Casey Segraves, Business Development & Marketing Manager from Smart Vision Lights, Muskegon, MI, US
Clara Dunning, Marketing Manager, ControlVision Ltd., Auckland, New Zealand
In fifty-nine countries around the world, Sistema Plastics Limited is well known for its range of stackable, food safe storage containers. Perhaps the best known brand, the company's Klip It collection with its distinctive blue clips allow containers of different sizes to be stacked in different configurations.
To produce these containers in quantity, the company has developed fully-automated systems that Include plastic molding injection systems to produce the containers, lids and plastic clips, robotic-guided vision systems that assemble each container and automated systems to label, pack and wrap the containers for shipment.
After each container and lid is manufactured, flexible plastic clips must be applied to seal the lid and the container. In the past, these clips had been manually attached on the base of each container. However when Sistema introduced a new range which featured smaller clips attached to the lid, issues in the manual production process led to the search for an automated solution to lower costs and increase efficiency.
Figure 1: To automate the process of applying clips to plastic storage containers, ControlVision has developed a vision-guided robotic system that uses two vision guided Adept robots to add the clips to the containers at the rate of one every two seconds.
Reduced cost
"While Sistema is always looking for ways to reduce costs through automation, there were other reasons for prioritizing the clip attaching process", says Oliver Jensen, Engineering Manager at Sistema. "It was difficult for workers to apply the clips to the lids, especially when they were working long shifts to keep up with demand. Applying the clips was a process that was also run offline, which means that that the lids are molded, collected and the clips added separately. What was needed was a system to automate this process for multiple shapes and sizes of products."
Having already worked with Sistema to install a camera-guided robotic labeling system, ControlVision was tasked with integrating the hardware and software to enable the automation of clip attachment (Figure 1). A major challenge of the project was ensuring precise accuracy for the clip placement while maintaining a high speed on a moving conveyor, as there was a tolerance of less than 0.5mm for the clip to be successfully applied. It was also vital that the system could handle a range of lid sizes, shapes and different clip colors.
Figure 2: In the design of the system, lids and clips are imaged as they move along two separate containers. After each clip is located, two clips are picked and placed onto the lid using an Adept robot. A second Adept robot picks and places the final two clips.
System design
In the system, two conveyor belts carry the lids and clips separately in parallel (Figure 2). Encoder feedback is employed to enable the accurate tracking of the clips and lids on the moving conveyors. Upstream of each robot, used to pick and place the clip, are a pair of scout scA640-74gm cameras from Basler with 640x480 resolution. With a 25mm focal length Fujinon lens from Fujifilm, these two cameras capture a 250mm x 200mm field of view of the clip, which are sent to Control Vision's VisionServer software to determine their position.
Once the position is determined, the VisionServer software guides a Cobra s600 robot from Adept Technology to pick up the clip. A separate, 1600 x 1200 Basler scout scA1600-14gm monochrome camera captures a 500mm x 350mm field of view of the corresponding lid using a shorter focal length Fujinon 16mm lens. This image is processed by the VisionServer software to locate its position and guide the robot into applying the clip. The process is repeated for the second clip. As all lids have either three or four clips, a second Adept Cobra s600 robot is paired with an identical vision system that applies the third and/or fourth clip to the same lid downstream.
Figure 3: Each camera is mounted to image the lids and clips through the center of a DLP-300x300-WHI, diffuse light panel from Smart Vision Lights.
To locate the clips, the ControlVision VisionServer software uses the VisionPro PatQuick geometric matching tool from Cognex. Further VisionPro edge and contrast tools are then used to identify the orientation of the clip and distinguish whether it was upside down or right side up. To determine whether a clip is already present on the lid and in which location, PatQuick geometric matching, and edge and contrast tools were used.
Diffuse lighting
Each Basler camera is mounted to image the lids and clips through the center of a DLP-300x300-WHI, diffuse light panel from Smart Vision Lights while the lower resolution camera is mounted upstream, next to the light source. This LED array provides homogeneous "cloudy-day" illumination covering the complete field of view for both cameras (Figure 3).
Figure 4: ControlVision's VisionServer framework acts as the human-machine interface (HMI) for the system, enabling system parameters to be configured and the complete clip placement process to be monitored.
Since a variety of clip colors may be used, white light was chosen for its versatility. "Diffuse ring light panels, such as the DLP & LLP-H Series, have become increasingly popular", says Dave Spaulding, President of Smart Vision Lights.
By using panels slightly larger than the inspection subject, they provide results similar to dome lighting by allowing light to come from multiple angles, but at a significant cost savings. Another advantage over dome lighting is that the panel light does not have to be placed directly over the target and can be mounted at a distance.
HMI Interface
As well as managing the robot cell, ControlVision's VisionServer framework also acts as the human-machine interface (HMI) for the system, enabling system parameters to be configured and the complete clip placement process to be monitored (Figure 4).
Adept ACE software is also running on the PC while VisionServer interacts with the robot through the ACE software sending positional data to the robot program. VisionServer also obtains variables from the robot in order to display them within the HMI.
Since the system has been installed, clips are applied to lids at a rate of one every two seconds - double the output of the previous process. Operators are now able to run twice the volume of product.
