IE271_Lecture14

# Time study equipment 1 stopwatch mechanical

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Time Study Equipment 1. Stopwatch Mechanical stopwatches Electronic stopwatches 1. Video cameras Provides visual and audio record of method used by worker 1. Computerized techniques in direct time study Use of PCs and PDAs

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Mechanical Stopwatch Calibrated in decimal minutes

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Prepare and clean the tools Load the tools to the machine Run the machine Recording the data Continuous timing Snapback (Repetitive) timing 1.2 2.0 5.2 1.2 0.8 3.2 1.4 7.3 10.5 6.6 0.7 3.2 1.2 12.7 15.9 11.7 1.0 3.2
13.2 Direct time study form

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Cycle-to-Cycle Time Variations Result from the following: Variations in hand and body motions Variation in the placement of parts and tools Variations in the quality of the starting work units Operator mistakes Variations in worker pace Timing errors by analyst
Number of Cycles to be Timed One of the practical issues in taking a time study is determining how many work cycles should be timed. The reason this issue arises is that there is statistical variation in the times of respective elements from one work cycle to the next. There is inherent variability in any human activity. Work element times vary from cycle to cycle because of the following reasons.

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Variations in hand and body motions Variations in the placement and location of parts and tools used in the cycle Variation in the quality of the starting work units Mistakes by the operator Number of Cycles to be Timed
Number of Cycles to be Timed By using the data collected for the most critical work element, find the necessary number of observations. If the most critical work element is not obvious, then find the necessary number of observations to be made for all work elements and make observations as much as the largest number.

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For analysis purposes, we assume that the observed work element times are normally distributed about the true value of the work element time. Our objective is to be able to identify the true value of the duration of the work element within a confidence interval. We might state that we want to be 95% confident that the true value of Te lies within ±10% of the observed average value of the element time Number of Cycles to be Timed
Number of Cycles to be Timed After several cycles, calculate sample standard deviation s s = Let k be the precision level. Then, the required number of observations in given by n = ( 29 1 2 - - n x x 2 2 / x k s t α

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Example Seven cycles have been observed during a direct time study. The mean for the most critical element time = 0.85 min, and the corresponding sample standard deviation s = 0.15 min, which was also the largest. If the analyst wants to be 95% confident that the mean of the sample was within ± 10% of the true mean, how many more observations should be taken?
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• Spring '10
• smith

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