Glenn K. Klute

The effects of extra vehicular activity (EVA) gloves on human performance

Abstract Human strength and capabilities such as dexterity, manipulability, and tactile perception are unique and render the hand as a very versatile, effective, multipurpose tool. This is especially true for unknown microgravity environments such as the EVA environment. Facilitation of these activities, with simultaneous protection from the cruel EVA environment, are the two, often conflicting, objectives of glove design. The objective of this study was to assess the effects of EVA gloves at different pressures on human hand capabilities. A factorial experiment was performed in which three types of EVA gloves were tested at five pressure differentials. The independent variables tested in this experiment were gender, glove type, pressure differential, and glove make. Six subjects participated in an experiment in which a number of dexterity measures such as time to tie a rope, and the time to assemble a nut and bolt, were recorded. Tactility was measured through a two-point discrimination test. The results indicate that (a) With EVA gloves there is a considerable reduction in both strength and dexterity performance; and (b) performance decrements increase with increasing pressure differential. Some interesting gender glove interactions were observed, some of which may have been due to the extent (or lack of) fit of the glove to the hand. The implications for the designer are discussed.

Tactility as a Function of Grasp Force: Effects of Glove, Orientation, Load and Handle

The objectives of this research were to ensure that a reduction in tactile sensitivity was causing a reduction in gloved performance, and to measure this reduction in tactile sensitivity through grasp force at the hand/handle interface under a variety of performance conditions. The effects of glove type, load lifted, handle size, and handle orientation on the initial grasping force and stable grasping force were determined through a factorial experiment in which 10 subjects participated. The working hypothesis was that grasp force would be a function of all the above mentioned factors. The most consistent findings of this experiment were: 1. Glove effect is marginal at submaximal exertions. 2. The magnitude of force exertions in the advanced glove and bare handed conditions were similar. 3. The magnitude of force exertion was the highest with meat packing gloves. 4. The ratio of peak to stable grasp force increased with increasing loads. 5. The glove effect for maximal exertions as seen in experiment 2 is consistent with published evidence. In conclusion, it is clear from these experiments that when people perform a grasping action, the maximal exertions are affected differently by gloves than sub-maximal or “just holding type of exertions.”

The Effects of Extra Vehicular Activity (EVA) Gloves on Dexterity and Tactility

Human capabilities such as dexterity, manipulability, and tactile perception are unique and render the hand as a very versatile, effective and a multipurpose tool. This is especially true for unknown microgravity environments such as the EVA environment. Facilitation of these activities, with simultaneous protection from the cruel EVA environment are the two, often conflicting, objectives of glove design. The objective of this study was to assess the effects of EVA gloves at different pressures on human hand capabilities, A factorial experiment was performed in which three types of EVA gloves were tested at five pressure differentials. The independent variables tested in this experiment were gender, glove type, pressure differential, and glove make. Six subjects participated in an experiment where a number of dexterity measures, namely time to tie a rope, and the time to assemble a nut and bolt were recorded. Tactility was measured through a two point discrimination test. The results indicate that a) With EVA gloves there is a considerable reduction in dexterity, b) performance decrements increase with increasing pressure differential, and c) some interesting gender glove interactions were observed, some of which may have been due to the extent (or lack of) fit of the glove to the hand. The implications for the designer are discussed.

Influence of a Pitch Adjustable Foot Restraint on Operator Induced Loads in Zero-Gravity

The zero-gravity environment creates a need for a proper human body restraint system to maintain a comfortable posture which lessens fatigue and maximizes productivity. In addition, restraint systems must be able to meet the loading demands of maintenance and assembly tasks performed on-orbit. The Shuttles primary intravehicular astronaut restraint system is currently a foot loop design that attaches to flat surfaces. This restraint system allows for variation in mounting locations and ease of ingress and egress. However, this design limits performance because it does not allow for elevation, pitch, or foot loop length adjustment. Several prototype foot restraint systems are being evaluated for use aboard Space Station and the Space Shuttle. A study was initiated using NASAs reduced gravity aircraft quantifying differences observed in operator performance while adjusting the pitch angle of a prototype foot restraint. Pitch angle adjustments were made from 5° to 35°. While operators performed a torque wrench task using a hand hold and foot restraint, the maximum axial forces and moments induced on the restraint systems and torque wrench were recorded. Overall this study did not see any significant difference in the force operators could place on the torque wrench or forces imparted to the foot restraint system due to the pitch orientation of the foot restraint. Thus in a work environment in which hand holds are available, no significant influence of the pitch angle existed for operator performance or forces imparted to the restraint system.

Evaluation of Crew Capabilities to Handle and Stabilize Heavy Masses in Microgravity

One of the purposes of NASAs Shuttle missions is to deploy and retrieve satellites. Some of these missions require extravehicular activities (EVAs). During EVAs, crew members wear pressurized suits for protection from hazardous conditions and use a Remote Manipulator System (RMS) to transfer heavy objects from one location to another. Prior to the Hubble Space Telescope repair mission (STS-61), concerns were raised whether crew members would be able to hold onto the modules if the RMS started or stopped unexpectedly. An experiment was conducted to measure the handle forces during such a scenario and to determine whether these forces and moments were well within the capabilities of the crew. Four subjects participated in the study. Mockups were built to represent the characteristics of the actual unit and tests were conducted at the Precision Air Bearing Facility (PABF) which simulates a nearly friction-free environment. Force plates were attached to the mockups to monitor forces and moments during the test. Controlled translation and rotation tasks were also conducted to compare the results with those of sudden RMS run start/stop tasks. The results from this study showed that the forces and moments exerted by subjects during sudden stopping and starting conditions were well within the capabilities of the crew members. This study thus provided quantitative data for NASA to be assured of a safe and successful mission.

Strength Capabilities While Performing Torquing Tasks in Weightlessness

Knowledge of individuals strength capabilities in weightlessness is of interest within many areas of NASA, including workplace design, tool development, and mission planning. This study was a generic examination of the loads produced by individuals performing maximal efforts with a torquing tool in zero-gravity. The study also examined the effects of orientation and direction of rotation of the tool on strength effectiveness. An experiment was conducted aboard NASAs reduced gravity aircraft which simulates brief periods of weightlessness. A test stand was developed and instrumented to measure the loads applied to fixed fittings. Eight male volunteers participated in this study in which they used a wrench to apply a maximum torque to fittings oriented along each of three orthogonal axes. It was seen that these subjects could produce approximately 400 to 750 N of force, depending on the orientation of the tool and the direction of effort. The most force could be produced when pushing the tool upwards. A force effectiveness ratio (FER) was defined as an indication of how much of the subjects total effort actually went into performing the desired task. Values of FER ranged from 0.55 to 0.90, with the greatest FER occurring with UP and DOWN efforts, and the lowest with AWAY and LEFT efforts. Designers can use these results to set specifications for craft structures; tools can be developed based on the known strength of the tool users; and tasks can be developed to not exceed the crewmembers capabilities.