Cold air thruster of microsatellite

Abstract

The invention provides a cold air thruster of a microsatellite. The cold air thruster is integrated with a valve assembly, a piezoelectric actuator, an elastic mechanism, a capacitance displacement sensor, a flow sensor and a control unit. The valve assembly is driven by the executing mechanism, the gap between the disc-shaped diaphragm and the valve port is accurately regulated and controlled, and fine adjustment of gas flow and thrust is achieved. And the piezoelectric ceramic and elastic design of the actuating mechanism ensures that the valve is normally opened and quickly responded. The sensor system optimizes the control accuracy through feedback of a capacitance sensor and a flow sensor. The double-closed-loop control strategy adjusts driving voltage based on displacement and flow information, improves dynamic response and reduces control noise. The shell assembly provides comprehensive protection. The problems that in the prior art, thrust control precision is low, dynamic response performance is poor, and control noise is large can be effectively solved.

Description

Technical Field

[0001] This invention belongs to the field of aerospace propulsion technology, specifically relating to a cold gas thruster for microsatellites. Background Technology

[0002] With the continuous advancement of microelectromechanical systems (MEMS) technology and the development of microsatellite technology, the scientific mission capabilities of small and microsatellites have been greatly enhanced. This has placed higher demands on microsatellite propulsion systems to meet the demands of these more demanding scientific missions. Cold gas thrusters for microsatellites are a propulsion technology that generates thrust by releasing high-pressure gas. Their core principle involves controlling the ejection of stored high-pressure gas (or liquefied gas) through valves, using the reaction force to adjust the satellite's attitude or control its orbit. Employing small-sized and simple-to-control cold gas propulsion technology on microsatellites to meet the needs of attitude adjustment, orbit maintenance, and deorbiting operations at the end of their lifespan has become an important choice for microsatellite propulsion systems.

[0003] However, traditional cold gas thruster design and control strategies have certain limitations. Currently, most cold gas thrusters used in microsatellites fail to meet the requirements of high-precision scientific missions in terms of size, control accuracy, response speed, thrust noise, and stability. Specifically, existing cold gas thrusters are typically large, making it difficult to adapt to the stringent space requirements of microsatellites. In terms of control, the lack of effective displacement and flow feedback mechanisms limits the thruster's control accuracy, especially in terms of micro-Newton thrust and sub-micro-Newton thrust resolution, failing to meet the needs of high-precision attitude adjustment and orbit control. Slow response speed is also a common problem with existing cold gas thrusters, directly affecting their applicability in rapid attitude adjustment missions. Furthermore, ensuring ultra-low noise and stability in thrust output is also a challenge. Existing solutions (such as those based on complex sensor fusion or multi-stage conical valve adjustment) struggle to effectively suppress thrust fluctuations (noise) introduced by valve nonlinearity, hydrodynamic disturbances (such as turbulence and cavitation), temperature sensitivity, and sensor noise when achieving nanometer-level displacement control or high-resolution flow measurement. This thrust noise is particularly deadly in high-precision attitude control (such as Earth staring and deep space exploration pointing) and ultra-fine orbit maintenance (such as gravitational measurement satellite formations). It can significantly reduce control accuracy, introduce unnecessary attitude disturbances, increase fuel consumption, and even interfere with the measurement data of precision scientific payloads (such as optics and interferometers).

[0004] Patent document CN 113738881 B discloses a piezoelectric cold gas variable thrust closed-loop control device with multi-sensor fusion. Through piezoelectric precision drive and interactive compensation from temperature and flow sensors, combined with displacement sensor feedback, it improves the reliability and anti-interference capability of the control system to some extent. However, its structure is complex, and there is still room for improvement in sensor integration and feedback control strategies, especially in achieving micro-Newton-level thrust and 0.1µN thrust resolution. Patent document CN 116620568 B discloses a micro-satellite device and its thruster. It designs a thruster including a shell, a valve core, and a piezoelectric ceramic unit. The size of the opening defined by the first and second conical surfaces is adjusted, and the piezoelectric ceramic unit achieves nanometer-level high-precision motion control of the valve core, thereby achieving micro-Newton-level thrust and 0.1µN thrust resolution. However, while this design utilizes a conical valve orifice for flow regulation, which improves thrust regulation accuracy, it may be challenged in terms of valve speed and reliability, especially in terms of thrust stability and low noise characteristics required for high-precision scientific missions.

[0005] In summary, the main problems faced by existing cold gas thrusters for microsatellites include: large size, low control precision, slow response speed, high thrust noise, and insufficient stability. These problems limit the widespread application of cold gas thrusters on microsatellites, especially their ability to perform high-precision scientific missions. Summary of the Invention

[0006] This invention provides a cold gas thruster for microsatellites to overcome the aforementioned technical obstacles, achieving smaller size, more precise control, and faster response, while ensuring low noise and stability of thrust in harsh space environments.

[0007] The technical solution of the present invention is as follows: A cold gas thruster for a microsatellite includes a valve assembly, an actuator, a sensor system, a gas flow path, a control unit, and a housing assembly. Wherein: The valve assembly includes a valve seat, a disc-shaped diaphragm, and a valve cover support. The valve seat consists of a central air inlet and a coaxially arranged cylindrical gas chamber, forming an annular valve port between the central air inlet and the gas chamber. The disc-shaped diaphragm is connected to the valve cover support and the actuator, forming a sealed contact with the valve port. Under the action of a drive signal, the gap between the diaphragm and the valve port is precisely adjusted, thereby controlling the gas flow rate and thrust. The valve cover support has a base surface for mounting the capacitive sensor stator and a position for fixing the disc-shaped diaphragm.

[0008] The actuator includes a piezoelectric actuator and an elastic mechanism that internally houses the piezoelectric actuator. The piezoelectric actuator drives the diaphragm to move, thereby changing the flow area of ​​the annular valve port, which remains normally open when no external force is applied. The elastic mechanism is connected to the valve cover bracket and provides a restoring force when the piezoelectric actuator is not in operation, causing the disc-shaped diaphragm to quickly return to its original position.

[0009] The sensor system includes a displacement sensor and a flow sensor. The displacement sensor comprises a capacitive sensor stator and a capacitive sensor mover. The capacitive sensor stator is mounted on the valve cover bracket, and the capacitive sensor mover is mounted on the bottom of the actuator. It detects the displacement of the piezoelectric actuator mechanism by measuring displacement changes. The flow sensor includes a flow sensor channel bracket and an integrated modulation circuit board for measuring gas flow velocity. The displacement sensor and flow sensor are connected to the control unit, providing displacement and flow feedback respectively.

[0010] The gas flow path includes an inlet pipe interface and an outlet nozzle. The inlet pipe interface is connected to the central inlet hole of the valve seat, and the outlet nozzle is connected to the flow sensor channel support, ensuring the gas flow path from the inlet to the outlet.

[0011] The control unit connects the actuator, displacement sensor, and flow sensor. It receives flow information from the flow sensor and displacement information from the capacitive sensor's mover. It adjusts the drive voltage of the piezoelectric actuator mechanism through a dual closed-loop control strategy, thereby adjusting the thrust magnitude and accuracy of the cold air thruster.

[0012] The housing assembly is used to encapsulate and protect the valve assembly, actuator, sensor system, and gas flow path of the thruster.

[0013] This technical solution combines a piezoelectric actuator with an elastic mechanism. The piezoelectric actuator utilizes the piezoelectric effect of piezoelectric ceramics to convert electrical energy into mechanical energy, thereby driving the movement of a diaphragm and achieving precise control of the disc-shaped diaphragm. Simultaneously, the integrated design of a capacitive sensor and a flow sensor ensures high efficiency and accuracy. The capacitive sensor measures the diaphragm displacement based on the principle of capacitance change, while the flow sensor detects gas flow rate to provide feedback to the control unit. This technical solution achieves precise flow control and rapid response in cold gas thrusters, improving the accuracy of attitude adjustment and orbit control for microsatellites.

[0014] In one embodiment of the present invention, the piezoelectric actuator of the gas-cooled thruster is a piezoelectric ceramic stack actuator, and the elastic mechanism is an elliptical elastic mechanism or a corrugated elastic mechanism. The outer diameter of the lower bottom surface of the elastic mechanism is consistent with the outer diameter of the annular valve port of the valve seat. Through the cooperation of the two, the working pressure difference of the gas-cooled thruster is improved and the overall flow-stopping characteristics of the gas-cooled thruster are enhanced. When the piezoelectric ceramic stack is in an inactive state, it can provide a return force, causing the disc-shaped diaphragm to quickly return to its initial position, thereby enabling the valve to open quickly and improving dynamic response performance. This design utilizes the combination of the expansion and contraction characteristics of the piezoelectric ceramic stack and the rebound force of the elastic mechanism to achieve rapid valve opening and closing, significantly improving the dynamic response speed of the gas-cooled thruster, enabling it to adapt more quickly to the needs of satellite attitude adjustment and orbit control.

[0015] In one embodiment of the present invention, a piezoelectric ceramic stack is embedded in an elastic mechanism, connected to the elastic mechanism by an interference fit, and pre-tightened by a pre-tightening screw to ensure that the piezoelectric ceramic stack can generate stable and predictable displacement during the driving process. In this solution, the use of interference fit and pre-tightening screws ensures a tight connection between the piezoelectric ceramic stack and the elastic mechanism, avoiding displacement deviation during the driving process. This connection method utilizes the piezoelectric effect and elastic properties of the piezoelectric ceramic stack, controlling the initial state of the piezoelectric ceramic stack through pre-tightening force, thereby achieving precise control of the diaphragm displacement and ensuring rapid reset of the actuator in the inactive state. This improves the displacement control accuracy of the cold gas thruster, reduces thrust fluctuations, and enhances the stability and reliability of the system.

[0016] In one embodiment of the present invention, a preset initial gap is maintained between the disc-shaped diaphragm and the annular valve port on the valve seat. This initial gap design ensures that the valve is normally open, while the flow rate is precisely controlled by changing the position of the disc-shaped diaphragm. The initial gap setting takes into account gas flow characteristics and valve control requirements. This design utilizes the influence of the gap change between the disc-shaped diaphragm and the valve port on the gas flow rate. By controlling the displacement of the diaphragm, precise flow rate control is achieved, improving the flow control accuracy of the cold gas thruster and enabling it to meet the precision propulsion requirements of microsatellites.

[0017] In one embodiment of the present invention, the cylindrical gas chamber and the central air inlet of the valve seat are machined from a single piece of material, employing an integrated design. This integrated design avoids leakage and displacement deviation that may result from connecting multiple components, ensuring the structural stability and sealing performance of the valve assembly. This design utilizes the material's processing characteristics and, through precision machining technology, achieves high-precision manufacturing of the valve seat, reducing the risk of gas leakage and enhancing the reliability and performance of the system.

[0018] In one embodiment of the present invention, the stator and mover of the capacitive sensor are respectively fixed on the base surfaces of the valve cover bracket and the elastic mechanism, forming a capacitive displacement sensor to ensure high-precision feedback of the displacement of the disc-shaped diaphragm. Here, the installation positions of the stator and mover of the capacitive sensor take into account the relative motion between the sensor and the actuator. Through precise installation and fixing, high-precision displacement measurement is achieved.

[0019] In one embodiment of the present invention, the control unit includes an inner loop control module and an outer loop control module. The inner loop control module employs a composite control algorithm combining feedforward and feedback to adjust the gap height between the disc-shaped diaphragm and the valve port on the annular surface of the valve seat, as well as the input voltage. The outer loop control module employs a PID control algorithm to adjust the difference between the actual flow rate and the desired flow rate generated by adjusting the actual gap height between the disc-shaped diaphragm and the valve port on the annular surface of the valve seat, thereby achieving high-precision control of the output flow rate and thrust. The control unit can optimize the response time and control accuracy of the piezoelectric actuator mechanism based on flow error and displacement error signals using advanced control algorithms, while compensating for the nonlinear hysteresis effect of the piezoelectric ceramic actuator and reducing thrust noise. In this scheme, a dual closed-loop control strategy combines the advantages of feedforward and feedback control. Through the synergistic effect of the inner and outer loops, precise control of flow rate and thrust is achieved, which can improve the control accuracy and response speed of the cold gas thruster, reduce thrust fluctuations and noise, and enhance the stability and reliability of the system.

[0020] In one embodiment of the present invention, the flow sensor channel bracket is glued and sealed to the flow sensor modulation circuit board manufactured using PCB technology, and connected to the base. The flow sensor chip on the flow sensor modulation circuit board is installed at the middle position of the flow channel on the flow sensor channel bracket, so that the flow channel is symmetrically distributed with respect to the position of the flow sensor chip, reducing fluid turbulence, improving the accuracy of flow measurement, and also ensuring the compactness and reliability of the entire cold gas thruster. The symmetrically distributed flow channel design takes into account the gas flow characteristics and sensor measurement requirements. Through the glued and sealed connection between the flow channel bracket and the modulation circuit board, high-precision measurement of gas flow velocity is achieved, enhancing the system's feedback control capability, reducing thrust fluctuations, and improving propulsion efficiency.

[0021] In one embodiment of the present invention, the valve seat air inlet and the flow sensor air outlet are respectively connected to the air inlet pipe interface and the air outlet nozzle by threads, thereby ensuring the sealing and stability of the gas flow path.

[0022] The working process of this invention is as follows: In the initial state, when the voltage applied externally to the cold gas thruster is 0, the piezoelectric ceramic stack is in a contracted state. At this time, gas at a certain pressure flows in through the inlet pipe interface, enters the chamber through the annular valve port, then flows through the chamber, enters the flow sensor inlet, and finally flows out from the outlet nozzle, generating thrust. When thrust needs to be adjusted, the control unit, based on the desired thrust magnitude, uses a dual closed-loop control strategy. First, it adjusts the drive voltage of the inner loop control module to change the gap height between the disc-shaped diaphragm and the annular valve port on the valve seat. Simultaneously, the outer loop control module adjusts the actual gap height between the disc-shaped diaphragm and the annular valve port on the valve seat based on the flow information obtained from the flow sensor, to achieve the desired flow output. During the control process, the displacement information obtained by the capacitive sensor generates a control signal after being processed by the control algorithm. After being amplified by the drive, the signal acts on the piezoelectric actuator, pushing the disc-shaped diaphragm, changing the flow area of ​​the annular valve port, and generating different flow outputs, thereby achieving precise control of the thrust. Throughout the operation, the rapid response of the piezoelectric actuator and the precise adjustment of the dual closed-loop control strategy ensured that the cold gas thruster could quickly and accurately adjust the thrust magnitude to meet the needs of microsatellite attitude adjustment and orbit control.

[0023] According to the above technical solution, the present invention has the following significant technical effects: 1. High-precision displacement feedback: Through a capacitive micro-displacement sensor, the displacement of the piezoelectric actuator mechanism is accurately measured and controlled, ensuring the fine-tuning accuracy of the valve gap. The dynamic resolution of the capacitive micro-displacement sensor is 0.4nm.

[0024] 2. Rapid response and reset capability: The combined use of the piezoelectric actuator mechanism and the elliptical elastic mechanism enhances the working pressure difference of the thruster and improves its flow-stopping characteristics, enabling the valve to reset quickly in the inactive state. This not only ensures the dynamic response performance of the system but also provides a return force when the power is off, allowing the disc-shaped diaphragm to reset quickly and ensuring the timely opening of the valve. The response speed can reach 5 ms.

[0025] 3. Precise flow control: The close cooperation between the flow sensor, capacitive micro-displacement sensor, actuator and control unit, through a high-precision dual closed-loop control strategy, achieves precise control of flow and thrust, significantly improving the accuracy and response speed of microsatellite attitude control. The precise flow control accuracy is ±0.332% FS, and the flow sensor has a flow resolution of 0.04 mL / min.

[0026] 4. High operating pressure differential and flow-stopping characteristics: The integrated valve seat design and the fit between the elliptical elastic mechanism and the annular valve port improve the operating pressure differential of the air-cooled thruster and enhance its flow-stopping characteristics, with a leakage rate ≤0.5% FS. This ensures structural stability and control accuracy under high pressure differential operating environments. 5. Compactness and reliability: The glued and sealed connection between the flow sensor channel bracket and the flow sensor modulation circuit board, as well as the overall compact design, ensure the adaptability and reliability of the cold gas thruster in confined space applications such as microsatellites.

[0027] 6. Reduce thrust noise: The dual closed-loop control strategy precisely adjusts the diaphragm gap through inner loop feedforward-feedback composite control and dynamically compensates for flow deviation through outer loop PID algorithm. The dual synergy suppresses the nonlinear hysteresis and dynamic disturbance of the piezoelectric actuator, thereby effectively reducing thrust noise.

[0028] This invention provides strong support for the precise orbit control and attitude adjustment of microsatellites and has significant engineering application value. Attached Figure Description

[0029] The accompanying drawings, which are included to provide a further understanding of the invention and form part of this invention, illustrate exemplary embodiments of the invention and are used to explain the invention, but do not constitute an undue limitation of the invention. In the drawings: Figure 1 This is a three-dimensional unfolded diagram of a cold gas thruster used in microsatellites; Figure 2 This is a three-dimensional partial cross-sectional view of a cold gas thruster used in microsatellites; Figure 3 This is a 3D diagram of a piezoelectric actuator used in a cold gas thruster for microsatellites. Figure 4 This is a 3D diagram of a valve cover support for a cold gas thruster used in microsatellites. Figure 5 This is a front view of a valve cover bracket for a cold gas thruster used in microsatellites; Figure 6 This is a top view of a valve cover support for a cold gas thruster used in microsatellites; Figure 7 This is a 3D diagram of a valve seat for a cold gas thruster used in microsatellites. Figure 8 This is a top view and a cross-sectional view of the valve seat of a cold gas thruster used in microsatellites; Figure 9 A three-dimensional diagram of the flow channel support for a cold gas thruster used in microsatellites; Figure 10This is a front view, bottom view, and sectional view of a novel cold air thruster flow channel support; Figure 11 It is another type of piezoelectric actuator used in cold gas thrusters for microsatellites; Figure 12 This is a dual closed-loop control block diagram for a cold gas thruster used in microsatellites.

[0030] Component numbers in the diagram: 1. Stud, 2. Stud mounting hole, 3. Housing, 4. Threaded hole, 5. Pre-tightening threaded hole, 6. Threaded hole, 7. Elliptical elastic mechanism, 8. Piezoelectric ceramic stack, 10. Valve cover bracket, 11. Stud, 12. Capacitive sensor stator, 13. Disc-shaped diaphragm, 14. Screw, 15. Sealing ring, 16. Valve seat, 17. Sealing ring, 18. Inlet pipe interface, 19. Threaded hole, 20. Flow sensor channel bracket, 21. Stud mounting hole, 22. Housing cover, 23. Stud, 24. Outlet nozzle, 25. Piezoelectric actuator mechanism, 26. Capacitive sensor mover, 27. Central air inlet, 28. Flow sensor modulation circuit board, 29. Cylindrical gas chamber, 30. Capacitive sensor mover mounting base, 31. Control unit, 32. Detailed Implementation

[0031] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other. The present invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0032] It should be noted that, unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0033] In this invention, unless otherwise stated, directional terms such as "upper," "lower," "top," and "bottom" are generally used in relation to the direction shown in the accompanying drawings, or in relation to the vertical, perpendicular, or gravitational direction of the component itself; similarly, for ease of understanding and description, "inner" and "outer" refer to the inner and outer contours of each component itself, but the above directional terms are not intended to limit this invention.

[0034] This embodiment provides a cold gas thruster for microsatellites, comprising a valve assembly, an actuator, a sensor system, a gas flow path, a control unit, and a housing assembly. Figure 1 and Figure 2 The diagram shows a three-dimensional unfolded view and a detailed cross-section of the cold gas thruster, clearly demonstrating the components mentioned above. These components are closely connected through a carefully designed assembly process, together forming a high-precision, high-response cold gas thrust system.

[0035] See also Figure 1 , Figure 2 as well as Figures 3-8 In one embodiment, the valve assembly mainly includes a valve seat 17, a disc-shaped diaphragm 13, and a valve cover bracket 10. The valve seat is composed of a central air inlet 28 and a cylindrical gas chamber 30 (connected to an outlet) arranged coaxially therewith. The outer cylindrical surface of the central air inlet 28 and the inner cylindrical surface of the coaxially arranged cylindrical gas chamber 30 form an annular valve port 16. The center of the disc-shaped diaphragm 13 is connected to the bottom of the piezoelectric actuator by a screw 14, and its periphery is also connected to the bottom surface of the valve cover bracket 10 by screws. The piezoelectric actuator and the valve cover bracket 10 are coaxially pressed together above the cylindrical gas chamber 30, forming a sealed contact with the valve port. Under the action of the drive signal, the gap between the piezoelectric actuator and the valve port is precisely adjusted, thereby controlling the gas flow and thrust.

[0036] In one embodiment, the valve seat 17, the sealing ring 16, the disc-shaped diaphragm 13, and the valve cover bracket 10 have corresponding threaded holes, and are connected and fixed by four symmetrically distributed studs 11.

[0037] See also Figure 1 , Figure 2 as well as Figures 3-6 In one embodiment, the actuator is formed by a piezoelectric ceramic stack 8 embedded in an elliptical elastic mechanism 7. The elliptical elastic mechanism and the valve cover bracket 10 have threaded holes 6 and are fixed by bolts. The piezoelectric ceramic stack 8 is used to drive the disc-shaped diaphragm 13 to move, thereby changing the flow area of ​​the annular valve port 16. The annular valve port 16 remains open when no external force is applied. The elastic mechanism 7 provides a rebound force when the piezoelectric ceramic stack 8 is not in action, causing the disc-shaped diaphragm 16 to quickly return to its original position. Specifically, when a certain voltage is applied externally, the actuator is in an extended state. At this time, the piezoelectric ceramic stack 8 extends, causing the valve port 16 to close, and the fluid cannot flow out through the chamber 30. The cold air thruster is in a closed state. Since the piezoelectric ceramic stack 8 can only provide downward thrust, the elliptical elastic mechanism 7 is designed to provide a certain return force when the piezoelectric ceramic is de-energized, so that the diaphragm 10 quickly returns to its initial position, realizing that the valve can be quickly opened after closing. By controlling the amplitude and frequency of the voltage applied to the piezoelectric ceramic stack, the opening height and speed of the inlet valve can be adjusted, thereby changing the outlet flow rate of the outlet nozzle and achieving precise control of the thrust.

[0038] In one embodiment, the piezoelectric ceramic stack 8 is embedded in an elliptical elastic mechanism 7 with an interference fit, and its pre-tightening is achieved by a pre-tightening screw in a pre-tightening threaded hole 5.

[0039] In one embodiment, the diaphragm 10 and the annular valve port 16 need to maintain a certain initial gap under natural conditions to ensure that the air inlet valve port is normally open. At the same time, the outer diameter of the lower bottom surface of the elliptical elastic mechanism 7 is consistent with the outer diameter of the annular boundary of the cold air thruster's annular valve port 16. Through the cooperation of the two, the working pressure difference of the cold air thruster can be increased and the overall flow control characteristics can be improved.

[0040] The sensor system includes a capacitive micro-displacement sensor and a flow sensor.

[0041] See also Figure 1 , Figure 2 as well as Figures 3-8 In one embodiment, the capacitive micro-displacement sensor includes a capacitive sensor stator 12 and a capacitive sensor mover 27. The capacitive sensor stator 12 is mounted on the capacitive sensor mounting base surface of the valve cover bracket 10, and the capacitive sensor mover 27 is mounted on the capacitive sensor mover mounting base surface at the bottom of the elliptical elastic mechanism 7. The capacitive sensor stator has bolt connection holes that are bolted to the bolt connection holes at the bottom of the valve cover bracket for bolt fixation. The capacitive sensor stator mounted at the bottom of the valve cover bracket constitutes the fixed electrode plate of the capacitive micro-displacement sensor. Movement of the piezoelectric actuator mechanism drives the capacitive sensor mover mounted at the bottom of the piezoelectric actuator mechanism to form a movable electrode plate, thereby realizing the sensing of the displacement of the piezoelectric actuator mechanism.

[0042] In one embodiment, the capacitive sensor plate of the capacitive micro-displacement sensor that realizes displacement feedback of the piezoelectric actuator mechanism is fabricated using PCB technology to realize displacement sensing of the piezoelectric actuator mechanism.

[0043] See also Figure 1 , Figure 2 , Figure 9 and Figure 10 In one embodiment, the flow sensor includes a flow sensor channel support 21 and an integrated modulation circuit board 29, which is connected to a control unit for measuring and providing feedback on gas flow rate. The flow sensor channel support 21 and the flow sensor modulation circuit board 29 are sealed together with epoxy resin. The sensor chip is installed in the middle of the flow channel inside the flow sensor channel support 21, so that the flow channels are symmetrically distributed around the center of the sensor chip.

[0044] In one embodiment, the four threaded holes 20 on the flow sensor channel bracket are connected and fixed to the mounting threaded holes on the base by studs. To ensure gas tightness, the base flow outlet and the inlet of the flow sensor channel bracket 21 are sealed by sealing rings 18.

[0045] In one embodiment, the flow sensor modulation circuit board 29 that realizes the flow feedback of the cold gas thruster is fabricated using PCB technology to realize the flow sensing of the cold gas thruster.

[0046] In one embodiment, the gas flow path includes an inlet pipe interface 19 and an outlet nozzle 25. The valve seat has a threaded hole in its central inlet port, which is threadedly connected to the inlet pipe interface 19. The flow sensor outlet port has a threaded hole, which is threadedly connected to the outlet nozzle 25, ensuring the gas flow path from the inlet to the outlet.

[0047] See Figure 12 In one embodiment, the control unit 32 includes an inner-loop control module and an outer-loop control module, employing a dual-closed-loop control strategy. The outer-loop module uses a PID feedback controller 321 to control the gap height between the disc-shaped diaphragm and the valve port on the annular surface of the valve seat, and the output flow rate. The inner-loop module uses a hybrid control algorithm based on a feedforward controller (hysteresis model 323) and a PI feedback controller 324 to control the gap height between the disc-shaped diaphragm and the valve port on the annular surface of the valve seat, and the input voltage. The flow information acquired by the flow sensor is processed by the control algorithm to generate a control signal, obtaining the desired gap height between the disc-shaped diaphragm and the valve port on the annular surface of the valve seat. The displacement information of the piezoelectric actuator acquired by the capacitive sensor is processed by the control algorithm to generate a control signal, which, after amplification, acts on the piezoelectric actuator to push the disc-shaped diaphragm, changing the gap height between the disc-shaped diaphragm and the valve port on the annular surface of the valve seat, generating the desired flow output, and finally obtaining different desired thrusts. The inner-loop feedforward control algorithm is mainly used to improve the fast response time of the piezoelectric actuator mechanism and to compensate for its nonlinearity based on the established nonlinear model of the piezoelectric ceramic actuator. The inner-loop feedback control (PI) algorithm is mainly used to precisely correct the displacement error signal. The outer-loop feedback control (PID) algorithm is mainly used to precisely correct the flow error signal.

[0048] Specifically, the control unit receives flow information from the flow sensor and displacement information from the capacitive sensor mover 27, and employs a dual closed-loop control strategy (inner and outer loops) to adjust the gap height between the disc diaphragm (13) and the valve seat (17) and the input voltage (inner loop), respectively, and to adjust the difference between the actual flow rate and the desired flow rate (outer loop). The inner loop uses a composite control algorithm of feedforward and feedback to improve the response speed of the disc diaphragm 13 and compensate for the nonlinear characteristics of the actuator; the outer loop uses a PID control algorithm to precisely correct the flow error and ensure that the output flow rate is consistent with the desired value. The combined use of the dual closed-loop control strategy significantly improves the control accuracy and response speed of the cold gas thruster, enabling it to meet the high requirements of attitude control for microsatellites.

[0049] See Figure 1 and Figure 2The housing assembly includes an outer shell 3 and an outer shell cover 23, used to encapsulate and protect the valve assembly, actuator, sensor system, gas flow path, and other components above the thruster. The control unit is located in an external host computer.

[0050] like Figure 11 As shown, in another embodiment, depending on actual needs, the elastic mechanism of the internally embedded piezoelectric actuator can be a corrugated elastic mechanism. This type of elastic mechanism can enhance stability, providing a more stable restoring force and ensuring that the actuator maintains high precision during long-term operation. It also has strong adaptability, able to adapt to different installation spaces and load requirements, improving the flexibility of the air-cooled thruster. Furthermore, it can improve durability, reduce mechanical stress, and extend the actuator's service life.

[0051] The following is how a cold air thruster works: Initially, the external voltage applied to the cold gas thruster is 0, and the piezoelectric ceramic stack is in a contracted state. Gas at a certain pressure flows in through the inlet pipe interface, then through the annular valve port into the chamber, and finally flows out of the chamber into the flow sensor inlet, and finally out of the outlet nozzle, generating thrust. The control unit receives flow information from the flow sensor and displacement information from the capacitive sensor, and adopts a dual closed-loop control strategy with inner and outer loops. It adjusts the gap height between the disc diaphragm 13 and the valve seat 17 and the input voltage (inner loop), and adjusts the difference between the actual flow rate and the desired flow rate (outer loop), ultimately achieving the desired thrust.

[0052] In summary, this novel cold gas thruster, through its precise structural design, efficient actuator, high-precision sensor system, and advanced dual-closed-loop control strategy, achieves high precision and high response in attitude control of microsatellites, possessing significant engineering application value and broad market prospects.

Claims

1. A cold gas thruster for a microsatellite, characterized in that, Includes valve assembly, actuator, sensor system, gas flow path, control unit, and housing assembly; The valve assembly includes a valve seat, a disc-shaped diaphragm, and a valve cover support. The valve seat consists of a central air inlet and a coaxially arranged cylindrical gas chamber. An annular valve port is formed between the central air inlet and the gas chamber. The disc-shaped diaphragm and the valve cover support are connected to the actuator and form a sealing contact with the valve port. Under the action of the drive signal, the gap between the diaphragm and the valve port is precisely adjusted to control the gas flow and thrust. The actuator includes a piezoelectric actuator and an elastic mechanism internally embedded with the piezoelectric actuator. The piezoelectric actuator is used to drive the diaphragm to move, thereby changing the flow area of ​​the annular valve port. The annular valve port remains open when no external force is applied. The elastic mechanism is connected to the valve cover bracket. When the piezoelectric actuator is not in action, the elastic mechanism provides a rebound force to cause the disc-shaped diaphragm to quickly return to its original position. The sensor system includes a displacement sensor and a flow sensor. The displacement sensor includes a capacitive sensor stator and a moving part. The capacitive sensor stator is mounted on the valve cover bracket, and the capacitive sensor moving part is mounted on the bottom of the actuator. It detects the displacement of the piezoelectric actuator mechanism by means of displacement change and provides displacement feedback. The flow sensor includes a flow sensor channel bracket and an integrated modulation circuit board for measuring gas flow rate and providing flow feedback. The gas flow path includes an inlet pipe interface and an outlet nozzle. The inlet pipe interface is connected to the central inlet hole of the valve seat, and the outlet nozzle is connected to the flow sensor channel support to ensure the gas flow path from the inlet to the outlet. The control unit is connected to the actuator, displacement sensor and flow sensor. It is used to receive flow information from the flow sensor and displacement information from the capacitive sensor mover. It adjusts the drive voltage of the actuator through a dual closed-loop control strategy, thereby adjusting the thrust and accuracy of the cold gas thruster. The housing assembly is used to encapsulate and protect the valve assembly, actuator, sensor system, and gas flow path of the thruster.

2. The cold gas thruster according to claim 1, characterized in that, The piezoelectric actuator is a piezoelectric ceramic stack actuator, and the elastic mechanism is an elliptical elastic mechanism or a corrugated elastic mechanism. The outer diameter of the lower bottom surface of the elastic mechanism is consistent with the outer diameter of the valve port of the annular surface of the valve seat. The cooperation between the two improves the working pressure difference of the cold air thruster and improves the overall flow-stopping characteristics of the cold air thruster. When the piezoelectric ceramic stack is in an inactive state, it can provide a return force, so that the disc-shaped diaphragm can quickly return to the initial position, thereby enabling the valve to open quickly and improving the dynamic response performance.

3. The cold gas thruster according to claim 1, characterized in that, The piezoelectric ceramic stack is embedded in the elastic mechanism and is connected to the elastic mechanism by an interference fit. It is pre-tightened by a pre-tightening screw to ensure that the piezoelectric ceramic stack can generate stable and predictable displacement during the driving process.

4. The cold gas thruster according to claim 1, characterized in that, The disc-shaped diaphragm maintains a preset initial gap with the annular valve port on the valve seat. This initial gap design ensures that the valve is normally open, while the flow rate can be precisely controlled by changing the position of the disc-shaped diaphragm.

5. The cold gas thruster according to claim 1, characterized in that, The cylindrical gas chamber that makes up the valve seat and the central air inlet are machined from a single piece of material, adopting an integrated design to improve structural stability and machining accuracy.

6. The cold gas thruster according to claim 1, characterized in that, The stator and mover of the capacitive sensor are fixed on the base surfaces of the valve cover bracket and the elastic mechanism, respectively, forming a capacitive displacement sensor to ensure high-precision feedback of the displacement of the disc-shaped diaphragm.

7. The cold gas thruster according to claim 1, characterized in that, The control unit includes an inner loop control module and an outer loop control module. The inner loop control module employs a composite control algorithm of feedforward and feedback (PI) to adjust the gap height between the disc-shaped diaphragm and the valve port on the annular surface of the valve seat, as well as the input voltage. The outer loop control module employs a PID control algorithm to adjust the difference between the actual flow rate and the desired flow rate caused by adjusting the actual gap height between the disc-shaped diaphragm and the valve port on the annular surface of the valve seat. This achieves high-precision control of the output flow rate and thrust. The control unit can optimize the response time and control accuracy of the piezoelectric actuator mechanism based on the flow error and displacement error signals through advanced control algorithms. At the same time, it compensates for the nonlinear hysteresis effect of the piezoelectric ceramic actuator and reduces thrust noise.

8. The cold gas thruster according to claim 1, characterized in that, The flow sensor channel bracket is glued and sealed to the flow sensor modulation circuit board made of PCB technology, and connected to the base. The flow sensor chip is installed in the middle of the channel, so that the channel is symmetrically distributed with respect to the position of the flow sensor chip, which reduces fluid turbulence, improves the accuracy of flow measurement, and also ensures the compactness and reliability of the entire cold gas thruster.

9. The cold gas thruster according to claim 1, characterized in that, The valve seat air inlet and the flow sensor air outlet are respectively connected to the air inlet pipe interface and the air outlet nozzle via threads.

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