Industrial Engineering & Ergonomics (ME-504 (A)) - Unit 4 Short Notes

UNIT 4: WORK STUDY, WORK MEASUREMENT & ERGONOMICS

1. Work Study: Foundation and Relevance

Definition:

Work Study is a systematic examination of methods of carrying out activities to improve productivity and effectiveness. It is the systematic investigation, analysis, and synthesis of the methods and factors affecting the efficiency of work with the aim of making improvements.

Scope & Objectives:

• Primary Objective: Improve productivity (more output for same or less input).

• Specific Objectives:

  • Improve methods and procedures.

  • Establish standard times for tasks.

  • Optimize utilization of men, material, and equipment.

  • Improve workplace layout and working conditions.

  • Reduce fatigue and improve operator well-being.

Benefits & Applications:

• Reduces production cost.

• Improves product quality and consistency.

• Increases output and capacity.

• Provides basis for sound incentive plans.

• Identifies and eliminates waste (motion, time, material).

• Essential for method engineering, capacity planning, and value engineering.

Relationship: Method Study vs. Work Measurement

[!TIP] Exam Focus: Always remember the sequence: Method Study first → establishes the "best way" → then Work Measurement sets the "standard time" for that best way. Questions often ask to distinguish them.

2. Method Study (Motion Study)

Steps in Method Study (Systematic Procedure):

1. SELECT: The job/process to be studied.

2. RECORD: All relevant data about the present method using appropriate charts/ diagrams.

3. EXAMINE: Critically analyze the recorded data to identify inefficiencies, unnecessary movements, and delays.

4. DEVELOP: Devise the best possible method considering principles of motion economy and ergonomics.

5. INSTALL: Implement the new method as a standard. Train personnel, change layouts.

6. MAINTAIN: Ensure the new method is followed and periodically review it.

Recording & Analysis Techniques (Key Charts):

Motion Study Symbols (Commonly Used - ASME):

• Operation (O): Changes shape or physical characteristics.

• Inspection (I): Checks for quality/quantity.

• Move (M): Material or person moves.

• Delay (D): Temporary hold (not operator's fault).

• Storage (S): Controlled storage (inventory).

• Combined Activity (⧈): Two or more simultaneous activities.

Principles of Motion Economy (Classification & Application):

1. Use of Body:

   • Use the highest classification (fingers < hand < arm < body).

   • Symmetrical and simultaneous motions.

   • Continuous, curved, rhythmic motions.

   • Minimize fatigue (balance work, use momentum).

2. Arrangement of Workplace:

   • Fixed, regular, and definite places for all tools/materials.

   • Tools/materials in "Gravity Feed" or "Finger-Tip Reach" zones.

   • Optimize height for sitting/standing.

   • Provide adequate illumination and visual focus.

3. Design of Tools & Equipment:

   • Combine tools, use jigs/fixtures.

   • Tools should be ergonomic, require minimal effort.

   • Use power assists where possible.

4. Workplace Layout:

   • Arrange tools/materials in sequence of use.

   • Minimize travel distance.

   • Use "U-shaped" or "cellular" layouts for team work.

[!TIP] Exam Focus: "Application in workplace design" means linking each principle directly to layout, tool design, or operator posture. Sketch a simple workstation showing "Gravity Feed" and "Finger-Tip Reach" zones.

Standardisation of Motions:

• Importance: Before time study, the method must be standardized. Time study measures the time for a specific, defined method. If the method varies, the time study data is invalid and cannot establish a fair standard.

• Ensures consistency, facilitates training, and provides a basis for comparison and incentive plans.

3. Work Measurement

Objectives of Work Measurement:

• To determine the standard time for a job.

• To set production standards for planning, scheduling, and costing.

• To compare the efficiency of workers/methods.

• To balance workloads and determine manpower requirements.

• To provide a basis for sound wage incentive schemes.

• To identify and eliminate ineffective time (idle time, delays).

Techniques:

1. Time Study (Stopwatch Time Study):

• Procedure:

  1. Obtain and record detailed job information.

  2. Divide the job into elements (clearly defined, repeatable).

  3. Time each element repeatedly (using stopwatch).

  4. Rating: Assess operator's performance relative to standard performance (100% = normal pace). Apply performance rating factor.

  5. Calculate Normal Time.

  6. Add Allowances (personal, fatigue, delay) to get Standard Time.

• Key Formulas:

  • Observed Time (OT): Direct stopwatch reading for an element.

  • Normal Time (NT) = Average Observed Time × Performance Rating Factor

  • Standard Time (ST) = Normal Time × (1 + Total Allowance Fraction)

$$\boxed{ST = NT \times (1 + \frac{A}{100})}$$

*   Where $A$ = Total Allowance percentage (e.g., 15%).

2. Work Sampling (Ratio Delay Study):

• Concept: Random observations over a period to determine the proportion of time spent on various activities (working, idle, delays).

• Calculation of Standard Time:

  1. Determine % Time Working ($$\displaystyle P_w $$) from observations.

  2. Normal Time is derived from the production rate during working time.

  3. Standard Time includes allowances.

  • Formula for Standard Time per Unit:

$$ST = \frac{\text{Total Observation Time} \times (1 - P_d) \times (1/R) \times (1 + A/100)}{N}$$

    Where:

    *   $$\displaystyle P_d $$ = Proportion of delay time (from observations).

    *   $R$ = Performance Rating factor (as decimal).

    *   $A$ = Allowance fraction.

    *   $N$ = Number of units produced during observation period.

*   **Simplified Approach (from past papers):**

    *   Find **Effective Working Time** = Total Obs. Time × % Working.

    *   Find **Normal Time per Unit** = Effective Working Time / (Units Produced × Rating Factor).

    *   Find **Standard Time per Unit** = Normal Time per Unit × (1 + Allowance).

3. Standard Data:

• Concept: Pre-determined time values for specific, elemental motions or tasks (e.g., "pick up nut", "tighten bolt") based on extensive historical data or PMTS.

• Advantages:

  • Very fast (no need for fresh time study).

  • Consistent and accurate (based on large data samples).

  • Useful for estimating new jobs, quoting, and planning.

  • Reduces cost of time study.

4. Predetermined Motion Time Systems (PMTS):

• Concept: Breaks down any manual task into basic motions (e.g., Reach, Grasp, Move, Position, Release). Each motion has a pre-determined time value (in TMU - Time Measurement Units, 1 TMU = 0.00001 min) based on human motion capabilities.

• Examples: MTM (Methods-Time Measurement), MOST (Maynard Operation Sequence Technique).

• Advantages:

  • Objective (no need for rating).

  • High accuracy and consistency.

  • Excellent for method design and comparison before production.

  • Provides a library of standard times for elements.

5. Work Factor:

• Concept: A system where a basic time for a task is modified by a work factor (a number < 1.0) to account for difficulty due to physical, environmental, or mental demands.

• Classification & Characteristics:

  • Physical Work Factor: Based on weight, force, posture.

  • Environmental Work Factor: Based on heat, noise, light, humidity.

  • Mental Work Factor: Based on complexity, visual/auditory demands.

  • Factor Value: Determined from tables/charts developed from experimental data. Applied as: Standard Time = Basic Time / Work Factor.

Key Distinction: Standard Time vs. Normal Time

Time Measuring Devices:

• Mechanical Stopwatch: Traditional, manual start/stop.

• Digital Stopwatch: Higher precision, easier reading.

• Computerized Time Study Systems: Uses data collection terminals, software for analysis, rating, and reporting. Reduces paperwork.

• Video Recording: Allows replay, detailed analysis, and multiple reviews.

4. Ergonomics (Human Factors Engineering)

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:

• Enhance human efficiency, safety, and comfort.

• Reduce operator fatigue, stress, and error.

• Improve quality and productivity.

• Adapt the job/task/system to the human, not vice-versa.

• Prevent work-related musculoskeletal disorders (WMSDs).

Anthropometry:

• Definition: The science of measurement of the human body.

• Types:

  • Static Anthropometry: Measurements of body dimensions in a static posture (standing, sitting). E.g., stature, sitting height, arm reach.

  • Dynamic Anthropometry (Functional Anthropometry): Measurements of body dimensions during motion or in working postures. E.g., maximum reach envelope, working height.

• Factors Affecting Data: Age, sex, ethnicity, nutrition, socioeconomic status, geographical region, posture/clothing.

• Purpose & Application:

  • Design of workstations (desk height, chair design, tool reach).

  • Design of tools and equipment (handle diameter, force requirements).

  • Design of protective clothing and equipment (helmets, gloves).

  • Design of vehicles and cockpits (clearance, visibility).

  • Design for the "5th Percentile Female to 95th Percentile Male" to accommodate most of the population.

Sensory Information Processing:

• Human Sensory Systems:

  • Visual (Primary): ~70% of information. Key for displays, inspection, navigation.

  • Auditory: Alarms, speech communication, machine noise.

  • Tactual (Haptic): Touch, vibration, temperature, kinesthesis (body position).

• Visual Displays:

  • Characteristics for Effectiveness:

    • Legibility: Clearness of individual characters/symbols.

    • Readability: Ease of understanding the message (font, spacing, contrast).

    • Discriminability: Ability to distinguish between different displays/symbols.

  • Design Guidelines:

    • Use simple, standard alphanumeric fonts.

    • High contrast (e.g., black on white/yellow).

    • Adequate size based on viewing distance.

    • Logical grouping and arrangement.

    • Use color coding consistently (red=danger, green=normal).

• Tactual Displays:

  • Characteristics: Shape, texture, size, temperature, vibration pattern, force feedback.

  • Design: Use distinctive shapes for controls (e.g., round knob vs. toggle), textured surfaces for identification without looking, force feedback to indicate resistance/limit.

• Human Information Processing Model:

  • A sequential model: Sensation → Perception → Processing (Cognition) → Response (Action).

  • Sensation: Physical detection by sensory organs.

  • Perception: Interpretation and organization of sensory input.

  • Processing: Decision-making, memory retrieval, problem-solving.

  • Response: Motor action to carry out the decision.

  • DiagramCANVAS: A simple flowchart with boxes: Stimulus -> Sensory Organs (Eye/Ear) -> Brain (Perception/Processing) -> Decision -> Motor System (Hands/Feet) -> Response/Output.

Work and Environment Design:

• Work Environment Design:

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

  • Noise: Control at source, use hearing protection. Keep A-weighted sound pressure level below 85 dB for prolonged exposure.

  • Climate (Thermal Environment): Control temperature, humidity, air velocity. Aim for thermal comfort (PMV/PPD indices).

  • Vibration: Isolate vibrating equipment, provide anti-vibration gloves/mats.

• Task and Work Organisation Design for Ergonomics:

  • Job Rotation: Vary tasks to reduce repetitive strain.

  • Job Enlargement/Enrichment: Add variety and responsibility.

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

  • Paced vs. Self-Paced Work: Allow operator control where possible.

  • Design for Whole-Body Movement: Avoid prolonged static postures.

Man-Machine Systems:

• Definition: A system where a human operator works in conjunction with a machine (simple tool to complex computer) to achieve a goal.

• Types:

  1. Manual Systems: Human provides all power and control (e.g., hand tool).

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

  3. Semi-Automatic Systems: Machine performs routine tasks; human monitors/intervenes (e.g., CNC machine with operator oversight).

  4. Automatic Systems: Machine operates autonomously; human role is monitoring, maintenance, and decision-making (e.g., power plant control room).

• Analysis: Focuses on feedback loops, information display, control devices, decision-making requirements, and allocation of functions (what the human does vs. what the machine does).

• Integration: Designing the system so that human capabilities (judgment, flexibility, pattern recognition) are utilized for tasks they excel at, while machine capabilities (speed, precision, strength) are used for their strengths.

Relative Capabilities of Humans and Machines:

[!TIP] Exam Focus: Be prepared to give examples for each capability comparison (e.g., Human: diagnosing a new machine fault; Machine: repetitive welding).

5. Integration, Incentives, and Human Factors

Integration of Operation and Operator:

• Meaning: Balancing the requirements of the task/operation (method, time, tools) with the capabilities and limitations of the operator (physical, mental, physiological).

• How to Achieve:

  • Apply ergonomic principles in workplace design.

  • Use standardized methods derived from method study.

  • Set realistic standard times with proper allowances.

  • Provide adequate training.

  • Design tasks for variety and reasonable workload.

  • Ensure proper feedback to the operator.

Wage Incentive Plans (Output-Based):

Human Factors in Work Study:

• The application of ergonomics principles throughout the work study process.

• During Method Study: Ensure the proposed method does not cause excessive physical/mental stress. Use motion economy principles.

• During Work Measurement: Set realistic allowances based on job demands (physical, environmental, mental). Do not use a single blanket allowance.

• Goal: Improve the system for the human operator, leading to sustainable productivity gains, not just short-term speed-up.

Allowances (in Standard Time):

• Definition: Additional time added to Normal Time to compensate the operator for necessary non-productive activities and to sustain performance over a full workday.

• Types & Determination:

  1. Personal Allowance: For personal needs (restroom, water). Fixed (e.g., 5%).

  2. Fatigue Allowance: To counteract physiological/psychological fatigue. Variable, based on job demands (physical effort, posture, visual strain, noise, temperature). Determined from tables/empirical data.

  3. Delay Allowance: For unavoidable delays (machine breakdown, material shortage). Based on historical records of such delays for that specific process.

  4. Policy Allowance: For company policy reasons (e.g., to meet a target output level). Not based on human factors.

• Total Allowance = Sum of all applicable allowances (usually 10-25%).

$$\boxed{Standard\ Time = Normal\ Time \times (1 + \frac{Total\ Allowance}{100})}$$