Rope-tied robot trajectory tracking method based on backstepping method

Abstract

The invention discloses a tethered robot trajectory tracking method based on a backstepping method, is suitable for tethered double-wheel differential drive robots in extreme terrain environments such as abrupt slopes, and belongs to the technical field of mobile robot motion control. According to the method, kinematics and dynamics models are established, the dynamic coupling relation between robot motion and rope tension is modeled into a two-stage cascade system, a hierarchical controller is designed through a backstepping method, and trajectory tracking error convergence and system global stability are achieved. The dynamic controller optimizes double-wheel torque and rope tension distribution based on power consumption minimization, meanwhile, a nonlinear disturbance observer is introduced to estimate and compensate external disturbance in real time, and the robustness and the anti-jamming capability of the system are remarkably enhanced.

Description

Technical Field

[0001] The invention belongs to the field of mobile robot motion control, and in particular relates to a trajectory tracking method of a cable-tethered dual-wheel differential drive robot in a steep slope environment. Background Art

[0002] As planetary exploration missions go deeper, more and more scientific studies have shown that some of the most valuable information in planetary exploration is often located in steep slopes, gullies and other extreme terrain areas, which has important scientific exploration value. However, most of the existing planetary exploration robots are based on the traditional six-wheel rocker structure (such as "Spirit" and "Opportunity", etc.). These robots perform well on terrain with low slopes, but have difficulty adapting to terrain areas with slightly larger slopes. Because wheeled robots rely on the support of the terrain, when the slope is too steep or the surface is soft, the robot will be at risk of sliding, losing stability or even overturning, which greatly limits its detection range and capabilities.

[0003] In response to the needs of extreme terrain exploration, a tethered mobile robot has been developed. This type of robot uses a rope with one end fixed to the mother robot or anchor point to provide the necessary tension or support, allowing it to descend along steep slopes and enter areas that ordinary wheeled robots cannot reach. This robot can perform in-situ scientific exploration tasks in extreme terrains, such as steep slopes, deep gullies and even caves. However, although tethered robots overcome some limitations of traditional wheeled robots in extreme terrains, they still face huge challenges in motion control, especially the problems of trajectory tracking and rope tension distribution and dealing with external interference.

[0004] Existing trajectory tracking control algorithms, including backstepping control, sliding mode control, intelligent control and their combination, mainly focus on the motion control of conventional wheeled robots. They usually ignore the influence of rope tension input on robot motion and cannot adapt to the dynamic coupling characteristics between rope and robot. In addition, in extreme terrain environments, the interference effect of terrain disturbance on the robot increases significantly, such as slope sliding, rolling stones or sudden changes in terrain. These external disturbances make traditional control methods obviously insufficient in trajectory tracking accuracy and system stability, making it difficult to meet actual mission requirements.

[0005] To solve the above problems, a control method is needed that can simultaneously achieve robot trajectory tracking and rope tension distribution. On the one hand, it is necessary to ensure that the robot moves along the planned trajectory in complex terrain to avoid motion deviation caused by terrain disturbance or control lag; on the other hand, it is necessary to consider the coupling effect of the dual-wheel torque and the rope tension to ensure that the rope is always in a tensioned state and assist the robot's movement in extreme terrain, thereby improving the safety and reliability of the system. In addition, the control method must also take into account external interference to improve the tracking performance and robustness of the system. Summary of the invention

[0006] The present invention proposes a trajectory tracking method for a tethered robot based on backstepping. This method fully considers the complex coupling relationship and external disturbances of the tethered robot when moving in extreme terrain, constructs a hierarchical control strategy through the backstepping control framework, and designs recursive control laws for the cascade system of robot kinematics and dynamics, ultimately achieving the global stability of the system and improved trajectory tracking accuracy. In addition, in response to the inevitable disturbances in extreme terrain environments, this method further integrates a nonlinear disturbance observer to estimate and compensate for the effects of external disturbances, thereby enhancing the robustness and anti-interference ability of the system. At the same time, the present invention jointly optimizes the distribution of dual-wheel drive torque and tether tension based on the principle of minimizing power consumption, so that the robot can reduce energy consumption while maintaining stable motion.

[0007] Specifically, the technical solution of the present invention is as follows:

[0008] Step 1: Kinematic modeling and dynamic modeling of the tethered mobile robot.

[0009] The robot kinematic modeling considers the relationship between the robot state and its speed control input, while the dynamic model considers the relationship between the robot motion state and its torque control input, and comprehensively considers the coupling between the rope tension and the dual-wheel drive torque. Through modeling methods such as the Lagrangian method, the kinematic model and the dynamic model can be modeled as a two-level cascade system to conform to the strict nonlinear feedback form:

[0010]

[0011] Where x is the system state, z is the introduced virtual control variable, and u is the control input. Each function f i (·) and g i (·) describes the dynamic relationship of the system at the i-th level, i = 1, 2, ..., k.

[0012] Step 2: Hierarchical control design using backstepping method.

[0013] In the control framework, the motion of the tethered robot is decomposed into two parts: the kinematic module and the dynamic module. Through the backstepping control method, the kinematic module controls the convergence of the robot's trajectory tracking error in the global coordinate system, while the dynamic module further optimizes the driving torque and tension distribution to ensure the global stability of the system. The recursive design method of backstepping control enables each level of controller to be independently designed according to its specific dynamic characteristics and constraints, and achieves the closed-loop stability of the entire system through layer-by-layer feedback.

[0014] Among them, the kinematic control law is designed first. The error between the position and posture of the robot in the target trajectory and the actual motion state is defined. By constructing the error Lyapunov function, the kinematic control law is designed so that the trajectory error converges asymptotically to zero. The expected motion speed generated by the kinematic control law is used as the input of the dynamic controller, laying the foundation for the high-precision trajectory tracking of the system. The dynamics module models the system dynamics equations, comprehensively considers the coupling between the rope tension and the dual-wheel drive torque, and designs the dynamic control law. While meeting the trajectory tracking requirements, this control law uses the power consumption minimization strategy to optimize the drive torque and tension distribution, thereby reducing energy consumption.

[0015] Step 3: Design a nonlinear disturbance observer.

[0016] In complex extreme terrain, robot motion is inevitably affected by slope sliding, terrain undulations and environmental disturbances. The present invention introduces a nonlinear disturbance observer, which estimates the size and characteristics of external disturbances in real time and feeds them back to the controller for compensation, thereby significantly enhancing the system's anti-interference ability in harsh environments. The design of the disturbance observer is based on a dynamic model and real-time state variables, which can quickly respond to disturbance changes and maintain the system's trajectory tracking performance under disturbances.

[0017] Compared with the prior art, the technical solution of the embodiment of the present invention has the following beneficial effects:

[0018] The model of the tethered robot is transformed into a cascade system of kinematic and dynamic modules. The kinematic and dynamic controllers are designed respectively using the backstepping method. The dual-wheel torque and tether tension are distributed according to the principle of minimizing power, thereby realizing the coordinated control of trajectory tracking and rope tension management, ensuring the overall stability of the system and the trajectory tracking accuracy. In the robot movement, considering that the rope tension in extreme terrain environments is easily affected by external disturbances, the present invention designs a nonlinear disturbance observer for real-time estimation and compensation of the influence of external disturbances. Through disturbance observation and compensation, the robustness and adaptability of the system in complex environments are significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a tethered robot model;

[0020] Figure 2 This is the motion control block diagram of the tethered mobile robot;

[0021] Figure 3 This is the coupling analysis of double wheel torque and rope tension. DETAILED DESCRIPTION

[0022] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

[0023] like Figure 1 As shown, the tethered robot of the present invention includes the following key components:

[0024] Drive system: The left and right drive wheels are connected to the middle connecting shaft through bearings and driven by independent motors, gearboxes and encoder systems. The motor controls the rotation of the wheels through the gear transmission system to achieve the robot's forward, backward and steering movements. Using the differential drive principle, the robot can flexibly adjust its direction by controlling the speed difference between the left and right drive wheels.

[0025] Caster Arm: The caster arm is connected to the connecting shaft and driven by an independent motor to support and guide the tether. The tether is passed through the pipe of the caster arm to ensure that the tether can be smoothly guided and maintained during the movement of the robot.

[0026] Winch system: The winch is installed in the center of the connecting shaft and driven by a motor. The tether is retracted and released by rotation. One end of the tether is fixed to the mother robot or a ground anchor point, and the other end is fixed to the winch. A force sensor is installed on the winch to monitor the tether tension in real time and feed it back to the control system to ensure that the tether tension remains within a reasonable range and avoids looseness or over-tightness.

[0027] Perception and feedback system: Force sensors, position sensors and encoders together constitute the perception and feedback system, which monitors the robot's position, speed and tether tension information in real time, and feeds the data back to the control system for optimizing motion control and tether management.

[0028] like Figure 2 The figure shows a control flow chart based on the backstepping method. The present invention adopts a hierarchical control structure, decomposing the robot system into a kinematic module and a dynamic module, and performing control design respectively.

[0029] The first step is kinematic control design. In the global coordinate system, the kinematic model of the robot is established as:

[0030]

[0031] Then define the error vector between the target trajectory and the actual trajectory, and establish the Lyapunov function of error convergence. Based on the backstepping method, design the kinematic control law, and adjust the robot driving speed and direction to gradually reduce the trajectory error and finally converge to zero. The designed control rate is:

[0032]

[0033] The dynamics controller is based on the dynamics equations of the system:

[0034]

[0035] in, is a symmetric positive definite inertia matrix, are the Coriolis force and centripetal force matrices, is the gravity vector acting on the system, is the input matching matrix, τ controls the input torque vector, and f is the external unknown disturbance including friction.

[0036] according to Figure 3 The relationship among It can be further decomposed into the coupling of the dual wheel torque and the tether tension:

[0037]

[0038] Taking into full consideration the coupling relationship between rope tension and driving torque, the optimized dynamic control law is designed as follows:

[0039]

[0040] Among them, F * The optimal tension distribution is obtained by minimizing the following energy function:

[0041]

[0042] In extreme terrain environments, external disturbances inevitably affect the robot's motion stability. The present invention designs a nonlinear disturbance observer to estimate and compensate for the impact of external disturbances in real time. The nonlinear disturbance observer is designed as follows:

[0043]

[0044] The current force of the system is calculated through the dynamic model and real-time state variables, and the size of the external disturbance is estimated using a nonlinear observer. The observed disturbance value is fed back to the dynamic controller, and the driving torque and rope tension are dynamically adjusted through the control law to achieve real-time compensation for external disturbances.

[0045] In the embodiment of the present invention, an effective solution is provided for the motion control and rope tension distribution of the tethered robot through a trajectory tracking control method based on the backstepping method, thereby improving the trajectory tracking accuracy and robustness of the system.

[0046] The specific application of the present invention is very extensive, and the above is only a preferred embodiment of the present invention. It should be pointed out that for those skilled in the art, various improvements or modifications thereof, without departing from the core technical concept of the present invention, should be deemed to belong to the protection scope of the present invention.

Claims

1. A tethered robot trajectory tracking method based on backstepping method, characterized in that: The following steps are involved: Step 1, establish the kinematic and dynamic models of the tethered robot, in which the coupling relationship between the robot state, control input and rope tension is comprehensively considered; Step 2: Based on the kinematic model, a backstepping kinematic controller is designed to make the robot trajectory tracking error converge to zero asymptotically by constructing the error Lyapunov function; Step 3: Based on the dynamic model, a backstepping dynamic controller is designed. The optimal distribution of rope tension and dual-wheel driving torque is combined, and the principle of power consumption minimization is adopted to ensure the robot's motion stability and energy consumption optimization. Step 4: Introduce a nonlinear disturbance observer to estimate and compensate for external disturbances in real time, thereby improving the robustness and anti-interference capability of the system. Step 5: Combine the kinematic and dynamic controllers to form a closed-loop control system, and finally achieve dynamic management of robot trajectory tracking and rope tension.

2. A tethered robot trajectory tracking method based on backstepping according to claim 1, characterized in that: The dynamic model is built using the Lagrangian method, and the coupling effect between the rope tension and the dual-wheel driving torque is expressed as a strictly nonlinear feedback form.

3. The tethered robot trajectory tracking method based on backstepping method according to claim 1, characterized in that: The dynamic controller minimizes energy consumption by optimizing the following objectives: And this principle is used to solve the optimal tether tension distribution.

4. The tethered robot trajectory tracking method based on backstepping method according to claim 1, characterized in that: The nonlinear disturbance observer calculates the current force condition of the system through the dynamic model and real-time state variables, and feeds back the observed disturbance value to the dynamic controller to compensate for external disturbance in real time.

5. The tethered robot trajectory tracking method based on backstepping method according to claim 1, characterized in that: The kinematic controller defines the error vector between the actual state of the robot and the target trajectory state, and designs the control law to adjust the robot's driving speed and direction to gradually reduce the error and improve the trajectory tracking accuracy.

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