[Total: 0    Average: 0/5]
Based on a real observation of the work, it allows to identify the standard times as well as potential improvements.

Introduction

Chrono-Analysis is the oldest and most widespread method. It consists of performing a direct timekeeping of the work cycle and then deducting a standard time from the operation by applying a Pace factor and a coefficient taking into account the notions of fatigue, rest… In the end, the time of the standard operation is broken down as follows:

  • to: the time observed. It corresponds to the timed time during the analysis.
  • TN: Normal time. It corresponds to the observed time adjusted according to the pace factor.
  • TS: Standard time. It corresponds to the Normal time more different increases such as unpredictable delays, rest or even personal needs.

The pace Factor

The pace Factor Is by definition the comparison of the performance observed with the concept of normal performance of the analyst. So we are talking about ” judgement ” of allure because it is a very subjective factor.

 

The increases

The increases are there to add time to the cycle time “normal” to take into account the working conditions (fatigue, unforeseeable delays, personal need…) and identify a standard time “supportable” when it makes a Average performance. They are most commonly found under the term DPMA coefficient (torque, posture, monotony, ambience).

Generally, a rate of 5% is granted for various personal needs, but as far as possible, these adjustments must be determined by a time study. The table below gives the rates to be added in function of the different situations.

 

Class

Type

Description

% to add

Constant

Personal: Pee break…

5%

Normal Fatigue

4%

Torque wrench

Use of force to lift, push…

2,3 kg

0%

4.5 kg

1%

6.8 kg

2%

9.1 kg 3%
11.4 kg 4%
13.6 kg 5%
16 kg 7%
18.2 kg 9%
20.5 kg 11%
22.7 kg 13%

27.3 kg

17%

32 kg

22%

Posture

Sitting/Standing

Standing

2%

Curvature Slightly bent 0%
Bend 2%
Very bend 7%
Monotony Concentration level Slightly complex process 1%
Complex process requiring attention 4%

Very complex process

8%

Monotony Low 0%
Average 1%
Strong 4%
Level of fatigue Normal 0%
Boring 2%
Very annoying 5%
Level of work accuracy Specific 2%
Very accurate 5%
Atmosphere Lack of brightness Slightly below recommendations 0%
well below 2%
Inadequate 5%
Weather Conditions Variable (humidity, heat…) 0 to 10%

Noise level

Continuous and normal 0%
Loud intermittently 5%
Very acute 5%

Source: S. O. Dufuaa, J. D. Campbell, A. Raouf (1998)-Planning and control of maintenance systems: Modeling and analysis

 

The stages of the Chrono-analysis

1. Select the operations and the operator to observe

All the details of the operations to be observed must be standardized before the study begins and the operator who will be observed must master these standards.

Indeed, if a minimum standardisation is not present, the results obtained will not be applicable to all and will leave to discuss.

The operator must be representative of the average and accept the fact of being observed.

2. Cut the work into sub-elements

To facilitate the measurement, the work must be divided into a sub-group of movements. An element is a part of the work that can be easily measured and identified. These different sub-groups of elements should preferably be identified in the phases upstream of the measurement. There are different types of1 :

  • Repetitive task: an item that returns multiple times in the same work cycle.
  • Occasional Task: an element that does not appear in each cycle and can come at regular intervals or not.
  • constant Task: an element whose time is always the same (a machine shutdown for example).
  • variable task: an identical element but whose time varies according to the characteristics of the product, the equipment… (Walk X metre for example).
  • Manual Task: An element made by the operator.
  • Machine Task: an element made only by a machine.
  • Housekeeping Task: an element that takes a while while others are being made in parallel.
  • Foreign task: an element made during the work cycle whereas after analysis it is not necessary to work.

To define the subgroups, some rules help us:

  • Make sure all items are needed.
  • The elements must be easily identifiable with a clear starting and ending point.
  • The elements should be as short as possible for the measurement to be the most accurate. The minimum unit used is 2.4 seconds2. For less trained observers, the unit is a minimum of 6 seconds.
  • The subgroups must respond to a logical and natural sequence.
  • The steps performed by machines must be separated from the manual.

3. Define the number of measures required

The number of observations is 10 for cycle times of less than 2 minutes and 5 observations for cycle times of more than 2mn.

However, the number of measurements can be statistically determined. In this case it is necessary to carry out a first series of measurements. This will also help to ” train ” and validate the different steps.

Once this first set of measures is made, the total number of measures depends on three factors

 

With:

  • N: The number of measurements
  • p: desired accuracy of the estimate (generally, a value of 5% is taken)
  • σ: standard deviation of the first time measurements
  • XBar : Average sample times
  • Z: standard deviation for the desiredConfidence interval . In the normal distribution, this value is:

Desired Confidence interval

Z Value

90

1,65

95

1,96

96

2,05

97

2,17

98

2,33

99

2,58

99,7

3

4. Taking measurement

During the measurement, the analyst can identify ways of improvement. Thus, for each of the phases observed, it can see if the tools are adapted, if there is possibility to reduce the movements… This is one of the strengths of this method where Gemba observation allows the analyst to make these remarks, contrary to methods such as the analysis of predetermined times (MTM…).

The two rules of a direct measure are recalled:

  • The staff observed must be aware of the project and be in agreement with it.
  • Timing must be done under normal production conditions.

Technique 1: Continuous taking

The watch runs continuously during the study. It starts at the beginning of the first stage of the studied cycle and ends at the end of it. At the end of each sub-group of the cycle, the Timekeeper notes the time played on the Chrono.

The interest of this method is that no second of the total cycle is lost. All the waiting times and even the ” foreign ” elements are measured. On the other hand, this technique requires more work in the analysis because it needs to deduct the times of each of the subgroups.

Technique 2: The Taking in sequence

The hand on the Chrono, after each sub-group, this one is reset to 0 and the time is transcribed directly by the timekeeper. This technique requires less time in the analysis but has various drawbacks:

  • Measuring short elements is complex.
  • The result cannot be verified on the overall cycle time by summing each of the tasks.
  • Wait times and foreign elements are not taken into account.

Technique 3: The plug with a system 3 watches

Combinations of the first two techniques, in addition to the two different watches, this technique adds a third watch. The goal is to be stopped at each stage as the sequence but rather than to continue the Chrono, it returns to 0. This gives a clear and precise view of the entire time of the cycle and thus facilitates the work of the analyst.

Difficulties in taking measurements

Taking measurement is a complex task. The timekeeper is often subject to 3 types of difficulties:

  • Missing elements: Sometimes the operator forgets a task or the timekeeper has had time to observe it. The first case indicates either a lack of standard or the fact that the task in question is not useful. The second case calls for the stop of the measure to avoid errors and misinterpretations.
  • The analyst sees elements that are not a priori part of the standard cycle.
  • A foreign element appears during the cycle.

5. Calculate the observed time-TO

First of all, we have to start by stripping the Times observed during the study phase. For this we have three possibilities:

  • Average calculation: For each phase, we come to average the observed times.
  • Frequency calculation: For each of the phases of work, we classify the different values measured and we look for the one that comes back most often. example, if 10 seconds is the time that comes up most often for the phase studied, it will be that value that will be retained as to.
  • calculation with the Michelin method: This is to put the values in ascending order and then to take the 1st value of the second third as the reference value. For example, on the next set of statements, the value taken as to will be 12. Reading in seconds: 10, 10, 11, 12, 12, 13, 13, 14, 14

Measure of the stability rate

At the margins of the observed time, an indicator called stability rate is measured. This is calculated with the following formula:

Below 50%, the position is considered to be stable.

6. Application of the speed factor and calculation of TN

Once measured and calculated, the Normal time will be inferred by applying to the observed time to the pace factor according to 2 techniques:

Arithmetic method

The previously calculated to be taken and the average of the allure factor is calculated. We’re deducting TN.

Example, if the average of the TB is 10 sec, the average of the allure factor is 70% then the TN time is 10 * 70/100 = 7 seconds.

Bedaux method

Very often used in the automotive sector, it takes place as follows:

  1. In a column, insert in ascending order the different measures
  2. On the other columns, check by bars the different paces for the time in question
  3. In another column, put bars to indicate the frequency at which this time was measured
  4. Gather by a straight line, passing through the lower left corner, the squares containing the highest number of observations
  5. Draw a horizontal line starting from the time for which the greatest number of observations was raised, up to the junction with the previous right
  6. The intersection point of the 2 straights gives time TO and the associated allure factor
In this example, it will take a time of operation of 15 secs, for a speed factor of 65%.

7. Standard Time Calculation – TS

Standard time, in addition to Normal time, takes into account a number of increases defined above. It is enough to add to the standard time TN these increases.

Strengths for a good measure

The necessary equipment

A rigid, lightweight support must be used to hold the reading sheet, pen and stopwatch on its own (preferably in the upper right).

A video can be a plus in the analysis especially when the work cycle requires many short movements. With the video, the analysis can be sequenced in sequence if necessary. The video may also look less intrusive and be more easily accepted.

The stopwatch must remember all measurements and display the time in seconds, hundredths of an hour and 10 000 thousandth of an hour.

The data sheet

It must include all the categories of items to be noted (task, time, descriptive). It must also provide a space to note any type of data (tools, working conditions…).

It consists of an introductory part (observation date, observed person, analyst, Process analyzed) and a series of columns indicating:

  • The process step number
  • A description of the operation
  • The machine/tools used in the operation
  • The time of the operation
  • The judgement of Allure associated
  • The increase
  • A comment part
  • A game with one or ideas of improvements and optimizations

Good advice

  • The timekeeper must be positioned to the left of the operator and in the same direction.
  • He must stand up to better observe the work, read the Chrono and write on the sheet of readings without making any head movements.
  • The Chrono, the work to be observed and the hand are in the field of view of the timekeeper.
  • It is necessary to avoid as far as possible, to time on Monday morning and on Saturdays.
  • You have to stop before the exit time and never clock at the beginning of the work.

Source

1-G. Salvendy (2001) – Handbook of Industrial engineering: Technology and Operations management

2 – B. W. Niebel, A. Freivalds (1999) – Methods, standards and work design

3-B. W. Niebel (1992) – Motion and Time Study

The Good timekeeper’s guide

Share This