This paper proposes a new rotary welding torch with a ball-jointed mechanical seal structure that simultaneously realizes the enclosure of CO₂ gas, the energization of welding current, and the insulation for system protection. In order to effectively compare the operation mechanism of the proposed device with the conventional rotary welding torch, a schematic technique is introduced to clearly visualize the operation and connection structure of the model. The kinematic state and constraint degrees of freedom of the tool are clearly shown, and it is easy to distinguish between the two designs that use different component parts and connection structures but result in the same final motion. In addition, the four dynamic characteristics of a rotary torch operating at 20 Hz (driving torque, vibration reaction force, natural frequency, and inertial mismatch) were analyzed to demonstrate superior performance to conventional products. The welding test showed that the tool normally operated even in a harsh welding environment, verifying its applicability in the field.

The gear ratio variable topology of a magnetic gear with an integrated harmonic modulator is analyzed using a magnetic permeance model. A dynamic characteristic equation is derived in consideration of the gear ratio between each layer constituting the magnetic gear: the driving side, the driven side, and the control side layer. Based on derived transfer function, the frequency characteristic between driving torque and angular speed of the driving side is analyzed. Theoretic model is compared with an experimental test result using the in-house dynamometer. In the general magnetic gears, the gear ratio is variable so that speed between each layer decelerates with gear ratio, but transmission torque is constant regardless of gear ratio. In this study, these characteristics are also verified through theoretical methods and experimental results, respectively.