Industrial Engineering & Ergonomics (ME-504 (A)) - Unit 1 Short Notes

UNIT 1: WORK STUDY, METHOD STUDY, MOTION STUDY & FUNDAMENTALS OF ERGONOMICS

1.0 FOUNDATIONS OF WORK STUDY

1.1 Definition, Objectives, and Scope

• Definition: Work Study is a systematic examination of existing or proposed ways of carrying out a job to make improvements. It is the systematic investigation, analysis, and synthesis of the work of men and machines to improve effectiveness and efficiency.

• Objectives:

  1. Improve the method of operation.

  2. Establish the standard time for the operation.

  3. Improve layout and working conditions.

  4. Reduce fatigue and increase safety.

  5. Train workers in the improved method.

• Scope: Covers all activities from procurement to distribution. It is applicable in manufacturing, offices, hospitals, service industries, etc.

1.2 Relevance and Benefits

• Relevance: Critical for competitiveness in modern industry due to global pressure for cost reduction, quality improvement, and flexibility.

• Benefits:

  • Higher productivity and output.

  • Reduced manufacturing costs.

  • Better product quality and consistency.

  • Improved working conditions and safety.

  • Provides basis for planning, scheduling, and costing.

  • Facilitates effective training.

1.3 Human Factors in Work Study

• Considers the physical and psychological capabilities and limitations of the worker.

• Aims to design jobs that are safe, efficient, and satisfying.

• Key Principle: "The right job for the right man" – matching task requirements with operator capabilities.

1.4 Integration of 'Operation and Operator'

• Concept: Work Study does not just study the machine or the process in isolation. It studies the entire man-machine system.

• The goal is to find the best method (operation) and then select/train the operator to perform it efficiently.

• It ensures the method is designed for the operator, not forcing the operator into an inefficient method.

[!TIP]

Exam Focus: "Integration of Operation and Operator" is a frequent 7-mark question. Emphasize that Work Study optimizes the method first, then matches the person to it, considering human factors.

2.0 METHOD STUDY (METHOD ENGINEERING)

2.1 Definition, Objectives, and Steps

• Definition: Method Study is the systematic recording and critical examination of existing and proposed ways of doing work to develop and apply easier, more effective, and less costly methods.

• Objectives: Eliminate unnecessary movements/materials, improve layout, reduce fatigue, improve process design.

• Six Steps:

  1. Select the work to be studied.

  2. Record the present method using appropriate charts/diagrams.

  3. Examine the recorded facts critically (ask "Why?", "What?", "Where?", "When?", "Who?").

  4. Develop the new, improved method.

  5. Install the new method (train workers, change layout).

  6. Maintain the new method through regular checks.

2.2 Recording Techniques for Method Study

A. Process Charts

• Use standardized symbols (O, D, I, S, T, etc.) to represent operations, inspections, delays, etc.

• Operation Process Chart (OPC):

  • Records operations and inspections only.

  • Used for macro-level analysis of a process (e.g., manufacturing sequence of a product).

  • Shows the sequence of operations on each component/assembly.

  • DiagramSEARCH: "Operation Process Chart example manufacturing"

• Flow Process Chart (FPC):

  • Records all activities: Operation, Inspection, Delay, Storage, Move (including distance).

  • Used for micro-level analysis of a specific operation or movement of material/person.

  • Highlights non-productive elements (D, S).

  • DiagramSEARCH: "Flow Process Chart example material movement"

• Distinction: OPC vs FPC

B. Motion Charts & Diagrammatic Tools

• Two-Hand Process Chart:

  • Records simultaneous motions of both hands against a time scale.

  • Construction: Two parallel columns (Left Hand, Right Hand) with rows for time increments. Uses motion symbols (Reach, Grasp, Move, Position, Release, etc.).

  • Utility: Analyzes detailed hand motions to eliminate, combine, or rearrange them. Basis for applying Principles of Motion Economy.

  • DiagramSEARCH: "Two-Hand Process Chart assembly operation"

• Activity Chart:

  • Records activities of one operator and one or more machines/equipment on a common time scale.

  • Construction: Separate columns for Operator and Machine(s). Shows idle times for both.

  • Utility: Balances work between operator and machine, identifies machine downtime causes.

• Distinction: Two-Hand Chart vs Activity Chart

• Flow Diagram:

  • A scaled drawing of the workplace showing the path followed by materials/workers.

  • Highlights excessive travel distances and layout problems.

• String Diagram:

  • A scale drawing with a thread/string used to measure the exact distance traveled by a worker/material during a cycle.

  • Utility: Quantifies travel distance for layout comparison and optimization.

  • DiagramCANVAS: "A workshop floor plan with a winding red string tracing the path of a worker moving between stations A, B, C, and back to A."

• Travel Chart:

  • A matrix (from-to chart) showing the frequency of movements between all pairs of departments/points.

  • Purpose: Analyze material flow patterns to design an optimal plant layout (minimize total travel distance/frequency).

• SIMO Chart (Simultaneous Motion Chart):

  • Combines a Two-Hand Chart for an operator with an Activity Chart for the associated machine(s) on a common time base.

  • Construction: Columns for Left Hand, Right Hand, Machine(s) Activity.

  • Utility: Provides a complete picture of operator-machine interaction to synchronize activities and eliminate delays.

2.3 Motion Study & Principles of Motion Economy

• Motion Study: The study of human motions used to perform an operation to find the most efficient method.

• Objectives: Eliminate wasteful motions, reduce fatigue, speed up the operation.

• Principles of Motion Economy (Detailed List & Application):

  • Use of Body:

    1. Both hands should start and finish motions simultaneously.

    2. Both hands should not be idle at the same time (except during rest).

    3. Motions of arms should be in opposite and symmetrical directions.

    4. Use the lowest possible classification of motion (finger > wrist > forearm > arm > shoulder).

    5. Use momentum to assist the worker.

    6. Continuous, curved motions are preferable to straight-line motions.

    7. Ballistic (free-swinging) movements are faster, more accurate, and less fatiguing than restricted or controlled movements.

  • Arrangement of Workplace:

    8. Fixed, defined places for all tools and materials.

    9. Tools and materials should be located to minimize search and reach.

    10. Provide proper height for work surface (elbow level for precision, shoulder for heavy).

    11. Provide adequate illumination.

    12. Provide a chair that allows good posture.

  • Design of Tools & Equipment:

    13. Combine tools whenever possible.

    14. Use jigs and fixtures to reduce the need for holding and positioning.

    15. Tools should be designed to require the least number of motions.

    16. Use passive motion (let gravity, springs, etc., assist).

2.4 Specialized Motion Study Techniques

• Micro-Motion Study:

  • Detailed study of very short-duration motions (sub-motions like reach, grasp).

  • Uses high-speed photography (motion pictures) to analyze, slow down, and study the motion cycle frame by frame.

  • Utility: Fundamental for developing and teaching the one best way for highly repetitive tasks.

• Memo Motion Study:

  • Study of long-duration operations using normal-speed motion pictures at a lower frame rate (e.g., 1-2 fps).

  • Utility: Economical for studying activities that take several minutes/hours (e.g., clerical work, maintenance, machine setup). Provides a permanent visual record for analysis.

• Memo Production Study:

  • A specific application of memo motion study to determine production rates over a longer period by counting the number of times a task is completed on the film.

3.0 WORK MEASUREMENT

3.1 Definition, Objectives, and Purpose

• Definition: Work Measurement is the application of techniques designed to establish the time for a qualified worker to carry out a specified job at a defined level of performance.

• Objectives:

  • Establish standard times for planning, scheduling, and costing.

  • Compare the efficiency of different methods.

  • Set realistic production targets and quotas.

  • Provide basis for incentive wage plans.

• Purpose: To determine how long a job should take under normal working conditions.

3.2 Techniques of Work Measurement

1. Time Study: Direct observation with a timing device.

2. Work Sampling (Ratio Delay Study): Statistical technique to estimate proportion of time spent on various activities.

3. Predetermined Motion Time Systems (PMTS): Uses pre-determined times for basic motions (e.g., MTM, MODAPTS).

4. Standard Data: Uses historical time data for similar elements.

3.3 Time Study in Detail

• Procedure:

  1. Select the job, operator, and conditions.

  2. Record all job elements and times using a time study form/stopwatch.

  3. Evaluate the worker's performance (Rating).

  4. Compute Normal Time.

  5. Add Allowances to get Standard Time.

• Performance Rating:

  • Definition: The process of comparing the observed performance of a worker against the standard performance (100% rating) and assigning a numerical value (Rating Factor).

  • Rating Methods:

    • Speed Rating: Rating based on the pace of working relative to standard pace.

    • Westinghouse System: Considers four factors: Skill, Effort, Conditions, Consistency. Uses a rating scale and factor table.

  • Concept of Average Rating: For multiple observations, the average of all rating factors is used.

• Allowances:

  • Definition: Extra time added to the Normal Time to compensate for non-productive but unavoidable factors.

  • Need: To make the Standard Time realistic and achievable.

  • Types:

    • Personal Allowance: For personal needs (rest, water).

    • Fatigue Allowance: To recover from physiological/psychological fatigue.

    • Delay Allowance: For unavoidable delays (machine breakdown, material shortage).

    • Policy Allowance: For company policy (e.g., union agreements).

  • Calculation: Total Allowance % = Sum of all applicable % allowances.

• Standard Time Calculation:

$$ \text{Normal Time} = \text{Observed Time} \times \text{Rating Factor} $$

$$ \text{Standard Time} = \frac{\text{Normal Time}}{1 - \text{Allowance Fraction}} $$

Where, Allowance Fraction = Total Allowance % / 100.

\boxed{\text{Standard Time} = \frac{\text{Sum of (Observed Time} \times \text{Rating)}}{\text{Number of Observations}} \times \frac{1}{1 - \text{Allowance Fraction}}}

[!TIP]

Common Pitfall: Students often add allowance to Normal Time. Correct Formula uses DIVISION by (1 - Allowance Fraction). Always convert allowance percentage to a fraction first.

3.4 Standard Data

• Definition: Pre-determined times for groups of motions or operations derived from previous time studies. Used when a new job contains elements that have been studied before.

• Advantages:

  • Drastically reduces time and cost of new time studies.

  • Increases accuracy and consistency.

  • Simplifies planning and estimating.

  • Provides a reliable database.

3.5 Predetermined Motion Time Standards (PMTS)

• Definition: A system where the time for a task is built up from the times of its constituent basic motions (e.g., reach, grasp, move, release) using a pre-established table of values.

• Examples: MTM (Methods-Time Measurement), MODAPTS.

• Advantages over Time Study:

  • Objectivity: No need for performance rating (times are fixed for a defined performance level).

  • Consistency: Same element always gets same time.

  • Method-focused: Forces detailed method study before timing.

  • Useful for: New jobs, non-repetitive work, setting standards where time study is difficult.

• Brief Explanation of MTM: The most widely used PMTS. Breaks down manual work into basic motions (Reach, Move, Turn, Grasp, Position, Release, etc.) and assigns a Time Measurement Unit (TMU) to each based on distance and motion type. 1 TMU = 0.000036 seconds (or 36 TMU = 1 second).

3.6 Gantt's Task and Bonus Plan

• A wage incentive plan linked to a standard time.

• Mechanism:

  • A standard time for the job is established via Time Study.

  • Worker is paid a higher hourly rate for time worked up to the standard time.

  • For any output beyond the standard time, the worker earns a bonus (typically 50% of the hourly rate for the bonus time).

• Formula: Total Earnings = (Hours Worked × Higher Rate) + (Bonus Hours × 50% × Higher Rate)

• Purpose: Incentivizes workers to achieve and exceed the standard while providing a guaranteed higher base rate.

4.0 FUNDAMENTALS OF ERGONOMICS (HUMAN FACTORS ENGINEERING)

4.1 Definition, Objectives, and Goals

• Definition: Ergonomics (Human Factors) is the scientific discipline concerned with the understanding of interactions among humans and other elements of a system, and the profession that applies theory, principles, data, and methods to design in order to optimize human well-being and overall system performance.

• Objectives:

  • Fit the job/task to the human (not vice-versa).

  • Maximize efficiency and productivity.

  • Ensure safety, health, and comfort.

  • Reduce errors and improve quality.

• Goals: Design of tasks, jobs, products, environments, and systems to be compatible with human needs, abilities, and limitations.

4.2 Man-Machine System

• Definition: A system consisting of a human operator (man) working in conjunction with a machine, tool, or process to achieve a specific goal.

• Model: Input (from environment) → Human (Senses → Processes → Acts) → Machine (Processes input) → Output → Environment.

• Types:

  • Open-Loop System: Output does not affect the input (e.g., simple drilling).

  • Closed-Loop System (Feedback System): Output is monitored and fed back to adjust the input (e.g., driving a car, process control).

• Relative Capabilities:

  • Human Strengths: Flexible, adaptable, can handle unexpected situations, creative, can use complex sensory input (vision, hearing).

  • Machine Strengths: High speed, high power, consistent, precise, can work in hostile environments, excellent memory for data.

  • Ergonomic Design Principle: Assign tasks to the component (human or machine) best suited for them.

4.3 Information Processing by Humans

• Human Sensory Information Reception:

  • Coding: The process of converting physical stimuli (light, sound) into neural signals. Different senses have different coding mechanisms.

  • Selection (Attention): The brain cannot process all incoming sensory data. Selective attention filters information based on intensity, novelty, relevance, etc. This is critical for display design (make important signals stand out).

• Model of Human Information Processing:

  • A three-stage model:

    1. Perception (Sensory Input): Receiving and registering stimuli via senses.

    2. Cognition (Central Processing): Interpretation, decision-making, memory retrieval.

    3. Action (Motor Output): Executing a response (e.g., pressing a button, moving a lever).

  • Feedback Loop: The result of the action is perceived, closing the loop.

  • DiagramCANVAS: "A flowchart: Sensory Input -> Perception -> Cognitive Processing (Decision) -> Motor Output -> Action -> Feedback -> Sensory Input. Arrows show the cycle."

4.4 Anthropometry

• Definition: The science of measurements of the human body (dimensions, mass, composition).

• Importance: Provides the essential data for designing workplaces, tools, equipment, and vehicles that fit the user population.

• Types of Body Measurements:

  • Static Anthropometry: Body dimensions in a static posture (standing, sitting). E.g., stature, sitting height, elbow height.

  • Dynamic Anthropometry (Functional Anthropometry): Body dimensions during motion or in a working posture. E.g., reach envelope, grip span. More relevant for workstation design.

• Factors Affecting Data: Age, Sex, Ethnicity, Nutrition, Socio-economic status, Posture, Clothing/footwear.

• Purpose & Application:

  • Determine design dimensions (clearance, reach, height).

  • Use percentiles (e.g., design for 5th percentile female to 95th percentile male for adjustability).

  • Ensure compatibility between human body and physical workspace.

4.5 Display Design

• Visual Displays:

  • Types: Analog (pointer/scale), Digital (numerical), Alphanumeric (text), Graphic (charts), Symbolic (icons).

  • Design Guidelines for Effectiveness:

    1. Legibility: Size, contrast, font must be easily readable.

    2. Discriminability: Different symbols/colors must be easily distinguishable.

    3. Meaningfulness: Use intuitive, conventional symbols (e.g., red for danger/stop).

    4. Location: Place in the operator's normal field of view (primary field of view is straight ahead ±15°).

    5. Grouping: Related information should be grouped (proximity, common region).

    6. Minimize Information Load: Show only essential information.

• Tactual Displays:

  • Use the sense of touch to convey information (e.g., Braille, vibration in mobile phones, control shape coding).

  • Characteristics & Design:

    1. Location: Must be on a body part with high tactile sensitivity (fingertips).

    2. Coding: Use shape, texture, vibration pattern, or location to code different signals.

    3. Force/Pressure: Should be within comfortable and discriminable limits.

    4. Feedback: Should provide clear feedback to the user.

4.6 Work Environment and Task Design for Ergonomics

• Work Environment Design:

  • Lighting: Adequate illuminance, uniform distribution, glare control, appropriate contrast.

  • Noise: Reduce at source, use barriers, provide hearing protection. Consider auditory displays.

  • Temperature & Humidity: Maintain within thermal comfort zone (approx. 20-25°C, 40-60% RH).

  • Vibration: Isolate vibrating tools/machines, provide anti-vibration gloves.

• Task and Work Organisation Design:

  • Job Rotation: To reduce monotony and localized muscle fatigue.

  • Work-Rest Schedules: Based on task demands to prevent fatigue.

  • Mental Workload: Balance tasks to avoid under-load (boredom) or over-load (stress).

  • Autonomy & Participation: Allow some control over work pace/method to increase satisfaction.

  • Goal: Design work that is safe, efficient, and satisfying for the worker, leading to higher quality and lower turnover.