A space truss climbing robot manipulator clamping stability control method and system

Abstract

The application discloses a space truss climbing robot manipulator clamping stability control method and system, belongs to the technical field of manipulator control, and aims to solve the problems of large contact impact, easy slippage instability, torque bias and clamping force out-of-range in the multi-point contact clamping process of the end gripper, and the insufficient clamping stability and reliability. The application takes the stably locked gripper as a fixed end equivalent base, realizes approach deceleration through a virtual admittance model in the non-contact stage; after contact is established, the local force of each discrete contact point is mapped into a six-dimensional overall load at the end, a stability criterion including normal contact, friction cone, overall force / torque balance and clamping force range is constructed; the end pose is corrected online by driving the overall load error to adapt the admittance model, and when the continuous satisfaction is constrained, stable clamping is determined, and corresponding processing is performed in abnormal states. The application is suitable for stable clamping and climbing operation of the space truss in the microgravity environment.

Description

Technical Field

[0001] This invention belongs to the field of robotic arm control technology, and in particular relates to a method and system for stabilizing the gripping of a robotic arm in a space truss climbing robot. Background Technology

[0002] With the continuous development of on-orbit servicing, on-orbit assembly, long-term operation and maintenance of space stations, and the construction of large space structures, the demand for space robots in tasks such as external inspection, component handling, structural assembly, and equipment maintenance is increasing. Space truss structures, due to their geometric regularity, high stiffness, strong load-bearing capacity, and clear connection methods, are widely used in external platforms of space stations, large space solar arrays, large space telescopes, and other large space deployment structures. When performing on-orbit inspection, maintenance, or assembly assistance tasks, space truss climbing robots rely on reliable clamping between their end effector and truss members to achieve support and movement.

[0003] In actual gripping processes, robot end effectors typically go through stages such as non-contact approach, initial contact, contact transition, and stable gripping. Due to factors such as microgravity, weak damping, structural flexibility, external disturbances, sensing errors, assembly errors, and control execution errors in the space environment, end effectors are prone to positional and attitude deviations when approaching truss members. These deviations can lead to uneven distribution of local contact forces between the gripper and the truss members, resulting in problems such as contact impact, frictional instability, torque misalignment, and gripping failure.

[0004] Existing gripping control methods mostly employ constant gripping force or simple force feedback control. While these methods can close the gripper and output a certain gripping force, they struggle to simultaneously handle local friction constraints, overall force / torque balance constraints, and force / position coordination issues after contact under multi-point contact conditions. This results in insufficient gripping reliability for program-controlled manipulators under complex conditions of microgravity and multi-point contact in space. If the controller cannot correct the end effector's pose online based on actual external load errors, problems such as local slippage, gripping force overload, or end effector oscillation can easily occur. Therefore, achieving rapid, compliant, and stable gripping of truss members by the end effector under complex conditions of microgravity and multi-point contact in space is a key technical challenge for space-based on-orbit service robots. Summary of the Invention

[0005] In view of this, the present invention aims to propose a method and system for stable control of gripping by a manipulator of a space truss climbing robot, so as to solve the problems of large contact impact, easy slippage and instability, torque bias and gripping force exceeding the limit, and insufficient gripping stability and reliability of the end gripper of the space truss climbing robot during multi-point contact gripping.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: a method for stabilizing and controlling the gripping of a manipulator on a space truss climbing robot, comprising the following steps:

[0007] Step 1: Determine the end effector that is currently locked stably between the robot and the space truss member as the fixed end. Use the fixed end as the robot's equivalent base to obtain the climbing robot's joint variables, joint velocities, end effector pose of the mobile end, end effector velocity of the mobile end, six-dimensional external load of the end effector, gripper status, geometric parameters of the truss member, and target gripping point.

[0008] Step 2: Identify the clamping stage based on the relative distance between the mobile terminal's end reference point and the target clamping point, and the six-dimensional combined external load of the end. When entering the non-contact flexible approach stage, construct a virtual interaction domain along the desired clamping direction, and generate the end desired pose deceleration correction amount along the target clamping direction through the non-contact virtual admittance model to obtain the corrected non-contact desired pose.

[0009] Step 3: After the end gripper establishes contact with the space truss member, obtain the normal contact force, two orthogonal tangential contact forces and position vectors relative to the end reference point at each discrete contact point, and map the local contact force into a six-dimensional resultant external load in the end tool coordinate system.

[0010] Step 4: Construct a multi-point contact clamping stability criterion that includes normal contact constraints, friction cone constraints, overall resultant force balance constraints, overall resultant moment balance constraints, and clamping force range constraints. Determine the desired stable resultant external load based on the stability criterion, and calculate the resultant external load error between the actual resultant external load and the desired stable resultant external load.

[0011] Step 5: Using the combined external load error as the admittance outer loop driving quantity, the end pose correction quantity is generated through the adaptive admittance model, the equivalent damping is adaptively adjusted, and the desired end pose of the moving end is corrected online to achieve force / position coordination adjustment during the clamping process.

[0012] Step 6: Repeat steps 3 to 5 until all constraints are satisfied simultaneously and the condition remains satisfied for a preset number of consecutive control cycles. When stable clamping is determined to be complete, when contact point slippage, clamping force exceeding the limit, end-effector load exceeding the limit, or admittance pose correction exceeding the limit is detected, perform unloading, retraction, or realignment abnormality handling operations.

[0013] Furthermore, the end gripper has a double V-shaped gripping surface, and the space truss member is a cylindrical member. After the double V-shaped gripping surface contacts the space truss member, eight discrete contact points are formed. Each contact point establishes a local contact coordinate system, which includes a normal direction and two tangential directions that are orthogonal to each other in the tangential plane.

[0014] Furthermore, the local contact force can be expressed as:

[0015]

[0016] In the formula: The local contact force at the i-th contact point; Let be the normal contact force at the i-th contact point; The first tangential contact force at the i-th contact point; The second tangential contact force at the i-th contact point;

[0017] The formula for calculating the six-dimensional combined external load of the mobile terminal is as follows:

[0018]

[0019] In the formula: W is the six-dimensional combined external load of the mobile terminal; N is the total number of discrete contact points; Let be the rotation matrix from the local contact coordinate system of the i-th contact point to the end-tool coordinate system; Let be the position vector of the i-th contact point relative to the end reference point; Let be the contact force vector of the i-th contact point in the end-tool coordinate system; It is the contact torque vector formed by the i-th contact point relative to the end reference point.

[0020] Furthermore, in step 4, the multi-point contact clamping stability criterion simultaneously satisfies the normal contact constraint, friction cone constraint, overall resultant force balance constraint, overall resultant moment balance constraint, and clamping force range constraint.

[0021] The formula for calculating normal contact constraints is:

[0022]

[0023] In the formula: Let be the normal contact force at the i-th contact point;

[0024] The formula for calculating friction cone constraints is:

[0025]

[0026] In the formula: The first tangential contact force at the i-th contact point; The second tangential contact force at the i-th contact point; Let be the equivalent friction coefficient at the i-th contact point;

[0027] The overall resultant force equilibrium constraint is calculated using the following formula:

[0028]

[0029] In the formula: N is the total number of discrete contact points; Let be the rotation matrix from the local contact coordinate system of the i-th contact point to the end-tool coordinate system; The local contact force at the i-th contact point; External disturbance force acting on the end; This is the allowable threshold for the resultant force balance error;

[0030] The formula for calculating the overall resultant moment equilibrium constraint is:

[0031]

[0032] In the formula: Let be the position vector of the i-th contact point relative to the end reference point; This refers to the external disturbance torque acting at the end. This is the allowable threshold for the resultant torque balance error;

[0033] The formula for calculating the clamping force range constraint is:

[0034]

[0035] In the formula: This refers to the actual clamping force of the gripper; This is the lower limit of the allowable clamping force. This represents the maximum allowable clamping force.

[0036] Furthermore, the equivalent friction coefficient is updated online based on the tangential relative velocity at the corresponding contact point, and the calculation formula is as follows:

[0037]

[0038] In the formula: The relative velocity at the i-th contact point in the tangential direction is The equivalent coefficient of friction at that time; Let be the tangential relative velocity at the i-th contact point; The static friction coefficient of the contact surface; The coefficient of kinetic friction of the contact surface; This is the characteristic velocity of Stribeck.

[0039] Furthermore, the lower limit of the clamping force is determined jointly based on the desired tangential contact force and the external disturbance torque to be resisted, and the calculation formula is as follows:

[0040]

[0041] In the formula: For clamping safety factor; Let be the first tangential contact force component of the i-th contact point under the desired steady state; Let be the second tangential contact force component of the i-th contact point under the desired steady state; This is a correction factor for the number of effective contact points; The comprehensive equivalent friction coefficient of the clamping contact surface; This is the equivalent anti-disturbance arm of the clamping structure.

[0042] Furthermore, in step 2, the calculation formula for the non-contact virtual admittance model is as follows:

[0043]

[0044] In the formula: For non-contact virtual equivalent quality; For non-contact virtual equivalent damping; The scalar correction acceleration is given along the desired clamping direction; The scalar correction speed is along the desired clamping direction; This is a virtual braking coefficient; The preset non-contact deceleration radius; The relative distance between the mobile terminal reference point and the target clamping point; This is the velocity damping coefficient; The velocity component of the mobile end along the desired clamping direction;

[0045] The revised formula for calculating the non-contact desired pose is as follows:

[0046]

[0047] In the formula: The corrected non-contact desired pose; This is the original planned end pose; This is a scalar trajectory correction amount along the desired clamping direction; Let be the unit vector along the desired clamping direction.

[0048] Furthermore, in step 5, the calculation formula for the adaptive admittance model is as follows:

[0049]

[0050] In the formula: The equivalent mass matrix of the contact phase admittance; The equivalent damping matrix varies with the combined external load error; The equivalent stiffness matrix of the admittance during the contact stage; Acceleration for end-effector pose correction; For end-effector pose correction speed; This is the end-effector pose correction amount; The resultant external load error is the difference between the actual resultant external load and the expected stable resultant external load, including the resultant external force error and the resultant external moment error. The equivalent stiffness matrix of the admittance during the contact stage;

[0051] The equivalent damping matrix is ​​a diagonal matrix, and is adaptively adjusted according to the following formula:

[0052]

[0053] In the formula: diag represents the diagonal matrix construction operator; This represents the basic damping value in the translational direction; This is the translational damping adjustment coefficient; This is the resultant external force error; This is the basic damping value in the direction of rotation; This is the rotational damping adjustment coefficient; This is the error of the resultant external torque.

[0054] Furthermore, in step 5, the end-effector pose correction is calculated using a discrete recursive method. The calculation method is as follows: within the k-th control sampling period, first calculate the combined external load error and the equivalent damping matrix for the current period:

[0055]

[0056]

[0057] In the formula: The combined external load error in the k-th control cycle; The actual end-point six-dimensional combined external load for the k-th control cycle; The desired stable external load for the k-th control cycle; Let be the equivalent damping matrix for the k-th control cycle; The adaptive equivalent damping matrix;

[0058] Then, calculate the pose correction acceleration based on the adaptive admittance model:

[0059]

[0060] In the formula: The end-position pose correction acceleration for the k-th control cycle; This is the inverse of the contact-phase admittance equivalent mass matrix; The end pose correction speed for the k-th control cycle; This is the end pose correction amount for the k-th control cycle;

[0061] The pose correction rate and pose correction amount for the next cycle are obtained through numerical integration recursion:

[0062]

[0063]

[0064] In the formula: The end pose correction speed for the (k+1)th control cycle; To control the sampling period; This is the end pose correction amount for the (k+1)th control cycle;

[0065] The final corrected end-effector pose is obtained as follows:

[0066]

[0067] In the formula: The desired end-effector pose is corrected for the (k+1)th control cycle sent to the inner loop controller; The original planned end pose for the (k+1)th control cycle;

[0068] Simultaneously, set the amplitude boundaries for the pose correction amount:

[0069]

[0070] In the formula: This is the end-effector pose correction amount; This represents the maximum permissible amplitude of the pose correction.

[0071] When the pose correction exceeds the amplitude boundary, stop the current clamping action and perform a backtracking or realignment operation.

[0072] The present invention also provides a manipulator gripping and stabilizing control system for a space truss climbing robot, comprising:

[0073] The status acquisition module is used to determine the end gripper that is currently stably locked with the space truss member as the fixed end, and use the fixed end as the robot's equivalent base to acquire the climbing robot's joint variables, joint velocities, end pose of the mobile end, end velocity of the mobile end, six-dimensional external load of the end, gripper status, geometric parameters of the truss member, and target gripping point.

[0074] The non-contact admittance control module is used to identify the clamping stage based on the relative distance between the end reference point of the mobile terminal and the target clamping point and the six-dimensional combined external load of the end. When entering the non-contact flexible approach stage, a virtual interaction domain is constructed along the desired clamping direction. The deceleration correction amount of the desired end pose along the target clamping direction is generated through the non-contact virtual admittance model to obtain the corrected non-contact desired pose.

[0075] The contact force mapping module is used to obtain the normal contact force, two orthogonal tangential contact forces and position vectors relative to the end reference point at each discrete contact point after the end gripper establishes contact with the space truss member, and to map the local contact force into a six-dimensional resultant external load in the end tool coordinate system.

[0076] The stability determination module is used to construct a multi-point contact clamping stability criterion that includes normal contact constraints, friction cone constraints, overall resultant force balance constraints, overall resultant moment balance constraints, and clamping force range constraints. Based on the stability criterion, the desired stable resultant external load is determined, and the resultant external load error between the actual resultant external load and the desired stable resultant external load is calculated.

[0077] The adaptive admittance correction module is used to use the combined external load error as the admittance outer loop driving quantity, generate the end pose correction quantity through the adaptive admittance model, adaptively adjust the equivalent damping and correct the desired end pose of the moving end online, so as to realize the force / position coordination adjustment during the clamping process.

[0078] The anomaly handling module is used to repeatedly execute the contact force mapping, stability determination and pose correction process until all constraints are satisfied at the same time and the state is maintained for a preset number of consecutive control cycles, at which point stable clamping is determined to be completed; when contact point slippage, clamping force exceeding the limit, end-effector load exceeding the limit or admittance pose correction amount exceeding the limit is detected, the anomaly handling operation of unloading, retraction or realignment is performed.

[0079] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention introduces a virtual admittance deceleration mechanism during the non-contact approach phase, enabling the end effector of the mobile end to reduce its speed in advance when approaching the space truss member, thereby reducing initial contact impact and sudden changes in joint forces. Based on a multi-point contact force aggregation model, this invention maps the normal force, tangential force, and contact position at each contact point into a unified six-dimensional external load at the end effector, reflecting the influence of local contact force distribution on overall clamping stability.

[0080] This invention integrates friction cone constraints, overall force balance constraints, overall torque balance constraints, and clamping force range constraints into a unified clamping stability criterion, effectively identifying unstable states such as slippage risk, torque offset, and insufficient clamping force. During the contact phase, this invention employs adaptive admittance control, adaptively adjusting the equivalent damping based on the combined external load error. This enhances vibration suppression when the contact force error is large and improves end-effector pose fine-tuning sensitivity when the error is small, achieving adaptive compliant control of the program-controlled robot's clamping process.

[0081] This invention uses a stable clamping criterion as the clamping completion condition, avoiding reliance solely on the clamper's closing signal or fixed clamping force to determine clamping success, thus improving the safety and reliability of the end effector of the space truss climbing robot. Attached Figure Description

[0082] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0083] Figure 1 This is a flowchart of a spatial truss climbing robot manipulator gripping stability control method according to the present invention;

[0084] Figure 2 This is a schematic diagram of the overall structure of the space truss climbing system described in this invention;

[0085] Figure 3 This is a schematic diagram of the equivalent clamping state structure of the end effector described in this invention;

[0086] Figure 4 This is a schematic diagram showing the contact and clamping of the end gripper with the equivalent truss member described in this invention;

[0087] Figure 5 The diagram shows the equivalent clamping contact process state diagram of the present invention. In the diagram, (a) is the non-contact state diagram, (b) is the contact adjustment state diagram, and (c) is the stable clamping state diagram.

[0088] Figure 6 This is a schematic diagram of the clamping contact coordinate system described in this invention;

[0089] Figure 7 This is a schematic diagram of the truss clamping state described in the present invention;

[0090] Figure 8 The diagram shows the different stages of truss clamping described in this invention. In the diagram, (a) is the non-contact stage, (b) is the contact adjustment stage, and (c) is the stable clamping stage.

[0091] Figure 9 This is a flowchart illustrating the admittance control determination process for the non-contact and contact stages as described in this invention.

[0092] Figure 10 This is a flowchart illustrating the multi-point contact clamping stability criterion of the present invention.

[0093] Figure 11 This is a flowchart of the adaptive admittance closed-loop control described in this invention;

[0094] Figure 12 This is a flowchart illustrating the calculation of the equivalent friction coefficient and the lower limit of the clamping force as described in this invention.

[0095] In the picture:

[0096] 1- Gripper base, 2- Equivalent lower left claw finger, 3- Equivalent upper left claw finger, 4- Equivalent upper right claw finger, 5- Equivalent truss member, 6- Equivalent lower right claw finger. Detailed Implementation

[0097] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other, and the described embodiments are only some embodiments of the present invention, not all embodiments.

[0098] See Figure 1-7 This embodiment describes a method for stabilizing the gripping of a manipulator on a space truss climbing robot, which includes the following steps:

[0099] Step 1: Determine the end effector that is currently locked stably between the robot and the space truss member as the fixed end. Use the fixed end as the robot's equivalent base to obtain the climbing robot's joint variables, joint velocities, end effector pose of the mobile end, end effector velocity of the mobile end, six-dimensional external load of the end effector, gripper status, geometric parameters of the truss member, and target gripping point.

[0100] Step 2: Identify the clamping stage based on the relative distance between the mobile terminal's end reference point and the target clamping point, and the six-dimensional combined external load of the end. When entering the non-contact flexible approach stage, construct a virtual interaction domain along the desired clamping direction, and generate the end desired pose deceleration correction amount along the target clamping direction through the non-contact virtual admittance model to obtain the corrected non-contact desired pose.

[0101] Step 3: After the end gripper establishes contact with the space truss member, obtain the normal contact force, two orthogonal tangential contact forces and position vectors relative to the end reference point at each discrete contact point, and map the local contact force into a six-dimensional resultant external load in the end tool coordinate system.

[0102] Step 4: Construct a multi-point contact clamping stability criterion that includes normal contact constraints, friction cone constraints, overall resultant force balance constraints, overall resultant moment balance constraints, and clamping force range constraints. Determine the desired stable resultant external load based on the stability criterion, and calculate the resultant external load error between the actual resultant external load and the desired stable resultant external load.

[0103] Step 5: Using the combined external load error as the admittance outer loop driving quantity, the end pose correction quantity is generated through the adaptive admittance model, the equivalent damping is adaptively adjusted, and the desired end pose of the moving end is corrected online to achieve force / position coordination adjustment during the clamping process.

[0104] Step 6: Repeat steps 3 to 5 until all constraints are satisfied simultaneously and the condition remains satisfied for a preset number of consecutive control cycles. When stable clamping is determined to be complete, when contact point slippage, clamping force exceeding the limit, end-effector load exceeding the limit, or admittance pose correction exceeding the limit is detected, perform unloading, retraction, or realignment abnormality handling operations.

[0105] like Figure 7 As shown, the method of the present invention is applied to a space truss climbing robot with an end effector, and is suitable for a program-controlled manipulator to stably grip and climb space truss structures in a microgravity environment.

[0106] like Figure 2 As shown, the space truss climbing robot includes a central body, a first branch manipulator, a second branch manipulator, a first end effector, and a second end effector. The first end effector is stably locked to the space truss members, serving as the fixed end; the second end effector needs to approach and grip the target member, serving as the mobile end. The controller uses the fixed end as an equivalent base to establish a closed-loop relationship between the end effector pose, contact force, gripping force, and admittance control of the mobile end.

[0107] The controller uses the fixed end as an equivalent base to read the robot's joint variables. Joint velocity Endpoint pose of mobile device Mobile terminal speed End-point six-dimensional combined external load The opening and closing state of the gripper and the target gripping point The endpoint reference point for mobile devices is... Then the distance between the mobile device and the target clamping point is .when At that time, the mobile device moves according to the planned trajectory; when Furthermore, when the external load at the end of the six dimensions does not exceed the contact threshold, the controller determines that the mobile terminal has entered the non-contact flexible approach stage.

[0108] During the non-contact flexible approach phase, the controller calculates the desired clamping direction:

[0109]

[0110] Scalar trajectory correction is calculated using a non-contact virtual admittance model. .

[0111] The calculation formula for the non-contact virtual admittance model is as follows:

[0112]

[0113] In the formula: For non-contact virtual equivalent quality; For non-contact virtual equivalent damping; The scalar correction acceleration is given along the desired clamping direction; The scalar correction speed is along the desired clamping direction; This is a virtual braking coefficient; The preset non-contact deceleration radius; The relative distance between the mobile terminal reference point and the target clamping point; This is the velocity damping coefficient; The velocity component of the mobile end along the desired clamping direction;

[0114] The revised formula for calculating the non-contact desired pose is as follows:

[0115]

[0116] In the formula: The corrected non-contact desired pose; This is the original planned end pose; This is a scalar trajectory correction amount along the desired clamping direction; Let be the unit vector along the desired clamping direction.

[0117] When the mobile device is closer to the target clamping point The larger the value of , the stronger the virtual braking effect, thereby achieving flexible deceleration when approaching the target member and reducing the risk of initial collision.

[0118] When the mobile end effector contacts the truss member, the controller enters the contact phase. The controller determines the set of contact points based on the contact detection results and calculates the contact force at each point. Subsequently, the controller determines whether the current gripping is stable based on a multi-point contact stability criterion. If unstable, an adaptive admittance model is used to correct the end effector pose, and the contact force and stability criterion are recalculated. If the stability criterion is continuous... If a control cycle is established, the controller outputs a stable clamping flag.

[0119] The mobile end effector has a double V-shaped clamping surface. The space truss members are cylindrical. After the double V-shaped clamping surface contacts the space truss members, eight discrete contact points are formed. Therefore, the number of contact points is taken as... A local contact coordinate system is established for each contact point. The coordinate system contains a normal direction and two tangential directions that are orthogonal to each other in the tangential plane.

[0120] Local contact force is expressed as:

[0121]

[0122] In the formula: The local contact force at the i-th contact point; Let be the normal contact force at the i-th contact point; The first tangential contact force at the i-th contact point; The second tangential contact force at the i-th contact point;

[0123] The normal contact force can be calculated using the penalized contact model:

[0124]

[0125]

[0126] in, For normal contact stiffness, For normal damping, For the first The contact gap at each contact point This is the equivalent pressure. For the first Equivalent pressure at each contact point The first derivative with respect to time.

[0127] The tangential resultant force is:

[0128]

[0129] No. The six-dimensional force spiral formed by the contact points and the end reference point is:

[0130]

[0131] The formula for calculating the six-dimensional combined external load of the mobile terminal is as follows:

[0132]

[0133] In the formula: W is the six-dimensional combined external load of the mobile terminal; N is the total number of discrete contact points; Let be the rotation matrix from the local contact coordinate system of the i-th contact point to the end-tool coordinate system; Let be the position vector of the i-th contact point relative to the end reference point; Let be the contact force vector of the i-th contact point in the end-tool coordinate system; This is the contact torque vector formed by the i-th contact point relative to the end reference point. This six-dimensional resultant external load is used to determine whether the gripper currently has a resultant force imbalance, resultant torque offset, or local contact force overload.

[0134] The stability criterion for multi-point contact clamping simultaneously satisfies the normal contact constraint, friction cone constraint, overall resultant force balance constraint, overall resultant moment balance constraint, and clamping force range constraint.

[0135] The formula for calculating normal contact constraints is:

[0136]

[0137] In the formula: Let be the normal contact force at the i-th contact point; this constraint indicates that the contact point can only withstand compression and cannot generate non-physical tensile force.

[0138] The formula for calculating friction cone constraints is:

[0139]

[0140] In the formula: The first tangential contact force at the i-th contact point; The second tangential contact force at the i-th contact point; Let be the equivalent friction coefficient of the i-th contact point; this constraint is used to determine whether there is a risk of tangential slippage at the i-th contact point.

[0141] The overall resultant force equilibrium constraint is calculated using the following formula:

[0142]

[0143] In the formula: N is the total number of discrete contact points; Let be the rotation matrix from the local contact coordinate system of the i-th contact point to the end-tool coordinate system; The local contact force at the i-th contact point; External disturbance force acting on the end; This is the allowable threshold for the resultant force balance error;

[0144] The formula for calculating the overall resultant moment equilibrium constraint is:

[0145]

[0146] In the formula: Let be the position vector of the i-th contact point relative to the end reference point; This refers to the external disturbance torque acting at the end. This is the allowable threshold for the resultant torque balance error;

[0147] The formula for calculating the clamping force range constraint is:

[0148]

[0149] In the formula: This refers to the actual clamping force of the gripper; This is the lower limit of the allowable clamping force. This represents the maximum allowable clamping force.

[0150] When the normal contact constraint, friction cone constraint, overall resultant force balance constraint, overall resultant moment balance constraint and clamping force range constraint are simultaneously established and remain established for L consecutive control cycles, the controller determines that the end effector has completed stable clamping.

[0151] To describe the transition from static to kinetic friction at the contact point, this embodiment uses a velocity-dependent equivalent friction coefficient. This equivalent friction coefficient is updated online based on the tangential relative velocity at the corresponding contact point, and the calculation formula is as follows:

[0152]

[0153] In the formula: The relative velocity at the i-th contact point in the tangential direction is The equivalent coefficient of friction at that time; Let be the tangential relative velocity at the i-th contact point; The static friction coefficient of the contact surface; The coefficient of kinetic friction of the contact surface; This is the characteristic velocity of Stribeck.

[0154] When the tangential velocity at the contact point is small Approaching the static friction coefficient; as the tangential velocity at the contact point increases... It gradually approaches the coefficient of kinetic friction. This approach can improve the continuity of friction constraint judgment.

[0155] The lower limit of the clamping force is determined jointly by the desired tangential contact force and the external disturbance torque to be resisted, and the calculation formula is as follows:

[0156]

[0157] In the formula: For clamping safety factor; Let be the first tangential contact force component of the i-th contact point under the desired steady state; Let be the second tangential contact force component of the i-th contact point under the desired steady state; This is a correction factor for the number of effective contact points; The comprehensive equivalent friction coefficient of the clamping contact surface; This is the equivalent anti-disturbance arm of the clamping structure.

[0158] If the actual clamping force The controller then increases the clamping force; if the actual clamping force If the controller restricts the gripper output or performs an unloading operation, it will prevent the gripper, lever, or joint mechanism from being overloaded.

[0159] like Figure 5As shown, the contact process between the end effector and the member can be equivalent to three states: non-contact state, contact adjustment state, and stable clamping state. When the end effector of the moving end contacts the truss member, the controller calculates the six-dimensional resultant external load on the end effector based on the multi-point contact forces. And according to the expected stable external load Error obtained:

[0160]

[0161] To account for the resultant external force error, This is the error of the resultant external torque.

[0162] The formula for calculating the adaptive admittance model is:

[0163]

[0164] In the formula: The equivalent mass matrix of the contact phase admittance; The equivalent damping matrix varies with the combined external load error; The equivalent stiffness matrix of the admittance during the contact stage; Acceleration for end-effector pose correction; For end-effector pose correction speed; This is the end-effector pose correction amount; The resultant external load error is the difference between the actual resultant external load and the expected stable resultant external load, including the resultant external force error and the resultant external moment error. This is the equivalent stiffness matrix of the admittance during the contact stage.

[0165] The equivalent damping matrix is ​​a diagonal matrix, and it is adaptively adjusted according to the following formula:

[0166]

[0167] In the formula: diag represents the diagonal matrix construction operator; This represents the basic damping value in the translational direction; This is the translational damping adjustment coefficient; This is the resultant external force error; This is the basic damping value in the direction of rotation; This is the rotational damping adjustment coefficient; This represents the net external torque error. When the net external load error is large, the damping increases, and the system's ability to suppress oscillations is enhanced; when the net external load error is small, the damping decreases, and the sensitivity of end-effector attitude fine-tuning is improved.

[0168] The controller adds the pose correction to the planned pose:

[0169]

[0170] And Send to the inner loop position controller or joint servo controller for execution.

[0171] In real-time control systems, adaptive admittance control can be implemented using the following discrete recursive form, calculated as follows: Within the k-th control sampling period, first calculate the net external load error and equivalent damping matrix for the current period:

[0172]

[0173]

[0174] In the formula: The combined external load error in the k-th control cycle; The actual end-point six-dimensional combined external load for the k-th control cycle; The desired stable external load for the k-th control cycle; Let be the equivalent damping matrix for the k-th control cycle; The adaptive equivalent damping matrix;

[0175] Then, calculate the pose correction acceleration based on the adaptive admittance model:

[0176]

[0177] In the formula: The end-position pose correction acceleration for the k-th control cycle; This is the inverse of the contact-phase admittance equivalent mass matrix; The end pose correction speed for the k-th control cycle; This is the end pose correction amount for the k-th control cycle; This is the equivalent stiffness matrix of the admittance during the contact stage.

[0178] The pose correction rate and pose correction amount for the next cycle are obtained through numerical integration recursion:

[0179]

[0180]

[0181] In the formula: The end pose correction speed for the (k+1)th control cycle; To control the sampling period; This is the end pose correction amount for the (k+1)th control cycle;

[0182] The final corrected end-effector pose is obtained as follows:

[0183]

[0184] In the formula: The desired end-effector pose is corrected for the (k+1)th control cycle sent to the inner loop controller; The original planned end pose for the (k+1)th control cycle;

[0185] Simultaneously, set the amplitude boundaries for the pose correction amount:

[0186]

[0187] In the formula: This is the end-effector pose correction amount; This represents the maximum permissible amplitude of the pose correction.

[0188] When the pose correction exceeds the amplitude boundary, stop the current clamping action and perform a backtracking or realignment operation.

[0189] This embodiment is a manipulator gripping and stabilizing control system for a space truss climbing robot, including:

[0190] The status acquisition module is used to determine the end gripper that is currently stably locked with the space truss member as the fixed end, and use the fixed end as the robot's equivalent base to acquire the climbing robot's joint variables, joint velocities, end pose of the mobile end, end velocity of the mobile end, six-dimensional external load of the end, gripper status, geometric parameters of the truss member, and target gripping point.

[0191] The non-contact admittance control module is used to identify the clamping stage based on the relative distance between the end reference point of the mobile terminal and the target clamping point and the six-dimensional combined external load of the end. When entering the non-contact flexible approach stage, a virtual interaction domain is constructed along the desired clamping direction. The deceleration correction amount of the desired end pose along the target clamping direction is generated through the non-contact virtual admittance model to obtain the corrected non-contact desired pose.

[0192] The contact force mapping module is used to obtain the normal contact force, two orthogonal tangential contact forces and position vectors relative to the end reference point at each discrete contact point after the end gripper establishes contact with the space truss member, and to map the local contact force into a six-dimensional resultant external load in the end tool coordinate system.

[0193] The stability determination module is used to construct a multi-point contact clamping stability criterion that includes normal contact constraints, friction cone constraints, overall resultant force balance constraints, overall resultant moment balance constraints, and clamping force range constraints. Based on the stability criterion, the desired stable resultant external load is determined, and the resultant external load error between the actual resultant external load and the desired stable resultant external load is calculated.

[0194] The adaptive admittance correction module is used to use the combined external load error as the admittance outer loop driving quantity, generate the end pose correction quantity through the adaptive admittance model, adaptively adjust the equivalent damping and correct the desired end pose of the moving end online, so as to realize the force / position coordination adjustment during the clamping process.

[0195] The anomaly handling module is used to repeatedly execute the contact force mapping, stability determination and pose correction process until all constraints are satisfied at the same time and the state is maintained for a preset number of consecutive control cycles, at which point stable clamping is determined to be completed; when contact point slippage, clamping force exceeding the limit, end-effector load exceeding the limit or admittance pose correction amount exceeding the limit is detected, the anomaly handling operation of unloading, retraction or realignment is performed.

[0196] The specific embodiments of the present invention disclosed above are merely illustrative of the invention. These embodiments do not exhaustively describe all details, nor do they limit the invention to the specific embodiments described. Many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention.

Claims

1. A method for stabilizing the gripping of a manipulator in a space truss climbing robot, characterized in that: It includes the following steps: Step 1: Determine the end effector that is currently locked stably between the robot and the space truss member as the fixed end. Use the fixed end as the robot's equivalent base to obtain the climbing robot's joint variables, joint velocities, end effector pose of the mobile end, end effector velocity of the mobile end, six-dimensional external load of the end effector, gripper status, geometric parameters of the truss member, and target gripping point. Step 2: Identify the clamping stage based on the relative distance between the mobile terminal's end reference point and the target clamping point, and the six-dimensional combined external load of the end. When entering the non-contact flexible approach stage, a virtual interaction domain is constructed along the desired clamping direction. The deceleration correction amount of the end desired pose along the target clamping direction is generated through the non-contact virtual admittance model to obtain the corrected non-contact desired pose. Step 3: After the end gripper establishes contact with the space truss member, obtain the normal contact force, two orthogonal tangential contact forces and position vectors relative to the end reference point at each discrete contact point, and map the local contact force into a six-dimensional resultant external load in the end tool coordinate system. Step 4: Construct a multi-point contact clamping stability criterion that includes normal contact constraints, friction cone constraints, overall resultant force balance constraints, overall resultant moment balance constraints, and clamping force range constraints. Determine the desired stable resultant external load based on the stability criterion, and calculate the resultant external load error between the actual resultant external load and the desired stable resultant external load. Step 5: Using the combined external load error as the admittance outer loop driving quantity, the end pose correction quantity is generated through the adaptive admittance model, the equivalent damping is adaptively adjusted, and the desired end pose of the moving end is corrected online to achieve force / position coordination adjustment during the clamping process. Step 6: Repeat steps 3 to 5 until all constraints are satisfied simultaneously and the condition remains satisfied for a preset number of consecutive control cycles. When stable clamping is determined to be complete, when contact point slippage, clamping force exceeding the limit, end-effector load exceeding the limit, or admittance pose correction exceeding the limit is detected, perform unloading, retraction, or realignment abnormality handling operations.

2. The method for stabilizing the gripping of a manipulator in a space truss climbing robot according to claim 1, characterized in that: The end gripper has a double V-shaped gripping surface. The space truss member is a cylindrical member. After the double V-shaped gripping surface contacts the space truss member, eight discrete contact points are formed. Each contact point establishes a local contact coordinate system, which includes a normal direction and two tangential directions that are orthogonal to each other in the tangential plane.

3. The method for stabilizing the gripping of a manipulator in a space truss climbing robot according to claim 1, characterized in that: Local contact force is expressed as: In the formula: The local contact force at the i-th contact point; Let be the normal contact force at the i-th contact point; The first tangential contact force at the i-th contact point; The second tangential contact force at the i-th contact point; The formula for calculating the six-dimensional combined external load of the mobile terminal is as follows: In the formula: W is the six-dimensional combined external load of the mobile terminal; N is the total number of discrete contact points; Let be the rotation matrix from the local contact coordinate system of the i-th contact point to the end-tool coordinate system; Let be the position vector of the i-th contact point relative to the end reference point; Let be the contact force vector of the i-th contact point in the end-tool coordinate system; It is the contact torque vector formed by the i-th contact point relative to the end reference point.

4. The method for stabilizing the gripping of a manipulator in a space truss climbing robot according to claim 1, characterized in that: In step 4, the multi-point contact clamping stability criterion simultaneously satisfies the normal contact constraint, friction cone constraint, overall resultant force balance constraint, overall resultant moment balance constraint, and clamping force range constraint. The formula for calculating normal contact constraints is: In the formula: Let be the normal contact force at the i-th contact point; The formula for calculating friction cone constraints is: In the formula: The first tangential contact force at the i-th contact point; The second tangential contact force at the i-th contact point; Let be the equivalent friction coefficient at the i-th contact point; The overall resultant force equilibrium constraint is calculated using the following formula: In the formula: N is the total number of discrete contact points; Let be the rotation matrix from the local contact coordinate system of the i-th contact point to the end-tool coordinate system; The local contact force at the i-th contact point; External disturbance force acting on the end; This is the allowable threshold for the resultant force balance error; The formula for calculating the overall resultant moment equilibrium constraint is: In the formula: Let be the position vector of the i-th contact point relative to the end reference point; This refers to the external disturbance torque acting at the end. This is the allowable threshold for the resultant torque balance error; The formula for calculating the clamping force range constraint is: In the formula: This refers to the actual clamping force of the gripper; This is the lower limit of the allowable clamping force. This represents the maximum allowable clamping force.

5. The method for stabilizing the gripping of a manipulator in a space truss climbing robot according to claim 4, characterized in that: The equivalent friction coefficient is updated online based on the tangential relative velocity at the corresponding contact point, and the calculation formula is as follows: In the formula: The relative velocity at the i-th contact point in the tangential direction is The equivalent coefficient of friction at that time; Let be the tangential relative velocity at the i-th contact point; The static friction coefficient of the contact surface; The coefficient of kinetic friction of the contact surface; This is the characteristic velocity of Stribeck.

6. The method for stabilizing the gripping of a manipulator in a space truss climbing robot according to claim 4, characterized in that: The lower limit of the clamping force is determined jointly based on the desired tangential contact force and the external disturbance torque to be resisted, and the calculation formula is as follows: In the formula: For clamping safety factor; Let be the first tangential contact force component of the i-th contact point under the desired steady state; Let be the second tangential contact force component of the i-th contact point under the desired steady state; This is a correction factor for the number of effective contact points; The comprehensive equivalent friction coefficient of the clamping contact surface; This is the equivalent anti-disturbance arm of the clamping structure.

7. The method for stabilizing the gripping of a manipulator in a space truss climbing robot according to claim 1, characterized in that: In step 2, the calculation formula for the non-contact virtual admittance model is as follows: In the formula: For non-contact virtual equivalent quality; For non-contact virtual equivalent damping; The scalar correction acceleration is given along the desired clamping direction; The scalar correction speed is along the desired clamping direction; This is a virtual braking coefficient; The preset non-contact deceleration radius; The relative distance between the mobile terminal reference point and the target clamping point; This is the velocity damping coefficient; The velocity component of the mobile end along the desired clamping direction; The revised formula for calculating the non-contact desired pose is as follows: In the formula: The corrected non-contact desired pose; This is the original planned end pose; This is a scalar trajectory correction amount along the desired clamping direction; Let be the unit vector along the desired clamping direction.

8. The method for stabilizing the gripping arm of a space truss climbing robot according to claim 1, characterized in that: In step 5, the calculation formula for the adaptive admittance model is as follows: In the formula: The equivalent mass matrix of the contact phase admittance; The equivalent damping matrix varies with the combined external load error; The equivalent stiffness matrix of the admittance during the contact stage; Acceleration for end-effector pose correction; For end-effector pose correction speed; This is the end-effector pose correction amount; The resultant external load error is the difference between the actual resultant external load and the expected stable resultant external load, including the resultant external force error and the resultant external moment error. The equivalent damping matrix is ​​a diagonal matrix, and is adaptively adjusted according to the following formula: In the formula: diag represents the diagonal matrix construction operator; This represents the basic damping value in the translational direction; This is the translational damping adjustment coefficient; This is the resultant external force error; This represents the basic damping value in the direction of rotation; This is the rotational damping adjustment coefficient; This is the error of the resultant external torque.

9. The method for stabilizing the gripping of a manipulator in a space truss climbing robot according to claim 8, characterized in that: In step 5, the end-effector pose correction is calculated using a discrete recursive method. The calculation method is as follows: In the k-th control sampling period, first calculate the combined external load error and the equivalent damping matrix for the current period: In the formula: The combined external load error in the k-th control cycle; The actual end-point six-dimensional combined external load for the k-th control cycle; The desired stable external load for the k-th control cycle; Let be the equivalent damping matrix for the k-th control cycle; The adaptive equivalent damping matrix; Then, calculate the pose correction acceleration based on the adaptive admittance model: In the formula: The end-position pose correction acceleration for the k-th control cycle; This is the inverse of the contact-phase admittance equivalent mass matrix; The end pose correction speed for the k-th control cycle; This is the end pose correction amount for the k-th control cycle; The pose correction rate and pose correction amount for the next cycle are obtained through numerical integration recursion: In the formula: The end pose correction speed for the (k+1)th control cycle; To control the sampling period; This is the end pose correction amount for the (k+1)th control cycle; The final corrected end-effector pose is obtained as follows: In the formula: The desired end pose is corrected for the (k+1)th control cycle sent to the inner loop controller; The original planned end pose for the (k+1)th control cycle; Simultaneously, set the amplitude boundaries for the pose correction amount: In the formula: This is the end-effector pose correction amount; This represents the maximum permissible amplitude of the pose correction. When the pose correction exceeds the amplitude boundary, stop the current clamping action and perform a backtracking or realignment operation.

10. A stabilization control system for the gripper of a space truss climbing robot, characterized in that, include: The status acquisition module is used to determine the end gripper that is currently stably locked with the space truss member as the fixed end, and use the fixed end as the robot's equivalent base to acquire the climbing robot's joint variables, joint velocities, end pose of the mobile end, end velocity of the mobile end, six-dimensional external load of the end, gripper status, geometric parameters of the truss member, and target gripping point. The non-contact admittance control module is used to identify the clamping stage based on the relative distance between the end reference point of the mobile terminal and the target clamping point and the six-dimensional external load of the end. When entering the non-contact flexible approach stage, a virtual interaction domain is constructed along the desired clamping direction. The deceleration correction amount of the end desired pose along the target clamping direction is generated through the non-contact virtual admittance model to obtain the corrected non-contact desired pose. The contact force mapping module is used to obtain the normal contact force, two orthogonal tangential contact forces and position vectors relative to the end reference point at each discrete contact point after the end gripper establishes contact with the space truss member, and to map the local contact force into a six-dimensional resultant external load in the end tool coordinate system. The stability determination module is used to construct a multi-point contact clamping stability criterion that includes normal contact constraints, friction cone constraints, overall resultant force balance constraints, overall resultant moment balance constraints, and clamping force range constraints. Based on the stability criterion, the desired stable resultant external load is determined, and the resultant external load error between the actual resultant external load and the desired stable resultant external load is calculated. The adaptive admittance correction module is used to use the combined external load error as the admittance outer loop driving quantity, generate the end pose correction quantity through the adaptive admittance model, adaptively adjust the equivalent damping and correct the desired end pose of the moving end online, so as to realize the force / position coordination adjustment during the clamping process. The anomaly handling module is used to repeatedly execute the contact force mapping, stability determination and pose correction process until all constraints are satisfied at the same time and the state is maintained for a preset number of consecutive control cycles, at which point stable clamping is determined to be completed; when contact point slippage, clamping force exceeding the limit, end-effector load exceeding the limit or admittance pose correction amount exceeding the limit is detected, the anomaly handling operation of unloading, retraction or realignment is performed.

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