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Partnering July, 2016 BellHawk Systems Provides WIP Tracking By Peter Green, CTO, BellHawk Systems Corp.
WIP (work-in-progress) tracking sys- tem for quick-turn manufacturing operations in the U.S., they consid- ered two options: RFID or barcodes. Each of these options had a similar problem; they were unable to track, in real-time, the status of every cus- tomer order as the jobs flowed from one work center to another. The three companies, a large manufac- turer of electrical panels, a manufac- turer of industrial thermostats, and a manufacturer of PCBs, approached BellHawk for a solution, since the company offers both barcode and RFID tracking systems. All three of the companies ini-
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tially thought about using RFID, as this would avoid the time required to scan barcodes manually. Ultimately, after considering the two systems’
hen three electronics manu- facturers approached Bell- Hawk Systems looking for a
time, cost and accuracy differences, they chose barcode scanning.
The RFID approach BellHawk looked into attaching
an RFID tag to each electrical panel, thermostat and PCB at the start of the assembly process, and placing RFID readers at the entrance of the work centers to record when each unit entered and left the work cell. Other than initially associating the RFID tag to be attached to each unit with the work order at the beginning of the line, this would avoid the need for any manual barcode scanning or data entry. However, a number of problems
arose with this approach. First, units traveled in batches ranging in size from one or two units to dozens of units at a time. As the number of RFID tags being read by the entry- way RFID portal increased, the read
accuracy decreased from 99.9 percent for one RFID tag on one unit to below 95 percent when dozens of units were scanned at the same time. Next, in every case, it was unac-
ceptable to the end customers to have RFID tags permanently attached to the units they were purchasing. With temporary tags there was still the real problem of tags becoming de- tached during the manufacturing process. Finally, in two out of the three
cases, products were exposed to high temperatures during the manufactur- ing process, which required that RFID tags be capable of withstanding those high temperatures. This requirement drove the cost of the RFID tags unac- ceptably high for these applications. The reason read accuracy
dropped with the increasing number of RFID tags is due to the physics of how RFID works: it takes a certain amount of time to read each tag reli- ably. When there are dozens of RFID tags being read at the same time, as when a person walks a batch of parts through an RFID portal for example, there is not enough time to read all the tags with a high degree of accu- racy.
To overcome this problem, plac-
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ing an RFID tag on each cart used to move the panels and each tote used to move the thermostats and PC boards was considered. This overcame the first two objections above by only hav- ing a single RFID tag read by each work center portal at a time and not requiring attachment to the units themselves. But ultimately, the need to equip
dozens of work centers with RFID entry way portals at a cost of several thousand dollars each eliminated RFID from consideration.
Keep It Simple In the end, the companies decid-
ed on the simplest solution to the tracking problems. In each case, the BellHawk system created a barcoded traveler, which was used to record the start and end of each operation. In two cases the work order was im- ported from an ERP system, and in the third it was manually set up in the work-in-process tracking system. This traveler had a barcode for
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the work order and a barcode for each operation to be performed. Em- ployees used barcode scanning equip- ment to scan the work order and the operation when they started and fin- ished work. Employees also scanned a barcode on their employee badge and recorded whether they had fin- ished the batch or were simply going on break and how many units they had processed. In this way the software was
able to track the real-time status of each batch and how much labor was involved for each operation. This en- abled performance metrics to be generated for each work center and
employee. As part of this solution, a bar-
code scanning device was employed at each work center. In many cases this was as simple as a low cost bar- code scanner plugged into a PC. In other cases, ruggedized PDA-style mobile computers with integral bar- code scanners were used because they were dust and moisture sealed. These units were kept in charging cradles and shared between users in each work center, which minimized the cost of deployment.
Trade Offs The big win for barcode track-
ing was in accuracy and cost. Once users were trained to do barcode scanning as part of their job, they did not forget to scan batches of units in or out of a work center. And, when they did scan, they got a confirming beep from the barcode scanner when it had read the barcode correctly. As a result, accuracy of record-
ing was high irrespective of the batch size. The barcode system was also able to record data such as labor time, as well as realtime status, in- cluding whether the units were being worked on or just in a wait-state. The cost of equipment deploy-
ment using barcodes versus RFID ranged between 10 and 40 percent. This would have dropped by another 50 percent if the cost of services in setting up and adjusting the RFID portals was included. In addition, the time taken for
users to do barcode scanning proved not to be an issue as it takes only a few seconds to scan into and out of a work center operation. In each case the time to perform the operation on a batch of units took tens of minutes. A drawback, however, is the in-
ability to track the flow of individual units down a line when using bar- code scanning. In each of the three cases here, the clients processed their units in batches, so this was not a problem. Currently, BellHawk is working on a potential deployment that would allow the client to track the flow of PC boards down a produc- tion line. In that case, placing barcodes
on each board and reading these using fixed station barcode scanners as they pass from station to station down the line is a possible solution. Attaching RFID tags to each of the carriers in which PC boards are placed to travel down the automated line would also help. The jury is out as to which will be the best approach. But, one thing has already been de- cided: Barcodes will definitely be used to track the boards through testing, packing and shipping after
they come off the line. Contact: BellHawk Systems
Corp., P.O. Box 300, Millbury, MA 05127 % 508-865-8070 E-mail:
info@bellhawk.com Web:
www.bellhawk.com r
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