Ergonomic principles basic to hand tool design

Investigating the trends and causes of changes in human anthropometric dimensions over the past three decades: a challenge for ergonomic design

Objectives. The present study aimed to review the changes in anthropometric dimensions around the world during the last 30 years.Methods. The search for this study was conducted in four databases with related keywords. Papers from 1990 to 2021 were reviewed and 4139 articles were identified, with 505 related titles. Of these, 187 articles met the eligibility criteria, and their whole text was examined; 132 articles were then included for the final review.Results. The reviewed studies showed that a large number of anthropometric dimensions of the human body have become larger than in the past, such as height. Although the increasing trend of anthropometric dimensions in the past has been faster than in recent years, decreasing changes have also been seen in some anthropometric dimensions, such as the human jaw, face width and head width. It should be noted that the main reasons for the changes mentioned in the studies are economics and family income, social conditions, health and nutrition.Conclusion. Since the process of changes in anthropometric dimensions is not always the same, anthropometric data should be updated regularly, and work environments and equipment should be reviewed or redesigned according to the new anthropometric data.

Investigating Whether the Mass of a Tool Replica Influences Virtual Training Learning Outcomes

Virtual Reality (VR) has emerged as a promising solution to address the pressing concern of transferring know-how in the manufacturing industry. Making an immersive training experience often involves designing an instrumented replica of a tool whose use is to be learned through virtual training. The process of making a replica can alter its mass, making it different from that of the original tool. As far as we know, the influence of this difference on learning outcomes has never been evaluated. To investigate this subject, an immersive training experience was designed with pre and post-training phases under real conditions, dedicated to learning the use of a rotary tool. 80 participants took part in this study, split into three groups: a control group performing the virtual training using a replica with the same mass as the original tool ($\mathrm{m}=100\%$), a second group that used a replica with a lighter mass than the original tool ($\mathrm{m}= 50\%$) and a third group using a replica heavier than the original tool ($\mathrm{m}=150\%$). Despite variations in the mass of the replica used for training, this study revealed that the learning outcomes remained comparable across all groups, while also demonstrating significant enhancements in certain performance measures, including task completion time. Overall, these findings provide useful insights regarding the design of tool replicas for immersive training.

Agricultural Farm-Related Injuries in Bangladesh and Convenient Design of Working Hand Tools

Injuries during cultivation of land are the significant causes of recession for an agricultural country like Bangladesh. Thousands of tools are used in agricultural farm having much probability of getting injury at their workplaces. For the injury prevention, proper hand tool designs need to be recommended with ergonomic evaluations. This paper represents the main causes of agricultural injuries among the Bangladeshi farmers. Effective interventions had been discussed in this paper to reduce the rate of injury. This study was carried out in the Panchagarh district of Bangladesh. Data on 434 agricultural injuries were collected and recorded. About 67% injuries of all incidents were due to hand tools, and the remaining 33% were due to machinery or other sources. Though most of the injuries were not serious, about 22% injuries were greater than or equal to AIS 2 (Abbreviated Injury Scale). The practical implication of this study is to design ergonomically fit agricultural hand tools for Bangladeshi farmers in order to avoid their injuries.

The Dibber: Designing a standardised handheld tool for lay-up tasks

We present an application of engineering and ergonomics principles in the design of a standardised tool, The Dibber, which is a tool with multiple geometric features to fit the diversity of lay-up tasks used in the composites industry. The Dibber is the result of a design process, which consists of a series of observations and prototyping to extract geometric requirements for lay-up tasks. To demonstrate that it is possible to design a standardised tool prototypes of the Dibber were distributed and 91 participants gave feedback. Our results are positive and show consistent patterns of use across industry sectors, as well as between novice and expert laminators.

A Hand Posture Measurement System for Evaluating Manual Tool Tasks

A measurement system of describing the loads in the hand during manual tool tasks is presented. The system consists of a network of force sensitive resistors and an angle transducer glove (CybergloveTM, Virtual Technologies). Eighteen different cylindrical grip tasks for six subjects were studied using the developed measurement system. Fourteen flexion and abduction angles and the ten force data from ten locations of the hand was measured for the sixteen tool tasks. The results showed that the flexion angle for the five fingers decreased with increasing grip span. Grip force was mainly controlled by the opposing action of the thumb and the index finger. The contribution of the thumb and index finger force to the total grip force was greater when the grip size was increased. A regression approach to estimate the joint flexion angle based on the hand anthropometry and grip characteristics showed significant results. It was possible to use the data from the measurement system as an input to the calculation of the joint torques and moments in the finger joints. The simultaneous measurement system of the finger joint angles and finger forces was useful in collecting the information on the hand force postures during the duration of the task. The system was also useful in providing detailed input data for the biomechanical analysis of the hand.

Using Force Sensitive Resistors to Evaluate Hand Tool Grip Design

The pressure distribution of the hand is an important element in evaluating hand tool grip. For measuring the pressure distributions of the hand, a portable sensor glove was developed using force sensitive resistors of the conductive polymer type. Pressure distributions of three hand tools for three male subjects were measured. The pressure distribution pattern varied significantly between type of grip, location, and subjective exertion level. Factor analysis was used to identify the relative importance of each area of the hand during grip action. The results showed that there is an ‘active' area involved in gripping the hand tool and a ‘control’ area which supports the hand motion for the given task. Studies about hand tool pressure distributions will provide an important guideline in designing a new tool or improving an existing one. A microcomputer based system is being developed that records data on grip pressure distribution throughout a tool grip task. The digitized data then will be analyzed both graphically and statistically and will be used to evaluate various hand tools for industrial settings.

Ergonomics evaluation of user-hand tool interaction

BACKGROUND

An in-depth evaluation of user hand tool interaction aids to derive strenuous areas for redesigning.

OBJECTIVE

In this paper, we examined user perception about the hand tool features and derived features that exert an influence on human system. This nature of study aids to reduce the risk and enhance the comfort.

METHODS

Workers from six occupational groups participated in the study. Ergonomic checkpoints pertaining tool features and a general health questionnaire that included musculoskeletal discomforts, stress symptoms and general health complaints were administered to check user's interaction with hand tools.

RESULTS

Risk estimates identified varied factors such as weight of tool, improperly designed handle and sharp edges associated with workers risk to pain in upper extremities, anxiety and injury. The workers' response indicated that handle redesign and protection against sharp-edged tools are crucial for improving comfort.

CONCLUSION

The study aims to provide an approach to examine the characteristics of tools for redesign and increase user's comfort and safety.

An fMRI-compatible multi-configurable handheld response system using an intensity-modulated fiber-optic sensor

Functional magnetic resonance imaging (fMRI) data should be interpreted in combination and in the context of relevant behavioral measurements. However, the strong magnetic environment of MRI scanner and the supine position of participants in the scanner significantly limit how participants' behavioral responses are recorded. This paper presents the design of a low-cost handheld response system (HRS) with a multi-configurable optomechanical design that utilizes a reflective-type intensity modulated fiber-optic sensor (FOS) and a programmable visual interface to accurately gather participants' behavioral responses during an fMRI experiment. Considering the effects of an input unit design on the participants' performance efficiency across age groups and physical and neurological (dis)ability, the optomechanical system is designed to provide flexibility in the range of an input module with easy change-out feature. Specifically, the input unit can be configured as a binary module such as push buttons or as an analog input device including a scrolling wheel, and one-dimensional joystick (lever arm). To achieve MRI-compatibility, all parts of the unit that are used inside the scanner bore are built from nonferromagnetic and off-the-shelf plastic materials. The MRI compatibility was evaluated on a 3.0 Tesla MRI scanner running echo planar imaging (EPI) and the average time-variant signal-to-noise ratio (tSNR) loss is limited to 2%.

Design and Ergonomics. Methods for Integrating Ergonomics at Hand Tool Design Stage

As a marked increase in the number of musculoskeletal disorders was noted in many industrialized countries and more specifically in companies that require the use of hand tools, the French National Research and Safety Institute (INRS) launched in 1999 a research project on the topic of integrating ergonomics into hand tool design, and more particularly to a design of a boning knife. After a brief recall of the difficulties of integrating ergonomics at the design stage, the present paper shows how 3 design methodological tools--Functional Analysis, Quality Function Deployment and TRIZ--have been applied to the design of a boning knife. Implementation of these tools enabled us to demonstrate the extent to which they are capable of responding to the difficulties of integrating ergonomics into product design.

Effects of glovebox gloves on grip and key pinch strength and contact forces for simulated manual operations with three commonly used hand tools

This study examined the effects of glovebox gloves for 11 females on maximum grip and key pinch strength and on contact forces generated from simulated tasks of a roller, a pair of tweezers and a crescent wrench. The independent variables were gloves fabricated of butyl, CSM/hypalon and neoprene materials; two glove thicknesses; and layers of gloves worn including single, double and triple gloving. CSM/hypalon and butyl gloves produced greater grip strength than the neoprene gloves. CSM/hypalon gloves also lowered contact forces for roller and wrench tasks. Single gloving and thin gloves improved hand strength performances. However, triple layers lowered contact forces for all tasks. Based on the evaluating results, selection and design recommendations of gloves for three hand tools were provided to minimise the effects on hand strength and optimise protection of the palmar hand in glovebox environments.

PRACTITIONER SUMMARY

To improve safety and health in the glovebox environments where gloves usage is a necessity, this study provides recommendations for selection and design of glovebox gloves for three hand tools including a roller, a pair of tweezers and a crescent wrench based on the results discovered in the experiments.

Job Analysis Techniques for Distal Upper Extremity Disorders

Distal upper extremity (DUE) work-related musculoskeletal disorders (WMSDs) are among the most costly injuries suffered in industry today. These WMSDs are reported in both office (computer use) and manufacturing environments. Job physical exposure analysis techniques for DUE WMSDs range from simple checklists to quantitative models. A summary of literature review of biomechanical, physiological, psychophysical and epidemiological bases for job physical exposure risk factors for DUE WMSDs is provided. Several job analysis methods suitable for manufacturing environments are reviewed and discussed. A comparative analysis of Rapid Upper Limb Assessment (RULA), Threshold Limit Value for Hand Activity Level (TLV for HAL), and the Strain Index is provided along with results from validation studies and advantages and disadvantages of each method. Three examples from industries are provided to demonstrate applications of RULA, TLV for HAL, and the Strain Index. Last, issues with current job analysis methods when a worker rotates to different jobs and/or when a job consists of several tasks are discussed as well as the need for more robust models to account for these variations in physical exposure in real-world environments.

Applications of biomechanics for prevention of work-related musculoskeletal disorders

This paper summarises applications of biomechanical principles and models in industry to control musculoskeletal disorders of the low back and upper extremity. Applications of 2-D and 3-D biomechanical models to estimate compressive force on the low back, the strength requirements of jobs, application of guidelines for overhead work and application of strain index and threshold limit value to address distal upper extremity musculoskeletal disorders are presented. Several case studies applied in the railroad industry, manufacturing, healthcare and warehousing are presented. Finally, future developments needed for improved biomechanical applications in industry are discussed. The information presented will be of value to practising ergonomists to recognise how biomechanics has played a significant role in identifying causes of musculoskeletal disorders and controlling them in the workplace. In particular, the information presented will help practising ergonomists with how physical stresses can be objectively quantified.

QFD: a methodological tool for integration of ergonomics at the design stage

As a marked increase in the number of musculoskeletal disorders was noted in many industrialized countries and more specifically in companies that require the use of hand tools, the French National Research and Safety Institute launched in 1999 a research program on the topic of integrating ergonomics into hand tool design. After a brief review of the problems of integrating ergonomics at the design stage, the paper shows how the "Quality Function Deployment" method has been applied to the design of a boning knife and it highlights the difficulties encountered. Then, it demonstrates how this method can be a methodological tool geared to greater ergonomics consideration in product design.

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 wrist orthoses on forearm muscle activity

A general hypothesis is that a wrist orthosis reduces the wrist extensor muscle load. The aim of this study was to investigate the effects of a completely stiff wrist orthosis (SO) and a commercially available wrist orthosis (CO) on flexor and extensor electromyographic (EMG)-activity in a standardised intermittent gripping task and during standardised manual work tasks. Surface EMG from two forearm flexor and two extensor muscles was recorded. The target grip forces were 5%, 20% and 40% of maximal voluntary contraction (MVC). During the grip contraction phase CO had no effect on the EMG-readings. SO resulted in higher EMG activity than when gripping with CO and with no orthosis (NO), especially when gripping with 40% MVC. During the relaxation phase neither CO nor SO had any effect on the extensors. For the flexors the SO gave higher EMG-readings than when gripping with CO and NO, especially at 40% MVC. In conclusion the wrist orthoses tested did not reduce the EMG-activity from the flexors or the extensors during gripping or manual tasks.

Ergonomics study on the handle length and lift angle for the culinary spatula

The culinary spatula (turning shovel) is one of the most common cooking tools used in the kitchen in Asia. However, the culinary spatula has seldom been ergonomically investigated. When a person uses a spatula to cook food, the operations involve repetitive bent-wrist motions, such as dorsiflexion, palmary flexion, and radial and ulnar deviations. These movements may cause cumulative trauma disorders in the upper extremities, and in particular carpal tunnel syndrome. A poorly designed culinary spatula will be ergonomically inefficient and cause injury to the hand and wrist. The purpose of this study was to investigate the effects of spatula handle length and lift angle on food-frying, food-turning, and food-shoveling performance. Eight female subjects were tested using 16 different culinary spatulas, with four different handle lengths (20, 25, 30 and 35 cm) and four different lift angles (15 degrees, 25 degrees, 35 degrees and 45 ). The criterion measures included cooking performance, and rating of perceived exertion. The subjects ranked their preference after all of the tasks in the tests were completed. The results showed that: (1) The handle length had a significant influence on the cooking performance, and rating of perceived exertion. The optimal handle lengths for frying food, turning food, and shoveling food were 20, 25 and 25 cm, respectively. (2) The lift angle significantly affected the cooking performance, and rating of perceived exertion. The optimal lift angles for frying food, turning food, and shoveling food were 15 degrees, 15 degrees and 25 degrees, respectively. (3) Both the handle length and lift angle had significant effects on subjective preference. For the handle length, the 20 cm length was the best. For the lift angle, the 25 angle was the best. (4) In general, a spatula with a 20 cm handle length and 25 degrees lift angle was the best. A spatula with a 25 cm handle length and 15 lift angle was the second most preferred. (5) However, to prevent subjects from touching the edge of a hot pan, a spatula with a 25 cm handle length and 25 lift angle is suggested.

Forearm muscular load and wrist angle among automobile assembly line workers in relation to symptoms

Electromyographic activity (EMG) from m. flexor carpi radialis (FCR) and m. extensor carpi radialis longus (ECRL) of the right forearm was recorded together with wrist angles in the flexion/extension and radial/ulnar plane in 20 healthy automobile assembly line workers during work. Eleven of these were randomly recruited from assembly stations with a low prevalence of subjective wrist/forearm symptoms (LPS), while the rest came from stations with a high prevalence of symptoms (HPS). The main EMG finding was a clear difference in activation pattern between flexors and extensors. ECRL was activated more statically, while FCR had a more dynamic pattern with more pauses but also higher peak loads. The main wrist angle finding was a difference in angle distribution as well as absolute angular velocity in the radial/ulnar plane between LPS and HPS work stations. Workers in HPS stations worked longer times in a more ulnar deviated hand position and had higher absolute deviation angular velocity compared to LPS workers, indicating ulnar deviation as a risk factor. Generally, ulnar deviation from a neutral position was more frequent than angular displacement in the flexion/extension plane.

An ergonomic design and performance evaluation of handy scanners by males

This paper describes the results of an investigation of the difference in performance, posture used, strain on forearm musculature, and subjective ratings of three handy scanners (models A, B and C). Both models A and B were scanners on the market. Model C was developed for validation. The gripping posture of the three models is distinct both in the anatomical and functional sense. Work with model A requires a thumb-forefinger side grip which induces an ulnar deviation angle; work with model B requires a thumb-finger grip; work with model C requires a thumb-finger-palmar grip. Performance evaluation of scanner models A, B and C on different scanning tasks (with and without stitch) using different resolution modes (100 and 400 dpi), indicated that using the proposed model C resulted in a 13% higher success rate, a 14% shorter completion time, the smallest self-selected working area, least strain on the forearm muscles, and highest subjective ratings among the three. Model C appeared to provide the greatest opportunity for delicate adjustments of posture in response to the activity of the skin receptors, justifying the ergonomic input into the design.

Occupation and the carpal tunnel syndrome

Repetitive physical tasks, particularly executed with force or using vibrating hand tools, carry the chief risk of carpal tunnel syndrome for workers. Treatment may require removing the worker from the task or redesigning the task for the worker, while proper attention to ergonomics can prevent carpal tunnel injuries in the first place.

Carpal tunnel syndrome among grocery store workers

The California Department of Health Services evaluated carpal tunnel syndrome (CTS), a median nerve entrapment condition associated with forceful and repetitive wrist motion, among grocery store workers at a large California supermarket where a CTS cluster had been reported. Forceful and repetitive wrist motion was measured, in three exposure levels, through a job classification scheme based upon type of work tasks and average time per week spent performing these tasks. A medical questionnaire and measurements of median sensory nerve conduction were used to measure CTS. CTS prevalence was 23% based upon a sample of 56 participants drawn from a workforce of 69 employees. A relative risk of 8.3 (95% confidence interval 2.6-26.4) for a history of CTS-like symptoms between the high and low exposure level groups held up after adjustment for the potential confounders of age, sex, alcohol consumption, and high-risk medical history. It was concluded that the basic principles of good ergonomic design should be used to prevent or diminish the risk of musculoskeletal injury in the workplace.

Design and sizing of ergonomic handles for hand tools

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.

A cube model for the classification of work with hand tools and the formulation of functional requirements

In an interdisciplinary research project, a model, visualized as a cube, was developed for the classification and analysis of work with hand tools and for communication of different ways of solving problems related to manual handling. The dimensions of the cube are demands of force, precision and time. Each dimension is divided into three levels of low, moderate and high demands respectively. Preliminary limits are proposed for acceptable and non-acceptable use situations and for situations that have to be investigated further. Using a case study of plate shears as a starting point, various measures of improving the position in the cube are discussed. The hand tool, the workplace, the work organization as well as the user of the hand tool are included in the analysis.

Sensitivity of the hand to surface pressure

A new method of measuring pain-pressure threshold (PPT) of the hand has been developed. Externally applied surface pressure (EASP) was exerted at a certain rate of increase and the level where the feeling of pressure turned into pain was recorded. Also, the effects of sustained EASP were elucidated. Sixteen healthy right-handed subjects (eight female, eight male) participated. The distribution of the hand's sensitivity to EASP is presented. The most sensitive areas were the thenar area, the skinfold between thumb and index finger and the area around os pisiforme. When the hand was repeatedly exposed to EASP, the PPT decreased with increasing number of pressure incidents. For sustained EASP, the time of exposure was found to be important also for the quality of the sensation. Our results show that sustained EASP does not hurt at once, but becomes painful after a short time. On average, the female PPT corresponded to two-thirds of the male PPT. Females experienced pain faster than males when exposed to sustained EASP, and chose lower levels when estimating acceptable sustained EASP.

A kinematic model of the human hand to evaluate its prehensile capabilities

A kinematic model has been developed for simulation and prediction of the prehensile capabilities of the human hand. The kinematic skeleton of the hand is characterized by ideal joints and simple segments. Finger-joint angulation is characterized by yaw (abduction-adduction), pitch (flexion-extension) and roll (axial rotation) angles. The model is based on an algorithm that determines contact between two ellipsoids, which are used to approximate the geometry of the cutaneous surface of the hand segments. The model predicts the hand posture (joint angles) for power grasp of ellipsoidal objects by 'wrapping' the fingers around the object. Algorithms for two grip types are included: (1) a transverse volar grasp, which has the thumb abducted for added power; and (2) a diagonal volar grasp, which has the thumb adducted for an element of precision. Coefficients for estimating anthropometric parameters from hand length and breadth are incorporated in the model. Graphics procedures are included for visual display of the model. In an effort to validate the predictive capabilities of the model, joint angles were measured on six subjects grasping circular cylinders of various diameters and these measured joint angles were compared with angles predicted by the model. Sensitivity of the model to the various input parameters was also determined. On an average, the model predicted joint flexion angles that were 5.3% or 2.8 degrees +/- 12.2 degrees larger than the measured angles. Good agreement was found for the MCP and PIP joints, but results for DIP were more variable because of its dependence on the predictions for the proximal joints.

Tenosynovitis of Hand and Wrist: A Literature Review

This literature review of tenosynovitis of hand and wrist concentrates on the definition of tenosynovitis, aetiology and causative factors, site of occurrence, general methods of treatment and specific occupational therapy procedures. Despite extensive research into tenosynovitis, very little is yet known about causative factors. There also continues to be much controversy surrounding how to use splinting and the usefulness of rest in the treatment of tenosynovitis. On the basis of descriptive studies it can be said that tenosynovitis mostly affects the wrist and hand and more commonly the extensor tendon of the right/dominant hand. It is suggested that tenosynovitis occurs more commonly in females and the peak incidence is in the 35–40 years age group. Common opinions regarding causative factors are work related, infections and manifestations of diseases. Treatment of tenosynovitis mostly lies in rest and splinting and some suggest that electrotherapy and diathermy may help. If conservative treatment fails, many advocate surgery.