Rexnord is a company specialized in the production and assembly of conveyor belts. They produce conveyor tracks and the components related to it. Currently they are using tiny clips to combine the different parts of the conveyor tracks.
This combining is done automatically for most of the standard tracks that Rexnord produces. Custom bowl feeders are used to properly align the clips for production. For the non-standard tracks, production is still done manually by picking the clips from the bins by hand. In the future Rexnord wants a single production cell to be able to produce different types of (non-)standard tracks. For this all the parts and their supply forms need to be usable for automated production.
The clips are manufactured using injection molding and are dropped into a bin directly from the mold, because of this it is virtually impossible to use these clips for automated production. To be able to use the clips in automated production the clips need to be placed in a defined position.
Rexnord has given the group the task to design a system to place two types of clips from an undefined position into a defined position. The target for speed is to place ten clips in the defined position within 30 seconds, since this is the same speed at which the clips are produced. Rexnord wants to know how close the proof of concept can come to this cycle time. For the proof of concept, the orientation will be defined by placing clips in a fixed orientation into a magazine.
Shape and view of the clips used for the proof of concept
Using a bowl feeder for supplying the robotic arm with clips in the correct orientation is not possible since they are clip specific. To get the same result, it was decided to divide the supply and pre-orientation of the clips in two different mechanisms: an auger-feeder would supply the different clips into the system and an orbital shaker would pre-orientate the clips.
The auger feeder would allow a worker to put as much clips as needed in the hopper. A stepper motor drives the auger that pushes the clips onto the shaker. This table will start rotating and places the clips into the correct position for the robot to be able to pick the clips. The top of the shaker is made from opaque acrylic and a RGB LED-strip is placed in the table. By using the correct color, the contrast between the clips and the table can be improved for the vision system.
Auger feeder and orbital shaker
The clips that are picked up by the robot needs to be placed into a defined position and orientation. For this defined position and orientation, a magazine was designed for each clip. These magazines can contain up to 16 of the red clips and 12 of the orange clips.
The magazines need to be swapped manually when they are filled.
Magazines for the orange (left) and red (right) clips
End of arm tool
To pick as much clips as possible at the same time, a hexagon shaped end of arm tool was designed to pick up six clips in one cycle. The tool uses blunt needles and vacuum to pick up the clips. Six needles are placed on the tool and are used to pick up the clips with vacuum. Each needle has its own vacuum generator connected to it. When the needle is placed above a clip its vacuum generator will be turned on and the needle will pick up the clip.
End of arm tool implemented into the robot
For the vision part of the system a Cognex camera with the Cognex In-Sight software was used. The software will detect the location and orientation of the clips. The software will then select the clips with the most optimal orientation and send the coordinates and orientation of these clips to the robot.
The PLC is the central part of the system and controls multiple parts of the system, the PLC can:
- Start and stop the robot
- Start and stop the auger feeder
- Start and stop the orbital shaker
- Control the color the orbital shaker
The operator can control the machine with an HMI (Human Machine Interface) via the status screen, the HMI can:
- Start and stop the system
- Show the number of clips placed into the magazine
- Reset the number of clips put into the magazine
- Manually control the feeder
- Manually control the orbital shaker
- Give information whether the vision system is activated or not.
Display of the HMI
The machine works as expected. The robot can place both clips in a defined position. The cycle time for the placement of twelve clips is 48 seconds for both clips. This is relatively close to the given speed target of ten clips per 30 seconds.
Overall image of the workspace
Further improvements to the system can improve this cycle time. The following improvements have been suggested:
- All-metal end of arm tool to prevent misalignment
- Increase the number of nozzles from six to ten
- The use of a robot with higher speed
- Use internal pneumatics instead of external