Text / Lee Kielblock, Senior Application Engineer, Banner Engineering, USA
Not long ago, engineers working on quality control systems had limited options, none of which were entirely satisfactory. These included costly single-use vision systems, multi-array low-function photo sensors, and human inspections that were prone to fatigue and inattention. However, modern vision sensors now combine the best of traditional methods with remarkable speed, accuracy, compact size, and cost efficiency.

Figure 1: Vision sensor checks if the correct part is being conveyed

This article explores the capabilities of different sensor technologies and explains why visual sensing is rapidly becoming the fastest-growing segment in the industrial sensor market.

The basic principle of visual sensing

A photo sensor detects light, while a vision sensor captures thousands of pixels from a single image. Image clarity and detail are usually measured by resolution, expressed in pixel count. For example, some vision sensors from Banner Engineering can capture up to 1.3 million pixels, allowing them to "see" even small targets from several meters away.

Figure 2: Broken pills in a blister pack detected by a backlit vision sensor


Once the image is captured, the vision sensor compares it with a reference image stored in memory. For instance, it can detect whether a machine part has eight correctly inserted bolts or if one is misaligned. Moreover, the sensor can make accurate judgments regardless of where the component is located in the field of view or its orientation, even if it's rotated 360 degrees.

Key elements of vision sensor applications

1. Lighting – In vision sensor applications, lighting is the most critical factor. The type and placement of the light source directly affect the contrast between the target and the background.

2. Tools – Vision sensors use algorithms (often referred to as tools) to analyze images. A versatile vision sensor offers multiple tools for different tasks, while lower-cost models may only have one. Each has its own specific use cases.

Figure 3: A vision sensor identifies if a bottle label is missing


Tools are generally divided into two categories: linear and flat. Both analyze image changes, but they do so in different ways.
(1) If the area to be monitored is predictable, a linear tool is ideal because it’s faster and more precise. For example, a vision sensor can use a linear tool like a cutting tool to ensure vials are properly sealed as they move along an assembly line.
(2) If the target’s position might vary, such as in a plastic bottle box that may be missing one or more bottles, a flat tool is more practical. It checks for deviations from the standard.

Advantages of vision sensors

Among available inspection alternatives—vision systems, photoelectric sensors, and manual checks—vision sensors often offer the best combination of accuracy, ease of use, rich functionality, and affordability.

Figure 4: Trained sensors monitor mislabeling in horizontal and vertical positions


As competition intensifies across industries, profit margins shrink, and manufacturers can no longer afford high scrap rates. To avoid costly errors, they're integrating inspection processes into the entire production cycle.
1. While complex vision systems provide detailed automatic inspection, their high cost and complexity often limit their use. These systems typically range from $5,000 to $50,000 and require cameras, custom software, and computers. They also need expert support and are not easily adaptable for other uses.
In contrast, vision sensors are more affordable, easier to use, and increasingly popular in inspection and verification tasks. Their compact size and flexibility help improve factory automation quality and production efficiency.
2. Compared to photoelectric sensors, vision sensors offer greater flexibility. Previously, multiple photoelectric sensors were needed for certain tasks, but a single vision sensor can now handle them all. Vision sensors can inspect larger areas and allow more flexibility in target positioning and orientation. This makes them ideal for applications that once relied solely on photoelectric sensors. Additionally, since the cost of a basic vision sensor is similar to that of several photoelectric sensors with expensive accessories, price is no longer a barrier.
Vision sensors also provide unmatched flexibility for application switching. For example, changing from a yogurt cup to an ice cream container can be done in seconds and remotely. Additional test conditions can be added easily.
3. When compared to manual inspections, vision sensors offer significant advantages. While many inspections are still done manually, vision sensors can work at higher speeds, perform consistent and repeated inspections at lower costs, and reduce human error.

Expanding applications of vision sensors

The affordability and ease of use of vision sensors have led to their integration into a wide range of applications previously handled by labor, multiple photoelectric sensors, or no inspection at all. Industrial applications include inspection, metrology, measurement, orientation, flaw detection, and sorting. Some examples include:
● At a car assembly plant, verifying that robot-applied door frame beads are continuous and of the correct width.
● In a bottling plant, checking that caps are properly sealed, filling levels are correct, and no foreign objects have entered the bottle before capping.
● On a packaging line, ensuring that the correct label is applied in the right location.
● In pharmaceutical packaging, detecting broken or missing tablets in aspirin blister packs.
● In a metal stamping facility, inspecting stamped parts at over 150 per minute—13 times faster than manual inspection.
For vision sensors, this is an exciting time. Technology once requiring specialized expertise is now more accessible and cost-effective. Future developments will continue to expand their potential. The challenge now is to raise awareness among industries about the full range of benefits vision sensors offer in quality control, measurement, and inspection processes.

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