13 Understanding Vision Sensors: Components and Edge Detection

Introduction

Vision sensors are an integral part of machine vision systems, utilizing various components to capture and process images for a wide range of applications. Some of the key components of vision sensors include lighting, lenses, image sensors, controllers, and communication protocols[1]. These sensors use images captured by a camera to determine the presence, orientation, and accuracy of parts, and they differ from image inspection systems in that the camera, light, and controller are integrated together, simplifying installation and operation[3]. Image sensors, a vital component of vision sensors, are responsible for converting incoming light into an electrical signal that can be analyzed or stored[4].

Figure1: Vision Sensor [6]

These sensors enable machines to “see” and interpret visual data, allowing for automation, quality control, and safety enhancement. In this reading material, we’ll delve into the components of vision systems and explore the concept of edge detection, a fundamental process in image analysis.

Components of Vision Systems:

1. Image Capture Device: At the heart of any vision system lies the image capture device, which could be a camera or an array of cameras. These devices capture visual information from the surroundings and convert it into digital signals for processing.
2. Lens: The lens focuses light onto the image sensor, ensuring clarity and precision in capturing images. Different lenses may be used depending on factors such as focal length, field of view, and depth of field requirements.
3. Light Source: Adequate illumination is essential for high-quality image capture. Vision systems often incorporate various lighting techniques, including LED arrays, strobes, or ambient lighting, to ensure optimal visibility of objects.
4. Image Processing Unit: This unit processes the digital signals received from the image capture device. It includes hardware and software components responsible for tasks such as image enhancement, feature extraction, and pattern recognition.
5. Communication Interface: Vision systems often integrate with other systems or networks for data sharing and decision-making. Common communication interfaces include Ethernet, USB, and industrial protocols like Modbus or Profinet.

In addition to the components, vision sensors are capable of performing various tasks such as edge detection, presence detection, orientation determination, and accuracy inspection. They can be used for multi-point inspections and are known for their wide field of view, allowing detection even when the target position is not consistent [3]. Furthermore, vision sensors can be integrated into different platforms, including PC-based systems, standalone vision systems, and simple vision sensors, offering flexibility in their application [2].

How does the vision sensor work?

Vision sensors work by utilizing various components to capture and process images for a wide range of applications. The main function of the image sensor (Figure 1) is to capture light and convert it to a digital picture while balancing noise, sensitivity, and dynamic range[1]. These sensors use images captured by a camera to determine the presence, orientation, and accuracy of parts, and they differ from image inspection systems in that the camera, light, and controller are integrated together, simplifying installation and operation [3]. Once the field of view is set, an operator can run vision tools within the entire range of the target to inspect multiple features, completeness, or orientation—all in a single image [4].

Vision sensors perform inspections by first capturing an image, finding an object or feature in the image, and then searching for certain characteristics on that object or feature. They can be used for tasks such as edge detection, presence detection, orientation determination, and accuracy inspection. These sensors can handle multiple inspection points per target and can detect products or packages by pattern, feature, and color [5].

In terms of components, vision sensors share common components with vision systems, including lighting, lenses, image sensors, controllers, vision tools, and communication protocols [5]. The lens captures the image and presents it to the sensor in the form of light, while the image sensor converts light into a digital image, which is then sent to the processor for analysis [5].

Different types of vision sensors and their applications

Vision sensors come in various types, each with its own set of applications. These sensors use images captured by a camera to determine the presence, orientation, and accuracy of parts, and they differ from other types of sensors such as fiber optic, proximity, and ultrasonic sensors. Some of the different types of vision sensors and their applications include:

Monochrome Model: This type of vision sensor captures images using a monochrome camera and is suitable for applications where the color of the object is not a critical factor. It is commonly used for tasks such as presence detection, orientation determination, and accuracy inspection [3].

Color Model: Vision sensors equipped with color cameras are capable of capturing and processing images in color. They are suitable for applications where color differentiation is important, such as identifying products or packages by their color or detecting variations in color intensity [3].

Measurement and Inspection: Vision sensors are commonly used for measurement, pass/fail decisions, and other observable characteristics relating to product quality. They can be utilized for tasks such as detecting defective objects, measuring the size of objects, and performing character recognition [2][3].

Pattern Searching: Vision sensors are equipped with image processing capabilities that allow them to perform pattern searching. This feature is useful for identifying specific patterns or features within an image, making them suitable for applications such as pattern matching and object recognition [4].

Flexibility and Multi-Point Inspections: Unlike other types of sensors, vision sensors can handle multiple inspection points per target and are known for their wide field of view, allowing detection even when the target position is not consistent. This makes them suitable for applications requiring flexibility and the ability to inspect multiple features within a single image [1][6].

In summary, vision sensors play an important role in automated inspection in manufacturing, offering benefits such as increased throughput, higher quality, and lower costs. Vision sensors come in different types, each tailored to specific applications such as monochrome or color-based inspections, measurement, pattern searching, and flexibility in handling multiple inspection points per target. These capabilities make vision sensors a versatile solution for a wide range of industrial inspection tasks across various industries. Understanding the various components and capabilities of vision sensors is essential for making informed choices when integrating them into industrial processes [7].

Deepen your understanding: Watch the accompanying lecture video to delve deeper into the concepts covered in the reading. The second part of this lecture video covers the vision sensor.

References:

1. Cognex. (n.d.). Vision sensors: Components. Retrieved from https://www.cognex.com/what-is/vision-sensors/components
2. Cognex. (2024, February 3). Introduction to Vision System Components. https://www.cognex.com/blogs/machine-vision/introduction-to-vision-system-components
3. Keyence. (n.d.). Vision Sensors. Retrieved from https://www.keyence.com/ss/products/sensor/sensorbasics/vision/info/
4. Lucid Vision Labs. (n.d.). Understanding Digital Image Sensors. Retrieved from https://thinklucid.com/tech-briefs/understanding-digital-image-sensors/
5. GlobalSpec. (n.d.). Vision Sensors Selection Guide: Types, Features, Applications. Retrieved from https://www.globalspec.com/learnmore/video_imaging_equipment/machine_vision_inspection_equipment/vision_sensors
6. Cognex. (n.d.). How Do Vision Sensors Work? Retrieved from https://www.cognex.com/blogs/machine-vision/how-do-vision-sensors-work
7. Optex FA. (n.d.). Vision Sensor Guide. Retrieved from https://www.optex-fa.com/tech_guide/vision/guide/