Inspection For Toothpaste Tubes
One of our customer relies on vision systems in its newest packaging machine, the tube feeding machine for 19mm to 40mm (0.75 to 1.57 inches) wide tubes. During the course of the filling process, vision systems check that the tubes are round, clean, and firmly sealed. In-process inspection has allowed the number of cameras to be reduced from the six conventional units required in the old process to just two per checking station.
The packaging materials have to be of high quality because the machine operates so quickly. Even though materials of high quality are used, there can still be contamination by small dirt particles, tubes may be deformed when the outer packaging is applied or there may be faulty seals at the base of the tube.
With a capacity of up to 500 tubes per minute, the high-performance newest tube feeding production line inspects, fills, and seals toothpaste tubes in record time. Based on the needs of a typical toothpaste user, a minute's production time on the new machine produces enough toothpaste for a lifetime of tooth brushing
During the first operation step, a 6-axis robot with an expanding gripper arm takes the tubes out of the boxes. The robot places them into the tube holders of the conveyor system with the open base of the tube pointing upwards. The robot arm is equipped with a special tool with pins which fit precisely into the partition in the box and picks up two rows with a total of 30 tubes each time. The screw cap is already in place at the top of the tube and the lower end is open for the filling procedure. The conveyor system moves the tubes clockwise towards the cleaning and filling station. Before they reach the cleaning and filling station, a scanner checks that the tubes are aligned correctly so that the printing is in the correct position when the base is sealed later. Two successive inspection stations check that the tubes are round in shape and clean before they go through cleaning and filling stage.
Two vision cameras installed above the conveyor and the work areas evaluate the tube ground coat, the shoulders of the tube, and the inside of the tube cap during the particle check. The cameras detect foreign bodies based on the contrast to their surroundings. A red, ring-shaped LED light illuminates the inside of the tube from above. Any undesired particles cast a shadow which is detected by the cameras making it possible to detect objects which are the same color as the tube itself.
During the subsequent tube roundness check, two vision cameras check whether the tubes are of the required shape. If the tubes do not have the specified roundness, the nozzles stay at the edge during the cleaning and filling process and ram the packages into the tube holders. The high-performance technology ensures that the nozzles enter the tubes accurately to within a tolerance of three millimeters (0.12 in.). The checking procedure takes place without the need for an additional operation step during the process. The individual cameras receive a trigger for every tube and record pictures of the packages as they move past. If a tube is out-of-round or outside of the tolerance range, it is identified as faulty and is not filled. Further on in the process, the packaging machine seals the tube and ejects it from the production line.
After cleaning and filling, the laminated plastic tubes are sealed with hot air. The ends of the tube are heated by hot air at a temperature of 380 to 450°C (716 to 842°F) and are then pressed together by cooled stamping jaws. The seal is either stamped smooth or in a corrugated pattern and may feature a serial number or code. Defects can occur at this stage of the packaging process. For example, if a knife becomes blunt and can no longer cut off the ends of the tubes correctly, the seal will be left with rough edges. In the trimming station, two cameras ensure that all faulty packages are detected without fail. The cameras also check the seal itself. If the seal is not complete, or if the printing is not properly aligned with the specified parameters, the faulty tube is ejected from the process.