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1、Chapter 28 STOPWATCH TIME STUDY,Stopwatch Time study should be preceded by a methods analysis so the resulting standard is a“should take” time not a “did take” time.,OVERVIEW,Stopwatch time study is one of the two methods to establish a type I time standard.,The analyst observes one or more operator
2、s continuously and records the time taken to accomplish a task. This is called Observed Time Observed Time x Rating = Normal Time,OVERVIEW,Standard time = (Normal time) * (100/100 pct Allowances),Example: Observed time = .01 hr./unit Rating = 120 % Normal time = .012 hr./unit Allowances = 10% Standa
3、rd time = (.012 hr./unit * 100/90) =.0133hr./unit,Time Study Sheets (from ERGO),PREPARATION,There are basically two steps involved in Preparation 1. Methods Analysis 2. Operator Selection,METHODS ANALYSIS,From a productivity standpoint, supervisors of industrial engineering department have to do job
4、 design. The primary reason for doing a methods analysis before doing a time study is to establish a safe, productive job. The secondary reason is to leave a permanent record of the methods for future audits and improvements.,The typical items that are recorded are : Date of observation(Improvement
5、curve) Person observed (Skilled) Person observing (Viewpoint) Machine used (Improvement curve) Tools used (Improvement curve) Part no. processed etc,METHODS ANALYSIS,METHODS ANALYSIS,After a good method has been established (using checklists), the job should be broken into Elements,METHODS ANALYSIS,
6、Five Reasons to divide the tasks into elements: Elements make it possible to reuse the data Elements permit different ratings for different elements(Machine time and manual time) Elements permit consistency checks, within the study and between studies Elements improve methods descriptions Data colle
7、ction is flexible,METHODS ANALYSIS,After the task is broken into elements, we write the element description on the time study form with a description of its EP (End points ) or also called TP (Termination point) (Example),OPERATOR SELECTION,It is very important to select the right operator for perfo
8、rming the time study There are two reasons: Rating Accuracy(average worker) Worker Acceptance( do the study at different times),TIMING,Timing Techniques (example) Videotape One watch, continuous One watch, snapback Three watch system Electronic watches,TIMING,Videotape: The primary advantage is havi
9、ng a permanent record of the method. Videotaping is less intrusive so there might not be any discrepancies. The tape counter does not give very accurate data as it gives continuous timing; use a stopwatch. The elements can also be performance rated If any dispute occurs then the tape can also be rep
10、layed,TIMING,One watch, continuous The stop watch does not stop, it is continuously run (Example) As the clock never stops, there is no time omitted and workers like that The disadvantage is that the observer does not know how individual elements vary and the observer tries to read a moving target.,
11、TIMING,One watch, Snapback As the element ends, the time is noted and the stop is reset (set back to zero). The advantage is that no subtraction to be done and the observer is able to see the pattern. If the observer is confused then he might stop the watch. Continuous is preferred over snapback.,TI
12、MING,Three-watch system As in the title there are three watches and it is a combination of snap back and continuous type Initially the hands of the first watch are moving, the seconds are stopped at some value, and the thirds are stopped at zero. The only disadvantage is that there are three watches
13、.,TIMING,Electronic watches These watches can be used either the snapback or the continuos mode The key feature is that, when the user depresses the button, the display time is frozen while the clock continues timing. Electronic watches with a computer built into the board, generally have replaced t
14、he traditional mechanical stop watch.,NUMBER OF OBSERVATIONS,There are two approaches to determining the number of observations Statistical Importance of Decision,NUMBER OF OBSERVATIONS,Statistical A time study of sequential observations is a sample from a population of times. The goal is to estimat
15、e the population mean from the sample mean. To minimize the differences between the sample and population means, increasing the sample size is one of the answers.,The number of sample size depends on three factors Accuracy Desired (absolute or relative) Confidence Desired (based on Z score) Data Var
16、iability (use subsample to determine) Calculation formula: (See Box 28.1) -Westinghouse/ General Electric and Niebels approaches are in Tables 28.2 and 28.3,NUMBER OF OBSERVATIONS,Irregular and Foreign Observations Irregular element (exp. Breakdown) Foreign element (exp. Customized part),NUMBER OF OBSERVATIONS,Recording Techniques Missed Readings Omitted Readings Element out of order Unexpected element,RATING,Normal Pace During the time study, the observer will rate the worker, t
