Sarrus Straight Line Polyhedral Linkage

The linkage shown above will keep the top plate parallel to the bottom plate as you raise and lower it. Pierre Frédéric Sarrus invented this linkage in 1853. It solves the problem of converting circular motion to straight-line motion that many people were still searching for.

Notes

• The two hinges do not have to be set at right angles to each other for this linkage to work. Here is a model with the two hinges at a larger angle.
  
• You can even make a collapsible Sarrus linkage out of one piece of paper without glue or tape using these patterns: 8½" × 11" Pattern or A4 Pattern or SVG Format. Cut along the solid lines and fold valley folds along the dashed lines and mountain folds along the dot-dashed lines. The small square near the center of the page will rise up parallel to the paper. Perhaps you can use a version of this to make a pop-up in a greeting card.
  

References

• (Goldberg, Polyhedral Linkages 1942)