Scheduling METHOD STUDY PART II METHODS by niusheng11

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									METHOD STUDY PART II
METHODS AND MOVEMENTS
 AT THE WORK STATION




     WORK STUDY
     (IE411- 2010/2011 Fall)
                            METHODS AND MOVEMENTS
                             AT THE WORK STATION

Until now, we have gradually moved from the wide field of “measures of performance” in relation with
the “productivity of a company” as a whole, to the general consideration of how the productivity of
manpover and machines can be improved through the use of work study.

Then, still moving from the broader to a more detailed approach, we have discussed methods of
studying the movements of material and men around the working area and the relationships between
men and machines or of men working together in groups. When doing this, we have emphasized the
principle that the picture of overall method of existing operation must be examined before an attempt for
making improvements in detail.

Now, we will look at a single man working at a work place. This work place may be a bench or a table
which is generally called a “work station”.
However, before going into the specifics of “IMPROVING THE EXISTING METHOD” in a
work station, we will spend some time on the “WORK STATION DESIGN”.


WORK STATION DESIGN
Each work station in this context has a “design”. Neither method study nor time study can be performed
if there is no “work station design”. The work station design is a drawing, normally top view, of the
work station including equipment, materials and operator/worker space. Examples of work station
designs are given on the next page. The design of work stations has been an activity for industrial
engineers and technologists for nearly a century.

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                               METHODS AND MOVEMENTS
                                AT THE WORK STATION

                     LAYOUT                   Layout




                                                                                     Scale




            PRODUCT OR PART SKETCH




                                U-Bolt
                                                                                Product or
                                                                                Part Sketch
                     Bracket



 Nut

       Lock washer



Work Station Design : Clamp Assembly       Work Station Design : Machine Operation
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                     METHODS AND MOVEMENTS
                      AT THE WORK STATION
The first question asked by a work station designer who is new in the field of study is,
“Where to start?”. No matter where you start in work station design, another idea will
come along and make the starting point absolete. Where to start depends a great deal on
what is to be accomplished at the work station.
                                                 “The cheapest way to get into production” is
                                                 the best rule for starting point. Here, the
                                                 cheapest way means, the simplest machines,
                                                 equipment, and work stations. Any
                                                 improvement on this cheapest method must
                                                 be justified by savings. Therefore, you are
                                                 free to start anywhere, and then improve on
                                                 the first method. When the design is
                                                 finalized, you will end up with the
                                                 “Machinery & equipment layout data sheet”
                                                 which represents your work station.
                                                 An example of such a work station description
                                                 is given on the left. Observe that, there is a
                                                 note on the sheet saying the specifications of
                                                 anything involved in the work center design
 Work Station : Muffler Clamp Assembly           are given on the back side of the sheet.
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                            METHODS AND MOVEMENTS
                             AT THE WORK STATION
In summary, for the “Mufler clamp assembly work station” case, the “Machinery & equipment
layout data sheet” (work station description) will include the following work station design
information ;

                                                   1.   Work table (dimensions: length x width x height)
                                                   2.   Incoming materials (bolt, clamp, washers, and
         1
                                                        nuts; packaging and quantity must be considered)
                                                   3.   Outgoing material (finished product)
                        2                          4.   Operator space and access to equipment (in this
                                                        case the fixture).
          2                                2
                            6                      5.   Location of waste and rejects.
   5                                           5
                                                   6.   Fixture and tools (if available, jigs, equipment and
                                                        machine).
              4
                                                   7.   Scale of drawing.

                                                   DEFINITIONS:

   3                                               A JIG holds part in exact position and guides the tool that
                                               3   works on them.
                  Scale : 1cm = 15cm   7           A FIXTURE is a less accurate device for holding a part
                                                   which would otherwise have to be held in one hand while
                                                   the other is working on it.



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                      METHODS AND MOVEMENTS
                       AT THE WORK STATION
The Principles of Motion Economy

Industrial engineers and technologists have been continually developing guidelines for
efficient and effective work station design. These guidelines are collectively called “the
principles of motion economy”.

“Effectiveness” is doing the right things (the job), and “efficiency” is doing the things
right (method). So, effectiveness and efficiency mean doing the right thins right.
Effectiveness is important to consider first, because doing a job which is not necessary is
bad, but, making a useless job efficient is the worst sin.

The principles of motion economy can be grouped under three headings;

                         A. Use of human body
                         B. Arrangement of the work place
                         C. Design of tools and equipment




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                       METHODS AND MOVEMENTS
                        AT THE WORK STATION

A. Principles Related with the Use of Human Body
  When possible,
  1.   The two hands should begin and complete their movements at the same time.
  2.   The two hands should not be idle at the same time except during periods of rest.
  3.   Motion of the arms should be symmetrical and in opposite directions and should be made
       simultaneously.
  4.   Hand and body motions should be made at the lowest classification (classification of human
       body movements will be discussed later in this document) at which it is possible to do the
       work satisfactorily.
  5.   Momentum should be employed to help the worker, but should be reduced to a minimum
       whenever it has to be overcome by muscular effort.
  6.   Continuous curved movements are to be preferred to straight line motions involving sudden
       and sharp changes in direction. Continuous motions are more natural. When the body has to
       change direction, speed is reduced, and the result is two separate motions. If direction is
       changed less than 120o, two motions are required. Forexample, reaching into a box of parts
       lying flat on the table requires two motions. One motion to the lip of the box and another
       down in the box. If the box were placed on an angle, one motion could be used.
  7.   Ballistic (free-swinging) movements such as throwing a part in a tub or hitting a panic button
       are faster, easier and more accurate than restricted or controlled movements such as placing
       parts carefully. Safety and quality considerations are the best justification for controlled
       motions.

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                     METHODS AND MOVEMENTS
                      AT THE WORK STATION

8.   Rthym is essential to the smooth and automatic performance of a repetetive operation. The
     work should be arranged to permit easy and natural rthym whenever possible.
9.   Work should be arranged so that the eye movements are confined to a comfortable area,
     without the need for continuous change of focus.




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                          METHODS AND MOVEMENTS
                           AT THE WORK STATION
DEFINITION: MOTION PATTERNS
When we are talking about the “motion economy principles related with the human body”, infact we are talking
essentially about the “motion patterns of the hands”.

A motion pattern is the path taken by both hands in the process of making one part or pair of parts (if making
two at a time).The path for each hand must be unbroken and a complete loop. It is much like a computer
program similar to the ones used for Numerically Controlled (NC) machines. Thus, a motion pattern is also a
blueprint of the work method and a Bill Of Material for a time standard. This second definition will prove to be
useful in application of Predetermined Time Standards (PTS) systems.
Work station designs and motion patterns are required before PTS can be applied, because the motion
pattern (which is drawn on the work station layout drawing) is the blueprint of the work method and bill of
material for the time standard.
The work station design must be completed before the motion pattern is drawn. The first motion pattern is
drawn on the work station and then redrawn on its own page to allow analysis. The motion pattern and the
cyclograph for the same job would look identical. Cyclographs are nice but too expensive to produce.



                                                                                Work station and
                                                                                motion pattern for pin
                                                                                board: from average
                                                                                pin location to average
                                                                                hole = 6 inches.

                                                                                (one-element job)




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                     METHODS AND MOVEMENTS
                      AT THE WORK STATION

                                           Each job is made of elements. An element is one indivisible
                                           piece of work, which usually includes areach, a grasp, a
                                           move, and an alignment/position. In more simple terms, an
                                           element is getting one part or tool and doing some thing with
                                           it.

                                           Number of elements in a job is equal to the number of loops
                                           per hand.



Cyclograph : six-element job




        Motion pattern for cable clamp : three-element job (since there are 3 loops per hand)



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                          METHODS AND MOVEMENTS
                           AT THE WORK STATION
B. Principles Related with the Arrangement of the Work Station
 1.   Definite and fixed positions / places should be
      provided for all tools and materials to permit habit
      formation.
 2.   Tools and materials should be prepositioned to
      reduce searching.
 3.   Gravity feed should be employed whereever
      possible so that bins and containers can deliver the
      materials as close to the point of use as possible.
 4.   Tools, materials and controls should be located
      within the maximum working area and as near to
      the worker as possible.
 5.   Materials and tools should be arranged to permit
      the best sequence of of motions.




                                                             As much as possible, materials should not be stored
                                                             in the area directly in front of worker. Stretching
                                                             forwards involves the use of back muscles, thereby
                                                             causing fatigue.


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                         METHODS AND MOVEMENTS
                          AT THE WORK STATION
6.  “Drop deliveries” or “ejectors” should be used
    wherever possible, so that the worker does not have to
    use his hands for disposal of finished work.
7. Provision must be made for adequate illumination.
8. A chair of the type and height to permit good posture                          Drop
                                                                                  delivery
    should be provided.
9. The height of the work place/bench/table and seat
    should be so arranged that it allows alternate standing
    and sitting.
10. The color of the work place should contrast with that
    of the work and thus reduce eye fatigue.




                                                                                 Chair must be
                                                                                 Adjustible &
                                                                                 comfortable




Wrong work height will        Proper work height will   Design a work station
create problems.              produce less fatigue.     for sitting & standing
                                                        but keep work height
                                                        constant.

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                           METHODS AND MOVEMENTS
                            AT THE WORK STATION

B. Principles Related with the Design of Tools and Equipment
   1.   The hands should be relieved of all work of “holding” the work piece where this can be done
        by a jig, fixture or foot operated device.
   2.   Two or more tools should be combined wherever possible.
   3.   Where each finger performs some specific movement, as in typewriting, the load should be
        distributed in accordance with the inherent capacities of the fingers.
   4.   Handles such as those on cranks or large screw drivers should be so designed that as much of
        the surface of the hand as possible can come into contact with the handle. This is especially
        necessary when considerable force is to be used on the handle.
   5.   Levers, crossbars and hand wheels should be so placed that the operative can use them with
        the least change in body position and the greatest “mechanical advantage.

   The above given principles of motion economy can be made the basis of a summary questionaire
   which will help in designing or reorganizing a work station, to ensure that nothing is overlooked.



 Classification of Movements

 The fourth rule of motion economy in the use of human body, as discussed above, calls for the
 movements to be of the lowest classification possible. This classification is built up on the pivots
 around which the body members must move. This classification is given as follows;


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                         METHODS AND MOVEMENTS
                          AT THE WORK STATION

                                  Classification of Movements

               Class             Pivot               Body member(s) moved
                  1              Knuckle         Finger
                  2               Wrist          Hand and fingers
                  3               Elbow          Forearm, hand and fingers
                  4              Shoulder        Upper arm, forearm,hand & fingers

                  5               Trunk          Torso, upper arm, forearm, hand & fingers



It is obvious that each movement above Class 1 will involve movements of all classes below it. Thus,
the saving in effort resulting from using the lowest class possible is obvious. If in designing a work
station, everthing needed is placed within easy reach, this will minimize the class of movement
which the work itself demands from the worker. (Think about the case when you are eating your
lunch : what happens if the dish is moved 1 cm away from you at each reaching out to the dish? )




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                         METHODS AND MOVEMENTS
                          AT THE WORK STATION

Further Notes on Work Station Design

  1.   If similar work is being done by each hand, there
       should be a separate supply of materials or parts for
       each hand.
  2.   If eyes are used to select the material, the material
       should be placed in a position so that there is no need
       to turn the head.
  3.   The shape and the nature of the material influence its
       position in the layout.
  4.   Hand tools should be picked up with the least possible
       disturbance to the rhythm and symmetry of movements               Similar work done by each hand:
                                                                         separate supply of materials for
       (mirror image of the motion pattern). As far as                              each hand.
       possible, the worker should be able to pick up or put
       down a tool as the hand moves from one part of the
       work to the next (hand should not make a special
       movement for the tool). Natural movements (motion
       patterns) are along a curved line, not straight line. Tool
       should be placed on the arc of movements, but clear of
       the path of movement of any material which has to be         Natural movements are along a curved line
       slid along the surface of the bench.

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                        METHODS AND MOVEMENTS
                         AT THE WORK STATION

5.    Tools should be easy to pick up and replace. They
      should have an automatic return where possible.
6.    Finished work should be;

      a)   dropped down a hole or chute (use of
           gravity),
      b)   dropped through a chute when the hand is
           starting the first motion of the next cycle.
      c)   put in a container which is placed such that
           hand movements kept to a minimum,
      d)   placed in a container in such a way that the
           next worker can pick it up easily if the
           operation is an intermediate one.
                                                              Counterbalance : pre-positions
 7.    Always search for the possibility of using pedals or   tool close to the point of use.
       knee operated levers for locking or indexing work
       on fixtures. Same applies for the disposal of
       finished work.




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                 METHODS AND MOVEMENTS
                  AT THE WORK STATION

An Example of a Work Station Layout

                                  Let’s now look at a work station from the perspective
                                  of motion economy principles as we have discussed in
                                  the previous sections.

                                  Picture on the left is a typical example of a work
                                  station where assembly of small electrical equipment
                                  (in this case, electric meters) is accomplished. Just by
                                  looking at the picture, certain points are noticed at
                                  once;
                                  a)   A fixture has been provided for holding the work
                                       piece (here, the chasis of the meter). Thus, both
                                       hands of the worker are left free for the assembly
                                       work. The use of one hand purely for holding the
                                       part being worked on should always be avoided.
                                       An exception to this rule can be valid for
                                       operations so short that a fixture would not be
                                       justified.



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METHODS AND MOVEMENTS
 AT THE WORK STATION


           b)   The power screwdriver and box spanner are
                suspended in front of the worker so that she has
                to make only very short and easy movement to
                grasp them and bring them to the work. Note that,
                they are clear of the surface of the table and of the
                work.
                The hammer and hand screwdriver for use with
                the left hand are within easy reach, so that the
                worker can pick them up without searching. They
                are in line with the bins but below them. So, they
                do not get in the way.
           c)   All the small parts are close to the worker, located
                within the “maximum working area”. Each part
                has a definite location and the bins are designed
                with “scoop” fronts for easy withdrawal. Thus,
                parts are drawn forward with the tips of the
                fingers and grasped as they come over the
                rounded edge.


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METHODS AND MOVEMENTS
 AT THE WORK STATION



                Bins are arranged for symmetrical movements of
                the arms. Thus, the parts which are assembled are
                simultaneously picked up from bins in the same
                relative position on either side of the worker.

           d)   It is seen that, the worker has taken a small
                number of formed wire parts normally kept in a
                bin to her left front and placed them conveniently
                in front of and to the side of the work piece, in
                order to make a shorter reach.
           e)   The backrest of the worker’s chair is an interesting
                and ingenious improvisation. Special chairs with
                this type of backrest were not produced locally.




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                           METHODS AND MOVEMENTS
                            AT THE WORK STATION

Work Station Environment

No matter how motivated the worker or how effective the design of the individual work station, the
climate of the plant must be considered for the health and well being of the employees.
Environmental topics include illumination, vibration, noise, climate, toxicology and safety. Only
extremely severe and unusual conditions have immediate observable effects. In most cases,
secondary (possibly chronic) effects may occur.
Details of above indicated topics are beyond our present scope. For this reason, we will see some
brief descriptions related with them.

ILLUMINATION
The effects of illumination depend on three things;
                    a)   The individual’s perception of the quantity and quality of light,
                    b)   The light source output, and
                    c)   The visual environment that is illuminated.
The light output from a light source is measured in “lumen”s. The amount of light which can be used is the
“lumens / m2” or “lux” reflected from the illuminated object.

People see differently. As one becomes older, the amount of light required to see and complete tasks
increases dramatically. An aging work force will generally mean an increase in the amount of light required
to operate the company.

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                            METHODS AND MOVEMENTS
                             AT THE WORK STATION

Some of the interesting points with respect to the illumination of work environment can be summarized as
follows;

      The perfect light source would be free, provide true color, come from the proper direction and give the
     right amount of light upon demand. There is no such thing.

      Using sunlight requires decisions about, noise, ventilation, heat loss and many costly side effects.
     Also, the amount and direction of sunlight often require supplementing and occasionally require blocking
     (blinds, shades and curtains).

      The visual environment affects the way the work is seen. With the same employee and same light
     source; the size and the shape of the room, the color of the walls, ceiling and floor, the color and shape
     of the equipment, even the amount of dust in the environment will affect how the things are seen.

      Backgrounds for color inspection should be the same color as the part being inspected to make
     changes in surface characteristics appearent.

      Effective inspection of shapes, prints and colored objects require a contrasting background color.
     Light colored walls, floors and ceilings increase lighting efficiency and reduce glare.
     Moving machine parts should be painted in matte color while work piece that is being worked on
     should be a contrasting color.

     Glare can be indirectly reflected from a surface illuminated by too much light. Metallic or gloss finishes
     can increase this glare.
     For all repetetive industrial work, overall light levels should be above about 500 lux for better detection
     of color. Insufficient light will cause eye muscle fatigue, bloodshot eyes and headaches.

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                           METHODS AND MOVEMENTS
                            AT THE WORK STATION
VIBRATION

Vibration conditions in industry can be studied under following headings;
                 a) Segmental vibration caused by hand tools,
                 b) Whole-body vibration associated by large machines, and
                 c) Whole-body vibration of trucks and other transportation vehicles.

Vibration can be reduced;
                a) By redesigning at the source, or
                b) By isolating the person from the source of vibration.

Some methods of vibration reduction can be summarized as;
          Equipment can be mounted on springs or compression devices which absorbe vibration.
          Materials can be substituted to have little vibration properties.
          Amplitude of vibration can be reduced with more frequent balancing and maintenance.
          Machine motions such as speed and feed can be modified.
          Persons can be isolated from vibration by means of gloves, by insulating materials on
           handles, by soft floor matts, or by springs or cushions on chairs.

 The severity of vibration effects is affected by exposure time, acceleration, and frequency. The effects of
 whole –body vibration is most severe at frequencies of 4 to 8 hertz and above 0.1 G (The gain, G, is
 assigned a value of 1 for vibration frequencies to which the hand-arm system has the highest sensitivity)
 include abdominal pain, loss of equilibrium, nausea, muscle contraction and chest pain. Effects of
 segmental vibration at frequencies over 8 Hz and above 1.5 G include loss of strength, numbness,
 stiffness, pain and blanching of fingers.

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                           METHODS AND MOVEMENTS
                            AT THE WORK STATION
NOISE

Noise provides a common source of annoyance in an industrial environment. It requires employees to
increase concentration and this tends to increase fatigue. Noise may effect people in the following ways;

                a)    Degrade task performance.
                b)    Distract or annoy nearby persons.
                c)    Interfere with communication.
                d)    Contribute to temporary or permanent hearing loss.

 Noise is measured by a logarithmic scale and is expressed as dBA (decibels in the A band). A living
 environment such as home, hospital or courtroom measures about 40 dBA; a conferance room about 50
 dBA; a loud office about 60 dBA. At about 80 dBA, noise is very loud but has no permanent effect. At about
 90 dBA, exposure is to be limited to 8 hours; at 100 dBA there is a two-hour limit; above 115 dBA, exposure
 is not permitted.

 Noise reduction is accomplished by planning and management.There are three techniques to reduce noise;

                 a)    Placing a barrier to reduce transmission through air or other materials.
                 b)    Absorbing the reflected or casual noise.
                 c)    Reducing the volume or spectrum of the noise generator.




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                          METHODS AND MOVEMENTS
                           AT THE WORK STATION
COLD or HOT SURFACES

 Cold surfaces when touched with bare skin, can tear and damage it. Metal below 7 oC and wood or
plastic below freezing point should be handled with gloves. Metals become uncomfortable at 43 oC and
cause burns at 60 oC. Wood and plastics can be over 93 oC before burn occurs. In an environment with a
hot or cold radiating material, radiated energy will increase the effects of climate.


 Changes in body heat affect comfort. Body heat is controlled by airflow, temperature and humidity. Cold
conditions increase manupulative task effort. Very wet climates may require special precautions and
clothing to maintain health. Hot, humid climates add to the demands of physical work. Dry conditions put
increased strain on the body.

 Individual perseption of comfort changes with behaviour, diet, season, time of the day, job stress and
expectations. If we can assume that, clothing can be adjusted for discomfort, and light work is to be done,
individuals will be comfortable between about 19 and 24,5 oC. If the humidity is below 30%, then
temperatures up to 26 oC can be tolerated. Humidity readings between 70% and 20% are preferable.
Increased air flow can be a benefit at higher temperatures. Airflows of 12 m/min are common in the comfort
zone. At velocities of 30,5 m/min, temperatures can increase to about 27,7 oC.

 As temperatures increase beyond the comfort zone, sweating increases and skin temperature rises. As
workload is increased, more body heat is produced and the immediate effect is that less work can be
performed. In two-hour exposures with a humidity of 60%,
                       at 26,6 oC, the worker can do work above 300 kcal/hr,
                       at 32 oC , up to 300 kcal/hr,
                       at 37,8 oC, below 120 kcal/hr

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                           METHODS AND MOVEMENTS
                            AT THE WORK STATION
 As temperatures decrease below the comfort zone, the range between comfort and freezing will effect
the ability to perform dexterity tasks. Although generally protected, the hands, feet and face are often
subjected to increased stresses. The combined effect of exposure and reduced blood flow cause such
discomfort. Skills start to degrade at 15,5 oC, and can have a severe reduction of 20% at about 7 oC. Use of
different kinds of clothing (fabrics such as wool, designs which cover body closely but allowing skin side
layer of air, hand pockets etc) is the general approach for correcting the cold exposure. Wet clothing
increase the risk, in which case a clothing drying cabinet between breaks is useful. Air velocity reduction is
provided by means such as wind breaks or portable tents. Work load should be leveled because short
spans of high activity cause sweat and periods of inactivity cause discomfort.


 When the core temperature of the body and skin temperature converge, the body becomes unable to
eliminate heat resulting in possible dehydration and heat stroke. Work practices for protection against heat
illness include;
                        radiant heat protective clothing,
                        flexibility in work and rest scheduling,
                        provision of tepid (not cold) drinking water,
                        scheduling the tasks in cooler hours of the day,
                        training the workers in heat illness first aid.

When core temperature cannot be maintained, serious hypothermia and subsequent death from exposure
can occur. At a body temperature below 35 oC, severe shivering occurs. Short term exposure of -23 oC is
dangerious if gloves are not worn.




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                                  METHODS AND MOVEMENTS
                                   AT THE WORK STATION

                                           HEAT DISCOMFORT REDUCTION


  Reduce the temperature (air conditioning) ..........                 Quickest, but often most expensive approach.
  Reduce the humidity (dehumidifying) ..................               Increases the ability to sweat, permitting increased
                                                                        temperature tolerance.

 Increase air velocity (fan) ....................................      Increases evaporative heat loss.
 Reduce the work load (method study) .................                 Additional fixtures and holding devices are needed.
 Adjust the clothing (protective clothing) ...............             Special cooling systems or fabrics are available.
 Work practices ....................................................   Rest periods in cool area (72 oF).
                                                                        Drinking water and eating salted food.
                                                                        Trainig in recognizing and eliminating heat illness
                                                                        symptoms.
                                                                        Acclimatization allowances.


Physiology and psychology of the worker is very important in his / her performance. For this reason,
it is a part of the engineering design process to ensure that nothing in the manufacturing system
impedes workers’ performance. It is not enough that the work station is ensured to be comfortable,
safe and simple, but it must be percieved so by the worker.


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                           METHODS AND MOVEMENTS
                            AT THE WORK STATION

THE STUDY OF A WORK PERFORMED BY A WORKER AT A BENCH
The study of the work of a worker at a bench, in other words in a work station, starts just as in the same
way as a method study starts for cleaning process of old bus engines or process of receiving aircraft
parts. Independent of scale of the process we start with a “process chart”.

In this case, the chart used is called “two-handed process chart” or “left/right hand process chart” which
mainly shows the sequence of operations in a process. This chart is a special version of “multiple
activity chart”. More formal definition is given as follows;

             “The two-handed process chart is a process chart in which the activities of
             a worker’s hands (or limbs) are recorded in relation to one another”.


Sometimes, a time scale can be used in these charts just to show what the two hands are doing at any
given moment in time.

The two-handed process chart is generally used when one complete cycle of a repetetive work is to be
recorded. Recording is carried out in far more detail than what we had experienced in other macro level
process charts. What may be shown as a single operation in a flow process chart may be broken down
into many elemental activities which make up the respective operation.


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                           METHODS AND MOVEMENTS
                            AT THE WORK STATION
When preparing the two-handed process charts we use the same process chart symbols which we had
previously used for other process charts. However, due to the details covered their meanings are slightly
different in this case.


       Symbol        Meaning           Description

                   OPERATION           Is used for the activities of grasp, position, use, release, etc. Of
                                       a tool, component part or material.
                   TRANSPORT           Is used to represent the movement of the hand (or limb) to or
                                       from the work, or tool or material.

                   DELAY               Is used to denote time during which the hand or limb being
                                       charted is idle.

                   HOLD                The symbol is redesignated as “hold” and is used to represent
                                       the activity of holding the work, a tool or material (that is, when
                                       the hand being charted is holding something).

The symbol for “inspection” is not used because the hand movements when a worker is inspecting an
item are classified as “operations” on the two-handed chart.




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                    METHODS AND MOVEMENTS
                     AT THE WORK STATION
Notes About Preparation of Two-Handed Process Charts

                                      The chart form should include;
                                        Usual heading information.
                                        Adequate space for a sketch of the layout of the
                                       work station or sketch of jigs, fixtures etc.
                                        Spaces for the movements of right and left hands.
                                        Space for summary of movements and analysis of
                                       idle time.
                                      Some points worth mentioning for recording activity;
                                       1.   Observe the operation cycle a few times before
                                            starting to record.
                                       2.   Chart one hand at a time.
                                       3.   Do not record more than a few symbols at a
                                            time.
                                       4.   The action of picking up or grasping a fresh
                                            part at the beginning of a cycle is a good point
                                            to start recording (starting point must be
                                            definite). Start with the hand which handles
                                            the part first or with the hand which does most
                                            of the work.

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METHODS AND MOVEMENTS
 AT THE WORK STATION




             5.   Record actions on the same level only when
                  they occur at the same moment.
             6.   Actions which occur in sequence must be
                  recorded at different horizantal levels on the
                  chart. Check the chart for time relation of the
                  hands.
             7.   Care must be taken to list everything the
                  worker does and to avoid combining
                  operations and transports or positionings,
                  unless they actually occur at the same time.




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                    METHODS AND MOVEMENTS
                     AT THE WORK STATION

Example of a Two-Handed Process Chart : Cutting Glass Tubes

                                         This simple example describes how a two-handed
                                         process chart is constructed for cutting off short
                                         lengths of glass tube with the aid of a jig. The
                                         operations involved are self explanatory.

                                         RECORDING THE FACTS :
                                         In the original method, the tube is pressed to the
                                         stop at the end of the jig, marked with the file and
                                         then eased back for notching. It is then taken out
                                         of the jig for breaking. The chart goes into detail
                                         in recording the movements of the hands, because
                                         in short cycle work of this kind, fractions of
                                         seconds when added together, may represent a
                                         large proportion of the total time needed for the
                                         job.
                                         CRITICAL EXAMINATION :
                                         An examination of the original method, using the
                                         questioning technique, at once raises certain
                                         points;

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METHODS AND MOVEMENTS
 AT THE WORK STATION

             Q. Why is it necessary to hold the tube in the jig?
             A. The tube will always have to be held because the length
             supported by the jig is short when compared to the total
             length of the tube.
              Q. Why the tube can not be notched while it is being
              rotated? The right hand is waiting at the time.
              A. There is no reason why the tube can not be rotated and
              notched at the same time.
              Q. Why the tube has to be taken out of the jig to break it?
              A. The tube has to be taken out, because, if the tube were
              broken by bending against the face of the jig, the short end
              would then have to be picked out (an awkward operation).
              If a jig were so designed that the short end would fall out
              when broken, it would not be necessary to withdraw the
              tube.

              Q. Why pick up and put down the file at he end of each
              cycle? Can it not be held?
              A. Both hands are needed to break the tube using the
              original method. This might not be necessary if a new jig
              could be designed.




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METHODS AND MOVEMENTS
 AT THE WORK STATION
             DEVELOPING THE NEW METHOD :

             Once the above questions have been asked and
             answered, it is fairly easy to find a more
             satisfactory alternative solution to the problem.
             Figure on the left shows such a solution.
             It is seen that, a new jig has been designed. This
             new design makes it possible to cut the notch on
             the right hand side of the supporting pieces, so that
             by a sharp tap the short end will break away. Thus,
             it won’t be necessary to withdraw the tube and use
             both hands to break it.
             By this new approach, the number of the operations
             and movements have been reduced from 28 to 6.
             The expected increase in productivity in this way is
             133%. In fact, there is more increase, since, the
             irritating work of “position tube in jig” is now
             eliminated. Also, the new method enables the
             worker to work without closely looking at the work
             piece. This means that, workers can be trained more
             easily and become less fatigued.

                                                                 33
                         METHODS AND MOVEMENTS
                          AT THE WORK STATION

Micromotion Study
There are certain type of operations, particularly having very short cycles which are repeated
thousands of times within a normal working day (such as packing sweets into boxes or packing food
cans into cartoons). For such operations, sometimes it worths to go into detail inorder to find out the
best possible pattern of movement so that savings can be made for reducing the effort spent and the
fatigue on behalf of the worker who does them repeatedly.

The techniques used for studying such operations are collectively called as “micromotion study”
which frequently employs filming as a tool.

These techniques are based on the idea of dividing human activity into divisions of movements or
groups of movements which are known as “therbligs”.

Above indicated divisions are devised by Frank B. Gilbreth. He differentiated 17 hand (or hand and
eye) motions to which 18th had been subsequently added. These 18 basic therbligs cover “movements”
and “reasons for the absence of movement”. Each therblig has a specific “color”, “symbol” and “letter
code” for recording purposes. These can be seen in the table as presented on the next page.




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                         METHODS AND MOVEMENTS
                          AT THE WORK STATION




                                                Therbligs
Important Note :
Therbligs primarily refer to the motions of human body at the work station and to the mental activities
associated with them. They permit a much more precise and detailed descrioption of the work than
any other method described so far.

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                          METHODS AND MOVEMENTS
                           AT THE WORK STATION
 SIMO (Simultaneous Motion) Chart

The SIMO Chart was invented by Gilbreths when they found the “two handed chart / left hand – right
hand chart” to be insufficient in one important detail. When a movement of 10 cm has occured, the
two handed chart would only tell which hand was used. When evaluating human effort and resultant
fatigue, this information was not enough. It was important to determine which body member was
used. One of the Gilbreths’ many principles of motion economy is that the body member requiring the
least effort is to be used. Thus, a new column was added to the two handed chart which is used for
recording the body member used.

The formal description of the SIMO Chart can be given as follows ;

   “A SIMO Chart is a chart which is often based on film analysis and used to simultaneous
   recording of the therbligs or group of therbligs performed by different parts of the body against a
   time scale.”

Since SIMO Charts are primarily used for operations of short duration which are often performed with
extreme rapidity, it is generally necessary to compile them from motion picture (film) of the operation.
Such a film can be stopped at any point or projected in slow motion for detailed study.

A sample SIMO Chart can be seen onthe next page.



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           METHODS AND MOVEMENTS
            AT THE WORK STATION




                           In the given SIMO Chart, it is seen that the
                           movements are recorded against a time scale
                           measured in “winks” (1 wink=1/2000 min).
                           These are recorded by a wink counter placed in
                           such a position that it can be seen rotating
                           during the filming.

                           Again In the given SIMO Chart, motions for
                           each hand are classified according to the
                           classification which can be seen from the table
                           of “Classification of Movements” as on page
                           14 of this section.




An Example of SIMO Chart
                                                                         37
            METHODS AND MOVEMENTS
             AT THE WORK STATION



                             SIMO charts can be prepared in different
                             forms. The one on the left is prepared for the
                             operation of lifting 30 kg bags from a skid to a
                             conveyor.

                             In this chart, the “classification of motions” is
                             indicated in the form of 2 columns on each
                             side of the time axis for left and right hand
                             respectively. Each of the 2 columns is
                             subdivided into 5 sections each showing the
                             classification of the respective movement
                             where the closest one to the time axis is the
                             easiest and farthest from the time axis is the
                             most complex movement.




SIMO Chart : Heavy Lifting
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                         METHODS AND MOVEMENTS
                          AT THE WORK STATION

EVALUATING THE SIMO CHART

The SIMO Chart must be evaluated for two conditions ;

                         Potential stress on trunk (torso), and
                         Potential stress on fingers and wrists.

     If the job has a considerable amount of type 4 and type 5 motions (shoulder and full arm), then a
     thorough study of the ;
                         Weight involved,
                          The heights of beginning and ending motions,
                          The distance away from the body, and
                          Frequency of the activity in the task

     should be evaluated to ensure the worker has sufficient recovery time.

     If the activity has a considerable number of type 1 and type 2 motions, the task should be studied
     for potential “repetetive motion stresses”.

From the perspective of our course, we will not discuss SIMO Chart in further depth. The student
is adviced not to try out such a study in practice without expert supervision.


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