Leakage detection method and device for hemispherical resonator gyroscope base

Abstract

The invention provides a hemispherical resonator gyroscope base leak detection device and method.The hemispherical resonator gyroscope base leak detection device comprises a leak detection seat, an O-shaped sealing ring and a process leak detection seat, the leak detection seat is of a different-diameter tubular structure, the two ends of the leak detection seat are provided with tubular structures, the leak detection seat is of a high-airtightness structure, and the leak detection seat is placed between a leak detector and a hemispherical resonator gyroscope base when used; the leak detection seat is used as a high-reliability sealed connection passage between the leak detector and the hemispherical resonator gyroscope base, one end of the leak detection seat is in high-airtight connection with the leak detector through the O-shaped sealing ring during leak detection, and the other end of the leak detection seat is in high-airtight connection with the hemispherical resonator gyroscope base through the O-shaped sealing ring, so that high-reliability quick leak detection of the hemispherical resonator gyroscope base is realized.

Description

Technical Field

[0001] This invention belongs to the field of hemispherical resonant gyroscope technology, specifically relating to a leak detection method and device for a hemispherical resonant gyroscope base. Background Technology

[0002] A hemispherical resonator gyroscope is a rotorless vibrating gyroscope that measures the rotation of its outer shell by measuring the circumferential precession of the standing wave of a hemispherical harmonic oscillator. Due to its simple structure, small size, light weight, low power consumption, high precision, high reliability, and good environmental adaptability, it can be widely used in aviation, aerospace, and marine fields, and is currently the most promising inertial gyroscope in these fields. Hemispherical resonator gyroscopes must operate in a high vacuum environment to ensure their ultra-high precision and long-term stability. High vacuum (typically below 1E-4 Pa) significantly reduces air damping, allowing the quality factor (Q value) of the resonator to reach tens of millions or more, thereby reducing energy loss, improving zero-bias stability, and reducing angular random walk error. Through metal or ceramic sealing, laser welding, and getter technology, hemispherical resonator gyroscopes can maintain an ultra-high vacuum state for decades in extreme environments, meeting the stringent precision and lifespan requirements of high-end applications in aviation, aerospace, and marine industries.

[0003] The hemispherical resonator gyroscope achieves an ultra-high airtightness connection between the metal casing and the base through brazing or laser welding, ensuring that the internal resonator operates in a high vacuum environment for extended periods. While ensuring a high airtight connection between the metal casing and the base, the airtightness of the metal casing and base themselves is crucial. The metal casing has an integral barrel-shaped structure; with stable materials and manufacturing processes, long-term reliability can be guaranteed through leak detection. The base, as another sealing structure, has a main structure of square or circular plates. Since it needs to connect 10 signals (8 internal detection / excitation signals, high-voltage signal, and ground signal) to the outside, it typically uses an insulator sintering process. While ensuring insulation and airtightness reliability, the internal and external signals are connected via metal pins. Due to the special manufacturing process of the insulators, there are significant differences in product quality consistency. Furthermore, due to the special structure of the metal base, with metal pins protruding from both sides, leak detection of the base itself is quite difficult.

[0004] Due to the unique structure of the base, checking the leakage rate of the insulator holes within the base itself is currently quite difficult. Generally, the base is supported by a bracket, and a sealing gasket or vacuum sealant is used to seal the space between the base and the bracket for leak detection. However, existing methods are difficult to standardize and involve significant time spent checking the reliability of the vacuum sealant itself, resulting in generally poor leak detection effectiveness. Consequently, most bases are only visually inspected for leaks, making it difficult to quantify the leakage rate. In conclusion, current leak detection methods cannot guarantee product quality and can seriously affect batch quality. Summary of the Invention

[0005] To address the difficulty of ensuring the sealing reliability of the base itself using existing technologies, this invention proposes a leak detection method and device for hemispherical resonant gyroscope bases, solving the problems of high difficulty and non-standardized leak detection processes in current methods, and achieving reliable and standardized leak detection for hemispherical resonant gyroscope bases.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: In a first aspect, this application provides a leak detection device for a hemispherical resonant gyroscope base, comprising a leak detection base 3, an O-ring seal 2, and a process leak detection base 5, wherein: Leak detection base 3 is a tubular structure with different diameters. Both ends of the leak detection base 3 are equipped with tubular structures. The leak detection base 3 is a highly airtight structure. When in use, it is placed between the leak detector 4 and the hemispherical resonant gyroscope base 1, serving as a highly reliable sealed connection channel between the leak detector 4 and the hemispherical resonant gyroscope base 1. During leak detection, one end of the leak detection base is connected to the leak detector 4 in a highly airtight manner through the O-ring seal 2, and the other end is connected to the hemispherical resonant gyroscope base 1 in a highly airtight manner through the O-ring seal 2, realizing highly reliable and fast leak detection of the hemispherical resonant gyroscope base 1.

[0007] Specifically, the leak detection base 3 has a leak detection end 3-1 and a leak detection connection end 3-2 at its two ends, respectively. The upper and lower end faces of the leak detection base 3 are parallel, and a through hole of the same or different diameter is opened in the center. Rectangular grooves of specified depth B and width C are machined on the upper and lower end faces of the leak detection base according to the diameter R specification of the O-ring seal. During leak detection, the rectangular groove is used to install the O-ring seal. The two ends are respectively connected to the leak detector 4 and the hemispherical resonant gyroscope base 1 with high airtightness.

[0008] Specifically, the leak detection seat 3 is made of a low-emission metal material.

[0009] Specifically, the rectangular grooves on both ends of the leak detection seat 3, including the leak detection end and the leak detection seat connection end, include dovetail grooves, open grooves, and narrow grooves.

[0010] Specifically, the base 1 serves as the structural support for the hemispherical resonant gyroscope. The base 1 is provided with mounting holes for mounting the hemispherical resonant gyroscope to the system's working surface, providing a mounting reference for the hemispherical resonant gyroscope.

[0011] Specifically, the base 1 includes at least 10 metal pins 1-1, which are used to mount the plate electrodes of the gyroscope, to connect the excitation and detection signals, and to isolate the influence of common vibration frequencies.

[0012] Specifically, the process leak detection seat 5 is a cylindrical structure with one end open, including the process leak detection seat connecting end 5-2.

[0013] Specifically, the process leak detection seat connection end 5-2 is a circular plane with a rectangular groove. According to the standard of O-ring diameter D, the rectangular groove is used to install the O-ring during leak detection to achieve a high airtight connection with the leak detector, and to determine the equipment's working status and background vacuum in advance.

[0014] Specifically, the O-ring 2, together with the rectangular structure on the leak detection seat 3 and the process leak detection seat 5, forms a sealing part, achieving a highly airtight connection with the leak detector 4 and the hemispherical resonant gyroscope base 1.

[0015] Secondly, this application provides a leak detection method for a hemispherical resonant gyroscope base, the method utilizing the aforementioned device, the method comprising: Step 1: The end faces of leak detection seat 3 and process leak detection seat 5 have rectangular groove structures; Step 2: Insert the O-ring 2 into the corresponding rectangular groove and confirm that the working surface of the leak detector 4 is flat; Step 3: First, use the process leak detection seat 5 to confirm the status of the leak detector. During leak detection, use the helium nozzle 6 to spray helium gas around the sealing ring and read the reading of the leak detector 4. This is used to confirm the limit leak rate detected by the leak detector 4. The limit leak rate is used as a benchmark value. During formal leak detection, it is used to screen the base 1 that has a small amount of leakage in advance. Step 4: Place the detection end of the leak detector 3 flat on the working surface of the leak detector, ensuring that the leak detection port is located in the center of the leak detector. Place the base 1 flat on the detection end of the leak detector 3, ensuring that the base 2 is basically aligned with the center of the leak detector 3. Step 5: Start the leak detector 4, draw the air pressure inside the leak detector 3 to the specified negative pressure, continue to maintain the negative pressure state of the detection base 3, and spray helium gas around the base 1 through the helium nozzle 6. During the spraying process, observe whether there is any change in the leak rate displayed by the leak detector 4. Step 6: During the process of spraying helium gas onto the base 1 using the helium nozzle 6, if the leak detector 4 indicates no change in the leak rate, the leak rate is deemed acceptable; if the leak detector 4 indicates a decrease in the leak rate, the helium nozzle 6 is used to hold the helium gas at each metal pin 1-4 for about 10 seconds, and the sudden change in the leak rate is observed when the gas is held at each metal pin 1-1 to further confirm the location of the leak. Step 7: After the initial leak detection of base 1 is completed, the ambient temperature of base 1 is screened according to the ambient temperature cycling conditions required by HRG gyroscope. Step 8: After the environmental temperature screening test, repeat steps 2 to 6, compare the leakage rates of the two tests, confirm whether base 1 meets the leakage rate requirements, screen out bases with reduced leakage rates, and eliminate bases 1 with potential hazards in advance.

[0016] In summary, this invention proposes a leak detection method and device for a hemispherical resonant gyroscope base, which has the following advantages and beneficial effects compared with the prior art: 1. Core Innovation Point 1: This invention uses a rectangular groove plus O-ring sealing ring structure as the sealing part as the core sealing part of the leak detection device, which can achieve high vacuum sealing and high reliability leak detection. 2. Core Innovation Point 2: The leak detection structure of this invention only has two O-rings for sealing, eliminating the need for auxiliary materials such as vacuum sealing mud and sealing silicone grease, thus achieving clean leak detection and avoiding the cleaning process after detection; 3. Core Innovation Point 3: The leak detection method and device of the present invention are simple and reliable to operate, greatly improving the leak detection efficiency and effect of existing bases and reducing detection costs; 4. Core Innovation Point 4: This invention provides a leak detection device for a hemispherical gyroscope base. The device is a tubular structure with varying diameters, which is simple in structure and applicable to leak detection equipment and hemispherical gyroscope bases of different specifications. 5. Core Innovation Point 5: The method of this invention adds a process leak detection seat to the traditional leak detection process. The process seat has a simple structure and low operation difficulty. It is used to confirm the status of the leak detector and the limit leak rate of the base before base leak detection. 6. Core Innovation Point 6: Based on the basic leakage rate of the process leak detection base, this invention can accurately screen out bases with micro-leakage. 7. Core Innovation Point 7: The method of this invention is designed for the actual use conditions of hemispherical resonant gyroscopes. It proposes a method of conducting temperature environment stress screening on the base and then conducting leak detection again, and compares the leakage rates of the two leak detections to screen bases with potential sealing hazards in advance. Attached Figure Description

[0017] Figure 1 Schematic diagram of leak detector working position Figure 2 Schematic diagram of the process leak detection seat Figure 3 Schematic diagram of the sealing part In the diagram: 1-Base, 1-1 Metal pin, 2-O-ring seal, 3-Leak detector seat, 3-1 Leak detector seat detection end, 3-2 Leak detector seat connection end, 4-Leak detector, 4-1 Leak detector exhaust port, 5-Process leak detector seat, 5-2 Process leak detector seat connection end, 6-Helium injection nozzle. Detailed Implementation

[0018] The present invention will now be described clearly and specifically with reference to the accompanying drawings.

[0019] Example 1 like Figures 1-3 As shown, this embodiment proposes a leak detection device for a hemispherical resonant gyroscope base, comprising a leak detection base 3, an O-ring seal 2, and a process leak detection base 5, wherein: The leak detector base 3 is a tubular structure with varying diameters at both ends. This design accommodates different specifications of leak detector interfaces and hemispherical resonator gyroscope base sizes. In special cases, the leak detector base 3 can also be designed as a round tube of equal diameter or other tubular structures. The specific shape of the leak detector base 3 depends on the specific structure of the hemispherical resonator gyroscope base 1. The leak detector base 3 itself is a highly airtight structure, and leaks in the base itself will not affect the leak detection results. During use, it is placed between the leak detector 4 and the hemispherical resonator gyroscope base 1, serving as a highly reliable sealed connection between them. During leak detection, one end of the leak detector base is connected to the leak detector 4 with a high airtight seal via an O-ring 2, and the other end is connected to the hemispherical resonator gyroscope base 1 with a high airtight seal via an O-ring 2, achieving highly reliable and rapid leak detection for the hemispherical resonator gyroscope base 1.

[0020] Specifically, the leak detector base 3 has a leak detector detection end 3-1 and a leak detector connection end 3-2 at its two ends. The leak detector base 3 is made of a common low-gas-emission metal material, such as stainless steel. The upper and lower end faces of the leak detector base 3 are parallel, with a through hole of the same or different diameter in the center. The surface roughness of the through hole is required to reach Ra0.4 to reduce internal gas adsorption and avoid affecting the leak detection effect. Rectangular grooves of specified depth B and width C are machined on the upper and lower end faces of the leak detector base according to the diameter R of the O-ring seal. The surface roughness of the rectangular grooves is required to reach Ra0.4, and the length of the rectangular grooves matches the length of the selected O-ring seal 2. During leak detection, this rectangular groove is used to install the O-ring seal, and the two ends respectively achieve a high-tightness connection with the leak detector 4 and the hemispherical resonator gyroscope base 1.

[0021] Specifically, the rectangular grooves on both ends of the leak detection seat 3, including the detection end and the connection end, can also be processed into other sealing structure shapes, such as dovetail grooves, open grooves, and narrow grooves. The above structures are all standard structures in the vacuum sealing industry. The specific dimensions of the groove are designed and processed according to the standard dimensions of the selected O-ring 2. The specific length of the groove can be matched with the selected O-ring.

[0022] Specifically, the base 1 can be designed as a square, triangular, or circular structure according to usage requirements. The material of base 1 is generally Kovar alloy or ceramic. Base 1 serves as the structural support for the hemispherical resonant gyroscope. It has mounting holes for mounting the hemispherical resonant gyroscope to the system's working surface, providing a mounting reference for the gyroscope. Base 1 includes at least 10 metal pins 1-1, typically made of Kovar alloy. These metal pins 1-1 are used to mount the gyroscope's planar electrodes, facilitating the connection of excitation and detection signals. Simultaneously, the structural design of the metal pins isolates common vibration frequency influences, providing a better working environment for the resonant components.

[0023] Specifically, the process leak detection seat 5 is a cylindrical structure with one open end, including the process leak detection seat connection end 5-2. The material is a common low-emission metal material, such as stainless steel. The process leak detection seat connection end 5-2 is a circular plane with a rectangular groove. According to the diameter D specification of the O-ring seal, a rectangular groove with a specified depth B and width C is machined on the process leak detection seat connection end. The surface roughness of the rectangular groove is required to reach Ra0.4. At the same time, the length of the rectangular groove matches the length specification of the selected O-ring seal 2. During leak detection, this rectangular groove is used to install the O-ring seal to achieve a high airtight connection with the leak detector, which is used to determine the working status and background vacuum of the equipment in advance.

[0024] Specifically, the O-ring 2 is a commonly used sealing component in the vacuum field. It has a circular cross-section and is usually made of rubber. Together with the rectangular structure on the leak detector 3 and the process leak detector 5, it forms a sealing part to achieve a high airtight connection with the leak detector 4 and the hemispherical resonant gyroscope base 1.

[0025] During leak detection, the O-ring 2 is inserted into the square grooves at both ends of the leak detection base 3. After installing the O-ring on the connecting end 3-2 of the leak detection base, it is placed horizontally on the leak detection port of the leak detector 4 to form a sealing part. The base 1 is placed horizontally on the O-ring at the detection end to form a sealing part.

[0026] Before the leak detection process begins, in order to quickly confirm the working status of the leak detector 4 and the limit leak rate of the leak detection seat 3, this embodiment designs a process leak detection seat 5. The process leak detection seat 5 is a cylindrical structure with one end open. The opening port is designed with a rectangular groove for placing the O-ring seal 2, which is used to confirm the working status of the leak detector 4 and the limit leak rate of the leak detection seat 3.

[0027] Example 2 like Figure 2 As shown, this embodiment proposes a leak detection method for a hemispherical resonant gyroscope base, including: Step 1: The end faces of leak detection seat 3 and process leak detection seat 5 have rectangular groove structures. Figure 3 The depth B and width C of the rectangular groove are related to the diameter R of the O-ring. The depth B of the rectangular groove is approximately 0.7R, the width C of the rectangular groove is approximately 1.6R, and the circumference of the rectangular groove is the same as the circumference of the O-ring. Step 2: Before installing the leak detection seat 1 or process leak detection seat 5 with the O-ring 2, confirm that the inside of the rectangular groove is smooth, intact and free of foreign objects. Check that the corresponding O-ring 2 is intact and free of foreign objects on its surface. Install the O-ring 2 into the corresponding rectangular groove and confirm that the working surface of the leak detector 4 is flat and free of foreign objects. Step 3: First, use the process leak detection seat 5 to confirm the status of the leak detector. During leak detection, use the helium nozzle 6 to spray helium gas around the sealing ring and read the reading of the leak detector 4 to confirm the limit leak rate that the leak detector 4 can detect. Use the limit leak rate as the benchmark value. During formal leak detection, it can be used to screen the base 1 with trace leaks in advance. Step 4: Place the detection end of the leak detector 3 flat on the working surface of the leak detector, ensuring that the leak detection port is located in the center of the leak detector. Place the base 1 flat on the detection end of the leak detector 3, ensuring that the base 2 is basically aligned with the center of the leak detector 3. Step 5: Start the leak detector 4, draw the air pressure inside the leak detector 3 to the specified negative pressure, continue to maintain the negative pressure state of the detection base 3, and spray helium gas around the base 1 through the helium nozzle 6. During the spraying process, observe whether there is any change in the leak rate displayed by the leak detector 4. Step 6: During the process of spraying helium gas onto the base 1 using the helium nozzle 6, if the leak detector 4 indicates no change in the leak rate, the leak rate is deemed acceptable; if the leak detector 4 indicates a decrease in the leak rate, the helium nozzle 6 is used to hold the helium gas near each metal pin 1-4 for about 10 seconds, and the sudden change in the leak rate when it is held near each metal pin 1-1 can be observed to further confirm the location of the leak. Step 7: After the initial leak detection of base 1 is completed, the ambient temperature of base 1 is screened according to the ambient temperature cycling conditions required by HRG gyroscope. Step 8: After the environmental temperature screening test, repeat steps 2 to 6 and compare the leakage rates of the two tests to confirm whether base 1 meets the leakage rate requirements. Further screening can identify bases with reduced leakage rates and eliminate bases 1 with potential risks in advance.

[0028] In summary, this embodiment discloses a precision leak detection method and apparatus for a hemispherical resonator base 1. The main structure of the apparatus, the leak detection base 3, is a tubular structure with varying diameters. Rectangular grooves matching O-ring seals 2 are machined on both ends of the tubular structure, at the detection end 3-1 and the connecting end 3-1. When using this apparatus for leak detection, firstly, corresponding O-ring seals 2 are installed in the rectangular grooves at both ends of the leak detection base 3. Then, the connecting end with the O-ring seal 2 is horizontally placed on the detection platform of the leak detector 4. Next, the base 1 is horizontally placed on the O-ring seal 2 at the detection end. When the leak detector 4 is working, the internal air pressure of the leak detection base 3 decreases, causing the O-ring seal to deform, achieving a high-vacuum reliable seal between the leak detection base 3, the leak detector 4, and the base 1. This enables high-precision leak detection of the hemispherical resonator gyroscope base 1 and accurately quantifies the leakage rate. By performing environmental stress screening on the base 1 and then performing leak detection again, bases with potential micro-leakage can be pre-screened, ensuring that the high-vacuum requirements of the resonator are met for subsequent use of the hemispherical resonator gyroscope.

[0029] The base leak detection device 3 described in this embodiment has a simple structure and simple operation method, can achieve standardized operation, and has high accuracy in leak detection results. It can be applied to different types of leak detectors 4 and base 1 structures, and solves the problems of high operation difficulty and low accuracy of existing leak detection methods for hemispherical resonant gyroscope base 1, as well as the inability to accurately quantify the leak rate due to the difficulty in standardizing existing leak detection operation methods.

Claims

1. A leak detection device for a hemispherical resonant gyroscope base, characterized in that, Includes a leak detection seat (3), an O-ring (2), and a process leak detection seat (5), wherein: The leak detection base (3) is a tubular structure with different diameters. The leak detection base (3) has tubular structures at both ends. The leak detection base (3) is a highly airtight structure. When in use, it is placed between the leak detector (4) and the hemispherical resonant gyroscope base (1) as a highly reliable sealed connection channel between the leak detector (4) and the hemispherical resonant gyroscope base (1). During leak detection, one end of the leak detection base is connected to the leak detector (4) with a highly airtight connection through the O-ring seal (2), and the other end is connected to the hemispherical resonant gyroscope base (1) with a highly airtight connection through the O-ring seal (2), so as to realize highly reliable and fast leak detection of the hemispherical resonant gyroscope base (1).

2. The apparatus according to claim 1, characterized in that, The leak detection base (3) has a leak detection end (3-1) and a leak detection connection end (3-2) at its two ends respectively; the upper and lower end faces of the leak detection base (3) are parallel, and a through hole of the same or different diameter is opened in the center; rectangular grooves of specified depth B and width C are machined on the upper and lower end faces of the leak detection base according to the diameter R specification of the O-ring seal. During leak detection, the rectangular groove is used to install the O-ring seal. The two ends are respectively connected to the leak detector (4) and the hemispherical resonant gyroscope base (1).

3. The apparatus according to claim 2, characterized in that, The leak detection seat (3) is made of a low-emission gas metal material.

4. The apparatus according to claim 1, characterized in that, The rectangular grooves on both ends of the leak detection seat (3) include dovetail grooves, open grooves, and narrow grooves.

5. The apparatus according to claim 1, characterized in that, The base (1) serves as the structural support for the hemispherical resonant gyroscope. The base (1) is provided with mounting holes for mounting the hemispherical resonant gyroscope to the system working surface, providing a mounting reference for the hemispherical resonant gyroscope.

6. The apparatus according to claim 1, characterized in that, The base (1) includes at least 10 metal pins (1-1) for mounting the plate electrodes of the gyroscope, for connecting excitation and detection signals, and for isolating common vibration frequency effects.

7. The apparatus according to claim 1, characterized in that, The process leak detection seat (5) is a cylindrical structure with one end open, including the process leak detection seat connection end (5-2).

8. The apparatus according to claim 1, characterized in that, The process leak detection seat connection end (5-2) is a circular plane with a rectangular groove. According to the standard of the diameter D of the O-ring seal, the rectangular groove is used to install the O-ring seal during leak detection to achieve a high airtight connection with the leak detector and to determine the working status and background vacuum of the equipment in advance.

9. The apparatus according to claim 1, characterized in that, Specifically, the O-ring (2) and the rectangular structure on the leak detection seat (3) and the process leak detection seat (5) form a sealing part, realizing a high airtight connection with the leak detector (4) and the hemispherical resonant gyroscope base (1).

10. A leak detection method for a hemispherical resonant gyroscope base, characterized in that, The method utilizes the apparatus according to any one of claims 1 to 9, and the method includes: Step 1: The end faces of the leak detection seat (3) and the process leak detection seat (5) have a rectangular groove structure; Step 2: Insert the O-ring (2) into the corresponding rectangular groove and confirm that the working surface of the leak detector (4) is flat; Step 3: First, use the process leak detection seat (5) to confirm the status of the leak detector. When leaking, use the helium nozzle (6) to spray helium gas around the sealing ring and read the reading of the leak detector (4) to confirm the limit leak rate detected by the leak detector (4). Use the limit leak rate as the benchmark value to screen the base (1) with trace leakage in advance during formal leak detection. Step 4: Place the detection end of the leak detector (3) flat on the working surface of the leak detector, ensuring that the leak detection port is located in the center of the leak detector. Place the base (1) flat on the detection end of the leak detector (3), ensuring that the base (2) is basically aligned with the center of the leak detector (3). Step 5: Start the leak detector (4), draw the air pressure inside the leak detector (3) to the specified negative pressure, continue to maintain the negative pressure state of the detection base (3), spray helium gas around the base (1) through the helium nozzle (6), and observe whether the leak rate displayed by the leak detector (4) changes during the spraying process. Step 6: During the process of spraying helium gas onto the base (1) with the helium nozzle (6), if the leak detector (4) indicates no change in the leakage rate, the leakage rate is deemed acceptable; if the leak detector (4) indicates a decrease in the leakage rate, the helium nozzle (6) is used to hold the helium gas at each metal pin (1-4) for about 10 seconds, and the sudden change in the leakage rate is observed when the gas is held at each metal pin (1-1) to further confirm the location of the leak. Step 7: After the initial leak detection of the base (1) is completed, the base (1) is subjected to environmental temperature screening in accordance with the environmental temperature cycling conditions required by the HRG gyroscope. Step 8: After the environmental temperature screening test, repeat steps 2 to 6, compare the leakage rates of the two tests, confirm whether the base (1) meets the leakage rate requirements, screen out the bases with reduced leakage rates, and eliminate the bases (1) with potential hazards in advance.

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