Journal of Ergonomics

Hand tools are a wide range of equipment used in many industrial, service and even household activities (1). The use of hand tools is accompanied by repeated movements. Repeated movements are the sources of musculoskeletal injury. Therefore, ergonomic principles are important in the design of these tools (5). Feeling comfortable working with handheld devices plays a huge part in helping users decide to continue using that tool. Important factors affect how comfortable users are with the tool. Beautiful design, performance, physical interaction with the tool, and physical injury caused by using the tool were the most important predictors of comfort and discomfort reported by Kuwait et al. (2014) (6). Two factors to consider in designing an ergonomic tool are performance and ease of use. The performance of a tool is related to its health and safety aspects. But user comfort when used is defined in terms of its usability, utility, and enjoyment. Usability is a measure of how easy and convenient a product is to use and how applicable it is to its users (13).
The socket wrench is a single-handle wrench that is most commonly used to open and close bolts that require high force and high operating speed. This tool is widely used in installation, mechanical and assembly jobs (11). The purpose of this study was to investigate the relationship between physical parameters of length, diameter and weight of several different models of wrench tool with their usability index score.

 

The present study is a descriptive-analytic one through correlation method. A total of 58 men working in the facilities of a university with a mean (SD) age of 36 (5.5) years and a mean (SD) height of 175.7 (6.12) cm participated in the study. Inclusion criteria included having at least one year of experience in the installation and repair departments and no upper limb injuries. Participants performed a simulated task using 6 wrench models. The simulated task consisted of opening the bolts in a standing position, using a plate equipped with 12 bolts on the desk. The height of this plate was 104 cm (ninety fifth percentile of the elbow height) and was adjustable and reduced by 6 cm for shorter participants. All bolts were fastened to 8 N / m using a torque meter. Different wrench models were coded with the letters A, B, C, D, E, and F, and were presented to participants for a random simulated task. Figure 1 illustrates the wrenches used in the study and Table 1 shows their physical properties. After performing the simulated task with each wrench model, participants responded to the SUS questionnaire with questions about the applicability of that model.
 

Figure 1. The socket wrenches used in the study
 
Table 1. Physical characteristics of the studied socket wrenches

 

Table 2 presents the usability score of the instruments under investigation. The highest and the lowest score of usability index belonged to C and B wrenches, respectively. Table 3 also presents the ranking of the studied wrench models in terms of their physical properties and their usability score.
 

Table 2. Mean and standard deviation score of the usability index of the socket wrenches studied


Table 3. Ranking of the wrench models studied in terms of physical properties and usability score

The results of the univariate and multiple regression tests are presented in Table 4 to investigate the relationship between the dimensional variables and the weight of the wrenches with their usability score. The results showed a significant relationship between physical parameters and usability index score (P<0.001).
 

Table 4. Investigation of Relationship between usability index and specifications of wrenches (length, diameter, weight)

The purpose of this study was to investigate the relationship between dimensional characteristics and wrench weight on the usability index score. The results of this study showed that there is a statistically significant relationship between dimensional parameters including handle length, diameter and wrench weight with usability index. The results also showed that the usability rating of the models under consideration was not similar to any of the ratings related to the physical properties of the tool. In his study, while investigating the influence of tool handle diameter on the comfort and maximum torque produced in 7 different tool batches, Sohrabi found out that maximum user comfort and maximum torque of the hand is obtained at an optimum diameter of 38 mm (11). In the design of the wrench C, in addition to the optimum diameter, the cross-section being elliptical, the tool bumps for finger placement have also been effective in achieving a higher usability score. Wang and Kai (2017) have introduced the best cross section for elliptic grip (20). Harry and Dolshak (2014) showed that the shape of the handle had a great impact on user’s comfort (21). The results of the present study are in line with the results of the study by Deanett et al. (2017) which aimed to influence the dimensions and shape of hand tools category on the usability index score. In their study, they concluded that there was a significant relationship (P=0.001) between the dimensions of the wrench handle (P=0.001) (22).

 

Users' perceptions of the convenience or usability of the tool are influenced by a set of physical and psychological variables. Tool design based solely on physical rules and anthropometric dimensions cannot guarantee the ergonomic quality of the product. The findings of the study confirmed the proper operation of the usability index questionnaire for measuring the quality of hand tools design. Using this low-cost method can accelerate ergonomic evaluations of handheld devices and avoid the high cost of laboratory studies. Using this index, you can choose the best and most suitable model with the most convenience and satisfaction for the users from different models of a handheld device. It should be noted, however, that the results of the study are applicable to simulated studies for short-term experiences of valid instrument use, and broader studies should be designed to extend these findings to longer-term applications of the tool.

 

The authors thank all those who helped them writing this article.

 

The authors declared that there are no conflicts of interest.