ERHS 540 chapters 14 and 15

what are some thoughts to consider in designing tools to be used by either hand?

- left handed operators should be as proficient as right handed operators (assuming workstations can be mirrored and tools can be used with either hand) -penalty of nonpreferred hand is minimal for simple tasks and increases with task difficulty/movement.

what percent performance would you expect for the non-preferred hand for bench assembly work without tools? What percent for use of a manual screwdriver?

-5-10% -50%

mechanical energy (motors) is 10 to 1,000 times cheaper than human energy because...:

1. people are running in and out of work whereas machines only run when they are on 2. worker energy cost is covered by wages, workers need to make enough to pay for family, living, food. 3. people are insufficient power sources

The amount of force (torque) that can be exerted on a control depends on two things:

1. people variables 2. control variables

what are the three types of grip?

1. power grip 2. semi-power grips 3. precision grips

give an example of a tool using power grip: -with force parallel to the forearm -with perpendicular angle to forearm -torque about the forearm

1. someone sawing 2. hammer, ice pick 3. wrench

what are the two reasons a tool should be usable with either hand?

1. the 10% of people who are left handed are not left out anymore 2. non-preferred hand can be used when preferred hand is engaged or resting

there are two types of reaction times in preventing unintended activation

1. the human 2. the machine

every tool has two ends:

1. the part working on the material 2. the part working on the hand

low conductivity materials (wood and rubber) are good for two reasons:

1. they release heat to the hand more slowly- can be held longer 2. gain heat more slowly- less likely to reach high temperature

four methods of limiting force reaction:

1. torque reaction bars 2. torque-absorbing suspension balancers 3. tool-mounted nut holding devices 4. tool support reaction arms

Give four design solutions that permit a person to use either foot on a foot pedal

1. wide pedal for either foot use 2. a pedal for each foot 3. lateral movement of chair 4. a wide chair- so operator can change positions

what are four design solution for using a pedal?

1. wide pedal for either foot use 2. a pedal for each foot 3. lateral movement of chair 4. a wide chair- so operator can change positions

what is an interlock?

a specific sequence must be followed before unlocking occurs (e.g. car transmission must be in neutral or park before starting)

should the control label be above or below the control?

above so that label is readable when hand is on the control

vibration syndrome

caused by prolonged or excessive vibration

For an automobile, give 5 continuous and 5 discrete controls

continuous: -radio volume -steering wheel -accelerator -temperature adjustment -electric seat adjustment discrete: -ignition (on-off) -headlight (low-high) -gear shift (1st, 2nd, reverse, etc) -seat heater (low-high)

what is an enabling control?

control A must be activated before controls B and C can be activated

what are control variables?

control's purpose and design -keys and pushbuttons -knobs -cranks -hand wheels: valve control, vehicle control -foot/leg control

people impose their will on machines through ___

controls

sketch a schematic controls, human, machine, and environment, display

controls->machine->displays->human->back to controls

Gloves _________ grip and grasp capabilities and _______ finger dexterity.

decrease, reduce

pedal force ___ as distance from the pedal ______

decreases, increases

information flows from machine to human through ____

displays

grips should not conduct____

electricity or temperature

give an example of a closed-loop system

feedback influences the display- traffic light: light controlled by magnetic sensors on pavement that detect a car

which wrist style should gloves handling chemicals have?

gauntlet style

How do the three elements of jobs affect the decision to use a general purpose or special purpose tool?

get ready do put away -general purpose tool may save on get ready and put away tasks since one tool does it all there is less search and select time -special purpose tools can increase all of these elements

location depends on whether the control will be used by ___ or ____

hands or feet

shape coding

helps identify controls even in the dark

what is an example of discrete controls?

in a car: -ignition (on-off) -headlights (high-low) -gear shift (1st, 2nd, 3rd, reverse)

what are continuous control examples?

in car: -radio volume -steering wheel -accelerator

what are people variables?

includes: -muscles used -user population -percentile of population designed for

For a standing person, summarize force capability at knee, waist, and shoulder heights

knee: pull is better than push, up is better than down shoulder: push is better than pull, down is better than up waist: best when person is braced, push is better than pull and up and down are equal

what are manipulative controls?

knobs, switches (low-force)

interlocks can be ____ or ____

mechanical or electrical

give an example of an open-loop system

no feedback-traffic light: light is on a timer

give an example of an oblique grip, a hook grip, and internal and external precision grips

oblique: carrying tray with handles hook grip: auto steering wheel internal precision grip: table knife use external precision grip: pencil or pen use

optimum tool angle depends on _____

posture

customized grip design

recommend a diameter 10mm less than inside grip diameter

compressible grip

reduces pressure on hand by: -increases contact area -reduces slippage -reduces vibration transmission -improves sanitation -rubber and hard wood are best EXAMPLE: polo mallet grip, tennis racquets

grip surfaces should be:

smooth compressible non-conductive

what are the best types of tools for industrial repetitive tasks?

special-purpose tools

what is the control/response ratio?

the distance the control moves/ the distance the display indicator moves

what is the exclusion percent?

the percent of the population that is not designed for -have to weigh pros and cons of designing for or against weak people -BUT percentile should be small 1 in 1,000 or less

you should design grip to be the proper ____, ______, and _____

thickness, shape, length

are trigger strips or trigger buttons preferred?

trigger strips b/c multiple fingers are stronger than one

bend the tool, not the _____

wrist

what is maintenance cost?

-maintenance of powered handtools- $100 per year would be considered high

what is a lockout/tagout system?

-require machine controls to be locked so the machine cannot be turned on by someone else while maintenance is performed -maintainer has only key -machine should be in zero mechanical state (zero potential energy)

how can human reaction time be divided?

-sensing (which sense is used- eyes, ears) -making a decision -carrying out the decision

what is capital cost?

-tends to be low for handtools -usually under $100 -consider having duplicates

what is the boundary between the human and the machine?

-user interface

what is utility cost?

-zero for non-power tools power tools: -depends on power source -energy used per minute -duty cycle -pretty low for air and electric motors

what are the two divisions in angles of forearm grip and tool?

1. angles: want wrist in neutral position 2. clearance

what three costs are handtool costs divided into?

1. capital cost 2. maintenance cost 3. utility cost

What are the three steps in determining what type of control is suitable?

1. decide whether the command to the machine will be discrete or continuous 2. decide what part of the body will implement the mental command (e.g. hand, arm, foot, voice command) 3. decide on mechanical interface between the human body and the machine interior

a job is composed of which three elements?

1. get ready 2. do 3. put away

Types of precision grip

1. internal precision grip 2. external precision grip

what are seven ways to prevent unintended activation?

1. key or special tool activation locks 2. interlocks 3. barriers/covers 4. recessing (placing below ground) 5. spacing 6. resistance 7. direction

what are the seven methods of reducing accidental activation of controls?

1. key or special tool activation locks 2. interlocks 3. barriers/covers 4. recessing (placing below ground) 5. spacing 6. resistance 7. direction

work gloves have three wrist styles:

1. knitwrist 2. safety cuff 3. gauntlet

what are six methods of reducing control identification errors?

1. labeling 2. colors 3. shape 4. size 5. mode of operation 6. location

what are the six methods of preventing incorrect identification of controls?

1. labeling 2. colors 3. shape 4. size 5. mode of operation 6. location

ways to reduce vibration syndrome (VS)

1. maintain equipment 2.put a pad under impact surface when using an impact tool 3. minimize handgrip force and push force on tool (suspended tools, etc) 4. rest the tool on a support or workplace as much as possible 5. avoid continuous vibration 6. keep body and hands warm and dry (prevents vasoconstriction). Gloves should cover fingers, not just palms b/c VS begins at fingertips 7. avoid smoking

three things to consider regarding gloves and chemicals. Chemicals can penetrate gloves if:

1. material degrades 2. through penetration via holes, seams, porous material 3. permeation- chemical penetration at molecular level

systems can be divided into two general types:

1. open-loop system 2. closed-loop system

what are the three reasons to use motors instead of humans?

1. people are more expensive 2. machines extend capability- humans get tired, machines are faster and stronger 3. machines permit a larger percent of the workforce to do the job e.g. women, small males

labels should be:

-legible -located properly -understandable -avoid abbreviations -be precise -if possible, use words with icons

what are some example controls?

-levers -wheels -pedals -cranks -switches -buttons -knobs

what is unintended activation?

-activating a control unintentionally

what is an open-loop system?

-desired input or setting of the device but there is no feedback of what the device is doing

what are types of controls?

-discrete -continuous

what is a closed loop system?

-feedback affects the desired input

population stereotypes

-habit patterns -designers cannot depend on controller to follow habitual patterns

handgrip strength facts:

-handgrip strength is less for the non-dominant hand -less for females than males -declines with age

how are hand controls divided?

-keyboards -manipulative controls -force controls

what are benefits of leg controls?

-leg is stronger -leg use leaves hands free

the precision grip is only about _____% of the power grip

20%

the leg is approximately how much stronger than the arm?

3 times

ideal power grip:

35-45mm

what percent of males have color perception problems?

8%

the preferred hand is the right hand for approximately what percent of the population?

90%

"Rule of thumb"

For male adults, the length of the last phalange of the little finger and the width of the thumb is one inch

are color stereotypes consistent across cultures?

NO

what are the pros and cons of multifunction tools?

PROS: can do multiple tasks e.g. camping shovel-hammer, saw, ax, bottle opener, wrench CONS: doesn't do any one task particularly well