Design of adjustable spherical four-bar linkages as continuous passive motion devices for anatomic joints rehabilitation

Continuous passive motion (CPM) is an important treatment in postoperative rehabilitation of human joints. It can improve the range of motion (ROM), reduce joint stiffness and accelerate the recovery process. The concept of CPM can be applied in many joint rehabilitation applications, including ankle joints, knee joints and elbow joints. However, even within a single type of joint, the ROM can be significantly different from person to person. Adjustable spherical linkage is appropriate for these applications. The following procedure is introduced: synthesize the first set of positions and selects the center point and circle point. Then, with the same center point and circle point, by altering some design parameters, i.e., the length of the input link and output link, a new set of positions can be synthesized. This idea is more practical in three-plustwo position synthesis, but can also be applied to four-plusthree position synthesis, with a significant increase in complexity.