9.1 Methods Analysis, Process Charting & Motion Study (Therbligs, 5S)

9.1 Methods Analysis, Process Charting & Motion Study (Therbligs, 5S)

Methods engineering is the systematic professional discipline focused on designing, analyzing, and improving work methods to produce goods and services with maximum human safety, optimal ergonomic comfort, minimum operational waste, and lowest unit cost. As the bedrock of classical industrial engineering, methods engineering bridges human capabilities with mechanical, digital, and organizational systems.

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1. Foundations and Objectives of Methods Engineering

Methods engineering originated through the pioneering research of Frederick Winslow Taylor and Frank and Lillian Gilbreth at the turn of the 20th century. Taylor introduced scientific task analysis, time study, and systematic tool standardization. Concurrently, Frank and Lillian Gilbreth pioneered motion study, developing photographic and micro-chronometer techniques to analyze manual movements down to fractions of a second.

While early practitioners focused heavily on manual pacing, modern methods engineering adopts a socio-technical systems approach. Its four overarching objectives are:

1. Eliminate Non-Value-Added Waste (Muda): Interrogate every stage of a process to strip away unnecessary movements, redundant handling, transit distances, and bureaucratic processing.
2. Enhance Ergonomics and Human Safety: Design workstations and task sequences to eliminate awkward joint postures, extreme biomechanical moments, contact stress, and repetitive strain injuries.
3. Standardize Best Practices and Tools: Establish unambiguous Standard Operating Procedures (SOPs), ensuring consistent product quality, predictable cycle times, and robust training frameworks.
4. Establish Reliable Baselines for Work Measurement: A work standard cannot be established until the method itself is stabilized and standardized. Measurement applied to an unstable method produces invalid, unrepeatable data.

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2. The Process Charting Hierarchy

Process charts are specialized graphical modeling tools used by industrial engineers to document, visualize, and critically evaluate the sequential steps of an industrial operation. They range in analytical granularity from enterprise value streams down to the simultaneous motions of an operator's hands.

Granularity Hierarchy of Process Analysis
├── 1. Value Stream Map (VSM) [Enterprise & Supply Chain Level]
├── 2. Operation Process Chart (OPC) [Component Flow & Assembly Level]
├── 3. Flow Process Chart (FPC) [Detailed Material / Worker Pathway Level]
└── 4. Two-Handed Process Chart (Operator Chart) [Micro-Motion Workstation Level]

The Operation Process Chart (OPC)

The Operation Process Chart (OPC) provides a macro-level overview of an entire manufacturing or assembly sequence. It charts only the points where raw materials or subcomponents enter the primary stream and the sequence of operations and inspections performed upon them.

• Allowed Symbols: Strictly limited to Operations (circles) and Inspections (squares).
• Omissions: Transports, delays, and storages are explicitly excluded from an OPC to preserve strategic visibility of manufacturing transformations.
• Conventions: The primary base component flows down a vertical line on the far right of the chart. Subassemblies and purchased parts enter horizontally from the left, joining the main vertical trunk at their exact point of assembly.

The Flow Process Chart (FPC)

The Flow Process Chart (FPC) magnifies a specific segment of the operation, tracing the minute-by-minute journey of either a material (material-type), a worker (worker-type), or an equipment asset (equipment-type). It incorporates all five standard symbols defined by ASME Standard 101:

Every FPC concludes with a Summary Table tallying the total number of operations, transports, inspections, delays, and storages, alongside the cumulative transport distance (feet or meters) and total elapsed cycle time. Engineering improvements are quantified by comparing current vs. proposed summary metrics.

The Two-Handed (Worker-Material) Process Chart

The Two-Handed Process Chart (also termed an Operator Process Chart) analyzes manual operations at a single workstation. It synchronizes the activities of the operator's left and right hands along a common vertical timeline.

• The chart utilizes modified ASME symbols (Operation, Transport, Hold, Delay) to identify balance discrepancies between hands.
• Its primary engineering objective is to identify instances where one hand is passive or serving merely as a holding device (Hold), freeing that hand to perform productive assembly work in tandem with the other.

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3. Principles of Motion Economy

Developed by Frank and Lillian Gilbreth and codified into industrial practice by Ralph M. Barnes, the Principles of Motion Economy comprise a set of practical guidelines designed to reduce worker fatigue, eliminate wasted effort, and increase task efficiency. They are categorized into three core domains:

Domain A: Use of the Human Body

1. Simultaneous and Symmetrical Motions: Both hands should begin and complete their motions at the same instant. Arm movements should be made in opposite and symmetrical directions simultaneously, balancing dynamic torque on the spine and minimizing trunk muscle fatigue.
2. Motion Classification: Human motions should be confined to the lowest practical classification level to minimize energy expenditure:
   • Class 1: Fingers only (knuckle pivots; minimal fatigue, highest precision).
   • Class 2: Fingers and wrist (wrist pivots).
   • Class 3: Fingers, wrist, and forearm (elbow pivot; ideal baseline for bench assembly).
   • Class 4: Fingers, wrist, forearm, and upper arm (shoulder pivot; causes upper trapezius fatigue if sustained).
   • Class 5: Fingers, wrist, forearm, upper arm, and torso/body (requires bending or twisting of the trunk; highly fatiguing, slowest velocity).
3. Continuous Curved Motions: Smooth, continuous curved hand trajectories are preferred over straight-line motions involving sudden, sharp reversals in direction. Reversals require the muscular system to decelerate the limb to zero velocity, hold static tension, and re-accelerate in the opposite direction, producing high muscular wear.
4. Ballistic vs. Controlled Motions: Free-swinging (ballistic) movements—propelled by a burst of agonist muscle activity and sustained by momentum—are faster, easier, and less fatiguing than restricted, controlled movements that require continuous opposing co-contraction of antagonist muscles.
5. Rhythm and Cadence: Work should be arranged to promote a natural, rhythmic cadence. Rhythmic performance diminishes mental hesitation and promotes neuromuscular automaticity.

Domain B: Arrangement of the Workplace

1. Fixed Locations for Tools and Materials: All tools, jigs, and components must possess fixed, definite, and marked locations. This develops proprioceptive muscle memory, allowing the operator to retrieve items without visual search.
2. Primary and Maximum Working Envelopes:
   • Normal Working Area (Horizontal): The semicircular area swept by the hands and forearms when the upper arms hang naturally at the sides and the elbows pivot (approximately 14 to 16 inches / 35 to 40 cm from the edge of the bench). High-frequency assembly must reside within this zone.
   • Maximum Working Area (Horizontal): The area swept by the fingertips when the arms are fully extended from the shoulder without bending the waist (approximately 24 to 28 inches / 60 to 70 cm). Items used occasionally should be placed here.
3. Gravity Feed and Point-of-Use Delivery: Bins should utilize gravity-feed hoppers to present components directly at the operator's fingertips, eliminating the need to reach deep into boxes.
4. Drop Delivery Chutes: Operators should release completed workpieces into drop chutes or air-ejection mechanisms adjacent to the assembly zone. Carrying finished items to distant storage bins is pure non-value-added transport waste.
5. Ergonomic Workstation Geometry: Set bench height relative to elbow height and the task (Grandjean's guidance: about 5–10 cm above elbow height for precision work, 10–15 cm below for light work, and 15–40 cm below for heavy work), and provide sit-stand flexibility where possible.

Domain C: Design of Tools and Equipment

1. Relieving Hands of Holding: Mechanical holding fixtures, toggle clamps, pneumatic vises, or foot-operated treadles should secure workpieces, liberating both hands for productive manipulation.
2. Multi-Function Tooling: Two or more tools should be integrated whenever feasible (e.g., dual-ended torquing bits, combined crimp-and-cut pliers).
3. Ergonomic Handle Profiles: Tool grips should maximize contact area with the palm and fingers to distribute mechanical pressure over the fleshy thenar and hypothenar eminences, preventing focal nerve compression at the carpal tunnel.
4. Power Assistance and Reaction Arms: High-torque power tools should be suspended from spring balancers and equipped with torque-reaction arms to absorb rotational recoil.

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4. Therblig Analysis (17 Elemental Micro-Motions)

Frank and Lillian Gilbreth decomposed manual work into elemental motions called Therbligs ("Gilbreth" spelled nearly backward). Most methods texts list 17 therbligs; some older lists add an 18th, Find, which is now usually merged into Search. Therbligs expose micro-level waste that standard process charts cannot show.

Therbligs are partitioned into two distinct categories: Effective Therbligs (which directly advance the progress of work) and Ineffective Therbligs (which generate operational delay without adding physical value):

17 Elemental Micro-Motions (Therbligs)
├── Effective Therbligs (Direct Value-Adding Transformations)
│   ├── Reach (RE) — Transporting empty hand toward object
│   ├── Move (M) — Transporting loaded hand / object through space
│   ├── Grasp (G) — Closing fingers to establish physical control
│   ├── Release (RL) — Relinquishing physical control of object
│   ├── Pre-position (PP) — Orienting object into position for subsequent use
│   ├── Use (U) — Manipulating a tool or executing mechanical transformation
│   ├── Assemble (A) — Bringing two or more mating parts together
│   └── Disassemble (DA) — Separating mating components from an assembly
└── Ineffective Therbligs (Non-Value-Adding Waste / Improvement Targets)
    ├── Search (Sh) — Eyes or hands actively hunting for an object
    ├── Select (St) — Choosing one specific item among mixed/jumbled items
    ├── Position (P) — Aligning an object for its final placement
    ├── Hold (H) — Static muscular retention of an object with one hand
    ├── Inspect (I) — Examining an object against quality standards
    ├── Plan (Pn) — Mental hesitation to decide upon next operational course
    ├── Unavoidable Delay (UD) — Waiting caused by external process factors
    ├── Avoidable Delay (AD) — Idling caused by operator disengagement
    └── Rest for Overcoming Fatigue (R) — Periodic physiological recovery

Industrial Engineering Intervention Strategies

• Eliminating Hold ($H$): Using a human hand as a clamp is the most common inefficient Therblig in manual manufacturing. It causes rapid isometric fatigue and locks 50% of the operator's manual capacity. Engineers eliminate Hold by implementing toggle clamps, magnetic nests, or vacuum chucks.
• Eliminating Search ($Sh$) and Select ($St$): Searching through mixed bins consumes extensive visual-cognitive processing. Engineers eliminate Search and Select by adopting standardized component kitting, compartmentalized tray organizers, and gravity-fed orientation tracks.
• Optimizing Pre-position ($PP$): Pre-positioning requires the operator to rotate or align a tool or part before it can be used. Engineers eliminate $PP$ by using spring-loaded tool balancers that park drivers in exact working orientation, or by designing symmetrical fasteners that require no rotational alignment.

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5. The 5S Workplace Organization Methodology

The 5S Methodology is a systematic framework originating within the Toyota Production System (TPS) that transforms workspaces into clean, visual, standardized, and safe operating environments. A stable 5S foundation is a mandatory prerequisite for methods engineering, time study, and standard work creation.

The 5S Continuous Improvement Cycle
Sort (Seiri) ──> Set in Order (Seiton) ──> Shine (Seiso)
     ^                                          │
     │                                          v
Sustain (Shitsuke) <────────────────── Standardize (Seiketsu)

The Five Pillars of 5S

1. Sort (Seiri): Separate necessary items from unnecessary items in the workplace. Apply the Red Tag Protocol: attach physical red tags to unneeded tools, excess inventory, scrap, or broken equipment; move them to a central holding area; and scrap, sell, or relocate them if unclaimed within a specified window (e.g., 48 hours). The objective is eliminating clutter and reclaiming floor space.
2. Set in Order (Seiton): Organize all remaining necessary items so they are instantly accessible, clearly identified, and easy to return. Adhere to the core maxim: "A place for everything, and everything in its place." Engineering tactics include:
   • Shadow Boards: Outlines of tools cut into contrasting backings to make missing tools immediately apparent.
   • Floor Striping & Demarcation: High-visibility boundary tape defining walkway corridors, pallet staging squares, and trash receptacle placements.
   • Point-of-Use Storage: Locating fasteners and tools directly within the operator's normal reach envelope.
3. Shine (Seiso): Clean the entire work area, machines, tools, and floor surfaces daily. Crucially, Shine treats cleaning as a rigorous form of inspection. While cleaning, operators detect oil leaks, loose bolts, frayed wiring, vibration damage, and early equipment failure before they trigger catastrophic breakdowns.
4. Standardize (Seiketsu): Establish formal rules, visual standards, audit checklists, and color codes to ensure the first three pillars are maintained consistently across all operating shifts. Standard operating procedures (SOPs) must be displayed visibly at the cell.
5. Sustain (Shitsuke): Build organizational discipline and commitment through recurring cross-departmental 5S audits, management Gemba walks, performance scorecards, and continuous improvement (Kaizen) cycles.

The Visual Workplace and Standardization

A mature 5S environment functions as a self-explaining, self-ordering, and self-improving visual workplace. Any deviation from standard conditions—such as a missing torque wrench, an overflowing scrap container, or an unauthorized pallet—is immediately visually conspicuous to any observer within five seconds, without requiring verbal explanation or data queries.