人因工程学Effect of wrenches on the operator's hand fatigue

Effect of wrenches on the operator's handfatigueClass: Mechatronic 1401Member: 汪培义Wang Peiyi 14222019刘翔天Liu Xiangtian 14222011高猛Gao Meng 142220062017年05月12日目录1 Introduction (3)1.1 Background (3)1.2 Object (3)2 Method (3)2.1 Participants (3)2.2 Experiment setup (4)2.3 Apparatus (5)2.4 Experimental design (5)2.5 Data analysis (5)2.5.1 Hand grip force (5)2.5.2 The Brog scale (6)2.5.3 FR index (6)2.5.4 Statistical method (6)3 Results (7)4 Discussion (7)4.1 The analysis of the wrench type effect (7)4.2 The analysis of Brog scale (8)4.3 The analysis of grip force difference (8)4.4 The analysis of FR index (9)4.5 The reasons of difference (10)5 Conclusion (11)1 Introduction1.1 BackgroundHand fatigue is best described as a person's inability to generate the desired amount of force necessary to perform a task with his or her hands. There are numerous reasons that the fatigue occurs. In many cases, it is because of a buildup of lactic acid in the muscle. A buildup of lactic acid in the muscles causes blood circulation in the hand to decrease. As blood decreases, so does oxygen. A person who is exposed to continual vibrations at work can also suffer from fatigue and pain. High vibration tools can damage nerves and blood vessels in the fingers and cause discomfort.Fatigue can also occur because a person has lost the energy or motivation needed to complete a task. There are many benefits to reducing and eliminating hand fatigue.If a person can reduce fatigue, he or she can increase their productivity. For the reasons above, it is necessary to select the appropriate operating tool to work.1.2 ObjectThrough this experiment, we will research the effect of types of wrenches on operator's hand fatigue. Also we need to research which types of wrenches is better in some condition. At the same time we should learn deeply to use Brog scale.2 Method2.1 ParticipantsThe participants were healthy, had no muscle fatigue and had no intense exercise within 24 hours before the experiment. Although the participants’ age and weight are different weight, but the final data analysis will take into account these individual differences, that is to say we think the participants before the test are all the same.2.2 Experiment setupSince the experiment condition, we just choose 12 participants from each group. Each participant needs to be adept in screwing the nut. All of them are healthy and had no intense exercise within 24 hours before the experiment. Both of the right-hand dominant and left hand dominant is ok. Besides since the restrict of the experiment, we just use water operation to do the experiment. Each group need one people to record, one person to tighten the bolt and two persons to screw the bolt.All the tests are conducted in the same experimental environment including the same gripforce is 8 N·M.The experiment includes the measure of wrist fatigue after the task and the grip test before and after the experiment. In the experiment, to ensure that each subject test independently, trying to avoid the outside interference.2.3 Apparatus1. A experimental table which has 30 bolts (M8) fixed with equal distance, and 60 hexagon nut;2. A torque wrench (EQ-3010001) with torque range of 20-110NM;3. A 13mm fixed size wrench;4. A 13mm socket wrench;5. Electronic grip gauges (EH101);6. Borg scale.2.4 Experimental designThe steps are as follows:1. Before each task, we set the torque of torque wrench, which is 8NM in this experiment. Using the torque wrench to screw all the nuts on the bolts, therefore the nuts will be remove by the same force.2. Before each test we explain the purpose, methods and procedures of this experiment to the participants.3. Measure subject's right hand or left hand grip 3 times, and take the average.4. Participants use the 13mm fixed size wrench to remove all the screws by rightor left hand.5. After the task, measure right or left hand grip immediately, and we record the hand grip force and Brog scale.6. Rest for 20 minutes, use socket wrench to remove all the screws by right hands;7. After the task, measure right hand grip immediately, and we record the hand grip force and Brog scale.2.5 Data analysis2.5.1 Hand grip forceSubjects will measure the hand grip before the experiment, and after each experiment they should immediately measure the grip at that time. Through the analysis of grip difference, we need to discuss the effect of the types of wrench on the opponent's grip and hand fatigue.2.5.2 The Brog scaleWhile doing physical activity, we want you to rate your perception of exertion. This feeling should reflect how heavy and strenuous the exercise feels to you, combining all sensations and feelings of physical stress, effort, and fatigue.Look at the rating scale below while you are engaging in an activity; it ranges from 6 to 20, where 6 means "no exertion at all" and 20 means "maximal exertion." Choose the number from below that best describes your level of exertion. This will give you agood idea of the intensity level of your activity, and you can use this information toher own pace for some minutes13 on the scale is "somewhat hard" exercise, but it still feels OK to continue.17 "very hard" is very strenuous. A healthy person can still go on, but he or she really has to push him- or herself. It feels very heavy, and the person is very tired.19 on the scale is an extremely strenuous exercise level. For most people this is the most strenuous exercise they have ever experienced.2.5.3 FR indexFR means that the ratio of grip force and the Brog scale. Sometimes we can’t get the exact result from single factor such as the single grip force. But the FR index is more accuracy to describe the effect on hand fatigue. The larger the index is, the less fatigue the hand has.2.5.4 Statistical methodPaired Sample T Test is used to analyze the data before and after the experiment, which is to find the significant difference between the wrench types and hand fatigue.Correlation analysis is used to analysis the correlation between the wrench types and hand force and the Brog scale.3 Results(1) The fixed size wrench(p=0.002<0.05) and the socket wrench(p=0.008<0.05) have a significant effect on operator’s hand fatigue.(2) The fixed size wrench and the socket wrench have significant correlation. (p=0.008<0.05) And the fixed size wrench is better than the socket wrench for screwing nut. (mean value of fixed-socket=0.65374>0, p=0.000<0.05).4 Discussion4.1 The analysis of the wrench type effect40.52 to 35.93 for fixed size wrench, and from 40.52 to 34.69 for socket wrench. We make asocketThis table tells that the mean value difference between initial force and fixed size wrenchfinal force, and socket wrench final force. Each pair mean value difference has a significant correlation.4.2 The analysis of Brog scale.We can know that from Table.4.2.2 the fixed Brog scale and the socket Brog scale have no significant correlation(p=0.409<0.05) which means fixed size wrench and socket wrench has no difference on Brog scale. But Table.4.2.3 show that mean value difference of fixed size wrench and socket wrench have significant correlation(p=0.000<0.05). So hypothesis that before is not true.4.3 The analysis of grip force differencesize wrench and socket wrench. We can’t ensure that the difference effect on hand fatigue through the grip force. Since the experiment condition is restricted, the result of grip force is not exact.4.4 The analysis of FR indexTable.4.4.1 shows that the fixed size wrench and the socket wrench have significant correlation(p=0.008<0.05). There is significant different on FR index between the fixed sizewrench and socket wrench. Table.4.4.2 tells us that FR index mean value between the both wrenches have significant effect(p=0.000<0.05). Since the mean difference value is 0.065374>0, the FR index of fixed size wrench is bigger than that of socket wrench, which means that in this condition the fixed size wrench is better than the socket wrench on hand fatigue.4.5 The reasons of differenceBefore the test, we set the torque of torque wrench, which is 8NM in this experiment. Using the torque wrench to screw all the nuts on the bolts, therefore the nuts will be remove by the same torque. As is shown in Fig.1, this is a fixed size wrench. The bolt is on the point A, and our hand is on the point B. As shown in Fig.2, that is a socket wrench. The bolt is on the point C, and our hand is on the point D. According to the formula T=F∙D, the distance of socket wrench is larger than that of fixed size wrench and the torque we need to screw the bolt is the same, so the socket wrench need much larger force to screw the nut. Since the force we need is difference, our hands will different fatigue under the same other conditions.BAFig.1DCFig.25 ConclusionThrough this experiment, we research that the effect on hand fatigue between the both wrenches. Both of the wrenches have significant difference on hand fatigue. We can’t avoid the fatigue, but we can reduce the fatigue and the damage through the propel tools. The fixed size wrench is better for reducing the fatigue on some extend than the socket wrench. But on some conditions the socket wrench is better. For example, if the operation space is restricted, the fixed size wrench can’t reach the target bolt.This experiment has some faults, which we can get improved in the next experiment. For example, we can’t get enough large data to analyze the result. And it’s too hard to screw the bolt by using the socket hand under one hand only condition. We can improve the experiment condition by using two hands but the larger torque.Through this experiment, all of us had learned that many methods we can use to analyze the collected data. Only the data is large enough, we can get the exact result based on reality.。