Diagrammatic Aids Used in Recording Work | Industries

There are two basic types of diagrammatic aids used in recording and explaining the work method. These are: 1. Process Charts 2. Diagrams.

 

Type # 1. Process Charts:

It is a graphical representation of the activities that occur during the manufacturing or servicing job. For a manufacturing work, a process chart usually beings with the issue of raw materials from store and ends with the completion of part or assembly.

These are of several types and can be categorized into two groups:

(a) The first type are used to record a process sequence (i.e., a series of events in the order in which they occur) but do not depict the events to time scale, and

(b) The second type are record events in their proper sequence and on a time scale, so that the interaction of related events may be more easily studied.

The various charts fall into following groups:

(A) Charts shows process sequence only:

(i) Outline process chart.

(ii) Flow process chart-man type.

(iii) Flow process chart-material type,

(iv) Flow process chart-equipment type.

(v) Operator chart (or two handed process chart).

(B) Charts show process sequence using time-scale:

(i) Multiple activity chart.

(ii) Simo chart.

Type # 2. Diagram:

A diagram is a pictorial plan of the flow of work and it is used to record the movement of man and material in a process. So it is very useful for the study of material handling or workplace-layout problems. It would show the location of tools, equipment’s and machines in the plant and the movement of men materials and parts.

The commonly used diagrams are:

(i) Flow-diagram.

(ii) String (or thread) diagram.

(iii) Cyclegraph.

(iv) Chrono-cyclegraph.

These diagrams are helpful in:

(i) Communicating a given method in a simple and compact way.

(ii) Examining and developing different process-stages.

(iii) As a source of process information.

(iv) In simplification of overall complicated process, and

(v) Training employees about the process.

After discussion of all these charts and diagrams which are frequently used in the method study, we have some of the examples to understand the real implementation of some of the diagrams and charts. They are basically used to show the process for understanding and controlling the process.

(I) Operation Process-Chart:

Part Name – Rivetted plate Assembly

Part Number – R40 x 10

Location – Plant 6

Method – Present

Charted By – VIVEKMISHRA

Charted Date – 06 October, 2005

It provides a compact overall view of the whole processes for manufacturing a product. It includes only the main operations and the inspections carried out to complete a job are recorded in the sequence of their occurrence but irrespective of where they are performed and by who they are performed.

Thus, only the symbols for operation and inspection are used in preparing the chart. Here also the entry of material or purchased part is shown by the horizontal lines, and processing of material is shown vertically in terms of operations and inspections.

(II) Flow-Process Chart:

It is a chart showing the sequence of flow of a job or a process by recording all events under review using the appropriate symbols. This chart is prepared in the same way as the chart of operation-process we have discussed, but it uses the symbols of operation, inspection, transportation, delay (i.e., temporary storage) and permanent storage. Operation times and distances moved may also be written alongside the symbols. Flow-process charts are of three types man-type, material-type and equipment-type.

Here, we are taking man-type flow-process chart as an example:

(III) Two-Handed Process-Chart:

It consists of two charts, one for right hand and other for the left hand. The simultaneous activities are recorded opposite to each other on the chart. This assists in analysing what right hand will be doing when left hand is working or vice-versa at any point of time. All the above mentioned five symbols are used.

It is used:

(i) To visualize the complete sequence of the activities in a repetitive task.

(ii) To study the work station layout

The two handed process chart is usually confined to work carried out at a single work-piece. For drawing the two-hand chart, we should consider the work-bench layout. As it is shown in fig. (1.12) then in fig (1.13) the two-hand chart formed.

(IV) Multiple-Activity Chart:

It is a very important chart where activities of more than subject (worker or equipment) are each recorded on a common time scale to show their inter-relationship.

Multiple activity chart is made to:

(a) Study idle time of man and machines.

(b) Determine number of machines handled by one operator.

(c) Determine the number of operators required in teamwork to perform the given job.

Multiple activity chart consists of a series of bars (columns) placed against a common time scale. Each subject is allocated one bar and activities related to the subjects are represented in this bar. The columns are placed against a common time scale which starts at zero and ends at cycle time of the job.

The task to be recorded is broken into smaller elements and time for each element is measured with the help of a stop-watch. The activities are then recorded in the chart in their respective columns. Two symbols are used in the chart one represent working and other idle. Working is represented by hatched column and idle is represented by blank (Fig. 1.14).

(V) Flow-Diagram:

It is a pictorial layout of floors and buildings on which the location of ail activities (as in the flow-process-chart) and the “flow-lines” representing the movement of materials or operators are indicated. The pictorial layout is valuable in improving the method. For example, before transportation, distance can be well shortened, it is useful to visualize where the space exists to add a facility. Fig. (1.16) shows the Flow-Diagram of “Gear-Manufacturing” activity.

The procedure to make the flow-diagram:

(i) The layout of the work-place is drawn to scale.

(ii) Relative positions of the M/Cs. storage, inspection etc. are marked on the scale.

(iii) Path followed by the subject under study is traced by drawing lines with arrows.

(iv) Each movement should be serially numbered and indicated by arrow for direction.

(v) Different colours are used to denote different types of movements.

(VI) String-Diagram:

The string diagram is a scale drawing on which length of a string (thread) is to record the extent as well as the pattern of movement of a worker working within a limited area during a certain period of time. It is especially valuable where the journeys are so irregular in distance and frequency to see exactly what is happening.

Examples of situation where string diagram find applications are – material handling man attending to the requirements of a groups of workers, a nurse carrying out routine work of checking temperature, giving medicines and reports. A quality engineer checks the products etc.

To prepare a string diagram, a scale layout plan of the work-area is first prepared. The travelling of men, materials equipment, is recorded on it by winding a string around the pins fixed along the path of movement. The length of path moved by resources is measured by the length of string used. Strings of different colours may be used to show the travel of different people or products.

A String diagram is very effective means of recording and presenting the facts regarding the existing layout. The paths between different work stations, which are too frequently traversed are highlighted.

If two diagrams arc made, one showing the original layout and one showing the improved layout. The string diagram are restricted to use where the number of workstations are large in number so that it becomes difficult to explain and in that case “Travel-Chart” is useful.

Micro-Motion Study:

It is the study of the fundamental elements (called Therbligs) or sub-division of an operation by means of a motion picture and a timing device which accurately shows the time intervals on the motion picture film. This study provides a technique for recording and timing an activity.

It is set of techniques intended to divide the human activities in a groups of movements or micro-motions. This study helps to find for an operator one best way of movements that consumes less time and requires less effort to accomplish the task.

Micro-motions study was originally employed for job-analysis but new uses have been found for this means. The motion data from the film is transferred to a chart called SIMO-CHART’. The data so recorded on the SIMO-CHART can be further analyzed, for example, for better workplace layout or the method improvement. One important thing which is associated with micro-motion study is that Mr. Frank B. Gilbreth is known as a founder of this study.

Micro-motion study can be used for following purposes:

(i) To study the relationship of two or more persons doing group work.

(ii) To study the relationship of the activities of the operator and machine.

(iii) To obtain motion time data for time standard.

(iv) To keep a permanent record of the method and time of various activities of the operator and machine.

(v) For research-work in the field of method and time study.

Micro-motion study involves following steps:

(I) Filming the operation to be studied.

(II) Analysis of the data from the films.

(III) Recording of the data.

(I) Filming the Operation:

It consists of taking motion pictures of the activity while being performed by an operator. The equipment required to make a film or video tape of the operation consists of 16 mm movie camera, 16 mm film, wink-Counter (micro-chronometer) and other usual photographic aids.

(II) Analysis of the Data from the Films:

Once the operation has been filmed and film is processed, then the film is viewed with help of projector for analysis of micro- operations.

The film is analysed in following way:

Film is run at normal speed so as to get familiar with the pattern of movement involved. A typical work cycle is selected from amongst the filmed cycles. Film is run at a very slow speed and is usually stopped or reversed frequently to identify the motions.

Therbligs:

It is term coined by Mr. Frank B. Gilbreth to denote the absolute division of movement of human body performing work. It is also sometimes referred to as fundamental element or subdivision of work. It is a set of activities along with its abbreviation, meaning, symbols, and colours. It is derived from the ‘reserve’ spelling of Gilbreth, i.e.

Glibreth differentiated (18) fundamental hand and eye motion under the given headings as:

Cyclegraph and Chrono-Cyclegraph:

Both cyclegraph and chrono-cyclegraph, are the records of the motion path of an operator. In making a cyclegraph, (Fig. 1.20) a small electric bulb is attached with the finger, hand or other parts of the body whose motion path is to be recorded. With the working area slightly illuminated, the path of light of bulb as it moves through space for one complete cycle is photographed by still photography.

The path traced by the body member appears as a closed loop of a white continuous line in the background of the working area on the cyclegraph. A cyclegraph does not indicate the direction of speed of motion. It can be used for improving method or for training purpose when the superiority of one motion pattern is shown as better than another one.

For making chrono-cycle graph, instead of giving a continuous power supply of bulb, an interrupter of known frequency is introduced in the electric circuit so that light flashes on quickly and off slowly. The bulb is attached to the body member whose motion path is to be recorded just in the same way as in the making of a cycle-graph.

When photographed, the path of the bulb appears as a dotted line with pear shaped dots on the photograph. The frequency of interruption is general 10-30 per second. The spacing of dots on the photograph is indicative of the speed of the motion here wide spacing indicates for fast moves and close spacing for slow moves.

The jumping of dots at one point indicating fumbling or hesitation of the body pan at that point. A proper study of graph can give accurate times Speed acceleration, retardation and also direction and path of motion. So a chrono-cyclegraph provides more information about the motion than just the .path. The chrono-cyclegraph is also used for comparing a method with another and for improving the workstation layouts.

Simo-Chart:

SIMO chart stands for Simultaneous Motion chart; which is a recording technique for micro-motion study. It is a chart, based on the film analysis, used to record simultaneously on a common time-scale the therbligs or a group of therbligs performed by different parts of the body of one or more operators. It is micro-motion form of the man-type flow process- chart.

A motion film is made of the operation for which are simo-chart is required to be prepared. The film is then analysed frame-by-frame. The sequence of the therbligs with their name values is determined and recorded on film-analysis sheet.

Parallel columns drawn on the chart for recording the activities of the various parts of the body. The symbols and the columns of therblig are then added on the chart for the length of the column which indicates the duration of the therbligs.

The simo-chart is used for sequence with cycle-time less than a minute. The duration of an activity represented by one therblig is indicated by the length of therblig symbol or colour column. Except for delays, which are, in fact, non-activities, all therbligs are lengthened by the complexity for the activity involved.

It is also called ‘therblig-time-chart’ and it is very useful for analysing the work in following situations:

(i) Large volume operations.

(ii) Greater economy of motions is desired than obtainable through method-study technique.

(iii) When hand and fingers perform motions, the exact nature of which is difficult to be specified by operator process-chart.

The format of SIMO-chart is shown in Fig. (1.22):

Basic Hand Motions:

Basic hand motions are generally classified as:

(i) Finger motion.

(ii) Motions involving fingers and wrist.

(iii) Motions involving fingers, wrist and forearm.

(iv) Motions involving fingers, wrist, forearm and upper-arm.

(v) Motions involving fingers, wrist, forearm, upper-arm and shoulder.

A better method to use of basic hand motions is consumed minimum of time and energy in performing motions.

Principles of Motion Economy:

A set of rules were designed by Mr. Frank B. Gilbreth in order to develop better methods. In order to make best use of man considerations are given to certain principles which are known as ‘Principles of Motion Economy’.

These principles can be considered under three different groups have 26 principles:

(I) Principles Related to the Use of the Human Body:

(i) Both hands should start and complete their motion at the same time.

(ii) Both hands should be used for productive work.

(iii) Both hands should not be idle at the same time except during rest period.

(iv) Hand and body motions should be confined to the lowest possible classification in order to reduce fatigue.

(v) Smooth, continuous and curved motions should be preferred over straight line motions.

(vi) Ballistic movements are faster, easier and more accurate than the restricted or controlled movement.

(vii) Hands should be relieved of all work that can be done by feet or other parts of the body.

(viii) Momentum should be employed to assist the body motion.

(ix) Work movement should be arranged to build rhythm and automaticity.

(II) Principles Related to the Arrangement of the Work-place:

(i) All tools and materials should be placed at definite and fixed place with easy reach.

(ii) As far as possible all tools and materials and other mechanical devices should be kept close to the worker.

(iii) Gravity feed bins and conveyor should be used to deliver the materials.

(iv) Wherever possible use drop deliveries so that the worker should not be employed for non-productive work.

(v) Tools and materials should be located in such a way to achieve the best sequence of motions.

(vi) Workplace should be illuminated properly for adequate seeing and visual perception.

(vii) The height of the workplace and seat should be arranged to allow alternate sitting or standing.

(viii) Chairs provided should make good posture.

(ix) Keep the shops in good order, neat and clean.

(x) The colour of workplace should contrast with that of the work to reduce eye

(III) Principles Related to the Design of Tools and Equipment:

(i) Jigs, fixtures and foot operated devices should be used to reduce work load on hands.

(ii) Two or more tools should be combined wherever possible.

(iii) Reduced noise-level gives increased speed of work with less energy.

(iv) Those tools should be used which can perform more than one operation.

(v) Handles on tool should be provided, particularly where force is applied like screw­driver, scraper, etc.

(vi) Where work is carried out by fingers, the load distribution on to each fingers should be as per the normal capacity of the finger.

(vii) Levers, cross-bars and hand-wheels should be placed so that operator can use them with least body efforts and get maximum mechanical advantages.