| 摘要 |
PROBLEM TO BE SOLVED: To eliminate the generation of noise due to a contact between a floor part and a back frame, by pressing a floor part against the back frame by means of the energizing force of a spring member, preferably, by energizing a locking rod in the pivoting shaft direction of the floor part by means of a coil spring. SOLUTION: A floor part 7 is rotatably pivoted to a pivoting shaft attached on the back frame side of a horizontal frame, positioned orthogonally to the back frame of a back surface, and is formed with a drilled slot 7c in a rib 7b positioned near a vertical wall 7a on the opposite side to the pivoting shaft to insert a locking rod c1. A locking member c3 engaging with one hook c2' of a coil spring c2 is formed at a position on the pivoting shaft side to the locking rod c1. The other hook c2" of the soil spring c2 is locked on the locking rod, and the locking rod c1 is energized toward the pivoting shaft. The coil spring c2 is tensed near both ends of the locking rod c1 and, as necessary, even near its central portion as well.
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