Date of Graduation

1989

Document Type

Dissertation/Thesis

Abstract

Many mechanical power presses are equipped for actuation with dual hand buttons. For these operations, most countries have safety regulations requiring the button location be at least a minimum distance from the hazardous area where the dies meet. This distance is called the "safe distance" (D{dollar}\\sb{lcub}\\rm s{rcub}{dollar}) because its purpose is to protect the operator in case of a sudden, instinctive reach into the die area after initiating the downstroke. According to most of these regulations, D{dollar}\\sb{lcub}\\rm s{rcub}{dollar} is determined (in meters) from the inequality D{dollar}\\sb{lcub}\\rm s{rcub}{dollar} {dollar}>{dollar} S T{dollar}\\sb{lcub}\\rm stop{rcub}{dollar} where S is an assumed hand speed of 1.6 m/s, and T{dollar}\\sb{lcub}\\rm stop{rcub}{dollar} is the time to stop the press ram (in seconds). Data from a prior study indicate that distances calculated from this formula are insufficient to protect many press operators from amputation if they happen to reach into the die area after initiating the downstroke. This project was undertaken to provide the manufacturing community with a better formula. An experiment was conducted in which subjects operated a simulated mechanical power press. At random times their routine operation was interrupted by a signal indicating than they should reach as rapidly as possible to touch the part being processed. Their reach times were used to develop a regression model that uses distance to predict the mean time expected for power press operators to complete such a movement. This regression model for after-reach time was then used to derive a new inequality for calculating D{dollar}\\sb{lcub}\\rm s{rcub}{dollar} from T{dollar}\\sb{lcub}\\rm stop{rcub}{dollar} and a variable called DELTA which accounts for the variability of after-reach time among press operators. The new inequality is D{dollar}\\sb{lcub}\\rm s{rcub}{dollar} {dollar}>{dollar} 0.127-0.125 ln(0.18 {dollar}-{dollar} T{dollar}\\sb{lcub}\\rm stop{rcub}{dollar} {dollar}-{dollar} DELTA). In addition to the research on safe distance, two epidemiologic investigations were conducted. The first compared three methods for estimating the total annual incidence of selected occupational injuries in the United States. All three methods estimated over 1000 power press related amputations in the year studied. The second epidemiologic study determined from workers' compensation data that young press operators were at greater risk of amputation than older press operators. Gender had no significant association with risk.

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