Grasping of deformable 3D objects under gravity

The research area of robotic grasping of soft objects is difficult for multiple reasons: high cost computation of deformation, and the changes of the wrench space, contact areas, as well as point wise contact modes inside the areas. This thesis describes modeling of grasped soft objects and recovering their gravity-free shapes. Chapter 1 will introduce the background and related work. Chapter 2 will focus on grasping and picking up soft objects. In the beginning, some results will be shortly described on resisting a third force applied on a 2D rigid body . The results will show that one of the forces must lie on an edge of the friction cone in order to achieve the optimized total normal force. Studying grasping of soft 2D objects will pave the way for picking up 3D objects. Even though there are some similar methods used in both situations, such as the four events of contact establishment, contact break, stick-to-slip and slip-to-stick, which can happen in the finger\u27s squeezing process, there is still some significant difference between the 2D and 3D cases. This difference goes beyond just adding one more dimension, because the gravity effect has to be considered in 3D cases. In Chapter 3, the focus will be on recovering the shape of a 3D object. Since we use its shape under gravity to construct the stiffness matrix and compute deformations, errors are observed in the experiment. The reason behind this, is that the stiffness matrix in conventional FEM practice already encodes the effect of gravity, which is considered again in the constitutive equation used for computing deformation. Then a numerical iteration method will be introduced to recover the gravity free shape

Literature Review on Changes of Professional Title Policy in Chinese Universities

This paper reviews the literature of research on policy changes of the professional titles in Chinese universities and summarizes the characteristics of policy changes of college professional titles in four aspects of connotation, function, mechanism and model: changing from identity assessment to contractual appointment, from academic performance identification and resource allocation to performance management and incentive restraints, from the administrative-oriented to academic-oriented and from a mandatory institutional transition to an induced institutional transition. On this basis, the paper proposes focus of future research

Computational modeling of impact and deformation

This thesis tackles several problems arising in robotics and mechanics: analysis and computation of two- and muti-body impacts, planning a contact velocity for robotic batting, impact of an elastic rod onto a fixed foundation, robotic pickup of soft three-dimensional objects, and recovery of their gravity-free shapes. Impact is an event that lasts a very short period of time but generates a very large interaction force. Assuming Stronge’s energy-based restitution, a formal impulse-based analysis is presented for the collision of two rigid bodies at single contact point under Coulomb friction in three dimensions (3D). Based on this analysis, we describe a complete algorithm to take advantage of fast numerical integration and closed-form evaluation. For a simultaneous collision involving more than two bodies, we describe a general computational model for predicting its outcome. Based on the impact model, we then look into the task of planning an initial contact velocity between a bat and an in-flight object to send the latter to a target. In certain situations, a closed-form solution can be found, while in others, a bounding triangle algorithm of iterative nature can be employed. An alternative way of modeling impact is to consider the engaged objects to be elastic rather than rigid. A damped one-dimensional wave equation can model an elastic rod bouncing off the ground at a given initial velocity, under the influence of gravity. We derive an explicit solution based on the Method of Descent and D’Alembert’s formula. We also obtain formulas for the time of contact and analyze the dependence of the energetic coefficient of restitution on the physical constants. I conclude the thesis with two pieces of work involving deformable objects. First, an algorithm for picking up a 3D object is introduced. Homotopy continuation method is applied to solve a non-linear system for slips between objects and fingers. Some simulation and experimental results are compared. Second, I discuss an iterative fixed-point method for recovering the gravity-free shape of an object. An experiment shows that the resulting stiffness matrix gives better predictions on deformations than the conventional stiffness matrix influenced by gravity