Straight guide trace STE

This image describes a curve traced by a coupler of a four bar linkage, where a major part of the curve is traced as a straight line. By adjusting the ratios of lengths , one solution is obtained where the entire curve traced is a straight line and the tracer of the coupler osciallates only between the dead centre positions in a linear way with constant velocity. The system has three bodies and four revolute joints and therefore one degree freedom.