In manufacturing, inspection is one of the essential processes for ensuring consistent product quality. In particular, surface inspection and visual inspection are commonly performed using machine vision systems with area cameras or line scan cameras, while in some industries visual inspection by human operators is still used. In recent years, as an alternative to large and complex camera systems, CIS (Contact Image Sensor) line scan cameras have increasingly been considered as a viable option in machine vision applications due to the following characteristics:
– Compact structure – Integrated design combining camera, lens, and light sources – No-distortion imaging using a 1:1 optical system – High stability and resistance to vibration
To improve inspection accuracy while also achieving a more compact inspection system, it is important to select a CIS line scan camera that fully leverages these characteristics. Understanding the specific features of line scan cameras and selecting specifications appropriate for the application are key factors in successful implementation. This article summarizes several fundamental points to consider when selecting a CIS line scan camera.
One of the most fundamental parameters when selecting a camera is resolution. While conventional cameras often express resolution based on the number of sensor pixels, CIS line scan cameras typically use dpi (dots per inch) as the resolution metric. The required resolution can be calculated as follows.
Another major difference compared with conventional cameras is the scanning width. CIS line scan cameras consist of multiple sensor chips arranged in a single line, and the total length of the sensor array corresponds directly to the scan width. Therefore, unlike conventional cameras where the field of view is adjusted using a combination of lens selection and working distance, CIS cameras require selecting a model with an appropriate scan width according to the width of the inspection target. For example, if the inspection object is 300 mm wide, selecting a CIS camera with a scan width that covers this dimension allows the entire object to be captured in a single pass.
Because the field of view does not need to be adjusted through optical parameters, the imaging range can often be determined more simply during machine design. This is one of the strengths of CIS systems. Furthermore, because CIS cameras use a 1:1 optical system, the scan width closely corresponds to the actual imaging width, making the field-of-view design more intuitive. By organizing the system layout in advance—such as the conveyor width and the size of the inspection target—it becomes easier to select the appropriate scan width.
In addition, the availability of different scan width options means that even large inspection objects can sometimes be inspected using a single camera. Compared with systems that require multiple cameras, this can simplify the overall system configuration and increase design flexibility.
Lighting is a critical factor in improving the accuracy of surface inspection. Appropriate illumination conditions must be selected depending on the reflectivity, transmissivity, and material properties of the inspection object. Traditionally, CIS line scan cameras incorporate an integrated light source combined with the sensor. This integrated design provides uniform illumination across the imaging area and allows a stable imaging environment to be built with a relatively simple system configuration.
In continuous inspection systems along production lines, the fixed positional relationship between the illumination and the sensor helps ensure highly repeatable image acquisition. However, depending on the inspection target or the type of defect, it may be necessary to adjust the illumination angle or light diffusion characteristics using external lighting. To support such applications, CIS cameras without a built-in light source have also been introduced in recent years. By combining these cameras with external lighting systems, the illumination angle and optical conditions can be adjusted to create lighting environments optimized for the inspection target.
Another important factor when designing lighting is the working distance (WD). Traditional CIS cameras are designed for near-contact imaging, typically requiring the distance between the protective glass and the object to be less than approximately 0.5 mm. However, advances in optical design have led to CIS cameras capable of operating at working distances of about 50 millimeters.This increased working distance allows more space for lighting equipment and enables the use of various illumination techniques such as low-angle (dark-field) lighting or diffuse illumination, depending on the application.
The wavelength of light is also an important factor in illumination design. In addition to white light, a variety of wavelengths may be used, including RGB, infrared (IR), and ultraviolet (UV). For example, certain wavelengths may enhance the visibility of fine surface textures, while others may highlight specific materials or contaminants. The optimal wavelength depends on the characteristics of the defect to be detected. In this way, the visibility of defects can change significantly depending on the combination of lighting conditions and optical configuration. To achieve stable inspection performance, it is important to comprehensively consider the relationships between lighting method, wavelength, and working distance based on the characteristics of the inspection target and the types of defects to be detected.
CIS line scan cameras can deliver their full potential when inspection conditions and system constraints are clearly defined. Proper resolution design, scan width selection, and lighting configuration are essential. By organizing these parameters during the early stages of system design, the overall efficiency of inspection system development can be improved. At WHEC, we offer customizable CIS line scan cameras with a wide range of options including resolution, scan width, integrated or external illumination, working distance, interface options, and mechanical dimensions. As a specialized CIS camera manufacturer, we can propose optimal solutions based on your application requirements. If you are considering CIS camera selection, please feel free to contact us.
For further details or questions regarding product characteristics, please call or send us an inquiry.
You are more than welcome to ask for samples! Feel free to ask about requests for samples or if there are any other questions.
