Previously, their customer had installed labels on beverage cans by hand and sorted them manually. This created a production bottleneck, and increased the risk of motion injuries for employees. The per-piece average cycle time for the new system had to be 1.4 seconds. Because the labels on the cans have more than 150 possible color schemes and background patterns, an additional challenge was finding and reading the bar code on each can.
The solution required tight integration among three cameras, three stepper motors, and 50 industrial digital I/O sensors and actuators. Also, the control system had to be capable of implementing complex vision algorithms. “We needed a PAC (programmable automation controller) that had the functionality of a PC (personal computer) and, at the same time, the reliability of a programmable logic controller (PLC),” says Innoventor Chief Engineer Sam Hammond.
The company chose the PXI platform from automation supplier National Instruments Corp., Austin, Texas. With it, says Hammond, “we could easily synchronize industrial digital I/O, motion, and vision and use a single controller. With LabView (National Instruments’ graphical programming environment) we could also use the same programming language for motion, vision and industrial digital I/O. Having one controller for all operations, as well as a single programming language, reduced the overall cost of the system, making it less expensive than PLCs.”
They designed a system featuring a six-position rotary indexing table that could be dropped into an existing conveyor line. This system removes the cans from the in-feed conveyor and loads them onto the rotary indexer. After sequencing through the top-seal operation, the cans are placed on an outgoing conveyor that carries them to one of six wide packing conveyor tables. Different types of can labels can all employ the same top-seal type, and the cans are automatically shunted to the packing conveyor to eliminate manual sorting. Pneumatic actuators are used to pick the cans and operate a customized label applicator. “We had to select pneumatics for their high speeds to meet overall cycle time,” reflects Hammond.
At station 1, a container is picked up from the in-feed conveyor and placed into a spindle base on the index table. Three cameras then take pictures of the can at station 2 and examine the images for the bar code. If the bar code cannot be read, the can is rotated for a better view. The seal is applied to the top of the can at station 3 and the seal wings are pressed against the side of the can at station 4. Station 5 removes the cans from the rotary index table and loads them onto the out-feed conveyor. Station 6 is a normally empty position that is monitored for the presence of a container that remains due to an out-of-tolerance diameter.
“Station 2 was difficult to implement and still achieve the desired performance,” recalls Hammond. At this station, the location of the bar code first had to be detected around the perimeter of the can. The background artwork of the label made this difficult due to the variety of color variations, surface finishes and patterns. A custom, three-level detection and discrimination scheme was developed to meet this challenge.
“This was further complicated by the distortion in the images off the center of the camera field of view (FOV). The presence of a bar code that was at the edge of the FOV could be identified, but the resolution and distortion prevented the reading of the bar code. In this case, the can was rotated to center the bar code in the nearest camera FOV.”
After reading the bar code, a second rotation of the can was required to orient the can for correct application of the top seal at the next station. Due to space constraints, the location and number of cameras did not allow for a full 360-degree viewing. If no bar code was detected in the first views by the cameras, the can was rotated to place the hidden parts of the cans in the view of the cameras. “Worst-case positions of a can may require seven images and three moves to complete the operation at the station.”
At station 2, a large stepper motor drove the spindle through a friction drive wheel. Once the rotary index table was near the index point, the stepper was driven in on a pneumatic slide. At nearly the same time, a spindle break was released with another pneumatic mechanism. While all of this was going on at station 2, the other operations at the other stations continued in parallel to achieve the part cycle time.
“This top-seal applicator allows the customer to run the facility at 30 percent to 50 percent greater throughput with the same number of people used for the hand-application of labels,” says Hammond. “These people now concentrate on the boxing of cans for shipment. The placement of the top seals is more consistent, preventing the label text from being obscured.”Related Feature - Culture Wars: Connectivity in PackagingTo read the feature article relating to this story, go to www.automationworld.com/feature-6346.
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