Evaluation of Fitts’ Throughput as a Possible Performance Measure for Manual Assembly Tasks

Abstract

Assembly lines are the backbone of the manufacturing sector. Workers at the assembly lines are expected to perform fast pace hand-arm exertions with precision and accuracy. To protect the workers from injuries, OSHA mandates the use of personal protective equipment (PPE) including gloves. Certain assembly operations require the use of special gloves. Some of these gloves can inhibit hand performance, further increasing the task difficulty. The Index of Difficulty (ID) is a metric measured in 'bits' quantifies task difficulty through the quotient of target width and target motion, i.e., distance travelled. The time required to complete the target motion is the Movement time (MT). The ratio of ID and MT was defined by Fitts as 'throughput' and is measured in bits/s. This study aims to evaluate Fitts' throughput as a possible performance measure for gloves used in the manual assembly tasks. An experimental study was performed using fifteen healthy participants with three types of gloves which were evaluated using two tests, Fitts' throughput test and a hand tool dexterity test (HTDT). The Fitts' throughput test was designed using ISO 9241-411 standard and involved a series of target transfer tasks with varying ID levels. In the HTDT test, participants performed a simulated assembly task with different glove conditions. Statistical analysis revealed that the effect of glove condition was significant for both throughput and assembly time. The mean throughput of 3.91 bits/s for bare hand was higher compared to the three glove conditions. Among the three glove conditions, Glove 2 was found to have a higher throughput of 3.72 bits/s followed by Glove 1 with 3.51 bits/s, and Glove 3 with 3.47 bits/s. The mean assembly times for Gloves 2, 1, 3 were 462.52 sec, 501.88 sec and 558.48 sec, respectively.In general, an inverse relationship between throughput and assembly time was observed, indicating that a glove with higher throughput produces lower assembly time. Thus, the study findings seem to indicate that Fitts' throughput can serve as a possible performance measure for manual assembly tasks.iii DEDICATIONTo my beloved family, Jagadish, Nalini, Prajwal and my grandparents for their endless compassion, support and guidance.