UNIT 1: WORK STUDY, METHOD STUDY, WORK MEASUREMENT & ERGONOMICS

I. INTRODUCTION TO WORK STUDY

Work Study is a systematic examination of activities to identify where improvements can be made in terms of efficiency, effectiveness, and economy. It is the generic term for Method Study (examining how work is done) and Work Measurement (determining how long it should take).

Objective: To achieve higher productivity with minimum waste of resources (men, material, machine, method, money).

Relevance in Modern Industry:

• Reduces cost and improves quality.

• Increases output and capacity without major capital investment.

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

• Improves working conditions and reduces fatigue.

• Forms the basis for wage incentive plans.

Human Factors & Role of Analyst:

The work study engineer must:

1. Observe without interfering initially.

2. Record facts accurately using appropriate techniques.

3. Analyze to eliminate, combine, or rearrange unnecessary elements.

4. Install the new method and maintain standards through training and supervision.

5. Integrate operator and method – the new method must be acceptable, safe, and ergonomic for the worker.

II. METHOD STUDY (Motion & Process Analysis)

A. Recording Techniques for Method Study

1. Process Charts:

• Definition: A symbolic representation of the sequence of activities in a process.

• Five Basic Symbols:

  | Symbol | Name | Meaning | | :--- | :--- | :--- | | O | Operation | A step where material is changed or assembled. | | □ | Inspection | Checking for quality, quantity, etc. | | → | Move | Transportation of material or worker. | | D | Delay | Temporary unplanned stoppage (e.g., waiting). | | ▽ | Storage | Controlled storage (recorded in files). |

• Operation Process Chart:

  • Records only the principal operations and inspections in sequence.

  • Utility: Gives a quick overview of the entire process from raw material to finished product. Used for macro-level analysis.

  • DiagramSEARCH: operation process chart example manufacturing

• Flow Process Chart:

  • Records all activities (operations, inspections, moves, delays, storage) for a single product or group of similar products.

  • Utility: Detailed analysis of a specific process to identify non-value-added activities (delays, unnecessary moves, storage). Used for micro-level improvement.

  • Distinction from Operation Chart: Flow chart is more detailed and uses all 5 symbols; Operation chart is a simplified summary.

  • DiagramSEARCH: flow process chart symbols example

2. Two-Hand Process Chart (Simultaneous Motion Chart):

• Definition: A chart that records the simultaneous activities of both left and right hands of an operator.

• Construction: Two parallel columns (Left Hand / Right Hand). Time scale on top. Activities plotted against time.

• Symbols: Uses the same 5 basic process chart symbols.

• Utility:

  • Reveals idle time of either hand.

  • Identifies unnecessary motions.

  • Basis for applying Principles of Motion Economy.

  • Helps in balancing the workload between hands.

• DiagramSEARCH: two hand process chart assembly operation

3. Multiple Activity Charts:

• Definition: Charts that record the activities of multiple resources (men, machines, materials) against a common time scale.

• SIMO Chart (Simultaneous Motion Chart):

  • A multiple activity chart for operators and machines.

  • Construction: Vertical columns for each operator/machine. A single time scale runs horizontally. Activities of each resource are plotted in its column.

  • Utility: To analyze and balance the activities in a man-machine system. Identifies machine idle time and operator idle time.

  • DiagramSEARCH: SIMO chart example operator machine

4. Memo Motion Study & Memo Production Study:

• Memo Motion Study:

  • Definition: A low-cost, quick motion study technique using a regular motion picture camera at slow speed (e.g., 1 frame per minute) to record long-cycle jobs.

  • Procedure: Film the operation. Project at normal speed for analysis.

  • Utility: For long-duration tasks (e.g., maintenance, construction) where micro-motion study is impractical. Identifies major delays and inefficient postures.

• Memo Production Study: An extension where the study focuses on output rate over a long period using the same filming technique.

• Distinction from Micro-Motion Study: Micro-motion uses high-speed cameras for short-cycle, precise motions. Memo motion is for long-cycle, overall analysis.

5. String Diagram:

• Definition: A scale diagram where a string is laid out to represent the actual path and distance traveled by a worker or material.

• Construction:

  1. Draw a scale plan of the workplace.

  2. Trace the exact path of movement with a string.

  3. Measure the length of the string to get total distance.

• Utility: To quantify travel distance, compare alternative layouts, and reduce unnecessary movement.

• DiagramCANVAS: A simple workshop layout with a string path traced from tool chest to workbench to inspection station

6. Travel Chart:

• Definition: A tabular record of the frequency of material movement between different departments or work centers.

• Purpose: To analyze material handling costs and design an efficient plant layout (e.g., using a From-To Chart).

• Utility: Identifies high-frequency movement pairs, which should be placed close together in a new layout.

B. Principles of Motion Economy & Micro-Motion Study

1. Principles of Motion Economy (3 Categories):

[!TIP] Exam Focus: Be prepared to list and apply all principles with examples.

Application in Workplace Design: These principles guide the design of workstations to minimize fatigue, reduce motion time, and improve comfort.

2. Micro-Motion Study:

• Definition: The detailed study and analysis of a short-cycle operation using a high-speed motion picture camera.

• Purpose: To break down an operation into its fundamental motions (Therbligs) for detailed analysis and improvement.

• Therbligs: The 18 basic elemental motions (e.g., Search, Reach, Grasp, Move, Assemble, Use, Disassemble, Inspect, Position, Rest, etc.). Each has a standard symbol and time value (in TMU - Time Measurement Units).

• Applications:

  • Eliminate, combine, or rearrange Therbligs.

  • Design the best method before it is installed.

  • Provide data for PMTS like MTM.

• Advantages over Conventional Motion Study:

  • Permanent record for repeated study.

  • Magnification of motions for slow-motion analysis.

  • Provides accurate timing data for each micro-motion.

  • Objective evidence for method changes.

3. Motion Study Symbols: The 5 basic process chart symbols (O, □, →, D, ▽) are used in motion study to record the nature of each activity.

C. Standardisation of Motions

• Importance: Before conducting a Time Study, the method must be standardized. A time study on a non-standard, variable method yields meaningless and unstable standards.

• Procedure: After Method Study identifies the one best method, it must be:

  1. Documented in detail (with charts, diagrams).

  2. Taught to all operators.

  3. Enforced through supervision and training.

  4. Maintained to prevent drift back to old methods.

• Result: Ensures that the Normal Time obtained from rating reflects the time for the standard method, not individual variations.

D. Man-Machine System Analysis

• Definition: A system where a human operator works in conjunction with one or more machines/equipment to perform a task.

• Types:

  1. Single Machine, Multiple Operators: e.g., a large press with a crew.

  2. Multiple Machines, Single Operator: The classic machine-paced or operator-paced system (e.g., an operator tending several automatic lathes).

  3. Multiple Machines, Multiple Operators: e.g., an assembly line.

• Analysis & Balancing:

  • Use a SIMO Chart to plot operator and machine activities on a common time scale.

  • Objective: To balance the workload so that:

    • Operator idle time is minimized.

    • Machine idle time is minimized.

    • The system operates at a smooth, continuous pace.

  • Solution: May involve machine modification, method change, adding/removing machines, or changing assignment.

III. WORK MEASUREMENT (Setting Standards)

A. Objectives & Techniques

• Primary Objectives:

  1. To determine the standard time for a job.

  2. To compare the effectiveness of different methods.

  3. To plan and schedule production (capacity planning).

  4. To set production targets and incentive rates.

  5. To estimate labor cost for tenders and quotations.

• Secondary Objectives: Labor budgeting, manpower planning, setting delivery dates.

• Techniques Overview:

  • Time Study (Stopwatch): Direct observation and timing of a skilled operator.

  • Work Sampling: Statistical technique to estimate proportion of time spent in various activities.

  • Standard Data: Using pre-determined times for similar elements from previous studies.

  • Predetermined Motion Time Systems (PMTS): Using established time values for basic motions (e.g., MTM, MODAPTS).

B. Time Study (Stopwatch Time Study)

• Procedure:

  1. Selection: Choose a qualified operator and a representative job.

  2. Breakdown: Divide the job into distinct, measurable elements.

  3. Timing: Use a stopwatch to record the observed time for each element over multiple cycles.

  4. Rating: Assess the operator's pace relative to a standard pace (100%). Apply a rating factor.

  5. Calculate Normal Time: For each element: Normal Time = Observed Time × Rating Factor.

  6. Total Normal Time: Sum of normal times for all elements.

  7. Add Allowances: Standard Time = Total Normal Time × (1 + Total Allowance Fraction).

• Performance Rating:

  • Concept: Comparing the observed pace of the operator to the standard pace (what an average, trained worker can maintain all day without undue fatigue).

  • Rating Factor: A multiplier (e.g., 0.90, 1.10, 1.25). Observed Time × Rating Factor = Normal Time.

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

• Allowances:

  • Purpose: To provide reasonable time for activities that are part of the job but not directly productive.

  • Types:

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

    • Fatigue Allowance: To recover from physical/mental fatigue (varies with job demands).

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

    • Policy Allowance: For company policy (e.g., union agreements, rest breaks).

  • Determination: Based on historical data, surveys, or negotiated rates.

Key Formulas:

Let $$\displaystyle T_{obs} $$ = Average observed time for an element, $R$ = Rating factor (as decimal), $A$ = Total allowance fraction.

Normal Time (per cycle): $$\displaystyle T_N = T_{obs} \times R $$

Standard Time (per cycle): $$\displaystyle T_{std} = T_N \times (1 + A) = (T_{obs} \times R) \times (1 + A) $$

C. Work Sampling (Statistical Sampling Technique)

• Definition: A statistical technique to estimate the proportion of time spent by a worker or machine in various defined activities by taking a large number of random observations.

• Principle: Based on the Binomial Probability Distribution. The proportion of time spent in a category equals the probability of observing that category at any random instant.

• Procedure:

  1. Define the activities (e.g., Working, Idle, Delay, Setup).

  2. Take random observations (by a observer or automatically) over a representative period.

  3. Tally the number of observations in each activity.

  4. Calculate percentage for each activity: $$\displaystyle P_i = \frac{n_i}{N} \times 100\% $$, where $$\displaystyle n_i $$ = observations in activity $i$, $N$ = total observations.

• Number of Observations Required (N):

$$N = \frac{Z^2 \times p(1-p)}{e^2}$$

Where:

*   $Z$ = Standard normal deviate for desired confidence level (e.g., 1.96 for 95%).

*   $p$ = Estimated proportion (use 0.5 for maximum sample size if unknown).

*   $e$ = Desired precision (e.g., 0.05 for ±5%).

• Problem Solving (Standard Time from Work Sampling):

  • Step 1: Find % of time actively working: $$\displaystyle P_{work} = 100\% - (\% \text{ delays} + \% \text{ idle}) $$.

  • Step 2: Find Observed Output Rate: $$\displaystyle \text{Rate}_{obs} = \frac{\text{Total Units Produced}}{\text{Total Observation Time}} $$.

  • Step 3: Find Effective Working Rate: $$\displaystyle \text{Rate}_{eff} = \text{Rate}_{obs} \times \frac{P_{work}}{100} $$.

  • Step 4: Apply Performance Rating (R) and Allowance (A):

$$\text{Standard Time per unit } (T_{std}) = \frac{1}{\text{Rate}_{eff} \times R \times (1-A)}$$

> **OR**

> 

$$\text{Standard Production Rate} = \text{Effective Rate} \times R \times (1-A)$$

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

• Standard Data:

  • Definition: Pre-determined times for standardized elements of work (e.g., "pick up bolt," "tighten nut") derived from previous detailed time studies.

  • Concept: Instead of timing a whole job, time the elements and use a lookup table of standard times for those elements.

  • Advantages:

    • Fast & economical for repetitive jobs.

    • Consistent and accurate.

    • Requires less skilled personnel for application.

    • Easy to update and maintain.

  • Applications: Estimating, quoting, routing, scheduling for high-volume, repetitive operations.

• Predetermined Motion Time Standards (PMTS):

  • Definition: A system where the time for a task is calculated by summing the pre-determined times for its basic motions (Therbligs), based on human motion capabilities.

  • Concept: Time is derived from motion analysis, not from observation of a specific worker.

  • Examples: MTM (Methods-Time Measurement), MODAPTS.

  • MTM: Breaks down motions into TMUs (Time Measurement Units). 1 TMU = 0.00001 minute (0.0006 sec). Has detailed tables for reach, move, turn, apply pressure, etc., based on distance and direction.

  • Advantages:

    • Objective & consistent (no rating needed).

    • Useful for method design before production.

    • Provides detailed motion analysis.

    • Excellent for ergonomic assessment (identifying stressful motions).

  • Limitations:

    • Expensive and time-consuming to implement initially.

    • Requires extensive training.

    • Less effective for non-repetitive, creative, or mentally demanding tasks.

E. Time Measuring Devices

• Stopwatch: Traditional, mechanical or digital. Used for continuous or snapback timing.

• Decimal Minute Watch: Stopwatch calibrated in 1/100 or 1/1000 of a minute for easier calculation.

• Electronic Timer: Computer-based systems with data acquisition, often linked to video recording.

• Movie Camera (High-Speed): For Micro-Motion Study to analyze fast, short-cycle motions frame-by-frame.

IV. 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:

1. Enhance human efficiency and productivity.

2. Ensure safety, health, and comfort.

3. Reduce fatigue, stress, and error.

4. Improve quality of work and life.

5. Design systems that are compatible with human capabilities and limitations.

A. Anthropometry

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

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

• Types of Measurements:

  1. Static Anthropometry: Body dimensions in a static posture (e.g., standing height, sitting elbow height).

  2. Dynamic Anthropometry: Body dimensions in motion or functional postures (e.g., maximum reach, grip span).

  3. Functional Anthropometry: Measurements related to specific tasks (e.g., eye height while operating a vehicle control).

• Factors Affecting Data:

  • Age, Sex, Ethnicity (genetic background).

  • Nutrition and health.

  • Socio-economic factors.

  • Posture (sitting vs. standing).

• Application: Design of chair height, workbench height, tool handle diameter, vehicle cockpit, doorway clearance, control reach envelopes. Use percentiles (e.g., design for 5th percentile female to 95th percentile male for adjustability).

B. Human Sensory Systems & Information Processing

• Sensory Inputs (Coding & Selection):

  • Visual: Most important. Coding by shape, color, size, position. Must consider illumination, glare, contrast.

  • Auditory: Coding by pitch, loudness, rhythm, location. Effective for warning signals and when vision is occupied.

  • Tactual (Tactile): Coding by texture, shape, temperature, vibration. Used for identification by feel (e.g., Braille, tool handles).

  • Selection: Design must consider attention, expectation, and relevance of the signal to avoid overload.

• Human Information Processing Model:

  DiagramCANVAS: A flowchart with boxes: Sensory Input (Stimulus) -> Sensory Register (Iconic/Echoic) -> Perception/Pattern Recognition -> Short-Term Memory (Limited Capacity) -> Decision/Response Selection -> Motor Output -> Long-Term Memory (Unlimited Capacity) -> Feedback

  • Stages: Input → Sensory Register → Perception → Short-Term Memory (Working Memory) → Decision → Motor Output → Long-Term Memory.

  • Key Implications: Design displays to match perceptual strengths (e.g., analog vs. digital). Avoid overloading Short-Term Memory (limit to 7±2 items). Provide clear feedback.

• Relative Capabilities of Humans and Machines:

  | Capability | Humans (Advantage) | Machines (Advantage) | | :--- | :--- | :--- | | Pattern Recognition | Excellent, flexible. | Poor, rigid. | | Decision Making | Good in novel, complex situations. | Excellent in routine, programmed tasks. | | Memory | Long-term associative memory good. Short-term limited. | Vast, precise, immediate recall. | | Sustained Attention | Poor, fatigues quickly. | Excellent, consistent. | | Strength & Endurance | Limited, fatigues. | High, consistent. | | Speed & Precision | Variable, slower. | Extremely fast, precise. | | Creativity & Improvisation | Excellent. | None. | | Sensitivity | To light, sound, temperature, pain. | To specific, measurable inputs only. | | Fatigue & Boredom | Prone to both. | Not applicable. |

C. Displays and Controls

• Visual Displays:

  • Types:

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

    • Quantitative: Indicate magnitude (e.g., speedometer, pressure gauge - analog or digital).

    • Warning/Alarm: Attract attention to abnormal condition (flashing light, audible alarm).

  • Characteristics of an Effective Visual Display:

    • High detectability: Bright, contrasting, large enough.

    • High discriminability: Clear coding (shape, color, position).

    • Immediate comprehension: Meaning should be obvious.

    • Compatibility: Display movement matches mental model (e.g., pointer up = increase).

    • Accuracy: Minimal parallax error.

• Tactual (Tactile) Displays:

  • Definition: Devices that convey information through the sense of touch.

  • Characteristics:

    • Shape/Texture Coding: Different shapes/textures for different controls (e.g., aircraft cockpit).

    • Location Coding: Controls placed in specific, memorized locations.

    • Force Feedback: Resistance or detents to indicate selection (e.g., keyboard keys, joystick).

  • Applications: When vision is heavily loaded (e.g., pilot, surgeon), in dark/noisy environments, for visually impaired.

• General Design Guidelines for Displays:

  • Match the display to the task and human information processing.

  • Use redundant coding (e.g., color + shape + position).

  • Place displays in the normal field of view.

  • Ensure adequate illumination and glare control.

  • Design for quick, accurate, and low-error interpretation.

D. Work Environment & Task Design

• Work Environment Design:

  • Lighting: Adequate illuminance (lux), uniformity, contrast, and glare control. Task-dependent.

  • Noise: Minimize unwanted sound. Use enclosures, absorbers, hearing protection. Consider speech interference.

  • Temperature & Humidity: Maintain within thermal comfort zone (approx. 20-25°C, 40-60% RH) to prevent heat/cold stress.

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

  • Vibration: Isolate sources, use anti-vibration mats/gloves to prevent health issues.

• Task and Work Organisation Design (to reduce fatigue & monotony):

  • Job Rotation: Cycle workers through different tasks to use different muscle groups and reduce mental fatigue.

  • Job Enlargement: Add more similar tasks to a job to increase variety (horizontal loading).

  • Job Enrichment: Add more responsibility, control, and variety (vertical loading - planning, checking).

  • Work-Rest Schedules: Design breaks based on task demands (physical vs. mental).

  • Autonomy & Participation: Allow workers some control over pace/method.

  • Feedback: Provide clear information on performance.

V. WAGE INCENTIVE PLANS & INTEGRATION

A. Wage Incentive Plans

• Output-Based Plans: Earnings depend on output above a standard.

  • Taylor's Differential Piece Rate System:

    • Two piece rates: Higher rate for output at or above standard, lower rate for output below standard.

    • Purpose: To strongly incentivize workers to achieve the standard.

    • Criticism: Punitive, creates two classes of workers.

  • Merrick's Multiple Piece Rate Plan:

    • Graduated piece rates. Output up to 83% of standard: low rate. 83%-100%: medium rate. Above 100%: high rate (premium).

    • Less severe than Taylor's. Rewards incremental improvement.

  • Gantt's Task and Bonus Plan:

    • High piece rate (150% of normal rate) for output at or above standard.

    • Time rate (100% of base rate) for output below standard.

    • Guaranteed minimum daily wage.

    • Bonus: 50% of wages earned on time work for the portion of output above standard.

    • Philosophy: "Task and bonus" – a clear task (standard) with a bonus for exceeding it. More cooperative than Taylor's.

B. Integration of 'Operation and Operator'

• Concept: Achieving harmony between the standardized method (operation) and the human worker (operator).

• How? Through the combined application of:

  1. Method Study: To determine the one best, standardized method that is efficient and ergonomic.

  2. Work Measurement: To establish a fair and attainable standard time for that method, including appropriate allowances.

  3. Ergonomics: To ensure the method and workplace are designed for human capabilities.

  4. Training: To teach the operator the standard method.

  5. Incentive Plans: To motivate the operator to work at the standard pace using the standard method.

  6. Supervision & Feedback: To maintain the standard and address problems.

• Goal: The operator is trained, motivated, and works in a designed environment to consistently perform the best method at a standard pace, leading to mutual benefit (higher pay for worker, higher output/quality for management).