Rigid-body equations (1) and (2) include only the effects oflink masses and inertias. Friction, dynamic coupling due tothe inertia of geared actuator rotors that spin at high velocity[12], as well as the effects of gravity-compensatingdevices if present contribute significantly to the dynamicbehavior of the robot manipulator. Gravity-compensatingdevices, which are preloaded springs mounted betweenthe first and second link, approximately compensate thestatic torque caused by the mass of the payload and robotwrist on the actuator of the second link, that is, the shoulderactuator [13]. Dynamic coupling and gravity-compensatingsprings can be described by mathematical