| 摘要 |
A copying machine which can reproduce convex or concave surfaces having smaller radii of curvature at the edge than at the center, for example the surfaces of moulds for making contact lenses, has a cam assembly including a cam with a part-cylindrical cam surface mounted on a base. The cam has a part-circular section in the plane perpendicular to the cam surface generatrices and a straight section tangential to and continuous with one end of the part-circular section. The latter is slidably mounted on a concentric part-circular guide on the base, allowing rotary movement about its geometric center. The guide and at least the part-circular section of the cam have complementary square profiles. The part-circular cam section may be locked in position on the guide by screws threaded into the guide and passing through a concentric part-circular slot in the cam. The machine has a feeler held against the cam surface, a work block movable perpendicularly to the cam surface generatrices, and a transmission for moving the work block in dependence on the movement of the feeler. The transmission is so arranged that when the feeler moves away from an axis parallel to the cam surface generatrices passing through the geometric center of the part-circular cam section the work block moves towards that axis. The transmission includes a pivoted lever. The work block and feeler may be pivoted to this on the same or opposite sides of its pivot. In the first case a tool carried by the work block is located on the opposite side of the axis to the lever, while in the second case it is located between the axis and the lever.
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