Finite Element Method (ME-504 (C)) - Unit 1 Short Notes

UNIT 1: FOUNDATIONS OF WORK STUDY, METHOD STUDY, AND ERGONOMICS

I. INTRODUCTION & DEFINITIONS

Work Study is a systematic examination of activities to improve efficiency and productivity.

• Objectives: Improve processes, reduce waste, optimize resource use, establish standards.

• Relevance: Essential for lean manufacturing, cost reduction, and competitive advantage.

Method Study (Motion Study) focuses on how a job is done. It seeks the "best method" for performing a task.

• Systematic Steps:

  1. Select the job.

  2. Record all facts (using recording techniques).

  3. Critically examine the recorded data.

  4. Develop the improved method.

  5. Install the new method.

  6. Maintain the standard method.

Ergonomics (Human Factors Engineering) studies the interaction between humans, tools, equipment, and the work environment.

• Objectives: Design tasks, jobs, products, and environments to fit human capabilities and limitations, enhancing safety, comfort, and performance.

Work Measurement determines the time a qualified worker should take to complete a specified task at a defined performance level.

• Key Output: Standard Time.

Standard Time vs. Normal Time:

• Normal Time: Observed Time × Performance Rating. Reflects the time for the work at the worker's pace, excluding allowances.

• Standard Time: Normal Time + Allowances. The time allowed for the job including personal, fatigue, and delay allowances. It is the time used for planning and costing.

\boxed{\text{Standard Time} = \text{Normal Time} \times (1 + \text{Total Allowance Fraction})}

II. RECORDING TECHNIQUES FOR METHOD STUDY

A. Process Chart Symbols (Basic 5 + Combined):

B. Types of Process Charts & Distinctions:

C. Other Motion Study Tools:

• SIMO Chart (Simultaneous Motion Chart): Records the simultaneous activities of multiple operators/body parts on a common time scale. Used for group work and crew balance.

  • Construction: Vertical columns for each operator/body part, horizontal time scale.

• Travel Chart: A matrix showing the frequency of movements between departments/places. Used for plant layout planning to minimize material handling.

• Memo Motion Study: A quick, low-cost observation technique using a pre-printed form (memo) to note down activities at regular intervals (e.g., every 5 minutes). Useful for preliminary surveys and work sampling.

• String Diagram: A scaled plan with a string/pin to trace and measure the path of movement (e.g., of a worker or material). Used to quantify travel distance and test new layouts.

• Memo Production Study: A variation where the memo records both activity and quantity produced at each observation interval. Helps correlate activity with output.

III. WORK MEASUREMENT TECHNIQUES

A. Time Study

1. Procedure: Select job → Break into elements → Time several cycles (with stopwatch) → Rate performance → Calculate Normal Time → Add Allowances → Standard Time.

2. Rating (Performance Rating): Assessing the worker's pace relative to standard pace.

   • Methods: Speed Rating, Westinghouse System (factor for skill, effort, conditions, consistency).

3. Allowances: Extra time added to Normal Time to get Standard Time.

   • Types: Personal (3-5%), Fatigue (4-8%), Delay (unavoidable), Process (included in element time).

   • Factors Influencing: Nature of work, environment, individual factors.

B. Work Sampling (Activity Sampling)

• Concept: Statistical technique to estimate the proportion of time spent on various activities by taking random observations.

• Procedure: Randomly observe worker at large number of instances → Classify activity (working/not working) → Calculate % time.

• Standard Time Calculation (with rating & allowance):

  Let:

  • $P$ = Fraction of time working (from observations)

  • $R$ = Performance Rating factor (as decimal, e.g., 1.10 for 110%)

  • $A$ = Total Allowance fraction (as decimal)

  • $T$ = Total available time for study

  • $N$ = Number of units produced in time $T$

  \boxed{\text{Standard Time per unit} = \frac{T \times P}{N \times R \times (1 - A)}}

  Alternatively:

  \boxed{\text{Standard Time} = \frac{\text{Normal Time per unit}}{(1 - A)} \quad \text{where} \quad \text{Normal Time} = \frac{T \times P}{N \times R}}

Common Pitfall: Forgetting to adjust the working time fraction ($P$) by the rating factor ($R$) before applying the allowance.

C. Standard Data

• Definition: Pre-determined time values for specific motions, elements, or operations based on past studies or PMTS.

• Advantages: Speeds up future studies, ensures consistency, reduces cost of measurement, useful for estimating.

D. Predetermined Motion Time Systems (PMTS) - e.g., MTM

• Method Time Measurement (MTM): Breaks down any manual task into basic motions (reach, grasp, move, release, etc.). Each motion has a pre-determined time value (in TMU - Time Measurement Units, 1 TMU = 0.000036 sec) based on the motion's class and distance/weight.

• Advantages: Objective, independent of worker pace, excellent for method comparison and design, detailed analysis of motions.

E. Work Factor

• Definition: A factor representing the difficulty of an element relative to a standard condition. Used to adjust basic times.

• Classification:

  1. Physical Effort Factor: Based on force, weight, posture.

  2. Mental & Sensory Factor: Based on visual/auditory attention, decision complexity.

  3. Environmental Factor: Based on temperature, noise, lighting.

IV. INTEGRATION & APPLICATION

• Integration of 'Operation and Operator': The goal is to design the operation (tools, layout, sequence) to perfectly suit the operator's physical and mental capabilities. This means the method should be designed first, then the operator is trained to follow it precisely.

• Standardisation of Motion: Critical prerequisite for a valid time study. All workers must perform the job exactly the same way (the best method). Without this, time data is meaningless as it reflects method variations, not pace.

V. ERGONOMICS / HUMAN FACTORS ENGINEERING

A. Man-Machine System

• Definition: A system where a human operator (man) works in conjunction with a machine/tool to achieve a goal.

• Types:

  1. Semi-Automatic: Human starts/stops machine, machine does the work.

  2. Automatic: Human monitors, machine operates.

  3. Skeletal: Human provides power, machine guides (e.g., hand tool).

  4. Manual: Human provides both power and control.

B. Anthropometry

• Definition: The science of measuring the human body's physical dimensions.

• Importance: Ensures fit between human body and workspace/equipment (e.g., chair height, tool grip, reach distances). Prevents discomfort, injury, and inefficiency.

• Types of Measurements:

  • Static: Body dimensions in a stationary posture (stature, sitting height, limb lengths).

  • Dynamic: Dimensions during movement (reach envelope, working postures).

• Factors Affecting Data: Age, sex, ethnicity, nutrition, socioeconomic status, posture.

• Purpose: Design for percentiles (e.g., design for 5th percentile female to 95th percentile male to accommodate most users).

C. Sensory Information Processing

1. Coding: Transducing physical stimuli (light, sound) into neural signals.

2. Selection (Attention): Filtering relevant from irrelevant stimuli. Limited channel capacity.

• Human Information Processing Model:

  Stimulus → Sensory Register → Perception/Processing → Decision → Response → Action

  • Includes feedback loops and memory (short-term/working, long-term).

D. Displays

• Visual Displays: Most common.

  • To be Effective: High contrast, appropriate size, clear symbols, placed in optimal field of view.

  • Design Guidelines: Use common symbols, minimize glare, group related info, use color meaningfully (red=danger).

• Tactual Displays: Use touch/pressure.

  • Characteristics: Must be distinguishable by shape/texture, require active exploration, limited information capacity.

E. Work Environment & Task Design

• Environment: Control noise, vibration, temperature, lighting, air quality.

• Task/Work Organisation: Design for variety, whole-body involvement, meaningful content, autonomy, and feedback.

F. Relative Capabilities: Human vs. Machine

VI. WAGE INCENTIVE PLANS (Output-Based)

• Differential Piece-Rate: Two rates - higher for meeting/exceeding standard, lower for below standard.

• Halsey's 50-50 Plan: 50% of time saved is given as bonus to worker.

• Rowan's Premium Plan: Bonus = (Time Saved / Standard Time) × Hourly Rate × Time Taken. (Bonus % decreases as more is saved).

• Barth's Plan: Fixed hourly rate + bonus based on standard minutes per unit (not time saved). Encourages high output.

• Gantt's Task and Bonus Plan:

  • Worker gets high piece-rate only if standard task is completed within standard time.

  • If task is not completed in standard time, worker gets minimum guaranteed day rate.

  • Key: Clear, achievable standard task.

• Merrick's Multiple Piece Rate Plan:

  • Three-tier piece-rate:

    1. Below 83% of standard: Low rate.

    2. 83% to 100% of standard: Medium rate.

    3. Above 100% of standard: High rate.

  • Encourages workers to reach at least the standard output.

VII. CALCULATION-BASED PROBLEMS (KEY FORMULAS)

1. Standard Time from Time Study Data:

\boxed{\text{ST} = \frac{\sum (\text{Observed Time}_i \times \text{Rating}_i)}{\sum \text{Observed Time}_i} \times (1 + A)}

Where $A$ = Total Allowance Fraction.

2. Standard Time from Work Sampling Data:

\boxed{\text{ST} = \frac{T \times P}{N \times R \times (1 - A)}}

• $T$ = Total observation time (or available time)

• $P$ = Fraction of observations where operator was working (not idle)

• $N$ = Number of units produced during $T$

• $R$ = Average Performance Rating (as decimal)

• $A$ = Total Allowance Fraction

3. Normal Time from Work Sampling:

\boxed{\text{NT} = \frac{T \times P}{N \times R}}

4. Production Rate from Standard Time:

\boxed{\text{Production Rate (units/day)} = \frac{\text{Available Time per day}}{\text{Standard Time per unit}}}

Exam Tip: In work sampling problems, carefully identify:

1. Total observation time vs. total available time.

2. Number of working observations vs. total observations to find $P$.

3. Whether rating is applied to the observed working time or the calculated normal time (standard formula applies rating to working time fraction).

4. Allowance is subtracted from 1 in the denominator (1 - A).