An omnidirectional controllable wheeled end effector for derotation of space debris

Abstract

The present invention discloses an omnidirectional, controllable wheeled end effector for derotating space debris. The end effector comprises a spherical wheel arm, three drive units, a universal bearing, a fastening bracket, and a connecting flange. One end of each drive unit is connected to the connecting flange, while the other end of each drive unit contacts the spherical wheel arm. One end of the fastening bracket is connected to the connecting flange, while the other end of the fastening bracket is connected to the spherical wheel arm via the universal bearing. By controlling the end effector, the present invention achieves derotation by slowly exchanging energy between the manipulator and the debris through friction, effectively improving operational safety.

Description

Technical Field

[0001] The present invention belongs to the technical field of supporting the development of space missions such as aerospace operations, lunar exploration, interstellar exploration, and on-orbit services, and in particular relates to an omnidirectional controllable wheeled end effector for derotating space debris. Background Art

[0002] Space debris primarily originates from large rocket upper stages, failed satellites, and secondary debris generated by collisions. According to statistics, there are approximately hundreds of millions of pieces of debris of varying sizes floating in Earth's orbit. It can be said that five percent of spacecraft are surrounded by ninety-five percent of the debris. These debris are often non-cooperative and have lost the ability to adjust their attitude. They operate in an uncontrolled state for extended periods, often experiencing tumbling motions due to perturbations such as solar pressure and gravity gradients, as well as their residual angular momentum before failure. Direct capture of these debris carries the risk of collision, so de-rotation followed by capture is a more appropriate approach to mitigate this risk.

[0003] Derotation methods can be categorized into contact and non-contact methods, depending on whether or not contact is established. Contact derotation is currently the mainstream derotation method due to its simplicity and low cost. Typical contact derotation methods include deceleration brush derotation, mechanical pulse derotation, and flexible tether derotation. The deceleration brush, a type of end effector for a robotic arm, was first proposed by JAXA[X] in Japan. It is a variable-stiffness brush that applies a derotation torque by gently touching the surface of the target debris. A typical example is the deceleration brush derotation device designed by Nishida[X]. Mechanical pulse derotation changes the target's posture by applying an impulse to the target. A typical example is Matungaga[X]'s use of an elastic ball as an end effector. Furthermore, Yoshikawa[X] utilized the pulse force generated by multiple contact collisions to attenuate the target debris's nutation angle and spin velocity, thereby suppressing angular momentum. However, due to its limited mechanism of action, this method cannot achieve on-orbit derotation of large targets. The European Space Agency [X] has proposed using a flying net system for debris removal. A capture mechanism releases the net approximately 15 meters from the target debris, sequentially completing five actions: launching, opening, enveloping, retracting, and dragging. The target is then captured and towed into a discarded orbit. After the net separates from the target, it returns to its mission orbit to prepare for the next mission. Flexible tethers are prone to tangling during the capture and despinning process, and once tangled, they are difficult to untangle on their own.

[0004] In summary, the tumbling and spinning of space debris poses significant risks to on-orbit operations. Currently, derotation technology remains at a theoretical level, with no mature technology capable of direct contact operation. Whether using deceleration brushes, mechanical pulses, continuum systems, or soft-body derotation solutions, none can effectively address the challenges posed by high-speed spin. Summary of the Invention

[0005] The technical problem solved by the present invention is: to overcome the shortcomings of the existing technology and provide an omnidirectional controllable wheeled end effector for derotation of space debris. By controlling the end effector, slow energy exchange between the robotic arm and the debris by friction is achieved to achieve the purpose of derotation, which can effectively improve the safety of operation.

[0006] The object of the present invention is achieved through the following technical solution: an omnidirectional controllable wheeled end effector for derotation of space debris, comprising: a spherical wheel arm, three drive devices, a universal bearing, a fastening bracket and a connecting flange; wherein, one end of each drive device is connected to the connecting flange, and the other end of each drive device is in contact with the spherical wheel arm; one end of the fastening bracket is connected to the connecting flange, and the other end of the fastening bracket is connected to the spherical wheel arm through the universal bearing.

[0007] In the above-mentioned omnidirectional controllable wheeled end effector for derotating space debris, each drive device includes a Mecanum wheel, a motor flange, a motor and a motor bracket; wherein one end of the motor bracket is connected to the connecting flange, and the other end of the motor bracket is connected to the motor; the output shaft of the motor is connected to the Mecanum wheel through the motor flange; and the Mecanum wheel is in contact with the spherical wheel hand.

[0008] In the above-mentioned omnidirectional controllable wheeled end effector for derotation of space debris, the three driving devices form an angle of 120° with each other on the horizontal projection plane; the angle between the axis of each driving device and the horizontal line is 60°.

[0009] In the above-mentioned omnidirectional controllable wheeled end effector for derotation of space debris, the center of the Mecanum wheel is defined as the origin O, the rotation axis is the z-axis, the parallel fastening bracket pointing to the outside of the wheel arm is the y-axis, and the x-axis is determined according to the right-hand rule; the radius r is the circumferential radius formed by the roller envelope of the Mecanum wheel; h is the wheel width; the roller axis is the line segment AB, the curve of the roller is the curve AB, point C is located on the curve AB and contacts the ground, the line segment OC is ⊥ the line segment AB, and the line segment OC intersects the line segment AB at point D; B′, C′, and D′ are the projections of points BCD, respectively; and α is the offset angle of the roller.

[0010] In the above-mentioned omnidirectional controllable wheeled end effector for derotation of space debris, the curve AB rotates around the axis AB to generate a roller surface, and the number N of rollers satisfies Nγ≥2π; where γ is the angle between the line segment AO′ and the line segment O′B′.

[0011] In the above-mentioned omnidirectional controllable wheeled end effector for derotation of space debris, the length of the line segment OD is:

[0012]

[0013] Among them, l OD is the length of line segment OD, θ is the angle between line segment AO′ and line segment O′C′, and γ is the angle between line segment AO′ and line segment O′B′.

[0014] In the above-mentioned omnidirectional controllable wheeled end effector for derotation of space debris, curve AB is represented as:

[0015]

[0016] Where θ is the angle between line segment AO′ and line segment O′C′, γ is the angle between line segment AO′ and line segment O′B′, and x, y, and z represent the projection of curve AB on the O′XYZ coordinate system.

[0017] In the above-mentioned omnidirectional controllable wheeled end effector for derotation of space debris, the motion speed v of the Mecanum wheel relative to the spherical surface ∑ of the spherical wheel hand is Σ for:

[0018] v Σ =v D +v DC +v CΣ ;

[0019] Among them, v D is the velocity of the roller center of the Mecanum wheel, v DC is the velocity of the Mecanum wheel roller and the spherical wheel hand contact point relative to the roller center, v CΣ is the slip speed between point C and the spherical surface of the spherical wheel.

[0020] In the above-mentioned omnidirectional controllable wheeled end effector for derotation of space debris, the speed of the roller of the Mecanum wheel and the contact point of the spherical wheel hand relative to the center of the roller is v DC for:

[0021]

[0022] Where θ is the angle between line segment AO′ and line segment O′C′, γ is the angle between line segment AO′ and line segment O′B′, and ω is the rotation speed of the Mecanum wheel driven by the motor.

[0023] In the above-mentioned omnidirectional controllable wheeled end effector for derotation of space debris, the motion speed v of the roller center of the Mecanum wheel is D for:

[0024] v D =[-l OD ·sinθ·ωl OD ·cosθ·ω0] T ;

[0025] Among them, lOD is the length of line segment OD, θ is the angle between line segment AO′ and line segment O′C′, and ω is the rotation speed of the Mecanum wheel driven by the motor.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] The present invention achieves the purpose of derotation by controlling the end effector to realize slow energy exchange between the robot arm and the debris in a frictional manner, thereby effectively improving the safety of operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiment below. The accompanying drawings are for illustration purposes only and are not to be considered as limiting the present invention. The same reference symbols are used throughout the drawings to represent the same components. In the drawings:

[0029] Figure 1 1 is a schematic structural diagram of an omnidirectional controllable wheeled end effector for derotation of space debris provided by an embodiment of the present invention;

[0030] Figure 2 Schematic diagram of the derotation working principle of an omnidirectional controllable wheeled end effector for derotation of space debris provided by an embodiment of the present invention;

[0031] Figure 3 Schematic diagram of a mathematical model of a Mecanum wheel provided by an embodiment of the present invention;

[0032] Figure 4 Schematic diagram of coordinate definition of a system consisting of multiple arms and target fragments provided by an embodiment of the present invention;

[0033] Figure 5 is a schematic diagram of the coordinate definition of the end effector provided by an embodiment of the present invention;

[0034] Figure 6 It is a stereoscopic diagram of an omnidirectional controllable wheeled end effector for derotating space debris provided by an embodiment of the present invention. DETAILED DESCRIPTION

[0035] The exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the accompanying drawings, it should be understood that the present disclosure can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to enable a more thorough understanding of the present disclosure and to fully convey the scope of the present disclosure to those skilled in the art. It should be noted that, unless there is a conflict, the embodiments of the present disclosure and the features described in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0036] Figure 1 1 is a schematic structural diagram of an omnidirectional controllable wheeled end effector for derotation of space debris provided by an embodiment of the present invention; Figure 6 FIG is a perspective view of an omnidirectional controllable wheeled end effector for derotating space debris provided by an embodiment of the present invention. Figure 1 and Figure 6 As shown, the omnidirectional controllable wheeled end effector for derotation of space debris comprises: a spherical wheel hand 1, three drive devices, a universal bearing 2, a fastening bracket 3 and a connecting flange 8; wherein,

[0037] One end of each driving device is connected to the connecting flange 8, and the other end of each driving device is in contact with the spherical wheel hand 1; one end of the fastening bracket 3 is connected to the connecting flange 8, and the other end of the fastening bracket 3 is connected to the spherical wheel hand 1 through the universal bearing 2; the three driving devices form an angle of 120° with each other on the horizontal projection plane.

[0038] like Figure 1 and Figure 6 As shown, each drive unit includes a Mecanum wheel 4, a motor flange 5, a motor 6, and a motor bracket 7. One end of the motor bracket 7 is connected to the connecting flange 8, and the other end of the motor bracket 7 is connected to the motor 6. The output shaft of the motor 6 is connected to the Mecanum wheel 4 through the motor flange 5. The Mecanum wheel 4 contacts the spherical wheel handle 1. The angle between the axis of the drive unit and the horizontal line is 60°.

[0039] A symmetrically distributed design achieves symmetrical decoupling between the power source and output, enabling better omnidirectional control. The motor is connected to the omnidirectional wheel via an adapter flange; the two together form a single drive source, with the three drive sources forming a 120° angle with each other in horizontal projection. Whether the omnidirectional wheel and the intermediate spherical wheel handle can achieve frictional control is a major factor limiting the performance of the designed end effector. A Mecanum wheel consists of a hub and several rollers arranged diagonally on its rim. These rollers have a unique generatrix, with a cylindrical envelope, enabling forward rolling. These rollers also convert the wheel's steering force into an axial force (i.e., normal force). By combining the different rotational speeds of the three wheels, the required torque and velocity on the spherical wheel handle surface can be synthesized, thus enabling omnidirectional control of the spherical wheel handle. Furthermore, the Mecanum wheel offers advantages such as compact structure, strong load-bearing capacity, and easy installation and control. Therefore, the Mecanum wheel was chosen as the omnidirectional wheel.

[0040] The point of tangency between the Mecanum wheels and the spherical hand is located at a 45° angle below the zenith of the sphere. Three Mecanum wheels support the central spherical hand. The hand's surface is roughened to minimize slippage between the Mecanum wheels and the hand during movement. A fastening bracket is mounted on the bottom flange at one end, and a universal bearing is installed on the other end, providing restraint for the spherical hand to prevent escape during derotation. The universal bearing gently contacts the spherical hand and has a low coefficient of friction, minimizing friction during hand rotation. Motor brackets corresponding to the three drive sources secure the motors and feature radial fine-tuning capabilities. By controlling the radial distance, the pressure between the Mecanum wheels and the hand is adjusted to achieve automatic disengagement of the mechanism. The entire system is mounted on a standardized connecting flange, enabling connection to different robot end-effectors and facilitating quick assembly and disassembly of the end effector. This end effector for target derotation boasts a lightweight structure, flexible actuation, and simple control.

[0041] Considering the characteristics of space debris, such as unknown large target mass, large external structure size, large residual angular velocity and angular momentum, and unknown surface shape, the omnidirectional controllable wheeled end effector designed in this paper can be installed at the end of multiple robotic arms to achieve dynamic adhesion, derotation, capture and manipulation of the target, such as Figure 2 As shown. The specific working principle is that a multi-arm composite aircraft equipped with the designed end effector of the present invention achieves dynamic "adhesion" by tracking and following large space debris. The aircraft and the target debris form multiple points of contact based on the end effector. These contact points form a virtual "ball and socket" that can adapt to targets with various surface morphological characteristics. When the target spins, the multi-arm dynamically adjusts through the appropriate disk structure to implement constraint-level control on the target, rather than holding it tightly, avoiding the risks brought by the violent momentum exchange caused by instantaneous contact. When passively following, the end effector can generate a small friction force between the contact surface and the target debris. When actively controlling, it can output the required direction and magnitude of the derotation torque to the target according to demand. Through active and passive control of the target momentum exchange process, the target is slowly and process-controlled "braking" operation, thereby achieving the purpose of debris derotation. When the residual angular velocity of the space debris is reduced, it becomes simple and easy to capture and manipulate it.

[0042] The kinematic mapping relationships between the motor and the spherical wheel arm, and vice versa, between the spherical wheel arm and the target object are key to achieving stable control of the end effector and achieving target derotation. A mathematical model of the Mecanum wheel was established, and its kinematic characteristics were analyzed. Based on this model, a kinematic model reflecting the constraint relationship between the motor and the target object was developed, revealing the mapping relationship between the two.

[0043] The first choice is to establish a mathematical model of the Mecanum wheel such as Figure 3 As shown. The center of the Mecanum wheel is defined as the origin O, the axis of rotation is the z-axis, the parallel fastening bracket pointing to the outside of the wheel handle is the y-axis, and the x-axis is determined according to the right-hand rule. The radius r is the radius of the circle formed by the envelope of the Mecanum wheel roller; h is the wheel width; line segment AB is the roller axis, curve AB is the curve of the roller, point C is located on the curve and in contact with the ground, OC⊥AB, OC intersects curve AB at point D; B′C′D′ are the projections of points BCD respectively; α is the offset angle of the roller. Rotating curve AB around axis AB generates the roller surface. The number of rollers N should satisfy Nγ≥2π to ensure that the envelope of the roller forms a continuous circle and that the Mecanum wheel operates normally and smoothly.

[0044] By analyzing the established mathematical model, the length of line segment OD can be obtained as:

[0045]

[0046] Where θ is the angle between line segment AO′ and line segment O′C′, and γ is the angle between line segment AO′ and line segment O′B′.

[0047] Curve AB can be expressed as:

[0048]

[0049] The Mecanum wheel and the wheel hand spherical surface ∑ are tangent at point C. The speed of the Mecanum wheel relative to the wheel hand spherical surface ∑ is defined as v Σ , according to the constructed model:

[0050] v Σ =v D +v DC +v CΣ (3)

[0051] Where, v DC The direction can be expressed as e OC ×e AB ·signω, sign represents the sign of the variable, representing v DC The same as the direction of rotation. The Mecanum wheel roller has a driven characteristic, and its angular velocity is affected by the direction and speed of the wheel rotation. When the direction of the Mecanum wheel movement changes, the direction of rotation of the roller will also change, showing a driven characteristic. From this, we can get:

[0052]

[0053] v D The direction can be expressed as z×e CD ·signω, of size:

[0054] vD =[-l OD ·sinθ·ω l OD ·cosθ·ω 0] T (5)

[0055] There is rolling friction between the Mecanum wheel and the wheel handle, and there is no relative displacement, so v CΣ =O.

[0056] In summary, we can get:

[0057]

[0058] The above establishes the relationship between the hand contact point and the rotational speed of the Mecanum wheel and the spherical wheel, laying the foundation for the subsequent system kinematic analysis.

[0059] The mapping relationship between the target object and the end effector, and between the spherical wheel hand and the contact point is established, and then Equation (6) is used to finally obtain the inverse kinematics relationship of the system, that is, the relationship between the target object and the motor speed. Based on this, the derotation operation of the target object can be completed stably and controllably.

[0060] The motion modeling of the system consisting of multiple arms and target fragments is carried out, such as Figure 4 and Figure 5 As shown. First define the relevant coordinate system: o x o y o z o is the target object coordinate system, O bi x bi y bi z bi is the wheel hand coordinate system of the i-th wheel hand, whose origin is O bi is the geometric center of the wheel. k x k y k z k The coordinate system of the kth Mecanum wheel of the designed end effector is the wheel system. Its origin is located at the geometric center of the Mecanum wheel, the z-axis is parallel to the output shaft of the drive motor, the y-axis is parallel to the fastening bracket and points to the outside of the wheel hand, and the x-axis is determined according to the right-hand rule. b The first wheel is on the first axis, and the order is counterclockwise.

[0061] Assume that any hand coordinate system O bi x bi y bi z bi From the target object coordinate system O o x o y o z o Around K iAxis rotation θ i Angle is obtained, where k i The axis can be represented as k i =[k xi k yi k zi ] T , the transformation matrix between the target object and the spherical wheel hand is:

[0062]

[0063] ω o =∑ O J bi ·ω bi (8)

[0064] Where, ω o is the moving speed of the target object, ω bi is the speed of the i-th wheel hand, k xi 、k yi 、k zi The rotation axis k i In coordinate system O o x o y o z o The projection on the image, cθ and sθ are the rotation angles θ i The above establishes the motion relationship between the target object and the end effector spherical wheel hand.

[0065] Assume that the gear train coordinate system O bi x bi y bi z bi In the wheel hand coordinate system O bi x bi y bi z bi The deflection angle is [α i β i γ i ], then the wheel hand coordinate system O of the i-th wheel hand bi x bi y bi z bi With the wheel hand coordinate system O bi x bi y bi z bi The transformation matrix between is:

[0066]

[0067] Combining equations (6) and (9), we can obtain:

[0068]

[0069] Where, O J bi is the transformation matrix between the target object and the spherical wheel hand, b J i is the transformation matrix between the i-th gear train and the spherical wheel hand, R is the radius of the spherical wheel hand, v Σ is the speed of the Mecanum wheel relative to the wheel hand spherical surface ∑, α i , β i , γ i is the gear train coordinate system O bi x bi y bi z bi In the wheel hand coordinate system O bi x bi y bi z bi The above equations establish the kinematic relationship between the target object and the end effector's spherical wheel. The above equations reflect the relationship between the end effector's motor speed and the target object's speed. Based on this, the position of the target fragment can be indirectly controlled by controlling the motor.

[0070] The present invention uses three Mecanum wheels symmetrically distributed to achieve omnidirectional control, and has the advantages of light structure, flexible drive, and simple control. The present invention indirectly controls the spherical wheel arm by controlling the Mecanum wheels, and on this basis uses the slow energy exchange of friction between the spherical wheel arm and the target object to achieve the purpose of derotation, subverting the traditional concept of robot control, and using the idea of ​​"using small to win big" to achieve the purpose of "using weak to control strong". Through the symmetrical structural distribution, the present invention achieves kinematic decoupling of the contact relationship between the robot arm and the target fragments in a certain dimension during the derotation process, thereby improving the safety of capturing high-speed spinning targets. The present invention applies slow and process-controllable friction to the target fragments through the central spherical wheel arm, which is a handleless control. It does not require the target to be equipped with a target hand that matches the end effector. It has low requirements on the "handle" and morphological characteristics of the target surface, and can implement control for any irregular target.

[0071] Although the present invention has been disclosed above in terms of preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications to the technical solutions of the present invention by using the methods and technical contents disclosed above without departing from the spirit and scope of the present invention. Therefore, any simple modifications, equivalent changes and modifications 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 scope of protection of the technical solutions of the present invention.

Claims

1. An omnidirectional controllable wheeled end effector for derotation of space debris, characterized by include: A spherical wheel handle (1), three drive devices, a universal bearing (2), a fastening bracket (3) and a connecting flange (8); wherein, One end of each driving device is connected to the connecting flange (8), and the other end of each driving device is in contact with the spherical wheel handle (1); One end of the fastening bracket (3) is connected to the connecting flange (8), and the other end of the fastening bracket (3) is connected to the spherical wheel handle (1) via the universal bearing (2); Each driving device includes a Mecanum wheel (4), a motor flange (5), a motor (6) and a motor bracket (7); wherein, One end of the motor bracket (7) is connected to the connecting flange (8), and the other end of the motor bracket (7) is connected to the motor (6); The output shaft of the motor (6) is connected to the Mecanum wheel (4) via a motor flange (5); The Mecanum wheel (4) is in contact with the spherical wheel handle (1); Define the center of the Mecanum wheel as the origin O, the rotation axis as the z-axis, the parallel fastening bracket pointing to the outside of the wheel as the y-axis, and the x-axis determined according to the right-hand rule; the radius r is the circumference radius of the circle formed by the roller envelope of the Mecanum wheel; h is the wheel width; the roller axis is line segment AB, the roller curve is curve AB, point C is located on curve AB and in contact with the ground, line segment OC ⊥ line segment AB, and line segment OC intersects line segment AB at point D; B′, C′, and D′ are the projections of points BCD respectively; α is the offset angle of the roller; The velocity v of the Mecanum wheel (4) relative to the spherical surface Σ of the spherical wheel hand Σ for: v Σ =v D +v DC +v CΣ ; Among them, v D is the velocity of the roller center of the Mecanum wheel, v DC is the velocity of the Mecanum wheel roller and the spherical wheel hand contact point relative to the roller center, v CΣ is the slip speed between point C and the spherical surface of the spherical wheel handle; The speed v of the contact point between the roller and the spherical wheel relative to the center of the roller DC for: Where θ is the angle between line segment AO′ and line segment O′C′, γ is the angle between line segment AO′ and line segment O′B′, and ω is the rotation speed of the Mecanum wheel driven by the motor.

2. The omnidirectional controllable wheeled end effector for derotation of space debris according to claim 1, characterized in that: The three driving devices form an angle of 120 degrees with each other on the horizontal projection plane; the angle between the axis of each driving device and the horizontal line is 60 degrees.

3. The omnidirectional controllable wheeled end effector for derotation of space debris according to claim 1, characterized in that: The curve AB rotates around the axis AB to generate a roller surface, and the number of rollers N satisfies Nγ≥2π; where γ is the angle between the line segment AO′ and the line segment O′B′.

4. The omnidirectional controllable wheeled end effector for derotation of space debris according to claim 1, characterized in that: The length of line segment OD is: Among them, l OD is the length of line segment OD, θ is the angle between line segment AO′ and line segment O′C′, and γ is the angle between line segment AO′ and line segment O′B′.

5. The omnidirectional controllable wheeled end effector for derotation of space debris according to claim 1, characterized in that: Curve AB is represented by: Where θ is the angle between line segment AO′ and line segment O′C′, γ is the angle between line segment AO′ and line segment O′B′, and x, y, and z represent the projection of curve AB on the O′XYZ coordinate system.

6. The omnidirectional controllable wheeled end effector for derotation of space debris according to claim 1, characterized in that: The velocity v of the roller center of the Mecanum wheel D for: v D =[-l OD ·sinθ·ωl OD ·cosθ·ω0] T ; Among them, l OD is the length of line segment OD, θ is the angle between line segment AO′ and line segment O′C′, and ω is the rotation speed of the Mecanum wheel driven by the motor.

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