Work Systems

1. 1
Work Systems and How They Work
Chapters:
2. Manual Work and Worker-Machine Systems
3. Work Flow and Batch Processing
4. Manual Assembly Lines
5. Logistics Operations
6. Service Operations and Office Work
7. Projects and Project Management
Part I

2. 2
Manual Work & Worker-Machine
Systems
Sections:
1. Manual Work Systems
2. Worker-Machine Systems
3. Automated Work Systems
4. Determining Worker and Machine
Requirements
5. Machine Clusters
Chapter 2

3. 3
Three Categories of Work Systems
1. Manual work system
 Worker performs one or more tasks without the aid
of powered tools (e.g. hammers, screwdrivers,
shovels)
2. Worker-machine system
 Human worker operates powered equipment (e.g.
a machine tool)
 Physical effort (less)
 Machine power(more)
3. Automated work system
 Process performed without the direct participation
of a human worker

4. 4
Manual Work System

5. 5
Worker-Machine System

6. 6
Automated System

7. 7
Some Definitions
 Work unit – the object that is processed by the work system
 Workpiece being machined (production work)
 Material being moved (logistics work)
 Customer in a store (service work)
 Product being designed (knowledge work)

8. 8
Manual Work Systems
 Most basic form of work in which human body
is used to accomplish some physical task
without an external source of power
 With or without hand tools
 Even if hand tools are used, the power to operate
them is derived from the strength and stamina ‫القدرة‬
‫التحمل‬ ‫على‬of a human worker
 Hairbrush vs hair dryer
 Of course other human faculties ‫بشرية‬ ‫قدرات‬are
also required, such as hand-eye coordination
and mental effort

9. 9
Pure Manual Work
Involves only the physical and mental
capabilities of the human worker without
machines or tools.
 Material handler moving cartons in a
warehouse
 Workers loading furniture into a moving van
without the use of dollies
 Office worker filing documents
 Assembly worker snap-fitting two parts
together

10. 10
Manual Work with Hand Tools
 Manual tasks are commonly augmented by
‫تعزز‬
‫ب‬ use of hand tools.
 Tool is a device for making changes to objects
(formally work units) such as cutting, grinding,
striking, squeezing
 Scissor, screwdriver, shovel
 Tools can also be used for measurement
and/or analysis purposes
 Workholder to grasp or poisiton work units

11. 11
Manual Work with Hand Tools
Examples:
 Machinist filing a part
 Assembly worker using screwdriver
 Painter using paintbrush to paint door trim
 QC inspector using micrometer to measure the
diameter of a shaft
 Material handling worker using a dolly to move
furniture
 Office worker writing with a pen

12. 12
Repetitive vs. Nonrepetitive Tasks
Nonrepetitive Task
Repetitive Task
•Work cycle takes a long time
•Work cycles are not similar
•Work cycle is relatively short
(usually a few minutes or less)
•High degree of similarity from
one cycle to the next
In either case, the task can be divided into work elements that
consist of logical groupings of motions

13. 13
Cycle Time Analysis
 Cycle time Tc
where
Tek = time of work element k, where k is used to
identify the work elements (min)
ne = number of work elements into which a cycle is
divided.
1
e
n
c ek
k
T T

 

14. 14
Example 2.1: A repetitive Manual Task
 Current method: An assembly worker performs a
repetitive task consisting of inserting 8 pegs ‫أوتاد‬into 8
holes in a board. A slightly interference fit is involved in
each insertion. The worker holds the board in one hand
and picks up the pegs from a tray with other hand and
inserts them into the holes, one peg at a time.

15. 15
 Current method and current layout:
Example 2.1: A repetitive Manual Task

16. 16
 Improved method and improved layout:
 Use a work-holding device to hold and position the
board while the worker uses both hands
simultaneously to insert pegs.
 Instead of picking one peg at a time, each hand will
grab ‫أمسك‬
‫ب‬ four pegs to minimize the number of
times the worker’s hands must reach the trays.
Example 2.1: A repetitive Manual Task

17. 17
 Improved method
 The cycle time is reduced from 0.62 min to 0.37 min.
 % cycle time reduction=(CTcurrent-CTimproved)/CTcurrent
=(0.62-0.37)/0.62=40%
Example 2.1: A repetitive Manual Task

18. 18
 Production ratecurrent=1/0.62 min=1.61 units per min
(throughput)
 Production rateimproved=1/0.37 min=2.70 units per min
 % increase in R =(Rimproved-Rcurrent)/Rcurrent
=(1.61-2.70)/1.61=68%
 It is important to design the work cycle so as to minimize
the time required to perform it.
 Of course there are many alterantive ways to perform a
given task. Our focus is on the best one.
Example 2.1: A repetitive Manual Task

19. 19
One Best Method Principle
 Of all the possible methods that can be used to perform a
given task, there is one optimal method that minimizes the
time and effort required to accomplish it
 Attributed to Frank Gilbreth
 A primary objective in work design is to determine the one
best method for a task, and then to standardize it
 This one best refers to an average worker with a moderate
level of skill, operating under normal working conditions with
nominal material quality and tool/equipment availability

20. 20
Cycle Time Variations
 Once the method has been standardized, the
actual time to perform the task is a variable
because of:
 Differences in worker performance
 Mistakes, failures and errors
 Variations in starting work units
 Variations in hand and body motions
 Extra elements not performed every cycle
 Differences among workers
 The learning curve phenomenon

21. 21
Worker Performance
 Defined as the pace (tempo) or relative speed
with which the worker does the task.

‫هى‬
‫الوتيرة‬
(
‫اإليقاع‬
)
،
‫أو‬
‫السرعة‬
‫النسبية‬
‫التي‬
‫يؤدى‬
‫بها‬
‫العامل‬
‫المهمة‬
.
 As worker performance increases, cycle time
decreases
 From the employer’s viewpoint ‫وجهة‬
‫نظر‬
‫صاحب‬
‫العمل‬ ,
it is desirable for worker performance to be high
 What is a reasonable performance/pace to
expect from a worker in accomplishing a given
task?

22. 22
Normal Performance (pace)
‫العادي‬ ‫األداء‬
 A pace of working that can be maintained by a properly
trained average worker throughout an entire work shift
without harmful short-term or long-term effects on the
worker’s health or physical well-being
 The work shift is usually 8 hours, during which periodic rest
breaks are allowed
 Normal performance = 100% performance
 Faster pace > 100%, slower pace < 100%
 Common benchmark of normal performance:
 Walking at 3 mi/hr (~4.83 km/hr)

23. 23
Normal Time
 The time to complete a task when working at
normal performance (Tn )
 Actual time to perform the cycle depends on
worker performance
Tc = Tn / Pw
where
Tc = cycle time,
Tn = normal time,
Pw = worker performance or pace

24. 24
Example 2.2: Normal Performance
 Given: A man walks in the early morning for
health and fitness. His usual route is 1.85 miles.
The benchmark of normal performance = 3 mi/hr.
 Determine:
(a) how long the route would take at normal
performance
)b( the man’s performance when he completes
the route in 30 min.

25. 25
Example 2.2: Solution
(a) At 3 mi/hr, normal time = 1.85 mi / 3 mi/hr
= 0.6167 hr = 37 min
(b) Rearranging equation, Pw = Tn / Tc
Pw = 37 min / 30 min = 1.233 = 123.3 %
 If worker performance > 100%, then the time required to
complete the cycle will be less than normal time.
 If worker performance < 100%, then the time required to
complete the cycle will be greater than normal time.

26. 26
Standard Performance
 Same as normal performance, but
acknowledges ‫يقر‬ that periodic rest breaks
must be taken by the worker
 Periodic rest breaks are allowed during the
work shift
 Lunch breaks (1/2 or 1 hour)
 usually not counted as part of work shifts
 Shorter rest beraks (15 mins)
 usually counted as part of work shifts

27. 27
Rest Breaks in a Work Shift
 A typical work shift is 8 hours (8:00 A.M. to 5:00 P.M.
with one hour lunch break)
 In Turkey work time is defined as 45 hours a week
(so 8:00 A.M. to 6:00 P.M. with one hour lunch break,
provided that workers work for 5 days)
 The shift usually includes one rest break in the morning
and another in the afternoon.
 The employers allows these breaks, because they know
that the overall productivity of a worker is higher if rest
breaks are allowed.
 In Turkey the rest periods are not included in daily work
hours in which employers are paid for.

28. 28
Standard Performance
 Of course other interruptions and delays also
occur during the shift
 Machine breakdowns
 Receiving instructions from the foreman
 Telephone calls
 Bathroom/toilette breaks etc.

29. 29
Personal time, Fatigue, Delay (PFD)
Allowance
 To account for the delays and rest breaks, an
allowance is added to the normal time in order
to determine allowed time for the worker to
perform the task throughout a shift
 Personal time (P)
 Bathroom breaks, personal phone calls
 Fatigue (F) ‫تعب‬
 Rest breaks are intended to deal with fatigue
 Delays (D)
 Interruptions, equipment breakdowns

30. 30
Standard Time
 Defined as the normal time but with an allowance added
into account for losses due to personal time, fatigue, and
delays
Tstd = Tn (1 + Apfd)
where
Tstd = standard time,
Tn = normal time,
Apfd = PFD allowance factor
 Also called the allowed time
 Now we are confident to say that a worker working at
100% performance during 8 hours can accomplish a task
of 8 hour standard time.

31. 31
Irregular Work Elements
 Elements that are performed with a frequency
of less than once per cycle
 Examples:
 Changing a tool
 Exchanging parts when containers become full
 Irregular elements are prorated into the regular
cycle according to their frequency

32. 32
Example 2.3: Determining Standard Time
and Standard Output
 Given: The normal time to perform the regular
work cycle is 3.23 min. In addition, an irregular
work element with a normal time = 1.25 min is
performed every 5 cycles. The PFD allowance
factor is 15%.
 Determine
(a) the standard time
(b) the number of work units produced during
an 8-hr shift if the worker's pace is consistent
with ‫بما‬
‫يتفق‬
‫مع‬ standard performance.

33. 33
Example 2.3: Solution
 Normal time of a task involves normal times
for regular and irregular work elements
(a) Normal time Tn = 3.23 + 1.25/5
= 3.48 min
Standard time Tstd = 3.48 (1 + 0.15)
= 4.00 min
(b) Number of work units produced during an 8-hr
shift
Qstd = Hsh / Tstd
Qstd = 8.0(60)/4.00 = 120 work units
Hsh =number of shift hours, hr

34. 34
Example 2.4: Determining Lost Time due
to the Allowance Factor
 Given: An allowance factor of 15% is used.
 Determine the anticipated amount of time lost per
8-hour shift.
 Solution:
Hsh =(Actual time worked) (1+ Apfd )
8.0 hour =(actual time worked) (1+0.15)
Actual time worked = 8 / 1.15 = 6.956 hr
Time lost = Hsh – Actual time worked
Time lost = 8.0 – 6.956 = 1.044 hr

35. 35
Example 2.5: Production rate when
worker performance exceeds 100%
 Given: From Ex. 2.3,Tstd = 4.00 min and Tn = 3.48
min. The worker’s average performance during an
8-hour shift is 125% and the hours actually worked
is 6.956 hr (which corresponds to the 15%
allowance factor).
 Determine daily production rate.

36. 36
Example 2.5: Solution
 Based on normal time Tn = 3.48 min, the actual
cycle time with a worker performance of 125%,
Tc =3.48 / 1.25 = 2.78 min. (see slide 23)
 Assuming one work unit is produced each cycle,
the corresponding daily production rate,
Rp = 6.956 (60) / 2.78 =150 work units
OR
 125% of 120 units (we know that from Ex. 2.3.b)
at 100% performance = 150 units

37. 37
Standard Hours and Worker
Efficiency
 Two (three) common measures of worker productivity
used in industry
1. Standard hours – represents the amount of work actually
accomplished during a given period (shift, week)
2. Quantity of work units (in terms of time) produced
Hstd = Q Tstd
where
Hstd =standard hours accomplished, hr
Q = quantity of work units completed during the period, pc
Tstd =standard time per work unit, hr/pc
3. Worker efficiency – work accomplished during the shift
expressed as a proportion of shift hours
Ew = Hstd / Hsh
Ew =worker efficiency, %
Hsh =number of shift hours, hr

38. 38
Example 2.6: Standard hours and worker
efficiency
 Given: The worker performance of 125% in the
previous example. Example 2.5
 Determine:
(a) number of standard hours produced
(b) worker efficiency
 Solution:
(a) Hstd = Q Tstd
Hstd =150 (4 min)=600 min= 10.0 hr
(b) Ew = Hstd / Hsh
Ew = 10hr / 8 hr =125 %

39. 40
Example 2.7: Standard hours and worker
efficiency as affected by hours actually worked
 Given: The worker performance of 125%, actual hours
worked is 7.42 hr. Tc = 2.78 min and Tstd =4 min
 Determine:
(a) number of pieces produced,
(b) number of standard hours accomplished,
(c) the worker’s efficiency
 Solution:
(a) Q =Actual time worked / cycle time
Q =7.42 (60) / 2.78 = 160 units
(b) Hstd = Q Tstd =160 (4 min) = 640 min = 10.67 hr
(c) Ew = 10.67hr / 8 hr =133.3 %