CHAPTER VIIFATIGUE MEASUREMENT AND FATIGUE ELIMINATION: HOW TO ATTACK THE PROBLEM SCIENTIFICALLY
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, inorder 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 methodof making them, we have also devices for measuring both activity and output and relative rate of output.
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 ofoutput, 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.
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 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 largenumber 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.
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.
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.
Fig 19 - original micromotion films at the motion study laboratory of the New England Butt Company
Fig.19This picture shows the examination of the original micromotion films at the motion study laboratory of the New England Butt Company.
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, appearon 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, representingthe 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.
Fig 20 - lamp attached to the hand for taking cyclegraphs or chronocyclegraphs of motions
Fig.20This 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.
Fig 21 - lamp attached to the hand for taking cyclegraphs or chronocyclegraphs of motions
Fig.21This 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 isuseful 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 establishedhabits 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.
Fig 22 and 23 - chronocyclegraph of the motion and fatigue studies of bricklayer and drill press
Fig.22Typical chronocyclegraph of the motion and fatigue study of a bricklayer, laying three bricks in the old method.
Fig.23Typical cyclegraph of motion and fatigue study on a drill press, showing cyclegraph of path of motions of the left hand.
Fig 24 - Typical chronocyclegraph of compositor setting type by hand.
Fig.24Typical chronocyclegraph of compositor setting type by hand.
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.
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 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 theart 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.
Too much credit can never be given toDr.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 oftime 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-continuedobservation, absolute accuracy and co-operation between all interested will reduce fatigue study to the science which motion study has become.
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. Thework 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 standingor 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 periodNo.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 producingan 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.
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.