Lecture 9 & 10 Flashcards
What are the different types of work measurement techniques?
What are Therbligs?
- Therbligs - are the 17 motion elements
- Basic building blocks of virtually all manual work performed at a single location
- With modifiation, use today in several work measurement systems.
Expalin Micromotion analysis
- Analyisis of therbligs that make up a repetitive task
- Objectives:
- Eliminate ineffective therbligs if possible
- Avoid holding objects with hand
- Use workholder
- Combine therbligs
- Perform right-hand and left-hand motions simultaneously
- Simplify overall method
- Reduce time for a motion, e.g., shorter distance.
What are predetermined motion time systems - PMTS?
A database of basic motion elements and their associated basic/normal time values, together with procedures for applying the data to analyze manual tasks and establish standard times for the tasks
- Basic motions include
- Reach
- Grasp
- Move
- Release
Give the steps of the PMTS Procedure?
- Synthesize method that would be used to perform the task - The method is described in terms of basic motion elements
- Retrieve basic time values for each motion element - Sum the element times to determine the task basic time
- Evaluate method to make improvements - Evaluate method to make improvements
- Apply allowances to determine standard time - Apply allowances to determine standard time
What is the methods-time measurement?
What are TMU’s?
“Procedure which analyzes any manual operation or method into the basic motions required to perform it and assigns to each motion a predetermined time standard which is determined by the nature of the motion and the conditions under which it is made.
- Time units are TMU’s
1 TMU = 0.00001 = 0.0006 min = 0.036 sec
1 sec = 27.8 TMU
- MTM is a family of products available through the MTM Association in Des Plaines, Illinois.
What the MTM motion elements?
- Reach
- Grasp
- Move
- Position
- Release
- Disengage
- Turn
- Apply pressure
- Eye travel, eye focus, and reading
- Body, leg and foot motions
- Simultaneous motions
What are the advantages of predetermined time standards?
- The detailed systems produce more detailed description of the work than other methods.
- As each basic motion is decribed along with its variables, so alternative methods can be readily compared using time as a criterion.
- Methods can be developed and standards established before production operations start.
- PTS do not require the assessment of rate of working and the use of the stop watch as is required in time study. This can remove one of impediments to good industrial relations.
- PTS are objective and consistent.
Define standard data system.
- A SDS is a database of basic/normal time values, usually organized by work elements, that can be used to establish time standards for tasks composed of work elements similar to those in the database.
- Basic times in the database are usually compiled from pervious direct time studies.
- Using a stanard data system, time standards can be established before the job is running.
When is a SDS most suitable to use?
-
Similarity in tasks
- With many similar tasks, it is more efficient to use a SDS than direct time study
-
Large mumber of standards to be set
- More productive than direct time study
-
Need to set standards before production
- Direct time study requires observations of actual task to be set, SDS does not.
Describe the SDS Database
- A catalog of basic/normal times, organized to allow the analyst to access the values corresponding to work elements performed under various work variables
- Work variables - factors that affect the basic time of the element
- Examples
- Work unit characteristics (e.g., size, weight)
- Task parameters (e.g., distances moved)
- Working conditions (e.g., illumination)
Define work sampling
- Stastistical technique for determining the proportions of time spent by subjects in various defined categories of activity.
- Subjects = workers, machines
- Categories of activity = setting up a machine, producing parts, idle, etc.
- For statistical accuracy
- Observations must be taken at random times.
- Period of the study must be representative of the types of activities performed by the subjects.
When is work sampling appropriate?
- Sufficient time is available to perform the study
- Several weeks usually required for a work sampling study
- Multiple subjects
- Work sampling suited to studies involving more than one subject
- Long cycle times for the jobs covered by the study
- Nonrepetitive work cycle
- Jobs consist of various tasks rather than a single repetitive task
What are aspects of measurement in work sampling applications?
- Machine utilization - how much time is spent by machines in various categories of activity
- Worker utilization - how workers spend their time
- Allowances for time standards - assessment of delay components in allowance
- When doing time studying - maybe no delays happen, this will give you the wrong impression - need to sit and analyse activity till they happen.
- Average unit time - determining the average time on each work unit
- Time standards - limited statistical accuracy when standards set by work sampling.
What are the steps in a work sampling study?
1. Define the problem - (e.g. how log a worker spends time on the phone)
- Determine the required accuracy and required confidence limits
- Make a preliminary estimate of the % occurrence of the desired activity. Usually done by carrying out a pilot study.
- Design the main study. Find number of observations required, design sampling plan with randomised times, determine number of observers.
- Carry out study according to above plan, summarising the data at the end of each shift.
(e.g. Cambridge does a large sample study every year, lecturers has to tell how much work they have done lecturing, teaching, researching. So what Cambridge can see what proprotion of time they have spent on these activities. )
Explain the statistical basis of work sampling.
Also explain the confidence intervals
Explain how to find the Z-Score using the 3P5 datasheet.
Calculate the 95% confidence interval for the proportion time for the machines in the previous example (proportion of running time p = 0.6)
Explain how the number of observations required to achieve a given confidence interval about the estimate of p can be calculated.
Example
Determine how many observations will be required to estimate the porportion of time used to set up the 10 machines. The confidence interval must be within +/- 0.03 ( c = 0.03 ) of the true proportion, which the line manager initially estimates to be p = 0.20. A 95% confidence level will be used.
