| 摘要 |
A head supporting device for a universal parallel ruler is disclosed. The head supporting device connects the operating head of the ruler, having the scales attached thereto, to the cursor of the ruler, which is movable along a longitudinal rail. When the operating head and the scales are in contact with the drawing board surface, and are forced in an upward direction, the mechanism in the head supporting device locks the operating head in a raised position above the drawing board surface. The drawing may then be removed from the drawing board surface, or the surface may be cleaned. In order to unlock the mechanism in the head supporting device, a slight external downward force should be exerted onto the top of the operating head. Once the downward force exceeds a certain amount, the operating head, with the scales attached thereto, snaps back into contact with the drawing board surface. The essential parts of the mechanism include a tiltable holding member, pivotable about a central axis, biased by a spring or other means against a rolling member. The tilted position of the holding member coupled with the shape of two surfaces of the holding member maintain the operating head in either a raised or lowered position relative to the drawing board surface.
|
