Finite Element Method (ME-504 (C)) - Unit 5 Short Notes

UNIT 5: WORK STUDY, METHOD STUDY, WORK MEASUREMENT & ERGONOMICS

A. FOUNDATIONS OF WORK STUDY & METHOD STUDY

Work Study: Definition, Scope & Relevance

• Definition: A systematic examination of activities to improve efficiency and effectiveness. It comprises Method Study (improving the method) and Work Measurement (establishing time standards).

• Objectives:

  • Improve processes and methods.

  • Establish standard times for tasks.

  • Reduce waste and unnecessary costs.

  • Enhance productivity and working conditions.

• Relevance in Modern Industry:

  • Foundation for lean manufacturing and process optimization.

  • Essential for capacity planning, costing, and incentive schemes.

  • Drives continuous improvement (Kaizen).

[!TIP] Exam Focus: Distinguish clearly between Method Study (the "what and how" of a task) and Work Measurement (the "how long").

Method Study: Definition & Procedure

• Definition: The systematic recording, analysis, and critical examination of existing and proposed ways of doing work to develop and apply more effective methods.

• Step-by-Step Procedure (Select, Record, Examine, Develop, Install, Maintain):

  1. Select: Choose the process/task to study (high volume, problem area).

  2. Record: Document the current method using appropriate charts/diagrams.

  3. Examine: Question every detail of the recorded method (5W1H: What, Why, Where, When, Who, How).

  4. Develop: Devise a new, improved method.

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

  6. Maintain: Ensure the new method is followed and periodically reviewed.

[!IMPORTANT] Standardisation of motion before time study is critical. A standard method must be established first; otherwise, time study data is meaningless and inconsistent.

B. RECORDING TECHNIQUES FOR METHOD STUDY

Process Charts: Symbols & Types

• Standard Symbols (ASME/ISO):

  | Symbol | Name | Meaning | | :--- | :--- | :--- | | ○ | Operation | A change in shape, size, or other physical characteristics. | | □ | Inspection | Checking for quality/quantity. | | → | Move | Transporting an object from one place to another. | | D | Delay | Temporary hold-up (e.g., waiting). | | ▽ | Storage | Controlled storage (e.g., warehouse). | | □+→ | Combined | Operation + Move (often used). |

• Operation Process Chart vs. Flow Process Chart:

  | Feature | Operation Process Chart | Flow Process Chart | | :--- | :--- | :--- | | Focus | Material (product/component) | Worker/Operator | | Records | Steps in manufacturing a single item. | Activities of one or more workers on a job. | | Utility | Planning material flow, process planning. | Studying operator motion, identifying delays. | | Primary Symbol | Operation (○) | All symbols used frequently. |

Two-Handed Process Chart & Activity Chart

• Two-Handed Process Chart:

  • Records the simultaneous activities of both hands of an operator.

  • Uses therblig symbols (basic motions like Reach, Grasp, Move, Assemble, etc.).

  • Utility: Micromotion study, identifying ineffective motions, balancing work between hands.

• Activity Chart:

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

  • Uses a time scale on the horizontal axis.

  • Utility: Identifying machine idle time, operator idle time, and opportunities for multi-machine tending.

  • Key Difference: Two-Handed focuses on hand motions (micro), Activity Chart focuses on operator-machine interaction over time (macro).

SIMO Chart & Travel Chart

• SIMO (Simultaneous Motion) Chart:

  • An extension of the two-handed chart for multiple limbs (hands, feet, eyes, body).

  • Records therbligs for each limb vertically against a common time scale.

  • Purpose: To achieve simultaneous, balanced motions and eliminate idle time for any body part.

• Travel Chart (From-To Chart):

  • A matrix showing the frequency of material or personnel movement between various departments/places.

  • Rows = origin, Columns = destination.

  • Purpose: Analyze material handling costs, optimize facility layout (minimize travel distance).

Other Recording Techniques

• String Diagram:

  • A scaled plan of the workplace with a string/thread traced along the actual path of movement.

  • Utility: Quantify and compare travel distances for different layouts or methods.

• Memo Motion Study:

  • Using a normal-speed motion picture camera (e.g., 16-64 fps) to study long-duration activities (e.g., a day's work).

  • Utility: Study overall work patterns, delays, and methods over an extended period economically.

• Micro Motion Study:

  • Using a high-speed camera (e.g., 1000+ fps) to study very short-duration hand/body motions.

  • Utility: Fundamental for developing Predetermined Motion Time Systems (PMTS) like MTM.

C. PRINCIPLES OF MOTION ECONOMY & MOTION STUDY

Principles of Motion Economy

• Classification & Application:

  | Category | Key Principles | Application Example | | :--- | :--- | :--- | | Use of Body | 1. Use lowest possible exertion.<br>2. Use symmetrical motions.<br>3. Use continuous curved motions.<br>4. Use momentum. | Avoid heavy lifting; use both hands; design curved handle grips. | | Arrangement of Workplace | 1. Fixed location for tools/materials.<br>2. Arrange in sequence of use.<br>3. Locate for minimum movement.<br>4. Provide optimal height. | Shadow boards; gravity feed bins; adjustable workbench. | | Design of Tools & Equipment | 1. Combine tools.<br>2. Use jigs/fixtures.<br>3. Distribute loads according to body strength. | Multifunction tool; pneumatic screwdriver for downward force. |

Motion Study: Fundamentals

• Definition: Analysis of the human element in a job to find the most efficient pattern of movements.

• Therbligs:

  • Definition: Basic, indivisible motions (18 original by Gilbreth). E.g., Search, Reach, Grasp, Move, Assemble, Use, Disassemble, Release, Position, Inspect, Pre-position, Rest, Delay, Plan, Unavoidable Delay, etc.

  • Use: To record, analyze, and improve micro-motions by eliminating, combining, or simplifying them.

• Memo Production Study:

  • A form of memo motion study applied to a group of workers or an entire production line.

  • Use: To study overall production flow, bottlenecks, and group coordination over a full shift or day.

D. WORK MEASUREMENT & TIME STUDY

Objectives & Techniques of Work Measurement

• Objectives:

  • Establish standard times for tasks (planning, costing, scheduling).

  • Compare worker performance.

  • Set realistic production targets.

  • Balance workloads.

• Techniques:

  1. Time Study (Stopwatch study).

  2. Work Sampling (Statistical sampling of activities).

  3. Standard Data (Using pre-determined times for similar elements).

  4. Predetermined Motion Time Systems (PMTS) (e.g., MTM, MODAPTS).

Time Study: Procedure & Equipment

• Procedure:

  1. Select and define the job.

  2. Ensure standard method is used.

  3. Record observed times for multiple cycles.

  4. Rate the operator's performance relative to standard.

  5. Compute Normal Time.

  6. Add Allowances to get Standard Time.

  7. Document and review.

• Equipment: Stopwatch (mechanical/digital), electronic timer, video recorder, process chart.

Rating & Allowances

• Rating:

  • Definition: The process of observing and assessing an operator's relative speed and effectiveness compared to a standard performer.

  • Purpose: To convert observed time to normal time for a standard performer.

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

• Allowances:

  • Definition: Extra time added to Normal Time to account for non-productive but legitimate needs of the worker.

  • Types:

    • Personal Allowance: Rest, hydration, personal needs (~5-10%).

    • Fatigue Allowance: Physiological/psychological tiredness (varies with work intensity).

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

    • Special Allowance: Training, contingencies, policy allowances.

• Normal Time vs. Standard Time:

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

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

Calculations & Standard Data

• Work Sampling Calculation (Standard Time):

  • Step 1: Calculate Performance Rating (PR) factor from study: $$\displaystyle PR = \frac{\text{Rating \%}}{100} $$

  • Step 2: Find Fraction of Time Working (P): $$\displaystyle P = \frac{\text{Number of "Working" observations}}{\text{Total observations}} $$

  • Step 3: Compute Normal Time per unit: $$\displaystyle NT = \frac{\text{Total Observation Time} \times P}{N \times PR} $$ where N = number of units produced.

  • Step 4: Add Allowance (A): $$\displaystyle ST = NT \times (1 + A) $$

  \boxed{\text{Standard Time (ST)} = \frac{(\text{Total Obs. Time} \times P)}{(N \times PR)} \times (1 + A)}

• Standard Data:

  • Definition: Pre-established times for standardized elements (e.g., "tighten nut," "drill hole 10mm") derived from extensive time studies.

  • Advantages: Speeds up new time studies, ensures consistency, reduces cost of measurement.

• PMTS (e.g., MTM):

  • Advantages: Objective, independent of operator pace, useful for new designs, facilitates method comparison.

  • MTM (Method Time Measurement): Breaks down manual motions into basic MTM elements (Reach, Move, Turn, Apply, Release, etc.) with pre-determined times (in TMU - Time Measurement Units, 1 TMU = 0.00001 min).

• Work Factor:

  • Definition: A multiplicative factor applied to a basic time to account for difficult working conditions (e.g., poor lighting, awkward posture, cramped space).

  • Classification: Based on the nature of the difficulty (visual, auditory, physical, mental).

E. WAGE INCENTIVE PLANS

Objectives & Types

• Objectives: Increase productivity, reward efficiency, improve morale, reduce labor cost per unit.

• Classification:

  • Output-Based: Earnings vary directly with output (piece rate).

  • Input-Based: Earnings vary with time saved (premium bonus plans).

Specific Plans

F. 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 design to optimize human well-being and overall system performance.

• Objectives:

  • Enhance human efficiency, safety, and comfort.

  • Reduce fatigue, error, and injury.

  • Adapt the system (job, product, environment) to the human.

Anthropometry

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

• Importance: Provides the fundamental data for designing workplaces, tools, equipment, and vehicles to fit the user population.

• Types of Measurements:

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

  • Dynamic: Body dimensions in motion or in a specific posture (e.g., reach envelope, grip span).

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

• Application: Design of chair height, tool handle diameter, control panel reach, vehicle cockpit, doorway height.

Human Information Processing & Sensory Inputs

• Model of Human Information Processing:

  • Stimulus → Sensory Register → Perception/Processing → Decision → Response → Motor Output.

  • Includes feedback loops and is affected by attention, memory, and experience.

  • DiagramSEARCH: "human information processing model diagram"

• How Humans Receive Sensory Information: Through sensory receptors (eyes, ears, skin, nose, tongue) which transduce physical stimuli into neural signals.

• Coding and Selection of Sensory Inputs:

  • Coding: Transforming sensory input into a meaningful form (e.g., shape, color, sound pitch).

  • Selection (Attention): The brain cannot process all stimuli. Salience (intensity, novelty, relevance) determines what is selected for conscious processing.

Displays & Controls

• Visual Displays:

  • Types: Analog (gauge, dial), Digital (numeric), Alphanumeric (text), Graphic (charts, maps).

  • Design Guidelines for Effectiveness:

    • Size & Brightness: Adequate for viewing distance/lighting.

    • Coding: Use color, shape, position for quick identification (e.g., red=danger).

    • Location: In primary field of view, grouped by function.

    • Simplification: Present only essential information.

• Tactual Displays:

  • Characteristics: Use touch/pressure. Can be active (operator feels) or passive (vibration alert).

  • Applications: Braille displays, vibration alerts in phones/tools, shape-coded controls for blind operation.

Man-Machine Systems

• Definition: A system where a human operator is in direct physical or informational contact with a machine to achieve a goal (e.g., driving, CNC machining, process control).

• Types:

  • Skeletal: Human provides only power (e.g., pedal-powered lathe).

  • Manual: Human provides power, control, and monitoring (e.g., hand tools).

  • Automatic: Machine does the work; human monitors and intervenes (e.g., automated assembly line).

  • Informational: Human makes decisions based on information from machine (e.g., air traffic control).

• Relative Capabilities:

  | Human Strengths | Machine Strengths | | :--- | :--- | | Pattern recognition, subjective judgment, flexibility, adaptability, handling unexpected situations. | Speed, precision, strength, consistency, repetitive operations, working in hostile environments. | | Design Implication: Assign tasks based on these strengths. Human should monitor, decide, and handle exceptions; machine should execute, measure, and repeat.

Work & Task Design for Ergonomics

• Work Environment Design Factors:

  • Lighting: Adequate illuminance, glare control, contrast.

  • Noise: Reduce at source, use hearing protection, auditory alarm design.

  • Temperature & Humidity: Maintain thermal comfort zone.

  • Vibration: Isolate vibrating tools/machines.

• Task and Work Organisation Design Principles:

  • Work-Rest Schedules: Balance to prevent fatigue.

  • Job Rotation: Vary tasks to reduce monotony and static muscle load.

  • Task Allocation: Match task demands to worker capabilities.

  • Participatory Design: Involve workers in designing their tasks.

• Human Factors in Work Study: Ergonomics provides the human-centric criteria for evaluating and improving methods identified by work study. It ensures that "efficient" methods are also safe, comfortable, and sustainable for the human operator.

[!TIP] Exam Integration: Questions often link Ergonomics to Method Study/Motion Study. E.g., "How do principles of motion economy relate to ergonomics?" (Answer: Both aim to reduce fatigue and improve efficiency through better motion/work design).