A photoelectric tracking system for composite axes of flexible joint mechanical arms and its control method

Abstract

The present invention provides a photoelectric tracking system of a composite axis of a flexible joint mechanical arm and a control method thereof, which mainly solves the problems of the photoelectric tracking system existing in the prior art, such as being too large in size, too high in power consumption, limited in control accuracy, and slow in response speed. The system comprises a control unit, a flexible joint mechanical arm connected to an external mechanism, a fine tracking sub-axis connected to the end of the flexible joint mechanical arm, and an optical load installed on the fine tracking sub-axis; the flexible joint mechanical arm comprises an azimuth motor and a first harmonic reducer, a pitch motor and a second harmonic reducer, a roll motor and a third harmonic reducer, and a coaxially arranged azimuth axis, pitch axis, and roll axis; a rate gyro is installed at the connection between the roll axis and the fine tracking sub-axis; the joint ends of the azimuth axis, pitch axis, and roll axis are all installed with joint end goniometers, and the azimuth motor, pitch motor, and roll motor are all installed with motor end goniometers; the control unit comprises a coarse tracking controller and a fine tracking controller.

Description

Technical Field

[0001] The invention relates to a photoelectric tracking system and a control method thereof, and in particular to a photoelectric tracking system for a composite axis of a flexible joint mechanical arm and a control method thereof. Background Art

[0002] With the increasing demand for space exploration, high-precision optoelectronic tracking systems are increasingly being used in the aerospace field. Optoelectronic tracking systems are mainly used to overcome the influence of various interference factors and ensure that the visual axis stably points to the target, thereby achieving image stabilization.

[0003] The optoelectronic tracking system is a combination of transmission system, sensor, control algorithm and optomechanical architecture. In space, optoelectronic tracking systems are mostly driven directly by the satellite body. However, due to the large volume, mass and flexible accessories (such as solar panels) of the satellite itself, its structural fundamental frequency is generally low, resulting in a slow response speed of the optoelectronic tracking system driven directly by the satellite body. In addition, the control accuracy of the optoelectronic tracking system driven directly by the satellite body is limited. Therefore, it is difficult to meet the requirements of fast visual axis movement and high-precision image stabilization control of the optoelectronic tracking system by directly driving the satellite body. Summary of the invention

[0004] The purpose of the present invention is to solve the technical problem that the method of directly driving the optoelectronic tracking system with a satellite body in the prior art is difficult to meet the requirements of rapid movement of the visual axis and high-precision image stabilization control of the optoelectronic tracking system, and to provide a flexible joint robotic arm composite axis optoelectronic tracking system and its control method.

[0005] To achieve the above purpose, the technical solution adopted by the present invention is:

[0006] A flexible joint mechanical arm composite axis photoelectric tracking system, which is special in that it includes a control unit, a flexible joint mechanical arm connected to an external mechanism, a precision tracking sub-axis connected to the end of the flexible joint mechanical arm, and an optical load installed on the precision tracking sub-axis;

[0007] The optical load includes a beam splitter and a CCD arranged in sequence along the optical path;

[0008] The flexible joint mechanical arm comprises an azimuth motor and a first harmonic reducer, a pitch motor and a second harmonic reducer, a roll motor and a third harmonic reducer, and a coaxially arranged azimuth axis, a pitch axis and a roll axis;

[0009] The azimuth motor is connected to an external mechanism, the output end of the azimuth motor is connected to the input end of the first harmonic reducer, the output end of the first harmonic reducer is connected to the joint end of the azimuth axis, the connecting end of the azimuth axis is connected to the pitch motor, the output end of the pitch motor is connected to the input end of the second harmonic reducer, the output end of the second harmonic reducer is connected to the joint end of the pitch axis, the connecting end of the pitch axis is connected to the roll motor, the output end of the roll motor is connected to the input end of the third harmonic reducer, the output end of the third harmonic reducer is connected to the joint end of the roll axis, the connecting end of the roll axis is connected to the fine tracking sub-axis, and a rate gyroscope is installed at the connection between the roll axis and the fine tracking sub-axis;

[0010] The joint ends of the azimuth axis, the pitch axis and the roll axis are all equipped with joint end goniometers, and the azimuth motor, the pitch motor and the roll motor are all equipped with motor end goniometers;

[0011] The control unit includes a coarse tracking controller and a fine tracking controller. The azimuth motor, pitch motor, roll motor, joint end goniometer, motor end goniometer and rate gyro are all connected to the coarse tracking controller, and the fine tracking sub-axis is connected to the fine tracking controller.

[0012] Furthermore, the transfer functions of the azimuth axis, pitch axis and roll axis are:

[0013]

[0014]

[0015] Where: L is the angular velocity of the joint end of the azimuth axis, pitch axis or roll axis; ω m J is the angular velocity of the azimuth motor, pitch motor or roll motor; m is the nominal moment of inertia of the azimuth motor, pitch motor or roll motor; J L is the nominal moment of inertia of the joint end of the azimuth axis, pitch axis or roll axis; S is the Laplace operator; is the equivalent resonant frequency; REF is the reference signal; ω a is the anti-resonance frequency.

[0016] Furthermore, the equivalent resonant frequency

[0017] Anti-resonance frequency

[0018] Where: K s The stiffness of the first harmonic reducer, the second harmonic reducer or the third harmonic reducer; is the equivalent moment of inertia of the azimuth motor, pitch motor or roll motor; N is the reduction ratio of the first harmonic reducer, the second harmonic reducer or the third harmonic reducer; kaL It is the acceleration feedback coefficient of the joint end of the azimuth axis, pitch axis or roll axis.

[0019] Furthermore, the equivalent moment of inertia of the azimuth motor, the pitch motor, or the roll motor

[0020] Where: It is the acceleration feedback coefficient of the azimuth motor, pitch motor or roll motor.

[0021] Furthermore, the output torque T of the flexible gear in the first harmonic reducer, the second harmonic reducer or the third harmonic reducer is fs Satisfies the following formula:

[0022]

[0023] Where: △θ fs is the elastic deformation of the flexible gear; C fs k is the local stiffness coefficient of the flexible gear; fs0 is the nominal stiffness of the flexible gear.

[0024] Furthermore, the precision tracking sub-axis is a fast-reflection mirror driven by a voice coil motor.

[0025] Furthermore, there are four voice coil motors, and the four voice coil motors are arranged in a four-point symmetrical manner.

[0026] Furthermore, the output length of the voice coil motor changes by ΔL max The rotation angle θ of the reflector in the fast mirror satisfies the following relationship:

[0027]

[0028] Where: R A is the distance between any voice coil motor and the symmetry center of the four voice coil motors.

[0029] At the same time, the present invention also provides a control method for a flexible joint mechanical arm composite axis photoelectric tracking system, which is special in that it includes the following steps:

[0030] 1) The coarse tracking controller controls the flexible joint manipulator to adjust the visual axis of the optical load over a large range, and points the visual axis to the vicinity of the position of the tracking target;

[0031] 2) Control the flexible joint robot arm through the coarse tracking controller to drive the optical load to scan, search and track the target in a small range;

[0032] 3) After the tracking target is found, the tracking target is imaged through the spectroscope of the optical load, and the first miss distance of the tracking target is obtained through the CCD;

[0033] 4) Use the miss distance of the tracked target to form an image closed-loop control, and use the coarse tracking controller to control the movement of the flexible joint manipulator to pull the tracked target into the center of the field of view;

[0034] 5) When the tracked target enters the center of the field of view, the precision tracking controller works, and the second miss distance obtained by the CCD eliminates the influence of high-frequency jitter, so that the tracked target is stabilized in the center of the field of view;

[0035] 6) Continuously track the target until the tracking task is completed.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] 1. The present invention adopts a flexible joint robot arm that indirectly drives the azimuth axis, pitch axis and roll axis respectively through the first harmonic reducer, the second harmonic reducer and the third harmonic reducer as a coarse tracking sub-axis, and a fast reflection mirror driven by a voice coil motor as a precision sub-axis, which together constitute a composite axis tracking system, give full play to the complementary advantages, and can obtain low power consumption, small size, light weight, high precision and stable tracking performance.

[0038] 2. The system transfer function adopted by the present invention can effectively suppress the inertia coupling and mechanical resonance of the flexible joint robot arm.

[0039] 3. The present invention adopts a flexible joint robot arm indirectly driven by a harmonic reducer to replace the traditional direct-drive tracking frame structure, which can greatly reduce the volume, power consumption and weight of the driving mechanism of the aperture space optical system, and provide convenience for the transportation and on-orbit assembly of large-aperture space optical systems.

[0040] 4. The present invention adopts a multi-flexible body modeling method to establish a refined model of the harmonic reducer, and estimates the precise joint torque based on the established model, thereby completing the acceleration feedback of the joint end. BRIEF DESCRIPTION OF THE DRAWINGS

[0041] Figure 1 It is a structural schematic diagram of an embodiment of a photoelectric tracking system for a composite axis of a flexible joint mechanical arm of the present invention;

[0042] Figure 2 It is a structural schematic diagram of an optical load and a FSM in an embodiment of a flexible joint mechanical arm composite axis photoelectric tracking system of the present invention;

[0043] Figure 3 It is a control principle diagram of the first harmonic reducer, the second harmonic reducer or the third harmonic reducer in an embodiment of a flexible joint mechanical arm composite axis photoelectric tracking system of the present invention;

[0044] Figure 4It is a principle block diagram of dual acceleration feedback in an embodiment of a flexible joint mechanical arm composite axis photoelectric tracking system of the present invention;

[0045] Figure 5 It is a principle diagram of the flexible transmission of the first harmonic reducer, the second harmonic reducer or the third harmonic reducer in an embodiment of a photoelectric tracking system for a composite axis of a flexible joint mechanical arm of the present invention;

[0046] Figure 6 It is a layout diagram of a fast-reflecting mirror voice coil motor in an embodiment of a flexible joint mechanical arm composite axis photoelectric tracking system of the present invention;

[0047] Figure 7 It is a control principle block diagram of a control unit in a photoelectric tracking system of a composite axis of a flexible joint mechanical arm of the present invention;

[0048] Figure 8 This is a control principle diagram of a coarse tracking controller in an embodiment of a flexible joint mechanical arm composite axis photoelectric tracking system of the present invention; (both the joint end control law and the motor end control law adopt PID controller)

[0049] Fig. 9 This is a control principle diagram of a precision tracking controller in an embodiment of a flexible joint mechanical arm composite axis photoelectric tracking system of the present invention. (Both the position loop controller and the speed loop controller use PID controllers)

[0050] In the figure, 1-aircraft, 2-shock absorber, 3-azimuth axis, 4-pitch axis, 5-roll axis, 6-precision tracking axis;

[0051] θ Lr Indicates the reference angle of the joint end of the azimuth axis, pitch axis, or roll axis, θ mr Indicates the reference angle of the azimuth motor, pitch motor and roll motor; e L =θ L -θ Lr Indicates the joint end tracking error of the azimuth axis, pitch axis, or roll axis; e m =θ m -θ mr Indicates the motor end tracking error of the azimuth motor, pitch motor or roll motor; a L * Indicates the joint end acceleration reference of the azimuth axis, pitch axis, or roll axis, a m * Indicates the acceleration reference of the azimuth motor, pitch motor, or roll motor; d L It represents the equivalent disturbance torque at the end of the azimuth axis, pitch axis or roll axis; d m represents the unknown external disturbance applied to the azimuth motor, pitch motor or roll motor; θ LIndicates the joint end angle position of the azimuth axis, pitch axis, or roll axis; θ m represents the motor end angle position of the azimuth motor, pitch motor or roll motor; FSM represents the fast response mirror; Γ L represents the model uncertainty on the azimuth axis, pitch axis, or roll axis, Γ m represents the model uncertainty of the azimuth motor, pitch motor, or roll motor; Indicates the angular velocity of the joint end of the azimuth axis, pitch axis, or roll axis, K wg represents the stiffness of the harmonic generator, J in It is the total inertia of the azimuth motor, pitch motor or roll motor rotor, the azimuth motor shaft, pitch motor shaft or roll motor shaft and the harmonic generator connected to the azimuth motor shaft, pitch motor shaft or roll motor shaft, T ft represents the friction torque. DETAILED DESCRIPTION

[0052] In order to make the purpose, advantages and features of the present invention clearer, the flexible joint robot arm composite axis photoelectric tracking system and its control method proposed in the present invention are further described in detail in combination with the drawings and specific embodiments. According to the following specific implementation methods, the advantages and features of the present invention will be clearer. It should be noted that: the drawings are all in a very simplified form and use non-precise proportions, which are only used to conveniently and clearly assist in explaining the purpose of the embodiments of the present invention; secondly, the structure shown in the drawings is often part of the actual structure.

[0053] In the description of the present invention, it should be noted that the terms “first” and “second” are only used for descriptive purposes and cannot be understood as indicating or implying relative importance.

[0054] like Figure 1-Figure 9 As shown, the flexible joint robot arm composite axis optoelectronic tracking system of the present invention includes a control unit, a flexible joint robot arm connected to an external mechanism, a precision tracking sub-axis connected to the end of the flexible joint robot arm, and an optical load installed on the precision tracking sub-axis. In this embodiment, the flexible joint robot arm is connected to the aircraft 1. In other embodiments of the present invention, the flexible joint robot arm can also be connected to a vehicle-mounted mechanism, a ship-mounted mechanism, a ground-mounted mechanism or an airborne mechanism.

[0055] like Figure 1 and Figure 3As shown, the flexible joint mechanical arm includes an azimuth motor and a first harmonic reducer, a pitch motor and a second harmonic reducer, a roll motor and a third harmonic reducer, and a coaxially arranged azimuth axis 3, a pitch axis 4 and a roll axis 5; the azimuth motor is connected to the aircraft 1 through a shock absorber 2, the output end of the azimuth motor is connected to the input end of the first harmonic reducer, the output end of the first harmonic reducer is connected to the joint end of the azimuth axis 3, the connecting end of the azimuth axis 3 is connected to the pitch motor, the output end of the pitch motor is connected to the input end of the second harmonic reducer, the output end of the second harmonic reducer is connected to the joint end of the pitch axis 4, the connecting end of the pitch axis 4 is connected to the roll motor The output end of the roll motor is connected to the input end of the third harmonic reducer, the output end of the third harmonic reducer is connected to the joint end of the roll axis 5, the connecting end of the roll axis 5 is connected to the fine tracking sub-axis, and a rate gyro is installed at the connection between the roll axis 5 and the fine tracking sub-axis, and the rate gyro is a fiber optic gyro, a laser gyro or a MEMS gyro, etc.; the joint ends of the azimuth axis 3, the pitch axis 4 and the roll axis 5 are all equipped with joint end goniometers, and the azimuth motor, the pitch motor and the roll motor are all equipped with motor end goniometers, and the joint end goniometers and the motor end goniometers both use encoders to measure the rotation angle of the joint end or the rotation angle of the motor; Figure 7 , Figure 8 and Fig. 9 As shown, the control unit includes a coarse tracking controller and a fine tracking controller. The azimuth motor, pitch motor, roll motor, joint end goniometer, motor end goniometer and rate gyro are all connected to the coarse tracking controller, and the fine tracking sub-axis is connected to the fine tracking controller.

[0056] like Figure 6 and Fig. 9 As shown, the fine tracking sub-axis 6 in this embodiment is a fast mirror driven by a voice coil motor. According to the fast mirror structure in the prior art, it includes a base connected to the roll axis on one side, a support mechanism connected to the other side of the base, multiple voice coil motors and multiple grating scales installed on the support mechanism, and a reflector connected to the output ends of the multiple voice coil motors, such as Figure 6 As shown (θ X is the rotation angle of the reflector in the X-axis direction, θ Yis the rotation angle of the reflector in the Y-axis direction), there are four voice coil motors, and a four-point symmetrical drive layout is adopted. The four voice coil motors are voice coil motor A, voice coil motor B, voice coil motor C and voice coil motor D. The displacements of the four voice coil motors are measured by setting grating rulers on the four voice coil motors respectively. The grating ruler and the four voice coil motors are connected to the precision tracking controller, and half of the maximum elongation displacement of the four voice coil motors after power is turned on is defined as the initial zero position. When the voice coil motors B and D are stationary, and the voice coil motors A and C are respectively extended and shortened by equal displacements, the reflector realizes rotation around the X-axis. When the voice coil motors A and C are stationary, and the voice coil motors B and D are respectively extended and shortened by equal displacements, the reflector realizes rotation around the Y-axis.

[0057] Output length change of voice coil motor △L max The relationship with the rotation angle θ of the reflector in the fast mirror is:

[0058]

[0059] Where: R A is the straight-line distance between any voice coil motor and the central symmetric point of the four voice coil motors;

[0060] It should be noted that the structure of the precision tracking sub-axis in this embodiment is only a preferred embodiment of the present invention. In other embodiments of the present invention, the precision tracking sub-axis may also adopt a piezoelectric ceramic driven fast response mirror, a fast response mirror of other driving forms or a rotating reflector in the prior art, or may be a lightweight and small-volume tracking frame structure.

[0061] like Figure 2 As shown, the optical load includes a beam splitter and a CCD arranged in sequence along the optical path, and a telescope is also provided. The light signal enters the fast mirror FSM through the telescope, is reflected by the reflector on the fast mirror FSM, and enters the beam splitter. The transmitted light of the light signal enters the signal detection and information processing module, and the refracted light enters the CCD.

[0062] In order to improve the control performance of the flexible joint manipulator, the present invention designs a dual acceleration feedback control method to eliminate the influence of inertia coupling and mechanical resonance. First, the transfer function of the single-joint flexible joint manipulator is given as follows:

[0063]

[0064]

[0065] Where: L is the angular velocity of the joint end of the azimuth axis, pitch axis or roll axis; ω m K is the angular velocity of the azimuth motor, pitch motor or roll motor; sThe stiffness of the first harmonic reducer, the second harmonic reducer or the third harmonic reducer; N is the reduction ratio of the first harmonic reducer, the second harmonic reducer or the third harmonic reducer; S is the Laplace operator; J L is the nominal moment of inertia of the joint end of the azimuth axis, pitch axis or roll axis; J m is the nominal moment of inertia of the azimuth motor, pitch motor or roll motor; τ m Output torque of azimuth motor, pitch motor or roll motor; resonant frequency Anti-resonance frequency Inertia ratio but

[0066] like Figure 4 As shown in FIG. 1 , it is a dual acceleration feedback control block diagram provided by the present invention. Combined with the transfer function of the single-joint flexible manipulator, the transfer functions of the azimuth axis 3, the pitch axis 4 and the roll axis 5 can be obtained as follows:

[0067]

[0068]

[0069] Where: k aL is the acceleration feedback coefficient of the joint end of the azimuth axis, pitch axis or roll axis; equivalent resonant frequency REF is the reference signal; the equivalent moment of inertia of the azimuth motor, pitch motor or roll motor

[0070] It can be seen that through the acceleration feedback of the azimuth motor, pitch motor or roll motor, the equivalent rotational inertia of the azimuth motor, pitch motor or roll motor becomes the original When the rotational inertia of the joint end of the system is too small or too large than R, the formula By adjusting the parameters To obtain the ideal moment of inertia ratio By changing the acceleration feedback coefficient k of the joint end of the azimuth axis, pitch axis or roll axis aL To arbitrarily configure the equivalent resonant frequency of the system so that the equivalent resonant frequency of the system falls outside the bandwidth of the system, the purpose of suppressing resonance can be achieved; on the other hand, adding acceleration feedback at the joint end of the azimuth axis, pitch axis or roll axis can effectively reduce the impact of inertia coupling.

[0071] Where: is the acceleration feedback coefficient of the azimuth motor, pitch motor or roll motor; R is the moment of inertia ratio of the joint end of the azimuth axis, pitch axis or roll axis; is the ideal moment of inertia ratio.

[0072] The premise of dual acceleration feedback is to obtain accurate angular acceleration information. In order to avoid increasing the cost and complexity of the system by adding accelerometers, an estimation method is used here to extract the acceleration of the azimuth motor, pitch motor, or roll motor and the joint end acceleration of the azimuth axis, pitch axis, or roll axis. The acceleration of the azimuth motor, pitch motor, or roll motor can be estimated by embedding a Lomborg state observer on the goniometer at the motor end, while the joint end acceleration of the azimuth axis, pitch axis, or roll axis is estimated by estimating the joint torque T s Equivalent acquisition, that is:

[0073] T s =J L a L ;

[0074] The key to joint torque estimation lies in the establishment of an accurate model of the harmonic reducer (referring to the first harmonic reducer, the second harmonic reducer or the third harmonic reducer). In the process of establishing the flexible joint manipulator model, the harmonic reducer is approximately equivalent to a linear spring, but the actual harmonic reducer transmission characteristic has nonlinear hysteresis characteristics. In order to estimate the accurate joint torque T s , it is necessary to carry out detailed modeling of the harmonic reducer. The harmonic reducer consists of a harmonic generator, a rigid gear and a flexible gear. The flexible behavior of the harmonic reducer in the transmission is as follows Figure 5 shown.

[0075] The flexibility of the harmonic generator can be determined by the angular displacement difference △θ on both sides of the harmonic generator. wg =θ wgo -θ wgi To express, where θ wgi is the angular displacement at the input of the harmonic generator, θ wgo is the angular displacement of the harmonic generator output end. Similarly, the flexibility of the flexible gear is also determined by the angular displacement difference △θ on both sides. fs =θ fso -θ fsi Given, where θ fsi and θ fso are the angular displacements of the input and output ends of the flexible gear respectively. wgo and θ fsi In addition, the third angular displacement is the kinematic error caused by the meshing clearance between the flexible gear and the rigid gear. Can be obtained from unloaded rotary joint testing.

[0076] The elastic deformation of the flexible gear is:

[0077]

[0078] Among them C wg , k wg0is the parameter to be determined, and the elastic deformation △θ of the flexible gear is obtained. fs After that, the output torque T of the flexible gear fs It can be given by the following formula:

[0079]

[0080] In actual use, current sensors are installed on the azimuth motor, pitch motor and roll motor. The current measured by the current sensor is used to estimate the harmonic generator torque T wg :

[0081] T wg =T m -T fm ;

[0082] Where: C fs k is the coefficient related to the local stiffness of the flexible gear; fs0 is the nominal stiffness of the flexible gear; C wg is the coefficient related to the stiffness of the harmonic generator; k wg0 is the nominal stiffness of the harmonic generator (k fs0 , C fs , C wg and k wg0 can be determined according to the manufacturer's instructions of the harmonic reducer); T m is the output torque of the azimuth motor, pitch motor or roll motor, T fm is the friction force of the azimuth motor, pitch motor or roll motor, and △θ is the total torsional deformation between the input and output of the harmonic reducer.

[0083] The output torque T of the flexible wheel is obtained fs The joint torque T s accurate estimate of .

[0084] Based on the dual acceleration feedback, the outer loop (speed loop, position loop, etc.) controller is designed to achieve high-precision control of the flexible joint robot arm.

[0085] A control method for a composite axis photoelectric tracking system of a flexible joint mechanical arm is based on a composite axis photoelectric tracking system of a flexible joint mechanical arm, and comprises the following steps:

[0086] 1) The coarse tracking controller controls the flexible joint manipulator to adjust the visual axis of the optical load over a large range, and points the visual axis to the vicinity of the position of the tracking target;

[0087] 2) Control the flexible joint robot arm through the coarse tracking controller to drive the optical load to scan, search and track the target in a small range;

[0088] 3) After the tracking target is found, the tracking target is imaged through the spectroscope of the optical load, and the first miss distance of the tracking target is obtained through the CCD ( Figure 7 off-target amount in );

[0089] 4) Use the miss distance of the tracked target to form an image closed-loop control, and use the coarse tracking controller to control the movement of the flexible joint manipulator to pull the tracked target into the center of the field of view;

[0090] 5) When the target enters the center of the field of view, the precision tracking controller starts to work and obtains the second miss distance of the target through CCD decoupling ( Figure 8 The high-frequency small-amplitude miss amount in the image is obtained by decoupling to eliminate the influence of high-frequency jitter and stabilize the tracked target in the center of the field of view;

[0091] 6) Continuously track the target until the tracking task is completed.

Claims

1. A photoelectric tracking system for composite axes of a flexible joint mechanical arm, characterized in that: It comprises a control unit, a flexible joint mechanical arm connected to an external mechanism, a precision tracking sub-axis (6) connected to the end of the flexible joint mechanical arm, and an optical load installed on the precision tracking sub-axis (6); The optical load includes a beam splitter and a CCD arranged in sequence along the optical path; The flexible joint mechanical arm comprises an azimuth motor and a first harmonic reducer, a pitch motor and a second harmonic reducer, a roll motor and a third harmonic reducer, and a coaxially arranged azimuth axis (3), a pitch axis (4) and a roll axis (5); The azimuth motor is connected to an external mechanism, the output end of the azimuth motor is connected to the input end of a first harmonic reducer, the output end of the first harmonic reducer is connected to the joint end of an azimuth axis (3), the connection end of the azimuth axis (3) is connected to a pitch motor, the output end of the pitch motor is connected to the input end of a second harmonic reducer, the output end of the second harmonic reducer is connected to the joint end of a pitch axis (4), the connection end of the pitch axis (4) is connected to a roll motor, the output end of the roll motor is connected to the input end of a third harmonic reducer, the output end of the third harmonic reducer is connected to the joint end of a roll axis (5), the connection end of the roll axis (5) is connected to a precision tracking sub-axis (6), and a rate gyroscope is installed at the connection between the roll axis (5) and the precision tracking sub-axis (6); The joint ends of the azimuth axis (3), the pitch axis (4) and the roll axis (5) are all equipped with joint end goniometers, and the azimuth motor, the pitch motor and the roll motor are all equipped with motor end goniometers; The control unit includes a coarse tracking controller and a fine tracking controller, the azimuth motor, pitch motor, roll motor, joint end goniometer, motor end goniometer and rate gyro are all connected to the coarse tracking controller, and the fine tracking sub-axis is connected to the fine tracking controller; The transfer functions of the azimuth axis (3), the pitch axis (4) and the roll axis (5) are: Where: L is the angular velocity of the joint end of the azimuth axis, pitch axis or roll axis; ω m J is the angular velocity of the azimuth motor, pitch motor or roll motor; m is the nominal moment of inertia of the azimuth motor, pitch motor or roll motor; J L is the nominal moment of inertia of the joint end of the azimuth axis, pitch axis or roll axis; S is the Laplace operator; is the equivalent resonant frequency; REF is the reference signal; ω a is the anti-resonance frequency.

2. The photoelectric tracking system for composite axes of a flexible joint mechanical arm according to claim 1, characterized in that: Equivalent resonant frequency Anti-resonance frequency Where: r is the resonant frequency; K s The stiffness of the first harmonic reducer, the second harmonic reducer or the third harmonic reducer; is the equivalent moment of inertia of the azimuth motor, pitch motor or roll motor; N is the reduction ratio of the first harmonic reducer, the second harmonic reducer or the third harmonic reducer; k aL It is the acceleration feedback coefficient of the joint end of the azimuth axis, pitch axis or roll axis.

3. The photoelectric tracking system for composite axes of a flexible joint mechanical arm according to claim 2, characterized in that: The equivalent moment of inertia of the azimuth motor, pitch motor or roll motor Where: It is the acceleration feedback coefficient of the azimuth motor, pitch motor or roll motor.

4. The photoelectric tracking system for composite axes of a flexible joint mechanical arm according to claim 3 is characterized in that: The output torque T of the flexible gear in the first harmonic reducer, the second harmonic reducer or the third harmonic reducer fs Satisfies the following formula: Where: Δθ fs is the elastic deformation of the flexible gear; C fs k is the coefficient related to the local stiffness of the flexible gear; fs0 is the nominal stiffness of the flexible gear.

5. The photoelectric tracking system for composite axes of a flexible joint mechanical arm according to claim 4, characterized in that: The precision tracking sub-axis (6) is a fast-reflecting mirror driven by a voice coil motor.

6. The photoelectric tracking system for composite axes of a flexible joint mechanical arm according to claim 5, characterized in that: There are four voice coil motors, and the four voice coil motors are arranged in a four-point symmetrical manner.

7. The photoelectric tracking system for composite axes of a flexible joint mechanical arm according to claim 6, characterized in that: The output length change of the voice coil motor is ΔL max The rotation angle θ of the reflector in the fast mirror satisfies the following relationship: Where: R A is the distance between any voice coil motor and the symmetry center of the four voice coil motors.

8. A control method for a photoelectric tracking system of a composite axis of a flexible joint mechanical arm, based on a photoelectric tracking system of a composite axis of a flexible joint mechanical arm according to any one of claims 1 to 7, characterized in that: The following steps are involved: 1) The coarse tracking controller controls the flexible joint manipulator to adjust the visual axis of the optical load over a large range so that the visual axis points to the vicinity of the position of the tracking target; 2) The coarse tracking controller controls the flexible joint manipulator to drive the optical load to scan and search for the tracking target in a small range; 3) After the tracking target is searched, the tracking target is imaged through the spectroscope of the optical load, and the first miss distance of the tracking target is obtained through the CCD of the optical load; 4) Use the miss distance of the tracked target to form an image closed-loop control, and use the coarse tracking controller to control the movement of the flexible joint manipulator to pull the tracked target into the vicinity of the center of the field of view; 5) When the tracked target enters the center of the field of view, the precision tracking controller works, obtains the second miss distance of the tracked target through the CCD to eliminate the influence of high-frequency jitter, and stabilizes the tracked target in the center of the field of view; 6) Continuously track the target until the tracking task is completed.

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