Revolving body outer diameter measuring system and measuring method based on low-coherence light common path

Abstract

The invention provides a high-precision revolved body outer diameter measuring system and method based on a low-coherence light common path. The high-precision revolved body outer diameter measuring system comprises a low-coherence light aiming module, an optical path difference scanning module, a dual-wavelength separation acquisition module and an upper computer processing system. According to the invention, high-precision aiming of the space position of the outer diameter of the rotary body is realized through the characteristic that the light intensity is maximum only when the optical path difference between the reference arm and the measuring arm is zero through low-coherence light interference; high-precision measurement is realized on optical path difference change caused by the change of the outer diameter of the rotary body in a mode of combining a series Michelson interference optical path and high-coherence light interference motor scanning. The system can realize zero-optical-path-difference position adjustment by measuring a high-precision revolving body standard component, and lossless measurement of the outer diameter of the revolving body is realized by high-precision aiming of low-coherence light interference; a high-precision motor required by traditional scanning measurement is replaced by high-coherence light interference, so that the cost and the measuring range of the system are reduced, and the measurement precision is further improved.

Description

Technical Field

[0001] The present invention relates to the field of optoelectronic detection, and specifically to an external diameter measurement system and method for a rotating body based on a common optical path of low-coherence light. Technical Background

[0002] Rotating body workpieces are the most important transmission and connection components, and are extremely common basic parts in fields such as industrial equipment, aerospace, etc. The accuracy of their shaft diameter or hole diameter directly affects the equipment performance and service life. Among the contact measurement methods for the diameter of rotating body parts, vernier calipers have a low cost. Due to the need for manual operation, the measurement accuracy is low, and they are mainly used for measuring rotating body workpieces with a small diameter. Coordinate measuring machines have high accuracy, but require professional personnel for operation, and the equipment is large in volume and expensive. Among the non-contact measurement methods, the laser Doppler measurement method calculates the workpiece diameter by extracting the Doppler shift information of the laser. This method has a high measurement accuracy, but the parameter requirements for the optical devices required by the optical path are harsh, so this optical path is less used in actual applications. The laser scanning measurement method calculates the workpiece diameter by obtaining the relationship between the signal time interval and the angular velocity of the mirror. This method has a high accuracy, and the small-size accuracy can reach 2 micrometers, but the measurement range is small. The projection imaging measurement method places the measured part in parallel light and calculates the diameter of the part to be measured through the shadow size. The current products of this method have high accuracy, but the measurement range is limited by the size of the detection surface.

[0003] In summary, in the field of high-precision measurement of rotating bodies, there is still a large gap between China and the world's advanced level. Buying mature foreign products as a solution, the independent R & D ability is weak, and there is no system that can simultaneously meet the current non-destructive measurement requirements of high precision, large measurement range, and low cost for rotating bodies. Summary of the Invention

[0004] One of the purposes of the present invention is to implement an external diameter measurement system for a rotating body based on a common optical path of low-coherence light, which is used to simultaneously meet the current non-destructive measurement requirements of high precision, large measurement range, and low cost for rotating bodies.

[0005] The implementation manner of one of the purposes of the present invention is: an external diameter measurement system for a rotating body based on a common optical path of low-coherence light, the measurement system includes a low-coherence light aiming module, an optical path difference scanning module, a dual-wavelength separation acquisition module, and a host computer processing system.

[0006] The low-coherence light aiming module, which is connected in series with the optical path difference motor scanning module, is a Michelson interference optical path, and is used to convert the change in the external diameter of the rotating body to be measured into the optical path difference of two beams of low-coherence light, and transfer the low-coherence light to the optical path difference scanning module.

[0007] The optical path difference scanning module, connected to the low-coherence light outer diameter aiming module and the dual-wavelength separation acquisition module, is a Michelson interference optical path. It is used to combine two low-coherence lights input by the high-coherence light and the low-coherence light outer diameter aiming module to form a common optical path structure. By means of the linear servo motor scanning in the measurement arm of the module's optical path and the property that the interference light intensity is maximum at the zero optical path difference of the low-coherence light interference, the outer diameter change amount is transferred from the low-coherence light optical path difference to the period and phase of the high-coherence light interference signal, and the interference signals of the two wavelengths are transmitted to the dual-wavelength separation acquisition module;

[0008] The dual-wavelength separation acquisition module, connected to the optical path difference scanning module and the host computer processing system, is used to separate the dual-wavelength interference signals input by the optical path difference motor scanning module according to the wavelength, and collect them by respective photodetectors, and then hand them over to the host computer system;

[0009] The host computer processing system processes the signals such as filtering. Finally, through the timestamp positioning of the acquisition card corresponding to the low-coherence light wave peak, the data within the corresponding timestamp is intercepted in the high-coherence light interference signal, and the periods and phases contained in the data are statistically analyzed to calculate the offset of the outer diameter of the measured rotating body compared with the standard part.

[0010] The described low-coherence light aiming module includes:

[0011] The fiber collimator is located at the fiber output end of the low-coherence light source with a central wavelength of 840 nm and a bandwidth of 48 nm;

[0012] The linear polarizer and the quarter-wave plate are located at the front end of the fiber collimator, and are used to prevent the laser from returning to the laser;

[0013] The beam splitter prism is located at the center of the Michelson interference optical path in the module;

[0014] The 30 / 70 beam splitting flat plate is located in the reference arm of the Michelson interference optical path in the module;

[0015] The double convex lens is located in the measurement arm of the Michelson interference optical path in the module, and is used to focus and weaken the speckle effect brought by the surface of the rotating body;

[0016] The air-bearing turntable is located behind the double convex lens, and a self-centering three-jaw chuck is installed on the turntable, which is used to clamp the measured rotating body and drive it to rotate for multi-point measurement.

[0017] The described optical path difference scanning module includes:

[0018] The 50 / 50 depolarization beam splitter prism I is located at the input of the two-wavelength laser, and is used to stabilize the laser light intensity and combine the two-wavelength lasers;

[0019] The 50 / 50 depolarization beam splitter prism II is located at the center of the Michelson interference optical path in the module;

[0020] A right-angle reflecting prism 1 is located in the reference arm of the Michelson interference optical path within the module;

[0021] A linear servo motor is located in the measurement arm of the Michelson interference optical path within the module and is used to scan the optical path difference. A right-angle reflecting prism 2 is mounted on the motor.

[0022] The dual-wavelength separation acquisition module includes:

[0023] A cold mirror is located on the output side of the optical path difference scanning module and is used to separate two-wavelength lasers;

[0024] A plano-convex lens 1 and a photodetector 1 are located on the transmission side of the cold mirror to collect low-coherence light interference signals;

[0025] A plano-convex lens 2 and a photodetector 2 are located on the reflection side of the cold mirror to collect high-coherence light interference signals;

[0026] A high-speed data acquisition card is used to simultaneously collect signals from two photodetectors and assign time stamps to the measurement points.

[0027] The upper computer processing system includes:

[0028] Measurement software can control the scanning of the linear servo motor in the hardware, the rotation of the air-bearing turntable, and the acquisition of the high-speed data acquisition card. The operation process of a single measurement software is

[0029] a. Control the air-bearing turntable to rotate to the initial position;

[0030] b. Control the linear servo motor to perform scanning;

[0031] c. Read the data from the high-speed data acquisition card;

[0032] d. Process the data and calculate the radius of the measurement point of the workpiece to be measured for the rotating body;

[0033] e. Control the air-bearing turntable to rotate to the next angle

[0034] f. Repeat the above steps until one full rotation is completed

[0035] g. According to the measured radii at each angle, calculate the final diameter value of the workpiece to be measured through least squares fitting.

[0036] The second object of the present invention is to provide a method for initializing and calibrating the system with a high-precision standard part to ensure the accuracy of the final result of the system.

[0037] The calibration method for the second object of the present invention is as follows:

[0038] a. Install the high-precision rotating body standard part on the self-centering three-jaw chuck of the air-bearing turntable in the low-coherence light aiming module;

[0039] b. Start the motor in the optical path difference scanning module to start scanning. The acquisition card obtains the dual-wavelength interference signal, which contains the optical path difference between the measuring arm standard and the reference arm 30 / 70 splitter plate in the low-coherence light aiming module. It is expressed as three peaks, one large and two small. The small peaks are symmetrically distributed on both sides of the large peak, and the spacing to the large peak is equal. The spacing is calculated by the number of cycles and phase size of the high-coherence light in this interval to obtain the specific distance as the system calibration parameter. Since the reference arm reflector is fixed and the standard part has higher precision, the results obtained from this measurement and the multiple rotations of the air-floating turntable are both fixed values. The fixed value is recorded as the system calibration, and the subsequent test results are calculated on this basis, and the calibration is completed.

[0040] The third purpose of the present invention is that because the central wavelength of the low-coherence light source is 840nm, which is in the invisible light band, the construction and adjustment of the system are inefficient and low-precision because the optical path is invisible. At the same time, the light source power is high, and when the optical fiber is invisible, it is difficult for the operator to realize that the light source is directly shining into the eyes during the optical path construction and system use. The dual-wavelength common optical fiber is used to achieve efficient optical path adjustment and safety warning.

[0041] The third object of the present invention is achieved by using a 1X2 fiber coupler, connecting a low-coherence light source and a 635nm red light source to its two input ends respectively, and connecting the output end to the fiber collimator in the low-coherence light aiming module. The 635nm semiconductor laser is also a high-coherence light, and the interference phenomenon at the photodetector can better reflect the accuracy of the optical path construction. When the red light is turned on and the low-coherence light is turned off, it can be used for system construction and adjustment. When the two light sources are turned on at the same time, the operator can confirm the current low-coherence light irradiation position through the red light, which plays a safety warning role.

[0042] The fourth purpose of the present invention is to avoid a significant change in the intensity of the interference signal caused by a change in the polarization state of the two wavelength light sources, thereby affecting the final data processing accuracy.

[0043] The fourth object of the present invention is achieved by using a 50 / 50 depolarizing beam splitter prism to split the high and low coherence lights in the common optical path.

[0044] The fifth object of the present invention is to provide a method for measuring the outer diameter of a rotating body based on a common optical path of low-coherence light, so as to simultaneously meet the current needs for high-precision, large-range, and low-cost non-destructive measurement of rotating bodies.

[0045] The outer diameter measurement method includes the following steps:

[0046] a. Outer diameter aiming of the rotating object to be measured. The system needs to be calibrated in advance. Install the object to be measured on the self-centering three-jaw chuck of the air-bearing turntable in the low-coherence light aiming module. This module consists of a Michelson interference optical path. The low-coherence light is emitted by an optical fiber collimator, and after passing through a linear polarizer and a quarter-wave plate, it is split into a measurement light and a reference light at the beam splitter prism, reaching the outer diameter of the object to be measured and the 30 / 70 beam splitter flat plate respectively. After being reflected by the two reflecting surfaces, they return to the beam splitter prism for beam combination and enter the 50 / 50 depolarizing beam splitter prism I in the optical path difference scanning module;

[0047] b. The high-coherence light enters the optical path difference scanning module from the 50 / 50 depolarizing beam splitter prism 1. The reflected part of the high-coherence light by the 50 / 50 depolarizing beam splitter prism I and the transmitted part of the combined low-coherence light by the 50 / 50 depolarizing beam splitter prism I are spatially collinear. After beam combination, they enter the Michelson interference optical path part of the optical path difference scanning module through the common optical path;

[0048] c. The combined light beam is split into a reference light and a measurement light at the 50 / 50 depolarizing beam splitter prism II, reaching the fixed right-angle reflecting prism I and the right-angle reflecting prism II on the linear servo motor respectively. After being reflected by the two right-angle reflecting surfaces, they return to the 50 / 50 depolarizing beam splitter prism II for beam combination and enter the dual-wavelength separation acquisition module;

[0049] d. The cold mirror in the dual-wavelength separation acquisition module separates the high- and low-coherence lights, and they enter the photodetectors I and II in the form of transmitted light and reflected light through the plano-convex lenses I and II;

[0050] e. The high-speed data acquisition card acquires the signals of the photodetectors I and II. The upper computer controls the linear servo motor to drive the right-angle reflecting prism II for a single scan, and the dual-wavelength interference signals are acquired. Among them, the low-coherence light interference signal contains the optical path difference between the object to be measured in the measurement arm and the reflecting mirror in the reference arm in the low-coherence light aiming module, showing three peaks of one large and two small. The small peaks are symmetrically distributed on both sides of the large peak, and the distance to the large peak is equal. This distance is the optical path difference between this measurement point of the object to be measured and the 30 / 70 beam splitter flat plate. This distance is calculated by the number of cycles and the phase size of the high-coherence light interference signal in this interval to obtain the specific distance, and the difference from the calibrated result can be used to calculate the radius size of this point;

[0051] f. Through the upper computer, control the air-bearing turntable and the three-jaw chuck in the low-coherence light aiming module to drive the object to be measured to rotate by a fixed angle and repeat the above measurement process. Fit the multiple measurement results with the corresponding angles to obtain the outer diameter size of the rotating object to be measured.

[0052] By combining the low-coherence light interference phenomenon where the interference signal has a peak only when the optical path difference is zero and the high-coherence light interference capable of achieving high-precision ranging, they are respectively used to achieve the aiming and positioning of the outer diameter of the rotating body to be measured and the high-precision measurement of the change in the outer diameter. By connecting two Michelson interference optical paths in series, the optical path difference generated by the change in the outer diameter in the low-coherence light aiming module is transferred to the optical path difference scanning module for compensation. The change in the outer diameter is reflected as multiple low-coherence light peaks in the interference signal, and the low-coherence light peaks are measured by the periodic sine interference signal of the high-coherence light interference, avoiding the high requirements for the positioning accuracy of the scanning motor and the ranging accuracy in the traditional low-coherence light aiming measurement method. The servo motor of the system only needs to perform a simple scan, without the need to be positioned at a special position, nor does it need to carry a ranging function, reducing the system cost, and the ranging accuracy of the high-coherence light interference can also reach within λ / 2.

[0053] Specifically, in the present invention, the rotating body to be measured is placed on an air-bearing turntable and is on the measurement arm of the Michelson interference optical path. There is an optical path difference between the optical path from the outer diameter of the measured part to the beam splitter prism and the optical path of the 30 / 70 beam splitter flat of the reference arm. Therefore, low-coherence light does not interfere in this Michelson interference optical path. The high-coherence light is combined with two beams of low-coherence light through a 50 / 50 depolarizing beam splitter prism, and the existing optical path difference is compensated through the second Michelson interference optical path, capable of generating three zero optical path difference points. The interference beams during the scanning process are separated by a cold mirror and are respectively collected by their own photodetectors. It can be observed that as the servo motor scans, the interference intensity of the high-coherence light is a periodic sine signal, while the interference intensity of the low-coherence light shows a symmetric distribution of three peak signals of "small, large, small", and the optical path difference is reflected within the peak-to-peak distance of any group. Since the two groups of signals are collected simultaneously by a high-speed data acquisition card, the effective interval of the high-coherence light can be obtained through the timestamps of the appearance of the large and small peaks in the data acquisition card. By calculating the number of cycles and the start and end phase information, the number of fringes N is obtained, and the optical path difference is Nλ / 2. This result only represents the optical path difference between the current measurement point of the measured part and the 30 / 70 beam splitter flat of the reference mirror. Since the position of the reference mirror does not change, a calibrated optical path difference can be obtained by calibrating a high-precision standard part with a known outer diameter using this system. By subtracting the optical path difference of the measured part from the calibrated optical path difference, the specific value of the outer diameter at the current measurement point can be obtained. Similarly, by driving the measured part to rotate with high precision through the air-bearing turntable, multiple-point measurements are carried out, and the outer diameter of the measured part is fitted by combining the rotation angles, and then the final result is obtained.

[0054] The outer diameter measurement of the rotating body in the present invention is carried out by means of optical aiming and optical ranging, achieving non-destructive detection while ensuring high precision. The method of using the common optical path of high and low coherence light reduces the performance requirements of the traditional method for the scanning motor, thereby reducing the system cost. Compared with the previous methods for measuring the outer diameter of the rotating body, the present invention has the following advantages: the high-precision aiming of low-coherence light interference realizes non-destructive measurement of the outer diameter of the rotating body; the high-coherence light interference replaces the high-precision motor required for traditional scanning measurement, reducing the cost and range of the system and further improving the measurement accuracy. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 It is a schematic diagram of the overall structure of the present invention.

[0056] In the figure: 1. 635nm semiconductor laser, 2. 840nm SLD laser, 3. 1X2 fiber coupler, 4. Fiber collimator, 5. Reflecting mirror, 6. Linear polarizer, 7. Quarter-wave plate, 8. Beam splitter prism, 9. 30 / 70 beam splitting flat plate, 10. Double convex lens, 11. Self-centering three-jaw chuck, 12. Air-bearing turntable, 13. Rotating body to be measured, 14. 632.8nm helium-neon laser, 15. Reflecting mirror, 16. Reflecting mirror, 17. 50 / 50 depolarization beam splitter prism 1, 18. 50 / 50 depolarization beam splitter prism 2, 19. Right-angle reflecting mirror 1, 20. Right-angle reflecting mirror 2, 21. Linear servo motor, 22. Cold mirror, 23. Plano-convex lens 1, 24. Plano-convex lens 2, 25. Photoelectric detector 1, 26. Photoelectric detector 2, 27. High-speed data acquisition card and upper computer. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0057] In order to deepen the understanding of the present invention, the following detailed description of this embodiment is made in conjunction with the accompanying drawings.

[0058] Embodiment 1: Refer to Figure 1 , a rotating body outer diameter measurement system based on the common optical path of low-coherence light, the measurement system includes a low-coherence light aiming module, an optical path difference scanning module, a dual-wavelength separation acquisition module and an upper computer processing system.

[0059] The low-coherence light aiming module is connected in series with the optical path difference motor scanning module. Its essence is a Michelson interference optical path, which is used to convert the change in the outer diameter of the rotating body to be measured into the optical path difference of two beams of low-coherence light and transfer the low-coherence light to the optical path difference motor scanning module.

[0060] The optical path difference scanning module is connected to the low-coherence light outer diameter aiming module and the dual-wavelength separation acquisition module. It is a Michelson interference optical path, which is used to combine the two low-coherence light beams input by the high-coherence light and the low-coherence light outer diameter aiming module into a common optical path. By means of the scanning of the optical path measurement arm motor and the property that the interference light intensity is maximum at the zero optical path difference of the low-coherence light, the outer diameter change amount is transferred from the low-coherence light optical path difference to the interference signal period and phase of the high-coherence light, and the interference signals of the two wavelengths are transmitted to the acquisition module;

[0061] The dual-wavelength separation acquisition module is connected to the optical path difference scanning module and the host computer processing system. It is used to separate the dual-wavelength interference signals input by the optical path difference motor scanning module according to the wavelength and input them into their respective photodetectors, and then hand them over to the host computer system;

[0062] The host computer processing system processes the signals such as filtering. Finally, through the positioning of the time stamp of the acquisition card corresponding to the peak of the low-coherence light wave, the signals within the corresponding time stamp are intercepted in the high-coherence light, and the period and phase of the signals are statistically analyzed to calculate the offset of the outer diameter of the measured rotating body compared with the standard part.

[0063] Specifically, the low-coherence light aiming module includes: a fiber collimating mirror 4, a linear polarizer 6, a quarter-wave plate 7, a beam splitting prism 8, a 30 / 70 beam splitting flat plate 9, a bi-convex lens 10, a self-centering three-jaw chuck 11 and an air-bearing turntable 12. Among them, the fiber collimating mirror 4 is located at the output end of the low-coherence light fiber with a central wavelength of 840 nm; the linear polarizer 6 and the quarter-wave plate 7 are located at the front end of the fiber collimator to prevent the laser from returning to the laser; the beam splitting prism 8 is located at the center of the Michelson interference optical path in the module; the 30 / 70 beam splitting flat plate 9 is located in the reference arm of the Michelson interference optical path in the module; the bi-convex lens 10 is located in the measurement arm of the Michelson interference optical path in the module to focus and weaken the speckle effect brought by the surface of the rotating body; the air-bearing turntable 12 is located behind the bi-convex lens, and a self-centering three-jaw chuck 11 is installed on the turntable to clamp the measured rotating body 13 and drive it to rotate for measurement.

[0064] Specifically, the optical path difference scanning module includes: 50 / 50 depolarization beam splitting prisms 17 and 18, right-angle reflecting mirrors 19 and 20, and a linear servo motor 21. Among them, the 50 / 50 depolarization beam splitting prism 17 is located at the input of the two-wavelength laser to stabilize the laser light intensity and combine the two-wavelength lasers; the 50 / 50 depolarization beam splitting prism 18 is located at the center of the Michelson interference optical path in the module; the right-angle reflecting prism 19 is located in the reference arm of the Michelson interference optical path in the module; the linear servo motor 21 is located in the measurement arm of the Michelson interference optical path in the module for scanning, and a right-angle reflecting prism 21 is installed on the motor.

[0065] The dual-wavelength separation acquisition module includes: a cold reflector 22, a plano-convex lens 1 23, a plano-convex lens 24, a photodetector 1 25, a photodetector 2 26, and a high-speed data acquisition card and a host computer 27. Among them, the cold reflector 22 is located at the output side of the optical path difference scanning module, and is used to separate the two wavelength lasers; the plano-convex lens 1 23 and the photodetector 1 25 are located at the transmission side of the cold reflector, and are used to collect low-coherence light interference signals; the plano-convex lens 2 24 and the photodetector 2 26 are located at the reflection side of the cold reflector, and are used to collect high-coherence light interference signals; the high-speed data acquisition card and the host computer 27 are used to simultaneously collect the signals of the two photodetectors and give the corresponding timestamps of the measurement points.

[0066] The host computer processing system includes:

[0067] Filtering algorithm is used to process the collected signal and remove interference;

[0068] The controller is used to control functions such as motor scanning, air-floating turntable rotation, photoelectric detector measurement, and acquisition card acquisition.

[0069] The coherence of light refers to the fact that two light waves maintain the same phase difference, have the same frequency, or have completely consistent waveforms during propagation. Such two beams of light can produce stable interference during propagation. When the spectral width of the light source is narrow, it is called a narrowband light source, and because of its good coherence, it is called high coherence light. Figure 1 As shown, the 632.8nm helium-neon laser 14 is a high coherence light source. At this time, the central wavelength of the light source can be considered to be unique and a monochromatic light source. The light intensity amplitude of the high coherence light interference fringes will not change with the change of the optical path difference, but always remain stable, and the fringe spacing is always λ / 2 (λ=632.8nm). When the outer diameter of the rotating body changes △l, resulting in a change in the optical path difference of the light path, the fringes will shift N (N can be a non-integer, and the decimal part is calculated by the phase change before and after the shift), satisfying the formula:

[0070] Δl=Nλ / 2

[0071] Through calculation, it is found that the system measurement accuracy can be better than 0.3μm.

[0072] When the spectral width of the light source is wide, it is called a broadband light source, and because of its coherence it is called low coherence light. Figure 1 As shown, the 840nm SLD laser is a low-coherence light source. At this time, the light source can be considered to be a combination of monochromatic lights of different wavelengths within the bandwidth range. During interference, monochromatic lights of different wavelengths will overlap and superimpose at the central zero-order (zero optical path difference) stripes to form peak stripes with the highest intensity and contrast. As the optical path difference gradually increases, the monochromatic interference stripes are staggered and superimposed on each other, and the intensity and contrast decrease synchronously until the interference stripes disappear completely. This feature enables it to have high-precision spatial positioning capabilities.

[0073] The high-precision ranging of high-coherence light interference and the high-precision spatial positioning ability of low-coherence light interference are combined by connecting two Michelson interference optical paths in series to realize the measurement of the outer diameter of a rotating body.

[0074] Embodiment 2

[0075] A rotating body outer diameter measurement system based on a common optical path of low-coherence light needs to be initialized and calibrated with a high-precision standard part. The calibration method is as follows:

[0076] a. Install the high-precision rotating body standard part 13 (the same as the rotating body to be measured 13) on the self-centering three-jaw chuck 11 of the air-bearing turntable 12 in the low-coherence light aiming module;

[0077] b. Start the linear servo motor 21 in the optical path difference scanning module to start scanning. The high-speed data acquisition card and the upper computer 27 obtain the dual-wavelength interference signals S 1 and S 2 , where the low-coherence light interference signal S 2 contains the optical path difference between the measurement arm standard part 13 and the reference arm 30 / 70 beam splitter flat 9 in the low-coherence light aiming module, and is manifested as one large (S 2 P 2 ) and two small (S 2 P 1 , S 2 P 3 ) three peaks. The small peaks are symmetrically distributed on both sides of the large peak, and the distances to the large peak are equal.

[0078] Only considering the reflected light of the reference arm 30 / 70 beam splitter flat 9 in the low-coherence light aiming optical path entering the scanning ranging optical path, according to the low-coherence light interference principle, when the optical path x4 = x3 (the optical path difference is zero), the photodetector 25 collects the interference peak, and the signal appears at S2P2. Similarly, only considering the reflected light of the rotating body 13 to be measured in the measurement arm of the low-coherence light aiming optical path, the interference peak will also be reached at this position. The two peaks are superimposed at the same position, forming a peak S2P2 with a relatively large amplitude in the middle of the interference signal S2. The optical path x4 = x3 is a fixed quantity of the second Michelson interference optical path. As long as the right-angle reflector 19 does not change, the right-angle reflector 20 on the linear servo motor 21 will always scan out this peak at a fixed position. Using this property, this peak will be used as the benchmark for subsequent rotating body measurements.

[0079] Interference signal S 2The small peaks on both sides contain information about the change in the outer diameter of the rotating body. It is known that there is an optical path difference between the reference arm optical path x2 and the measuring arm optical path x1 of the aiming optical path. When considering the low-coherence light reference arm beam incident on the right-angle reflector 20 and the low-coherence light measuring arm beam incident on the right-angle reflector 19, according to the principle of low-coherence light interference, when x2+x3=x1+x4, that is, x3=x4+(x1-x2), a peak will appear. Among them, x4 and x2 are constants, and only x1 changes due to the change in the diameter of the rotating body. Therefore, the optical path difference between x1 and x2 causes the second peak to have a certain offset compared to the fixed highest peak. The light beam at the depolarizing beam splitter prism 18 will be divided into two beams. Only one path is considered above. Similarly, the other path will also be offset at the highest peak. The two peaks have the same offset and are distributed on both sides of the highest peak.

[0080] The distance between any small peak and the large peak is measured by the high coherence light interference signal S 1 The number of cycles and phase size in this interval are solved to obtain the specific distance (through S 1 P 1 -S 1 P 2 or S 1 P 2 -S 1 P 3 The number of fringes N in the range is calculated) as the system calibration parameter. Since the reference arm reflector is fixed and the standard part has higher precision, the results of this measurement and the multiple rotations of the air-floating turntable are both fixed values. This fixed value is recorded as the system calibration, and the subsequent test results are calculated based on this, and the calibration is completed.

[0081] Example 3

[0082] A rotating body outer diameter measurement system based on low-coherence light common optical path realizes efficient optical path adjustment and safety warning through dual-wavelength common optical fiber. The specific contents are as follows:

[0083] The central wavelength of the low-coherence light source is 840 nm, which is in the non-visible light band. The setup and adjustment of the system are inefficient and inaccurate due to the invisibility of the optical path. At the same time, the light source power is high, and it is difficult for operators to realize that the light source is directly shining into the eyes during the optical path setup and system use when the optical fiber is invisible. Therefore, in the present invention, a 1X2 fiber coupler 3 is used, and an 840 nm SLD laser 2 and a 635 nm semiconductor laser 1 are respectively connected to its two input ends, and the output end is connected to the fiber collimator 4 in the low-coherence light aiming module. The 635 nm semiconductor laser 1 is also a high-coherence light, and the interference phenomenon at the photodetector 26 can better reflect the accuracy of the optical path setup. When the red light of the 635 nm semiconductor laser 1 is turned on and the low-coherence light is turned off, it can be used for system setup and adjustment. When both light sources are turned on, the operator can confirm the current irradiation position of the low-coherence light through the red light, playing a safety warning role.

[0084] Embodiment 4

[0085] A method for measuring the outer diameter of a rotating body based on a common optical path of low-coherence light includes the following steps:

[0086] a. Aiming at the outer diameter of the rotating body to be measured. The system needs to be calibrated in advance. The workpiece to be measured is installed on the self-centering three-jaw chuck 11 on the air-bearing turntable 12 in the low-coherence light aiming module. This module is composed of a Michelson interference optical path. The low-coherence light is emitted by the fiber collimator 4, and after passing through the linear polarizer 6 and the quarter-wave plate 7, it is divided into a measurement light and a reference light at the beam splitter prism 8 and respectively reaches the outer diameter of the rotating body 13 of the workpiece to be measured and the 30 / 70 beam splitter flat plate 9. After being reflected by the two reflecting surfaces, it returns to the beam splitter prism 8 for beam combination and enters the 50 / 50 depolarizing beam splitter prism 17 in the optical path difference scanning module;

[0087] b. The high-coherence light enters the optical path difference scanning module from the 50 / 50 depolarizing beam splitter prism 17. The reflected part of the high-coherence light in the 50 / 50 depolarizing beam splitter prism 17 and the transmitted part of the low-coherence light in the 50 / 50 depolarizing beam splitter prism 17 are collinear in space. After beam combination, they enter the Michelson interference optical path of the optical path difference scanning module through the common optical path;

[0088] c. The combined light is divided into a reference light and a measurement light at the 50 / 50 depolarizing beam splitter prism 18, and respectively reaches the fixed right-angle reflecting prism 19 and the right-angle reflecting prism 20 on the linear servo motor 21. After being reflected by the two right-angle reflecting surfaces, it returns to the 50 / 50 depolarizing beam splitter prism 18 for beam combination and enters the dual-wavelength separation acquisition module;

[0089] d. The cold mirror 22 in the dual-wavelength separation acquisition module separates the high- and low-coherence lights, and they respectively pass through the first double convex lens 23 and the second double convex lens 24 in the form of reflected light and transmitted light, and after interference, they are collected by the first photodetector 25 and the second photodetector 26;

[0090] e. The high-speed data acquisition card and the host computer 27 collect the signals of the photodetector 1 - 25 and the photodetector 2 - 26. The host computer controls the linear servo motor 21 to drive the right-angle reflecting prism 20 for a single scan, and collects the dual-wavelength interference signal S 1 and S 2 . Among them, the low-coherence light interference signal S 2 contains the optical path difference between the standard part 13 of the measuring arm and the beam splitter flat 9 of the reference arm 30 / 70 in the low-coherence light aiming module, which is manifested as one large (S 2 P 2 ) and two small (S 2 P 1 , S 2 P 3 ) three peaks. The small peaks are symmetrically distributed on both sides of the large peak, and the distances to the large peak are equal. This distance is obtained by resolving the number of periods and the phase size of the high-coherence light interference signal S 1 in this interval to obtain the specific distance (obtained by calculating the number of fringes N within the range of S 1 P 1 -S 1 P 2 or S 1 P 2 -S 1 P 3 ). By taking the difference from the calibrated fixed value and knowing the outer diameter size of the standard part used for calibration, the radius size of this point can be calculated;

[0091] f. The host computer controls the air-bearing turntable 12 in the low-coherence light aiming module to drive the measured rotating body 13 to rotate by a fixed angle. The multiple measurement results are fitted with the corresponding angles, and the outer diameter size of the measured rotating body is calculated.

[0092] It should be noted that the above embodiments are not used to limit the protection scope of the present invention. Any equivalent transformation or substitution made on the basis of the above technical solutions falls within the protection scope of the claims of the present invention.

Claims

1. A rotating body outer diameter measurement system based on low coherence light common optical path, characterized in that: The measurement system includes a low-coherence light aiming module, an optical path difference scanning module, a dual-wavelength separation acquisition module and a host computer processing system. The low-coherence light aiming module is connected in series with the optical path difference motor scanning module, and is used to convert the change in the outer diameter of the rotating body to be measured into the optical path difference of two beams of low-coherence light, and transfer the low-coherence light to the optical path difference scanning module; The optical path difference scanning module is connected to the low coherence light outer diameter aiming module and the dual-wavelength separation acquisition module, and is used to combine the two low coherence light beams input by the high coherence light and the low coherence light outer diameter aiming module to form a common optical path structure, and through the linear servo motor scanning located in the optical path measurement arm of the module and the property that the interference light intensity is the largest at the zero optical path difference of the low coherence light interference, the outer diameter change is transferred from the low coherence light optical path difference to the high coherence light interference signal period and phase, and the interference signals of the two wavelengths are transmitted to the dual-wavelength separation acquisition module; The dual-wavelength separation acquisition module is connected to the optical path difference scanning module and the host computer processing system, and is used to separate the dual-wavelength interference signal input by the optical path difference motor scanning module according to the wavelength, and collect it by respective photoelectric detectors and hand it over to the host computer system; The host computer processing system filters the signal and finally locates the timestamp of the acquisition card corresponding to the low coherent light peak, intercepts the data in the corresponding timestamp in the high coherent light interference signal, performs statistics on the period and phase contained in the data, and calculates the offset of the outer diameter of the rotating body to be measured compared with the standard part.

2. According to claim 1, a rotary outer diameter measurement system based on low coherent light common optical path is characterized in that: The low-coherence light aiming module comprises: The optical fiber collimator is located at the output end of the low-coherence optical fiber with a central wavelength of 840nm; A linear polarizer and a quarter wave plate are located at the front end of the optical fiber collimator to prevent the laser from returning to the laser; A beam splitter prism located at the center of the Michelson interference optical path in the module; 30 / 70 beam splitter, located in the reference arm of the Michelson interferometer optical path in the module; The double convex lens is located in the Michelson interference optical path measurement arm in the module, which is used to focus and weaken the speckle effect caused by the rotating body surface; The air-floating turntable is located behind the double convex lens. A self-centering three-jaw chuck is installed on the turntable to clamp the rotating body to be measured and drive it to rotate for multi-point measurement.

3. The outer diameter measurement system of a rotating object based on a low-coherence light common optical path according to claim 1 is characterized in that: The optical path difference scanning module comprises: 50 / 50 depolarizing beam splitter prism 1, located at the input of two-wavelength lasers, used to stabilize the laser intensity and combine the two-wavelength laser beams; 50 / 50 depolarizing beam splitter prism 2, located at the center of the Michelson interference optical path in the module; Right-angle reflecting prism 1, located in the reference arm of the Michelson interference optical path in the module; The linear servo motor is located in the Michelson interference optical path measurement arm in the module and is used to scan the optical path difference. A right-angle reflection prism 2 is installed on the motor.

4. The outer diameter measurement system of a rotating object based on a low-coherence light common optical path according to claim 1 is characterized in that: The dual-wavelength separation acquisition module comprises: A cold reflection mirror, located at the output side of the optical path difference scanning module, used for separating two wavelength lasers; A plano-convex lens 1 and a photodetector 1 are located on the transmission side of the cold reflector to collect low-coherence light interference signals; Plano-convex lens 2 and photodetector 2 are located on the reflection side of the cold reflector to collect high coherence light interference signals; High-speed data acquisition card, used to simultaneously collect signals from two photoelectric detectors and give time stamps to the measurement points.

5. The outer diameter measurement system of a rotating object based on a low-coherence light common optical path according to claim 1 is characterized in that: The host computer processing system includes: The measurement software can control the linear servo motor scanning, air-floating turntable rotation, and high-speed data acquisition card acquisition in the hardware. The running process of a single measurement software is as follows: a. Control the air-floating turntable to rotate to the initial position; b. Control the linear servo motor to scan; c. Read data from the high-speed data acquisition card; d. Process the data and calculate the radius of the measuring point of the rotating workpiece to be measured; e. Control the air-floating turntable to rotate to the next angle f. Repeat the above steps until one rotation g. According to the radius measured at each angle, the final diameter value of the test piece is calculated by least square fitting.

6. The outer diameter measurement system of a rotating object based on a low-coherence light common optical path according to claim 1 is characterized in that: The system needs to be calibrated by high-precision standard parts. The calibration method is as follows: a. Install the high-precision rotary body standard parts on the self-centering three-jaw chuck of the air-floating turntable in the low-coherence light aiming module; b. Start the motor in the optical path difference scanning module to start scanning. The acquisition card obtains the dual-wavelength interference signal. The signal contains the optical path difference between the measuring arm standard and the reference arm 30 / 70 splitter plate in the low coherent light aiming module, which is manifested as three peaks, one large and two small. The small peaks are symmetrically distributed on both sides of the large peak, and the spacing to the large peak is equal. The specific distance is calculated by the number of cycles and phase size of the high coherent light in this interval to obtain the system calibration parameter. Since the reference arm reflector is fixed and the standard part has higher accuracy, the results of this measurement and the multiple rotation air-floating turntable measurements are both fixed values. The fixed value is recorded as the system calibration, and the subsequent test results are calculated on this basis, and the calibration is completed.

7. The outer diameter measurement system of a rotating object based on a low-coherence light common optical path according to claim 1 is characterized in that: The dual-wavelength common fiber realizes efficient optical path adjustment and safety warning. The specific features are as follows: The central wavelength of the low-coherence light source is 840nm, which is in the invisible light band. The construction and adjustment of the system are inefficient and of low precision because the optical path is invisible. At the same time, the light source power is high. A 1X2 fiber coupler is used, and the two input ends are connected to the 840nm SLD low-coherence light source and the 635nm semiconductor light source respectively. The output end is connected to the fiber collimator in the low-coherence light aiming module. The 635nm semiconductor laser is also a high-coherence light. The interference phenomenon at the photodetector can better reflect the accuracy of the optical path construction. When the red light is turned on and the low-coherence light is turned off, it can be used for system construction and adjustment. When the two light sources are turned on at the same time, the operator can confirm the current low-coherence light irradiation position through the red light, which serves as a safety warning.

8. The outer diameter measurement system of a rotating object based on a common optical path of low coherent light according to claim 1 is characterized in that: The outer diameter measurement method includes the following steps: a. Aiming at the outer diameter of the rotating object to be measured, the system needs to be calibrated in advance, and the object to be measured is installed on the self-centering three-jaw chuck of the air-floating turntable in the low-coherence light aiming module. The module is composed of a Michelson interference optical path. The low-coherence light is emitted by the fiber collimator, and after passing through the linear polarizer and the 1 / 4 wave plate, it is divided into the measuring light and the reference light at the beam splitter prism and reaches the outer diameter of the object to be measured and the 30 / 70 beam splitter plate respectively. After being reflected by the two reflecting surfaces, it returns to the beam splitter prism for beam combination and enters the 50 / 50 depolarizing beam splitter prism 1 of the optical path difference scanning module; b. The high coherent light enters the optical path difference scanning module from the 50 / 50 depolarization beam splitter prism 1. The reflected part of the high coherent light 50 / 50 depolarization beam splitter prism 1 and the transmitted part of the combined low coherent light 50 / 50 depolarization beam splitter prism 1 are spatially collinear. After the beams are combined, the common optical path enters the Michelson interference optical path part of the optical path difference scanning module. c. The combined light beam is divided into reference light and measurement light at the 50 / 50 depolarizing beam splitter prism 2, and reaches the fixed right-angle reflection prism 1 and the right-angle reflection prism 2 on the linear servo motor respectively. After being reflected by two right-angle reflection surfaces, it returns to the 50 / 50 depolarizing beam splitter prism 2 for beam combination and enters the dual-wavelength separation acquisition module; d. The cold reflector in the dual-wavelength separation acquisition module separates the high-coherence light and the low-coherence light, and enters the photodetectors 1 and 2 through the plano-convex lenses 1 and 2 in the form of transmitted light and reflected light; e. The high-speed data acquisition card collects the signals of the first and second photodetectors. The host computer controls the linear servo motor to drive the right-angle reflection prism two to perform a single scan, and collects the dual-wavelength interference signal. The low-coherence light interference signal contains the optical path difference between the measuring arm to be tested and the reference arm reflector in the low-coherence light aiming module, which is manifested as three peaks, one large and two small. The small peaks are symmetrically distributed on both sides of the large peak, and the spacing to the large peak is equal. The spacing is the optical path difference between the measuring point of the to-be-tested object and the 30 / 70 splitter plate. The spacing is solved by the number of cycles and phase size of the high-coherence light interference signal in this interval to obtain the specific distance, and the radius of the point can be calculated by subtracting it from the calibration result; f. Control the air-floating turntable and three-jaw chuck in the low-coherence light aiming module through the host computer to drive the workpiece to be measured to rotate at a fixed angle and repeat the above measurement process. Fit the multiple measurement results with the corresponding angles to obtain the outer diameter of the rotating body to be measured.

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