Industrial Engineering & Ergonomics (ME-504 (A)) - Unit 2 Short Notes

UNIT 2: INDUSTRIAL ENGINEERING & ERGONOMICS

I. FOUNDATIONS OF WORK STUDY & METHOD STUDY

A. Definition, Scope & Relevance

• Work Study: A systematic examination of activities to improve productivity and efficiency. It has two core components:

  1. Method Study: Seeking the best method for doing work.

  2. Work Measurement: Determining the standard time for a qualified worker to complete a task at a defined performance level.

• Relevance in Modern Industry: Essential for lean manufacturing, process optimization, cost reduction, quality improvement, and ergonomic workplace design in both manufacturing and service sectors (hospitals, IT, logistics).

• Objectives/Benefits:

  • Improve processes and methods.

  • Establish standard times for planning & costing.

  • Reduce fatigue and improve working conditions.

  • Train new workers effectively.

  • Provide basis for wage incentives.

B. Method Study (Motion Study)

Definition: The systematic recording, analysis, and critical examination of existing and proposed ways of doing work to develop and apply more effective methods.

Systematic Procedure (6 Steps):

1. Select: The work to be studied.

2. Record: All relevant facts about the current method using appropriate charts.

3. Examine: Critically question the recorded facts to identify improvements.

4. Develop: The new, improved method.

5. Install: Implement the new method (training, new tools, layout changes).

6. Maintain: Ensure the new method is followed and periodically reviewed.

[!TIP]

Exam Focus: Distinguishing between OPC and FPC is a high-frequency question. Know the symbols and utility of all charts listed.

Recording Techniques & Charts:

Micro-Motion Study:

• Definition: Detailed analysis of an operation into its basic thebl motions (reach, move, turn, grasp, release, etc.) using high-speed photography.

• Purpose: To eliminate unnecessary motions, design better methods, and provide data for PMTS.

• Principles of Motion Economy (Workplace Design):

  1. Use of Human Body: Use symmetrical motions, maintain continuous curved motions, minimize muscular effort.

  2. Arrangement of Workplace: Locate tools/materials in fixed, optimal positions (within normal work area - "Golden Circle"). Use gravity feed.

  3. Design of Tools & Equipment: Design tools for the job, combine tools, use jigs/fixtures, minimize gripping force.

Memo Motion Study: A hybrid technique using cine film at slow speed (e.g., 1-4 fps) for longer duration studies. Useful for capturing infrequent events or overall activity patterns economically.

Integration of Operation & Operator: The concept that the method (operation) and the person performing it (operator) must be designed as a single system. A good method is useless if the operator is not trained, motivated, or physically suited to it. Approaches include standardizing methods, training, ergonomic design, and linking to incentive plans.

II. WORK MEASUREMENT & TIME STUDY

A. Objectives & Purpose

• Work Measurement: To determine the time a qualified worker should take to carry out a specified task at a defined performance level. Used for planning, scheduling, costing, and incentive schemes.

• Time Study: The technique of work measurement using a stopwatch to establish the standard time for a specific task.

B. Time Study Procedure

1. Selection: Choose the job/operation to be studied.

2. Recording: Use a time study sheet to record all elements of the job, including delays.

3. Rating: Assess the worker's performance relative to standard performance (see Section C).

4. Calculation:

   • Observed Time (OT): Sum of recorded times for all elements.

   • Normal Time (NT): NT = OT × Rating Factor

   • Basic Time: Often synonymous with Normal Time.

5. Extension: Convert Normal Time to time per unit if study was on a sample.

6. Allowance: Add personal, fatigue, and delay allowances to Normal Time.

7. Standard Time (ST): ST = NT + Allowances

Time Measuring Devices: Stopwatch (digital/analog), electronic timers, video recording with time stamp.

C. Performance Rating

• Definition: The process of evaluating a worker's rate of working relative to a standard performance (the performance of a worker skilled in the method, working at a sustainable pace).

• Rating Factor: A decimal multiplier (e.g., 1.10 for 110% performance).

• Common Methods:

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

  • Westinghouse System: A factor rating system considering skill, effort, conditions, and consistency.

D. Allowances

• Definition: Additional time added to Normal Time to account for legitimate, unavoidable activities not part of the job itself.

• Purpose: To arrive at a realistic Standard Time that a worker can maintain without undue fatigue.

• Types:

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

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

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

  • Special Allowance: For specific policies (e.g., clean-up, training).

E. Standard Time & Standard Data

• Standard Time (ST): \boxed{ST = NT + \text{Total Allowances}}

  • The time allowed for a qualified worker to complete a task including allowances, working at a standard performance.

• Normal Time (NT): Time for a worker at standard performance with no allowances.

• Distinction: NT is the "pure" work content at standard pace. ST is the "practical" time including legitimate non-work time.

• Standard Data: Pre-determined times for basic motions, elements, or entire operations derived from PMTS or extensive time studies.

  • Development: Built by analyzing a job into its fundamental components and assigning times from a database (e.g., MTM tables).

  • Advantages: Faster than fresh time study, consistent, objective, useful for estimating new jobs.

F. Predetermined Motion Time Systems (PMTS)

• Definition: Systems that assign pre-determined times to basic human motions and their conditions (tool, weight, etc.). No stopwatch needed.

• Concept: Job time = Sum of times for all constituent motions (from tables).

• Advantages over Time Study: Objective, independent of worker pace, excellent for method comparison and design, no need for rating.

• Method Time Measurement (MTM): The most widely used PMTS. Breaks down any manual activity into a sequence of TMUs (Time Measurement Units; 1 TMU = 0.000036 sec). Uses detailed tables for motions like Reach, Move, Turn, Grasp, Release, Position, Apply Pressure, Disengage.

G. Work Sampling (Activity Sampling)

• Definition: A statistical technique to estimate the proportion of time spent on various activities (working, idle, delays) by taking a large number of random observations.

• Statistical Basis: Based on the Binomial Probability Distribution. The number of observations (n) required for a given confidence level (e.g., 95%) and accuracy (e.g., ±5%).

• Procedure:

  1. Define activities (e.g., "working", "idle").

  2. Take random observations at unpredictable times.

  3. Record the activity at each instant.

  4. Calculate fraction/proportion of time for each activity.

• Key Formula (for % Working):

  P = (N_w / N) × 100

  Where P = % of time spent working, N_w = No. of observations worker was working, N = Total observations.

• Calculating Standard Time from Work Sampling Data:

  1. Find fraction of time working (P).

  2. Find Normal Time (NT) per unit: NT = (Time of observation period × P) / Number of units produced

  3. Apply rating factor (R) if observations were rated: NT_rated = NT × R

  4. Add allowances (A): ST = NT_rated + (NT_rated × A) or ST = NT_rated × (1 + A)

[!TIP]

Calculation Focus: This is a repeated, high-mark question. Master the sequence: Observed % -> Time spent working -> NT (per unit) -> Apply Rating -> Add Allowances -> ST.

H. Other Techniques

• Memo Production Study: A short-duration, intensive study (often 1-2 days) to establish quick, approximate standard times for a new or changed job. Less rigorous than full time study.

III. ERGONOMICS (HUMAN FACTORS ENGINEERING)

A. Definition, Objectives & Scope

• Definition: 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.

• Primary Objectives:

  1. Enhance human efficiency, safety, and comfort.

  2. Reduce fatigue, error, and stress.

  3. Improve system reliability and productivity.

• Man-Machine System: A system where a human operator interacts with a machine/tool/process to achieve a goal.

  • Types: Open/Closed loop, Manual/Automatic/Semi-automatic.

B. Human Capabilities & Limitations

• Relative Capabilities:

  • Humans: Flexible, adaptable, creative, can handle unexpected situations, superior in pattern recognition & complex decision-making.

  • Machines: Consistent, fast, strong, precise, superior in repetitive tasks, memory storage, and computation.

• Human Information Processing Model:

  DiagramCANVAS: A flowchart showing: Sensory Input (Visual/Auditory/Tactual) -> Short-Term Sensory Store (very brief) -> Perception & Recognition -> Short-Term Memory (limited capacity, ~20 sec) -> Decision & Response Selection -> Motor Output. Long-Term Memory feeds into Perception/Decision. Feedback loop from Output to Sensory Input.

• Sensory Inputs:

  • Coding: Presenting information in a form (visual, auditory, tactual) suitable for the sensory channel.

  • Selection: Choosing the most appropriate channel for the task (e.g., visual for detailed inspection, auditory for alarms).

C. Anthropometry

• Definition: The science of measurement of the human body's dimensions (static, dynamic, functional).

• Importance: Provides the data basis for designing workplaces, tools, equipment, vehicles, and clothing to fit the user population.

• Types of Measurements:

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

  • Dynamic: Dimensions during motion (e.g., reach envelope while operating a control).

  • Functional: Measurements related to specific tasks (e.g., grip strength, lift capacity).

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

• Purpose/Application: To determine percentiles (e.g., design for 5th percentile female to 95th percentile male - "Design for the Extremes"), set workstation heights, reach distances, clearances, and tool sizes.

D. Display Design

• Visual Displays:

  • Types:

    • Qualitative: Indicate condition (e.g., "ON/OFF" light, warning flag). Design for quick recognition.

    • Quantitative: Indicate magnitude (e.g., speedometer, pressure gauge). Design for accurate reading.

  • Design Guidelines for Effectiveness:

    • Use standard, familiar symbols.

    • Ensure high contrast (e.g., dark on light).

    • Size and viewing distance appropriate.

    • Location in operator's field of regard.

    • Analog displays better for trend/relative value; digital displays better for precise value.

• Tactual Displays:

  • Characteristics: Use touch/pressure/vibration. Useful in visual or auditory overload situations (e.g., cockpit, heavy machinery).

  • Design Considerations: Location must be unambiguous and distinct (different shapes/textures for different signals). Must not interfere with other manual tasks.

E. Work & Task Design

• Work Environment Design:

  • Lighting: Adequate illuminance (lux), uniformity, glare control, appropriate color rendering.

  • Noise: Control at source, use hearing protection. Auditory alarms must be distinctive and not mask speech.

  • Temperature & Humidity: Within thermal comfort zone (approx. 20-25°C, 40-60% RH) to prevent heat/cold stress.

  • Vibration: Minimize whole-body and hand-arm vibration to prevent health issues.

• Task & Work Organisation Design (to reduce fatigue, monotony, stress):

  • Job Rotation: Vary tasks to use different muscle groups.

  • Job Enrichment: Add responsibility, variety, and feedback.

  • Work-Rest Schedules: Design based on task demands (physical/mental).

  • Autonomy: Allow worker some control over pace/method.

  • Social Interaction: Design tasks to allow communication where appropriate.

IV. INTEGRATION WITH WAGE INCENTIVE PLANS

A. Need for Incentive Plans

• To motivate workers to increase output.

• To share productivity gains with workers.

• To link pay directly to performance.

• Foundation: Requires a reliable, accepted Standard Time for the job.

B. Types of Output-Based Wage Incentive Plans

[!TIP]

Exam Focus: Be prepared to explain the working of any plan, especially Gantt's, Halsey, and Differential Piece Rate. Know the key distinction between Standard Time (used as benchmark) and Normal Time.