Kevin B. Fite

Transparency and Stability Robustness in Two-Channel Bilateral Telemanipulation

This paper presents a two-channel architecture and design approach that enables a simultaneous increase in the transparency and stability robustness of a bilateral teleoperation system, and additionally provides a high degree of transparency robustness to uncertainty in the operator and environment dynamics. The former is provided by the use of a loop-shaping filter incorporated on the master-to-slave motion command, and the latter by local feedback loops around both the master and slave manipulators. The proposed architecture and design approach are illustrated on a single-degree-of-freedom example with and without a communication channel time delay. Finally, the implications of scaling on the stability of the teleoperator loop are discussed. @DOI: 10.1115/1.1387018#

Design and Control of an Electrically Powered Knee Prosthesis

This paper describes the design and control of a transfemoral prosthesis with an electrically powered knee joint. This paper details the design of the active-knee prototype and presents an impedance-based control approach with which to coordinate the interaction between the prosthesis and user during level walking. The control methodology is implemented on the prosthesis, and experimental results and video frame sequences are shown that demonstrate the effectiveness of the prosthesis and control approach for level walking.

Loop shaping for transparency and stability robustness in bilateral telemanipulation

This paper presents and experimentally demonstrates a control methodology that provides transparency and stability robustness in bilateral telemanipulator systems. The approach is based upon a previously published method that structures the human-manipulators-environment system in a manner that enables the application of frequency-domain loop-shaping methods. This paper reformulates the human-manipulator interaction described in the previously published work, and experimentally demonstrates the approach on a single degree-of-freedom telemanipulation system. Experimental measurements indicate significant improvements offered by the method in both the stability robustness and transparency of the human-manipulators-environment system. Finally, experimental results are presented that demonstrate the robustness in the transparency to significant changes in the environment dynamics.

A Gas-Actuated Anthropomorphic Prosthesis for Transhumeral Amputees

This paper presents the design of a gas-actuated anthropomorphic arm prosthesis with 21 degrees of freedom and nine independent actuators. The prosthesis utilizes the monopropellant hydrogen peroxide as a gas generator to power nine pneumatic type actuators. Of the nine independent actuators, one provides direct- drive actuation of the elbow, three provide direct-drive actuation for the wrist, and the remaining five actuate an underactuated 17 degree of freedom hand. This paper describes the design of the prosthesis, including the design of small-scale high-performance servovalves, which enable the implementation of the monopropellant concept in a transhumeral prosthesis. Experimental results are given characterizing both the servovalve performance and the force and/or motion control of various joints under closed-loop control.

Stair Ascent With a Powered Transfemoral Prosthesis Under Direct Myoelectric Control

This paper presents experimental results of a myoelectric controller designed for reciprocal stair ascent using a transfemoral prosthesis with an actively powered knee joint. The control architecture is derived from able-bodied gait data and estimates knee torque with a linear two-state (stance/swing) impedance control form that includes proportional myoelectric torque control combined with a state-determined knee impedance. The experimentally implemented control interface affords the amputee subject with direct control of knee torque using surface electromyogram (EMG) measurements of muscles in the residual thigh supplemented with a nominal knee impedance whose set-point switches based on the detection of ground contact at the foot. Preliminary clinical evaluations of the EMG-based control system with a single subject with unilateral transfemoral amputation show robust and repeatable performance for alternating stair ascent. The amputee subject effectively modulates power output at the knee using EMG commands during stance, while leveraging the knees nominal swing-phase impedance and only modest EMG influence to achieve the desired knee trajectories during swing.

Design and energetic characterization of a proportional-injector monopropellant-powered actuator

This paper describes the design and energetic characterization of an actuator designed to provide enhanced system energy and power density for self-powered robots. The proposed actuator is similar to a typical compressible gas fluid-powered actuator, but pressurizes the respective cylinder chambers via a pair of proportional injector valves, which control the flow of a liquid monopropellant through a pair of catalyst packs and into the respective sides of the double-acting cylinder. This paper describes the design of the proportional injection valves and describes the structure of a force controller for the actuator. Finally, an energetic characterization of the actuator shows improvement relative to prior configurations and marked improvement relative to state-of-the-art batteries and motors.

Design, control, and energetic characterization of a solenoid-injected monopropellant-powered actuator

This paper describes a direct-injection configuration of a monopropellant-powered actuator that is intended to provide high-energy-density actuation for a self-powered position- or force-controlled human-scale robot. The proposed actuator is pressurized by a pair of solenoid injection valves (each of which control the flow of a monopropellant through a catalyst pack and directly into the respective side of a pneumatic-type cylinder), and depressurized via a three-way hot-gas proportional exhaust valve. A controller is described that coordinates the control of the two solenoid propellant injection valves, together with the control of the proportional hot-gas exhaust valve, in order to provide actuator force tracking. Experimental results are presented that validate the effectiveness of the force-control approach. Finally, energetic performance of the proposed actuator is experimentally assessed and shown to provide an energetic figure of merit, an order of magnitude greater than that of a battery-powered servomotor approach

A unified force controller for a proportional-injector direct-injection monopropellant-powered actuator

This paper describes the modeling and control of a proportional-injector direct-injection monopropellant powered actuator for use in power-autonomous human-scale mobile robots. The development and use of proportional (as opposed to solenoid) injection valves enables a continuous and unified input/output description of the device, and therefore enables the development and implementation of a sliding-mode-type controller for the force control of the proposed actuator that provides the stability guarantees characteristic of a sliding mode control approach. Specifically, a three-input, singleoutput model of the actuation system behavior is developed, which takes a nonlinear noncontrol-canonical form. In order to implement a nonlinear controller, a constraint structure is developed that effectively renders the system single-input, single-output and control canonical, and thus of appropriate form for the implementation of a sliding mode controller. A sliding mode controller is then developed and experimentally implemented on the proposed actuator. Experimental results demonstrate closed loop force tracking with a saturation-limited bandwidth of approximately 6 Hz.

Transparent telemanipulation in the presence of time delay

This paper presents a method for providing stability and robust transparency in bilateral teleoperator loops that include a time delay in the communication channel. Specifically, the proposed approach incorporates an adaptive Smith predictor within a frequency domain loop shaping approach that addresses both stability and transparency of the teleoperator loop. Experimental results are presented that demonstrate the effectiveness of the approach.

Position control of a compliant mechanism based micromanipulator

This paper addresses the modeling and control of a compliant micromanipulator for use in such fields as microsurgery, telesurgery, and microassembly. The unique flexure-based manipulator utilizes revolute flexure joints in achieving well-behaved kinematic characteristics, without the backlash and stick-slip phenomena that would otherwise impede precision control. A mathematical model of the micromanipulator is formulated, and a controller for positioning of the manipulator is derived. The model and resulting controller are unlike typical manipulator models and controllers since this manipulator is actually a controlled large range-of-motion structure with nonlinear structural dynamics. Following the development of the controller, computer simulations of the proposed controller on the manipulator are used to verify the positioning performance.