UNIT 3: METHOD STUDY, WORK MEASUREMENT & ERGONOMICS

I. FOUNDATIONS OF WORK STUDY & METHOD STUDY

Definition & Scope

• Work Study: A systematic examination of activities to improve productivity and efficiency. It is the generic term for Method Study (improving the method) and Work Measurement (establishing standard time).

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

• 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.

Relationship

• Method Study comes first: It seeks the best method.

• Work Measurement follows: It determines how long the best method should take.

• They are complementary and iterative. A new method requires new measurement; measurement may reveal need for method improvement.

Systematic Procedure for Method Study (6-Step Approach)

1. Select: Identify the job/process with high potential for improvement (e.g., frequent, costly, problematic).

2. Record: Use appropriate charts/diagrams to document the current method (all facts: movements, delays, materials).

3. Examine: Critically question every detail of the recorded method (Purpose, Place, Sequence, Person, Means). Use "5W1H" (What, Why, Where, When, Who, How).

4. Develop: Design, evaluate, and select the best new method (most economical, effective, safe).

5. Install: Implement the new method (train personnel, change layouts, provide tools).

6. Maintain: Ensure the new method is standardised and sustained through regular checks.

Human Factors in Work Study

• Work study must consider the human element (physical/psychological capabilities, limitations, attitudes).

• Goals: Reduce fatigue, improve safety, increase job satisfaction, and secure worker acceptance of changes. Ergonomics is the scientific discipline that addresses this.

[!TIP] Exam Focus: The 6-step procedure is frequently asked. Be ready to explain each step with a simple example (e.g., improving a nut-bolt assembly).

II. RECORDING TECHNIQUES FOR METHOD STUDY (CHARTS & DIAGRAMS)

A. Process Charts

• Purpose: To represent a process sequentially using standard symbols, focusing on operations, inspections, moves, delays, and storage.

• Common Symbols (ASME/ISO):

  | Symbol | Name | Meaning | | :--- | :--- | :--- | | O | Operation | Value-adding change to material/product | | D | Inspection | Check for quality/quantity | | → | Move | Physical movement of material/worker | | □ | Delay | Unplanned stoppage (waiting) | | ▽ | Storage | Controlled accumulation (inventory) | | S | Combined Activity | Operation + Inspection, etc. |

• 1. Operation Process Chart (Outline/Flow Process Chart)

  • Use: High-level overview of the entire process from raw material to finished product.

  • Construction: Only Operation (O) and Inspection (D) symbols are used. Moves are implied by sequence.

  • Utility: Planning, scheduling, costing, and identifying major operations/inspections.

• 2. Flow Process Chart (Detailed Process Chart)

  • Use: Detailed analysis of a specific operation or workstation. Records all activities of the worker/machine/material.

  • Construction: Uses all five symbols (O, D, →, □, ▽). Tracks material, worker, and equipment flow.

  • Utility: Identifying non-value-adding activities (delays, unnecessary moves, storage) for method improvement.

• Distinction: Operation vs. Flow Process Chart

  | Feature | Operation Process Chart | Flow Process Chart | | :--- | :--- | :--- | | Level | Macro (entire process) | Micro (single operation/station) | | Symbols Used | Only O & D | All 5 symbols (O, D, →, □, ▽) | | Focus | Sequence of operations/inspections | Detailed activity of worker/material | | Analytical Depth | Low | High |

B. Motion Study Charts

• 1. Two-Hand Process Chart (Simultaneous Motion Chart)

  • Purpose: To record the simultaneous activities of both hands of an operator.

  • Construction: Two vertical columns (Left Hand, Right Hand) against a common time scale. Uses therblig symbols (see Section III).

  • Utility: Reveals imbalance in hand motions, idle time, and opportunities for better coordination. Foundation for micro-motion study.

• 2. Multiple Activity Chart (SIMO Chart)

  • Definition: A chart that records the activities of multiple operators and/or machines against a common time scale.

  • Construction: Vertical columns for each operator/machine. Time proceeds horizontally. Activities are plotted.

  • Utility: Balancing work between operators, identifying machine idle time, studying group dynamics, and improving layout for multi-person tasks.

• 3. Activity Chart

  • Definition: A simplified multiple activity chart for one operator and one machine.

  • Utility: To study the relationship between operator activity and machine cycle. Identifies if the operator is overburdened or underutilized relative to the machine.

C. Other Diagrams

• Flow Diagram: A scaled drawing of the workplace layout showing the path of movement (material/worker) using flow lines. Useful for studying travel distances.

• String Diagram:

  • Definition: A scale model using a string or thread to measure the actual distance traveled by a worker or material during a process.

  • Construction: Pin a scaled layout on a board. Use a pin and string to trace the exact path. Measure string length.

  • Utility: Quantifying travel distance for layout optimisation. High-frequency exam topic.

• Travel Chart: A matrix (table) showing the frequency of movement between different departments/points. Used for planning plant layout to minimise material handling.

• Cyclegraph & Chronocyclegraph: Photographic techniques. Cyclegraph uses a light to trace a path. Chronocyclegraph adds a timing device to show speed/direction. Used for complex motion analysis.

[!TIP] Exam Focus: Distinctions between charts (Operation vs. Flow, Two-Hand vs. Activity) are very common. Sketch the basic chart format and label symbols. For String Diagram, describe the pin-and-string method.

III. MICRO-MOTION STUDY & PRINCIPLES OF MOTION ECONOMY

Micro-Motion Study

• Definition: Detailed analysis of an operation into its basic elemental motions (therbligs) using high-speed photography and slow-motion playback.

• Objectives: To eliminate unnecessary motions, combine motions, and arrange the most efficient sequence. Provides data for PMTS (like MTM).

Principles of Motion Economy (3 Categories)

A. Use of the Body:

1. Use both hands simultaneously, symmetrically, and with continuous, curved motions.

2. Use lowest possible classification of motion (Finger > Wrist > Arm > Body).

3. Minimise the number of limbs involved.

4. Use momentum to assist the worker; avoid sudden changes in direction.

5. Rhythmic motions are easier and less tiring.

B. Arrangement of the Workplace:

1. Fixed locations for all tools and materials (consistent place).

2. Arrange tools/materials in fixed, logical sequence of use.

3. Provide adequate illumination and height for work (elbow height for precision, hip height for heavy work).

4. Use gravity (drop deliveries, chutes).

5. Combine tasks where possible.

C. Design of Tools & Equipment:

1. Use jigs, fixtures, and guides to reduce the need for positioning.

2. Combine tools where possible.

3. Design tools to maximise the use of momentum and minimise muscular effort.

4. Segregate cutting edges from non-cutting surfaces.

5. Provide proper handles (shape, size, location).

Memo Motion Study

• Definition: A low-cost, simplified version of micro-motion study using normal-speed photography or direct observation with a stopwatch to record the sequence and timing of major motions.

• Utility: For studying long-cycle, complex operations where high-speed photography is impractical. Identifies major motion patterns and delays.

Therbligs

• Definition: The 18 basic elemental motions (named from "Gilbreth" spelled backwards) identified by Frank and Lillian Gilbreth.

• Classification:

  • Effective Therbligs (Value-Adding): Reach, Grasp, Move, Position, Assemble, Use, Disassemble, Release.

  • Ineffective Therbligs (Non-Value-Adding): Hold, Rest, Plan, Unavoidable Delay, Search, Find, Select, Inspect, Pre-position, Avoidable Delay.

• Utility: Each therblig has a symbol and color code. Used in Two-Hand Process Charts to identify and eliminate waste.

[!TIP] Exam Focus: Memorise the 3 categories of Motion Economy principles. Be able to apply them to a simple task (e.g., packing an item). Know the difference between Effective and Ineffective Therbligs with 2 examples of each.

IV. WORK MEASUREMENT: OBJECTIVES, TECHNIQUES & STANDARD DATA

Objectives of Work Measurement

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

2. To compare efficiency of workers/methods.

3. To balance the workload.

4. To set realistic production targets and incentives.

5. To identify and eliminate idle time and delays.

Objectives of Time Study

1. To determine the basic time for a task under standard conditions.

2. To rate the operator's performance.

3. To establish standard time including allowances.

Techniques of Work Measurement

1. Time Study (Stopwatch Study):

   • Procedure: Select job → Obtain worker consent → Record all elements using stopwatch → Rate operator performance → Calculate Observed Time and Normal Time → Add Allowances → Get Standard Time.

   • Steps: (i) Define task, (ii) Break into elements, (iii) Time elements (repeated readings), (iv) Rate performance, (v) Compute.

2. Work Sampling (Activity Sampling):

   • Theory: Based on statistical probability. A large number of random observations over time gives a reliable picture of how time is spent.

   • Calculation of % Idle Time:

$$\% \text{ Idle Time} = \frac{\text{Number of "Idle" Observations}}{\text{Total Observations}} \times 100$$

*   **Standard Time Calculation (from Work Sampling):**

    Let:

    *   `P` = Proportion of time working (from sample)

    *   `R` = Average performance rating (as decimal, e.g., 110% = 1.10)

    *   `A` = Allowance fraction (e.g., 30% = 0.30)

    *   `N` = Number of units produced in observed period

    *   `T` = Total observation time (in hours/minutes)

    Then:

$$ \text{Standard Time per unit} = \frac{T \times (1 - P) \times R}{N} + \text{Allowance} \quad \text{or more directly:} $$

$$ \text{Normal Time per unit} = \frac{T \times P \times R}{N} $$

$$ \text{Standard Time} = \text{Normal Time} \times (1 + A) \quad \text{or} \quad \text{ST} = \text{NT} + (\text{NT} \times A) $$

3. Predetermined Motion Time Systems (PMTS):

   • Concept: Uses pre-established times for basic human motions (therbligs) from extensive studies. Time for a task is built by synthesising the times of its constituent motions.

   • Common Systems: MTM (Methods-Time Measurement), MODAPTS (Modular Arrangement of Predetermined Time Standards).

   • Advantages: Objective, consistent, independent of operator speed, useful for new designs.

4. Standard Data:

   • Definition: A compiled set of standard times for similar tasks/elements, derived from previous time studies or PMTS analysis.

   • Development: Group similar tasks → Analyse → Establish elemental times → Compile into a table/database.

   • Advantages: Fast, inexpensive, consistent for repetitive tasks. Reduces need for full time study every time.

Rating of Performance

• Definition: The process of evaluating a worker's pace and effectiveness relative to a standard performer (100% rating = standard pace).

• Methods:

  • Speed Rating: Focuses on the pace of movement.

  • Pace Rating (Westinghouse System): Considers pace, skill, effort, and consistency.

  • Objective Rating: Uses objective criteria (e.g., number of units produced).

  • Synthetic Rating: Uses standard data to compare observed method against a standard method.

Allowances

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

• Types:

  • Personal Allowance: For rest, toilet, etc. (2-5%).

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

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

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

• Determination: Based on empirical studies, company policy, or union agreements.

Method Time Measurement (MTM)

• Brief Explanation: The first and most famous PMTS. Breaks down any manual task into a sequence of basic motions (Reach, Move, Turn, Grasp, Release, etc.). Each motion is assigned a time value (TMU - Time Measurement Unit, 1 TMU = 0.000036 sec) based on distance and nature of motion. Sum of TMUs gives basic time. High-frequency exam topic.

[!TIP] Exam Focus: The formula Standard Time = Normal Time + Allowance is CRITICAL. Know:

• Normal Time = Observed Time × Performance Rating

• Work Sampling problems are common. Practice the formula: ST = (Total Obs. Time × % Working × Rating) / Output + Allowance.

• Distinguish clearly: Observed Time (stopwatch reading), Normal Time (observed time adjusted for rating), Standard Time (normal time + allowances).

V. INTEGRATION, STANDARDISATION & INCENTIVES

Importance of Standardisation of Motions before Time Study

• Purpose: To ensure the time study is based on the best, most efficient method, not a random or poor method.

• Process: Method Study must first establish, document, and train on the standard method. Only then is the standard time for that method measured.

• Benefit: Prevents setting a standard for an inefficient method, which would lock in poor performance.

Integration of 'Operation and Operator'

• Concept: The method (operation) and the worker (operator) must be perfectly matched.

• How? The method study engineer designs the job (tools, layout, sequence) considering human capabilities and limitations (ergonomics). The worker is then trained to perform this integrated method efficiently. It's a system approach.

Standard Time vs. Normal Time

Wage Incentive Plans

• Purpose: To motivate workers to produce more by linking earnings to output, while ensuring a fair day's work is compensated fairly.

• Types:

  • Individual Plans: Reward based on individual output.

  • Group Plans: Reward based on group/department output.

• Gantt's Task and Bonus Plan:

  • Mechanism: A two-tier rate system.

    1. Task Rate: A high piece rate for output above the standard quantity.

    2. Time Rate: A guaranteed hourly wage for output up to the standard.

  • Example: If standard is 10 units/day. Worker makes 8 units → paid hourly. Makes 12 units → paid 12 × (high piece rate). Earnings increase sharply only after standard is exceeded.

• Merrick's Multiple Piece Rate Plan:

  • Mechanism: A sliding scale of piece rates.

    • Output below 83% of standard → Low piece rate.

    • Output 83% to 100% of standard → Medium piece rate.

    • Output above 100% of standard → High piece rate.

  • Utility: Encourages even below-standard workers to produce more (they get a higher rate than pure time rate), while strongly rewarding high performers.

• Other Plans (Brief):

  • Halsey 50-50 Plan: Worker gets 50% bonus of the time saved (measured at the hourly rate).

  • Rowan Plan: Bonus = (Time Saved / Standard Time) × Hourly Rate. Earnings never exceed those under a pure piece-rate system for the same output.

  • Barth Plan: Bonus based on ratio of worker's speed to standard speed. Used for speed-critical tasks.

  • Emerson Plan: Bonus increases gradually as efficiency exceeds 66.67%. Includes a minimum guaranteed base.

[!TIP] Exam Focus: Gantt's and Merrick's plans are high-frequency. Draw a simple graph for each showing earnings vs. output. Know the key feature: Gantt's has a sharp breakpoint at standard; Merrick's has graduated rates.

VI. 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 optimise human well-being and overall system performance.

• Objectives:

  1. Enhance human efficiency and productivity.

  2. Ensure safety, health, and comfort.

  3. Reduce fatigue, error, and stress.

  4. Improve job satisfaction and quality of work life.

Human Information Processing Model

DiagramCANVAS: A simple box-and-arrow flowchart: "Sensory Input (Visual, Auditory, etc.)" → "Perception & Processing (Brain/CNS)" → "Decision & Response Selection" → "Motor Output (Action)" → "Feedback (to Sensory Input & Processing)"

• Stages: Input (Sensation) → Processing (Perception, Cognition) → Output (Action) → Feedback.

• Application: Design systems that match human capabilities at each stage (e.g., clear displays for input, simple controls for output).

Anthropometry

• Definition: The science of measuring the dimensions of the human body.

• Purpose: To design workstations, tools, and equipment that fit the user population (e.g., chair height, reach distances, control clearances).

• Types of Measurements:

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

  • Dynamic: Body dimensions during movement or work (functional reach, working envelope).

• Factors Affecting Data: Age, Sex, Ethnicity, Nutrition, Socio-economic status. Data must be population-specific (e.g., Indian anthropometric data for Indian workforce).

Man-Machine System

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

• Types:

  1. Sensory: Human senses monitor machine output (e.g., watching a gauge).

  2. Motor: Human operates machine controls (e.g., driving).

  3. Cognitive: Human makes decisions based on machine information (e.g., air traffic control).

• Relative Capabilities:

  | Human Strengths | Machine Strengths | | :--- | :--- | | Pattern recognition, flexibility, creativity, common sense | Speed, power, precision, consistency, repetitive tasks, memory | | Design Implication: Assign tasks based on strengths. Machine handles repetitive/precise work; human handles monitoring, decision-making, and handling exceptions.

Workstation & Environment Design

• A. Work Environment Design Factors:

  • Lighting: Adequate intensity, glare-free, proper contrast.

  • Noise: Minimise unwanted sound; use absorptive materials.

  • Temperature & Humidity: Maintain thermal comfort (typically 20-24°C, 40-60% RH).

  • Vibration: Isolate vibrating equipment.

  • Air Quality: Ventilation, remove contaminants (dust, fumes).

• B. Task and Work Organisation Design Principles:

  1. Use natural body movements (avoid twisting, reaching).

  2. Work within the "normal work area" (within easy reach of both hands from a fixed position).

  3. Maintain neutral postures ( wrists straight, back supported).

  4. Alternate muscle groups and provide micro-breaks.

  5. Minimise the number of ** motions** and force required.

  6. Sequence tasks to balance load and reduce monotony.

Displays

• Visual Displays:

  • Types:

    • Qualitative: Indicate condition (e.g., "ON/OFF", "FAULT").

    • Quantitative: Indicate magnitude (e.g., speedometer, pressure gauge).

  • Design Guidelines for Effectiveness:

    1. Location: Within primary field of view.

    2. Size & Shape: Large enough to be seen clearly; shape can indicate meaning (circular for speed, vertical for level).

    3. Scale: Counterclockwise for increasing values (natural). Zero at bottom or 9 o'clock.

    4. Colour: Use standard meanings (Red=danger/stop, Green=go/safe, Yellow=caution).

    5. Digital vs. Analogue: Digital for precision reading; analogue for quick pattern recognition of rate of change.

• Tactual Displays:

  • Characteristics: Use touch/pressure (vibration, shape, texture, temperature).

  • Use: Complementary to visual/auditory in high-noise, high-vibration, or visually-demanding environments (e.g., cockpit controls, wearable tech alerts).

Controls

• Principles of Control Design:

  1. Location: Within easy reach (within the normal work area). Group by frequency and sequence of use.

  2. Movement: Natural, compatible with expected response. E.g., push for "on/forward", pull for "off/back". Rotary for continuous adjustment.

  3. Resistance: Provide feedback (tactile). Resistance should increase with the degree of activation (e.g., spring-loaded). Avoid requiring excessive force.

[!TIP] Exam Focus: Be ready to sketch the Human Information Processing model. Know the difference between Qualitative and Quantitative displays with examples. For Work Environment, list the 5 factors. For Controls, remember the 3 principles: Location, Movement, Resistance.

VII. WORK FACTOR & SYNTHETIC SYSTEMS

Work Factor

• Definition: A numerical value assigned to a basic motion element based on the difficulty or effort required to perform it. It is the foundation of synthetic systems.

• Concept: Instead of timing each element, you rate its difficulty against a standard and multiply by a base time unit.

Classification of Work Factors (with Characteristics)

• Application: Each basic motion in a task is analysed, assigned a Work Factor for each of the 5 categories, and a total WF is calculated. This total is multiplied by a time unit per WF (determined from calibration studies) to get the standard time for that element.

[!TIP] Exam Focus: Be able to list and briefly explain all 5 Work Factor classifications. Understand that it's a synthetic rating system for motion difficulty, alternative to PMTS like MTM.