A buoyancy adjustment device for a small underwater robot based on electrolyzed seawater

Abstract

The present invention discloses a buoyancy adjustment device for a small underwater robot based on electrolyzed seawater, which is fixed on the upper part of the sealed cavity end cover of the small underwater robot and includes a flow guide cover fixed to the sealed cavity end cover; an exhaust hole and an electric control switch module for controlling the opening and closing of the exhaust hole are provided at the top of the flow guide cover; the electric control switch module is connected to the circuit in the sealed cavity through a watertight cable; an electrolytic anode and an electrolytic cathode arranged in a nested manner are provided inside the flow guide cover, and the electrolytic anode and the electrolytic cathode are respectively fixed to the sealed cavity end cover through an anode watertight connector and a cathode watertight connector and are connected to the electrolysis control circuit in the sealed cavity; a water permeable hole is provided on the sealed cavity end cover. The structure of the present invention is simple, without additional sensors. The flow guide cover structure is used as a buoyancy adjustment gas container, reducing the external oil bag or air bag of the traditional buoyancy adjustment device. It can detect the gas volume during the gas production and exhaust processes, facilitating the quantitative control of buoyancy.

Description

Technical Field

[0001] The present invention belongs to the field of buoyancy adjustment devices, and in particular relates to a buoyancy adjustment device for a small underwater robot based on electrolyzed seawater. Background Art

[0002] As an unmanned ocean exploration platform, a small underwater robot has the advantages of low cost and convenient use, and can conduct diverse research on the marine environment and resources.

[0003] In the structure of an underwater robot, the buoyancy adjustment device is an important component for controlling the robot to complete ascending and descending movements. Currently, the buoyancy adjustment devices applied to small underwater robots mainly change their own drainage volume by changing the volume of an oil bladder or air bladder located outside the pressure-resistant cavity to adjust buoyancy. Generally, it is divided into two methods: hydraulic and pneumatic. The hydraulic method uses a hydraulic pipeline connecting an oil bladder located outside the cavity with an oil cylinder, solenoid valve, hydraulic pump, drive motor, etc. located inside the cavity. By controlling the operation of the pump and solenoid valve, hydraulic oil flows between the oil bladder and the oil cylinder, increasing or decreasing the volume of the oil bladder. The pneumatic method uses an air bladder located outside the cavity connected to a valve, high-pressure gas cylinder or air pump located inside the cavity to increase and decrease the volume of the air bladder.

[0004] However, both of the above two devices have the disadvantages of requiring many components, complex structure, large weight, and large occupation of the internal volume of the robot cavity. Therefore, there is an urgent need for a device with a simple structure, small size, light weight, and stable reliability to achieve the buoyancy adjustment of small underwater robots.

[0005] Chinese patent document with publication number CN108327855A discloses a deep-sea buoyancy adjustment system and its method. The system includes a glass float pressure-resistant cabin, an outer oil bladder, an outer air bladder, an inner oil bladder, a DC motor, a high-pressure piston pump, an air pump, a ball valve, and an electromagnetic air valve. This system realizes increasing buoyancy by discharging oil in the deep sea by using the air pump to provide inlet pressure for the high-pressure piston pump, and realizes reducing buoyancy by generating a pressure difference in the vacuum cavity, solving the problem of buoyancy adjustment of intelligent buoys in the deep-sea environment. However, this system still has the following disadvantages:

[0006] (1) This system uses an inner oil bladder, a high-pressure piston pump, an air pump, two DC motors, two solenoid valves, and two one-way valves. These components require a large amount of space in the sealed cavity of the underwater robot, and at the same time, they have a large weight and are not suitable for small underwater robots.

[0007] (2) The volume compression of the outer oil bladder and outer air bladder in this system under deep-sea pressure is huge, and it is easy for the connection between the oil bladder, air bladder and metal to rupture and cause leakage.

[0008] (3) This system uses multiple motors, pumps, and valves, with a complex system, high power consumption, and low reliability.

[0009] (4) All the hydraulic devices used in this system need to be able to withstand high pressure, with few product options and high costs, and are not suitable for small underwater robots.

[0010] (5) The system requires a vacuum environment in the sealed cavity, which is inconvenient for actual operation and is not conducive to heat dissipation of the devices in the sealed cavity during operation. Summary of the Invention

[0011] The present invention provides a buoyancy adjustment device for a small underwater robot based on electrolyzing seawater, which has a simple structure, does not require additional sensors, can detect the gas volume during gas production and exhaust processes, and is convenient for quantitative control of buoyancy.

[0012] A buoyancy adjustment device for a small underwater robot based on electrolyzing seawater is fixed on the upper part of the sealed cavity end cover of the small underwater robot, and includes a diversion cover fixed to the sealed cavity end cover; an exhaust hole is provided at the top of the diversion cover and an electric control switch module for controlling the opening and closing of the exhaust hole; the electric control switch module is connected to the circuit in the sealed cavity through a watertight cable;

[0013] An electrolytic anode and an electrolytic cathode are arranged in a nested manner inside the diversion cover, and the electrolytic anode and the electrolytic cathode are respectively fixed on the sealed cavity end cover through an anode watertight connector and a cathode watertight connector and are connected to the electrolysis control circuit in the sealed cavity; a water permeable hole is provided on the sealed cavity end cover.

[0014] The entire device body of the present invention is located outside the pressure-resistant cavity of the underwater robot and inside the structure of the diversion cover, without occupying the internal space of the underwater robot cavity and without occupying additional external cavity space, thus saving space and facilitating the miniaturization of the underwater robot volume. At the same time, using the diversion cover structure as a buoyancy adjustment gas container reduces the external oil bag or air bag of the traditional buoyancy adjustment device, reduces the system weight and avoids structural damage caused by the action of seawater pressure on the oil bag or air bag.

[0015] Furthermore, the electric control switch module mainly controls gas discharge through an electromagnet and a spring structure. Specifically, the electric control switch module includes a bracket fixed to the top of the diversion cover, an electromagnet fixed on the bracket, a pull rod with its lower end fixed to the moving core of the electromagnet, and a sealing cover fixed to the upper end of the pull rod. A pre-compression spring is connected between the lower end face of the sealing cover and the upper end face of the electromagnet, and the electromagnet is connected to the watertight cable;

[0016] When the electromagnet is not energized, the pre-compression spring presses the sealing cover on the diversion cover to block the exhaust hole; when the electromagnet is energized, the moving core of the electromagnet drives the pull rod to separate the sealing cover from the diversion cover, opening the exhaust hole.

[0017] The present invention mainly uses electrolytic electrodes and electromagnets. Compared with the oil cylinders, pumps, motors, and solenoid valves used in traditional buoyancy adjustment devices, it has a simple structure, small volume, low cost, is not easily damaged, and has high reliability.

[0018] In order to obtain a larger specific surface area, both the electrolytic anode and the electrolytic cathode adopt a long cylindrical mesh structure.

[0019] In order to obtain a smaller seawater resistance and improve the electrolysis efficiency, the distance between the electrolytic anode and the electrolytic cathode is 3 mm to 8 mm.

[0020] A plurality of fixing blocks are evenly arranged on the outer edge of the sealing cavity end cover, and the lower end of the flow guide cover is fixed to the fixing blocks by bolts.

[0021] To obtain higher electrolysis efficiency, the electrolytic cathode needs to have good hydrogen evolution ability and corrosion resistance at the same time, and a pure titanium electrode can be selected; the electrolytic anode can select an iridium tantalum titanium electrode.

[0022] In the present invention, by controlling whether the electromagnet is energized and the magnitude of the electrolysis current, the increase and decrease of buoyancy are controlled. No additional sensors are required, and the gas volume can be detected during the gas production and exhaust processes, which is convenient for the quantitative control of buoyancy. The specific control process is as follows:

[0023] When the underwater robot needs to increase its own buoyancy, the electromagnet is not energized. The sealing cover seals the exhaust hole under the action of the pre-compressed spring. The electrolysis control circuit applies a voltage between the electrolytic anode and the electrolytic cathode to generate a large electrolysis current. At this time, the gas generated by the electrolysis of seawater rises to the top of the flow guide cover under the action of buoyancy, and the seawater drains out from the bottom water permeable hole. The gas volume in the upper part of the flow guide cover increases, the seawater liquid level drops, the overall drainage volume of the underwater robot increases, and the buoyancy increases; at the same time, the electrolysis control circuit continuously detects the voltage across the electrodes and the electrolysis current, calculates the seawater resistance between the electrolytic anode and the electrolytic cathode, and further calculates the gas volume in the flow guide cover. When the target gas volume is reached, that is, the buoyancy required by the underwater robot is reached, the voltage applied to the electrolytic anode and the electrolytic cathode is stopped, the seawater electrolysis stops, the gas stops being generated, the gas volume in the flow guide cover remains unchanged, and the buoyancy of the robot remains constant;

[0024] When the underwater robot needs to reduce its own buoyancy, the electromagnet is energized, and the moving core drives the pull rod to separate the sealing cover from the fairing. The gas overflows from the exhaust hole, the gas volume in the fairing decreases, the sea water level rises, the overall drainage volume of the underwater robot decreases, and the buoyancy decreases. At the same time as exhausting, the electrolysis control circuit applies a voltage to the electrolysis anode and the electrolysis cathode to generate a small current. By detecting the voltage across the electrodes and the electrolysis current, the sea water resistance between the electrolysis anode and the electrolysis cathode is calculated, and then the gas volume inside the fairing is obtained. At this time, only a small amount of gas is generated on the two electrodes. When the measured gas volume decreases to the target value, the electromagnet is powered off, and the sealing cover reseals the exhaust hole under the action of the pre-compressed spring, the gas stops overflowing, the volume remains unchanged, and the buoyancy of the robot remains constant.

[0025] The sea water resistance between the electrolysis anode and the electrolysis cathode is inversely proportional to the immersion height of the electrolysis anode and the electrolysis cathode in sea water. After the quantitative relationship between the sea water resistance between the electrolysis anode and the electrolysis cathode and the voltage across the electrodes and the electrolysis current is measured by the initial experiment, the sea water resistance between the electrolysis anode and the electrolysis cathode is calculated through the voltage across the electrodes and the electrolysis current, and then the immersion height of the electrodes in the fairing in sea water is obtained from the sea water resistance between the electrolysis anode and the electrolysis cathode. Finally, the gas volume inside the fairing above the sea water level is calculated from the geometric dimensions of the fairing and its internal structure.

[0026] Further, the calculation formula for the immersion height h of the electrolysis anode and the electrolysis cathode in the fairing in sea water is:

[0027]

[0028] In the formula, U e is the voltage across the electrolysis anode and the electrolysis cathode, and I is the electrolysis current; according to the formula U e =U r +U p +IR e , the equivalent ohmic internal resistance R e of the device and the theoretical decomposition voltage U r and the sum of the two, denoted as U p and the electrode polarization voltage U rp are obtained by linear regression method for the experimental data of the device at different immersion heights h of the electrodes in sea water, U rp =U r +U p ; according to the formula the equivalent ohmic internal resistance R e of the device at different immersion heights h of the electrodes in sea water, the resistance coefficient K r and the resistance R m of the metal conductor of the device are obtained through linear regression analysis.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1) The present invention utilizes the fairing structure commonly possessed by underwater robots as the electrolytic reaction vessel and gas container, which does not occupy the precious internal space of the sealed cavity of the underwater robot, and at the same time does not increase the external volume of the cavity, thus reducing the overall volume and weight of the underwater robot.

[0031] 2) The present invention uses the fairing as the gas container to replace the commonly used airbag in existing products, which can avoid the leakage of the sealed cavity of the underwater robot caused by the rupture of the airbag under the action of water pressure and improve the system reliability.

[0032] 3) The system structure of the present invention is simple, and the main components are electrolytic electrodes and an electromagnet. Compared with the pumps, valves, and motors commonly used in existing products, the cost is greatly reduced, the failure rate is reduced, and the system reliability is high.

[0033] 4) The electrolytic electrode adopts a long cylindrical mesh structure, which increases the specific surface area, improves the electrolysis efficiency, reduces the weight of the electrode, and is convenient for gas volume measurement.

[0034] 5) The present invention indirectly obtains the gas volume in the device by measuring the voltage and current during the electrolysis process, without the need to install additional sensors, solving the difficulty of gas volume measurement and facilitating the quantitative control of the buoyancy of the underwater robot. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Figure 1 It is a schematic diagram of the overall structure of a buoyancy adjustment device for a small underwater robot based on electrolysis of seawater according to the present invention.

[0036] In the figure: 1 - exhaust hole; 2 - O-ring seal; 3 - sealing cover; 4 - bracket; 5 - electromagnet; 6 - watertight cable; 7 - anode watertight connector; 8 - end cover of the sealed cavity; 9 - permeable hole; 10 - fixing block; 11 - cathode watertight connector; 12 - fairing; 13 - electrolytic cathode; 14 - electrolytic anode; 15 - pull rod; 16 - pre-compression spring. DETAILED DESCRIPTION OF THE INVENTION

[0037] The following further describes the present invention in detail with reference to the drawings and embodiments. It should be noted that the following embodiments are intended to facilitate the understanding of the present invention and do not limit it in any way.

[0038] As Figure 1 shown, a buoyancy adjustment device for a small underwater robot based on electrolysis of seawater includes: a fairing 12 fixed to the end cover 8 of the sealed cavity of the underwater robot (a cross-sectional view of the fairing is shown in the figure). The electrolytic anode 14 is connected to the end cover 8 of the sealed cavity through the anode watertight connector 7 and is connected to the electrolysis control circuit in the sealed cavity (not shown in the figure). The electrolytic cathode 13 is connected to the end cover 8 of the sealed cavity through the cathode watertight connector 11 and is connected to the electrolysis control circuit in the sealed cavity (not shown in the figure).

[0039] There are water permeable holes 9 on the upper surface of the end cover 8 of the sealed cavity. The inside of the flow guide cover 12 is communicated with the seawater outside. There is an exhaust hole 1 opened at the top of the flow guide cover 12, which is communicated with the seawater outside. A plurality of fixing blocks 10 are evenly arranged along the outer edge of the end cover 8 of the sealed cavity. The lower end of the flow guide cover 12 is fixed to the fixing blocks 10 by bolts.

[0040] The electromagnet 5 is fixed to the bracket 4 by bolts, and the bracket 4 is fixed to the inner top surface of the flow guide cover 1 by bolts. The sealing cover 3 equipped with an O-ring 2 is connected to the moving core of the electromagnet 5 by a pull rod 15, and the electromagnet 5 is connected to the circuit inside the sealed cavity by a watertight cable 6. A pre-compression spring 16 is installed between the sealing cover 3 and the electromagnet 5. In the state where the electromagnet 5 is not energized, the pre-compression spring 16 presses the sealing cover 3 on the flow guide cover 12 to block the exhaust hole 1.

[0041] To obtain higher electrolysis efficiency, the cathode needs to have good hydrogen evolution ability and corrosion resistance. A pure titanium electrode can be selected, and an iridium tantalum titanium electrode can be selected for the anode. In order to obtain a larger specific surface area, both the electrolysis anode 14 and the electrolysis cathode 13 adopt a mesh structure. The distance between the electrolysis anode 14 and the electrolysis cathode 13 is 5 mm.

[0042] In the present invention, the method for measuring the gas volume inside the flow guide cover is as follows: The resistance of the seawater between the electrolysis anode 14 and the electrolysis cathode 13 is inversely proportional to the height of the immersed electrolysis electrodes, that is, the greater the height of the two electrodes immersed in seawater, the smaller the resistance of the seawater between the electrolysis anode 14 and the electrolysis cathode 13. After the quantitative relationship between the seawater resistance between the electrolysis anode 14 and the electrolysis cathode 13, the voltage at both ends of the electrodes, and the electrolysis current is measured through initial experiments, during the use of the device, the seawater resistance between the electrolysis anode 14 and the electrolysis cathode 13 can be obtained by the voltage at both ends of the electrodes and the electrolysis current. Then, the height h of the electrolysis anode 14 and the electrolysis cathode 13 immersed in seawater inside the flow guide cover 12 is obtained from the seawater resistance. Finally, the gas volume inside the flow guide cover 12 above the seawater level is calculated from the geometric dimensions of the flow guide cover 12 and its internal structure.

[0043] The following introduces the calculation process of the height h of the electrodes immersed in seawater inside the flow guide cover:

[0044] According to the electrolysis theory, the voltage-current relationship between the electrolysis anode 14 and the electrolysis cathode 13 during seawater electrolysis can be expressed as follows:

[0045] U e = U r + U p + IR e (Ⅰ)

[0046] Among them, U e is the voltage at both ends of the electrolysis anode 14 and the electrolysis cathode 13, U r is the theoretical decomposition voltage, U pis the electrode polarization voltage, I is the electrolysis current, and R e is the equivalent ohmic internal resistance of the device, which consists of the following two parts:

[0047] R e = R s + R m (Ⅱ)

[0048] Among them, R m is the metal conductor resistance of the device, including wire resistance, electrolytic electrode metal resistance, etc., which remains unchanged during the operation of the device. R s is the seawater resistance between the electrolytic anode 14 and the electrolytic cathode 13, which can be calculated by the following formula:

[0049]

[0050] Among them, d is the distance between the electrolytic anode 14 and the electrolytic cathode 13, κ is the seawater conductivity, S is the area of the electrolytic electrode immersed in seawater. For electrodes with a consistent cross-section in the vertical height direction, the immersed area S is proportional to the height h of the electrode immersed in seawater, and the proportionality coefficient is k.

[0051] Substituting Equation (Ⅲ) and Equation (Ⅱ) into Equation (Ⅰ) can obtain the relationship between the voltage U e across the electrolytic anode 14 and the electrolytic cathode 13, the electrolysis current I, and the height h of the electrode immersed in seawater:

[0052]

[0053] According to Equation (Ⅳ), the calculation formula for the height h of the electrode immersed in seawater is obtained:

[0054]

[0055] Since the electrode polarization voltage U p , the proportionality coefficient k, and the metal conductor resistance R m of the device are related to the electrolysis device and difficult to obtain through direct measurement, the parameters required in Equation (Ⅴ) can be calculated by fitting the experimental data of the device.

[0056] The following method is adopted in this embodiment:

[0057] Step 1: Before using the device, complete the electrolysis experiment of the device with simulated seawater. Apply different voltages at the electrolytic anode 14 and the electrolytic cathode 13 to generate different electrolysis currents at different heights h of the electrode immersed in seawater. According to Equation (Ⅰ), the equivalent ohmic internal resistance R e of the device and the theoretical decomposition voltage U r and the sum of the electrode polarization voltage U p can be obtained by using the linear regression method, which is denoted as U rp . Urp The values ​​of the electrodes at different immersion heights h are approximately equal, and the mean of the values ​​obtained by regression analysis at different immersion heights is taken as the final calculation value.

[0058] Step 2: According to formula (II) and formula (III), the equivalent ohmic internal resistance R of the device is e It can be expressed as a linear relationship of the inverse of the electrode immersion height h in seawater:

[0059]

[0060] According to the equivalent ohmic internal resistance R of the device at different electrode immersion heights h obtained in step 1 e The resistivity K can be obtained by linear regression analysis. r The resistance R of the metal conductor of the device m .

[0061] Step 3: According to the device parameters experimentally fitted in steps 1 and 2, the height h of the electrode immersed in seawater can be expressed as:

[0062]

[0063] During the use of the device, the voltage U between the electrolysis anode 14 and the electrolysis cathode 13 is detected by the electrolysis control circuit. e and the electrolysis current I passing through, combined with the device parameter resistivity K obtained by fitting in step 1 and step 2 r , Device metal conductor resistance R m , Theoretical decomposition voltage U r With electrode polarization voltage U p The sum of U rp According to formula (VII), the height h of the electrode immersed in seawater can be calculated, and the volume of the gas inside the flow guide cover 12 above the seawater surface can be further calculated based on the geometric dimensions of the flow guide cover 12 and its internal structure.

[0064] In this embodiment, the parameters of the experimental device fitted by the above method are: U rp =2.77V, K r =2.38×10 -3 Ω·m,R m =0.0779Ω.

[0065] The implementation process of the device of the present invention includes two stages: buoyancy increase and buoyancy decrease.

[0066] Increasing buoyancy: When the underwater robot needs to increase its own buoyancy, the electromagnet 5 is de-energized. The sealing cover 3 equipped with the O-ring seal 2 seals the exhaust hole 1 under the action of the pre-compression spring 16. The internal electrolysis control circuit applies a voltage (about 3.7V) between the electrolysis anode 14 and the electrolysis cathode 13 to generate a large electrolysis current (about 10A). At this time, seawater is electrolyzed to rapidly generate gas. The generated gas rises to the top of the fairing 12 under the action of buoyancy, and seawater is discharged from the bottom water-permeable hole 9. The gas volume in the upper part of the fairing 12 increases, the seawater liquid level drops, the overall drainage volume of the underwater robot increases, and the buoyancy increases. At the same time, the internal control circuit continuously detects the voltage across the electrodes and the electrolysis current and indirectly calculates the gas volume inside the fairing 12. When the target gas volume is reached, that is, when the buoyancy required by the underwater robot is reached, the voltage applied to the electrolysis anode 14 and the electrolysis cathode 13 is stopped, the seawater electrolysis stops, the gas generation stops, the gas volume in the fairing 12 remains unchanged, and the buoyancy of the robot remains constant.

[0067] Decreasing buoyancy: When the underwater robot needs to reduce its own buoyancy, the electromagnet 5 is energized. The moving core drives the pull rod 15 to separate the sealing cover 3 from the fairing 12, and the gas overflows from the exhaust hole 1. The gas volume in the fairing 12 decreases, the seawater liquid level rises, the overall drainage volume of the underwater robot decreases, and the buoyancy decreases. While exhausting the gas, the internal electrolysis control circuit applies a voltage (about 2.6V) between the electrolysis anode 14 and the electrolysis cathode 13 to generate a small electrolysis current (about 0.5A). At the same time, the internal control circuit continuously detects the voltage across the electrodes and the electrolysis current and indirectly calculates the gas volume inside the fairing 12. At this time, only a small amount of gas is generated on the two electrodes. When the measured gas volume decreases to the target value, the electromagnet 5 is de-energized, and the sealing cover 3 seals the exhaust hole 1 again under the action of the pre-compression spring 16, the gas stops overflowing, the volume remains unchanged, and the buoyancy of the robot remains constant.

[0068] The above-described embodiments have described in detail the technical solutions and beneficial effects of the present invention. It should be understood that the above are only specific embodiments of the present invention and are not used to limit the present invention. Any modifications, supplements, and equivalent replacements made within the scope of the principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A buoyancy adjustment device for a small underwater robot based on electrolyzed seawater, characterized in that It is fixed on the upper part of the end cover (8) of the sealed cavity of the small underwater robot, and includes a fairing (12) fixed to the end cover of the sealed cavity; an exhaust hole (1) is provided at the top of the fairing (12), and an electric control switch module for controlling the opening and closing of the exhaust hole (1); the electric control switch module is connected to the circuit in the sealed cavity through a watertight cable (6); An electrolytic anode (14) and an electrolytic cathode (13) which are sleeved with each other are arranged inside the fairing (12). The electrolytic anode (14) and the electrolytic cathode (13) are respectively fixed on the end cover (8) of the sealed cavity through an anode watertight connector (7) and a cathode watertight connector (11) and are connected to the electrolytic control circuit in the sealed cavity; a water permeable hole (9) is provided on the end cover (8) of the sealed cavity; The electric control switch module includes a bracket (4) fixed to the top of the fairing (12), an electromagnet (5) fixed on the bracket (4), a pull rod (15) whose lower end is fixed to the moving core of the electromagnet (5), and a sealing cover (3) fixed to the upper end of the pull rod (15). A pre-compression spring (16) is connected between the lower end face of the sealing cover (3) and the upper end face of the electromagnet (5). The electromagnet (5) is connected to the watertight cable (6); when the electromagnet (5) is not powered on, the pre-compression spring (16) presses the sealing cover (3) on the fairing (12) to block the exhaust hole (1); when the electromagnet (5) is powered on, the moving core of the electromagnet (5) drives the pull rod (15) to separate the sealing cover (3) from the fairing (12), so that the exhaust hole (1) is opened; The increase and decrease of buoyancy are controlled by controlling whether the electromagnet is powered on and the magnitude of the electrolytic current. The specific control process is as follows: When the underwater robot needs to increase its own buoyancy, the electromagnet (5) is not powered on. The sealing cover (3) seals the exhaust hole (1) under the action of the pre-compression spring (16). The electrolytic control circuit applies a voltage between the electrolytic anode (14) and the electrolytic cathode (13) to generate a large electrolytic current. At this time, the gas generated by the electrolysis of seawater rises to the top of the fairing (12) under the action of buoyancy, and the seawater is discharged from the bottom water permeable hole (9). The gas volume in the upper part of the fairing (12) increases, the seawater liquid level drops, the overall drainage volume of the underwater robot increases, and the buoyancy increases; at the same time, the electrolytic control circuit continuously detects the voltage and electrolytic current at both ends of the electrolytic anode (14) and the electrolytic cathode (13), calculates the seawater resistance between the electrolytic anode (14) and the electrolytic cathode (13), and further calculates the gas volume in the fairing (12). When the target gas volume is reached, that is, the buoyancy required by the underwater robot is reached, the voltage applied to the electrolytic anode (14) and the electrolytic cathode (13) is stopped, the seawater electrolysis stops, the gas stops generating, the gas volume in the fairing (12) remains unchanged, and the buoyancy of the robot remains constant; When the underwater robot needs to reduce its own buoyancy, the electromagnet (5) is energized. The moving core drives the pull rod (15) to separate the sealing cover (3) from the fairing (12). Gas overflows from the exhaust hole (1). The volume of gas in the fairing (12) decreases, the sea water level rises, the overall drainage volume of the underwater robot decreases, and the buoyancy decreases. At the same time of exhausting, the electrolysis control circuit applies a voltage to the electrolysis anode (14) and the electrolysis cathode (13) to generate a tiny electrolysis current. By detecting the voltage across the electrolysis anode (14) and the electrolysis cathode (13) and the electrolysis current, the sea water resistance between the electrolysis anode (14) and the electrolysis cathode (13) is calculated, and then the gas volume in the fairing (12) is obtained. At this time, only a small amount of gas is generated on the two electrodes. When the measured gas volume decreases to the target value, the electromagnet (5) is de-energized. The sealing cover (3) reseals the exhaust hole (1) under the action of the pre-compressed spring (16). The gas stops overflowing and the volume remains unchanged, and the buoyancy of the robot remains constant; The sea water resistance between the electrolysis anode (14) and the electrolysis cathode (13) is inversely proportional to the immersion height h of the electrolysis anode (14) and the electrolysis cathode (13) in sea water; After the quantitative relationship between the sea water resistance between the electrolysis anode (14) and the electrolysis cathode (13), the voltage across the electrodes and the electrolysis current is measured by the initial experiment, the sea water resistance between the electrolysis anode (14) and the electrolysis cathode (13) is calculated by detecting the voltage across the electrolysis anode (14) and the electrolysis cathode (13) and the electrolysis current. Then, the immersion height h of the electrodes in the fairing (12) in sea water is obtained from the sea water resistance between the electrolysis anode (14) and the electrolysis cathode (13). Finally, the gas volume inside the fairing (12) above the sea water level is calculated from the geometric dimensions of the fairing (12) and its internal structure; The calculation formula for the immersion height h of the electrolysis anode (14) and the electrolysis cathode (13) in the fairing (12) in sea water is: Where U e is the voltage across the electrolytic anode (14) and the electrolytic cathode (13), and I is the electrolytic current; according to the formula U e =U r +U p +IR e , the equivalent ohmic resistance R e of the device at different immersion heights h of the electrodes in seawater and the sum of the theoretical decomposition voltage U r and the electrode polarization voltage U p are obtained by linear regression on the experimental data of the device, denoted as U rp , U rp =U r +U p ; according to the formula the equivalent ohmic resistance R e of the device at different immersion heights h of the electrodes in seawater, the resistance coefficient K r and the resistance R m of the metal conductor of the device are obtained by linear regression analysis.

2. The buoyancy adjustment device for a small underwater robot based on electrolyzed seawater according to claim 1, characterized in that, Both the electrolysis anode (14) and the electrolysis cathode (13) adopt long cylindrical mesh structures.

3. The buoyancy adjustment device for a small underwater robot based on electrolyzed seawater according to claim 1, characterized in that, The distance between the electrolysis anode (14) and the electrolysis cathode (13) is 3 mm to 8 mm.

4. The buoyancy adjustment device for a small underwater robot based on electrolyzed seawater according to claim 1, characterized in that, A plurality of fixing blocks (10) are uniformly arranged on the outer edge of the sealing cavity end cover (8). The lower end of the fairing (12) is fixed to the fixing blocks (10) by bolts.

5. The buoyancy adjustment device for a small underwater robot based on electrolyzed seawater according to claim 1, wherein The electrolysis anode (14) adopts an iridium tantalum titanium electrode, and the electrolysis cathode (13) adopts a pure titanium electrode.

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