WorkStudy
From Industrial Engineering
- Work Study
Is a generic term for techniques used for the examination of human work and systematic investigation of all the factors which affect the efficiency of the process, in order to seek improvements.
Work study investigates the work done in an organization and aims at finding the best and the most efficient way of utilizing the available resources (man, material, money and machinery) to achieve best possible quality work in minimum possible time.
- which involves least possible time and causes least possible fatigue to the worker
[edit] Method study or Motion study
Work Study ----------
[edit] Work Measurement or Time 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
- Outline Process chart (or operation process chart)
- Flow Process chart (Man type; Material type; Equipment type)
- Multiple activity chart
- Two handed process chart (or Left hand-Right hand chart)
- SIMO chart (Simultaneous Motion Cycle chart)
- Diagrams
- Flow diagram
- String diagram
- Cyclegraph
- 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 is 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)
A2
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
TIME & MOTION STUDY : A NEW PARADIGM
In theory there is no difference between theory and practice,
In practice there is …….
I realized it by myself when I undertook a project on time & motion study during my summer internship. On paper it looks very easy to do timestudy with a stopwatch. But when you actually do it you realize the practical difficulties associated with the traditional method.
That’s why I picked up the cause in my final year project and developed a software which automates the process of time & motion study.
Details about it can be seen at the following URL -:
http://in.geocities.com/time_motion_study
Please go through it; its worth a watch……
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