The effectiveness of a machine vision system is crucial for maintaining consistent performance and minimizing downtime. While these systems may perform optimally in controlled lab environments, they face numerous challenges when deployed in industrial settings. This article will explore the complexities of industrial environments, providing valuable insights to ensure your machine vision system remains robust and efficient in real-world applications. We will discuss strategies for overcoming obstacles and optimizing system performance, ultimately allowing you to make the most of your vision system in the demanding world of manufacturing.
Ambient Lighting: Managing Unpredictable Light Sources
In an industrial environment, ambient lighting can be a significant challenge to overcome. Unlike the controlled lab setting, unanticipated light sources from overhead lights or sunlight streaming through windows can compromise image quality. Fortunately, there are a few strategies to mitigate the impact of ambient lighting on your machine vision system.
- Block external or stray light sources: Create a controlled lighting environment around the inspection area by using enclosures, shrouds, or curtains. Adjusting the positioning of your camera and lighting can also help minimize the impact of external light.
- Utilize single-wavelength LED illumination: By choosing a specific wavelength (red, green, blue, etc.) for your LED lighting, you can reduce interference from other wavelengths. This approach can be particularly useful for increasing the contrast for the product in the acquired image.
- Implement strobing light techniques: Overdriving an LED for a very short duration produces 10x-100x brighter light, effectively drowning out interference from external light sources. Strobing can also help reduce motion blur in high-speed applications. Lights that are strobed can easily have a 7+ year lifespan. Lights left on 24/7 decrease intensity, requiring replacement in 2-3 years. When buying surplus or decommissioned lights off of eBay, this is what you are getting.
- Use polarized lighting and filters: Aligning the polarization of both the light source and the camera lens reduces glare and reflections, improving image contrast and quality. This technique is especially helpful when inspecting shiny or reflective surfaces. (Edmund Optics)
Dust, Dirt & Water: Protecting Your Vision System in Harsh Conditions
Industrial environments can expose machine vision systems to contaminants like dust, dirt, and water. These elements can affect image quality and potentially damage your vision system's sensitive components. To maintain optimal performance and ensure the longevity of your equipment, consider the following protective measures:
- IP-rated cameras: Choose cameras that, at minimum, are IP 65 rated (Ingress Protection dust tight). Dust impacts thermal efficiency to bleed off the heat on electronic components—the better the thermal management, the longer the camera's life span.
- Enclosures and housing: Placing an enclosure around the whole vision inspection system can help keep the system cleaner for longer. It can also help to block any strobing lights from affecting operators nearby. If working in a food & beverage or pharmaceutical environment where the equipment needs to be watertight, the camera must be placed in an enclosure. Although selection may be limited, the washdown version of lights does exist. (Smart Vision Lights)
- Air Purging: In particularly dusty environments, consider using an air purging system to keep the camera lens and lighting elements clean. Maintaining a constant flow of clean, filtered air across the lens can prevent dust and dirt from accumulating and affecting image quality. When using an industrial PC for a vision system, positive pressure in the cabinet can help to keep the heat fins clean.
- Sealed Connectors: Utilize sealed connectors for both cameras and lights to maintain the integrity of your electrical connections in the presence of moisture or other contaminants. This can help prevent signal degradation or even damage to your camera and other components.
- Lens Protection: Use protective lens covers or filters to shield your camera lens from direct contact with dust, dirt, or water. These accessories can be easily replaced if they become damaged or excessively dirty, protecting the more expensive components of your vision system.
- Regular Cleaning and Maintenance: Implement a preventative maintenance schedule for your machine vision system. Regularly inspect and clean protective filters on lenses and wipe down emission zones on LED lights to maintain optimal image quality. At a minimum quarterly, wipe down all surfaces of cameras, lights, and lenses for continued thermal efficiency, and don't skip checking if the control cabinet could use internal cleaning too.
Motion & Vibration: Stabilizing Your Vision System
In industrial environments, motion and vibration are inevitable factors that can significantly impact the performance of your machine vision system. To address these challenges, consider the following strategies:
- Camera Mounting: Carefully choose where to mount your camera. Attaching it directly to a vibrating surface, like a conveyor, can cause image blur and reduce the lifespan of the camera lens. Instead, opt for mounting the camera on a stable, isolated structure or the floor, away from vibration sources.
- Vibration Isolation: Utilize vibration isolation techniques such as mounting the camera on shock-absorbing or damping materials, which can help minimize the transfer of vibrations from the equipment to the camera. This can include rubber mounts, filling cavities of a structure with stainless shot, increasing the thickness of bracketry, or for really challenging environments, specialized vibration-isolating mounts designed for industrial applications.
- Shorter Exposure Times: Reducing the camera's exposure time can help minimize the impact of motion blur in high-speed applications. This can be achieved by increasing the camera's frame rate along with strobing light sources to "freeze" the motion of the object being inspected.
- Robust Lens Assembly: Select lenses with robust, industrial-grade assemblies designed to withstand vibrations and maintain focus. Lenses with locking mechanisms can help keep the focus and aperture settings fixed, even in the presence of vibrations. Consider replacing the thumb screws on the focus and aperture ring with set screws. In general, once a system is commissioned, the aperture should never be adjusted again; add a little bit of Loctite before installing the setscrew.
- Regular Maintenance: Implement a preventive maintenance schedule to inspect and maintain mounting hardware, damping materials, and other components that may wear over time, leading to increased vibrations.
Fixturing & Product Positioning: Ensuring Precision and Consistency
In machine vision applications, consistent and accurate product positioning is crucial for reliable inspection, measurement, and decision-making processes. The following strategies can help you optimize fixturing and product positioning within your industrial vision system:
- Camera and Light Fixtures with Repeatable Positioning: Design or purchase quality, durable fixtures to securely hold the cameras and lights during the inspection process. Minimize the degrees of freedom. Swivel/knuckle and rod-type mounting is great for quick prototyping, but we do not recommend it for permanent installation. If something gets knocked out of position, it is easier to realign the camera or light. Consider using precision adjustment mechanisms when fine-tuning alignment is needed.
(Foveal Mounts) - Product Fixtures: Design the fixturing system to enable repeatable positioning of products with minimal variation. This may involve using mechanical stops, guide rails, or custom-designed nests to align products consistently.
- Calibration: Regularly verify the alignment of your vision system and fixtures. This may involve using calibration objects or reference patterns to verify the system's accuracy and make necessary adjustments. At a minimum, quarterly archive images of both good and non-conforming products. This way, you can compare how a part or fixture changes over time.
- Regular Maintenance: Implement a preventive maintenance schedule to inspect and maintain fixtures, feeders, and other positioning components. Document and have reference guides to aid the maintenance team so they know what the captured image should look like. This helps ensure consistent product presentation and minimizes the impact of wear and tear on system performance.
Cabling: Ensuring Reliable Data Transmission in Industrial Environments
High-quality cabling is crucial for the successful operation of a machine vision system, as it directly affects data transmission, reliability, and overall system performance. When choosing and implementing cabling solutions for your vision system, consider the following aspects:
- Cable Quality: Select high-quality cables designed for industrial applications that can withstand harsh conditions, such as temperature extremes, humidity, and chemical exposure. Look for cables with proper shielding and insulation to minimize the impact of electromagnetic interference (EMI) from nearby equipment, such as motors, power lines, or welders.
- Cable Quality: Select high-quality cables designed for industrial applications that can withstand harsh conditions, such as temperature extremes, humidity, and chemical exposure. Look for cables with proper shielding and insulation to minimize the impact of electromagnetic interference (EMI) from nearby equipment, such as motors, power lines, or welders.
- Connector Quality: Select high-quality connectors that can withstand the rigors of an industrial environment. This includes connectors that resist bending, impacts, and excessive tension to ensure a stable connection and minimize the risk of data loss or garbled packets.
- Environmental Protection: Choose cables with appropriate ratings for the specific industrial environment, such as IP-rated cables for dust and water protection or cables with chemical-resistant jackets for harsh chemical environments. PUR cables resist cutting fluids, oil, and repeatable flexing, which is ideal for an automotive environment. Whereas PVC cables are resistant to cleaning chemicals used in the food and beverage industry. (Turck)
- Cable Management: Implement effective cable management practices to prevent damage, reduce connector strain, and maintain an organized workspace. This may include using cable trays, conduits, or cable chains to route and protect cables, as well as implementing strain relief mechanisms to minimize tension on connectors. Avoid tight bend radiuses in the cable raceways or at the devices. Most importantly, plan for and implement service loops. Guaranteed at some point in the life of a Vision System, something will need to get moved or added.
- Pre-terminate all Cables: Terminating/Landing cables in the control panel on site, stated bluntly, sucks. With most manufacturing operations 24/7, and limited scheduled downtime, the installation of a Vision System needs to be tight and efficient. Pre-termination and strategizing with quick disconnects allow a Vision System to be fully checked out before delivery, installation, and commission in production. The cost saving on labor and travel expenses far outweighs the extra cabling costs. Lay any excess cable in a cable tray or in the skirt under the control panel.
- Regular Maintenance: Implement a preventive maintenance schedule to inspect, clean, and maintain cables and connectors. This helps identify potential issues, such as damaged insulation, loose connections, or signs of wear before they cause system failure or downtime.
Conclusion
In the demanding world of manufacturing, ensuring your machine vision system is robust and reliable is critical for achieving consistent performance and minimizing downtime. By addressing the challenges posed by ambient lighting, harsh conditions, motion, and vibration, fixturing and product positioning, and cabling, you can create a vision system that thrives in the unforgiving industrial environment. Regular preventative maintenance is essential to the long-term success of your vision system, so be proactive and help the maintenance team out by having documentation and reference images. With careful planning, consideration, and execution, you can optimize your machine vision system to withstand the rigors of the manufacturing plant and deliver exceptional results.
