Lecture 7 & 8

Question 1

What are the functions of having time standards?

Answer 1

• They define a “fair day’s work”
• They provide a means to convert workload into staffing and equipment needs
• They allow alternative methods to be compared objectively
• They provide a basis for wage incentives and evaluation of worker performance
• They provide time data for:
  
  • Production planning and scheduling
  • Cost estimating
  • Material requirements planning

Question 2

What are the different methods to determine time standards?

Answer 2

• Estimation - Used when you don’t have time to work the time out.
• Historical records - Records of times for similar products/processes. Better than estimated times but still not great.
• Direct time study - Focused on the work elements.
• Predetermined motion time system - Focused on the motion elements (more detail)
• Work sampling - E.g. Cambridge asks lecture each month to give work sample of one week, (what he did during his day, how much time he spent lecturing/working etc.)

Question 3

What are the prerequisites for valid time standards?

Answer 3

• When developing a time study make sure method study is standardized/correct
• Factors that must be standardized before a time standard can be set.

Question 4

What are the assumptions made about the average workers - how are they defined?

Answer 4

• A worker who is representative of the persons who usually perform tasks similar to the task being measured
  
  • If the work is performed mostly by men, then the average worker is male
  • If the work is performed mostly by women, then the average worker is female
• Assumed to have learned the task and is practiced and proficient at it.
• Well into the learning curve (we’ll talk about this later).
• Jam company (meant to go on industrial visit) - In factory line, worker has to pick up slab of jelly and move it on to another line. They found that women are much better at this then men despite all the training they gave them. This exemplifies to observe the correct people for the work times.

Question 5

Define the term Standard Performance

Answer 5

A pace of working that can be maintained by an average worker throughout an entire work shit without harmful effects on the worker’s health or physical well-being.

Question 6

What is performance rating?

Answer 6

• The analyst judges the performance or pace of the worker relative to the definition of standard performance used by the orginzation.
  
  • Standard performance PR = 100%
    
    • Slow pace than standard PR < 100%
    • Faster pace than standard PR > 100%
  • Basic (or normal) time T_b = T_obs x PR
• E.g. An analysit observes a worker arrying out a task. The worker does the job in 5 minutes. According to the analyst’s judgement, the worker is ‘below standard’ (maybe he is a newbie) and rates him at 80% standard performance.
  
  • Hence, he sets the ‘basic/normal time’ to do the job at 5*0.8 = 4 mins. Therefore, a standard worker should be able to do the job in 4 minutes.

Question 7

What is a standard method?

Answer 7

• Must include all of the details on how the task is performed, including:
  
  • Procedure - hand and body motions
  • Tools
  • Equipment
  • Workplace layout
  • Irregular work
  • Working conditions
  • Setup

Question 8

What are standard work units?

Answer 8

• The time needed to process the work unit depends on its starting condition.
  
  • Therefore this conditions must be specified
  • If the actual condition deviates from the specification, then extra time may be required to accomplish the task.
• Exactly what changes are made in the work unit by the task?
• What is the final state of the completed work?

Question 9

What are the two approaches used by companies to deal with employees breaks?

Answer 9

• Scheduled rest breaks during the shift
  
  • Typical - one 15-minute break in mid-morning and another in mid-afternoon.
  • Mainly used where worker interaction is essential.

OR

• An allowence is added to the basic time
  
  • This allows the worker to take breaks as required.
  • Only where there is minimal interaction among workers.

Note: Not both! - Also, lunch time does not count towards breaks.

Question 10

What are allowances?

What is the purpose of them?

Answer 10

• Basic time is adjusted by allowance factors to obtain the standard time.
• Purpose of allowances is to account for fatigue, to recognise that workers will not spend the whole shift working, and to cope with other contigencies.
• Allowances are additions to the basic time intended to provide the worker with the oppor- tunity to recover from the physiological and psychological effects of carrying out specified work under specified conditions and to allow for personal needs. The amount of the allow- ance will depend on the nature of the job. The way in which relaxation allowance is calculated, and the exact allowances given for each of the factors which determine the extent of the allowance, varies between different organizations.

Question 11

Explain the type of fixed allowances.

Answer 11

• Personal time
  
  • Toilet breaks, getting drinks, (6% typical)
• Basic fatigue
  
  • rest allowance to overcome general fatigue (4% typical)

Question 12

Explain Variable allowances

Answer 12

• These are given when the working conditions vary from those which are assumed in the basic allowances. There are three main areas which these allowances generally cover.
• Physical Strains
  
  • Force exerted
  • Posture
  • Vibration
  • Short cycle
  • Restrictive clothing
• Mental Strains
  
  • Concentration/ anxiety Monotony
  • Eye strain
  • Noise
• Nature of Working Conditions
  
  • Temperature and humidity Ventilation, Fumes
  • Dust, Dirt
  • Wet

Question 13

What are other types of allowances?

Answer 13

• Contingency Allowance
  
  • Additional allowance due to a problem with the task (e.g., raw material problem ) - not greater than 5%
  • Temporary basis - solve the underlying problem
• Training allowance - for teaching new workers
• Learning allowance - learning a new task
• Policy allowance (set by company policy, perhaps in wage negotiations, e.g., machine allowance)

Question 14

What are the equations for:

Basic Time

Standard Time

Answer 14

• Basic Time = Observed time x Rating/Standard Rating
• Standard Time = Basic Time + Allowances

Question 15

The average observed time for a repetitive work cycle of packing boxes in a direct time study was 3.27min. The worker performance was rated by an analyst at 90%. The company uses an allowance factor of 13%. What is the standard time for this task?

How many boxes can the company expect a standard worker to pack in a 8 hour working day with a 30min lunch break?

Answer 15

Observed time = 3.27 mins

Basic time = 3.27 x 0.90 = 2.94 mins

Standard time = 2.94 * 1.13 = 3.33 mins

Standard time = 3.33 mins/box. Therefore, a standard worker can pack 135 boxes in 7.5hrs.

Question 16

Draw the different rating scales

Answer 16

Question 17

Define direct time study.

Answer 17

• Time study is a technique for measuring the times and rates of working for the elements of a specified job, and for analysing the data to establish the time necessary for carrying out the job at a defined level of performance.
  
  • Direct and continous observation of a task using a stopwatch or other timekeeping device to record the time taken to accomplish the task.
  • While observing and recording the time, an appraisal of the worker’s performance level is made to obtain the basic take for the task
  • The data are then used to compute a standard for the task.

Question 18

What is the procedure for direct time study?

Answer 18

1. If the purpose of the time study is to establish a standard then it is essential tha the operation has been subjected to method study first.
2. Obtain and record basic information about the part/operation, the details of the process e.g., equipment used, jigs, tools, speeds & feeds etc., the operation, the working environment.
3. Define and document the standard method
4. Divide the task into work elements
5. Over a number of cycles, time the work elements and calculate the mean value to obtain the observed time T_obs
6. Evaluate worker’s pace relative to standard performance to obtain basic time (or normal time) (T_b = T_obs x PR)
7. Apply allowance factor to compute standard time (T_std = T_b + Allowances)

Question 19

What are reasons for breaking operation into elements?

Answer 19

• The analysis of the operation by elements may show slight variations in method that could not be detected so easily from an over-all study.
• An operator may not work at the same tempo throughout the cycle. An elemental time study permits seperate performance ratings to be applied to each element of the job.

Question 20

Answer 20

Question 21

What are the measurement problems associated with direct time study?

Answer 21

• How can we be sure that the limited “sample” of times observed is actually representative of the truth?
  
  • Is the mean of the observed times equal to the true value of the time to perform the task.
  • Unless you make a very large number of observations, you cannot make that claim.
• However, the number of observations that can be made during a direct time study is limited (cost, time , effort)
• So, the question is how many observations mus be made so that we are ‘fairly’ confident about the outcome of the study?

Question 22

Illustrate accuracy and precision.

Answer 22

Question 23

What does the term precision mean in work measurement?

Answer 23

• Precision is concerned with the expected variability within a single time study.
• Precision of a time standard is determined at a certain confidence level.
  
  • For example, the standard time calculated based on a time study for a task is 4.00 min, and we are 98% confident that the actual time is within 5% of that time.

Question 24

Explain how confidence is calcualted - using probability density function.

Answer 24

Question 25

A total of 9 cycles of an assembly operation have been observed during a direct time study.

The mean time = 1.30 min, and the corresponding sample standard deviation s = 0.20 min.

Calculate 95% confidence limits for the assembly time.

Answer 25

Question 26

Show by reaarranging a certain formula - we can find how many observations we need to take to get within certain error limits at a given level of confidence.

Answer 26

Question 27

Explain the learning curve phenomenon.

Answer 27

• Reduction in cycle time that occurs in a repetitive work activity as the number of cycles increases
• When a worker accomplishes a task over and over, the time required for each successive cycle decreases as he or she learns the task
  
  • At first the learning effect is rapid, and the cycle time decreases
  • As more and more cycles are completed, the cycle time reduction becomes less and less.

Question 28

learning curve theroy - Explain what the learning rate is.

what is the relationship between m and LR?

Answer 28

Question 29

Plot a learning curve for LR = 80%

Answer 29

Question 30

What are typical learning rates?

Answer 30

• Machining/Welding - where there are machines involved in tasks the LR is higher because the machines can’t get faster.

Question 31

What are the sources of learning curves (what makes improve) ?

Answer 31

• Self
  
  • ​Practice - Workers becomes familiar with the task - (moves from conscious to sub-conscious)
  • Worker makes fewer mistakes as the task is repeated
  • Hand and body motions become more efficient, and there is rhythm and pattern developed - strengthening of muscles
  • Minor adjustment in workplace layout to reduce distances - better tools and equipment.
• Organisation
  
  • ​Methods improvements
  • Fine-tuning of machinery and tooling
  • Development of special tooling
  • Technological improvements
  • Product design improvements
  • Leadership and better motivation of workers.

Question 32

What are factors impeding learning curves?

Answer 32

• Physical and mental limits
• Frustration
• Inertia
• Interruption/ forgetting
• Constraints imposed by other members of group
• Shortage of resources, lack of investment in new technology.
• Lack of Leadership
• Low motivation of workers.

Question 33

What things cause interruptions to the learning curve

Answer 33

• Learning curve effect tends to be disrupted by interruptions in production.
• For example due to:
  
  • Batch production, in which there are extended periods between repeat orders
  • Vacations
  • Raw material shortages.

Question 34

What are other factors affecting learning?

Answer 34

• Product complexity
  
  • More oppotunities for learning - higher T₁ and lower LR
• Preproduction planning
  
  • Fewer opportunities for learning - lower T₁ and higher LR
• Labour turnover - slower learning (higher LR)
• Plateau model - learning curve consists of two phases:
  
  • Start-up - log-linear model applies
  • Steady state - no further improvement

Question 35

Why does the plateau model occur (why does learning stop?)

Answer 35

• In a worker-machine system, worker is finally limited by the speed of the machine.
• No incenties for worker to make further improvements
• Management is unwillling or unable to invest in newer production technologies
• Management does not believe that learning can continue indefinitely.