A fast tracking device for gravity unloading system

Abstract

The present invention provides a fast tracking device applied to a gravity unloading system, aiming to improve the tracking accuracy of the servo system while avoiding the internal vibration and impact of the system caused by the sudden acceleration of the two-degree-of-freedom motion platform; the device comprises a two-degree-of-freedom tracking slide platform, an active constant force system and a three-degree-of-freedom motion system; the two-degree-of-freedom tracking slide platform realizes the sliding motion of the active constant force system along the x-axis and the y-axis; the active constant force system controls the motion distribution to reduce the acceleration of the two-degree-of-freedom tracking slide platform; the three-degree-of-freedom motion system is used to install a simulation object and realize the movement of the simulation object in the three-degree-of-freedom directions.

Description

Technical Field

[0001] The invention belongs to the technical field of spacecraft space environment simulation, and in particular relates to a fast tracking device applied to a gravity unloading system. Background Art

[0002] Gravity unloading technology provides a spacecraft with a microgravity environment and full degrees of freedom, reconstructing the spacecraft's motion in outer space on the ground to enhance the fidelity of ground-based verification. Currently, various gravity unloading methods have been proposed, including drop towers, air bearings, neutral buoyancy, and suspension.

[0003] The suspension method is widely used due to its advantages, including simple implementation, adjustable force, high simulation accuracy, and low added inertia. A suspended gravity unloading system primarily consists of a horizontal servo system that maintains the vertical position of the cable and a constant force system that maintains a constant cable force. Compared to a constant force system, a servo system has more degrees of freedom and a more complex structure, often employing rectangular or polar coordinates. This results in a large mass. This limits its dynamic performance, leading to large following errors under conditions of sudden acceleration, such as rapid spacecraft deployment, docking, and collision. When a spacecraft contacts or collides with another object, the two horizontal accelerations at the upper end of the cable, resulting in drastic changes in the avoidance force, cause the servo system to provide sufficient acceleration to the upper end of the cable to ensure good control accuracy. This places very stringent demands on the stiffness of the drive mechanism and the power of the active components in large servo systems. Excessive acceleration and sudden changes in acceleration can cause vibration and shock in the mechanical structure, shortening its service life. Summary of the Invention

[0004] In view of the technical drawbacks of the suspension method, the present invention provides a fast tracking device applied to the gravity unloading system, aiming to improve the following accuracy of the servo system while avoiding the internal vibration and impact of the two-degree-of-freedom motion platform caused by sudden acceleration changes.

[0005] The technical solution adopted by the present invention is as follows: a fast tracking device applied to a gravity unloading system, comprising a two-degree-of-freedom tracking slide platform, an active constant force system and a three-degree-of-freedom motion system;

[0006] The dual-degree-of-freedom tracking slide platform realizes the sliding motion of the active constant force system along the x-axis and the y-axis;

[0007] The active constant force system includes a sliding seat, which is slidably mounted on the third slide rail, a winding motor is fixedly installed above the sliding seat, and an upper connecting plate is fixedly installed below the sliding seat, a circular hole is reserved in the center of the upper connecting plate, and a parallel mechanism is installed along the circumference of the upper connecting plate, the upper connecting plate is connected to the lower connecting plate through the parallel mechanism, and a circular hole is also opened in the center of the lower connecting plate; a winding wheel is installed on the output shaft of the winding motor, and the cable is wound on the winding wheel, and the free end of the cable passes downward through the guide wheel on the sliding seat, the upper connecting plate and the central circular hole of the lower connecting plate in sequence, and then is connected to the three-degree-of-freedom motion system;

[0008] The parallel mechanism includes two active action arms and one passive arm, and the active action arms include an active arm and a passive arm. The upper end of the active arm is fixed to the output shaft of the action motor, and the action motor is installed on the upper connecting plate. The lower end of the active arm is hinged to the passive arm, and the lower end of the passive arm is hinged to the lower connecting plate. The two active action arms are respectively driven by an action motor to rotate the active arm; the upper end of the passive arm is hinged to the upper connecting plate, and the lower end is hinged to the lower connecting plate. The passive arm cooperates with the two active action arms to drive the lower connecting plate to move.

[0009] The three-degree-of-freedom motion system is used to install a simulation object and realize the movement of the simulation object in three degrees of freedom directions.

[0010] A cable pulling device and an angle measuring device are installed above and below the lower connecting plate, respectively. The cable passes through the cable pulling device, and its swing angle is measured by the angle measuring device.

[0011] The cable traction device includes two upper guide wheels and two lower guide wheels, the axis lines of the two upper guide wheels are perpendicular to the axis lines of the two lower guide wheels, and the cable passes between the two upper guide wheels and between the two lower guide wheels in sequence;

[0012] The angle measuring device is installed under the lower connecting plate, and the first measuring rod and the second measuring rod are installed respectively through two brackets. The two measuring rods are L-shaped, and the cross bar parts below them are provided with strip holes. The strip holes of the two measuring rods are perpendicular to each other, and the cable passes through the overlapping part of the two strip holes; and the first digital encoder and the second digital encoder are also installed on the two brackets respectively.

[0013] The passive arm includes two vertically parallel first and second long rods, and two horizontally parallel first and second short rods. The upper and lower ends of the first and second long rods are hinged to the upper and lower connecting plates, respectively. The ends of the first and second short rods are hinged to the first and second long rods, respectively. The four rods form a four-bar linkage structure. The structural composition of the driven arm is the same as that of the passive arm.

[0014] The dual-degree-of-freedom tracking slide platform consists of two mutually parallel first slide rails, a second slide rail, and a third slide rail that crosses the first and second slide rails; the third slide rail can slide along the first and second slide rails, and the active constant force system can slide along the third slide rail.

[0015] The three-degree-of-freedom motion system includes a hinge, a U-shaped frame and a ring frame. The upper part of the U-shaped frame is hingedly mounted on the hinge and can rotate circumferentially relative to the hinge. The two arms of the U-shaped frame are respectively hingedly connected to one side of the ring frame. The ring frame can flip relative to the U-shaped frame. The simulation object is mounted inside the ring frame and can rotate around its central axis.

[0016] The advantages of the technical solution of the present invention are:

[0017] (1) Through the motion distribution control of the parallel mechanism, the acceleration of the dual-degree-of-freedom tracking slide platform is minimized to reduce the inertial force within the entire system, avoid vibration and impact within the system, and at the same time improve the horizontal following speed.

[0018] (2) A cable traction device is installed at the bottom of the parallel mechanism, which promotes the rapid movement of the cable in the horizontal plane through the four guide wheels inside. The parallel mechanism has the characteristics of high stiffness, low inertia and good dynamic performance. It can quickly push the cable to the desired position, so that the cable hanging point can achieve rapid changes in acceleration within a small range. The control accuracy of the servo system is improved through the joint operation of the dual-degree-of-freedom tracking slide platform and the parallel mechanism, while avoiding the vibration and impact caused by the sudden change of acceleration of the dual-degree-of-freedom tracking slide platform. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic diagram of the overall structure of the fast tracking device of the present invention;

[0020] Figure 2 It is a schematic diagram of the framework structure of the dual-degree-of-freedom tracking slide platform of the present invention;

[0021] Figure 3 It is a schematic diagram of the overall structure of the active constant force system of the present invention;

[0022] Figure 4 This is a partial view of the parallel mechanism of the present invention. Figure 1 ;

[0023] Figure 5 This is a partial view of the parallel mechanism of the present invention. Figure 2 ;

[0024] Figure 6 Schematic diagram of the structure of the cable pulling device of the present invention, wherein (a) is an external view and (b) is a view of the internal components;

[0025] Figure 7 It is a structural schematic diagram of the angle measuring device of the present invention;

[0026] In the figure: 1. Double-degree-of-freedom tracking slide platform, 2. Active constant force system, 3. Three-degree-of-freedom motion system, 4. Simulator, 5. First slide rail, 6. Second slide rail, 7. Third slide rail, 8. Slide rail motor, 9. Winding motor, 10. Winding wheel, 11. Cable, 12. Guide wheel, 13. Upper connecting plate, 14. Action motor, 15. Active arm, 16. Driven arm, 17. Passive arm, 18. Lower connecting plate, 19. Cable traction device, 20. Angle measuring device, 21. First long rod, 22. Second long rod, 23. First short rod, 24. Second short rod, 25. Upper guide wheel, 26. Lower guide wheel, 27. First measuring rod, 28. Second measuring rod, 29. First digital encoder, 30. Second digital encoder. DETAILED DESCRIPTION

[0027] Figure 1 It is a schematic diagram of the overall structure of the rapid tracking device of the present invention. The supporting structure is not shown in the figure. A conventional frame can be used to support the entire rapid tracking device. As shown in the figure, the rapid tracking device applied to the gravity unloading system of the present invention includes a dual-degree-of-freedom tracking slide platform 1, and an active constant force system 2 is slidably installed on the dual-degree-of-freedom tracking slide platform 1. The dual-degree-of-freedom tracking slide platform 1 drives the active constant force system 2 to move in the x-axis and y-axis directions. The cable of the active constant force system 2 is downwardly connected to the three-degree-of-freedom motion system 3, and the simulated object 4 (generally an artificial satellite) is installed and supported by the three-degree-of-freedom motion system 3.

[0028] The structure of each part will be described in detail below with reference to the accompanying drawings.

[0029] See also Figure 2 , is a schematic diagram of the frame structure of the dual-degree-of-freedom tracking slide platform of the present invention, wherein the dual-degree-of-freedom tracking slide platform 1 is composed of two mutually parallel first slide rails 5, a second slide rail 6, and a third slide rail 7 horizontally placed on the first slide rail 5 and the second slide rail 6. The three slide rails are all equipped with a slide motor 8, which is driven by the motor to slide the third slide rail 7 along the first slide rail 5 and the second slide rail 6 in conjunction with a transmission structure such as a belt or chain, and drives the active constant force system 2 to slide along the third slide rail 7, thereby realizing dual-degree-of-freedom movement of the active constant force system 2.

[0030] See also Figure 3, is a schematic diagram of the overall structure of the active constant force system of the present invention. The active constant force system includes a sliding seat, which is slidably mounted on the third slide rail 7. A winding motor 9 is fixedly mounted above the sliding seat, and an upper connecting plate 13 is fixedly mounted below the sliding seat. A circular hole is reserved in the center of the upper connecting plate 13, and parallel mechanisms are installed along the circumference of the upper connecting plate 13. The upper connecting plate 13 is connected to the lower connecting plate 18 through the parallel mechanism. The center of the lower connecting plate 18 also has a circular hole. The output shaft of the winding motor 9 is mounted with a winding wheel 10. The cable 11 is wound on the winding wheel 10. Its free end passes downward through the guide wheel 12 on the sliding seat, the upper connecting plate 13, and the central circular hole of the lower connecting plate 18, and is connected to the hinge 31 of the three-degree-of-freedom motion system. A cable traction device 19 and an angle measuring device 20 are installed above and below the lower connecting plate 18, respectively. The cable 11 passes through the cable traction device 19, and its swing angle is measured by the angle measuring device 20.

[0031] Figure 4 This is a partial view of the parallel mechanism of the present invention. Figure 1 , Figure 5 This is a partial view of the parallel mechanism of the present invention. Figure 2 ; Combine Figure 3 The parallel mechanism includes two active action arms and one passive arm. The active action arms include an active arm 15 and a passive arm 16. The upper end of the active arm 15 is fixed to the output shaft of the action motor 14, which is mounted on the upper connecting plate 13. The lower end of the active arm 15 is hinged to the passive arm 16, and the lower end of the passive arm 16 is hinged to the lower connecting plate 18. The two active action arms are each driven by an action motor 14 to rotate the active arm 15, thereby causing the lower connecting plate 18 to move. The passive arm 17 has no power components. Its upper end is hinged to the upper connecting plate 13 and its lower end is hinged to the lower connecting plate 18. The passive arm 17 cooperates with the two active action arms to drive the lower connecting plate 18 to move, thereby following the movement of the cable 11.

[0032] In the parallel mechanism, see Figure 5 The frame structures of the driven arm 16 and the passive arm 17 are the same, the difference is that the overall size of the passive arm 17 is larger than that of the driven arm 16, so as to adapt to the size of the active action arm. They both include two vertically parallel first long rods 21 and second long rods 22, and two horizontally parallel first short rods 23 and second short rods 24. The upper and lower ends of the first long rod 21 and the second long rod 22 are respectively hinged to the upper connecting plate 13 and the lower connecting plate 18, and the two ends of the first short rod 23 and the second short rod 24 are respectively hinged to the first long rod 21 and the second long rod 22. The four rods form a four-bar structure.

[0033] See also Figure 6, is a structural schematic diagram of the cable traction device of the present invention, wherein (a) is an external view and (b) is an internal component view; the cable traction device 19 includes two upper guide wheels 25 and two lower guide wheels 26, the axis center lines of the upper guide wheels 25 and the axis center lines of the lower guide wheels 26 are perpendicular to each other, and the cable 11 passes between the two upper guide wheels 25 and between the two lower guide wheels 26 in sequence.

[0034] See also Figure 7 , a schematic diagram of the structure of the angle measuring device according to the present invention, shows a first measuring rod 27 and a second measuring rod 28 mounted below the lower connecting plate 18 via a bracket. Both measuring rods are L-shaped, with strip holes defined in their lower crossbars. The strip holes in the two measuring rods are perpendicular to each other, and the cable 11 passes through the overlapping portion of the two strip holes. A first digital encoder 29 and a second digital encoder 30 are also mounted on the brackets, with the first digital encoder 29 corresponding to the second measuring rod 28 and the second digital encoder 30 corresponding to the first measuring rod 27, respectively, to measure the swing of the cable 11 in both directions.

[0035] The three-degree-of-freedom motion system includes a hinge 31, a U-shaped frame 32 and a ring frame 33, see Figure 3 The upper part of the U-shaped frame 32 is hingedly mounted on the hinge 31 and can rotate circumferentially relative to the hinge 31. The two arms of the U-shaped frame 32 are respectively hingedly connected to one side of the annular frame 33. The annular frame 33 can flip relative to the U-shaped frame 32. The simulant 4 is mounted inside the annular frame 33 and can realize circumferential rotation of the simulant 4 relative to the annular frame 33, that is, rotation along its own axis. The annular frame 33 can drive the simulant 4 to realize flipping movement relative to the U-shaped frame 32, and the U-shaped frame 32 can drive the simulant to realize its overall rotation movement in the horizontal plane.

[0036] This paper constructs a virtual prototype to verify the effectiveness and correctness of the proposed control method. The constant-force system utilizes the sliding membrane control method from existing references, while the follower system utilizes the impedance controller proposed in this paper. The initial sling length (suspension height) of the virtual prototype is set to 1 meter. To simulate spacecraft collision conditions, a rigid body with a mass of 10 kg is used to simulate the target spacecraft to be unloaded. A rigid body of equal mass is used to impact the target spacecraft at a horizontal velocity of 0.5 m / s to simulate a sudden acceleration change. The simulation results are as follows: The interference force provided by the collision causes a sudden change in the acceleration of the unloaded target, resulting in a significant deviation in the cable's swing angle of approximately ±0.047 rad. The two rigid bodies then separate and remain floating. Throughout the process, the cable's deflection angle remains within a range of ±0.02 rad, and the time integral of each swing angle also remains within ±0.02. The parallel mechanism within the follower system actuator provides a sufficiently large acceleration to the suspension point during impact. Throughout the entire process, the acceleration of the dual-degree-of-freedom tracking slide platform remains low, with a maximum value of approximately 0.6 m / s. 2 , approximately one-quarter of the maximum acceleration at the upper end of the cable. Throughout this process, the parallel mechanism's maximum displacement relative to the end of the dual-DOF tracking slide platform was 0.105 m, followed by a rapid reset. The horizontal force error of the servo system was less than 5% of the force due to gravity. This validates the effectiveness and correctness of the rapid tracking device and control method of the present invention.

Claims

1. A fast tracking device for a gravity unloading system, comprising a two-degree-of-freedom tracking slide platform, an active constant force system, and a three-degree-of-freedom motion system; The dual-degree-of-freedom tracking slide platform realizes the sliding motion of the active constant force system along the x-axis and the y-axis; The active constant force system includes a sliding seat, which is slidably mounted on the third slide rail, a winding motor is fixedly installed above the sliding seat, and an upper connecting plate is fixedly installed below the sliding seat, a circular hole is reserved in the center of the upper connecting plate, and a parallel mechanism is installed along the circumference of the upper connecting plate, the upper connecting plate is connected to the lower connecting plate through the parallel mechanism, and a circular hole is also opened in the center of the lower connecting plate; a winding wheel is installed on the output shaft of the winding motor, and the cable is wound on the winding wheel, and the free end of the cable passes downward through the guide wheel on the sliding seat, the upper connecting plate and the central circular hole of the lower connecting plate in sequence, and then is connected to the three-degree-of-freedom motion system; The parallel mechanism includes two active action arms and one passive arm, and the active action arms include an active arm and a passive arm. The upper end of the active arm is fixed to the output shaft of the action motor, and the action motor is installed on the upper connecting plate. The lower end of the active arm is hinged to the passive arm, and the lower end of the passive arm is hinged to the lower connecting plate. The two active action arms are respectively driven by an action motor to rotate the active arm; the upper end of the passive arm is hinged to the upper connecting plate, and the lower end is hinged to the lower connecting plate. The passive arm cooperates with the two active action arms to drive the lower connecting plate to move. The three-degree-of-freedom motion system is used to install a simulation object and realize the movement of the simulation object in three degrees of freedom directions.

2. The fast tracking device for a gravity unloading system according to claim 1, further characterized in that: A cable pulling device and an angle measuring device are installed above and below the lower connecting plate, respectively. The cable passes through the cable pulling device, and its swing angle is measured by the angle measuring device. The cable traction device includes two upper guide wheels and two lower guide wheels, the axis lines of the two upper guide wheels are perpendicular to the axis lines of the two lower guide wheels, and the cable passes between the two upper guide wheels and between the two lower guide wheels in sequence; The angle measuring device is installed under the lower connecting plate, and the first measuring rod and the second measuring rod are installed respectively through two brackets. The two measuring rods are L-shaped, and the cross bar parts below them are provided with strip holes. The strip holes of the two measuring rods are perpendicular to each other, and the cable passes through the overlapping part of the two strip holes; and the first digital encoder and the second digital encoder are also installed on the two brackets respectively.

3. The fast tracking device for a gravity unloading system according to claim 1 or 2, further characterized in that: The passive arm includes two vertically parallel first long rods and second long rods, and two horizontally parallel first short rods and second short rods. The upper and lower ends of the first long rod and the second long rod are hinged to the upper connecting plate and the lower connecting plate respectively, and the two ends of the first short rod and the second short rod are hinged to the first long rod and the second long rod respectively. The four rods form a four-bar structure.

4. The fast tracking device for a gravity unloading system according to claim 3, further characterized in that: The structural composition of the driven arm is the same as that of the passive arm.

5. The fast tracking device for a gravity unloading system according to claim 1 or 2, further characterized in that: The dual-degree-of-freedom tracking slide platform consists of two mutually parallel first slide rails, a second slide rail, and a third slide rail that crosses the first and second slide rails; the third slide rail can slide along the first and second slide rails, and the active constant force system can slide along the third slide rail.

6. The fast tracking device for a gravity unloading system according to claim 1, further characterized in that: The three-degree-of-freedom motion system includes a hinge, a U-shaped frame and a ring frame. The upper part of the U-shaped frame is hingedly mounted on the hinge and can rotate circumferentially relative to the hinge. The two arms of the U-shaped frame are respectively hingedly connected to one side of the ring frame. The ring frame can flip relative to the U-shaped frame. The simulation object is mounted inside the ring frame and can rotate around its central axis.

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