Psychophysically Determined Horizontal and Vertical Forces of Dynamic Pushing on High and Low Coefficient of Friction Floors for Female Industrial Workers

Abstract

The purpose of this experiment was to investigate horizontal and vertical components of maximum acceptable initial and sustained forces while performing pushcart tasks on high and low coefficient of friction (COF) floors. Eleven female industrial workers performed two sessions of 120 pushcart tasks on a high COF (.68) floor and one session of 120 pushcart tasks on a low COF (.26) floor. Each pushcart task was 7.6 meters long and initiated once a minute. A psychophysical methodology was employed whereby the workers were asked to select a work load they could sustain for 8 hours without "straining themselves or without becoming unusually tired, weakened, overheated, or out of breath." The results revealed that maximum acceptable weights of the pushcart task on the low COF floor were significantly lower (20%) than the maximum acceptable weights on the high COF floor, which coincided with a significant reduction in the initial and sustained horizontal forces of push (28% and 29%, respectively) on a low COF floor. Push durations on the low COF floor were also significantly longer (36%) than on the high COF floor. Vertical forces and ratios of the vertical to horizontal forces were not significantly different comparing both floors. Calculated probabilities of slipping were supported by observations of repeated slipping by some workers during pushing on the low COF floor. Ergonomic strategies should include the maintenance of sufficient COF on floors to maximize the psychophysical pushing capabilities of the industrial worker.

Comparison of psychophysiological responses in healthy men and women workers during cart pushing on two walkways of high and low coefficient of friction

“…2, Tables 1a and b). When encountering a slippery surface (i.e., Teflon walkway), participants selected lower cart weights, and such workloads during cart pushing are in agreement with previous psychophysics literature (Ciriello et al, 2001;Ciriello, 2005). It is established that participants anticipate the characteristics of the floor due to prior slip experience and knowledge (Marigold and Patla, 2001;Heiden et al, 2006) and modify posture and effort accordingly so as to avoid any potential slip (Redfern et al, 2001).…”

“…The diameter of each wheel was 20 cm, and was inflated to a pressure of 207 kPa. At this inflation pressure, the rubber wheels minimized the rolling of the cart after each push, and thus did not require the participant to exert any force to stop the cart (Ciriello et al, 2001;Ciriello, 2005). Instrumented handles that can be adjusted between 66 and 127 cm in height were attached to both ends of the cart (Fig.…”

“…A resultant force on the instrumented handle was then calculated as the square root of the sum of the squared horizontal and vertical integrated forces. To measure the slipperiness of the walkway during cart pushing, the difference in COF (COF diff ) for each walkway was determined (Ciriello, 2005;Ciriello et al, 2001;Hanson et al, 1999). These authors defined COF diff as the difference between measured COF (obtained from a Brungraber Slip-Tester (Model Mark II, Lowisburg, PA, USA), Plywood ¼ 0.68; Teflon ¼ 0.26) and required COF.…”

“…The required COF was the minimum friction that is necessary to perform pushing without slipping on the walkway, and was expressed as the ratio of the sum of forces applied in the horizontal direction on the handle and the sum of the vertical forces acting at the interface. According to Hoozemans et al (1998), force applied on the cart handle in the horizontal direction can be assumed to be equivalent to sum of forces applied in the horizontal direction, whereas forces applied in the vertical direction was calculated as the difference between body weight (in Newtons) and force applied on the cart handle in the vertical direction (Ciriello, 2005;Ciriello et al, 2001). Therefore, required COF and COF diff for each walkway were determined at the end of 2 h of pushing.…”

The evaluation of force exertions and muscle activities when operating a manual guided vehicle

“…For maximum acceptable initial and sustained pushing forces, both forces exerted by females while pushing a cart are about 70 percent of that of males (Ciriello, 2004;Ciriello et al, 2007). When pushing a cart on a low coefficient of friction floor, the acceptable initial pushing force for males and females are about 65 percent and 72 percent of that of a high coefficient of friction floor, respectively (Ciriello, 2005;Maikala et al, 2009). Beside the strength capability difference between genders, other factors such as motivation and working skill may also affect force exertion.…”