Methods of Time Study/Work Measurement
Time study or work measurement is used to specify a
time required to do each operation and to determine an
operation standard.
Use of the human body
1. The two hands should begin as well as complete their motions at the same
time.
2. The two hands should not be idle at the same time except during rest
periods.
3. Motions of the arms should be made in opposite and symmetrical directions
and should be made simultaneously.
4. Hand motions should be confined to the lowest classification with which it is
possible to
perform the work satisfactorily. General classifications of hand motions are as
follows:
(a) finger motions;
(b) motions involving fingers and wrist;
(c) motions involving fingers, wrist, and forearm;
(d) motions involving fingers, wrist, forearm, and upper arm;
(e) motions involving fingers, wrist, forearm, upper arm, and shoulder.
5. Momentum should be employed to assist the worker
wherever possible, and it should be reduced to a minimum if
it must be overcome by muscular effort.
6. Smooth continuous motions of the hands are preferable to
zigzag motions or straight-line motions involving sudden and
sharp changes in direction.
7. Ballistic movements are faster, easier, and more accurate
than restricted or controlled movements.
8. Rhythm is essential to the smooth and automatic
performance of an operation, and the work should be
arranged to permit easy and natural rhythm wherever
possible.
(ii) Arrangement of the workplace
9. There should be a definite and fixed place for all tools and materials.
10. Tools, materials, and controls should be located close to and directly in front of
the operator.
11. Gravity feed bins and containers should be used to deliver material close to the
point of use.
12. Drop deliveries should be used wherever possible.
13. Materials and tools should be located to permit the best sequence of motions.
14. Provisions should be made for adequate conditions for seeing. Good illumination
is the first requirement for satisfactory visual perception.
15. A chair of the type and height to permit good posture should preferably be
arranged so that alternate sitting and standing at work are easily possible.
16. A chair of the type and height to permit good posture should be provided for
every worker
.
(iii) Design of tools and equipment
17. The hands should be relieved - by a jig, a fixture, or a foot-operated
device.
18. Two or more tools should be combined wherever possible.
19. Tools and materials should be pre-positioned wherever possible.
20. Where each finger performs some specific movement, such as
typewriting, the load should be distributed
21. Handles such as those used on cranks and large screwdrivers should be
designed to permit
22. Levers, crossbars, and hand wheels should be located in such positions
that the operator can manipulate them with the least change in body position
and with the greatest mechanical advantage.
2) Methods-time measurement (MTM). This is a procedure which analyses any
manual operation into the basic motions of reach, move, make a crank motion,
turn, apply pressure, grasp, position, release, disengage, make a body motion,
and eye motion.
This system assigns to each motion at normal pace a predetermined time standard
measured in time units of 0.000 01 hours which is determined by the nature of the
motion and the conditions under which it is made.
The steps of MTM are: first, all motions required to perform the job are
summarised properly for both the left and the right hands, and then the standard
time for each motion is determined from the methods-time data tables.
Two principal procedures for establishing predetermined time standards are:
(1) Work-factor (WF). This system recognises the following major variables that
influence operation time, such as
(a) the body member making the motion,
(b) the distance moved,
(c) the weight carried, and
(d) the manual control required.
Work-factor motion-time values measured in units of 0.0001 minutes are
determined as an incentive pace and enable the effect of these major variables
to be determined.
(
2) Methods-time measurement (MTM). This is a procedure which analyses any
manual operation into the basic motions of reach, move, make a crank motion,
turn, apply pressure, grasp, position, release, disengage, make a body motion,
and eye motion.
This system assigns to each motion at normal pace a predetermined time
standard measured in time units of 0.000 01 hours which is determined by the
nature of the motion and the conditions under which it is made.
The steps of MTM are: first, all motions required to perform the job are
summarised properly for both the left and the right hands, and then the standard
time for each motion is determined from the methods-time data tables.
Optimum Routing Analysis
Meaning of Optimum Routing Analysis
It is usual that there are several alternative process routes or
patterns for converting raw material into the finished mechanical
product. To select one best process route from among the
alternatives is optimum routing analysis (or optimum process
planning).
Procedures for Optimum Routing Analysis
1. An optimum routing problem has a finite number of
combinations, and a solution for this type of combinatorial
problem can be always obtained by calculating the total
selecting a route with a least time (or cost).
2. This complete-enumeration procedure requires a substantial
computational effort when the problem includes a large number of
arrows.
3. Dynamic programming and the network technique are two
methods for solving this type of problem with less computational
effort.
<NOTATION) L: LATHE, B: BORING MACHINE, D: DRILLING MACHINE, G:
GRINDER, M: MILLING MACHINE, MC: MACHINING CENTRE, P: PLANER,
S: SHAPER
Line Balancing
Scope of Line Balancing
Meaning of Line Balancing
In assembly lines production stages are tightly connected e.g. by conveyor
lines; each production stage is dependent on prior stages such that the
production time must be equalised for all stages, to assure smooth
production flow.
This type of continuous production is called a line-production system. Line
balancing is concerned with this system and aims at optimum decisionmaking in regard to:
• cycle time;
• number of workstations or production stages;
• grouping of work elements by assigning them on a same workstation such
that their precedence order is assured.
Problems of Line Balancing
In order to determine a proper line balance, the following basic
information is Required
• Product items and their production quantities;
• operations or work elements, their times and their sequence
for completing each product item;
• structure of assembly line (number of workstations) and its
technological abilities, etc.
Then the following two approaches to the assembly-linebalancing problem may be adopted
(1) Find the optimal number of workstations under a fixed cycle
time.
(2) Minimise the cycle time, hence, the total delay or idle time
Layout Design
• Meaning of Layout Planning After the optimum work flow has
been determined to change the form from raw material and
bought-in components to the finished product through the
conversion process, as established by process planning, the next
problem is to determine a spatial location for a collection of
physical production facilities associated with that specified work
flow, in connection with the operators, the plant location and
the site.
• This decision system is called layout planning/design. In
particular, when referring to the design of layouts for production
Aims of Layout Planning
(1) Efficiency of production
(2) Stability of utilisation of production facilities.
(3) Small work-in-process inventories.
(4) Flexibility and adaptability o f production.
(5) Economy of production.
Fundamental Patterns of Plant
Layout
(I) Product (or flow-line or
production-line) layout.
(II) Process (or functional) layout
(III) Group (- technology) (or
cellular) layout.
Plant Layout Design
The design of plant layout is mostly made in a heuristic way by a
choice of one layout from among the above alternatives such that
appropriate criteria may be ‘satisfied’. Some of the objectives for this
layout planning are (Francis et a i, 1992):
(1) minimise the overall production time;
(2) minimise the overall production cost;
(3) minimise the material-handling time and cost;
(4) minimise variation in types of material-handling equipment;
(5) minimise investment in equipment;
(6) utilise existing space most effectively;
(7) maintain flexibility of arrangement and operation.
 Systematic Layout Planning (SLP)
 Basics of SLP
 Various procedures for layout planning have been proposed and
developed.
 Most of them use some sort of heuristic approach, since
optimisation analysis is rather difficult for both process and layout
planning.
 An organised approach, referred to as systematic layout planning or
simply SLP, developed by Muther (1973), has received considerable
publicity due to its practical application in determining an
appropriate ‘best’ layout plan.
 Layout planning proceeds in the following four phases:
Layout planning proceeds in the following four phases:
(1) location—determining the plant site to be laid out;
(2) general overall layout— establishing the general arrangement
of the area to be laid out from the basic flow patterns;
(3) detailed layout plans—establishing the detailed actual
placement of each specific physical machine and equipment;
(4) installation— executing the layout plan.
The following five key factors are considered in this layout design
process.
• Product P : What is to be produced?
• Quantity Q : How much of each item will be made?
• Routing R : How will each item be produced?
• Supporting services S : With what support will production be
backed?
• Time T: When will each item be produced?
The layout procedure is based directly on three fundamentals, which
are always at the heart of any layout project:
(1) relationships— the relative degree of closeness desired or
required among things;
(2) space—the amount, kind, and shape or configuration of the
things being laid out;
(3) adjustment— the arrangement of things into a realistic best fit.
The SLP Procedure
Basic steps involved in SLP are as follows
(1) Input data
(2) Flow of materials
(3) Activity relationships
(4) Flow and/or activity relationship diagram
(5) Space determination
(6) Space relationship diagram.
(7) Adjusting the diagram
(8) Optimisation analysis.
(9) Evaluating and determining the best layout.
Production Flow Analysis
• Cellular Layout by Production Flow Analysis A method of
constructing a cellular (or GT) layout is production flow analysis
originated by Burbidge (1989).
• This classifies work flows logically and arranges production
facilities to several cells, using, e.g. cluster analysis which
• deals with ‘similarity’.
Logistic Planning and Design
Transportation Problems
Problems such as the allocation of the raw materials purchased
from various suppliers to various manufacturing divisions and
delivery of the finished goods produced in various factories to
various distribution depots/markets are called transportation
problems.
Obtaining an Initial Feasible Solution for the Transportation-type
Linear Program
(1) Northwest corner rule
(2) Least unit transportation cost rule
(3) VAM (Vogel’s approximation method)
Travelling Salesperson Problems
A distribution for minimising the total transportation distances (or times) needed to
circulate the products made in a factory among several places (markets) is called the
travelling salesperson problem.
Solving Travelling Salesperson Problems
 The branch-and-bound method for obtaining the optimal solution. However,
this method requires a great deal of computation time as the size of the problem
becomes large (NP-hard problems).1 This algorithm will be explained in
Section 14.2.4, being applied to solving large-scale flow-shop scheduling
problems.
 The dynamic programming approach for obtaining the optimal solution, by
constructing the recursive functional equation based upon the principle of
optimality, which was discussed in Section 8.4.2.
 The heuristic approach by starting from the factory and, first, taking a route to
the nearest market from the factory, then to the nearest market from the current
market, and so on, ... until all the places have been visited.
Manufacturing Optimisation
The optimisation analysis of manufacturing has been studied
since Gilbert’s first work on the economics of machining (Gilbert,
1950). He introduced the ‘maximum production rate’ and the
‘minimum production cost’ criteria, under which optimal
machining speeds were analysed by developing mathematical
models for single-stage manufacturing
The following three basic criteria (or principles) are utilised in
manufacturing optimization
(I) Maximum-production-rate or minimum-time criterion.
(II) Minimum-cost criterion
(III) Maximum-profit-rate criterion.
Ideally, optimisation should be applied to a total manufacturing
system such as material fabrication (casting, forging, etc.)— part
machining (cutting, grinding, etc.)—product assembly; however, the
present theory has not been extended to this kind of analysis for total
optimisation of a manufacturing system.
Basic Factors in Machining Operation
Optimisation analysis of single-stage manufacturing is the
fundamental of optimisation of integrated manufacturing
systems. For constructing basic mathematical models based upon
three evaluation criteria mentioned in the previous section the
following three important factors are formulated:
• unit production time;
• unit production cost;
• profit rate.
Unit Production Time
Unit production time is the time needed to manufacture a unit of
product. The shorter this time, the higher the productivity; and the
machining conditions for the least unit production time are based
upon the minimum-time criterion.