Keywords: Pinch technique, Pinch effort, Pinch grip, Pilot study, Grip force, Manufacturing firm

Transcription

1 s and Their Effects on Pinch Effort: A Pilot Study Poh Kiat Ng 1,a, Meng Chauw Bee 1,b, Qiao Hui Boon 1,c, Ka Xuan Chai 1,d, Shiong Lung Leh 1,e and Kian Siong Jee 1,f 1 Faculty of Engineering and Technology, Multimedia University, Malacca, Malaysia a pkng@mmu.edu.my, b charles_bee28@hotmail.com, c qiaohui07@gmail.com, d ka_xuan_1990@hotmail.com, e ivanleh@live.com, f ksjee@mmu.edu.my Keywords: Pinch technique, Pinch effort, Pinch grip, Pilot study, Grip force, Manufacturing firm Abstract. Hands are important tools for manual work. Although researchers have identified factors that influence the grip efforts of an entire hand, there appears to be limited research concerning the use of different pinch techniques and how they affect the performance of pinch effort. Therefore, the aim for this pilot study is to determine the effects of different pinch techniques on pinch effort. A total of 110 manual workers from a wooden pallet manufacturing firm participated in this study, which involved an experiment and survey to investigate the most preferred pinch technique applied on screw knobs. The techniques used were the 3-jaw chuck, pulp-2 and lateral pinch. A total of 6 screw knobs of different shapes and sizes were used. After the data were collected, descriptive and Cronbach's alpha reliability analyses were carried out. The results show that the preferred pinch technique for the small cylindrical knob, small sphere knob and all large knobs is the lateral pinch. However, the 3-jaw chuck pinch is preferred for the small 5-lobes knob. This study provides preliminary information for further research on pinch techniques and their influences on the pinching outcomes of individuals. Introduction In many industries, the involvements of skilled and manual workers in manual handling operations create a concern for workplace safety and health. Compensation claims for upper body injuries such as hand-related musculoskeletal disorders are the highest in the manufacturing, construction, transportation and warehousing industry [1]. It was found that billions of dollars are paid to workers by employers for medical compensations on hand-related injuries each year. The rate of incidence of hand injuries alone in the workplace is as high as 0.25, implying that 25 hand injuries occur on average for every 10,000 workers per year [2]. The preceding literature [1, 2] clearly shows that hand-related injuries are very prevalent in the workplace. Since the use of the hand is vital for manual work in many industries, it is of interest for researchers to conduct more focused studies to better understand the capacities of the human hand and the factors that influence its performance among manual workers. Although some researchers have looked into various factors that influence the grip forces of an entire hand [3-7], there appears to be a lack of research done in the area concerning the use of different pinch techniques and how they affect the performance of pinch effort. This is important to industries since some manual operations only require the workers to use pinch grips. Hence, this pilot study aims to determine the effects of different pinch techniques on pinch effort. In practice, finger pinching or pinch grip is used for both precision control and high force applications, for example, opening a cylindrical jar cover. Although there have been some theoretical groundwork done on various types of pinches [8], it may still be difficult for researchers to classify pinch grips based on only the above definitions seeing as there appears to be limited data to describe the pinch effort of individuals. The 3 most commonly applied pinch techniques include the pulp-2, lateral and 3-jaw chuck pinches [9].

2 The pulp-2 pinch is defined as a pinch technique where the pad of the distal phalange of the thumb opposes the pad of the distal phalange of the index finger [3]. The number 2 in this term indicates the second finger or index finger. Magee [10] defines a lateral pinch as an act where the thumb comes into contact with the lateral side of the index finger. The 3-jaw chuck pinch refers to an act where the pad of the distal phalange of the thumb opposes the pad of the distal phalange of both the index finger and the middle finger [10]. Even though numerous reviews have been carried out on various factors that may affect pinch effort [8, 11, 12], it is still imperative for researchers to quantify the possible contributions of these factors in pinch effort. Research Method Surveys were used to facilitate this study. A total of 6 prototype industrial screw knobs of different shapes and sizes were used. Screw knobs were chosen for this study due to its frequent usage in various industrial applications [13]. There were 3 types of knob shapes used (cylindrical, sphere and 5-lobes) and each of them came in 2 sizes. Participants were asked to pinch and turn these knobs and answer the questions written in the questionnaire. The types of pinch techniques used in this study were the pulp-2, 3-jaw chuck and lateral pinches. The participants of this survey study were manual workers from a wooden pallet manufacturing firm located in Penang, Malaysia. All the participants involved were males, with the majority being right-handed and having no significant hand injuries that can affect their right hand movements. Figures of the pinch techniques used were also shown to all participants before the survey commenced for them to understand the correct way to conduct the experiment. Figure 1 (Source: developed for the study) shows the correct methods of performing the pinch techniques. Participants were requested to strictly follow the protocol stated below: Use the right hand to execute the pinch technique. Ensure that an upright standing posture is assumed. Ensure that the elbow is flexed at a 90 angle, and the forearm is in a neutral position. 3-Jaw Chuck Pinch Pulp-2 Pinch Lateral Pinch Figure 1: s Performed for the Study Participants were requested to perform a pulp-2 pinch to pinch and turn one of the 6 screw knobs provided. The participants were then asked to rate the effort used to pinch and turn the screw knob from a scale of 0 to 10. This scale was modified from the Borg CR10 scale [14], where 0 indicates no effort at all and 10 indicates tremendous effort. The effort rated by the participants was recorded in a feedback form. The participants were then asked to perform the same procedures on every remaining screw knob as well, using the 3-jaw chuck pinch and lateral pinch. The data were analyzed with Cronbach s alpha reliability analysis, a type of reliability analysis that determines the internal consistency of items in a survey instrument to gauge its reliability [15]. Descriptive analyses were carried out using data such as mean, maximum and minimum values via Microsoft Excel 2010.

3 Results and Discussion The test model was then evaluated by a total of 110 manual workers. The response rate was approximately 69% (based on a total number of 160 workers employed in the firm). This percentage is satisfactory seeing as a response rate of more than 30% is acceptable in most studies [16]. The data collected from the survey study were entered into a Cronbach s alpha Excel spreadsheet used for reliability analysis that was retrieved from an online source [17]. Table 1 shows the result of the reliability analysis. Table 1: Cronbach s Alpha Reliability Analysis Results Test results Values Alpha Standard Deviation Standard Error of Mean (SEM) From the results, the Cronbach s alpha coefficient is 0.826, which is adequately above 0.7. Hence, the internal consistency is excellent [18, 19] and the data is reliable enough for further analysis. The responses provided by the participants in terms of mean effort used to pinch and turn the small knobs are summarized in Table 2. Table 2: Mean Effort for Small Knobs Mean Effort [Rating 1-10] Cylindrical Sphere 5-Lobes 3-Jaw Chuck Pulp Lateral Small Cylindrical Knob. It is clear that the mean effort needed to pinch and turn the small cylindrical knob using the lateral pinch is the lowest, followed by the 3-jaw chuck pinch and pulp-2 pinch respectively. The maximum effort exerted using the 3-jaw chuck, pulp-2 and lateral pinches are 6.0, 8.0 and 5.0 respectively. On the other hand, the minimum effort exerted using the 3-jaw chuck, pulp-2 and lateral pinches are 2.0, 2.0 and 1.0 respectively. Small Sphere Knob. It is found that the mean effort needed to pinch and turn the small sphere knob using the lateral pinch is the lowest, followed by the 3-jaw chuck pinch and pulp-2 pinch respectively. The results regarding the sequence in the efforts obtained are almost similar to the results for the small cylindrical knob. The maximum efforts recorded for the 3-jaw chuck, pulp-2 and lateral pinches are 7.0, 9.0 and 6.0 respectively. The minimum efforts recorded for 3-jaw chuck, pulp-2 and lateral pinches are 1.0, 3.0 and 1.0 respectively. The results show that the lateral pinch is the most effortless pinch technique for both the small cylindrical and sphere knobs compared to the other two pinch techniques due to the fact that lesser mean effort is exerted by the users with this technique compared to the other two techniques. This is due in part to the thumb which is more adducted while exerting the lateral pinch, thus providing a better hold on the object [20]. Besides that, it is reasonable to say that the pulp-2 pinch is the most undesirable technique to be applied on both of the small cylindrical and sphere knobs as the results show that they require the highest mean effort. According to Swanson, et al. [21], this is because only 25% of individuals prefer to use the pulp-2 pinch technique when pinching small objects. Small 5-Lobes Knob. It appears that the mean effort needed to pinch and turn the small 5-lobes knob using the 3-jaw chuck pinch is the lowest. However, the pulp-2 pinch technique is still the one with the highest mean effort scored. It is also observed that the mean effort scored by using the pulp-2 pinch for the small 5-lobes knob is the smallest compared to the previous two small knobs. The mean effort scored by the 3-jaw chuck pinch on this small 5-lobes knob is the lowest compared to the mean effort scored by the lateral pinch on both of the small knobs discussed earlier. For the small 5-lobes knob, the maximum efforts recorded for the 3-jaw chuck, pulp-2 and lateral pinches are 6.0, 8.0 and 6.0 respectively. The minimum effort recorded for all 3 pinch techniques is

4 1.0. The responses provided by the participants in terms of mean effort used to pinch and turn the large knobs are summarized in Table 3. Table 3: Mean Effort for Large Knobs Mean Effort [Rating 1-10] Cylindrical Sphere 5-Lobes 3-Jaw Chuck Pinch Pulp-2 Pinch Lateral Pinch Large Cylindrical Knob. The mean effort needed to pinch and turn the large cylindrical knob using the 3-jaw chuck pinch is the lowest. The maximum effort exerted using the 3-jaw chuck, pulp-2 and lateral pinches are 6.0, 8.0 and 7.0 respectively. The minimum efforts recorded for all 3 pinch techniques are 2.0. Large Sphere Knobs. It appears that the mean effort needed to pinch and turn the large sphere knob using the 3-jaw chuck pinch is the lowest, followed by the lateral pinch and pulp-2 pinch respectively. For the large sphere knob, the maximum efforts recorded for the 3-jaw chuck, pulp-2 and lateral pinches are 6.0, 8.0 and 6.0 respectively. The minimum effort recorded for all 3-pinch techniques is 1.0. Large 5-Lobes Knob. It is observed that the mean effort needed to pinch and turn the large 5- lobes knob using the 3-jaw chuck pinch is the lowest. However, the pulp-2 pinch technique is still the one with the highest mean effort scored. It is also observed that the mean effort scored by the pulp-2 pinch for the large 5-lobes knob is the smallest compared to the two large knobs (large sphere and cylindrical knobs). The mean effort scored by 3-jaw chuck pinch on the large 5-lobes knob is the lowest compared to the mean efforts recorded from the previous large knobs discussed. For the large 5-lobes knob, the maximum efforts recorded for 3-jaw chuck, pulp-2 and lateral pinches are 7.0, 7.0 and 8.0 respectively. The minimum effort recorded for all 3-pinch techniques is 1.0. The results shown for the small 5-lobes knob and all the large knobs support that the 3-jaw chuck pinch is the most effortless pinch technique for these knobs compared to the other two pinch techniques due to the fact that lesser mean effort is exerted with this technique. According to Imrhan and Rahman [22], this is because the 3-jaw chuck pinch is generally stronger compared to the lateral and pulp-2 pinch, while the lateral pinch is stronger than the pulp-2 pinch. Besides that, it is reasonable to say that the pulp-2 pinch is the most undesirable technique to be applied on the small 5-lobes knob and all the large knobs as the results show that it requires the highest mean effort to pinch and turn these knobs. Conclusion Overall, the preferred pinch technique for the small cylindrical knob, small sphere knob and all large knobs is the lateral pinch. However, the 3-jaw chuck pinch is preferred for the small 5-lobes knob. This study provides researchers with fundamental knowledge on pinch techniques for further research on pinch force measurement. This study also provides designers with preliminary information to create design guidelines on ergonomic knobs. For future work on this area, an experiment can be done to determine the forces exerted by each pinch technique. Measurement equipment such as tactile pressure sensors can be used to collect data on forces exerted by the fingers while pinching. References [1] Information on [2] Information on [3] S. Kumar, Biomechanics in Ergonomics, 2nd ed., CRC Press, Boca Raton, 2008.

5 [4] N. J. Seo, T. J. Armstrong, D. B. Chaffin, and J. A. Ashton-Miller, The Effect of Handle Friction and Inward or Outward Torque on Maximum Axial Push Force, Human Factors, 50 (2008) [5] P. K. Ng, Q. H. Boon, K. X. Chai, S. L. Leh, M. C. Bee, and A. Saptari, The Roles of Shape and Size in the Pinch Effort of Screw Knobs, presented at the 4th International Conference on Mechanical and Manufacturing Engineering, Bangi, Putrajaya, Malaysia, [6] P. K. Ng, K. X. Chai, S. L. Leh, M. C. Bee, Q. H. Boon, and A. Saptari, Applying Clockwise and Counterclockwise Torque Directions in Pinch Grips: A Descriptive Study, presented at the 4th International Conference on Mechanical and Manufacturing Engineering, Bangi, Putrajaya, Malaysia, [7] P. K. Ng, S. L. Leh, M. C. Bee, Q. H. Boon, K. X. Chai, and K. S. Jee, The Effects of Different Tactile Sensations on Pinch Effort, presented at the 4th International Conference on Mechanical and Manufacturing Engineering, Bangi, Putrajaya, Malaysia, [8] P. K. Ng, M. C. Bee, A. Saptari, and N. A. Mohamad, A Review of Different Pinch Techniques, Theoretical Issues in Ergonomics Science, (2013), doi: / X [9] R. O. Smith, Pinch and Grasp Strength: Standardization of Terminology and Protocol, The American Journal of Occupational Therapy, 39 (1985) [10] D. J. Magee, Orthopedic Physical Assessment, 5th ed., Saunders Elsevier, St. Louis, Missouri, [11] P. K. Ng and A. Saptari, A Review of Shape and Size Considerations in Pinch Grips, Theoretical Issues in Ergonomics Science, (2012), doi: / X [12] P. K. Ng, A. Saptari, and J. A. Yeow, Synthesising the Roles of Torque and Sensation in Pinch Forces: A Framework, Theoretical Issues in Ergonomics Science, (2012), doi: / X [13] Information on [14] G. A. V. Borg, Psychophysical Bases of Perceived Exertion, Medicine and Science in Sports and Exercise, 14 (1982) [15] Information on [16] U. Sekaran, Research Methods for Business: A Skill Building Approach, 4th ed., John Wiley & Sons, New York, [17] Information on [18] L. J. Cronbach and R. J. Shavelson, My Current Thoughts on Coefficient Alpha and Successor Procedures, Educational And Psychological Measurements, 64 (2004) [19] J. Nunnally and I. Bernstein, Psychometric Theory, McGraw-Hill Publication, New York, [20] H. M. Clarkson, Musculoskeletal Assessment: Joint Range of Motion and Manual Muscle Strength, 2nd ed., Lippincott Williams & Wilkins, Philadelphia, [21] A. B. Swanson, I. B. Matev, and G. de Groot, The Strength of the Hand, Inter-Clinic Information Bulletin, 13 (1974) 1-8. [22] S. N. Imrhan and R. Rahman, The Effects of Pinch Width on Pinch Strengths on Adult Males Using Realistic Pinch-Hand Coupling, International Journal of Industrial Ergonomics, 16 (1995)