Ödev Amaçlıdır - Yabancı Kaynak 2

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Ödev Amaçlıdır

Method study or Motion study

Method Study – Systematic recording & critical examination of the way of doing a work as a mean for developing more effective methods & reducing costs.

Work Measurement – Establishing the time required by a qualified worker to carry out a specified job at a defined level of performance

Steps in Method Study - :

Select	job or process to be studied
Record	All the details concerning job
Examine	Recorded facts	Develop	Most economical method
Define	New method
Install	New method
Maintain	New method

Recording Techniques - :

Process Charts
1. Outline Process chart (or operation process chart)
2. Flow Process chart (Man type; Material type; Equipment type)
3. Multiple activity chart
4. Two handed process chart (or Left hand-Right hand chart)
5. SIMO chart (Simultaneous Motion Cycle chart)
Diagrams
1. Flow diagram
2. String diagram
3. Cyclegraph
4. Chronocyclegraph
Models

i) Outline Process chart – Gives bird’s eye view of the process; considers only main operations and inspections

ii) Flow Process chart – Detailed version of operation process chart

Man type – Sequence of activities performed by worker

Material type – Sequence of activities performed on material

Equipment type – Sequence of activities performed by equipment

iii) Multiple Activity chart – Activities of more than one man or machine are recorded on a common time scale

iv) Two handed Process chart – Activities performed by two hands of worker are recorded on a common time scale

v) SIMO chart – Detailed version of two handed process chart (micromotion study)

vi) Flow diagram – Shows the relative position of machines and equipments and marks the path followed by man and material

vii) String diagram – similar to flow diagram except that path ie traced by a continuous string or thread

viii) Cycle graph – To study the path of movement of operators hands;

A small electric bulb is attached to hand and photograph is taken by a still camera

ix) Chronocycle graph – Similar to cycle graph except that along with path it also shows direction and speed of movement. This is done by interrupting the light source so that path appears as a series of dots.

SIMO chart is Micromotion study whereas

cycle graph and chronocycle graph are Memo Motion Study

Memo Motion study involves time-lapse photography ie a still camera takes pictures of the activity at regular intervals (1 to 5 sec) unlike micromotion study which involves making a continuous motion film

Memo motion study is used for activities which are not required to be examined in fine detail but are still too fast to be recorded accurately by human eye.

Therbligs – are the fundamental hand motions which are performed over and again in any manual work, eg Search, find, select, hold, grasp, use, assemble, dissemble, inspect, release

-developed by Mr. Gilbreth (Therblig is his name spelled backward) -used in micromotion study

Work Measurement

Std. time for any job may be established by 3 methods-

Time Study (stop watch) Short cycle ; Repetitive jobs Work Sampling Long cycle ; Heterogeneous operations PMTS Short cycle ; Highly-repetitive jobs

Work sampling

Time

study

Synthetic time

P.M.T.S.

Analytical

estimating

Direct

Indirect

Work

Measurement

Work Sampling

In this a no. of observations are made over a period of time of any worker or m/c and each observation records what is happening at that instant. The percent of observations recorded for a particular activity is a measure of the percentage of time during which that activity occurs.

Work Sampling is used for activities of very long duration which cannot be measured with stopwatch. Eg to find out actual working time of an operator in one shift.

It is based on Statistical theory of sampling – ie adequate random samples of observations spread over a period of time can construct an accurate picture of the actual situation of system.

No. of observations required for 95% confidence level and ±5% accuracy (ie we are sure that 95% of the time the average value will not be having error more than 5% of the true value.

N = 4p(100-p) (p = percent of occurance)

--------------- (A = Accuracy required)

StopWatch TimeStudy

Why do we break down the activity to be studied into elements?(why not measure time straightly)

To provide a detailed work specification

To separate value adding & non-value adding activities

To select best method by comparing work elements of different methods

Stopwatch – one revolution = 1 minute (1 deciminute = 1/100th of minute)

Normal time = Observed time * rating factor

Standard time = Normal time + allowances

Rating – Comparing the pace rate or performance of a worker against standard performance level

to take into account different operators’ performance level

Rating techniques-

Speed- Worker’s speed/speed expected

However assigning a rating factor and allowances are largely subjective in nature and depends on personal judgment of timestudy engineer

Allowances- it is the additional time provided over and above normal time to take into account time for relaxation, attending personal needs

Rest and personal allowances (to overcome fatigue incurred during working)
Interference allowances (to take into account m/c stoppages etc)
Special allowances (for activities which are generally not a part of work cycle)

Indirect (Without actually measuring)

In this we build up the total time for a job by summing up the times for different elements

Particularly useful for operations which are still in the planning phase and have not yet started (helpful in planning and scheduling)

Synthesis
PMTS (Predetermined Motion Time System)
Analytical estimating

Synthesis

Element time values are taken from a catalogue of elements time built from timestudies done in the past

PMTS also make use of previously collected data but it deals with basic human motions (or therbligs) of duration 0.1 seconds or less. Whereas in synthesis duration may be 3-4 seconds

Analytical estimating is used when past time data is not available and estimator has to rely on his past experience.

PMTS

For short cycle & highly repetitive jobs
Uses video film (micromotion study)
More accurate than stopwatch timestudies
No rating factor required but allowances need to be added
But can deal with only manual motions of the operation

Method Time Measurement

Work Factor Systems

1 TMU = 0.0006 minutes (TMU = Time Measurement Unit)

1 wink = 0.0005 minutes (used in SIMO chart/micromotion study)

Analytical Estimating

For long and non-repetitive operations ; Least accurate

(Machine elements – calculated from information of feed, speed, depth of cut etc)

Comparison

It is difficult to compare different work measurement techniques, as each technique has its own set of application

Work sampling is used for long cycles eg amount of time actually spent working by a worker in a shift

Time study is used for short repetitive cycles eg worker working on a assembly line

PMTS is used for very short cycles which require a very detail analysis (micromotion study)

Time

study

Work sampling

Synthetic time

P.M.T.S.

Analytical

estimating

Time Required

MAX

MIN

Accuracy

MAX

MIN

ESOGÜ

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