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.

This paper proposed the simulation model of the servo system with three-stage reducer and presented the result of frequency analysis of the servo system considering backlash ratios and motor input voltage. By virtue of this work, we realized that if the motor input voltage of the system was large, the influence of each stage backlash ratio could be minimized or removed. Besides, we also found that if the motor input voltage was small, this created an optimal backlash ratio combination which could maximize the anti-resonance and resonance frequency of the servo system. This paper could be useful for determining each stage backlash ratio in designing a three-stage geared servo system with fast response.

Precision positioning stages are devices for precisely positioning objects according to required degrees of freedom and performance. Precision positioning stages are classified into serial and parallel mechanisms. Except for specific applications, the parallel mechanism is preferred. In serial mechanism, dynamic characteristics such as resonant frequency are clearly different from axis to axis and the first resonance frequency is distinctly low compared to the second. These make the control performance different for each axis and incurs limitation in control. In this study, the first and second resonant frequencies in a serial 2-DOF precision positioning stage were increased while maintaining their approximal value. Compliance analysis for the stage was performed by applying the matrix based method. A new concept of resonant frequency isotropy (RFI) was introduced and design optimization was performed in which first and second resonant frequencies almost coincided. This optimization allowed for the design of a serial 2-DOF precision positioning stage with enhanced first resonance frequency by 50.8% and RFI by 80.2% compared to the initial design. This paper is expected to increase the use of precision positioning stages based on serial mechanism and apply the concept of RFI to the positioning stages with more than 2-DOF.

This paper investigated the influence of the backlash ratio on frequency response characteristic in servo systems with twostage gear reducer, according to the change of magnitude of motor input voltage. The backlash ratio is defined as the ratio of the first gear stage backlash magnitude in relation to total backlash magnitude. This paper presents that the maximum anti-resonance and resonance frequency of the system can take place at the maximum backlash ratio if the motor input voltage of the system is large. On the other hand, if the motor input voltage is small, the maximum anti-resonance and resonance frequency of the system will occur at an arbitrary backlash ratio. In order to develop the geared servo system with fast response, it is effective to increase the maximum allowable motor input voltage and to reduce the magnitude of backlash on the second gear reduction stage.