pantograph

pantograph

1. an instrument consisting of pivoted levers for copying drawings, maps, etc., to any desired scale

2. a sliding type of current collector, esp a diamond-shaped frame mounted on a train roof in contact with an overhead wire

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Pantograph

A four-bar parallel linkage, with no links fixed, used as a copying device for generating geometrically similar figures, larger or smaller in size, within the limits of the mechanism. In the illustration the curve traced by point T will be similar to that generated by point S. This similarity results because points T and S will always lie on the straight line; triangles and are always similar because lengths, and are constant and is always parallel to. Distance always maintains a constant proportion to distance because of the similarity of the above triangles. Numerous modifications of the pantograph as a copying device have been made.

A second use of the pantograph geometry is seen in the collapsible parallel linkage used on electric locomotives and rail cars to keep a current-collector bar or wheel in contact with an overhead wire. Two such congruent linkages in planes parallel to the train's motion are affixed securely on the top of the locomotive with joining horizontal members perpendicular to each other. The uppermost member collects the current, and powerful springs thrust the configuration upward with sufficient pressure normally to make low-resistance contact from wire to collector.