Scott Russell Straight Line Mechanism
The mechanism to the right can be refered to as the Scott Russell Mechanism or a more descriptive name is the Scott Russell Exact Straight Line Mechanism. For this description to be true the acting length of the short link, the blue one, needs to be half as long as the active length of the green one and the pin that connects them must be concentric with the mid point of the long or green link. One more requirement is that the slider's connection pin needs to be sliding in a line that would intersect the static pivot end of the short link. I have seen this link represented on the web in proportions which prevent it from producing an exact straight line. I have tested one of these and it is was surprising how close to a line it made over a given range. Of coarse often a aproximate line is close enough. On the other hand one should remember that real linkages bend under load and joints have play; so even exact straight line mechanisms will not be exact in practice. In the animation above the slider stops short of that blue link's pivot point. But if the mechanism was made so that the links were in different planes then it it would be possible for this mechanism to 'flip' on the vertical axis as the slider passes through the traced line. Again if the links are in different planes, the long link could pass through the horizontal axis and continue to draw a straight line that would run down below the x or horizontal axis.
My interest in straight line generators is partly the result of looking for mechanisms that could help drive the "Uniport Valve", for which I own a patent. If you happened to land on this page, please visit my home page at: http://www.inventhp.com and learn more about this double acting valve. Anyway, during my research I came across the Peaucellier Mechanism, one example is to the left. It produes a straight line having only linkages and pivot points. In testing the conditions for this mechanism, some unusual variations of this mechanism were found. Please view some of these at Peaucellier Mechanisms.
Should you have any comments about how I represented these straight line generators or anything else on my site please contact me at: Contact Invent Horsepower