To guide users in considering the key, fundamental characteristics they should consider when selecting a machine vision system, here are ten aspects to prioritize:
1 Positioner
Precise object or feature localization is a crucial function of any detection system or vision-guided motion system. Traditional object localization uses grayscale correction to identify objects. While this technique is widely used, it lacks stability when image quality deteriorates. Image quality deterioration can be caused by factors such as clutter, varying brightness, and occlusion. In contrast, geometric object localization is a more recent approach that uses the object's contour to identify the object and its features. Adept's HexSight software and AdeptVisionsAVI system both utilize highly advanced contour detection technology for object identification. A reliable locator eliminates the need for fixtures to position parts, thus saving costs.
2 Light and Illumination
As is well known, proper lighting and illumination are crucial for the success of vision applications. Sometimes, even with the most suitable lighting and illumination chosen, slight changes in the monitored object or features necessitate adjustments to the brightness. Examples include variations in the polished surface of a chip or the quality of laser-etched markings in OCR applications. A stable positioning tool, such as Adept's Geometric Object Positioner, can easily handle situations where changes in light focus and brightness degrade image quality. Using appropriate software allows you to eliminate the need for necessary dimming operations, regardless of changes in image quality.
3. A complete toolset for multiple tools
Machine vision software is primarily sold in two typical forms—complete vision toolsets and application tools for specific tasks, such as BGA inspection. The end-user's application will determine whether to use a complete vision toolset or numerous specific tools. Vision tools are general applications or algorithms that perform predetermined tasks on an image or a part of an image. For example, a blob detection tool can identify a set of dark or bright pixels and measure the various dimensions of the blob. A key point in choosing a vision system is having a complete vision toolset. While you may not need all the tools at the beginning of a project, your requirements will change over the years, and new applications may require different tools. Adept's HexSight software is a comprehensive machine vision library based on popular software platforms such as Visual Basic, Visual C++, and Activision controls. Optional HexSight symbol tools are provided along with OCR, digit matrix, and barcode decoding tools. The AdeptVisionsAVI system comes with a simple graphical interface for programming vision and motion applications.
4. Convenient programming and operation: A simple and intuitive graphical interface is key to ease of use and setup.
The main difference between machine vision products today lies in their graphical interfaces. Interfaces should be evaluated in terms of both "setup" and "operation." For an engineer, it should be very complex, but for an operator, it should be extremely simple. For example, calibrating a vision system should be as simple as clicking a mouse a few times, not like an exercise in rocket science.
5 sub-pixel precision
The resolution of a vision system is the smallest feature that the system can distinguish. For example, a visual field of view (FOV) of '1' using a 640x480 pixel computer image will yield a resolution of 1/640, or '0.00156'. In fact, machine vision algorithms have sub-pixel capabilities. That is, these algorithms can measure or derive units smaller than a single pixel. Adept's geometric object localization tool is accurate to 1/40th of a pixel. All other vision system tools are only accurate to 1/10th to 1/20th of a pixel. The sub-pixel accuracy of vision tools depends on the image quality and the power of the algorithm.
6 Future Upgrades
Machine vision systems have a wide range of applications, from high-end cameras to surveillance systems. When selecting a system, future upgrades should be considered. Several vendors offer general-purpose vision software that allows end-users to configure suitable lighting, optics, and vision tools. Specialized software packages such as BGA inspection and OCR are also sold as pre-configured software. General-purpose vision software systems are easier to upgrade. End-users should consider future system needs based on additional cameras, changes in lighting, and changes in vision tools. For example, if a system requires multiple cameras, the price and flexibility of a frame acquisition-based system should be compared to that of a high-end camera-based system. Adept's HexSight software is compatible with many third-party frame acquisition devices and cameras, including FireWire cameras.
7 Image Preprocessing
Detecting feature points and defects is crucial, regardless of brightness or differences in object surface or material. Image preprocessing algorithms can amplify feature points in an image, enabling vision tools to detect them more effectively. Conversely, feature points can be reduced in size so that vision tools can ignore them. For example, HexSight's morphological operations can be used to remove or fill holes in objects, separate objects at sparse points, or connect adjacent objects. Similarly, filtering operations can be used for convolution of input images. This wide range of preprocessing algorithms is key to the success of complex vision applications.
8 Visually Guided Movement
If your application requires a vision system, then you must understand how the vision system is integrated with the motion system. For calibration and operation, an unintegrated motion system and vision system constitute a preliminary system; the robot or mechanism and vision system are calibrated separately. In operation, a standalone vision system calculates the offset of the part's position based on its known location in the vision coordinate system, and then instructs the robot arm to pick up the part at an offset from the initially programmed pick-up position. Conversely, an integrated system, such as the AdeptvisionsAVI controller, calibrates both the vision system and the machine within a single coordinate system. Part positioning can then be defined in the same six-DOF coordinate space as programmed into the machine.
9 System Integration
If you're not very proficient in machine vision technology, you'll need a system integrator for your project. Ideal vision products are widely accepted by system integrators. Adept has a program called Adept Preferred Vision Integrators (PVIs) that trains system integrators on Adept's products. These system integrators have application engineering resources to handle even the most challenging machine vision projects. Furthermore, these PVIs are well-suited for working with Adept's robotics and motion products. This is an ideal resource for projects requiring both motion and vision.
10-Plant Layer Connection
Currently, various methods exist for communicating with vision systems, including common interfaces such as serial ports (RS-232), RS-485, parallel ports, Ethernet, DeviceNet, and digital I/O. Newer interfaces like IEEE-1394 and USB are also widely used. When evaluating a vision system, factory-level connectivity must be considered. Typically, a machine vision system is a data acquisition system that interfaces with other factory-level equipment and the factory's information systems. Some vendors' software allows for remote operation of vision systems over a local area network (LAN) or the Internet. In specific industries, such as pharmaceuticals, machine vision systems are required to be application-independent to ensure setup is unaffected by remote operation. The communication interface of a vision system is a crucial consideration and should not be overlooked when selecting one. AdeptVisionsAVI controllers can connect to RS-232, RS-485, DeviceNet, Ethernet, and Firewire interfaces.
