Impedance control of two d.o.f. CPM device for elbow joint

Recently, new technology that supports human will be an emergent issue as population ages and birthrate declines. As human having a lot of joints utilizes many degrees of freedom (d.o.f.) for living and working, reduction or loss of d.o.f. will deteriorate the quality of life. So, it will be important to recover joint functions immediately after injury or operation. Accordingly, many studies have been performed on the development and application of orthopedic treatment or rehabilitation training devices (Furusho et al., 2005; Duong et al., 2005; Mavroidis et al., 2005; Hogan et al., 2006). In the tendency, continuous passive motion (CPM) was proposed as an orthopaedic treatment and a physiotherapy method that promotes recovery from the injuries after surgery of joints (Salter et al., 1960). The CPM is intended to accelerate the regeneration of periarticular tissues, to prevent contracture, and to correct range of motion (ROM) (Salter, 1993), and is more effective than conventional treatment method with casts (Salter, 1993; O'Driscoll et al., 2000). There are many works on the CPM devices for the lower limbs. Particularly, the CPM devices for the knee joint have been widely used. It was reported that these devices induce quick recovery and improve the joint ROM more effectively (Tanaka, 1998; Sakaki et al., 2000; Akdogan et al., 2006). The knee joint has a simple hinged joint, which is the same structure as the CPM devices for the knee joint, so that the CPM devices can perform effective CPM by easy setting. On the other hand, there are few researches about CPM devices for the upper limbs because of the musculoskeletal complexity. Most conventional CPM devices for the elbow joint have only one d.o.f., and perform the flex-/extension with fixed forearm to avoid the complex setting of the device (Kawaji, 2006). The human’s elbow joint, which consists of a radius, ulna, humerus and biological tissues, has complex structure, and is structurally different from the conventional CPM devices for the elbow. This difference causes some problems such as fluctuation of rotation center of the flex-/extension, excessive reaction force due to the inappropriate pose of the forearm, etc. For the former, Usui et. al. have proposed an algorithm that compensates the fluctuation of the rotation center while the rehabilitation(Usui et al., 2004). But, for the latter there are few researches about the variation of the reaction force due to the forearm position i.e., the pro/supination. 13