Characterizing the Human Wrist for Improved Haptic Interaction

Haptic displays provide the user with a sense of touch in both simulation of virtual environments and teleoperation of remote robots. The instantaneous impedance of the user’s hand affects this force interaction, changing the transients experienced during activities such as exploratory tapping. This research characterizes the behavior of the human wrist joint while holding a stylus in a three-fingered grasp. Nonparametric identification methods, evaluating frequency-and time-responses, support a second-order system model. Further analysis shows a positive linear correlation between grip force and wrist impedance for all subjects, though each individual’s trend is unique. These findings suggest that a quick calibration procedure and a realtime grip force measurement could enable a haptic display to predict user response characteristics throughout an interaction. Such knowledge would enable haptic control algorithms to adapt continuously to the user’s instantaneous state for improved performance.

Fuzzy Logic Control of a Laboratory Magnetic Levitation System

This paper deals with the Fuzzy Logic control of a Magnetic Levitation system [1] available in the Robotics and Control Laboratory at Duke University. The laboratory Magnetic Levitation system primarily consists of a metallic ball, an electromagnet and an infrared optical sensor. The objective of the control experiment is to balance the metallic ball in a magnetic field at a desired position against gravity. The dynamics and control complexity of the system makes it an ideal control laboratory experiment. The student can design their own control schemes and/or change the parameters on the existing control modes supplied with the Magnetic Levitation system, and evaluate and compare their performances. In the process, they overcome challenges such as designing various control techniques, choose which specific control strategy to use, and learn how to optimize it. A Fuzzy Logic control scheme was designed and implemented to control the Magnetic Levitation system. Position and rate of change of position were the inputs to Fuzzy Logic Controller. Experiments were performed on the existing Magnetic Levitation system. Results from these experiments and digital simulation are presented in the paper.

Development of an Electro-Rheological Fluidic Actuator and Haptic Systems for Vehicular Instrument Control

Force-feedback methanisms have been designed to simplify and enahance the human-vehicle interface. The increase in secondary controls within vehicle cockpits has created a desire for a simpler, more efficient human-vehicle interface. Haptic system, or systems that interact with the operator’s sense of touch, can be used to consolidate various controls into fever, haptic feedback control devices, so that information can be transmitted to the operator and the operator can change control settings without requiring the driver’s visual attention. In this paper an Electro-Rheological Fluid (ERF) based actuator and mechanisms are presented that provide haptic feedback. ERSs are fluids that change their viscosity in response to an electric field. Using the electrically controlled rheological properties of ERFs, haptic devices have been developed that can resist human operator forces in a controlled and tunable fashion. The design of an ERF-based actuator and its application to a haptic knob and haptic joystick is presented. The analytical model is given, analyses are performed, and experimental systems and data are presented for the actuator. Conceptual methods for the application to the haptic devices are presented.

Multivariable Control of an Earthmoving Vehicle Powertrain Experimentally Validated in an Emulated Working Cycle

The operation of an earthmoving vehicle involves the coordination of a multivariable powertrain and the execution of specific tasks in a repetitive fashion. The performance and efficiency depend heavily on human expertise. The purpose of this research is to automate the coordination of a multi-input multi-output (MIMO) nonlinear electro-hydraulic powertrain and to validate the performance and efficiency improvements in a human-machine interaction. Firstly, a robust gain scheduling method is developed to design a powertrain controller and to analyze its robust stability and robust performance. The gain scheduling is based on a Local Controller Network strategy and its satisfactory properties are analytically confirmed using robust control theories. Secondly, the improvement of performance and efficiency are validated through two experiments performed on an Earthmoving Vehicle Powertrain Simulator (EVPS). This testbed is a Hardware-In-the-Loop HIL environment representative of a class of electro-hydraulic systems with multiple loads. The two human-operated experiments include a reference tracking test and a working cycle test. In the second test, three types of loads are modeled for a typical wheel loader and emulated on EVPS for a 180-degree loading cycle. These models include the steering, the drive, and the implement. The load emulation technique ensures that the HIL working cycles are representative of real life cycles. The reference tracking and loading cycle results show the significant improvement in productivity in terms of performance, efficiency, and ease of operation.

Optimal Path Planning of Redundant Cooperative Robots Under Equality and Inequality Constraints

Using kinematic resolution, the optimal path planning for two redundant cooperative manipulators carrying a solid object on a desired trajectory is studied. The optimization problem is first solved with no constraint. Consequently, the nonlinear inequality constraints, which model obstacles, are added to the problem. The formulation has been derived using Pontryagin Minimum Principle and results in a Two Point Boundary Value Problem (TPBVP). The problem is solved for a cooperative manipulator system consisting of two 3-DOF serial robots jointly carrying an object and the results are compared with those obtained from a search algorithm. Defining the obstacles in workspace as functions of joint space coordinates, the inequality constrained optimization problem is solved for the cooperative manipulators.

GPC-Based Stable Reconfigurable Control

This paper presents development of multi-input multi-output (MIMO) Generalized Predictive Control (GPC) law and its application to reconfigurable control design in the event of actuator saturation. The stability of the GPC control law without reconfiguration is first established using Riccati-based approach and state-space formulation. A novel reconfiguration strategy is developed for the systems which have actuator redundancy and are faced with actuator saturation type failure. An elegant reconfigurable control design is presented with stability proof. A numerical example with application to reconfigurable flight control is presented to demonstrate the results presented in the paper.

On a Finger Model Actuated With Shape Memory Alloy Artificial Muscles

The simulation of a flexible finger, actuated with the shape memory alloys (SMAs) artificial muscles, is presented in the paper. The finger is modeled as a cylindrically rod with three embedded NiTi wires in a n aluminum matrix. Forces between NiTi wires causes bending in any plane perpendicular to the longitudinal axis of the finger. The NiTi wires are heated above the austenitic start temperature by passing an electrical current, and the deflected wire tends to return to the initial configuration. Using characteristics of SMAs such as high damping capacity, super-elasticity, thermo-mechanical behavior and shape memory, the actuation for the finger is theoretically introduced and discussed.

Pelton Turbine Needle Control Model Development, Validation, and Governor Designs

Underspeed needle control of two Pelton turbine hydro units operating in a small power system has caused many incidents of partial system blackouts. Among the causes are conservative governor designs with regard to small signal stability limits, non-minimum phase power characteristics, and long tunnel-penstock traveling wave effects. A needle control model is developed from “water to wires” and validated for hydro-turbine dynamics using turbine test data. Model parameters are tuned with trajectory sensitivity. Proposed governor designs decompose the needle regulation gains into the power and frequency governor loops with a multi-time-scale approach. Elements of speed loop gain scheduling and a new inner-loop pressure stabilization circuit are devised to improve the frequency regulation and to damp the traveling wave effects. Simulation studies show the improvements of the proposed control designs.

Optimal Rollover Prevention With Steer by Wire and Differential Braking

This paper uses Model Predictive Control theory to develop a framework for automobile stability control. The framework is then demonstrated with a roll mode controller which seeks to actively limit the peak roll angle of the vehicle while simultaneously tracking the driver’s yaw rate command. Initially, control law presented assumes knowledge of the complete input trajectory and acts as a benchmark for the best performance any controller could have on this system. This assumption is then relaxed by only assuming that the current driver steering command is available. Numerical simulations on a nonlinear vehicle model show that both control structures effectively track the driver intended yaw rate during extreme maneuvers while also limiting the peak roll angle. During ordinary driving, the controlled vehicle behaves identically to an ordinary vehicle. These preliminary results shows that for double lane change maneuvers, it is possible to limit roll angle while still closely tracking the driver’s intent.

A Control-Oriented Polytropic Model of SI Engine Intake Manifold

The paper presents experimental results which show significant changes of the intake manifold air temperature during fast tip-in/tip-out engine transients. An adequate two-state polytropic manifold model is developed and experimentally validated. An emphasis is on the derivation and parameterization of a time-variant structure of the heat transfer coefficient. The polytropic manifold model is extended to a three-state form for the more general case of different heat transfer properties for the manifold plenum and runners. An influence of the engine back flow on the runner thermal transients is observed. A simple extension of the three-state model with the back flow effect is proposed.