Advanced Materials Research Online: 2014-02-06 ISSN: 1662-8985, Vols. 889-890, pp 1227-1230 doi:10.4028/www.scientific.net/amr.889-890.1227 2014 Trans Tech Publications, Switzerland Analysis and simulation of one worker with multi-machine mode LIU Jinfei 1, a, CHEN Ming 2, b, QI Xianglong 3, c 1 Postdoctoral Scientific Research Flow Stands of Control Science and Engineering of school of Electronics and Information, Tongji Univ., Shanghai, 201804, China; 2,3 Sino-German College of Applied Sciences, Tongji Univ., Shanghai, 201804, China; a jinfeil@tongji.edu.cn, b chen.ming@tongji.edu.cn, c qxl071858@163.com Keywords: Operator-machine work; One operator with multi-machine; Process simulate&verify Abstract. One operator with multi-machine operating mode is an important part of the analysis of operator-machine work, because it takes it into consideration that the utilization of both machines and operators. It is necessary to study its classification, application and analysis process, besides, a mathematical model is constructed to analyze the differences in efficiency for operators and machines, which are caused by the difference of machine assignment amount. Finally, The process simulation and verification is based on the platform of Plant simulation. Introduction The analysis of operator-machine work is one of techniques for mechanical work research, and it helps to find a reasonable operation method to make the coperation between operators and machines more coordinated by field observation, the records and analysis of operators and machines work in the same time, which contributes to allow full play of the efficiency of operators and machines. The main purposes of analysis of operator-machine work are as follows: 1. Find the reason that affects the operating efficiency. It will easily find the reason if there exists some non-harmonious interaction between operators and machines. 2. Determine the number of machines that one operator can handle simultaneously, and make full use of operators free energy. 3. Help to judge which is better to improve the efficiency, operator or machine. 4. Ensure operators safety. Because it will threat the safety of operators when the running speed of the machine is very fast and the utilization of the equipment is improved too much. 5. Transform equipments, achieve automation and improve the layout of the operation area. Operator-machine work can be divided into two categories: 1. Internal operation: Machines must be stopped before the operation; 2. External operation: Operations can be performed without the stop of machines. Basic steps flowchart is as below Fig.1. Fig 1. Flowchart of operator-machine analysis All rights reserved. No part of contents of this paper may be reproduced or transmitted in any form or by any means without the written permission of Trans Tech Publications, www.ttp.net. (ID: 130.203.136.75, Pennsylvania State University, University Park, USA-17/05/16,21:41:44)
1228 Engineering Solutions for Manufacturing Processes IV Mathematical model of one operator with multi-machine This operating model refers that one operator can handle several equipments simultaneously in order to save time when it runs itself to operate other devices, and it will help to shorten waiting time, improve operation enrichment degree and achieve the goal of reducing operators. It has been applied to machining and the production line of automobile gearbox steel workpiece and the camshaft of engine. Assuming that the free time of operators is rich, and the task is to utilize the free energy, so that it needs the operator to handle several machines. The parameters to be used are defined as follows: α---- Parallel operating time. (eg: The machine loading and unloading operation) β----operating time independently for workers. (eg: walking, testing, packing) t---- Operating time independently for machines. (eg: machining) p----the number of machines actually assigned to one operator. q----the number of machines ideally assigned to one operator. T c ----Repeated cycle time. T o ----Free time of an operator in one cycle time. I p ---- Free time of a machine in one cycle time. 2.1 The analysis of free energy of the operator Igonring the free time, the cycle time is (α+t)minutes, and the operator need (α+β)minutes to finish the work in one cycle. Therefore, the ideal number of machines assigned to the operator is q= ( α+ t)/( α+ β). Tc = α+ t If p q, then I p = 0 T o p( α+ β) Tc = p( α + β) If p>q, then I p ( α + t) To = 0 Here is an example: There is a worker operating an automatic machine and he needs to load and unload the workpiece, and both of loading and unloading take 1 minute. The processing time of automatic machine is 5 minutes. The whole follow-up work including dimension inspection and product packing takes 0.5 minute. His walking time is 0.5 minute between each two machines if he has to operate several machines. Obviously,α =1+1=2minutes, β =0.5+0.5=1 minute and t=5 minutes, then q= ( α+ t)/( α+ β) 2.33. Because the machine can not be counted by a decimal number, p must be an integer. If p=2(p q), thent c = α + t =7minutes and To p( α + β) =7-2(2+1)=1 minute. So the actual utilization for the machine is 5/7 71.5% and for the operator it is 6/7 85.7%. This allocation approach is consistent with the principles of people-centered basically. If p=3(p>q), then Tc = p( α + β) =9 minutes and Ip ( α + t) =9-5=4 minutes, and in this situation there will be no free time for the operator and the actual utilization of each machine is 5/9 55.6%. At this point,operating units must be carefully designed in order that there shall be enough time for the operator to deal with materials, machine maintenance and walk. 2.2 The analysis of economical efficiency C o is set for the hourly labor cost of the operator, C p is set for the hourly cost of the machine and (p) is set for the cost of each machine that is operated by one worker. So there are p machines and one operator and the total cost is C o +p C p. Assume that one machine can just produce one product in a cycly time and the cost of this product is : (1)
Advanced Materials Research Vols. 889-890 1229 ( p) = + p )( α t) p p )( α β) +, p q + +, p> q If p q, then p should be as big as possible to make (p) tend to be the minimum, while if p>q, then on the contrary, p should be as small as possible. In case that q is not an interger, Q (Q is the interger part of q)or(q+1)shall be the answer that makes (p) achieve the minimum. Set Φ as the ratio of (Q) and (Q+1), then the formula above can be transformed as follows: + Q )( α+ t) + + 1 ( α+ β) ( Q) Φ= = ( Q+ 1) Q Co ( Q ) (2) (3) Set ε=c o /C p, and it can be simplified: q ε + Q Φ = (4) Q ε + Q + 1 If Φ<1, that means (Q) < (Q+1), and the operator should handle Q machines; If Φ>1, that means (Q) > (Q+1) and the operator should handle (Q+1)machines; If Φ=1, either is OK. The simulation of the system with one operator and two machines The work can be described as that one operator handle machine tool and he must finish clamping and alignment of the roughcast before the processing, and during the period of processing, he can do some external operations, such as dimension measurement, inspection and deburring, and then he should stop the machine and upload the product when the processing is completed. In Plant simulation, there are four kinds of logistics objects that are able to apply for resources: SingleProc, ParallelProc, Assembly and DismantleStation. And Worker, WorkerPool, Exporter can work as resource objects to provide services. As to Worker, it can provide different kinds of services but can only serve one object at the same moment. WorkerPool is a collection of Workers in this production system. It is necessary to give a good coordination and arrangement when there are several applications, and to arrange the order of execution. Borker is the object that can manage it. In this case, the operator needs to imitate clamping and handling, so it is important to define the traverse path and the operation related for the operator. The length of time of providing service must be defined by other methods because of the lack of operating time definition for Worker. Besides, the clamping operation usually includes picking up materials, and the Worker should walk to the place where the roughcast exists and then get back. The consumed time is determined by the round-trip distance and the speed of the operator. Take the data above as an example to simulate a system with one operator and two machines in Plant simulation. In order to avoid the situation that the Worker comes out from the WorkerPool when the processing is finished and the machine applies for carry, after clamping the roughcast in one machine(m1), the operator must wait for the command in front of another machine(m2).if not, the walking time of the operator from WorkerPool to the machine will be included in the working time, which has a bad influence on the result. The model is shown as below Fig.2.
1230 Engineering Solutions for Manufacturing Processes IV Fig.2 The simulation model Based on the consideration above, virtual machines(tm1, TM11) and virtual workplaces(tw1, TW11) are set in the model. When the operator finish his virtual job in TM11, he won t go back to WorkerPool but will stay at TW11 and wait for some other applications. The simulation time is set to 24h and start simulating the model. When it stops, open the statistics Tabs of Machine_1 and Machine_2, and it shows that the utilization of machines is the same as that we got from the theoretical calculation, 71.46%.The statistics Tab is shown in Fig.3. Fig. 3 The utilization of Machine_1 in the model Conclusions In this paper we analyze the production model of one operator with multi-machine in the aspects of free energy of the operator and the economical efficiency by setting up mathematical models. to propose a quantitative distribution plan. Then we build a simulation model for the system with one operator and two machines, in which we successfully solve the distortion problem by adding virtual workplaces. The same result shows that we have achieved the purpose of the simulation. References [1] (USA) Tompkins, John A, White, et al. Facilities Planning [M]. Beijing: Machinery Industry Press, 2007(9). Yin Junmin, Yuan Haibo, et al. translated. [2] Liu Liwen. A queueing model of a production system with one operator and two machines, Journal of system engineering, Vol.10(1995), p.21-30. [3] Yang Jun. Dynamic allocation model of One-man-multi-machine system and its solution, Chinese journal of management science, Vol.4(1996), p.36-41. [4] Wang Guoxin, Ning Ruxin, Wang Aimin. Production optimal scheduling technology based on simulation, Vol.13(2007), p.1419-1427. [5] Ma Hanwu. The planning and designing of logistics and facilities [M]. Beijing: Higher Education Press, 2005.
Engineering Solutions for Manufacturing Processes IV 10.4028/www.scientific.net/AMR.889-890 Analysis and Simulation of One Worker with Multi-Machine Mode 10.4028/www.scientific.net/AMR.889-890.1227