hand tool design for ergonomics

Hand Tool Design

Submitted toDr. Engr. Mohammad IqbalProfessorIndustrial & Production Engineering,Shahjalal University of Science & Technology,Sylhet

Industrial & Production Engineering,Shahjalal University of Science & Technology

Submitted ByGroup B4Tanni Das 2013334054 Kyaw Zaw Thowai 2013334055Aminul Islam 2013334056K A M Shahrier 2013334057Mahbub Alam 2013334058Ali Akbar Tanim 2013334060


and tool is any tool that is powered by . hand (manual labor) rather than by an engine.

Hand tool aid the Human forCutting, smashing, scraping, and piercing.Fit the work.Fit the user and hand.Not create injuries.

Hand tool design

H

Special Purpose Hand Tool


Handled with power grip or with a precious grip. Small or large Flexible or, stiff One can design special purpose hand tool for specific task Possible to combine several hand tools into one.

Fig: A special Handtool

A tool use in multipurpose task at a time can be said as a specialHand tool. It saves time and make work easier.E.g. Hammer with an extension pulling nails, pliers with Hammer parts etc.

Hand tool designFitting the task

Power Grip The hand makes a fist with the forefinger on one side and the

thumb reaching around. It can be differentiate by direction of force i)Force parallel to the forearm. E.g. saw; ii) Force at angle to fore arm. E.g. Hammer iii)Torque about the fore arm. E.g. Screwdriver


Saw

Hammer

Screw driver

Hand tool designPrecision Grip


Internal Precision Grip The tool is held inside the hand. E.g. A table knife

External Precision Grip The tool is pinched by the thumbs . against the index finger and the middle finger. E.g. A pen.

Fig: Gripping a table Knife

Fig: Writing by pen

Hand tools and Power hand tools


Hand Tools Power Tools

Hand tools are devices for performing work on a material or a physical system using only hands

Power tools are tools powered by an electric motor

Hand tools are propelled only by human power

Power tools always have a motor

Hand tools mechanism is very easy Power tools mechanism is not easy as hand tools

It is environment friendly and cheaper but take more time than power tools

Power tool save a considerable amount of time and effort in a larger project.

Hand tool Design For the User


GoodPistol HandleVertical surfaceElbow height

BadPistol HandleHorizontal surfaceElbow height

BadStraight HandleVertical surfaceElbow height

GoodStraight HandleHorizontal surfaceElbow height

BadStraight HandleHorizontal surfaceBelow elbow height

GoodPiston HandleHorizontal surfaceBelow elbow height

Grip force vs Handle opening


Fig: Maximum grip strength for male and female employees in electronics manufacturing

Hand -anthropometry


Awkward situation Right handed tools for left handed users

create awkward situation. Awkward postures may cause to use more

force. Cut-outs for the fingers are responsible Awkward wrist position results in a loss of

strength It is responsible for CTD It affects torque exertion capability

Awkward wrist position (Terrell and Pursell-1976) :

Decreases grip strength by 12% Flexion/extension by 25% Radial/ulnar deviation by 15%

Prevention: Hand-tool should be designed both the

left handed & right handed user. Design hand-tools by hand

anthropometry Industrial & Production Engineering,Shahjalal University of Science & Technology

Injuries


Cumulative Trauma disorder (CTD) Repetitive usage of hand tools Wear & tear on tissue on the joint. Vibration-Induced Injuries Hand tool vibration 1)Reynaud’s disease: Hand tool vibration in the frequency range 50-100 Hz 2)Dart’s disease: Vibration frequencies around 100 Hz

Reynaud’s disease


2)Stiffness and numbness Reduction of blood flow Gradual loss of muscle control of the

hand

1)White finger disease Reduction in blood flow to the hand and

the finger

Fig: White finger disease

Fig: Stiffness and numbness


Several Guidelines for Hand tools design

Aim:To increase operator comfort, convenience and controllability of hand tools .

Guidelines: For precision grip

Grip between thumb and fingerGrip thickness is 8 to 13 mmGrip length minimum 100 nmToll weight maximum 1.75 kgTrigger activated by distal phalanges of fingers with fast release mechanism.



For power grip

Grip with entire handGrip thickness 50-60 mmGrip length minimum 125 mmGrip force maximum 100 mGrip shape non-cylindrical Tool weight maximum 2.3 kg, 1.2 kg is preferableTrigger activated by thumb with locking mechanism



Grip surface smooth Slightly compressible and non conductive Avoid vibration, Particularly in the range of 50-100 Hz Design Handles for use by either handsKeep the wrist straight in the handshake orientationTool weight balanced about the grip axisEliminate pinching hazard

The End