The term “high-speed web inspection” can be broken down into its constituent terms “high speed” and “web inspection” for a more profound understanding. Machine vision systems are leveraged to address a customer’s high-speed web inspection issues, but what is the objective description of high speed? Vision systems capable of operating at rates above 30 fps are considered high-speed vision inspection systems. When people think about these high-speed vision inspection systems, they visualize hundreds of objects being inspected every minute. This, however, is a misconception. What makes these applications fast is not the speed of the production line but the concerned processing requirements.
The term “web inspection” refers to the detection of anomalies or the dimensional gauging of continuously processed products such as paper, film, foil, or textiles. The web material defects include stains, physical deformities, and several contaminants. Historically, laser scanning, cameras, or spectrometers were used in web inspection systems.
Let’s take a moment to understand laser scanning. So, laser scanning can be understood as the controlled deflection of laser beams, visible or invisible. This laser scanning technology is used in some 3D printers, barcode scanners, etc.
Nowadays, cameras are the primary sensing technology in most web applications because of their price-performance ratio. A typical web inspection system consists of a sensor for inspection, a means of tracking position, and a user interface for monitoring the system’s performance.
Hardware Involved in High-Speed Web Inspection
Qualitas Technologies delivers powerful solutions in high-speed webs. This solution is primarily based on online scanning technology, utilizing line scan cameras operating at speeds up to 90kHz line rates. The basic architecture of our high-speed web inspection system consists of the following hardware:
- Line Scan Cameras with Lens
Line scan cameras work on the principle of scanning only a single row of pixels with high resolution (up to 12,000 pixels). The latest TDI sensors are based on the revolutionary TDI (Time Delay Interfacing) technology. This method of line scanning offers dramatically enhanced responsivity compared to other video scanning techniques.
- Frame Grabber
We use a suitable CameraLink frame grabber after adequately evaluating the concerned application. The right set of boards needs to be selected after a thorough analysis of the requirements depending on throughput, required processing power, and the number of cameras to be interfaced into the system. The use of this frame grabber has been extended to interfaces directly with the shaft encoder and the trigger from a laser scanning/ photoelectric sensor. This ensures high accuracy of pixel-perfect synchronization and scanning between the image capturing hardware and the conveyor. This technology can also help achieve line speeds greater than 5 m/s.
- High-Intensity Line Light
For line scan systems to work at the optimal productivity levels, line lights of greater than 100,000 lux are required for accurate scanning. With the right combination of the wavelength of light and the output power – we can choose the apt lighting for the application.
- Industrial PC
Based on the processing power and integration requirements of the concerned application, you need an Industrial PC tailored according to your needs. In extremely high-speed environments, you also need offline processing in a separate process. This decouples the software from the capture process so that the frames are not skipped due to delays in image processing.
- Shaft Encoder
Selection of the apt shaft encoder and resolution is critical to ensure proper synchronization between the grabber and the conveyor. If the resolution is too high, then the frame rates surpass the scanning speeds. And if the resolution is too low, then the sharpness of the image is affected. Thus, it is crucial that the encoder be compatible with the requirements of the system.
- Photo Electric/ Laser Sensor
These are used in signaling the start and stop commands of the frame. It is critical to choose the right sensor technology, especially in cases where high scanning speeds are concerned.
Problem Analysis & Solution Setup
Qualitas Technologies has recently devised a solution for web inspection. Let’s consider the print industry as an example. We needed to inspect a web spool with labels printed on the web with multiple columns. The line speed demanded a maximum cycle time of 20ms to complete the inspection of one complete frame in the web.
While this could have been easily accomplished with a line scan system, we instead chose three high-speed area scan cameras to minimize the costs. Three 120 FPS firewire cameras, a high-speed 2nd generation desktop PC, and two linear lights seemed to suit the purpose well. A photoelectric sensor acted as the external trigger to activate all three cameras simultaneously for every frame.
Benefits of High-Speed Web Inspection
Thanks to the massive leaps in technology, today’s low-cost vision inspection systems have gained traction in a vast number of industries, helping them reap considerable benefits. Some of the prominent benefits are:
- Enhanced Quality Control
Web inspection vision systems can inspect a variety of continuously processed materials with tremendous accuracy and high precision, helping generate only quality products in compliance with the set standards.
- Saving on Costs and Time
Web inspection systems are capable of operating at high speeds and, therefore, increasing the net throughput. By replacing manual labor, these low-cost vision inspection systems help reduce operational and maintenance costs while eliminating the room for manual errors.
- Higher productivity
By freeing the employees from the mind-numbing and taxing tasks involved in the inspection processes, their efforts can now be directed to a more valuable purpose to the company.
In this post, we gained an in-depth understanding of high-speed web inspection systems, their components, and their benefits. We also performed problem analysis based on the issue of inspection in the print industry and outlined the basic architecture of a suitable solution to the problem.