Highly stationary focal plane multi-stage multi-channel switching control method with dynamic constraints

Abstract

A highly stable focal plane multi-stage / multi-channel switching control method with dynamic constraints is proposed. This method addresses the switching stability problem during the satellite acquisition and stable tracking phases of moving target tracking. It designs a focal plane trajectory planning strategy based on real-time adjustment of constraint capability and image shift terminal deviation, and a weighted forgetting angular velocity command control algorithm. For the stability problem of multi-channel switching during the stable tracking phase, a unified coordinate scale focal plane control method is proposed by utilizing the consistency of the physical position of the focal plane at the switching point. This is combined with a visual feedback control algorithm based on sliding mode vectors to achieve high-precision, high-dynamic tracking.

Description

Technical Field

[0001] This invention relates to a highly stable focal plane multi-stage / multi-channel switching control method with dynamic constraints, belonging to the field of spacecraft control technology. Background Technology

[0002] Rapid acquisition and high-precision tracking of space targets are the prerequisites and foundations for utilizing and controlling space. To achieve the tasks of discovering, tracking, and identifying space targets, one design approach involves using a two-dimensional turntable to drive a camera for highly stable target tracking. Throughout the tracking process, the satellite maintains a zero attitude to ensure the normal operation of other onboard payloads. This model can be equivalent to a three-link free-flying robot system. Unlike traditional satellite platform attitude control, the camera's target tracking process involves the kinematic characteristics of the non-cooperative target, as well as the parameters of the satellite platform, the two-dimensional turntable, and the camera. The object is complex, and nonlinearity and uncertainty are more prominent, posing challenges to the design of the control system.

[0003] The satellite's tracking process of non-cooperative targets is divided into two stages:

[0004] (1) Acquisition phase: In this phase, the desired angular trajectory of the turntable is calculated based on the guidance information. The target is acquired by angle control to ensure that the target enters the field of view and the turntable attitude meets the imaging conditions of the camera.

[0005] (2) Stable tracking phase: This phase no longer relies on guidance information, but instead uses the camera's miss distance as feedback to achieve stable tracking of non-cooperative targets. Both the miss distance and the rate of change of miss distance must meet the specified requirements. The seamless transition between these two phases presents the following challenges to the control strategy:

[0006] (1) The turntable adopts an angular trajectory feedback control strategy during the acquisition phase and a miss amount feedback control strategy during the stable tracking phase. It is necessary to ensure the smoothness of the switching process between the two control strategies.

[0007] (2) During the stable tracking phase, since the camera has multiple channels, each channel has different imaging parameters and different field of view centers, it is necessary to ensure the smoothness of the channel switching process. Summary of the Invention

[0008] The technical problem to be solved by this invention is to overcome the shortcomings of the prior art and propose a high-stability focal plane multi-stage / multi-channel switching control method to ensure the focal plane tracking performance in dynamic processes and seamless and stable switching between multiple channels.

[0009] The technical solution adopted in this invention is as follows:

[0010] on the one hand,

[0011] This invention proposes a high-stability focal plane multi-stage / multi-channel switching control method with dynamic constraints, comprising:

[0012] Perform focal plane desired trajectory planning;

[0013] Perform multi-channel unified scale processing: project the output of each channel onto a unified focal plane coordinate system to ensure the control stability of the multi-channel switching process;

[0014] Design of a high-stability capture / tracking full-process switching control law based on the kinematics of the projected focal plane position.

[0015] Furthermore, the focal plane desired trajectory planning uses the rate of change of miss distance and the acceleration of change as design parameters to ensure that the desired miss distance value smoothly transitions from the initial capture miss distance to the desired value with the desired rate of change of miss distance.

[0016] Furthermore, the focal plane desired trajectory planning specifically includes:

[0017] e = y r (t)-y f (t)

[0018] Among them, y r (t) represents the original expected off-target distance, y f (t) represents the expected miss distance after planning, and e is the error vector; introducing...

[0019]

[0020] Wherein, the coefficient k = k0 + k1exp(-k2|e|), and k0, k1, and k2 are adjustable design parameters; a tmp , For temporary variables, The expected rate of change of the miss distance;

[0021] The planned values ​​are constrained and limited based on the rate of change of the focal plane position and angular acceleration, i.e.

[0022]

[0023] Where Δt is the turntable control cycle. for The limiting value is determined based on the camera's imaging requirements; t represents time. This represents the rate of change in the amount of data that misses the target.

[0024] Furthermore, a unified coordinate system for the focal plane is established, and an imaging kinematic model is built on this basis;

[0025] Let the pixel size on the image plane be D. x D yIf the camera focal length is f, then in coordinate system O, the image point A(x,y,z) mapped onto the image plane has image coordinates A'(x',y') in coordinate system O, with units of pixels; the feature point's position y on the camera focal plane... f The uniform scale coordinates used in the focal plane are represented as

[0026]

[0027] z(t) = m T C eo (q)x(t)

[0028] in, The projection of the relative trajectory of x(t) and the satellite onto the orbital system, y∈R 2 C represents the projected position of the feature point on the camera's focal plane. eo Let P be the transformation matrix between the satellite orbital system and the end-camera coordinate system. 2×3 m∈R 3×1 These are all camera projection parameters. q s ∈R 3×1 Let q be the three-axis attitude angles of the satellite relative to its orbital system. z ∈R 2×1 Z represents the azimuth and pitch angle of the turntable, and z(t) represents the camera depth information.

[0029] Furthermore, the design of the highly stable acquisition / tracking switching control law based on the kinematics of the projected focal plane position is as follows:

[0030] When switching to stable tracking mode, the control law will be switched and optimized as follows:

[0031]

[0032] in, This is the real-time angular velocity command for the turntable. This is the turntable angular velocity command before switching to stable tracking mode. The current turntable angular velocity command is obtained based on the miss distance feedback. r is an adjustable parameter, and t is the time to enter the stable tracking mode.

[0033] on the other hand,

[0034] This invention also proposes a highly stable focal plane multi-stage / multi-channel switching control system with dynamic constraints, comprising:

[0035] Trajectory planning module: performs desired trajectory planning in the focal plane;

[0036] Multi-channel unified scale processing module: projects the output of each channel onto a unified focal plane coordinate system to ensure the control stability of the multi-channel switching process;

[0037] Control law design module: Design of a highly stable capture / tracking control law for the entire switching process based on the kinematics of the projected focal plane position.

[0038] Compared with the prior art, the present invention has the following advantages:

[0039] (1) This invention proposes a novel control method for multi-channel switching in non-cooperative target visual tracking with focal plane image movement velocity output constraints. By planning the real-time expected miss distance based on constraint capability and image movement terminal deviation, the focal plane tracking performance in the dynamic process is guaranteed. To address the stability problem of multi-channel switching in the stable tracking phase, a focal plane control method with a unified coordinate scale is proposed by utilizing the consistency of the physical position of the focal plane at the switching point, which guarantees seamless and stable switching between multiple channels. To address the jump problem that may be caused by the switching of control laws between the acquisition phase and the stable tracking phase, a switching logic is designed, and the two controls are fused and forgotten through mode time parameters, which guarantees the stability of control mode switching.

[0040] (2) This invention effectively improves upon traditional satellite control and traditional visual servo control by introducing miss trajectory planning, weighted forgetting of control laws, and a unified focal plane scale strategy. This solves the problem of non-cooperative target focal plane tracking control with dynamic image movement velocity constraints under multi-stage, multi-channel switching. The improved control strategy effectively meets the fast and stable performance requirements of the entire switching process. The algorithm design is simple, and parameter debugging requires minimal effort.

[0041] (3) This invention proposes a new solution for the problem of moving target tracking with visual servo tracking requirements. It does not require additional data input, is simple to calculate, and can be adapted to a large class of military and civilian satellite systems with non-cooperative moving target tracking requirements. It has strong engineering practicality. Attached Figure Description

[0042] Figure 1 This is a flowchart of the method of the present invention;

[0043] Figure 2 This is a schematic diagram of the camera imaging mode of the present invention;

[0044] Figure 3 This is a schematic diagram of the projection of the relative trajectory of the target and the satellite in the satellite orbital system.

[0045] Figure 4 This is a schematic diagram of the camera channel and control mode switching of the present invention;

[0046] Figure 5 This is a schematic diagram illustrating the rate of change of the target miss distance at the focal plane in this invention.

[0047] Figure 6 This is a schematic diagram illustrating the tracking error of the miss distance in this invention. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0049] This invention addresses the switching smoothness problem during the acquisition and stable tracking phases by designing a focal plane trajectory planning strategy based on constraint capability and real-time adjustment of image shift terminal deviation, and a weighted forgetting angular velocity command control algorithm. For the smoothness problem of multi-channel switching during the stable tracking phase, a focal plane control method with a unified coordinate scale is proposed, utilizing the consistency of the physical position of the focal plane at the switching point. Finally, for the smooth switching problem during acquisition and tracking, a smooth switching control law based on weighted forgetting of miss distance is proposed, which can guarantee the camera's imaging requirements even when the target angular velocity at the switching point is large. The control algorithms proposed in this invention are simple and effective, possessing strong engineering application value.

[0050] Specifically, such as Figure 1 As shown, the present invention proposes a high-stability focal plane multi-stage / multi-channel switching control method with dynamic constraints, comprising the following steps:

[0051] Step 1: Focal plane desired trajectory planning;

[0052] The satellite maneuvers to bring the target into the camera's field of view. After identifying the target, the satellite system autonomously switches to a stable tracking mode, using focal plane position feedback for turntable pointing control. When the camera initially acquires the target, the control law switches from angular trajectory feedback to miss distance position feedback. This switching process must meet the long-term stability (speed at which the target moves to the center after initial acquisition) index, meaning the target cannot move to the center too quickly, otherwise the camera will be unable to image.

[0053] The specific process of step one is as follows:

[0054] To ensure the stability of the miss distance in the dynamic process, a focal plane desired trajectory planning strategy was designed. This strategy uses the miss distance change rate and acceleration as design parameters to ensure that the desired miss distance smoothly transitions from the initial capture miss distance to the desired value at the desired miss distance change rate. The specific planning algorithm is as follows:

[0055] e = y r (t)-y f (t)

[0056] Among them, y r(t) represents the original expected off-target distance, y f (t) represents the expected miss distance after planning, and e represents the miss distance error. Next, we introduce...

[0057]

[0058] Where k = k0 + k1exp(-k2|e|), k0, k1, and k2 are adjustable design parameters, a tmp , For temporary variables, This represents the expected rate of change in the off-target amount.

[0059] The planned values ​​are constrained and limited based on the rate of change of the focal plane position and angular acceleration, i.e.

[0060]

[0061] Where Δt is the turntable control cycle, and t is time. The rate of change of the miss distance. for The limiting value is determined based on the camera's imaging requirements.

[0062] Step 2: Multi-channel unified scale processing;

[0063] During the stable tracking phase, since the camera parameters differ for each channel, designing control laws directly based on the image coordinate system would result in abrupt changes in the control laws when switching between channels, leading to deteriorated control performance during the switching process. To ensure the smoothness of control during multi-channel switching, the outputs of each channel are projected onto a unified focal plane coordinate system, and the control laws are designed based on the kinematics of the projected focal plane position, effectively avoiding control abrupt changes introduced by channel switching.

[0064] In step two, a unified coordinate system for the focal plane is established, and an imaging kinematic model is built on this basis.

[0065] like Figure 2 As shown, let the pixel size on the image plane be D. x D y If the camera focal length is f, then in coordinate system O, the image of point A(x,y,z) mapped onto the image plane will have image coordinates A'(x',y') in coordinate system O, with units of pixels. The position y of the feature point on the camera focal plane... f It can be represented by a uniform scale coordinate system on the focal plane as follows

[0066]

[0067] z(t) = m T C eo (q)x(t)

[0068] in, Imaging errors such as geometric distortion and spherical aberration of the optical system are ignored here, y∈R 2 C represents the projected position of the feature point on the camera's focal plane. eo Let P be the transformation matrix between the satellite orbital system and the end-camera coordinate system. 2×3 m∈R 3×1 These are all camera projection parameters. q s ∈R 3×1 Let q be the three-axis attitude angles of the satellite relative to its orbital system. z ∈R 2×1 Z represents the azimuth and pitch angle of the turntable, and z(t) represents the camera depth information.

[0069] Step 3: Design of high-stability capture / tracking full-process switching control logic.

[0070] During the stabilization phase of the maneuvering capture mode, the pointing angular velocity of the turntable basically matches the desired angular trajectory velocity. Once the mode transitions to stable tracking, the control law will switch. To ensure the smoothness of the switching process and the capture-tracking stability index during the switching process, the control law is optimized as follows:

[0071]

[0072] in, This is the turntable angular velocity command before switching to stable tracking mode. The current turntable angular velocity command is obtained based on the miss distance feedback, where r is an adjustable parameter and t is the time to enter stable tracking mode. This strategy can effectively avoid control jumps caused by the turntable control law under high desired angular velocities, achieving a smooth transition.

[0073] The present invention will be further described below with reference to the embodiments.

[0074] Example:

[0075] Taking a certain satellite as an example, a multi-channel switching control strategy was simulated and verified using a set of typical trajectories. The simulation process considered the time delays of each sensor and actuator, with a focal plane information processing delay of 400ms. Figure 3 The projection of the relative trajectories of the target and the satellite onto the satellite's orbital system. Figure 4 In this application, the camera has two channels with expected miss distances of [-362, -298]. T and [0 0] T Pixel, ControlMode indicates the control mode word, 1 is the angular trajectory control mode, 2 is the miss distance control mode. Figure 5The curve showing the rate of change of the miss distance. Figure 6 This diagram illustrates the tracking error of the miss distance. During multiple channel switching processes, the rate of change of the miss distance is better than the constraint of 65 pixels / s, which meets the dynamic imaging requirements of the camera.

[0076] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make possible changes and modifications to the technical solutions of the present invention by utilizing the methods and techniques disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the content of the technical solutions of the present invention shall fall within the protection scope of the technical solutions of the present invention.

Claims

1. A high-stability focal plane multi-stage multi-channel switching control method with dynamic constraints, characterized in that, include: Perform focal plane desired trajectory planning; Perform multi-channel unified scale processing: project the output of each channel onto a unified focal plane coordinate system to ensure the control stability of the multi-channel switching process; Design of a high-stability capture and tracking full-process switching control law based on the kinematics of the projected focal plane position; The focal plane desired trajectory planning uses the rate of change of miss distance and the acceleration of change as design parameters to ensure that the desired miss distance value smoothly transitions from the initial capture miss distance to the desired value with the desired rate of change of miss distance. The focal plane desired trajectory planning is specifically as follows: in, The off-target distance is the originally expected amount. The expected miss distance after planning. For error vector; Introduction Among them, coefficient , k 0、 k 1. k 2 represents adjustable design parameters; , For temporary variables, The expected rate of change of the miss distance; The planned values ​​are constrained and limited based on the rate of change of the focal plane position and angular acceleration, i.e. in, For the turntable control cycle, for The limiting value is determined based on the camera's imaging requirements; For time, The rate of change of the miss distance; Establish a unified coordinate system for the focal plane, and then build an imaging kinematics model based on this system. Let the pixel size on the image plane be... , If the camera focal length is f, then in coordinate system O, the image point A(x,y,z) mapped onto the image plane has image point coordinates A'(x',y') in coordinate system O, with units of pixels; the position of the feature point on the camera focal plane... The uniform scale coordinates used in the focal plane are represented as in, ; The projection of the relative trajectory of the satellite onto the orbital system. This indicates the projection position of the feature point onto the camera's focal plane. This is the transformation matrix between the satellite orbital system and the end-camera coordinate system. , These are all camera projection parameters. , Let be the satellite's three-axis attitude angles relative to its orbital frame. For the turntable's azimuth and pitch angle, This is the camera depth information.

2. The high-stability focal plane multi-stage multi-channel switching control method with dynamic constraints according to claim 1, characterized in that: The design of the high-stability acquisition and tracking full-process switching control law based on the kinematics of the projected focal plane position is as follows: When switching to stable tracking mode, the control law will be switched and optimized as follows: in, This is the real-time angular velocity command for the turntable. This is the turntable angular velocity command before switching to stable tracking mode. The current turntable angular velocity command is obtained based on the miss distance feedback. r is an adjustable parameter, and t is the time to enter stable tracking mode.

3. A high-stability focal plane multi-stage multi-channel switching control system with dynamic constraints, characterized in that, include: Trajectory planning module: performs desired trajectory planning in the focal plane; Multi-channel unified scale processing module: projects the output of each channel onto a unified focal plane coordinate system to ensure the control stability of the multi-channel switching process; Control law design module: Design of a high-stability capture and tracking full-process switching control law based on the kinematics of the projected focal plane position; The focal plane desired trajectory planning uses the rate of change of miss distance and the acceleration of change as design parameters to ensure that the desired miss distance value smoothly transitions from the initial capture miss distance to the desired value with the desired rate of change of miss distance. The focal plane desired trajectory planning is specifically as follows: in, The off-target distance is the originally expected amount. The expected miss distance after planning. For error vector; Introduction Among them, coefficient , k 0、 k 1. k 2 represents adjustable design parameters; , For temporary variables, The expected rate of change of the miss distance; The planned values ​​are constrained and limited based on the rate of change of the focal plane position and angular acceleration, i.e. in, For the turntable control cycle, for The limiting value is determined based on the camera's imaging requirements; For time, The rate of change of the miss distance; Establish a unified coordinate system for the focal plane, and then build an imaging kinematics model based on this system. Let the pixel size on the image plane be... , If the camera focal length is f, then in coordinate system O, the image point A(x,y,z) mapped onto the image plane has image point coordinates A'(x',y') in coordinate system O, with units of pixels; the position of the feature point on the camera focal plane... The uniform scale coordinates used in the focal plane are represented as in, ; The projection of the relative trajectory of the satellite onto the orbital system. This indicates the projection position of the feature point onto the camera's focal plane. This is the transformation matrix between the satellite orbital system and the end-camera coordinate system. , These are all camera projection parameters. , Let be the satellite's three-axis attitude angles relative to its orbital frame. For the turntable's azimuth and pitch angle, This is the camera depth information.

4. The high-stability focal plane multi-stage multi-channel switching control system with dynamic constraints according to claim 3, characterized in that: The design of the high-stability acquisition and tracking full-process switching control law based on the kinematics of the projected focal plane position is as follows: When switching to stable tracking mode, the control law will be switched and optimized as follows: in, This is the real-time angular velocity command for the turntable. This is the turntable angular velocity command before switching to stable tracking mode. The current turntable angular velocity command is obtained based on the miss distance feedback. r is an adjustable parameter, and t is the time to enter stable tracking mode.

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