H. Kazerooni

Biomechanical design of the Berkeley lower extremity exoskeleton (BLEEX)

Wheeled vehicles are often incapable of transporting heavy materials over rough terrain or up staircases. Lower extremity exoskeletons supplement human intelligence with the strength and endurance of a pair of wearable robotic legs that support a payload. This paper summarizes the design and analysis of the Berkeley lower extremity exoskeleton (BLEEX). The anthropomorphically based BLEEX has 7 DOF per leg, four of which are powered by linear hydraulic actuators. The selection of the DOF, critical hardware design aspects, and initial performance measurements of BLEEX are discussed.

Human-robot interaction via the transfer of power and information signals

Constrained motion in a class of human-controlled robotic manipulators called extenders is discussed. Extenders are defined as a class of robot manipulators worn by humans to increase mechanical strength while the wearers intellect remains the central control system for manipulating the extender. The human, in physical contact with the extender, exchanges power and information signals with the extender. The present analysis focuses on the dynamics and control of human-robot interaction in the sense of the transfer of power and information signals. General models for the human, the extender, and the interaction between the human and extender are developed. The stability of the system of human, extender, and the object being manipulated is analyzed, and the conditions for stable maneuvers are derived. An expression for the extender performance is defined to quantify the force augmentation. The trade-off between stability and performance is described. The theoretical predictions are verified experimentally. >

On the Control of the Berkeley Lower Extremity Exoskeleton (BLEEX)

The first functional load-carrying and energetically autonomous exoskeleton was demonstrated at U.C. Berkeley, walking at the average speed of 1.3 m/s while carrying a 34 kg (75 lb) payload. Four fundamental technologies associated with the Berkeley Lower Extremity Exoskeleton (BLEEX) 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 (bLAN) to host the control algorithm and an on-board power unit to power the actuators, sensors and the computers. This article 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 tradeoffs between having sensors to measure human variables and the lack of robustness to parameter variation are described.

Robust compliant motion for manipulators, part I: The fundamental concepts of compliant motion

A method for the design of controllers of constrained manipulators in the presence of model uncertainties is developed. The controller must carry out fine maneuvers when the manipulator is not constrained, and compliant motion, with or without interaction-force measurement, when the manipulator is constrained. At the same time stability must be preserved if bounded uncertainties are allowed in modelling the manipulators. Stability of the manipulator and environment as a whole and the preservation of stability in the face of changes are two fundamental issues that have been considered in the design method. A set of practical design specifications in the frequency domain is presented that is meaningful from the standpoint of control theory and assures the desired compliant motion in the Cartesian coordinate frame and stability in the presence of bounded uncertainties. This approach also assures the global stability of the manipulator and its environment. The consequence of inexact achievement of performance specifications on stability is also specified. Part I concerns the fundamentals of compliant motion, while Part II is devoted to the controller design method.

The Berkeley Lower Extremity Exoskeleton

The first functional load-carrying and energetically autonomous exoskeleton was demonstrated at U.C. Berkeley, walking at the average speed of 1.3 m/s while carrying a 34 kg (75 lb) payload. Four fundamental technologies associated with the Berkeley Lower Extremity Exoskeleton (BLEEX) 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 (bLAN) to host the control algorithm and an on-board power unit to power the actuators, sensors and the computers. This article 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 dynamics and control of a haptic interface device

Haptic interface devices are machines that are controlled by the human arm contact forces. These devices are necessary elements of virtual reality machines. These devices may be programmed to give the human arm the sensation of forces associated with various arbitrary maneuvers. As examples, these devices can give the human the sensation that he/she is maneuvering a mass, or pushing onto a spring or a damper. In general, these devices may be programmed for any trajectory-dependent force. To illustrate and verify the analysis of these machines, a two-degree-of-freedom electrically-powered haptic interface device was designed and built at the Human Engineering Laboratory (HEL) of the University of California-Berkeley. >

Human/robot interaction via the transfer of power and information signals. I. Dynamics and control analysis

Extenders, a class of robot manipulators worn by humans to increase human mechanical strength while the wearers intellect remains the central intelligent control system for manipulating the extender, are characterized, with a focus on the issues of the dynamics and control of human-machine interaction in the sense of the transfer of power and information signals. General models of the human, the extender, and the interaction between the human and the extender are developed. Unstructured modeling is chosen to include all the dynamics in the systems and to avoid specific models. The stability of the system of human, extender, and object being manipulated is analyzed, and the conditions for stable maneuvers derived. An expression for the performance of the extender is defined as a means to quantify the force augmentation. The tradeoff between stability and performance is described.<<ETX>>

Robust compliant motion for manipulators, part II: Design method

A controller design methodology to develop a robust compliant motion for robot manipulators is described. The achievement of the target dynamics (the target impedance is introduced in Part I) and preservation of stability robustness in the presence of bounded model uncertainties are the key issues in the design method. State-feedback and force-feedforward gains are chosen to guarantee the achievement of the target dynamics, while preserving stability in the presence of the model uncertainties. In general, the closed-loop behavior of a system cannot be shaped arbitrarily over an arbitrarily wide frequency range. It is proved that a special class of impedances that represent our set of performance specifications are mathematically achievable asymptotically through state-feedback and interaction-force feedforward as actuator bandwidths become large, and we offer a geometrical design method for achieving them in the presence of model uncertainties. The design method reveals a classical trade-off between a systems performance over a bounded frequency range and its stability relative to model uncertainties via multivariable Nyquits criteria. Two classes of such uncertainties are dealt with. While the first class of model uncertainties is formed from the uncertainties in the parameters of the modeled dynamics, the high-frequency unmodeled dynamics form the second class of model uncertainties. The multivariable Nyquist criterion is used to examine trade-offs in stability robustness against approximation of desired target impedances over bounded frequency ranges.

Dynamics and Control of Robotic Systems Worn by Humans

This article describes the dynamics, control, and stability of extenders, robotic systems worn by humans for material handling tasks. Extenders are defined as robot manipulators which extend (i.e., increase) the strength of the human arm in load maneuvering tasks, while the human maintains control of the task. Part of the extender motion is caused by physical power from the human; the rest of the extender motion results from force signals measured at the physical interfaces between the human and the extender, and the load and the extender. Therefore, the human wearing the extender exchanges both power and information signals with the extender. The control technique described here lets the designer define an arbitrary relationship between the human force and the load force. A set of experiments on a two-dimensional non-direct-drive extender were done to verify the control theory.

On the Robot Compliant Motion Control

The work presented here is a nonlinear approach for the control and stability analysis of manipulative systems in compliant maneuvers. The general stability condition has been extended to the particular case where the environment is very rigid in comparison with the robot stiffness. A fast, light-weight, active end-effector (a miniature robot) which can be attached to the end-point of large commercial robots has been designed and built to verify the control method