RFID Based Management of Manufacturing Line

RFID Based Management of Manufacturing Line Bin Huang Abstract: In this paper, an in-process tracking system is proposed to track the status of semi-finished products and coordinate the manufacturing forces. Since its reliability and flexibility, RFID technique has shown big advantages than the conventional Bar-code systems, especially to automate of floor shop management. Based on this availability, RFID solutions are ideal for manufacturers who build several products on a single production line, or manufacture complex or customized products. This report propose a novel form of RFID based manufacturing line with distributed stations 1. Introduction Radio frequency (RF) technology is commonly used to transmit and receive information without wires. A wide variety of electronic devices such as television, radio, and wireless telephone use radio frequency technology to transmit or receive information. It is predicted that in retail alone, spending on RFID will swell to $1.3 billion a year by 2008 ( http://www.brooks.com/pages/210_factoryworks.cfm ). The optical nature of barcode requires labels to be seen by lasers. That line-of-sight between label and reader is often difficult, impractical, or even impossible to achieve in industrial environments. In order to function properly, a barcode reader must have clean, clear optics, the label must be clean and free of abrasion, and the reader and label must be properly oriented with respect to each other. RFID technology enables tag reading from a greater distance, even in harsh environments. In addition, the information imprinted on a barcode is fixed and cannot be changed. RFID tags, on the other hand, have electronic memory similar to what is in your computer or digital camera to store information about the inventory or equipment. This information can be dynamically updated responsive to changes in supply demand and shop-floor requirements.. The advantages of RFID vs. barcode technology include: No line of sight requirement. The tag can stand a harsh environment. Long read range Portable database Multiple tag read/write. Tracking people, items, and equipment in realtime. 1.1. Advancement of RFID The core of the system is built around the RFID tags or transponders, RFID readers, host computer, and Windows based software. RFID tags contain micro electronic circuits that store product information. The tags transmit this information to a remote RFID reader The RFID tag is attached or placed inside of the equipment or inventory. Each tag sends its data periodically. The RFID reader will cross-reference the tag s data within its self-contained database. After the reader receives new data, it will send the data to the host. The readers and the host communicate through a secure wireless link. 2

Recent developments in extremely miniaturized integrated-circuit (IC) technology have allowed for the development of miniature and intelligent RFID tags. Recent breakthroughs in very low power IC technology have allowed us to develop small low power active tags. While passive tags operate by generating energy from the field without any battery, these tags can be used only over a short read range. In the past RFID active tags have been large and have had a short life due to large demand for power. Low power active tags that use the latest technologies have a long read range combined with the long life and reliability of passive tags. Whether we are concerned with tracking inventory in a warehouse or maintaining a fleet of vehicles, there is a clear need for a fully automated data capture and analysis system that will help to keep track of the valuable assets and equipment. RFID technologies provide unique solutions to difficult logistical tracking of inventory or equipment, particularly in applications where optically based systems fail and when read/write capabilities are required. The technology is stable, and evolving, with open architectures becoming increasingly available. Recent RFID systems have multi-tag capability. This means an RFID system can read several tags in the field at the same time. The read range between the tag and the reader is 100 to 140 feet. A single reader can cover a total area of up to 30,000 square feet. While passive RFID has a few of meters. The RFID reader s wireless connection to the host computer has a range of approximately 500 to 1000 feet. 1.2. Existing RFID deployment for manufacturing Manufacturing is not just machine control but also to obtain, store and display information, distributing it to the users who need it in a way that they can use it and in a timely manner. It may even need to identify and track individual components as they move through the production process. Finally, the factory must to document all these processes and equipments, keeping this documentation up-to-date and available for use. A well-designed manufacturing system can do all of these things efficiently, allowing the manager to monitor and control an entire plant to make the best use of the expensive resources with maximum benefit. According to Jonathan [6], The automotive industry has long used RFID in closed-loop systems with lowfrequency (125 khz) tags and readers. Because of the growing interest in deploying passive UHF (866 MHz to 960 MHz) RFID in the supply chain driving adoption and lower equipment prices for that technology, however, RFID systems developer Advanced Research Co. believes there is also a role for UHF RFID in automotive and manufacturing environments. The OpenCrib application developed by them supports a check-in/check-out station comprised of either a PC or a handheld computer deployed at the crib and connected to an UHF RFID reader. Reader antennas deployed on shelves can detect when tagged items are placed in the crib s storage area, and an antenna at the doorway to the crib can detect when items leave the crib. To standardize the digital structure and coding semantics for data capture is an inevitable trend in global scope. EPC Network (http://www.epcglobalinc.org, as a set of technologies that enable immediate, automatic identification and sharing of information on items in the supply chain, has gained more and more 3

popularity. EPC is divided into numbers that identify the manufacturer and product type. But, the EPC uses an extra set of digits, a serial number, to identify unique items. The EPC is the key to the information about the product it identifies that exists in the EPCglobal Network. An EPC number contains: 1. Header, which identifies the length, type, structure, version and generation of EPC 2. Manager Number, which identifies the company or company entity 3. Object Class, similar to a stock keeping unit or SKU 4. Serial Number, which is the specific instance of the Object Class being tagged 2. Distributed Manufacturing System Since its reliability and flexibility, RFID technique has shown big advantages than the conventional Barcode systems, especially to automate of floor shop management. Based on this availability, RFID solutions are ideal for manufacturers who build several products on a single production line, or manufacture complex or customized products. In the next sections, I propose a distributed manufacturing system based on RFID deployment, which is capable of tracking and assist the real-time manufacturing processes, especially for the prototype manufacturing. Advances in solid modeling systems offer a better environment for the generation of the NC cutting paths. This development has improved the feasibility of the CAD/CAM integration, however, the complexity of existing CAD models has, on the other hand, introduced the new problems and challenges for the automatic generation of manufacturing plan. For Computer Integrated Manufacturing System (CIMS), the manufacturing implementations generally include: 1), one is the duplication of a physical object from the measured data [1-3], where the object is measured and rebuilt virtually via the interpolation techniques. The geometrical information is partially unavailable due to the discreteness of measured points. Procedure of duplication generally involves three phases: (1) digitizing the physical object with measuring devices, (2) obtaining a shape model of the digitized object in form of geometric model and (3) actualizing the geometric model by means of prototyping or NC machining. The second phase bottlenecks the automation of duplication procedure. It falls into an open area involving many disciplines. 2), another category is to actualize the CAD models, where the geometrical information of the design is interpolated into the controlling commands of CNC machine. Differing from the first case, the graphical data has to be identified as a sequence of features. Each of them will be processed individually with different set-up instructions, tools and cutting methods. The architectures of the integration manufacturing systems usually consist of CAD, CAPP and CAM, as indicated in Fig.1. The designed concept represented in form of graphic model is sent to the manufacturing site through a translation block called CAPP, by which the design information on the CAD site is interpolated to a set of manufacturing instructions, such as the fixture setup, motion command in case of CNC machining, environmental requirement, and heat treatment etc. CAPP bridges CAD and manufacture forces with highly sophisticated intelligence. In the distributed manufacture systems, CAPP is composed of 4

two blocks: One embedded into the CAD modeler, is used to identify the features to be manufactured. For each of these features, a detailed scheme of fabrication is planed based on many considerations (productivity, materials, fabrication method and quality). Eventually the description of CAD model is represented as a sequence of manufacturing instructions. Another one locates in the job floor, where the process plan from the CAD modeler is analyzed and translated into the commands that are executable for the specified machine. Product process from the initial concepts to final product involves design, planning and manufacture activities. CAD, CAPP and CAM, as the independent systems, accommodate each of these phases. However, the links/interface between them is weak. The information from CAD and CAPP systems is not exchangeable with CAM systems. The expertise interactions have to be involved to interpret the information, create machining operations, and prepare geometry for tool path generation or NC part programs according to a process plan generated in CAPP systems. As a matter of fact, although the efforts to integrate CAD/CAM systems has been taken for 20 years, until now a part represented in form of solid model still cannot be directly processed on a CNC machine. The time cost on generating tool path and preparing a NC program is considerably longer than the actual machining time. The emergence of STEP_NC (ISO 14649) addresses this problem [3], but it is still in the initial phase and there are many traditional NC machines taking G-codes as inputs. The transition to STEP_NC will not be an evolution in short-term. 2.1. Distributed manufacturing system and its architecture Fig.2 shows a CNC-machine oriented distributed manufacturing system explored in this report. The longterm vision is to completely integrate design and manufacturing process, automate the process planning and provide the rapid manufacturing service through a distributed manufacturing system. The design concepts can thereby be converted into real product automatically without the constraints of location, resources, and technical expertise etc. It supplies an interface for the designer to monitor and control the manufacture CAD CAPP CAM Definition: Computer aided design: graphic modeling of parts and assembly, including the estimation of mechanical and kinematics behavior. Commercial Software: Solid works, Pro/E, UG and FEA programs Definition: Computer aided process Planning: translating design information into the process commands and instructions Commercial Software: CIMx, Cimplan, MetCAPP, HMS-CAPP, LOCAM Definition: Computer aided manufacture: Use of computer-based systems to control the machinery in manufacturing processes, often combined with CAD Commercial Software: EdgeCAM, CATIA, UG, VERICUT, MasterCAM, Pro/E Fig. 1 Architecture of CIMS 5

process. It is a highly effective technology for discrete manufacturers to shorten the development cycle of products. It is designed to be a networked and fully automated system with workshop-managing modules and seamless communication flow. For the conventional remote manufacturing system, the normal practices give the designer flexibility, via on a remote person, a skilled set-up engineer at the CAM facility, to manage the manufacturing process. By contrast, the new distributed manufacturing system requires the designer to put more concerns on the manufacturability. Similar to VLSI-MOSIS [4] and CyberCut [5], a software module needs to be installed on the client site. But one evolution of the proposed infrastructure from these systems is that the design to manufacture is interfaced by a Workshop management package and Re-configurable virtual CNC machine. As shown in Fig. 2, the architecture of proposed system comprises three main factors: Client Site Agent, Workshop Managing Module, and virtual CNC machine. Client Site Agent (CSA): Most of the existing CAD programs have powerful capabilities of Application Programming (API). Therefore, this module can be achieved by a client program that is embeds into a commercial CAD modeler. Based on this platform, the users are able to access directly to functionalities of CAD tools and manipulate every feature of designed model. CSA will reconstruct the CAD model into a feature sequence with a format that is exchangeable to the server. The reconstruction can be finished automatically; however technologies of these areas are not well developed yet, and have to introduce a lot of AI type works that will sophistically increase the data occupation. Therefore a more feasible way is via the dialogs, i.e. through a serial of interactions, the designer is required to determine the manufacturing sequence of features manually. User CAD Client Sites Agent Internet (STEP-NC) Workshop Management CAPP/CAM Virtual CNC machine Virtual CNC machine Virtual CNC machine STEP_NC STEP_NC STEP_NC Fabrication Station 1 Fabrication Station 2 Fabrication Station 3 Fig. 2 Architecture of CNC milling based distributed manufacturing system 6

The output of this module is not just a machining feature, but the manufacturing flow that also gives important connectivity information bridging one feature to another. Information required for individual features includes geometrical parameters, tolerance, coordinate, and basis set, etc. Virtual CNC Machine is a configurable robotic analysis pack with additional functions for process planning. Its capability is determined by the specifications of the CNC machine that it is attached to. The output data of this module is the detailed manufacturing commands for individual features including G-code, fixtures, tool selection, and coordinate selection etc. With the technologies of forward and inverse kinematical analysis, Virtual CNC machine will also simulate the fabrication process and all sorts of problems that probably happen in the manufacturing process will be reported to designer. Workshop Management System (WMS) is a RFID based monitoring system implemented to track the in-process status of each semi-finished materials. When the design is finish, a manufacturing request will be sent to WMS, which plays the role of coordinating the floor resources, facilities and materials etc. First of all, it needs to check the availability of local manufacturing stations. If there is a local manufacturing facility non-operation, WMS will forward the request to Virtual CNC machine that is connected to the specified facility. If all the manufacturing stations are busy, WMS will append the request and the information of client design into a waiting list. Sequencing the manufacturing order is the main function of WMS. In case of some complicate part models that cannot be completed in one location, WMS needs to arrange the transportation of semi-manufactured goods, monitor the stock and synchronize inventory database. Basically, WMS contains sophisticated technology with high intelligence. 3. WMS and manufacturing line based on RFID tracking. RFID solutions are ideal for manufacturers who build several products on a single production line, or manufacture complex or customized products. Manufacturers can track and record in-process manufacturing information into the RFID tag as an item progresses along the line. The tag information could later be read to produce a shipping list and invoice. The tag could also remain with the item for later use by field personnel during installation and maintenance. WMM host database Next Stop. Reader Reader Fig. 4 Infrastructure of RFID based Fabrication station 7

The major application RFID in manufacturing field is oriented to assembly. Assembly line personnel could use an RFID reader to verify which processes have been completed, to determine which inspections or tests are required and to automatically update the central production database. And production planners and inventory control personnel could use the RFID tags to automatically update the customer database and finished goods inventory, using an RFID reader and PC, rather than manually creating data entry sheets, which could introduce errors into the system. As a matter of fact, RFID techniques also validate in the manufacturing process, especially for distributed manufacturing of complex or customized models. Where the production is not in a massive scale, some of the features requested by customer can hardly be finished in one factory or fabrication station, the semifinished products is transported to the different locations. The main advantage of distributed manufacturing is that all these discrete resources work together to minimize the manufacturing cost. 3.1. Infrastructure: Fig.4 depicts the infrastructure of RFID based WMS and Fig. 4 illustrates the identifications stored in the RFID tag and the corresponding information in WMS host. As we discuss before, CAPP abstract the design concept into a set of to-be-manufactured features, which is assigned an identification number. The ID will be stored into the RFID tag representing the current to-be manufactured feature. The detailed information can be retrieved from the WMS host base with IP authentication. Right after each step finish, the tag is updated with the next feature, meanwhile the inventory of WMS host is synchronized spontaneously. Since the limit of the bandwidth, the detailed information about each feature is retrievable from the WMS WMS host database Product Name Costumer information Process status Material Overall steps.. XML Internet Geometrical Description Feature Name Fixture setup Tolerance Heat treatment Surface finish.. XML IP of Fabrication Station Physical Location Tools Motion commands Lubrication requirement Environmental requirement Status and waiting list. Product ID ID of Current feature ID of Fabrication Station Fig. 5 Information of RFID system 8

sever. Fig. 5 gives the expanded view of the inventory database located in the WMS host, where RFID tag is updated with the in-process status of the product. When one feature get finished, the ID of next feature to be manufactured is stored and replace the finished one. According to the location of next fabrication station retrieved from the host database, delivery personnel will move/ship the part to the location of the station for manufacturing. The host will check the availability of the next fabrication station. If it is occupied, the rough part will be put into the waiting list until the station get ready. All other pertinent information can also be accessed in order to help CAM to setup the detailed manufacturing plan with respect to specific fabrication station. From the discussion, we can see that RFID is an ideal solution for WMM. Differing from the traditional bard code system, RFID can be writing and reading. Meanwhile its performance is not influenced by the working environments 3.2. Benefits By establishing distributed manufacturing system, the manufacturer will benefit from the high efficiency of workshop management and minimization of the manufacturing cost. Actually many academic efforts have been invested into this field. However, to realize the smooth data flow and the instant data capture is the main barrier. RFIT is the ideal solution for these problems. Following is the main advantages of RFID applied to manufacturing line. Maintaining current item information on the tag is ideal for managing production of complex or customized products and assemblies, eliminates the need for separate paperwork on manufacturing status and content. With RFID, the manufacturing planning is actually a dynamic response to changes in supply demand and shop-floor requirements. RIFD deployment can simultaneously notify the central product database when each process has been completed with optimized capacity and resource utilization through real-time accurate visibility into production resources and supply chain Field personnel could use RFID tag to determine product features, date of manufacture, revision levels, etc. 4. Remarks As a conclusion, a synthesis form of the RFID based CIMS is established. Through the wireless connection, RFID provide an circumstance for fully integration of manufacturing and design. Also, only via RFID techniques, the distributed manufacturing is applicable to the real world industry. Reference: [1]. TOOL-PATH GENERATION FROM MEASURED DATA Sang C. Park, [2]. A Multiple-Tool Approach to Rough Machining of Sculptured Surfaces, A.C.Lin and R. Gian, International Journal of Advanced Manufacutring Technology, 1999, Volume 15, pp: 387-398 [3] http://www.step-nc.org The official page of STEP-NC 9

[4] MOSIS, University of Southern California s Information Science Ins. The MOSIS VLSI Fabrication Service http://www.isi.edu/mosis/, 2000 [5] Wright, P.K. and Sequin, C.H., CyberCut: A networked manufacturing system, Proceedings of the managing Enterprise Conference, Loughborough University, England, July, pp605-614, 1997 [6] Jonathan Collins, Using UHF RFID in Auto Factories, http://www.rfidjournal.com/article/view/1198, 10