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taguchi approach in optimizing environment factors human
Taguchi Approach in Optimizing Environmental Factors Human towards Productivity A.R. Ismail 1 , M.H.M. Haniff 2 , B.M. Deros 2 , R.A. Bakar 1 1 Faculty of Mechanical Engineering, Universiti Malaysia Pahang, 26600 Pekan, Pahang, Malaysia Phone: +609-4242268, Fax: +609-4242202 Email: arasdan@gmail.com, rasdan@ump.edu.my 2 Department of Mechanical and Material Engineering, Faculty of Engineering and Build Enviroment, Universiti Kebangsaan Malaysia, 43600 UKM Bangi, Selangor, Malaysia ABSTRACT Environmental factors such as lighting, temperature and relative humidity are important factors affecting the performance of workers in the automotive industry. Therefore, the optimal parameters must be obtained to get the best production rate. The objective of this study is to determine the dominance effects of environmental factors such as Illuminance, humidity and wet-bulb globe temperature (WBGT) on the workers’ performance at Malaysian automotive industry. A case study was carried out at an automotive components assembly factory. The environmental factors examined were the Illuminance (lux), humidity and WBGT of the surrounding workstation area. The production rate data were collected through observations and survey questionnaires while the illuminance level was measured using photometer model RS 180-7133, the humidity and WBGT level were measured by using Quest Temp apparatus and humidity. Taguchi Method was utilized to find the sequence of dominant factors that contributed to the production rate of operator at that specified production workstation. These results indicate that the optimum parameter relative humidity level at level 1 (<60%), illuminance level at level 1 (<500lux) and WBGT at level 2 (>23°C). Revenue contribution from this study will be used to improve the performance for our country's automotive industry. Keywords: humidity, illuminance, WBGT, taguchi method, performance INTRODUCTION Automotive industry is one of the dominant industries, which contributes to the Malaysian economic growth. Therefore, healthy competition and there should be competitive in the industry to compete in the global market. Time is a factor that is often an issue on the productivity of an industry. Various research methods have been discovered and applied to optimize the productivity of industry as well as high quality products. According to the study, several factors have been identified as the cause of the decline in labor productivity. Therefore, the parameters must be obtained for the workstation environment is not only aimed to increase productivity and even ensure the comfort, health and safety of workers involved (Juslen 2007).Environment and a comfortable atmosphere is an important point because it can maintain focus and employee performance for a long time. If the focus of their impairment, this is what led to the decline in productivity, or worse, can result in accidents. Therefore, the values should be applied in ergonomic working environment for a comfortable environment and quality. The utility of ergonomics research is not limited to predicting and eliminating workplace injuries but can also be used to enhance productivity (Resnick & Zanotti, 1997). Relative humidity is a term used to describe the water vapor pressure of the air at given temperature (Bridger, 1995). It is one of the environmental factors that could give an influence towards workers’ performance. Previous research done by Gavhed & Klasson (2005) showed that the low relative humidity resulted in more discomfort and more frequent symptoms in facial skin and the mucous membranes such as dryness of the mouth and throat, facial skin, more frequent symptoms of the eyes, lips and running nose. According to the Ishii et al. (1993), Japanese people might be more sensitive to humidity than westerners and so different methods from those used in the western countries should be required for human thermal environmental studies with respect to the hot humid summer in Japan. Tsutsumi et al. (2007) conducted a study to evaluate the effect of humidity on human comfort and productivity after step changes from warm and humid environment. The results of the study revealed that workers’ performance was found to be at the same level under all conditions but to more tired at 70% RH after humidity step change meanwhile more evaporation of sweat from human body at lower humidity. Humans can attempt to maintain their internal (core) temperature within an optimum range at around 37ºC and if the body is subjected to thermal stress the thermoregulatory system responds by changing its state in a way which is consistent with maintaining core temperature within this range (Parsons, 2000). Wijewardane & Jayasinghe (2008) had conducted the study of thermal comfort temperature range for factory workers in warm humid tropical climates. The results from this study showed that the ability to operate factory buildings as free running will be very useful in the context of saving energy needed from providing adequate thermal comfort for workers in warm humid tropical climatic conditions. A study on impact of lighting level on productivity by Juslen (2006) indicated that at higher illumination level (1200 lux as against 800 lux) shows increase in productivity. This study shows a change and improvement in lighting can have an effect on productivity. Juslen (2006) also found that by increasing an illumination levels it is possible to increase a person’s productivity. This result in line with finding by Nicol et.al (2006) who claimed that there was a general satisfaction with the environment at higher level of illuminance. Previous research done by Cajochen (2007) show that the human alertness increase directly propotional with the increase of illuminance. The objective of this study was to determine the dominance effects of environmental factors such as illuminance, humidity and WBGT on the workers performance at Malaysian manufacturing plant. METHODOLOGY Selection of Location and Subjects The study is conducted on a selected work station in the automotive industry where it refers mainly towards the assembly section or the manual production line where human energy are involve for in the manufacturing activity. Figure 1 shows the production line layout. Figure 1: Handle Assembly Door Outside production line The production is desired to be the repeated production of the same component throughout the entire shift and this is to ensure on the consistency of the data collected towards the data analysis later. Priority of study will be given to the work station where the environmental factors will sponsor the most towards effect of the performance. One automotive vendor has been selected as a place of study. A line producing a product over a period of time and under the effects of certain relative humidity,illuminance and WBGT was chosen. Figure 2 shows the flow chart of work sequences on the production line. Figure 2: The works sequence to assemble complete Handle Assembly Door Outside This criterion is essential in order to obtain the which factors contribute utmost to the worker performance based on output of assemblies among operators. The production line was consist of 10 woman operators. The task is to assemble an automotive parts which is known as handle assembly door outside. The standard production rate determined by the previous feasibility study to assemble a complete handle assembly door outside was 240 units for every hour of production. Experimental Method The Taguchi design of experiment was employed in this experiment with two factors at two levels each. The fractional factorial designs used was a standard L 8 orthogonal array (Park, 1996). This orthogonal array was chosen because of its minimum number of experimental trials. Each row of the matrix represented one trial. However, the sequence in which those trials were carried out was random. The factors and levels identified in this study were shows in Table 1. Table 1: Factors and levels used in the experiment Symbol Factors Unit Level 1 Level 2 A Illuminance lux <500 >500 B Relative Humidity (%) <60 >60 C WBGT °C <23 >23 RESULTS AND DISCUSSIONS The result of this study was based on the case study conducted on the production line in the automotive vendor factory. The hypotheses for this study was the production rate have a direct relationship with the illuminance, humidity and WBGT level. The levels of illuminance, humidity and WBGT were taken to identify their effect on the worker performances. Table 1 shows the data of production rate, illuminance, WBGT and humidity level collected during the experimental work taken for every 30 minutes. Table 1: Results of Average Workers’ Production Rate Time Level of Parameters Production Illuminance (lux) Relative Humidity, (%) WBGT (˚C) Target (units) Rate (units) 09.05 – 09.35 497.65 60.76 22.98 120 119 09.35 – 10.05 505.20 59.85 23.19 120 123 10.05 – 10.35 504.65 59.21 23.13 120 121 10.35 – 11.05 503.95 59.55 23.25 120 115 11.05 – 11.35 503.83 59.29 23.15 120 121 12.05 – 12.35 501.16 59.61 22.86 120 124 12.35 – 01.05 492.45 55.98 23.25 120 108 02.10 – 02.40 489.89 55.84 23.82 120 112 The objective of the experiment is to obtain the optimize the environmental parameters (WBGT, illuminance and humidity) in order to obtain the better results for production rate (high value) and therefore the optimum characteristic of environment should be quantify Taguchi Approach Taguchi recommends analyzing the means and S/N ratio using conceptual approach that involves graphing the effects and visually identifying the factors that appear to be significant, without using ANOVA, thus making the analysis simple (Park, 1996). The bigger the better characteristic S/N ratio graph for the production rate is shown in Figure 3. It shows that the relative humidity is the most significant factor in controlling the production rate, followed by the illuminance and WBGT. Figure 3 also shows the optimum condition for the production rate are at level 1 (less than 60%) of humidity, level 1 (less than 500 Lux) of illuminance and level 2 of WBGT (more than 23°C ). The L8 orthogonal array for environment parameters and production rate were show in Table 2 Table 2: Experimental Result for Production Rate and S/N Ratio Experiment Number Level of Parameters Production Rate (units) S/N Ratio, (dB) Illuminance, (lux) Relative Humidity, (%) WBGT, (˚C) 1 <500 <60 <23 119 41.51 2 <500 <60 >23 123 41.80 3 <500 >60 <23 121 41.66 4 <500 >60 >23 115 41.21 5 >500 <60 <23 121 41.66 6 >500 <60 >23 124 41.87 7 >500 >60 <23 108 40.67 8 >500 >60 >23 112 40.98 Table 3: Response Table for Signal to Noise Ratios (Larger is Better) Symbol Factors Mean S/N ratio (dB) Level 1 Level 2 Rank A Illuminance 41.54 41.29 2 B Relative Humidity 41.71 41.13 1 C WBGT 0.58 41.47 3 Table 3 shows the mean S/N ratio for each factor at two levels. From this table, the highest value for each mean S/N ratio for each factor can be identified clearly. For the illuminance level, the level 1 of <500 lux give the highest value, for the relative humidity the level 1 of <60% gives the highest value and WBGT, level 2 of >23°C gives the highest value. Figure 3 shows the S/N graph for the experimental results. Figure 3: S/N Graph for Production Rate Analysis of Variance (ANOVA) The purpose of ANOVA is to investigate which of the factors significantly affect the workers’ production rate. Table 4 shows the results of analysis of variance. Statistically F- test can be used to determine which factors have significant effect on the workers’ production rate. The sequential sums of squares (Seq SS) measure the reduction in the residual sums of squares provided by each additional term in the model. The adjusted sums of squares (Adj SS) measure the reduction in the residual sums of squares provided by each term relative to a model containing all the other terms. The F value for each factor is then a ratio of the MS to the mean square of error. The larger the F value, the greater the effect on the performance characteristics (productivity of workers) due to change of operating factors. Usually, when F>4 it means that the change of operating factors has a significant effect on the quality characteristics (Ismail et al., 2010). Table 4: Results of the Analysis of Variance for S/N Ratios Symbol Factors DF Seq SS Adj SS Adj MS F P A Illuminance 1 0.125 0.125 0.125 1.11 0.351 B Relative Humidity 1 0.667 0.667 0.667 5.93 0.042 C WBGT 1 0.017 0.017 0.017 0.16 0.714 Error 4 0.450 0.450 0.113 Total 7 1.260 From the results of the ANOVA presented in Table 4, it can be seen that only relative humidity is statistically significant. However, each factor contributes to the quality characteristics and the rank order is relative humidity (rank 1), illuminance (rank 2) and WBGT (rank 3) respectively. Therefore, based on the S/N ratio and ANOVA analysis, the optimal parameters for achieving optimum production rate in terms of environmental factors are relative humidity level at level 1 (<60%), illuminance level at level 1 (<500lux) and WBGT at level 2 (>23°C). Relative humidity is the most significant factors impact on workers’ production rate while the second biggest factor affecting production rate is followed by the brightness and WBGT. This parameter is valid as well as standards set by ISO 7730 which states that the temperature at 24 °C - 27 °C is the best temperature for the convenience of employees. According to Tsutsumi et al (2007), the best relative humidity range is between 40% to 50%. For the results of brightness, the brightness of 500 lux is meeting the standards set by the European Standard (EN 12464-1:2002), which states that the brightness 500lux is best used for assembly works in the automotive industry. The finding also will be useful to engineers in design humidity systems in order to improve the comfort in the workstation area and control the productivity of workers. The dominant environmental parameter obtain in this study is only applicable to present the current condition for the selected area of assembly workstation at Malaysian automotive industries. CONCLUSION Overall, this study has met the objectives and scope of the target. From the data analysis was performed by Taguchi method, the relationship between environmental factors to production rate have been obtained. The optimum relative humidity level at level 1 (<60%), illuminance level at level 1 (<500lux) and WBGT at level 2 (>23°C). This study was done to prove empirically the previous perception studies, which based on the role of environmental factors to human performance. The results might vary for test carried out for different sample sizes, type of industries and countries. 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