Optical Sensing Techniques for Color Analysis in Industrial SettingsColor matching and color consistency are important quality control parameters for finished products in many markets. For example, in the textile industry, a continuous swath of fabric moving through production equipment may be tested for dye variability, or different batches may be compared for consistency. In food quality control, the desired product color is carefully adjusted to consumers’ tastes, and the product must look the same despite being produced at different factories. In commercial lighting, bulb-to-bulb consistency to within the limits of human detection is extremely important. This is particularly true for banks of color LEDs, or any type of lighting array.
To control color as a quality parameter, color measurement must be repeatable from one production location to another. A well-defined method of comparing color, either within a batch or to an acceptable standard, is also required. Ocean Optics optical sensing solutions for inline color measurement offer both, providing the flexibility to configure the measurement system for various sample types and needs, as well as the software to perform quantifiable color comparisons.
Optical Sensing and Color Measurement
Measuring color is challenging, as the way our eyes detect color is not directly related to easily measured parameters such as light intensity. Color is dependent on the sample, on the illuminant and on subjective human perception. However, spectral sensing makes color measurement quantifiable, repeatable and consistent.
Optical sensing tools like spectrometers, cameras and multispectral sensors are well suited for monitoring color in process environments, whether the application requires full spectral analysis or measurement of only a few wavelengths of interest.
Where full spectral analysis is required, measuring the amount of light across the entire visible wavelength range brings real advantages compared with colorimetry due to the higher resolution and wider bandwidth of the measurement.
Simple colorimeters use red, green and blue filters in combination with diodes or sensor pixels for measurement. More advanced systems use tristimulus filters that mimic CIE color matching functions.
But to detect small color changes, very high color resolution is necessary. By capturing the complete spectrum, the color measurement made by a spectrometer allows careful, detailed analysis of data.
When color measurements are made with a spectrometer, a full reflected or emissive spectrum is the starting point for all calculations. Capturing the complete spectrum allows the data to be analyzed in different ways, offering a degree of flexibility not available using other measurement methods. Consider these additional advantages:
- Provides quantitative measurements. Optical sensing is far more accurate than the human eye, with detailed spectral information available.
- Monitors color in real time. Optical sensing measurements can be used inline to provide continuous, real-time results for output to a PLC or other control system.
- Is non-contact, non-destructive and versatile. Fiber optics -- including light sources and accessories that connect to the spectral system -- allow setups to be deployed in hostile environments without affecting the spectrometer or the sample. Also, optical sampling setups can be designed for parts and components with unusual shapes, sizes or glossy versus matte finishes.
- Offers flexibility. Data acquired can be used to calculate multiple color parameters, varying factors such as the observer and illuminant.
- Can be used to measure other sample parameters. Other sample characteristics can be measured spectrally, such as brightness and output power for lighting efficiency calculations.
More recently, digital tools like artificial intelligence and machine learning are being applied to massive data sets generated from spectral measurements or used for complex spectral analysis, providing users with real-time insight into sample color and appearance, authenticity and other criteria.
Color Measurement in Process Environments
In process environments, the sensing instrument must be able to provide real-time monitoring, otherwise the solution is of no greater benefit than other approaches. As with any monitoring and analytical solution, the creation of fast and repeatable results is the goal. This is particularly true for long production lines, where downtime can be minimized by accurate measurements.
Spectroscopy offers a much better alternative to current color measurement methods that revolve around post-processing inspection. With post-processing inspection methods, if the product is not up to standard, the potential exists for significant product loss, as it is often too late to fix any issues. This waste can be mitigated using real-time spectroscopy monitoring.
Reliability is a key factor for many production lines. There are two ways in which an industrial-grade instrument can be reliable. These criteria are longevity, often expressed as a high mean time between failures (MTBF), and robustness (how well the instrument holds up to shock, vibration, humidity and so on). Environments where an instrument could be exposed to dirt and other particulate matter can lead to frequent replacement of instrument components. For many companies, this disturbance leads to an increase in both downtime and costs.
Manufacturers also want easy to service components. While minimizing the downtime of instruments is a key factor to obtaining high efficiencies, all instruments will require maintenance at some point. When the time comes, components from a reliable source that can be swapped easily enable technicians to minimize downtime and speed up maintenance protocols. Here are additional criteria for spectral systems in process environments:
- In high-speed environments such as process lines, spectral instruments can acquire spectra quickly and process and store data onboard the instrument to save data transfer time.
- Maintaining instrument fidelity despite challenging conditions (temperature extremes and more) is managed through careful instrument design and system setup.
- Our spectral systems have a small footprint and are designed for simple integration into process instrumentation or the process line.
- Spectral instruments can be connected to industrial control systems via interfaces including Gigabit Ethernet, Wi-Fi, USB and RS-232.
Examples of Inline Color Measurement using Optical Sensing
High-Speed QC Processes
Solution: With high scan rates, robust communications capabilities and onboard processing, Ocean Optics spectrometers overcome limitations of some devices for processing environments.
Inline Fruit Sorting and Grading
Challenge – Grading of fruit based on color, sweetness and the presence of defects requires a solution capable of measuring both external (surface) and internal fruit characteristics.
Solution – Reflectance spectroscopy system capable of deriving color and sub-surface information about the fruit without contact and non-destructively.
Applications – Sorting and grading of apples, dates, grains, soybeans
Consumer Finished Goods Color Quality
Challenge – Maintaining color consistency in high volume production of consumer goods requires fast, reliable measurement systems.
Solution – Inline, real-time optical sensing systems are configured to capture diffuse reflection while minimizing variation in material color finish.
Applications – Color quality of consumer electronics, automotive parts and components
Inline Color Measurement for Paint, Solvents and Pigments
Challenge – Simple to use, customized inline color measurement system is required across multiple plants to maintain consistent colors in paint products.
Solution – Inline optical sensing solutions and custom algorithm development provide precise, reliable results, saving manufacturers time and reducing waste.
Applications – Color consistency in paints, pigments and colorants