Ultrasonic signal-based point contact micro-area center accurate positioning control system and method

Abstract

The invention discloses a point contact micro-area center accurate positioning control system and method based on ultrasonic signals, and relates to the technical field of lubricating film thickness ultrasonic testing. The invention solves the problems of large error, low efficiency and insufficient precision caused by incapability of realizing high-precision and high-efficiency automatic positioning of the center of the point contact micro-area due to the fact that the existing probe positioning for measuring the thickness of the lubricating film in the point contact micro-area adopts a manual adjustment mode. The test piece system is used for forming a ball disc point contact micro-area; the ultrasonic measurement system is used for exciting an ultrasonic signal and collecting and processing a reflected signal from the contact micro-area; the multi-stage displacement table is used for bearing and driving an ultrasonic probe of the ultrasonic measurement system to carry out pose adjustment, and the motion control module can drive the multi-stage displacement table to carry out coarse positioning and accurate positioning on the ultrasonic probe according to the characteristics of a reflected signal, so that the center of a sound field focusing focal spot coincides with the center of a point contact micro area. The method is used for realizing high-precision and high-efficiency automatic positioning of the point contact micro-area center.

Description

Technical Field

[0001] This invention relates to the field of ultrasonic testing technology for lubricating film thickness, and specifically to a point contact micro-area center precise positioning control system and method based on ultrasonic signals. Background Technology

[0002] Friction pairs are widely present in basic components, and lubrication is an important means to reduce friction and wear. The quality of lubrication performance mainly depends on the thickness of the lubricating film. Dynamic measurement of the lubricating film thickness can completely and accurately reveal the evolution of the lubrication state. Ultrasonic measurement technology, as a non-invasive and non-destructive measurement technique, has the advantages of strong penetration and high measurement accuracy. It is often used to measure the thickness of submicron-level elastohydrodynamic films. Among them, the water immersion focusing probe is used to measure the thickness of lubricating films in point contact micro-regions due to its small detection area. In order to improve the measurement accuracy of the film thickness at the center of the contact micro-region, increase the test sensitivity, and enhance the signal-to-noise ratio, when using the water immersion focusing probe to measure the lubricating film thickness, it is necessary to adjust the position of the probe so that the center of the sound field focusing spot coincides with the center of the contact micro-region. However, the current positioning method is achieved by manually adjusting the probe position using a displacement stage and relying on visual observation of the reflected signal. Manual adjustment and visual observation will produce large errors, resulting in the sound field focusing spot center and the center of the contact micro-region not necessarily coinciding precisely, thus making it impossible to accurately measure the film thickness at the center of the contact micro-region. Furthermore, under light load conditions, the contact radius may only be tens of micrometers. For such extremely small contact micro-areas, manual displacement stages are difficult to achieve precise positioning due to their low accuracy, thus failing to meet the accuracy requirements for testing the film thickness at the center of the contact micro-area. Summary of the Invention

[0003] The purpose of this invention is to address the problems of existing point contact micro-area lubricating film thickness measurement probe positioning using manual adjustment, which cannot achieve high-precision and high-efficiency automatic positioning of the center of the point contact micro-area, resulting in large errors, low efficiency, and insufficient accuracy. Therefore, based on LabVIEW programming and ultrasonic reflection signal analysis, this invention provides a point contact micro-area center precise positioning control system and method based on ultrasonic signals.

[0004] The technical solution of this invention is:

[0005] This invention provides a precise positioning and control system for the center of a point contact micro-region based on ultrasonic signals, comprising a specimen system, an ultrasonic measurement system, and a probe posture control system. The specimen system is used to form a ball-and-disc point contact micro-region. The ultrasonic measurement system is used to excite ultrasonic signals and acquire and process reflected signals from the contact micro-region. The probe posture control system includes a multi-stage displacement stage 1 and a motion control module. The multi-stage displacement stage 1 is used to support and drive the water-immersion focusing ultrasonic probe 2 of the ultrasonic measurement system for posture adjustment. The multi-stage displacement stage 1 includes a micrometer-level motorized displacement stage for coarse positioning. The system includes a nanoscale piezoelectric displacement stage for precise positioning; the motion control module is connected to the host computer 9 of the ultrasonic measurement system, and the host computer 9 transmits motion commands to the motion control module based on the reflected signal; the motion control module is also connected to the multi-stage displacement stage 1; the motion control module is configured to: drive the micrometer-level electric displacement stage to perform coarse positioning of the water immersion focused ultrasonic probe 2 based on the characteristics of the reflected signal, and drive the nanoscale piezoelectric displacement stage to perform precise positioning of the water immersion focused ultrasonic probe 2, so that the center of the sound field focusing focal spot coincides with the center of the point contact micro-area.

[0006] Furthermore, the specimen system includes a ball specimen 3, a disc specimen 4, and a corresponding clamping fixture. The disc specimen 4 is located above the ball specimen 3. The clamping fixture of the ball specimen 3 is installed on a vertical guide mechanism, which can drive the ball specimen 3 to move in the vertical direction to contact or separate from the disc specimen 4.

[0007] Furthermore, the multi-stage displacement stage 1 also includes a manual displacement stage, on which the micron-level electric displacement stage and the nano-level piezoelectric displacement stage are sequentially mounted. The manual displacement stage is used for the initial coarse positioning of the water immersion focused ultrasound probe 2.

[0008] Furthermore, the motion control module includes a motion control card 5 and a motor driver 6. The motion control card 5 is connected to the ultrasonic measurement system via signal, and the motor driver 6 is connected to the micron-level electric displacement stage via control. The nano-level piezoelectric displacement stage is connected to a voltage driving device via control.

[0009] Furthermore, the multi-stage displacement stage 1 has five degrees of freedom, enabling adjustment of the pitch angle, tilt angle, vertical height, front-back displacement, and left-right displacement of the water immersion focused ultrasound probe 2.

[0010] Furthermore, the ultrasonic measurement system includes a water immersion focused ultrasonic probe 2, a pulse transceiver 7, a data acquisition and storage device 8, and a host computer 9; the pulse transceiver 7 is connected to the water immersion focused ultrasonic probe 2; one end of the data acquisition and storage device 8 is connected to the pulse transceiver 7, and the other end is connected to the host computer 9, and the host computer 9 is signal-connected to the motion control module.

[0011] This invention also provides a precise positioning control method for the center of a point contact micro-region based on ultrasonic signals. This method uses the precise positioning control system for the center of a point contact micro-region based on ultrasonic signals as described above, and includes the following steps:

[0012] Step 1: Initial positioning of the manual displacement stage:

[0013] The position of the immersion focused ultrasound probe 2 is adjusted by manually adjusting the displacement stage to make its central axis as close to vertical as possible and pass through the center of the spherical specimen 3. At the same time, the distance between the immersion focused ultrasound probe 2 and the disc specimen 4 is adjusted to make it as close as possible to the theoretically calculated value. The theoretical calculated value The calculation is as follows:

[0014]

[0015] in, To ensure the correct distance between the water immersion focused ultrasound probe 2 and the disc specimen 4, The underwater focal length of the ultrasonic transducer. The thickness of disc specimen 4 The velocity of sound in disk specimen 4. The speed of sound in water;

[0016] Step 2: Coarse positioning using a micron-level electric displacement stage:

[0017] The pose of the water immersion focused ultrasound probe 2 is adjusted using a micrometer-level electric displacement stage, and high-precision positioning of the center of the contact micro-region is achieved by analyzing the ultrasonic reflection signal. Specifically, this includes:

[0018] Based on the actual time difference and theoretical time difference of the reflected signals from the upper and lower surfaces of the disk specimen 4 received by the water immersion focused ultrasonic probe 2. The comparison, and / or the comparison between the actual center frequency and the theoretical center frequency, adjusts the pitch and roll angles of the water immersion focused ultrasound probe 2 until the ultrasound is perpendicularly incident on the oil film layer, the theoretical time difference. The calculation is as follows:

[0019]

[0020] The actual time difference between the reflected signals from the upper and lower surfaces of the disk specimen (4) received by the water immersion focused ultrasound probe (2) is tested as follows: the initial time of the pulses corresponding to the upper and lower surfaces of the disk specimen (4) in the ultrasound reflection signal curve is obtained respectively, and the difference between the two is the actual time difference; if the actual time difference obtained by the test is different from the theoretical time difference obtained by the calculation, the actual time difference is determined by the actual time difference obtained by the test. If the time difference is equal within the allowable error range, then the ultrasound is incident perpendicularly to the oil film layer; if the actual time difference is greater than the theoretical time difference... If the ultrasound is obliquely incident on the oil film layer, the reflected signal is converted from the time domain to the frequency domain using a fast Fourier transform. The center frequency of the ultrasonic transducer is used to determine whether the ultrasound is perpendicularly incident on the oil film layer. If the actual center frequency obtained by the test is equal to the theoretical center frequency within the allowable error range, the ultrasound is perpendicularly incident on the oil film layer. When the result shows that the ultrasound is obliquely incident on the oil film layer, the appropriate motion parameters are set on the host computer (9), and the motion control signal is transmitted to the motor driver (6) through the motion control card (5), thereby controlling the electric displacement stage to adjust the pitch angle and flip angle of the water immersion focusing ultrasonic probe (2) until the result shows that the ultrasound is perpendicularly incident on the oil film layer.

[0021] Based on the actual time and theoretical time of the reflected signal from the upper surface of the disk specimen 4 received by the water immersion focused ultrasonic probe 2. By comparison, the vertical height of the water immersion focused ultrasound probe 2 was adjusted until the distance was correct, and the theoretical time was determined. The calculation is as follows:

[0022]

[0023] The actual time of the reflected signal from the upper surface of the disk specimen (4) received by the water immersion focused ultrasonic probe (2) is tested as follows: The pulse corresponding to the upper surface of the disk specimen (4) is searched from the ultrasonic reflection signal curve, and the initial time of this pulse, i.e., the actual time, is obtained; if the actual time obtained by the test differs from the calculated theoretical time... If the distances are equal within the allowable error range, then the distance between the immersion focused ultrasound probe (2) and the disc specimen (4) is too large. In this case, the electric displacement stage is controlled to move the immersion focused ultrasound probe (2) downwards. If the actual time is less than the theoretical time, the immersion focused ultrasound probe (2) is moved downwards. If the distance between the water immersion focused ultrasound probe (2) and the disc specimen (4) is too small, then the electric displacement stage is controlled to move the water immersion focused ultrasound probe (2) upward.

[0024] Lubricating film thickness With reflection coefficient amplitude The relationship is as follows:

[0025]

[0026] in, , The acoustic impedances of the spherical specimen (3) and the disc specimen (4) are respectively. The angular frequency of the sound wave. The density of the lubricating oil, The velocity of sound in the oil film;

[0027] According to Hertzian contact theory, the contact micro-region of the ball-disc is circular. When the contact micro-region is completely immersed in lubricating oil, the oil film thickness varies at different locations within and near the contact micro-region. The closer the distance to the center of the contact micro-region, the thinner the oil film and the smaller the reflection coefficient amplitude. The oil film thickness is thinnest at the center of the contact micro-region, so the reflection coefficient amplitude should be the smallest there. Therefore, when the ultrasonic probe is moved through the contact micro-region in a certain step along the straight line containing the chord of the circular contact micro-region, the peak value of the oil film reflection signal should first decrease and then increase. The closer the chord of the circle is to the center, the greater the gradient of the change in the peak value of the oil film reflection signal. The gradient of the change in the peak value of the oil film reflection signal is the largest in the diameter direction. Therefore, by checking whether the gradient of the change in the peak value of the oil film reflection signal is the largest, we can find the diameter passing through the center or the chord closest to the center. Then, by checking whether the peak value of the oil film reflection signal is the smallest, we can find the center position or the point closest to the center along the found path. This point is the center of the contact micro-region determined by coarse positioning.

[0028] Step 3: Precise positioning using a nanoscale piezoelectric displacement stage:

[0029] The position of the water immersion focused ultrasonic probe 2 in the horizontal plane is adjusted by a nanoscale piezoelectric displacement stage, and high-precision positioning of the center of the contact micro-area is achieved by analyzing the ultrasonic reflection signal. Specifically, this includes: using the approximate area determined by coarse positioning as the center, setting the movement range and movement step size of the water immersion focused ultrasonic probe 2 in the horizontal plane; driving the nanoscale piezoelectric displacement stage to make the water immersion focused ultrasonic probe 2 scan each point within the movement range according to the movement step size and collect the oil film reflection signal at each point; searching for the position with the minimum peak value of the oil film reflection signal, which is the center of the precisely positioned contact micro-area, and moving the water immersion focused ultrasonic probe 2 to this position.

[0030] Furthermore, the step of coarse positioning using the micron-level electric displacement stage, specifically "determining the approximate area of ​​the center of the contact micro-region based on the gradient of the change in the peak value of the oil film reflection signal," involves: driving the micron-level electric displacement stage to move the water immersion focused ultrasound probe 2 along different chord paths and acquiring the peak value of the oil film reflection signal in real time; comparing the gradient of the change in the peak value of the signal on different paths, identifying the path with the largest gradient of the change in the peak value as the diameter passing through the center of the contact micro-region; moving the water immersion focused ultrasound probe 2 along the identified diameter path, and determining the point with the smallest peak value of the oil film reflection signal as the approximate area of ​​the center of the contact micro-region.

[0031] Furthermore, in the coarse positioning step of the micron-level electric displacement stage, the operation of adjusting the pitch and roll angles of the water immersion focused ultrasonic probe 2 until the ultrasonic waves are perpendicularly incident on the oil film layer is achieved by the host computer 9 automatically comparing the actual time difference with the theoretical time difference. The system calculates the actual center frequency and the theoretical center frequency, and automatically generates control commands to drive the micron-level electric displacement stage to perform adjustments when a deviation is detected.

[0032] Furthermore, in the precise positioning step of the nanoscale piezoelectric displacement stage, the moving step size is set according to the acoustic field focusing focal spot size of the water immersion focusing ultrasonic probe 2, and the moving step size must be small enough to ensure that the acoustic field focusing focal spot can scan to the center of the contact micro-area.

[0033] Compared with the prior art, the present invention has the following advantages:

[0034] 1. The present invention utilizes an electric displacement stage to make the movement of the water immersion focused ultrasound probe 2 more stable.

[0035] 2. The present invention drives the electric displacement stage to adjust the position of the water immersion focused ultrasound probe 2 based on the relevant precise values ​​of the collected ultrasonic reflection signals, rather than relying solely on visual observation, thus making the positioning of the center of the contact micro-area more accurate.

[0036] 3. This invention combines ultrasonic film thickness measurement technology with motion control technology using LabVIEW software. A single software interface can both acquire relevant data information of the reflected signal and drive the water immersion focusing ultrasonic probe 2 to move, making the operation simpler and more convenient.

[0037] 4. This invention utilizes a manual displacement stage, a micron-level electric displacement stage, and a nanometer-level piezoelectric displacement stage to sequentially adjust the position and orientation of the water immersion focusing ultrasonic probe 2, completing three levels of adjustment from low precision to higher precision and then to high precision, significantly improving the positioning accuracy of the center of the contact micro-area and effectively saving positioning time. Attached Figure Description

[0038] Figure 1 This is a schematic diagram of the structure of the point contact micro-area center precise positioning control system based on ultrasonic signals of the present invention;

[0039] Figure 2 This is a schematic diagram of sound field focusing during effective measurement according to the present invention;

[0040] Figure 3 This is a schematic diagram of the height and angle adjustment of the water immersion focused ultrasound probe 2 of the present invention;

[0041] Figure 4 This is a schematic diagram of the water immersion focused ultrasound probe 2 of the present invention scanning and moving in the horizontal plane;

[0042] Figure 5 This is a schematic diagram of the search path of the water immersion focusing ultrasonic probe 2 in the horizontal plane during coarse positioning according to the present invention;

[0043] Figure 6This is a schematic diagram of the water immersion focusing ultrasonic probe 2 scanning grid points in the horizontal plane during precise positioning according to the present invention;

[0044] Figure 7 This is a time-domain diagram of the oil film reflection signal when the sound field focusing focal spot of the present invention is located at different positions;

[0045] Figure 8 This is a flowchart of the positioning control process of the present invention;

[0046] Figure 9 This is a schematic diagram of the ball specimen 3, the disc specimen 4, and the corresponding clamping fixture structure in the specimen system of the present invention.

[0047] In the figure: 1-Multi-stage displacement stage; 2-Immersion focused ultrasonic probe; 3-Ball specimen; 4-Disc specimen; 5-Motion control card; 6-Motor driver; 7-Pulse transceiver; 8-Data acquisition and storage device; 9-Host computer; 10-Ball clamp; 11-Disc clamp; 12-Support arm. Detailed Implementation

[0048] Specific implementation method one: Combining Figures 1 to 9 This embodiment describes a precise positioning and control system for a point contact micro-area center based on ultrasonic signals. The system includes a specimen system, an ultrasonic measurement system, and a probe posture control system. The specimen system forms a ball-and-disc point contact micro-area. The ultrasonic measurement system excites ultrasonic signals and collects and processes reflected signals from the contact micro-area. The probe posture control system includes a multi-stage displacement stage 1 and a motion control module. The multi-stage displacement stage 1 carries and drives the water-immersion focusing ultrasonic probe 2 of the ultrasonic measurement system for posture adjustment. The multi-stage displacement stage 1 includes a micrometer-level electrical component for coarse positioning. The system includes a dynamic displacement stage and a nanoscale piezoelectric displacement stage for precise positioning; the motion control module is connected to the host computer 9 of the ultrasonic measurement system, and the host computer 9 transmits motion commands to the motion control module based on the reflected signal; the motion control module is also connected to the multi-stage displacement stage 1; the motion control module is configured to: drive the micrometer-level electric displacement stage to perform coarse positioning of the water immersion focused ultrasonic probe 2 based on the characteristics of the reflected signal, and drive the nanoscale piezoelectric displacement stage to perform precise positioning of the water immersion focused ultrasonic probe 2, so that the center of the sound field focusing focal spot coincides with the center of the point contact micro-area.

[0049] Specific Implementation Method Two: Combining Figures 1 to 9This embodiment describes a specimen system comprising a ball specimen 3, a disc specimen 4, and corresponding clamping fixtures. The disc specimen 4 is positioned above the ball specimen 3. The clamping fixture for the ball specimen 3 is mounted on a vertical guide mechanism, enabling the ball specimen 3 to move vertically to contact or separate from the disc specimen 4. This configuration, with the disc specimen 4 above the ball specimen 3 and the ball specimen 3 able to move vertically, serves two purposes: firstly, to separate the ball and disc to a sufficient distance for specimen replacement; and secondly, to bring the ball and disc into contact and apply a contact load. Other components and connections are the same as in Specific Embodiment One.

[0050] like Figure 9 As shown, both the spherical specimen 3 and the disc specimen 4 in the specimen system are equipped with corresponding clamping fixtures, wherein:

[0051] The ball clamping fixture corresponding to the ball specimen 3 includes a ball clamping member 10, a transverse movement mechanism, and a longitudinal movement mechanism. The ball clamping member 10 is used to clamp the ball specimen 3. The ball clamping member 10 is installed at the moving end of the transverse movement mechanism. The fixed end of the transverse movement mechanism is installed at the moving end of the longitudinal movement mechanism, and the fixed end of the longitudinal movement mechanism is installed on the frame (not shown in the figure). Both the transverse movement mechanism and the longitudinal movement mechanism employ a screw-nut transmission mechanism and a guide rail-slider mechanism.

[0052] The disc clamping fixture corresponding to the disc specimen 4 includes a disc clamping component 11 and a support arm 12. The disc clamping component 11 is a circular cylindrical structure. The bottom of the disc clamping component 11 is provided to clamp the disc specimen 4 (the disc specimen 4 and the disc clamping component 11 can be an integral structure or a separate structure, sealed by an O-ring and connected by multiple screws). The outer side of the disc clamping component 11 is provided with a flange ring arranged coaxially along the circumferential direction. The flange ring is connected to the support arm 12, which is mounted on the frame (not shown in the figure).

[0053] Specific implementation method three: Combining Figures 1 to 9 This embodiment further includes a manual displacement stage 1. The micrometer-level electric displacement stage and the nanometer-level piezoelectric displacement stage are sequentially mounted on the manual displacement stage. The manual displacement stage is used for the initial coarse positioning of the water immersion focused ultrasound probe 2. Other components and connections are the same as in specific embodiments one or two.

[0054] Specific implementation method four: Combination Figures 1 to 9This embodiment describes a motion control module comprising a motion control card 5 and a motor driver 6. The motion control card 5 is signal-connected to the ultrasonic measurement system, and the motor driver 6 is control-connected to the micron-level electric displacement stage. The nanon-level piezoelectric displacement stage is control-connected to a voltage driving device. In this configuration, the multi-stage displacement stage 1 is assembled from a manual displacement stage, a micron-level electric displacement stage, and a nanon-level piezoelectric displacement stage in a bottom-to-top order. The motion control card is connected to both the host computer and the motor driver. Motion control signals are transmitted from the host computer to the motor driver via the motion control card, thereby driving the micron-level electric displacement stage and the nanon-level piezoelectric displacement stage to adjust their poses according to the given motion control signals. Other components and connections are the same as in specific embodiments one, two, or three.

[0055] Specific Implementation Method Five: Combining Figures 1 to 9 This embodiment describes a multi-stage displacement stage 1 with five degrees of freedom, capable of adjusting the pitch angle, tilt angle, vertical height, forward / backward displacement, and left / right displacement of the water immersion focused ultrasound probe 2. Other components and connections are the same as in specific embodiments one, two, three, or four.

[0056] In this embodiment, the manual displacement stage, micron-level electric displacement stage, and nano-level piezoelectric displacement stage of the multi-stage displacement stage 1 are all commercially available products. The manual displacement stage is the XYZ60-L / C / R and GFW60-60 manual displacement stage manufactured by Ximu Precision Technology (Dongguan) Co., Ltd.; the micron-level electric displacement stage is the LPAA601 micron-level electric displacement stage manufactured by Beijing Laiwei Instrument Co., Ltd.; and the nano-level piezoelectric displacement stage is the XY-axis piezoelectric displacement stage manufactured by Shanghai Nadong Nano Displacement Technology Co., Ltd.

[0057] Specific Implementation Method Six: Combination Figures 1 to 9 This embodiment describes an ultrasonic measurement system comprising a water immersion focused ultrasonic probe 2, a pulse transceiver 7, a data acquisition and storage device 8, and a host computer 9. The pulse transceiver 7 is connected to the water immersion focused ultrasonic probe 2. One end of the data acquisition and storage device 8 is connected to the pulse transceiver 7, and the other end is connected to the host computer 9. The host computer 9 is signal-connected to the motion control module. In this configuration, the host computer sends pulse control signals to the pulse transceiver, which, connected to the ultrasonic probe, triggers the ultrasonic signal and receives the echo signal. The echo signal is then transmitted to the host computer via the data acquisition and storage device. Other components and connections are the same as in specific embodiments one, two, three, four, or five.

[0058] Specific implementation method seven: Combination Figures 1 to 9This embodiment describes a precise positioning and control method for the center of a point contact micro-area based on ultrasonic signals. The method uses the precise positioning and control system for the center of a point contact micro-area based on ultrasonic signals as described above, and includes the following steps:

[0059] Step 1: Initial positioning of the manual displacement stage:

[0060] The position of the immersion focused ultrasound probe 2 is adjusted by manually adjusting the displacement stage to make its central axis as close to vertical as possible and pass through the center of the spherical specimen 3. At the same time, the distance between the immersion focused ultrasound probe 2 and the disc specimen 4 is adjusted to make it as close as possible to the theoretically calculated value. The theoretical calculated value The calculation is as follows:

[0061]

[0062] in, To ensure the correct distance between the water immersion focused ultrasound probe 2 and the disc specimen 4, The underwater focal length of the ultrasonic transducer. The thickness of disc specimen 4 The velocity of sound in disk specimen 4. The speed of sound in water;

[0063] Step 2: Coarse positioning using a micron-level electric displacement stage:

[0064] The pose of the water immersion focused ultrasound probe 2 is adjusted using a micrometer-level electric displacement stage, and high-precision positioning of the center of the contact micro-region is achieved by analyzing the ultrasonic reflection signal. Specifically, this includes:

[0065] Based on the actual time difference and theoretical time difference of the reflected signals from the upper and lower surfaces of the disk specimen 4 received by the water immersion focused ultrasonic probe 2. The comparison, and / or the comparison between the actual center frequency and the theoretical center frequency, adjusts the pitch and roll angles of the water immersion focused ultrasound probe 2 until the ultrasound is perpendicularly incident on the oil film layer, the theoretical time difference. The calculation is as follows:

[0066]

[0067] The actual time difference between the reflected signals from the upper and lower surfaces of the disk specimen (4) received by the water immersion focused ultrasound probe (2) is tested as follows: the initial time of the pulses corresponding to the upper and lower surfaces of the disk specimen (4) in the ultrasound reflection signal curve is obtained respectively, and the difference between the two is the actual time difference; if the actual time difference obtained by the test is different from the theoretical time difference obtained by the calculation, the actual time difference is determined by the actual time difference obtained by the test. If the time difference is equal within the allowable error range, then the ultrasound is incident perpendicularly to the oil film layer; if the actual time difference is greater than the theoretical time difference... If the ultrasound is obliquely incident on the oil film layer, the reflected signal is converted from the time domain to the frequency domain using a fast Fourier transform. The center frequency of the ultrasonic transducer is used to determine whether the ultrasound is perpendicularly incident on the oil film layer. If the actual center frequency obtained by the test is equal to the theoretical center frequency within the allowable error range, the ultrasound is perpendicularly incident on the oil film layer. When the result shows that the ultrasound is obliquely incident on the oil film layer, the appropriate motion parameters are set on the host computer (9), and the motion control signal is transmitted to the motor driver (6) through the motion control card (5), thereby controlling the electric displacement stage to adjust the pitch angle and flip angle of the water immersion focusing ultrasonic probe (2) until the result shows that the ultrasound is perpendicularly incident on the oil film layer.

[0068] Based on the actual time and theoretical time of the reflected signal from the upper surface of the disk specimen 4 received by the water immersion focused ultrasonic probe 2. By comparison, the vertical height of the water immersion focused ultrasound probe 2 was adjusted until the distance was correct, and the theoretical time was determined. The calculation is as follows:

[0069]

[0070] The actual time of the reflected signal from the upper surface of the disk specimen (4) received by the water immersion focused ultrasonic probe (2) is tested as follows: The pulse corresponding to the upper surface of the disk specimen (4) is searched from the ultrasonic reflection signal curve, and the initial time of this pulse, i.e., the actual time, is obtained; if the actual time obtained by the test differs from the calculated theoretical time... If the distances are equal within the allowable error range, then the distance between the immersion focused ultrasound probe (2) and the disc specimen (4) is too large. In this case, the electric displacement stage is controlled to move the immersion focused ultrasound probe (2) downwards. If the actual time is less than the theoretical time, the immersion focused ultrasound probe (2) is moved downwards. If the distance between the water immersion focused ultrasound probe (2) and the disc specimen (4) is too small, then the electric displacement stage is controlled to move the water immersion focused ultrasound probe (2) upward.

[0071] Lubricating film thickness With reflection coefficient amplitude The relationship is as follows:

[0072]

[0073] in, , The acoustic impedances of the spherical specimen (3) and the disc specimen (4) are respectively. The angular frequency of the sound wave. The density of the lubricating oil, The velocity of sound in the oil film;

[0074] According to Hertzian contact theory, the contact micro-region of the ball-disc is circular. When the contact micro-region is completely immersed in lubricating oil, the oil film thickness varies at different locations within and near the contact micro-region. The closer the distance to the center of the contact micro-region, the thinner the oil film and the smaller the reflection coefficient amplitude. The oil film thickness is thinnest at the center of the contact micro-region, so the reflection coefficient amplitude should be the smallest there. Therefore, when the ultrasonic probe is moved through the contact micro-region in a certain step along the straight line containing the chord of the circular contact micro-region, the peak value of the oil film reflection signal should first decrease and then increase. The closer the chord of the circle is to the center, the greater the gradient of the change in the peak value of the oil film reflection signal. The gradient of the change in the peak value of the oil film reflection signal is the largest in the diameter direction. Therefore, by checking whether the gradient of the change in the peak value of the oil film reflection signal is the largest, we can find the diameter passing through the center or the chord closest to the center. Then, by checking whether the peak value of the oil film reflection signal is the smallest, we can find the center position or the point closest to the center along the found path. This point is the center of the contact micro-region determined by coarse positioning.

[0075] Step 3: Precise positioning using a nanoscale piezoelectric displacement stage:

[0076] The position of the water immersion focused ultrasonic probe 2 in the horizontal plane is adjusted by a nanoscale piezoelectric displacement stage, and high-precision positioning of the contact micro-area center is achieved by analyzing the ultrasonic reflection signal. Specifically, this includes: setting the movement range and step size of the water immersion focused ultrasonic probe 2 in the horizontal plane, using the approximate area determined by coarse positioning as the center; driving the nanoscale piezoelectric displacement stage to make the water immersion focused ultrasonic probe 2 scan each point within the movement range according to the step size and collect the oil film reflection signal at each point; searching for the position with the minimum peak value of the oil film reflection signal, which is the precisely positioned contact micro-area center, and moving the water immersion focused ultrasonic probe 2 to this position. Other components and connections are the same as in specific embodiments one, two, three, four, five, or six.

[0077] Specific implementation method eight: Combination Figures 1 to 9 In this embodiment, the coarse positioning step of the micron-level electric displacement stage, specifically "determining the approximate area of ​​the contact micro-region center based on the gradient of the oil film reflection signal peak value," involves: driving the micron-level electric displacement stage to move the water immersion focused ultrasonic probe 2 along different chord paths and acquiring the oil film reflection signal peak value in real time; comparing the gradient of the signal peak value change on different paths, identifying the path with the largest gradient as the diameter passing through the contact micro-region center; moving the water immersion focused ultrasonic probe 2 along the identified diameter path, and determining the point with the smallest oil film reflection signal peak value as the approximate area of ​​the contact micro-region center. Other components and connections are the same as in specific embodiments one, two, three, four, five, six, or seven.

[0078] Specific Implementation Method Nine: Combining Figures 1 to 9In this embodiment, the coarse positioning step of the micron-level electric displacement stage, specifically the adjustment of the pitch and rotation angles of the water immersion focused ultrasonic probe 2 until the ultrasound is perpendicularly incident on the oil film layer, is achieved by the host computer 9 automatically comparing the actual time difference with the theoretical time difference. The system calculates the actual center frequency and the theoretical center frequency, and automatically generates control commands to drive the micron-level electric displacement stage to perform adjustments when a deviation is detected. Other components and connections are the same as in specific embodiments one, two, three, four, five, six, seven, or eight.

[0079] Specific Implementation Method Ten: Combining Figures 1 to 9 In this embodiment, the precise positioning step of the nanoscale piezoelectric displacement stage is set according to the size of the acoustic field focusing focal spot of the water immersion focused ultrasonic probe 2. The step size must be small enough to ensure that the acoustic field focusing focal spot can scan to the center of the contact micro-region. Other components and connections are the same as in embodiments one, two, three, four, five, six, seven, eight, or nine.

[0080] Example 1: See Figure 1 A precise positioning device for point-contact micro-area centers based on ultrasonic signals includes a spherical specimen and its clamping fixture, a disc specimen and its clamping fixture, an ultrasonic probe, a probe fixture, a displacement stage, a motor driver, a motion control card, a pulse transceiver, a data acquisition and storage device, and a host computer. The disc specimen is positioned above the spherical specimen. The host computer sends pulse control signals to the pulse transceiver, which is connected to the ultrasonic probe to trigger the ultrasonic signal and receive the echo signal. The echo signal is then transmitted to the host computer via the data acquisition and storage device. The motion control card is connected to both the host computer and the motor driver. Motion control signals are transmitted from the host computer to the motor driver via the motion control card, thereby driving the electric displacement stage to adjust its posture according to the given motion control signals. The displacement stage has five degrees of freedom, allowing control of the ultrasonic probe's pitch angle, roll angle, vertical height, forward / backward displacement, and left / right displacement.

[0081] Example 2: See Figure 2 This diagram illustrates the focused sound field for effective measurement. When measuring lubricating film thickness using a water-immersion focused ultrasonic probe, the measurement result is accurate and effective only when the entire ultrasonic pulse is incident within the contact micro-area. Therefore, it is necessary to ensure that the ultrasonic wave is incident perpendicularly to the oil film layer and that the center of the focused sound field coincides with the center of the contact micro-area. To achieve this coincidence, the vertical distance between the ultrasonic probe and the disc specimen must first be adjusted. To achieve the appropriate size, the ultrasonic probe's displacement in the horizontal plane must be adjusted to the correct position. This should be based on the thickness of the disc specimen. The theoretical time difference between the reflected signals from the upper and lower surfaces of the disk received by the ultrasonic probe is calculated. The actual time difference is obtained from the measured ultrasonic reflection signal curve. By comparing the actual time difference with the calculated theoretical time difference, and by comparing the actual center frequency with the theoretical center frequency, it is determined whether the ultrasonic wave is perpendicularly incident on the oil film layer. The time difference between the reflected signals from the upper surface of the disk received by the ultrasonic probe and... The distance between the ultrasonic probe and the disc specimen is directly proportional to the actual time obtained from the test, and the distance is compared with the calculated theoretical time to determine whether the distance is correct. The oil film thickness is thinnest at the center of the contact micro-area, so the amplitude of the reflection coefficient should be the smallest at this point. Therefore, the position of the ultrasonic probe in the horizontal plane is determined by whether the peak value of the reflected signal from the oil film layer received by the ultrasonic probe is the smallest.

[0082] Example 3: See Figure 3 , Figure 4 , Figure 5 , Figure 6 , Figure 3 This is a diagram illustrating probe height and angle adjustments. Figure 4 This is a schematic diagram of the probe scanning and moving in the horizontal plane. Figure 5 This is a schematic diagram of the probe's search path in the horizontal plane during coarse positioning. Figure 6 This is a schematic diagram illustrating the probe scanning grid points in the horizontal plane during precise positioning. Figure 7 This is a time-domain plot of the oil film reflection signal when the focal spot of the sound field is located at different positions. (Example:) Figure 3 As shown, the displacement stage can adjust the pitch and tilt angles to ensure the ultrasonic probe's sound field is perpendicularly incident on the oil film layer, and adjust the height to ensure a suitable distance between the ultrasonic probe and the disc specimen. Figure 4 As shown, the displacement stage can move the ultrasonic probe arbitrarily to various points within a certain range on the horizontal plane, thereby locating the center of the contact micro-region. For example... Figure 5 As shown, when the ultrasonic probe is moved along different paths with a certain step size, the gradient of the change in the peak value of the oil film reflection signal is different, with the gradient being the largest in the diameter direction. Figure 6 As shown, the movement range and step size (including lateral movement step size) of the ultrasound probe are set. and longitudinal movement step size The step size must be small enough to allow the focused spot of the acoustic field to scan to the center of the contact micro-area. The grid points in the diagram represent all the locations searched by the ultrasonic probe. For example... Figure 7 As shown, the peak value of the oil film reflection signal is different when the focal spot of the sound field is located at different positions. As the center of the focal spot of the sound field approaches the center of the contact micro-area, the peak value becomes smaller and smaller. When the center of the focal spot of the sound field coincides with the center of the contact micro-area, the peak value is the smallest.

[0083] Example 4: See Figure 8 The following is a flowchart of the positioning control process. Specifically, it includes the following steps: (1) Adjust the position of the ultrasonic probe by manually moving the stage to make the ultrasonic probe as close as possible to the correct position state, and complete the initial positioning; (2) Set the ultrasonic acquisition parameters and ultrasonic probe movement parameters, and continuously acquire ultrasonic reflection signals; (3) Observe the time difference and actual center frequency of the ultrasonic waves arriving at the upper and lower surfaces of the disk given by the reflected signals. If the time difference or center frequency is incorrect, drive the electric stage to adjust the pitch angle and lateral tilt angle of the ultrasonic probe until the time difference and center frequency are correct; (4) When the time difference of the ultrasonic waves arriving at the upper and lower surfaces of the disk is correct, observe the time of the ultrasonic waves arriving at the upper surface of the disk. If the time is incorrect, drive the electric stage to adjust the ultrasonic waves. (5) When the ultrasound reaches the upper surface of the disk at the correct time, drive the electric displacement stage to move the ultrasound probe to the origin position, and set the movement path and movement step of the ultrasound probe in the horizontal plane. Drive the electric displacement stage to move the ultrasound probe along different paths according to the movement step to search for the position of the contact micro-area diameter and the center of the circle, and complete the coarse positioning; (6) Set the movement step and movement range of the ultrasound probe in the horizontal plane, drive the electric displacement stage to move the ultrasound probe to scan each point in the movement range according to the movement step, and output the position of the peak value and minimum peak value of the oil film reflection signal at each point; (7) Drive the electric displacement stage to move the ultrasound probe to the point where the peak value of the oil film reflection signal is the minimum, and complete the precise positioning. The positioning ends.

[0084] The following is a real-world example of the test:

[0085] GCr15 steel ball-GCr15 steel disc point contact, 4050 aviation lubricating oil spray lubrication, steel ball diameter 30mm, sliding speed 0.628m / s, contact force 100N: theoretical result of center film thickness 0.1582μm; when relying on visual observation and manual adjustment, the center positioning of the contact micro-area takes more than 10 minutes, and the measured center film thickness is 0.1738μm; when adjusting the probe with this invention, the center positioning of the contact micro-area takes about 2-3 minutes, and the measured center film thickness is 0.1602μm.

[0086] GCr15 steel ball-GCr15 steel disc point contact, 4050 aviation lubricating oil spray lubrication, steel ball diameter 30mm, sliding speed 0.628m / s, contact force 200N: theoretical result of center film thickness is 0.1475μm; when relying on visual observation and manual adjustment, the center positioning of the contact micro-area takes more than 10 minutes, and the center film thickness measurement result is 0.1621μm; when adjusting the probe with this invention, the center positioning of the contact micro-area takes about 2-3 minutes, and the center film thickness measurement result is 0.1499μm.

[0087] GCr15 steel ball-GCr15 steel disc point contact, 4050 aviation lubricating oil spray lubrication, steel ball diameter 30mm, sliding speed 0.942m / s, contact force 200N: theoretical result of center film thickness is 0.1996μm; when relying on visual observation and manual adjustment, the center positioning of the contact micro-area takes more than 10 minutes, and the center film thickness measurement result is 0.2192μm; when adjusting the probe with this invention, the center positioning of the contact micro-area takes about 2-3 minutes, and the center film thickness measurement result is 0.2036μm.

[0088] As can be seen from the above practical examples, the present invention can effectively save more than 70% of the time required for center positioning of contact micro-areas. Furthermore, the film thickness measured by the present invention is closer to the theoretical film thickness, thus demonstrating that the present invention has higher positioning accuracy when performing center positioning of contact micro-areas.

[0089] Working principle

[0090] Combination Figures 1 to 9 The working principle of the point contact micro-area center precise positioning control system based on ultrasonic signals described in this invention is as follows: When measuring the thickness of the lubricating film using the water immersion focusing ultrasonic probe 2, the measurement result is accurate and effective only when all ultrasonic pulses are incident inside the contact micro-area. Therefore, it is necessary to ensure that the ultrasonic waves are incident perpendicularly to the oil film layer and that the center of the focused acoustic field coincides with the center of the contact micro-area. To ensure that the ultrasonic waves are incident perpendicularly to the oil film layer, the pitch and rotation angles of the water immersion focusing ultrasonic probe 2 need to be adjusted so that the central axis of the water immersion focusing ultrasonic probe 2 is perpendicular to the upper (lower) surface of the disk; to ensure that the center of the focused acoustic field coincides with the center of the contact micro-area, the following two adjustments need to be made: first, adjust the vertical distance between the water immersion focusing ultrasonic probe 2 and the disk specimen 4 so that the height of the focused acoustic field spot is consistent with that of the contact micro-area; second, adjust the horizontal displacement of the water immersion focusing ultrasonic probe 2 so that the central axis of the water immersion focusing ultrasonic probe 2 passes through the center of the contact micro-area. To achieve the above adjustment goals, initial positioning is first performed using a manual displacement stage, followed by coarse positioning using a micrometer-level electric displacement stage, and finally precise positioning using a nanometer-level piezoelectric displacement stage.

[0091] I. Initial Positioning of Manual Displacement Stage

[0092] Manual stage initial positioning refers to adjusting the ultrasonic probe's orientation using a manual stage during installation, while simultaneously relying on visual observation or measurements using mechanical tools such as calipers, to bring the probe as close as possible to the correct orientation. Although the manual stage used for initial positioning has low precision, and the errors introduced by visual observation or mechanical tool measurements are significant, manual stage initial positioning can provide a rough position for the ultrasonic probe, greatly contributing to the efficiency of subsequent coarse and fine positioning. The specific method for manual stage initial positioning is as follows:

[0093] When the disc specimen is installed horizontally, the central axis of the ultrasonic probe is perpendicular to the upper (lower) surface of the disc, meaning the central axis of the ultrasonic probe is vertical. If the central axis of the ultrasonic probe passes through the center of the contact micro-area, it must also pass through the center of the spherical specimen. Therefore, after installing the spherical specimen, use a manual displacement stage to adjust the relative position of the ultrasonic probe and the spherical specimen. Through visual observation and measurement with tools such as calipers, achieve the adjustment goal of ensuring the central axis of the ultrasonic probe is vertical and passes through the center of the spherical specimen to the greatest extent possible.

[0094] To ensure that the focused spot of the sound field is aligned with the height of the contact micro-area, a correct vertical distance must be maintained between the ultrasonic probe and the disc specimen. The theoretical calculation of this correct distance is as follows:

[0095]

[0096] in, To ensure the correct distance between the ultrasonic probe and the disc specimen, The underwater focal length of the ultrasonic transducer. The thickness of the disc specimen. The velocity of sound in the disk specimen. The speed of sound in water. After installing the disc specimen, use a manual displacement stage to adjust the distance between the ultrasonic probe and the disc specimen. Use tools such as vernier calipers to measure and adjust the distance between the ultrasonic probe and the disc specimen to the correct value.

[0097] II. Coarse Positioning Using a Micron-Level Electrodynamic Displacement Stage

[0098] Micrometer-level motorized stage coarse positioning refers to using a micrometer-level motorized stage to adjust the ultrasonic probe's pose and simultaneously relying on ultrasonic reflection signal analysis to achieve high-precision adjustment of the probe's pose, thereby achieving high-precision positioning of the contact micro-area center. Micrometer-level motorized stage coarse positioning not only compensates for the initial low positioning accuracy but also provides a more accurate contact micro-area center position for subsequent precise positioning. The specific method of micrometer-level motorized stage coarse positioning is as follows:

[0099] First, the time difference between the reflected signals from the upper and lower surfaces of the disk received by the ultrasonic probe is used to determine whether the ultrasound is incident perpendicularly to the oil film layer. The theoretical time difference between the reflected signals from the upper and lower surfaces of the disk received by the ultrasonic probe... The calculation is as follows:

[0100]

[0101] The actual time difference between the reflected signals from the upper and lower surfaces of the disk received by the ultrasonic probe is tested as follows: The initial times of the pulses corresponding to the upper and lower surfaces of the disk in the ultrasonic reflection signal curves are obtained respectively; the difference between the two is the actual time difference. If the measured actual time difference is equal to the calculated theoretical time difference within the allowable error range, the ultrasound is incident perpendicularly to the oil film layer. If the actual time difference is greater than the theoretical time difference, the ultrasound is incident obliquely to the oil film layer. Simultaneously, a Fast Fourier Transform is used to convert the reflected signal from the time domain to the frequency domain, and the center frequency of the ultrasonic transducer is used to determine whether the ultrasound is incident perpendicularly to the oil film layer. If the measured actual center frequency is equal to the theoretical center frequency within the allowable error range, the ultrasound is incident perpendicularly to the oil film layer. When the result shows that the ultrasound is incident obliquely to the oil film layer, appropriate motion parameters are set on the host computer, and the motion control signal is transmitted to the motor driver through the motion control card, thereby controlling the electric displacement stage to adjust the pitch and tilt angles of the ultrasonic probe until the result shows that the ultrasound is incident perpendicularly to the oil film layer.

[0102] Then, the distance between the ultrasonic probe and the disk specimen is determined by the time it takes for the ultrasonic probe to receive the reflected signal from the upper surface of the disk. The theoretical time for the ultrasonic probe to receive the reflected signal from the upper surface of the disk is... The calculation is as follows:

[0103]

[0104] The actual time of the reflected signal from the upper surface of the disk received by the ultrasonic probe is tested as follows: Search for the pulse corresponding to the upper surface of the disk from the ultrasonic reflection signal curve, and obtain the initial time of that pulse, i.e., the actual time. If the measured actual time is equal to the calculated theoretical time within the allowable error range, the distance between the ultrasonic probe and the disk specimen is correct. If the actual time is greater than the theoretical time, the distance between the ultrasonic probe and the disk specimen is too large, and the electric displacement stage is controlled to move the ultrasonic probe downwards. If the actual time is less than the theoretical time, the distance between the ultrasonic probe and the disk specimen is too small, and the electric displacement stage is controlled to move the ultrasonic probe upwards.

[0105] Lubricating film thickness With reflection coefficient amplitude The relationship is as follows:

[0106]

[0107] in, , The acoustic impedances are those of the disk specimen and the sphere specimen, respectively. The angular frequency of the sound wave. The density of the lubricating oil, Let be the speed of sound in the oil film. According to Hertzian contact theory, the contact micro-region of the ball-disc is circular. When the contact micro-region is completely immersed in lubricating oil, the oil film thickness varies at different locations within and near the micro-region. The closer the distance to the center of the contact micro-region, the thinner the oil film and the smaller the reflection coefficient amplitude. The oil film thickness is thinnest at the center of the contact micro-region, therefore the reflection coefficient amplitude should be the smallest there. Therefore, when the ultrasonic probe is moved through the contact micro-region in a certain step along the straight line containing the chord of the circular contact micro-region, the peak value of the oil film reflection signal should first decrease and then increase. The closer the chord is to the center, the greater the gradient of the oil film reflection signal peak value; the gradient is greatest along the diameter. Therefore, by checking if the gradient of the oil film reflection signal peak value is maximum, we can find the diameter passing through the center or the chord closest to the center. Then, by checking if the oil film reflection signal peak value is minimum, we can find the center position or the point closest to the center along the found path. This point is the center of the contact micro-region determined by coarse positioning.

[0108] III. Precise Positioning by Nanoscale Piezoelectric Displacement Stage

[0109] Due to the limited accuracy of micron-level electric displacement stages, the determined center of the contact micro-area exhibits a certain deviation during coarse positioning. Therefore, a more precise nanometer-level piezoelectric displacement stage is chosen for accurate positioning. Precise positioning using a nanometer-level piezoelectric displacement stage involves adjusting the ultrasonic probe's position in the horizontal plane using the stage, while simultaneously relying on ultrasonic reflection signal analysis to achieve high-precision adjustment of the probe's position, thereby realizing high-precision positioning of the contact micro-area center. The specific method for precise positioning using a nanometer-level piezoelectric displacement stage is as follows:

[0110] The accuracy of the ultrasonic probe's position in the horizontal plane is determined by minimizing the peak value of the reflected signal from the oil film layer received by the ultrasonic probe. Using the center determined by coarse positioning as the center, the movement range and step size of the ultrasonic probe in the horizontal plane are set. The step size must be small enough to ensure that the focused spot of the sound field can scan to the center of the contact micro-region. The ultrasonic probe scans each point within the movement range according to the step size and collects the oil film reflection signal at each point. The position with the minimum peak value of the oil film reflection signal is found; this position is the precisely located center of the contact micro-region, and the ultrasonic probe is moved to this position.

[0111] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A point-contact micro-area center precise positioning control system based on ultrasonic signals, characterized in that, The system includes a specimen system, an ultrasonic measurement system, and a probe posture control system. The specimen system is used to form a ball-and-disc point contact micro-region. The ultrasonic measurement system is used to excite ultrasonic signals and collect and process reflected signals from the contact micro-region. The probe posture control system includes a multi-stage displacement stage (1) and a motion control module. The multi-stage displacement stage (1) is used to support and drive the water immersion focusing ultrasonic probe (2) of the ultrasonic measurement system to perform posture adjustment. The multi-stage displacement stage (1) includes a micron-level electric displacement stage for coarse positioning and a nanometer-level piezoelectric displacement stage for precise positioning. The motion control module is connected to the host computer (9) of the ultrasonic measurement system. The host computer (9) sends motion commands to the motion control module according to the reflected signal. The motion control module is also connected to the multi-stage displacement stage (1). The motion control module is configured to drive the micron-level electric displacement stage to perform coarse positioning of the water immersion focused ultrasonic probe (2) according to the characteristics of the reflected signal, and drive the nano-level piezoelectric displacement stage to perform precise positioning of the water immersion focused ultrasonic probe (2) so that the center of the sound field focusing spot coincides with the center of the point contact micro-area.

2. The point contact micro-area center precise positioning control system based on ultrasonic signals according to claim 1, characterized in that: The test specimen system includes a ball specimen (3), a disc specimen (4) and a corresponding clamping fixture. The disc specimen (4) is located above the ball specimen (3). The clamping fixture of the ball specimen (3) is installed on a vertical guide mechanism, which can drive the ball specimen (3) to move in the vertical direction so as to contact or separate from the disc specimen (4).

3. The point contact micro-area center precise positioning control system based on ultrasonic signals according to claim 2, characterized in that: The multi-stage displacement stage (1) also includes a manual displacement stage. The micron-level electric displacement stage and the nano-level piezoelectric displacement stage are sequentially mounted on the manual displacement stage. The manual displacement stage is used for the initial coarse positioning of the water immersion focused ultrasound probe (2).

4. The point contact micro-area center precise positioning control system based on ultrasonic signals according to claim 3, characterized in that: The motion control module includes a motion control card (5) and a motor driver (6). The motion control card (5) is connected to the ultrasonic measurement system via signal, and the motor driver (6) is connected to the micron-level electric displacement stage via control. The nano-level piezoelectric displacement stage is connected to a voltage driving device via control.

5. The point contact micro-area center precise positioning control system based on ultrasonic signals according to claim 4, characterized in that: The multi-stage displacement stage (1) has five degrees of freedom and can adjust the pitch angle, flip angle, vertical height, front-back displacement and left-right displacement of the water immersion focused ultrasound probe (2).

6. The point contact micro-area center precise positioning control system based on ultrasonic signals according to claim 5, characterized in that: The ultrasonic measurement system includes a water immersion focused ultrasonic probe (2), a pulse transceiver (7), a data acquisition and storage device (8), and a host computer (9); the pulse transceiver (7) is connected to the water immersion focused ultrasonic probe (2); one end of the data acquisition and storage device (8) is connected to the pulse transceiver (7), and the other end is connected to the host computer (9); the host computer (9) is connected to the motion control module via signal connection.

7. A method for precise positioning and control of the center of a point-contact micro-region based on ultrasonic signals, characterized in that, The method uses a point-contact micro-area center-precision positioning control system based on ultrasonic signals as described in any one of claims 1-6, and includes the following steps: Step 1: Initial positioning of the manual displacement stage: The position of the immersion focused ultrasound probe (2) is adjusted by manually adjusting the displacement stage so that the central axis of the immersion focused ultrasound probe (2) is as close as possible to a vertical state and passes through the center of the spherical specimen (3). At the same time, the distance between the immersion focused ultrasound probe (2) and the disc specimen (4) is adjusted to be as close as possible to the theoretical calculation value. The theoretical calculated value The calculation is as follows: in, To ensure the correct distance between the water immersion focused ultrasound probe (2) and the disk specimen (4), The underwater focal length of the ultrasonic transducer. The thickness of the disc specimen (4) is... The velocity of sound in the disk specimen (4) The speed of sound in water; Step 2: Coarse positioning using a micron-level electric displacement stage: The pose of the water immersion focused ultrasound probe (2) is adjusted by a micrometer-level electric displacement stage, and high-precision positioning of the center of the contact micro-area is achieved by relying on the analysis of ultrasound reflection signals. Specifically, this includes: Based on the actual time difference and theoretical time difference of the reflected signals from the upper and lower surfaces of the disk specimen (4) received by the water immersion focused ultrasonic probe (2). The comparison, and / or the comparison between the actual center frequency and the theoretical center frequency, adjusts the pitch and roll angles of the water immersion focused ultrasound probe (2) until the ultrasound is perpendicularly incident on the oil film layer, the theoretical time difference The calculation is as follows: The actual time difference between the reflected signals from the upper and lower surfaces of the disk specimen (4) received by the water immersion focused ultrasound probe (2) is tested as follows: the initial time of the pulses corresponding to the upper and lower surfaces of the disk specimen (4) in the ultrasound reflection signal curve is obtained respectively, and the difference between the two is the actual time difference; if the actual time difference obtained by the test is different from the theoretical time difference obtained by the calculation, the actual time difference is determined by the actual time difference obtained by the test. If the time difference is equal within the allowable error range, then the ultrasound is incident perpendicularly to the oil film layer; if the actual time difference is greater than the theoretical time difference... If the ultrasound is obliquely incident on the oil film layer, the reflected signal is converted from the time domain to the frequency domain using a fast Fourier transform. The center frequency of the ultrasonic transducer is used to determine whether the ultrasound is perpendicularly incident on the oil film layer. If the actual center frequency obtained by the test is equal to the theoretical center frequency within the allowable error range, the ultrasound is perpendicularly incident on the oil film layer. When the result shows that the ultrasound is obliquely incident on the oil film layer, the appropriate motion parameters are set on the host computer (9), and the motion control signal is transmitted to the motor driver (6) through the motion control card (5), thereby controlling the electric displacement stage to adjust the pitch angle and flip angle of the water immersion focusing ultrasonic probe (2) until the result shows that the ultrasound is perpendicularly incident on the oil film layer. The actual time and theoretical time of the reflected signal from the upper surface of the disk specimen (4) received by the water immersion focused ultrasonic probe (2) are based on the water immersion focused ultrasonic probe (2). By comparison, the vertical height of the water immersion focused ultrasound probe (2) was adjusted until the distance was correct, and the theoretical time was determined. The calculation is as follows: The actual time of the reflected signal from the upper surface of the disk specimen (4) received by the water immersion focused ultrasonic probe (2) is tested as follows: The pulse corresponding to the upper surface of the disk specimen (4) is searched from the ultrasonic reflection signal curve, and the initial time of this pulse, i.e., the actual time, is obtained; if the actual time obtained by the test differs from the calculated theoretical time... If the distances are equal within the allowable error range, then the distance between the immersion focused ultrasound probe (2) and the disc specimen (4) is too large. In this case, the electric displacement stage is controlled to move the immersion focused ultrasound probe (2) downwards. If the actual time is less than the theoretical time, the immersion focused ultrasound probe (2) is moved downwards. If the distance between the water immersion focused ultrasound probe (2) and the disc specimen (4) is too small, then the electric displacement stage is controlled to move the water immersion focused ultrasound probe (2) upward. Lubricating film thickness With reflection coefficient amplitude The relationship is as follows: in, , The acoustic impedances of the spherical specimen (3) and the disc specimen (4) are respectively. The angular frequency of the sound wave. The density of the lubricating oil, The velocity of sound in the oil film; According to Hertzian contact theory, the contact micro-region of the ball-disc is circular. When the contact micro-region is completely immersed in lubricating oil, the oil film thickness varies at different locations within and near the contact micro-region. The closer the distance to the center of the contact micro-region, the thinner the oil film and the smaller the reflection coefficient amplitude. The oil film thickness is thinnest at the center of the contact micro-region, so the reflection coefficient amplitude should be the smallest there. Therefore, when the ultrasonic probe is moved through the contact micro-region in a certain step along the straight line containing the chord of the circular contact micro-region, the peak value of the oil film reflection signal should first decrease and then increase. The closer the chord of the circle is to the center, the greater the gradient of the change in the peak value of the oil film reflection signal. The gradient of the change in the peak value of the oil film reflection signal is the largest in the diameter direction. Therefore, by checking whether the gradient of the change in the peak value of the oil film reflection signal is the largest, we can find the diameter passing through the center or the chord closest to the center. Then, by checking whether the peak value of the oil film reflection signal is the smallest, we can find the center position or the point closest to the center along the found path. This point is the center of the contact micro-region determined by coarse positioning. Step 3: Precise positioning using a nanoscale piezoelectric displacement stage: The position of the water immersion focused ultrasonic probe (2) in the horizontal plane is adjusted by a nanoscale piezoelectric displacement stage, and high-precision positioning of the center of the contact micro-area is achieved by relying on ultrasonic reflection signal analysis. Specifically, this includes: Using the approximate area determined by coarse positioning as the center, set the movement range and movement step of the water immersion focused ultrasound probe (2) in the horizontal plane; drive the nanoscale piezoelectric displacement stage to make the water immersion focused ultrasound probe (2) scan each point in the movement range according to the movement step and collect the oil film reflection signal of each point; search for the position with the minimum peak value of the oil film reflection signal, which is the center of the contact micro-area for precise positioning, and move the water immersion focused ultrasound probe (2) to this position.

8. The precise positioning and control method for the center of a point contact micro-region based on ultrasonic signals according to claim 7, characterized in that, The "determining the approximate area of ​​the center of the contact micro-region based on the gradient of the change of the peak value of the oil film reflection signal" step in the micron-level electric displacement stage specifically involves: driving the micron-level electric displacement stage to move the water immersion focused ultrasound probe (2) along different chord paths and acquiring the peak value of the oil film reflection signal in real time; comparing the gradient of the change of the peak value of the signal on different paths, identifying the path with the largest gradient of the change of the peak value as the diameter passing through the center of the contact micro-region; moving the water immersion focused ultrasound probe (2) along the identified diameter path, and determining the point with the smallest peak value of the oil film reflection signal as the approximate area of ​​the center of the contact micro-region.

9. The precise positioning and control method for the center of a point contact micro-region based on ultrasonic signals according to claim 8, characterized in that, In the coarse positioning step of the micron-level electric displacement stage, the operation of adjusting the pitch and roll angles of the water immersion focused ultrasonic probe (2) until the ultrasonic waves are perpendicularly incident on the oil film layer is performed by the host computer (9) automatically comparing the actual time difference with the theoretical time difference. The system calculates the actual center frequency and the theoretical center frequency, and automatically generates control commands to drive the micron-level electric displacement stage to perform adjustments when a deviation is detected.

10. The precise positioning and control method for the center of a point contact micro-region based on ultrasonic signals according to claim 9, characterized in that, In the precise positioning step of the nanoscale piezoelectric displacement stage, the moving step length is set according to the acoustic field focusing focal spot size of the water immersion focusing ultrasonic probe (2). The moving step length must be small enough to ensure that the acoustic field focusing focal spot can scan to the center of the contact micro-area.

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