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Voxin Tech manufacturer and supplier of many sensors—including ultrasonic, photoelectric, capacitive, and inductive—this discussion will focus on specialty photoelectric sensors.


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Eye Color Mark Contrast Sensor Photocell / Registraton Mark Sensor As demand for packed products are increasing in India have led in increase in demand for color mark sensor which are a part of the automation in providing packaged material. One of the key components in this high-speed production environment is the sensor evaluating many of the features and characteristics of products at rates as fast as hundreds of items a second. Although we are manufacturer and supplier of many sensors—including ultrasonic photoelectric capacitive and inductive—this discussion will focus on specialty photoelectric sensors. This article is intended to guide readers color mark sensor working principalcolor mark sensor applications eye mark sensor installation contrast level comparison color mark sensor applications and in what kind of machines it used . How Photoelectric Sensors Work The basic functions of a photoelectric sensor are to react to a change in light produced by or characteristic of a target and to generate an analog or digital electrical signal that interfaces to external equipment for control purposes. Typically the sensor is set to diferentiate between two conditions or characteristics exhibited by the target e.g. detection of a light or dark mark on a label or the presence/absence of an adhesive on a part. More advanced sensors such as color sensors react not only to the change in light produced by the target but also evaluate the color content of the light allowing multiple colors to be recognized. All photoelectric sensors have a limited feld of view FOV defned by their spot size. As a result its necessary to guide the target through the light spot—a photoelectric sensor cannot detect a 1 cm 2 mark placed randomly in a 100 cm 2 area without being directly "aimed" at the mark. Best results are achieved by maintaining a fxed sensor-to-target distance.

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Nearly all photoelectric sensors modulate their light source to prevent ambient light from afecting the sensors measurement. This technique involves measuring the signal with the light source on and with the light source of then calculating the diference. The result is a signal level that is attributed solely to the sensors light source i.e. ambient light is subtracted out. Sensor Commissioning Considerations Sensor commissioning involves selecting the Voxin Tech sensor for the job installing it and evaluating it. . The good part about our sensor is that you need to only teach the eye mark rather than teaching both mark and background .Although this technique works in all applications where there is a or no signifcant diference between a good part and a bad part it is also useful in many other applications where the diference is less marked. For all the applications a successful implementation is more likely if the sensor selected provides the user with visual feedback allowing the user to determine and set the optimum threshold level. Our sensors even provide visual feedback such as a display of bar graph that indicates the signal strength. This Visual feedback aids in the set-up and evaluation process by indicating the signal strength to the operator allowing the operator to determine the optimum location within the sensors range for reliable operation. This feature is also a valuable troubleshooting aid when evaluation of marginal targets is necessary. Voxin Tech Contrast sensor. 1. Dark Mark dark background our sensor works 2. Light mark light background our sensor works 3. Dark mark light multi-color background our sensor works. 4. Light Mark dark multi-color background our sensor works. 5. Sensor for Joint detection or splice detection in a roll or flm. Our Contrast sensors detect a diference in contrast between the presence and absence of an object or mark Figure 1 and are available in a variety of spot sizes ranging from a few millimeters to more than 25 mm. Most contrast sensors use a red or green LED light source and often use both. Because diferent colors absorb diferent amounts of light the wavelength of the light source can be selected to provide the highest amount of contrast for a given application. Unfortunately this approach is not very fexible requiring both a specifc background and mark color. Sensors that provide both red and

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green light sources ofer a greater degree of fexibility but require a fxed selection of one or the other light source during operation. This is frequently accomplished automatically using the teach function. Figure 1. A broad-spectrum white light source provides the versatility to detect any color target on any color background The reason why Voxin Tech contrast sensor is most versatile of all the contrast sensors available in the market is because our sensor provide broad-spectrum white light source. Voxin Tech white light sensors provide good diferentiation on all color and background combinations and also allow for quick changeover in production by adjusting the threshold level to one that has been previously established. Color Sensors These sensors separate the refected light from a target into its constituent red green and blue components each of which is then evaluated to determine whether or not it is within the range of tolerances set for specifc color recognition. They are efective in monitoring of color consistency in applications such as textile production plastics and other continuous output processes. A color recognition channel allows you to associate the specifc characteristics of the target with a discrete output line with the values stored in the sensors internal memory. Response time for these sensors can be as fast as 300 µs and spot sizes can vary from several millimeters to 25 millimeters. Color sensors integrate the signal over the entire area of the light spot. Therefore if the light spot spans two colors the sensor will "see" the combination of the colors rather than each separate color. This is an important consideration in applications where the target has a texture or pattern such as wood grain or the multicolor crosshatch often

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used in automobile seat covers. While a small light spot would not be suitable for this application a large light spot with its ability to average the signal over a large area would likely do the job. Available features range from simple teach functionality to a full-featured GUI Figure 2 that allows real-time display access to tolerance settings for each color and general sensor controls. While simple applications such as sorting—based on a few very diferent colors—can often be accomplished with lower-end color sensors more complicated applications will require the more comprehensive control of settings provided by full-featured sensors. Figure 2. A Windows-based application program provides extensive control of sensor settings such as illumination level and individual red green and blue tolerance settings for color recognition channels Voxin Tech Color mark sensors. Our sensors are designed to detect color marks at high speeds. They do not typically identify a specifc color rather they react to a change from the background color and provide a discrete output signal to indicate the presence of a mark Figure 3. Our Color mark sensors provide spot sizes from a circular spot 0.5 mm dia. to a 2 mm x 5 mm rectangular spot. Sensors that use rectangular-shaped

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spots require you to mount the sensor so that its spot has the proper orientation with respect to the mark these are limited to detecting larger marks. A smaller circular spot size is suitable for use on 0.5 mm wide and larger marks. Figure 3. An example of a color mark. A small spot size combined with fast sensor response allows reliable detection of 0.5 mm wide marks at process speeds exceeding 2000 ft./min. Key to the successful color mark sensor implementation is a careful analysis of the particular requirements of the application. For best results select a sensor with a spot size that is no larger than the smallest mark being detected to achieve the highest level of contrast. Target speed is also a major factor in the selection process for color mark sensors. Many processes such as printing and converting require precise detection at high production speeds. For example a 1 mm wide mark moving at 2000 ft./min. translates into the linear travel of 1 mm in 98 µs. Because the light source is modulated it may be on or of as the mark enters the sensors FOV. Therefore the sensors response must be sufciently fast to make a measurement before the mark leaves the sensors FOV. Selecting a sensor with a response that is four times faster than the time required for a mark to move the distance equal to its width will generally guarantee detection. In this example a sensor with a maximum spot size of 0.5 mm and a response time of 25 µs or faster would be a suitable choice. Color mark sensor eye mark sensor contrast sensor registration mark sensor - 1. Packaging machines Flour rap machines FFS machines 2. labelling machines 3. Inkjet printers 4. Bottling machine 5. Paper roll and flm roll printing machines

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6. Re-winding machines 7. Rotary type machines . Ultra violet sensor /U.V sensors /fourescent detection sensor /Luminescence sensors –Both Analog and digital output enabled sensors. Voxin Tech sensors respond to materials such as paints greases inks and adhesives that have luminescent tracers which emit light in the visible spectrum when stimulated by a UV light source. These sensors are useful in applications where the presence of these materials needs to be accurately verifed. The technique of applying a luminescent marking is often useful in applications where there is signifcant variation in the background that needs to be ignored such as text and graphics printed on labels. A luminescent mark can be printed using an invisible ink anywhere on a label without afecting the labels aesthetics and still allow a luminescence sensor to detect the mark to verify presence orientation and positioning of the label. Often clear flms such as those used in tamper-evident seals contain optical brighteners that cause them to luminesce in the presence of a UV light source. Gluedetergent adhesives plastics fuorescent chalksmarkers-crayons greese and leaking oil detection sensor Ultra violet pigments or brighteners and most hydro carbon based materialsensor to detect tamper evident seals. Many commonly used packaging and production materials use luminescent tracers as a means of providing presence verifcation. Among these materials are adhesives gums flms inks and greases. Since many of these materials are clear or nearly clear other types of sensors are not suitable for reliable verifcation. Background or substrate luminescence is an important consideration in luminescent sensor applications. It is recommended that substrates be checked to verify that they do not possess a substantial luminescent property that will adversely afect the reliable detection of the intended luminescent markings. Some materials such as white paper contain optical brighteners that have a strong luminescent characteristic it is often

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difcult to provide a luminescent mark that will exceed the background luminescence of high-quality white paper. In these cases luminescent inks that emit light in the yellow/green spectrum may be useful to allow diferentiation between the mark and the paper. Other materials such as wood have a natural luminescence marks on wood need to have stronger luminescent properties than the wood for reliable detection. Sensor Selection Considerations Generally selecting the proper sensor involves carefully assessing the target characteristics and determining what constitutes the acceptance criteria. 1. What is the characteristic that is to be detected The table in Figure 4 shows many common materials and the type of sensor typically used for detection. Figure 4. Certain sensor types lend themselves to use with various common materials SENSOR TYPE CHARACTERISTIC TO BE DETECTED Luminescence sensor Luminescent tracer in: Adhesive Gum Grease Inks Crayon Chalk Thread Oil detection Leaking oil Detection Tampered seals Color sensor Color consistency verifcation and sorting of: Tiles sorting machine Painted products

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Automotive interior trim components Plastics Tinted flms Stained wood Packaging materials Labels Printed products Carpet Textiles Color mark sensor Precise high-speed color mark detection for: Printing processes Packaging applications Print-to-cut triangle for gluer- folder Color registration mark verifcation Contrast sensor Detects marks or contrast changes of: Registration marks Objects 2. Is there one condition or are there multiple conditions that constitute acceptance of the part With the exception of the color sensor all of the other sensor types detect a single characteristic or condition that causes the refected light signal to be above or below the threshold. Multiple characteristics can often be diferentiated using a color sensor or several contrast sensors. 3. Is the surface glossy or matte

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Glossy highly refective surfaces generally require mounting the sensor on a slight angle relative to the target surface e.g. 15° from perpendicular. If the glossy characteristic is the feature that needs to be detected then the sensor should be mounted perpendicular to the target surface. Matte surfaces difuse light in a relatively uniform manner improving detection consistency. 4. What is the size of the feature The mark or object should be larger than the sensor spot size for reliable operation. The size of the feature and the speed of the target must be considered in all but static or slow-moving processes. Reliable detection requires that the target be present in the sensor light spot long enough to be acknowledged by the sensor. 5. How fast is the target moving Reliable detection is a function of the sensors response time sampling rate size of the target and the speed of the target as it moves through the sensors light spot. Simply put the target needs to be present in the sensors light spot long enough for the sensor to respond. Sensors that have response times faster than 100 µs are generally suitable for all but the highest speed/small target applications. 6. What is the distance—minimum and maximum—from the sensor mounting position to the target While some sensors operate at distances 100 mm most do not. Greater distance operation requires the use of higher sensitivity sensors. Some color sensors contrast sensors and luminescence sensors provide large light spots allowing their use at greater distances from the target. Generally it is best to select a sensor that will provide reliable detection and place it at the optimum distance rather than to fx on a distance requirement and try to fnd a sensor that will work. 7. Is the sensor-to-target distance fxed or does it vary Variation in sensor-to-target distance typically referred to as "futter" is a factor in successful detection. Since all photoelectric sensors measure the diferences in light collected by the sensor optics changes in distance will cause changes in the amount of

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light incident on the collection lens. Whether or not this results in a problem with detection reliability depends on the diference between presence and absence levels: the greater the diference the greater the allowable distance variation. Closing Thoughts While applications are sufciently diferent from one another applying the guidelines discussed in this paper will help to make the sensor selection process a bit easier. Photoelectric sensors are powerful tools that when properly applied can produce highly reliable solutions to some tough automation challenges.