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This paper investigates the motion of a free ball with initial velocity and angular velocity on a horizontal plane under friction. The ball will first slide along a parabolic trajectory (with its contact velocity in constant direction) and then roll along a straight trajectory. Curving of the sliding trajectory can be utilized for obstacle avoidance in path planning. A one-to-one correspondence exists...
This paper presents an impulse-based model for n-body collisions with or without friction. In the frictionless case, impulses at all the contacts, initialized via solution of a non-linear system, accumulate over different phases (compression and restitution) tracked through numerical integration. Experiment over Newton's cradle, using vision-based velocity estimation, achieves a close agreement with...
This paper describes a strategy to lift up a deformable 2D object resting on a horizontal plane. Inspired by human hand lifting behavior, the strategy plans grasping trajectories of two fingertips using modified Rapidly-exploring Random Trees (RRT). Compared to a straight squeeze, a planned finger movement not only enlarges the graspable region, but also minimizes the work. Improvements on control...
This paper investigates the free motion of a sphere with initial velocity and angular velocity on a plane under sliding and rolling friction. The sphere will first slide along a parabolic trajectory (with a constant direction of its contact velocity), and then roll along a straight trajectory. Such a curved trajectory can be utilized for obstacle avoidance in path planning. A one-to-one correspondence...
This paper describes a simple strategy for a robot hand to grasp and lift a deformable 3D object resting on a table. Inspired by the human hand grasping, the strategy employs two rigid hemispherical fingers to first squeeze the object until a secure grip is achieved under contact friction, and then translate vertically upward. During the squeeze, a lift test is repeatedly conducted to determine if...
Robotic grasping of a deformable object is difficult not simply due to the high computational cost of deformable modeling. More fundamentally, the difficulty lies in a wrench space that changes under deformation, with growing contact areas, and subject to varying slip/stick modes in these areas. This paper presents a grasping strategy by squeezing the object with two fingers. An analysis based on...
Grasping a deformable object instantaneously requires maintaining equilibrium of its pre- and post-deformed shapes using the same set of forces. This paper studies the type of grasps generated by squeezing a planar object with two fingers. It is shown that the success of such a grasp is independent of the applied forces in the case of small deformation. Numerical algorithms are introduced to compute...
The friction and wear behaviors of various polymer–polymer combinations were examined by means of a pin-on-disc type apparatus. The worn surfaces of the polymers were observed by using Scanning Electron Microscope (SEM). The relationships between the tribological properties and cohesive energy density (CED) of the two mated polymers were found. For the similar polymer combinations, the increasing...
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