DPT Laboratories, a full-service outsourcing company for prescription drugs, OTC drugs, and cosmetics, specializes in the development and manufacture of creams, lotions, gels, ointments, suspensions, powders, and oral liquids. The company continually reviews and updates its manufacturing methods, implementing proven technology to increase quality and improve production efficiency.
To deliver the highest quality products to its customers, DPT has a program in place to inspect a large percentage of the bottles to verify the presence of labels on both the front and back. Previously, DPT had relied on line workers to visually check each bottle for label presence before packing it in the case. Then, to automate and error-proof this process, the DPT engineering department began evaluating various vision systems and sensors.
DPT found a quality vision system that detected whether each bottle had a label by measuring the label area, locating its center, and determining the height of the bottle. However, it had a complex set of tools not required for the label-presence application. And in addition to its initial cost -- tens of thousands of dollars -- the vision system presented significant training and maintenance costs. DPT concluded that the vision system represented a level of cost and technology that was not needed for the task of detecting label presence.
DPT also evaluated a teachable, low-contrast fiber optic sensor from Banner Engineering. Another photoelectric sensor was used as a "gate" sensor, sending a signal to the machine''s PLC when it sensed the leading edge of each bottle. The PLC then triggered the fiber optic sensor to inspect and determine whether it was receiving light reflected from a label (label present) or from a bottle (label missing). This sensor triggered a light and alarm when it did not sense a label. The system''s initial cost was tiny, compared with the vision system, and its operation was much simpler.
If each of DPT''s machines had been used for only one type of bottle, each with the same label, the fiber optic system would have been both cost-effective and reliable. However, DPT packages more than 400 types of bottles, of many shapes, sizes, colors, and materials. In addition, the labels themselves take many shapes, sizes and colors. Thus with each line change the fibers would need to be physically repositioned to sense each new bottle size and shape, and the sensor amplifier would then need to be recalibrated. Some bottle-and-label combinations would require changing to another sensor amplifier to emit a different color beam (green, blue, red, or white). These line-change complications made the fiber optic system time-consuming and costly.
Finally, in March 2000, DPT began to evaluate Banner''s new PresencePLUS pixel-counting sensor for its label-detection processes. As with the fiber optic system, a photoelectric gate sensor was used to sense each bottle''s leading edge and trigger the PresencePLUS to inspect. But unlike the single-point fiber optic sensor, the PresencePLUS scanned an area measuring 1.3 in. by 1 in., allowing line changes without mechanical repositioning of the sensor.
The PresencePLUS sensor captures a 512 by 384-pixel grayscale image of the bottles processed on DPT''s lines. PresencePLUS technology then converts the grayscale image to black or white pixels (depending on a user-adjusted threshold), counts the pixels and renders a "pass" or "fail" judgment. When a bottle is missing one or more labels, the PresencePLUS lights a warning light and sounds an alarm.
DPT now uses more than 20 PresencePLUS sensors to inspect bottles for label presence. The production lines run continuously, three 8-hour shifts per day. As many as four times each shift, the line is changed over to another label-and-bottle combination. DPT has over 40 technicians who conduct these line changes; part of their line-change routine is to run several bottles with labels and several bottles without labels to "teach" the PresencePLUS which bottles to pass or fail. The PresencePLUS Teach feature really makes the sensor easy and practical to use.
The handheld PresencePLUS teaching pendant may be removed and given only to authorized technicians; it is not needed for sensor operation. The absence of buttons or potentiometers on the sensor itself prevents line workers from inadvertently taking the sensor out of calibration and causing downtime. However, because of the frequent product changes and the abundance of technicians at DPT, the PresencePLUS teaching pendants remain connected to their sensors, attached to each machine. A security code allows only authorized technicians to teach the sensor new run-time parameters. While the line is running, the teaching pendants are configured to continually display the RUN JUDGE screen-dynamically showing current condensed images and numeric pixel counts with the PASS or FAIL percentage.
DPT is so pleased with the practicality and reliability of the PresencePLUS sensors that they are evaluating additional applications. The PresencePLUS pixel-counting sensor is now being evaluated for inspecting bottles for the presence of date code printing.