18534970 mistake proofing technique

8/8/2019 18534970 Mistake Proofing Technique

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Mistake proofing

Mistake proofing is a scientific technique for improvement of operatingsystems including materials, machines and methods with an aim of

preventing problems due to human error. The term error means a

sporadic deviation from standard procedures resulting from loss of

memory, perception or motion.


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Examples of mistake proofing

Gas pumps are equipped with hose couplings that break away

and quickly shutoff the flow of gasoline.


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The bathyscaph is a deep water submarine used to explore the verylowest parts of the ocean.It is electrically powered.Once at the bottom,if

the batteries or electrical system fail the best outcome would be for the

submarine to return to the surface.The designers made this outcome

occur by holding the ballast in place with electromagnets.When power

is lost,the ballast drops off automatically and sub starts it ascent.


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File cabinet can pull over if too many

drawers are pulled out.

For some file cabinets,opening one

drawer locks all the rest ,reducing the

chance of the file cabinet tipping.


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Fuelling area of the car has three

mistake proofing devices :

Filling pipe insert keeps larger,leadedfuel nozzle from being inserted

Gas cap tether does not allow the

motorist to drive off with out the cap

Gas cap is fitted with ratchet to signal

proper tightness and prevent overtightening.


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Automobiles controls have a mistake

proofing device to ensure that the key

in the on position before allowing the

driver to shift out of park.The keys can

not be removed until the car is in park.


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3.5 inch diskette can not be inserted

unless diskette is oriented

correctly.This is as far as diskette can

be inserted upside-down.

The beveled corner of the diskette

pushes a stop in the disk drive out of

the way allowing diskette to beinserted.This feature,along with the fact

that the diskette is not square,prohibit

incorrect orientation.


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Electronic car locks can have three

mistake proofing devices:

Ensures that no door is left unlocked.

Door automatically locks when car

exceeds the speed of 18mile an hour.

Lock wont operate when door is open

and engine is running.


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New lawn mowers are required to have

a safety bar on the handle that must be

pulled back in order to start the

engine.If you let go of the safety bar,the mowers blade stops in 3

seconds or less.This is an adaptation of

thedead man switch from railroad

locomotives.


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Retail stores use electronic

article surveillance to

ensure that no one walksaway without making

payment.


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This device continuously monitors the water

level. If the level is too low, a valve opens to

add water to the pool.

You can see more examples on www.mistakeproofing.com


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Defect Vs errors

It is important to understand that defects and errors are not

the same thing. A defect is the result of an error, or an

error is the cause of defects as explained below.

Error Defect

Cause Result


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Prevention of defects

Machine

or

human error

Detect error

Take

corrective

action

zero

defect

Analyze for

preventive action

Cause Intermediate result End result

Modify work

procedure to

prevent such errors

Work

Procedure


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Types of error

Error in memory of PLAN : Error of

forgetting the sequence/ contents operations

required or restricted in standard procedures.

Error in memory ofEXECUTION : Errors

of forgetting the sequence/contents of

operations having been finished.

Error in PERCEPTION of type : Error of

selecting the wrong object in type orquantity.


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Types of error

Error in perception of MOVEMENT :

Error of misunderstanding/misjudging the

shape, position, direction or othercharacteristics of the objects.

Error in motion of HOLDING : Error in

failing to hold objects.

E

rror in motion ofCHANGING :E

rrorsof failing to change the shape , position ,

direction , or other characteristics of

object according to the standard.


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Human error

provoking situations

Complex design

Inadequate written standards

Too many parts

Mix up

Too many steps

Specifications or critical conditions

Too many adjustments Frequent repetition


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The principles of mistake proofing can be categorized into groups:

A. Prevention of occurrence

B. Minimization of effects

Principles of mistake proofing


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A. Prevention of occurrence

Methods under this principle aim to prevent the occurrence of human errors from all

stages of operations and make corrections unnecessary.This can be done through the

following 3 methods:-

I. Elimination

II. Replacement

III. Facilitation


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I. Elimination

Elimination method aims to remove the system properties which generate

operations/restrictions susceptible to human errors so as to make them

unnecessary. Consider the error of an operator touching a high temperature pipe

and getting burnt. One method of preventing this error is to make the pipe safe by

covering it with insulating material. This improvement removes the property of

the pipe which generates the restriction.


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Elimination - Example

Alternative design has baffle

function stamped into sheet

metal cover eliminating

troublesome assembly step

Air baffles needed to be

attached to cover to direct

airflow over hot components.

Adhesive could come loose ifnot properly applied. Baffle

also prone to damage during

assembly.


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Replacement

Replacement substitutes a more reliable process to improve

consistency.

Examples: use of robotics or automation that prevents a manual

assembly error, automatic dispensers or applicators to insure thecorrect amount of a material such as an adhesive is applied.


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Replacement- Example

Alignment of the adhesive

overlay on the faceplate was

critical over a series of port

holes. If mis-aligned, the

overlay would need to bestripped off, the surface

cleaned, and a new overlay

applied.

The new model replaced this

process by eliminating the

adhesive overlay and using a

more reliable silk screenprocess.


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III. Facilitation

The principles of elimination and replacement described above make it

unnecessary for operators to perform operations or note restrictions. Incontrast to these, the purpose of facilitation is to make such functions as

memory, perception and motion required in operations easy for the

operators by well designed work stations and thus reduce the occurrence

rate of human errors.


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Board orientation on bottom row 180 different from top row. Color

coded board insertion screws and panel color-coding facilitate correct

board orientation for insertion.

Facilitation - Example


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B. Minimization of effects*

Methods under this principle aim to minimize the effects of human error and focus

on processes where the errors develop into serious problems of quality,safety orefficiency. This can be divided into two categories :

I. Detection and

II. Mitigation

*This principle is also known as Stop-in-time.


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I. Detection

The concept of detection is that even if a human error occurs, the deviations from

standard states caused by it can be detected and corrected in the succeedingoperation steps. The methods of correcting the detected deviations are classified

into two types :

1. Operators are informed or find by themselves the deviations and take necessary

corrective action.

2. The deviations are automatically corrected without operators


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Detection

There are two methods of informing the operator. The first method is to bring errors

to the operators notice by visual or audible alarms, and the second method is by

making the successive operations impossible.


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A conveyor carries the product under a pivoting flag. A correctly

assembled product passes under the flag. An incorrectly assembled

product tips the flag, and a sensor detects the flag movement.

Detection - Example


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The mitigation method aims to make operations redundant or incorporate shock

absorbing/protecting materials so as to mitigate the effects of human errors in

their development process.Example : Consider the error of burning out the motor of a production machine

by forgetting to switch off the power supply. The mitigation countermeasure is to

install a fuse which cuts off the power supply when the temperature reaches

certain point.

II. Mitigation

18534970 mistake proofing technique

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