In an experiment to measure and identify postural arm reflexes, subjects hold in their hands a linear hydraulic manipulator. A load cell is attached to the actuator handle to measure resulting forces. At the application of a force, subjects try to maintain a fixed posture. Figure P5.37 shows a block diagram for the combined arm-environment system.

In the diagram, H_r(s) represents the reflexive length and velocity feedback dynamics; H_act (s) the activation dynamics, H_i(s) the intrinsic act dynamics; H_h(s) the hand dynamics; H_e(s) the environmental dynamics; X_a(s) the position of the arm; X_h(s) the measured position of the hand; F_h(s) the measured interaction force applied by the hand; F_int (s) the intrinsic force; F_ref (s) the reflexive force; A(s) the reflexive activation; and D(s) the external force perturbation (de Vlugt, 2002).

a. Obtain a signal-flow diagram from the block diagram.

b. Find F_h(s)/D(s).

Transcribed Image Text:

F(s) Hs AG) Environment - Arm FIGURE P5.37