Mobile robot multi-machine self-reconfiguration mechanical arm system based on kinematics coupling control and cooperative control method

Abstract

The invention discloses a mobile robot multi-machine self-reconfiguration mechanical arm system based on kinematics coupling control and a cooperative control method, and belongs to the field of robots and intelligent manufacturing. The system comprises a mobile mechanical arm unit, an omnidirectional physical coupling docking mechanism and an integrated cooperative controller. The mobile mechanical arm unit comprises an omnidirectional chassis and a multi-joint mechanical arm, the docking mechanism integrates tolerance guidance, rigid locking, force perception and high-speed communication contacts, and the controller is a multi-core real-time industrial control computer. Multi-machine rigid combination and high-speed communication are achieved through physical and information coupling butt joint, an assembly unified coupling kinematics / dynamics model is constructed, motion distribution is conducted based on the optimal instantaneous rotation center and gravity center compensation, and non-internal-force cooperative operation is achieved in combination with distributed impedance control. The defects that in the prior art, rigidity and flexibility are opposite, dynamic precision is poor, and communication dependence is high are overcome, the synchronization precision reaches the nanosecond level, the load capacity is remarkably improved, and the method is suitable for collaborative carrying and precise assembling of large workpieces.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary field of robotics and intelligent manufacturing, specifically relating to a reconfigurable mobile operation robot system, and more particularly to a system and method that achieves dynamic combination and separation of multiple mobile robotic arms through deep integration of physics and information, and performs high-precision collaborative control based on a unified kinematic model. It is suitable for complex working conditions such as collaborative handling of large workpieces, precision assembly, and heavy-duty operations, and can realize hot-swappable flexible reconfiguration and high-rigidity strong coupling collaborative motion. Background Technology

[0002] With the rapid development of flexible manufacturing, aerospace assembly, automotive manufacturing, and large workpiece logistics, single mobile robotic arms (AGV / AMR with a single robotic arm) are limited by load capacity and operating space, and can no longer meet the complex operation requirements such as collaborative handling and precise assembly of large structural components. Therefore, high-rigidity and high-precision collaborative operation of multiple mobile robotic arms has become a key direction to overcome current technological bottlenecks.

[0003] Current multi-mobile robot collaborative solutions suffer from the following significant technical shortcomings, which severely limit their application in high-precision, heavy-duty scenarios:

[0004] 1. Lack of strong real-time performance and bottleneck of synchronization accuracy: Existing technologies mostly rely on wireless communication such as WiFi / 5G to achieve multi-machine collaboration. The inherent delay and jitter of wireless communication will cause unacceptable dynamic errors in the trajectory of the robotic arm end in communication-limited environments or tasks with high synchronization requirements (such as collaborative lifting of rigid long shafts), which cannot meet the requirements of high-precision force-position hybrid control.

[0005] 2. Fragmented kinematic model leads to insufficient dynamic accuracy: Traditional control methods treat the kinematics of the mobile chassis and the robotic arm as independent systems and solve them sequentially. Without establishing an overall coupled dynamic model under a unified world coordinate system, the dynamic disturbance of the robotic arm end effector caused by the chassis motion cannot be effectively compensated in the "operation while moving" mode, resulting in a significant decrease in positioning accuracy.

[0006] 3. The rigid-flexible duality of combination and separation mechanisms: Existing multi-robot combinations are mostly rigid mechanical connections or software master-slave following. Rigid connections lack terrain adaptability and are prone to internal stress; software following has insufficient physical rigidity, making it difficult to transmit large torques and has poor anti-disturbance capabilities, and cannot cope with heavy-load collaborative scenarios.

[0007] Therefore, developing a multi-machine self-reconfiguration cooperative control scheme that balances rigidity and flexibility, has high dynamic accuracy, and low communication dependence has become an urgent technical problem to be solved in this field. Summary of the Invention

[0008] I. Purpose of the Invention

[0009] This invention aims to overcome the shortcomings of existing technologies, such as the inability to balance rigidity and flexibility, poor dynamic accuracy, and strong communication dependence when multiple mobile robotic arms work together. It provides a mobile robot multi-machine self-reconfigurable robotic arm system and collaborative control method based on kinematic coupling control, which realizes flexible reconfiguration and high-rigidity strong coupling motion from independent units to a super-redundant mobile operation platform, meeting the collaborative operation requirements under high precision, heavy load, and complex working conditions.

[0010] II. Technical Solution

[0011] (I) Multi-machine self-reconfigurable robotic arm system for mobile robots

[0012] A multi-machine self-reconfigurable robotic arm system for mobile robots includes at least two mobile robotic arm units. Its distinguishing feature is that it further includes an omnidirectional physical and information coupling docking mechanism and an integrated collaborative controller based on model prediction. The structure and function of each component are as follows:

[0013] 1. Mobile robotic arm unit

[0014] 1.1 Omnidirectional Mobile Robot Module: It adopts a high-precision servo-driven omnidirectional mobile chassis, driven by Mecanum wheels or four independent steering / drive wheels. The chassis integrates a multi-source fusion navigation sensor consisting of LiDAR, IMU, and encoder, which has millimeter-level positioning capability (static positioning accuracy ±0.5mm) and a maximum unloaded moving speed of 1.2m / s.

[0015] 1.2 Redundant Degrees of Freedom Robotic Arm Module: Rigidly mounted on the mobile robot chassis, it is a high-performance collaborative robotic arm with at least 6 degrees of freedom, a repeatability accuracy of ±0.1mm, a maximum single-unit load of ≥100kg, and an end effector integrated with an intelligent quick-change tool system that can be adapted to tools such as grippers, vision cameras, and force-controlled milling spindles.

[0016] 2. Omnidirectional physical and information coupling docking mechanism

[0017] The docking mechanism is located at the front and rear ends and sides of the chassis of each mobile robotic arm unit, enabling omnidirectional docking of multiple units. It includes an active tolerance guide, a rigid locking part, a flexible force sensing part, and high-speed physical communication contacts.

[0018] 2.1 Active tolerance guide: It is a large-chamfered conical guide structure with a built-in proximity sensor and a docking deviation tolerance of ±10mm, realizing deviation correction during the docking process;

[0019] 2.2 Rigid locking part: It is an integrated electromagnetic / mechanical locking pin with a locking force ≥50kN, shear force bearing capacity ≥30kN, no mechanical backlash, ensuring the rigidity of the combined structure;

[0020] 2.3 Flexible Force Sensing Unit: Based on the principle of series elastic actuator (SEA), it has a built-in high-precision six-dimensional force / torque sensor (accuracy ±0.1N / ±0.01N・m) for active and compliant absorption of impact during docking (impact buffer ≤50N) and real-time detection of docking force;

[0021] 2.4 High-speed physical communication contacts: Automatically connect after docking and locking, forming a wired communication link with a delay of ≤1μs, supporting EtherCAT industrial bus, and realizing nanosecond-level synchronous communication.

[0022] 3. Integrated Collaborative Controller

[0023] It adopts a multi-core industrial control computer (≥8 cores) with a real-time operating system (RTOS), integrates core algorithm modules such as coupled kinematics calculation, ICR dynamic programming, center of gravity compensation, and distributed impedance control, and establishes communication connections with each unit actuator and sensor through a high-speed industrial bus (EtherCAT). It supports synchronous drive of ≤32 axes (chassis wheel set + robotic arm joint), and is responsible for processing all sensor information, running core algorithms and synchronously issuing control commands.

[0024] (II) Collaborative Control Methods

[0025] A cooperative control method based on the above system, characterized by comprising the following steps:

[0026] 1. Steps for Physical and Information Coupling and Integration

[0027] The master control mobile robotic arm unit sends docking commands to the slave unit via a high-speed bus. The slave unit approaches the master control unit via visual servo or laser guidance. The active tolerance guidance unit corrects deviations, and the flexible force sensing unit detects six-dimensional contact forces in real time. The controller fine-tunes the docking posture based on the force information to achieve a soft landing. When docking is detected, the rigid locking unit locks, and the high-speed physical communication contacts are activated to establish an integrated coupling of mechanical, electrical, and information systems.

[0028] 2. Steps for constructing a unified coupling model

[0029] The collaborative controller treats the combined multi-machine multi-arm system as a super-redundant degree-of-freedom robot with a movable base. It collects the geometric and kinematic parameters of each mobile chassis, the DH parameters of each robotic arm, and the precise relative pose of the docking point in real time. Combining the influence of the current pose of the robotic arm on the system's center of gravity and inertia, it constructs a fully coupled kinematic and dynamic model in the world coordinate system.

[0030] 3. Centralized optimization of solution steps

[0031] The controller calculates the optimal instantaneous center of rotation (ICR) that satisfies kinematic and dynamic constraints in real time based on the target mission trajectory; by solving a constrained quadratic programming problem, it synchronously generates the optimal speed commands for each mobile chassis drive wheel and the optimal angular velocity commands for each robotic arm joint.

[0032] 4. Dynamic center of gravity compensation steps

[0033] Real-time monitoring of the overall center of gravity change of the system caused by the movement of each robotic arm joint, and feedforward adjustment of the speed and torque distribution of each drive wheel based on the coupled dynamics model, to compensate for the impact of the center of gravity offset on the instantaneous rotation center stability of the assembly and suppress dynamic disturbances.

[0034] 5. Synchronous execution steps

[0035] The collaborative controller sends the calculated control commands to all actuators (chassis wheel assembly + robotic arm joints) with microsecond-level synchronization accuracy via a high-speed wired communication link, driving the combined assembly to move in a coordinated manner.

[0036] 6. Multi-arm cooperative impedance control steps

[0037] When multiple robotic arms work together to operate the same rigid load, the system automatically switches to distributed impedance control mode: at least one robotic arm acts as the master arm for high-precision position control, while the other slave arms use six-dimensional force sensors at the end and joints to provide real-time feedback and perform impedance control with self-tuning parameters. This dynamically absorbs small position errors and vibrations between the multiple arms, enabling collaborative operation of the load with no or minimal internal force.

[0038] III. Beneficial Effects

[0039] Compared with the prior art, the present invention has the following significant advantages:

[0040] 1. Breakthrough in synchronization accuracy: The wired high-speed bus communication established through the physical docking mechanism completely eliminates the delay and uncertainty of wireless communication, and the multi-axis synchronous control accuracy reaches nanosecond-level synchronization and microsecond-level response, meeting the stringent requirements of ultra-precision collaborative assembly.

[0041] 2. Increased load and stiffness: Multiple robots are rigidly connected to form an integrated mobile platform. The system's structural stiffness, load capacity, and anti-overturning moment increase exponentially, enabling heavy-duty handling and processing that far exceeds the physical limits of a single machine.

[0042] 3. Leap in dynamic stability: Based on the coupled model of ICR and dynamic center of gravity compensation, real-time feedforward and feedback coupled control of the movement of the robotic arm and the chassis is realized, which effectively suppresses dynamic disturbances during the movement process and makes the accuracy and stability of "cooperative operation in motion" reach the level of practical application.

[0043] 4. The dialectical unity of rigidity and flexibility: The combination of active tolerance guidance and the flexible sensing of the SEA principle makes the rigid connection process smooth and shock-free; distributed impedance control ensures that the multi-arm rigid grip has compliant force control characteristics when grasping heavy objects, perfectly protecting the workpiece and equipment, and achieving a balance between rigidity and flexibility. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below:

[0045] Figure 1 , Figure 2 : A schematic diagram of the structure of the two mobile robotic arm units before combination in this embodiment of the invention (labeled: omnidirectional mobile robot, redundant degree-of-freedom robotic arm, omnidirectional physical information coupling docking mechanism, flexible force sensing unit, active tolerance guidance unit);

[0046] Figure 3 , Figure 4 : A diagram showing the collaborative handling state of two mobile robotic arm units rigidly combined in this embodiment of the invention (labeled: rigid locking part engagement state, high-speed industrial bus data flow, and internal module interaction of the collaborative controller).

[0047] Figure 5 The present invention is based on the coupled kinematic control flowchart of ICR and dynamic center of gravity compensation.

[0048] The above figures are only used to illustrate the technical solutions of the present invention and do not constitute a limitation on the scope of protection of the present invention. The same or similar parts in each figure are referred to by the same reference numerals. Detailed Implementation

[0049] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. This embodiment takes the collaborative handling and assembly of a 3-meter-long automotive chassis longitudinal beam by two mobile robotic arms as an example:

[0050] 1. System Initial State

[0051] Two mobile robotic arm units (AGV Master main control unit and AGV Slave slave unit) are located below the longitudinal beams of the vehicle chassis at both ends. Each unit is in standby mode, the docking mechanism locking pins are unlocked, the force sensor and navigation sensor are working normally, and the integrated collaborative controller completes self-test.

[0052] 2. Load grabbing and impedance control activation

[0053] 2.1 The main control unit and the slave unit confirm the position of the longitudinal beam through visual positioning, and the controller issues a synchronous grasping command.

[0054] 2.2 The two robotic arms move synchronously to the gripping position, and the end grippers close to grip both ends of the longitudinal beam;

[0055] 2.3 When the six-dimensional force sensor at the end of the driven unit detects the contact force signal, the system immediately and automatically switches to the distributed impedance control mode. The driven arm smoothly follows the movement of the master arm based on force feedback, ensuring that there is no impact or internal force during the grasping process.

[0056] 3. Multi-machine self-reconfiguration docking

[0057] 3.1 The main control unit sends combined commands to the slave unit through high-speed physical communication contacts to set the tail docking position;

[0058] 3.2 The slave unit autonomously moves to the preset docking area at the rear of the main control unit based on the fusion navigation of lidar and IMU;

[0059] 3.3 The active tolerance guide enters the conical guide port corresponding to the main control unit, the proximity sensor triggers the deceleration signal, the flexible force sensing unit monitors the docking force in real time (controlled within ≤50N), and the controller fine-tunes the attitude of the driven unit;

[0060] 3.4 When the force sensor detects that the docking is in place, the locking pin of the rigid locking part pops out and locks (locking force ≥ 50kN). At the same time, the high-speed communication contact is turned on to form an in-vehicle local area network, and the docking is completed (total time ≤ 10s). At this time, the two units form a mechanical-electrical-information integrated coupling combination.

[0061] 4. Cooperative movement and dynamic compensation

[0062] 4.1 The collaborative controller activates the unified coupled kinematics / dynamics model and calculates the optimal instantaneous rotation center (ICR) in real time based on the target trajectory of the longitudinal beam being rotated 90 degrees horizontally and sent into the assembly station.

[0063] 4.2 Based on ICR, the precise rotational speeds of the four drive wheels and the compensation motion commands for each joint of the two robotic arms are calculated and sent out via the EtherCAT bus with microsecond-level synchronization accuracy.

[0064] 4.3 During the turning process of the longitudinal beam, centrifugal force is generated. Based on the dynamic model, the controller actively controls the shoulder joints of the two robotic arms to generate a small reverse torque to suppress the overall vibration of the system.

[0065] 4.4 Real-time monitoring of the center of gravity changes caused by the swing of the longitudinal beam, dynamic adjustment of the driving force distribution of the inner and outer wheels, ensuring that the longitudinal beam always maintains the preset horizontal posture, and the positioning accuracy is controlled within ±0.5mm.

[0066] 5. Precision assembly operation

[0067] 5.1 After the assembly is moved to the assembly station, the main control arm carries one end of the longitudinal beam to perform precise position control of the insertion of the hole shaft;

[0068] 5.2 The boom is completely switched to pure force control mode, which acts as an "intelligent flexible fixture" to follow the movement of the main control boom, absorb all positional errors, and ensure a smooth and jam-free assembly process;

[0069] 5.3 After assembly is completed, the boom gripper is released and the main control arm exits the assembly area.

[0070] 6. System disconnection and reset

[0071] 6.1 When the co-controller issues a separation command, the rigid locking part unlocks, and the driven unit slowly separates from the main control unit (separation force ≤ 20N).

[0072] 6.2 The slave unit returns to its initial standby position via autonomous navigation, and the main control unit completes the tool reset;

[0073] 6.3 The collaborative controller shuts down the coupled control mode, and the two units return to independent single-machine status, waiting for the next operation command.

[0074] This embodiment verifies the effectiveness of the system and method of the present invention in heavy-duty, high-precision collaborative assembly scenarios. Through the synergistic effect of self-reconfiguration docking, coupled kinematic control, dynamic center of gravity compensation and distributed impedance control, collaborative operation with zero communication delay, high rigidity and high precision is achieved, solving the core defects of the prior art.

[0075] It should be noted that the scope of protection of this invention is not limited to the above embodiments. Any modifications, equivalent substitutions, or extensions based on the technical solutions of this invention shall fall within the scope of protection of this invention. For example, the number of mobile robotic arm units can be expanded to three or more, the docking direction can be selected as front-end, rear-end, or side docking according to the operation requirements, and the end tool can be replaced with a welding gun, spraying device, etc., depending on the operation type.

Claims

1. A multi-machine self-reconfigurable robotic arm system for mobile robots based on kinematic coupling control, comprising at least two mobile robotic arm units, each mobile robotic arm unit including an omnidirectional mobile chassis and a multi-joint robotic arm mounted thereon, characterized in that, Also includes: An omnidirectional physical information coupling and docking mechanism is set on the chassis of each mobile robotic arm unit to realize mechanical rigid connection and high-speed electrical communication between adjacent units; An integrated collaborative controller is integrated into at least one mobile robotic arm unit and establishes communication connections with the actuators and sensors of all units. The collaborative controller is configured to: when at least two mobile robotic arm units are connected to form a combination through the docking mechanism, treat the combination as a whole, establish its unified coupled kinematics / dynamics model, and calculate the motion control commands of the combination in real time according to the task objective. The commands are then synchronously sent to the drive modules of each unit through the high-speed communication link established by the docking mechanism.

2. The system according to claim 1, characterized in that, The omnidirectional physical information coupling docking mechanism includes: an active tolerance guide, which is a conical guide structure with a large chamfer and a built-in proximity sensor, used to provide a wide range of mechanical guidance in the early stage of docking; a rigid locking part, which is an integrated electromagnetic / mechanical locking pin structure, used to provide a high-rigidity mechanical connection to transmit large loads after docking; and a flexible force sensing part, connected between the rigid locking part and the chassis body, which has a built-in high-precision force / torque sensor and elastic element, used to detect and actively buffer impact forces in real time during docking, and feed the force information back to the cooperative controller.

3. The system according to claim 2, characterized in that, The docking mechanism also includes a high-speed physical communication contact. When the rigid locking part is in the locked state, the high-speed physical communication contact is automatically connected, forming a wired communication link with a delay of less than 1ms between the connected mobile robotic arm units.

4. The system according to claim 1, characterized in that, The collaborative controller establishes a coupled kinematic / dynamic model, specifically including: collecting the geometric and kinematic parameters of each mobile chassis in the assembly, the DH parameters of each robotic arm, and the precise relative pose relationships between each unit determined by the docking mechanism, and constructing a full-state coupled model describing the overall motion state of the assembly.

5. The system according to claim 1, characterized in that, The omnidirectional mobile chassis adopts a Mecanum wheel structure or a four-wheel independent steering / drive structure, and integrates multi-source fusion navigation sensors, including lidar, inertial measurement unit (IMU) and encoder, enabling the chassis to have millimeter-level positioning capability.

6. The system according to claim 1, characterized in that, The multi-joint robotic arm is a collaborative robotic arm with at least 6 degrees of freedom, a repeatability accuracy of ≤ ±0.1 mm, a maximum single-machine load of ≥100 kg, and an end effector integrated with an intelligent quick-change tool system, which includes at least one of a gripper, a vision camera, and a force-controlled milling spindle.

7. A multi-machine self-reconfiguration cooperative control method for mobile robots based on kinematic coupling control, characterized in that, The system applied to any one of claims 1 to 6 includes the following steps: Step 1: Physical and information coupling and docking: Control the first mobile robotic arm unit and the second mobile robotic arm unit to approach each other through their respective docking mechanisms, complete mechanical locking under force guidance, and establish a high-speed wired communication link; Step 2: Unified Model Construction: The collaborative controller acquires the real-time structural parameters of the assembly and constructs an overall coupled kinematic / dynamic model; Step 3: Centralized optimization calculation: Based on the target task trajectory and the coupled kinematics / dynamics model, considering the dynamic constraints of the system, the optimal instantaneous rotation center (ICR) of the assembly is calculated in real time, and the drive wheel speed commands of each mobile chassis and the joint motion commands of each robotic arm are generated based on the ICR. Step 4: Synchronous Execution: The cooperative controller sends the calculated instructions to all execution components with microsecond-level synchronization accuracy through a high-speed communication link, driving the combined body to move in a coordinated manner.

8. The method according to claim 7, characterized in that, It also includes a dynamic center of gravity compensation step: real-time monitoring of the overall center of gravity change of the system caused by the movement of each robotic arm joint, and dynamic adjustment of the speed and / or torque distribution of each drive wheel based on this to compensate for the impact of center of gravity offset on the instantaneous rotational center stability of the assembly.

9. The method according to claim 7, characterized in that, It also includes a multi-arm collaborative impedance control step: when two or more robotic arms are operating the same load in a collaborative manner, the system switches to a master-slave or distributed impedance control mode, in which at least one robotic arm performs high-precision position control, and the other robotic arms perform impedance control based on force sensor feedback, so as to dynamically absorb the synchronization error between the multiple arms and realize the collaborative operation of the load with no internal force or low internal force.

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