Window-shaped obstacle avoidance for a redundant manipulator

The window-shaped obstacle avoidance problem is studied in this paper. Several research papers regarding obstacle avoidance including the method proposed by Zghal et al., which we believe is the most suitable for three-dimensional (3-D) window-shaped obstacle avoidance are studied. Consequently, several shortcomings of the Zghal's method are discovered. The Zghal's method will produce chattering solution sequences in joint rates due to its deficiency in determining the shortest distance between the manipulator links and the window edges. This paper proposes a new scheme to determine the shortest distance. This new scheme will remedy the chattering problem. Moreover, the nearest link (NL) method is developed for further improvement. Because the NL method only considers the nearest link in the performance criterion, the on-line weighting assignment problem of the Zghal's method is removed, also, less redundancy is required to accomplish the goal for obstacle avoidance. Therefore, the NL method will allow more redundancy to be useful for the other goals under multiple-goal application environments.

Modeling and analysis of equipment managers in manufacturing execution systems for semiconductor packaging

Equipment Managers (EMs) play a major role in a Manufacturing Execution System (MES). They serve as the communication bridge between the components of an MES and the equipment. The purpose of this paper is to propose a novel methodology for developing analytical and simulation models for the EM such that the validity and performance of the EM can be evaluated. Domain knowledge and requirements are collected from a real semiconductor packaging factory. By using IDEFO and state diagrams, a static functional model and a dynamic state model of the EM are built. Next, these two models are translated into a Petri net model. This allows qualitative and quantitative analyses of the system. The EM net model is then expanded into the MES net model. Therefore, the performance of an EM in the MES environment can be evaluated. These evaluation results are good references for design and decision making.

Evolution of surface roughness of some metallic materials in cavitation erosion

The evolution of surface roughness of three common metallic materials (316L stainless steel, CP titanium, and brass) in ultrasonic vibratory cavitation tests was monitored using profilometric measurements. Three stages of roughness change, based on the rate of change of the mean surface roughness d(Ra)/dt, may be identified. In stage I (initial stage), Ra increases almost linearly with the test time; in stage II (transition stage), the rate decreases until stage III (steady-state stage) is reached, in which Ra remains unchanged. Concurrent measurements of mass loss in the ultrasonic cavitation test indicated that stage I approximately coincides with the incubation stage, stage II approximately coincides with the acceleration stage, and stage III approximately coincides with the maximum erosion rate stage as defined by ASTM Standard G 32. Compared with conventional mass loss measurements in assessing material degradation in cavitation erosion, surface roughness measurements provide an alternative and convenient method which possesses several advantages. In the first place, change in surface roughness provides information of material response before mass loss is detected. Secondly, there is no restriction of the size of the component, while weighing is suitable for small samples only. Thirdly, mass loss reflects erosion of the whole surface under cavitation attack, and the mean depth of penetration or erosion only gives an average loss, while in roughness measurement, damage in specific locations may be studied. The present study indicates that roughness measurement may constitute a practical method for monitoring damage in industrial ultrasonic cleaners.

An efficient method for obtaining the general solution for the force balance equations with hard point contacts

A compact formulation which is more efficient than the traditional pseudoinverse formulation for obtaining the general solution for the force balance equations has been presented (Cheng and Orin, 1991). With hard point contacts considered, the force balance equations can be decomposed into two sets of rank 3, smaller linear equations if proper coordinate frames of the reference member and at the contact points are chosen. This decomposition, together with the compact formulation, can reduce the steps of the Gaussian elimination process, increase parallelism of the algorithm, and therefore, keep the computation time for obtaining the general solution for the force balance equations to a minimum.