PANTOGRAPH

A pantograph is a four-bar linkage used to produce paths exactly similar to the ones traced out by a point on the linkage. The paths so produced are, usually, on an enlarged or reduced scale and may be straight or curved ones.

Pantograph is a geometrical instrument used in drawing offices for reproducing given geometrical figures or plane areas of any shape, on an enlarged or reduced scale. It is also used for guiding cutting tools. Its mechanism is utilized as an indicator rig for reproducing the displacement of cross-head of a reciprocating engine, which, in effect gives the position of displacement.

Fig. (a) shows the line diagram of a pantograph in which AB = CD, BC = AD and ABCD is located/jointed in such a way that it remains in a parallelogram position. OQP is a straight line and P describes a path similar to that described by Q.

Proof : To prove that the path described by P is similar to that described by Q, let us consider similar triangles ΔOAQ and ΔOBP in which ∠BOP is common.

Hence, OQ₁ is similar to OP₁ or they are parallel. Thus, path traced by P is similar to that of Q.

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