How to Select the Right Protective Optical Window
Safeguards
Protective windows are an essential element in any automation system. Although they may not be a fundamental component, they serve an integral purpose in safeguarding critical components. Protective windows are one of the most cost-effective ways to ensure system longevity, repeatability and reliability. With so many material and coating options, here's how to select the best protective window for our system.
Bild: Midwest Optical SystemsMaterial Options
When choosing a protective window, we first need to select the substrate material. For applications where the optics may be prone to scratches or used as a wear plate, a scratch resistant material should be selected. If the window will be exposed to high temperatures, like in a hot steel or glass factory, a material with a higher temperature rating is important. If the system uses a thermal or LWIR sensor, a material that can withstand harsh environments should be chosen. Let's take a closer look at the available materials:
- • Acrylic: Abrasion-, breakage- and solvent-resistant; durable, economical and laser-able; optical-grade and anti-reflection coated; oleophobic coating available.
- • Fused Silica/Quartz: Ultra-low thermal expansion; withstands temperatures of up to 1,100°C; superior transmission in the UV; multi-layer anti-reflection coating available.
- • Borofloat: Impact-, chemical- and alkali-resistant; withstands temperatures of up to 450°C, wavelengths range from UV, visible (VIS) and NIR; durable multi-layer anti-reflection coating; oleophobic coating available.
- • Precision Windows: Made with precision polished N-BK7; low image distortion and stain-resistant; free of bubbles and inclusions; ideal for low power laser applications; excellent transmission in the VIS and NIR.
- • Sapphire: Stronger than standard glass windows; durable to withstand harsh environments; impact-, chemical- and alkali-resistant; transmits wavelengths ranging from UV, VIS and SWIR.
- • Germanium: Diamond-like carbon (DLC) coating; can withstand harsh environments; ideal for thermal camera enclosures; 7.5 to 12.5 micron useful range.
Bild: Midwest Optical SystemsOptical Coating Options
Coatings play an important role in how the protective window interacts with the vision system and environment. Choosing the correct coating combination is key to both optical performance and maintenance. Anti-reflection (AR) coatings can have direct impacts on light transmission of an optical window and clarity. By decreasing the amount of light reflecting off the surface, a higher percentage of light will pass through the protective window.
Without an AR coating, reflected light can create glare or hot spots on the window, which can lead to a loss of clarity - especially when used in front of a vision sensor. But when it comes to AR coatings, it's not always one size fits all. Different AR coatings provide optimal transmission in the intended wavelength spectrum. For substrates that can be used in both the VIS and NIR range, Broadband Anti-Reflection (BBAR) coating is recommended. BBAR coating has a larger optical working range compared to standard AR coating while still providing all the AR benefits.
For protective and maintenance coatings, MidOpt offers a variety of solutions. Options like hard coating can provide the benefits of high scratch resistance and durability. This is commonly used to not only protect the window itself, but also protect other coatings such as AR and interference coatings. This will provide overall improved durability and longevity of the optics. For maintenance, an oleophobic coating resists moisture, oils, grease and smudging from fingerprints. This can prevent buildup of substances that could interfere with the clarity of the window.
Bild: Midwest Optical SystemsAdditional Lens Protection
Machine vision lenses can be fragile. Made up of a series of optical components, they help focus light onto the eye of a machine vision camera, the sensor. Many optical lenses are designed based on function and affordability rather than convenience, like adding a flat surface for easier cleaning. For this reason, many lens manufacturers include a filter thread on the front of the lens. While this filter thread is typically used for a machine vision filter, for applications where a filter isn't in use, MidOpt can utilize this filter thread for a protective window. If it is in use, all MidOpt filters and protective windows have male and female threads for easy stackability. For additional lens protection, there is the LE110 Lens Enclosure. It not only protects the front of the lens, but also the entire body of the lens from dust and impact. The LE100 also prevents tampering. Once installed, settings put in place by a technician it cannot be inadvertently changed, making this an easy, low-cost insurance for the lens and vision system.
Camera & Lighting Enclosures
Depending on the setting, machine vision components can be exposed to harsh elements such as corrosive chemicals, high temperatures, and water submersion. Putting these components into ruggedized enclosures protects them from the elements and maintains system reliability. Enclosures house cameras and/or light sources in sealed metal shrouds are usually aluminum or stainless steel. Many enclosures often also feature a protective window, which allows the camera to see out, doesn't interfere with image quality and serves as a protective barrier. Choosing the correct window material for the environment is key to providing adequate protection while keeping costs low. For example, light weight and shatter-resistant acrylic is ideal for food-grade / FDA-compliant applications. Acrylic provides an easy-to-clean surface while minimizing the risk of falling shards if the window was to be subjected to impact. For harsher environments, glass windows are the optimal choice, as additional options are available for impact, scratch and heat resistance.
Custom Solutions
Some vision systems may require a custom protective window to fit the design or application requirements such as autonomous mobile robots or drones for aerial landscape imaging. Custom options include:
- • Silk Screen Printing in a variety of colors and opacities for printing borders, masks, logos and other information. Inks that can act as optical longpass filters are also offered. (Ex: ink that blocks visible light but passes NIR light.)
- • Chemical Strengthening for applications where the glass is placed in front of a camera lens and optical distortion and surface quality are important. It's ideal for thinner glass (less than 3mm thick) and is most commonly used for Gorilla Glass, soda lime glass, some filter glasses and B270 and BK7 glasses.
- • Thermal Tampering/Heat Strengthening is offered for glass that exceeds 3mm in thickness to improve resistance to impact (up to eight times), high temperatures and scratches.
- • Assembly Mounting Tapes for easy assembly when screws are not an option. Very high bonding (VHB) tape is an easier and more convenient option than difficult to work with cements or liquid adhesives.
- • Specialized Shapes and Sizes can be precision cut to fit a specific radius or hole.
Protective windows are an essential element in any automation system. Although they may not be a fundamental component, they serve an integral purpose in safeguarding critical components. Protective windows are one of the most cost-effective ways to ensure system longevity, repeatability and reliability. With so many material and coating options, here's how to select the best protective window for our system.
Bild: Midwest Optical SystemsMaterial Options
When choosing a protective window, we first need to select the substrate material. For applications where the optics may be prone to scratches or used as a wear plate, a scratch resistant material should be selected. If the window will be exposed to high temperatures, like in a hot steel or glass factory, a material with a higher temperature rating is important. If the system uses a thermal or LWIR sensor, a material that can withstand harsh environments should be chosen. Let's take a closer look at the available materials:
- • Acrylic: Abrasion-, breakage- and solvent-resistant; durable, economical and laser-able; optical-grade and anti-reflection coated; oleophobic coating available.
- • Fused Silica/Quartz: Ultra-low thermal expansion; withstands temperatures of up to 1,100°C; superior transmission in the UV; multi-layer anti-reflection coating available.
- • Borofloat: Impact-, chemical- and alkali-resistant; withstands temperatures of up to 450°C, wavelengths range from UV, visible (VIS) and NIR; durable multi-layer anti-reflection coating; oleophobic coating available.
- • Precision Windows: Made with precision polished N-BK7; low image distortion and stain-resistant; free of bubbles and inclusions; ideal for low power laser applications; excellent transmission in the VIS and NIR.
- • Sapphire: Stronger than standard glass windows; durable to withstand harsh environments; impact-, chemical- and alkali-resistant; transmits wavelengths ranging from UV, VIS and SWIR.
- • Germanium: Diamond-like carbon (DLC) coating; can withstand harsh environments; ideal for thermal camera enclosures; 7.5 to 12.5 micron useful range.
Midwest Optical Systems
Dieser Artikel erschien in inVISION E-Magazin inVISION International (english) 2023 - 18.10.23.Für weitere Artikel besuchen Sie
