Wireless optical communication module suitable for underwater robot and autonomous hovering control method

Abstract

The invention belongs to the technical field of underwater wireless optical communication (UWOC) and underwater robot control, and aims at solving the problems that an existing underwater optical communication system is high in alignment dependence and poor in communication link stability in a high-dynamic environment. The invention discloses a wireless optical communication module suitable for an underwater robot and an autonomous hovering control method for the underwater robot. The communication module can be integrated in an underwater robot frame and sealed cabins (1-1 and 1-13), and the hardware design of the communication module comprises a high-precision and low-distortion visible light modulation transmitting circuit (Figure 5), the circuit is powered by 3A constant current with low power ripple (Figure 4) and is combined with current feedback to ensure that the light intensity of a transmitting end LED (3-4) is controllable and the modulated signal is low in distortion; and the core of the visible light receiving circuit is that a trans-impedance amplifier (6-5) of the receiving circuit adopts an independent power supply to filter and supply power (figure 7), so that electromagnetic interference generated by digital equipment in a cabin is isolated, and the signal-to-noise ratio and the receiving reliability of analog signals are greatly improved. According to the autonomous hovering control method provided by the invention, a dual feedback mechanism is constructed by fusing an external accurate relative distance D (provided by stereoscopic vision guidance of a base station) and an internal real-time communication bandwidth B (measured in real time by tools such as Iperf and the like). According to the method, the problem that excessive correction or drifting is easily generated under underwater turbidity and water flow disturbance by only depending on navigation data or instantaneous visual data is solved. When the communication bandwidth B is reduced, the system firstly uses the distance D to carry out rapid correction; and when the connection is completely interrupted, entering a text {PROBING} exploration mode. According to the method, intelligent sensing and high-robustness autonomous position keeping of the underwater robot on a communication link are realized, and an efficient and high-bandwidth stable optical communication link can be continuously maintained in a complex underwater environment.

Description

TECHNICAL FIELD

[0001] The present application relates to the cross-technical field of underwater wireless optical communication, underwater robot navigation and control, and visible light communication circuit design, and is particularly applied to improving the robustness of underwater mobile platform communication links and high-precision dynamic position keeping. BACKGROUND

[0002] Existing underwater wireless communication technologies mainly include underwater acoustic communication, underwater radio frequency communication, and underwater wireless optical communication. Although underwater acoustic communication is suitable for long-distance communication, it has a low communication bandwidth and high latency, making it difficult to meet the high-bandwidth application requirements of high-definition video backhaul and real-time data acquisition. Underwater radio frequency communication suffers from exponential attenuation, and the effective transmission distance in seawater is strictly limited to a few meters, lacking practical value. In contrast, underwater wireless optical communication can provide high-bandwidth rates of Mbps or even Gbps, making it an ideal solution to the underwater bandwidth bottleneck. However, underwater wireless optical communication has a high degree of direction dependence and is easily affected by beam alignment deviations caused by water flow disturbances and platform motion, resulting in poor robustness and stability of the communication link, which is a key technical obstacle to its practical application. To solve the alignment problem, existing research has mainly focused on underwater positioning and visual guidance technology. Traditional underwater robots use inertial navigation systems and Doppler speedometers for positioning, but these systems mainly provide the absolute position of the robot. Some research has attempted to use underwater vision systems (such as binocular stereo vision) to identify markers on the optical communication base station to provide relative distance D However, in actual lake or ocean environments, factors such as water turbidity, suspended particle scattering, and uneven lighting can severely interfere with the accuracy of visual recognition, causing instantaneous positioning data to jump, which in turn can worsen the stability of the communication link. In addition, in the hardware design of the communication module, underwater robots have integrated PLC control boards, switches, and other high-speed digital devices in the cabin, which generate spatial electromagnetic interference and power network noise that can severely affect the signal-to-noise ratio of the weak light reception signal in the optical communication reception circuit, reducing the hardware reliability of the communication system.

[0003] Position holding and hovering control of underwater robots (AUVs / ROVs) are crucial for maintaining the stability of underwater wireless communication. Existing control methods generally suffer from several shortcomings: First, traditional control algorithms such as PID and LQR typically only use the robot's position or attitude error as input, lacking the ability to perceive real-time communication quality (e.g., bandwidth, bit error rate). This means that even if the robot's positioning error is within acceptable limits, the system cannot make intelligent, targeted corrective actions based on the communication status once the optical communication link is lost. Second, in situations of severe water current disturbances or momentary failure of visual positioning data, control systems relying on single position information exhibit poor robustness and are prone to drift or instability. In summary, current technology lacks a method that possesses high anti-interference capabilities at the hardware level and can integrate high-precision external guidance data (e.g., visual ranging) with real-time internal communication quality feedback (e.g., bandwidth) at the control level. B The combination of these factors to achieve intelligent, robust, and high-precision dynamic hovering control methods for underwater robots directly restricts the practical application of underwater wireless optical communication systems in highly dynamic environments. Summary of the Invention

[0004] The purpose of this invention is to overcome the technical shortcomings of existing underwater wireless optical communication systems, such as strong alignment dependence and poor communication link stability in dynamic underwater environments. It provides a highly robust underwater wireless optical communication module and an autonomous hovering control method for underwater robots capable of achieving high-precision dynamic position maintenance. This invention solves the communication stability problem of underwater mobile platforms under water flow disturbances and visual interference by integrating external high-precision relative positioning with internal real-time communication quality feedback.

[0005] The robot is equipped with a sealed cabin structure, which consists of a front cover (1-10), a rear cover (1-4), and a support frame (2-8). Inside the sealed cabin are an internal frame (1-5) and internal support columns (1-6) for fixing and vibration-resistant support of the electronic equipment. The sealed cabin houses a PLC control board (1-7), an internal switch (1-8), a robot control board (2-4), and a robot camera control board (2-3). The PLC control board (1-7) is electrically connected to the external system via a PLC watertight connector (2-6). The sealed cabin also has an airtightness detection connector (2-5) for detecting the cabin's sealing status.

[0006] To achieve passive attitude stability of the underwater robot, multiple buoyancy blocks are installed on the outside of the robot's skeleton and sealed cabin, including buoyancy block (front left) (2-8), buoyancy block (front right) (1-12), buoyancy block (rear left) (2-7), and buoyancy block (rear right) (2-2). The spatial distribution of the buoyancy blocks achieves a reasonable match between the center of gravity and the center of buoyancy of the entire robot.

[0007] The wireless optical communication module (1-9) is located inside the sealed chamber and interacts with the external water environment through the light-transmitting structure provided at the front cover (1-10) or rear cover (1-4) of the chamber.

[0008] Based on the above system structure, the wireless optical communication module (1-9) of the present invention includes a visible light modulation transmitting circuit and a visible light receiving circuit, which together constitute a highly reliable wireless optical communication hardware unit suitable for underwater environments.

[0009] At the transmitting end, the visible light modulation transmitting circuit includes a transmitting LED and its driving power supply. The driving power supply is a 3A constant current power supply with low power supply ripple characteristics, and combined with a current feedback control mechanism, it realizes precise control of the luminous intensity of the transmitting LED, thereby ensuring the low distortion characteristics of the modulated light signal during high-speed transmission.

[0010] At the receiving end, the visible light receiving circuit includes a photodiode and a transimpedance amplifier. The photodiode converts the received optical signal into an electrical signal, and the transimpedance amplifier amplifies the weak, high-speed electrical signal. To address the electromagnetic interference and power supply noise issues caused by the coexistence of multiple digital devices within the underwater robot's sealed cabin, the transimpedance amplifier employs an independent power supply with filtering, isolating it from the power supply networks of high-power digital devices such as the PLC control board and the cabin switch.

[0011] The above-mentioned independent power supply and filtering design can effectively suppress the influence of power supply noise and electromagnetic interference on the analog received signal, and ensure the linear amplification performance of the transimpedance amplifier under high sensitivity operation, thereby significantly improving the signal-to-noise ratio and overall communication reliability of the wireless optical communication module.

[0012] Based on this communication module, this invention further discloses an autonomous hovering control method for an underwater robot. This method constructs a dual real-time feedback mechanism as the decision-making basis for position maintenance: one is an external high-precision relative distance... D The first factor is the accurate identification of positioning markers by the base station's stereo vision system; the second is the internal instantaneous communication bandwidth. B This method, derived from real-time testing tools like Iperf for robotics, assesses the quality of optical links. It addresses the overcorrection or drift issues that easily arise under underwater turbidity and current disturbances when relying solely on navigation or vision data. Specifically, it considers the instantaneous communication bandwidth... B When a slight decrease occurs (but is still greater than zero), the system prioritizes using relative distance. D The changing trend allows for precise position correction to quickly restore alignment; and when the communication bandwidth... B Complete interruption ( BWhen the timeout counter reaches a preset threshold and the value is 0, the system initiates an exploration mode, using a preset spiral or scanning path to find and quickly reconnect the optical communication link. The beneficial effects of this invention are significant. By integrating high-precision visual ranging with real-time communication quality feedback, the underwater robot can achieve highly robust autonomous hovering and position maintenance under water flow disturbances and instantaneous visual interference, effectively avoiding overcorrection and drift. Experiments demonstrate that this fusion strategy can maintain a high-bandwidth stable communication link for a longer period in complex underwater environments, significantly improving the availability, reliability, and practical engineering application value of the underwater wireless optical communication system compared to traditional control methods. Attached Figure Description

[0013] Figure 1 This is a rear view of the underwater robot of the present invention.

[0014] Figure 2 This is a front view of the underwater robot of the present invention.

[0015] Figure 3 This is a schematic diagram of the visible light modulation emission circuit of the present invention.

[0016] Figure 4 The LED power supply of the transmitter of this invention is provided with a constant current of 3A.

[0017] Figure 5 This is a schematic diagram of the visible light modulation emission circuit of the present invention.

[0018] Figure 6 This is a schematic diagram of the visible light receiving circuit of the present invention.

[0019] Figure 7 This is the independent power supply for the transimpedance amplifier of the present invention. Detailed Implementation

[0020] This invention aims to describe in detail the implementation process of a wireless optical communication module and an autonomous hovering control method suitable for underwater robots through specific embodiments, so as to provide a highly robust underwater high-bandwidth communication system.

[0021] (1) Hardware integration and anti-interference design of the optical communication module: The wireless optical communication module (1-9) of this invention is integrated inside the underwater robot shown in Figure 1, located in the airtight chamber, and the optical signal enters and exits through the watertight light-transmitting window on the rear cover (1-4) or front cover (1-10) of the chamber. The module consists of a high-precision, low-distortion visible light modulation transmitting circuit (Figure 5) and a high-performance visible light receiving circuit (Figure 6). At the transmitting end, the module is driven by a 3A constant current power supply (Figure 4) with low power supply ripple, and combined with a current feedback mechanism, the light intensity of the transmitting LED (3-4) is controllable, which significantly ensures the low-distortion transmission of the modulated signal. At the receiving end, to overcome the electromagnetic interference (EMI) and power supply noise generated by digital devices such as the in-cabin PLC control board (1-7) and in-cabin switch (1-8) during high-speed switching, the core technical feature of this module is that its visible light receiving circuit uses a transimpedance amplifier (6-5) to amplify the small high-speed signal from the photodiode (6-4), and this transimpedance amplifier (6-5) is powered by an independent power supply with filtering (Figure 7). This independent power supply design can effectively isolate the interference sources in the cabin, ensure that the transimpedance amplifier is in a pure analog power supply environment, and ensure that the received weak analog signal is not distorted during amplification, thereby significantly improving the signal-to-noise ratio and overall reliability of the optical communication module.

[0022] (2) Implementation of autonomous hovering control method: The autonomous hovering control method proposed in this invention is based on the software and firmware integration of the robot control board (2-4) and the PLC control board (1-7). This method regards the position holding of the underwater robot as a dual feedback closed-loop control problem, and its control output is the instruction to drive the lower thruster (1-2) and the upper thruster (1-11) to perform position correction.

[0023] This method first obtains a dual basis for decision-making: external relative distance. D After real-time calculation via the base station's binocular stereo vision system, the data is transmitted to the robot via an optical communication link; internal instantaneous communication bandwidth... B Real-time measurements are then performed using network performance testing tools such as Iperf, which run internally within the robot. The core of the autonomous hovering control method lies in its integrated control logic.

[0024] 1) High bandwidth stability period: When the instantaneous bandwidth B When the bandwidth remains consistently above a preset high bandwidth threshold (e.g., greater than 300 Kbits / s), the system enters the CONTROLLING state. In this state, the control system primarily relies on minute changes in the curve to drive the thrusters to maintain high-precision hold, ensuring centimeter-level alignment accuracy.

[0025] 2) Bandwidth fading correction period: When bandwidth B Instantaneously drop below the threshold (0 <B When the bandwidth is less than 300 Kbits / s, the system immediately initiates the correction strategy. Due to the inherent measurement delay in bandwidth feedback, if the system relies on... B Making large corrections can easily cause oscillations. Therefore, the system prioritizes reference distance. D The direction of correction is determined by the trend of change (i.e., whether it is increasing or decreasing) to avoid overcorrection.

[0026] 3) Link interruption exploration period: When communication bandwidth... B Complete interruption ( B =0) and continues to exceed the preset value. TIMEOUT The robot will stop relying on the count after 3 seconds. D Upon receiving data, the robot enters PROBING exploration mode. In this mode, the robot will execute preset spiral or scanning path movements (such as small up / down loops or small-radius rotations) and remain in listening mode. Once any non-zero data is received... B If the value is not specified, the system immediately exits PROBING mode and returns to CONTROLLING state, utilizing... D Rapid alignment is achieved. By integrating the above-mentioned autonomous hovering control methods and strategies, this invention effectively enhances the underwater wireless optical communication system's resistance to water flow disturbances and its robustness in the event of momentary failure of visual positioning in complex dynamic environments such as lakes and oceans, ensuring the continuous and efficient maintenance of high-bandwidth communication links.

Claims

1. A wireless optical communication module suitable for underwater robots, characterized in that, This module is integrated into the underwater robot frame and sealed chamber (1-1, 1-13), and includes a visible light modulation and transmission circuit (Figure 5) and a visible light receiving circuit (Figure 6), wherein: a. The visible light modulation emission circuit (Figure 5) is powered by the LED power supply (Figure 4). The power supply has low power ripple and provides a constant current of 3A. Combined with the current feedback mechanism, it ensures that the light intensity of the LED (3-4) at the emission end is controllable, so as to ensure low distortion transmission of the modulated signal. b. The visible light receiving circuit (Figure 6) includes a photodiode (6-4), a transimpedance amplifier (6-5), and an analog-to-digital converter (6-6). The transimpedance amplifier (6-5) is powered by an independent power supply filter (Figure 7) to isolate electromagnetic interference and power supply noise generated by digital devices in the cabin (such as PLC control board 1-7 and switch 1-8), thereby ensuring the signal-to-noise ratio and reception reliability of the received original small signal (6-1).

2. An autonomous hovering control method for an underwater robot, characterized in that, This method, by fusing external positioning information and internal communication quality feedback, drives the thrusters to perform position corrections in real time, and includes the following steps: a. Receive external positioning data: Receive relative distance D data provided by the underwater base station stereo vision system; b. Receive internal feedback data: Receive instantaneous communication bandwidth B data measured in real time from the optical communication module (1-9); c. Constructing a dual decision-making basis: The relative distance D and the instantaneous communication bandwidth B are used as the dual decision-making basis for robot position holding control; d. Perform fusion control: Based on the real-time changes of D and B, drive the lower thruster (1-2) and upper thruster (1-11) to make corrections, so as to keep the robot's position error and communication link quality within a preset threshold range at the same time.

3. The control method according to claim 2, characterized in that, The execution fusion control step further includes: a. When the communication bandwidth B drops instantaneously, the system prioritizes the trend of distance D change for directional correction to avoid overcorrection caused by bandwidth feedback lag; b. When the communication bandwidth B is completely interrupted and the timeout counter reaches the preset value, the system starts the exploration mode, searches for and quickly reconnects the optical communication link through the preset spiral or scanning path.

4. The wireless optical communication module according to claim 1, characterized in that, The communication module is integrated into the rear end cover (1-4) or front end cover (1-10) of the robot's sealed cabin, and is connected to the PLC control board (1-7) through a watertight connector (2-6). The robot skeleton (1-1, 1-13) adopts a buoyancy block (1-12, 2-1, 2-2, 2-7) layout to ensure the passive stability of the robot's posture, thereby providing basic posture assurance for active hovering control.

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