| 摘要 |
PURPOSE: A blackboard eraser and a gear structure thereof are provided to minimize the floating of dust by using a clean cotton part in order to erase a blackboard. CONSTITUTION: A plurality of saw blades are formed in an outer circumference around a rotary shaft. A lower gear has a saw blade having a streamlined convex one side and a streamlined concave other side. A movable guide hole(4) is formed along a fixed shaft inside. At least two teeth(3) has a pitch less than the pitch of a lower gear in a direction contacting the lower gear. The side between the teeth includes an upper gear(1) having a streamlined concave side. When the lower gear is rotated around the rotary shaft, a rotational angle in a one direction should be greater than a rotational angle in an opposite direction.
|
