Combining a specialized optical head with off-the-shelf cameras, frame grabbers, and PC allows barcode data to be rapidly read.
By Andrew Wilson, Editor
According to a Worldwide Optical Media Market Intelligence Service Report, published by the International Recording Media Association, worldwide sales for optical media in 2001 were nearly 10 billion units. Roughly equally divided among Europe, North America, and the Far East, the markets include optical media for CD-audio, CD-ROM, DVD-video, and DVD-ROM. To accommodate the production of these media types, a number of companies, including Bronway, offer machinery to automate the packaging and inspection of optical-disk products.
Initially founded in 1991 by Martin O'Malley to target the floppy-disk market, Bronway provides end-of-line automation equipment for the compact-disk (CD), CD-rewritable (CD-R/CD-RW), digital-video-disk (DVD), and software-manufacturing industries. The company designs and manufactures products including disk counters, collators, and automatic sleeving equipment in Ireland for distribution in Europe, North America, and the Far East. The company first entered the optical-disk industry in 1996 with a device designed to count the number of disks on a CD spindle.
Bronway now offers several products for industrial automation of CD and DVD manufacturing, including the SoftPack-260, a packaging and inspection system designed for mid- to high-end automated CD/DVD soft-box packaging (see Fig. 1). Capable of handling a variety of soft-box types for DVD disks at rates of up to 60 per minute, the machine includes a title-sheet-insertion module; up to three booklets can be inserted into each box. Currently, the design of the machine allows one disk to be inserted into the box.
At the disk-loading station, an optical-code reader safeguards against mixed product being accidentally shipped to the customer. Any disks that fail code checking are placed on a reject spindle and not loaded into the box. At the exit station of the machine, the user can opt to either close the boxes automatically or leave them open for the later manual insertion of additional components. Typically, one operator can run the entire machine, and this may be a cost-effective alternative to two operators running one high-speed machine.
Up to 400 empty DVD boxes are stacked ready for packaging (see Fig. 2). After the machine is initialized, the DVD boxes are opened so that the cover material can be inserted automatically. After insertion, a vacuum-assisted picker places any booklet material in the lefthand side of the package.
After both cover material and booklets are inserted, a conveyor belt moves the boxes to the disk-insertion stage. Here, a stack of approximately 150 disks placed on a rotary mechanism with eight spindles coupled to a vacuum picker that places the DVDs in their boxes. Before packaging, however, the code on the inner mirror band of the DVD must be read to ensure that the correct disk is placed in the right package. If the data are identified as being correct, the disk is packed into the package and the box closed for shipping. If the code on the DVD is incorrect, the disk is automatically transferred to a separate reject spindle.
ADDING VISION
To add automated visual inspection to its SoftPack-260 packaging and inspection system, Bronway enlisted the help of its UK-based subsidiary Bronway Technology UK. There, Peter Ramsden, general manager, and his colleagues developed a specialized optical head and PC-based vision system based on off-the-shelf cameras, frame grabbers, and CPUs— dubbed the IDV-120 Ident Code reader.
"In the design of the optical head," says Ramsden, "it was necessary to properly position and illuminate the inner mirror band of the CD before any imaging could occur." To accomplish this, Pro/ENGINEER from PTC was used to design a specialized optical head to hold each disk in position.
"In the prototype version of the system," says Chris Sanby, a senior development engineer with Bronway, "this head used a vacuum to hold the CD on the head of the fixture." In the latest incarnation, the system uses the Venturi effect to accomplish this task (see Fig. 3). "By pumping a stream of air from approximately 1 in. under the optical head through three holes located at the top of the fixture, a low-pressure vacuum is created that holds the CD firmly in place." While the previous vacuum-based designed drew dust into the optical head, the Venturi-based method can liberate the optical head from any dust buildup.
Once placed on the optical head, the optical disk must be properly illuminated before imaging can occur. To achieve this, a ring of eighty 3-mm white-light LEDs with constant current drivers is mounted in the head of the optic. "By mounting an optical diffuser and Perspex light guide on top of the LEDs," says Tony Bland, senior engineering manager with Bronway, "we achieve an extremely uniform light source with which to illuminate the disk."
After the disk has been properly illuminated, it is necessary to capture images from the mirror band located inside the data area of the disk. This mirror band contains data in alphanumeric and barcode formats that must be interpreted by the system. "To properly capture these data," says Sanby, "it is imperative that the end user cannot alter the focus or the aperture of the imaging system. Because of this restriction, Bronway uses a fixed-focus, fixed-aperture lens to focus images of the CD mirror band onto a CS 3910 progressive-scan camera from Tokyo Electronic Industry. Featuring a 1.3-Mpixel, 2/3-in. sensor, the progressive-scan camera outputs data in EIA 644 format to a PCI-based Phoenix frame grabber from Active Silicon.
Since there can be an order-of-magnitude difference between the reflectivity of DVD-disk surfaces as a result of the different materials used to coat the disks, the LEDs located in the optical read head must be strobed at more than their rated maximum. Says Ramsden, "It is necessary to strobe the LEDs for up to a 5 ms to produce a bright, intense light pulse. To do this, Bronway manufactured specialized driver circuitry in the base of the optical head that consists of monostable triggers that stop trigger pulses of longer than 7 ms. "By driving this circuitry from the I/O of the Phoenix frame grabber, we can control the cameras exposure and the strobe lighting from a single board," says Ramsden.
To control the frame grabber and provide an interface to an LCD display, Ethernet, programmable logic controllers, and a hand-held barcode scanner, Bronway chose the SBC-658, a single-board computer from AAEON Europe. Supporting Intel's Pentium III processors and the 440BX chip set, the SBC features one DIMM socket with 256-Mbytes SDRAM, support for TFT LCD panels with a 1024 × 768 resolution, one
Ethernet port, and DiskOnChip. "When interfaced to the Phoenix frame grabber," says Bland, "the two-board solution provides a cost-effective imaging, computing, display, and processing platform."
SOFTWARE SOLUTIONS
Once images are captured by the frame grabber, they must be processed in the PC to read the data located in the inner mirror band. With a front-end developed in Microsoft Visual Basic, Bland, Sanby, and Ramsden use Common Vision Blox (CVB) software from Stemmer Imaging to capture images and transfer them to the host PC memory. "After images are captured," says Sanby, " the alphanumerics and barcode data in the circular image must be unwrapped." Using royalty-free image-processing libraries from Intel, an algorithm was developed to detect the two circumferences enclosing the mirror band of the CD.
After the mirror band is successfully isolated, a bilinear interpolation algorithm (also modified from the Intel libraries) unwraps the image. According to Sanby, custom coding of the interpolation algorithm allows each band to be unwrapped in approximately 10 ms. "This is considerably faster than if we had implemented the same algorithm using CVB. However, to use the Intel algorithm, it was necessary to first convert the CVB image-data format to one that could be read by the Intel image-processing libraries," he adds.
Once the bilinear interpolation unwraps the mirror band, optical-character-recognition (OCR) and optical-character-verification (OCV) algorithms are required to read the alphanumeric and barcode data. To perform the OCR, Bronway's engineers use the Minos OCR package found in CVB to perform OCR training and recognition on the alphanumerics and barcodes. For the development of the OCV algorithm, Intel image-processing libraries are again used and are incorporated as subroutines in the final software package.
For ease of use, the system presents the user with a simple interface developed in Visual Basic (see Fig. 4). To operate the machine, the user must have a work-order number that can be entered either by typing or using an optional hand-held barcode scanner interfaced to the SBC via the RS-232 serial port. After this code is entered, the user is prompted to start the machine. The interface can then display each image as it is processed, the total number of disks, the batch, and recent yield of the host machine.
"Adding the IDV-120 Ident Code reader to the SoftPack-260 packaging and inspection system allows the system to verify that correct optical media are placed in the DVD cases," says Ramsden. "In addition to using the machine-vision system in our range of CD and DVD packaging systems, we will also be offering the unit to other manufacturers requiring CD/DVD inspections." According to Ramsden, these may include CD/DVD printing companies who want to verify that the correct label has been placed on each disk before packaging occurs. "By modifying the algorithms used," he adds, "we can tailor the IDV-120 to meet the needs of such applications."
Company Info
Active Silicon, Uxbridge, UK www.activesilicon.co.uk
AAEON Europe, Limburg, Germany www.aaeon.com.tw
Bronway, Bray, Ireland, and Gorham, ME, USA www.bronway.com
Bronway Technology UK, Cranfield, UK www.bronway.com
Intel, Santa Clara, CA, USA www.intel.com
International Recording Media Association, Princeton, NJ, USA www.recordingmedia.org
PTC, Needham, MA, USA www.ptc.com
Stemmer Imaging, Pucheim, Germany www.commonvisionblox.de
Tokyo Electronic Industry, Tokyo, Japan www.teli.co.jp
