Cover of optical system with guiding structures

A cover, being covered on an optical system, comprising:

• a first surface, configured to face a working surface when the optical system is moving on the working surface in a moving direction;
• a first opening, having a width in the moving direction;
• a second opening, arranged adjacent to the first opening in a first direction perpendicular to the moving direction;
• and one first guiding protrusion, protruded out from the first surface toward the working surface and arranged opposite to one of two opposite sides of the second opening in the moving direction, wherein a range of the first guiding protrusion in the moving direction does not exceed the width of the first opening.

A cover, being covered on an optical system, comprising:

• a first surface, configured to face a working surface when the optical system is moving on the working surface;
• a first opening;
• a second opening, arranged adjacent to the first opening in a first direction;
• and one first guiding protrusion, protruded out from the first surface toward the working surface and arranged only adjacent to one of two opposite sides of the second opening in a second direction without adjacent to the first opening in the second direction, wherein the first guiding protrusion has a first branch extending toward the first opening and a second branch extending away from the first opening, and a distance between the first branch and the second branch becomes larger from a connection point of the first branch and the second branch.