Predetermined motion time systems: MTM and MOST

Why it matters

A stopwatch needs a job that already exists and a worker to rate. Predetermined motion time systems (PMTS) let you set a standard time for a job that is still on the drawing board, compare alternative methods before buying fixtures, and avoid the rating arguments of time study. MTM and MOST are the systems used most in automotive, electronics and appliance assembly.

Key ideas

Principle. Almost all manual work is made of a small set of basic motions (reach, grasp, move, position, release, body motions). The time for each basic motion, performed by a trained worker at a defined standard pace, depends only on a few variables such as distance, weight and the difficulty of control. These times were found once from large film studies and published in tables. To time a new job, you list its motions, read each time from the table and add them up.

What the result means. A PMTS time is a normal (basic) time at the system's built-in standard performance, so no performance rating is needed. Allowances must still be added to get a standard time.

Time unit. MTM and MOST use the time measurement unit: 1 TMU = 0.00001 h = 0.0006 min = 0.036 s, so 1 h = 100,000 TMU and 1 min = 1,666.7 TMU.

MTM-1 (Methods-Time Measurement). Developed by Maynard, Stegemerten and Schwab (1948). Hand and arm motions: Reach (R), Move (M), Turn (T), Apply pressure (AP), Grasp (G), Position (P), Release (RL), Disengage (D); plus eye travel and eye focus, and body, leg and foot motions. Each motion is coded with its variables, for example R30B means a 30 cm reach to an object whose location varies slightly from cycle to cycle (case B). Times are read from the MTM-1 data card; they are not something to memorise or invent. MTM-1 is very detailed and suits short, highly repetitive cycles where seconds matter. Simplified, faster levels exist: MTM-2, MTM-3, MTM-UAS and MTM-MEK, which group motions and trade precision for speed.

MOST (Maynard Operation Sequence Technique). Developed by Zandin at H. B. Maynard (1970s). Instead of single motions it uses a few standard sequence models describing how objects are moved:

• General move (object moved freely through the air): A B G A B P A (action distance, body motion, gain control, action distance, body motion, placement, action distance).
• Controlled move (object stays in contact or is guided, e.g. pushing a lever): A B G M X I A (M = move controlled, X = process time, I = align).
• Tool use: A B G A B P * A B P A, where * is a tool parameter such as fasten, loosen, cut, measure, record or think.

Each parameter gets an index number (0, 1, 3, 6, 10, 16, 24, 32, 42, 54 …) from the BasicMOST data card according to distance, difficulty and so on. Time of a sequence in TMU = (sum of indices) × 10. If the sequence is repeated f times, multiply by f. Variants: MiniMOST for very short, highly repetitive cycles (multiplier 1), BasicMOST for general work, and MaxiMOST for long, non-repetitive operations such as maintenance and heavy assembly (multiplier 100). MOST is far faster to apply than MTM-1 with acceptable accuracy for medium and long cycles.

Other systems: Work-Factor, and MODAPTS (1 MOD = 0.129 s), which codes motions by body part.

Advantages: standards before production starts, no rating, consistent results between analysts, method comparison on paper, and a built-in method description. Limitations: trained analysts needed; mainly manual, not machine or process, time; analysis of long jobs with MTM-1 is slow; the job description must be exact, or the time is wrong.

Formulas

Time (s) = TMU × 0.036; Time (min) = TMU × 0.0006; Time (h) = TMU × 0.00001

BasicMOST: TMU = 10 × Σ(index values) × frequency

Standard time ST = NT × (1 + A)

• NT = PMTS normal time; A = allowance fraction of normal time.

Output per shift = Available time / ST

Worked examples

Example 1 (standard). An analyst reads the following from the MTM-1 data card (given data): reach 13.4 TMU, grasp 2.0 TMU, move 15.2 TMU, position 16.2 TMU, release 2.0 TMU. Allowances are 12 %. Find the normal time in seconds and the standard time in minutes.

1. Σ = 13.4 + 2.0 + 15.2 + 16.2 + 2.0 = 48.8 TMU.
2. NT = 48.8 × 0.036 = 1.757 s (= 48.8 × 0.0006 = 0.02928 min).
3. ST = 0.02928 × 1.12 = 0.0328 min.

No rating factor appears: the table values are already at standard performance.

Example 2 (GATE level). A BasicMOST analysis of one cycle gives two general-move sequences:

• Pick a washer from a bin within reach and place it loosely on a stud, done 4 times per cycle: A1 B0 G1 A1 B0 P3 A0.
• Walk to a rack, pick up a cover and bring it back to place it with light adjustment, once per cycle: A6 B0 G1 A6 B0 P1 A0.

Allowances are 15 %, and the shift has 480 productive minutes. Find the cycle time and the output per shift.

1. Sequence 1: Σ index = 1 + 0 + 1 + 1 + 0 + 3 + 0 = 6, so 6 × 10 = 60 TMU; × 4 = 240 TMU.
2. Sequence 2: Σ index = 6 + 0 + 1 + 6 + 0 + 1 + 0 = 14, so 140 TMU.
3. Cycle: 240 + 140 = 380 TMU = 380 × 0.036 = 13.68 s = 0.228 min.
4. ST = 0.228 × 1.15 = 0.262 min per cycle.
5. Output = 480 / 0.2622 = 1,830 cycles per shift.

Common mistakes

• Forgetting the × 10 multiplier in BasicMOST (index sum is not TMU).
• Applying a performance rating to PMTS times; they are already normal times.
• Mixing TMU conversions: 1 TMU = 0.036 s, not 0.036 min.
• Treating PMTS as a standard time: allowances still have to be added.
• Saying MOST is for short, high-volume cycles; MTM-1 or MiniMOST suit very short cycles, BasicMOST and MaxiMOST suit longer ones.

For GATE PI

Expect conversions between TMU, seconds and minutes, a BasicMOST sequence total with frequency, standard time and output from PMTS data, and one-mark questions on the features of PMTS versus time study (no rating, usable before production). Practise index sums and keep track of which result is normal time.

Quick check

1. Convert 250 TMU to seconds.
2. A BasicMOST sequence A1 B0 G1 A1 B0 P1 A0 is done twice. Total TMU?
3. Why is no performance rating used with MTM?
4. Which MOST variant is used for long, non-repetitive maintenance work?

Answers: 1. 9.0 s; 2. 4 × 10 × 2 = 80 TMU; 3. The table times are already at the standard pace of a trained worker; 4. MaxiMOST.