Machine vision lighting for pharmaceutical and medical device inspection

The continued existence of the new coronavirus epidemic has made people more aware of the importance of the pharmaceutical and medical device industry. In the pharmaceutical and medical device industries, machine vision inspection technology is often used for quality control in high-volume manufacturing environments. For example, in the production of medical products such as syringes and medicine bottles, machine vision is often used for quality monitoring. The global new coronavirus vaccination plan will eventually cover about 7.8 billion people and will require a large amount of vaccines, and the production of vaccines is inseparable from visual inspection.

In the broader pharmaceutical and medical device industries, machine vision can start from inspecting raw materials, all the way up to inspecting finished products and their packaging. Product inspection can include size, shape, color, completeness, and the presence of defects or foreign objects. Packaging inspection ranges from checking the fill levels of vials and bottles to ensuring the filling of blister packs. The presence and location of tamper-evident seals can also be detected, as well as other details about the integrity of the package. It is also important to confirm the presence of labels, as well as to read and verify 1D/2D codes and human-readable text. Using a serialized QR code on each package can be traced back to production from the point of sale. Machine vision lighting is a critical component in ensuring accurate and repeatable measurements while performing all of these tasks.

Lighting Considerations in Pharmaceutical and Medical Device Production Machine vision lighting needs to provide the illumination intensity and uniformity required by the application in order to produce images with good contrast and signal-to-noise ratio that highlight features of interest. These characteristics are determined by the application itself. Factors such as the color, surface texture, shape and reflectivity of the imaged object all affect its interaction with light, which also determines which light source form and wavelength is best suited for a specific inspection task. The geometric position between the object, light source, and camera determines the direction, lighting angle, and angle at which the camera collects light. Machine vision lighting solutions can be designed based on the unique needs of each application. Pharmaceutical and medical manufacturers require light sources that: High-speed, high-volume production requires precise pulses to "freeze" motion in the image. High lighting intensity is required to clearly capture smaller target information on moving objects, such as one- and two-dimensional codes. Used for lighting in clean room environments, the heat generation should be small to prevent product aging.

To maintain stable levels of lighting intensity and uniformity to ensure good production practices. Product Quality Control Many pharmaceutical powders need to be tested for the presence of foreign matter before being compressed into tablets. Traditional dome lighting provides uniform illumination of the powder, and the wavelength can be selected to provide optimal contrast between powder and contaminants. Foreign matter in a solution filled into a vial can be identified by examining the liquid using high-intensity directional illumination from a spotlight located at the bottom of the vial. Some opaque liquids may be transparent to infrared light, allowing infrared illumination to reveal contaminants. Tablets can also be inspected for dirt or other surface defects using a high-angle ring light, which provides bright on-site illumination. Light from surface textures and features (such as scratches and imperfections) reflects off the camera, so they appear as dark features on a bright background. Low-angle ring lights provide darkfield illumination that highlights surface features because the camera only receives light scattered by surface imperfections. This is useful in applications such as internal inspection of vial caps, edge detection, identifying defects in O-rings, and reading dosage and other information printed on the surface of tablets .

A major problem with packaging inspection is reflection from packaging materials, which makes it difficult to obtain acceptable images, especially when the packaging surface is uneven. Traditional dome lights and flat top lights provide even diffused lighting to minimize glare and shadows, making uneven surfaces appear flat, enabling imaging of codes and text printed on packaging. Flat dome lights create the effect of a dome light in a thin housing package, do not require a hole for the camera, and take up less space than a dome light. In addition, the choice of wavelength is also crucial to enhance the contrast between the print and the background. In some cases, code and text may be cross-printed and cannot be imaged separately using traditional methods. This is where photometric stereovision (part of the broader multi-lens computational imaging technology) can provide a solution. A single image is acquired by illuminating each segment of a four-segment ring or square light in sequence. Key data is extracted from each image and combined with the object's 2D texture or surface color to isolate the object's shape. In this way, the overlaid code and text can be separated.

Sometimes it is necessary to detect the amount of liquid loaded into a container. To measure the fill level of clear liquids in transparent containers with reflective surfaces, such as vials, ampoules, and IV bags, a flat panel light is used to illuminate the container from behind. The meniscus of the liquid is clearly shown in the image as a black line. Sometimes, the container containing the liquid is not completely transparent, in which case it is necessary to use wavelengths outside the visible range for measurement. For example, some contact lenses absorb ultraviolet light, and a high-output UV light source can be used to image the contact lenses within the package. Near-infrared (NIR) and short-wave infrared (SWIR) light can also penetrate many packaging materials, making them important in viewing the contents of a package.

SWIR and Hyperspectral Imaging Materials such as plastic and glass are transparent to illumination in certain areas of the SWIR band. Other materials, such as water and lipids, show strong absorption at specific wavelengths in this region, which can make them easier to see within packaging. For example, 1450nm light can image the moisture content in disinfecting wipes. Light in the 1450~1550nm band can also penetrate plastic. For medical products that use opaque packaging (such as bottles) to maintain efficacy, SWIR can be an effective solution for detecting substance information inside sealed products. Recent technological developments have greatly improved the intensity of SWIR light sources compared to those of just a few years ago.

Another powerful imaging technology is hyperspectral imaging. Hyperspectral imaging combines imaging with spectroscopy using broadband light sources. Because drug formulations absorb specific wavelengths of light, images can be generated based on these unique "fingerprints." Hyperspectral imaging enables product quality assessment based on chemical composition, such as differentiating similar-looking tablets and detecting contaminants and foreign matter. Using an appropriate illumination source that provides uniform illumination across the entire wavelength range in a manner similar to sunlight is absolutely critical to providing high-quality measurements. Traditional white LEDs are not suitable for these applications because they have a strong blue component, an intensity drop around 480nm, and a very weak red component. Natural light LEDs do have a similar spectral distribution to sunlight and offer a high color rendering index of Ra98. This ensures that the observed color of the illuminated object is very close to that of nature, making natural light LEDs the light source of choice for applications requiring accurate color reproduction.

However, since hyperspectral imaging requires illumination wavelengths exceeding 700nm, CCS has developed a single LED illumination source that provides a nearly flat spectrum between 400 and 900nm. The range can be further extended to 1000nm by adding two LEDs with outputs of 930nm and 970nm. High-Speed ​​Imaging In high-volume, high-speed applications, pulsed illumination at the appropriate speed to prevent motion blur in the image requires the use of specialized lighting controllers. Constant current lighting controllers not only allow lights to be pulsed, but also enable overdrive, which is driving LEDs with short pulses of current above the specified maximum to increase the intensity of the light's output. This is particularly useful when, under normal operating conditions, there is not enough light intensity to obtain adequate image detail. These lighting controllers are available with a variety of output channels to drive multiple light sources when required and ensure consistent light output from pulse to pulse, a key requirement to ensure repeatability of machine vision measurements. High-speed online inspection requires very fast stroboscopic lighting to avoid motion blur. Machine vision lighting system Manufacturers have developed high-power strobe light sources designed specifically for these high-speed inspections. The brightness of these light sources ranges from 2 million lux to 10 million lux. When strobe, they are noticeably brighter than standard lights. Available in a variety of form factors, they provide very high illumination intensities and a response time of less than 1µs from trigger input to maximum light emission, enabling ultra-fast strobing.

The high brightness not only provides the illumination intensity required for these extremely short strobes, but also allows the use of smaller apertures to increase depth of field. Machine vision inspection is a powerful tool for the pharmaceutical and medical device industries. Each specific application requires the right lighting to make target information clearly visible and enable inspection to achieve the required speed, consistency, uniformity and accuracy. As the range of LED lighting configurations expands, having the support and advice of a machine vision lighting expert is critical to ensuring the best lighting solution is achieved.