Chapter 28 swts
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Stopwatch time studies involve observing operators performing tasks and recording the times taken to establish standard times. The key steps are to first analyze methods to establish efficient workflows, select appropriate operators, time task elements using techniques like continuous watches or snapback, determine the required number of observations statistically, and rate operators to adjust times to normal levels.
Chapter 28 swts
- 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.
- 2. OVERVIEW Stopwatch time study is one of the two methods to establish a type I time standard. The analyst observes one or more operators continuously and records the time taken to accomplish a task. This is called Observed Time Observed Time x Rating = Normal Time
- 3. OVERVIEW Standard time = (Normal time) * (100/{100 – pct Allowances}) Example: Observed time = .01 hr./unit Rating = 120 % Normal time = .012 hr./unit Allowances = 10% Standard time = (.012 hr./unit * 100/90) =.0133hr./unit
- 4. Time Study Sheets (from ERGO)
- 5. PREPARATION There are basically two steps involved in Preparation 1. Methods Analysis 2. Operator Selection
- 6. METHODS ANALYSIS From a productivity standpoint, supervisors of industrial engineering department have to do job 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.
- 7. METHODS ANALYSIS The typical items that are recorded are : Date of observation (Improvement curve) Person observed (Skilled…..) Person observing (Viewpoint) Machine used (Improvement curve) Tools used (Improvement curve) Part no. processed etc..
- 8. METHODS ANALYSIS After a good method has been established (using checklists), the job should be broken into Elements
- 9. METHODS ANALYSIS 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 collection is flexible
- 10. 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)
- 11. OPERATOR SELECTION It is very important to select the right operator for performing the time study There are two reasons: Rating Accuracy (average worker) Worker Acceptance ( do the study at different times)
- 12. TIMING Timing Techniques (example) Videotape One watch, continuous One watch, snapback Three watch system Electronic watches
- 13. TIMING Videotape : The primary advantage is having 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 replayed
- 14. 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.
- 15. 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.
- 16. TIMING 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 second’s are stopped at some value, and the third’s are stopped at zero. The only disadvantage is that there are three watches.
- 17. 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 the traditional mechanical stop watch.
- 18. NUMBER OF OBSERVATIONS There are two approaches to determining the number of observations Statistical Importance of Decision
- 19. NUMBER OF OBSERVATIONS Statistical A time study of sequential observations is a sample from a population of times. The goal is to estimate 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….
- 20. The number of sample size depends on three factors Accuracy Desired (absolute or relative) Confidence Desired (based on Z score) Data Variability (use subsample to determine) Calculation formula: (See Box 28.1) -Westinghouse/ General Electric and Niebel’s approaches are in Tables 28.2 and 28.3
- 21. NUMBER OF OBSERVATIONS Irregular and Foreign Observations Irregular element (exp. Breakdown) Foreign element (exp. Customized part)
- 22. NUMBER OF OBSERVATIONS Recording Techniques Missed Readings Omitted Readings Element out of order Unexpected element
- 23. RATING Normal Pace During the time study, the observer will rate the worker, that is, determine the adjustment to convert the observed time to a time that a normal, experienced worker would take APL = MPL - Expectancy
- 24. RATING MPL (Motivated productivity level) : The work pace of a motivated worker possessing sufficient skill and effort to do the job, physically fit to do the job after adjustment to it, and working at an incentive pace that can be maintained day after day without harmful effect.
- 25. RATING Acceptable productivity level (APL): The work pace established by management or jointly by management and labor at a level that is considered satisfactory; it is established at a given relationship to motivated productivity level. Expectancy is the expected level of productivity, it is also related to allowance, if allowance is low expectancy discount tends to be high and vice-versa.
- 26. RATING TECHNIQUES There cannot be a set method to rate as different tasks within an activity requires different levels of skills and ways All tasks cannot be rated at a same scale (example)
- 27. RATING TECHNIQUES Pace Rating: The observer estimates the speed and concentrate on dynamic micromotions such as reach or move rather then stationary like position and grasp. Objective Rating: (three steps) (example) The observer rates the speed Observer estimates the task difficulty task difficulty factor is multiplied with speed to get actual pace.
- 28. RATING PROCEDURES Divide the elements and take multiple readings Categorize mental, fine manipulative and muscular jobs Categorize skilled, unskilled and semi skilled labor Categorize time of the day Rating is a very specialized task and enough training via videotapes, practice tests, different paces etc should be carried out before actual assignment
- 29. RATING TECHNIQUES Actual pace Estimated Pace 0 20 40 60 80 100 120 140 120 100 80 60 40 20 0 Identity Line Cte Error Flat Rating Consistency