Adaptive hybrid position/force control of robotic manipulators

The problem of position and force control for the compliant motion of the manipulators is considered. The external force and the position of the end-effector are related by a second order impedance function. The force control problem is then translated into a position control problem. For that, an adaptive controller is designed to achieve the compliant motion. The design uses the Liapunov's direct method to derive the adaptation law. The stability of the process is guaranteed from the Liapunov's stability theory. The controller does not require the knowledge of the system parameters for the implementation, and hence is easy for applications

Collision-free trajectory planning algorthm for manipulators

Collision-free trajectory planning for robotic manipulators is investigated. The task of the manipulator is to move its end-effector from one point to another point in an environment with polyhedral obstacles. An on-line algorithm is developed based on finding the required joint angles of the manipulator, according to goals with different priorities. The highest priority is to avoid collisions, the second priority is to plan the shortest path for the end effector, and the lowest priority is to minimize the joint velocity for smooth motion. The pseudo-inverse of the Jacobian matrix is applied for inverse kinematics. When a possible collision is detected, a constrained inverse kinematic problem is solved such that the collision is avoided. This algorithm can also be applied to a time-variant environment

CRYSTAL ORIENTATION EFFECTS DURING FABRICATION OF SINGLE OR MULTI-CRYSTAL NB SRF CAVITIES*

Abstract Single and large-grain Nb SRF cavities are of interest due to possible reduction of cost and problems associated with inconsistent texture and surface finish among batches of rolled polycrystalline Nb sheet. The effect of crystal orientation on dislocation density, surface quality, and recrystallization after plastic deformation and e-beam welding was investigated, as understanding of their interrelations is needed. These were evaluated for three samples of different orientations at steps similar to those in typical cavity forming, with deformation modeled using a crystal plasticity approach. Initial dislocation density was higher than expected, increased with deformation, after welding was reduced in recovered areas, and was similar to initial density in recrystallized grains; there was also evidence that Nb has a higher tolerance for dislocations than other metals. Surface quality depends on a complex relation of crystal orientation, slip system activity, and prior surface treatment. Recrystallization nucleated outside the melt pool, and the new orientations grew both epitaxially into the weld as it solidified, and away until heat and time were insufficient to continue growth

FINITE ELEMENT ANALYSIS OF ALUMINUM TUBE HYDROFORMING BASED ON NON-QUADRATIC YIELD FUNCTION

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Plastic anisotropic modeling for sheet forming design applications

Abstract not available

A 3D hybrid membrane/shell method with kinematic hardening to predict the springback of sheet metals

Abstract not available

A hybrid membrane/shell method for rapid estimation of springback of stamped anisotropic sheet metals

Abstract not available

Influence of initial back stress on the earing prediction of drawn cups for planar anisotropic aluminum sheets

Anisotropy is closely related to the formability of sheet metal and should be considered carefully for more realistic analysis of actual sheet metal forming operations. In order to better describe anisotropic plastic properties of aluminum alloy sheets, a planar anisotropic yield function which accounts for the anisotropy of uniaxial yield stresses and strain rate ratios simultaneously was proposed recently. This yield function was used in the finite element simulations of cup drawing tests for an aluminum alloy 2008-T4. Isotropic hardening with a fixed initial back stress based on experimental tensile and compressive test results was assumed in the simulation. The computation results were in very good agreement with the experimental results. It was shown that the initial back stress as well as the yield surface shape have a large influence on the prediction of the cup height profile