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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
10
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)
3.2 ObjectivesThe objectives of this laboratory experiment are as follows:
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
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 4).
3.4 Experiment Procedures (simple repetitive 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 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 4: Digital stopwatch. (Dad-7141, Japan)
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.
3.5 Results of the Experiment
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
5.2 ObjectivesThe objectives of this laboratory experiment are as follows:
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
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).
5.4 Experiment Procedures (Cutting saw machine 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 insert the pegs inside the holes.
22
Figure 3: Digital stopwatch. (Dad-7141, Japan)
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.
5.5 Results of the Experiment
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
6.2 ObjectivesThe objectives of this laboratory experiment are as follows:
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).
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 2).
6.4 Experiment Procedures (Cutting saw machine task) The experiment procedures are as follows (group work):
26
Figure 2: Digital stopwatch. (Dad-7141, Japan)
Figure 1: Roeder Board (Model 32026; Lafayette Inst. Company) and four receptacles for holding washers, rods, caps, and nuts.
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. 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.
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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:
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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).
7.2 ObjectivesThe objectives of this laboratory experiment are as follows:
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
8.2 ObjectivesThe objectives of this laboratory experiment are as follows:
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.
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).
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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):
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 insert the pegs inside the holes.
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):
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 insert the pegs inside the holes.
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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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Figure 2: Roeder Board (Model 32026; Lafayette Inst. Company) and four receptacles for holding washers, rods, caps, and nuts.
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