Aerosol cans are ubiquitous in the modern household. Look at the cleaning products under a kitchen sink or at the spray paint on a basement workbench, and you are likely to find an aerosol can or two.
A critical part of these aerosol cans are their caps — the often color-coded or marked plastic closures that cover the dispensing nozzles. The cap serves to protect the nozzle, to simplify storage and packaging, and to minimize the unintended dispensing of the can’s contents.
Sensing the attributes of these aerosol caps is a common application in industrial automation. Engineers must often perform an error-checking, sorting, or positioning operation before or after placing the cap on the aerosol can. Over the years, some solutions have emerged as the go-to sensors or technologies for these applications. Now, let’s take a look at five sensing tasks and the different types of sensors used to detect differences between caps.
1. Color sensors
If you need to see the difference in color between caps, a color sensor is typically the best product for the job. You can sort multiple caps so they are either routed to the correct packaging location or rejected if they are an incorrect color. For color detection, a DF12 Series color sensor can be taught to recognize up to three different colors, and a VCS110 Series color sensor can be taught up to ten different colors. For example, DF12 color sensors can be taught a red cap, a yellow cap, and a blue cap to trigger three different discrete outputs that correlate to three different sensing channels. If a line is running in which red-capped products are processed, the presence of a blue cap triggers a reject of that cap.
2. Background suppression sensors
If you are detecting the skew of the cap position, consider using multiple background suppression sensors like the ML6 Series. Sometimes a cap is not fully seated onto its container, resulting in the upper surface of the cap not being parallel to the surface that the cap is on. In this instance, mount several background suppression sensors looking down onto the cap’s upper surface. If the cap is fully seated, then none of the sensors will detect the cap as it passes by. But if the cap sticks up on one side, then one or more of the sensors will detect the cap as it passes and indicate a skewed cap.
3. Luminescence sensors
If you need to detect the presence of invisible markings, then a DK50-UV Series luminescence sensor is often the best approach. Sometimes a mark is purposely made on the cap using ink that is not visible to human eyesight. This mark can help prevent counterfeiting by identifying the cap as the real thing while preserving the aesthetic of the product. A luminescence sensor detects this mark to verify its authenticity or to align the cap to correctly position a molding seam relative to the can.
4. Contrast sensors
To sense a label or coupon on the cap, a contrast sensor like the DK12 Series may be the right solution. If something is glued to the cap, whether it is promotional or safety information, it is often necessary to confirm that the label is present on the cap before it’s packaged. If the label is present, the cap and the can pass the error-check and are placed into a carton. If the label is missing, the product is rejected from the line to be reworked. Contrast sensors are designed for two colors and can handle situations where the cap is one color and the label or a section of the label is a second color.
5. Laser distance measurement sensors
If sorting by cap height is the challenge, a laser distance measurement sensor from the VDM18 Series could be the correct approach. A sensor looks down onto the cap as the cap passes by. This sensor could be used for sorting caps so that only the correct-sized cap is used. A distance measurement sensor can be used overhead to measure the cap height to within 0.5 mm accuracy.