PROBLEM TO BE SOLVED: To hold an upper frame capable of oscillating along the motion trajectory of a quadric crank chain that takes an inclined posture and an approximately horizontal posture in the approximately horizontal posture by a simple operation when necessary.SOLUTION: An upper frame 20 capable of oscillating along the motion trajectory of a quadric crank chain between an inclined posture and an approximately horizontal posture is forcibly displaced to the approximately horizontal posture and held. A front link mechanism control means 100 applies external force for pushing down an operation member 120 to thereby control a front link mechanism 30 such that the front side of the upper frame 20 is displaced backward while being lowered. The direction of the displacement for bringing the upper frame 20 into the approximately horizontal posture and the direction of an operation for locking the front link mechanism 30 or a back link mechanism 40 by the operation of the operation member become approximately the same direction as each other, and consequently two movements, a displacement movement to the approximately horizontal posture and a lock movement, can be performed only by operating the operation member in a predetermined direction.COPYRIGHT: (C)2013,JPO&INPIT【課題】傾斜姿勢と略水平姿勢となる四節回転連鎖の運動軌跡に沿って揺動可能な上部フレームを、必要な場合に簡易な操作で、略水平姿勢で保持する。【解決手段】傾斜姿勢と略水平姿勢との間で、四節回転連鎖の運動軌跡に沿って揺動可能な上部フレーム20を、強制的に略水平姿勢に変位させて保持する。前部リンク機構制御手段100は、操作部材120を押し下げる外力を付与することで、上部フレーム20の前方側を下降させながら後方に変位させるように前部リンク機構30を制御する。上部フレーム20を略水平姿勢にするための変位方向と、操作部材の操作によって前部リンク機構30又は後部リンク機構40をロックするための操作方向とが略同方向となるため、操作部材を所定方向に操作するだけで、略水平姿勢への変位動作とロック動作という2つの動作を共に行うことができる。【選択図】 図14
