| 摘要 |
A wheel structure includes a central sleeve, a central controlling shaft joined to the central shaft, a wheel pivoting on an extension portion of the central shaft, and a braking unit; the central controlling shaft includes a controlling piece, and a connecting part for controlling the controlling piece; a position-limiting element is secured in the central sleeve, which is next to the controlling piece, and has a position-limiting hole having the same outline as the controlling piece; the braking unit is arranged in the central sleeve in a movable manner, and biased upwards by springs; the central controlling shaft is operable to change the wheel into first, second, and third configurations; in the first configuration, the wheel can move and turn left and right freely; in the second one, the wheel can only move in a direct course; in the third one, the wheel is immobile.
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