A human's ability to perform physical tasks is limited not by intellect but by physical strength. If, in an appropriate environment, a machine's mechanical power is closely integrated with a human arm's mechanical strength under the control of the human intellect, the resulting system will be superior to a loosely integrated combination of a human and a fully automated robot.
Extenders are defined as a class of robot manipulators that extend the strength of the human arm while maintaining human control of the task [23].The defining characteristic of an extender is the transmission of both power and information signals. The extender is worn by the human; the physical contact between the extender and the human allows the direct transfer of mechanical power and information signals. Because of this unique interface, control of the extender trajectory can be accomplished without any type of joystick, keyboard, or master-slave system. The human provides a control system for the extender, while the extender actuators provide most of the strength necessary for the task. The human becomes a part of the extender and "feels" a scaled-down version of the load that the extender is carrying. The extender is distinguished from a conventional master-slave system; in that type of system, the human operator is either at a remote location or close to the slave manipulator, but is not in direct physical contact with the slave in the sense of transfer of power. An extender is shown in Figure AP6.7(a) [23]. The block diagram of the system is shown in Figure AP6.7(b). Consider the proportional plus integral controller

Determine the range of values of the controller gains KP and KI such that the closed-loop system is stable.
Figure AP6.7
Extender robot control.

G,(s) = Kp + Ki Actuator Yis) Output RIS s(2s (0.05s 1) mpue