Finite Element Method (ME-504 (C)) - Unit 4 Short Notes

UNIT 4: WORK STUDY AND ERGONOMICS

I. WORK STUDY: FOUNDATIONS

A. Definition and Scope of Work Study

• Definition: Work Study is the systematic examination, analysis, and improvement of existing or proposed methods of work to achieve greater efficiency and productivity at lower cost. It is a tool of method study (finding the best method) and work measurement (finding the standard time for the method).

• Scope: Covers all activities from procurement to dispatch, focusing on:

  • Methods of manufacturing/processing.

  • Materials handling.

  • Plant and equipment layout.

  • Work design and human factors.

  • Working conditions.

B. Objectives of Work Study (High Frequency)

1. Improve processes: Simplify, standardize, and eliminate waste.

2. Determine standard time: For planning, costing, and incentive schemes.

3. Improve layout: Reduce material handling and movement.

4. Improve working conditions: Enhance safety and reduce fatigue.

5. Increase productivity: Achieve more output with the same or less effort.

6. Reduce costs: By eliminating non-value-added activities.

C. Relevance and Benefits in Modern Industry (High Frequency)

• Relevance: Critical in today's competitive global market for cost reduction, quality improvement, and lean manufacturing.

• Benefits:

  • Higher productivity & output.

  • Lower unit costs of production.

  • Better quality through standardized methods.

  • Improved delivery schedules (due to better planning).

  • Enhanced worker morale (fairer workloads, better conditions).

  • Reduced waste of materials, time, and effort.

  • Provides basis for wage incentives and training.

D. Human Factors in Work Study

• Work Study must consider human capabilities and limitations (physical and mental).

• Ergonomics/Human Factors Engineering is an integral part, ensuring work methods and workplaces are designed to fit the worker, not vice-versa.

• Goals: Reduce fatigue, prevent accidents, improve comfort, and increase job satisfaction.

II. METHOD STUDY (MOTION STUDY)

A. Definition and Steps in Method Study (High Frequency)

• Definition: The systematic recording and critical examination of existing and proposed ways of doing work to find and implement the best, most economical method.

• The 6-Step Procedure:

  1. Select the work to be studied.

  2. Record all facts about the existing method (using recording techniques).

  3. Examine the recorded facts critically (ask "why?", "what?", "where?", "when?", "who?").

  4. Develop the new, improved method.

  5. Define the new method and install it (train workers, change layout).

  6. Maintain the standard method through audits and supervision.

B. Recording Techniques (Very High Frequency)

1. Process Charts (Very High Frequency)

• Definition: A graphical representation of a process using standard symbols to show the sequence of activities.

• ASME/ANSI Standard Symbols:

  | Symbol | Operation | Inspection | Move | Delay | Storage | Combined Activity | | :--- | :--- | :--- | :--- | :--- | :--- | :--- | | Shape | ▭ | ⬜ | ⇨ | D | □ | ⌛ | | Meaning | A step that changes object | Check for quality/quantity | Physical movement | Object waits | Object stored | Two or more activities |

a. Operation Process Chart vs. Flow Process Chart (High Frequency)

b. Two-Hand Process Chart vs. Activity Chart (High Frequency)

2. Simultaneous Motion Chart (SIMO Chart)

• Definition: A two-handed chart extended to show all limbs of an operator (hands, feet, eyes, body) on a common time scale.

• Utility: Used for micro-motion study of complex tasks involving multiple body parts. Helps in balancing workload across limbs and improving motion coordination.

3. Memo Motion Study / Memo Production Study (High Frequency)

• Definition: A quick, low-cost motion study technique using a video camera to record an operation at a high speed (e.g., 5-10 fps).

• Procedure: Film operation → Play back at normal speed → Observe and record on a two-handed process chart.

• Utility: For preliminary analysis, studying short-cycle repetitive jobs, and training. Less detailed than micro-motion but faster to set up.

4. Micro Motion Study (High Frequency)

• Definition: The detailed study of a task by filming it at very high speed (e.g., 16-100 fps) and analyzing it using basic motion elements (Therbligs).

• Utility: For high-volume, short-cycle operations. Provides precise time data for each basic motion. Foundation for PMTS like MTM.

5. Motion Study Symbols (Therbligs/ASME Symbols) (High Frequency)

• Therbligs: 18 basic hand motions identified by Gilbreth (e.g., Search, Grasp, Hold, Transport Loaded, Assemble, Use, Disassemble, Rest).

• Purpose: To break down any manual activity into its fundamental, indivisible elements. Enables critical analysis to eliminate, combine, or simplify motions.

• ASME Symbols: The 5 standard process chart symbols (▭, ⬜, ⇨, D, □) used for recording.

6. String Diagram

• Definition: A scaled plan of the workplace showing the actual path traveled by a worker or material, represented by a string or thread.

• Utility: To measure and compare distances traveled under different layout/method proposals. Identifies excessive movement.

7. Travel Chart

• Definition: A matrix (table) showing the frequency of movement between departments or workstations.

• Utility: For analyzing material flow in a plant layout. Helps in departmental placement to minimize total material travel distance.

C. Principles of Motion Economy (High Frequency)

Fundamental Rules to Design Efficient Manual Work:

1. Use the fewest number of motions possible for the task.

2. Balance motions of both hands (they should start/end together).

3. Use the lowest possible classification of motion (e.g., finger motion > wrist > arm > body).

4. Design for curved, continuous, rhythmic motions (avoid sharp, jerky changes).

5. Use momentum to assist the worker (e.g., let gravity help).

6. Minimize eye travel and focus changes.

7. Provide proper workplace arrangement (tools/materials in fixed, optimum locations - "A place for everything and everything in its place").

8. Combine motions where possible (e.g., two-handed simultaneous work).

D. Standardisation of Motion (High Frequency)

• Definition: Establishing and maintaining the one best method for performing each task, and ensuring all workers use it.

• Importance BEFORE Time Study:

  • Ensures the time measured is for the most efficient method.

  • Eliminates variability due to different personal methods.

  • Provides a fair basis for setting standard times and incentives.

  • Facilitates training of new workers.

E. Integration of Operation and Operator (High Frequency)

• Goal: To achieve a balanced production line where the machine cycle time and the operator cycle time are synchronized.

• How:

  • Use Activity Charts to identify machine idle time and operator idle time.

  • Redistribute work among operators or between operator and machine.

  • Adjust machine speeds or add/remove work elements to achieve balance.

  • Result: Maximum utilization of both human and machine resources, minimizing bottlenecks.

III. WORK MEASUREMENT

A. Objectives of Work Measurement and Time Study (Very High Frequency)

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

2. Compare worker efficiency (actual time vs. standard time).

3. Balance workloads among workers/machines.

4. Provide basis for wage incentive schemes.

5. Estimate costs and set prices.

6. Identify and eliminate idle time.

B. Time Study Procedure (High Frequency)

1. Select & Define: Choose the job and break it into elements.

2. Record: Use a time study form to record time for each element over multiple cycles.

3. Rate Performance: Assess the worker's pace relative to standard performance (see Section C).

4. Calculate Basic Time (Normal Time): Basic Time = Observed Time × Performance Rating

5. Determine Allowances: Add appropriate allowance fractions for personal, fatigue, delay, etc. (see Section D).

6. Compute Standard Time: Standard Time = Normal Time × (1 + Total Allowance Fraction)

7. Review & Document: Verify data, state assumptions, and document the standard.

C. Performance Rating (Rating Methods and Factors) (High Frequency)

• Definition: The process of comparing the observed pace of a worker to the concept of "standard performance" (a worker with average ability working at a sustainable pace) and expressing it as a numerical factor.

• Rating Factor: >1.0 (faster than standard), =1.0 (standard), <1.0 (slower).

• Methods:

  • Speed Rating: Assesses the pace of movement.

  • Westinghouse System: Considers skill, effort, conditions, and consistency (using a factor table).

  • Objective Rating: Uses predetermined data (like MTM) to calculate rating.

• Factors Affecting Rating: Skill, experience, effort, consistency, working conditions, personal attributes.

D. Allowances (Types: Personal, Fatigue, Delay, etc.) (High Frequency)

• Definition: Extra time added to the Normal Time to get Standard Time to account for legitimate, unavoidable losses.

• Types & Typical % (Varies by Industry/Job):

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

  • Fatigue Allowance (4-10%+): For physiological/psychological recovery. Increases with poor environment (heat, noise, poor lighting) and stress.

  • Delay Allowance (Variable): For unavoidable delays (machine breakdown, material shortage). Can be policy-controlled.

  • Process Allowance: For inherent job requirements (e.g., tool setting, cleaning).

  • Special Allowance: For training, new methods etc.

E. Standard Time Calculation (High Frequency)

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

Where:

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

\boxed{Observed Time = \frac{\text{Total Time Recorded for an Element}}{\text{Number of Cycles}}}

F. Work Sampling (Calculation of Standard Time from Sampling Data) (High Frequency)

• Definition: A statistical technique to estimate the proportion of time spent on various activities by taking a large number of random observations.

• Procedure:

  1. Take random observations (e.g., every 10 mins) over a period.

  2. Record the activity (Working, Idle, Delay, etc.).

  3. Calculate % Working Time = (No. of "Working" observations / Total observations) × 100.

  4. Calculate Standard Time:

     • Step 1: Find Normal Time per Unit.

       Normal Time per Unit = (Total Observation Time × % Working Time) / Number of Units Produced

     • Step 2: Add Allowances.

       Standard Time per Unit = Normal Time per Unit × (1 + Allowance Fraction)

• Key Formula for Sample Size (n):

$$n = \frac{Z^2 \cdot p(1-p)}{e^2}$$

(Where Z = confidence level, p = estimated proportion, e = desired error).

G. Standard Data (Definition, Uses, Advantages) (High Frequency)

• Definition: Predetermined time values for elements, operations, or entire jobs based on historical data, PMTS, or extensive time studies.

• Uses:

  • Quickly set standards for new, similar jobs.

  • Cost estimation and bidding.

  • Scheduling and capacity planning.

• Advantages:

  • Very fast standard setting (no fresh time study needed).

  • Consistency across similar jobs.

  • Reduces cost of time study.

  • Fairer as it's based on broad data, not one worker.

H. Predetermined Motion Time Systems (PMTS)

1. Method Time Measurement (MTM) (High Frequency)

• Definition: A PMTS that assigns time values (in TMUs - Time Measurement Units, 1 TMU = 0.00001 min) to basic hand and body motions (Reach, Move, Turn, Apply, Release, etc.) based on distance and nature of motion.

• Procedure: Analyze task → Break into TMU motions → Sum TMUs → Add body motion and tool use allowances → Convert to minutes.

• Utility: Setting standards without a time study; for method design (compare alternative methods by summing TMUs); training.

2. Advantages of PMTS over Time Study (High Frequency)

I. Time Measuring Devices

• Stopwatch: Traditional, for direct timing.

• Electronic Timers: Digital, with memory and statistical functions.

• Video Recording: For later analysis (Memo/Micro Motion).

• Computer-Aided Systems: Automated data collection from machines.

J. Work Factor

• Definition: A percentage allowance applied to the basic time to account for job difficulty factors not inherent in the motion (e.g., poor lighting, awkward posture, heavy material).

• Classification:

  • Physical Factors: Weight, height, temperature.

  • Mental Factors: Complexity, visual strain.

  • Environmental Factors: Noise, dust, humidity.

• Use: Often used in PMTS as a final adjustment factor.

K. Wage Incentive Plans (Output-Based) (High Frequency)

1. Merrick's Multiple Piece Rate Plan

• Mechanism: Two-tier piece rate.

  • Normal output (up to a standard %): Lower piece rate.

  • Above normal output: Higher piece rate (e.g., 120% of standard).

• Purpose: To reward higher output more generously, encouraging workers to exceed the standard.

2. Gantt's Task and Bonus Plan

• Mechanism: Worker receives straight hourly rate up to standard time. If task is completed in less than standard time, they receive a bonus (typically 25-50% of the hourly rate for the time saved).

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

• Key Feature: Guarantees minimum hourly wage, reducing risk for worker. Bonus is on time saved, not output.

IV. ERGONOMICS (HUMAN FACTORS ENGINEERING)

A. Definition and Objectives of Ergonomics (High Frequency)

• 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:

  1. Enhance human performance and productivity.

  2. Improve safety and reduce errors/accidents.

  3. Increase comfort and reduce fatigue/discomfort.

  4. Promote health and well-being.

  5. Improve quality of life.

B. Anthropometry (Very High Frequency)

1. Definition and Importance

• Definition: The science of measuring the dimensions (size, shape, strength, range) of the human body.

• Importance: Provides the quantitative data needed to design workplaces, tools, equipment, and products that fit the user population. Prevents mismatch (e.g., too high desk, too small control).

2. Types of Body Measurements

• Static Anthropometry: Body dimensions at rest (e.g., stature, sitting height, arm reach, hand grip span). Used for space allocation.

• Dynamic Anthropometry (Functional Anthropometry): Body dimensions during motion (e.g., reach envelope while seated, lifting posture). Used for workspace design involving movement.

3. Factors Affecting Anthropometric Data

• Genetics & Ethnicity: Different population groups have different body proportions.

• Nutrition & Health: Affects growth and body composition.

• Age: Body dimensions change (e.g., height decreases, weight may increase).

• Gender: Significant differences in body size and proportions.

• Posture: Measurement posture (standing, sitting) must be standardized.

• Clothing/Equipment: Must account for what is worn (e.g., safety shoes, space suit).

4. Application in Design

• Use percentile data (e.g., design for 5th percentile female to 95th percentile male to accommodate most users).

• Adjustability: Design for range of adjustability (e.g., chair height, steering wheel).

• Design for extremes: Critical dimensions (e.g., clearance height) based on largest user; reach distances based on smallest user.

C. Human Information Processing

1. Sensory Inputs (Coding and Selection)

• Sensory Channels: Visual (most used), Auditory, Tactual (touch, vibration), Olfactory/Gustatory (rare in work).

• Coding: Presenting information in a meaningful form (e.g., color for warning, shape for identification, sound pitch for urgency).

• Selection: Human attention is limited. Design must highlight critical information and minimize irrelevant stimuli (signal-to-noise ratio).

2. Human Information Processing Model (Stimulus → Processing → Response)

• Stages:

  1. Sensation: Sensory organs detect stimulus.

  2. Perception: Brain interprets the stimulus (recognizes pattern, meaning).

  3. Decision: Choose a response (based on memory, rules).

  4. Response: Motor action (press button, move lever).

• Implications: Design displays for easy perception, controls for easy operation, and tasks to match cognitive load.

3. Relative Capabilities of Humans and Machines (High Frequency)

D. Display Design

1. Visual Displays (Design Guidelines, Effectiveness Factors) (High Frequency)

• Guidelines:

  • Legibility: Adequate size, contrast, font.

  • Discriminability: Different displays must be easily distinguishable (shape, color, location).

  • Meaningfulness: Use conventional codes (red=stop/danger, green=go/safe).

  • Simplicity: Minimize information clutter.

  • Location: Place in primary field of view.

  • Feedback: Provide immediate, clear feedback on system status.

• Effectiveness Factors: Accuracy, Speed, Operator Acceptance, Cost.

2. Tactual Displays (Characteristics and Applications) (High Frequency)

• Definition: Displays that use the sense of touch (skin, proprioception).

• Characteristics:

  • High spatial resolution on skin (fingers).

  • Temporal resolution is lower than vision.

  • Directional sensitivity (e.g., vibration direction).

  • Can be used when vision/audition are overloaded or unavailable.

• Applications:

  • Vibration alerts in mobile phones/controllers.

  • Braille displays for the visually impaired.

  • Tactile maps for navigation.

  • Shape-coded controls (knobs, buttons with different textures) for blind operation.

E. Work and Task Design for Ergonomics

1. Work Environment Design (Lighting, Noise, Temperature, etc.) (High Frequency)

• Lighting: Adequate quantity (illuminance in lux), quality (glare-free, uniform), and color rendering.

• Noise: Control at source, use enclosures/barriers. Maintain speech intelligibility (Signal-to-Noise Ratio > 15 dB).

• Temperature & Humidity: Maintain within thermal comfort zone (ASHRAE standards). Prevent heat stress.

• Vibration: Isolate vibrating equipment; provide anti-vibration gloves.

• Air Quality: Ventilation, control of fumes/dust.

2. Task and Work Organisation Design (Job Rotation, Enrichment, etc.) (High Frequency)

• Job Rotation: Periodically switching workers between tasks.

  • Purpose: Reduce musculoskeletal strain from repetitive tasks, increase skill variety, reduce monotony.

• Job Enrichment: Adding more responsibility, variety, and autonomy to a job.

  • Purpose: Improve motivation, satisfaction, and mental well-being.

• Work-Rest Schedules: Designing break frequency and duration based on task demands (physical/mental) to manage fatigue.

• Team-Based Design: Organizing work around self-managing teams for flexibility and engagement.

F. Man-Machine Systems (Types: Manual, Automated, Hybrid; Analysis Considerations) (High Frequency)

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

• Types:

  1. Manual System: Human provides all power and control (e.g., hand tools).

  2. Automated System: Machine operates autonomously; human monitors and intervenes only for exceptions.

  3. Hybrid (Semi-Automated) System: Shared control; human and machine perform different sub-tasks.

• Analysis Considerations (for Design):

  • Allocation of Function: Decide which tasks are done by human vs. machine (based on relative capabilities - see Section C.3).

  • Information Flow: Design displays for machine status and controls for human input.

  • Feedback: Ensure clear, timely feedback to the operator.

  • Error Management: Design to prevent errors (forcing functions, interlocks) and detect/recover from them.

  • Training & Procedures: Provide adequate training and clear procedures for normal and emergency operation.