TQM and SQC (ME-504 (B)) - Unit 5 Short Notes

UNIT 5: METHOD STUDY, WORK MEASUREMENT & ERGONOMICS

I. WORK STUDY (FOUNDATION & OVERVIEW)

Definition:

Work Study is a systematic examination of existing or proposed ways of doing work to make improvements in effectiveness and efficiency. It is the generic term encompassing Method Study (seeking the best method) and Work Measurement (determining standard time for the method).

Purpose & Scope:

• Improve processes and methods.

• Establish standard times for planning and costing.

• Reduce waste (motion, time, materials).

• Improve workplace layout and working conditions.

• Provide basis for wage incentives and production scheduling.

Relevance in Modern Industry:

• Foundation for Lean Manufacturing and Kaizen.

• Essential for process optimization and cost reduction.

• Integrates with automation and technology implementation.

• Supports sustainable practices by eliminating non-value-added activities.

Relationship:

• Method Study comes first: It finds the "best method".

• Work Measurement follows: It determines "standard time" for that best method.

[!TIP] Exam Focus: Always state that Method Study and Work Measurement are complementary. You cannot measure time for a poor method and expect meaningful results.

II. METHOD STUDY (MOTION & METHOD IMPROVEMENT)

Steps in Method Study (The 6-Step Cycle)

1. Select: Identify the process, operation, or job with potential for improvement.

2. Record: Use appropriate charts/diagrams to document the existing method in detail.

3. Examine: Critically question the recorded facts. Challenge the purpose, place, sequence, and person for each element.

4. Develop: Design and evaluate alternative improved methods. Select the best one.

5. Install: Implement the new method. Train personnel, change layouts, and install new tools.

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

Recording Techniques (Process Charts & Diagrams)

Process Chart Symbols (ASME Standard):

• O - Operation: A main step where material is changed.

• I - Inspection: Checking for quality/quantity.

• D - Delay: Temporary hold (material waiting).

• M - Move: Transportation of material/person.

• S - Storage: Controlled storage (inventory).

• ⊞ - Combined Activity: Two or more activities occur simultaneously.

Motion Study & Therbligs

• Micro-Motion Study: Detailed study of sub-divisions of a motion using high-speed photography and Therbligs. Used for designing highly repetitive tasks.

• Memo Motion Study / Memo Production Study: Uses normal-speed film (16-64 fps) to study long-cycle, non-repetitive jobs. Faster and cheaper than micro-motion study. Useful for overall method analysis.

• Therbligs: 18 basic theoretical motions (e.g., Search, Grasp, Hold, Release, Position, Assemble, Use, Inspect, etc.). Each has a symbol and color. They are the building blocks of any manual task.

  Classification: Effective (towards job) vs. Ineffective (delay, hold, rest).

Motion Economy Principles

A. Fundamental Principles (Use of Body):

1. Both hands should start and end their motions simultaneously.

2. Both hands should not be idle at the same time except during rest.

3. Motions of the hands should be made in opposite and symmetrical directions.

4. Use lowest possible classification of motion (Finger > Wrist > Elbow > Shoulder > Body).

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

B. Detailed Principles (Workplace & Tool Design):

1. Fixed locations for all tools/materials.

2. Gravity feed bins and drop deliveries.

3. Optimal workplace height for visual and manual tasks.

4. Tools and materials pre-positioned for sequential use.

5. Combine tools where possible.

6. Sequence motions to establish a rhythm.

7. Minimize eye focus and head movements.

Method Improvement: Integration of 'Operation and Operator'

• This means designing the workstation and method so that the operator and the machine/operation are in perfect harmony.

• Goal: Eliminate waiting (operator or machine idle). Ensure smooth, balanced flow.

• Application: Use Activity Charts to identify imbalances. Redesign layout, adjust machine cycle times, or allocate tasks to synchronize the human and machine elements.

[!TIP] Exam Focus: Be ready to list all 18 Therbligs (names/symbols) and all 7-8 Motion Economy principles with a one-line explanation. Distinguishing Memo Motion (normal film, long cycles) from Micro-Motion (high-speed film, short cycles) is common.

III. WORK MEASUREMENT (TIME & PERFORMANCE STANDARDS)

Objectives of Work Measurement

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

2. To compare worker performance against the standard.

3. To set production targets and incentive rates.

4. To balance workloads and determine manpower requirements.

5. To provide a basis for labor cost estimation.

Techniques of Work Measurement

Key Concepts & Calculations

1. Normal Time vs. Standard Time:

• Normal Time (NT): Time required by a qualified worker to perform the task at a normal pace (without fatigue or delays).

$$ \text{Normal Time} = \text{Observed Time} \times \text{Performance Rating} $$

• Standard Time (ST): Time allowed for a qualified worker to complete the task including all necessary allowances (personal, fatigue, delay).

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

> **Crucial Difference:** NT = "pure work" at normal pace. ST = NT + **allowances**.

2. Performance Rating:

• Definition: The process of adjusting observed time to what it should have been for a worker operating at a standard (100%) performance level.

• Purpose: To eliminate the effect of the operator's individual pace (fast/slow) from the time study.

• Common Methods: 60/40 Rating, Westinghouse System (skill, effort, conditions, consistency).

3. Allowances:

• Purpose: To add to Normal Time to get Standard Time, covering unavoidable delays and personal needs.

• Types:

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

  • Fatigue Allowance: To recover from physiological/psychological strain (varies with job demands).

  • Delay Allowance: For unavoidable machine/process delays (e.g., tool change, material not ready).

  • Policy Allowance: For company policies (e.g., rest breaks).

• Total Allowance is expressed as a fraction or percentage (e.g., 15% = 0.15).

Standard Time Calculation from Work Sampling (Frequent Problem)

Formula Chain:

1. Proportion of Working Time (P): P = (Number of Working Observations) / (Total Observations)

2. Normal Time per Unit: NT = (Total Available Time for Production) / (Number of Units Produced) × P

   • Total Available Time = (Observation Period in hours) × (Number of workers observed).

3. Standard Time per Unit: ST = NT / (1 - Total Allowance Fraction) OR ST = NT × (1 + Total Allowance Fraction)

   Note: The second formula (ST = NT × (1+A)) is more common and direct.

Example (from Past Paper - Jun 2025):

• Work week = 48 hours.

• Avoidable delays = 25% → Working Proportion (P) = 1 - 0.25 = 0.75.

• Rating = 110% = 1.10.

• Units produced = 80.

• Total Available Time = 48 hours (for the operator).

• Step 1: Observed Time per Unit = 48 hours / 80 units = 0.6 hours/unit.

• Step 2: Normal Time (NT) = Observed Time × Rating = 0.6 × 1.10 = 0.66 hours/unit.

• Step 3: Standard Time (ST) = NT × (1 + Allowance). Allowance not given in this specific problem statement? (Typically, if not given, assume a standard like 15%. But the problem says "avoidable delays" are 25% - this is part of the proportion. The allowance for personal/fatigue is separate. Clarification needed in exam context. Usually, the 25% "avoidable delays" are part of the non-working time captured by Work Sampling. The P=0.75 already accounts for it. Then we apply separate allowance (e.g., 15%) on the NT derived from P.

  • Correct Interpretation: The 25% is the idle time from sampling. So P = 0.75. NT is based on the working component. Then ST = NT / (1 - Allowance). If no separate allowance is given, ST = NT / P? No.

  • Standard Formula for WS: ST = (Total Observed Time) / (Number of Units × P × (1 - A)) is messy.

  • Simpler Path: The observed time per unit is based on total clock time. The working fraction (P) tells us what portion of that clock time was actual work. So effective work time per unit = Observed Time per unit × P. Then Normal Time = (Effective work time per unit) / Rating. Then Standard Time = NT / (1 - A).

  • Let's apply: Observed Time/unit = 0.6 hr. Work content = 0.6 × 0.75 = 0.45 hr. NT = 0.45 / 1.10 = 0.409 hr/unit. If A=15%, ST = 0.409 / (1-0.15) = 0.482 hr/unit.

  • ⚠️ Common Pitfall: Students often multiply NT by (1+A) instead of dividing by (1-A). Remember: Allowances are added to the working time, so ST = NT / (1 - A) is the correct formula when A is the fraction of NT added. The formula ST = NT × (1+A) is incorrect if A is defined as a fraction of NT. It's correct only if A is a fraction of ST. Most textbooks define: ST = NT × (1 + Total Allowance), where Allowance is a fraction of NT. This is the convention to use. So ST = NT × (1.15) if A=15%. Be consistent with your textbook's definition.

Time Study Equipment:

• Stopwatch: Manual (split-second), digital.

• Film/Videography: For later analysis (micro/memo motion).

• Electronic Devices: Data collection terminals, PC-based systems, RFID, video analysis software.

[!TIP] Exam Focus: Standard Time calculation is THE most frequent numerical problem. Be absolutely clear on the sequence: Observed Time → Normal Time (apply Rating) → Standard Time (apply Allowance). Know the difference between rating (adjusting pace) and allowance (adding for fatigue/delays).

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, safety, and comfort.

2. Reduce fatigue, error, and injury.

3. Improve quality and productivity.

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

Anthropometry

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

• Purpose: To design workplaces, tools, equipment, and products that fit the user population.

• Types of Measurements:

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

  • Dynamic: Body dimensions during movement or task performance (e.g., functional reach, grip span).

• Factors Affecting Data: Age, Sex, Ethnicity/Region, Socio-economic status, Nutrition, Posture (sitting/standing).

• Application: Design of chair height, desk depth, tool handles, control panel reach, vehicle cockpits. Use percentiles (e.g., design for 5th percentile female to 95th percentile male for adjustability).

Human Information Processing & Sensory Inputs

Sensory Channels: Visual (most common), Auditory, Tactual (touch/pressure), Olfactory, Gustatory. Coding & Selection: Information must be encoded (e.g., light color, sound pattern, shape). Selection depends on:

• Importance of the signal.

• Ambient conditions (noise, light).

• Task demands (visual vs. auditory load).

• Human capabilities (e.g., auditory for warnings in high-visual-load tasks).

Model of Human Information Processing:

1. Sensory Input: Stimulus received via senses.

2. Perception & Recognition: Brain interprets the stimulus.

3. Decision/Processing: Comparison with memory, choice of response.

4. Response Selection: Choosing motor program.

5. Motor Output: Physical action (press button, move lever).

6. Feedback: Sensory input from the action to close the loop.

DiagramCANVAS: Draw a simple box-and-arrow flowchart with the 6 stages above, labeled clearly.

Displays

• Visual Displays:

  • Analog: Continuous display (e.g., speedometer, thermometer). Good for relative change.

  • Digital: Discrete numerical display (e.g., digital clock). Good for precise reading.

  • Design Guidelines: Size, brightness, contrast, location (in normal field of view), coding (color, shape), minimize glare.

• Auditory Displays: Use sound (beeps, tones, speech). Effective for alerting/warning. Must be distinct from background noise.

• Tactual Displays: Use touch/pressure/vibration (e.g., Braille, steering wheel vibration for lane departure).

  • Characteristics: Location must be natural (e.g., controls under fingers), stimulus must be unambiguous, suitable intensity and duration.

Man-Machine System

• Definition: An integrated system where a human operator interacts with a machine/device to achieve a goal.

• Types:

  1. Semi-Automatic: Human starts/stops machine, monitors.

  2. Automatic: Human monitors and intervenes only on exception.

  3. Manual: Human provides all power and control.

• Relative Capabilities:

  | Human | Machine | | :--- | :--- | | Excellent pattern recognition, flexibility, judgment. | Excellent speed, strength, precision, repeatability. | | Tires, gets bored, makes errors. | Does not tire, but can malfunction, needs maintenance. | | Learns and adapts. | Follows programmed instructions only. | | Goal: Design system to use human strengths (monitoring, decision-making) and machine strengths (precision, endurance).

Work Environment & Task Design

• Work Environment Design:

  • Lighting: Adequate intensity, uniform distribution, minimize glare/reflection.

  • Noise: Control at source, use hearing protection. Auditory signals must be above noise floor.

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

  • Vibration: Minimize; can cause fatigue and injury.

• Task & Work Organisation Design:

  • Job Rotation: Reduce monotony and localized fatigue.

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

  • Ergonomic Workstations: Adjustable chairs, desks, monitor arms. Neutral postures (wrists straight, elbows at ~90°, back supported).

  • Cognitive Load: Balance mental demands; avoid underload (boredom) and overload (stress).

[!TIP] Exam Focus: Anthropometry and Displays are huge. Be ready to define, list types, and give 2-3 design guidelines for each. For Man-Machine System, always contrast human vs. machine capabilities in a table form.

V. WAGE INCENTIVE PLANS (RELATED TO WORK MEASUREMENT)

Objective: To increase productivity by linking earnings directly to output beyond a standard level.

Specific Plans

1. Gantt's Task and Bonus Plan:

   • Worker gets straight time rate up to standard output.

   • For output above standard, worker gets bonus = 75% of the time saved × hourly rate.

   • Formula: Earnings = (Hours Worked × Hourly Rate) + 0.75 × (Time Saved × Hourly Rate)

   • Focus: Rewards efficiency; bonus increases with more time saved.

2. Merrick's Multiple Piece Rate Plan:

   • Two-tier piece rate:

     • Output below standard → Lower piece rate (e.g., 80% of standard rate).

     • Output at or above standard → Higher piece rate (e.g., 120% of standard rate).

   • Purpose: Penalizes slow workers, rewards efficient ones. More motivating than straight piece rate.

3. Taylor's Differential Piece Rate System:

   • Two-tier piece rate (similar to Merrick's but more severe).

     • Output below standard → Very low piece rate (e.g., 50% of standard rate).

     • Output at or above standard → High piece rate (e.g., 150% of standard rate).

   • Purpose: Strong incentive to achieve standard; "drastic" penalty for not meeting it.

[!TIP] Exam Focus: Be able to distinguish these three plans in a table: Basis of Payment (time vs. piece), Treatment of output below standard, Treatment of output above standard, Primary Objective. Gantt's is unique as it has a time-rate base with a bonus on saved time.