Finite Element Method (ME-504 (C)) - Unit 2 Short Notes

UNIT 2: WORK STUDY, METHOD STUDY & ERGONOMICS

1.0 FOUNDATIONS OF WORK STUDY

1.1 Definition, Objectives, and Scope

• Definition: Work Study is a systematic examination of methods of carrying out activities to improve productivity and reduce waste. It is the generic term for Method Study (finding the best method) and Work Measurement (establishing standard time for the method).

• Primary Objectives:

  1. Improve processes and methods.

  2. Set standards for performance (time, output).

  3. Increase productivity with less effort.

  4. Reduce costs and improve quality.

  5. Provide data for planning, scheduling, and wage incentives.

• Scope: Applicable to all activities—manufacturing, offices, hospitals, services—anywhere human effort is applied.

1.2 Relevance in Modern Industry

• Competitiveness: Essential for lean manufacturing, cost reduction.

• Automation: Provides baseline data for designing automated systems.

• Quality: Links method standardization to consistent quality.

• Safety & Ergonomics: Integrates human factors to reduce fatigue and injury.

• Flexibility: Enables quick assessment of new processes.

1.3 Relationship: Method Study vs. Work Measurement

The Core Principle: Method Study comes FIRST. You cannot measure a poor method.

• Method Study: Answers "WHAT is the best way to do the job?" (Focus: Method).

• Work Measurement: Answers "HOW LONG should it take?" (Focus: Time for the standard method).

• Integration: The output of Method Study (the standard method) becomes the input for Work Measurement.

2.0 METHOD STUDY (METHOD ENGINEERING)

2.1 Definition & Steps

• Definition: Systematic recording and critical examination of existing and proposed ways of doing work to develop and apply easier, more effective, and economical methods.

• The 6-Step Procedure:

  1. SELECT the job to be studied.

  2. RECORD all facts about the current method (using recording techniques).

  3. EXAMINE the recorded facts critically (question every detail: Purpose? Place? Sequence? Person? Means?).

  4. DEVELOP the new, improved method.

  5. INSTALL the new method (train personnel, implement changes).

  6. MAINTAIN the standard method (audit, prevent regression).

2.2 Recording Techniques: Classification & Purpose

2.2.1 Process Charts: Symbols & Types

• Basic Symbols (ASME/ISO):

  • Operation (O): Main work done on product (change shape, property).

  • Inspection (I): Check for quality/quantity.

  • Move (→): Transport of material/product.

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

  • Storage (□): Controlled storage (inventory).

  • Combined Activity (⊞): Two or more simultaneous activities.

• Types & Distinction:

  • Operation Process Chart (OPC): Shows sequence of operations & inspections for a single product/component. Focus: Product journey.

  • Flow Process Chart (FPC): Shows sequence of activities for a group of products or a whole process. Can include material, operator, or equipment flow. Focus: Overall process flow.

  • Two-Hand Process Chart (THPC): Records simultaneous motions of right & left hands against a time scale. Used for detailed analysis of a single operator's task.

  • Activity Chart: A type of Multiple Activity Chart showing one operator's activities against time, often compared with machine/cycle time.

DiagramCANVAS: Draw a simple process chart for making tea, using O, I, D, → symbols. Show an FPC for a batch of tea vs an OPC for a single cup.

2.2.2 Multiple Activity Charts & SIMO Chart

• Multiple Activity Chart: Records activities of multiple resources (operators, machines) on a common time scale to identify idle time, bottlenecks, and coordination needs.

• SIMO Chart (Simultaneous Motion Chart):

  • Construction: Combines two or more Two-Hand Process Charts on a single time base. Each operator's hand motions are plotted vertically against common horizontal time.

  • Operation: Allows direct visual comparison of motions between operators or between operator and machine. Used to balance work and eliminate idle time in group work.

2.2.3 Other Techniques

• Travel Chart (From-To Chart): A matrix where rows = origins, columns = destinations. Entries = number of trips or loads. Used to analyze material handling frequency and evaluate layout alternatives.

• String Diagram: A scaled floor plan with pins at key locations. A string traces the actual path of a worker/material. The string length gives total distance traveled. Used to measure & compare travel distances for different layouts.

• Memo Motion Study: Use of motion picture camera at very low frame rate (1-5 frames per minute) to record long-duration activities (e.g., a day's work) economically. Useful for initial survey and recording idle periods.

• Micro Motion Study: Use of high-speed camera (16-100+ fps) to record short-duration, rapid motions. Forms the basis for therblig analysis and developing Predetermined Motion Time Systems (PMTS).

2.3 Principles of Motion Economy

Basic Principles (9): Focus on use of the human body.

1. Both hands should begin and end motions simultaneously.

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

3. Motions should be made in opposite, symmetrical directions.

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

5. Use momentum to assist, but not to be overcome.

6. Use continuous, curved motions rather than straight-line, jerky motions.

7. Ballistic (free-swing) movements are faster, more accurate than restricted.

8. Minimize the number of units of motion (e.g., one tool for multiple functions).

9. Hands should not meet in the same line of motion; one should enter the work area as the other leaves.

Detailed Principles (4): Focus on workplace & tool design.

1. Fixed, defined, and conveniently located workplaces and tool depositories.

2. Gravity bins, drop delivery for tools/materials.

3. Optimal heights for work and tool locations (elbow height for precision, shoulder for force).

4. Good illumination, adequate visual acuity, and proper seating.

2.4 Application in Workplace Design

• Arrange tools/materials in fixed, logical sequence.

• Use gravity feed for parts.

• Position work at optimal height (elbow for fine work, knuckle for heavy).

• Provide proper seating with back support, footrests.

• Ensure adequate lighting (no glare, shadows).

• Design tools with ergonomic handles to reduce grip force.

• Combine tools to reduce motion units.

• Minimize walking by bringing work to the operator.

2.5 Standardisation of Motions

• Definition: Establishing the one best method for a task, documented in a standard method sheet with standardized tools, fixtures, and workplace layout.

• Importance before Time Study:

  1. Eliminates method variation between operators.

  2. Ensures the time measured is for the standard, most efficient method.

  3. Provides a fair basis for performance rating and incentive plans.

  4. Facilitates training and maintenance of standards.

2.6 "Operation and Operator" Integration

• Concept: The design of the work system must integrate the capabilities and limitations of the human operator with the requirements of the operation/process.

• Methods:

  • Task Allocation: Assign tasks based on human vs. machine strengths (humans: judgment, flexibility; machines: speed, power, repetition).

  • Workplace Design: Apply motion economy & anthropometry.

  • Display & Control Design: Match sensory and response capabilities.

  • Scheduling: Balance workload, provide rest breaks.

  • Training: Ensure operator proficiency with the standard method.

3.0 WORK MEASUREMENT (TIME STUDY)

3.1 Definition & Objectives

• Definition: Application of techniques to establish the time for a qualified worker to complete a specified task at a defined level of performance.

• Objectives:

  1. Establish standard times for planning, scheduling, costing.

  2. Set baseline for performance comparison.

  3. Provide basis for wage incentive plans.

  4. Balance workloads and determine manpower needs.

  5. Set realistic delivery promises.

3.2 Time Study Procedure (Steps)

1. Select & Define Job: Clearly state the task and boundaries.

2. Obtain Operator Consent & Ensure Standard Method: Operator must be trained on the standard method.

3. Record: Use stopwatch/time study form to record element times over multiple cycles.

4. Rate Performance: Assess operator's speed/effort relative to standard (see 3.4).

5. Compute: Calculate Observed Time, Normal Time, and Standard Time (see 3.6).

6. Allowances: Add appropriate allowances (see 3.5).

7. Define & Document: State standard time, method, conditions, and allowances.

3.3 Time Measuring Devices

• Stopwatch: Mechanical, digital. Basic tool.

• Electronic Timer: Integrated with data collection systems.

• Predetermined Motion Time Systems (PMTS): Use tabulated times for basic motions (MTM, MODAPTS).

• Work Sampling: Statistical technique for estimating proportions of time (see 3.6).

3.4 Performance Rating

• Definition: The process of evaluating the worker's speed and effort relative to a standard performer (100% rating = standard pace).

• Concept: Adjusts the observed time to reflect what the time would have been if the worker was performing at the standard level.

• Rating Factor: Expressed as a decimal (e.g., 1.10 for 110%).

  • Observed Time × Rating Factor = Normal Time.

• Common Rating Methods:

  • Speed Rating: Compare overall speed of worker to standard.

  • Westinghouse System: Considers Skill, Effort, Conditions, Consistency (rated as letters A=120%, B=100%, etc.). Factor applied to observed time.

  • Objective Rating: Uses pace (speed) and adjustment (job difficulty) factors.

3.5 Allowances

• Definition: Extra time added to Normal Time to arrive at Standard Time to account for legitimate, unavoidable delays and personal needs.

• Purpose: To make the standard time achievable and fair.

• Types & Influencing Factors:

  | Allowance Type | Purpose | Typical % Range | Influencing Factors | | :--- | :--- | :--- | :--- | | Personal | Toilet, phone, smoking. | 2-5% | Company policy, local customs. | | Fatigue | Physical/mental recovery. | 0-10% | Work intensity, environment (heat, noise), posture. | | Delay | Unavoidable external delays (machine breakdown, material shortage). | Job-specific | Reliability of equipment, material supply system. | | Process/Policy | Administrative tasks, meetings. | Varies | Organizational rules. |

3.6 Standard Time Calculation & Work Sampling

Core Formulas:

1. Normal Time (NT): $$\displaystyle NT = \sum (\text{Observed Time}_i \times \text{Rating Factor}_i) $$

2. Standard Time (ST): $$\displaystyle ST = NT \times (1 + \text{Total Allowance Fraction}) $$

   or $$\displaystyle ST = NT + (\text{Allowance Time}) $$

   \boxed{ST = NT \times (1 + A)} \quad \text{where A = total allowance (decimal)}

Work Sampling Application:

• Used to estimate proportion of time spent in various activities (working, idle, delays).

• Formula for % Delay: $$\displaystyle \% \text{Delay} = \left( \frac{\text{Number of "Idle" Observations}}{\text{Total Observations}} \right) \times 100 $$

• This % Delay can be used to quantify the "Delay Allowance" or to improve methods.

Numerical Example (From JUN 2025 Paper):

• Work week = 48 hrs.

• Avoidable delays = 25% → Productive time fraction = 0.75.

• Operator Rated at 110% → Rating Factor = 1.10.

• Production = 80 units.

• Step 1: Find Observed Time for one unit.

Total time available for production = 48 hrs × 0.75 = 36 hrs.

Observed Time per unit (OT) = 36 hrs / 80 units = **0.45 hrs/unit**.

• Step 2: Find Normal Time.

NT = OT × Rating Factor = 0.45 × 1.10 = **0.495 hrs/unit**.

• Step 3: Apply Allowances. (Assume standard 15% total allowance unless given).

ST = NT × (1 + 0.15) = 0.495 × 1.15 = **0.56925 hrs/unit**.

\boxed{\text{Standard Time per unit} = 0.569 \text{ hours (or 34.15 minutes)}}

3.7 Standard Data

• Definition: Pre-determined times for specific elements or groups of elements (e.g., "pick up part from bin," "tighten nut") based on historical data, PMTS, or detailed studies.

• Advantages:

  1. Speeds up future time studies (no need to time every element).

  2. Improves accuracy (based on larger data set).

  3. Ensures consistency across studies/jobs.

  4. Reduces cost of time study function.

  5. Useful for estimating and costing new jobs.

3.8 Predetermined Motion Time Systems (PMTS)

• Definition: Systems that assign standard times to basic human motions (therbligs) based on extensive laboratory studies. Total time for a task is the sum of times for its constituent motions.

• Example: MTM (Methods-Time Measurement). Assigns TMU (Time Measurement Unit) to motions like "Reach," "Grasp," "Move," "Position," "Release." 1 TMU = 0.00001 min = 0.000036 sec.

• Advantages over Conventional Time Study:

  1. No need for performance rating (times are for a "100% performer").

  2. No need for allowances (built into system or added simply).

  3. Objective, consistent, and defendable.

  4. Excellent for method comparison and designing new work.

  5. Not influenced by operator's pace or observer's bias.

3.9 Work Factor

• Definition: A multiplicative factor applied to a basic standard time to account for difficult working conditions that affect performance.

• Classification:

  1. Physical Work Factor: Based on weight lifted, force required, posture.

  2. Mental Work Factor: Based on complexity, visual/auditory stress, decision-making.

  3. Environmental Work Factor: Based on temperature, humidity, noise, vibration.

• Use: $$\displaystyle Adjusted Time = Basic Standard Time \times Work Factor $$.

3.10 Standard Time vs. Normal Time

4.0 ERGONOMICS (HUMAN FACTORS ENGINEERING)

4.1 Definition & Objectives

• Definition: The scientific discipline concerned with understanding 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. Ensure safety, health, and comfort.

  3. Reduce fatigue, error, and stress.

  4. Improve satisfaction and quality of work life.

  5. Design compatible man-machine systems.

4.2 Human Information Processing Model

DiagramCANVAS: Draw a 4-stage box diagram: 1. INPUT (Sensory Organs) -> 2. PROCESSING (Perception, Cognition, Decision) -> 3. OUTPUT (Motor Response) -> 4. FEEDBACK (System response to output). Show environmental factors influencing each stage.

• Explanation: A human receives stimuli (visual, auditory) via sensory organs → perceives and interprets (cognitive processing, memory, decision-making) → initiates motor response (action on controls) → receives feedback from the system. Ergonomics optimizes each stage.

4.3 Human Sensory Capabilities & Information Reception

• Visual: Primary channel (~85% of info). Factors: acuity, color perception, field of view, adaptation (dark/light).

• Auditory: Important for warnings, communication. Factors: frequency range (2k-5k Hz most sensitive), directionality.

• Tactual: Touch, pressure, vibration, temperature. Used for controls, Braille, warnings.

• Olfactory/Gustatory: Less used in industry (hazard detection, quality).

• Coding & Selection: Information must be coded (shape, color, sound, label) to be quickly and accurately selected by the appropriate sensory channel. Principle: Match code to task and sensory capability.

4.4 Displays

• Types:

  • Visual: Gauges, dials, lights, CRTs, digital readouts.

  • Auditory: Bells, buzzers, voice messages, alarms.

  • Tactual: Vibrating surfaces, raised patterns, force feedback.

• Characteristics of Effective Displays (General):

  1. Salience: Attention-getting (for warnings).

  2. Legibility: Clear, high contrast, appropriate size.

  3. Interpretability: Meaning is clear and unambiguous.

  4. Compatibility: Display matches user's mental model and control movement (e.g., moving control up increases display up).

  5. Feedback: Immediate, clear indication of system response.

• Characteristics of Tactual Displays:

  1. Location: On or near the control hand.

  2. Coding: Use shape, texture, temperature differences.

  3. Force/Displacement: Should be discriminable (e.g., detents, spring force).

  4. Application: Used when vision/audition are overloaded or unavailable (e.g., cockpit, surgery).

4.5 Anthropometry

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

• Purpose: To design workplaces, tools, equipment, and vehicles that fit the user population, ensuring comfort, safety, and efficiency.

• Types of Measurements:

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

  • Dynamic: Body dimensions during movement or task (functional reach, workspace envelope, joint angles).

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

• Importance & Application (Examples):

  • Chair Design: Seat height (popliteal height), depth (buttock-knee length), backrest lumbar support.

  • Workbench Height: Based on elbow height for standing work, or thigh height for seated.

  • Tool Design: Handle diameter (grip span), length (based on hand length).

  • Vehicle/Control Panel Design: Based on percentile ranges (e.g., 5th percentile female to 95th percentile male) to accommodate most users.

4.6 Man-Machine System

• Definition: An integrated system where a human operator interacts with a machine (or process) to achieve a common goal.

• Types:

  1. Open-Loop: No feedback from machine to operator (e.g., simple on/off switch).

  2. Closed-Loop (Feedback): Operator receives feedback from machine output and adjusts input (e.g., driving a car, CNC machining).

  3. Semi-Automatic: Operator performs some tasks, machine others (e.g., assembly line).

  4. Fully Automatic: Machine operates autonomously; human role is monitoring and intervention.

4.7 Relative Capabilities: Humans vs. Machines

4.8 Work Environment Design

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

• Noise: Control at source, barriers, hearing protection. Avoid masking speech/auditory signals.

• Temperature & Humidity: Maintain within thermal comfort zone (approx. 20-24°C, 40-60% RH) to prevent heat/cold stress.

• Vibration: Isolate vibrating sources, provide anti-vibration gloves/ seating. Prevents "white finger" and fatigue.

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

4.9 Task & Work Organisation Design

• Task Design: Job rotation to reduce monotony, enlargement/enrichment to increase responsibility, autonomy.

• Work Organisation: Design of work schedules (shift patterns, breaks), team structures, communication channels, participation in decision-making. Aims to match work demands with human rhythms and social needs.

5.0 APPLICATIONS & WAGE INCENTIVE PLANS

5.1 Objectives of Wage Incentive Plans

1. Increase productivity and output.

2. Link pay to performance fairly.

3. Motivate workers to achieve or exceed standards.

4. Reduce labor cost per unit.

5. Provide opportunity for higher earnings.

6. Simplify labor cost estimation.

5.2 Types of Output-Based Wage Incentive Plans

5.3 Human Factors in Work Study

• Integration: Work Study must consider human limitations and capabilities (ergonomics) to be effective and sustainable.

• Link: A method that is technically efficient but causes fatigue, injury, or stress is not truly efficient.

• Application:

  • Use motion economy to reduce fatigue.

  • Apply anthropometry to prevent MSDs.

  • Design displays & controls to minimize error.

  • Set realistic allowances for fatigue.

  • Design incentive plans that are fair and do not encourage unsafe speed.

  • Goal: Achieve safe, healthy, and sustainable productivity.