Chapter 10: Time Studies Presented by Andira. Time study topics What are they? What can you accomplish with them? What methods and equipment do you need?

Chapter 10: Time StudiesChapter 10: Time StudiesPresented by

Andira

Time study topicsTime study topics

What are they?What can you accomplish with them?What methods and equipment do you need?What do data sheets (for recording times)

look like?How many observations do you need?How do you calculate allowances and

standard times (ST)?

Time StudyTime Study

Time studies are:– Observations of work and the time it takes to

perform it.– Method of determining a “fair” day’s work.

Frederick Taylor popularized times studies in the late 1800’s. Founder of the modern time study.

Work is divided into “elements” which are timed.

Time Study MethodsTime Study Methods Time studies can be conducted with

simply, low-cost equipment:– Stop watch (or other time recording devices:

time study board, computer, etc.)– Video and/or audio tape,– Time study forms, and other written notes,

Time study often combined with motion study (e.g. additionally looks at how motions are made)

Early studies analyzed physical work, but many of the principles/methods apply equally well to analysis of cognitive work (e.g. using verbal protocol studies.)

Functions of Time StudiesFunctions of Time StudiesEstablish work standards: e.g. recommended

times in which tasks should be completed by qualified, trained operators, without excessive fatigue,

Set expectations which are fair to both employee and company.

Identify sources of error, difficulties, sub-optimal aspects,

Improve existing processes, tools, or work environments,

Functions of Work StandardsFunctions of Work Standards

Establish reasonable productivity targets for experienced workers,

Provide productivity goals for training purposes,

Eliminate waste,Make processes more consistent,Reduce variability, improve quality.

Establishing Work StandardsEstablishing Work Standards Need to use “work measurement procedures” (e.g.

time studies) to set accurate work standards. Data must be specific to a particular

– process, – work environment, – tool set and – operator population

Estimates that are not based on data may not be sufficiently accurate for setting standards which have a large impact on company and employees.

Preparing for a Time StudyPreparing for a Time StudyThe steps in the process studied must already

be standardized; e.g. sequences have been determined.

Operator must be fully qualified, trained, and acquainted with standardized process being studied.

Must inform supervisor, union steward, department head.

Make sure all materials are available for the process.

Time Study ProcedureTime Study Procedure Select operator(s) Break task down into elements (before you start

study) Observe operators performing task: record time taken

for each element, over several cycles. Assign appropriate allowances (e.g. allow time for

necessary but non-productive activities, such as rest, cleaning eye-glasses, etc.

Determine appropriate work standards.

Selecting an OperatorSelecting an Operator

Get supervisor to help in identifying appropriate operators,

Ideally, you want someone qualified, trained and very familiar with process (may need to provide training before study) if your goal is to set standards.

Prefer an average or slightly above average operator.

Sometimes you have no choice of operator – only one person is available who does the job.

Divide Task into ElementsDivide Task into Elements

Work Element: a group of motions that is relevant to the experimenter’s study objectives.

(For cognitive work, divide verbal protocol into “utterances” roughly equivalent to a single thought.)

Watch for several cycles (before study starts) to identify useful work elements for the task.

Look for easily identifiable start and end signals, often auditory or visual. Examples:– The “clink” of a part being set on the fixture,– Setting a cup on the counter in front of the customer,– The moment when a customers hand touches the credit card as the

cashier hands it back.

Divide task into elements (cont)Divide task into elements (cont)

This is not so easy to do! Preparatory observations: Devote a half hour or so to

observation of the task: start to identify relevant operations, and practice recording them.

Data sheets: Create a spread sheet or recording scheme to help you record elements quickly and easily.

Work element revisions: new elements may keep popping up over several days! You may also find that two or more elements should really be combined. Example: for cashiers, cleaning and organizing, chatting with co-workers are just different ways of “waiting” for customers.

Level of abstraction. The size of the divisions between elements depend on what you need to do in the analysis.

Record Significant InformationRecord Significant Information

Time Study Observation form provides space for: – Study date– Observer Name– Operator Name– Department,– Study Start Time– Study End Time

Also useful to record:

– Machines– Jigs, fixtures– Working conditions– Sketch of work area

layout

Positioning ObserverPositioning Observer

Stand slightly behind operator, usually easier than sitting – easier to follow movements of operator or get out of way).

Try not to distract or interfere with operator.

Avoid distracting conversation that may upset routines.

Divide Task into ElementsDivide Task into Elements

Smallest unit that can be accurately timed is about 0.04 minutes (approx 2 to 3 sec).

Breakpoints: use sound and sight both to identify breakpoints between elements, (e.g. sound of a part clinking in “finished” bin, sound of a latch clicking shut, etc.)

ExampleExampleCaribou coffee study: Corporate GoalsCaribou coffee study: Corporate Goals

Stated goals: To streamline operations so that employees will have more time to interact with the customers.

Additional benefits: customers will be happier if they do not have to wait as long.

ExampleExampleCaribou coffee study: Analysts’ GoalsCaribou coffee study: Analysts’ Goals

To understand how long each activity took, To identify what “typical” processes were, To streamline processes, where possible, To set work performance standards, and customer

expectations, – How long should customers expect to wait for a cup of

coffee?– How should performance of stores be assessed?– What performance goals should trainee’s aim for?

Identifying work elementsIdentifying work elements

It can take several hours or days of observation to identify all work elements and to come up with a consistent naming.

New elements may keep appearing, over time,

Two methods for recording Two methods for recording element timeselement times

Snapback method: after recording the end of an operations, “snapback” or reset the stopwatch to zero.– Advantages: don’t need to compute element duration, don’t need to record delays or “foreign elements.”– Disadvantages: may loose some time during

“snapback” Continuous method: Start timer at zero at start of

all observations, let it run continuously. Record elapsed time at element breakpoints.– Advantages: all time is recorded, operators and unions

like that, makes method easy to sell,– Disadvantages: may take more computational effort

Data recording sheetsData recording sheets

You may need to devise data recording sheets that fit the study goals, the task and the type of data.

You may use the example data recording sheets in the book, but they are not meant to fit all situations,

Examples:– Recording a fixed sequence of operations.– Recording a variable sequence of operations,– Recording arrival and wait times in a line,

Recording a fixed sequence of operations

Foreign Elements

Repeated cycles of the sequence

Examples of Data Recording Sheets:Examples of Data Recording Sheets:for recording operations that happen in an for recording operations that happen in an unpredictableunpredictable

order: custom assembly of one-off productsorder: custom assembly of one-off products

Time and Motion Study. Site 2: Regular Machine Page

Barista: employee observations Friday, mo/day/year

T 2.35 3.56 4.31 5:04 5:23 5:42

Op Wash Fill Steam Wait Pour C Check M

T 5:55 6:14 6:21 7:55

Op Pour M Finish Place Super.

T

Op

Examples of data recording sheets:Examples of data recording sheets: for sampling length of time customers wait in a linefor sampling length of time customers wait in a line

Time and Motion Study. Site 3: Drive Thru page ________

Coffee Order Line: customer observations Date ____, 20__

Entry clock time (in min and second) when car enters line or turns away

Short description (color, type: sedan, station wagon, SUV, pick-up, etc.)

"X" if car turns away from line or exits line prematurely

No# already in first part of line.

Order Clock Time (in min and seconds) when car stops at order kiosk.

Other types of dataOther types of data Chanhassen: Customer Arrival Rates

Ave. for 1/30/06 and 1/31/06, 6:30 - 10:30 AM

23

3832

39 39

27 28

20

0

10

20

30

40

50

6:30

- 6:

59

7:00

- 7:

29

7:30

- 7

: 59

8:00

- 8:

29

8:30

- 8:

59

9:00

- 9:

29

9:30

- 9:

59

10 -

10:3

0

Time

Nu

mb

er#

En

teri

ng

Ca

sh

ier

Lin

e

How many cycles should be How many cycles should be observed?observed?

There are several ways of estimating the number of cycles that should be observed in order to obtain accurate standard:

The statistical method. The General Electric (G.E.) method,

The Statistical Method The Statistical Method Estimate numbers of observations required Estimate numbers of observations required

Goal: to limit the error in the estimate for the mean operation time (OT) to plus or minus a given percentage, k.

Equation to estimate n, no# of observations needed:

n = t s

k x Problem: If you haven’t taken any observations yet, how can

you know x and s ? You can’t. Must estimate them first with a small pilot study.

2




n = t s



2




n = t s



2


Procedure: it takes two steps to calculate sample size:1. Pilot study: Take small set of observations or use historical

data to estimate the parameters: Mean OT: xp (mean operation time observed in the pilot study), use

xp as an estimate of x for the full scale study Sample standard deviation, s.

2. Full scale study. Use these parameters to calculate sample size of a larger study.

ExampleExampleEstimation of number of ObservationsEstimation of number of Observations

1. Pilot study: you take n = 25 readings for an element. You get 25 readings, x1 through x25: 0.28, 0.24, 0.33, 0.33, etc.

When you summarize your data, you find: xp = Σ xi /25 = 0.30, where xp is the average time required

to perform the work element. s = Σ (xi – xp)2 = [(.28-.30) + (.24-.30) + …]2 = 0.09 √ n – 1 √ 25 – 1 Use s = 0.09 from the pilot study to estimate s for the larger

study.




to perform the work element. s = Σ (xi – xp)2 = [(.28-.30) + (.24-.30) + …]2 = 0.09 √ n – 1 √ 25 – 1 Use s = 0.09 from the pilot study to estimate s for the larger

study.




s = Σ (xi – xp)2 = [(.28-.30) + (.24-.30) + …]2 = 0.09 √ n – 1 √ 25 – 1 Use s = 0.09 from the pilot study to estimate s for the

larger study.




s = Σ (xi – xp)2 = (.28-.30)2 + (.24-.30)2 + … = 0.09 √ n – 1 √ 25 – 1 Use s = 0.09 and xp from the pilot study to estimates to

“jump start” the calculation for the larger study.

Example (continued)Example (continued)Estimation of number of ObservationsEstimation of number of Observations

1. Full scale study: how many observations of an element do you need to take in a larger time study, in order be 95% confident that your measurement of x is within k = 5% of the true value?

k = 5% (acceptable error) α = 1 – confidence level = 1 - .95 = .05 From pilot study we estimated: xp = Σ xi = 0.30, s =0.09 Now you need to look up t. You can look up t if you know α and the

degrees of freedom (d.o.f):

d.o.f. = np - 1 = 25 – 1 = 24

n = t s = 2.064 x 0.09 = 153.3 observations

k x 0.05 x 0.30 (round up to integer)

2 2





d.o.f. = np - 1 = 25 – 1 = 24



2 2





d.o.f. = np - 1 = 25 – 1 = 24



2 2

The t-distribution (pg. 701)The t-distribution (pg. 701)Look up t-value in the tableLook up t-value in the table (or use the Excel function)(or use the Excel function)

Degrees of freedom, d.o.f.

Alpha, α

The t-distribution (pg. 701)The t-distribution (pg. 701)

Degrees of freedom, d.o.f.

Alpha, α

d.o.f = 24t = 2.064





d.o.f. = np - 1 = 25 – 1 = 24. From table: t = 2.064



2 2

The General Electric (G.E.) Method The General Electric (G.E.) Method Assumes more error in smaller measurements – not much Assumes more error in smaller measurements – not much

attention to typical variability in the operation itself)attention to typical variability in the operation itself)

Using the data Using the data from our in-class pilot studyfrom our in-class pilot study

Task: collating & stapling 3 sheets of paper Operations:

1. Assemble sheets 1, 2, 3

2. Hand-off/Align/Staple

Can you the data from our in-class pilot study to estimate no# observations needed to insure that we are:

– 95% confident (α = 0.05) that our answer is within:– 10% error (k=.10)

Time Study Data Sheet

Process: Collating and Stapling

Day: Wed. November 17, 2010

Start time: 11:14 AM

Location: Room 108, Mechanical Engineering Bldg., Minneapolis, MN

cycle Operation 1 Operation 2

1 5 2

2 5 4

3 6 5

4 5 5

5 4 4

Average 5.0 4.0

StDev 0.7 1.2

Calculate Calculate nn, sample size needed , sample size needed for operation 1for operation 1

xp = 5.0

s = 0.71

k = 0.10 (10% error); Let alpha = 0.05

n = t s 2 = ? *0.71 2

k xp .10 * 5.0

What value should we use for t?


xp = 5.0

s = 0.71

k = 0.10 (10% error); Let alpha = 0.05

n = t s 2 = 2.776 * 0.71 2 = 15.4 obs.

k xp 0.10 * 5.0

What if we decrease k to 5% ?


xp = 5.0

s = 0.71

k = 0.05 (5% error)

n = t s 2 = 2.776 * 0.71 2 = 62.7 obs.

k xp 0.05 * 5.0

The no# of observations greatly increases!

““Foreign” ElementsForeign” Elements

A foreign element is one that does not explicitly belong in the sequence

Typically one subtracts them from observations (when possible) to get a more “true” time.

Examples:– Worker has to adjust glasses,– Must speak to supervisor,– Rest break, lunch break,– Equipment search: must find new wrench.

Foreign ElementsForeign Elements

Some foreign elements can be eliminated, But others cannot or should not be:

– Foreign elements can an idea of how much extra time (e.g. allowances) is reasonable to allow in an operation.

AllowancesAllowances

Allowances refers to extra time allowed, beyond completion of the task itself

Some allowances are necessary for health and long term efficiency (like rest breaks),

Others are pragmatically necessary, (like time for picking up dropped tools or consulting with supervisor)

Computing Standard TimesComputing Standard Times

A standard time is a combination of:– The time it takes to complete a task– Allowances.

This approach recognizes that it is not possible to work at top efficiency all day, all the time.

Methods for computing Methods for computing standard timesstandard times

Method 1: Add in allowances: compute required rest.

ST = NT + NT x allowance

= NT (1 + allowance) Method 2: Compute allowances as a % of task time.

ST = NT / (1 – allowance)

ST = Standard Time: the time in which you expect workers to complete an operation.NT = Normal Time: time required to complete an operation for a given operatorOT = Mean Observed Time to complete an operation (from time study). For an experienced operator who works at a 100% rate (R), OT = NT, and NT = OT x R/100 where R = the performance rating of the operator.

Example: Method 1Example: Method 1

Suppose that your time study shows that it takes 3.5 minutes on average to complete a task. Rule of thumb for manual tasks: 15% allowances.

ST = NT + (NT * allowance) = 3.5 min + (3.5 min * .15) = 3.5 min + 0.525 min = 4.03 minutes.

Experienced operators will be expected to complete the task in this time.

But how can you estimate But how can you estimate allowances?allowances?

Observe foreign elements – what percentage of total time do they comprise?

Chapter 11 outlines many additional methods for calculating allowances:– For personal needs,– For fatigue reduction

Next, identify possible sources Next, identify possible sources of fatigueof fatigue

Abnormal posture, Muscular force, Ventilation, Lighting, Visual strain Mental strain, Etc.

(see check list, Table 11 – 2).

Question:Question:

Does it make sense to estimate:– Allowances– Standard time– Efficiency

for a cashier who may spend much time waiting for customers to arrive?

How should Standard Times be used How should Standard Times be used to Evaluate and Motivate People?to Evaluate and Motivate People?

What happens when you set up a reward system? – All jobs have same standard time, but some are

more difficult,– Busy-time often results in slower production

because you are exceeding capacity,Do you always get the behavior you expect?

Time Sheet Time Sheet

Operation Start time End time Total time

Average:

Date: Study start time:

Chapter 10: Time Studies Presented by Andira. Time study topics What are they? What can you accomplish with them? What methods and equipment do you need?

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