Today, Wuxi Rihuan Sensing Technology Co., Ltd. will introduce to us how color mark sensors are used in the packaging and printing industry? - Color marking, cutting positioning, presence/absence detection.

Color mark sensors are a type of photoelectric sensor specifically designed to identify the contrast difference between printed marks (color marks) and the background. They are widely used in automatic control systems in industries such as packaging, printing, pharmaceuticals, and textiles, and can achieve functions such as automatic positioning, fixed length, cutting, deviation correction, and counting. They do not recognize the color itself, but distinguish color marks from the background by detecting changes in the intensity of reflected light and output switch signals to the control system. In the packaging and printing industry, color mark sensors mainly undertake three tasks: color marking detection, cutting positioning, and label presence/absence detection. The process requirements and selection priorities for each scenario are different.

1. Color marking detection: The "scale" of printing quality

Process requirements

In multicolor printing, each color plate roller needs to precisely align the color marks on the substrate. If the color alignment deviations are too large, the printed product will have problems such as ghosting and color shifts. Currently, the automatic color alignment system uses photoelectric sensors (commonly known as "photoelectric eyes") to detect the position deviation of the color marks and combines encoder signals to calculate the error. The color alignment accuracy can reach 0.1mm. In the dual photoelectric eye structure, the center distance between the two focal points is usually 20mm, which is used to increase the detection and adjustment speed.

Selection points

Light source type: The printed product has rich colors, including low contrast, matte film, color aluminum foil, laser hot stamping film, etc. Therefore, RGB three-color light source color mark sensors should be selected. The system automatically selects the best emission color to improve the contrast resolution. Single-color light sources are prohibited.

Response speed: The printing machine runs at a high speed, so the color mark sensor needs to have an extremely short response time. The response time of mainstream products is in the range of 35μs to 50μs.

Gray scale resolution: The contrast between the color mark and the background may be very low. The sensor needs to have high gray scale resolution. Some products can reach 20 levels of gray scale, which can reliably detect subtle gray scale differences.

Light source lifespan: Color mark sensors usually use LED light sources instead of incandescent lamps, which have a longer lifespan and are suitable for continuous production environments.

II. Capping and positioning: The "starting gun" for packaging accuracy

Process requirements

The feeding speed of equipment such as pillow packaging machines, bag-making machines, and slitting machines can reach 100 to 300 meters per minute. The color mark sensors need to accurately track each color mark signal during high-speed feeding to provide triggering signals for the cutting knives, ensuring consistent cutting positions. If the sensor response is delayed, the cutting position will deviate from the color mark, resulting in inconsistent bag lengths and misaligned seals, leading to batch waste.

Selection Tips

Response Time: This is the core parameter for selecting the cutting positioning. On high-speed production lines, a 1ms delay in the sensor could mean a deviation of several millimeters in the cutting. The time for the color mark to pass through should be calculated based on the production line speed, and the sensor response time should be much shorter than this time. For high-speed bag-making, printing, and rewinding production lines (300 to 600 meters per minute), a 15kHz high-frequency model should be selected to prevent marking loss and omission.

Switching Frequency: High switching frequency means that the sensor can complete more on-off switching per second. For example, a 10kHz switching frequency can support 10,000 detections per second, suitable for most high-speed cutting scenarios.

Anti-shake Algorithm: The roll material will shake during high-speed feeding, and the sensor needs to have anti-shake capabilities to avoid false triggering due to shaking.

Depth of Field Tolerance: A sensor with a larger depth of field (such as ±3mm) can better adapt to the up and down shaking of the material or installation errors, and the signal is more stable.

III. Label Presence/absence Detection: The "gatekeeper" for quality control

Process requirements

During processes such as labeling, bag-making, and winding, it is necessary to confirm in real time whether the labels or color marks exist and if their positions are correct. For example, in the labeling machine, if the label position is incorrect or the printed marks are missing, the product should be automatically rejected. In the lithium battery winding process, if defective labels or warning labels are not detected, it may lead to defective products being wound into the battery cells.

Selection

Spot size： Labels are usually small in size， so a small spot sensor should be selected to ensure that the spot completely falls within the label range. Some products have spots as small as millimeter level， which is suitable for detecting fine marks.

Adaptive function： The contrast between the label and the base film may vary due to batch differences. Sensors with adaptive digital logic can automatically distinguish between the label and the base film without frequent adjustments.

Output mode： It needs to support NPN/PNP dual output or push-pull output to facilitate connection with different brands of PLC systems.

Installation flexibility： Some sensors support a 90° rotation of the optical system， allowing for installation on the top or side based on the installation space.

Quick reference for selection parameters

Application scenarios Key parameters Recommended configuration

Multi-color marking detection Light source type， grayscale resolution RGB three-color light source， grayscale ≥ 20 levels

Cutting positioning Response time， switching frequency Response time ≤ 50 μs， switching frequency ≥ 10 kHz

Label presence detection Spot size， adaptive function Small spot (mm level)， supports ADL automatic adaptation

Core selection principles for color mark sensors： The selection of color mark sensors is not "the higher the parameter， the better"， but rather it should be comprehensively matched based on three dimensions： production line speed， color mark contrast， and installation space. Low contrast materials must use RGB three-color light sources， high-speed production lines must select high-frequency models， and transparent films need to be paired with limited-mode optical fiber probes. During installation， a debugging space must be reserved to avoid direct strong light shining on the sensor receiving surface.

Rihuan Sensing provides color mark sensor products covering scenarios such as multi-color detection， cutting positioning， and label presence detection. It supports automatic switching of RGB three-color light sources， microsecond-level response time， and multi-mode teaching functions， and is suitable for various high-speed production lines in the packaging and printing industry. Welcome to follow Rihuan Sensing to obtain professional color mark detection selection guidance and technical support.