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

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

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

4. Manual Work System

5. Worker-Machine System

6. Automated System

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. 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 على التحمل of a human worker
Hairbrush vs hair dryer
Of course other human faculties قدرات بشريةare also required, such as hand-eye coordination and mental effort

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. Manual Work with Hand Tools
Manual tasks are commonly augmented by تعزز بuse 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. 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. Repetitive vs. Nonrepetitive Tasks
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. 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.

14. Example 2.1: A repetitive Manual Task
Current method: An assembly worker performs a repetitive task consisting of inserting 8 pegs أوتاد into 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. Example 2.1: A repetitive Manual Task
Current method and current layout:

16. Example 2.1: A repetitive Manual Task
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.

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

18. Example 2.1: A repetitive Manual Task
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=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.

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. Cycle Time Variations Differences in worker performance
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. Worker Performance
Defined as the pace (tempo) or relative speed with which the worker does the task.
هى الوتيرة (الإيقاع)، 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. Normal Performance (pace) الأداء العادي
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. 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. 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. Example 2.2: Solution (a) At 3 mi/hr, normal time = 1.85 mi / 3 mi/hr
= hr = 37 min
(b) Rearranging equation, Pw = Tn / Tc
Pw = 37 min / 30 min = = %
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. 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. 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. 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. 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. 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. 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. 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. Example 2.3: Solution
Normal time of a task involves normal times for regular and irregular work elements
Normal time Tn = /5
= 3.48 min
Standard time Tstd = 3.48 ( )
= 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. 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 = hr
Time lost = Hsh – Actual time worked
Time lost = 8.0 – = hr

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 hr (which corresponds to the 15% allowance factor).
Determine daily production rate.

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 = (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. Standard Hours and Worker Efficiency
Two (three) common measures of worker productivity used in industry
Standard hours – represents the amount of work actually accomplished during a given period (shift, week)
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
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. 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. 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 = hr
(c) Ew = 10.67hr / 8 hr =133.3 %