2026-10-20
How position, velocity, and current control work together to achieve precise, repeatable gun motion. In automated stud welding, the welding gun must reach programmed positions, follow a defined motion profile, and respond quickly to changes in mechanical load. These requirements are managed by a cascaded three-loop servo control architecture: the position loop, velocity loop, and current loop. Hongbai’s servo control architecture combines MCU and FPGA processing to coordinate motion commands, feedback regulation, and gun movement throughout the welding cycle. 1. The Three Loops of Servo Control Position Loop: Accurate Positioning The outermost loop controls the position of the gun’s lifting mechanism using feedback from a high-resolution optical linear encoder. Its main functions are to track commanded positions, reduce positioning errors, and maintain the required position during designated stages of the welding cycle. Accurate positioning helps ensure that the gun follows the programmed movement sequence and establishes the intended lift conditions for the welding process. Velocity Loop: Motion Profile Tracking The velocity loop regulates motor speed according to the trajectory generated by the motion planner. Velocity feedback, derived from position measurements or dedicated estimation, enables the controller to correct tracking errors. The specified motion configuration includes: Maximum velocity: adjustable range of approximately 50–800 mm/s (recommended 400 mm/s) Acceleration: adjustable range of approximately 20–80 m/s² (recommended 50 m/s²) These are application-specific settings. Actual motion performance depends on the gun mechanism, moving mass, stroke, and load conditions. Current Loop: Fast Torque Response The innermost loop regulates servo motor phase current, which is closely related to motor torque. It enables the drive to respond to acceleration commands and changes in mechanical load. The specified servo-drive parameters are: Parameter Value Current-loop control period 20 μs Switching frequency 50 kHz Maximum current command/output ±20 A Specified current response 10 A within 40 μs These figures apply to the…
