Industrial Engineering & Ergonomics (ME-504 (A)) - Unit 3 Short Notes

UNIT 3: Industrial Engineering & Ergonomics (ME-504 A)

I. WORK STUDY & METHOD STUDY FOUNDATIONS

Work Study: Definition & Components

• Definition: A systematic examination of activities to identify and eliminate waste, improve effectiveness, and set standards. It has two main components:

  1. Method Study (Motion Study): The systematic recording and critical examination of existing and proposed ways of doing work to develop and apply easier, more effective methods.

  2. Work Measurement: The application of techniques to establish the time for a qualified worker to carry out a specified task at a defined level of performance.

Relevance in Modern Industry

• Increases productivity and reduces cost without major capital investment.

• Improves product quality and consistency through standardisation.

• Enhances worker safety and morale by designing better methods.

• Provides reliable data for planning, scheduling, and costing.

• Forms the basis for wage incentive plans and capacity planning.

Method Study: Objectives & Steps

• Objectives: To improve processes, reduce human effort, minimise material waste, utilise resources better, and improve working conditions.

• Steps (SERIM):

  1. Select: Choose the process, operation, or activity to study.

  2. Record: Use appropriate charts/diagrams to document all facts about the current method.

  3. Examine: Critically question each recorded element (Purpose, Place, Sequence, Person, Means).

  4. Develop: Design a new, improved method based on elimination, combination, rearrangement, or simplification.

  5. Install: Implement the new method through training, new layouts, and procedures.

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

[!TIP] Exam Focus: Be prepared to explain each step with a simple example (e.g., studying a nut-bolt assembly operation).

II. MOTION STUDY & PROCESS CHARTING TECHNIQUES

Principles of Motion Economy (Gilbreth)

These are fundamental rules for designing efficient, fatigue-reducing motions. They are grouped into three categories:

Application in Workplace Design: Principles guide the layout of workstations, tool placement, and tool design to minimise reach, grasp, and move actions, reducing fatigue and cycle time.

Micro-Motion Study

• Definition: Detailed study of a short operation cycle using motion picture cameras to analyse and improve the basic therbligs (fundamental hand/body motions like Search, Grasp, Hold, Release, etc.).

• Purpose: To eliminate unnecessary motions, combine motions, and establish a definitive method for time study. Provides a permanent visual record.

Recording Techniques & Process Charts Classification of Recording Techniques:

1. Charts & Diagrams: Process charts, flow diagrams, string diagrams.

2. Templates & Models: Scale models, manikins, templates for layout planning.

3. Motion Pictures & Video: High-speed cameras for micro-motion study, standard video for memo motion study.

Process Charts (Symbols & Application)

Standard symbols (ASME/ISO):

• O - Operation

• D - Delay

• I - Inspection

• S - Storage

• M - Move

• ─ - Combined Operation & Inspection (sometimes used)

Other Diagrams

• String Diagram: A scale drawing of the workplace layout with a string/thread traced along the actual path of movement. Its length is measured to compare different layouts and minimise travel distance.

• Travel Chart (From-To Chart): A matrix showing the number of trips or volume of material moved between each pair of workstations/areas. Used to optimise facility layout by minimising total travel.

Motion Study Symbols (Therbligs)

Fundamental elements of motion (e.g., Search, Reach, Grasp, Hold, Release, Position, Assemble, Use, Disassemble, Inspect, Plan, Rest). Each has a standard symbol and colour.

Standardisation of Motion

• Importance: Before a valid time study can be conducted, the best method must be standardised (tools, parts, workstation layout, sequence). This ensures the recorded time reflects the method, not variations in workplace or tool availability. It is the foundation for establishing a reliable Normal Time.

III. WORK MEASUREMENT & TIME STUDY

Objectives of Work Measurement

1. To establish standard times for tasks (planning, scheduling, costing).

2. To compare operator performance against the standard.

3. To set production targets and incentive rates.

4. To identify and eliminate inefficiencies (delays, idle time).

5. To balance workloads and determine manpower requirements.

Specific Objectives of Time Study

1. To determine the time required for a qualified worker to perform a task at a defined performance level.

2. To provide data for labour-cost estimation.

3. To enable effective production control.

Time Study Procedure

1. Select & Define: Choose the job and break it into elements (distinct, measurable steps).

2. Obtain Acceptance: Ensure worker and management agree on the study.

3. Record: Use a time study sheet to record observed times for multiple cycles (usually 10-20+).

4. Evaluate (Rate): Assess the worker's performance relative to standard (e.g., 90%, 110%). Convert observed time to normal time.

5. Compute: Determine allowances (personal, fatigue, delay).

6. Set Standard Time: Add allowances to normal time.

7. Document & Install: Write the standard and implement.

Rating of Performance (Performance Rating)

• Concept: The process of comparing a worker's observed pace and effectiveness against the "standard" worker concept (100% rating = standard pace, working efficiently).

• Methods:

  • Speed Rating: Rating based solely on the speed of motion.

  • Westinghouse System: Considers skill, effort, conditions, and consistency. Uses letters (A=Excellent, B=Good, C=Average, etc.) and factors.

  • Objective Rating: Uses predetermined data (like MTM) to compare observed method against a standard method.

Allowances

• Definition: Additional time added to Normal Time to account for unavoidable personal needs, fatigue, and delays.

• Purpose: To set a realistic Standard Time that a worker can maintain over a full shift without undue stress.

• Types:

  • Personal Allowance: For physiological needs (e.g., 5-7%).

  • Fatigue Allowance: For physical/mental tiredness (varies with job demands).

  • Delay Allowance: For unavoidable interruptions (machine breakdowns, material delays).

• Factors Influencing Allowances: Nature of work (physical/mental), environment (heat, noise), shift patterns, company policy.

Standard Time Calculation

The fundamental relationship:

$$ \text{Observed Time} \xrightarrow{\text{Rating}} \text{Normal Time} \xrightarrow{\text{Allowances}} \text{Standard Time} $$

Formulas:

1. Normal Time (NT): $$\displaystyle NT = \text{Observed Time} \times \frac{\text{Rating (\%)}}{100} $$

2. Standard Time (ST): $$\displaystyle ST = NT \times (1 + \text{Total Allowance Fraction}) $$ or $$\displaystyle ST = NT + (\text{NT} \times \text{Allowance \%}) $$

[!TIP] Common Pitfall: Students often add allowance to Observed Time instead of Normal Time. Always convert to Normal Time first.

Work Sampling (Ratio Delay Study)

• 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 confidence interval for the proportion is given by:

$$ p = \frac{\text{Number of observations in activity}}{\text{Total observations}} \pm Z \sqrt{\frac{p(1-p)}{n}} $$

where $Z$ is the standard normal variate (1.96 for 95% confidence), $n$ is total observations.

• Procedure:

  1. Define the activities to be studied (e.g., "working", "idle").

  2. Take a large number of random observations (n) over a representative period.

  3. Calculate the percentage of time spent on each activity.

  4. Determine normal time for the productive activity: $$\displaystyle NT = \frac{\text{Total Productive Time}}{\text{Units Produced}} $$.

  5. Apply performance rating (if used during observation) and allowances to get Standard Time.

• Calculation Example (from past paper):

  • Given: Total obs. period = 48 hrs/week. Avoidable delays = 25% → Productive time = 75% of 48 hrs = 36 hrs.

  • Rating = 110%. Units produced = 80.

  • Normal Time per unit = (Total Productive Time / Units) × (Rating/100) = (36 hrs / 80) × 1.10.

  • Standard Time = Normal Time × (1 + Allowance %). (Allowance % must be provided to complete calculation).

Standard Data

• Definition: Pre-determined times for basic motions or elements (e.g., "reach 20 cm", "tighten nut") derived from extensive time studies or PMTS. These are stored in tables or databases.

• Advantages:

  • Drastically reduces time for new time studies (just sum relevant standard data).

  • Ensures consistency and accuracy across studies.

  • Useful for cost estimation and planning before a job exists.

  • Facilitates method comparison.

Predetermined Motion Time Systems (PMTS)

• Definition & Need: Systems that assign time values (in TMU - Time Measurement Units, 1 TMU = 0.00001 min) to basic human motions based on extensive laboratory studies. Needed for method design before production and for objective rating.

• Advantages:

  • Provides objective, consistent times independent of observer rating.

  • Enables method design and timing at the planning stage.

  • Excellent for ergonomic assessment (identifying high-TMU motions).

  • Forms the basis for Standard Data.

• Method Time Measurement (MTM): The most widely used PMTS. Breaks down any manual task into a sequence of fundamental motions (Reach, Move, Position, Release, etc.) with defined time values based on distance, weight, and control required.

• Work Factor: Another PMTS. Classifies motions into categories (A, B, C) based on difficulty and assigns a Work Factor number. Time is read from a table using the Work Factor and the number of cycles.

Time Measuring Devices

• Stopwatch: Mechanical, decimal (1/100 min), or electronic. Most common for direct time study.

• Electronic Timers: Integrated with data collection systems, often used with video recording for later analysis.

• Video Recording: Allows replay, slow-motion analysis, and multiple reviews. Essential for Memo Motion Study and complex tasks.

IV. ERGONOMICS (HUMAN FACTORS ENGINEERING)

Definition & Objectives

• 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.

• Objectives:

  1. Enhance human efficiency, safety, and comfort.

  2. Reduce fatigue, error, and injury.

  3. Improve productivity and quality.

  4. Adapt the task, equipment, and environment to the human user.

Design Applications

• Work Environment Design: Control of physical factors - illumination, noise, temperature, humidity, vibration, air quality. Goal: Provide a comfortable, safe environment.

• Task and Work Organisation Design: Designing jobs considering mental workload, task variety, autonomy,休息 breaks, work-rest schedules. Aims to prevent monotony, stress, and overexertion.

Anthropometry

• Definition: The science of measurement of the human body (dimensions, mass, volumes).

• Purpose: To obtain body size data for designing workplaces, tools, equipment, and protective gear that fit the user population.

• Types of Body Measurements:

  • Static Anthropometry: Measurements of the body in a stationary posture (e.g., standing height, sitting height, arm reach).

  • Dynamic Anthropometry (Functional Anthropometry): Measurements of the body in motion or in a working posture (e.g., maximum reach envelope, lifting capacity, field of vision).

• Factors Affecting Data: Age, sex, ethnicity, nutrition, socio-economic status, generation (secular trend). Data must be population-specific (e.g., Indian male/female percentiles).

• Importance & Applications:

  • Workstation Design: Adjustable chair height, desk height, monitor position based on popliteal height, eye height.

  • Tool Design: Handle diameter based on hand grip span.

  • Vehicle/Equipment Design: Clearance, seat design, control reach based on body dimensions.

  • Protective Clothing/Equipment: Sizing for helmets, gloves, respirators.

  • Use of Percentiles: Design for the 5th percentile female to 95th percentile male to accommodate most of the population (e.g., reach, clearance). Adjustability is key for extremes.

Displays Visual Displays

• Types:

  • Qualitative: Indicate condition (e.g., "ON/OFF", red/green light).

  • Quantitative: Provide numerical value (e.g., speedometer, digital readout).

  • Analogue: Continuous scale with pointer (good for trend detection).

  • Digital: Discrete numerical readout (precise, good for exact value).

• How to Make Effective:

  • Accuracy & Legibility: Clear symbols, appropriate size, high contrast.

  • Location: Within the normal field of vision (30° cone of gaze).

  • Coding: Use shape, colour, position to differentiate information quickly.

  • Consistency: Standardise symbols and layouts.

• General Design Guidelines:

  • Minimise visual accommodation (focusing) shifts.

  • Avoid glare and reflection.

  • Use colour meaningfully (red=danger, green=safe) but not as sole indicator (consider colour-blindness).

  • Provide backup (e.g., digital with analogue).

Tactual Displays

• Characteristics: Use the sense of touch (skin, proprioception). Information is conveyed through vibration, pressure, shape, texture, temperature.

• Applications: Warning signals (steering wheel vibration for lane departure), guidance devices for the visually impaired, control knobs with distinct shapes, surgical tools with force feedback.

Man-Machine System

• Definition: An integrated system where a human operator (man) works in conjunction with tools, machines, or computers (machine) to perform a task. Focus is on the interface and information flow.

• Types:

  1. Manual Systems: Human provides power & control (e.g., hand tools).

  2. Powered Systems: Human provides control, machine provides power (e.g., car, crane).

  3. Semi-Automatic: Human sets up, machine runs (e.g., CNC machine loading).

  4. Automatic: Human monitors and intervenes only on exception (e.g., process control room).

• Integration of 'Operation and Operator': Achieved through ergonomic design of controls, displays, and workspace to match human capabilities and limitations, ensuring smooth, efficient, and safe interaction.

Human Capabilities & Information Processing

• Relative Capabilities:

  • Humans excel at: Pattern recognition, flexible decision-making, handling unexpected situations, learning, applying common sense, sensory perception (touch, vision).

  • Machines excel at: High-speed repetitive operations, precise calculations, working in hostile environments, sustained vigilance, data storage/retrieval.

  • Goal: Allocate functions to what each does best.

• Human Sensory Information Reception:

  • Coding: The process of assigning meaning to sensory inputs (e.g., red light = stop, siren = emergency).

  • Selecting: The human sensory system is limited; it selectively attends to certain stimuli. Design must ensure critical information is salient (bright, moving, audible) to be selected.

• Human Information Processing Model (Block Diagram):

  
  [Stimulus (Input)] → [Sensory Register (Brief storage)] → [Perception & Interpretation] → [Decision Making (Central Processor)] → [Motor Response (Output)] → [Action]
  
  

  • Key Points: Limited short-term memory (7±2 items), reaction time varies with stimulus complexity, feedback is crucial for learning and correction.

• Human Factors in Work Study: Consider worker's physical/mental capabilities, learning curve, fatigue, and motivation when designing methods and setting standards. A method that is ergonomically poor will lead to low performance, errors, and injury.

V. WAGE INCENTIVE PLANS & INTEGRATION

Integration of Operation and Operator

Achieved by:

1. Scientific Method Design: Providing the best standard method with proper tools, layout, and instructions.

2. Training: Ensuring the worker is skilled in the standard method.

3. Fair Standards: Setting realistic, achievable standards based on work measurement.

4. Effective Incentives: Linking pay to performance to motivate the worker to achieve the standard.

5. Good Working Conditions: Providing an environment that supports efficient work.

Output-Based Wage Incentive Plans Individual Plans:

1. Gantt's Task and Bonus Plan:

   • Worker receives straight hourly rate up to 100% of standard output.

   • For output above 100%, worker earns a bonus of 20-75% of the hourly rate (on the excess time).

   • Formula: Earnings = (Hours Worked × Hourly Rate) + [ (Actual Time - Standard Time) × Bonus Rate × Hourly Rate ].

   • Feature: Guarantees minimum wage. Bonus increases with efficiency.

2. Merrick's Multiple Piece Rate Plan:

   • Uses three piece rates based on output level:

     • Below 83% of standard: Low rate (discourages low output).

     • 83% to 100%: Middle rate (standard rate).

     • Above 100%: High rate (incentive).

   • Feature: Penalises very low output, rewards high output.

3. Taylor's Differential Piece Rate System:

   • Uses two piece rates:

     • Below standard output: Lower rate.

     • At or above standard output: Higher rate.

   • Worker's earnings depend entirely on output. No guaranteed minimum.

   • Feature: Strong incentive to achieve standard, but no safety net.

Group/Plant-Wide Plans (General Awareness)

• Examples: Scanlon Plan, Rucker Plan, Improshare (Improved Productivity Share).

• Concept: Bonus is based on improvement in productivity or cost savings for a group, department, or whole plant. Encourages cooperation and teamwork. Sharing formula typically involves payroll cost vs. sales value of production.