Contact type three-dimensional scanning probe with mechanical self-decoupling function

Abstract

The invention discloses a contact type three-dimensional scanning probe with a mechanical self-decoupling function, which is composed of an XY-direction sensing module and a Z-direction sensing module, adopts a spherical hinge type mechanical self-decoupling structure, and realizes separation of Z-direction and XY-direction displacement paths by taking a central rotating ball in a fixed fisheye joint rod as a spherical hinge center; an XY-direction reed is arranged to be of an inner and outer ring structure, and the XY-direction reed and the center of the center rotating ball are located on the same plane; when a probe in the Z-direction sensing module moves along an X direction or a Y direction, an inner ring in an XY-direction reed deflects around a sphere center, a sensor in a corresponding direction outputs a strain signal, and meanwhile, a sensor in an orthogonal direction only slightly rotates along with a structure and does not generate effective output, so that mechanical decoupling of X-direction measurement and Y-direction measurement is realized, and a coupling error in a plane is reduced. The device is compact in structure, simple and convenient to assemble, high in sensitivity, low in coupling error and excellent in stability, and is suitable for high-precision contact measurement in a three-coordinate measuring machine and a micro-nano three-dimensional shape detection system.

Description

Technical Field

[0001] This invention relates to the field of micro-nano measurement, and more specifically to a contact-type three-dimensional scanning measurement probe with mechanical self-decoupling function applied to a coordinate measuring machine, which can be used for scanning and measuring the three-dimensional shape of an object surface. Background Technology

[0002] With the rapid development of modern manufacturing technology, microelectronics processes, and precision instrument engineering, the trend towards miniaturization of product structures and high precision of performance is becoming increasingly apparent, placing higher demands on the accuracy of dimensional inspection and geometric shape measurement. To achieve precise inspection of the surface morphology, position, and assembly errors of parts at a microscale, coordinate measuring machines (CMMs), micro / nano measurement systems, and various high-end precision manufacturing equipment are widely used in scientific research and industrial fields. Contact scanning probes, as key detection devices in such equipment, primarily achieve high-precision acquisition of spatial position or morphology by generating minute displacements through contact between the probe and the surface being measured, followed by detection of the probe's deflection by an internal sensing mechanism.

[0003] Currently, the contact scanning probes that have been announced mainly include those from the German Federal Institute of Physics (PTB), the Technical University of Eindhoven in the Netherlands, the Swiss Federal Institute of Metrology (METAS), and Hefei University of Technology. Among them: The miniature contact probe developed by S. Bütefisch et al. at the Federal Institute of Physics and Technology in Germany (Bütefisch S, Büttgenbach S, Kleine-Besten T, et al. Micromechanical three-axial tactileforce sensor for micromaterial characterization. Microsystem Technologies 7,171–174 (2001).Cao S, Brand U, Kleine-Besten T, et al. Recent developments indimensional metrology for microsystem components. Microsystem Technologies8,3–6 (2002) employs an integrated structure of silicon film and probe. When the end of the probe is subjected to external force, the silicon film undergoes slight deformation. The deformation is detected by 24 piezoresistive elements distributed on the silicon film, enabling three-dimensional force and displacement measurement. This structure has high sensitivity and good temperature stability. However, due to uneven stress distribution in the thin film and intersecting force transmission paths, mechanical coupling still exists between the axial and radial directions of the probe. Furthermore, the silicon film is prone to local stress concentration and fracture, limiting its reliability.

[0004] H. Haitjema et al. from the Technical University of Eindhoven in the Netherlands proposed a strain gauge-based three-dimensional micro-contact sensing probe (Haitjema H, Pril WO, Schellekens PH J. Development of asilicon-based nanoprobe system for 3-D measurements[J]. CIRP Annals, 2001, 50(1): 365-368.). The strain gauge, circuitry, and elastic element are integrated into a single unit using microfabrication processes such as deposition, lithography, and etching, enabling simultaneous detection of minute forces and displacements in multiple directions. This probe is small in size and highly sensitive, but its triangular topological support structure results in strong coupling between directions, making decoupling analysis and assembly complex.

[0005] F. Meli et al. of the Swiss Federal Institute of Metrology (METAS) developed an electromagnetic micro-contact probe (Küng A, Meli F, Thalmann R. Ultraprecision micro-CMM using a low force 3D touchprobe[J]. Measurement Science and Technology, 2007, 18(2): 319-327.ThalmannR, Meli F, Küng A. State of the art of tactile micro coordinate metrology[J].Applied Sciences, 2016, 6(5): 150 (13pp).). The probe has three degrees of freedom, and displacement detection in each direction is achieved using the inductive principle. The main body of the structure is made of aluminum alloy. The probe has high lateral sensitivity and low contact force, but its internal structure is complex, difficult to assemble and adjust, and has directional coupling problems due to its triangular suspension layout.

[0006] A research team from Hefei University of Technology has proposed a contact scanning probe with a double-layer flexible support structure (Xu Peng. Key Technologies and Systems for Three-Dimensional Nanoscale Measurement Probes with High Aspect Ratio Micro-Size [D]. Hefei University of Technology, 2023. DOI:10.27101 / d.cnki.ghfgu.2023.000052.), which achieves the detection of minute displacements in three dimensions through two-stage flexible beams. This structure has certain advantages in terms of sensitivity and manufacturing controllability, but there is still a coupling effect between force and displacement in multiple directions, which limits the further scanning measurement accuracy. Summary of the Invention

[0007] To avoid the shortcomings of the prior art, the present invention provides a contact-type three-dimensional scanning probe with mechanical self-decoupling function, in order to achieve a detection effect with low coupling error, while having the advantages of simple processing technology and convenient assembly and adjustment.

[0008] The present invention adopts the following technical solution to solve the technical problem: The contact-type 3D scanning probe of this invention with mechanical self-decoupling function is characterized by: it consists of an XY-axis sensing module and a Z-axis sensing module, and adopts a ball-joint mechanical self-decoupling structure. The central rotating ball in the fixed fisheye connector rod is used as the center of the ball joint, realizing the separation of the displacement paths in the Z-axis and XY-axis directions; the XY-axis spring is set as an inner and outer ring structure, and the center of the XY-axis spring and the center rotating ball are located in the same plane; when the probe in the Z-axis sensing module moves along the X or Y direction, the inner ring of the XY-axis spring deflects around the center of the ball, and the sensor in the corresponding direction outputs a strain signal. At the same time, the orthogonal direction sensor only rotates slightly with the structure and does not produce an effective output, thus realizing the mechanical decoupling of X and Y-axis measurements and reducing in-plane coupling errors.

[0009] The contact-type three-dimensional scanning probe with mechanical self-decoupling function of this invention is also characterized by the following: The structure of the XY-direction sensing module is as follows: the central rotating ball is set in the bottom joint of the fixed fisheye connector rod, and the connecting rod passes through the central rotating ball radially; the XY-direction spring for mounting the strain sensor is a rectangular inner and outer ring structure, with four beam segments arranged in a cross shape connecting the inner and outer rings to form a cross beam; the inner ring is connected to the end of the connecting rod and deflects around the center of the ball with the central rotating ball, while the outer ring is fixed; the X-direction strain sensor and the Y-direction strain sensor are distributed on the cross beam in the X and Y directions; The structure of the Z-direction sensing module is as follows: a connecting cylinder for mounting the Z-direction spring is set at the bottom of the inner ring of the XY-direction spring, the Z-direction sensor is set on the Z-direction spring, a vertical guide sleeve is set below the connecting cylinder, and a guide post is set in the vertical guide sleeve. The probe is fixedly set at the bottom end of the guide post, and Z-direction displacement detection is achieved by the relative sliding between the guide post and the guide sleeve.

[0010] The contact-type three-dimensional scanning probe with mechanical self-decoupling function of this invention is also characterized in that: the XY direction sensing module adopts a rectangular shell, and the screw rod of the fixed fisheye connector rod is fixedly set at the center of the upper panel of the rectangular shell by a nut; the XY direction spring is installed in the following way: the inner ring of the XY direction spring is fixedly installed at both ends of the connecting rod by the upper inner ring pressure plate and the lower inner ring pressure plate; the outer ring of the XY direction spring is fixedly installed on the bottom surface of the rectangular shell by the outer ring pressure plate.

[0011] The contact-type three-dimensional scanning probe with mechanical self-decoupling function of the present invention is also characterized in that: in the Z-axis sensing module, a guide cylinder is provided at the bottom of the connecting cylinder, the guide cylinder is an upper cylinder and a lower cylinder connected together, and the guide sleeve is provided in the upper cylinder; the spring spring fitted on the guide post is provided in the lower cylinder, and the spring spring, the guide sleeve and the guide post constitute a spring mechanism. When the guide post is subjected to Z-axis force, it slides in the Z-axis with the guide sleeve and is rebounded to the initial position by the spring spring.

[0012] The feature of the contact three-dimensional scanning probe with mechanical self-decoupling function of the present invention is that: a differential sensing structure is set up, in which the X-axis strain sensor and the Y-axis strain sensor are set up in pairs, and the output signals of the pair of X-axis strain sensors and the pair of Y-axis strain sensors are respectively processed by differential signal processing.

[0013] Compared with existing technologies, the beneficial effects of this invention are reflected in: 1. The present invention comprises X and Y direction sensing modules and Z direction sensing module, and adopts ball joint mechanical self-decoupling structure to realize the separation of displacement paths in Z direction and X and Y direction, thereby reducing mechanical coupling between directions at the source.

[0014] 2. In this invention, the X and Y direction reeds and the center of the central rotating sphere are located in the same plane. When the probe is displaced along the X (or Y) direction, the inner ring of the reed deflects around the center of the sphere, and the sensor in the corresponding direction undergoes bending deformation and outputs a strain signal. The sensor in the orthogonal direction (Y direction) only undergoes a slight rotation with the structure, and its bending strain is extremely small, producing virtually no effective output. Since the sensor is primarily sensitive to bending stress, the response in the orthogonal direction is significantly suppressed, thereby achieving mechanical decoupling of X and Y direction measurements and reducing in-plane coupling errors.

[0015] 3. This invention employs a differential sensing structure, with two sets of strain-sensing sensors arranged on opposite beams of the reed. When the probe is subjected to an external force in the X direction, the two sensors are in symmetrical positions with opposite sensing directions, and their output signals exhibit a differential relationship. Through differential output, the measurement sensitivity and linearity of the probe can be effectively improved, while simultaneously offsetting the influence of temperature changes and common-mode interference on the measurement results. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the overall structure of the present invention; Figure 2 This is a schematic diagram of the X and Y direction sensing module structure in this invention; Figure 3 This is an exploded view of the X and Y direction sensing module structure in this invention; Figure 4a This is a schematic diagram of the external structure of the Z-axis sensing module in this invention; Figure 4b This is a schematic diagram of the internal structure of the Z-axis sensing module in this invention; Figure 5 This is a schematic diagram of the assembly of the two modules and the upper shell in this invention; Figure 6 This is a distribution diagram of the XY-direction reeds and the X-direction sensor and Y-direction sensor of the present invention; Figure 7 This is a schematic diagram of the XY-direction spring strain when the probe is subjected to a horizontal triggering force in this invention; Figure 8 This is a schematic diagram of Z-axis sensing when the probe is subjected to a vertical triggering force in this invention; The diagram is labeled as follows: 1 Rectangular housing, 2 XY direction sensing module, 3 Z direction sensing module, 4 Fixed fisheye connector rod, 5 Nut, 6 Center ball, 7 Connecting rod, 8 XY direction spring, 9 X direction strain sensor, 10 Y direction strain sensor, 11 Outer ring pressure plate, 12 Inner ring upper pressure plate, 13 Inner ring lower pressure plate, 14 Connecting cylinder, 15 Z direction spring, 16 Z direction sensor, 17 Upper cylinder, 18 Lower cylinder, 19 Vertical guide sleeve, 20 Guide post, 21 Return spring, 22 Probe. Detailed Implementation

[0017] like Figure 1 and Figure 5 As shown, the contact-type three-dimensional scanning probe with mechanical self-decoupling function in this embodiment consists of an XY-axis sensing module and a Z-axis sensing module. It adopts a ball-joint mechanical self-decoupling structure, with the central rotating ball 6 in the fixed fisheye connector rod 4 as the center of the ball joint, realizing the separation of the displacement paths in the Z-axis and XY-axis. The XY-axis spring 8 is set as an inner and outer ring structure, and the center of the XY-axis spring 8 and the center rotating ball 6 are located in the same plane. When the probe 22 in the Z-axis sensing module is displaced along the X or Y direction, the inner ring in the XY-axis spring 8 deflects around the center of the ball, and the sensor in the corresponding direction outputs a strain signal. At the same time, the orthogonal direction sensor only rotates slightly with the structure and does not produce an effective output, realizing the mechanical decoupling of X and Y-axis measurements and reducing the coupling error in the plane.

[0018] In specific implementation: such as Figure 2 and Figure 3As shown, the structure of the XY direction sensing module 2 is as follows: the central rotating ball 6 is set in the bottom joint of the fixed fisheye connector rod 4. The fixed fisheye connector rod 4 is a rod end joint bearing structure, and its lower part is a shell with an inner spherical surface. The central rotating ball 6 is constrained in it and can rotate freely with low friction, but its center position is fixed in space. The connecting rod 7 passes through the central rotating ball 6 radially. Any deflection of the central rotating ball 6 will be directly and equally transmitted to the connecting rod 7. The XY direction spring 8 used to install the strain sensor is a rectangular inner and outer ring structure. Specifically, it is a thin sheet elastic metal part (such as beryllium bronze) that is machined as a whole. The inner ring and the outer ring are connected by four beam segments distributed in a cross shape to form a cross beam. The inner ring of the XY direction spring 8 is fixed to the rod end of the connecting rod 7 and deflects around the center of the ball with the central rotating ball, while its outer ring is fixed to the shell by a pressure plate. Furthermore, the neutral plane of the XY direction spring 8 (i.e. the center plane of the inner ring) is precisely installed so as to be coplanar with the center of the central rotating ball 6; the X direction strain sensor 9 and the Y direction strain sensor 10 are distributed on the cross beam in the X and Y directions.

[0019] like Figure 4a and Figure 4b As shown, the structure of the Z-axis sensing module 3 is as follows: a connecting cylinder 14 for mounting the Z-axis spring 15 is set at the bottom of the inner ring of the XY-axis spring 8, and the Z-axis sensor 16 is set on the Z-axis spring 15. A guide cylinder is connected to the bottom of the connecting cylinder 14. The guide cylinder consists of an upper cylinder 17 and a lower cylinder 18 connected coaxially. A vertical guide sleeve 19 is set below the connecting cylinder 14. The guide sleeve 19 is pressed into the upper cylinder 17, and a guide post 20 is set in the vertical guide sleeve 19. The probe 22 is fixedly set at the bottom end of the guide post 20. The Z-axis displacement detection is achieved by the relative sliding of the guide post 20 and the vertical guide sleeve 19.

[0020] like Figure 1 and Figure 2 As shown, the XY direction sensing module 2 adopts a rectangular housing 1. The screw rod body of the fixed fisheye connector rod 4 is fixedly set at the center of the upper panel of the rectangular housing 1 by the nut 5. The installation form of the XY direction spring 8 is as follows: the inner ring of the XY direction spring 8 is fixedly installed at both ends of the connecting rod 7 by the upper inner ring pressure plate 12 and the lower inner ring pressure plate 13, so as to ensure the reliable connection between the inner ring and the connecting rod 7 to transmit motion; the outer ring of the XY direction spring 8 is fixedly installed on the bottom surface of the rectangular housing 1 by the outer ring pressure plate 11 to achieve complete fixation.

[0021] like Figure 4b and Figure 8As shown, in the Z-axis sensing module 3, a guide cylinder is set at the bottom of the connecting cylinder 14. The guide cylinder is the upper cylinder 17 and the lower cylinder 18 connected together. The vertical guide sleeve 19 is set in the upper cylinder 17. In order to enable the probe to automatically reset and maintain a stable initial contact force after measurement, a spring 21 is fitted on the guide post 20. The spring is placed in the cavity of the lower cylinder 18, with one end abutting against the lower end of the guide sleeve 19 or the inside of the upper cylinder 17, and the other end abutting against the bottom of the guide post 20. The spring 21 fitted on the guide post 20 is set in the lower cylinder 18. The spring 21, the guide sleeve 19, and the guide post 20 form a spring mechanism. When the probe 22 contacts the workpiece surface and is subjected to an upward Z-axis force, the guide post 20 overcomes the spring force and slides upward relative to the guide sleeve 19. The Z-axis spring 15 deforms, and the sensor outputs a signal. After the force is removed, the guide post 20 can accurately spring back to the initial position under the action of the spring 21.

[0022] like Figure 6 As shown, to further improve the signal-to-noise ratio and temperature compensation performance, a differential sensing structure is set up, in which X-axis strain sensors 9 and Y-axis strain sensors 10 are set up in pairs. For example, one strain sensor is set at a symmetrical position on each side of the X-axis beam segment of the cross beam, forming a half-bridge or full-bridge; the same applies to the Y-axis. Then, the output signals of the pair of sensors in the same direction are connected to the measurement circuit for differential signal processing. This not only amplifies the useful strain signal, but also effectively cancels noise caused by temperature changes and common-mode interference, making the measurement system more stable and accurate.

[0023] The three-dimensional sensing principle in this embodiment is as follows: Figure 7 and Figure 8 As shown: When probe 22 is subjected to a small horizontal triggering force and undergoes displacement, the entire Z-axis sensing module 3 deflects angularly. During this process, probe 22 is fixed to guide post 20, and there is no relative sliding between guide post 20 and guide sleeve 19. Therefore, Z-axis spring 15 remains in its initial state, and Z-axis sensor 16 does not generate displacement or strain signals. At the same time, the inner ring of XY-axis spring 8 is fixed together with its upper and lower pressure plates 12 and 13, and rotates around the center of the central rotating ball 6 with the Z-axis sensing module 3; while the outer ring of XY-axis spring 8 is fixed by outer ring pressure plate 11 and upper shell 1, remaining stationary. As a result, the beams of XY-axis spring 8 undergo bending or torsional deformation. For example, when probe 22 deflects along the X-axis, beams 1 and 3 of spring 8 undergo bending deformation, and the corresponding X-axis sensor 9 generates a strain response; while beams 2 and 4 only undergo slight self-deflection deformation, and the corresponding Y-axis sensor 10 is almost unaffected by stress and does not generate a significant response. Similarly, when probe 22 is offset along the Y direction, sensor 9 in the X direction does not produce a significant strain response, thus achieving good decoupling in the plane.

[0024] When probe 22 is displaced along the Z-axis, guide post 20 undergoes axial displacement with probe 22 and slides relative to guide sleeve 19. Simultaneously, the return spring 21 is compressed, causing Z-axis spring 15 to bend under force. Z-axis sensor 16, arranged on it, generates strain output, and then returns to its initial position by return spring 21. Since XY-axis sensing module 2 only undergoes angular deflection around the center of central rotating ball 6, without translation along the Z-axis or probe 22 axis, X and Y-axis sensors 9 and 10 remain in a strain-free state.

Claims

1. A contact three-dimensional scanning probe with mechanical self-decoupling function, characterized in that: The XY direction sensing module and the Z direction sensing module are composed, a spherical hinge type mechanical self-decoupling structure is adopted, the center rotating ball (6) in the fixed fisheye joint rod (4) is taken as the spherical hinge center, the displacement paths of the Z direction and the XY direction are separated, the XY direction spring leaf (8) is arranged as an inner and outer ring structure, the spherical center of the XY direction spring leaf (8) and the center rotating ball (6) are located in the same plane, when the probe (22) in the Z direction sensing module is displaced along the X or Y direction, the inner ring of the XY direction spring leaf (8) deflects around the spherical center, the strain signals of the corresponding direction sensors are output, at the same time, the orthogonal direction sensors only slightly rotate with the structure and do not produce effective output, the mechanical decoupling of the X and Y direction measurements is realized, and the in-plane coupling error is reduced.

2. Contact three-dimensional scanning probe with mechanical self-decoupling function according to claim 1, characterized in that: The structure of the XY direction sensing module (2) is that the center rotating ball (6) is arranged in the bottom joint of the fixed fisheye joint rod (4), the connecting rod (7) penetrates the center rotating ball (6) along the radial direction of the center rotating ball (6), the XY direction spring leaf (8) for installing strain sensors is a rectangular inner and outer ring structure, four beam segments in cross distribution are connected between the inner ring and the outer ring to form a cross beam, the inner ring is connected with the rod end of the connecting rod (7) and deflects around the spherical center with the center rotating ball, and the outer ring is fixed, the X direction strain sensor (9) and the Y direction strain sensor (10) are distributed on the cross beam according to the X and Y directions, and the structure of the Z direction sensing module (3) is that the connecting cylinder (14) for installing the Z direction spring leaf (15) is arranged at the bottom of the inner ring of the XY direction spring leaf (8), the Z direction sensor (16) is arranged on the Z direction spring leaf (15), the vertical guide sleeve (19) is arranged below the connecting cylinder (14), the guide column (20) is arranged in the vertical guide sleeve (19), the probe (22) is fixedly arranged at the bottom end of the guide column (20), and the relative sliding of the guide column (20) and the guide sleeve (19) realizes Z direction displacement detection.

3. The contact 3D scanning probe with mechanical self-decoupling function according to claim 1, characterized in that: The XY direction sensing module (2) adopts a rectangular shell (1), the screw rod body of the fixed fisheye joint rod (4) is fixedly arranged on the upper panel center of the rectangular shell (1) through a nut (5), the mounting form of the XY direction spring leaf (8) is that the inner ring of the XY direction spring leaf (8) is fixedly mounted at the two ends of the connecting rod (7) by using the inner ring upper pressing plate (12) and the inner ring lower pressing plate (13), and the outer ring of the XY direction spring leaf (8) is fixedly mounted on the bottom surface of the rectangular shell (1) by using the outer ring pressing plate (11).

4. The contact 3D scanning probe with mechanical self-decoupling function according to claim 1, characterized in that In the Z direction sensing module (3), a guide cylinder is arranged at the bottom of the connecting cylinder (14), the guide cylinder is a connected upper cylinder (17) and lower cylinder (18), the guide sleeve (19) is arranged in the upper cylinder (17), the rebound spring (21) sleeved on the guide column (20) is arranged in the lower cylinder (18), the rebound mechanism is formed by the rebound spring (21), the guide sleeve (19) and the guide column (20), the guide column (20) forms Z direction sliding with the guide sleeve (19) when subjected to Z direction force, and is rebounded to the initial position by the rebound spring (21).

5. The contact three-dimensional scanning probe having a mechanical self-decoupling function according to claim 1, characterized in that: The differential sensing structure is arranged by arranging the X-direction strain sensors (9) and the Y-direction strain sensors (10) in pairs respectively, and the output signals of one pair of X-direction strain sensors (9) and one pair of Y-direction strain sensors (10) are respectively subjected to differential signal processing.

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