SynopsisPostpolymerization was obtained in solid PBT sheets, by annealing in a dry nitrogen stream a t 214°C. After different reaction times, the samples were cut into thin slices. The M , profile within the sample was obtained through intrinsic viscosity measurements in a phenol-TCE mixture. At each location inside the sample, the [q] vs. time curve typically shows a maximum, which is rather broad at the midplane and much sharper at the external surface. The phenomenon was mathematically described by accounting for both diffusion and chemical reactions within the slab; five simultaneous chemical reactions have been considered. The observed behavior is found to be essentially due to two competing processes, i.e., the diffusion of the low molecular weight species generated during the polycondensation and the thermal degradation reaction. The model predictions are compared with the experimental data showing a satisfactory agreement.
This work presents an automated and dedicated system aiming at the measurement of straightness errors of mechanical components, using an industrial robot. A multi-probe error separation technique was used to make measurements independent from the coordinate system of the robot. A mathematical model that takes into account the readings from three sensors was specifically designed for the proposed measurements and produces inspection results by means of the solution of a system of linear equations, in only one operation. Also in this work, a new approach was developed to minimize the influence of the zero-adjustment errors of the sensors, which represent the major source of errors in the separation process. Experimental tests applied to the measurement of straightness errors of mechanical components were accomplished, which demonstrated the effectiveness of the employed methodology.
Dimensional inspections in manufactured workpieces allow assess the quality of the manufacturing process, in this context the quality and development of measurement systems are issues addressed by many researchers. The coordinate measuring machines (CMMs) are versatile systems, can measure complex geometries quickly and accurately. Positional errors are parts of volumetric error and affect the correct positioning of probe in CMMs or of the tool in machine tools. Faced with this, the purpose this investigation is show a method to calibrate the positional errors in a bridge-type coordinate measuring machine, this method collects data in dynamic mode and reduces cyclic errors. The calibration of positional errors was performed using laser interferometry in the “on-the-fly” mode and a method to reduce cyclic errors was applied. The highest value of position error occurred in x axis with value positive of 10μm in the position of 220mm, while in the y and z axis the higher absolute values were 2μm and 6μm respectively. From calibration and compensating of positional errors it is possible to reduce the effects of the volumetric errors in machines with axis of linear displacements as the CMMs and machine tools.
With the relentless quest for improved performance driving ever tighter tolerances for manufacturing, machine tools are sometimes unable to meet the desired requirements. One option to improve the tolerances of machine tools is to compensate for their errors. Among all possible sources of machine tool error, thermally induced errors are, in general for newer machines, the most important. The present work demonstrates the evaluation and modelling of the behaviour of the thermal errors of a CNC cylindrical grinding machine during its warm-up period.
The CMM (coordinate measuring machines) are able to perform dimensional inspections in workpieces with complex geometries, in a short time compared to conventional methods, however, errors on volume of CMM harm the performance of measurement. Faced with this, the purpose this investigation is to identify regions in the machine with large and small values of volumetric errors. The mapping of volumetric error is performed by optimization of objective function with SQP method. The objective function is defined by modeling errors of the CMM using a method of the homogeneous transformation, and, by calibration curves of individual errors. The optimization allowed to obtain the smallest value of volumetric error, 1.1796 μm, located near the linear encoder of the y axis. The mapping the volumetric error by optimization allows to know regions with minor harm the performance of measurement, therefore, it's possible to select regions of measurement to obtain reliable results.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.