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Table of contents

1. Laboratory Introduction------------------------------------------------2

2. Operation Analysis-Flow Process Chart-----------------------------5

3. Activity Chart (Right/Left Hand Activity Chart)-----------------12

4. String Diagram ----------------------------------------------------------16

5. Motion Study (Therbligs Technique)-------------------------------20

6. Direct Time Study Method-------------------------------------------25

7. Work Sampling Measurement Method---------------------------30

8. Learning Curves Theory-----------------------------------------------38

1

1. Laboratory Introduction

1.1 Introduction

This laboratory class aims to provide students with a general knowledge of

work study and methods engineering. Also, the laboratory session is an

introductory laboratory in which students obtain general knowledge of human

factor engineering as well as the nature of experiments and laboratory

exercises that are covered throughout the semester. Safety instructions that

must be followed during each laboratory session will be explained and

discussed with students.

Work is an activity in which one exerts physical and mental effort to accomplish

a given task or perform a duty. In fact, work study or methods engineering

refers to the analysis and design of work methods, including the tooling,

equipment, workplace layout, human activity, and environment. Work study

aims to analyse a task’s contents to determine the time that should be allowed

for a qualified worker to perform the task. Generally, there are several

engineering methods to analyse task contents as well as different charts and

diagrams to measure task time.

Main objectives in methods engineering or work studyare:

Increase productivity and efficiency

Reduce cycle time

Reduce product cost

Reduce labour content

Generally, there are six main steps to accomplish methods engineering or work study:

1. Define the problem and objectives

2. Analyse the problem

3. Formulate alternatives

4. Evaluate alternatives and select the best solution

5. Implement the best method

6. Audit the study (review the success of the method)

2

In general, there are four main types of charts and diagrams that are used to

analyse the task and operations:

- Operation chart: Graphical and symbolic representation of the

operations used to produce a product.

- Process chart: Graphical and symbolic representation of the processing

activities performed on something or by somebody. It includes a flow

process chart, a worker process chart, and a form process chart.

- Flow diagram: represents the drawing of the facility layout with the

addition of lines that represent the movement of materials or workers

within the facility.

- Activity chart: A listing of the activities of one or more subjects (e.g.,

workers, machines) plotted against a time scale to indicate graphically

how much time is spent on each activity

These charts and diagrams are commonly used to analyse existing operations,

sequences of operations, or other work activities to make improvements.

The main objectives of charting and diagramming techniques are: • Reduce cycle time

• Eliminate unnecessary steps in an operation

• Mitigate safety hazards

• Improve product quality

• Propose new way to complete the operation or design new operations

1.2 ObjectivesThe objectives of this laboratory session are as follows:

To gain a general background and knowledge about work study definitions,

work study methods, and its applications.

To gain a wide description regarding to work study laboratory experiments,

tools, and equipment that will be used in the experiments.

To learn the various types of charts and diagrams used in work study and in

this laboratory.

3

1.3Requirements (Individual lab report)

A short laboratory report includes the following(Internet search lab):

1. Work study definitions, objectives, methods, and applications

2. The different types of charts/diagrams that are used in work study to

analyse operations and tasks.

3. In brief, provide an explanation of the work measurements and

methods (time study).

4. A list of commercially available software tools that are used in the work

study field to motion and time study.

4

2. Operation Analysis-Flow Process Chart

2.1 IntroductionThe Flow Process Chart was developed many years ago as a means of listing

out the activities performed by a worker, with quantities, times, and movement

distances. In fact, flow Process Chart is chart that uses 5 symbols to analysis

and detail the work performed on a material or work part through a sequence of

operations and other activities. It uses five symbols to detail the work performed

on a material or workpart as it is processed through a sequence of operations

and activities (ASME, 1972):

Operation ( O) – Processing of a material, an object is changed

intentionally, assembled or dis-assembled to/from another, or prepared

for another process, or information is given or received.

Inspection ( ) – Check for quality or quantity, an object is examined for

identity, quality, or quantity.

Move ( ) – Transport of material to new location, an object is moved

from place to place, except as part of an operation

Delay ( D) – Material waiting to be processed or moved, The next

planned step cannot take place immediately

Storage ( ) – Material kept in protected location, an object is stored

under some control

In addition, the flow process chart is a simple half-text, half-picture method of

showing the steps in a process, using symbols to indicate the type of action

being taken and text to give details of the action. The Standard form for flow

process chart is showed in Figure 1.

This exercise plays an important part in forming a critical way of thinking about

the design of work, that is, making full use of both hands, eliminating

unnecessary tasks and delays, shortening distances, and simplifying the tasks

involved. Such experiences aim to make the student critically aware of

deficiencies and avoidable effort whenever work designs are examined, and

help to develop a consciousness of the need for high productivity.

5

Questions Related to Material Make or buy decisions: Should the part be produced in the factory

or purchased from an outside vendor? Questions Related to Operations and Inspections

Is the operation time too high? Is the inspection operation necessary?

Questions Related to Moves How can moves be shortened or eliminated by combining or

eliminating operations? Can the level of mechanization in material handling be increased? Questions Related to Delays Is the delay avoidable? What is the reason for the delay? Can the reason be eliminated? Questions Related to Storage Is the storage necessary? Why can’t the material be move immediately to the next

operation?

There are five important questions that are used to improve the steps of

process and contents of the flow process charts in order to reduce the waste

time, effort and cost of the specific process. These questions are:

There are three principal types of process charts:1. Flow process chart – analysis of a material or workpiece being

processed

2. Worker process chart – analysis of a worker performing a task

3. Form process chart – analysis of the processing of paperwork

forms

2.2 ObjectivesThe objectives of this laboratory experiment are as follows:

To use the flow process chart type of task analysis to describe a two-

operation process:

6

First: to describe a simple assembly process task in a laboratory

setting which simulates an industrial task process (laboratory

experiment).

Second: to describe a task process of changing a flat tire, this

demonstrates a non-industrial task. This task will be given to a student

with a text and video (non-laboratory experiment).

Obtain an improved solution and recommendations through critical

questioning of the contents of the chart for the both tasks: assembly and tire

change.

7Figure 1: Standard form of flow process chart

2.3 InstrumentA wooden plate and two uprights have small wooden plates with 6 bolts for

each upright plate and each bolt has nuts and washers (Hand tool dexterity

test, model 32521, Lafayette Instrument, US; see Figure 2) for a total of 12

bolts. The device has the following dimensions: 0.76×0.40×0.40 m. The

wooden plate simulates the assembly task because this type of task is common

in many different factory jobs, particularly in the industrial sector, and the

operator can assume an awkward posture to perform this type of task. Two

types of hand tools (10-inch Crescent wrench and screwdriver) are used to fix

the bolts to the wooden plate (see Figure 2).

A digital stopwatch (Dad-7141, China) also records the time to complete a task.

The stop watch has these features: 10-500 laps and split memory with

1/100sec memory recall during operation, calendar and time (12/24 hour

format), 5 daily alarms, countdown and repeat (9h 59m 59s) and water

resistance (See Figure 3).

8

Figure 3: Digital stopwatch. (Dad-7141, Japan)

Assembly wooden plate, hand tools and bolts with nuts and washers.

2.4 Experiment Procedures (assembly task)The experiment procedures are as follows (group work):

1. Participants are given a brief introduction to the experiment in order to

familiarize themselves with the procedure. They are provided with

instructions and advised on how to assemble the wooden plates.

2. Participants devise an assembly procedure in which the work is done

largely by the dominant hand, and helped by the other hand.

3. One student in the group assembles all the components supplied

(without any arrangements for the bolts, nuts, washers and hand tools). In one plate assembly the student is required to fix 12 complete

bolts sets (consisting of bolts, nuts and washers) with different sizes on

both upright plates.

4. The students must work at a pace that can be maintained for an 8

hours shift. Assuming that pay is $25 per hour; he needs to complete

75 assembled plates during the shift.

5. A second student records the time to complete each assembly (i.e., the

cycle time) as well as the time to affix each bolt as an element times or

subgroups of element times. These times are recorded in the flow

process chart as illustrated previously in Figure 1.

6. A third student records the order of operations in the flow process chart

and any events of note, such as bad parts or a difficult insertion task.

7. As the group repeats the assembly task and similar measurements,

they need to arrange the components in individual bins depending on the type and size of bolt and hand tools in a line in front of the student.

9

2.5 Non-industrial process task (Tire change task)In this exercise, the group needs to use the flow process chart to describe the steps of the service task which is changing a flat tire (non-industrial task). The exercise is:

A motorist experienced a flat tire on the driver side rear wheel of his car and

went through the following procedure to replace the flat tire with the spare. The

tire change occurred in the middle of the day in his own driveway about six

metres in front of his garage.

He first secured the other three wheels of the car with three bricks from his

garage to prevent the vehicle from rolling (two trips back and forth to the

garage) with a distance of 11.5m. He then took out the jack, crank, and lug nut

wrench from the trunk of the car, traveling a distance of 1.5m. He then removed

the spare tire from the trunk and placed it near the rear left wheel with a time of

1.04 min. Next, he proceeded to position the jack under the car at the

recommended support beam on the car frame with a time of 0.44 min. He then

began to turn the crank to elevate the car with a time of 1.09 min. After the left

rear portion of the car was lifted a few inches, but before the flat tire was lifted

from the driveway surface, he used the lug nut wrench to loosen the five lug

nuts securing the tire to the wheel hub with time 0.85 min. He then returned to

the task of elevating the car, turning the jack crank until the flat tire was

completely off the driveway surface (0.92 min).

The next step was to remove the loosened lug nuts, placing them in a nearby

position within reach (0.12 min). The flat tire was then removed with time 0.10

min and lifted into the trunk with a distance of 2.5 m. The motorist then moved

the spare tire into position with a distance of 2.5 m and lifted it onto the five

studs protruding from the wheel hub with a time 0.22 min. He then reached for

the five lug nuts, one at a time, placing them onto the studs and rotating them

until finger tight (0.60 min). The lug nut wrench was then used to tighten the five

nuts with a time of 1.01 min. With the tire secure, he proceeded to lower the car

by cranking the jack down slowly until the spare tire supported the car with a

time of 1.14 min. For good measure, he again tightened the five lug nuts now

that the car was securely on the ground (0.62 min). He then collected the

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hardware (0.09 min), put it back into the trunk (2.5 m), and removed the bricks

from the other three rear right tire, front right tire and front left tire wheels with a

distance of 1.5, 3.6 and 1.5, respectively. Then, he put them back into his

garage with distance 9 m.

Document this tire changing procedure using a worker process chart.

2.6 Results of the Experiment

A laboratory report includes the following:

a. Compile a description of the assembly task on the Flow Process Chart (Figure 1). Get the mean time for the cycle; add in the transport distances (if possible) and totals and list all the actions required. Also, you need to add the worker costs for an 8-hours shift.

b. Provide the flow process chart for the new design of the assembly task as mentioned in step 7 (section 2.4). Get the mean time for the cycle; add in the transport distances (if possible) and totals and list all the actions required.

Compile a description of the tire change task on the Flow Process Chart (Figure

1). Get the mean time for the cycle; add in the transport distances (if possible)

and totals and list all the actions required.

11

3. Activity Chart (Right/Left Hand Activity Chart)

3.1 IntroductionIn general, the activity chart is a listing of the activities of one or more subjects

(e.g., workers, machines) plotted against a time scale to indicate graphically

how much time is spent on each activity. There are various types of activity

charts and the right/left hand activity chart is one of the common activity charts

that are used to describe the manual repetitive task such as manual assembly

task.

The usual is to provide brief descriptions of the work activities against a vertical

time scale. The activities in the activity charts are indicated by vertical lines or

bars instead of using symbols for the work activities as in the other charting

such as process charts. When the bars are used, they are shaded or colored to

indicate the kind of the activity being performed as illustrated in Figure 1.

However, the right-hand/left hand activity chart explains the left and right

activities during performing a task that is highly repetitive. The chart includes

four columns one column for the right hand, second column for the left hand

and the other two columns for the time (min) and total task cumulative time

(min) as shown in Figure 2 also, represents the Standard Form for

right-hand/left hand activity chart. The right-hand/left hand activity chart is also,

12

Figure 1: Shading Formats for Activity Chart

called Workplace Activity Chart since it is usually describes a repetitive task

which is performed at single place such as assembly task in production line.

The main objective of this activity chart is to achieve a more even balance of

the workload during task performing between the right and left hands.

Left hand (activity description)

Time (min)

Right hand (activity description)

Cumulative time (min)


To understand and use the activity chart (Right/Left Hand Activity Chart) while

performing a task:

To describe a simple assembly process task in a laboratory setting

that simulates a simple repetitive task, such as a basic assembly task

(laboratory experiment) and create an appropriate right/left hand

activity chart for the simple repetitive task.

Understand how to improve the simple repetitive task's activities and create

the proposed right/left hand activity chart for the improved activities.

3.3 InstrumentThe Grooved Pegboard (Simple assembly tool test, model 32025, Lafayette

Instrument, US; see Figure 3) is a manipulative dexterity test that consists of 25

holes with randomly positioned slots. the pegs are keyhole-shaped must be

rotated to match the hole before they can be inserted, requiring more complex

visual-motor coordination.

13

Figure 2: Standard Form of Right /left Hands Activity Chart


The stop watch has these features: 10–500 laps and split memory with




3.4 Experiment Procedures (simple repetitive assembly task)

The experiment procedures are as follows (group work):



instructions and advised on how to insert the pegs inside the holes.

2. In the first part of the experiment (present method), one student in

the group needs to hold the board with his left hand and is required to

14


Figure 3:Grooved pegboard tool and pegs.

pick up the peg and then insert it into the hole in the board with his right

hand.

3. The student needs to insert 25 pegs in order to complete the assembly.

4. A second student records the order of left- and right-hand activities in

the right/left hand activity chart form. At the same time a third student

records the time for each activity that the subject needs to complete the

assembly task.

5. The group then repeats the repetitive assembly task and similar

procedures, but in the second part of experiment (proposed method), the student needs to put the board on the table and then put

the first 12 pegs near his right hand and the other 13 pegs near his left

hand. After that, the subject he needs to pick up the pegs and insert

them into the holes with both hands, simultaneously. The other two

students are required to record the descriptions of the activities for both

hands as well as the time, as mentioned in step 4.


The laboratory report includes the following:

a. Construct a right-hand/left-hand activity chart for the present method and

record the cumulative time of the task.

b. Construct a right-hand/left-hand activity chart for the proposed method

and record the cumulative time of the task.

c. State the results summary for both the present and the proposed

methods.

15

4. 4. String Diagram

4.1 Introduction

The string diagram is a scale plan or model on which a thread is used to trace and

measure the path of workers, material or equipment during a specified sequence of

events. The string diagram is mostly used for studying workers’ movement.

The work study person observes the movement of a worker over enough period of

time. The observations may be recorded in a simple movement study sheet. Then, the

string diagram can be constructed. The examination of the diagram and the

development of the new layout can now proceed with templates being used and the

pins and templates being moved around until an arrangement are found by which the

same operations can be performed with a minimum movement between them.

The string diagram is a useful aid in explaining proposed changes to management,

supervisors and workers.

4.2 Objectives

The objectives of this laboratory experiment are as follows:

To understand the concept and the technique of String diagram.

To let students practice on the construction of string diagram from data submitted in

a movement study sheet.

Figure 1: movement study sheet

16

4.3 Materials

Pieces of cork (50cm*50cm) or bigger

Pinpoints

Piece of string

Figure 2: Pieces of cork Figure 3: Pinpoints

Figure 4: Piece of string

4.4 Experiment Procedures

Each group has to construct 2 string diagrams using the tools given:

1. Participants are given a brief introduction to the experiment. They are

provided with instructions and advised on how to construct a string diagram

2. Using the data presented in the submitted movement study sheet. The

students required to put the pinpoints on the cork as the work layout and

17

make connection between the pinpoint using the string step by step. After that

they need to determine the length of the string used in the process.

3. The students will construct another string diagram by using another piece of

cork and pin points but they need to make a change in the position of

pinpoints to make the string used shorter than before by the same way of

connections. In other words, the second diagram shows the proposed

improvement in layout.

Figure 5: work layout

4.5 Requirements

A. Construct a string diagram for the work layout given in the class by using the material described above.

B. Construct a string diagram for the work developed (improved) layout by using similar set of material.

C. Make a comparison between the diagrams and the length of the strings used to show how long moving distance you saved.

5. Motion Study (Therbligs Technique)

18

5.1 IntroductionMotion study is an analysis of the basic hand, arm, and body movements of

workers as they perform work. Frank Gilbreth was the first to analyze and

classify the basic motion elements. He called each hand motion a therblig.

Therbligs is spelled backward except for “th”. Therbligs are Basic building

blocks of virtually all manual work performed at a single location (so the primary

interest is the hand motions). Therbligs involved 17 letters symbols that are

descriped the hands motion (right and left hands motion) of worker while

perform a manual task (i.e. hand tasks). The list of 17 therbligs symbols are:

1. Transport empty (TE) – reach for an object with empty hand – today we

call it “reach”.

2. Grasp (G) – grasp an object by contacting and closing the fingers until

control has been achived.

3. Transport loaded (TL) – move an object with hand and arm – today we

call it “move”.

4. Hold (H) – hold an object with one hand.

5. Release load (RL) – release control of an object.

6. Use (U) – manipulate/use a tool.

7. Pre-position (PP) – position object for next operation.

8. Position (P) – position object in defined location.

9. Assemble (A) – join two parts

10.Disassemble (DA) – separate multiple parts that were previously joined

11.Search (Sh) – attempt to find an object using eyes or hand

12.Select (St) – choose among several objects in a group (hand-eye

coordination is involved)

13.Plan (Pn) – decide on an action (a short pause or hesitation تردد in the

motions)

14. Inspect (I) – determine quality of object using the eyes

15.Unavoidable delay (UD) – waiting due to factors beyond worker control

16.Avoidable delay (AD) – worker waiting

17.Rest (R) – resting to overcome fatigue.

19

Effective therbligs:Physical Basic Motion Elements:

Transport empty Grasp Transport loaded Release load Use Assemble Disassemble

Mental B asic E lements : Inspect

Delay Elements : Rest

Ineffective therbligs:Physical Basic Motion Elements:

Hold Pre-position

Physical and Mental Basic Motion Elements:

Position Search Select

Mental Basic Elements: Plan

Delay elements: Unavoidable delay Avoidable delay

The therbligs classified into two main sections; effective therbligs and

ineffective therbligs and these classifications are:

In general, Therbligs include physical elements such as transport, grasp

assembly and it refers to any activity that needs physical hands movements.

Also, therbligs include mental elements such as position, search and select and

it refers to any activity that needs to information process and visual effort rather

than physical effort.

Micromotion Analysis is analysis of therbligs that make up a repetitive task and

the standard form of therbligs showed in Figure 1. The objectives of therbligs

analysis are:

Eliminate ineffective therbligs if possible; for example, eliminate the need to search for parts or tools by positioning them in a known & fixed location in the workplace.

Avoid holding objects with hand – Use workholder Combine therbligs – Perform right-hand and left-hand motions

simultaneously Simplify overall method resequence of therbligs in the cycle Reduce time for a motion, e.g., shorten distance of therbligs such as

transport loaded

20

Seq. of activities

Left hand Therbligs Right hand Cumulative Time


To understand and use the therblig analysis technique for hands motion while

manual assembly task and create the present therbligs list of right and lift

hands while perform a simple assembly task.

To learn the various symbols of therbligs that used to analysis the hands

motion activities.

Understand how can make improve in the therbligs symbols in order to

improve the hands motion activities and create the proposed list of therbligs

chart for an improved activities of right and left hands activties.

5.3 InstrumentRoeder Board Manipulative Aptitude Test (Model 32026; Lafayette Inst.

Company; see Figure 2) is the test that uses to measure hand, arm, finger

dexterity, and speed. The board of the roeder board has four receptacles for

holding washers, rods, caps, and nuts. The performance board also is

comprised of a horizontal T-bar and 40 inserts arranged in a predetermined

pattern.

21

Figure 1: Standard Form of Therblig Analysis Sheet






5.4 Experiment Procedures (Cutting saw machine task) The experiment procedures are as follows (group work):




22


Figure 2: Roeder Board (Model 32026; Lafayette Inst. Company) and four receptacles for holding washers, rods, caps, and nuts.

2. In the first part of the experiment (present method), one student in

the group needs to assemble all four parts washers, rods, caps, and

nuts together and insert into the hole in the board after pick-up these

parts from pin that placed in the front of the student. Note: In the current

method all the four parts washers, rods, caps, and nuts are placed in

one pin together.

3. The student requires to repeat this activity for 8 times which means that

he needs to complete 8 assembly tasks and assemble only 8 holes in

the board.

4. A second student records the order of hand motions (right and left

hands) of the student activities (e.g., reach, search, grasp, transport

loaded, position, assemble and etc.) as mentioned previously. At the

same time a third student records only the cumulative time of each

complete assembly cycle that means he needs to records the

cumulative time for 8 cycles.

5. The group need to complete all the hands motions data of both hands

as well as the cumulative time in the form of Therblig Analysis Sheet.

6. As the group repeats the assembly task and similar procedures, but in

second part of experiment (proposed method) the students need to

arrange and separate the four parts washers, rods, caps, and nuts and

place each part the identified location on the board and also, they can

combine the washers and nut together and put both on the T-bars to

reduce the time and effort of search and assemble.


A laboratory report includes the following:

a. Construct a Therblig analysis sheet chart for the present method and complete the cumulative time of the task.

b. Construct a Therblig analysis sheet chart for the proposed method.

23

6. Direct Time Study Method

6.1 IntroductionDirect Time Study is a direct and continuous observation of a task using a

stopwatch or other timekeeping device to record the time taken to accomplish

the task. Direct time study is also known as stopwatch time study method. The

direct time is one of the most work measurements that uses to determine the

standard time of a task. However, while observing and recording the time, an

appraisal of the worker’s performance level is made to obtain the normal time

for the task. Since, the performance rating in this method is important in order

to determine the standard time. The normal time in this method obtain by

multiply the observation time of the work element with worker performance

rating in percentage. The data are then used to compute a standard time for the

task after adding the PFD allowances (personal needs, fatigue and delay

allowance time). The direct time study is much more appropriate for repetitive

tasks (batch and mass production).

- In order to implement the direct time study (DTS) the work study engineer should follow the following procedures:

1. Define and document the standard method

2. Divide the task into work elements

3. Time the work elements to obtain the observed time Tobs

4. Evaluate worker’s pace relative to standard performance to obtain

normal time Tn

Called performance rating (PR %)

Tn = Tobs(PR) (1)

5. Apply allowance factor to compute standard time

Tstd = Tn(1 + Apfd) (2)

24

- The engineer should be consider the following guidelines while divide task into work elements:

• Each work element should consist of a logical group of motion elements.

• Beginning point of one element should be the end point of the preceding

element.

• Each element should have a readily identifiable end point.

• Work elements should not be too long nor too short (less than 3 sec).

• Separate irregular elements (non-frequent element) from regular

elements.

• Separate manual elements from machine elements.

• Separate internal elements (during machine work) from external

elements.

- There are two important stopwatch timing methods used in direct time study to record the observation time:

1. Snapback timing method Flyback – stopwatch is reset to zero at the

start of each work element

2. Continuous timing method – stopwatch is allowed to run continuously

throughout the duration of the work cycle


To understand the concept and the technique of direct time study method in

time measurement.

To learn the direct time study in order to determine the normal time and

standard time for a task.

To learn and understand the calculation of the appropriate number of time

readings (i.e., number of time observations) that are need to give an accurate

standard time value for a task.

6.3 Instrument

25

A wooden plate and two uprights have small wooden plates with 6 bolts for

each upright plate and each bolt has nuts and washers (Hand tool dexterity

test, model 32521, Lafayette Instrument, US; see Figure 2) for a total of 12

bolts. The device has the following dimensions: 0.76×0.40×0.40 m. Two types

of hand tools (10-inch Crescent wrench and screwdriver) are used to fix the

bolts to the wooden plate (see Figure 1).






6.4 Experiment Procedures (Cutting saw machine task) The experiment procedures are as follows (group work):

26





instructions and advised on how to assemble the wooden plates.

2. The students need to divide task into work elements. The assembly task

includes 12 bolts so; the student should consider each bolt as a one

work element (12 work elements).

3. They need to use the Form of Direct Time Study (see Figure 3) to record

the observation time and performance rating for the task. Also, they

require to write all work elements in the form.

4. One student in the group assembles all the components supplied. In one

plate assembly the student is required to fix 12 complete bolts sets

(consisting of bolts, nuts and washers) with different sizes on both

upright plates. The student needs pick up the small bolts and nuts in

order to fix them and he requires to check the tight quality of the

assembly. After that he needs to pick up the large bolts and nuts and fix

them and also, he needs to check it. Finally, the student to needs to lift

the plate (assembled object) and put it in other location.

5. The other students record the observation time to complete each work

element (fix one bolt) as well as the performance rating for each work

element. The performance rating of the student depends on the speed

and the quality of assembly task. Therefore, the students require to

check the tight quality of the assembly. The student should assign PR =

100% for the normal performance, greater than 100% for the faster and

good accuracy performance and lower 100% for the slower student

performance and poor accuracy.

6. Each group have to collect the data of observation time and performance

rating for each work element from all other class groups and complete

these data in cycle columns as illustrated in the form direct time study.

27

7. Then the students need to compute the normal time for each work

element by using the previous equation (1) in section 6.1. After that,

they require to add all normal time for all work elements to determine the

total normal time for the task.

6.5 Results of the ExperimentA laboratory report includes the following:

28

Figure 3: Direct Time Study Form

1. Determine the total normal time (Tn) of the task in min.

2. Determine the standard time (Tstd) of the task if the PFD allowance is 12% (see equation 2 in section 6.1).

Determine the number of cycles that should be timed for the assembly task at a

95% confidence level and the actual element time is within ± 11% of the mean.

7. Work Sampling Measurement Method

7.1 IntroductionWork sampling is one of the work measurements most used to determine the

standard time of a task. In particular, it aims to find the standard task time for

different numbers of workers or machines. Work sampling is a statistical

technique for determining the proportions of time spent by subjects (e.g.,

workers, machines) in various defined categories of activity (setting up a

machine, producing parts, idling, etc.). Therefore, the work sampling is useful to

determine the idle time of machine or worker in a task as well as their work

time. In a work sampling study, a large number of observations are made over

an extended period of time, and statistical inferences are drawn about the

proportion of time spent by subjects (workers/machines) in various defined

categories of activity.

The following general characteristics of work situations are particularly well-suited for work sampling:

Sufficient time should be available to perform the study .

Several weeks are usually required for a work-sampling study.

Multiple subjects should be used.

Work sampling is suited to studies involving more than one

subject.

Long cycle times should be used for the jobs covered by the study .

Nonrepetitive work cycles should be used.

Jobs consist of various tasks rather than a single repetitive task.

In fact, for highly repetitive jobs with short cycle times performed by one worker,

an alternative work measurement method such as a direct-time study,

predetermined time system, or standard data system is preferred over work

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sampling. There are other names used for work sampling, such as activity

sampling and ratio delay study.

There are various applications for the work - sampling method:

Machine utilisation: how much time is spent by machines in various

categories of activity

Previous example

Worker utilisation: how workers spend their time

Allowances for time standards : assessment of delay components in PFD

allowance factor

Average unit time : determining the average time on each work unit

Time standards : limited statistical accuracy when standards are set by

work sampling

Different guidelines are used to define categories in a work-sampling study:

First, the categories must be defined to be consistent with the objectives of the

work-sampling study. Second, they must be immediately recognizable by the

observer (mutually exclusive). Third, if output measures are included, then

activity categories must correlate with those measures (i.e., the machine idle

time is considered the output measure for machine utilisation). Fourth, if there

is more than one output measure, then an activity category must be defined for

each. Finally, it is helpful to minimize the number of activity categories to

reduce the level of confusion for the study observer (work-study engineer).


To understand the concept and the technique of the work-sampling study

method in time measurement.

To use the work-sampling study in order to determine the average time of a

task.

To use the work-sampling study in order to determine the normal and

standard times of a task.

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To understand the implementation of a work-sampling study in the evaluation

of various workers’ utilisation.

7.3 Experiment Exercise (First part of the experiment)

A work-sampling study was performed on nine workers in the milling production

department in a steel factory. The task was divided into four activity categories:

‘worker operates on machine’ (producing units), ‘worker waits for raw

materials’, ‘worker talks with advisor and co-workers’, and ‘worker inspects

unit’. The below table 1 shows the work-sampling data study form that was

used in the study and contained the data collection for the nine workers with

randomised time and time of data collection. The factory approved 13% as an

allowance factor Apfd. A total of 438 work units were produced during the two

weeks. Furthermore, 753 were inspected during the two weeks.

7.4 Results of the ExperimentA laboratory exercise report includes the following:

1. Construct a 90% confidence interval for the true proportion of time spent producing units.

2. Construct a 95% confidence interval for the true proportion of time spent inspecting units.

3. Determine the average time per day that each worker spends producing units as well as inspecting unit.

4. Determine the standard time for the ‘worker operates on machine’ category.

5. Determine the total percentage of idle time (delay time) for each worker.

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Date: 2/5/2011 Work Sampling Data Collection FormPage 1 of

1Period of Study : Two weeks

Activity Category (AC) 1. Worker operates on machine (producing units) 2.Worker waiting the raw materials 3.Worker Talking with advisor and coworkers 4. Worker inspects unit

Observer: Eng. MarkDepartment: Milling production departmentNotes: all workers have same levels of training and experiences

Subjects

Observation Date and Time

Worker#1 Worker#2 Worker#3 Worker#4 Worker#5 Worker#6 Worker#7 Worker#8 Worker#9

ACPR (%) AC PR AC PR AC PR AC PR AC PR AC PR AC PR AC PR

2/5/11 (10:05 am) 3 3 2 1 95 1 93 3 3 1 90 24/5/11 (11:15 am) 4 95 3 2 3 3 3 4 100 4 101 1 9412/5/11 (4:11 pm) 3 3 1 92 2 4 98 3 4 102 4 99 1 916/5/11 (4:30 pm) 1 90 2 4 105 3 2 1 92 2 4 101 2

3/5/11 (10:44 am) 1 90 3 4 102 1 95 1 90 1 94 1 93 4 100 32/5/11 (3:10 pm) 4 99 4 103 3 2 4 100 3 2 1 89 1 934/5/11 (8:20 am) 4 102 4 105 4 103 3 3 3 3 1 93 4 1042/5/11 (2:14 pm) 1 92 3 3 3 1 91 1 90 4 100 4 97 29/5/11 (9:30 am) 3 2 2 3 1 93 3 1 90 2 4 100

11/5/11 (11:10 am) 3 1 94 4 109 1 94 2 2 2 2 1 924/5/11 (4:12 pm) 1 90 4 102 4 100 3 1 90 2 3 3 4 98

11/5/11 (2:00 pm) 4 100 2 4 100 3 3 3 4 103 4 100 4 9510/5/11 (11:30 am) 4 101 2 2 4 102 1 94 1 91 2 2 1 915/5/11 (10:20 am) 4 98 1 96 1 90 3 3 1 91 1 92 4 101 4 1014/5/11 (8:16 am) 4 105 2 2 4 100 2 4 97 1 89 2 1 903/5/11 (3:45 pm) 3 3 2 1 92 2 4 100 4 102 2 4 103

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Table 1: Work Sampling Data Form for the Study

9/5/11 (1:30 pm) 4 99 1 93 4 99 2 1 89 4 98 3 4 102 212/5/11 (2:50 pm) 1 89 3 1 93 1 93 1 91 3 2 3 1 9111/5/11 (9:38 am) 1 88 2 3 2 1 90 4 98 1 90 1 92 4 1006/5/11 (9:58 am) 1 92 2 2 3 1 89 3 1 94 1 91 4 100

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7.5 Practical Exercise (Second part of the experiment)

For this part, as a group you need to conduct a work sampling study on one of

the jobs listed below. Select any one of the listed jobs and implement the study

on at least four subjects (i.e. workers OR machines).

- Any job in an industrial factory (production lines)

- Barber shop jobs

- Reception employees at a hospital or hotel

- Bank teller at a bank

- Supermarket cashier or restaurant cashier

- Workshop jobs (woodworking, painting, or forge workshop)

- Your choice (discussed with me in advance)

Each group needs to collect 100 observations as a total in one week. The

group must use the work sampling data form to collect the data from the job. In

addition, groups must use the scheduling observations technique and pseudo

random number generators in Excel (see the class’s slides 22-25, chapter 9) in

order to ensure randomization in observation dates, times, and workers.

The group must determine the following:a. Determine the proportion of time spent on each activity category

b. Determine the hours spent on each category by all workers/machines

c. Determine the average time that each worker/machine spends on each

producing unit (worker/machine activation) activity category.

d. Determine the normal time of worker/machine work activity category

(worker/machine activation category)

e. Determine the percentage of utilization of each worker/machine

You may use figures and photos to illustrate your description (if needed).

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8. Learning Curves Theory

8.1 IntroductionLearning Curve Phenomenon as in term of task time refers to the Reduction in

cycle time that occurs in a repetitive work activity as the number of cycles

increases. It means that when a worker accomplishes a task over and over, the

time required for each successive cycle decreases as he or she learns the task.

Learning Curve analysis has been applied for different areas rather than cycle unit time such as estimates the product cost, product quality and occupational

safety. According to theory, there is a constant learning rate that applies to a

given repetitive task. Learning Rate means that the proportion by which the

dependent variable (e.g., task time) is multiplied every time the number of task

cycles doubles. The learning curve effect is inherent in any work system that

continuous to seek improvement in its operations. There is other alternative

term for the learning curves used for organizations learning and technology

improvement which is experience curve.

Improvement time of task over time during a repetitive task was pointed out by

Wright and Crawford those developed a number of equations to express the

time improvement mathematically (Grover, 2007). They plotted the results of

time against the number of cycles on log-log paper and that gave a straight line.

The plotted showed that the time of cycle was significantly decreased while the

number of cycles is doubled. There is one important term related to the learning

rate which is called improvement rate. It defines as the parentage of

improvement in cycle time of the unit (dependent variable) as the number of

unit doubles.

In fact, the occurring of learning curve related to two important factors which

are: workers and organization. The workers can contribute in occurring

learning curves with different ways such as: worker becomes familiar with the

task - the worker learns the task, worker makes fewer mistakes as the task is

repeated, hand and body motions become more efficient, and there is a rhythm

and pattern developed and minor adjustments in workplace layout to reduce

distances. In contract, the organization can contribute in occurring learning

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curves with different ways such as: methods improvements by the IE

Department (i.e., layout and design methods, process optimization and just-in-

time method), technological improvements, development of special tooling,

better scheduling, improved logistical support and better motivation of workers.

Learning curves can be also useful in showing how differences in work design

can have an effect on the rate of learning


To learn how to draw learning curve for more than one subject and task.

To understand the concept of learning curves theory.

To learn how calculate the time of any specific unit in the task as well as the

cumulative time of the task.

To calculate the learning rate for the subject for different two tasks.

8.3 InstrumentThe Grooved Pegboard (Simple assembly tool test, model 32025, Lafayette

Instrument, US; see Figure 1) is a manipulative dexterity test consisting of 25

holes with randomly positioned slots. Pegs with a key along one side must be

rotated to match the hole before they can be inserted, requiring more complex

visual-motor coordination.

Roeder Board Manipulative Aptitude Test (Model 32026; Lafayette Inst.

Company; see Figure 2) is the test that uses to measure hand, arm, finger

dexterity, and speed. The board of the roeder board has four receptacles for

holding washers, rods, caps, and nuts. The performance board also is

comprised of a horizontal T-bar and 40 inserts arranged in a predetermined

pattern.






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8.4 Experiment Procedures (group work)

Each student will perform two different experiments since; the student

needs to perform the Grooved Pegboard simple assembly tool test(task no. 1) as well as also, he needs to do other task which is Roeder Board

Manipulative Aptitude Test (task no. 2):

First of all, the lab section needs to divide into two groups and each group

needs to select one student to perform the both tasks.

In the first experiment (task no. 1):




2. One student of the group needs to pick up the peg and insert to the

board hole with random orientation (see Figure 1) and uses both hands.

3. The student needs to insert 25 pegs in order to complete the assembly.

4. The students requires to timed 15 cycles.

5. The other members of the group need to record the time for each cycle

(i.e., time record for 15 cycles).

In the second experiment (task no. 2):




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Figure 1:Grooved Pegboard tool and pegs.

2. One student of the group (i.e., same student who performs the first

task) needs to assemble all four parts washers, rods, caps, and nuts

together and insert into the hole in the board after pick-up these parts

from pin that placed in the front of the student see Figure 2.

3. The student requires to complete 25 assembly parts out of 40 which

means that he needs to assemble only 25 holes in the board.

4. The students requires to timed 15 cycles.

5. The other members of the group need to record the time for each cycle

(i.e., time record for 15 cycles).

8.5 Results of the ExperimentA laboratory exercise report includes the following:

a. Record the times for each task using snapback method.

b. Present the data in a tabular form database.

c. Plot the learning curve for both students and both tasks (i.e., 2 graphs with 4 learning curves). Use simple and log-log graph paper.

d. Determine the learning curve slope (m) via the graph using the following equation:

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m =lnTN2– lnTN1ln(N2) – ln(N1)

e. Determine the learning rate (%) using the following equation:

f. The total cumulative time and the average total cumulative time, using the following equation of Crawford model.

g. Compare the results of both tasks as well as results of the both students and provide your comments.

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LR = 2m

audimetry - web viewrest (r) – resting to overcome fatigue. ... a work-sampling study was...

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