Mechanical & Materials Engineering, Department of


Date of this Version

Spring 1-2015


Sri Harsha Kavuri (2015). Size Effects in Human Visual Inspection for Micro/Meso Scale Parts. MS thesis. University of Nebraska-Lincoln


A THESIS Presented to the Faculty of The Graduate College at the University of Nebraska In Partial Fulfillment of Requirements For the Degree of Master of Science, Major: Mechanical Engineering and Applied Mechanics, Under the Supervision of Professor Ram Bishu. Lincoln, Nebraska: January, 2015

Copyright (c) 2015 Sri Harsha Kavuri


Visual inspection has been a major method of quality control in conventional manufacturing processes for the last fifty years. Utilizing trained human inspectors to perform this visual inspection has been the most effective means of maintaining quality control. Extensive research has been performed to understand the factors that influence the human inspection process.

In the recent years, there has been a significant emphasis on manufacturing at the smaller end of the size-spectrum such as Micro and Meso scale manufacturing. Quality control at becomes a challenging task due to the extremely small sizes. Several automated visual inspection techniques have been proposed to increase inspection capability. However, the implementation of these automated techniques requires a largecapital investment which makes it unviable for small/medium scale manufacturing companies. Human visual inspection continues to be the major inspection method for these organizations.

Due to the extremely small sizes, some level of magnification is required to facilitate through visual inspection. Visual aids such as microscopes, borescopes are extensively used for this purpose. The level of magnification depends on the size and the detail of the object being inspected. There is no established procedure to choose the level of magnification required for a certain inspection task.

There have been no studies attempted to model the relationship between inspection time and the level of magnification being used. Such a model would help better understand the effective levels of magnification required for a certain inspection task. This study attempts to model the relationship between inspection time and the level of magnification.

A visual inspection experiment was developed with a combination of the major factors that influenced visual inspection accuracy. This was tested on a group of sixty subjects from two distinctive age groups in a PC based environment. The time taken for inspection and the accuracy of responses were recorded in real-time through this experiment.

A MANOVA and ANOVA was performed on the data obtained from the visual inspection experiment. It was observed that magnification was not a significant factor for the data considered for this experiment. This indicates that the above mentioned approach may not be valid to model the relationship between inspection time and magnification.

Advisor: Ram Bishu