| 摘要 |
A compass for drawing geometric figures including ellipses and polygons of different sizes and shapes. The compass includes an upstanding center post having a lower point which supports the compass on the drawing surface. A disc forming a peripheral cam track is detachably mounted on a holder which in turn is pivotally mounted on a medial portion of the post. The disc is connected with a plunger which is slidable in the post for selectively adjusting the angle of the disc. A head member is rotatably mounted on an upper portion of the post. An adjustable multiplier link carrying a marking element is pivotally mounted at its upper end to the head member at a point which is radially spaced from the post a distance greater than the maximum radius of the cam track. In one embodiment a cam follower is suspended from the head member by a parallelogram linkage, and spring means is provided to urge the roller into contact with the cam track. In another embodiment the cam follower comprises a ring which turns in positive engagement about the disc, with stabilizer fingers being mounted to turn about the post. An alternate stylus arm is mounted below the cam follower for use in drawing figures of short radii. In both embodiments disc can be detached from its holder for replacement with parts having a varied cam track for drawing a different geometric figure.
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