Chapter 25 Time Study Supplementary Material from: Learning Objective 6 Determine the time required to do a job using standard data, occurrence sampling, time study, and predetermined time systems. Supplementary Material from: Groover, M.P. (2007). Work Systems and the Methods, Measurement, and Management of Work, Upper Saddle River, NJ: Pearson Prentice Hall, pp. 319 - 360.

Time Study Also known as Involves Allowances made for Direct Time Study Stopwatch Time Study Involves direct, continuous observation of a task using a time measurement instrument to record time taken to complete task. Allowances made for personal needs fatigue unavoidable delays Dates back to 1883 Inextricably connected with origins and early history of IE

Direct Time Study Procedure Define and Document Standard Method Divide Task Into Work Elements Time Work Elements Rate Worker’s Performance Apply Allowances

Define and Document Standard Method Goal: “one best method” Seek worker’s advice, if appropriate Elements of Document Procedure (steps, actions, work elements, hand/body motions) Tools, equipment Machine settings (e.g., feeds, speeds) Workplace layout Frequency of irregular elements Working conditions Setup

Reasons For Thorough Documentation Batch production (likely to be repeated) Methods improvement by operator Disputes about method (too tight?) Data for standard data system

Divide Task Into Work Elements Series of motion activities logically grouped because of unified purpose. Guidelines Each work element should consist of a logical group of motion elements. e.g., reach, grasp, move, place Beginning point of one element should be end of previous. No time gap between elements. Each element should have readily identifiable end point. i.e., easily detected, no ambiguity Work elements should not be too long. < “several” min

Divide Task Into Work Elements Guidelines (continued) Work elements should not be too short. > 3 sec Irregular elements should be identified & distinguished. i.e., not every cycle Manual elements should be separated from machine elements. generally constant values Internal elements should be separated from external elements. i.e., performed by operator during machine cycle

“Irregular” and “Foreign” Elements Elements that occur routinely, but not every cycle – should be included: irregular elements (Groover) Elements that the observer didn’t anticipate –probably should be included: irregular elements (Konz & Johnson) Elements that are not normal work – should not be included: foreign elements (Konz & Johnson)

Time Work Elements Collect data on time study form (on clipboard).

Time Work Elements (2) Collect data on time study form (on clipboard).

Time Work Elements (3) Use stopwatch calibrated in 0.01 minutes: Snapback method Start watch at beginning of every element. “Snap” watch back to zero at end of element. Record time. Advantages Element variations easily observable No subtraction Continuous method Start watch at beginning of observation (or beginning of each cycle) Record elapsed time at end of each element. Let it run … Not so much manipulation of stopwatch Elements not so easily omitted Regular/irregular elements more readily distinguished (?)

Rate Worker’s Performance Standard performance = 100% Rate Individual elements Or entire work cycle Most difficult & controversial step in time study Requires analyst’s judgment

Apply Allowance Pure Manual Work Work Element a b c d* Obs. Time 0.56 min 0.25 min 0.50 min 1.10 min Perf. Rating 100% 80% 110% * irregular element performed every 5 cycles PFD Allowance = 15%

Apply Allowance Pure Manual Work Work Element a b c d* Obs. Time 0.56 min 0.25 min 0.50 min 1.10 min Perf. Rating 100% 80% 110% * irregular element performed every 5 cycles PFD Allowance = 15% Normal Time: NT = 0.56(1.00) + 0.25(0.80) + 0.50(1.10) + 1.10(1.00)/5 = 0.56 + 0.20 + 0.55 + 0.22 = 1.53 min Standard Time: ST = 1.53(1 +0.15) = 1.76 min

Apply Allowance Task Including Machine Cycle Work Element a b c d* Obs. Time 0.22 min 0.65 min 0.47 min 0.75 min Perf. Rating 100% 80% Mach. Time (idle) m 1.56 min PFD Allowance = 15% Machine Allowance = 20% * irregular element performed every 15 cycles

Apply Allowance Task Including Machine Cycle Work Element a b c d* Obs. Time 0.22 min 0.65 min 0.47 min 0.75 min Perf. Rating 100% 80% Mach. Time (idle) m 1.56 min PFD Allowance = 15% Machine Allowance = 20% * irregular element performed every 15 cycles Normal Time: NT = 0.22(1.00) + Max{0.65(0.80), 1.56} + 0.47(1.00) + 0.75(1.00)/15 = 0.22 + 1.56 + 0.47 + 0.05 = 2.30 min Standard Time: ST = (0.22 +0.47 + 0.05)(1 + 0.15) + Max{0.52(1 + 0.15), 1.56(1 + 0.20)} = 0.85 + 1.87 = 2.72 min

Number of Cycles To Be Timed Let X be a random variable, time of one work element in a task. Time several cycles to estimate true mean: close estimate α/2 1-α x α/2 1-α x α/2 1-α x low estimate high estimate μX Overall, P(μx lies within x + zα/2 [σ/√nc ]) = 1 – α where nc = number of cycles timed But σ unknown, so take preliminary sample of ns observations and use ∑(x-x)2 s = ns-1

Number of Cycles To Be Timed (2) P(μ lies within x + tα/2 [s/√nc ]) = 1 – α Interval size = x + kx where k = proportion of sample mean (e.g., if k = 10%, interval size = x + 0.10 x) kx = tα/2 [s/√nc ] (remember, s is an estimate of σ based on preliminary sample of ns) So, rearranging, nc = (tα/2s / kx)2

Number of Cycles To Be Timed: Example From preliminary study, engineer has collected ns=10 samples on one work element x = 0.40 min s = 0.07 (an estimate of σ based on preliminary sample of ns=10) How many cycles should be timed to ensure actual element time is + 10% of the sample mean, with 95% confidence? df = (ns – 1) = 10 – 1 = 9 α = 0.05, α/2 = 0.025 tα/2 = t0.025 = 2.262 Number of cycles = nc = (tα/2s / kx)2 = [2.262(0.07) / 0.10(0.40)]2 = 15.7 ≈ 16 cycles If 16 observed cycles yields x = 0.45 min P(μx lies within x + kx) = P(μx lies within 0.45 + 0.10(0.45)) = P(μx lies within [0.405, 0.495]) = 95%

Performance Rating Also called performance leveling. Performance relative to engineer’s concept of “standard” performance. Most common method based on speed or pace: speed rating. > 100% means faster than standard pace engineer must use judgment must consider degree of difficulty of work element worker’s pace relative to standard Standards Walk 3 mi/hr on flat, level ground, no load, 27-in steps. Problem: few work situations lend themselves to such precise measurement. However, many situations in which experts judge (e.g., gymnastics, dog shows) Solutions Experience (including feedback) Training (e.g., using training films)

Performance Rating (2) Pace depends on worker’s skill experience exertion level attitude toward time study So, select skilled worker familiar with job Accepts time study as necessary management tool Characteristics of good performance rating system consistency among tasks (one task to another) consistency among engineers easily understood related to standard performance (well-defined concept) machine-paced elements rated at 100% (no worker control of machine) rating recorded during observation, not after worker notification

Time Study Issue Why is time study important to the organization? What are some worker concerns? How can they be resolved?

Time Study Equipment: Mechanical Stopwatch 1

Time Study Equipment: Mechanical Stopwatch 2

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Time Study Results (from text)