John R. Etherton

A robot safety experiment varying robot speed and contrast with human decision cost

An industrial robot safety experiment was performed to find out how quickly subjects responded to an unexpected robot motion at different speeds of the robot arm, and how frequently they failed to detect a motion that should have been detected. Robotics technicians risk being fatally injured if a robot should trap them against a fixed object. The value of the experimentation lies in its ability to show that this risk can be reduced by a design change. If the robot is moving at a slow speed, during programming and troubleshooting tasks, then the worker has sufficient time to actuate an emergency stop device before the robot can reach the person. The dependent variable in the experiment was the overrun distance (beyond an expected stopping point) that a robot arm travelled before a person actuated a stop pushbutton. Results of this experiment demonstrated that the speed of the robot arm and the implied decision cost for hitting an emergency stop button had a significant effect on human reaction time. At a fairly high level of ambient lighting (560 lux), fixed-level changes in the luminance contrast between the robot arm and its background did not significantly affect human reaction time.

Foreseeable errors in the use of foot controls on industrial machines

Foot controls are a productive actuator for many tasks on reciprocating action industrial machines such as power presses, spot welders and press brakes. However, amputations sometimes occur when a foot control is inadvertently depressed when an operator reaches into the danger point of the machine. This report uses occupational injury statistics, workplace observations and a review of selected literature to propose a model of inadvertent use of foot controls. This model serves as the basis for conducting a subsequent machine safety simulation experiment in a metal products fabricating factory. Primary model elements are unmediated hand movement, mental slips associated with task rhythm, and loss of balance. To avoid injury due to inadvertent use of pedals, workstation designers may wish to consider using automated or hand control devices in lieu of foot controls. Alternatively, if foot control is the selected method for actuation, then they may wish to consider mitigating the error-inducing effects of machine tooling problems and repetitiveness by using safeguarding which is difficult to circumvent or redundant safeguarding devices at the point of danger.

Machinery Risk Assessment for Risk Reduction

New avenues are reviewed and discussed for preventing industrial machine-related injury by means of realistic risk evaluation and reduction processes at the design and application stages of machinery development and use. U.S. guidelines and European standards on machinery risk assessment procedures are described. Applications of risk assessment for machine-related injury risk management and teaching machine-risk control are discussed.

The use of simulation for developing safe workstation designs for mechanical power presses

Simulation can provide a nonhazardous method for testing various equipment designs before selecting an option for implementation. A power press simulator was developed to evaluate workstation design options for foot switch and dual palm button actuation devices. Two experiments were performed with the simulator, reproducing several causal events that can result in amputations on mechanical power presses. Safety implications for workstation designers are discussed, as well as general considerations on the use of simulation for achieving a design that is as safe as possible.

Machine-cycling errors with foot switches in repetitive tasks. A workstation design simulation experiment.

In this experiment a non-hazardous industrial machine simulator was used to evaluate errors made when using a foot switch to initiate dangerous, repetitive machine motions. Subjects were experienced employees who normally operated metalworking presses and similar hazardous machines on jobs matching the simulation. Four variables (force needed to push switch to closure, the switchs force feedback felt by the subject, subject working posture, and hand task involved in stamping a simulated workpiece) were evaluated for their main and interactive effects upon frequency of machine-cycling errors in a repetitive task. Equipment problems which required immediate correction were introduced at a rate of 4.9 events/h. Also, three covariables (the rate of repetitive use of the switch to make hits on simulated workpieces, subject age and subject experience at foot switch-controlled workstations) were examined for their contribution to cycling errors. Although hand task was a significant effect in error prediction models containing the four primary variables, it was found that a model containing the hit rate covariate (rate of repeated use of the foot switch) provided the best predictor of the frequency of inadvertent actuation errors. An error threshold was observed at about 17.5 hits/min with a high linear correlation between hit rate and machine-cycling errors at higher hit rates. Based on results of the experiment, this report presents design considerations for workstations which use foot controls to help minimise the chance of machine-cycling errors and injury.

A case study of the occupational stress implications of working with two different actuation/safety devices.

A case study was conducted using an automatic sphygmomanometer to compare the stress encountered by workers using two different machine actuation/safety devices. The experiment took place in a small metal stamping plant as part of a government authorized comparison of the devices. Six experienced female workers separately performed the same task on the same power presses using either a photo electronic or a two-hand button device. These two devices perform dual duty as both machine actuators and machine safeguards. Blood pressure at the ankle and heart rate were measured periodically and a questionnaire was administered. The case study approach to this experiment was necessitated by government restrictions which limit the population of workers experienced with both devices. The results of the case study are twofold: (1) For the small population tested no significant difference was found in the stress measures examined for machine operators; and (2) A feasible in-plant methodology is demonstrated for unobtrusively monitoring worker populations exposed to machine related stress.

Design Recommendations for Controlling the Jam-Clearing Hazard on Recycling Industry Balers

Between 1986 and 2002, there were 43 fatalities in the United States to operators of recycling industry balers. Of these fatalities, 29 involved horizontal balers that were baling paper and cardboard (Taylor, 2002). Balers often become jammed while the baling process is occurring, and the only way to remove the jam is manually. This requires an employee to place a limb of their body into the jamming area and remove the material that is causing the jam. While lockout and tagout procedures reduce the risk of hazardous energy being released, they can still be easily bypassed, ignored, or forgotten. Recent efforts to reduce machine-related injury and death involve the development of a control system for these machines that automatically detects hazardous operating conditions and responds accordingly. The system is being developed at the National Institute for Occupational Safety and Health (NIOSH). This system, JamAlert, automatically terminates the power to the machine when a jam is detected. JamAlert detects a jam by observing both the strain that is experienced by the shear bar of the baler and the hydraulic pressure at which the ram is operating. The strain that is experienced by the baler shear bar when a jam is initiated was calculated in this study through laboratory testing and finite element modeling. Design recommendations are presented on how best to tune the JamAlert’s operating program to most effectively control the jam-clearing hazard.Copyright

NIOSH AutoROPS 3rd Generation Static Testing and Human Interaction Element

To address the need for rollover protective structures (ROPS) on farm tractors that are easily adapted to low overhead clearance situations, the Division of Safety Research (DSR), National Institute for Occupational Safety and Health (NIOSH), developed an automatically deploying, telescoping ROPS (AutoROPS). The NIOSH AutoROPS at the present is in the third generation design and static testing phase, and the first phase of human subject (human operator) testing and manufacturing. The static testing is based on the SAE J2194 standard for testing ROPS for agricultural tractor use. The nature of the NIOSH AutoROPS is to be in a retracted position until an overturn is determined to be imminent. It is during the deployment time period that potential safety hazards exist that are not present in a traditional fixed ROPS and not addressed in the standards. Human interaction is a key ingredient in refining the design to be both functional and desirable while considering possible hazards. Feedback from farmers who have operated a tractor with the NIOSH AutoROPS installed and in the ready state will enhance the design and acceptability. NIOSH’s goal is to reduce the number of fatal agricultural overturns by increasing the percentage of tractors with ROPS and seatbelts which operate in low clearance environments. This design has met laboratory static testing criteria of the SAE J2194 standard for ROPS on agricultural tractors. Field evaluation of the AutoROPS use by poultry farmers (N=32) in eastern West Virginia showed favorable results and a preference for wanting to purchase and use the NIOSH AutoROPS compared with a currently available manually foldable ROPS. This paper discusses the overall performance of the NIOSH AutoROPS as subjected to the SAE J2194 standard and human interaction/feedback of operating an agricultural tractor with this added safety device.© 2003 ASME

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.

NIOSH AutoROPS Research to Practice: Zero Turn Commercial Mowers

Marketing new safety devices is a critical function on the research-to-practice path. This path to adoption of new safety technology is not always straightforward. The National Institute for Occupational Safety and Health (NIOSH) Automatically deployable Rollover Protective Structure (AutoROPS) is a passive safety device developed to protect tractor operators in an overturn event. Tractor overturns kill more than 100 farmers each year in the United States (Myers, 2003). This technology was first designed to target the agricultural low-clearance environments involving “low-profile” tractors where traditional ROPS may not be feasible. These tractors are exempted from ROPS use as stated in OSHA 1928.51(b) (5) (i & ii). The upper portion of the AutoROPS remains retracted under low clearance areas but deploys to full height when an overturn is detected. The AutoROPS has been tested under both field and laboratory conditions prescribed in the ROPS performance standard, SAE J2194. To translate successful research into occupational practice, NIOSH formed a partnership with FEMCO, a ROPS manufacturer, in 2003. FEMCO’s efforts found Scag Power Equipment, a zero-turn commercial mower manufacturer. NIOSH has partnered with them as well. The Scag AutoROPS has been successfully laboratory tested to industry standards. Preliminary field evaluations of the deployment system have been conducted in preparation for field upset tests. Product development, test procedures, test results, and current marketing efforts are presented on this innovative safety device.