Jeffrey C. Woldstad

Floor/shoe slip resistance measurement

A variety of slip measurement devices exist that provide estimates of both static and dynamic coefficient-of-friction (COF) values between ones shoes and the floor. Unfortunately, different shoe sole/heel materials, floor conditions, and contaminants will affect the tests in ways that result in widely varying COF estimates. This paper reviews the basic physics of such tests and describes a set of experiments to determine the static and dynamic COF values under operating conditions known to exist in different jobs. The results define a set of conditions wherein low (hazardous) COF values would exist (e.g., hard Neolite shoe material in contact with a wet, smooth walking surface). The results also question the use of light-load testing devices and static and slow speed reference COF values in the literature.

DYNAMIC PUSH AND PULL FORCES WHILE USING A MANUAL MATERIAL HANDLING ASSIST DEVICE

Movement assist devices are quickly replacing traditional manual methods of material handling. By providing these devices, ergonomists assume they are substantially reducing the musculoskeletal strain associated with completing the task. Unfortunately, assist devices usually only minimize the gravitational force components of the task, and by their additional inertia, tend to increase dynamic manual requirements. The experiment reported here examines the dynamic force levels produced by inexperienced operators symmetrically pushing and pulling a small material handling assist device. Values are presented as a function of system and task parameters, such as load transported, movement distance, final placement accuracy and system friction. The results demonstrate that subjects performed the task using remarkably high push and pull forces. Experimental manipulations had only relatively small effects on the force levels observed. These results are discussed in terms of the ergonomic issues that may affect ind...

Forces applied to large hand wheels

This is a report of a study conducted to establish the population isometric strength capabilities of subjects generating force using a hand wheel. Wheel force strength of 125 males and 125 females was measured using two different handgrip configurations: grasping the rim of the wheel and grasping the spoke. In addition, two separate procedures for generating and measuring strength were used: a 3 s average during a 6 s trial, and a ramp to maximum exertion level and then relax. The task simulated setting a handbrake on a typical railroad box car. Results indicated that grip characteristics and grip strength play an important role in isometric wheel force strength capabilities. The average tangential forces ranged from 393 to 614 N for males, and from 235 to 348 N for females, depending upon the grip configuration and the method used to measure strength. Standard whole-body strength measures for the legs, arms, torso and grip were also measured and demonstrated to be effective in predicting the wheel force strength capabilities of the subjects.

Effects of wheel design on the torques applied to large hand wheels

This paper reports the results of an experiment to evaluate the isometric wheel torque strength of human subjects using four different hand wheel designs. Three of the wheels were new designs, while the fourth was a wheel currently used on many railroad car hand brakes. The three new designs were a cylindrical tube (4.3 cm in diameter), a cylindrical tube (2.5 cm in diameter) with spheres mounted along the edge, and a circular zig-zag design. The strength capabilities for 12 male and 12 female subjects were measured using two methods. The first method used a three-second average during a six-second sustained exertion following recommended isometric strength testing procedures. The second used the maximum value for a trial that had subjects slowly increase the magnitude of their exertion to a maximum and then relax. Results showed that the torque generated by the subjects was highest for the zig-zag design, followed in order by the wheel with the spheres, the cylindrical wheel, and the standard wheel; average torque values were 156 Nm, 118 Nm, 106 Nm, and 101 Nm, respectively. Further, the hand forces generated by the subjects during the wheel-turning task indicate that not only were subjects able to generate more wheel-turning torque using the new wheel designs, but they were also more efficient in producing this torque.

Isometric Strength Capability for a Vertical Wheel Turning Task

This paper reports on the measured isometric strength capability of 125 male and 125 female college students performing a one-handed wheel turning task. Three measures of isometric strength were used: (1) a three-second average of steady state levels taken from a six-second exertion, (2) the largest value (peak) from the same six-second exertion, and (3) a maximum exertion level taken from a separate “ramp-to-peak” exertion. Standardized whole-body strength measurements for the legs, arms, and torso as well as grip strength were also taken for each subject. The results presented in this paper demonstrate average isometric wheel turning strengths (torques) ranging from 109 to 152 N-m for males and 66 to 91 N-m for females, depending upon the strength measure used. The three strength measures were highly correlated, but produced significantly different estimates of strength. The three-second average produced the lowest estimate while the ramp-peak value produced the highest. Wheel turning strengths were also highly correlated with the standardized whole-body strength measures and with grip strength. Multiple regression models developed to predict wheel turning strength using these values accounted for 69 to 71 percent of the variation in the measures. The model results also suggest that grip strength plays an important role in determining wheel turning strength capability.

A computer-based method for recording three-dimensional body postures

Abstract A computer-based posture recording method was developed to allow users to record three-dimensional human body postures from a videotape recording for use in ergonomics. To evaluate the method, a validation experiment was performed using 30 male and female subjects. Subjects were asked to record body postures for a videotaped model which were compared to standardized recordings made by the experimenter. Results showed that the method was reliable between subject and moderately accurate. The overall average recording error for each link was approximately 11 degrees, but was highly dependent on the link being recorded, the posture and the viewing angle. The time required to record each posture ranged from 2.55 to 5.98 minutes.

Wheel Turning Strength for Four Wheel Designs

This paper reports the results of an experiment to evaluate the isometric wheel turning strength of 12 male and 12 female subjects using four different wheel designs. Three of the wheels investigated were new designs developed specifically for this study, while the fourth was a wheel currently used on many railroad car hand brakes. The three new designs considered were a cylindrical tube (4.3 cm in diameter), a cylindrical tube (2.5 cm in diameter) with spheres mounted along the edge, and a circular zig-zag design. Strength data were collected using a mock-up of the ladder and platform arrangement found on most railroad hopper and box cars. The task simulated the final tightening exertion required to secure railroad car hand brakes. Strength capabilities were measured using two methods: 1) a three second average during a six-second trial; 2) the peak reached on a separate trial in which subjects did not sustain an exertion. Results showed that the torque generated by the subjects was highest for the zig-zag design, followed in order by the wheel with the spheres, the cylindrical wheel, and the standard wheel; average torque values were 191 Nm, 147 Nm, 132 Nm, and 95 Nm, respectively. The average strength values (three-second average) for six-second maximum exertions produced lower average torque values (122 Nm) than the ramp to maximum exertion (161 Nm).

Coordination of Kinematic Events during Simple Arm Movements

This paper examines the pattern of kinematic events underlying repeated performance of simple rapid elbow flexion movements to a fixed target. The limb positions and time samples of kinematic indices are derived from forearm movement trajectories and measurements of the forces tangent to the arch described by the forearm during motion. The pattern of kinematic events are compared for different levels of the inertial load moved, distance traveled and target width. Results demonstrate that both time samples and limb positions corresponding to peak acceleration, peak velocity and peak deceleration varied significantly with inertial load and movement distance, but were relatively unaffected by changes in target width. Changes in the timing of kinematic events demonstrated no clear pattern across manipulations. Forearm positions, however, were highly proportional to the movement distance, with peak acceleration approximately 7% of the distance to the target, and peak velocity and deceleration approximately 47% and 87% of the distance to the target, respectively. These results are interpreted as indicating that the control processes governing the construction of motor commands are organized in terms of limb position instead of more traditional force-time representations. Mechanisms of this type are consistent with recent mass-spring models of muscle control.