Snap-on-handles for a non-powered hacksaw: an ergonomics evaluation, redesign and testing

Based on the ergonomics evaluation of existing non-powered hacksaws with original/horizontal and conventional/market handles, ergonomically designed hacksaw handles are proposed. To accommodate the entire male and female populations, the hand dimensions are categorized into three groups: small, medium and large. The proposed handles give special emphasis to hand size, length, cross-section dimension and curvature. The three-sized handles for both the preferred (rear) and non-preferred (front) hands are interchangeable to suit the individual hand size. Thus, the concept of 'snap-on-handles' with a fixed hacksaw (blade) can be promoted. The ergonomically designed hacksaw handles were tested/compared with original/horizontal and conventional/market hacksaw handles, in terms of performance or productivity (depth of cut), muscular effort or strain (EMG) and subjective scores (acceptance/comfort). The experimental results conclusively proved that the ergonomically designed hacksaw handles were significantly better than the other handles in terms of the stated criteria. The performance or productivity improvements of the ergonomically designed handles were about 25 and 148%, when compared with the conventional/market and original/horizontal handles, respectively. Furthermore, when the ergonomically designed handle was not matched with the proper or appropriate hand size, there was a significant reduction in performance or productivity, increase in muscular effort and decrease in subjective scores of acceptance/comfort.     

The effect of hand tools’ handle shape on upper extremity comfort and postural discomfort among hand-woven shoemaking workers

Hand tools are widely used in a large number of occupations. Many workers have to use hand tools to accomplish their duties. This may cause work-related Upper Extremities Musculoskeletal Disorders (UEMSDs). The present study was conducted in Iranian hand-woven shoe industry to (a) investigate the design of hand tools currently used in hand-woven shoemaking operation and (b) design/redesign the tools' handles based on anthropometric tables and ergonomic principles. Based on Iranian workers' anthropometric tables, new handles with different shapes were designed and made for hand tools currently used in hand-woven shoemaking operation (e.g., awl and cloth cutting tool). Hand postures and postural comfort and discomfort were investigated via rating technique using Comfort Questionnaire for Hand Tools (CQH) and upper extremities body map. The results of CQH showed that the handle shape had a significant influence on the hand posture and perceived postural discomfort in the upper extremities. The new ergonomically designed handles were perceived to be more comfortable compared to the traditional ones. Additionally, the new handles improved the hand posture during the operation and reduced the severity of discomfort in the upper extremities compared to the tools with conventional handles. The findings of this study revealed that designing the hand tools’ handles based on ergonomic principles and using anthropometric tables could improve the hand posture, increase comfort, and decrease discomfort in the upper extremities. By this means, reduction in work-related UEMSDs is expected.     

Ergonomic design and evaluation of the handle for an endoscopic dissector

The purpose of this study was to design an endoscopic dissector handle and objectively assess its usability. The handles were designed with increased contact area between the fingers and thumb and the eye rings, and the eye rings were modified to have a more perpendicular insertion angle to the finger midline. Four different handle models were compared, including a conventional product. Subjects performed dissection, exclusion, grasping, precision manipulation and precision handling tasks. Electromyography and subjective evaluations were measured. Compared to conventional handles, the designated handle reduced the muscle load in the extensor and flexor muscles of the forearm and increased subjective stability. The activity of the first dorsal interosseous muscle was sometimes influenced by the shape of the other parts. The ergonomically designed endoscopic dissector handle used in this study achieved high usability. Medical instrument designs based on ergonomic concepts should be assessed with objective indices.

Practitioner Summary: The endoscopic dissector handles were designed with increased contact area and more suitable insertion angle between the fingers and thumb and the eye rings. Compared to conventional handles, the designated handle reduced the muscle load in the extensor and flexor muscles of the forearm and increased subjective stability.     

Measurement of coupling forces at the power tool handle-hand interface

This study explored a low-cost system for measurement of coupling forces imposed by the hand on a handle under static and dynamic conditions, and its feasibility for applications to hand-held power tools. The properties of thin-film, flexible and trim-able resistive sensors (FlexiForce) were explored in view of their applicability for measurements of the hand-handle interface forces. The sensors showed very good linearity, while considerable differences were evident in the sensitivity amongst different sensors. The appropriate locations of the sensors on the handle surface were subsequently determined on the basis of the hand-handle geometry and reported force distributions. The validity of the measurement system was investigated for measuring the hand grip and push forces with eight subjects grasping five different stationary instrumented handles (cylindrical: 32, 38 and 43 mm diameter; and elliptical: 32 × 38 and 38 × 44 mm) considering two different positions of the sensors on the handle. The validity of the measurement system was also investigated under vibration for the 38 and 43 mm diameter cylindrical handles. The results showed good linearity and repeatability of the sensors for all subjects and handles under static as well as vibration conditions, while the sensors' outputs differed for each handle. The feasibility of the measurement system was also examined for measurements of hand forces on a power chisel hammer handle. The evaluations were conducted with three subjects grasping the power chisel handle under stationary as well as vibrating conditions, and different combinations of hand grip, push and coupling forces. The measurements revealed very good correlations between the hand forces estimated from the FlexiForce sensors and the reference values for the stationary as well as the vibrating tool.Relevance to industryThe measurement of hand-handle interface forces is vital for assessing the hand-transmitted vibration exposure and musculoskeletal loads. The low cost and flexible sensors, proposed in the study, could be conveniently applied to the curved surfaces of real power tool handles in the field to measure hand grip and push forces, and the forces exerted on the palm and the fingers. The most significant benefits of the sensors lie with its minimal cost and applicability to the real tool handles.     

Experimental study on fist-ellipse for Chinese auto drivers

Sub-workspaces and the fist-ellipse of auto drivers are new concepts in the fields of ergonomics and automotive engineering. The paper introduces measurement, generation, application and location of the 95th percentile fist-ellipse (i.e., 95th sub-workspace for gearshift) for Chinese car drivers. It is a rigorous scientific approach to locate gearshift handles in conventional motor vehicles or locate a central control handle sidestick in a recent non-steering wheel conceptual car, expanding the concepts of the design tool contours of SAE.     

User-centered evaluation of handle shape and size and input controls for a neutron detector

Current neutron detectors are big, heavy, difficult to use and are not ergonomically designed. Good handle design and easy to use control mechanisms are imperative for comfort, usability and accuracy for hand-held tools. Two studies were performed to assess these factors; Study I explored handle design (shape and size) preference and Study II evaluated the effects of control mechanisms, device orientations and word orientation on performance time. According to research findings, the recommended handle perimeter is 11 cm with a diameter range of 3.5–4.0 cm. These results demonstrated that as the handle perimeter decreased the handle becomes less preferred by first responders when using layered gloves. For control type, the fastest performance time was found with vertical push buttons and a vertical word orientation. These objective results matched the subjective results, which showed that the most preferred controller was a vertical push button control.     

A survey of the optimal handle position for boxes with different sizes and manual handling positions

Handles on objects are very important for enhancing the safety and efficiency of manual handling for people who use them. In this study, four different prototype boxes with auxiliary handles were designed to determine the optimal handle position of a box based on the evaluated user preferences and body part discomfort (BPD). Twenty male students participated in the experiment. Likert-5 point summated rating was applied to evaluate user preferences for the provided boxes with handles in upper, middle, and lower positions, in four different sizes and manual handling positions. Ten additional subjects were asked to indicate their BPD on a body chart after performing a similar experiment. The results show that the subjects preferred the upper part of the handle on a small box regardless of handling position; while the mid to upper parts of the handle on a big box were preferred for handling above the waist height. BPD also indicated that an upper handle was less stressful for a relatively smaller box than a big one; and mid to upper handles were less comfortable for a big box. The optimal handle positions depending on box size and handling position were suggested based on the results of the evaluation. It is thus recommended that a box provides a handle according to its relevant position, depending on size and manual handling condition, to reduce the musculoskeletal stress and in turn to increase user satisfaction.     

The influence of rice plow handle design and whole-body posture on grip force and upper-extremity muscle activation

A previous job screening study revealed ergonomics risk factors in rice field plowing. This work motivated the present experimental investigation of the influence of plow handle design and farmer whole-body posture on grip force and arm muscle activity. A total of 24 experienced farmers performed a simulated plowing task, including walking on even and uneven ground while rolling a tiller equipped with conventional horizontal and proposed vertical handles. Results revealed the proposed handles, designed to promote neutral wrist posture, to increase upper-arm muscle use between 47% and 70% across ground types, as compared with conventional handles. The ratio of grip force to forearm muscle activity (or efficiency in muscle use) increased from 1.85 when using conventional handles on uneven ground to 2.16 when using the proposed handles with symmetrical body posture on even ground. However, participants perceived higher discomfort when using the proposed handles, as they were accustomed to the conventional design.     

Effects of user experience, working posture and joint hardness on powered nutrunner torque reactions

Powered hand tools produce reaction forces that may be associated with upper extremity musculoskeletal disorders. The handle displacement, grip force and upper limb muscle activity (electromyography (EMG)) due to the effects of operator experience, working height and distance, type of tool and fastener joint hardness were measured in this study with 15 experienced and 15 novice nutrunner users. The results show that when pistol grip handles were used to work on a horizontal surface, experienced users allowed an average handle displacement of 7.9 degrees, while novice users allowed 11.5 degrees. Average EMG scaled by reference voluntary contraction (RVC) at forearm flexors, forearm extensors and biceps were greater for experienced users (318% RVC, 285% RVC, 143% RVC, respectively) than for novice users (246% RVC, 219% RVC, 113% RVC, respectively). Experienced users exerted more grip force than novice users when using right angle handles, but less force when using pistol grip handles. The results suggest that it is possible to minimize tool handle displacement by adapting the workplace layout to permit different working postures for each user group.     

Effects of user experience,working posture and joint hardness on powered nutrunner torque reactions

Powered hand tools produce reaction forces that may be associated with upper extremity musculoskeletal disorders. The handle displacement, grip force and upper limb muscle activity (electromyography (EMG)) due to the effects of operator experience, working height and distance, type of tool and fastener joint hardness were measured in this study with 15 experienced and 15 novice nutrunner users. The results show that when pistol grip handles were used to work on a horizontal surface, experienced users allowed an average handle displacement of 7.9°, while novice users allowed 11.5°. Average EMG scaled by reference voluntary contraction (RVC) at forearm flexors, forearm extensors and biceps were greater for experienced users (318% RVC, 285% RVC, 143% RVC, respectively) than for novice users (246% RVC, 219% RVC, 113% RVC, respectively). Experienced users exerted more grip force than novice users when using right angle handles, but less force when using pistol grip handles. The results suggest that it is possible to minimize tool handle displacement by adapting the workplace layout to permit different working postures for each user group.     

Design of liquid container handles in accordance with user preferences

In this study, a prototype liquid container combined with auxiliary handles was designed to increase the safety of manual handling and to protect users of these containers from hand contamination. A Likert summated rating method as well as a pairwise ranking test was applied to evaluate the user preferences for handles provided for the container under the conditions of different shapes and positions. The results show that the participants preferred perpendicular orientation of the handle on the top of the liquid container while carrying the containers and the crosswise position of the handle at the side of the container while pouring the liquid. In order to satisfy both conditions, the container needs to be designed with handles in perpendicular as well as crosswise positions for selective application. A prototype liquid container with provided auxiliary handles was developed based on the results of the evaluation. It is recommended that a liquid container provides extra handles to reduce musculoskeletal stress and in turn increase user satisfaction.     

Design of liquid container handles in accordance with user preferences

In this study, a prototype liquid container combined with auxiliary handles was designed to increase the safety of manual handling and to protect users of these containers from hand contamination. A Likert summated rating method as well as a pairwise ranking test was applied to evaluate the user preferences for handles provided for the container under the conditions of different shapes and positions. The results show that the participants preferred perpendicular orientation of the handle on the top of the liquid container while carrying the containers and the crosswise position of the handle at the side of the container while pouring the liquid. In order to satisfy both conditions, the container needs to be designed with handles in perpendicular as well as crosswise positions for selective application. A prototype liquid container with provided auxiliary handles was developed based on the results of the evaluation. It is recommended that a liquid container provides extra handles to reduce musculoskeletal stress and in turn increase user satisfaction.     

Evaluation of handle design characteristics in a maximum screwdriving torque task

The purpose of this study was to evaluate the effects of screwdriver handle shape, surface material and workpiece orientation on torque performance, finger force distribution and muscle activity in a maximum screwdriving torque task. Twelve male subjects performed maximum screw-tightening exertions using screwdriver handles with three longitudinal shapes (circular, hexagonal and triangular), four lateral shapes (cylindrical, double frustum, cone and reversed double frustum) and two surfaces (rubber and plastic). The average finger force contributions to the total hand force were 28.1%, 39.3%, 26.5% and 6.2%, in order from index to little fingers; the average phalangeal segment force contributions were 47.3%, 14.0%, 20.5% and 18.1% for distal, middle, proximal and metacarpal phalanges, respectively. The plastic surface handles were associated with 15% less torque output (4.86 Nm) than the rubber coated handles (5.73 Nm). In general, the vertical workpiece orientation was associated with higher torque output (5.9 Nm) than the horizontal orientation (4.69 Nm). Analysis of handle shapes indicates that screwdrivers designed with a circular or hexagonal cross-sectional shape result in greater torque outputs (5.49 Nm, 5.57 Nm), with less total finger force (95 N, 105 N). In terms of lateral shape, reversed double frustum handles were associated with less torque output (5.23 Nm) than the double frustum (5.44 Nm) and cone (5.37 Nm) handles. Screwdriver handles designed with combinations of circular or hexagonal cross-sectional shapes with double frustum and cone lateral shapes were optimal in this study.     

Effects of BMI and task parameters on joint angles during simulated small parts assembly

Functional limitations of persons classified into different obesity categories were evaluated while performing a simulated small parts assembly tasks. Joint angles (measured using electro-goniometers) and maximum forward function reach (MFFR) were used to quantify function limitations, and tasks were completed on three workstations designed for the 5th, 50th, and 95th percentile workers based on anthropometric data tables. Results revealed that BMI category did not significantly affect measured joint angles. Results also indicated that joint angles when working at the 95th percentile workstation configuration were significantly larger than those measured at the 5th percentile workstation configuration. Further, obese class 2 and obese class 3 groups MFFRs were significantly shorter than the normal weight group, which was expected. These results imply that workstation design considerations should include obesity levels, and that work should be placed near the worker and should be elevated to reduce pressure on joint angles while working for larger (obese) individuals.     

Ergonomic assessment of handle design by means of electromyography and subjective rating

Stress and strain during manual tool handling not only depend on factors such as weight to be handled, but are also determined by the design of the man-machine interface. In this study, three different handles of electric hedge-clippers were analysed; the results of a comparative investigation into the physiological cost demanded by the use of the different handles are discussed. Muscular strain was measured via surface electromyography in laboratory experiments with nine male subjects. The results showed significant differences in physiological cost depending on both work height and the handles' shape. Systematic differences in muscular strain between the utilized tools were found, despite the fact that all clippers were compensated with respect to weight and location of the centre of gravity. One of the handle designs enabled working under varying conditions (work height and direction) at a reduced level of muscular strain of the right arm. Results from the physiological evaluation were partly supported by the working persons' own subjective experience. The results of this investigation show that further ergonomic tool and handle design is necessary.     

Ergonomics evaluation and redesign of a hospital meal cart

The ergonomic, design and other problems of a conventional hospital meal cart were evaluated with a view to redesign a hospital meal cart by incorporating ergonomic principles and data. The operators encountered difficulty in setting the cart in motion, seeing over the cart, turning the cart and stopping the cart while in motion. The operators expressed postural discomfort in the shoulder, neck, back, lower back, knee and leg, and ankle and foot. The cart with meal trays and food was found to exceed the acceptable initial turning push force requirement of 5th percentile females. Recommendations were made for proper placement of cart handles and handle diameter, provision of large-diameter cart wheel made of hard rubber tire, reduction of cart height, use of plastic material for cart construction, provision of emergency brake, provision of individually (electrically) heated plates for soup and main meal, provision of thick air-tight transparent plastic doors, and reduction of the meal tray size. Several recommendations were adopted by the manufacturer in the new model.     

Power grip strength as a function of tool handle orientation and location

Thirty male volunteers participated in a study evaluating the effect of workspace envelope (work height and reach distance) and handle orientation on grip force capacity. Maximum voluntary power grip exertions were recorded using instrumented tool handles under three conditions: a pistol grip tool handle oriented horizontally and vertically and a right angle tool handle oriented horizontally. Significant main effects of handle height and reach location on normalized grip force capacity were observed with the horizontally oriented pistol grip and right angle handles, whereas only an interaction effect was observed with the vertically oriented pistol grip handle. Comparison of results to scores produced with a job assessment tool (RULA) is included as an appendix. The proposed methodology can provide information useful to job, workstation or tool design directed toward best accommodating the physical capacities of workers performing hand tool tasks.     

Power grip strength as a function of tool handle orientation and location

Thirty male volunteers participated in a study evaluating the effect of workspace envelope (work height and reach distance) and handle orientation on grip force capacity. Maximum voluntary power grip exertions were recorded using instrumented tool handles under three conditions: a pistol grip tool handle oriented horizontally and vertically and a right angle tool handle oriented horizontally. Significant main effects of handle height and reach location on normalized grip force capacity were observed with the horizontally oriented pistol grip and right angle handles, whereas only an interaction effect was observed with the vertically oriented pistol grip handle. Comparison of results to scores produced with a job assessment tool (RULA) is included as an appendix. The proposed methodology can provide information useful to job, workstation or tool design directed toward best accommodating the physical capacities of workers performing hand tool tasks.     

Evaluation of handle design characteristics in a maximum screwdriving torque task

The purpose of this study was to evaluate the effects of screwdriver handle shape, surface material and workpiece orientation on torque performance, finger force distribution and muscle activity in a maximum screwdriving torque task. Twelve male subjects performed maximum screw-tightening exertions using screwdriver handles with three longitudinal shapes (circular, hexagonal and triangular), four lateral shapes (cylindrical, double frustum, cone and reversed double frustum) and two surfaces (rubber and plastic). The average finger force contributions to the total hand force were 28.1%, 39.3%, 26.5% and 6.2%, in order from index to little fingers; the average phalangeal segment force contributions were 47.3%, 14.0%, 20.5% and 18.1% for distal, middle, proximal and metacarpal phalanges, respectively. The plastic surface handles were associated with 15% less torque output (4.86 Nm) than the rubber coated handles (5.73 Nm). In general, the vertical workpiece orientation was associated with higher torque output (5.9 Nm) than the horizontal orientation (4.69 Nm). Analysis of handle shapes indicates that screwdrivers designed with a circular or hexagonal cross-sectional shape result in greater torque outputs (5.49 Nm, 5.57 Nm), with less total finger force (95 N, 105 N). In terms of lateral shape, reversed double frustum handles were associated with less torque output (5.23 Nm) than the double frustum (5.44 Nm) and cone (5.37 Nm) handles. Screwdriver handles designed with combinations of circular or hexagonal cross-sectional shapes with double frustum and cone lateral shapes were optimal in this study.     

Hand tool handle size and shape determination based on hand measurements using a contour gauge

The purpose of this study is to provide a novel approach to tool handle design and development based on measurements of hand shape using a contour gauge. In general, traditional design techniques, designing based on anthropometric data, and derived mathematical models do not incorporate enough subject data to design a customized product. First, anthropometric measurements on the right hand of 60 participants were collected with a contour gauge to manufacture matching handles. A curved handle fitting the human hand was constructed with common computer‐aided design software, and cylindrical handles and elliptical handles were added for comparison. All of the handles were used to record the participants' grip force to evaluate the operating efficiency of the handles. Finally, the participants completed a comfort‐rating questionnaire. The results show that contours based on the hand provided the highest operating performance and the best overall comfort‐rating compared to cylindrical handles and elliptical cylindrical handles. The newly developed handles in the grip force tasks have the highest push performance and the best comfort ratings compared to traditional cylindrical and elliptical handles. The developed handles could provide the hand tool industry information on developing and manufacturing many other similar handle designs (such as those for saws and electric screwdrivers).