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Case study: CRS Gate Queue Reduction

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This is a case study on system improvement of material receiving operation with time-non-homogeneous queue.

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Case study: CRS Gate Queue Reduction

  1. 1. Improvement of Service Quality of Material Receiving System Soumyanath Chatterjee & Ashit Ghosh Productivity Services Division Tata Engineering & Locomotive Co. Ltd. Jamshedpur - 831 010
  2. 2. ABSTRACT : This paper is a Case study on how principles of Operations Research has been applied to improve the Quality of Service in Material receiving Area. In TELCO Jamshedpur, all Trucks arriving with material comes to CRS(Gate). At CRS(Gate) these trucks are checked for existance of proper purchase Order and Delivery Point through an On-line inventory control system. Then the trucks are given a "Priliminary Goods Inward Note ". After this, laden weight of the trucks are taken and they are allowed to go to store for unloading. After unloading material, unladen weight of the truck is taken and it is allowed to go out. This whole process used to take several hours to complete, causing lot of inconvenience to the transporter. As around two hundred trucks comes in the Works every day for delivering material the Management felt the need to improve quality of service in this area. A study was conducted to find out the extent of the problem and the reason of delay. The study brought out a small lacuna in the queuing system at the very beginning of the process. This was getting magnified by the physical system and resulting in hours of delay at the end. The system was suitably redesigned to eleminate those problems. A simulation study was carried out to validate some of the assumptions made to design the new system. BACKGROUND: TELCO Jamshedpur manufactures Commercial vehicle Chasis and Excavator. It has over fifteen stores spread over an area of six square kilometers. In most of the places stores are situated adjacent to production shops. This makes the shops vulnerable to pilferage. A central checking and control agency, CRS(Gate) was set up to check whether material being brought in belongs to TELCO and the delivery point of these material. In addition this agency also collects Excise Gate Pass for taking MODVAT credit. All trucks that enter in the works has to report to CRS(Gate) . At the start of the study on an average it used to take 2.5 Hrs to inward a truck at CRS(Gate) and 22.8% of the trucks were held up for more than 4 hours. In totality a truck used to spend 20 Hrs. inside works on an average. This delay causes loss of revenew to the transporter. Accumulation of large number of trucks inside works also causes problems for movement inside works. Top management felt the need to improve quality of service for the material receiving.
  3. 3. OLD SYSTEM: - The system of operation at the begining of study was as follows: 1. Transporter's men deposit challan and other document at the CRS(Gate) counter. 2. At CRS(Gate) the documents are fed in computer and Priliminary GIN are printed. A Movement Control Form with details of store location, item and quantity are manually 3. prepared for monitoring movement of truck. These are sent to security office. 4. After receiving documents trucks are called by security. 5. Security officer checks incoming material on a sampling plan 6. After checking, laden weight of trucks are taken and a weighment card is given to the transporter. 7. Trucks then unload material in the store. 8. After unloading material transporter hands over road permit and PGIN to stores Incharge and obtain signature on MCF. 9. After unloading material, the truck has to get unladen weighment done and then it goes out after handing over a copy of MCF to security person. DATA COLLECTION AND ANALYSIS: In order to analyse causes of delay a sample of thirty seven trucks were taken and time spend between various points were noted. Upon analysis percentage of delay was found to be: - LOCATION %GE DELAY At CRS(GATE) office 14.3 Queue between CRS & Security 6.1 Security checking 0.3 Weighment, travelling to first store 30.9 Movement between store 28.8 Unloading material in store 10.5 Exit weighment & checking 9.1 As weighment was found to consume the maximum time this place was observed physically. Physical observation brought out the fact that at weighment point trucks comes irregularly. As a result of this a long queue builds up at weigh bridge. Moreover trucks after unloading come for unladen weighment. On further exploration it was found that documents are sent from CRS(Gate) office in bundles. As a result calling of trucks and arrival of trucks at weigh bridge was irregular. This analysis made it clear, CRS(Gate) was the controling factor in the whole process. Further work was done in CRS(Gate) office system. OLD SYSTEM OF CRS(GATE) : At the time of study the transporters used to deposit all papers at a counter of CRS(Gate) . The recieving clerk used to a give Seniority number after checking all documents and making entries regarding truck number, arrival time, number of boxes etc. After this, the clerk used to send the documents to terminal room for feeding into computer. At terminal room, terminal operator
  4. 4. would fill purchase order number and other details to print Priliminary Goods Inward note. In case there was some error in Purchase Order number then the terminal operator will correct it before printing PGIN. For non computerised material PGIN were made by typing and updated on computer at a later date. Printed PGIN were passed on to supervisor for checking and signature. After signature the bunch of PGIN were passed on to security for calling trucks. Only Excise Gate pass used to be retained at CRS(Gate) office for further processing. Shift-wise manning of the office was: SHIFT TIME %GE STAFF 6:00 AM - 2:00 PM 12 % 7:00 AM - 4:00 PM 64 % 8:00 AM - 5:00 PM 24 % Against this arrival and release pattern of the trucks were as follows :- TIME INTERVAL ARRIVAL %GE RELEASE %GE (CUMM) (CUMM) 6:00 - 7:00 10.1 2.5 7:00 - 8:00 22.4 5.0 8:00 - 9:00 40.2 16.0 9:00 - 10:00 57.0 30.0 10:00 - 11:00 71.0 45.0 11:00 - 12:00 80.5 50.0 12:00 - 1:00 85.8 55.0 1:00 - 2:00 94.0 70.0 2:00 - 3:00 98.5 80.0 3:00 - 4:00 99.7 95.0 4:00 - 5:00 100.0 100.0 Graph of arrival and release of trucks are given in Figure 2. ANALYSIS OF THE SYSTEM: It may be observed from the graph of Fig. 1. that arrival rate and service rates do not match. Moreover these rates changes with time. At 6:00 AM when the office starts approximately ten percent of the vehicles comes within one hour. Whereas only 2.5% of the vehicles are cleared. This difference generate a queue right from the starting of the day.
  5. 5. As little work has been done in the field of "time-non-homogenious queue" graphical analysis was done at first to understand the mechanism later on a simulation study was carried out. Graphically, total time spent by all trucks is the area enclosed by the arrival and release curve in Fig. 2. for FCFS queue. From the graph it is clear that slow rate of release between 6:00 AM to 8:00AM and 11:00 AM to 1:00 PM attributes for large increase of area enclosed by the curves. This area can be reduced by 76.4% by maintaing steady release rate of 16 trucks per hour which is already achieved by CRS(GATE). As a result the waiting time will also be reduced by 76.4%. This proposed curve is shown in Fig 3. In order to achieve this change of service rate Shift wise manning was changed as follows :- SHIFT TIME %GE STAFF 6:00 AM - 2:00 PM 56 % 7:00 AM - 4:00 PM 16 % 8:00 AM - 5:00 PM 28 % During study it was also found that alongwith manual documents some erroneous documents also comes. Correcting these erroneous documents takes lot of time. It is a well known fact that mixed queue takes more waiting time than queue with seperate channel for large and small service time. However to validitate result of time-homogenious queue on time-non- homogenious queue a simulation study was carried out. SIMULATION: The simulation was carried out to test the hypothesis - "In a multiple server situation seggregating queue for slow processing and fast processing will result in reduced waiting time" holds good for the time-non-homogenious queue prevalent at CRS(GATE) . Following assumptions are taken for simulation: - 1. Arrival rate of trucks follows Poission distribution where mean arrival rate is a function of time. 2. Service rate is time-homogenious and follows Gauessian distribution. 3. Ten percent of trucks has erroneous documents which takes ten minutes to process and it also follows Gauessian distribution. 4. There are seven server.
  6. 6. Two hypothesis were tested. These are as follows: - HYPOTHESIS - I In the first case both normal and erroneous documents were processed in the same queue. Allocation of the trucks to the server was as follows: - 1. When a truck arrives it is first allocated to first server. If the first server is busy then it is allocated to second and so on. 2. When all server are busy the truck waits in a queue and it is allocated to a server when it becoms free. HYPOTHESIS - II In second case normal and erroneous documents are processed in different queue. On the basis of equal utilisation six server are ear marked for normal document and one server is ear marked for erroneous documents. In order to take care of excegency there is a provision of overlapping amongst these. Allocation scheme to server is as follows :- a) When a truck arrives with normal document then it is allocated to first server. If first server is busy then it is allocated to second server and so on. b) For erroneous document allocation is first made to seventh server then to sixth and so on. c) In case all servers are busy the document is put on a queue. There are seperate queue for normal and erroneous documents. d) When a server becomes free documents are allocated from the queue. For server one to five first preference is given from normal queue if normal queue is empty documents are alloted from erroneous queue. Similarly for seventh preference is given for erroneous documents. When queue for erroneous is empty then normal documents are allocated to seventh server. With this logic the simulation is carried out for a period of thirty days. Average waiting time for Case-I is 1.58 time units and for Case-II is 1.50 time units. Distribution of waiting time for the two is shown in Figure-4. which shows superiority of Case- II over Case-I. Flow-chart of the Simulation program is given in Figure-4(a). RECOMMENDATION: 1. Shift-wise manning at CRS(GATE) office should be changed to - SHIFT TIME %GE STAFF 6:00 AM - 2:00 PM 56 % 7:00 AM - 4:00 PM 16 %
  7. 7. 8:00 AM - 5:00 PM 28 % 2. All error transaction should be processed separately. Two terminal may be ear marked for this. Document Allocation scheme to terminal will be as follows: - a) When a truck arrives with normal document then it is allocated to first server. If first server is busy then it is allocated to second server and so on. b) For erroneous document allocation is first made to seventh server. c) In case all servers are busy the document is put on a queue. There are seperate queue for normal and erroneous documents. d) When a server becomes free documents are allocated from the queue. For server one to six first preference is given from normal queue if normal queue is empty documents are alloted from erroneous queue. Similarly for seventh server preference is given for erroneous documents. When queue for erroneous is empty then normal documents are allocated to seventh server. 3. Administrative control should be excercised to reduce formation of bunches as far as possible. ACTUAL ACHIEVEMENT: This study result was implemented in the year 1989-90. In the table below delay distribution of trucks at CRS(Gate) is given for period before and after the study recommendations were implemented. DELAY IN UNITS BEFORE STUDY AFTER STUDY (1990) OF TIME (1989) 0 - 1 9.3 % 61.5 % 1 - 2 30.2 % 24.6 % 2 - 3 18.6 % 7.7 % 3 - 4 2.3 % 1.5 % 4 - 5 7.0 % 0.0 % 5 - 6 9.3 % 3.1 % 6 and more 23.3 % 1.5 % TOTAL 100.0 % 100.0 % AVERAGE 3.26 1.18
  8. 8. Figure - 5 clearly shows the reduction in average waiting time and the shift of distribution pattern. However, it will be unwise to attribute the big improvement solely on th Operations Research study. The actual improvement is a combined effect of greater motivation of the staff of CRS(Gate), awareness of the total system and the implication of delays and recommend changes. ACKNOWLEDGEMENT: The authors wish to thank the top management of TELCO for the continued support for improving the service quality of material recieving function. Mr.M K Sengupta, AGM(Central Materials) and Mr.B N Sahay, Asst. Manager CRS(Gate) and the staff of CRS(Gate) for support in providing data and effective implementation of the recommendations. Without their support this study would have been impossible. BIBLIOGRAPHY 1. Gordon Geoffrey; " System Simulation " [1980]; Prentice-Hall (India) 2. Joseph J Moder and Salah E Elmaghraby; "Handbook of Operations Research - Foundations and Fundamentals" [1978]; Von Nostrand Reinhold Co. 3. Wagner H. M.; " Principles of Operations Research "[1969]; Prentice-Hall (India).
  9. 9. ANNEXURE - I AREA ENCLOSED BY ARRIVAL AND RELEASE CURVE ========================================== EXISTING CURVE :- TIME ARRIVAL RELEASE HEIGHT OF % % CURVE 06:00 - - 0% 07:00 10.1 2.5 7.6 % 08:00 22.4 5.0 17.4 % 09:00 40.2 16.0 24.2 % 10:00 57.0 30.0 27.0 % 11:00 71.0 45.0 26.0 % 12:00 80.5 50.0 30.5 % 13:00 85.8 55.0 30.8 % 14:00 94.0 70.0 24.0 % 15:00 98.5 80.0 18.5 % 16:00 99.7 95.0 4.7 % 17:00 100.0 100.0 0% Area by Trapizoidal rule 210.7 PROPOSED CURVE :- TIME ARRIVAL RELEASE HEIGHT OF % % CURVE 06:00 - - 0% 07:00 10.1 10.1 0% 08:00 22.4 21.9 0.5 % 09:00 40.2 33.7 6.5 % 10:00 57.0 45.5 11.5 % 11:00 71.0 57.3 13.7 % 12:00 80.5 69.1 11.4 % 13:00 85.8 80.9 4.9 % 14:00 94.0 92.7 1.3 % 15:00 98.5 98.5 0% 16:00 99.7 99.7 0% 17:00 100.0 100.0 0%
  10. 10. Area by Trapizoidal rule 49.8 Reduction in area = (210.7 - 49.8) ö 210.7 x 100 = 76.4 %

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