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As the core driving component of robot joints, what characteristics of different robot joints (base joints, arm joints, end effector joints) should be focused on when selecting and matching parameters of servo motors? How to achieve a balance between joint motion accuracy and dynamic performance through parameter optimization?
I. Core Principle of Servo Motor Adaptation: Aligning with Differentiated Joint Requirements
Servo motors are the preferred choice for driving joints of various robots such as industrial robots and collaborative robots, thanks to their advantages of high precision, fast response, and high torque density. Different joints of robots have significant differences in functional positioning, force-bearing conditions, and motion requirements. Therefore, selection and parameter matching must be tailored to specific needs, and parameters should be optimized to resolve the contradiction between accuracy and power, ensuring the overall operational stability of the robot.
II. Joint-Specific Selection Strategy: Matching Motor Characteristics with Core Demands
Firstly, it is necessary to clarify the core demands for selection based on the characteristics of different joints. As the load-bearing foundation of the robot, the base joint bears the weight of the entire machine and the load torque after the arm extends. Its core requirements are high torque and high stability, with relatively low requirements for rotational speed. When selecting a servo motor for the base joint, priority should be given to rated torque, peak torque, and continuous working time. Generally, a servo motor with large rated torque and large rotor moment of inertia is selected, combined with a precision planetary reducer to improve torque output. Meanwhile, the motor stall torque must be verified to avoid step loss during startup or load-bearing. The arm joint is responsible for the attitude adjustment and range movement of the robot, requiring a balance between torque and flexibility. Its motion trajectory is mostly in variable acceleration and variable load modes. When selecting a motor for the arm joint, key considerations include dynamic response speed, moment of inertia matching, and overload capacity. It is recommended to choose a servo motor with small rotor moment of inertia and excellent acceleration performance to ensure that the joint can quickly follow control commands. Meanwhile, the transmission ratio of the reducer should be optimized to balance torque output and motion flexibility. The end effector joint (such as the driving joint of a gripper or welding torch) mainly focuses on high-precision positioning and light-load rapid movement, with low torque requirements but extremely high requirements for position accuracy, repeat positioning accuracy, and low-speed stability. For this joint, a small-power servo motor with a high-resolution encoder (with an accuracy of no less than 23 bits) should be preferred. Additionally, the low-speed crawling performance of the motor should be optimized to avoid low-speed jitter affecting operation accuracy.
III. Parameter Optimization Path: Achieving Dynamic Balance Between Accuracy and Dynamic Performance
Secondly, achieving a balance between accuracy and dynamic performance through key parameter optimization involves three dimensions. First, optimization of moment of inertia matching. The ratio of motor rotor moment of inertia to load moment of inertia directly affects joint response speed and control accuracy, and the matching ratio should be set differently for different joints: for base joints with large load moment of inertia, the ratio can be controlled at 1:5~1:10; for arm joints requiring a balance between response and stability, the ratio is recommended to be 1:3~1:5; for end joints with small load moment of inertia, the ratio should be 1:1~1:3. Reasonable matching reduces inertial impact and improves control stability. Second, collaborative optimization of torque and rotational speed parameters. Calculate the peak load torque and rated load torque based on the joint motion trajectory to ensure that the motor’s peak torque can cover instantaneous impact loads and the rated torque meets continuous working requirements. Meanwhile, adjust the rotational speed to match the joint motion speed: the rotational speed of the base joint is set at 50~200r/min, the arm joint at 200~500r/min, and the end joint can be increased to 500~1500r/min, avoiding power waste due to excessively high speed or reduced operation efficiency due to excessively low speed. Third, calibration of control parameters. Optimize dynamic performance through gain adjustment and filter parameter setting of the servo driver. For end joints with high precision requirements, increase the position loop gain to improve positioning accuracy and enable the low-speed smoothing function to suppress jitter. For base joints with high power requirements, appropriately reduce the position loop gain and increase the speed loop gain to enhance anti-load disturbance capability, achieving a dynamic balance between accuracy and power.
IV. Auxiliary Adaptation Points: Considering Environmental and Collaborative Compatibility
In addition, environmental adaptability and reliability should be considered in selection. Industrial robots may operate in environments with dust and vibration, so servo motors with a protection level of IP65 or higher and strong vibration resistance should be selected. For collaborative robots, safety is a key consideration, so low-inertia servo motors with rapid braking should be adopted, combined with torque detection modules to achieve overload protection. Meanwhile, the collaborative adaptation of the motor, reducer, and encoder is crucial. It is necessary to ensure parameter compatibility among the three and further optimize motion accuracy and dynamic performance through integrated debugging to meet the differentiated working requirements of different robot joints.
