Results obtained on the Madison Symmetric Torus (MST) reversed-field pinch [Fusion Technol. 19, 13 1 ( 199 1) ] after installation of the design poloidal field winding are presented. Values of Be, = 2~, nd) T&/B s (a) -12% are achieved in low-current (I = 220 kA) operation; here, n, and T, are central electron density and temperature, and Be (a) is the poloidal magnetic field at the plasma edge. An observed decrease in pod) with increasing plasma current may be due to inadequate fueling, enhanced wall interaction, and the growth of a radial field error at the vertical cut in the shell at high current. Energy confinement time varies little with plasma current, lying in the range of OS-l.0 msec. Strong discrete dynamo activity is present, characterized by the coupling of m = 1, n = 5-7 modes leading to an m = 0, n = 0 crash (m and n are poloidal and toroidal mode numbers). The m = 0 crash generates toroidal flux and produces a small (2.5%) increase in plasma current.

Grasping an object with a multifingered robot hand requires complete constraint of its motion by contacts. Complete con straint of an object can also be described using force equilib rium. If any external force on the object can be balanced by applicable contact forces, a stable grasp has been achieved. A force closure grasp is such a grasp. This article presents a simple and efficient algorithm to find an optimum force clo sure grasp of a planar polygon using a three fingered robot hand. The optimum grasp is defined as a grasp that has the minimum value of a heuristic function. The heuristic function is formulated from the consideration of the possible uncertainties inherent in implementation. Even though a planar force clo sure grasp can be obtained using only two friction contacts, we consider only grasps where all three friction contacts explicitly participate. To find the optimum grasp, all feasible combina tions of edges and/or vertices are identified first. An edges and/or vertices combination is feasible when a stable grasp is attainable by an appropriate selection of three contacts on them. Then, using computational geometry, a single grasp is constructed on each feasible combination. Finally, the grasps obtained are compared using the heuristic quality measure. A test of our algorithm on several different polygons shows that the resulting grasp is realistic and is obtained fast enough for real-time use.

No abstract

Objects which cannot be directly grasped by the end effector of a robot manipulator and must be carried by a hook or similar device are susceptible to swinging during transport. For a simply suspended object, it is possible to use a path-controlled manipulator to achieve a swing-free motion. The trajectory consists of an initial acceleration to an intermediate velocity, then a secondary acceleration to final velocity. An experimental demonstration of the method is presented.