FATIGUE MEASUREMENT AND FATIGUE ELIMINATION: HOW TO ATTACK THE PROBLEM
SCIENTIFICALLY
History of Fatigue Measurement.
Accurate fatigue measurement is in its infancy as applied to the
industries. Such measurement can take place only where there is
complete co-operation between the man measured and the man making
the measurements. With the co-operation, that is the natural result
of measured functional management, comes the possibility of making
accurate measurements of fatigue under either laboratory or shop
conditions. It is as easy to pretend to be tired as to pretend to be
working. There is little or no profit in measuring pretended states.
Under the scientific form of management there is no incentive to
pretend anything. The incentive is, rather, to show exactly what one
is doing and how one feels, in order that accurate records may be
made, and that the offered rewards may be received. We have, then,
at this stage, where every member of the organization realizes that
co-operation is necessary for the good of all, the opportunity to
measure fatigue with considerable accuracy.
We have also the means. The psychologists and physiologists who
have measured fatigue rely almost solely upon output as the unit of
measurement. Decrease in output in a comparable unit of time, and all
other working conditions remaining the same, is taken as indicative
of being the result of fatigue. The observed man who is measured may
add introspections, he may tell how he feels while working and at
the close of work; but this testimony of his, while interesting and
worthy to be recorded with the other data, cannot be submitted to the
accurate measurement of the observer. In applying fatigue measurement
to the industries in the same way that we measure activity and what
it produces, we try to discover at the same time the condition of
the worker by his own accounts as to how he feels. We have not only
conditions under which scientific observations can be made and a
method of making them, we have also devices for measuring both
activity and output and relative rate of output.
Fatigue, a Test of Efficient Activity.
As for the relation between fatigue and activity, practically all of
our knowledge of fatigue is derived from our knowledge of the activity
that produces it. We measure the activity itself, and its product. We
then measure the interval of time that elapses before the organism has
gained enough activity to perform the same work in the same amount of
time and with the same results. A study such as this cannot extend over
a short space of time only. It must be carried on until any fatigue
that is accumulated shows itself; but it is simply a question of
extending the time over which the experiment stretches, and of varying
the length of rest periods until the desired information is recorded
in the data. As we come to compare various activities and their
results, we find that the fatigue is a measurement of the efficiency
of the activity. If two methods of doing the same piece of work take
the same amount of time and produce the same amount of output, and
if the interval needed to recover from the second is longer than that
needed to recover from the first, then, other conditions being equal,
the first method is the more efficient. A close study of the variables
that affect the two methods will be necessary to show exactly why the
first method is more efficient than the second, but the excess fatigue
certainly shows that it is more efficient.
Fatigue can, then, be looked at in two ways:
1. As a product of doing work.
2. As a test of efficiency in doing work.
The amount of work done and the product are affected by various
elements which affect the activity.
The Activity.
The activity is affected by the amount of practice that one has had.
It is affected by the extent to which the action has become a habit.
It is affected by the degree with which one has got into the swing of
the work. This may be an individual difference. Some workers find it
possible to start at work at very much the pace that they will use when
they are well into it. A large number of our records shows that most
workers never get into the swing at the beginning of a work period. Not
only the hour of the workday, but the time in the work period will have
a strong effect upon the amount of work turned out. Again we have the
question of spurt, when for some reason or other the activity is being
performed at a pace that is above the normal pace. The effect of all
these elements of the activity upon the fatigue itself depends upon the
relation between mental fatigue and bodily fatigue. This relationship
must be worked out by psychologists and physiologists. It is for the
observer who measures fatigue in the industries to attempt to discover,
as far as he can, what fatigue exists, and why it exists, and then to
make both physical and mental conditions under which the activity is
carried on as favorable to efficient activity as possible.
Motion Study, Micromotion Study, the Cyclegraph, and the
Chronocyclegraph Method as Measurers of Activity.
We measure activity in two ways:
1. By motion study, which records in great detail the methods used in
doing the work.
2. By records of outputs when using the various methods.
[Illustration: FIG. 19
This picture shows the examination of the original micromotion films at
the motion study laboratory of the New England Butt Company.]
[Illustration: FIG. 19]
Motion study consists of dividing the activity into the smallest units
possible, measuring the variables of these units, studying the data,
and deducing methods by which the activity may express itself more
efficiently. Motion study, whatever its type, implies time study, in
that the time the motion occupies is one test of the efficiency of the
motion.
Micromotion study is the name we have given to our method of recording
motions and their surrounding conditions by means of a cinematograph
and one of our special clocks which registers extremely small intervals
of time, smaller than the elapsed time between any two pictures of the
cinematograph film. The micromotion method enables us to record easily
motions down to less than a ten-thousandth of a minute. This gives us
all the information we could desire for purposes of time study, and the
record is absolutely free from the errors in time due to the personal
element. Although many of the various elements, or units, that comprise
the path of a complete motion, or cycle of activity, appear on
different pictures in the film, it is difficult to visualize or measure
the orbit or exact path of the motions by means of the film.
The cyclegraph method permits us to record, measure, and see this orbit
or exact path of a motion or cycle of motions. Small electric lights
are attached to the hands, or any other members of the body involved
in the motion. A photographic plate or film is then exposed while the
motion is made, with the result that a path of light, which resembles
a white wire, is seen upon the developed plate, representing the path
of the motion. The effect is best gained by a stereoscopic photograph,
which shows this path in three dimensions.
The chronocyclegraph method enables us not only to see the path of
the motion, but also its directions, and the duration of the entire
motion and of its elements. These chronocyclegraphs are made by
attaching lights to the moving parts of the body, or machine, as
in the cyclegraph, and by introducing a properly timed, pulsating
interrupter in the circuit, which may be adjusted not only to record
the time and duration, but also to record these with different graphs,
representing the paths of each of several motions made by various
parts of the body and their exact distances, exact times, relative
times, exact speeds, relative speeds, and directions.
[Illustration: FIG. 20
This picture shows a lamp attached to the hand for the purpose of
taking cyclegraphs or chronocyclegraphs of motions in connection with
obtaining motions of least fatigue.]
[Illustration: FIG. 21
This picture shows an experiment that was carried on by us some time
ago for determining the laws pertaining to the times and fatigue of
motions of different lengths.
The operation studied is that of moving a seven pound weight. The times
are divided into three parts: Length of time from starting to picking
up weight; length of time from picking up weight to depositing; and
length of time of recovery to standing position from depositing. The
experiment proved that the time of motions of different lengths is
practically the same unless those of the same length are consecutively
repeated. The quantity of work that can be done in a day is, of course,
much less with long motions than with short ones, due to extra time
needed to overcome the fatigue of the long motions.]
By means of the “penetrating screen,” it is possible to pass a
cross-sectioned plane in any direction through any desired plane, or
through any number of planes in the cubic space under observation.
This makes it possible to record the data with great accuracy in three
dimensions, and to read the information from the data easily.
These various types of motion study supplement rather than supplant one
another. Motion study is primarily for the purpose of observing the
variables that affect such study, and for arousing such co-operation
between observed and observer, as will make possible the testing of
the differences of the effects of the variables. Micromotion study
provides for an accurate record of what happened, with all such
attending circumstances as appeal to the eye. It is the greatest aid
in transference of skill and experience from a worker who has it to
one who does not possess such skill and experience. The cyclegraph is
useful in providing a simple, easily understood record of the path
that any activity followed. The chronocyclegraph is most valuable
when the activity is complicated, and when the time and direction
of the elements of the motion must be visualized continuously in
order to analyze, measure, synthesize, and standardize the process.
The penetrating screen, finally, is useful in recording the three
dimensional paths and speeds of even the smallest unit of activity.
These methods of applying motion study have been patented, but have
been for years freely at the disposal of the colleges, which have
begun to use them as means for recording accurately scientific data of
various kinds. They have justified themselves as more accurate than
ordinary records of activity, and have within recent times been put on
a basis which makes their cost compare favourably with less accurate
methods of measurement. What is more, we have discovered in our data,
especially in the chronocyclegraphs, direct records of fatigue,
that we believe are the first records of fatigue ever made under
industrial conditions. The micromotion films also show breaks in well
established habits of several motions that are undoubtedly due to
fatigue, but the irregularities in the orbit line, that appear in the
cyclegraphs, and that must, because of close control of the variables,
be due to the fatigue alone, are more impressive from the physiological
viewpoint.
[Illustration: FIG. 22
Typical chronocyclegraph of the motion and fatigue study of a
bricklayer, laying three bricks in the old method.]
[Illustration: FIG. 23
Typical cyclegraph of motion and fatigue study on a drill press,
showing cyclegraph of path of motions of the left hand.]
[Illustration: FIG. 24
Typical chronocyclegraph of compositor setting type by hand.]
Testing the Work by Motions Required.
It is for motion study to explain the methods of deducing standard
methods by using activity records obtained through the various types
of motion study data. Many such standards have been derived. We have
in our motion study data many elementary motions with records of the
space they cover and the amount of time they require. With these we can
test the given work to see which of these motions it includes. Having
tabulated this, we can make an intensive study of the motions that
remain. When this study has been made, we can combine the resulting
elementary motions that have proven themselves most efficient into the
working method, and classify the work as work of a type requiring a
certain set combination of motions.
Testing Workers by Motion Capabilities.
In the same way we may test a worker by motion learning capabilities,
before assigning him to any kind of work. Having reduced activities
to their motions, we can test the worker’s physical capability; his
mental capability we can test by determining his learning curve. To
these results we add a record of his interest in various types of work.
From the resulting three types of records, we can make placements that,
we believe, are far in advance of any that have been made up to the
present time.
The Use of Activity Records as Data for Eliminating Fatigue.
The fact that activity records are made of extremely small elements
moving through a short path in a small amount of time means that the
fatigue records cover the same short periods. This is a great help
in making fatigue study. A new combination of elements of activity
will also mean a combination of concurrent, or included, elements of
fatigue. The combination may have some effect on the activity. If so,
it will also affect the fatigue, but at the present state of the art
the most accurate and satisfying work can be done by making use of
activity records to eliminate unnecessary fatigue, without waiting
for some hypothetical, direct records of fatigue, that may be worked
out in the future. In other words, if you have accurate records of
fatigue included in your activity records, use these immediately,
without attempting to make separate records of the fatigue, that, while
valuable, will mean delaying fatigue elimination, perhaps indefinitely.
The Time Element.
Too much credit can never be given to Dr. Taylor for his emphasis
on the laws of the time element. He was the first to call to our
attention the fact that operations should be divided into the smallest
possible, timable units for setting tasks. In this way it is possible
for timed elements to be used in many combinations, thus eliminating
an enormous amount of unnecessary work. Dr. Taylor also recommended
that work periods should be timed separately from the rest periods.
Our new measuring devices for time study make it possible to record
much shorter intervals of time than were heretofore known, and now the
limiting factor in the problem is no longer the quickness with which we
can use a stop-watch.
Our methods and devices have been criticised as being specially adapted
to problems involving the minutia of motions, but too expensive for the
general time study purposes. A moment’s consideration will show that
the turning of the crank of the cinematograph may be done as slowly as
the requirements of the particular case of time study demand. In fact
we have films that were taken at the rate of one picture every ten
minutes. With the sixteen pictures to the foot, a foot will last one
hundred and sixty minutes, or two hours and forty minutes, at a total
maximum cost of six cents. If desired, the speed of the crank can be
instantly changed to any desired speed to enable one to take pictures
too quickly to be seen with the eye, and more accurately than the
highest-priced time study man can take by means of a stop-watch.
Our methods, devices, and records of activity and of output fulfil
every requirement, and are now perfectly satisfactory. Fatigue still
remains the elusive factor. Nothing but long-continued observation,
absolute accuracy and co-operation between all interested will reduce
fatigue study to the science which motion study has become.
The Standardization of Work and Rest.
Meantime, in standardizing work and rest periods, it is customary and
proper to make a larger allowance for fatigue than the records show to
be necessary. We cite as an example a case of folding handkerchiefs.
The old method of folding was to have the workers seated at low tables
in chairs of ordinary height, working throughout the entire day, with
the only rest periods an hour at noon and such ceasing from folding as
took place when the workers went for supplies, or took back finished
product to be checked, or other rest periods that they took at will,
as the work was piece work. After an intensive study of the problem,
made not only to increase their output but to better their working
conditions and allow them to earn more money with less fatigue, the
following schedule of work and rest periods was adopted.
Each hour was divided into ten periods. The work was placed on a
work table of the proper height. The handkerchiefs already folded,
those being folded, and those to be folded were arranged in the most
convenient and efficient manner. All variables of the work had been
studied, and the results of the study standardized. The first four
periods, that is, the first twenty-four minutes, the girl remained
seated. She worked five minutes and rested one; again worked five
minutes and rested one. That is to say, she had four minutes’ rest out
of the twenty-four, and spent this rest seated so that she might lose
no time in getting back to the work. The next two periods, that is for
twelve minutes, the girl was standing. Again she worked five minutes
and rested one minute, and for the second time worked five minutes and
rested one minute. That is, she rested two out of the twelve minutes
in the same position in which she worked. The third group, a space
of eighteen minutes, she spent either sitting or standing, as she
pleased. Here also she worked five minutes, rested one minute; worked
five minutes, rested one minute; worked five minutes, and rested one
minute in the position, either standing or sitting, which she herself
had chosen. The last period, which consisted also of six minutes, was
spent by the girl walking about and talking, or amusing herself as
she otherwise chose. With this might be combined the last rest minute
or period No. 9, which thus gave her seven consecutive minutes for
unrestricted rest activity.
This was the schedule for all hours of the day except the hour before
noon and the hour before closing time at night. In these hours the
first nine periods resembled the first nine periods of the other hours;
but the tenth period was spent in work, as a long rest period was to
follow.
At the end of the day’s work under these conditions the girls
accomplished more than three times the amount of their previous best
work, with a greater amount of interest and with no more fatigue. It
may be stated here that the primary aim in this investigation was
not to eliminate fatigue, but to increase the wages of the girls by
raising the output. The operators had not seemed overfatigued at the
start. They maintained that they were less tired at the close of the
day when using the new method, and certainly the amount of fatigue
caused by producing an amount of output such as was made under the old
method was reduced to an enormous extent. With further practice these
preliminary results will be further improved.
It is of fundamental importance in making an investigation of this type
that the allowance for fatigue be greater than the physical condition
of the worker at the end of the day seems to indicate necessary.
It is also fundamental that the results of the investigation be at
once incorporated into actual shop practice. If each member of the
organization is at once placed under such working conditions that he
can enjoy the rest periods along with the high pay that comes from
a large product, he will co-operate most fully in the progressive
work of fatigue elimination. It is a fundamental rule of scientific
management that the rate once set must never be cut. It should also
be a fundamental principle of our management that rest periods once
established should not be abolished or shortened. Let the error, if
error there is, always result to the advantage of the worker, never
to that of the employer. If you have not allowed enough rest, make
the allowance larger, then reinvestigate. If you have allowed too
much rest, let the job stand as one to be given for special merit, and
attack some other problem. The result will be an increased co-operation
which will more than compensate for the occasional over allowance for
fatigue.
Summary.
Fatigue measurement, as applied to the industries, is a new science. It
is being developed through a study of the data of activity. The methods
of measurement of activity are motion study, micromotion study, the
cyclegraph, the chronocyclegraph, and the penetrating screen. Through
the data derived by these, we standardize motion paths, motion habits,
and all other motion variables. These enable us to test and classify,
select and place, both work and workers, and to eliminate unnecessary
fatigue. Through the time element we compare our various data, and
finally arrive at results that enable us to standardize work and rest
periods. Any errors in length of rest periods must result to the
advantage of the worker.