Saturday, February 18, 2012

Variables of Motion Related to the Operator - Description by Frank Gilbreth

Frank Gilbreth in his book Motion Study (1911) discussed variable that are to be studied in motion study. He identified a group of variable as variables related to motion.

VARIABLES OF THE MOTION


Gilrbreth commented that discussion of variables of the motion by him only shows that each vari-
able is a necessary factor in making motions standard.  He left  to the universities and to properly created and  equipped bureaus of the national government the task of  reducing motion study to an exact science.

ACCELERATION

In considering acceleration of a motion as a variable, issues of interest are: 
1. The amount of acceleration that it is possible or economical to obtain.
2. The means by which the acceleration can be obtained.
3. The effect of the acceleration on
a. Economy in time required to make the motion.
b. Economy in time required for rest to overcome the fatigue of having made the motion.
Examples. i. Laying brick on a wall from a floor, from the height of the floor level up to three feet eight
inches high above the floor, can be done with greatest speed  when the brick to be picked up are each maintained at a height of one foot three inches, plus two-thirds the height that the wall is higher than the level of t he floor on which the bricklayer stands. The brick to be picked up should never be higher than three feet eight inches under any circumstances.
By maintaining the height of the brick to be laid in this relative position to the height of the wall, the brick will always be in a position that permits the bricklayer to accelerate the speed of transportation of the brick by using the path of the quickest speed.  Greater outputs will be noticeable as an immediate result of maintaining the brick as nearly as possible at the heights above stated. 
2. In laying the filling tiers in any one course, it is most economical to lay the farthest filling tier first and the next farthest tier second, and so on. This enables the brick- layer to accelerate the speed of transportation of the brick up to the instant that it is deposited in the mortar. The above practice is, of course, much more important on shove-joint work than on brick-and-brick construction.
3. The possible benefits from acceleration should be taken into consideration when determining the sequence in which the tiers shall be laid. The position of the feet of the bricklayer is an important factor in obtaining the acceleration desired. For the best results the feet should be on separate springy planks, so that the transportation of the brick can be speeded up, in addition to the speed of the arms by simply throwing the body by the aid of the spring of the plank. 

AUTOMATICITY

Nearly all often-repeated motions become automatic. This is especially true of motions that require no careful supervision of mind or eye.
The automaticity of motions is of great assistance to the worker whose training and methods conform to standardized motions. This fact makes it necessary to have the apprentice taught the right motions first, last, and always. 
When work is done by both hands simultaneously, it can be done quickest and with least mental effort if the work is done by both hands in a similar manner; that is to say, when one hand makes the same motions to the right as the other does to the left. Most work is accomplished when both hands start work
at the same time, and when the motions can be made at the same relative position on each side of a central fore and aft vertical plane dividing the worker's body symmetrically.
Even if motions cannot be planned to be similar for each hand and performed simultaneously, the plane in
which the work is to be done should be carefully located. If motions are so arranged as to be balanced, as sug- gested, it is possible not only to take advantage of automa- ticity, but also to cut down jar to the body. It is on this well-known principle that the shockless jarring machine is built. Balanced motions counteract each other. The result is, less bracing of the body is necessary, and less fatigue ensues. 

COMBINATION WITH OTHER MOTIONS, AND SEQUENCE

A motion may be combined with motions that are (a) similar to it, and (b) dissimilar to it.
(a) If the motions combined are similar to it, advantage must be taken of the automaticity. Care must also be taken that all the motions made in a series of similar motions are necessary. Sometimes one effective motion is preferable to several not so effective.
Examples. i . When tapping a brick down to grade with a trowel, one brisk tap will do the work as well as
several light taps, and with much less time and effort.
2. If it is necessary to spread mortar on a face tier, one stroke of the trowel will do the work as well as several.
(b) If the motions combined are dissimilar, two motions may often be transformed into one.
Example. - - The motion used to spread mortar may be combined with the motion used to butter the end of the brick laid just before the mortar was thrown. Thus, the two operations may be transformed into one, and a saving of time and motions will result. In fact, so doing may have other distinct advantages, such as leaving better keying for plastering direct upon the wall.
This subject of combinations of motions is barely touched here. Its full treatment involves all other vari- ables, and it can never be considered standardized till each separate motion is a standard. 
DIRECTION
In most cases, the direction of a motion that is most economical is the one that utilizes gravitation the most. Oftentimes delivering material to a high-priced workman by leaving the material in a high position also makes easy unloading for the low-priced workman.
Example. Stacking up packs 2 feet high saves motions, and saves stooping when the laborer unloads his trucket.
" Direction" admirably serves as an illustration of the close interrelation of the variables. It is closely con-
nscted with "path." It involves discussions of anatomy, acceleration, and speed. It demands consideration of all variables of surroundings, equipment, and tools. The best ''direction of motion" is not only important
in itself for increase of output; it must also be kept constantly in mind in standardizing the placing of both
materials and men.

EFFECTIVENESS

Effectiveness has been touched upon in discussing " combination with other motions."  An effective motion is one that produces the desired result. Oftentimes whole processes, methods, and operations can be so changed as to make the succeeding motions much more effective.
Example. The introduction of the fountain trowel, used in connection with an ordinary trowel, made each
motion in handling mortar much more effective.

FOOT-POUNDS OF WORK ACCOMPLISHED


After all, a human being or a work animal is a power plant, and is subject to nearly all the laws that govern
and limit the power plant. It is a law of motion study that, other things being equal, the less number of foot- pounds of work done by the workman, the smaller percentage of working hours he must devote to rest to overcome fatigue.
It is therefore of great importance in obtaining the largest possible output that the work shall be so arranged and the workman so placed that he can do his work with the least possible amount of foot-pounds of work done per unit of output accomplished. This is where the philanthropic employer has often been rewarded without knowing it. In his desire to make conditions such that the workman was most confortable while working, he reduced the number of foot-pounds of work to that which was absolutely necessary to do the work. He surrounded the workman with conditions that enabled him to have no
fatigue, except that which was acquired from the motions of the work itself. He made conditions such that the workman was enabled to overcome the fatigue from his motions in the quickest possible time. 

INERTIA AND MOMENTUM OVERCOME

There are two ways by which the amount of inertia and momentum may be reduced.
i. By standardizing surroundings and equipment so
that the inertia and the momentum are limited to practi-
cally that of the materials, and not the materials plus
arms and body.
Example. Picking up ninety pounds of brick at one lifting.
2. By so standardizing motions that as few starts and stops as possible occur from the time the material leaves the stock pile till the time it is in its final resting place in the work.
Example. In laying brick by the " pick-and-dip " method on face tiers, a brick is lifted in one hand and a
trowel full of mortar in the other. The brick must come to a full stop in the bricklayer's hand while the mortar is being laid and the bed prepared, and then move to its final resting place, unless brick and mortar are dropped in two different places.
In laying brick by the " stringing-mortar " method, the mortar is laid and the bed prepared before the bricks are lifted. The brick are conveyed from the pack to the wall without interruption or delay.
Standard methods of performing work may enable the worker to utilize the momentum.
Example. If the bricks are conveyed from the stock platform or pack to the wall with no stops, the momentum can be made to do valuable work by assisting to shove the joints full of mortar. If, instead of being utilized, the momentum must be overcome by the muscles of the bricklayer fatigue, not full joints, will result. The ideal case is to move the brick in a straight path and make the contact with the wall overcome the momentum. 

LENGTH

A general rule of motion economy is to make the shortest motions possible.
Eliminating unnecessary distances that workers' hands and arms must travel, will eliminate miles of motions that operators make everyday. 
Example. Put the wheelbarrow body as close as possible to the pile that is to be put into it, so that the distance the packets are carried from the pile to the barrow, or the sand from the pile to the barrow, will be the shortest distance possible.
Standard tools, equipment, and surroundings are essential if length of motions is to be made standard.
As already said when discussing clothes, the workman of the present should have even his overalls, belt, and clothes so designed that they will hold the different kinds of tools that are oftenest used, so that they may be picked up in the shortest time that is, with pockets for nails, clips, clamps, etc. The tools should be so placed that the least and shortest motions can be used after they are picked up, as cartridges are placed in a cartridge belt. 

PATH

The determination of the path which will result in the greatest economy of motion and the greatest increase of  output is a subject for the closest investigation and the most scientific determination.  The laws underlying physics, physiology, and psychology must be considered and followed. The path most desirable is usually that which permits gravitation to assist in carrying the material to place.
Example. We have found that the most economical height for laying brick is twenty-four inches above where the bricklayer stands, while it is most economical to pick the brick from a height about three feet above where the bricklayer stands; that is, about one foot higher than the top of the wall where the brick is to be laid. The path is affected by the direction that the material is to be shoved as it moves into its final resting place.
Examples. When the packet is placed on the wall it should be placed so that the brick can be picked up and moved in a comparatively straight line with the direction that the brick will be shoved for filling a joint.
In theory the ideal path would be in a line of quickest speed from the stock platform to the wall.
In practice it is seldom that the most economical path for carrying a brick or mortar from the stock platform to the wall is exactly a straight line from one to the other. It will generally be most economical to move the brick in the path that will bend the arms the least and that will permit almost a swing from the shoulder.

PLAYING FOR POSITION

Each motion should be made so as to be most economically combined with the next motion, like the bil-
liard player who plays for position. The direction in which a motion is made may affect the time required for a subsequent motion.
Example. In laying brick the motion of placing the mortar for the end joint can be done quickest if it is done in the direction of the next motion, such, for example, as the next motion that puts the trowel in the position to cut off the hanging mortar.
The sequence of motions in bricklaying, that determines when the particular motion is to be made that puts the mortar in the end joint, depends upon whether the "pick-and-dip" or the " stringing-mortar " method is used. When the motions are made in the correct sequence, many of them can be combined so that two, and in some cases three, motions can be made as one motion, in but little more time than is required for one motion.
Example. Cutting off mortar, buttering the end of the laid brick, and reaching for more mortar all as one motion, in the " pick-and-dip " method.

SPEED

Usually, the faster the motions, the more output. There are other advantages to speed of motions besides the fact that they require less time. Speed increases momentum, and this momentum may be utilized to do work.
Example. The momentum of the brick helps to shove the mortar better into the joint.
Again, high outputs are generally the result of the habit of speed in motions. Habits of speed are hard to
form, and they are hard to break. Next to fewest motions, speed of motions is the most important factor of high record of outputs.
The list of variables here given makes no claim to being complete. The field of study is so immense that it is impossible as yet to give a complete and detailed method of attack.
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Source:
Motion study : a method for increasing the efficiency of the workman (1911)
Download from
http://www.archive.org/details/motionstudymetho00gilbrich
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Originally posted be me in http://knol.google.com/k/narayana-rao/variables-of-motion-related-to-the/ 2utb2lsm2k7a/ 2366

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