Task and reliability analysis of lathe operation

Abstract

As machine tools have become larger, faster, and more automated, the role of the machinist has changed from a primary operator to a system monitor, who is further removed from the machining process. Estimation of system reliability must still consider the human monitor as an integral component, but human failure estimates are harder to make as the operator is further removed from direct system control. To illustrate system reliability analysis for specific machining tasks, the reliahility of both manual and computer-numerical controlled (CNC) lathe operation tasks were evaluated. A task analysis was initially completed, detailing common failure modes in each suhtask.Using the Technique for Human Error Prediction (THERP), human operator reliability was estimated at 0.90 for a 30-element manual task, and 0.95 for an 18-element CNC task. These estimates were considered acceptable for nonproduction work. Further decreases in reliability in the CNC task are expected as the result of operator program changes during machining. THERP was most useful in developing initial estimates of human reliability for the tasks, hut additional studies are recommended in the areas of operator scanning strategies and human reliahility in performance of more complex machining tasks. 1

Semi‐Markov reliability model of manufacturing systems considering machine degradation, human errors, and their mutual facilitation effects

“…However, the human errors in safety zone, such as failure to engage gearing or power feed, cannot influence the turret. 36 The degradation of the mechanical components increases the vibration intensity of the turret. Turret vibration worsens the work characteristics, that is, it decreases the machining accuracy and causes a nosier work environment.…”

“…Therefore, human errors in damage and fatal zones can contribute to turret degradation and turret failure, respectively. However, the human errors in safety zone, such as failure to engage gearing or power feed, cannot influence the turret 36 …”

“…To describe the facilitation effects of human errors on machine degradation, the human error model is extended to a zoned human error model. For operator errors in a manufacturing system, Pines and Goldberg 36 concluded that they can be divided into four categories: perceptual, conceptual, motor skill, and discretionary errors. Each possible human error is associated with a system impact or likelihood of creating a defective unit.…”

“…They can be obtained based on the method reported in Ref. 36 They conducted task analysis of a machining task using the Nardini TT 1230-E manual lathe and determined 24 operations. They then calculated the probability of error on each operation 𝑃 𝑖 based on the HRA method, and determined the effect of each error, that is, (a) no system impact, (b) some system impact, and (c) critical system impact or failure.…”