Terrence J. Stobbe

The effects of factors on human performance in the event of an unexpected robot motion

This study evaluates factors that could effect human performance in the event of an unexpected robot motion. The results of the study demonstrated many things. First, robot speed and task had an important impact on robot overrun distance. A longer overrun distance was observed with both increasing robot speed or task complexity. Second, illumination affected subjects performance; a longer overrun distance was observed with a low illumination level (10 Lux). Overrun distance, however, remained unaffected with increasing illumination level above 100 Lux. Furthermore, unexpected robot motions initiated in the peripheral field resulted in a longer overrun distance than motions initiated in the central field. The analysis of the robot speed by illumination interaction suggested that a low illumination level may further increase overrun distance with increasing robot speed. The analysis also suggested that when increasing robot motion speed, the overrun distance increases with low background-to-robot-arm luminance contrast ratios.

Facial hair and respirator fit: a review of the literature.

The effect of facial hair on the quality of fit obtained while wearing a tight-fitting respirator has been and continues to be a controversial subject. Many people hold strong opinions on both sides of the issue, but it is not opinion that is needed. Rather what is needed is quantitative study of the situation to determine precisely what effect facial hair has on respirator fit. The results of fourteen studies of the facial hair leakage question have been summarized. All but two of the fourteen studies found that in the presence of facial hair, face seal leakage increases from 20 times to 1000 times. In addition both intersubject and interrespirator face seal leakage variability increased when facial hair was present. In the other two studies, one completed with positive pressure SCBAs and the other completed in the workplace, no statistically significant leakage differences were found.

Determination of a safe slow robot motion speed based on the effect of environmental factors

The goal of this research was to determine a safe slow robot motion speed to be used for intervention tasks conducted in proximity to an industrial robot (e.g., programming and maintenance) when environmental factors were considered. The relevant factors associated with a robot station were dictated by previous research (Beauchamp and Stobbe, 1990). They were the illumination level, the luminance contrast between the robot and its background, the motion speed of the robot, and the field in which unexpected motions were initiated. The dependent variable measured was the distance the robot moved before the subject detected and responded to the unexpected robot motion. From the results, a multiple regression model was derived for predicting robot overrun distance. The model suggested that speeds in excess of 17 cm/s do not provide an adequate safety margin, and that 17 cm/s should be recommended as the maximum robot slow speed for work conducted in the vicinity of an industrial robot not equipped with dead-man switches.

A Test-Retest Criterion for Isometric Strength Testing:

Isometric strength testing has commonly been used to evaluate human strength capability. Recently it has been proposed by NIOSh as a form of administrative control for injury prevention. Historically, the number of trials used for each person-test combination has been arbitrarily selected and is often undocumented. This paper proposes a criterion for isometric testing and reports some results from using this criterion.

Prediction of elderly seating comfort from physical condition, chair type and gender

Many persons over 60 years of age have unique problems sitting on chairs. These problems which are caused by decreased mobility, strength or disease suggest that the chairs should be selected carefully with some scientific basis that incorporates the varying demands of the elderly community. Identification of the proper chair for a particular individual, especially if it has to be low cost and nonmotorized, is a difficult job for institutions, elderly themselves, their families and the furniture industry. Keeping in view these problems a prediction model is developed using established statistical methods to predict comfort of sitting of a particular individual sitting in a particular chair. The study is based on experimental data collected on 18 male and female subjects over the age of 64. The equation uses chair type, body fat %, i.e. above average fat etc., body size, i.e. lean etc., and gender as inputs. The equation was tested on new female and male elderly subjects sitting on two new chairs. The model holds out excellent on the validation despite a low coefficient of determination value obtained for the equation. The paper not only presents a comfort prediction model but also shows a new direction for elderly seating research by employing statistical methods and elderly variables which do not appear in the published literature on elderly seating in the manner presented in this paper. This model will have wide applications especially for practioners (e.g., human factors engineers, occupational therapists, product developers) who need such information in a hurry. This approach also has heuristic value for the researcher in providing guidelines for the testing of other critical variables that may impact on the use of a chair or of other pieces of equipment.

A Methodology for Determining the Mineral Content and Particle Size Distribution of Airborne Coal Mine Dust

Abstract Exposure to airborne dust in coal mines has caused respiratory disease in coal miners. The causal agent in these diseases remains unknown, although the minerals found in and around the coal seam have been implicated. Toxicological studies designed to establish the effect of different mineral combinations and concentrations are lacking because the mineral content of coal mine dust has not been defined. This paper reports the initial results of a study done to characterize the mineral content of the coal mine dust found in a mine in the Upper Freeport seam in Northern West Virginia. Coal mine dust samples were collected using 4-stage cassette impactors at nine locations in the mine. The samples were analyzed by an x-ray microdiffraction film technique supplemented by energy dispersive scanning electron microscopy. Primary size modes of about 17 to 20 micrometers from the samples collected at the haulageway and the returnside of the continuous miner were found. From the returnside of the roof bolter...

Handtool-task strength comparison between younger and older tractor operators using adjustable rollover protective structures

A fault tree analysis indicates that human strength limitations when using hand tools could lead to misuse of adjustable-type rollover protective structures (ROPS) for farm tractors. Manually adjustable designs for ROPS offer one way to provide wider protection against the hazard of farm tractor rollover. A task-strength study of working orchard farmers (n = 23) ranging in age from 21 to 70 was undertaken. Two age groups of working orchardists were studied: younger than 5.5 years of age (n = 12), and 55 and older (n = 11). Pulling tasks similar to those used for adjusting ROPS using wrenches with 12-, 18-, and 24-inch handles were evaluated. The torque (applied force at a given wrench handle length) and consequently the human strength needed to adequately tighten threaded fasteners, becomes easier as threaded-fastener-diameter decreases. For overhead pulling tasks, the older groups mean strength (133.8 lb) was 97% of the younger groups strength (137.4 lb). However, when the pull was shoulder-height, there was a statistically significant difference in capabilities. The older groups mean strength was 78% of the younger groups mean. Results of the study suggest that for working men between the ages of 55 and 70, (1) easy to use coarse-threaded fasteners no larger than 1/2-inch diameter/ 13 threads per inch will not compromise safety when the expected handtool is a 12-inch wrench and (2) fine-thread fasteners should be no larger than 1/2inch diameter/20 threads per inch for the same expected wrench. Larger diameter fasteners would be appropriate if it is expected that longer wrench handle extensions will be used.

Case study: ergonomic and hazard evaluation of a new consumer product

The introduction of a new, powerful, mechanical home-use tool carries with it a high risk of product liability. This liability stems from both planned and unanticipated use of the product. In view of this, it is imperative that designers and manufacturers carefully analyze their proposed product to insure that possible failures and hazards have been evaluated and corrected, that current ergonomic principles have been used in the design, that instructions and warning signs clearly document the hazards associated with use of the product, and that the advertising describe only safe methods of handling and using the product. This paper describes the analyses that were performed on a tool prior to its production. The purpose of the analyses was to identify and solve as many of the hazardous operating problems of the tool as possible. To this end, a series of system safety analyses was performed to define the user, user-machine interface, and mechanical problems associated with the ditcher-saw.

A methodology to assess the upper extremity strength in a chair egress posture

In this paper a method is presented which can be used to analyse the force distribution resulting from the application of force on the left and right armrest of a chair during the action of sitting down or standing up. The peak data for both hands can be combined to obtain the maximum for a trial on a specific chair configuration. This method is useful to assess the upper extremity limitations of an elderly or disabled population when rising from a seated position. The method involved the instrumentation, with strain gauges, of armrests of a prototype lounge chair obtained from a manufacturer of seating for the elderly. Provision for hand placement was included and the system was appropriately calibrated. The methodology presented may have a variety of applications, such as the assessment of seating requirements for the elderly or disabled, and the relative evaluation of a range of seats for nursing homes, clinics, hospitals and rehabilitation or recreational lounges.

Human Performance in Man-Robot System

The use of industrial robots and computerized automation in industry has increased considerably during the last few years, and the importance of these types of flexible automation is expected to increase very rapidly in the future. The increase in the robot population will, of course, have a favorable influence on working conditions as it will relieve the human of heavy and/or repetitious tasks and free him from hostile environments. On the other hand, it may create new problems, such as psychological problems for the worker displaced to a less challenging position, and a high frequency of robot related accidents. Already, many such accidents have been reported. Surveys conducted in Japan, West Germany and Sweden have indicated that programming, maintenance and inspection tasks were implicated in the majority of reported accidents, that require the individual to be placed within the operation envelope of the robot. An unexpected movement of the robot was among the most likely cause of accidents. Despite this, few studies have been conducted with the purpose of assessing human performance in the event of an unexpected or unsafe motion by a robot. The lack of knowledge concerning the human capacities and limitations in this situation is great, and many of the factors that could affect human performance have not yet been investigated. The goal of this paper is to review studies that dealt with human performance in man-robot system. Recommendations will be provided on safe working methods in realizing tasks that require the worker to be in vicinity of the robot.