TQM and SQC (ME-504 (B)) - Unit 4 Short Notes

UNIT 4: WORK STUDY, METHOD STUDY, TIME STUDY & ERGONOMICS

1.0 WORK STUDY (FOUNDATION)

Definition: Work Study is a systematic examination of the methods and elements of work to improve efficiency, reduce costs, and optimize resource utilization. It encompasses Method Study (improving how work is done) and Work Measurement (determining how long work should take).

Objectives & Benefits:

• Improve processes and methods.

• Reduce waste and non-value-added activities.

• Establish standard times for planning and costing.

• Enhance productivity and quality.

• Improve working conditions and safety.

Relevance in Modern Context:

• Lean Manufacturing & Six Sigma: Eliminates muda (waste) and supports process optimization.

• Service Industries: Applies to administrative, healthcare, and IT processes for workflow efficiency.

• Automation & Industry 4.0: Provides baseline data for robotic process design and human-machine collaboration.

• Sustainability: Reduces energy and material consumption through efficient methods.

Human Factors in Work Study:

• Considers physical and mental capabilities of workers.

• Aims to reduce fatigue, monotony, and ergonomic risks.

• Integrates ergonomic principles in method design to improve well-being and performance.

[!TIP]

Exam Focus: Work Study is the umbrella term—always link Method Study (how) and Work Measurement (how long) in answers.

2.0 METHOD STUDY (METHOD ENGINEERING)

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

Steps in Method Study:

1. Selection of Job/Process: Prioritize based on volume, complaints, or cost impact.

2. Recording of Facts: Use charts, diagrams, and video to document current method.

3. Critical Examination: Question purpose, sequence, location, and execution using "ECRS" (Eliminate, Combine, Rearrange, Simplify).

4. Development of Improved Method: Design new method incorporating motion economy and ergonomics.

5. Installation of New Method: Train operators, update documentation, and implement changes.

6. Maintenance of Improved Method: Ensure adherence through supervision and audits.

Importance of Standardisation of Motion before Time Study:

• Time study measures a specific, standardized method. Variability in motions invalidates time data.

• Standardization ensures consistent performance, enabling reliable standard time setting.

• Provides a baseline for future improvements and training.

Integration of 'Operation and Operator':

• Design work to harmonize machine capabilities with human skills.

• Balance machine-paced tasks with operator-paced tasks.

• Assign tasks based on comparative advantages: machines for speed/accuracy, humans for judgment/adaptability.

Task and Work Organisation Design (Ergonomic Perspective):

• Design tasks to fit human physical and cognitive limits.

• Rotate tasks to prevent repetitive strain.

• Structure work-rest cycles based on fatigue studies.

3.0 RECORDING TECHNIQUES FOR METHOD STUDY

3.1 Process Charts

Common Symbols (ASME/ISO):

• Operation (○): Changes shape or properties.

• Transport (→): Move material/person.

• Inspection (□): Check quality/quantity.

• Delay (D): Unplanned waiting.

• Storage (△): Controlled storage.

• Combined Activity (⦿): Operation + Inspection.

3.1.1 Operation Process Chart

• Definition: Charts the sequence of operations and inspections for a single product/component.

• Utility: Identifies non-value-added steps; simplifies process flow.

• Construction: List steps vertically; use symbols horizontally for each component.

3.1.2 Flow Process Chart

• Definition: Shows the sequence of all activities (operations, transport, inspection, delays, storage) for a group of products or a department.

• Utility: Analyzes material flow and identifies bottlenecks.

• Construction: Plot activities against distance/time; often uses a scaled layout.

3.1.3 Distinction: Operation vs. Flow Process Chart

3.1.4 Two-Hand Process Chart

• Definition: Records the simultaneous motions of both hands during an operation.

• Utility: Analyzes motion coordination; identifies idle time; applies motion economy principles.

• Construction: Two columns (left/right hand) with time scale; use therblig symbols.

3.1.5 Activity Chart

• Definition: Records the activity of an operator and machine(s) over time to show utilization.

• Utility: Identifies machine/operator idle time; balances workloads.

• Construction: Time-based chart with rows for operator and each machine; shade active periods.

3.1.6 Distinction: Two-Hand vs. Activity Chart

3.1.7 Flow Diagram / Travel Chart

• Definition: A scaled drawing showing the path of movement of workers, materials, or equipment.

• Utility: Identifies excessive travel; optimizes layout; reduces transportation time.

3.2 Multiple Activity Charts

3.2.1 SIMO Chart (Simultaneous Motion Chart)

• Definition: Combines multiple activity charts on a common time scale to show interactions.

• Construction: Multiple rows (operator, machines, materials) with synchronized time columns.

• Operation: Records start/end of activities; highlights conflicts and idle periods.

3.3 Motion Study

3.3.1 Principles of Motion Economy (Gilbreth)

1. Both hands should start and finish simultaneously.

2. Hands should not be idle at the same time.

3. Use continuous, curved motions instead of straight lines.

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

5. Use momentum to assist motion.

6. Minimize the number of motions.

7. Use rhythmic motions where possible.

8. Place tools and materials in fixed, optimal locations.

9. Use proper fixtures to free hands.

10. Combine motions when feasible.

11. Design workplace to allow good posture.

12. Use both feet if applicable.

3.3.2 Micro-Motion Study

• Definition: Detailed analysis of short-cycle operations using high-speed photography and therbligs.

• Applications: Designing workstations, reducing fatigue, establishing standard times for repetitive tasks.

3.3.3 Memo Motion Study / Memo Production Study

• Definition: A simplified motion study using timed video recordings at low frame rates to analyze longer cycles.

• Utility: Cost-effective for non-repetitive or longer tasks; identifies major delays and inefficient sequences.

3.3.4 Symbols of Motion Study (Therbligs)

• Basic Therbligs (18): Search (🔍), Find (✓), Select (→), Grasp (✊), Hold (✋), Transport Empty (↗), Transport Load (⇢), Position (◎), Assemble (🔩), Use (⚙), Disassemble (🔧), Inspect (👁), Pre-position (⤵), Release (⇠), Rest (💤), Delay (⏸), Plan (💡), Unavoidable Delay (⏳).

• Purpose: Universal language for motion analysis; enables quantification and improvement.

3.3.5 String Diagram

• Definition: A scaled plan with strings/pins tracing the path of movement to measure travel distance.

• Construction: Draw layout, mark paths with strings, measure total length.

• Utility: Quantifies travel; compares alternative layouts; reduces transportation waste.

[!TIP]

Exam Focus: Distinctions (Operation vs Flow, Two-Hand vs Activity) and Principles of Motion Economy are 7-mark questions—use tables and list principles clearly.

4.0 WORK MEASUREMENT

Definition: Work Measurement is the application of techniques to establish the time for a qualified worker to complete a task at a defined performance level.

Purpose:

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

• Compare efficiency and identify variances.

• Balance workloads and set incentive rates.

Objectives of Time Study:

• Determine basic time for a task.

• Establish performance standards.

• Provide data for labor costing and capacity planning.

Standard Data:

• Definition: Pre-determined times for basic elements of tasks (e.g., "reach 30 cm" = 0.12 min).

• Types:

  • Elemental: Times for basic motions (from PMTS).

  • Synthetic: Sum of elemental times for a complete task.

• Advantages: Speeds up time studies; ensures consistency; useful for similar tasks.

Predetermined Motion Time Standards (PMTS):

• Concept: Break tasks into fundamental motions; assign times from tables (no stopwatch needed).

• Method Time Measurement (MTM): Most common PMTS; assigns TMU (Time Measurement Units, 1 TMU = 0.00001 min) to motions like reach, grasp, move, release.

• Advantages: Objective, independent of observer; valid for new designs; facilitates method comparison.

Work Factor:

• Definition: A multiplicative factor adjusting basic time for skill, effort, and conditions.

• Classification:

  • Skill Factor: Worker proficiency (e.g., 0.8–1.2).

  • Effort Factor: Willingness to work (e.g., 0.9–1.1).

  • Condition Factor: Work environment (e.g., 0.85–1.15).

• Characteristics: Applied to normal time; based on historical data or expert judgment.

Time Study Procedure:

1. Selection: Choose representative job and worker.

2. Recording: Use stopwatch or video; break job into elements.

3. Performance Rating: Assess worker's pace relative to standard (e.g., 100% = standard pace).

   • Methods: Speed rating, pace rating, Westinghouse system (skill, effort, conditions).

4. Allowances: Add to normal time for:

   • Personal needs (5–7%).

   • Fatigue (4–10% based on conditions).

   • Delays (unavoidable, e.g., machine breakdown).

   • Total Allowance typically 15–25%.

Time Measuring Devices:

• Stopwatch: Manual or digital; continuous or snap-back.

• Film/Videography: High-speed for micro-motion; normal speed for longer cycles.

• Computerized Systems: Automated data collection with sensors.

Normal Time vs. Standard Time:

• Normal Time: Time required at 100% performance, excluding allowances.

$$\text{Normal Time} = \text{Observed Time} \times \frac{\text{Rating Factor}}{100}$$

• Standard Time: Normal time plus allowances; time allowed for the task.

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

[!TIP]

Common Pitfall: Forgetting to convert rating percentage to decimal (e.g., 110% → 1.10). Always box final formulas in calculations.

5.0 WORK SAMPLING (RANDOM OBSERVATION METHOD)

Definition: A statistical technique to estimate the proportion of time spent on various activities by random observations.

Purpose & Application:

• Determine idle time, delay fractions.

• Estimate performance levels.

• Low-cost method for non-repetitive tasks.

Procedure:

1. Define activities (working, idle, delays).

2. Determine number of observations (using statistical formula for desired accuracy).

3. Take random observations over sufficient period.

4. Tabulate counts for each activity.

5. Calculate fractions and estimate time proportions.

Calculation of Standard Time:

1. Total Observation Period: \( T \) (e.g., total hours observed).

2. Number of Observations: \( n \); Working Observations: \( n_w \).

3. Fraction Working: \( p = n_w / n \).

4. Estimated Working Time: \( T_w = T \times p \).

5. Units Produced: \( U \).

6. Observed Time per Unit: \( T_w / U \).

7. Normal Time per Unit: \( \text{Observed Time per Unit} \times \frac{100}{\text{Rating}} \) (if rating >100%, normal time < observed).

8. Standard Time per Unit: \( \text{Normal Time} \times (1 + \text{Allowance}) \).

Final Formula:

$$\boxed{\text{Standard Time per Unit} = \frac{T \times p \times \frac{100}{\text{Rating}}}{U} \times (1 + \text{Allowance})}$$

Example (May 2024):

T = 20 days × 4 hrs/day = 80 hrs; n = 400, n_w = 300 → p = 0.75; U = 20; Rating = 140%; Allowance = 30% = 0.3.

Normal Time/unit = (80 × 0.75 × 100/140) / 20 = (60 × 0.7143)/20 = 42.857/20 = 2.1429 hrs.

Standard Time = 2.1429 × 1.30 = 2.7857 hrs/unit.

[!TIP]

Exam Focus: Work sampling calculations are 14-mark questions. Show all steps: find p, compute working time, adjust for rating, add allowance.

6.0 ERGONOMICS (HUMAN FACTORS ENGINEERING)

Definition: Ergonomics is the scientific discipline concerned with understanding interactions among humans and system elements, and the profession of designing to optimize human well-being and system performance.

Objectives:

• Enhance safety, health, and comfort.

• Improve productivity and quality.

• Reduce errors and fatigue.

• Adapt systems to human capabilities.

Human Capabilities vs. Machines:

• Humans: Excellent pattern recognition, judgment, adaptability, learning; poor at repetitive, high-precision, continuous tasks.

• Machines: Superior in speed, strength, consistency, precision; lack creativity and flexibility.

• Integration: Design tasks to leverage strengths of both.

Man-Machine System:

• Definition: A system where human and machine interact to achieve a goal.

• Models: Input → Processor → Output; with feedback loops.

• Types:

  • Manual: Human provides power/control (e.g., hand tool).

  • Mechanical: Machine augments human effort (e.g., bicycle).

  • Semi-automatic: Human starts/monitors, machine executes (e.g., CNC with setup).

  • Automatic: Machine operates, human supervises (e.g., assembly line).

Human Information Processing Model:

Sensory Inputs: Coding and Selection:

• Coding: How information is presented (visual: shape, color, size; auditory: pitch, loudness; tactual: vibration, texture).

• Selection: Human attention filters stimuli; design displays to attract attention to critical information (e.g., alarms, color coding).

Anthropometry:

• Definition: Measurement of human body dimensions.

• Types:

  • Static: Measurements in fixed postures (standing, sitting).

  • Dynamic: Measurements during movement (reach, grip).

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

• Purpose/Application: Design workstations, tools, clothing, vehicle cabins; ensure fit for target population (use percentiles, e.g., 5th–95th).

Displays:

• Visual Displays:

  • Types: Analog (gauge), digital (numeric), symbolic (icon), graphical (chart).

  • Design Guidelines: Size appropriate for viewing distance; high contrast; intuitive coding; minimize glare; place in primary field of view.

• Tactual Displays:

  • Characteristics: Shape, texture, vibration, temperature; used when vision/audition overloaded (e.g., cockpit controls).

  • Design: Distinct shapes for identification; location within natural reach; feedback for confirmation.

Work Environment Design:

• Control lighting (intensity, glare), noise (below 85 dB), temperature (20–24°C), vibration.

• Ensure air quality and space.

Task and Work Organisation Design for Ergonomics:

• Job rotation to vary muscle use.

• Task variety to prevent monotony.

• Adjustable workstations.

• Match task demands to worker capabilities.

7.0 WAGE INCENTIVE PLANS (OUTPUT-BASED)

Gantt's Task and Bonus Plan:

• Mechanism: Set a standard time for a task. Worker receives guaranteed hourly rate up to standard time. If completed early, bonus = 50% of time saved (i.e., 150% of normal rate for saved time).

• Example: Standard time = 2 hrs, hourly rate = $$\displaystyle 10. If done in 1.5 hrs: pay = (2 × $$10) + (0.5 × $$\displaystyle 10 × 1.5) = $$20 + $$\displaystyle 7.5 = $$27.5.

• Focus: Rewards efficiency; simple to understand.

Merrick's Multiple Piece Rate Plan:

• Mechanism: Different piece rates for different output levels.

  • Up to 83% of standard output: lower rate.

  • 83%–100%: normal rate.

  • Above 100%: higher rate (e.g., 120% of normal rate).

• Purpose: Encourages workers to reach and exceed standard output; provides safety net for beginners.

Other Output-Based Plans:

• Halsey Plan: Bonus = 50% of time saved (similar to Gantt but no guaranteed minimum? Actually, Halsey pays hourly rate plus bonus on saved time).

• Rowan Plan: Bonus = (Time Saved / Standard Time) × Hourly Rate × Time Saved. Earnings increase with output but at diminishing rate.

• Bedeaux Plan: Standard time in "B" units (1 B = 1 min). Bonus = 75% of B's saved.

8.0 CALCULATION-BASED PROBLEMS (HIGH FREQUENCY)

8.1 Standard Time from Time Study Data

Steps:

1. Compute Observed Time per element (average of readings).

2. Normal Time = Observed Time × (Rating/100).

3. Standard Time = Normal Time × (1 + Total Allowance).

Example Problem:

Element observed times: 0.8, 0.9, 0.7 min. Rating = 125%. Allowance = 20%.

Observed avg = (0.8+0.9+0.7)/3 = 0.8 min.

Normal Time = 0.8 × 1.25 = 1.0 min.

Standard Time = 1.0 × 1.20 = 1.2 min.

8.2 Standard Time from Work Sampling Data

Use formula from Section 5.0.

8.3 Normal Time vs. Standard Time

• Normal Time: Performance-rated time, no allowances.

• Standard Time: Includes allowances; used for planning and incentives.

8.4 Production Units, Observation Periods, Rating Factors

• Key Relationships:

  • Total Working Time = Observation Period × Fraction Working.

  • Normal Time per Unit = (Total Working Time × Rating/100) / Units.

  • Always ensure consistent time units (hours/minutes).

[!TIP]

Exam Strategy: For calculation problems, first write down given data, identify unknown, choose correct formula, show unit conversions, and box final answer.