UNIT 3: WORK STUDY, METHOD STUDY, WORK MEASUREMENT & ERGONOMICS

A. WORK STUDY: FOUNDATIONS & OVERVIEW

Definition & Core Concept

Work Study is a systematic examination of activities to identify where improvements can be made in terms of efficiency, economy, and safety. It is the generic title for Method Study (seeking the best method) and Work Measurement (determining standard time for the method).

Objectives

1. Improve productivity (output per unit input).

2. Improve quality of product/service.

3. Reduce operational costs.

4. Improve safety and working conditions.

5. Provide reliable data for planning, costing, and scheduling.

Scope & Relevance in Modern Industry

• Applies to all sectors: manufacturing, services, healthcare, offices.

• Foundation for Lean Manufacturing, Six Sigma, and Business Process Re-engineering.

• Enables capacity planning, estimation, and performance benchmarking.

• Promotes standardization and continuous improvement (Kaizen).

Human Factors in Work Study

• Work Study must consider the physical and psychological capabilities and limitations of the operator.

• Goals: Reduce fatigue, monotony, and stress; increase job satisfaction.

• Poorly designed work leads to errors, accidents, high turnover, and low morale.

[!TIP] Exam Focus: Be prepared to define Work Study and list its objectives. The integration of human factors is a recurring theme, especially in Ergonomics.

B. METHOD STUDY (MOTION STUDY)

1. Recording Techniques for Existing/Proposed Methods

Process Charts

Distinction:

• Operation Process Chart: Focuses on what happens to the material (operations/inspections). It's a summary.

• Flow Process Chart: Focuses on how, where, and when it happens (including transport, delays, storage). It's a detailed sequence.

Motion Charts & Diagrams

• Two-Hand Process Chart (Simultaneous Motion Chart):

  • Records simultaneous activities of left and right hands of a single operator.

  • Uses a vertical time scale. Columns for each hand and a "Description" column.

  • Utility: Identifies unbalanced motions, idle hands, and unnecessary movements. Foundation for micro-motion study.

• Activity Chart:

  • Records activity of an operator and the machine(s) they tend over time.

  • Shows periods of machine work, operator work, and idle time for both.

  • Utility: Balances operator and machine workload, identifies machine idle time.

• SIMO Chart (Simultaneous Motion Chart for Multiple Operators):

  • Extension of two-hand chart for multiple operators working together.

  • Records left/right hand activities of each operator on parallel columns.

  • Utility: Analyzes team activities, identifies coordination problems.

• Travel Chart (From-To Chart):

  • A matrix showing the frequency of material or person movement between departments or workstations.

  • Rows = "From" locations, Columns = "To" locations.

  • Utility: Plans efficient facility layout by highlighting high-frequency movements.

• String Diagram:

  • A scaled plan of the workplace showing the actual path (string/thread) taken by a worker or material during an operation.

  • Utility: Visually demonstrates excessive travel distance and awkward postures. Used for layout redesign.

Motion Study Symbols & Terminology (Standard Set)

[!TIP] Common Pitfall: Confusing Delay (D) (temporary, unexpected) with Storage (∇) (planned, controlled). Delay is usually non-productive; storage may be necessary.

2. Micro-Motion Study & Motion Economy

Micro-Motion Study

• Definition: Detailed study and analysis of the smallest elemental motions (e.g., reach, grasp, move, position, release) of a worker.

• Purpose: To eliminate, combine, or sequence these basic motions for maximum efficiency. Forms the basis for PMTS.

• Tools: High-speed photography, video recording, therbligs (18 basic motion elements).

Principles of Motion Economy (Detailed Classification)

A. Principles Related to the Use of the Human Body:

1. Both hands should begin and end motions simultaneously.

2. Both hands should be symmetrically and simultaneously active.

3. Use lowest possible classification of motion (e.g., finger > wrist > elbow > shoulder).

4. Use momentum to assist the worker; minimize static muscle effort.

5. Use continuous, curved, and ballistic motions rather than straight-line, zigzag motions.

B. Principles Related to the Arrangement of the Workplace:

1. Arrange tools, materials, and controls in fixed, definite locations.

2. Locate tools, materials, and controls close to and in front of the operator.

3. Provide gravity feed for materials.

4. Design workplace for both sitting and standing if possible.

5. Ensure adequate illumination, minimize glare.

C. Principles Related to the Design of Tools and Equipment:

1. Combine tools whenever possible.

2. Design tools to reduce grip effort and maintain neutral wrist posture.

3. Use progressive indexing (e.g., jigs, fixtures) to eliminate searching/positioning.

4. Distribute required force over largest possible number of muscles.

5. Design handles for minimum grip strength.

Memo Motion Study / Memo Production Study

• Definition: A quick, low-cost method of motion study using video recording at high speed (e.g., 1/10th normal speed) for later analysis.

• Procedure: Record operation, play back slowly, record observations on a two-hand chart or activity chart.

• Utility: Less disruptive than live observation, allows repeated viewing, useful for infrequent or long-cycle operations.

3. Method Study Procedure (6-Step Approach)

1. SELECT: Identify the job/process to study (based on economic importance, problems, or new design).

2. RECORD: Use appropriate charts/diagrams (process, two-hand, flow) to objectively document the current method. All facts, no opinions.

3. EXAMINE: Critically question every detail of the recorded method. Use "ECRS" principle:

   • Eliminate: Can this step be removed?

   • Combine: Can this step be combined with another?

   • Rearrange: Can the sequence be changed for better flow?

   • Simplify: Can the step be made easier/safer?

4. DEVELOP: Design, evaluate, and select the best new method. Involve operators and stakeholders.

5. INSTALL: Implement the new method. Requires training, new layouts, documentation (standard operating procedure).

6. MAINTAIN: Ensure the new method is adhered to and periodically reviewed for further improvement.

[!TIP] Exam Key: The ECRS principle is a must-know for developing new methods. "Integration of 'operation and operator'" means designing the work system so that the task, tools, environment, and operator's capabilities are perfectly matched.

C. WORK MEASUREMENT

1. Time Study

• Objective: To determine the time required for a qualified worker to complete a specified task at a defined level of performance.

• Procedure:

  1. Select job & obtain operator consent.

  2. Record detailed job breakdown & timing (using stopwatch - continuous or snap-back method).

  3. Assess Performance Rating: Compare operator's speed/effort to a standard (100% = normal pace). Methods:

     • Speed Rating: Based on relative speed of motion.

     • Pace Rating: Based on output rate over a period.

     • Westinghouse System: Considers skill, effort, conditions, consistency.

  4. Calculate Normal Time: Normal Time = Average Observed Time × (Performance Rating / 100)

  5. Add Allowances to get Standard Time.

• Standard Time Calculation:

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

Where:

*   `NT = Average Observed Time × (Rating Factor)`

*   `Total Allowance = Personal % + Fatigue % + Delay % + Special %`

• Allowances (Types & Purpose):

  • Personal Allowance (2-5%): For personal needs (water, restroom).

  • Fatigue Allowance (4-10%): To recover from physiological/psychological strain.

  • Delay Allowance: For unavoidable delays (machine breakdown, material shortage). Not for operator-caused delays.

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

• Distinction:

  • Normal Time: Time required by operator working at standard performance (100% rating), excluding allowances.

  • Standard Time: Time allowed for the job including all legitimate allowances. It is the target time for planning and costing.

2. Work Sampling (Activity Sampling)

• 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 Binomial Distribution. The number of observations n needed for a given confidence level and precision is:

$$ n = \frac{p(1-p)}{\sigma^2} $$

Where:

*   `p` = estimated proportion (from pilot study or 0.5 for max sample size).

*   `σ` = desired **standard error** (precision). For 95% confidence & ±5% precision, σ ≈ 0.05.

• Calculation Steps:

  1. % Time for Activity: % = (Number of observations of activity / Total observations) × 100

  2. Number of Units Produced: Units = (Total working time / % working time)

  3. Average Time per Unit (from WS): T_u = (Total observation time × % working) / Number of units produced

  4. Normal Time: NT = T_u × (Performance Rating / 100)

  5. Standard Time: ST = NT × (1 + Allowance Fraction)

[!TIP] Exam Problem Pattern: A classic problem gives: total observations, working/idle counts, total hours observed, units produced, rating, allowance. You must calculate Standard Time per unit. Always convert all time to consistent units (minutes/seconds).

3. Predetermined Motion Time Systems (PMTS) & Standard Data

Predetermined Motion Time Standards (PMTS)

• Definition: Systems that assign time values (in TMU - Time Measurement Units) to basic motions (reach, move, turn, grasp, release, etc.) based on extensive laboratory studies.

• Advantages (High-Frequency Question):

  1. High Accuracy & Objectivity: No need for performance rating; times are predetermined.

  2. Consistency: Same analysis by different analysts yields same time.

  3. Basis for Standard Data: Builds comprehensive databases for similar tasks.

  4. Useful at Design Stage: Can estimate time for new methods before production.

  5. Identifies Non-Value-Added Motions: Highlights inefficient motion patterns.

  6. Facilitates Method Comparison: Quantifies improvement potential.

Brief: Method Time Measurement (MTM)

• The most widely used PMTS.

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

• Each motion's time depends on distance, weight, difficulty, and body part used.

• Times are tabulated in TMU (1 TMU = 0.00001 minute = 0.036 milliseconds).

• Application: Requires extensive training; used for detailed method engineering and standard data development.

Standard Data

• Definition: Pre-determined time values for groups of activities or complete operations (e.g., "drill 10mm hole in 5mm steel plate" = 0.25 min), derived from PMTS analysis or historical time study data.

• Advantages:

  1. Saves Time: No need for fresh time study for repetitive tasks.

  2. Consistency & Fairness: Same standard for all workers/plants.

  3. Quick Estimation: Useful for quoting, planning, and costing.

  4. Basis for Incentives: Reliable standard for wage plans.

  5. Simplifies Work Measurement: Reduces need for frequent, expensive time studies.

D. ERGONOMICS (HUMAN FACTORS ENGINEERING)

1. Introduction

• 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 efficiency and productivity.

  2. Ensure safety and reduce accidents.

  3. Improve comfort and reduce fatigue.

  4. Promote health and prevent musculoskeletal disorders (MSDs).

  5. Improve quality by reducing human error.

2. Anthropometry

• Definition: The science of measurements of the human body (dimensions, mass, composition).

• Importance: Provides the physical data for designing workplaces, tools, equipment, and vehicles that fit the user.

• Types:

  • Static Measurements: Body dimensions in a stationary posture (e.g., stature, sitting height, arm span, limb lengths).

  • Dynamic Measurements: Body dimensions and ranges of motion during activity (e.g., reach envelope, working postures, joint angles).

• Factors Affecting Data: Age, sex, ethnicity, nutrition, socioeconomic status, regional variations.

• Application & Percentiles:

  • Design for a target population (e.g., 5th percentile female to 95th percentile male).

  • Adjustable designs are preferred to accommodate a wide range.

  • Example: A chair height adjustable for 5th percentile female (short) to 95th percentile male (tall).

3. Human Information Processing & Sensory Systems

• Sensory Inputs: Humans receive information via Visual (80%+), Auditory, Tactual, Olfactory, Gustatory systems.

• Human Information Processing Model:

  
  [Stimulus] --> [Sensory Input] --> [Perception/Recognition] --> [Decision/Judgment] --> [Response/Motor Output] --> [Action]
  
  

  • Sensory Input: Physical stimulus detected by senses.

  • Perception: Interpreting and organizing sensory information.

  • Decision: Choosing a course of action.

  • Response: Physical action taken.

• Coding & Selection of Sensory Inputs:

  • Coding: Assigning meaning to signals (e.g., red=stop, green=go; shape coding for different valves).

  • Principles: Use multiple channels (visual + auditory) for critical signals. Ensure signal stands out from background (contrast). Use meaningful, standard codes. Minimize information load.

4. Displays & Controls

Visual Displays

• Types: Analog (pointer/scale), Digital (numeric), Graphical (trend charts), Symbolic (pictograms).

• Characteristics of Effective Displays:

  • Size & Shape: Appropriate for viewing distance and task.

  • Color: Use standard meanings (red=danger, green=ok). Avoid color as sole cue (color blindness).

  • Location: Within normal field of view (directly ahead).

  • Coding: Use shape, size, color to differentiate.

  • Accuracy & Precision: Match required task need.

  • Illumination: Adequate, glare-free.

Tactual Displays

• Definition: Devices that convey information through touch.

• Characteristics & Applications:

  • Braille: For reading by visually impaired.

  • Vibration Alerts: In mobile phones, gaming controllers, vehicle seat (for collision warning).

  • Shape/Texture Coding: For identification by feel (e.g., tools in a dark toolbox, control knobs).

  • Force Feedback: In advanced joysticks/steering wheels (e.g., video games, flight simulators).

General Design Guidelines for Displays:

1. Match display to task requirements.

2. Minimize visual search time.

3. Use standardized formats.

4. Provide immediate feedback.

5. Design for error tolerance (e.g., "Are you sure?" prompts).

5. Man-Machine Systems

• Definition: A system where a human operator interacts with a machine or technology to achieve a goal.

• Classification:

  • By Function:

    • Continuous Control: e.g., driving a car, piloting an aircraft (smooth, ongoing adjustments).

    • Discrete Control: e.g., operating a crane, typing (distinct, separate actions).

    • Supervisory Control: Human sets goals, plans, and monitors an automated system (e.g., plant operator monitoring SCADA).

  • By Degree of Automation: From fully manual to fully automatic (with human override).

• Relative Capabilities:

  | Human Strengths | Machine Strengths | | :--- | :--- | | Pattern recognition, subjective judgment, flexibility, creativity, common sense. | Speed, power, precision, repetition, consistency, operation in hazardous environments. | | Design Implication: Design system to use human strengths for non-routine, cognitive tasks and machine strengths for routine, physical tasks.

6. Work Environment & Task Design

Work Environment Design (Physical & Psychological)

• Physical Factors:

  • Lighting: Adequate illuminance, uniform distribution, glare control.

  • Noise: Reduce at source; use hearing protection. High noise causes stress and masks auditory signals.

  • Temperature & Humidity: Maintain within comfort zone (approx. 20-25°C, 40-60% RH).

  • Vibration: Isolate sources; can cause fatigue and health issues.

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

• Psychological Factors:

  • Stress: Manage workload, deadlines, role ambiguity.

  • Workload: Balance between underload (boredom) and overload (anxiety).

  • Shift Work: Minimize disruption to circadian rhythms; provide adequate rest.

Task & Work Organisation Design

• Job Rotation: Periodically shifting workers between different tasks.

  • Purpose: Reduce monotony, balance muscle use, cross-train workforce.

• Job Enlargement: Adding more similar tasks to a job (horizontal loading).

  • Purpose: Reduce repetitiveness, increase task variety.

• Job Enrichment: Adding more responsibility, autonomy, and challenge to a job (vertical loading).

  • Purpose: Increase motivation, satisfaction, and sense of achievement (Herzberg's motivators).

E. WAGE INCENTIVE PLANS & PRODUCTIVITY

Objectives of Incentive Plans

1. Increase output and productivity.

2. Provide fair reward for higher effort/skill.

3. Reduce labor cost per unit.

4. Improve morale and reduce turnover.

5. Establish clear performance standards.

Types of Output-Based Wage Incentive Plans

[!TIP] Distinction: Piece Rate plans pay directly per unit. Bonus plans (Gantt, Halsey, Rowan, Barth) pay a base time rate plus a bonus for exceeding standard.

F. CALCULATION-BASED PROBLEMS (HIGH FREQUENCY)

1. Standard Time from Work Sampling Data

Given: Total observations N, Working observations n_w, Total observation time T_obs (e.g., 5 days × 4 hrs/day), Units produced U, Performance Rating R%, Allowance A%. Steps:

1. % Working Time: %_w = (n_w / N) × 100

2. Total Effective Working Time: T_eff = T_obs × (%_w / 100)

3. Average Time per Unit (Observed): T_u_obs = T_eff / U

4. Normal Time: NT = T_u_obs × (R / 100)

5. Standard Time: ST = NT × (1 + A / 100)

\boxed{ST = \left( \frac{T_{obs} \times (n_w / N)}{U} \right) \times \frac{R}{100} \times \left(1 + \frac{A}{100}\right)}

2. Standard Time from Time Study Data

Given: Set of observed times for a cycle, Performance Rating R%, Allowance A%. Steps:

1. Average Observed Time: T_avg = (Σ Observed Times) / Number of Cycles

2. Normal Time: NT = T_avg × (R / 100)

3. Standard Time: ST = NT × (1 + A / 100)

\boxed{ST = T_{avg} \times \frac{R}{100} \times \left(1 + \frac{A}{100}\right)}

3. Number of Observations in Work Sampling

Formula for desired precision d (e.g., ±5% = 0.05) at confidence level (usually 95%):

$$ n = \frac{Z^2 \times p(1-p)}{d^2} $$

Where:

• Z = Z-score for confidence level (1.96 for 95%).

• p = estimated proportion (from pilot study, or 0.5 for maximum n).

• d = desired precision (e.g., 0.05).

Example: For 95% confidence, ±5% precision, with p=0.5:

\boxed{n = \frac{(1.96)^2 \times 0.5 \times 0.5}{(0.05)^2} = \frac{3.8416 \times 0.25}{0.0025} = 384.16 \approx 385 \text{ observations}}

[!TIP] Exam Tip: In work sampling problems, always check the observation period. If it says "observed for 4 hours/day for 5 days", T_obs = 20 hours. Convert to minutes for consistency with time units.

G. DISTINCTIONS & COMPARISONS (FREQUENTLY ASKED)

H. SHORT NOTES & DEFINITIONS (RECURRING THEMES)

Principles of Motion Economy (List)

1. Both hands start/end together.

2. Hands used symmetrically & simultaneously.

3. Use lowest classification of motion.

4. Use momentum; minimize static effort.

5. Use continuous, curved, ballistic motions.

6. Tools/materials in fixed, definite locations.

7. Tools/materials close to and in front of operator.

8. Provide gravity feed.

9. Design for sitting/standing.

10. Combine tools.

11. Design handles for minimal grip.

12. Use progressive indexing.

Symbols of Motion Study (Table from B.1)

• ○ Operation, □ Inspection, → Transport, D Delay, ∇ Storage, ⊗ Combined Activity.

String Diagram

• Utility: To measure and analyze the actual path of a worker or material, identifying excessive travel distance and awkward postures.

• Procedure: Draw scaled plan of workplace. Have worker perform task with a string tied to finger/pencil, tracing path. Measure string length.

Allowances

• Purpose: To provide reasonable time for personal needs, fatigue recovery, and unavoidable delays.

• Types: Personal (2-5%), Fatigue (4-10%), Delay (variable), Special (task-specific).

Rating (Time Study)

• Definition: The process of assessing the operator's speed and effort relative to a standard performance (100% = normal pace).

• Methods: Speed Rating, Pace Rating, Westinghouse System (Skill, Effort, Conditions, Consistency).

Travel Chart (From-To Chart)

• Purpose: To quantify and analyze material or personnel movement between departments/workstations for facility layout planning.

• Construction: Matrix with "From" locations as rows, "To" locations as columns. Fill cells with frequency of trips.

SIMO Chart

• Construction: Records left/right hand activities of multiple operators on parallel columns against a common time scale.

• Operation: Used to analyze team-based operations, identify idle time for any member, and balance team workload.

Micro-Motion Study

• Applications: Detailed analysis of short-cycle, repetitive operations; development of PMTS data; training for method improvement; identifying and eliminating unnecessary micro-motions.

Work Factor

• Definition: A predetermined element of a task (e.g., a reach, a grasp) to which a time value is assigned based on influencing factors (distance, weight, etc.).

• Classification: Often classified by body member used (finger, hand, arm) and type (reach, move, turn, grasp, release, position).

• Characteristics: Time values are empirically derived and independent of operator pace.

Ergonomics (Objectives)

1. Optimize human well-being (health, safety, comfort).

2. Optimize system performance (efficiency, productivity, quality).

3. Ensure compatibility between human capabilities and system demands.

Standard Data (Advantages)

1. Time-saving: No fresh study for repetitive tasks.

2. Consistency & Fairness: Uniform standards.

3. Quick Estimation: For quoting, planning.

4. Basis for Incentives: Reliable standard.

5. Simplifies Work Measurement.

[[END OF UNIT 3 NOTES]]