Two Omron E3X-NL photoelectric sensors distinguish variations in glossiness between labels on consumer products.

Integrating sensors and vision systems with motion is common in assembly applications; less so in packaging. But that’s beginning to change.

As with other areas of manufacturing, efforts at improving quality are having a big impact on packaging technology. As line speeds get faster, product must get into its package with minimal error. Sensors and vision systems can assure that the right product is in the right package, in the right orientation, and with the right labeling information.

One less bottleneck

When it comes to motion applications, the speed at which a sensor or vision system detects an object is no longer the issue it was a few years ago. The reason: Sensor manufacturers are taking advantage of miniaturization and optical technologies to develop products that can routinely detect over 1,400 objects/minute. For comparison, previous sensing rates were 300 to 400 objects/ minute.

The Passport DSL digital vision system uses a two-way digital serial communications network for simultaneous image capture and data transfer. From PPT Vision Inc., communication speeds are to 330 Mbps, letting the system simultaneously operate up to 16 cameras and several remote IO devices. With such a system, users can detect over 10,000 moving objects per minute.

Response rates of sensors have improved too. Some of the newer photoelectric sensors respond in as little as 0.02 msec when detecting features on the order of 20 microns or so.

If an application moves objects at faster speeds, the typical solution is a vision system. These sensing devices, usually a more expensive choice, detect objects moving at speeds ranging from 2,000 to over 12,000/ min. In addition, digitalbased vision systems can achieve realtime (microsecond) response rates.

Thus, says one application engineer, most system designers don’t worry about the speed of the motor-drive because sensing speed is no longer the bottleneck. As a result, designers can now focus on product orientation and alignment, whether it’s relative to the production line or the package.

Towards better positioning

Cognex Corp.’s Checkpoint 900C vision system uses a PCI board architecture that accelerates image analysis for color vision applications. In sorting, for example, the system recognizes subtle differences in parts that a grey-scale system might miss.

As technology improves, making it possible to develop smaller products with tighter tolerances, new concerns crop up. Laser sensors, for example, can measure objects or parts of objects as small as 0.01 in. But to fully use the tight focus and faster speeds, object orientation is crucial.

To deal with orientation problems, some packaging systems use sensors in combination with actuation devices. In some simple sensor-actuator combinations, the sensor signal may cause an actuator or linear slide to move the object a predetermined amount. A more common application is coordinating with an ejection motion system, such as an actuator or linear slide. The sensor, set up to detect a specific flaw, sends a signal to the ejection system, which moves to eject the defective object from the line.

One potential flaw is an incorrect label. Labels are an indispensable packaging component in food, consumer product, and pharmaceutical industries. A wrong label, especially on medicine, is grounds for legal action. But with packaging line speeds increasing, manual label inspection is impossible. Sample inspection can also be inadequate because defective labels may get through the process. Vision systems are an alternative that can provide 100% inspection.

Whether labels are inspected before or after being placed on products, whether they’re printed using ink-jet or hotstamping methods, and whether or not the labels are skewed, vision sensing can catch and offer fixes for all defects prior to shipment.

In more complex sensor-motion coordination arrangements, sensors may provide data for microprocessor-based controllers, which then issue commands to pick-andplace units to twist, turn, or otherwise properly align the objects. The recent development of device-level buses provides the communication necessary to coordinate such actions between sensing devices and motion systems.

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