PERFORMANCE EVALUATION OF THE UT AUTOMATED ROAD MAINTENANCE MACHINE
This final report mainly focuses on evaluating the overall performance of the University of Texas' (UT's) Automated Road Maintenance Machine (ARMM). First, the ARMM's man-machine-balanced control loop was further developed then rigorously tested and evaluated based on (1) accuracy, (2) time, and (3) quality of the resultant seal. For the efficiency evaluation, thirty pavement crack images, which included longitudinal, transverse, and block cracking, were collected from a UT research campus, and field trials were completed at five locations (Austin, San Antonio, Dallas, Corpus Christi, and Travis County) in the state of Texas. Several additional significant improvements were made to the ARMM during the course of this project. Second, the ARMM's productivity was estimated based on (1) the results of the efficiency evaluation of the man-machine control loop, (2) observations made during the series of field trials, and (3) a productivity model. The mathematical model that predicts the productivity of the ARMM under various work conditions was developed as a means for job estimating and for rating the performance of the ARMM. The ARMM's estimated productivity was then compared with the typical productivity rate associated with conventional crack sealing methods. Evaluation results from the field trials and implementation recommendations are also made in this final project report. It was concluded that the introduction of automated methods to the pavement crack-sealing process will improve productivity and quality and can reduce costs and safety risks. The latter is a direct result of reducing normal crew sizes of seven to eight workers to only three to four workers. The reduction in crew size and the increase in productivity of the sealing process translate directly into significant potential cost savings. By automatically recording work completed, the ARMM should help improve project controls; by its ability to work at night, the ARMM should reduce road user costs.
Advances in control systems for construction manipulators
Abstract Fundamental advances in sensors, actuators, and control systems technology are creating opportunities to improve the performance of traditional construction equipment. New capabilities are being developed as well. These improvements in performance and new capabilities are resulting in better safety and efficiency. However, selecting control strategies can be confusing, and measuring and predicting their performance can be difficult. This paper identifies emerging control paradigms and describes methods for measuring their performance. Many control schemes and corresponding example applications are identified, including single degree of freedom control sticks, multiple degree of freedom joysticks, operating and safety constraints, teach/learn capability, resolved motion with internal and external sensors, spatially correspondent controllers, tele-operation, graphical programming and control, and autonomous controls. Methods described for measuring performance are based on American National Standard Institute (ANSI) standard tests, applications analysis, and ergonomics. Examples focus on the University of Texas at Austin's large scale hydraulic manipulator (LSM) and Automated Road Maintenance Machine (ARMM) with the results of performance tests on these manipulators being presented.
Evolution of carbide precipitates in Hastelloy N joints during welding and post weld heat treatment
Abstract The effects of welding and post weld heat treatment (PWHT) on the morphology, composition and lattice parameter of the precipitates in the welding joints of Hastelloy N alloy have been investigated. Joint samples were prepared using a gas tungsten arc welding process with ERNiMo-2 fillers, and then solid-solution treated at 1100 °C for 20 min. After welding, eutectic M6C carbides can be observed in the heat affected zones (HAZ) and weld zones (WZ). These eutectic M6C carbides become spheroidized during the following PWHT. The concentration of Si decreases during the transformation from the primary ones to eutectic ones, and then increases during the spheroidizing process. The total concentration of Si + Cr in M6C carbides remains stable during welding and PWHT. At the same time, the heat leads to the outward diffusion of Mo from the M6C carbides, which results in a decrease of the lattice parameter.