Hand Tool Ergonomics – past and Present (original) (raw)
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An approach to ergonomics evaluation of hand tools
Applied Ergonomics, 1993
Based on current knowledge of cumulative trauma disorders in the hand and forearm, related to the use of hand tools, an analysis was undertaken of variables to be considered in ergonomics evaluation of hand tools. Measurement methods were developed and an evaluation station was implemented. Measurement methods are physical, physiological or psychophysical. They focus on the tool, and on the effect of typical use of the tool on the operator. The evaluation station serves as a resource in the development, selection, and testing of tools for a given purpose.
A Checklist for the Ergonomic Evaluation of Nonpowered Hand Tools
Journal of Occupational and Environmental Hygiene, 2004
A checklist was developed to evaluate nonpowered hand tools for basic features related to good ergonomic tool design. The checklist contains 16 items to which a yes/no response is required. The checklist is intended to be used by tradespersons and is written in clear, simple language. This column reports on a study conducted to examine the reliability of the checklist questions in identifying the presence or absence of the basic ergonomic design features that are believed to be important for nonpowered hand tools. Using the checklist, 14 ergonomists and 126 carpenters evaluated 18 typical hand tools. Agreement among the carpenters and ergonomists was high for most of the checklist items. A few checklist questions were associated with relatively low agreement among raters in terms of the presence or absence of a design feature. Lack of agreement between raters indicates that the criterion was not explicit or that users had difficulty identifying whether the tool satisfied the particular criterion. The majority of the 18 hand tools evaluated were deemed to be lacking in multiple highly important ergonomic design features. Additional studies are being conducted to make appropriate revisions to the checklist criteria based on quantitative measures of musculoskeletal loading.
Design and sizing of ergonomic handles for hand tools
Applied Ergonomics, 1993
In this paper, handles for two commonly used hand tools, the chisel and the off-set pliers, are designed using ergonomic principles. These were sized for both males and females falling in the 5th percentile, 50th percentile and 95th percentile groupings. The stresses developed in the ergonomically designed chisel handle while in use were analysed to verify the validity of the design. This chisel handle was then manufactured, and preliminary evaluation using electromyography was conducted. In these tests, the stresses exerted on the flexor and extensor muscles of the arm were measured and compared with those obtained during the use of a conventional handle. Under similar working conditions, results clearly showed that the ergonomically designed handle allows higher working efficiency than existing handles.
Ergonomics Applications of a Mechanical Model of the Human Operator in Power Hand Tool Operation
Journal of Occupational and Environmental Hygiene, 2005
Applications of a new model for predicting power threadedfastener-driving tool operator response and capacity to react against impulsive torque reaction forces are explored for use in tool selection and ergonomic workplace design. The model is based on a mechanical analog of the human operator, with parameters dependent on work location (horizontal and vertical distances); work orientation (horizontal and vertical); and tool shape (in-line, pistol grip, and right angle); and is stratified by gender. This model enables prediction of group means and variances of handle displacement and force for a given tool configuration. Response percentiles can be ascertained for specific tool operations. For example, a sample pistol grip nutrunner used on a horizontal surface at 30 cm in front of the ankles and 140 cm above the floor results in a predicted mean handle reaction displacement of 39.0 (SD = 28.1) mm for males. Consequently 63% of the male users exceed a 30 mm handle displacement limit. When a right angle tool of similar torque output is used instead, the model predicted that only 4.6% of the male tool users exceed a 30 mm handle displacement. A method is described for interpolating individual subject model parameters at any given work location using linear combinations in relation to the range of modeled factors. Additional examples pertinent to ergonomic workstation design and tool selection are provided to demonstrate how the model can be used to aid tool selection and workstation design.
International Journal of Occupational Safety and Ergonomics, 2021
The present study was conducted to review the literature on the effects of handle characteristics of manual hand tools including handle diameter, shape and material on forearm supination/pronation, wrist flexion/extension and wrist ulnar/radial deviation torque strengths to assist ergonomists and designers in developing guidelines to improve workstations and hand tool designs. Twenty-seven papers meeting the inclusion criteria were reviewed. The study provides different points that can be applied to improve the design of hand tools with an emphasis on handle diameter, shape and material, and highlights various methodological issues including interactions among variables affecting maximum torque strength, posture, torque exertion using one or two hands, torque exertions in multiple anatomical axes, using gloves, upper extremity anthropometry and test protocols, which should be considered in future research.
International Journal of Industrial Ergonomics, 1997
Reaction force and workstation design aspects of right angle nutrunner operation were studied in order to better understand their effects on handle kinematics and muscle activity. Tool reaction force factors included spindle target torque (25 Nrn and 50 Nm) and joint hardness (35 ms and 900 ms build-up time). Workstation factors included orientation (horizontal and vertical) and operator distance (10 cm and 35 cm) from the tool. Dependent variables included handle displacement and velocity, work done on the tool-hand system, power involved in doing work, and EMG activity in the forearm and upper arm muscles. Isometric and eccentric strength corresponding to exertions against the tool for velocities of 0 m/s, 0.084 m/s, 0.251 m/s, 0.503 m/s and 0.754 m/s were measured and the relationship between strength and handle kinematics during tool operation was studied. Six inexperienced volunteers (four males and two females) participated. Subjects operated a 58.5 cm long, 3.6 kg right angle nutrunner on a fastener 120 cm off the floor using the fight hand while standing. The handle was most stable (defined as minimum average peak velocity and displacement) when torque was 25 Nm, when vertical workstations were closest (10 cm) to the operator, or when horizontal workstations were farthest (35 cm) from the operator. Greater handle stability was observed for the horizontal workstation than for the vertical workstation. The hard joint (35 ms build-up) resulted in 307% greater peak handle velocity and 195% greater average power acting against the operator compared to the soft joint, however total work against the operator was 134% less for the hard joint. Little correlation was observed between static or dynamic strength and handle kinematics. EMG latency was measured from the onset of torque build-up. The average latency was 38 ms for the hard joint and 171 ms for the soft joint.
Ergonomic Design of Hand Tool (Screwdriver) for Indian Worker Using Comfort Predictors: A Case Study
The purpose of this paper is to focus on certain important aspects of screwdriver use in occupational work situations, with an emphasis on comfort/discomfort in using screwdriver according to users. Descriptors of comfort/discomfort in using hand tools were collected from literature and interviews. Six comfort factors could be distinguished (functionality, posture and muscles, irritation and pain of hand and fingers, irritation of hand surface, handle characteristics, aesthetics). These six factors can be classified into three meaningful groups: functionality, physical interaction and appearance. It is concluded that functionality and physical interaction are the most important factors of comfort in using screwdriver. Thus the designers can use to address the appropriate comfort descriptors in the hand tool design process; an attempt is made to illustrate the relevance of anthropometric data in the design of handle of hand tools (screwdriver) using ergonomic principles. The modified...
Evaluation of handle diameters and orientations in a maximum torque task
International Journal of Industrial Ergonomics, 2005
The effects of gender, handle diameter (25-50 mm), and handle orientation (horizontal and vertical) on the perceived comfort, torque, total finger force, and efficiency of flexor and extensor muscle activity were examined in a maximum torque task. A 16-force sensor glove system was applied to measure finger and phalangeal forces, and a surface EMG was recorded to investigate muscle activities in the torque task. Average maximum torque in the horizontal orientation was about 23.4% more than that in the vertical orientation. The maximum torque was the largest with the 45 and 50 mm diameter handles and least with the 25 mm diameter handle. In both orientations, torque increased as the handle diameter increased, whereas total finger force showed a decreasing pattern which can explain the positive and non-linear correlation between torque output and handle diameter. The efficiency of muscle activity in both orientations followed a similar trend with the torque output for the handle diameters (i.e., the efficiency increased when the handle diameter increased). 35-45 mm handles were rated as the most comfortable for maximum torque exertions. According to a polynomial regression, 37-44 mm and 41-48 mm diameter handles (23.3% of the user's hand length) maximized perceived comfort and were thus recommended for females and males, respectively in this study. Relevance to industry This study will provide guidelines for designing better workstations and hand-tools maximizing performance, muscle efficiency, and user's comfort in manual torque tasks.
An ergonomic comparison of pneumatic and electrical pistol grip hand tools
International Journal of Industrial Ergonomics, 2004
The purpose of this study was to compare the ergonomic demands associated with air and DC pistol grip hand tool use. Seven channels of EMG data were collected from 15 male and 15 female subjects to estimate the muscular demands on the forearms, biceps, shoulders and neck. An accelerometer was also used to estimate the torque reaction transmitted to the hand. Subjects performed drilling with five pistol grip tools obtained from two tool suppliers. This resulted in two air tools, one non-transducerized electric ðDC NT Þ and two transducerized electric ðDC T Þ tools. Three types of joints were simulated: (1) 2 Nm=720 , (2) 7 Nm=720 and (3) 7 Nm=30 . Subjects were asked to drill five joints to completion within a 60 s period, and to repeat this five times for each condition (25 joints per condition). Results of a three factor repeated measures ANOVA indicated that, in comparison to air tools, pistol grip DC tools do not pose an additional risk of musculoskeletal injury to the upper limbs. In fact, the data suggest that the use of pistol grip DC tools will reduce the demands on the forearms during horizontal drilling.
Procedia Manufacturing, 2015
The variety of different manual tasks performed in industry is infinite. In many circumstances, these tasks are carried out under difficult conditions with ergonomic concerns about the postures, force or repetitions involved. These tasks are sometimes performed using a dedicated special purpose tool, often developed by the workers themselves. These special tools are generally task-oriented only, with very little consideration of basic ergonomics. Therefore, in many cases, the design of a new or improved special purpose tool is one of the solutions that could enhance the ergonomics of the performed task.However, developing and implementing a new or improved tool is not an easy assignment and the ergonomist could face many unexpected challenges and pitfalls. This paper discusses the pitfalls that could compromise these ergonomic interventions and the critical success factors that should be considered. The main difficulties that could arise during such a project include the poor understanding of the user's needs, the hidden constraints related to the requirements of the task to be performed, the construction and testing of the prototypes, and the users' resistance to change.Critical success factors related to worker participation, needs and constraints analysis, and the implementation of prototypes,are presented. Examples from industrial projects involving the development and implementation of special purpose tools areused to support the discussion. This paper should provide some guidance in this particular field of applied ergonomics.