Rapid tracking device applied to gravity unloading system

Abstract

The invention provides a rapid tracking device applied to a gravity unloading system, and aims to improve the following precision of a follow-up system and avoid vibration and impact in the system caused by sudden acceleration change of a two-degree-of-freedom motion platform at the same time. Comprising a two-degree-of-freedom tracking slide rail platform, an active constant force system and a three-degree-of-freedom motion system, the two-degree-of-freedom tracking slide rail platform realizes the sliding motion of the active constant force system along the x axis and the y axis; the active constant force system is used for controlling motion distribution so as to reduce the acceleration of the two-degree-of-freedom tracking slide rail platform; and the three-degree-of-freedom motion system is used for installing a simulant and realizing actions of the simulant in 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 freedom, and reconstructs the movement of the spacecraft in outer space on the ground to improve the fidelity of its ground verification. Currently, a variety of gravity unloading methods have been proposed, such as the drop tower method, air bearing method, neutral buoyancy method, and suspension method.

[0003] The suspension method is widely used because of its advantages such as simple implementation, adjustable force, high simulation accuracy and small additional inertia. The suspension gravity unloading system is mainly composed of a horizontal position follower system that keeps the rope vertical and a constant force system that keeps the rope force constant. Compared with the constant force system, the follower system has more degrees of freedom and complex structure. It mostly uses rectangular coordinates or polar coordinates, and its mechanism mass is huge. This limits its dynamic performance, resulting in large following errors under working conditions with sudden acceleration changes such as rapid deployment, docking and collision of spacecraft. When the spacecraft contacts or collides with other objects, the two accelerations of the upper end of the cable in the horizontal plane and the avoidance force will change dramatically. At this time, the follower system needs to provide sufficient acceleration to the upper end of the cable to ensure good control accuracy. This places very demanding requirements on the stiffness of the drive mechanism and the power of the active components in the large follower system. Excessive acceleration and sudden changes in acceleration may cause vibration and shock in the mechanical structure, thereby 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 a gravity unloading system, aiming to improve the tracking accuracy of the follow-up system and avoid the vibration and impact inside the system caused by the sudden change of acceleration of the two-degree-of-freedom motion platform.

[0005] The technical solution adopted by the present invention is as follows: a fast tracking device applied to a gravity unloading system, comprising a dual-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 comprises a sliding seat, which is slidably mounted on the third slide rail, a winding motor is fixedly installed above the sliding seat, an upper connecting plate is fixedly installed below the sliding seat, a circular hole is reserved in the center of the upper connecting plate, 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, 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 turn, and then is connected to the three-degree-of-freedom motion system;

[0008] The parallel mechanism comprises two active action arms and one passive arm, the active action arm comprises an active arm and a passive arm, the upper end of the active arm is fixed on the output shaft of the action motor, the action motor is mounted 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, and 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 the simulation object and realize the movement of the simulation object in three degrees of freedom.

[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 comprises 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 a first measuring rod and a second measuring rod are installed respectively through two brackets. The two measuring rods are both L-shaped, and strip holes are provided in the cross bar parts below them. The strip holes of the two measuring rods are perpendicular to each other, and the cable passes through the overlapping parts of the two strip holes; and a first digital encoder and a second digital encoder are also installed respectively on the two brackets.

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

[0014] The dual-freedom tracking slide platform consists of two mutually parallel first slides, a second slide, and a third slide transversely placed on the first and second slides; the third slide can slide along the first and second slides, and the active constant force system can slide along the third slide.

[0015] The three-degree-of-freedom motion system includes a hinge, a U-shaped frame and an annular frame. The upper part of the U-shaped frame is hingedly installed 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 annular frame. The annular frame can flip relative to the U-shaped frame. The simulation object can be installed inside the annular frame so as to 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, and the four guide wheels inside it jointly promote the rapid movement of the cable in the horizontal plane. 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 follow-up 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 an internal component view;

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

[0026] In the figure: 1. dual-degree-of-freedom tracking slide platform, 2. active constant force system, 3. three-degree-of-freedom motion system, 4. analog object, 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. The entire rapid tracking device can be supported by a conventional frame. 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 suspended and 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 is 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, and each of the three slide rails is equipped with a slide rail motor 8, which cooperates with a transmission structure such as a belt or chain to drive the third slide rail 7 to slide along the first slide rail 5 and the second slide rail 6, and drives the active constant force system 2 to slide along the third slide rail 7, thereby realizing the 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, the sliding seat is slidably mounted on the third slide rail 7, a winding motor 9 is fixedly installed above the sliding seat, and an upper connecting plate 13 is fixedly installed below the sliding seat, a circular hole is reserved in the center of the upper connecting plate 13, and a parallel mechanism is 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, and a circular hole is also opened in the center of the lower connecting plate 18. The output shaft of the winding motor 9 is installed with a winding wheel 10, and the cable 11 is wound on the winding wheel 10, and 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 in turn, 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, and the active action arms include an active arm 15 and a passive arm 16. The upper end of the active arm 15 is fixed on the output shaft of the action motor 14, and the action motor 14 is installed 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 driven by an action motor 14 to rotate the active arm 15, thereby driving the lower connecting plate 18 to move. The passive arm 17 has no power components, and 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 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, and they both include two first long rods 21 and second long rods 22 arranged vertically in parallel, and two first short rods 23 and second short rods 24 arranged horizontally in parallel, 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, 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, and the four rod bodies form a four-bar structure.

[0033] See also Figure 6, is a schematic diagram of the structure 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 lines of the upper guide wheels 25 and the axis 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 , is a schematic diagram of the structure of the angle measuring device of the present invention. A first measuring rod 27 and a second measuring rod 28 are installed below the lower connecting plate 18 through a bracket. Both measuring rods are L-shaped, and a strip hole is provided in the cross bar below them. The strip holes of the two measuring rods are perpendicular to each other, and the cable 11 passes through the overlapping part of the two strip holes. A first digital encoder 29 and a second digital encoder 30 are also installed on the bracket, wherein the first digital encoder 29 is installed corresponding to the second measuring rod 28, and the second digital encoder 30 is installed corresponding to the first measuring rod 27, so as to measure the swing of the cable 11 in two directions respectively.

[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 installed 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 installed inside the annular frame 33, and the simulant 4 can rotate circumferentially relative to the annular frame 33, that is, rotate 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] The present invention verifies the effectiveness and correctness of the control method of the proposed system by building a virtual prototype. The constant force system adopts the synovial control method in the existing references, and the follower system adopts the impedance controller proposed in this paper. The initial sling length (suspension height) of the virtual prototype is set to 1m. In order to simulate the collision condition of the spacecraft, a rigid body with a mass of 10kg is used to simulate the target spacecraft that needs to be unloaded. A rigid body of equal mass is used to hit the target spacecraft at a horizontal speed of 0.5m / s to simulate the working condition of the acceleration mutation. The simulation results are as follows: the interference force provided by the collision causes the acceleration of the unloading target to change suddenly, and the swing angle deviation of the cable is large during this process, which is about ±0.047rad. Then, the two rigid bodies are separated and kept floating. In the subsequent process, the deflection angle of the cable is kept within the range of ±0.02rad, and the time integral of each swing angle is also kept within ±0.02. The parallel mechanism in the actuator of the driven system provides a sufficiently large acceleration for the suspension point during the impact. Throughout the process, the acceleration of the dual-degree-of-freedom tracking slide platform is kept at a low level, and its maximum value is about 0.6m / s 2 , which is about one-fourth of the maximum acceleration of the upper end of the cable. During the whole process, the maximum displacement of the parallel mechanism relative to the end of the dual-freedom tracking slide platform is 0.105m, and then it is quickly reset. The force error of the follow-up system in the horizontal direction is less than 5% of the gravity. The effectiveness and correctness of the fast tracking device and its control method of the present invention are verified.

Claims

1. A fast tracking device applied to a gravity unloading system, comprising a dual-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 comprises a sliding seat, which is slidably mounted on the third slide rail, a winding motor is fixedly installed above the sliding seat, an upper connecting plate is fixedly installed below the sliding seat, a circular hole is reserved in the center of the upper connecting plate, 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, 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 turn, and then is connected to the three-degree-of-freedom motion system; The parallel mechanism comprises two active action arms and one passive arm, the active action arm comprises an active arm and a passive arm, the upper end of the active arm is fixed on the output shaft of the action motor, the action motor is mounted 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, and 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 the simulation object and realize the movement of the simulation object in three degrees of freedom.

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 comprises 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 a first measuring rod and a second measuring rod are installed respectively through two brackets. The two measuring rods are both L-shaped, and strip holes are provided in the cross bar parts below them. The strip holes of the two measuring rods are perpendicular to each other, and the cable passes through the overlapping parts of the two strip holes; and a first digital encoder and a second digital encoder are also installed respectively on the two brackets.

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 first long rods and a second long rod arranged vertically in parallel, and two first short rods and a second short rod arranged horizontally in parallel. The upper and lower ends of the first long rod and the second long rod are respectively hinged to the upper connecting plate and the lower connecting plate, and the two ends of the first short rod and the second short rod are respectively hinged to the first long rod and the second long rod, and the four rod bodies 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-freedom tracking slide platform consists of two mutually parallel first slides, a second slide, and a third slide transversely placed on the first and second slides; the third slide can slide along the first and second slides, and the active constant force system can slide along the third slide.

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 an annular frame. The upper part of the U-shaped frame is hingedly installed 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 annular frame. The annular frame can flip relative to the U-shaped frame. The simulation object can be installed inside the annular frame so as to rotate around its central axis.

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