Optical high-precision analytical balance

Abstract

This invention proposes a high-precision optical analytical balance, relating to the field of precision measuring instruments. It includes a base upon which interconnected optical, weighing, and display units are sequentially mounted. This invention achieves measurement through pure optical detection of the mass-to-displacement conversion process, eliminating any additional electromagnetic contact and thus completely eradicating measurement errors introduced by feedback forces and electrostatic adsorption in traditional balances. Furthermore, by using the fundamental physical constants of laser wavelength and gravitational acceleration as references, the measurement chain is short, fundamentally eliminating the long-term drift problem caused by component aging and magnetic flux changes in electromagnetic balances, achieving absolute measurement with "wear-free scale." In addition, the measurement results can be directly traced back to the basic units of length (speed of light / wavelength) and acceleration, conforming to the trend of quantization and constantization in the International System of Units (SI), which has significant metrological implications.

Description

Technical Field

[0001] This invention relates to the field of precision measuring instrument technology, and more specifically, to an optical high-precision analytical balance. Background Technology

[0002] Currently, high-precision mass measurement mainly relies on electromagnetic micro / analytical balances, which achieve measurement by balancing the mass being measured using electromagnetic force. Although such balances have achieved relatively high resolution, they still have inherent drawbacks: First, there are long-term stability and drift issues. The measurement reference relies on electromagnetic force calibration, which is susceptible to factors such as temperature, magnetic fields, and component aging, requiring frequent calibration. Second, contact measurement introduces interference. Mechanical contact points may introduce non-target forces such as electrostatic adsorption, affecting the accuracy of micro-measurements. Third, the traceability chain is indirect. Measurement results need to be transferred through standard weights at each level for traceability, resulting in a long chain and large accumulated uncertainty.

[0003] While some cutting-edge research (such as the Kibbull balance) has achieved mass measurement based on quantum benchmarks, the systems are extremely complex and costly, and are only applicable to national metrology laboratories, making it difficult to promote them to scientific research and industrial applications.

[0004] Therefore, there is an urgent need to develop a new type of mass measurement device that combines high precision, high stability, relatively simple structure, and measurement results that can be directly traced back to basic physical constants. Summary of the Invention

[0005] The purpose of this invention is to provide an optical high-precision analytical balance that uses laser wavelength as a natural length reference and achieves accurate measurement of mass by measuring the minute displacement caused by the mass being measured and obtained through a mass-displacement conversion system.

[0006] The embodiments of the present invention are implemented as follows: An optical high-precision analytical balance includes a base, on which are arranged the following in sequence: Optical unit: includes a housing, with a beam splitter plate at the center of the bottom of the housing, and a reference mirror, a frequency-stabilized helium-neon laser and a photodetector arranged sequentially on the inner side wall of the housing. The reference mirror and the photodetector are directly opposite the beam splitter plate and are on the same horizontal line. It also includes a support located directly in front of the beam splitter plate, with a movable mirror slidably mounted on the support. Weighing unit: includes a weighing platform, on which a mass weighing pan is provided, and a sleeve rod is connected to the bottom end of the mass weighing pan. A first return spring is also provided inside the weighing platform, and the sleeve rod is connected to the first return spring; it also includes a sliding rod, which is mounted on a support, with one end abutting against the sleeve rod and the other end fixed to a moving mirror; Display unit: includes a touch display located in front of the weighing platform and a controller located on the top of the enclosure. The controller is electrically connected to a frequency-stabilized helium-neon laser, a photodetector, and the touch display.

[0007] Furthermore, the beam splitter has a beam splitting film on the front and an anti-reflection film on the back, with the front of the beam splitter facing the frequency-stabilized helium-neon laser.

[0008] Furthermore, a sliding channel is provided on the support, and a guide rail is provided at the bottom of the sliding channel. Several sliding balls are provided in the guide rail, and the sliding rod and the guide rail are slidably connected.

[0009] Furthermore, the inner wall of the sliding channel is also provided with a groove, and a number of sliding balls are provided in the groove.

[0010] Furthermore, the sleeve includes an integrally formed vertical rod and a diagonal rod. The vertical rod is provided with a first bracket for connecting the first return spring. One end of the sliding rod abuts against the diagonal rod, and its slope is consistent with the slope of the diagonal rod.

[0011] Furthermore, a second bracket is provided on the sliding rod, and a second return spring is connected to the second bracket. The other end of the second return spring is connected to the support.

[0012] Furthermore, it also includes a wind shield, which houses the optical unit and the weighing unit.

[0013] Compared with the prior art, the embodiments of the present invention have at least the following advantages or beneficial effects: 1. This invention uses the two fundamental physical constants of laser wavelength and gravitational acceleration as a reference. The measurement chain is short, which fundamentally eliminates the long-term drift problem caused by the aging of components and changes in magnetic flux of electromagnetic balances, and realizes absolute measurement with "no wear on the scale". 2. This invention completely eliminates measurement errors introduced by feedback force, electrostatic adsorption, etc. in traditional balances by using pure optical detection of the mass-displacement conversion process without any additional electromagnetic contact. In addition, the measurement results can be directly traced through the basic units of length (speed of light / wavelength) and acceleration, which is in line with the trend of quantization and constantization of the International System of Units (SI), and has great metrological significance. Attached Figure Description

[0014] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1 This is a schematic diagram of the overall structure of the balance in an embodiment of the present invention; Figure 2 This is a schematic diagram of the internal structure of the balance according to an embodiment of the present invention; Figure 3This is a schematic diagram of the structure of the balance optical unit in an embodiment of the present invention; Figure 4 This is a schematic diagram of the structure on the support in an embodiment of the present invention; Figure 5 This is a schematic diagram of the structure of the balance weighing unit in an embodiment of the present invention.

[0016] Icons: 1 - Base; 2 - Optical Unit; 3 - Cover; 4 - Beam Splitter; 5 - Reference Mirror; 6 - Frequency Stabilized Helium-Neon Laser; 7 - Photodetector; 8 - Support; 9 - Moving Mirror; 10 - Weighing Unit; 11 - Weighing Pan; 12 - Sleeve Rod; 1201 - Vertical Rod; 1202 - Diagonal Rod; 13 - First Return Spring; 14 - First Support; 15 - Sliding Rod; 16 - Sliding Channel; 17 - Guide Rail; 18 - Sliding Ball; 19 - Second Return Spring; 20 - Second Support; 21 - Windproof Cover; 22 - Display Unit. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations.

[0018] Therefore, the following detailed description of the embodiments of the invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the invention without inventive effort are within the scope of protection of the invention.

[0019] Example Please refer to Figure 1 - Figure 5This embodiment provides an optical high-precision analytical balance, including a base 1, on which a display unit 22, a weighing unit 10, and an optical unit 2 are sequentially arranged. The optical unit 2 includes a cover 3, which is a cuboid shape made of acrylic sheet. A beam splitter 4 is fixedly arranged at the center of the bottom of the cover 3. A reference mirror 5, a frequency-stabilized helium-neon laser 6, and a photodetector 7 are sequentially arranged on the inner sidewall. The reference mirror 5 and the photodetector 7 are directly opposite the beam splitter 4 and are on the same horizontal line. The beam splitter 4 is a cubic prism made of fused silica, with a surface flatness λ / 10 and a surface shape accuracy PV<0.1μm. The surface of the beam splitter 4 facing the frequency-stabilized helium-neon laser 6 is coated with a 50:50 beam splitting film (R / T=50 / 50±2%), while the opposite back side is coated with an anti-reflection film with an extinction ratio >100:1 (R<0.2%). In actual use, the beam splitter 4 can split a beam of light from the frequency-stabilized helium-neon laser 6 into two beams that are emitted perpendicularly to each other. One beam is directed toward the reference mirror 5, while the other beam is emitted in a straight line through the anti-reflection coating.

[0020] Furthermore, a support 8 is provided directly in front of the beam splitter 4. The support 8 is fixed to the base 1 and passes through the cover 3. A sliding channel 16 is provided above the support 8, and a guide rail 17 is provided at the bottom of the sliding channel 16. Several sliding balls 18 are arranged in the guide rail 17. It also includes a sliding rod 15 laid on the guide rail 17. A moving mirror 9 is fixed to one end of the sliding rod 15, and the moving mirror 9 is directly opposite the beam splitter 4. Reference mirror 5, frequency-stabilized helium-neon laser 6, photodetector 7, and moving mirror 9 are at the same horizontal height, and moving mirror 9, beam splitter 4, and frequency-stabilized helium-neon laser 6 are on the same axis. In use, light of a fixed wavelength emitted by the frequency-stabilized helium-neon laser is split into two beams by beam splitter 4. One beam is directed towards reference mirror 5, and the other towards moving mirror 9. At this point, the optical path difference between these two beams is zero. After being reflected back by reference mirror 5 and moving mirror 9, these two beams re-merge at photodetector 7 to form interference fringes. When moving mirror 9 is displaced, the optical path difference between the two beams directed towards reference mirror 5 and moving mirror 9 changes, and the interference fringes also shift accordingly. When the optical path difference is equal to half an integer multiple of the wavelength of the light, the two beams are out of phase, resulting in destructive interference and forming dark fringes on the screen. When the moving mirror 9 moves by half a wavelength (λ / 2), the optical path difference changes by one wavelength (λ). The interference pattern on the screen will undergo a periodic change from bright to dark to bright (or vice versa). By measuring the number of times this interference fringe moves, we can deduce the distance the moving mirror 9 moves due to the mass being measured, and thus deduce the mass of the object being measured.

[0021] Furthermore, the weighing unit 10 includes a weighing platform with a weighing pan 11. A sleeve rod 12 is connected to the bottom end of the weighing pan 11. The sleeve rod 12 includes an integrally formed vertical rod 1201 and an inclined rod 1202. One end of the vertical rod 1201 is fixedly connected to the bottom end of the weighing pan 11, while one end of the inclined rod 1202 is suspended. The vertical rod 1201 and the inclined rod 1202 form a 135° angle. A first support 14 extends from one side of the vertical rod 1201, and a first return spring 13 is fixedly connected to the first support 14. The other end of the first return spring 13 is fixed to the weighing platform. The elastic coefficient of the first return spring 13 is 50 N / m. Additionally, the other end of the sliding rod 15 is also sloped, with the slope matching that of the inclined rod 1202. When in contact, the slopes of the two rods coincide. In addition, it is worth noting that the contact surfaces of the sliding rod 15 and the inclined rod 1202 are both made of a smooth material with minimal friction. Thus, when the inclined rod 1202 moves downward, it will push the sliding rod 15 to produce a horizontal displacement, which in turn will cause the moving mirror 9 to move. When the weight is removed, the sleeve rod 12 is reset under the action of the first return spring 13 and returns to its initial position.

[0022] Additionally, a second bracket 20 is provided on the sliding rod 15. The second bracket 20 is symmetrically arranged on the left and right sides of the sliding rod 15, and a second return spring 19 is fixed to each of them. The other end of the second return spring 19 is fixedly connected to the support 8. It should be noted that the second return spring 19 and the first return spring 13 can be springs with the same elastic coefficient. Before weighing, calibration is performed. Based on the weight of the item, the relationship between the elastic force of the first return spring 13 and the downward displacement of the sleeve 12, the force on the sliding rod 15 is analyzed. Because the sliding rod 15 and the sleeve 12 are in contact, its displacement is directly linked to the displacement distance of the sleeve 12. However, since the second return spring 19 will generate a corresponding elastic force during the movement of the sliding rod 15, it is necessary to first calculate the influence of the second return spring 19 on the actual weight of the item, and then incorporate it into the calculation formula according to the calibrated structure.

[0023] Furthermore, in this embodiment, the display unit 22 includes a touch display located in front of the weighing platform and a controller (not shown in the figure) located on the top of the cover 3. The controller can be controlled by a Field-Programmable Gate Array (FPGA) chip in a hardware parallel pipeline manner. The photodetector 7 is equipped with a CMOS linear array sensor, an external quartz glass window, and an amplifier and AD converter integrated inside. Its spectral response range is 200-1000nm (peak sensitivity @700nm), dynamic range is 10000:1, dark current is <10pA, and signal-to-noise ratio is >250:1. The photodetector 7 is communicatively connected to the controller, converting the sensed light intensity into a two-dimensional digital matrix and transmitting it to the controller for processing.

[0024] Furthermore, to ensure the accuracy of the interferometric image results, the materials of both the reference mirror 5 and the moving mirror 9 in this embodiment have specific requirements. For example, the reference mirror 5 is a plane mirror with a microcrystalline glass substrate, a gold-plated surface, a thickness of 6 mm, a flatness of λ / 20, and a reflectivity >99.5%, used to reflect one beam of light from the beam splitter 4. The moving mirror 9 is also a plane mirror made of synthetic quartz, with a thickness of 6 mm, a flatness of λ / 20, and a reflectivity >99.5%, used to reflect another beam of light from the beam splitter 4. The balanced beam reflection loss ensures both optical path stability and reflection accuracy, while also allowing for flexible adjustment of the optical path, effectively reducing detection errors and improving the optical detection performance of the equipment.

[0025] Furthermore, the touch display uses an OLED screen that is electrically connected to the controller. It can display the current mass, convert units, automatically adjust decimal places, and display the current interference fringes via touch.

[0026] In this embodiment, the CMOS linear array sensor discretizes the light intensity distribution of the interference fringes into a grayscale digital image. The FPGA first preprocesses this image: environmental and sensor noise is removed by median filtering through a 3×3 sliding window, and background correction is used to eliminate fixed-pattern noise and uneven illumination. Then, the grayscale centroid method is used to extract the fringe center line position at the subpixel level, obtaining a one-dimensional signal reflecting the light intensity change. Next, the FPGA internally splits the signal into two parallel paths: one path enters the integer cycle counting module, which performs zero-crossing comparison and shaping on the sinusoidal interference signal, uses a digital phase detector to determine the direction of movement, and performs 32-bit reversible counting on the square wave pulse after frequency quadrupling, outputting the integer cycle number N; the other path enters the phase subdivision module, which uses the CORDIC algorithm to calculate the phase fraction θ less than one fringe cycle in 14-16 iterations within 22 clock cycles, thereby avoiding the need for multiple frame image acquisitions required by the traditional four-step phase shift method and realizing single-frame phase extraction. Subsequently, the displacement synthesis module calculates the phase fraction θ according to the formula... The total displacement of the moving mirror 9 is calculated (λ=632.8nm). The mass conversion is based on the calibration data pre-stored in the FPGA's on-chip Block RAM (establishing a displacement-mass mapping relationship through known mass weights) to obtain the mass value to be measured, which is then displayed on the touchscreen. The entire processing flow runs in a pipeline manner within the FPGA, with the acquisition and processing time for each frame of image being less than 50 microseconds and a frame rate exceeding 24,000 frames / second, far exceeding the moving speed of the moving mirror 9, thus ensuring no stripe-like omissions. Finally, after the object to be measured is removed, the weighing pan and the moving mirror 9 are reset by two springs. The spring stiffness coefficient is 25N / m, and the material is beryllium bronze. This material is widely used in electronic balances due to its extremely high elastic limit. At the same time, the stiffness coefficient of 25N / m will not reduce the sensitivity due to excessive stiffness, nor will it cause long-term instability of the system during reset due to insufficient stiffness. For example, when loading a 200g object, it will only cause the vertical bar to shift down by 19.6mm, producing a normal millimeter-level displacement. Ultimately, a measurement range of 200g can be achieved with a resolution of 0.1mg.

[0027] It is worth mentioning that, in order to minimize errors in this embodiment, in addition to the sliding balls 18 arranged in the guide rail 17, the inner sidewall of the sliding track is also provided with a groove, which is also provided with a number of sliding balls 18. In actual use, the sliding rod 15 and the sliding balls 18 are in contact. When it moves horizontally, the sliding balls 18 rotate synchronously, thereby reducing the friction generated by the sliding rod 15 during the displacement process and making the results more accurate.

[0028] As a preferred embodiment, the device is also provided with a windproof cover 21, which houses the optical unit 2 and the weighing unit 10 to further avoid interference from external factors.

[0029] Optionally, in this embodiment, a temperature sensor and a pressure sensor can be added inside the windproof cover 21. Both are electrically connected to the touch display to display the temperature and pressure inside the device in real time, ensuring that the environment inside the entire device is always under constant temperature and pressure, and avoiding the influence of temperature or pressure on the interference results.

[0030] In summary, the embodiments of the present invention provide an optical high-precision analytical balance, which uses the two fundamental physical constants of laser wavelength and gravitational acceleration as a reference. It has a short measurement chain and fundamentally eliminates the long-term drift problem caused by component aging and magnetic flux changes in electromagnetic balances, thus achieving absolute measurement with "no wear on the scale". This invention completely eliminates measurement errors introduced by feedback force and electrostatic adsorption in traditional balances by using pure optical detection of the mass-displacement conversion process without any additional electromagnetic contact. In addition, the measurement results can be directly traced through the basic units of length (speed of light / wavelength) and acceleration, which is in line with the trend of quantization and constantization of the International System of Units (SI), and has great metrological significance.

[0031] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. An optical high-precision analytical balance, characterized in that, Includes a base, on which are arranged in sequence: Optical unit: includes a housing, a beam splitter is provided at the center of the bottom of the housing, a reference mirror, a frequency-stabilized helium-neon laser and a photodetector are sequentially provided on the inner side wall of the housing, the reference mirror and the photodetector are directly opposite the beam splitter and are on the same horizontal line; also includes a support provided in front of the beam splitter, a movable mirror is slidably provided on the support; Weighing unit: includes a weighing platform, on which a mass weighing pan is provided, and a sleeve rod is connected to the bottom end of the mass weighing pan. A first return spring is also provided inside the weighing platform, and the sleeve rod is connected to the first return spring; it also includes a sliding rod, which is mounted on the support, with one end abutting against the sleeve rod and the other end fixing the moving mirror; Display unit: includes a touch display located in front of the weighing platform and a controller located on the top of the cover, wherein the controller is electrically connected to the frequency-stabilized helium-neon laser, the photodetector and the touch display.

2. The optical high-precision analytical balance according to claim 1, characterized in that, The beam splitter is provided with a beam splitting film on the front and an anti-reflection film on the back, with the front of the beam splitter facing the frequency-stabilized helium-neon laser.

3. The optical high-precision analytical balance according to claim 1, characterized in that, The support has a sliding channel, the bottom of the sliding channel has a guide rail, and the guide rail has a number of sliding balls. The sliding rod and the guide rail are slidably connected.

4. The optical high-precision analytical balance according to claim 3, characterized in that, The inner wall of the sliding channel is also provided with a sliding groove, and a number of sliding balls are provided in the sliding groove.

5. The optical high-precision analytical balance according to claim 1, characterized in that, The sleeve includes an integrally formed vertical rod and a diagonal rod. The vertical rod is provided with a first bracket for connecting the first return spring. One end of the sliding rod abuts against the diagonal rod, and its slope is consistent with that of the diagonal rod.

6. The optical high-precision analytical balance according to claim 1, characterized in that, The sliding rod is provided with a second bracket, and a second return spring is connected to the second bracket. The other end of the second return spring is connected to the support.

7. The optical high-precision analytical balance according to claim 1, characterized in that, It also includes a windproof cover, which covers the optical unit and the weighing unit.

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