Flexible cables are connected to a movable member at a first end and a fixed member at a second end, each having a curve in between the first end and the second end. The flexible cables each include a first positioning system near the first end in the curve and a second positioning system near the second end in the curve, and they have different distances between the first positioning system and the second positioning system. The first positioning system and the second positioning system are fixed to a first positioning portion and a second positioning portion respectively. The flexible cables are spaced from each other to define clearances thereamong at the curve.