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TECHNICAL PAPERS

The Berkeley Lower Extremity Exoskeleton

[+] Author and Article Information
H. Kazerooni

University of California, Berkeley, Berkeley, CA 94720

R. Steger

University of California, Berkeley, Berkeley, CA 94720exo@berkeley.edu

J. Dyn. Sys., Meas., Control 128(1), 14-25 (Sep 17, 2005) (12 pages) doi:10.1115/1.2168164 History: Received March 31, 2005; Revised September 17, 2005

Abstract

The first functional load-carrying and energetically autonomous exoskeleton was demonstrated at the University of California, Berkeley, walking at the average speed of $1.3m∕s$$(2.9mph)$ while carrying a $34kg$$(75lb)$ payload. Four fundamental technologies associated with the Berkeley lower extremity exoskeleton were tackled during the course of this project. These four core technologies include the design of the exoskeleton architecture, control schemes, a body local area network to host the control algorithm, and a series of on-board power units to power the actuators, sensors, and the computers. This paper gives an overview of one of the control schemes. The analysis here is an extension of the classical definition of the sensitivity function of a system: the ability of a system to reject disturbances or the measure of system robustness. The control algorithm developed here increases the closed-loop system sensitivity to its wearer’s forces and torques without any measurement from the wearer (such as force, position, or electromyogram signal). The control method has little robustness to parameter variations and therefore requires a relatively good dynamic model of the system. The trade-offs between having sensors to measure human variables and the lack of robustness to parameter variation are described.

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Figures

Figure 2

Simple 1-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.

Figure 3

The exoskeleton’s angular velocity is shown as a function of the input to the actuators and the torques imposed by the pilot onto the exoskeleton

Figure 4

Feedback control loop is added to block diagram of Fig. 3. C is the controller operating only on the exoskeleton variables.

Figure 5

This block diagram shows how an exoskeleton moves. The upper loop shows how its pilot moves the exoskeleton through applied forces. The lower loop shows how the controller drives the exoskeleton.

Figure 6

The pilot vests shown here and in Fig. 1 are designed to uniformly distribute the BLEEX-pilot force on the pilot’s upper body

Figure 7

Rigid attachment bindings between (a) the pilot boot and (b) the BLEEX foot

Figure 8

The sensory system in one prototype BLEEX foot sole is composed of pressure sensitive semi-conductive rubber embedded in a polyurethane sole (Fig. 7). This foot measures the ground reaction force profile at four locations: toe, ball, midfoot, and heel.

Figure 1

Berkeley lower extremity exoskeleton (BLEEX) and pilot Ryan Steger. (1) Load occupies the upper portion of the backpack and around the power unit, (2) rigid connection of the BLEEX spine to the pilot’s vest, (3) power unit and central computer occupies the lower portion of the backpack, (4) semi-rigid vest connecting BLEEX to the pilot, (5) one of the hydraulic actuators, and (6) rigid connection of the BLEEX feet to the pilot’s boots (more photographs can be found at http://bleex.me.berkeley.edu).

Figure 11

Sagittal-plane representation of BLEEX in (a) the double-support phase and (b) the double-support phase with one redundancy

Figure 12

The controller relies on a high-speed synchronous ring network topology where several remote input/output network nodes (shown as I/O Module #1) collect local sensor data and distribute local actuation commands

Figure 13

Each RIOM (shown here) is in communication with several sensors and one actuator in close proximity

Figure 14

BLEEX degrees of freedom

Figure 15

Human power required for walking. The flexion/extension direction requires the most power for all three joints (ankle, knee, and hip). Besides these sagittal plane directions, the hip abduction/adduction requires the next most power (31).

Figure 16

Power required for ascending/descending Stairs. The knee requires power when ascending stairs instead of absorbing power as it does during level walking (35).

Figure 9

Three phases of the BLEEX walking cycle

Figure 10

Sagittal plane representation of BLEEX in the single-stance phase. The “torso” includes the combined exoskeleton torso mechanism, payload, control computer, and power source.

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