Q&A: Color Mark Sensing Ask Peter Applications Engineer 1-888-3-SENSORS Description: The R58E color registration mark sensor is a convergent, non-contact sensor that contains both the emitter and receiver elements. Designed for use in the printing and packaging industries, the R58E represents an advancement in color registration mark technology with the inclusion of 3 color LEDs in one sensor. This allows the R58E to automatically select the correct LED to use in any sensing situation, based on the contrast between the background and the registration mark being sensed. Additionally, the R58E has a very fast response speed of 10,000 actuations per second. Q: What’s the difference between a true color sensor and a color registration mark sensor? A: True color sensors can be taught to detect minute color differences (for example, it can tell dark blue from black), while color mark sensors detect a gray scale change in color. True color sensors reflect light off a target using a white LED and red, green and blue filter elements. A color value is then assigned to the light returning to the sensor based on the amount of light reflecting off the target. Click here to see Banner's QC50 true color sensor. With color mark sensors, the sensor uses just an LED and no filters. The sensor distinguishes between the target color based on how it contrasts with the background color. Q: Isn’t it better to use a true color sensor rather than a color mark sensor? A: Not always. A large number of color sensing applications can be done quite effectively by detecting a gray scale change in the color mark. In these instances, we recommend you use a color mark sensor like the R58E, especially in high-speed applications. A true color sensor is required when sorting out targets that differ only in color, for example, when you need to distinguish between light blue and dark blue. However, when distinguishing a registration mark on a constant background, a color mark sensor is your best choice. Q: I’ve used the R55F in the past. Should I consider upgrading to an R58E? A: The R58E represents Banner’s commitment to continuous product improvement and it benefits from the newest technology. If you’ve used the R55 or R55F and are satisfied with it, there is really no reason to upgrade, unless your application has changed. Remember too that R55F fiber optic units offer the convenience of a tiny sensing point and the ability to work in wet or extremely hot environments. Q: Why would I choose an R58E over another Banner color mark sensor? A: With the R58E, you can have the convenience of using one device for multiple applications at a very affordable price. It also is especially useful in applications that involve multiple substrate challenges and have high speed requirements. Q: How can I maximize sensing in my high-sensitivity applications? A: Use the dynamic TEACH function to teach the sensor a series of conditions on the fly. The R58E takes multiple samples of a registration mark against its background and is able to automatically set the sensitivity at the optimum level. Q: Is it true that processing time for the color mark sensor affects speed? A: Speed is more of an issue for a true color sensor rather than a color mark sensor. The R58E can perform 10,000 actuations per second, which is really pretty fast! Q: Does having 3 LED colors affect the sensor’s response time? A: No. After the initial TEACH process, the R58E’s response time is the same as comparable registration mark sensors. The R58E has a 50 microsecond response time which allows 15 microsecond repeatability. Q: How do I pick the right LED color for my application? A: With the R58E, you do not need to choose an LED color. The R58E selects the proper LED color automatically during the initial TEACH function. However, when using a monochromatic color mark sensor, resources such as color selection charts are used to select the proper LED color.

Q: How do I sense a registration mark on clear material? A: Clear materials (e.g. a clear poly web) don’t reflect light very well, so when sensing a registration mark on a clear material, position a reflective surface directly behind the clear material to return light to the R58E. The registration mark will block the light from reaching the reflective surface and will be detected by the sensor. To avoid the shine from clear materials, you might consider mounting your sensor at a 15° skew angle. Q: How do I switch between the different LED colors? A: You don’t need to manually switch LEDs. The R58E will automatically select LED colors during the TEACH function. Q: Why do you use the red, green, and blue combination of LED colors? A: The R58E uses this combination so that it may reliably sense virtually any registration mark/background combination. The RGB (red, green and blue) combination can be combined to create almost any color. Your monitor, for example, which is capable of millions of colors uses the RGB technology. The R58E, using these three colors, is able to determine the color of the registration mark and the color of the background. The sensor will then use the LED that provides the best contrast between the registration mark and the background. Q: Can I choose the LED colors in the R58E? A: No. The R58E comes with only the possibility of three LED colors: red, green and blue. Q: I never understood the 16 gray scale contrast levels specification. What does this mean? A: One way to spec a color mark sensor is to understand how many levels of gray scale it can detect. The more levels, the finer the sensor’s resolution. A commercial gray scale printer's chart is divided into 20 segments between black, white and the shades of gray between. Many sensors are able to detect the first 16 segments starting at white. Q: Does the R58E have a spec for gray scale contrast levels? A: The R58E can easily meet the spec for 16 levels of gray scale. Because of the combination of RGB LEDs, the R58E’s resolution capability far exceeds gray scale charts. The R58E’s capability for subtle contrast changes far surpasses the specification for 16 levels of gray scale. Let us show you how! Contact a Banner Representative for more information. Q: Other than registration mark, what other applications can I use the R58E in? A: In addition to printing and packaging applications, you can use the R58E in high-speed applications in counting and in positioning applications. Q: What's the difference between a color mark sensor and a registration mark sensor? A: There is no difference; these terms are synonymous. The R58E goes by either designation and also by color registration mark sensor. Related Links: Get more information about the R58E sensor. Learn more about the R55F here. Download a handy reference with more color theory information. Download a handy reference on selecting a color mark sensor LED color. Need a true color sensor? Check out Banner's QC50 product page for more information.