1. Worker-Machine Systems
Worker operates a powered equipment
Examples:
Machinist operating a milling machine
Construction worker operating a backhoe حفار
Truck driver driving an 18-wheel tractor-trailerجرار ومقطورة
Worker crew operating a rolling mill ماكينة درفلة
Clerical worker entering data into a PC

2. Relative Strengths Humans Machines
Sense unexpected stimuli
الشعور بالمؤثرات الغير متوقعه
Solve problems
Adapt to change
Generalize from observations
Learn from experience
Make decisions on incomplete data
Machines
Perform repetitive operations consistently
Store large amounts of information
Retrieve data from memory reliably
Perform multiple tasks at the same time
Apply high forces and power
Perform computations very quickly
Make routine decisions quickly

3. Relative Strengths
In a worker-machine system the worker and the machine both contribute their own strengths and capabilities
The result is synergistic التآزرية
Types of worker-machine systems:
Types of powered machinery used in the system
Numbers of workers and machines in the system
Level of operator attention required to run the machinery

4. Types of Powered Equipment
Powered machinery: A source of power other than human (or animal) strength is used to operate that tool (or machine).
Portable power tools
Light enough in weight so that they can be easily carried
Mobile powered equipment
Heavy pieces of equipment but transportable
Stationary powered machines
Perfom functions in a stationary location

5. Classification of Powered Machinery
Portable power drills, chain saws, electric hedge trimmers
Cars, buses, trucks, airplanes
Tractor, bulldozers, backhoes, forklifts
Electric power generators
Turning, drilling, milling
PCs, photocopiers, telephones
Ovens, cash register

6. Numbers of Workers and Machines
One worker and One machine
Taxicab driver and taxi
One worker and Multiple machines
A worker operating several machines

7. Numbers of Workers and Machines
Multiple workers and One machine
A crew on a ship
Multiple workers and Multiple machines
Emergency repair crew responding to machine breakdowns in a factory

8. Level of Operator Attention
Full-time attention
Welders performing arc welding
Part-time attention during each work cycle
Worker loading and unloading a production machine on semi-automatic cycle

9. Level of Operator Attention
Periodic attention with regular servicing
Worker loading a machine every 20 cycles
Periodic attention with random servicing
Firefighters responding to alarms
Maintenance worker repairing machines

10. Good Work Design for Machine-Worker Systems
Design the controls of the machine to be logical and easy to operate for the worker.
Design the work sequence so that as much of the worker’s task as possible can be accomplished while the machine is operating.
Minimize the idle times of both the worker and the machine.
Design the task and the machine to be safe for the worker.
If the system is a multiple worker or/and multiple machine system, optimize the number of workers or machines in the system according to a specified objective.

11. Cycle Time Analysis A typist typing a list of names on a typewriter
Two categories of worker-machine systems in terms of cycle time analysis
Cases:
Systems in which the machine time depends on operator control
A typist typing a list of names on a typewriter
Carpenter using power saw to cut lumber
A construction worker operating a backhoe
Cycle time analysis is same as for manual work cycle
Systems in which machine time is constant and independent of operator control
Operator loading semi-automatic production machine
Our focus is on this 2nd type
Two types:

12. Case 2.a: Cycle Times with No Overlap Between Worker and Machine
Worker elements and machine elements are sequential
There is no overlap in work elements between the worker and the machine
While worker is busy, machine is idle
While machine is busy, worker is idle
Normal time for cycle
Tn = Tnw + Tm,
where
Tnw = Normal time for the worker-controlled portion of the cycle time, min
Tm = Machine cycle time (assumed to be constant)

13. Case 2.a: Cycle Times with No Overlap Between Worker and Machine
Standard time for cycle
Tstd = Tnw (1 + Apfd) + Tm (1 + Am)
where
Am = Machine allowance factor
Am=30%: Workers love that since efficiencies are overestimated
Am=0%: Workers hate that since efficiencies are underestimated
Am= Apfd

14. Example 2.8: Effect of machine allowance on standard time
Given: The work cycle consists of several manual work elements (operator controlled) and one machine element performed under semiautomatic control. The manual work elements: a normal time of 1 min and the semiautomatic machine cycle time is 2 min. Apfd=15%.
Determine: the standard time using
(a) Am =0,
(b) Am=30%.

15. Example 2.8: Solution
The normal time for the work cycle: Tn= =3.0 min
(a) Tstd = Tnw (1 + Apfd) + Tm (1 + Am)
Tstd=1.0(1+0.15)+2.0=3.15 min
Workers
(b) Tstd = Tnw (1 + Apfd) + Tm (1 + Am)
Tstd=1.0(1+0.15)+2.0(1+0.30) =3.75 min

16. Example 2.9: Effect of machine allowance on worker efficiency
Given: Standard times in the previous example (Example 2.8).
Determine: The worker efficiencies if 150 units are produced in an 8-hour shift.
Solution:
(a) Hstd = Q Tstd
Hstd=150(3.15)=472.5min=7.875hr
Ew = Hstd / Hsh
Ew=7.875/8.0=0.984= 98.4%
(b) Hstd = Q Tstd
Hstd=150(3.75)=562.5min=9.375hr
Ew=9.375/8.0=1.172= 117.2%

17. Case 2.b: Internal Work Elements
Some worker elements are performed while machine is working
Internal work elements performed simultaneously with machine cycle
External work elements performed sequentially with machine cycle
Desirable to design the work cycle with internal rather than external work elements
If it is possible, include operator work elements that are performed while machine is running.

18. Normal Time and Standard Time
Tn = Tnw + Max{Tnwi , Tm}
Standard time
Tstd = Tnw (1 + Apfd) +Max{Tnwi (1 + Apfd) , Tm (1 + Am)}
Actual cycle time
Tc = Tnw / Pw + Max{Tnwi /Pw , Tm}
where
Tnw = normal time for the worker’s external elements, min
Tnwi = normal time for the worker’s internal elements, min
Tm = machine cycle time, min

19. Example 2.10: Internal vs external work elements in cycle time analysis
0.75
0.73
Total
(idle)
0.15
Worker transports finished part and deposits into tote pan 6
0.10
Worker unloads finished part from machine 5
Machine semiautomatic cycle 4
0.12
Worker loads part into machine and engages machine semiautomatic cycle 3
0.23
Worker picks up raw workpart and transports to machine 2
0.13
Worker walks to tote pan containing raw stock 1
Machine Time (min)
Worker Time
(min)
Work Element Description
Seq.
Tc= =1.48 min

20. Example 2.10: Internal vs external work elements in cycle time analysis
0.75
0.73
Total
(operating)
0.15+
0.13+
0.23=
0.51
Worker transports finished part and deposits it into tote pan, walks to tote pan containing raw stock, and picks up raw workpart and transports it to machine. (This element is internal to the machine semiautomatic cycle.) 4
(idle)
Machine semiautomatic cycle 3
0.12
Worker loads part into machine and engages semiautomatic machine cycle 2
0.10
Worker unloads finished part from machine 1
Machine Time (min)
Worker Time
(min)
Work Element Description
Seq.
Tc= =0.97 min

21. Example 2.10: Internal vs external work elements in cycle time analysis
The cycle time is reduced from 1.48 min to 0.97 min.
% cycle time reduction=(CTcurrent-CTimproved)/CTcurrent
=( )/1.48=34%
Rcurrent=1/1.48 min=0.68 units per min
Rimproved=1/0.97 min=1.03 units per min
% increase in R=(Rimproved-Rcurrent)/Rcurrent
=( )/0.68=53%

22. Automated Work Systems
Automation is the technology by which a process or procedure is accomplished without human assistance
Implemented using a program of instructions combined with a control system that executes the instructions
Power is required to drive the process and operate the control system

23. Automated Work Systems
Automated robotic spot welding cell (photo courtesy of Ford Motor Company)

24. Levels of Automated Systems
There is not always a clear distinction between worker-machine systems and automated systems, because many worker-machine systems operate with some degree of automation.
Semiautomated machine
Performs a portion of the work cycle under some form of program control
Human worker tends the machine for the rest of the cycle by loading unloading etc.
Operator must be present every cycle
Same characteristics with worker-machine system
e.g.,an automated lathe requires a worker to unload parts at every cycle, although changing tools may not be required at every cycle

25. Levels of Automated Systems
Fully automated machine
Operates for extended periods of time with no human attention (longer than one work cycle, e.g. every hundredth cycle كل مائة دورة )
e.g., periodically the molded parts at a molding machine must be collected.

26. Determining worker and machine Requirements
How many workers/machines are required to achieve the organization’s work objectives?
If too few workers are assigned to perform a given amount of work
The work cannot be completed on time, customer service will suffer.
If too many workers are assigned to perform a given amount of work
The payroll costs are higher than needed, and productivity will suffer.

27. Determining worker and machine Requirements
Workload (WL): Total hours required to complete a given amount of work or to produce a given number of work units scheduled during the period
Available time (AT): The number of hours (in the same period) available from one worker or worker-machine system

28. Case 3.1: When Setup is not a Factor
Workload
WL=QTc
where
WL = workload scheduled for a given period, hr,
Q = quantity to be produced during the period. pc/period,
Tc = work cycle time required per work unit, hr/pc. (Tc =Tstd)
If the workload includes multiple part or product styles that are produced by the same work system:
Qj =quantity of part or product style j, pc,
Tcj =cycle time of part or product style j, hr/pc.

29. Case 1: When Setup is not a Factor
Number of workers and number of machines required:
W = WL / AT, or n = WL / AT
where
w = number of workers,
n = number of workstations,
AT = available time of one worker in the period, hr / period / worker

30. Example 2.11: Determining Worker requirements
Given: 800 shafts must be produced in the lathe section of a machine shop in particular week. Each shaft is identical and Tstd=11.5min. All the lathes are identical. There are 40 hours of available time on each lathe.
Determine: Number of lathes and lathe operators must be devoted during that week.

31. Example 2.11: Solution Workload: WL=800(11.5 min)=9200 min=153.33hr
Machine (and worker) requirements
w =n =153.3/40=3.83 (round up)
=4 lathe operators and lathes

32. Factors that affect the workload
Learning effect: As learning occurs in repetitive manual work, worker efficiency increases, cycle time decreases so that the workload is reduced.
Worker efficiency: Worker may perform either above or below standard performance.
Ew = Workload actually completed
Workload completed at standard performance
Worker efficiency greater than 1.00 reduces the workload.

33. Factors that affect the workload
Defect rate: Fraction of parts produced that are defective.
A defect rate greater than zero increases the quantity of work units that must be processed to yield the desired quantity. So workload increases with defect rate.
The relationship between the starting quantity and the final quantity produced:
Q =Q0 (1-q)
where
Q= quantity of good units made in the process,
Q0 =original or starting quantity; q=fraction defect rate.
The combined effect of worker efficiency and defect rate is given by
WL=(QTstd) / (Ew(1-q))

34. Availability A common measure of reliability for equipment
Defined as the proportion of time the equipment is available to run relative to the total time it could be used.
Available time increases as availability increases
AT=Hsh A
where
AT =available time, hr/worker,
Hsh=shift hours during the period, hr,
A =availability, expressed as a decimal fraction.

35. Example 2.12: Effect of worker efficiency defect rate, and availability
Given: Previous example. Anticipated availability of the lathes 95%. Expected worker efficiency during production=110%. The fraction defect rate=3%.
Determine: Number of lathes required.

36. Example 2.12: Solution Total workload WL=(QTstd) / (Ew(1-q))
WL =( 800 (11.5/60) ) / ( 1.10 (1-0.03) ) = hr
Available time
AT=Hsh A
AT=40(0.95)=38hr/machine
n=WL/AT
n=143.7/38=3.78 lathes (and lathe operators)
=4 lathes (and lathe operators)

37. We omit
2.4.2 When setup time is included-Case 2
2.5 Machine Clusters