782 Part D Manipulation and Interfaces Taking into account this new approach,the goal is stabilizing the exoskeleton and preventing it from falling to develop a controller for the exoskeleton with high in response to external forces depends on the pilot's sensitivity.One is faced with two realistic concerns; ability to move quickly (e.g.,step back or sideways)to the first was that an exoskeleton with high sensitivity create a stable situation for himself and the exoskeleton. to external forces and torques would respond to other For this,a very wide control bandwidth is needed so that external forces not initiated by its pilot,for example,if the exoskeleton can respond to both pilot's voluntary someone pushed against an exoskeleton that had high and involuntary movements(i.e.,reflexes). sensitivity,the exoskeleton would move just as it would The second concern is that systems with high sen- in response to forces from its pilot.Although the fact that sitivity to external forces and torques are not robust to it does not stabilize its behavior on its own in response variations and therefore the precision of the system per- to other forces may sound like a serious problem,if it formance will be proportional to the precision of the did (e.g.,using a gyro)the pilot would receive motion exoskeleton dynamic model.Various experimental sys- from the exoskeleton unexpectedly and would have to tems in Berkeley have proved the overall effectiveness of struggle with it to avoid unwanted movement.The key to the control method in shadowing the pilot's movement. 33.7 The Control Scheme of an Exoskeleton The control of the exoskeleton is motivated here through therefore considered unknown values in this analysis.In the simple one-degree-of-freedom (1-DOF)example fact,one of the primary objectives in designing BLEEX shown in Fig.33.11.This figure schematically depicts was to ensure a pilot's unrestricted interaction with the a human leg attached or interacting with a 1-DOF exo- exoskeleton.The equivalent torque on the exoskeleton skeleton leg in a swing configuration(no interaction with leg,resulting from the pilot's applied forces and torques, the ground).For simplicity,the exoskeleton leg is shown is represented by d. as a rigid link pivoting about a joint and powered by a sin- In the absence of gravity,(33.9)and the block dia- gle actuator.The exoskeleton leg in this example has an gram of Fig.33.12 represent the dynamic behavior of actuator that produces a torque about pivot point A. the exoskeleton leg regardless of any kind of internal Although the pilot is securely attached to the exo- feedback the actuator may have skeleton at the foot,other parts of the pilot leg,such as v=Gr+Sd, (33.9) the shanks and thighs.can contact the exoskeleton and impose forces and torques on the exoskeleton leg.The where G represents the transfer function from the ac- location of the contacts and the direction of the con- tuator input r to the exoskeleton angular velocity v tact forces (and sometimes contact torques)vary and are (the actuator dynamics are included in G).In the case where multiple actuators produce controlled torques on the system,r is the vector of torques imposed on the exoskeleton by the actuators.The form of G and the type of internal feedback for the actuator is immaterial for the discussion here.Also bear in mind the omission Human of the Laplace operator in all equations for the sake of leg compactness. BLEEX leg Part Fig.33.11 Simple one-DOF exoskeleton leg interacting D33.7 with the pilot leg.The exoskeleton leg has an actuator that produces a torque T about the pivot point A.The total Fig.33.12 The exoskeleton's angular velocity is shown as equivalent torque associated with all forces and torques a function of the input to the actuators and the torques from the pilot on the exoskeleton is represented by d imposed by the pilot on the exoskeleton782 Part D Manipulation and Interfaces Taking into account this new approach, the goal is to develop a controller for the exoskeleton with high sensitivity. One is faced with two realistic concerns; the first was that an exoskeleton with high sensitivity to external forces and torques would respond to other external forces not initiated by its pilot, for example, if someone pushed against an exoskeleton that had high sensitivity, the exoskeleton would move just as it would in response to forces from its pilot. Although the fact that it does not stabilize its behavior on its own in response to other forces may sound like a serious problem, if it did (e.g., using a gyro) the pilot would receive motion from the exoskeleton unexpectedly and would have to struggle with it to avoid unwanted movement. The key to stabilizing the exoskeleton and preventing it from falling in response to external forces depends on the pilot’s ability to move quickly (e.g., step back or sideways) to create a stable situation for himself and the exoskeleton. For this, a very wide control bandwidth is needed so that the exoskeleton can respond to both pilot’s voluntary and involuntary movements (i. e., reflexes). The second concern is that systems with high sen￾sitivity to external forces and torques are not robust to variations and therefore the precision of the system per￾formance will be proportional to the precision of the exoskeleton dynamic model. Various experimental sys￾tems in Berkeley have proved the overall effectiveness of the control method in shadowing the pilot’s movement. 33.7 The Control Scheme of an Exoskeleton The control of the exoskeleton is motivated here through the simple one-degree-of-freedom (1-DOF) example shown in Fig. 33.11. This figure schematically depicts a human leg attached or interacting with a 1-DOF exo￾skeleton leg in a swing configuration (no interaction with the ground). For simplicity, the exoskeleton leg is shown as a rigid link pivoting about a joint and powered by a sin￾gle actuator. The exoskeleton leg in this example has an actuator that produces a torque about pivot point A. Although the pilot is securely attached to the exo￾skeleton at the foot, other parts of the pilot leg, such as the shanks and thighs, can contact the exoskeleton and impose forces and torques on the exoskeleton leg. The location of the contacts and the direction of the con￾tact forces (and sometimes contact torques) vary and are T, d A + Human leg Actuator BLEEX leg Fig. 33.11 Simple one-DOF exoskeleton leg interacting with the pilot leg. The exoskeleton leg has an actuator that produces a torque T about the pivot point A. The total equivalent torque associated with all forces and torques from the pilot on the exoskeleton is represented by d therefore considered unknown values in this analysis. In fact, one of the primary objectives in designing BLEEX was to ensure a pilot’s unrestricted interaction with the exoskeleton. The equivalent torque on the exoskeleton leg, resulting from the pilot’s applied forces and torques, is represented by d. In the absence of gravity, (33.9) and the block dia￾gram of Fig. 33.12 represent the dynamic behavior of the exoskeleton leg regardless of any kind of internal feedback the actuator may have v = Gr + Sd , (33.9) where G represents the transfer function from the ac￾tuator input r to the exoskeleton angular velocity v (the actuator dynamics are included in G). In the case where multiple actuators produce controlled torques on the system, r is the vector of torques imposed on the exoskeleton by the actuators. The form of G and the type of internal feedback for the actuator is immaterial for the discussion here. Also bear in mind the omission of the Laplace operator in all equations for the sake of compactness. S r υ d ++ G Fig. 33.12 The exoskeleton’s angular velocity is shown as a function of the input to the actuators and the torques imposed by the pilot on the exoskeleton Part D 33.7