Quality 101: Using Machine Vision
January 15, 2007
A machine vision system acquires images of an object, and then uses computers to process, analyze and measure various characteristics of that object. The purpose may be to enhance the image to see characteristics undetected to the human eye, or to analyze image data for measurement purposes. The decisions made from this information are often related to quality. For example, production line parts can be qualified as good or bad based on their shape or size, but almost any industry can benefit from machine vision systems designed for their application.
Today, the costs of implementing a machine vision system have decreased significantly because of the lower cost of high-performance processors and improvements in sensors, cameras, lasers, embedded systems and illumination methods. With Six Sigma quality initiatives and the constant drumbeat of “better, faster, cheaper,” now may be the time to take a look at machine vision and determine if integrating a machine vision inspection system should be part of the quality improvement plan.
According to the Frost & Sullivan report, “Advances in Machine Vision Systems,” published in July 2005, “Machine vision systems are emerging as a superior alternative to human labor in process and quality control and are extremely sought after to create lean and flexible manufacturing systems. With its ability to deliver high accuracy while ensuring throughput on the production line, vision systems also serve as efficient quality control tools.”
Although the first machine vision systems were introduced in the 1970s, machine vision is now on the cusp of mainstream adoption across many industries. The semiconductor and electronics industries spearheaded the adoption of machine vision for inspection because of their complexity and miniaturization, but many other industries are following suit, and machine vision inspection has become cost-effective for the majority of applications.
For most products today, inspection is a necessity. Machine vision can add value by increasing the productivity and accuracy of the manufacturing process and reducing costs for the system’s operator. Today, industries from automotive to paper processing to food and beverage packaging are relying on machine vision to inspect products and increase the quality of the output. Industry experts predict that within the next 20 to 50 years, machine vision will become a universal factor across all industries, and that almost every product produced will be inspected by a machine vision system.
Machine vision is increasingly being used during the manufacturing process rather than just at the end to validate final quality. Products that are built in stages can heavily benefit from inspection throughout the process. Take, for example, electronic components. Electronic components are made in many stages from the initial silicon wafer to the final packaged chip. Using machine vision, a company can find bad parts and eliminate them early in the manufacturing chain so that the remaining production stages are never performed on the parts that are destined to be defective. Each production stage has a cost per unit associated with it, so if a company can eliminate the bad parts early, it can save money and improve efficiency.
Building BlocksThere are four main reasons for using machine vision:
• Accuracy. Machines have clear advantages in precision over the human eye. Even when humans rely on a magnifying glass or microscope, machines are still more accurate because they can “see” and measure parts to a tolerance of thousandths of an inch.
• Repeatability. Machines can conduct an inspection task over and over again in the exact same way without fatigue. In contrast, human inspectors tend to view an object slightly differently and may measure slightly differently each time, even if all the parts are exactly the same. Studies show that humans are 85% effective in visual detection of product quality concerns, while vision systems catch virtually 100% of these conditions.
• Speed. Machines can inspect parts faster. Particularly when inspection takes place at high speed, such as on a production line, machines offer an advantage in productivity and efficiency.
• Cost. Because machines are faster than humans, an automated inspector is worth several human inspectors. Machines also deliver higher uptime because they do not take breaks, do not get sick and are just as efficient in the middle of the night.
After a company determines the need for machine vision, the next challenge is to assemble the building blocks of the system. The essential components include: lighting, part positioning, cameras, optics and control logic, image acquisition hardware, processing software and engineering services.
Machine vision system components and configuration can vary from one application to another. For example, the frame grabber acquiring the image data from the camera could just as easily show a digital camera that sends images to the computer using a standard digital interface such as Gigabit Ethernet. In this case, the frame grabber’s duties of digitization, buffering and transfer of data to computer memory are all performed by the digital camera.
There are various components and system integration issues related to setting up a machine vision system. Most vendors are not expert in all of these areas, so look for a supplier who not only knows its core competencies, but has developed long-standing partnerships with other suppliers to provide other components needed for the system. Ask to speak to customers in the same industry, as well as in others that have successfully implemented machine vision inspection.
Inspection has become an important requirement during the manufacturing process to prevent poor quality products from being used in the value chain and from ultimately reaching-and potentially harming-the consumer.
Machine vision systems can yield significant benefits in the quest for improved quality including reduced scrap and rework, improved productivity, greater product reliability, increased consumer safety and greater customer satisfaction. As companies endeavor to increase quality and decrease costs, machine vision inspection may the next accelerant in the quest for perfection.