Neck pain is common among occupations requiring static neck flexion. Therefore, this project develops and tests a neck support to alleviate occupational neck pain. The design supports workers' heads during neck flexion to reduce neck muscle activity. Surface electromyography tests and workplace tests using a prototype yielded promising efficacy results. We designed and tested a new, wearable device to support workers' heads during neck flexion. The device acts as a headrest to reduce neck pain in people like dentists who hold their heads bent forward. Lab test results showed a reduction in muscle loads while workplace testing validated market potential.

The development of a semi-automated haptic device for installing cables is a promising application for ship building industry, as well as in other industries which require power cable installations. The most critical tasks of this device involve quickly and reliably grasping and releasing cables. In this study, we design a device with an end-effector that uses a self-locking mechanism based on rope elements. Here, the pulling force is directly transferred to the cable using a frictional connection. The modules of this device are designed for one-person-operation, and optimize for the harsh environment of shipyards. A set of equations of motions were derived from a mathematical model of the connection between rope elements of the end effector and the cable, which show that the presented design provides the necessary no-slip condition between the end effector and the cable. A printed circuit board with an 8-bit microcontroller controls the induction motor which gives 0.6 horsepower, in combination with an AC motor driver. Thereby sensor signals are processed to ensure the desired functions by the operator's commands. This device has been shown to perform with enhanced efficiency in cable-installing tasks throughout the field test in a shipyard.

This paper proposes a design for a knee-ankle prosthesis which ultimately controls two linear hydraulic actuators using a single pump. The design takes advantage of the fact that the knee and ankle never produce large positive powers simultaneously during stair-climbing, and that the ankle produces more positive power than the knee during walking. This makes the prosthesis lighter and smaller. During walking, the ankle joint adds forward propulsive power similar to that of an intact ankle. During stair climbing, the knee joint provides assistance like that of an intact knee. The hydraulic nature of the prosthetic allows it to function in a semi-active mode, where it behaves similar to a microcontroller controlled passive transfemoral prosthesis.

Current advancements in exoskeleton robotics allow those with mobility disorders to walk again. The user conveys his or her desired motion to the exoskeleton using a Human Machine Interface (HMI). This allows the users to stand up, walk, and sit down independently. Existing HMIs require unnatural motions that inhibit the gait. The HMI developed here uses natural gestures while ensuring the safety of the user. This method utilizes a unique sensor suite and a finite state automaton to allow a spinal cord injury patient to easily use an exoskeleton for mobility.

Current state-of-the-art prostheses for transfemoral amputees operate exclusively through controlled damping or through fully powered gait imitation. The passive devices cannot restore a natural gait, and the active devices are large and inefficient. This paper summarizes the design of a new semi-active prosthetic knee that combines the proven safety and power efficiency of a passively damped hydraulic device with the improved gait and advanced mobility of a fully active device.

The exoskeleton is an autonomous robotic device whose function is to increase the strength and endurance of a human pilot. In order to achieve an exoskeleton controller which reacts compliantly to external forces, an accurate model of the dynamics of the system is required. In this report, a series of system identification experiments are designed and carried out for the Berkeley lower extremity exoskeleton. As well as determining the mass and inertia properties of the segments of the legs, various non-ideal elements such as friction, stiffness and damping forces are identified. The resulting dynamic model is found to be significantly more accurate than the original model predicted from the designs of the robot

The Berkeley lower extremity exoskeleton (BLEEX) is a load-carrying and energetically autonomous human exoskeleton that, in this first generation prototype, carries up to a 34 kg (75 Ib) payload for the pilot and allows the pilot to walk at up to 1.3 m/s (2.9 mph). This article focuses on the human-in-the-loop control scheme and the novel ring-based networked control architecture (ExoNET) that together enable BLEEX to support payload while safely moving in concert with the human pilot. The BLEEX sensitivity amplification control algorithm proposed 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 tradeoffs between not having sensors to measure human variables, the need for dynamic model accuracy, and robustness to parameter uncertainty are described. ExoNET provides the physical network on which the BLEEX control algorithm runs. The ExoNET control network guarantees strict determinism, optimized data transfer for small data sizes, and flexibility in configuration. Its features and application on BLEEX are described

Many places in the world are too rugged or enclosed for vehicles to access. Even today, material transport to such areas is limited to manual labor and beasts of burden. Modern advancements in wearable robotics may make those methods obsolete. Lower extremity exoskeletons seek to supplement the intelligence and sensory systems of a human with the significant strength and endurance of a pair of wearable robotic legs that support a payload. This paper outlines the use of Clinical Gait Analysis data as the framework for the design of such a system at UC Berkeley.

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.

Energetic autonomy of a hydraulic-based mobile field robot requires a power source capable of both electrical and hydraulic power generation. While the hydraulic power is used for locomotion, the electric power is used for the computer, sensors and other peripherals. An internal combustion engine was used as the prime mover due to the high energy density of gasoline. The primary specification for this hybrid hydraulic-electric power unit (HEPU) is that it must output constant pressure hydraulic power and constant voltage electric power. An on-board computer uses a pressure sensor and a speed sensor to regulate the pressure and voltage by modulating a hydraulic solenoid valve and an engine throttle. The speed regulation also results in a system noise with predictable frequency band which allows for optimal muffler design. A novel characteristic of this power source is its cooling system in which hydraulic fluid is used to cool the engine cylinders. Several hydraulic-electric power units were built and successfully demonstrated on the Berkeley Lower Extremity Exoskeleton (BLEEX) shown on bleex.me.berkeley.edu/bleex.htm. A prototype power unit weighs 27 Kg, outputs 2.3 kW (3.0 hp) hydraulic power at 6.9 MPa (1000 psi), and 220 W of electric power at 15 VDC.

The first load-bearing and energetically autonomous exoskeleton, called the Berkeley Lower Extremity Exoskeleton (BLEEX) walks at the average speed of two miles per hour while carrying 75 pounds of load. The project, funded in 2000 by the Defense Advanced Research Project Agency (DARPA) tackled four fundamental technologies: the exoskeleton architectural design, a control algorithm, a body LAN 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 the BLEEX project.

The first energetically autonomous lower extremity exoskeleton capable of carrying a payload has been demonstrated at U.C. Berkeley. This paper summarizes the mechanical design of the Berkeley Lower Extremity Exoskeleton (BLEEX). The anthropomorphically-based BLEEX has seven degrees of freedom per leg, four of which are powered by linear hydraulic actuators. The selection of the degrees of freedom and their ranges of motion are described. Additionally, the significant design aspects of the major BLEEX components are covered.

This paper describes a novel robotic end-effector and a method for grasping deformable objects with undefined shapes and geometry, such as sacks and bags. The first prototype end-effector, designed for applications in the U.S. Postal Service, is comprised of two parallel rollers with gripping surfaces in which the rollers are pushed toward each other. When the end-effector comes into contact with any portion of the deformable object, the rollers turn inwardly so that a graspable portion of the object is dragged between the rollers. The rollers stop rotating when a graspable portion of the material/object is caught in between, allowing the object to be maneuvered by the robot. The object is released when the rollers turn outwardly. The end-effector described in this article can grab and hold filled sacks from any point on the sack, regardless of the sack's orientation. Experimental evaluation of the end-effector has proven the design and implementation remarkably effective. This article describes the hardware, control method, and design issues associated with the end-effector. Note to Practitioners - Delivery and postal services around the world currently use sacks to hold letters, magazines, and small boxes. The considerable weight of these sacks, their lack of handles, eyelets, or other operator interfaces, and the unpredictable shape and size of the packages within create awkward and uncomfortable handling predicaments for mail handlers at all U.S. Postal Service distribution centers. Currently, no robotic hand or end-effector is commercially available to grab and hold sacks effectively, so sacks must be handled manually by postal employees in distribution centers. This paper describes the design of a novel robotic end-effector for manipulating deformable objects with undefined shapes, such as sacks and bags. This device, which does not mimic human hand architecture, is simple and practical; it makes use of the friction between two rotating rollers to grab sack material when it is in close proximity of the end-effector. The rollers cease rotation when sufficient sack material is collected between the rollers to support the sack. They reverse their rotation, and turn outwardly to release the sack again. This end-effector is able to grab a sack at any point, does not require the edge of the sack to be gathered and flattened prior to grasp, does not require the sack to be placed on its bottom, needs no operator intervention, does not use the weight of the sack to lock and secure the sack in the end-effector, and does not damage the sack contents.

We have developed a novel device to supply hydraulic power for anaerobic mobile robotic systems. This power source demonstrates the possibility of operation in oxygen-free environments, such as underwater or in space. Unlike the internal combustion engine, the design produces power on demand, eliminating idling when there is no load on the system. This monopropellant-powered free piston hydraulic pump (FPHP) was designed as a human scale (1.0-3.0 kW) power source, and produces only steam and oxygen as its byproducts. The FPHP utilizes high concentration hydrogen peroxide as the monopropellant energy source, which decomposes into hot gas when exposed to a catalyst. Energy is extracted from the hydrogen peroxide and transferred directly to hydraulic fluid by expanding the hot decomposition gas in an integrated piston/cylinder arrangement. Based on a specific power and specific energy analysis using a Ragone plot, the performance of the FPHP potentially exceeds that of a battery-based hydraulic power source for short operation times. Note to Practitioners-This project was motivated by the need for a simple free piston engine that is capable of producing hydraulic power. A free piston engine has no crankshaft or rotating motion, only a piston assembly that is constrained to move in a linear fashion within a bore. The energy of the free piston can be harnessed by pressurizing a working fluid or generating electrical power. Instead of relying on the combustion of gasoline or diesel fuel to move the free piston, which involves problems with fuel/air mixing and ignition timing, we created a device that is powered by the catalytic decomposition of a monopropellant. This concept overcomes the problems with a combustion powered free piston engine and also affords operation in environments with no atmosphere, such as underwater or in space. The device we constructed is an integrated free piston engine and hydraulic pump with very few moving parts. This monopropellant free piston engine could be adapted for use with any source of pressurized gas (preferably one with a high specific energy) and could be scaled to varying power outputs. The largest hurdle to overcome before realizing reliable operation of the free piston hydraulic pump (FPHP) is ensuring that the catalyst effectively decomposes the monopropellant.

This article introduces an instrumented glove and its application for robotic and human-assisted material handling manipulators. In its simplest form, worn by an operator, the sensory glove measures the force the wearer imposes on any part of the material handling robot or the object being maneuvered by the material handling robot This measured force is then transmitted as radio frequency (RF) signals to the controller of the material handling robot, which in turn maneuvers the load so that the human operator only needs to exert a small portion of the force, leaving the actuator of the system to provide the remaining force required. Therefore, the actuators of the material handling system add exertion only in response to the operator's hand force on the material handling system, or on the object maneuvered by the robot. Our experimental glove has proven entirely effective in manipulating objects naturally similar to the way we manipulate objects manually without activating many switches and pushbuttons to command the device.

We have developed a novel device to supply hydraulic power for anaerobic mobile robotic systems. This power source is capable of operation in environments with no oxygen, such as underwater and space. The design, unlike the internal combustion engine, produces power on demand, eliminating idling when there is no load on the system. Steam and oxygen are the only byproducts of this power supply. This monopropellant-powered free piston hydraulic pump (FPHP) was designed as a human scale (1.0 to 3.0 kW) power supply. The FPHP utilizes high concentration hydrogen peroxide, which decomposes into hot gas when exposed to a catalyst, as the monopropellant energy source. Energy is extracted from the hydrogen peroxide and transferred directly to hydraulic fluid by expanding the hot decomposition gas in an integrated piston/cylinder arrangement. Based upon a specific power and specific energy analysis using a Ragone plot, the performance of the FPHP potentially exceeds that of a battery based hydraulic power supply for short operation times.

This article models a pneumatic system consisting of double-acting or single acting cylinder and a servovalve with the goal of providing an insight into pneumatic design and control requirements for Berkeley Exoskeleton (http://www.me.berkeley.edu/hel/). The modeling approach uses the thermodynamic principles of energy and mass conservation. We demonstrate that pneumatic systems suffer from two effects: unwanted dynamics due to gas compressibility and discontinuous nonlinearities in the servovalves due to choked flow. To obtain a wide control bandwidth, one needs to model these effects thoroughly.

The study aims to reduce the complexity of autonomous walking robots by involving the human in the operation of the machine. By taking advantage of the intelligence of the operator, the complexity of bipedal locomotion was reduced to tractable problem. The result of this research is that a two-legged, single actuated degree of freedom, walking machine was designed, built, and tested. The robot successfully navigated terrain including steep inclines and stairs. Additionally, a mechatronic control system was added to provide for smooth speed control and regulation. The leg driving architecture, the double four-bar linkage, designed for this machine can be extended to produce simplified fourand six-legged walking machines. The preliminary results can be used to extend this concept to a machine with an actuated balance assist system based on the human operator's interaction with the machine.

In this paper, a novel material handling system is presented. An overview of the hardware is provided, and issues related to control of the arms are discussed. It is believed that when it is completed, use of this material handling system will help reduce or eliminate workplace back injuries due to repetitive lifting.

The focus of this paper is to investigate the feasibility of stabilizing an underactuated double inverted pendulum. This preliminary investigation is motivated by the desire to construct a two-legged walking robot. The pendulum represents a single leg in a walking robot. The design of a stabilizing controller using a /spl mu/-synthesis approach is explained in detail and conditions for controllability and observability of the system are given.

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.>

The dynamic behavior of a hand controller when it is maneuvered by a human is described. A general control architecture is developed which guarantees various impedances on the hand controller. It is shown that some compliancy either in the hand controller or in the human arm is necessary to achieve stability of the hand controller and the human arm taken as a whole. The actuators' backdrivability and the dynamics of the hand controller mechanisms are discussed as they relate to system stability. A set of experiments performed on a prototype hand controller is presented to show the system performance.>

A control algorithm is defined for a telerobotic system in which the dynamic behaviors of the slave robot and the master robot are functions of each other. These functions, which are the designer's choice and depend on the application, are described. A control architecture that guarantees that the specified functions govern the dynamic behavior of the telerobotic system is presented. The stability of the closed-loop system (i.e., master robot, slave robot, human, and the load being manipulated) is analyzed, and sufficient conditions for stability are derived. Experimental results that verify the theoretical predictions are given.>

The dynamic behaviour of a harmonic drive, in particular the non-backdrivability, is developed in terms of a sensitivity transfer function (or 1/impedance). The instrumentation of the harmonic drive with torque sensor is described. This leads to a description of the control algorithm which allows modulation of the sensitivity transfer function within the limits established by the closed-loop stability criteria. A set of experiments on an active hand controller, powered by a DC motor coupled to an instrumented harmonic drive, is given to verify the theoretical predictions.>

A description is given of the dynamics, control, and stability of extenders, robotic systems worn by humans for material handling tasks. Extenders are defined as robot manipulators which extend 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 lets the designer define an arbitrary relationship between the human force and the load force. Experiments on a two-dimensional non-direct-drive extender were done to verify the control theory.>

The authors present a nonlinear stability analysis for constrained robotic motion, a maneuver where the manipulator contacts the environment. The external disturbances, sensor noises, parameter uncertainties, and the dynamics of the total system composed of the robot and the environment have been modeled. The control of the manipulator is divided into two components: a computed torque trajectory controller that regulates the robot position and a compliance controller that modulates contact forces. Three sufficient conditions for stability have been derived. The first condition guarantees the stability of the system of robot and finite stiff environment when no force sensor and, consequently, no force feedback is considered for the system. The second condition guarantees stability of the robot and environment when a compliance compensator (operating on the contact force) supplements the trajectory controller. The third stability criterion shows that, for a robot contacting a very stiff environment, the gain of the compliance compensator must vary in inverse proportion to the gain of the trajectory compensator.>

The dynamics and control of robotic systems worn by humans are analyzed. General models for the human, the extender, and the interaction between the human and the extender are developed. The stability of the system of human, extender, and 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 tradeoff between stability and performance is described. The theoretical predictions are verified experimentally.>

Extenders, a class of robot manipulators worn by humans to increase human mechanical strength while the wearer's 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.>

For pt.I see ibid., vol.3, p.1632-40. The author presents concepts involving constrained motion of a class of human-controlled robotic manipulators called extenders. Extenders amplify the strength of the human operator, while utilizing the intelligence of the operator to generate spontaneously the command signal to the system. A single-degree-of-freedom extender has been built for theoretical and experimental verification of the dynamics and control involved in this hardware. The system performance is defined as the amplification of the human power. It is shown that the more amplification is required, the smaller is the stability range of the system.>

In the work presented, extenders are defined as a class of robot manipulators worn by humans to increase human mechanical strength, while the wearer's 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 author gives a summary of the ongoing research work on human-machine interaction in the sense of the transfer of power and information signals. A single-degree-of-freedom extender has been built for theoretical and experimental verification of the extender dynamics and control. System performance is defined as amplification of human force. It is shown that the greater the required amplification, the smaller the stability range of the system is. A condition for stability of the closed-loop system (extender, human and environment) is derived, and, through both simulation and experimentation, the sufficiency of this condition is demonstrated.>

A practical architecture, using a four-bar-linkage, is considered for the University of Minnesota direct-drive robot. This statically-balanced direct-drive robot has been constructed for stability analysis of the robot in constrained manipulation. As a result of the elimination of the gravity forces (without any counterweights), smaller actuators and consequently smaller amplifiers were chosen. The motors yield acceleration of 5g at the end point without overheating. High torque, low speed, brushless AC synchronous motors are used to power the robot. Graphite epoxy composite material is used for the construction of the robot links. A four-node parallel processor is used to control the robot. The dynamic tracking accuracy with the computed torque method as a control law has been derived experimentally.>

The control strategy of two cooperating robots is described. A two-fingered hand is an example of such a system. A control architecture is proposed that guarantees: (1) each robot end-point follows its position input command vector 'closely' when the robots are not in contact with each other, and (2) when the two robots come in contact with each other, one robot controls the position of the contact point, while the other controls the contact force. The controller does not need any hardware or software switch for the transition between unconstrained and constrained maneuvering of each robot.>

A nonlinear approach for the stability analysis of robot manipulators in constrained maneuvers is presented. Stability of the environment and the manipulator taken as a whole has been investigated, and a bound for stable manipulation has been derived. The authors show that for stability of the robot, there must be some initial compliancy either in the robot or in the environment. The general stability condition has been extended to the particular case where the environment is very rigid in comparison with the robot stiffness. The stability analysis has been investigated using unstructured models for the dynamic behaviour of the robot manipulator and the environment. This unified approach of modeling robot dynamics is expressed in terms of sensitivity functions as opposed to the Lagrangian behavior of all the elements of a robot manipulator (i.e., actuators, sensors, and the structural compliance of the links) in addition to the rigid body dynamics.>

A fast, lightweight, active end-effector, which can be attached to the endpoint of a commercial robot manipulator, has been designed and built using an impedance-control method. This control method causes the end-effector to behave dynamically as a two-dimensional remote center compliance (RCC). The compliancy is in this active end-effector is electronic and can be modulated by an online computer. The device is planar and five-bar linkage, and is driven by two direct-drive, brushless DC motors. A two-dimensional, piezoelectric force cell on the endpoint of the device, two 12-bit encoders, and two tachometers on the motors form the measurement system. The high structural stiffness and light weight of the material used in the system allow for a 15-Hz-bandwidth impedance control.>

The work presented here is a practical, non-linear controller design methodology for robot manipulators that guarantees: 1) the robot end-point follows an input command vector "closely" when the robot is not constrained by the environment, and 2) the contact force is a function of the same input command vector (used in the unconstrained environment) when the robot is constrained by the environment. The controller is capable of "handling" both types (constrained and unconstrained) of maneuverings, and is robust to bounded uncertainties in robot dynamics. The controller does not need any hardware or software switch for transition between unconstrained and constrained maneuvering. In this design method, the structural compliancy of the manipulator has also been considered. A set of experiments were carried out to describe how this unified approach can develop electronic compliancy in a robot manipulator. The control architecture has been described by two different methods; frequency domain, and input/output time domain properties.[25,26]

A new strategy has been developed for precision deburring and grinding to guarantee burr removal while compensating for robot oscillations and small uncertainties in the location of the part relative to the robot. This problem has been posed as a frequency domain control problem. Electronic compliancy (impedance control) is demanded as an "adaptive" mechanism to satisfy the requirements of this new strategy. This paper examines the development and implementation of impedance control methodology [7,8,9,10,16] on an active end-effector[15] (or the whole robot if it is possible) for precision deburring and grinding tasks.

The design and construction of a fast, light-weight, active end-effector which can be attached to the end-point of a commercial, robot manipulator is presented here. Electronic compliancy (Impedance Control) [11] has been developed on this device The end-effector behaves dynamically as a two-dimensional, Remote Center Compliance (RCC). The compliancy in this active end-effector is developed electronically and can therefore be modulated by an on-line computer. The device is a planar, five-bar linkage which is driven by two direct drive, brush-less DC motors. A two-dimensional, piezoelectric force cell on the end-point of the device, two 12-bit encoders, and two tachometers on the motors form the measurement system For this device. The high structural stiffness and light weight of the material used in the system allows For a 25 Hertz bandwidth Impedance Control.

Manipulators are subject to interaction forces when they maneuver in a constrained work-space. Our goal is to develop a method for the design of controllers or constrained manipulators in the presence of model, uncertainties. 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. We start with conventional controller design specifications concerning the treatment of external forces when the manipulator is not constrained. Generalizing this concept to include cases when the manipulator is constrained, we state a set of practical, design specifications in the frequency domain 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. While this paper concerns the fundamentals of compliant motion, part 2 of this paper [Reference 24] is devoted to the controller 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 system's 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.

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.