| 摘要 |
PROBLEM TO BE SOLVED: To reduce the weight of a swing board in a state of maintaining strength to load transmitted to the swing board. SOLUTION: A swivel base 3 disposed on a travel device 2 rotatably around a turning axis X through a swing bearing 4 is partitioned into a center part where the swing board 40 is disposed on the swing bearing 4, and into both right and left side parts of the center part. The right and left side parts are formed by welding side plates 51 thinner in wall thickness than a main plate 45 forming the center part, to the main plate 45. COPYRIGHT: (C)2007,JPO&INPIT
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