pantograph (redirected from Eidograph)

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 [′pan·tə‚graf]

(engineering)

A device that sits on the top of an electric locomotive or cars in an electric train and picks up electricity from overhead wires to run the train.

(graphic arts)

A drawing instrument used for copying and consisting of four rigid bars linked together in a parallelogram form; one arm, equipped with a pencil, is connected through the bars to a pointer that is used to trace the original drawing.

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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.