Biomimetic fish-like propulsion using polyelectrolyte ion-exchange membrane metal composites as a propulsion fin for a robotic swimming structure, such as a boat swimming in water medium, was investigated. The membrane was chemically plated with platinum. The resulting membrane was cut in a strip to resemble fish-like caudal fin for propulsion. A small function generator circuit was designed and built to produce approximately /spl plusmn/2.0 V amplitude signal at desired frequency up to 50 Hz. The circuit board was mounted on a buoyant Styrofoam shaped like a boat or a tadpole. The fin was attached to the rear of the boat. By setting the signal frequency to the desired value and thereby setting the frequency of bending oscillation of the membrane, a proportional forward propulsion speed could be obtained. The speed was then measured using a high speed camera. Several theoretical hydrodynamic models were then presented to characterize speed-frequency of the forward motion using available theories on biological fish motion. The results were compared to experimental data which showed close agreement.

A mathematical model is presented for the dynamic response of contractile fiber bundles embedded in or around elastic springs that are either linear helical compression springs or hyperelastic springs such as rubber-like materials. The fiber bundle is assumed to consist of a parallel array of contractile fibers made form either contractile polymeric muscles such as polyacrylic acid plus sodium acrylate cross-linked with bisacrylamide (PAAM) or polyacrylonitrile (PAN) fibers. The proposed model considers the electrically or pH-induced contraction of the fibers which may include resistive heating of the fiber in case of shape-memory alloys. The theory then branches out to two different descriptions of such processes for ionic polymeric gel fiber bundles and shape-memory alloy fiber bundles. The governing equations have been derived and numerical simulations are carried to understand the dynamic response of such actuators.>

A simplified dynamic model for a one-link tip force-controlled flexible manipulator is simulated. Experimental work is then carried out and comparisons are made with the theoretical dynamic simulations. Results show that, during the initial contact process, separation between the manipulator and the environment occurs to the link elastic motion. This nonlinear effect causes a delay of force actuation and the occurrence of impacts, which are significant and detrimental to the system dynamic stability. It is shown that the nonlinear effects can be minimized by preloading an initial contact force through open-loop control.>

Governing equations for the dynamics of peg-in-hole insertion for six distinct cases are derived. It is shown that there exist generalized inequalities that govern the processes of successfully inserting a peg in a hole in computer-aided assembly processes. Exact inequalities are obtained for no-wedging and/or no-jamming conditions in computer-controlled dynamic assembly. An algorithm is also described for successful implementation of computer-aided dynamic insertion through the use of optimal trajectories pertaining to the dynamic motion of the peg in the hole.>

The effect of link flexibility on the dynamic stability of a two-link force-controlled robot manipulator is investigated. Assuming that the contact point is locked, the nonlinear open-loop equations for the compliant motion are derived. By using the hybrid force-position control law, the closed-loop dynamic equations are explicitly derived and linearized about some equilibrium configuration. Stability analyses are carried out by computing the eigenvalues of the linearized system equations. Results are verified by numerical simulations using the complete nonlinear dynamic equations. The effect of the wrist force sensor stiffness on the dynamic stability is also investigated. Results show that the link flexibility is an important source of dynamic instability in the motion of force-controlled manipulators. Moreover, the system stability is dominated by the effect of the distributed flexibility of the first link.>

The effects of joint and link flexibilities on the dynamic stability of two-link force-controlled manipulators are investigated. The complaint equations of motion involving joint and link flexibilities are presented. Three force control methods, which include the stiffness method, the damping method, and the hybrid method, are considered for the analysis. The linearized equations of motion about the equilibrium positions are used for stability analysis. Depending on the control method used and the distribution of system flexibility, different dynamic behaviors are predicted. Flexibility, which causes the instability problem of force-controlled manipulators, is inherent in every robotic structure. Thus, more sophisticated control strategies using different sensors which can compensate the flexibility effects are needed to improve the dynamic performance of force-controlled flexible-joint manipulators.>

The kinematics and the quasistatics of the stable grasping of an object by a planar two-fingered robotic gripper are considered. The object is assumed to be quasistatically manipulated in a fine-motion manufacturing work space while experiencing external forces and moments. Each finger is assumed to be a generalized two-axis revolute robot manipulator moving in harmony with another similar robot situated nearby. The quasistatics of the object are directly related to four-joint torques for servo-control purposes. Both the direct and inverse kinematics and statics are solved completely.>