| 摘要 |
The two side supports (12,13), fixed with a drive wheel (18,19) and a runner wheel (20,21), which are rigidly joined by a horizontal main cross-bar (34) and a subsidiary cross-bar (12,13). The main cross-bar is formed by two arms (38,39) at right angles to the main cross-bar, and linked to the side supports and joined by a hinge link. At least one of the arms is adjusted parallel with the pivot axle of the drive wheels (19). The one arm (38) has a locking piece in the form of a swivelling locking lug (56). The other arm has an elongated catch, from which part of the catch surface facing the locking lug is formed. |
