2 -x cs1 , z cs2 -z cs1 ) (1)

[0068] In step S11 of this embodiment, the coordinates (x cs1 , z cs1 ) and step S12) calculates the center coordinates (x) of the standard ball in the second posture coordinate system according to the set of second coordinates. cs2 , z cs2 ) all use the same method, and calculating the center coordinates of the standard sphere according to the set of coordinates includes the following steps: calculating the eccentricity error of the standard sphere relative to the rotation center line of the C-axis, adjusting each coordinate in the set of coordinates according to the eccentricity error, that is, subtracting the coordinate value in each coordinate from the eccentricity error to separate the eccentricity error, and then fitting the center coordinates of the standard sphere in the corresponding coordinate system using the least squares method for all adjusted coordinates. Fitting the center coordinates using the least squares method is a method commonly used by technical personnel in this field. This scheme does not involve improvements to its specific calculation process, and its specific calculation process is not the focus of this scheme, so it will not be repeated.

[0069] For step S2) of this embodiment, as Figure 5 As shown, after the hemispherical resonator is precisely ground and a certain margin is left, in-situ measurement is performed. The specific measurement process is similar to step S1). For the target points selected on the inner and outer spheres of the hemispherical resonator, the C-axis of the first spindle 11 is first controlled to rotate so that the target point reaches a preset position, such as the XZ plane where the C-axis rotation centerline is located. The first spindle 11 is controlled to move along the X-axis of the machine tool coordinate system, and the second spindle 12 is controlled to move along the Z-axis of the machine tool coordinate system. When the inductive lever probe in the first posture / second posture contacts the target point on the target meridian (close to the target point and the reading is zero), the corresponding XZC-axis displacement is obtained as the coordinate P of the target point on the outer sphere in the first posture coordinate system. i,1 (x i,1 , z i,1 ) / coordinates of the target point on the inner sphere in the second posture coordinate system Q j,2 (x j,2 , z j,2), and then use the following formula to transform the inner sphere target point from the second attitude coordinate system to the first attitude coordinate system:

[0070] Q j,1 =Q j,2 -ΔC (2)

[0071] Where i = 1, 2, ..., m, j = 1, 2, ..., n. m and n are the number of sampling points.

[0072] Similar to step S11) and step S12), in step S2), the concentricity of the hemispherical resonator to be measured is calculated based on the coordinates of the outer spherical target point and the inner spherical target point in the first coordinate system, specifically comprising: using the least squares method to calculate the outer spherical target point coordinate set P in the first coordinate system respectively. i,1 and the inner sphere target point coordinate set Q j,1 Performing spherical fitting to obtain the best fitting radius and sphere center position of the outer sphere and inner sphere of the hemispherical resonator to be measured, and calculating the concentricity of the outer sphere and inner sphere of the hemispherical resonator to be measured based on the best fitting radius and sphere center position of the outer sphere and inner sphere. Calculating the concentricity of the inner and outer spheres based on the best fitting radius and sphere center position of the inner and outer spheres is a method commonly used by those skilled in the art. This solution does not involve improvements to its specific calculation process, and its specific calculation process is not the focus of discussion in this solution, so it will not be repeated here.

[0073] For step S3) of this embodiment, we adopt the contour measurement method of separating the longitude and latitude and integrating them, and the sampling trajectory is as follows: Figure 6 As shown, for longitude, multiple sampling points on the meridian are selected, and the inductive lever probe is used to contact these sampling points respectively. The XZC axis displacement corresponding to the zero reading when close to the sampling point is collected as the coordinates of the sampling point. For latitude, the sampling points of the same dimension are used as the basis for selecting the target latitude. Then, a parallel scanning method is used, and the C axis rotates at a constant linear speed. The inductive lever probe is brought close to or in contact with the target latitude to measure the roundness runout value of the target latitude. Finally, the measurement value of the spherical profile is generated based on the coordinates of the sampling points on the meridian and the roundness runout value of the latitude. The specific steps include:

[0074] S31) selecting at least two sampling points on a target meridian of the spherical surface, and for each sampling point, moving the inductive lever probe along the Z axis at a first speed from the current sampling point to the vicinity of the next sampling point, and then moving the inductive lever probe along the X axis at a second speed until the inductive lever probe reads zero, and collecting displacement signals along the X axis and the Z axis at this time;

[0075] S32) taking the displacement signals of the X-axis and Z-axis corresponding to each sampling point as the sampling point coordinate measurement value, and returning to step S31) until all sampling points are measured;

[0076] S33) rotating the spherical surface along the C-axis at a constant linear velocity, moving the inductive lever probe to the vicinity of the target latitude to measure the roundness runout;

[0077] It should be noted that in step S31) and step S33), for the outer spherical surface, the inductive lever probe is always in the first posture, and for the inner spherical surface, the inductive lever probe is always in the second posture;

[0078] S34) Calculating the spherical profile based on the coordinate measurement values ​​of the sampling points on the spherical target meridian and the roundness runout value of the target latitude.

[0079] In step S31), we developed a zero-position trigger method for the probe according to the aforementioned "zero-position trigger mode", that is, collecting the coordinates of the point when the probe indication becomes inherent zero. When moving only along the X-axis and Z-axis of the machine tool coordinate system, the position of the probe coordinate system relative to the machine tool coordinate system is constant, and no linear error of the probe is introduced. Based on the fact that the repeatable positioning accuracy of the machine tool axis (0.015μm) is higher than the repeatable positioning accuracy of the probe (0.03μm), theoretically, the accuracy of the collected value at a certain point is determined by the repeatability of the probe, that is, 0.03μm (ignoring the error of the probe). The detection method of the probe is to fix the feed of the Z-axis, move the X-axis close to the surface of the workpiece, and trigger the collection of the displacement signals of the X-axis and Z-axis. The trigger condition is that the voltage signal of the probe becomes zero, that is, the probe reading is zero.

[0080] like Figure 7 As shown, step S31 of this embodiment specifically includes the following steps:

[0081] S311) calculating the Z-axis coordinate of each sampling point. In this embodiment, the sampling points are artificial sampling points on the target meridian. The artificial sampling points on different meridians are distributed according to the same latitude to provide a basis for subsequent parallel measurement of the latitude. The Z-axis coordinate of each sampling point is determined by the sampling interval;

[0082] S312) From the current sampling point P i Starting from the corresponding position point 1', the second spindle 12 is moved along the Z axis at the first speed so that the inductive lever probe reaches the next sampling point P i+1 The Z-axis coordinate of the corresponding position point 2';

[0083] S313) Fix the second spindle 12, that is, fix the feed of the Z axis, and move the first spindle 11 along the X axis at the first speed so that the inductive lever probe approaches the sampling point P i+1 Until the inductive lever probe is relative to the sampling point P i+1 Move a preset distance to position point 3', where the distance between position point 3' and position point 2' can be a preset fixed value;

[0084] S314) Move the first spindle 11 along the X-axis at a second speed, which is less than the first speed, so that the inductive lever probe continues to approach the sampling point P i+1 , until the reading returned by the inductive lever probe is zero, at which point the position reached by the inductive lever probe is the sampling point P i+1 The position point 4' is set, and the Z-axis displacement of the second spindle 12 and the X-axis displacement of the first spindle 11 corresponding to the position point 4' are triggered; in this step, considering the existence of processing errors, the sampling point P i+1 The actual surface of the workpiece to be measured has a machining tolerance of ±T compared to the theoretical surface, that is, the estimated range of the actual machining point of the workpiece deviates from the nominal machining point. However, the value of T cannot exceed the sensing range of the inductive lever probe to prevent damage to the inductive lever probe. And because the acquisition of the probe reaching zero position and the triggering of the acquisition of the XZ axis coordinates cannot be completely synchronized, the inductive lever probe is relative to the sampling point P. i+1 The faster the forward speed, the greater the delay in triggering the acquisition of displacement coordinates. Therefore, in this step, the trigger delay is minimized by reducing the speed. The theoretical maximum trigger accuracy of the inductive lever probe is 0.03μm, so the trigger delay corresponding to the second speed is less than the preset threshold trigger delay of 0.03μm.

[0085] S315) Move the first spindle 11 along the X-axis at a first speed so that the inductive lever probe is away from the sampling point P i+1 And arrive at position 5', so the sampling point P i+1 The sampling is completed, and the sampling point P i+2 The sampling starts at the sampling point Pi+2. In this embodiment, the position 1' of the sampling point Pi+2 is the same as the sampling point P i+2 Position 3' and position 5' coincide with each other, and position 5' indicates the end of this sampling and the beginning of the next sampling;

[0086] S316) The sampling point P i+1 As the current sampling point, return to step S312 until the Z-axis displacement of the second spindle 12 and the X-axis displacement of the first spindle 11 corresponding to the position point 4' of each sampling point are collected, thereby obtaining the XZ plane coordinates of all sampling points on the current arc in the machine tool coordinate system.

[0087] In step S3) of this embodiment, when measuring the sampling points on the target meridian, it is necessary to rotate the C-axis so that the target meridian reaches a preset position, such as the XZ plane where the central rotation axis of the C-axis is located. Therefore, each sampling point collected corresponds to a coordinate on the C-axis, and the coordinates of all sampling points in the machine tool XZC coordinate system can be obtained.

[0088] In step S33 of this embodiment, considering that the support rod of the hemispherical resonator interferes with about two-thirds of the range of the hemisphere, a sampling trajectory of parallel continuous circular lines is formed according to the target latitude determined by the sampling point, and the sampling density can increase the frequency, providing a circumferential profile of a comprehensive shape. In theory, the zero-position triggering method will not bring about the linear error of the probe, and the high-precision spindle rotation level of the machine tool is within 10nm, and the radial shape error of the processed parts is generally within microns. In the scanning measurement, the linear error of the probe ranging at the micron level is almost zero. Without reducing the theoretical measurement accuracy, the parallel scanning measurement improves the measurement efficiency and sampling density. In addition, when scanning the target latitude, the C-axis rotates at a constant linear speed to make the sampling density of the entire sphere uniform.

[0089] like Figure 8 As shown in the figure, when the inductive lever probe approaches the target latitude and conducts parallel scanning measurements, the direction misalignment between the probe center axis and the measured error cannot be ignored. There is a proportionality factor between the measured value and the actual value. The actual normal runout error of the workpiece surface (i.e., the inner / outer sphere of the hemispherical resonator) is:

[0090]

[0091] In the above formula, the roundness runout directly measured by the inductive lever probe is r0(θ), θ is the latitudinal circumferential angle, and γ is the angle between the normal direction of the workpiece contact point and the C-axis rotation centerline, which is calculated by the normal equation on the fitting curve of the target meridian sampling point in the previous step. is the center axis of the probe and the center line of C-axis rotation, and k1 is the correction coefficient for roundness measurement.

[0092] Regarding step S34) of this embodiment, calculating the spherical contour based on the coordinates of the sampling points on the longitude and the roundness runout value on the latitude is a method commonly used by those skilled in the art. This solution does not involve improvements to its specific calculation process, and its specific calculation process is not the focus of this solution, so it will not be repeated here.

[0093] It should be noted that, in step S34), the outer spherical contour calculated based on the coordinate measurement values ​​of the outer spherical target sampling points and the roundness runout values ​​of the target latitude is in the first posture coordinate system, and the inner spherical contour calculated based on the coordinate measurement values ​​of the inner spherical target sampling points and the roundness runout values ​​of the target latitude is in the second posture coordinate system. Therefore, it is also necessary to convert the coordinates of the inner spherical contour to the first posture coordinate system according to formula (2) before the subsequent difference calculation can be performed.

[0094] In summary, in the method of this embodiment, an inductive lever probe is used for in-situ measurement to test the inner and outer surfaces of a hemispherical resonator. The inductive lever probe uses a contact measurement method, which has high precision, is less affected by environmental changes, and can adapt to the harsh processing environment on machine tools. In addition, the inductive lever probe has good angular adaptability and can measure most of the inner and outer spherical surfaces of the hemispherical resonator without interference from the resonator support rod.

[0095] The method of this embodiment also uses a standard sphere to unify the coordinate systems of the inductive lever probes in different postures, thereby increasing the detection range of the probe and achieving the measurement of the concentricity and thickness uniformity of the non-transparent spherical shell.

[0096] Finally, the method of this embodiment improves sampling speed by sampling separately along the warp and weft. From the perspective of hemispherical resonator performance, the uniformity of the weft is more important. Therefore, scanning measurement is used along the weft to increase sampling density, while trigger measurement is used along the warp to save sampling time. This is a performance-based in-situ measurement.

[0097] The above description is merely a preferred embodiment of the present invention and does not constitute any form of limitation to the present invention. Although the present invention has been disclosed above with reference to the preferred embodiment, it is not intended to limit the present invention. Therefore, any simple modifications, equivalent variations, and modifications to the above embodiment that do not depart from the technical solution of the present invention and are based on the technical essence of the present invention shall fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for measuring the concentricity and thickness uniformity of the inner and outer spherical surfaces of a hemispherical resonator, characterized in that: The invention is applied to an in-situ measurement system, the in-situ measurement system comprising a machine tool (1), a first spindle (11) of the machine tool (1) linearly moving along the X-axis of the machine tool coordinate system and rotating along the C-axis of the machine tool coordinate system, a second spindle (12) of the machine tool (1) moving along the Z-axis of the machine tool coordinate system and rotating along the B-axis of the machine tool coordinate system, a hemispherical resonator to be measured and / or a standard ball is mounted on the C-axis of the first spindle (11), and an inductive lever probe and a grinding wheel are mounted on the B-axis of the second spindle (12). The method comprises the following steps: S1) controlling the second spindle (12) to adjust the inductive lever probe to a first posture and a second posture respectively, and using the inductive lever probe in the first posture and the second posture to measure the coordinates of the center of the standard sphere respectively, and calculating the coordinate difference ΔC between the first posture coordinate system and the second posture coordinate system according to the measurement results; S2) after the hemispherical resonator to be measured is processed, the coordinates of the outer spherical target point of the hemispherical resonator to be measured are measured with the inductive lever probe in a first posture, the coordinates of the inner spherical target point of the hemispherical resonator to be measured are measured with the inductive lever probe in a second posture, and then the coordinates are converted to the first posture coordinate system according to the coordinate difference ΔC, and the concentricity of the hemispherical resonator to be measured is calculated according to the coordinates of the outer spherical target point and the coordinates of the inner spherical target point in the first coordinate system; S3) measuring the outer spherical profile of the hemispherical resonator to be measured using the inductive lever probe in a first posture, measuring the inner spherical profile of the hemispherical resonator to be measured using the inductive lever probe in a second posture, and then converting the outer spherical profile and the inner spherical profile in the first posture coordinate system according to the coordinate difference ΔC to obtain the thickness distribution of the hemispherical resonator to be measured by taking the difference between the outer spherical profile and the inner spherical profile in the first coordinate system.

2. The on-site measurement method for the concentricity and thickness uniformity of the inner and outer spherical surfaces of a hemispherical resonator according to claim 1, characterized in that: Step S1) comprises the following steps: S11) controls the B axis of the second spindle (12) to rotate so that the inductive lever probe reaches a first posture, controls the C axis of the first spindle (11) to rotate so that the target meridian of the standard ball reaches a preset position, controls the first spindle (11) to move along the X axis of the machine tool coordinate system, and controls the second spindle (12) to move along the Z axis of the machine tool coordinate system. When the inductive lever probe in the first posture contacts the target point on the target meridian, the corresponding XZC axis displacement is obtained as the first coordinate of the target point, and the spherical center coordinate (xZC) of the standard ball in the first posture coordinate system is calculated based on the set of the first coordinates. cs1 , z cs1 ); S12) controlling the B axis of the second spindle (12) to rotate so that the inductive lever probe reaches a second posture, controlling the C axis of the first spindle (11) to rotate so that the target meridian of the standard ball reaches a preset position, controlling the first spindle (11) to move along the X axis of the machine tool coordinate system, and controlling the second spindle (12) to move along the Z axis of the machine tool coordinate system, when the inductive lever probe in the second posture contacts the target point on the target meridian, obtaining the corresponding XZC axis displacement as the second coordinate of the target point, and calculating the spherical center coordinate (xZC) of the standard ball in the second posture coordinate system according to the set of the second coordinates. cs2 , z cs2 ); S13) Calculate the center coordinates (x cs1 , z cs1 ) and the coordinates of the center of the standard ball in the second posture coordinate system (x cs2 , z cs2 ) is used as the coordinate difference ΔC between the first posture coordinate system and the second posture coordinate system.

3. The on-site measurement method for the concentricity and thickness uniformity of the inner and outer spherical surfaces of a hemispherical resonator according to claim 2, characterized in that: Step S11) and step S12) include the steps of calculating the coordinates of the center of the standard sphere based on the set of coordinates, specifically including: calculating the eccentricity error of the standard sphere relative to the center line of rotation of the C-axis, adjusting each coordinate in the set of coordinates according to the eccentricity error, and fitting all the adjusted coordinates using the least squares method to obtain the coordinates of the center of the standard sphere in the corresponding coordinate system.

4. The on-site measurement method for the concentricity and thickness uniformity of the inner and outer spherical surfaces of a hemispherical resonator according to claim 1 is characterized in that: Step S2) includes the step of converting the coordinate system according to the coordinate difference ΔC, specifically including: converting the coordinate Q in the second posture coordinate system j,2 (x j,2 , z j,2 ) minus the coordinate difference ΔC to obtain the corresponding coordinate Q in the first posture coordinate system j,1 (x j,1 , z j,1 ).

5. The on-site measurement method for the concentricity and thickness uniformity of the inner and outer spherical surfaces of a hemispherical resonator according to claim 1 is characterized in that: In step S2), the concentricity of the hemispherical resonator to be measured is calculated based on the coordinates of the outer spherical target point and the inner spherical target point in the first coordinate system, which specifically includes: using the least squares method to calculate the coordinate set P of the outer spherical target point in the first coordinate system. i,1 and the inner sphere target point coordinate set Q j,1 Spherical fitting is performed to obtain the best fitting radius and sphere center position of the outer sphere and inner sphere of the hemispherical resonator to be measured, and the concentricity of the outer sphere and inner sphere of the hemispherical resonator to be measured is calculated based on the best fitting radius and sphere center position of the outer sphere and inner sphere.

6. The on-site measurement method for the concentricity and thickness uniformity of the inner and outer spherical surfaces of a hemispherical resonator according to claim 1 is characterized in that: Step S3) includes the step of measuring the spherical profile with an inductive lever probe, specifically comprising: S31) selecting at least two sampling points on a target meridian of the spherical surface, and for each sampling point, moving the inductive lever probe along the Z axis at a first speed from the current sampling point to the vicinity of the next sampling point, and then moving the inductive lever probe along the X axis at a second speed until the inductive lever probe reads zero, and collecting displacement signals along the X axis and the Z axis at this time; S32) taking the displacement signals of the X-axis and Z-axis corresponding to each sampling point as the sampling point coordinate measurement value, and returning to step S31) until all sampling points are measured; S33) rotating the spherical surface along the C-axis at a constant linear velocity, moving the inductive lever probe to the vicinity of the target latitude to measure the roundness runout; S34) Calculating the spherical profile based on the coordinate measurement values ​​of the sampling points on the spherical target meridian and the roundness runout value of the target latitude.

7. The on-site measurement method for the concentricity and thickness uniformity of the inner and outer spherical surfaces of a hemispherical resonator according to claim 6, characterized in that: Step S31) specifically includes the following steps: S311) calculating the Z-axis coordinate of each sampling point; S312) starting from position point 1' corresponding to the current sampling point, moving the second spindle (12) along the Z-axis direction at a first speed so that the inductive lever probe reaches position point 2' corresponding to the Z-axis coordinate of the next sampling point; S313) fixing the second spindle (12) and moving the first spindle (11) along the X-axis at a first speed so that the inductive lever probe approaches the next sampling point until the inductive lever probe moves a preset distance relative to the next sampling point to position point 3'; S314) moving the first spindle (11) along the X-axis direction at a second speed so that the inductive lever probe continues to approach the next sampling point until the reading returned by the inductive lever probe is zero, and collecting the Z-axis displacement of the second spindle (12) corresponding to the position point 4' of the inductive lever probe at the next sampling point, and the X-axis displacement of the first spindle (11); S315) moving the first spindle (11) along the X-axis at a first speed so that the inductive lever probe moves away from the next sampling point and reaches position point 5'; S316) Return to step S312 until the Z-axis displacement of the second main axis (12) and the X-axis displacement of the first main axis (11) corresponding to the position point 4' of each sampling point are collected.

8. The on-site measurement method for the concentricity and thickness uniformity of the inner and outer spherical surfaces of a hemispherical resonator according to claim 7, characterized in that: Position 1' of the current sampling point coincides with positions 3' and 5' of the previous sampling point.

9. The on-site measurement method for the concentricity and thickness uniformity of the inner and outer spherical surfaces of a hemispherical resonator according to claim 7, characterized in that: In step S24), the trigger delay corresponding to the second speed is less than a preset threshold.

10. The on-site measurement method for the concentricity and thickness uniformity of the inner and outer spherical surfaces of a hemispherical resonator according to claim 9, characterized in that: The threshold value is 0.03 μm.

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