PRE-DETERMINED MOTION TIME SYSTEMS (PMTS)
EW. Taylor, was a pioneer in this field of PMTS. His idea was to establish a library of predetermined element times so that the correct job method could be planned, and its time be established, before the job reached the production floor. He managed to go only part of the way in this, for his approach was to establish element times by time study.
A work measurement technique whereby times established for basic human motions (classified according to the nature of the motion and the conditions under which it is made) are used to build up the time for a job at a defined level of performance. PMT systems are an important development within the field of time and motion study
F B Gilbrethâ€™s therblig and filming techniques opened up another avenue with the possibility of identifying and timing the types of motions that are the fundamental ingredients of any manual element. It was seen that this could provide a greater potential for judging the effectiveness of a motion pattern structure, as well as determining the time required for its performance. American research in this field came to fruition after 1940. Now there are a number of systems in existence such as Motion Time Analysis, Basic Motion Time Study, Work Factor and MTM are the best known.
MTM itself came into prominence in 1948 on the publication of the American book â€˜Methods Time Measurementâ€™ by Maynrd, Stegmerton, and Schwab. By their definition: â€˜Methods time measurement is a procedure which analyses any manual operations or method into the basic motions required to perform it and assign to each motion a predetermined time standard which is determined by the nature of the motion and the conditions under which it is madeâ€™
The motion classification and times for this system were derived from the analysis of many micro-motion films taken at 16 frames a second on a cine camera actuated by a constant speed motor. From this research the essential data was set out in ten small tables with the captions:
3. Turn and apply pressure
8. Eye travel and eye focus
9. Body, leg and foot motions.
10. Simultaneous motions.
Each table classifies the sub-divisions of its topic, and tabulates the time to be assigned according to the category of motion and the factor that causes the time to vary. These times are expressed in â€˜Time Measurement Unitsâ€™, where one TMU is equal to 0.00001 hour.
When using this system, the analyst may either establish the sequence of motions for the job by observation, or he may visualize what should take place and plan the best sequence or motions according to the data that gives simplest and economical movements. To enable him to pursue either course and to explore alternative sequences quickly, each category of movement possesses a letter code to give it a distinct identity, e.g. R12ACD would mean â€˜Reach, 12 inches, Case A with Change Direction. Given this the MTM tables can then be referred to and the relevant times calculated and assigned to their sequence on the chart.
Both Work Factor and simplified PMT operate in much the same way as MTM. Mainly, it is the classification of detail and the units recommend it in its simplicity and in the units of time used. Although simplified PMT system recognizes the BS rating scale and expresses its standards in milli-minutes that is 0.00001 minutes.
The advantages of such system are numerous
1. Evaluating time standards before the job is running.
2. Comparing method alternatives with the minimum need for experimentation.
3. Aiding tool and product design.
4. Setting targets and motion pattern in operator training, and so on.
There are, of course, limitations. These systems can deal only with manual content of a job. If the manual activities control and dictate the time of a job cycle, then PMT can produce a standard for the job, otherwise it can contribute to different objectives only.
There are instances where certain categories of movement are subject to a restraint not catered for in the data. An article may have to be moved with caution, or a controlled movement may be necessary to obtain a desired quality of finish. There are occasions where it is difficult to decide the sequence of finger movements that will act on a job. These examples can be regarded as minor problems on some jobs because careful approximation is often a satisfactory expedient. The main disadvantages are the time it takes to analyze a job into its very small constituents, calculate the times that apply, find the necessary RA, and add al the data to reach a standard. If the job detail is established by observation, then there is additional difficulty of making an accurate recording of fast and intricate motions. This, too, may increase recording time.