Methodology
Films were taken using constant speed cameras, running at 16 frames per second, of the work performed by qualified workers on the shop floor at the Westinghouse Brake and Signal Corporation. Each sequence was rated during filming by three qualified Industrial Engineers. These ratings had to agree within a close band, otherwise the sequence was not used.
The rating, or Levelling, system used was the Westinghouse or LMS system – so called after its originators Lowry, Maynard and Stegemerten. This system considers four factors independently:
- Skill – Proficiency in following the given method
- Effort – The will to work
- Conditions – The general work surroundings
- Consistency – of performance
Each factor is assigned an alpha rating, e.g. “B-“, “C+”, “A”, etc. which has a numeric value which is applied later. This reduces the possibility of “clock rating” and ensures that all factors are considered in the composite rating. Appendix 1 shows the model for Causes of Difference in Output on which the LMS system is based.
Layout, distances, sizes of parts and tools and tolerances were accurately measured and recorded on the shop floor to complement the later analyses.
The films were then projected frame-by-frame and analysed and classified in to a predetermined format of Basic Motions. These Basic Motions were Reach, Grasp, Move, Position, Release, etc. A motion was taken to begin on the frame in which the hand first started performing the motion and was taken to end on the frame in which the motion was completed. This allowed a time for each recorded motion to be calculated in seconds, by means of a frame count, and then “levelled” to a common performance.
Plots of the levelled times for the various motions were drawn. Analysis determined the best definitions of limits of motions and their major, time-determining variables, and resulted in, more or less, the structure which the manual motions of MTM-1 have today. Later work, using Time Study, gave the table of Body Motions.
In 1949, Cornell University conducted an independent study of MTM for the American Society of Mechanical Engineers. It used camera speeds of 64fps. The MTM data was replicated within very close limits. Minor discrepancies revealed by the faster camera speeds have since been corrected in the MTM-1 data.
Detailed research conducted under the auspices of the USA / Canada MTM Association have resulted in minor changes to the data and the application rules and in a greater understanding of the nature of the motions. The last change was made to the detail of the Apply Pressure data in 1973.
MTM is complementary to other Industrial Engineering charting analytical techniques; it does not replace them. It should be used after broader techniques have established the Necessity and Purpose, Place, Sequence, Person and Means of the tasks to be evaluated.
Read more about this topic: Methods-time Measurement
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