Impedance control of a hydraulic servoactuator joint system is discussed in this paper. Impedance control imparts a desired behavior to a system, rather than it controls position or force individually. Due to nonlinear properties of hydraulic actuators, impedance control is difficult. The control strategy presented here involves a combined feedforward and feedback control. An impedance filter modifies a desired trajectory according to a specified behavior. The modified trajectory is fed to a reduced-order model of the servoactuator hydraulic joint in order to reduce the effects of the nonlinear hydraulic dynamics. Position, velocity and pressure feedback loops compensate for the unmodeled dynamics. Simulation results show the strategy to be promising in providing impedance control to the joint. Special attention is given to the careful choice of impedance and control parameters to ensure smooth transition between contact and non-contact regimes, and to avoid actuator saturation. The developed controller is useful in achieving a desired behavior of hydraulic manipulators in contact tasks. It will provide the basis for a robust impedance control of the SARCOS high-performancehydraulic manipulator.

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This thesis describes the implementation of a telerobotic control architecture to manipulate a standard six degree of freedom industrial robot via a unique seven degree of freedom force-reflecting exoskeleton which is located in the Human Sensory Feedback Laboratory at Wright-Patterson Air Force Base. This is the first time that the robot and exoskeleton have been interfaced. The novel Naturally-Transitioning Rate-to-Force Controller is included in the irnplementation. Background for the control architecture and modes of operation are presented as well as the specific system description and operating procedures. Peg-insertion experiments were conducted to compare the performance of rate control, Naturally-Transitioning Rate-to-Force Control, and Naturally- Transitioning Rateto-Force Control with force reflection. Task completion time and manipulator work due to contact forces and moments through Cartesian displacements were the basis for comparison, The control architecture has been completely implemented. Experimental results displayed no clear differences among the three control modes; this indicates that a reduction in system time delays and more precise gain tuning are needed.

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Confocal microscopy methods have been employed to image the metathoracic trochanter, a small exoskeleton segment between the coxa and femur, of an adult cockroach, Periplaneta americana. The confocal images represent planar sections through the exoskeleton of the trochanter. Specia-lized software was implemented to convert the section images into a complete three-dimensional geometric model of the trochanter. The raster image data of the confocal model was exported in a vector file format. Custom software was developed to resample the vector data and to automatically create a finite element mesh. The resulting mesh contained first-order, three-dimensional, triangular plate elements and also encoded data for element thicknesses. The Algor finite element package was used to analyze the model under the conditions of several biologically pertinent experiments. Special emphasis was placed on the strain analysis of the four groups of campaniform sensilla on the trochanter. These sensory organs respond to strains in the exoskeleton and are instrumental in the control of natural walking in insects. The results were compared to data from biological experiments which confirmed hypotheses and answered questions that have been difficult to determine experimentally on the animal. Functional differentiation both between groups and within groups of sensilla was observed. Further evidence that strain measurements are used in positive feedback control of the trochanteral extensor muscles was discovered. The structure of the trochanter was analyzed in the context of the function of the campaniform sensilla. Previously undescribed quantitative stress and strain data for insect cuticle was recorded.

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This paper describes the development of a system for dexterous telemanipu-lation and presents the results of tests involving simple manipulation tasks. The user wears an instrumen-ted glove augmented with an arm-grounded haptic feedback apparatus. A linkage attached to the user’s wrist measures gross motions of the arm. The movements of the user are transferred to a two fingered dexterous robot hand mounted on the end of a 4-DOF industrial robot arm. Forces measured at the robot fingers can be transmitted back to the user via the haptic feedback apparatus. The results obtained in blockstacking and object-rolling experiments indicate that the addition of force feedback to the user did not improve the speed of task execution. In fact, in some cases the presence of incomplete force information is detrimen-tal to performance speed compared to no force information. There are indications that the presence of force feedback did aid in task learning.

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