WORK MEASUREMENT TECHNIQUES Soumya Subhra De Research Scholar ,SIF, CUSAT
What is Work Study / Work Measurement:• Organized common sense• 10% technique and 90% psychologyObjectives of Work Study:Obtain the optimum use of the human and material resources available to the organization for the accomplishment of the work
DEFINITION• According to the British Standards Institute “work study is a generic term for those techniques, particularly method study and work measurement, which are used in examination of human work in all its contexts and which lead systematically to the investigation of all factors which affect the efficiency and economy of the situation being renewed, in order to effect improvement.”• Work study consists of as already mentioned in the above definition of two steps –• Method study (motion study)• Work measurement (time study)
Principles of Work Study:• Must come from the top level management.• People made aware of the objectives and the need of the exercising such study.• Method study must precede work measurement
Scheduling A Work / Task WAGE PLANNINGJOB DESIGN Work METHOD STUDY Schedule WORK MEASUREMENT
PRINCIPLES OF MOTION ECONOMYAlso called “the characteristicsof easy movement” (BritishStandards)Developed by Frank GilbrethAs a young building contractor,he found ways to makebricklaying faster and efficientprocess.He find ways to increase outputand make jobs easier.
Principles concerning the economy of movements which have been developed from direct experimentation Form a good basis for the development of improved methods at the workplace. Classified as three main types:A.Use of human body,B.Arrangement of the workplace,C.Design of tools and equipment
USE OF HUMAN BODY:The two hands should begin andcomplete their movements at the sametime.The two hands should not be idle at thesame time except during periods of rest.Motion of arms - symmetrical and inopposite directionsHand and body motion - lowestclassification
USE OF HUMAN BODY:Continuous curved movements areto be preferred than straight-linemotionRhythm is essential to the smoothand automatic performance of arepetitive operation.Work should be arranged so thateye movements are confined to acomfortable area, without theneed for frequent changes offocus.
ARRANGEMENT OF WORK PLACE:Definite and fixed station for all toolsand materialsTools and materials should be pre-positioned to reduce searching. Gravityfeed, bins and containers should beused wherever possibleMaterials and tools should be arrangedto permit the best sequence of motions.The color of workplace should contrastwith that of the work and thus reduceeye fatigue.
ARRANGEMENT OF WORK PLACE:“Drop deliveries” or ejectors should beused whereverProvision should be made for adequatelighting, and a chair of the type andheight to permit good posture shouldbe provided.The height of the workplace and seatshould be arranged to allow alternativestanding and sitting.
DESIGNS OF TOOLS AND EQUIPMENTS: Two or more tools should be combined wherever possible. Where each finger performs specific movements, the load should be distributed Handles such as those on cranks and large screwdrivers should be designed Levers, crossbars and hand-wheels should be so placed that the operator can use them with the least change in body position and the greatest “mechanical advantage.”
DEFINITION According to British Standard Institution “Motion Study is the systematic recording and critical examination of existing and proposed ways for developing more effective and easier methods to reduce cost.”
STEPS IN MOTION STUDYSELECT RECORD EXAMINE DEVELOP INSTALL
SELECTION OF JOBS Economic Aspects Technical Aspects Human AspectsEconomic Basis of Job Selection Bottleneck of Operation Activity involves excessive labors Operation producing larger amount of scraps Backtracking of materials.Human Basis of Job Selection Workers complaining about unnecessary and tiring of work More frequency of accidents Inconsistent earning
RECORDING CHARTS DIAGRAMS AND MODELS PHOTOGRAPHIC AID
CHARTS Outline process char ts Flow process char ts Multiple activity char ts Two handed process char ts Simultaneous motion cycle
OUTLINE PROCESS CHARTPrincipal operationsand inspections ofthe processes arediagrammaticallyrepresented in thechart
FLOW PROCESS CHART OPERATION INSPECTION TRANSPORT DELAY STORAGE
MULTIPLE ACTIVITY CHARTSimultaneous / interrelated activities of operators and machinesare described on a common time scale.
TWO HANDED PROCESS CHARTActivities of a worker’s hands are recorded intheir relationship to one another is called“Two handed process charts”Advantages:1. Enables the work study person to gain intimate knowledgeabout the details of the job.2. Enables to study each element of the job by itself and in itsrelation to other elements.3.From this study, ideas for improvements are developed.4. The chart can be applied to assembly, machining and evenclerical jobs
SIMO CHART It is a graphic representation of the sequence of the therbligs or group of therbligs performed by body members of operator. It is drawn on a common time scale. In other words, it is a two-hand process chart drawn in terms of therbligs and with a time scale.
DIAGRAMS AND MODELS Flow diagram String diagram Two and three dimensional diagrams, models and templates
PHOTOGRAPHIC AIDS CYCLOGRAPH To make a cycle graph, a small electric bulb is attached to the finger, hand, or any other part of the body whose motion is to be recorded. By using still Photography, the path of light of bulb (in other words, that of the body member) is photographed by keeping the working area relatively less illuminated. The resulting picture (cycle graph) shows a permanent record of the motion pattern employed in the form of a closed loop of white continuous line with the working area in the background.
CHRONO CYCLOGRAPH The Chrono cycle graph is similar to the cycle graph, but the power supply to the bulb is interrupted regularly by using an electric circuit. The bulb is thus made to flash. The procedure for taking photograph remains the same. The resulting picture instead of showing continuous line of motion pattern, shows short dashes of line spaced in proportion to the speed of the body member photographed. Wide spacing would represent fast moves while close spacing would represent slow moves. The jumbling of dots at one point would indicate fumbling or hesitation of the body member. A chrono cycle graph can thus be used to study the motion pattern
EXAMININGo Examine facts without any biaso Avoid hasty judgments / conclusionso Do not consider new method until all undesirable features of existing method have been exposedFunction: If unnecessary, eliminate the activity altogether Combine activities, if feasible Change sequence of activities so that work or delay is reduced Simplify the activity to reduce the work content or the time consumed by examinationTOOLS Questions: Primary (What is to be done?) Secondary (What else can be done?) Alternatives (What should be done?)
DEVELOPING Draw a framework of an improved method by arranging in sequence the essential ‘do’ operations. Fill up ancillary work in a way as efficient as possible Try out mock ups of the new method (make dry runs) Draw up improved method in process chart form
INSTALLING It involves two phases. They are Preparation of plan like who will plan? how to plan? Arrangement for working according to plan like Training, Advise MAINTAINING It requires to make allowances for changes. Result of suggestion schemes and Minor innovations introduced by workers / supervisors were added to the core findings in subsequent time
UTILITY1. Recording the times and rates of working for the elements of a specified job carried out under specified conditions.2. Analyzing the data so as to obtain the time necessary for carrying out the job at a defined level of performance.
STEPS IN TIME STUDY 1. Select the Job for Study2. Break the operation into small elements orTherbligs depending upon the nature of the joband the purpose of the study 3. Determine number of cycles to be timed 4. Observe and record time at each therbligs 5. Calculate Normal Time 6. Calculate performance Rating 7. Determine Allowances 8. Derive Standard Time
Selecting a job for time study The job in question is a new one If a change in material or method of working has been made then a new time standard is required. A complaint has been received about the time standard for an operation. A particular operation appears to be “bottleneck” Standard times are required prior to the introduction of an incentive scheme.
Qualified worker One who is accepted as having the necessary physical attributes, who possesses the required intelligence, education, and has acquired the necessary skill and knowledge to carry out the work in hand to satisfactory standard of safety, quantity and quality. A representative worker is one whose skill and performance is the average of the group under consideration. She/He may not necessarily be a qualified worker.
Breaking The Job Into Elements The job in question is a new one If a change in material or method of working has been made then a new time standard is required. A complaint has been received about the time standard for an operation. A particular operation appears to be “bottleneck” Standard times are required prior to the introduction of an incentive scheme.
Reasons for breakdown of job To ensure that productive work (or effective time) is separated from unproductive activity (or ineffective time). To permit the rate of working to be assessed more accurately than would be possible if the assessment were made over a complete cycle. To enable elements involving high fatigue to be isolated and to make the allocation of fatigue allowances more accurate.
ELEMENTS• A repetitive element is an element which occurs in every work cycle of the job.• An occasional element does not occur in each work cycle of the job, but which may occur at regular or irregular intervals. e.g. machine setting.• For a constant element, the basic time remains constant whenever it is performed. e.g. switch the machine on.• A variable element is an element for which the basic time varies in relation to some characteristics of the product, equipment or process, e.g. dimensions, weight, quality etc. e.g. push trolley of parts to next shop.
• A manual element is an element performed by a worker.• A machine element is automatically performed by a power- driven machine (or process).• A governing element occupies a longer time than any of the other elements which are being performed concurrently. e.g. boil kettle of water, while setting out teapot and cups.• A foreign element is observed during a study which, after analysis, is not found to be necessary part of the job. e.g. degreasing a part that has still to be machined further.
Recording Time For ActivitiesCumulative timing• The watch runs continuously throughout the study.• At the end of each element the watch reading is recorded.• The individual element times are obtained by subsequent subtractions.• The purpose of this procedure is to ensure that all the time during which the job is observed is recorded in the study.• Typically, most work-study persons attain fair degree of accuracy quickly when using the cumulative method.
Flyback time• The hands of the stopwatch is returned to zero at the end of each element and are allowed to start immediately, the time for each element being obtained directly.• In a comparative study of two methods carried out the Purdue University, the average error in reading the watch using the cumulative method was +0.000097 min per reading and using the flyback method was -0.00082 min per reading.
Differential timingThe elements are timed in groups, first including and then excluding each small element.• Typically used for short element short cycle work, where elements are so short that there is not enough time for study-person to look at the watch and make a recording.• In this process, either the cumulative or the flyback method of watch manipulation may be used.
Rating• Rating is the assessment of the worker’s rate of working relative to the observer’s concept of the rate corresponding to the standard pace.• It is a comparison of rate of working observed by the work-study person with a picture of some standard level.• The standard level is the average rate at which qualified workers will naturally work at a job, when using the correct method and when motivated to apply themselves to their work.• This rate of working is called standard rating.
• If the standard pace is maintained and the appropriate relaxation is taken, a worker will achieve standard performance over the working day.• Standard performance is the rate of output which qualified workers will naturally achieve without over-exertion as an average over the working shift provided they know and adhere to the specified method and, they are motivated to apply themselves to their work.• This performance is denoted as 100 on the standard rating and performance scales.
• The purpose of rating is to determine from the time actually taken by the operator being observed the standard time which can be maintained by the average qualified worker and which can be used as a realistic basis for planning, and incentive schemes.• Time study is concerned with speed at which operator carries out the work, in relation to the concept of normal speed.• “Speed” here means the effective speed of operation.
Factors affecting rate of working1. Variation in the quality or other characteristics of the material used, although they be within the prescribed tolerance limit.2. Changes in the operating efficiency of tools or equipment within their normal life.3. Minor and unavoidable changes in methods or conditions of operations.4. Variation in the mental attention for the performance of elements.5. Changes in the climatic and other conditions.
Rating factor• The figure 100 represents standard performance.• If the operator is apparently performing with less effective speed, than the assigned factor is less than 100.• If, on the other hand, the effective rate of working is above standard, the operator gets a factor above hundred.• Essential idea being: Observed time x Rating = Constant
• This constant is known as the basic time: Rating Observed time x = Basic Time Standard Rating• So, depending on the rating assigned for the operator, the basic time can either be less than or greater than the observed time.
Selected timeConstant element• A very high or short observed time for a given element of job should be treated with caution.• An exceptionally high observed time could be due to incorrect recording, but most common reason is material or environment variation.• In such as case, it should be checked whether such a variation is frequent or rare.• Excess observed time because of rarely occurring events is typically not included as a representative.
Variable element• In general more observations will be necessary of a variable element than of a constant element before reliable representative basic times can be established.• The analysis of factors affecting the time to complete the element should be closely studied.• Some relationship should be established between the observed time and the variable factors.• Multiple factors could be affecting the observed time variation and establishing relationships amongst multiple factors is difficult.
Work content• The work content of a job or operation is defined as: basic time+ relaxation allowance+ any allowance for additional work (e.g. the part of relaxation allowance that is work related).• Standard time is the total time in which a job should be completed at standard performance – i.e. work content, contingency allowance for delay, unoccupied time and interference allowance.• Allowance for unoccupied time and interference may not be frequently included in the standard time calculations; however, the relaxation allowance is.
Standard time constituents• A contingency allowance is a small allowance of time which may be included in a standard time to meet legitimate and expected items of work or delays, precise measurement of which is uneconomical because of their infrequent or irregular occurrence.• Contingency allowance for work could include fatigue allowance; whereas the allowance for delay could be dependent on the workers.• Typically contingency allowances are very small and are generally expressed as percentage of the total repetitive minutes of the job.• 5%
• Relaxation allowance is an addition to the basic time intended to provide the worker with the opportunity to recover from the physiological and psychological effects of carrying out specified work under specified conditions and to allow attention to personal needs.• The amount of the allowance will depend on the nature of the job.• One of the major additions to the basic time.• Industrial fatigue allowance, in turn, forms a major portion of the relaxation allowance.• Relaxation allowances are also given as percentages of the basic times.• 12-20%
Other allowances Start-up / shut-down allowance Cleaning allowance Tooling allowance Set-up / change-over allowance Reject / excess production allowance Learning / training allowance Policy allowance is an increment, other than the bonus increment, applied to standard time to provide a satisfactory level of earning for certain level of performances under exceptional conditions.
Standard time Calculation• Now, we can add all the constituents to arrive at the standard time for a job.Standard time = observed time + rating factor + relaxation allowance + work related contingency allowance + delay related contingency allowance.