Model: T02 Parallel Link Mechanism
This model contains several variations of the so-called 'lazy tongs' mechanism. The principal constraint consists of crossed links with a center pin and slider pins in slots in two parallel links. Closing the angle between the crossed links moves the two parallel links apart while maintaining the vertical orientation of these two links. An extension of this mechanism is the connection of two or more pairs of crossed links with center pins that will amplify the relative motion of the two parallel links for a given change in angle of the crossed links. This constitutes an exact parallel mechanism in contrast to the approximate parallel mechanism of Models T3-T10. Variations of the lazy tongs mechanism have appeared in the history of machines including the manuscripts of Leonardo da Vinci (c.1500), and the machine books of Jacque Besson (C. 1570), and Ramelli (c. 1580).

A similar mechanism has been used in electric trains in the power pickup mechanism sometimes called a pantograph. It has also been used in hydraulic lift devices from automobile jacks to mobile worker lift platforms.

Francis Moon 2003-07-01