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

2. Three Categories of Work Systems
Manual work system
Worker performing one or more tasks without the aid of powered tools
Worker-machine system
Human worker operates powered equipment
Automated work system
Process performed without the direct participation of a human worker

3. Manual Work System

4. Worker-Machine System

5. Automated System

6. Some Definitions Workpiece being machined (production work)
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)
Unit operations – tasks and processes that are treated as being independent of other work activities

7. Manual Work Systems
Human body accomplishing some physical task without an external source of power
With or without hand tools
When hand tools are used, the power to operate them is derived from the strength of a human worker
Other human faculties are required, such as hand-eye coordination and mental effort

8. Pure Manual Work
Involves the physical and mental capabilities of the human worker, and no machines, tools, or other implements are employed in performing the task.
Material handler moving cartons in a warehouse
Workers loading furniture into a moving van without the use of dollies
Dealer at a casino table dealing cards
Office worker filing documents
Assembly worker snap-fitting two parts together

9. Manual Work with Hand Tools
Manual tasks are commonly improved by the use of hand tools. A tool is a device or implement for making changes to some object (e.g., the work unit), such as cutting, grinding, striking, squeezing, or other process. A hand tool is a small tool that is operated by the strength and skill of the human user. Examples of manual tasks involving the use of hand tools include the following:
Machinist filing a part
Assembly worker using screwdriver
Painter using paintbrush to paint door trim
QC inspector using micrometer to measure a shaft diameter

10. Repetitive vs. Nonrepetitive Tasks
Relatively short duration (usually a few minutes or less)
High degree of similarity from one cycle to the next
Nonrepetitive Task
Takes a long time
Work cycles are not similar

11. Cycle Time Variations
A main objective in work design is to determine the one best method for a task, and then to standardize its use
Once the method has been standardized, the actual time to perform the task is a variable because of:
Differences in worker performance
differences in hand and body motions
Mistakes by worker
Variations in starting work units
The learning curve phenomenon
Differences in the physical and cognitive attributes among workers performing the task
Variations in the methods used by different workers to perform the task

12. Worker Performance Defined as the pace or relative speed of working
As worker performance increases, cycle time decreases
From the employer’s viewpoint, it is desirable for worker performance to be high
What is a reasonable pace to expect from a worker?

13. Normal Performance
A pace of working that can be maintained by a properly trained average worker throughout an entire work shift without injurious effect 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
Common benchmark of normal performance:
Walking at 3 miles/hr

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

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

16. Example: Solution (a) At 3 miles/hr, time = 1.85 miles / 3 miles/hr
= hr = 37 min
(b) Rearranging equation, Pw = Tn / Tc
Pw = 37 min / 30 min = = %
Alternative approach in (b):
Using velocity = 1.85 miles / 0.5 hr = 3.7 miles/hr
Pw = 3.7 miles/hr / 3.0 miles/hr = %

17. Standard Performance
Same as normal performance, but acknowledges that periodic rest breaks must be taken by the worker
Periodic rest breaks are allowed during the work shift
Federal law requires employer to pay the worker during these breaks
Other interruptions and delays also occur during the shift

18. PFD Allowance Bathroom breaks, personal phone calls
To account for the delays due to:
Personal time (P)
Bathroom breaks, personal phone calls
Fatigue (F)
Rest breaks are intended to deal with fatigue
Delays (D)
Interruptions, equipment breakdowns

19. Standard Time
Defined as the normal time but with an allowance added in to account for losses due to personal time, fatigue, and delays
Tstd = Tn (1 + Apfd)
where Tstd = standard time, Tn = normal time, and Apfd = PFD allowance factor
Also called the allowed time

20. Irregular Work Elements
Elements that are performed with a frequency of less than once per cycle
Examples:
periodic changing of tools (e.g., changing a knife blade)
Irregular elements are prorated into the regular cycle according to their frequency

21. Example: Determining Standard Time
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 and (b) the number of work units produced during an 8-hr shift if the worker's pace is consistent with standard performance.

25. Standard Hours and Worker Efficiency
Two common measures of worker productivity used in industry to assess a worker’s productivity are standard hours and worker efficiency
Standard hours – represents the amount of work actually accomplished
Hstd = Q Tstd
Hstd = standard hours accomplished; Q = quantity of work units completed; Tstd = standard time per work unit
Worker efficiency – work accomplished as a proportion of shift hours
Ew = Hstd / Hsh
Ew = worker efficiency; Hstd = # of standard hours of work accomplished; Hsh = # of shift hours (8 hr)

28. Worker efficiency
Worker efficiency is commonly used to evaluate workers in industry.
In many incentive wage payment plans, the worker’s earnings are based on his or her efficiency or the number of standard hours accomplished.
Worker efficiency and standard hours are easily computed, because the number of hours in the shift and the standard time are known, and the number of work units produced can be readily counted.

29. Worker-Machine Systems
When worker operates a powered equipment we refer to the arrangement as a worker-machine system.
Examples:
Machinist operating a milling machine
Factory worker loading and unloading parts at a machine tool.
Truck driver driving an 18-wheel tractor-trailer
Worker crew operating a rolling mill that converts hot steel blocks into flat plates.
Clerical worker entering data into a PC

30. Types of Powered Equipment
Distinguished from hand tools by the fact that a source of power other than human strength is used to operate it. Common power sources are electric, pneumatic, hydraulic, and fossil fuel motors
Portable power tools are light enough in weight
portable power drills, rotary saws, chain saws, and electric hedge trimmers.
Mobile powered equipment are generally heavy pieces of equipment
Transportation equipment, agricultural and lawn-keeping, forklift trucks, electric power generator at construction site
Stationary powered machines stand on the floor or ground and cannot be moved while they are operating
Machine tools (e.g., turning, drilling, milling); office equipment (personal computers, photocopiers, telephones, fax machines); cash registers, heat treatment furnaces

31. Classification of Powered Machinery

32. Numbers of Workers and Machines Means of classifying worker-machine systems is according to whether there are one or more workers and one or more machines
One worker and
One machine
Taxicab driver and taxi
One worker & Multiple machines
A worker tending several production machines
Multiple workers and
One machine
Ship's crew
Multiple workers and
Multiple machines
Emergency repair crew responding to machine breakdowns in a factory

33. One Worker and One Machine
Good work design attempts to achieve the following objectives:
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, thereby minimizing worker idle time.
Minimize the idle times of both the worker and the machine.
Design the task and the machine to be safe for the worker.

34. 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
Periodic attention with regular servicing
Crane operator in steel mill
Periodic attention with random servicing
Firefighters responding to alarms

35. Two welders performing arc welding on pipe - requires full-time attention of workers (photo courtesy of Lincoln Electric Co.)

36. Cycle Time Analysis in Worker Machine System
In terms of cycle time analysis, worker-machine systems fall into two categories:
systems in which the machine time depends on operator control, the task can be either repetitive or nonrepetitive
systems in which the machine time is constant and independent of operator control, and the work cycle is repetitive.

37. Cycle Time with no Overlap between Worker and Machine
If there is no overlap in work elements between the worker and the machine, then the normal time for the cycle is simply the sum of their respective normal times:
Normal time for cycle
Tn = Tnw + Tm
Where Tnw = normal time for the worker-controlled portion of the cycle, min: and Tm = machine cycle time (assumed constant).
Standard time for cycle
Tstd = Tnw (1 + Apfd) + Tm (1 + Am)
where Tnw = normal time of the worker, min; Tm = constant time for the machine cycle, min; Am = machine allowance factor, used in the equation as a decimal fraction

41. Worker-Machine Systems with Internal Work Elements
In the operation of a worker-machine system, it is important to distinguish between the operator’s work elements that are performed in succession with the machine’s work elements and those that are performed simultaneously with the machine elements.
Operator elements that are performed sequentially are called external work elements while those that are performed simultaneously with the machine cycle are called internal work elements.

42. Example 2.10 Internal Versus External Work Elements in Cycle Time Analysis
The work cycle in a worker-machine system consists of the elements and associated times given in the table below.
All of the operator’s work elements are external to the machine time.
Can some of the worker’s elements be made internal to the machine cycle, and if so, what is the expected cycle time for the operation?

45. Comment
Although the total times for the worker and the machine are the same as before, element 4 in the revised cycle (which Consists of elements 1, 2, and 6 from the original work cycle) is performed simultaneously with the machine time, resulting in the following new cycle time:
Tc = = 0.97 min
This represents a 34% reduction in cycle time, which translates into a 53% increase in production rate.
When internal elements are present in the work cycle, it must then be determined whether the machine cycle time or the sum of the worker’s internal elements take longer.

46. 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

47. Levels of Automated Systems
Semiautomated machine
Performs a portion of the work cycle under some form of program control
Human worker tends the machine for the remainder of the cycle, by loading and unloading it
Operator must be present every cycle
Fully automated machine
Operates for extended periods of time with no human attention

48. Automated robotic spot welding cell (photo courtesy of Ford Motor Company)