Jan D. Wolter

On the automatic generation of assembly plans

The author describes a level of assembly process-planning in which a task-level plan is generated directly from a model of the proposed assembly. This involves not only the generation of a series of operations to build the assembly but also the selection or design of an appropriate workspace with suitable fixtures and tools. The author introduces the assembly planning problem and describes an experimental assembly planning system which is capable of rapidly generating plans for most assemblies. The structure of the proposed assembly planner, XAP/1, is described and the performance of the XAP/1 is discussed.<<ETX>>

Optimal algorithms for symmetry detection in two and three dimensions

Exact algorithms for detecting all rotational and involutional symmetries in point sets, polygons and polyhedra are described. The time complexities of the algorithms are shown to be θ (n) for polygons and θ (n logn) for two- and three-dimensional point sets. θ (n logn) time is also required for general polyhedra, but for polyhedra with connected, planar surface graphs θ (n) time can be achieved. All algorithms are optimal in time complexity, within constants.

Automatic generation of gripping positions

The problem of automatically determining gripping positions for objects based upon geometrical knowledge of the object and its environment is addressed. Both the question of what constitutes a good grip and the efficiency of the computational algorithms are considered. Two new criteria for the stability of a grip are proposed: resilience to slippage, and twisting in the gripper due to external forces and torques. Resilience to slippage is expressed in terms of friction effects of the surfaces involved, the shape of the contact between the gripper and object, and the distance of the grip point from the center of mass of the object. Two new performance measures are introduced to reflect resilience to twisting. A general grip planning strategy is introduced that is both run-time efficient and robust.

A constant expected time, linear storage data structure for representing three-dimensional objects

The interrogation of spatial relations and properties of three-dimensional objects are often involved in applications programs for CAD/CADM and robotics. These interrogations can be expressed in terms of low-level data retrieval queries called access primitives (APs). A data structure is presented for storing spatial relations of three-dimensional objects such that the amount of storage is linearly proportional to the number of entities, and the response time for the APs is constant on the average. Linear storage for this data structure is the lower bound. The data structure is in the form of a symmetric graph. Using E, the total number of edges of the object, as the unit, it is shown that the storage requirement of the symmetric data structure is 6E. By defining nine general data structure accessing primitives, it is shown that any local topological query can be answered in constant time, on the average.

Automatic two-fingered grip selection

Grip determination is essential to any task level planning process and to situations in which the pose of the part to be grasped is not known a priori. This paper presents the complete force/moment equations for grasping via a rigid two-fingered gripper. Surface contact is modeled as a linear pressure variation. The quality measure of a grip is taken to be the coefficient of friction needed to keep it from slipping under applied forces and moments, the lower the coefficient of friction, the better the grip. The incorporation of this evaluation into a general grip selection strategy is discussed and several examples given.

Automatic evaluation of two-fingered grips

Grip determination is essential to any task-level planning process. The complete force/moment equations are presented for grasping employing a rigid two-fingered gripper with a thin elastic layer on the contacting surface. The surface contact is modeled as a linear pressure variation. The quality measure of a grip is taken to be the coefficient of friction needed to keep the held object from slipping between the fingers under applied forces and moments. The lower the coefficient of friction, the better the grip. Incorporation of this evaluation into general grip selection strategy is discussed, and several examples are given.

CAD, Robot Programming and Ada

This paper addresses two topics which on the surface are unrelated, the use of CAD to assist robot and sensor programming, and the use of Ada as the basis for robot programming. The association between them arises from the fact that they are being combined in an experimental facility. The facility consists of an Intel iAPX 432 multiprocessing microcomputer system, a GE TN2500 camera, an ASEA RB 6 robot and a link to a VAX 11/780 off-line computer system. The facility is being used as a testbed for various robot programming and interface strategies, and to investigate the utility of object based systems as the computer foundation of manufacturing cells. Experimental verification of techniques using information extracted from CAD models to assist in robot programming and the use of Ada are important parts of the experiment.