Modeling Human Arm Movements Constrained by Robotic Systems

Fundamental difierences in human arm :>ehavior can be related to two types of movements: constrained and unconstrained. III constrained moveme Its, the human arm moves in such a way that the environment continuously exerts a dynamic constraint on the arm. The "environment", in this instance, is the object that is in continuous coptact with the human arm. In unconstrained movem~nts, the arm moves in its workspace without contact with the environment and, therefore, without cont~ ct forces between the arm and the environment. Exarr.ples of constrained movements can be seen when thE' arm is moving an exercise machine or is constrained by an orthotic device. In systems of this nature, the human arm dynamics are integrated with the mbchine dynamics, resulting in behavior specific to the total system. Therefore, the performance and stabilit,' of the system taken a.:. a whole are both functions of not only the machine dynwnics, but also the human arm dynamics. Instability of nlachines that interact with humans has been rep\.' -ted in (Kazerooni 1990). In this article, we examine the dynamics of constrained movements of the hunlan arm, where the environment dictates the position, while the human maintains a desired contact force. The human arm in constrained movements, is in continuous contact with its environment. The defining characteristic of the human arm in such movements is associated with the ability of the human to impose desired forces. Examples of con!trained movements can be seen in telerobotic systems, orthotic evices, and robotic systems worn by humans \Kazerooni 1991). We describe a theoretical and experimental analysis for constrained movements of the human arm.