Unit 5: Industrial Engineering & Ergonomics - Short Notes

I. Work Study: Foundation & Relevance

Work Study is a systematic investigation of work to improve efficiency and productivity. It encompasses method study (improving methods) and work measurement (establishing time standards).

Objectives in Industry

• Improve methods and procedures.

• Set realistic time standards.

• Reduce production costs.

• Enhance productivity and quality.

• Provide basis for wage incentives and planning.

Relevance in Modern Context

• Supports lean manufacturing and continuous improvement.

• Reduces waste (muda) and non-value-added activities.

• Enables accurate capacity planning and scheduling.

• Integrates with ergonomics for human-centered design.

Relationship: Method Study vs. Work Measurement

• Method Study designs the best method → Work Measurement determines standard time for that method.

• Iterative: improved methods require re-measurement; time standards may prompt method review.

[!TIP] Work study is not about speeding up workers arbitrarily—it’s about eliminating waste and designing efficient, safe methods.

II. Method Study: Systematic Analysis & Improvement of Methods

A. Method Study Process

Steps:

1. Select the job to study.

2. Record all details using appropriate techniques.

3. Examine critically to identify improvements.

4. Develop the best method.

5. Install the new method (train, implement).

6. Maintain through regular audits.

Recording Techniques: Process charts, flow diagrams, templates, models, video recording, activity charts.

B. Process Charts

ASME/ISO Symbols:

Types, Construction, and Utility

Operation Process Chart vs Flow Process Chart:

Two-Hand Process Chart vs Activity Chart:

Travel Chart: Matrix showing frequency of trips between departments. Used for facility layout planning. Rows = from, columns = to.

C. Motion Study & Micro Motion Analysis

Principles of Motion Economy (Key Gilbreth Principles)

1. Use both hands simultaneously.

2. Motions should be symmetrical and opposite.

3. Use lowest possible classification of motion (finger → wrist → arm → body).

4. Use momentum.

5. Continuous, curved motions.

6. Minimize number of motions.

7. Proper tool design: combine tools, use gravity feed.

8. Locate materials and tools in fixed positions.

9. Provide good workplace arrangement (optimal heights, reaches).

10. Ensure proper lighting and reduce fatigue.

11. [Full list: 22 principles]

[!TIP] Apply these principles to design ergonomic workstations—e.g., keep tools within "normal reach zone" to avoid excessive stretching.

Standardisation of Motions Before Time Study

• Ensures consistent method across observations.

• Eliminates unnecessary motions.

• Establishes the "one best way" before timing.

• Reduces variability in time study data.

Motion Study Symbols (Therbligs)

18 basic elements: Search, Find, Select, Grasp, Hold, Transport Loaded, Transport Empty, Position, Assemble, Use, Disassemble, Inspect, Delay, Rest, Unavoidable Delay, Plan, Pre-position, Rest for overcoming fatigue. Each has a symbol.

Techniques and Applications

SIMO Chart (Simultaneous Motion Chart):

• Construction: Columns for left hand, right hand, and time. Each row represents a time interval. Record Therbligs with time values for each hand simultaneously.

• Operation: Observe task, record motions frame-by-frame (from video) or by stopwatch. Identify simultaneous vs. alternating motions.

• Utility: Analyzes bimanual coordination, identifies idle hands, balances workload.

• DiagramCANVAS: SIMO chart example with Therbligs and times

Memo Motion Study:

• Quick, inexpensive motion study using video at high speed or normal speed with frequent sampling.

• Less detailed than micro motion; used for initial screening or jobs with long cycles.

• Utility: Identify major inefficiencies, train analysts, document methods.

String Diagram:

• Scale model of workplace with string traced along operator’s path.

• Measures travel distance, frequency.

• Utility: Layout planning, optimizing material locations, reducing motion travel.

Micro Motion Study:

• Use of motion pictures (film or video) at high frame rates (e.g., 100-1000 fps).

• Frame-by-frame analysis for precise timing of fast motions.

• Application: Detailed analysis of rapid manual tasks, developing standard data.

D. Work Factor & Work Factor Rating

Work Factor: Numerical value representing task difficulty based on factors like weight handled, distance carried, height of lift, etc. Used in some time study systems (e.g., Barnes’ Work Factor System).

Classification:

• Constant Factors: Always present (e.g., weight of object).

• Variable Factors: Depend on conditions (e.g., horizontal/vertical distance, height of lift).

• Environmental Factors: Lighting, noise, temperature.

Characteristics & Application:

• Each factor has a rating scale (e.g., weight 0-10 lbs = factor 1, 10-20 lbs = factor 2).

• Sum of factors = total work factor.

• Basic time (from standard data) is multiplied by a factor based on total work factor.

• Used to rate operator performance or set standards without stopwatch timing.

III. Work Measurement: Establishing Time Standards

A. Objectives of Work Measurement

• Establish standard times for tasks.

• Set production targets and schedules.

• Determine labor requirements and capacity.

• Provide basis for wage incentive plans.

• Estimate costs and pricing.

• Compare efficiency across methods.

B. Time Study Procedure

1. Job selection: Repetitive, stable jobs.

2. Operator selection: Average skilled, willing to cooperate.

3. Conditions: Normal working conditions, no interruptions.

4. Element breakdown: Divide job into observable elements.

5. Recording: Use stopwatch or electronic device; record multiple cycles.

6. Rating of performance: Assess operator’s speed/pace relative to standard.

7. Calculation: Compute normal time, add allowances for standard time.

8. Installation: Communicate standards, train workers.

9. Maintenance: Periodic review and update.

Rating of Performance (Methods)

• Speed Rating: Compare speed of motions to a standard (e.g., “operator working at 110%”).

• Pace Rating: Compare overall pace (e.g., “operator maintaining a brisk pace”).

• Westinghouse System: Rate on factors: Skill (S), Effort (E), Conditions (C), Consistency (C). Each rated 0-100%; overall rating = (S+E+C)/3 × (C/100).

• Objective Rating: Use predetermined data (e.g., from PMTS) to avoid subjectivity.

Allowances

• Personal: 5-7% for personal needs (toilet, water).

• Fatigue: 4-5% for physiological/psychological recovery.

• Delay: For unavoidable delays (machine breakdown, material shortage). Varies by job.

• Calculation: Total allowance = sum of individual allowances as % of normal time.

C. Standard Time Calculation

Normal Time = Observed Time × (Rating / 100)
Standard Time = Normal Time × (1 + Total Allowance)

\boxed{\text{Standard Time} = \text{Observed Time} \times \frac{\text{Rating}}{100} \times (1 + \text{Allowance})}

Work Sampling Technique

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

Procedure:

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

2. Determine sample size (using binomial formula for desired confidence).

3. Take random observations over representative period.

4. Record activity at each observation.

5. Calculate fractions: \( p = \frac{n}{N} \) (n = observations for activity, N = total).

6. Compute time spent: \( T \times p \) (T = total observation period).

7. Derive standard time if units produced known.

Application: Estimate machine/utilization, idle time, performance, staffing needs.

Calculation Example (May 2024):

• Days = 20, hours/day = 4 → T = 80 hours.

• Observations: total N=400, working n=300 → p = 300/400 = 0.75.

• Units produced U = 20.

• Rating R = 140% = 1.4.

• Allowance A = 30% = 0.3.

• Observed time per unit = (T × p) / U = (80 × 0.75) / 20 = 3 hours.

• Normal time = 3 × 1.4 = 4.2 hours.

• Standard time = 4.2 × (1 + 0.3) = 5.46 hours.

[!TIP] In work sampling, ensure observations are truly random and over a period that represents normal variability. Common error: using too few observations.

D. Predetermined Motion Time Systems (PMTS)

Definition: Systems assigning standard times to basic motions from pre-established data, without timing.

MTM (Method Time Measurement):

• Breaks task into basic motions (reach, move, turn, grasp, release, etc.).

• Each motion assigned a time in TMU (Time Measurement Unit; 1 TMU = 0.000036 sec).

• Requires detailed analysis and lookup tables.

MODAPTS:

• Similar but uses MODs (1 MOD = 0.0006 min = 0.036 sec).

• Simpler than MTM; groups motions into broader categories.

Advantages:

• Objective, no performance rating needed.

• Consistent standards across analysts.

• Useful for method comparison and design before production.

• Can be used for non-repetitive tasks with data development.

Limitations:

• Time-consuming to apply initially.

• Requires extensive training.

• May not capture all situational factors (e.g., fatigue, environmental).

• Not suitable for highly variable or creative tasks.

E. Standard Data

Definition: Pre-determined times for similar tasks/elements, developed from historical time studies.

Development Process:

1. Collect time data for a family of similar tasks.

2. Analyze to identify controlling factors (e.g., length of weld, number of bolts).

3. Develop formulas or tables (e.g., time = a + b×length).

4. Validate and update periodically.

Advantages:

• Saves time in future studies.

• Ensures consistency and fairness.

• Reduces cost of time studies.

• Useful for estimating, planning, and incentive schemes.

Industrial Applications:

• Estimating job costs and bids.

• Setting piece rates.

• Capacity planning.

• Performance evaluation.

IV. Ergonomics: Human-Centered Design

A. Definition and Objectives

Definition: Scientific discipline studying human capabilities, limitations, and interactions with systems, products, environments to optimize human well-being and performance.

Objectives:

• Enhance safety, health, comfort.

• Improve efficiency and productivity.

• Reduce errors, accidents, and fatigue.

• Adapt systems to human needs and characteristics.

B. Anthropometry

Definition: Measurement of human body dimensions (static and dynamic).

Importance: Ensures designs fit the user population, preventing discomfort, injury, and inefficiency.

Types of Body Measurements:

• Static: Body dimensions at rest (e.g., stature, sitting height, arm span).

• Dynamic: Dimensions during movement (e.g., reach envelope, joint angles, clearance during motion).

Factors Affecting Anthropometric Data:

• Age (growth, aging).

• Sex (males generally larger).

• Ethnicity/race (genetic variations).

• Nutrition and health.

• Posture (sitting, standing, crouching).

• Clothing and equipment.

• Population (regional differences).

Application in Workplace and Equipment Design:

• Workstation dimensions (desk height, chair size).

• Tool handles (grip diameter).

• Vehicle design (seat adjustment, pedal reach).

• Clothing sizes (uniforms, protective gear).

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

C. Human Information Processing

Sensory Inputs:

• Visual: Most used; for detail, color, movement, spatial awareness.

• Auditory: For warnings, communication, feedback.

• Tactual: For texture, shape, vibration, temperature.

• Olfactory: For detecting hazards (smoke, gas).

• Gustatory: Rare in industry (e.g., tasting contaminants).

Coding and Selection of Sensory Inputs:

• Coding: Representing information meaningfully (e.g., shape coding for controls, color coding for status: red=danger, green=normal).

• Selection: Human attention is limited; important signals must be salient (high contrast, movement, auditory alerts) to stand out from noise.

Model of Human Information Processing:

Stimulus → Sensory Memory → Short-Term Memory (Working Memory) → Long-Term Memory → Response

          (iconic/echoic)   (limited capacity, 15-30 sec)      (unlimited)

With feedback loops for error correction.

D. Displays and Controls

Visual Displays:

• Design Guidelines:

  • Size: Large enough for easy viewing at intended distance.

  • Contrast: High contrast (e.g., black on white) for readability.

  • Location: Within optimal visual field (30° horizontal, 20° vertical).

  • Movement: Use motion to attract attention (e.g., flashing warning).

  • Color: Use meaningfully (red=stop/danger, green=go/safe).

  • Simplicity: Uncluttered, minimal extraneous information.

• Effectiveness: Depends on task, ambient lighting, user’s vision, and display type (digital vs analog).

Tactual Displays:

• Characteristics:

  • Shape: Distinctive for identification without vision (e.g., knob shapes).

  • Texture: Different surfaces for discrimination.

  • Vibration: For alerts (e.g., mobile phone).

  • Location: Within easy reach, intuitive mapping.

  • Force: Required pressure should be within comfortable range.

• Applications: Emergency stop buttons (large, red, textured), Braille signage, haptic feedback in controls.

Relative Capabilities of Human Beings and Machines:

Design should leverage strengths: humans for decision/adaptation, machines for speed/precision.

E. Man-Machine Systems

Definition: System where human and machine (computer, vehicle, tool) interact to achieve a common goal.

Types:

• Open Loop: No feedback from output (e.g., simple on/off switch).

• Closed Loop: Feedback used to adjust input (e.g., driving a car, process control).

• Manual: Human directly operates machine (e.g., hand tool).

• Automated: Machine operates automatically; human monitors (e.g., CNC machine).

Integration of Operation and Operator:

• Design tasks to match human cognitive and physical capabilities.

• Provide clear, timely feedback (visual, auditory, tactual).

• Minimize mental workload (avoid information overload).

• Allow for human control and override in automated systems.

• Use automation to reduce fatigue, not to eliminate meaningful work.

F. Work Environment & Task Design

Work Environment Design:

• Lighting: Adequate illuminance (300-500 lux for offices, higher for precision work); avoid glare; uniform distribution.

• Noise: Below 85 dB; use absorption, isolation, hearing protection.

• Temperature: Comfortable range (20-25°C); humidity 40-60%.

• Vibration: Minimize from machinery; isolate sources.

• Air Quality: Proper ventilation; remove contaminants (dust, fumes).

Task and Work Organisation Design for Ergonomics:

• Job Rotation: Vary tasks to reduce monotony and static muscle loads.

• Work-Rest Cycles: Schedule breaks based on task intensity (e.g., microbreaks every 30 min for repetitive tasks).

• Adjustable Workstations: Chairs, desks, monitors to fit individual anthropometry.

• Teamwork: Distribute physical/mental workload.

• Pace Control: Allow self-pacing where possible; avoid forced pacing that causes fatigue.

V. Human Factors in Work Study

Considerations in Method and Time Study:

• Physical: Avoid awkward postures, excessive reach, forceful exertions, repetitive motions.

• Cognitive: Consider attention, memory load, decision points; simplify information.

• Psychological: Account for fatigue, stress, motivation; design methods to reduce mental strain.

• Limitations: Humans have limited attention span, vary in performance, fatigue over time, susceptible to error under stress.

Application:

• In method study, apply ergonomic principles to design safe, efficient methods (e.g., use gravity feed, optimal tool placement).

• In time study, include appropriate allowances for fatigue and personal needs; avoid setting unrealistic standards that compromise health.

• Use anthropometric data to set workstation dimensions.

• Evaluate displays and controls for effectiveness and error prevention.

VI. Wage Incentive Plans

A. Objectives and Classification

Objectives:

• Motivate workers to higher output.

• Increase productivity and reduce labor cost per unit.

• Reward superior performance.

• Improve morale and job satisfaction.

Classification:

• Output-based: Pay proportional to units produced (piece rate).

• Time-based: Bonus for completing within standard time.

• Hybrid: Combination of hourly rate plus bonus.

B. Specific Plans

1. Gantt’s Task and Bonus Plan

• Standard time determined for job.

• Task time set at 100% of standard (sometimes 120% for learning curve).

• Worker paid hourly rate for actual time taken.

• If job completed within task time, bonus of 25-50% on time saved.

• Earnings = (Time taken × Hourly rate) + (Time saved × Hourly rate × Bonus %)

• Time saved = Task time – Time taken.

• If time taken > task time, no bonus (only regular pay for time taken).

2. Merrick’s Multiple Piece Rate Plan

• Multiple piece rates for different output levels.

• Example:

  • Up to 100% of standard output: rate \( R_1 \).

  • 100–120% of standard: rate \( R_2 > R_1 \).

  • Above 120%: rate \( R_3 > R_2 \).

• Encourages higher output with increasing rates.

3. Other Common Plans

• Halsey Plan: Bonus = 50% of (Time saved × Hourly rate).

  Earnings = (Time taken × Hourly rate) + Bonus.

• Rowan Plan: Bonus = \( \frac{\text{Time saved}}{\text{Standard time}} \times (\text{Time taken} \times \text{Hourly rate}) \).

  Earnings = Time taken × Hourly rate × \( \left(1 + \frac{\text{Time saved}}{\text{Standard time}}\right) \).

• Barth Plan: Fixed bonus per unit above a certain output threshold.

C. Calculation of Earnings

Example 1: Gantt’s Plan

• Standard time = 10 min/unit.

• Task time = 10 min (100%).

• Hourly rate = ₹600 → ₹10/min.

• Operator takes 8 min.

• Time saved = 2 min.

• Bonus = 30% on time saved = 2 × 10 × 0.3 = ₹6.

• Earnings = (8 × 10) + 6 = ₹80 + ₹6 = ₹86 per unit.

Example 2: Merrick’s Plan

• Standard output = 6 units/hour.

• Rates: ≤6 units: ₹100/unit; 6–7 units: ₹120/unit; >7 units: ₹150/unit.

• Operator produces 8 units/hour.

• Earnings = (6 × 100) + (1 × 120) + (1 × 150) = ₹600 + ₹120 + ₹150 = ₹870.

[!TIP] In incentive plans, ensure standards are fair and attainable to avoid demotivation. Gantt’s guarantees minimum hourly earnings; Merrick’s strongly rewards high output.

Diagrams Reference:

• Process chart symbols:

  DiagramSEARCH: ASME process chart symbols

• SIMO chart:

  DiagramCANVAS: SIMO chart with Therblig times

• Human information processing:

  DiagramCANVAS: human information processing model

• Travel chart:

  DiagramCANVAS: travel matrix for layout

• String diagram:

  DiagramCANVAS: string diagram on floor plan