The purpose of this paper is to investigate the properties of the coupler c
urves generated by all 3R2C linkages. First, the 3x3 matrix with dual eleme
nts is used to derive the loop closure equation, the displacement equations
are derived, and all joints variables are expressed in terms of input and
output variables. Then, the parametric equations of the coupler curve are f
ound by the D-H matrix. Finally, homogeneous coordinate is introduced to th
ose displacement equations, and the order and some critical properties of t
he coupler curve are investigated based on the theories of algebraic curve
and analytical geometry of three dimensions. In addition, RCRCR and RRCCR l
inkages are used as examples for illustration. Moreover, the results on the
application of dimensional synthesis are discussed.