Motion Study and Work Design Sections: Basic Motion Elements and Work Analysis Principles of Motion Economy and Work Design Chapter 10

Definitions Motion study Work design Analysis of the basic hand, arm, and body movements of workers as they perform work Work design Design of the methods and motions used to perform a task Design of the work system Includes: Workplace layout and environment Tooling and equipment used in the task such as workholders, fixtures, power tools, etc.

Basic Motion Elements Frank Gilbreth – first to analyze and classify the basic motion elements “Therblig”s – 17 basic motion elements Spelled backward except for “th” Basic building blocks of virtually all manual work performed at a single location (so the primary interest is the hand motions) Some of the motion element names and definitions have been revised Involves both physical and mental elements Although it is first used in production and logistics, the principles are also applicable to service industry.

17 Therbligs Transport empty (TE) – reach for an object with empty hand – today we call it “reach” Grasp (G) – grasp an object by contacting and closing the fingers until control has been achived Transport loaded (TL) – move an object with hand and arm – today we call it “move” Hold (H) – hold an object with one hand Release load (RL) – release control of an object Use (U) – manipulate/use a tool Pre-position (PP) – position object for next operation Position (P) – position object in defined location

17 Therbligs (continued) Assemble (A) – join two parts Disassemble (DA) – separate multiple parts that were previously joined Search (Sh) – attempt to find an object using eyes or hand Select (St) – choose among several objects in a group (hand-eye coordination is involved) Plan (Pn) – decide on an action (a short pause or hesitation تردد in the motions) Inspect (I) – determine quality of object using the eyes Unavoidable delay (UD) – waiting due to factors beyond worker control Avoidable delay (AD) – worker waiting Rest (R) – resting to overcome fatigue

Therbligs

Therbligs

Therbligs

Therbligs

Therbligs

Therbligs

Example

Classification of Therbligs Effective therbligs: Physical Basic Motion Elements: Transport empty Grasp Transport loaded Release load Use Assemble Disassemble Mental Basic Elements: Inspect Delay Elements: Rest Ineffective therbligs: Physical Basic Motion Elements: Hold Pre-position Physical and Mental Basic Motion Elements: Position Search Select Mental Basic Elements: Plan Delay elements: Unavoidable delay Avoidable delay

Micromotion Analysis Analysis of therbligs that make up a repetitive task Objectives: Eliminate ineffective therbligs if possible Avoid holding objects with hand – Use workholder Combine therbligs – Perform right-hand and left-hand motions simultaneously Simplify overall method Reduce time for a motion, e.g., shorten distance

Principles of Motion Economy Developed over many years of practical experience in work design Guidelines to help determine Work method Workplace layout Tools, and equipment Objective: to maximize efficiency and minimize worker fatigue

Three Categories of Principles Principles that apply to the use of the human body Principles that apply to the workplace arrangement Principles that apply to the design of tooling and equipment

1. Use of Human Body Most applicable to manual work Design work to fully utilize both hands The two hands should begin and end their motions at the same time to distribute the work equally to hands Hand and arm motions should be symmetrical and simultaneous to minimize hand/arm-eye coordination Avoid different independent motions of hands/arms Design work to favor preferred hand Work units should enter the workplace on the side of the worker’s preferred hand Worker’s two hands should not be idle at the same time except for the rest breaks Don’t forget that not all tasks can be organized according to these principles.

An experiment A relatively simple task Reaching, selecting, grasping, transporting, releasing small parts. Two types of containers A rectangular bin A bin with a tray The worker performed the work cycle with each container using Only the right hand Only the left hand Both hands performing symmetrical and simultaneous motions.

0.72 sec / work unit 0.54 sec / work unit

1. Use of Human Body Utilize laws of physics Method should consist of smooth continuous curved motions rather than straight motions with abrupt changes in direction Although shortest distance between two points is a straight line Because straight-line path sequence includes start and stop actions (accelerations and decelerations) consume worker’s time and energy Use momentum (mass * velocity) to facilitate task Carpenter using a hammer to strike a nail Take advantage of gravity – Don’t oppose it Method should achieve a natural rhythm of the motions involved

1. Use of Human Body Use lowest classification of hand and arm motion (five classifications) Finger Finger and wrist Finger, wrist, and forearm Finger, wrist, forearm, and upper arm Finger, wrist, forearm, upper arm, and shoulder

1. Use of Human Body I Movement of the fingers only as when picking up a cotton roll. II Fingers and wrist motion as used when transferring an instrument to the operator, or manipulating a hand instrument.

1. Use of Human Body III Fingers, wrist, and forearm as when reaching for a handpiece.   IV       The entire arm when reaching for supplies away from the work area, or to adjust the operating light.

1. Use of Human Body V The entire arm and shoulder as when turning around to reach for equipment from adjacent fixed cabinetry.

1. Use of Human Body For using body members other than the hands, and arms Minimize eye focus and travel Minimize the distance between the object Design method to utilize feet and legs where appropriate Since they are stronger than arms

2. Workplace Arrangement Design of the workplace Locate tools and materials in fixed positions within the work area Locate tools and materials close to where they are used To minimize the distances to be covered Locate tools and materials to be consistent with sequence of work elements Decrease the time required for searching

2. Workplace Arrangement Normal and maximum working areas in the workplace Design for average user

Illustration of First Three Principles Good arrangement of parts and tools in workplace Poor arrangement of parts and tools in workplace Numbers indicate the sequence of operations

2. Workplace Arrangement Use gravity feed bins to deliver small parts and fasteners Two types of bins used for small parts and fasteners in the workplace: (a) gravity feed bin (b) conventional rectangular bin Use gravity drop chutes for completed work units where appropriate Provide adequate illumination Also color, constrast among items, location of the light source are important

2. Adjustable Chair for Workplace A proper chair should be provided for the worker Adjustable to the size of the worker Seat height and back adjustments Padded seat and back

3. Design of Tooling and Equipment Workholding devices should be designed for the task Hands should be relieved of work elements that can be performed by the feet using foot pedals sewing machine Combine multiple functions into one tool where possible Pencils designed for writing and erasing Perform multiple operations simultaneously rather than sequentially Multiple-spindle drill presses to drill holes in PCBs

Design of Tooling and Equipment Where feasible, perform operation on multiple parts simultaneously Machines in a cake factory Design equipment controls for operator convenience and error avoidance Controls should be located within easy reach to minimize the body motions required to access them Hand tools and portable power tools should be designed for operator comfort and convenience e.g. tools that can accomodate both right-handed and left-handed workers Mechanize or automate manual operations if economically and technically feasible