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Some of manufacturing tasks, such as sawing, often require continuous impulsive motion. In the case of sawing, such impulsive motions can be observed between the teeth of the saw and the object. The amount of the external impulse exerted on the object has been treated as an important control parameter. At the same time, the internal impulses experienced at the joints should be taken into account to avoid serious damage or injury at the joints of robot. The purpose of this paper is to improve the efficacy of sawing by using dual arms. For this, we suggest an external impulse model, and introduce a new concept of effective mass that accounts for the hardness of the object to corroborate the effectiveness of the proposed chip model employed in the derivation of the external impulse model. Closed-form internal impulse models are also proposed for both single and dual arms. Based on these models, the paper proposes a new measure for internal impulse. A normalized impulse ellipsoid reflecting the velocity direction is employed to visualize the impact geometry. Finally, we identify the optimal sawing region, wherein there is a maximum amount of external impulse and a minimal amount of the internal impulse. Simulation and experimentation demonstrate that the dual arm exhibits a better sawing performance than a single arm, in terms of external and internal impulses.

We have operated the 22.9-kV high temperature superconductor cable system installed at Icheon Substation of Korea Electric Power Corporation (KEPCO), which consists of a conductor and a shield using YBCO-NiW wires. We prepared the same 5-m cable sample as the Icheon Substation in order to understand its ac loss characteristic. Especially, the contact resistance between copper current leads and YBCO wires was minimized through the increased soldering surface between them. Besides, four voltage leads are attached to both the conductor and the shield with an equal angle of 90°. Under ac transport current, which was supplied to the conductor and shield in opposite direction, losses of the 5-m sample were tested for various contact positions of voltage leads, frequencies, and transport periods. The result shows that the measured ac losses for various contact positions in the conductor and shield are the same. However, their loss exponents are very different. More details will be presented in this work.